Conjugated inter-polyelectrolyte complexes with exciton transfer

Abstract

Presented are conjugated polyelectrolyte complexes including an electronic energy transfer acceptor conjugated polyelectrolyte polymer and an electronic energy transfer donor conjugated polyelectrolyte copolymer. The electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer can be oppositely charged. The conjugated polyelectrolyte complexes can be applied to convert photon energy into another form of energy.

Description

[0001] Attorney Docket 8883-0013 CONJUGATED INTER-POLYELECTROLYTE COMPLEXES WITH EXCITON TRANSFER This invention was made with government support under Grant No.1848069 awarded by ^^ the National Science Foundation. The government has certain rights in the invention. FIELD OF THE EMBODIMENTS This specification pertains to the field of harvesting energy from light. Artificial light harvesting, a process which involves converting light, such as sunlight, ^^^ into electrical energy and / or chemical potential energy, can address global energy challenges. SUMMARY Some embodiments of the invention include the following: [1] a conjugated polyelectrolyte complex (CPEC), comprising: ^^^ an electronic energy transfer (EET) acceptor conjugated polyelectrolyte (CPE) polymer; and an electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer, wherein the electronic energy transfer acceptor conjugated polyelectrolyte ^^^ polymer comprises an acceptor repeat unit, wherein the acceptor repeat unit comprises aryl or heteroaryl functionalized with an acceptor ionic group comprising an acceptor electrical charge, wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer comprises an ionic donor repeat unit and a second donor repeat unit, ^^^ wherein the ionic donor repeat unit comprises an aryl or heteroaryl group functionalized with a donor ionic group comprising a donor electrical charge, wherein the donor electrical charge is opposite to the acceptor electrical charge, wherein the second donor repeat unit comprises aryl or heteroaryl, and wherein the ionic donor repeat unit is bonded to the second donor repeat unit through ^^^ a linkage bond, such as a covalent linkage bond; [2] the conjugated polyelectrolyte complex of [1], wherein the ionic donor repeat unit and the second donor repeat unit are in an induced torsion about the linkage bond; Attorney Docket 8883-0013 [3] the conjugated polyelectrolyte complex of [2], wherein the torsion reduces an exciton radius; ^^ [4] the conjugated polyelectrolyte complex of [2], wherein the torsion reduces overlap of an ionic donor repeat unit aryl or heteroaryl group ^-orbital with a second donor repeat unit aryl or heteroaryl ^-orbital; [5] the conjugated polyelectrolyte complex of [4], wherein the reduced overlap reduces ^^^ an exciton radius; [6] the conjugated polyelectrolyte complex of [3] or [5], wherein the reduced exciton radius increases excitonic coupling between the electronic energy transfer donor conjugated polyelectrolyte polymer and the electronic energy transfer acceptor ^^^ conjugated polyelectrolyte copolymer; [7] the conjugated polyelectrolyte complex of [6], wherein the increased excitonic coupling increases the rate of electronic energy transfer from the electronic energy transfer donor conjugated polyelectrolyte copolymer to the electronic energy transfer ^^^ acceptor conjugated polyelectrolyte polymer; [8] the conjugated polyelectrolyte complex of any one of [1] through [7], wherein a ratio of a number of the ionic donor repeat units : a number of the second donor repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer is ^^^ in the range of from about 1:5, 1:3, 1:2, 1:1.5, 1:1, 1.5:1, 2:1, or 3:1 to about 1:3, 1:2, 1:1.5, 1:1, 1.5:1, 2:1, 3:1, or 5:1; [9] the conjugated polyelectrolyte complex of any one of [1] through [7], wherein the ratio of the number of the ionic donor repeat units : the number of the second donor ^^^ repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer is in the range of from about 1:2 to about 2:1; Attorney Docket 8883-0013

[0010] the conjugated polyelectrolyte complex of any one of [1] through [7], wherein the ratio of the number of the ionic donor repeat units : the number of the second donor repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer is about 1:1; ^^

[0011] the conjugated polyelectrolyte complex of any one of [1] through

[0010] , wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer is a random copolymer; ^^^

[0012] the conjugated polyelectrolyte complex of any one of [1] through

[0010] , wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer is a statistical copolymer;

[0013] the conjugated polyelectrolyte complex of any one of [1] through

[0010] , wherein the ^^^ electronic energy transfer donor conjugated polyelectrolyte copolymer is a block copolymer comprising at least one ionic donor repeat unit block and at least one second donor repeat unit block;

[0014] the conjugated polyelectrolyte complex of any one of [1] through [7], wherein the ^^^ ionic donor repeat unit and the second donor repeat unit alternate in the electronic energy transfer donor conjugated polyelectrolyte copolymer;

[0015] the conjugated polyelectrolyte complex of any one of [1] through

[0014] , wherein the acceptor repeat unit comprises thiophene functionalized with the acceptor ionic ^^^ group;

[0016] the conjugated polyelectrolyte complex of any one of [1] through

[0014] , wherein the acceptor repeat unit comprises benzothiadiazole, thienothiophene, dithiophene, or dithienothiophene functionalized with the acceptor ionic group; ^^^

[0017] the conjugated polyelectrolyte complex of any one of [1] through

[0014] , wherein the acceptor repeat unit comprises phenylene functionalized with the acceptor ionic group; Attorney Docket 8883-0013

[0018] the conjugated polyelectrolyte complex of any one of [1] through

[0014] , wherein the acceptor repeat unit comprises 3,4-ethylenedioxythiophene, pyrrole, or furan functionalized with the acceptor ionic group; ^^

[0019] the conjugated polyelectrolyte complex of any one of [1] through

[0018] , wherein the acceptor ionic group is an anionic group;

[0020] the conjugated polyelectrolyte complex of any one of [1] through

[0018] , wherein the ^^^ acceptor ionic group comprises an alkyl carboxylate;

[0021] the conjugated polyelectrolyte complex of any one of [1] through

[0018] , wherein the acceptor ionic group comprises butylcarboxylate; ^^^

[0022] the conjugated polyelectrolyte complex of any one of [1] through

[0018] , wherein the acceptor ionic group comprises ethylcarboxylate, propylcarboxylate, or pentylcarboxylate;

[0023] the conjugated polyelectrolyte complex of any one of [1] through

[0018] wherein the ^^^ acceptor ionic group comprises an alkyl sulfonate;

[0024] the conjugated polyelectrolyte complex of any one of [1] through

[0018] , wherein the acceptor ionic group is a cationic group; ^^^

[0025] the conjugated polyelectrolyte complex of any one of [1] through

[0018] and

[0024] , wherein the acceptor ionic group comprises a quaternary alkyl ammonium;

[0026] the conjugated polyelectrolyte complex of any one of [1] through

[0018] and

[0024] through 25, wherein the acceptor ionic group comprises a trimethyl alkyl ^^^ ammonium; Attorney Docket 8883-0013

[0027] the conjugated polyelectrolyte complex of any one of [1] through

[0018] and

[0024] through 26, wherein the acceptor ionic group comprises a quaternary alkyl phosphonium; ^^

[0028] the conjugated polyelectrolyte complex of any one of [1] through

[0027] , wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer is regioregular;

[0029] the conjugated polyelectrolyte complex of any one of [1] through

[0014] , wherein the^^^ electronic energy transfer acceptor conjugated polyelectrolyte polymer is poly(3-(4- butanoate)thiophene-2,5-diyl);

[0030] the conjugated polyelectrolyte complex of any one of [1] through

[0029] , wherein the ionic donor repeat unit comprises a phenylene functionalized with the donor ionic ^^^ group;

[0031] the conjugated polyelectrolyte complex of any one of [1] through

[0029] , wherein the ionic donor repeat unit comprises a biphenylene functionalized with the donor ionic group; ^^^

[0032] the conjugated polyelectrolyte complex of any one of [1] through

[0029] , wherein the ionic donor repeat unit comprises fluorene functionalized with the donor ionic group;

[0033] the conjugated polyelectrolyte complex of any one of [1] through

[0029] , wherein the ^^^ ionic donor repeat unit comprises carbazole functionalized with the donor ionic group;

[0034] the conjugated polyelectrolyte complex of any one of [1] through

[0029] , wherein the ionic donor repeat unit is fluorene functionalized at the 9-carbon with the donor ionic ^^^ group;

[0035] the conjugated polyelectrolyte complex of any one of [1] through

[0023] and

[0028] through 34, wherein the donor ionic group is a cationic group; Attorney Docket 8883-0013

[0036] the conjugated polyelectrolyte complex of any one of [1] through

[0023] and

[0028] through

[0035] , wherein the donor ionic group comprises a quaternary alkyl ammonium; ^^

[0037] the conjugated polyelectrolyte complex of any one of [1] through

[0023] and

[0028] through

[0036] , wherein the donor ionic group comprises a trimethyl alkyl ammonium;

[0038] the conjugated polyelectrolyte complex of any one of [1] through

[0023] and

[0028] ^^^ through

[0037] , wherein the donor ionic group comprises a gem-di(trimethyl alkyl ammonium);

[0039] the conjugated polyelectrolyte complex of any one of [1] through

[0023] and

[0028] through

[0038] , wherein the donor ionic group comprises a quaternary phosphonium ^^^ alkyl;

[0040] the conjugated polyelectrolyte complex of any one of [1] through

[0018] ,

[0024] through

[0028] , and

[0030] through

[0034] , wherein the donor ionic group is an anionic group; ^^^

[0041] the conjugated polyelectrolyte complex of any one of [1] through

[0018] ,

[0024] through

[0028] ,

[0030] through

[0034] , and

[0040] , wherein the donor ionic group comprises an alkyl carboxylate;

[0042] the conjugated polyelectrolyte complex of any one of [1] through

[0018] ,

[0024] through ^^^

[0028] ,

[0030] through

[0034] , and

[0040] through

[0041] , wherein the donor ionic group comprises an alkyl sulfonate;

[0043] the conjugated polyelectrolyte complex of any one of [1] through

[0023] and

[0028] through

[0034] , wherein the donor ionic group is gem-di(N,N,N-trimethylpropan-1- ^^^ ammonium-3-yl); Attorney Docket 8883-0013

[0044] the conjugated polyelectrolyte complex of any one of [1] through

[0023] and

[0028] through

[0029] , wherein the ionic donor repeat unit is 9,9-di(N,N,N-trimethylpropan-1- ammonium-3-yl)-9H-fluorene-2,7-diyl; ^^

[0045] the conjugated polyelectrolyte complex of any one of [1] through

[0044] , wherein the second donor repeat unit is nonionic;

[0046] the conjugated polyelectrolyte complex of any one of [1] through

[0045] , wherein the second donor repeat unit is functionalized with an electron-withdrawing group; ^^^

[0047] the conjugated polyelectrolyte complex of any one of [1] through

[0045] , wherein the second donor repeat unit comprises a phenylene functionalized with an electron- withdrawing group; ^^^

[0048] the conjugated polyelectrolyte complex of any one of [1] through

[0045] , wherein the second donor repeat unit comprises a phenylene functionalized with a halogen;

[0049] the conjugated polyelectrolyte complex of any one of [1] through

[0045] , wherein the second donor repeat unit comprises a phenylene functionalized with a fluorine; ^^^

[0050] the conjugated polyelectrolyte complex of any one of [1] through

[0045] , wherein the second donor repeat unit comprises a phenylene functionalized with two or three fluorines; ^^^

[0051] the conjugated polyelectrolyte complex of any one of claims [1] through

[0045] , wherein the second donor repeat unit is 2,3-difluorophenyl-1,4-diyl;

[0052] the conjugated polyelectrolyte complex of any one of [1] through

[0045] , wherein the second donor repeat unit comprises a phenylene functionalized with four fluorines; ^^^

[0053] the conjugated polyelectrolyte complex of any one of [1] through

[0045] , wherein the second donor repeat unit is 2,3,5,6-tetrafluorophenyl-1,4-diyl; Attorney Docket 8883-0013

[0054] the conjugated polyelectrolyte complex of any one of [1] through

[0053] , wherein a torsional angle about the linkage bond is greater than about 40 degrees;

[0055] the conjugated polyelectrolyte complex of any one of [1] through

[0053] , wherein a ^^ torsional angle about the linkage bond is greater than about 43.8 degrees;

[0056] the conjugated polyelectrolyte complex of any one of [1] through

[0053] , wherein a torsional angle about the linkage bond is greater than about 44 degrees; ^^^

[0057] the conjugated polyelectrolyte complex of any one of [1] through

[0053] , wherein a torsional angle about the linkage bond is at least about 50 degrees;

[0058] the conjugated polyelectrolyte complex of any one of [1] through

[0053] , wherein a torsional angle about the linkage bond is at least about 53 degrees; ^^^

[0059] the conjugated polyelectrolyte complex of any one of [1] through

[0049] and

[0052] through

[0053] , wherein a torsional angle about the linkage bond is at least about 60 degrees; ^^^

[0060] the conjugated polyelectrolyte complex of any one of [1] through

[0049] and

[0052] through

[0053] , wherein a torsional angle about the linkage bond is at least about 61 degrees;

[0061] the conjugated polyelectrolyte complex of any one of [1] through

[0023] and

[0028] ^^^ through

[0029] , wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer is poly(9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene- 2,7-diyl)-alt-(2,3-difluorophenyl-1,4-diyl)) (PFNF2);

[0062] the conjugated polyelectrolyte complex of any one of [1] through

[0023] and

[0028] ^^^ through

[0029] , wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer is poly(9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene- 2,7-diyl)-alt-(2,3,5,6-tetrafluorophenyl-1,4-diyl)) (PFNF4); Attorney Docket 8883-0013

[0063] the conjugated polyelectrolyte complex of any one of [1] through

[0062] , wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is in a range of from about 20:80 to about 80:20; ^^

[0064] the conjugated polyelectrolyte complex of any one of [1] through

[0062] , wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is in a range of from about 40:60 to about 95:5, in a range of from about 50:50 to about 90:10, in a range of from about 60:40 to about 80:20, or in a range of from about 65:35 to about 75:25; ^^^

[0065] the conjugated polyelectrolyte complex of any one of [1] through

[0062] , wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is at least about 70:30; ^^^

[0066] the conjugated polyelectrolyte complex of any one of [1] through

[0062] , wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is about 70:30;

[0067] the conjugated polyelectrolyte complex of any one of [1] through

[0066] , wherein the ^^^ electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in solution;

[0068] the conjugated polyelectrolyte complex of any one of [1] through

[0066] , wherein the ^^^ electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in aqueous solution;

[0069] the conjugated polyelectrolyte complex of any one of [1] through

[0066] , wherein the ^^^ electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in solution in water; Attorney Docket 8883-0013

[0070] the conjugated polyelectrolyte complex of any one of

[0067] through

[0069] , wherein the solution has a predetermined ionic strength;

[0071] the conjugated polyelectrolyte complex of any one of [1] through

[0069] , further ^^ comprising a salt;

[0072] the conjugated polyelectrolyte complex of any one of

[0067] through

[0069] further comprising a salt at a concentration of at most about 5 M in the solution; ^^^

[0073] the conjugated polyelectrolyte complex of [1], comprising: the electronic energy transfer acceptor conjugated polyelectrolyte polymer; and the electronic energy transfer donor conjugated polyelectrolyte copolymer, wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer comprises the acceptor repeat unit, ^^^ wherein the acceptor repeat unit comprises a poly(3-(4-butanoate)thiophene- 2,5-diyl) of the acceptor electrical charge of -1 e (1 electron), wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer comprises the ionic donor repeat unit and the second donor repeat unit, wherein the ionic donor repeat unit comprises 9,9-di(N,N,N-trimethylpropan-1- ^^^ ammonium-3-yl)-9H-fluorene-2,7-diyl of the donor electrical charge of +2 e (-2 electrons), and wherein the second donor repeat unit comprises phenyl;

[0074] the conjugated polyelectrolyte complex of

[0073] , wherein a ratio of a number of the ^^^ ionic donor repeat units : a number of the second donor repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer is in a range of from about 1:2 to about 2:1;

[0075] the conjugated polyelectrolyte complex of

[0073] , wherein a ratio of a number of the ^^^ ionic donor repeat units : a number of the second donor repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer is about 1:1; Attorney Docket 8883-0013

[0076] the conjugated polyelectrolyte complex of any one of

[0073] through

[0075] , wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer is a random copolymer; ^^

[0077] the conjugated polyelectrolyte complex of any one of

[0073] through

[0075] , wherein the ionic donor repeat unit and the second donor repeat unit alternate;

[0078] the conjugated polyelectrolyte complex of any one of

[0073] through

[0077] , wherein the second donor repeat unit comprises 2,3-difluorophenyl-1,4-diyl; ^^^

[0079] the conjugated polyelectrolyte complex of any one of

[0073] through

[0078] , wherein the second donor repeat unit comprises 2,3,5,6-tetrafluorophenyl-1,4-diyl;

[0080] the conjugated polyelectrolyte complex of any one of

[0073] through

[0079] , wherein a ^^^ ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is in the range of from about 80:20 to about 20:80;

[0081] the conjugated polyelectrolyte complex of any one of

[0073] through

[0079] , wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical ^^^ charges is in a range of from about 40:60 to about 95:5, in a range of from about 50:50 to about 90:10, in a range of from about 60:40 to about 80:20, or in a range of from about 65:35 to about 75:25;

[0082] the conjugated polyelectrolyte complex of any one of

[0073] through

[0079] , wherein a ^^^ ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is at least about 70:30;

[0083] the conjugated polyelectrolyte complex of any one of

[0073] through

[0079] , wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical ^^^ charges is about 70:30;

[0084] the conjugated polyelectrolyte complex of any one of

[0073] through

[0083] , wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer and the Attorney Docket 8883-0013 electronic energy transfer donor conjugated polyelectrolyte copolymer are in a solution;

[0085] the conjugated polyelectrolyte complex of any one of

[0073] through

[0083] , wherein the ^^ electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in an aqueous solution;

[0086] the conjugated polyelectrolyte complex of any one of

[0073] through

[0083] , wherein the ^^^ electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in a solution in water;

[0087] the conjugated polyelectrolyte complex of any of

[0085] through

[0086] , wherein the ^^^ solution has a predetermined ionic strength;

[0088] the conjugated polyelectrolyte complex of any of

[0084] through

[0087] , wherein the solution further comprises a salt; ^^^

[0089] the conjugated polyelectrolyte complex of

[0085] , further comprising a salt at a concentration of at most about 5 M in the aqueous solution. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1A at top shows a first step of a synthetic scheme for the PFNX polymer series, the ^^^ synthesis of the monomer FNB. At bottom center is shown the structure of the anionic CPE poly(butylcarboxythiophene) (poly(3-(4-carboxybutyl)thiophene-2,5-diyl), regioregular) (PTAK), which was used as the electronic energy transfer (EET) acceptor conjugated polyelectrolyte (CPE) polymer. At bottom right is shown the structure of an alternative anionic CPE, poly(propylcarboxythiophene) (poly(3-(3-carboxypropyl)thiophene-2,5-diyl), regioregular) ^^^ (PTAK’), which can be used as an electronic energy transfer (EET) acceptor conjugated polyelectrolyte (CPE). FIG.1B shows a second step of a synthetic scheme for the PFNX polymer series. That is, once synthesized, monomer FNB is coupled to one of the aryl co-monomers shown via Attorney Docket 8883-0013 Suzuki cross-coupling to produce the neutral precursor polymers. The final conjugated polyelectrolyte (CPE) series is obtained by reacting all neutral polymers with methyl iodide. FIG.2A shows optical properties of isolated donor and acceptor CPEs as normalized absorption (optical density, OD) spectra. The progression in peak OD wavelength illustrates the ^^ systematic variation in the bandgap and, thus, the electronic states comprising the low-lying exciton transition. FIG.2B shows optical properties of isolated donor and acceptor CPEs as normalized photoluminescence (PL) spectra. The progression in peak OD wavelength illustrates the systematic variation in the bandgap and, thus, the electronic states comprising the low-lying ^^^ exciton transition. FIG.3A shows optical spectroscopy of conjugated polyelectrolyte complexes (CPECs) as the OD spectra normalized to the PTAK absorption band on the red side. Spectra have been normalized on the red side, exclusively corresponding to direct PTAK excitation. The specific choice of the fixed wavelength was made to ensure a vanishing probability that donor PL would ^^^ be detected. The shape of the photoluminescence excitation (PLE) spectra provide unambiguous evidence of electronic energy transfer (EET). The contribution on the blue side due to EET from the donor can be isolated and used to quantify a relative EET efficiency. FIG.3B shows optical spectroscopy of CPECs as the PLE spectra collected at a fixed emission wavelength on the red side of the PTAK PL spectrum. Spectra have been normalized ^^^ on the red side, exclusively corresponding to direct PTAK excitation. The specific choice of the fixed wavelength was made to ensure a vanishing probability that donor PL would be detected. The shape of the PLE spectra provide unambiguous evidence of EET. The contribution on the blue side due to EET from the donor can be isolated and used to quantify a relative EET efficiency. ^^^ FIG.4A shows transient absorption (TA) spectra obtained with the uncomplexed (isolated) donor CPE F4. Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (360 nm for F4). Spectral dynamics are discussed in the Detailed Description. The same data are presented as a contour plot in Fig.33A. FIG.4B shows transient absorption spectra obtained with the uncomplexed (isolated) ^^^ donor CPE F2. Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (360 nm for F2). Spectral dynamics are discussed in the Detailed Description. The same data are presented as a contour plot in Fig.33B. Attorney Docket 8883-0013 FIG.4C shows transient absorption spectra obtained with the uncomplexed (isolated) donor CPE T1. Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (400 nm for T1). Spectral dynamics are discussed in the Detailed Description. The same data are presented as a contour plot in Fig.33C. ^^ FIG.4D shows transient absorption spectra obtained with the uncomplexed (isolated) donor CPE T2. Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (400 nm for T2). Spectral dynamics are discussed in the Detailed Description. The same data are presented as a contour plot in Fig.33D. FIG.5A shows transient absorption (TA) spectra obtained with a PFNX:PTAK CPEC ^^^ (70:30 ratio) of F4 (i.e., PFNF4:PTAK CPEC). Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (360 nm for F4). Spectral dynamics are discussed in the Detailed Description. The same data are presented as a contour plot in FIG.34A. FIG.5B shows transient absorption spectra obtained with a PFNX:PTAK CPEC (70:30 ^^^ ratio) of F2 (i.e., PFNF2:PTAK CPEC). Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (360 nm for F2). Spectral dynamics are discussed in the Detailed Description. The same data are presented as a contour plot in FIG.34B. FIG.5C shows transient absorption spectra obtained with a PFNX:PTAK CPEC (70:30 ^^^ ratio) of T1 (i.e., PFNT1:PTAK CPEC). Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (400 nm for T1). Spectral dynamics are discussed in the Detailed Description. The same data are presented as a contour plot in FIG.34C. FIG.5D shows transient absorption spectra obtained with a PFNX:PTAK CPEC (70:30 ^^^ ratio) of T2 (i.e., PFNT1:PTAK CPEC). Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (400 nm for T2). Spectral dynamics are discussed in the Detailed Description. The same data are presented as a contour plot in FIG.34D. FIG.6A shows transient absorption (TA) spectra obtained for isolated PTAK excited at ^^^ 600 nm, which exclusively excited PTAK. Spectral dynamics are discussed in the Detailed Description. FIG.6B shows transient absorption spectra obtained for a representative CPEC (PFNT1:PTAK) excited at 600 nm, which exclusively excited PTAK. Spectral dynamics are Attorney Docket 8883-0013 discussed in the Detailed Description. Data for all^CPECs excited at 600 nm are presented in FIGs.35A, 35B, 35C, and 35D. FIG.7A shows Species Associated Difference Spectra (SADS) obtained from global analysis of transient absorption spectra collected with a PFNX:PTAK CPEC of F4 (i.e., ^^ PFNF4:PTAK CPEC) using the four-state kinetic interconversion model expressed by Equation 5 (see Detailed Description). Lifetimes corresponding with the SADS are listed in Table 4 (see Detailed Description). FIG.7B shows Species Associated Difference Spectra (SADS) obtained from global analysis of transient absorption spectra collected with a PFNX:PTAK CPEC of F2 (i.e., ^^^ PFNF2:PTAK CPEC) using the four-state kinetic interconversion model expressed by Equation 5 (see Detailed Description). Lifetimes corresponding with the SADS are listed in Table 4 (see Detailed Description). FIG.7C shows Species Associated Difference Spectra (SADS) obtained from global analysis of transient absorption spectra collected with a PFNX:PTAK CPEC of T1 (i.e., ^^^ PFNT1:PTAK CPEC) using the four-state kinetic interconversion model expressed by Equation 5 (see Detailed Description). Lifetimes corresponding with the SADS are listed in Table 4 (see Detailed Description). FIG.7D shows Species Associated Difference Spectra (SADS) obtained from global analysis of transient absorption spectra collected with a PFNX:PTAK CPEC of T2 (i.e., ^^^ PFNT2:PTAK CPEC) using the four-state kinetic interconversion model expressed by Equation 5 (see Detailed Description). Lifetimes corresponding with the SADS are listed in Table 4 (see Detailed Description). FIG.8A shows a comparison of transients obtained with a donor CPE of F4 (i.e., PFNF4 CPE) (upper graph) and a PFNX:PTAK CPEC of F4 (i.e., PFNF4:PTAK CPEC) (lower graph) ^^^ by probing at 740 nm, within the region of photoinduced (transient) absorption of the donor. Data are shown by the hollow circle symbols, and the fits are shown by the curves through the data. Transients at more wavelengths for the PFNF4 CPE donor are in FIG.39A and for the PFNF4:PTAK CPEC are in FIG.37A. FIG.8B shows a comparison of transients obtained with a donor CPE of F2 (i.e., PFNF2 ^^^ CPE) (upper graph) and a PFNX:PTAK CPEC of F2 (i.e., PFNF2:PTAK CPEC) (lower graph) by probing at 740 nm, within the region of photoinduced (transient) absorption of the donor. Transients at more wavelengths for the PFNF2 CPE donor are in FIG.39B and for the PFNF2:PTAK CPEC are in FIG.37B. Attorney Docket 8883-0013 FIG.8C shows a comparison of transients obtained with a donor CPE of T1 (i.e., PFNT1 CPE) (upper graph) and a PFNX:PTAK CPEC of T1 (i.e., PFNT1:PTAK CPEC) (lower graph) by probing at 740 nm, within the region of photoinduced (transient) absorption of the donor. Transients at more wavelengths for the PFNT1 CPE donor are in FIG.39C and for the ^^ PFNT1:PTAK CPEC are in FIG.37C. FIG.8D shows a comparison of transients obtained with a donor CPE of T2 (i.e., PFNT2 CPE) (upper graph) and a PFNX:PTAK CPEC of T2 (i.e., PFNT2:PTAK CPEC) (lower graph) by probing at 740 nm, within the region of photoinduced (transient) absorption of the donor. Transients at more wavelengths for the PFNT2 CPE donor are in FIG.39D and for the ^^^ PFNT2:PTAK CPEC are in FIG.37D. FIG.9 shows azimuthally averaged small-angle X-ray scattering (SAXS) intensities as a function of the scattering vector length Q for all CPECs. All CPECs show monotonically decreasing intensities with no visible Guinier plateau regions. FIG.10 shows time-resolved photoluminescence (TRPL) decays of selectively excited ^^^ PTAK (600 nm) within each CPEC. The instrument response function (IRF) is shown as the set of data at bottom. FIG.11 shows normalized ground state bleach (GSB) spectra of CPECs at a 1-ps pump / probe delay excited at 600 nm. This wavelength corresponds to exclusive PTAK excitation. Small shifts in the absolute value of the peak are apparent across the donor series. ^^^ FIG.12 shows the transition density for each donor repeat unit on the electronic transition from the ground state to the lowest excited state. The darker gray and lighter gray regions correspond to negative and positive isosurfaces, respectively. The isovalue is 8x10−4in a.u. (atomic units). FIG.13A illustrates the electronic energy transfer (EET) from the donor CPE PFNX ^^^ (with X being B, F2, F4, T1, or T2) to the acceptor CPE PTAK (poly(butylcarboxythiophene) (poly(3-(4-carboxybutyl)thiophene-2,5-diyl, regioregular))). FIG.13B illustrates electronic energy transfer (EET) from the donor CPE PFNX (with X being B, F2, F4, T1, or T2) to an acceptor CPE PTAK’ (poly(propylcarboxythiophene) (poly(3- (4-carboxypropyl)thiophene-2,5-diyl, regioregular))). ^^^ FIG.14 shows a1H 500 MHz NMR in CDCl3 spectrum of the FNB monomer. FIG.15 shows a1H 800 MHz NMR in D2O of the PFNT1 CPE with a small water suppression peak at ~4.7 ppm and trace amounts of acetone. Attorney Docket 8883-0013 FIG.16 shows a1H 800 MHz NMR in D2O of the PFNT2 CPE with a small water suppression peak at ~4.7 ppm and trace amounts of acetone. FIG.17 shows a1H 800 MHz NMR in D2O of the PFNF2 CPE with a small water suppression peak at ~4.7 ppm and trace amounts of acetone. ^^ FIG.18 shows a1H 800 MHz NMR in D2O of the PFNB CPE with a small water suppression peak at ~4.7 ppm and trace amounts of acetone and hexanes. The broadening of baseline observed around 6.5-7.3 ppm is due to low solubility. FIG.19 shows a1H 800 MHz NMR in D2O of the PFNF4 CPE with a small water suppression peak at ~4.7 ppm and trace amounts of acetone. ^^^ FIG.20 shows a^distribution plot for extraction of neutral conjugated polymer molecular weight for nPFNF2. Polymer molecular weight parameters are summarized in Table 1 (see Detailed Description). FIG.21 shows a PLE fit for the CPEC PFNB:PTAK and native PTAK OD. FIG.22 shows as the Subtracted PLE curve the calculated PFNB donor contribution to ^^^ the PLE curve. The Difference Curve is the difference of the peak-normalized experimental PTAK OD and the fitted peak-normalized PTAK contribution. The half of this Difference Curve, i.e., the Half Difference Curve, was used to calculate the background and the error in Erel. FIG.23 shows a PLE Fit for the CPEC PFNF2:PTAK and the native PTAK OD. FIG.24 shows as the Subtracted PLE curve the calculated PFNF2 donor contribution to ^^^ the PLE curve. The Difference Curve is the difference of the peak-normalized experimental PTAK OD and the fitted peak-normalized PTAK contribution. The half of this Difference Curve, i.e., the Half Difference Curve, was used to calculate the background and the error in Erel. FIG.25 shows a PLE fit for the CPEC PFNT2:PTAK and native PTAK OD. FIG.26 shows as the Subtracted PLE curve the calculated PFNT2 donor contribution to ^^^ the PLE curve. The Difference Curve is the difference of the peak-normalized experimental PTAK OD and the fitted peak-normalized PTAK contribution. The half of this Difference Curve, i.e., the Half Difference Curve, was used to calculate the background and the error in Erel. FIG.27 shows a PLE fit for the CPEC PFNT1:PTAK and native PTAK OD. FIG.28 shows as the Subtracted PLE curve the calculated PFNT1 donor contribution to ^^^ the PLE curve. The Difference Curve is the difference of the peak-normalized experimental PTAK OD and the fitted peak-normalized PTAK contribution. The half of this Difference Curve, i.e., the Half Difference Curve, was used to calculate the background and the error in Erel. FIG.29 shows a PLE fit for the CPEC PFNF4:PTAK and native PTAK OD. Attorney Docket 8883-0013 FIG.30 shows as the Subtracted PLE curve the calculated PFNF4 donor contribution to the PLE curve. The Difference Curve is the difference of the peak-normalized experimental PTAK OD and the fitted peak-normalized PTAK contribution. The half of this Difference Curve, i.e., the Half Difference Curve, was used to calculate the background and the error in Erel. ^^ FIG.31A illustrates the donor-acceptor CPEC PFNF2-PTAK optimized by a semiempirical method, GFN2-xTB, to extract the Förster distance (R). FIG.31B illustrates the donor-acceptor CPEC PFNF4-PTAK optimized by a semiempirical method, GFN2-xTB, to extract the Förster distance (R). FIG.31C illustrates the donor-acceptor CPEC PFNT1-PTAK optimized by a ^^^ semiempirical method, GFN2-xTB, to extract the Förster distance (R). FIG.31D illustrates the donor-acceptor CPEC PFNT2-PTAK optimized by a semiempirical method, GFN2-xTB, to extract the Förster distance (R). FIG.31E illustrates the donor-acceptor CPEC PFNB-PTAK optimized by a semiempirical method, GFN2-xTB, to extract the Förster distance (R). ^^^ FIG.32 shows the normalized PL of 70:30 electrical charge ratio of CPECs excited at 545 nm. FIG.33A shows transient absorption (TA) spectra obtained with the uncomplexed (isolated) donor CPE F4 presented in a contour representation. Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (excitation ^^^ wavelength is indicated). Spectral dynamics are discussed in the text. The same data are presented as a spectral waterfall plot in FIG.4A. FIG.33B shows transient absorption spectra obtained with the uncomplexed (isolated) donor CPE F2 presented in a contour representation. Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (excitation wavelength is ^^^ indicated). Spectral dynamics are discussed in the text. The same data are presented as a spectral waterfall plot in FIG.4B. FIG.33C shows transient absorption spectra obtained with the uncomplexed (isolated) donor CPE T1 presented in a contour representation. Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (excitation wavelength is ^^^ indicated). Spectral dynamics are discussed in the text. The same data are presented as a spectral waterfall plot in FIG.4C. FIG.33D shows transient absorption spectra obtained with the uncomplexed (isolated) donor CPE T2 presented in a contour representation. Spectra were collected following excitation Attorney Docket 8883-0013 near the peak of the steady-state absorption spectrum of the donor (excitation wavelength is indicated). Spectral dynamics are discussed in the text. The same data are presented as a spectral waterfall plot in FIG.4D. FIG.34A shows transient absorption (TA) spectra obtained with a PFNX:PTAK CPEC ^^ of F4 (i.e., PFNF4:PTAK CPEC) presented in a contour representation. Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (excitation wavelength is indicated). Spectral dynamics are discussed in the text. The same data are presented as a spectral waterfall plot in FIG.5A. FIG.34B shows transient absorption spectra obtained with a PFNX:PTAK CPEC of F2 ^^^ (i.e., PFNF2:PTAK CPEC) presented in a contour representation. Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (excitation wavelength is indicated). Spectral dynamics are discussed in the text. The same data are presented as a spectral waterfall plot in FIG.5B. FIG.34C shows transient absorption spectra obtained with a PFNX:PTAK CPEC of T1 ^^^ (i.e., PFNT1:PTAK CPEC) presented in a contour representation. Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (excitation wavelength is indicated). Spectral dynamics are discussed in the text. The same data are presented as a spectral waterfall plot in FIG.5C. FIG.34D shows transient absorption spectra obtained with a PFNX:PTAK CPEC of T2 ^^^ (i.e., PFNT2:PTAK CPEC) presented in a contour representation. Spectra were collected following excitation near the peak of the steady-state absorption spectrum of the donor (excitation wavelength is indicated). Spectral dynamics are discussed in the text. The same data are presented as a spectral waterfall plot in FIG.5D. FIG.35A shows transient absorption (TA) spectra obtained through selective excitation ^^^ of PTAK in a PFNX:PTAK CPEC of F4 (i.e., PFNF4:PTAK CPEC) at 600 nm. FIG.35B shows transient absorption spectra obtained through selective excitation of PTAK in a PFNX:PTAK CPEC of F2 (i.e., PFNF2:PTAK CPEC) at 600 nm. FIG.35C shows transient absorption spectra obtained through selective excitation of PTAK in a PFNX:PTAK CPEC of T1 (i.e., PFNT1:PTAK CPEC) at 600 nm. ^^^ FIG.35D shows transient absorption spectra obtained through selective excitation of PTAK in a PFNX:PTAK CPEC of T2 (i.e., PFNT2:PTAK CPEC) at 600 nm. FIG.36A shows transient absorption (TA) spectra obtained with pure PTAK. Spectra were collected at 425 nm excitation. Attorney Docket 8883-0013 FIG.36B shows time-dependent cuts at selected (indicated) probe wavelengths from the transient absorption spectra obtained with pure PTAK shown in FIG.36A. FIG.37A shows time-dependence at selected (indicated) probe wavelengths with excitation of the PFNX:PTAK CPEC of F4 (i.e., PFNF4:PTAK CPEC). Data are shown with ^^ symbols; fits determined by global analysis are shown as lines. Lifetimes corresponding with fitted kinetic models are summarized in Table 4 (see Detailed Description). FIG.37B shows time-dependence at selected (indicated) probe wavelengths with excitation of the PFNX:PTAK CPEC of F2 (i.e., PFNF2:PTAK CPEC). Data are shown with symbols; fits determined by global analysis are shown as lines. Lifetimes corresponding with ^^^ fitted kinetic models are summarized in Table 4 (see Detailed Description). FIG.37C shows time-dependence at selected (indicated) probe wavelengths with excitation of the PFNX:PTAK CPEC of T1 (i.e., PFNT1:PTAK CPEC). Data are shown with symbols; fits determined by global analysis are shown as lines. Lifetimes corresponding with fitted kinetic models are summarized in Table 4 (see Detailed Description). ^^^ FIG.37D shows time-dependence at selected (indicated) probe wavelengths with excitation of the PFNX:PTAK CPEC of T2 (i.e., PFNT2:PTAK CPEC). Data are shown with symbols; fits determined by global analysis are shown as lines. Lifetimes corresponding with fitted kinetic models are summarized in Table 4 (see Detailed Description). FIG.38A shows^Species Associated Difference Spectra (SADS) obtained from global ^^^ analysis of transient absorption (TA) spectra collected with the donor CPE F4 (i.e., PFNF4 CPE) using the four-state kinetic interconversion model expressed by Equation 5 (see Detailed Description). Lifetimes corresponding with the SADS are listed in Table 5 (see Detailed Description). FIG.38B shows^Species Associated Difference Spectra (SADS) obtained from global ^^^ analysis of transient absorption (TA) spectra collected with the donor CPE F2 (i.e., PFNF2 CPE) using the four-state kinetic interconversion model expressed by Equation 5 (see Detailed Description). Lifetimes corresponding with the SADS are listed in Table 5 (see Detailed Description). FIG.38C shows^Species Associated Difference Spectra (SADS) obtained from global ^^^ analysis of transient absorption (TA) spectra collected with the donor CPE T1 (i.e., PFNT1 CPE) using the four-state kinetic interconversion model expressed by Equation 5 (see Detailed Description). Lifetimes corresponding with the SADS are listed in Table 5 (see Detailed Description). Attorney Docket 8883-0013 FIG.38D shows^Species Associated Difference Spectra (SADS) obtained from global analysis of transient absorption spectra (TA) collected with the donor CPE T2 (i.e., PFNT2 CPE) using the four-state kinetic interconversion model expressed by Equation 5 (see Detailed Description). Lifetimes corresponding with the SADS are listed in Table 5 (see Detailed ^^ Description). FIG.39A shows time-dependence at selected (indicated) probe wavelengths with excitation of the donor CPE F4 (i.e., PFNF4 CPE). Data are shown with symbols; fits determined by global analysis are shown as lines. Lifetimes corresponding with fitted kinetic models are summarized in Table 5 (see Detailed Description). ^^^ FIG.39B shows time-dependence at selected (indicated) probe wavelengths with excitation of the donor CPE F2 (i.e., PFNF2 CPE). Data are shown with symbols; fits determined by global analysis are shown as lines. Lifetimes corresponding with fitted kinetic models are summarized in Table 5 (see Detailed Description). FIG.39C shows time-dependence at selected (indicated) probe wavelengths with ^^^ excitation of the donor CPE T1 (i.e., PFNT1 CPE). Data are shown with symbols; fits determined by global analysis are shown as lines. Lifetimes corresponding with fitted kinetic models are summarized in Table 5 (see Detailed Description). FIG.39D shows time-dependence at selected (indicated) probe wavelengths with excitation of the donor CPE T2 (i.e., PFNT2 CPE). Data are shown with symbols; fits ^^^ determined by global analysis are shown as lines. Lifetimes corresponding with fitted kinetic models are summarized in Table 5 (see Detailed Description). FIG.40A shows photoluminescence excitation (PLE) spectra of the PFNX:PTAK CPEC series when the complexes (CPECs) were freshly made. FIG.40B shows photoluminescence excitation (PLE) spectra of the PFNX:PTAK CPEC ^^^ series two (2) weeks after the complexes (CPECs) were made. FIG.41 shows torsional angles about linkage bonds of the ground-state equilibrium geometries of co-monomer units for the CPE donors PFNF2 (F2), PFNF4 (F4), PFNT1 (T1), PFNT2 (T2), and PFNB (B) as from density functional theory (DFT) calculations. FIG.42A shows the electrical charge difference density for the repeat unit of the donor ^^^ PFNF2 on the electronic transition from the ground state to the lowest excited state. The darkest (some kidney-shaped) regions and the intermediate dark (some heart-shaped) regions correspond to negative and positive isosurfaces, respectively. The isovalue is 8x10−4in a.u. (atomic units). Attorney Docket 8883-0013 FIG.42B shows the electrical charge difference density for the repeat unit of the donor PFNF4 on the electronic transition from the ground state to the lowest excited state. The darkest (some kidney-shaped) regions and the intermediate dark (some heart-shaped) regions correspond to negative and positive isosurfaces, respectively. The isovalue is 8x10−4in a.u. (atomic units). ^^ FIG.42C shows the electrical charge difference density for the repeat unit of the donor PFNT1 on the electronic transition from the ground state to the lowest excited state. The darkest (some kidney-shaped) regions and the intermediate dark (some heart-shaped) regions correspond to negative and positive isosurfaces, respectively. The isovalue is 8x10−4in a.u. (atomic units). FIG.42D shows the electrical charge difference density for the repeat unit of the donor ^^^ PFNT2 on the electronic transition from the ground state to the lowest excited state. The darkest (some kidney-shaped) regions and the intermediate dark (some heart-shaped) regions correspond to negative and positive isosurfaces, respectively. The isovalue is 8x10−4in a.u. (atomic units). DETAILED DESCRIPTION ^^^ Light-harvesting materials include polymeric semiconductors. An approach is solution- processed organic photovoltaics cast from volatile organic solvents and deposited as thin films.1-3There is a complementary need to form self-assembled systems capable of converting photon energy into chemical potential energy4-8; it is desirable to do so using environmentally benign aqueous processing. Conjugated polyelectrolytes (CPEs) are interesting for such an application^^^ because, in addition to their highly delocalized electronic states, they can be made to be water- soluble and to have the potential for hierarchical self-assembly given the diversity of their noncovalent interactions.9-16Exciton transfer between extended electronic states in conjugated inter-polyelectrolyte complexes is presented herein. Conjugated polyelectrolyte complexes (CPECs) (also termed ^^^ conjugated inter-polyelectrolyte complexes) can be used for artificial light harvesting because of their extended electronic states, tunable assembly thermodynamics, and sensitivity to their local environment. Ionically assembled complexes of conjugated polyelectrolytes can act as efficient donor / acceptor pairs for electronic energy transfer (EET). That is, oppositely electrical charged CPEs in a CPEC (also termed an inter-CPE complex (inter-CPEC)) can be electrostatically ^^^ assembled in water over a broad range of ionic strengths.17,18If the two CPEs comprising the CPEC are chosen to act as an exciton donor / acceptor pair, they may undergo extremely rapid electronic energy transfer (EET) from the donor CPE to the acceptor CPE. The EET timescale can be commensurate with natural photosynthetic pigments.18Since EET is critical to high- Attorney Docket 8883-0013 performance light-harvesting systems,19-21CPECs can be attractive artificial light-harvesting antennae in overarching, aqueous light-harvesting systems. EET between a model donor and acceptor CPE within a CPEC can be ultrafast.18However, how the EET timescale responds to changes in the chemical structures of complexed ^^ CPEs is complex. Depending on the desired material, it may be necessary to tune the electronic bandgap or the emission spectrum to harvest a particular wavelength range. Doing so requires modifying the backbone chemical structure, which may affect the CPEC excitonic coupling. That is, tuning the backbone chemistry modifies the excitonic wavefunction and thus the excitonic coupling that determines the EET rate. ^^^ The F^rster model can be used to evaluate how the EET rate responds to changes in chemical structure.22,23Within this model, changes in chemical structure are encoded in the emission spectrum of the isolated exciton donor and the absorption spectrum of the isolated exciton acceptor. An assumption implicit to this model is that the separation between the donor and the acceptor is significantly larger than the spatial extent of their excitonic wavefunctions. ^^^ However, within a CPEC, the separation between donor and acceptor chains can be comparable to or smaller than the exciton delocalization radius, or mean chromophore length.24,25In such a case, the F^rster model may break down, making it challenging to determine how changes in backbone chemical structure will influence the EET rate. This knowledge gap complicates the application of CPECs as energy transfer antennae. ^^^ The Examples below report on the interrogation of the dependence of EET within a CPEC on the chemical structure of the CPEs that form the CPEC. In the Examples below, the anionic acceptor CPE polymer was fixed and a series of cationic, alternating donor CPE copolymers having identical ionic donor repeat units (monomers) but differing in subtle modifications of the second donor repeat units (comonomers) was synthesized. Variation of the ^^^ second donor repeat unit (monomer) while keeping the linear electrical charge density nearly fixed allows manipulation of the excitonic wavefunction on the donor CPE without significantly changing the thermodynamics of electrostatic self-assembly. A combination of steady-state and ultrafast optical probes were then used to characterize the relative EET efficiencies and rates. The results of the examples showed that relatively subtle changes in the chemical structure of a ^^^ second donor repeat unit (monomer) can lead to large differences in EET. Without being bound by theory, and as discussed further below, the nonionic second repeat unit (monomer) of the donor CPE may alter the exciton delocalization radius and, in turn, influence the exciton transfer integral. Manipulating EET between proximal conjugated polymer chains requires Attorney Docket 8883-0013 considerations that go beyond the spectral overlap. The results of the Examples below have implications for the choice of CPEC constituents in water-based light-harvesting materials. Definitions ^^ Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the provided compositions, suitable methods and materials are described below. Each publication, patent application, patent, and other reference mentioned ^^^ herein is herein incorporated by reference in its entirety as if each such publication, patent application, patent, and other reference had been individually incorporated. In case of an inconsistency, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be limiting. Other features and advantages of the methods and compositions discussed herein will be ^^^ apparent from the following written description, drawings, and claims. It is understood that wherever embodiments are described herein with the language “comprising”, then otherwise analogous embodiments, described in terms of “containing” “consisting of”, and / or “consisting essentially of” are also provided. However, when used in the claims as transitional phrases, each should be interpreted separately and in the appropriate ^^^ legal and factual context (e.g., in claims, the transitional phrase “comprising” is considered more of an open-ended phrase while “consisting of” is more exclusive and “consisting essentially of” achieves a middle ground). As used herein, the terms "approximately" and "about," as applied to one or more values of interest, refer to a value that is similar to a stated reference value. In certain ^^^ embodiments, the term "approximately" or "about" refers to a range of values that fall within 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value). For example, when used in the context of an amount of a ^^^ given compound in a composition, "about" may mean + / -10% of the recited value. For instance, a composition including a compound having about 40% of a given compound may include 30- 50% of the compound. Attorney Docket 8883-0013 The term “and / or” as used in a phrase such as “A and / or B” herein is intended to include each of the following: both A and B; A or B; A (alone); and B (alone). Likewise, the term “and / or” as used in a phrase such as “A, B, and / or C” is intended to encompass each of the following: A, B, and C; A, B, or C; A or C; A or B; B or C; A and C; A and B; B and ^^ C; A (alone); B (alone); and C (alone). Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. ^^^ Where embodiments of the disclosure are described in terms of a Markush group or another grouping of alternatives, the disclosed composition or method encompasses not only the entire group listed as a whole but also encompasses each member of the group individually and all possible subgroups of the main group and also encompasses the main group absent one or more of the group members. The disclosed methods and compositions also envisage the explicit ^^^ exclusion of one or more of any of the group members in the disclosed compositions or methods. Unless otherwise indicated or indicated by the context, a singular form is to be understood as also encompassing the plural form, and a plural form is to be understood as also encompassing the singular form. An embodiment may include one or more described elements and may optionally include ^^^ one or more additional elements that are not specifically described. An embodiment may be essentially free of or completely free of non-described elements; that is, non-described elements may optionally be essentially omitted or completely omitted from an embodiment. A polymer is composed of two or more identical (or identical other than terminal groups) repeat units. In some contexts, a repeat unit may be termed a monomer (although it is within a ^^^ polymer). A copolymer includes two or more chemically distinct repeat units. A polyelectrolyte includes a repeat unit that is or includes an electrolyte group, which dissociates in a solution, e.g., an aqueous solution, so that the polyelectrolyte is then electrically charged. A conjugated polymer (or copolymer), such as a conjugated polyelectrolyte (CPE), ^^^ includes connected p-orbitals with delocalized electrons. A conjugated polyelectrolyte complex (CPEC) can include a conjugated polyelectrolyte (CPE) having an electrical charge of one sign (i.e., either positive or negative) and another Attorney Docket 8883-0013 conjugated polyelectrolyte (CPE) having an electrical charge of the opposite sign (i.e., either negative or positive). A bond can be a chemical bond, such as a covalent bond, an ionic bond, a polar covalent bond that is intermediate between a covalent bond and an ionic bond, a coordinate covalent ^^ (dipolar) bond, a metallic bond, or a hydrogen bond. An exciton can be described as a quasiparticle that includes an electron and an electron hole (hole) attracted to each other by the Coulomb force. The exciton can form from promotion of an (negatively electrically charged) electron from the highest occupied molecular orbital to lowest unoccupied molecular orbital with the positively electrically charged hole being formed ^^^ in the highest occupied molecular orbital. A distance between the electron and hole defines an exciton radius. An exciton has an associated exciton energy. An exciton on a donor molecule may transfer (transferring energy) to an acceptor molecule through nonradiative electronic energy transfer (EET). A halogen is an element (an atom) that is in the Group 17 of the periodic table; the ^^^ halogens include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Embodiments In some embodiments, a conjugated polyelectrolyte complex (CPEC) includes an electronic energy transfer (EET) acceptor conjugated polyelectrolyte (CPE) polymer and ^^^ an electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer. The electronic energy transfer acceptor conjugated polyelectrolyte polymer can include an acceptor repeat unit, and the acceptor repeat unit can include aryl or heteroaryl functionalized with an acceptor ionic group including an acceptor (electrical) charge. The electronic energy transfer donor conjugated polyelectrolyte copolymer can include an ionic donor repeat unit and a second ^^^ donor repeat unit. The ionic donor repeat unit can include an aryl or heteroaryl group functionalized with a donor ionic group comprising a donor (electrical) charge, and the donor electrical charge can be opposite to the acceptor electrical charge. The second donor repeat unit can include aryl or heteroaryl. The ionic donor repeat unit can be bonded to the second donor repeat unit through a linkage bond, such as a covalent linkage bond. ^^^ In some embodiments, the ionic donor repeat unit and the second donor repeat unit are in an induced torsion about the linkage bond. The torsion can reduce an exciton radius. The torsion can reduce overlap of an ionic donor repeat unit aryl or heteroaryl group ^-orbital with a second donor repeat unit aryl or heteroaryl ^-orbital. The reduced overlap can reduce an exciton Attorney Docket 8883-0013 radius. The reduced exciton radius can increase excitonic coupling between the electronic energy transfer donor conjugated polyelectrolyte polymer and the electronic energy transfer acceptor conjugated polyelectrolyte copolymer. The increased excitonic coupling can increase the rate of electronic energy transfer from the electronic energy transfer donor conjugated ^^ polyelectrolyte copolymer to the electronic energy transfer acceptor conjugated polyelectrolyte polymer. In some embodiments, a ratio of a number of the ionic donor repeat units : a number of the second donor repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer is in the range of from about 1:5, 1:3, 1:2, 1:1.5, 1:1, 1.5:1, 2:1, or 3:1 to about 1:3, ^^^ 1:2, 1:1.5, 1:1, 1.5:1, 2:1, 3:1, 5:1. For example, the ratio of the number of the ionic donor repeat units : the number of the second donor repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer can be in the range of from about 1:2 to about 2:1. For example, a conjugated polyelectrolyte complex (CPEC) can have the ratio of the number of the ionic donor repeat units : the number of the second donor repeat units in the electronic energy ^^^ transfer donor conjugated polyelectrolyte (CPE) copolymer as about 1:1. In some embodiments, the electronic energy transfer (EET) acceptor conjugated polyelectrolyte (CPE) polymer is a linear polymer. In some embodiments, the electronic energy transfer acceptor conjugated polyelectrolyte (CPE) polymer is regioregular, for example, the acceptor repeat units are arranged head-to-tail in the backbone (chain) of the electronic energy ^^^ transfer acceptor conjugated polyelectrolyte polymer. If there is some deviation from heat-to-tail regioregularity, for example, if occasionally two acceptor repeat units in the backbone are head- to-head or tail-to-tail, then the electronic energy transfer acceptor conjugated polyelectrolyte polymer might still be considered to be regioregular. In some embodiments, the electronic energy transfer acceptor conjugated polyelectrolyte polymer is not regioregular, for example, ^^^ whether a pair of adjacent acceptor repeat units in the backbone are heat-to-tail, head-to-head, or tail-to-tail is random or can be statistically described (other than uniformly head-to-tail). In some embodiments, the electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer is a linear copolymer. In some embodiments, the electronic energy transfer donor conjugated polyelectrolyte copolymer is a random copolymer. In some ^^^ embodiments, the electronic energy transfer donor conjugated polyelectrolyte copolymer is a statistical copolymer. A random copolymer can be considered to be a limit of a statistical copolymer in which the probability of finding a repeat unit of a given chemical type (e.g., an ionic donor repeat unit or a second donor repeat unit) is equal to the mole fraction of that repeat Attorney Docket 8883-0013 unit in the copolymer. In some embodiments, the electronic energy transfer donor conjugated polyelectrolyte copolymer is a gradient copolymer. In some embodiments, the electronic energy transfer donor conjugated polyelectrolyte copolymer is a block copolymer; the block copolymer can include at least one ionic donor repeat unit block and at least one second donor repeat unit ^^ block. If there is more than one ionic donor repeat unit block, those blocks may be identical or different, for example, in length (number of ionic donor repeat units). If there is more than one second donor repeat unit block, those blocks may be identical or different, for example, in length (number of second donor repeat units). In some embodiments, the ionic donor repeat unit and the second donor repeat unit ^^^ alternate in the electronic energy transfer donor conjugated polyelectrolyte copolymer. That is, the ionic donor repeat unit and the second donor repeat unit can alternate in the backbone (chain) of the electronic energy transfer donor conjugated polyelectrolyte copolymer, so that the electronic energy transfer donor conjugated polyelectrolyte copolymer is an alternating copolymer. If there is some deviation from alternation, for example, if occasionally an ionic ^^^ donor repeat unit is followed by another ionic donor repeat unit, or if occasionally a second donor repeat unit is followed by a second donor repeat unit, the electronic energy transfer donor conjugated polyelectrolyte copolymer might still be considered to be an alternating copolymer. In some embodiments, the electronic energy transfer donor conjugated polyelectrolyte copolymer includes (combines) elements of a random copolymer, a statistical copolymer, a ^^^ gradient copolymer, a block copolymer, and / or an alternating copolymer. In some embodiments, in the electronic energy transfer acceptor conjugated polyelectrolyte polymer, the acceptor repeat unit includes thiophene functionalized with the acceptor ionic group. In some embodiments, the acceptor repeat unit includes benzothiadiazole, ^^^ thienothiophene, dithiophene, dithienothiophene, phenylene, 3,4-ethylenedioxythiophene, pyrrole, and / or furan functionalized with the acceptor ionic group. In some embodiments, the acceptor ionic group is an anionic group. For example, the acceptor ionic group can include a carboxylate alkyl, such as butylcarboxylate. For example, the acceptor ionic group can include ethylcarboxylate, propylcarboxylate, and / or pentylcarboxylate. ^^^ For example, the acceptor ionic group can include an alkyl sulfonate. In some embodiments, the acceptor ionic group is a cationic group. For example, the acceptor ionic group can include a quaternary alkyl ammonium, such as a trimethyl alkyl ammonium. For example, the acceptor ionic group can include a quaternary alkyl phosphonium. Attorney Docket 8883-0013 In some embodiments, the electronic energy transfer acceptor conjugated polyelectrolyte polymer includes poly(3-(4-butanoate)thiophene-2,5-diyl). In some embodiments, in the electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer, the ionic donor repeat unit includes a phenylene functionalized ^^ with the donor ionic group. For example, the ionic donor repeat unit can include a biphenylene functionalized with the donor ionic group. For example, the ionic donor repeat unit can include carbazole functionalized with the donor ionic group. In some embodiments, the ionic donor repeat unit includes fluorene functionalized with the donor ionic group. For example, the ionic donor repeat unit can include fluorene ^^^ functionalized at the 9-carbon with the donor ionic group. In some embodiments, the donor ionic group is a cationic group. For example, the donor ionic group can include a quaternary alkyl ammonium, such as a trimethyl alkyl ammonium, for example, a gem-di(trimethyl alkyl ammonium). For example, the donor ionic group can include a quaternary phosphonium alkyl. ^^^ In some embodiments, the donor ionic group is an anionic group. For example, the donor ionic group can include an alkyl carboxylate. For example, the donor ionic group can include an alkyl sulfonate. In some embodiments, the donor ionic group is gem-di(N,N,N-trimethylpropan-1- ammonium-3-yl). ^^^ In some embodiments, the ionic donor repeat unit is 9,9-di(N,N,N-trimethylpropan-1- ammonium-3-yl)-9H-fluorene-2,7-diyl. In some embodiments, in the electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer, the second donor repeat unit is nonionic. In some embodiments, the second donor repeat unit is functionalized with an electron-withdrawing ^^^ group. In some embodiments, the second donor repeat unit includes a phenylene functionalized with an electron-withdrawing group. For example, the second donor repeat unit includes a phenylene functionalized with a halogen. In some embodiments, the second donor repeat unit includes a phenylene functionalized with a fluorine. For example, the second donor repeat unit includes a phenylene functionalized with two or three fluorines. In some embodiments, the ^^^ second donor repeat unit includes 2,3-difluorophenyl-1,4-diyl. In some embodiments, the second donor repeat unit includes a phenylene functionalized with four fluorines. In some embodiments, the second donor repeat unit includes 2,3,5,6-tetrafluorophenyl-1,4-diyl. Attorney Docket 8883-0013 In some embodiments, in the electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer of the conjugated polyelectrolyte complex (CPEC), a torsional angle about the linkage bond is greater than about 40 degrees. For example, the torsional angle about the linkage bond can be greater than about 43.8 degrees, greater than about 44 degrees, at ^^ least about 50 degrees, at least about 53 degrees, at least about 60 degrees, or at least about 61 degrees. For example, the torsional angle about the linkage bond can be at least about 20 degrees, at least about 30 degrees, at least about 40 degrees, at least about 45 degrees, at least about 50 degrees, at least about 55 degrees, at least about 60 degrees, at least about 65 degrees, at least about 70 degrees, at least about 75 degrees, at least about 80 degrees, or at least about 85 ^^^ degrees. (Zero) (0 degrees, 0°) torsion about the linkage bond can correspond to aromatic moieties on either side of the linkage bond being coplanar, and 90° torsion about the linkage bond can correspond to aromatic moieties on either side of the linkage bond being perpendicular to each other. In some embodiments, the electronic energy transfer donor conjugated polyelectrolyte^^^ copolymer includes poly(9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7- diyl)-alt-(2,3-difluorophenyl-1,4-diyl)) (PFNF2). In some embodiments, the electronic energy transfer donor conjugated polyelectrolyte copolymer includes poly(9,9-di(N,N,N- trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7-diyl)-alt-(2,3,5,6-tetrafluorophenyl-1,4- diyl)) (PFNF4). ^^^ In some embodiments, in the conjugated polyelectrolyte complex, a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is in a range of from about 20:80 to about 80:20. For example, a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges can be in a range of from about 40:60 to about 95:5, in a range of from about 50:50 to about 90:10, in a range of from about 60:40 to about 80:20, or in a range of ^^^ from about 65:35 to about 75:25. For example, a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges can be at least about 70:30. In some embodiments, in the conjugated polyelectrolyte complex, a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is about 70:30. In some embodiments, in the conjugated polyelectrolyte complex, the electronic energy ^^^ transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in solution, for example, in aqueous solution. In some embodiments, the electronic energy transfer acceptor conjugated polyelectrolyte polymer and the Attorney Docket 8883-0013 electronic energy transfer donor conjugated polyelectrolyte copolymer are in solution in water. In some embodiments, the solution has a predetermined ionic strength. In some embodiments, the conjugated polyelectrolyte complex can include a salt. For example, the conjugated polyelectrolyte complex can include an alkali metal halide, sodium ^^ chloride, an alkali metal bicarbonate, potassium bicarbonate, an alkali metal carbonate, lithium carbonate, an alkali metal sulfate, sodium sulfate, an alkaline earth metal halide, magnesium bromide, an alkaline earth metal bicarbonate, magnesium bicarbonate, an alkaline earth metal carbonate, calcium carbonate, an alkaline earth metal sulfate, and / or calcium sulfate. For example, the conjugated polyelectrolyte complex can include a salt at a concentration of at least ^^^ about 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 M, 0.7 M, 1 M, 2 M, 3 M, 4 M, 5 M, 6 M, 8 M, 10 M, or 15 M in the solution and / or of at most about 0.1, 0.2, 0.3, 0.4, 0.5 M, 0.7 M, 1 M, 2 M, 3 M, 4 M, 5 M, 6 M, 8 M, 10 M, 15 M, or 20 M in the solution. In some embodiments, the conjugated polyelectrolyte complex includes the electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer ^^^ donor conjugated polyelectrolyte copolymer. For example, the electronic energy transfer acceptor conjugated polyelectrolyte polymer includes the acceptor repeat unit, which includes a poly(3-(4-butanoate)thiophene-2,5-diyl) of the acceptor electrical charge of -1 e (1 electron). For example, the electronic energy transfer donor conjugated polyelectrolyte copolymer includes the ionic donor repeat unit and the second donor repeat unit. For example, the ionic donor repeat ^^^ unit includes 9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7-diyl of the donor electrical charge of +2 e (-2 electrons), and the second donor repeat unit includes phenyl. For example, a ratio of a number of the ionic donor repeat units : a number of the second donor repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer is in a range of from about 1:2 to about 2:1 or about 1:1. For example, the electronic energy transfer ^^^ donor conjugated polyelectrolyte copolymer is a random copolymer. For example, the ionic donor repeat unit and the second donor repeat unit alternate. For example, the second donor repeat unit includes 2,3-difluorophenyl-1,4-diyl or 2,3,5,6-tetrafluorophenyl-1,4-diyl. For example, a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is in the range of from about 80:20 to about 20:80, in a range of from about 40:60 to ^^^ about 95:5, in a range of from about 50:50 to about 90:10, in a range of from about 60:40 to about 80:20, in a range of from about 65:35 to about 75:25, at least about 70:30, or about 70:30. For example, the electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in a solution, for Attorney Docket 8883-0013 example, in an aqueous solution, for example, in a solution in water. For example, the solution has a predetermined ionic strength. For example, the solution includes a salt. For example, the salt is at a concentration of at most about 5 M in the aqueous solution. ^^ Examples In these Examples, it is shown how modifying the chemical structure of a conjugated polyelectrolyte (CPE) backbone alters the EET rate beyond spectral overlap considerations. The dependence of the EET efficiency and rate on the electronic structure and excitonic wavefunction of the CPE backbone are investigated. As discussed in the Examples, a series of ^^^ alternating copolymers where the electronic states are systematically altered by introducing comonomers with electron withdrawing and electron-rich character while keeping the linear ionic electrical charge density nearly fixed were synthesized. As discussed below, the excitonic coupling may be significantly affected by the exciton delocalization radius; analytical models based on the line-dipole approximation and quantum chemistry calculations are considered to ^^^ elucidate this. The results implied that care should be taken when selecting CPE components for optimal CPEC EET. CPECs can be used as components in water-based light-harvesting materials, for example, as standalone assemblies or as adsorbates on nanoparticles and thin films. Conjugated Polyelectrolyte (CPE) Synthesis ^^^ Details of the synthesis of monomers and polymers and their characterization are provided below. Reagents and materials utilized in this study were obtained directly from distributors without further modification. 2,7-dibromofluorene and 4-toluenesulfonyl chloride were obtained from Oakwood Chemical. Poly[3-(potassium-4-butanoate)thiophene-2,5-diyl] regioregular was ^^^ obtained from Rieke Metals. The monomers 3,6-dibromothieno[3,2-b]thiophene (98.0%) and 1,4-dibromo-2,3-difluorobenzene, (98.0%) were purchased from TCI America. The monomer 1,4-dibromotetrafluorobenzene (99%) was purchased from Sigma Aldrich. The monomer 1,4- dibromobenzene (97.0%) was purchased from Spectrum Laboratory Products Inc. SlideALyzer Dialysis Flasks, 10K MWCO, 250 mL were obtained from Fisher Scientific Company LLC. ^^^ Bis(pinacolato)diboron (98%) and 1,4-dioxane (anhydrous, 99.8%) were obtained from Alfa Aesar. Tetraethylammonium bromide (100%) was obtained from Chem-Impex International Inc. Palladium catalyst [1,1’- bis(diphenylphosphino)ferrocene] dichloropalladium (II) and dimethyl aminopropyl chloride hydrochloride (96%) were obtained from Sigma-Aldrich. Methyl iodide Attorney Docket 8883-0013 (99.5%), tetrahydrofuran (HPLC grade), and dichloromethane (99.5%) were obtained from Spectrum Laboratory Products. Sodium hydroxide, sodium hydroxide solution (50% w / w), potassium carbonate (anhydrous, 99.7%), triethylamine (99%), diethyl ether (99%), methanol (99.9%), acetone (HPLC grade), chloroform (99.9%), ethyl acetate (99.5%), hexanes (98.5%), ^^ and potassium acetate (>99%) were obtained from Fisher Scientific Company LLC. Deuterated solvents CDCl3 (D 99.8%) and D2O (D 99.9%) were purchased from Cambridge Isotope Laboratories. Nuclear magnetic resonance (NMR) spectra of the polymers were collected on a Bruker Avance III HD 4 channel 800 MHz NMR with a cryoprobe. Due to solubility restrictions of the conjugated polymers,13C NMR spectra were not obtained. The1H NMR spectra of the ^^^ materials synthesized are provided below. Conjugated Polyelectrolyte PTAK The anionic CPE poly(butylcarboxythiophene) (poly(3-(4-carboxybutyl)thiophene-2,5- diyl), regioregular) (PTAK) with a molecular weight (MW) of 16,000 Da was obtained from ^^^ Rieke Metals and used as received. The chemical structure of PTAK is shown in the lower portion of Fig.1A. The acceptor repeat unit is the heteroaryl thiophene functionalized with the anionic group butylcarboxylate as the acceptor ionic group. The acceptor ionic group includes an acceptor electrical charge of -1 e (i.e., a 1- electrical charge, 1 negative elementary electrical charge). The PTAK was used as the electronic energy transfer (EET) acceptor conjugated ^^^ polyelectrolyte (CPE) polymer. For the electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymers, a series of polyfluorene-based exciton−donors containing identical cationic sidechains but differing in their backbone chemical structures was synthesized, as illustrated in ^^^ Figs.1A (upper portion) and 1B. This PFNX series was formed via Suzuki polycondensation reactions between propyl dimethylammine-functionalized fluorene pinacol boryl ester (FNB) and aryl co-monomers; synthetic details are provided below. Subsequently, the resulting neutral CPEs’ pendant alkyl amines on the FN monomer were quaternized and immediately dialyzed using a membrane with a 10,000 dalton molecular weight (MW) cutoff. The purity of all ^^^ synthesized products was ensured via proton (1H) NMR spectroscopy, the details of which are provided below. Synthesis of Monomer FN Attorney Docket 8883-0013 The synthesis of (2,7-dibromo-9,9-bis(3’-(N,N-dimethyl-amino)-propyl)-fluorene) (FN) is described (see Fig.1A). To a clean, dried, 100 mL two-neck round bottom flask, a Teflon coated stir bar, dimethyl sulfoxide (DMSO, 30.9 mL, 434.6 mmol), 2,7- dibromofluorene (F, 2 g, 6.2 mmol), tetrabutylammonium bromide (TBAB, 39.8 mg, 0.12 mmol), and 4 mL of a 50 wt. % ^^ aqueous sodium hydroxide solution (50 wt. % aq. NaOH, 4 mL, 154.3 mmol) were added under an atmosphere of N2(g). An additional aliquot of dimethylsulfoxide (DMSO, 10.5 mL, 145.1 mmol) was added to the reaction flask, followed by dimethyl aminopropyl chloride hydrochloride salt (DAPCl, 2.6 g, 16.4 mmol). The reaction was carried out with stirring and heating at 60 °C for 12 hours. Reaction progress was monitored by thin-layer chromatography ^^^ (TLC). Deionized (DI) H2O (40 mL, 2.216 mmol) was added to the reaction flask to dissolve precipitated salts as well as to solvate the DMSO. The product (FN) was extracted from the wet DMSO layer with diethyl ether (Et2O, 8 x 25 mL) and washed with 10 wt.% aqueous NaOH (2 x 50 mL). The organic layer was washed with DI H2O (3 x 50 mL), followed by a brine wash (1 x 50 mL), and then dried over Na2SO4. Concentration of the anhydrous organic layer under ^^^ reduced pressure led to a crude solid which was purified with a silica gel column (hexanes: ethyl acetate: triethylamine, 49:49:2) to obtain FN (72% yield). Synthesis of Monomer FNB The synthesis of 2,7-diboryl pinacol ester-9,9-bis(3’-(N,N-dimethyl-amino)-propyl)- ^^^ fluorene) (FNB) is described (see Fig.1A). To a clean, dried, 100 mL two neck round bottom flask, a Teflon coated stir bar, dimethylformamide (DMF, 39 mL, 505.8 mmol), FN(1 g, 2.0 mmol), bis(pinacolato)diboron (B2Pin2, 2.26 g, 8.9 mmol), potassium acetate (KOAc, 3.53 g, 17.8 mmol), and [1,1’- bis(diphenyl-phosphino)ferrocene]dichloro-palladium(II) (Pd(dppf)Cl2, 0.296 g, 0.40 mmol) were added under an atmosphere of N2(g). The solution for reaction was ^^^ stirred and heated at 80 °C for 24 hours. Reaction progress was monitored by TLC. Upon completion, the reaction was concentrated to dryness, and the crude solid was extracted with hot HPLC-grade hexanes (7 x 100 mL). The combined hexanes layer was filtered, concentrated to dryness, reextracted with hot hexanes, and re-concentrated to dryness. Acetone was used to extract the product from the re-dried hexanes layer and was allowed to crystallize out of the ^^^ solution as an off-white solid. The crystals of FNB were collected via filtration and washed with a minimal amount of cold acetone to obtain FNB (82.5% yield). The1H NMR spectrum of FNB (obtained in CDCl3 at 500 MHz) is shown in Fig. 14. Attorney Docket 8883-0013 Synthesis of Neutral Polymer nPFNT1 The polymerization of 3,3'-(2-methyl-7-(5-methylthiophen-2-yl)-9H-fluorene-9,9- diyl)bis(N,N-dimethylpropan-1-amine) is described (see Fig.1B). To a clean pressured vial 2,5- dibromothiophene (350 mg, 1 mmol), FNB (500 mg, 0.84 mmol), potassium carbonate (K2CO3, ^^ 1.25 g, 9.6 mmol), 1,4-dioxane (dioxane, 8 mL, 90.4 mmol), DI H2O (7.0 mL, 277.0 mmol), and Pd(dppf)Cl2 (4 mg, 0.005 mmol) were added. The entire reaction vessel, including the solution, was flushed with N2(g). The pressured vial was placed into a silicon oil bath, stirred, and heated at 100°C for 48 hours. To stop the reaction, the stirring function was turned off and the polymer in the dioxane layer was pipetted into DI H2O to induce precipitation of poly((9,9-di(N,N- ^^^ dimethylpropan-1-amine-3-yl)-9H-fluorene-2,7-diyl)-alt-(thiophen-2,5-diyl)) (nPFNT1), decanted, and vacuum filtrated. Synthesis of Conjugated Polyelectrolyte PFNT1 The synthesis of the conjugated polyelectrolyte 3,3'-(2-methyl-7-(5-methylthiophen-2- ^^^ yl)-9H-fluorene-9,9-diyl)bis(N,N,N-trimethylpropan-1-aminium) (PFNT1) is described (see Fig.1B). In-situ quaternization of nPFNT1 was done with the addition of iodomethane (MeI, 4 mL, 62 mmol) directly to the remaining dioxane layer containing nPFNT1 and was left to react for 2 hours before the addition of DI H2O, to assist in the dissolution of the polymer. The solution for reaction was then heated to 50 °C for 5 days and aliquots of DI H2O were ^^^ systematically added until there was no more headspace in the 250 mL pressured vial and the polymer was well dissolved. The solution was then dialyzed via the Thermo Scientific™ Slide- A-Lyzer Dialysis Cassette (10,000 dalton molecular weight cutoff (MWCO)) submerged in a vat of DI H2O. The DI H2O was exchanged with fresh DI H2O every day for 3 days. After 3 days, the dialyzed solution of PFNT1 was concentrated under reduced pressure, filtered, transferred^^^ into multiple 25 mL Falcon tubes, and lyophilized to yield poly((9,9-di(N,N,N-trimethylpropan- 1-ammonium-3-yl)-9H-fluorene-2,7-diyl)-alt-(thiophen-2,5-diyl)) (PFNT1) as a rusty-brown solid (71.2% yield). The1H NMR spectrum of PFNT1 (obtained in D2O at 800 MHz) is shown in Fig.15 (1H NMR: ^ 2.07, 2.13, 2.22, 2.28, 2.85, 3.01, 3.07, 3.13, 7.03, 7.20, 7.47, 7.34, 7.40, 7.51, 7.997.57, 7.59, 7.70, 7.81, 7.90, 8.04); the spectrum indicates a^small water suppression^^^ peak at ~4.7 ppm and trace amounts of acetone. The 9,9-di(N,N,N-trimethylpropan-1- ammonium-3-yl)-9H-fluorene-2,7-diyl is the ionic donor repeat unit, and the thiophen-2,5-diyl is the second donor repeat unit. The ionic donor repeat unit is the aryl fluorene functionalized at the 9-carbon with the cationic quaternary group, a gem-di(trimethyl alkyl ammonium) group, Attorney Docket 8883-0013 di(N,N,N-trimethylpropan-1-ammonium-3-yl) as the donor ionic group. The donor ionic group includes a donor electrical charge of +2 e (i.e., a 2+ electrical charge, 2 positive elementary electrical charges). The second donor repeat unit, thiophen-2,5-diyl, is nonionic. The PFNT1 was used as an electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) ^^ copolymer. Synthesis of Neutral Polymer nPFNT2 The polymerization of 3,3'-(2-methyl-7-(5-methylthieno[3,2-b]thiophen-2-yl)-9H- fluorene-9,9-diyl)bis(N,N-dimethylpropan-1-amine) is described (see Fig.1B). To a clean ^^^ pressured vial, 2,5-dibromothieno[3,2-b]thiophene (300 mg, 1 mmol), FNB (500 mg, 0.84 mmol), potassium carbonate (K2CO3, 1.25 g, 9.6 mmol), 1,4-dioxane (dioxane, 8 mL, 90.4 mmol), DI H2O (7.0 mL, 277.0 mmol), and Pd(dppf)Cl2(4 mg, 0.005 mmol) were added. The entire reaction vessel, including the solution, was flushed with N2(g). The pressured vial was placed into a silicon oil bath, stirred, and heated at 100 °C for 48 hours. To stop the reaction, ^^^ the stirring function was turned off, and the polymer in the dioxane layer was pipetted into DI H2O to induce precipitation of poly((9,9-di(N,N-dimethylpropan-1-amine-3-yl)-9H-fluorene-2,7- diyl)-alt-(thieno[3,2-b]thiophen-2,5-diyl)) (nPFNT2), decanted, and vacuum filtrated to dry. Synthesis of Conjugated Polyelectrolyte PFNT2 ^^^ The synthesis of the conjugated polyelectrolyte 3-(2-methyl-7-(5-methylthieno[3,2- b]thiophen-2-yl)-9-(3-(trimethylammonio)propyl)-9H-fluoren-9-yl)propyl)-l4- azaneyl)methylium (PFNT2) is described (see Fig.1B). In-situ quaternization of nPFNT2 was done with the addition of iodomethane (MeI, 4 mL, 62 mmol) directly to the remaining dioxane layer containing nPFNT2 and was left to react for 2 hours before the addition of DI H2O, to ^^^ assist in the dissolution of the polymer. The solution for reaction was then heated to 50 °C for 5 days and aliquots of DI H2O were systematically added until there was no more headspace in the 250 mL pressured vial and the polymer was well dissolved. The solution was then dialyzed via the Thermo Scientific™ Slide-A-Lyzer Dialysis Cassette (10,000 dalton MWCO) submerged in a vat of DI H2O. The DI H2O was exchanged with fresh DI H2O every day for 3 days. After ^^^ 3 days, the dialyzed solution of PFNT2 was concentrated under reduced pressure, filtered, transferred into multiple 25 mL Falcon tubes, and lyophilized to yield poly((9,9-di(N,N,N- trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7-diyl)-alt-(thieno[3,2-b]thiophen-2,5-diyl)) (PFNT2) as a rusty-brown solid (65.03% yield). The1H NMR spectrum of PFNT2 (obtained in Attorney Docket 8883-0013 D2O at 800 MHz) is shown in Fig.16 (1H NMR: ^ 2.07, 2.13, 2.16, 2.24, 2.85, 3.01-3.13, 7.05, 7.10, 7.30-7.46, 7.38, 7.57, 7.71, 7.76, 7.81, 7.90, 7.94, 8.01, 8.09); the spectrum indicates a small water suppression peak at ~4.7 ppm and trace amounts of acetone. The 9,9-di(N,N,N- trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7-diyl is the ionic donor repeat unit, and the ^^ thieno[3,2-b]thiophen-2,5-diyl is the second donor repeat unit. The ionic donor repeat unit is the aryl fluorene functionalized at the 9-carbon with the cationic quaternary group, a gem- di(trimethyl alkyl ammonium) group, di(N,N,N-trimethylpropan-1-ammonium-3-yl) as the donor ionic group. The donor ionic group includes a donor electrical charge of +2 e (i.e., a 2+ electrical charge, 2 positive elementary electrical charges). The second donor repeat unit, ^^^ thieno[3,2-b]thiophen-2,5-diyl, is nonionic. The PFNT2 was used as an electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer. Synthesis of Neutral Polymer nPFNF2 The polymerization of 3,3'-(2-(2,3-difluoro-4-methylphenyl)-7-methyl-9H-fluorene-9,9- ^^^ diyl)bis(N,N-dimethylpropan-1-amine) is described (see Fig.1B). To a clean pressured vial 1,4- dibromo-2,3-difluorobenzene (300 mg, 0.98 mmol), FNB (500 mg, 0.84 mmol), potassium carbonate (K2CO3, 1.25 g, 9.6 mmol), 1,4-dioxane (dioxane, 8 mL, 90.4 mmol), DI H2O (7.0 mL, 277.0 mmol), and Pd(dppf)Cl2 (4 mg, 0.005 mmol) were added. The entire reaction vessel, including the solution, was flushed with N2(g). The pressured vial was placed into a ^^^ silicon oil bath, stirred, and heated at 100 °C for 48 hours. To stop the reaction, the stirring function was turned off and the polymer in the dioxane layer was pipetted into DI H2O to induce precipitation of poly((9,9-di(N,N-dimethylpropan-1-amine-3-yl)-9H-fluorene-2,7-diyl)-alt-(2,3- difluorophenyl-1,4-diyl)) (nPFNF2), decanted, and vacuum filtrated to dry. ^^^ Synthesis of Conjugated Polyelectrolyte PFNF2 The synthesis of the conjugated polyelectrolyte 3,3'-(2-(2,3-difluoro-4-methylphenyl)-7- methyl-9H-fluorene-9,9-diyl)bis(N,N,N-trimethylpropan-1-aminium) is described (see Fig.1B). In-situ quaternization of nPFNF2 was done with the addition of iodomethane (MeI, 4 mL, 62 mmol) directly to the remaining dioxane layer containing nPFNF2 and was left to react for ^^^ 2 hours before the addition of DI H2O, to assist in the dissolution of the polymer. The solution for reaction was then heated to 50 °C for 5 days and aliquots of DI H2O were systematically added until there was no more headspace in the 250 mL pressured vial and the polymer was well dissolved. The solution was then dialyzed via the Thermo Scientific™ Slide-A-Lyzer Dialysis Attorney Docket 8883-0013 Cassette (10,000 dalton MWCO) submerged in a vat of DI H2O. The DI H2O was exchanged with fresh DI H2O every day for 3 days. After 3 days, the dialyzed solution of PFNF2 was concentrated under reduced pressure, filtered, transferred into multiple 25 mL Falcon tubes, and lyophilized to yield poly((9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7- ^^ diyl)-alt-(2,3-difluorophenyl-1,4-diyl)) (PFNF2) as a light grey solid (79.08% yield). The 1H NMR spectrum of PFNF2 (obtained in D2O at 800 MHz) is shown in Fig.17 (1H NMR: ^ 2.07, 2.10, 2.13, 2.15, 2.28, 2.33, 2.33, 2.85, 3.01, 3.07, 3.18, 7.48, 7.58, 7.60, 7.63, 7.73- 7.89, 8.13, 8.21); the spectrum indicates a small water suppression peak at ~4.7 ppm and trace amounts of acetone. The 9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7- ^^^ diyl is the ionic donor repeat unit, and the 2,3-difluorophenyl-1,4-diyl is the second donor repeat unit. The ionic donor repeat unit is the aryl fluorene functionalized at the 9-carbon with the cationic quaternary group, a gem-di(trimethyl alkyl ammonium) group, di(N,N,N- trimethylpropan-1-ammonium-3-yl) as the donor ionic group. The donor ionic group includes a donor electrical charge of +2 e (i.e., a 2+ electrical charge, 2 positive elementary electrical ^^^ charges). The second donor repeat unit, 2,3-difluorophenyl-1,4-diyl, is nonionic and is phenylene functionalized with two (2) fluorine atoms, which are halogen electron-withdrawing groups. The PFNF2 was used as an electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer. ^^^ Synthesis of Neutral Polymer nPFNB The polymerization of 3,3'-(2-methyl-7-(p-tolyl)-9H-fluorene-9,9-diyl)bis(N,N- dimethylpropan-1- amine) is described (see Fig.1B). To a clean pressured vial 1,4- dibromobenzene (300 mg, 0.74 mmol), FNB (500 mg, 0.84 mmol), potassium carbonate (K2CO3, 1.25 g, 9.6 mmol), 1,4-dioxane (dioxane, 8 mL, 90.4 mmol), DI H2O (7.0 mL, 277.0 mmol), and ^^^ Pd(dppf)Cl2(4 mg, 0.005 mmol) were added. The entire reaction vessel, including the solution, was flushed with N2(g). The pressured vial was placed into a silicon oil bath, stirred, and heated at 100 °C for 48 hours. To stop the reaction, the stirring function was turned off and the polymer in the dioxane layer was pipetted into DI H2O to induce precipitation of poly((9,9-di(N,N- dimethylpropan-1-amine-3-yl)-9H-fluorene-2,7-diyl)-alt-(phenyl-1,4-diyl)) (nPFNB), decanted ^^^ and vacuum filtrated to dry. Synthesis of Conjugated Polyelectrolyte PFNB Attorney Docket 8883-0013 Conjugated polyelectrolyte 3,3'-(2-methyl-7-(p-tolyl)-9H-fluorene-9,9-diyl)bis(N,N,N- trimethylpropan-1-aminium). In-situ quaternization of nPFNB was done with the addition of iodomethane (MeI, 4 mL, 62 mmol) directly to the remaining dioxane layer containing nPFNB and was left to react for 2 hours before the addition of DI H2O, to assist in the dissolution of the ^^ polymer. The reaction was then heated to 50 °C for 5 days and aliquots of DI H2O were systematically added until there was no more headspace in the 250mL pressured vial and the polymer was well dissolved. The solution was then dialyzed via the Thermo Scientific™ Slide- A-Lyzer Dialysis Cassette (10,000 dalton MWCO) submerged in a vat of DI H2O. The DI H2O was exchanged with fresh DI H2O every day for 3 days. After 3 days, the dialyzed solution of^^^ poly((9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7-diyl)-alt-(phenyl-1,4- diyl)) (PFNB) was concentrated under reduced pressure, filtered, transferred into multiple 25 mL Falcon tubes, and lyophilized to yield PFNB as a light-yellow solid (61.41% yield). The 1H NMR spectrum of PFNB (obtained in D2O at 800 MHz) is shown in Fig.18 (1H NMR: ^ 2.07, 2.10, 2.13, 2.15, 2.28, 2.33, 2.33, 2.85, 3.01, 3.07, 3.18, 7.48, 7.58, 7.60, 7.63, 7.73- 7.89, ^^^ 8.13, 8.21); the spectrum indicates a small water suppression peak at ~4.7 ppm and trace amounts of acetone and hexanes, with broadening of the baseline observed around 6.5-7.3 ppm due to low solubility. The 9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7- diyl is the ionic donor repeat unit, and the phenyl-1,4-diyl is the second donor repeat unit. The ionic donor repeat unit is the aryl fluorene functionalized at the 9-carbon with the cationic^^^ quaternary group, a gem-di(trimethyl alkyl ammonium) group, di(N,N,N-trimethylpropan-1- ammonium-3-yl) as the donor ionic group. The donor ionic group includes a donor electrical charge of +2 e (i.e., a 2+ electrical charge, 2 positive elementary electrical charges). The second donor repeat unit, phenylene, is nonionic. The PFNB was used as an electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer. ^^^ Synthesis of Neutral Polymer nPFNF4 The polymerization of 3,3'-(2-(2,3,5,6-tetrafluoro-4-methylphenyl)-7-methyl-9H- fluorene-9,9-diyl)bis(N,N-dimethylpropan-1-amine) is described (see Fig.1B). To a clean pressured vial, 1,4-dibromo-2,3,5,6- tetrafluorobenzene (300 mg, 1.05 mmol), FNB (500 mg, ^^^ 0.84 mmol), potassium carbonate (K2CO3, 1.25 g, 9.6 mmol), 1,4-dioxane (dioxane, 8 mL, 90.4 mmol), DI H2O (7.0 mL, 277.0 mmol), and Pd(dppf)Cl2 (4 mg, 0.005 mmol) were added. The entire reaction vessel, including the solution, was flushed with N2(g). The pressured vial was placed into a silicon oil bath, stirred, and heated at 100 °C for 48 hours. To stop the Attorney Docket 8883-0013 reaction, the stirring function was turned off and the polymer in the dioxane layer was pipetted into DI H2O to induce precipitation of poly((9,9-di(N,N-dimethylpropan-1-amine-3-yl)-9H- fluorene-2,7-diyl)-alt-(2,3,5,6-tetrafluorophenyl-1,4-diyl)) (nPFNF4), decanted, and vacuum filtrated to dry. ^^ Synthesis of Conjugated Polyelectrolyte PFNF4 The synthesis of the conjugated polyelectrolyte 3,3'-(2-(2,3,5,6-tetrafluoro-4- methylphenyl)-7-methyl-9H-fluorene-9,9-diyl)bis(N,N,N-trimethylpropan-1-aminium) is described (see Fig.1B). In-situ quaternization of nPFNF4 was done with the addition of ^^^ iodomethane (MeI, 4 mL, 62 mmol) directly to the remaining dioxane layer containing nPFNF4 and was left to react for 2 hours before the addition of DI H2O, to assist in the dissolution of the polymer. The reaction was then heated to 50 °C for 5 days and aliquots of DI H2O were systematically added until there was no more headspace in the 250 mL pressured vial and the polymer was well dissolved. The solution was then dialyzed via the Thermo Scientific™ Slide- ^^^ A-Lyzer Dialysis Cassette (10,000 dalton MWCO) submerged in a vat of DI H2O. The DI H2O was exchanged with fresh DI H2O every day for 3 days. After 3 days, the dialyzed solution of poly((9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7-diyl)-alt-(2,3,5,6- tetrafluorophenyl-1,4-diyl)) (PFNF4) was concentrated under reduced pressure, filtered, transferred into multiple 25 mL Falcon tubes, and lyophilized to yield PFNF4 as a grey solid ^^^ (74.6% yield). The1H NMR spectrum of PFNF4 (obtained in D2O at 800 MHz) is shown in Fig.19 (1H NMR: ^ 2.07-2.20, 2.13, 2.16, 2.30-2.41, 2.35, 2.85-2.94, 3.01-3.13, 3.07, 7.48, 7.49- 7.67, 7.72, 7.59, 7.61, 7.73-7.85, 7.79, 8.02-8.14, 8.13); the spectrum indicates a small water suppression peak at ~4.7 ppm and trace amounts of acetone. The 9,9-di(N,N,N-trimethylpropan- 1-ammonium-3-yl)-9H-fluorene-2,7-diyl is the ionic donor repeat unit, and the 2,3,5,6- ^^^ tetrafluorophenyl-1,4-diyl is the second donor repeat unit. The ionic donor repeat unit is the aryl fluorene functionalized at the 9-carbon with the cationic quaternary group, a gem-di(trimethyl alkyl ammonium) group, di(N,N,N-trimethylpropan-1-ammonium-3-yl) as the donor ionic group. The donor ionic group includes a donor electrical charge of +2 e (i.e., a 2+ electrical charge, 2 positive elementary electrical charges). The second donor repeat unit, 2,3,5,6-tetrafluorophenyl- ^^^ 1,4-diyl, is nonionic and is phenylene functionalized with four (4) fluorine atoms, which are halogen electron-withdrawing groups. The PFNF4 was used as an electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer. Attorney Docket 8883-0013 Molecular Weight Determination To measure molecular weights of CPEs, neutral precursor conjugated polymers can be formed, and these can be quaternized to form CPEs. Standard size-exclusion chromatography (SEC) measurements (e.g., high-temperature size exclusion chromatography (HT-SEC) measurements) ^^ may then be able to be conducted (doable) on the neutral precursors. SEC measurements were able to be performed on nPFNF2 with tertiary dimethylamine sidechains – the neutral precursor to the PFNF2 CPE. The calculated number-average molecular weight (Mn) was ~84,000 g / mol, weight-average molecular weight (Mw) was ~140,000 g / mol, and polydispersity (Mw / Mn) was ~1.7. Such a molecular weight (MW) corresponds to a degree of polymerization (DP) of ~311. ^^^ The molecular weight distribution for nPFNF2 is shown in Fig.20, and the calculated statistics are shown in Table 1. The other neutral precursor polymers were insufficiently soluble in both warm tetrahydrofuran (THF) and hot (150 °C) trichlorobenzene to obtain data of quality comparable to that obtained for nPFNF2. However, the synthetic procedures for all donor CPEs were identical. Thus, it is reasonable to expect that the molecular weights of all the donor ^^^ polymers are comparable (similar). Table 1. Polymer Molecular Weight ^^^ Conjugated Polyelectrolyte Complex (CPEC) (Sample) Preparation For the conjugated polyelectrolyte complex (CPEC), the electronic energy transfer (EET) acceptor conjugated polyelectrolyte (CPE) polymer and the electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer can be in a solution, for example, in an aqueous solution, such as in solution in water. CPEC solutions with the electronic energy ^^^ transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer and the electronic energy transfer (EET) acceptor conjugated polyelectrolyte (CPE) polymer at a predetermined electrical charge ratio of donor (e.g., PFNX) electrical charges : acceptor (e.g., PTAK) electrical charges can be prepared based on the number of electrical charges per (co-)monomer unit (the PFNX co- monomer (ionic donor repeat unit and second donor repeat unit together) carries an electrical Attorney Docket 8883-0013 charge of 2+ (2 positive elementary electrical charges, +2 e), and the ionized PTAK monomer (acceptor repeat unit) carries a 1− electrical charge (1 negative elementary electrical charge, -1 e)). For example, CPEC solutions can be formed with the ratio of donor electrical charges : acceptor electrical charges in a range of from about 20:80 to about 80:20, in a range of from ^^ about 40:60 to about 95:5, in a range of from about 50:50 to about 90:10, in a range of from about 60:40 to about 80:20, or in a range of from about 65:35 to about 75:25. For example, the ratio of donor electrical charges : acceptor electrical charges can be at least about 70:30. For example, the ratio of donor electrical charges : acceptor electrical charges can be about 70:30. In these studies, stock solutions of PFNX CPEs and PTAK (3.0 mg / mL) were prepared in ^^^ HPLC-grade water (Sigma-Aldrich) and complexed in desired molar ratios to form CPECs. To ensure optical clarity, the PTAK stock solution was stirred at ^70 °C for 24 h, and the PFNX stock solutions were stirred at ^70 °C for 72 h. Exposure to ambient light was minimized, and CPEC solutions were vigorously degassed with argon prior to performing optical measurements. CPEC solutions with PFNX / PTAK at an electrical charge ratio of 70:30 (donor (PFNX) ^^^ electrical charges : acceptor (PTAK) electrical charges) were prepared based on the number of electrical charges per (co-)monomer unit, as the PFNX co-monomer (ionic donor repeat unit and second donor repeat unit together) carries an electrical charge of 2+ (2 positive elementary electrical charges, +2 e), and the ionized PTAK monomer (acceptor repeat unit) carries a 1− electrical charge (1 negative elementary electrical charge, -1 e). 0.25 mg / mL PFNX and ^^^ 0.1072 mg / mL PTAK solutions were mixed to make samples. PFNX was added directly to PTAK at the desired electrical charge ratio. CPEC solutions were then stirred at 70 °C for 24 h. Steady-State Spectroscopic Measurements Optical density (OD, absorption) measurements were collected from the above-discussed ^^^ solutions using a UV-2700 Shimadzu spectrometer. Spectra were collected over the 300−800 nm wavelength range in 1.0-nm increments, with a 1-mm pathlength quartz cuvette. Photoluminescence (PL) and photoluminescence excitation (PLE) spectra were collected using a Horiba Fluoromax-4 spectrometer in a right-angle geometry. In photoluminescence measurements, the excitation wavelength was set to each respective CPE’s peak absorption ^^^ wavelength, ranging from 330-445 nm for PFNX donors and 550 nm for the acceptor PTAK. The PL intensity was then collected in the 350−800 nm range in 1-nm increments, with excitation and emission slit widths set to 1 nm bandpass. For photoluminescence excitation measurements, the fixed emission wavelength was set to 715 nm, and the excitation wavelength Attorney Docket 8883-0013 was scanned from 300 to 800 nm in 1-nm increments, with excitation and emission slit widths set to 2 nm bandpass. Time-Resolved Photoluminescence (TRPL) ^^ Time-correlated single photon counting (TCSPC) measurements were carried out on a laboratory-built setup.9The excitation source was a pulsed picosecond SuperK EXTREME (NKT Photonics) supercontinuum laser coupled to a SuperK SELECT (NKT Photonics) acousto- optic filter and external radio-frequency (RF) driver (NKT Photonics) to select the wavelength of the excitation pulse. With the supercontinuum laser, both the native thiophene-containing sub- ^^^ family and the corresponding CPEC samples were excited at wavelengths relative to the donor and acceptor PTAK: 425 nm and 600 nm, respectively. Some PFNX samples were excited at 375 nm by a pulsed picosecond diode laser (BDS-SM Series, Becker and Hickl, GmbH). Emission was measured on a hybrid photomultiplier tube (Becker and Hickl, GmbH). The signals were then sent to a Simple Tau SPC-130 (Becker and Hickl, GmbH) for initial data ^^^ visualization and analysis. Long-pass filters were used on the detection arm with either a 400 nm, 475 nm, or 590 nm onset, depending on either the donor or acceptor excitation wavelength in CPEC or native CPE solutions. Subsequently, the monochromator was set to collect emission intensity at 410 nm, 475 nm, and 620 nm. All measurements were taken with a right angle Starna Cell quartz cuvette, while the excitation and detection Glan-Thompson ^^^ polarizers were offset from each other by the magic angle (54.7º) to minimize polarization effects. Small Angle X-ray Scattering Small angle X-ray scattering (SAXS) measurements were conducted at the Stanford ^^^ Synchrotron Radiation Lightsource at beamline 4-2. This beamline is equipped with a Pilatus 3X detector and a robotic autosampler that feeds samples from a 96-well plate to a thin-walled quartz capillary cell. To avoid degradation, each sample was oscillated during the duration of exposure to X-ray radiation. The samples were irradiated with 10 consecutive 1-second (1-s) exposures at 11 keV at a sample distance of 1.7 m. This setup yielded an effective Q-range of ^^^ 0.0068-0.67 ^-1. With the aid of the SAStools software suite, averaged, totaled, and background-subtracted datasets were used in the analysis and plotting of SAXS data. Ultrafast Transient Absorption Spectroscopy Attorney Docket 8883-0013 Transient absorption (TA) measurements were obtained on a provided setup.26Experimental details follow. Ultrafast excitation and probe pulses were generated using the amplified output of a Ti:sapphire laser (Coherent Legend Elite, 800 nm center wavelength, ^35 fs pulse duration, 3.5 mJ / pulse, 1 kHz repetition rate). Excitation pulses at 400 nm were ^^ generated by second harmonic generation (SHG) of the 800 nm laser output in a ^-phase barium borate (Ba(BO2)2) (BBO) crystal. Excitation pulses at 360 nm and 600 nm were generated through fourth harmonic and second harmonic generation with the near-infrared (NIR) signal from an optical parametric amplifier (OPA, Coherent OperaSolo). Broadband (continuum) probe pulses (450−750 nm) were obtained via white-light generation in a 2 mm sapphire crystal ^^^ driven by a few nanojoules of the 800-nm laser fundamental. Probe pulses were transmitted through a wire-grid polarizer (Thorlabs) set at the magic angle (54.7°) with respect to the pump- pulse polarization. The polarizer is the last probe optic before the sample and is used to eliminate time-dependent polarization effects in transient absorption spectra. The path of the pump beam was aligned via a corner-cube retroreflector mounted to the carriage of a motorized ^^^ translation stage (Newport); a time delay between the pump and the probe pulses ranging from ^10 ps to 1400 ps was obtained by varying the carriage position. The effective time resolution of our experiments was determined to be 160 fs based on the resolution-limited rise of long-lived donor CPE excited-state features (vide infra). Excitation fluences that ensured limited fluence dependence in measured signals were used; for 360 and 400 nm, weak fluence dependence ^^^ below 4 mJ / cm2was found, whereas fluences below 20 uJ / cm2were used at 600 nm excitation due to a greater sensitivity to fluence at this excitation wavelength. Computational Details To calculate the center-to-center distance between the donor and acceptor backbones, the ^^^ PFNX:PTAK complexes were fully relaxed with the semiempirical quantum mechanical method GFN2-xTB with balanced treatment of non-covalent interactions, including multipole electrostatics and density-dependent dispersion contributions.27Each complex was modeled with a single PFNX donor chain with four repeat units and a single PTAK acceptor chain with five repeat units. The calculations were performed using the DFTB+ software package,28and the ^^^ relaxed structures were visualized using the VESTA program.29To calculate refined structures and transition properties of PFNX donors, density functional theory (DFT) calculations were performed using the ORCA quantum chemistry package.30The ground-state structures of isolated repeat units for PFNX (X = F4, F2, B, T1, T2) were fully optimized with the range- Attorney Docket 8883-0013 separated hybrid functional ^B97X-D3 that incorporates the DFT-D3 dispersion correction and the diffuse augmented def2-TZVPD basis set.31,32Time-dependent DFT (TDDFT) calculations with the same density functional and basis set were performed on the optimized geometries to determine oscillator strengths and transition dipole moments of their lowest excited states. ^^ Transition densities and electrical charge difference densities were computed to visualize the character of the electronic transitions. The visualization plots of electrical charge differences, transition densities, and natural transition orbitals were produced using the VMD program.33Experimental Results ^^^ Results were obtained for oppositely electrically charged CPEs in CPECs, the CPECs composed of variable cationic CPEs, which act as exciton donors, and a common anionic exciton-acceptor CPE. The synthesized exciton-donor CPE set was composed of a series of alternating copolymers, abbreviated PFNX, containing chemically identical electrically charged fluorene monomers but differing in the chemical structure of the co-monomer X. That is, X ^^^ refers to the variable monomer in the alternating copolymer series. The chemical structures of all CPEs are shown in Figs.1A and 1B. The variable monomer choice was motivated by the following. (1) It was desired to systematically vary the electronic wavefunction along the donor backbone in a tractable manner while ensuring that there would be spectral overlap with the fixed exciton acceptor. (2) It was aimed to keep the donor counterion identity and linear ionic ^^^ electrical charge density along the donor contour similar across the series. Doing so helped ensure that the electrostatic free energy of inter-polyelectrolyte complexation, which includes both the inter-polyelectrolyte binding energy and the change in entropy upon counterion release, was similar across the series. The linear electrical charge densities of the donor CPEs are (in units of e / ^) 0.34, 0.34, 0.34, 0.36, and 0.28 for PFNF4, PFNF2, PFNB, PFNT1, and PFNT2, ^^^ respectively. The common electronic energy transfer (EET) acceptor conjugated polyelectrolyte (CPE) polymer, PTAK, is a regioregular polythiophene derivative with butylcarboxylate sidechains. The choice of PTAK as the anionic acceptor CPE was partially motivated by the fact that its homo-polythiophene backbone is relatively simple compared to other anionic CPEs that could ^^^ function as exciton acceptors. Additionally, the PTAK PL quantum yield (PLQY), while low in isolation due to its collapsed coil structure, becomes substantially higher upon complexation to the donor due to the extension of the PTAK backbone.18,34 Attorney Docket 8883-0013 Without being bound by theory, at relatively early times after being formed (of order of a few days), the complexes are to a good approximation believed to be largely composed of at most a few oppositely electrically charged chains. This is consistent with the lack of significant light scattering from CPEC solutions shortly after complexation. The scattered light intensity ^^ from fresh CPEC solutions was evaluated by measuring the sample turbidity. Here turbidity is defined as the negative logarithm of the ratio of the transmitted to the incident light intensity at a nonabsorptive wavelength, which was 800 nm in this work. The turbidity in fresh CPEC solutions was negligible: the scattered light intensity increased monotonically with decreasing wavelenth, and the CPEC absorption spectrum was seen to decay to zero by 650 nm (vide infra). ^^^ Furthermore, without being bound by theory, the thermodynamic driving force for CPEC formation across the CPE series was expected to be dominated by electrostatic sidechain interactions and the increase in solution entropy due to counterion release upon complexation. Without being bound by theory, because of these factors, it was believed that the average number of chains per complex was similar and likely near two. Thus, care was taken to ensure that all ^^^ measurements were performed relatively shortly after preparing the CPEC solutions. The relative EET efficiencies were interrogated by analyzing photoluminescence (PL) excitation spectra of the complexes. The ultrafast EET dynamics were then measured using pump / probe spectroscopy. Finally, the potential differences in CPEC structure using both structural and optical probes were characterized. Figure 13A illustrates the electronic energy ^^^ transfer (EET) from the donor CPE PFNX (with X being B, F2, F4, T1, or T2) to the acceptor CPE PTAK. Photoluminescence Excitation (PLE) Spectrum Fitting for Obtaining Energy Transfer Efficiency (EET) ^^^ To extract relative energy transfer efficiencies (Erel) from PTAK photoluminescence excitation (PLE) spectra, the optical density (OD) spectrum of a dilute isolated PTAK solution was first fit to a sum of 4 Gaussian functions with unconstrained fitting parameters over the 300 nm to 700 nm range. These fitting parameters were then used as starting inputs for a constrained fit of CPEC PLE spectra. First, for each CPEC (PFNX:PTAK), the longest ^^^ wavelength above which the donor energy transfer efficiency (EET) contribution to the PTAK photoluminescence (PL) was approximately zero, such that the PLE in this region was due to directly excited PTAK alone, was identified. Then the PLE spectrum above this wavelength cutoff was fit to a sum of 4 Gaussian functions where each fitting parameter (amplitude, center, Attorney Docket 8883-0013 and width) was allowed to vary by ~10-15% of the values found in the PTAK OD fit. An additional common multiplicative scaling factor was applied identically to each Gaussian fitting function. The need to allow each OD fitting parameter to vary by ~10-15% relative to the OD fit arose because the PTAK spectrum underwent a qualitative change upon binding to a cationic ^^ donor CPE. Although a fully constrained fit was also attempted, it was clear that such a functional form was qualitatively inappropriate given the change in PLE peak position and spectrum shape on the red side compared to the isolated PTAK OD spectrum. Fits to the red side of the PLE are shown in Figs.21-30. Above the lower wavelength cutoff the PLE fit is of excellent quality. ^^^ The red-side PLE fit was then subtracted from the measured PLE spectrum to obtain the raw contribution to the PTAK PLE due to EET from the donor CPE (Subtracted PLE curves), see Figs.21-30. The integral under the resulting curve is related to the relative EET efficiency (Erel). A complication that accompanies this estimation stems from the fact that the behavior of the PLE spectrum in the donor EET region is not known. The fitted PLE on the red side, which ^^^ forms the background intensity on top of which the donor EET contribution sits, is a reasonable guess. A conservative estimate of the donor EET contribution that would partially and systematically account for the fact that the fitted background intensity corresponded to an estimate was obtained. To do so, it was observed that the normalized PTAK OD spectrum lies ^^^ well above the fitted PLE spectrum, see Figs.21-30. Thus, it was reasoned that the true PLE background intensity on top of which the donor EET contribution sits lies somewhere between the fitted spectrum and the measured OD spectrum. To obtain a minimally biased estimate of the relative EET efficiency, the (peak-normalized) PLE fit was subtracted from the (peak- normalized) OD spectrum to form a difference curve which, point by point, represented the ^^^ effective uncertainty in the true background intensity of the EET contribution. The least biased estimate was determined to be obtained by taking the background intensity as equal to half the difference curve. That is, the estimated background intensity at every wavelength was taken to lie exactly halfway between the fitted PLE spectrum and the measured OD spectrum. This contribution was further subtracted from the extracted donor EET peak (Subtracted PLE curve), ^^^ and the remaining curve was integrated to form Erel. Steady-State Photophysics Attorney Docket 8883-0013 Figure 2A shows the peak-normalized ground-state absorption spectra (or optical density, OD) of both the native anionic acceptor CPE, PTAK, and the isolated cationic donor CPE series, PFNX, in dilute, salt-free aqueous solution. By keeping the ionic fluorene monomer fixed and varying the other monomer, it was aimed to systematically alter the electronic states and thus the ^^ bandgap along the polymer series without inducing significant changes in the ionic linear electrical charge density of the CPEs. The progression in bandgap is clearly demonstrated in the shift in ^max among the donor CPEs. It is convenient to partition the PFNX donor series into two sub-families: (i) the poly(fluorene-alt-phenylene) family, with increasing fluorine content on the phenyl monomer (PFNB, PFNF2, PFNF4), and (ii) the thiophene family containing ^^^ poly(fluorene-alt-thiophene) (PFNT1) and poly(fluorene-alt-thienothiophene) (PFNT2). In what follows, the polymers are referenced by their shorthand X monomer abbreviation. The phenyl sub-family CPEs exhibit absorption spectra that are quite similar, only differing in a slight blueshift of approximately 20 nm between the polymers: ^maxfor B, F2, and F4 was 375, 348, and 332 nm, respectively. This corresponds to a slight increase in bandgap as a^^^ function of increasing fluorine substitution. The ^max for the two CPEs in the thiophene sub- family are shifted by ~30 nm corresponding to 405 nm and 435 nm for T1 and T2, respectively. The change in bandgap reflects both a change in the electronic structure of the variable monomer and any differences in the torsional potential. The latter can influence the delocalization radius of the exciton and thus the splitting between frontier orbital energy levels.35^^^ Figure 2B shows normalized photoluminescence (PL) spectra of the exciton donor series and the common exciton acceptor in isolated aqueous solution. Interestingly, although the OD peaks for fluorinated polymers are blueshifted with respect to B, the F2 and F4 peaks are effectively on top of each other. The T1 and T2 emission bands also encompass a comparable wavelength range albeit with substantially different apparent vibronic structure. All donor emission bands ^^^ have spectral overlap with the PTAK absorption spectrum, as quantified below. The native PTAK PL spectrum lies to the red of the donor polymers as expected. The large noise level given the comparable solution concentration reflects the fact that the native conformation of regioregular PTAK chains is highly coiled, leading to a very low PLQY.34With the OD and PL spectra of isolated CPE solutions characterized, CPECs were ^^^ formed. This was done by combining the polymers at the fixed molar polycation : polyanion electrical charge ratios of 70:30, respectively. Thus, in all cases the donor polymer was in molar excess. This choice was made for the following reasons: (i) this CPEC ratio produced extended PTAK chains within the complex with a PLQY that increased substantially compared to isolated Attorney Docket 8883-0013 PTAK solution; and (ii) having the acceptor CPE be the limiting component minimizes the probability that any PTAK chains remain uncomplexed. This in turn allowed PL excitation spectroscopy to be used to compare relative EET efficiencies (vide infra) by monitoring the PTAK PL signal. Figure 3A shows OD spectra of CPECs prepared with all the donor CPEs and ^^ the common acceptor CPE (PTAK). The spectra show the characteristic peak for each of the donor and acceptor components of the CPEC. The absorption bands spanning the 300 nm to 550 nm range correspond to the PFNX donors, while the broader peak centered about 525 nm corresponds to the PTAK acceptor. The steady-state EET efficiency, ^, within the CPEC across the donor CPE series was ^^^ then characterized. A way of calculating ^ from steady-state measurements is to calculate the ratio of the difference in PL intensity of the donor when it is isolated versus when it is in the presence of acceptor relative to the donor PL signal in isolation.36However, this method may lead to inaccuracies for CPECs because it relies on assuming that the PLQY of the donor is unchanged when it is electrostatically bound to the acceptor. In the CPEC this is likely a severe ^^^ assumption, as complex formation may lead to differences in the ensemble of thermally accessible conformations of the donor polymer and thus its PLQY.18Instead, it is desirable to extract ^ directly from spectra of the complex without the need to compare these to control donor-only measurements. To bypass the need to rely on such an assumption, PL excitation (PLE) spectroscopy was ^^^ used. In this measurement, the emission wavelength on the red side of the PTAK PL spectrum was fixed (715 nm) to ensure that this wavelength was significantly redshifted relative to the tail of all the donor PL spectra. The acceptor PL intensity was then measured as a function of excitation wavelength ^^^across the CPEC OD spectrum from 300 nm to 700 nm, encompassing both the donor and acceptor absorption windows. The choice to limit the lower integration ^^^ bound to 300 nm was made largely to avoid the region where the S0 ^ S2 absorption band of PTAK, T1, and T2 begins to acquire substantial amplitude. PLE spectra for all PFNX:PTAK CPECs are shown in Fig.3B. The PLE spectrum qualitatively resembles the corresponding OD spectrum of the CPEC for all donor CPEs. Since only PTAK emission is monitored in this experiment, it is expected that the PLE spectrum on the ^^^ red side will reflect the OD spectrum of PTAK. The fact that the PLE spectrum traces out the donor OD spectrum on the blue side is evidence of EET from the exciton donor to the exciton acceptor. To compare ^ across the donor series, the PLE spectra was first normalized to the intensity in the acceptor-only region, i.e., in the region to the red of ~525 nm, and it was then Attorney Docket 8883-0013 attempted to isolate the donor contribution to the PLE, ^^^^^. This procedure provides not an absolute but a relative EET efficiency, ^^^^, which can be defined as where the limits of integration encompass the 300 – 700 nm range. This approach allows ^^ elucidation of how varying monomer X while keeping the rest of the donor CPE chemical structure fixed influences ^. In estimating ^^^^from PLE spectra, calculating ^^^^^necessitates subtracting the contribution to the PLE that comes from native PTAK PL within the complex. That is, there is nonzero PTAK absorption at excitation wavelengths where the donors primarily absorb, giving ^^^ rise to a PTAK PLE background due to direct excitation of PTAK. The PLE signal due to direct PTAK excitation must then be subtracted off, but this presents a complication: on the blue side of the PLE spectrum the precise functional form of the acceptor PL signal due to direct acceptor excitation, ^^^^^^^^^^ is not known. The approach was to estimate the wavelength dependence of ^^^^^in the blue by using the Gaussian fit parameters of an isolated PTAK OD spectrum as an ^^^ initial guess for a constrained fit of the red side of the PLE spectra. The PLE fitting range was bounded from below by the excitation wavelength above which the donor contribution went to zero. More information on the procedure of fitting PLE spectra for estimating ^^^^^is provided in the section “Photoluminescence Excitation (PLE) Spectrum Fitting for Obtaining Energy Transfer Efficiency (EET)”, above. ^^^ The PLE fits together with the isolated PTAK OD spectrum are shown in Figs.21-30. The red side of the PLE spectrum is fit very well for all CPECs. Subtracting the PLE fit from the measured PLE spectrum gives the contribution to PTAK PL that comes from exciting the donor CPEs, ^^^^^^^^^^, i.e., the contribution due to EET. Although the fits on the red side of the ^^^ spectrum are of good quality, there is intrinsically an error associated with inferring ^^^^^^^^^^ in the donor region, which will give rise to an error associated with estimating the donor contribution and thus an error in ^^^^. To obtain an estimate of this error, the ^^^^^^^^^^ fit was subtracted from the PTAK OD spectrum (both normalized to the PTAK peak on the red side) to form a difference curve, the magnitude of which at every wavelength was associated with the ^^^ standard deviation of ^^^^^^^^^^. The section “Photoluminescence Excitation (PLE) Spectrum Fitting for Obtaining Energy Transfer Efficiency (EET)”, above, describes the rationale and justification for this means of estimating the error and the background intensity on top of which ^^^^^^^^^^ sits. Setting the lower limit of the integral in ^^^^^^^^^^ to 300 nm will almost Attorney Docket 8883-0013 certainly preferentially underestimate this quantity for F4 and F2. However, this should be the appropriate conservative choice for systematically avoiding having to account for potential EET between higher-energy excitonic states. To obtain insight into the ordering of ^^^^across the donor series, it is desirable to ^^ compare it to the ordering predicted by the F^rster EET model. The model assumes that the average distance between the donor and the acceptor is large compared to the spatial extent of the excitonic wavefunctions. The excitonic coupling is then assumed to be described by a dipole-dipole interaction between the point transition dipole moments of the donor and the acceptor. A natural length scale characterizing ^ called the F^rster radius ^^emerges; at this ^^^ distance the F^rster EET rate and the radiative relaxation rate are equal.37^^is determined by ^^ ^ ^^^^^^^ ^ !^ ^ ^^^ " (2)Here, ^^is in nm, ^^is the transition dipole orientation factor, is the PLQY of the donor, ^ is the refractive index of the medium taken to be that of pure water, and " is the spectral overall integral given by^^^ " ^ ^ ^^^^^#^^^^^!^^ (3)where ^^is the PL spectrum of the isolated exciton donor normalized to unit area, #^is the extinction coefficient spectrum of the isolated acceptor in units of M-1cm-1, and ^ is in nm. The transition dipole orientation factor ^2ranges from 0 to 4, where a value of 1 corresponds to parallel transition dipoles, 2 / 3 represents a random orientation, and 4 is a ^^^ consequence of dipoles that are both parallel and collinear.38^2was set to 1 for all F^rster model calculations. This was considered to be the least biased choice as it is expected that the donor and acceptor CPEs assemble to be approximately parallel. Such local complex structures are consistent with structures obtained to calculate mean separations between donor and acceptor CPE backbones (see Figs.31A-31E). ^^^ The F^rster EET efficiency ^$is related to the F^rster radius via where ^ (F^rster distance) is separation between the donor and the acceptor. To estimate ^, the center-to-center distance between the backbones was found by using semiempirical quantum mechanical calculations. Results from these calculations are shown in Table 2. ^^^ Attorney Docket 8883-0013 Table 2. Distance between the donor and acceptor CPEs as shown in Figs.31A-31E. Shown in Table 3 are the calculated values of ^$(indicated as “FRET Efficiency” in %) and the estimated values of ^^^^. The ordering of ^^^^does not follow that of ^$. ^^ PFNF4 43 2.29 17.3 13.0 84.7 142 7 6.18 PFNF2 44 2.53 17.7 12.7 87.9 99 11 3.91PFNB 41 2.93 17.9 13.2 86.1 139 14 4.27PFNT1 69 4.81 21.2 13.7 93.2 132 19 2.74PFNT2 67 5.60 21.6 13.1 94.7 218 22 3.89 ^ ^ Table 3. Measured and calculated quantities used to compute relative EET efficiencies and predictions from the F^rster model. ^ For incoherent exciton transfer described by the Fermi Golden Rule, the EET rate scales ^^^ as the product of the square of the excitonic coupling, ,^-, and a factor that ensures energy conservation between initial and final states participating in the EET process. To a first Attorney Docket 8883-0013 approximation, the latter is proportional to ", which tracks the position of the donor emission spectrum relative to that of the acceptor OD. Arguably the more interesting quantity is ,^-^ Here / ^ is the wavefunction of the donor, is that of the acceptor, ,2 is theoperator that describes the electronic coupling between the donor and the acceptor, and 0 ^^ indicates an excited state. It is ,^-that will reflect the precise excitonic wavefunctions of the donor and the acceptor and thus will encode the dependence of the delocalized electronic states on monomer X. It is instructive to divide out " to form a normalized (relative) EET efficiency ^45^6 quantity most directly related to (the square of) ,^-. Doing so implicitlyassumes that the donor exciton population undergoes rapid relaxation within its density of states ^^^ before EET takes place, since " is based on the steady-state PL spectrum of the donor. Interestingly, although ^^^^is largest for T2, ^45^6(Table 1) is largest for F4. Ultrafast Energy Transfer Dynamics Having characterized the relative EET efficiency via steady-state measurements, the ^^^ timescale over which EET occurred across the donor series was investigated. Excitons were transferred from the donor PFNB to the acceptor PTAK in approximately 240 fs.4Characterization of EET dynamics in the PFNF4:PTAK, PFNF2:PTAK, PFNT1:PTAK, and PFNT2:PTAK CPECs is discussed below. Figures 4A-4D present transient absorption spectra measured at various pump-probe ^^^ delays with the dilute aqueous solutions of the donor CPEs (isolated / no acceptors present). The gradient scale to the right of each panel maps to the pump-probe time delay in ps (corresponding contour representations of these data are presented in Figs.33A-33D). The uncomplexed polymers were excited near their absorption maxima: 360 nm for the phenyl sub-family (F2 and F4), and 400 nm for the thiophene sub-family (T1 and T2). All pump-probe spectra are ^^^ comprised of primarily two features in the wavelength range probed (450-750 nm): (1) a negative signal arising from stimulated emission of the excited donor, which has a spectral profile that approximately matches the steady-state PL spectrum of each donor; and (2) a positive signal due to excited-state transient absorption (TA) from the low-lying exciton state S1 to higher-lying states Sn. For T1 and T2, the stimulated emission signal is likely to be ^^^ overlapped partially with ground-state bleach (GSB), which lies to the blue of the emission signal. For F2 and F4, only the very red tail of the stimulated emission is observed in the spectral range probed. Attorney Docket 8883-0013 The time-dependent spectral evolution for the donor CPEs following photoexcitation appears to be qualitatively similar, involving a decay of excited donor absorption and stimulated emission over 10s-100s of picoseconds. However, the spectral evolution of PFNT1 appears to be qualitatively different from the rest of the polymers, with a rise in excited-state absorption ^^ signal in the region of ~650-700 nm and a blueshift of the absorption maximum with a corresponding reduction in the stimulated emission (450-650 nm). This spectral evolution is characteristic of intersystem crossing (ISC) from singlet to triplet excitons. Without being bound by theory, the yield for ISC may be greater for thiophene-containing conjugated polymers compared to the phenyl sub-family because of increased spin-orbit coupling due to the presence^^^ of the relatively heavy sulfur atoms. Coupling to the triplet manifold is likely promoted by intra- ring nuclear motions of the thiophene monomer. Close inspection of transient spectra for the other donor CPEs 1 ns after excitation, which reveals a weak and somewhat blue-shifted absorption relative to that of the initially populated singlet excited state, suggests that ISC may take place in all donor CPEs, but with ISC quantum yields that are less significant than the ^^^ excited T1. Without being bound by theory, the rigidity of the fused bithiophene ring in T2 may reduce vibrationally enhanced coupling, thereby lowering the ISC rate relative to T1. Figures 5A-5D present pump-probe spectra obtained with the PFNX:PTAK CPECs, which were collected under identical conditions as those used with solutions of uncomplexed donor CPE. (Contour representations of these data are presented in Figs.34A-34D). In addition ^^^ to the donor features seen in Figs.4A-4D, there are additional contributions from PTAK GSB and stimulated emission spanning from below 500 nm to above 650 nm that appear rapidly after photoexcitation (vide infra).9Without being bound by theory, the possibility that the appearance of PTAK features in transient spectra may arise from both EET from the donor CPE and direct excitation of PTAK chromophores within complexes given that the ground-state absorption of ^^^ the uncomplexed acceptor extends down to 360 nm cannot be discounted. However, the donor absorption dominates the absorption spectrum of CPECs with F2 / F4 and T1 / T2 at 360 nm or 400 nm, respectively, such that the rapid appearance of these significant features is expected to arise predominantly from EET. To assess whether the observed spectral dynamics reflect EET, the signal time ^^^ dependence at wavelengths that correspond to TA features associated with the donor CPEs was examined. When compared to the TA spectra of uncomplexed donors, a pronounced, rapid decrease in transient signals attributable to the excited donor in multiple spectral regions immediately following excitation was observed. Differences are observed in the blue at Attorney Docket 8883-0013 ~450 nm, a region that contains contributions from stimulated emission from donor CPEs, as well as in the 600-750 nm range, the region of donor TA (Figs.4A-4D) and where signal due to directly excited PTAK is minimal (cf. Figs.6A and 6B).9For T1 and T2 CPECs, there are rises at 450 nm which correspond to a rapid (sub-ps) reduction in the donor stimulated emission. The ^^ spectral dynamics that occur at 650-700 nm likewise reflect a sub-ps drop in the donor TA. The dynamics in this spectral region were noted for F2 and T2: for these complexes, an ultrafast flip from positive to negative signals was observed, consistent with an interconversion from excited donor CPEs (absorption) to excited PTAK (stimulated emission). Without being bound by theory, given that all four complexes were prepared at the same donor:acceptor ratios, the fact ^^^ that such an ultrafast flip from positive to negative signal was not observed for the F4 and T1 complexes likely indicates that there are chain regions for these donors that are not fully complexed to the acceptor. Electrically charged donor sidechains in such regions likely have partially condensed counterions as described by the Manning-Oosawa model.39The acceptor’s stimulated emission subsequently disappears as a result of PTAK exciton dynamics; without ^^^ being bound by theory, there may be some PTAK-to-PFNX electron transfer, similar to what has been observed for PFNB previously, based on the relative energies of donor and acceptor frontier orbitals.40,41In order to examine spectral contributions from directly excited PTAK, the photophysics of CPECs excited directly at 600 nm, which selectively excites the PTAK component, was ^^^ studied and these compared to the photophysics of uncomplexed PTAK. Transient absorption (TA) data for PTAK and the PFNT1:PTAK complex are presented in Figs. 6A-6B. Transient absorption data for all complexes excited at 600 nm are presented in Figs.35A-35D. Transient absorption date for pure PTAK excited at 425 nm are presented in Figs.36A-36B. The spectrum of uncomplexed PTAK exhibits signatures of both H-like excitons and “free coil” states; ^^^ excitation at 600 nm is selective for the former and gives rise to the characteristic polaron-pair absorption feature at 650 nm that is associated with electrical charge separation in ^-stacked polymer regions.18In contrast, polaron-pair absorption is not observed for PTAK in a CPEC when excited at 600 nm; instead, the region of 650-700 nm is dominated by stimulated emission. Without being bound by theory, this difference and the change in the vibronic structure of the ^^^ PTAK bleach with complexation reflect an isolation of PTAK chain segments, as discussed in more detail below. The stimulated emission observed with 600-nm excitation matches the feature observed within a few hundred femtoseconds following donor excitation (F2 and T2). The polaron-pair absorption feature observed for uncomplexed PTAK (650-700 nm) has a much Attorney Docket 8883-0013 slower spectral evolution (decay) than the ultrafast spectral evolution observed in this region for all CPECs, supporting assignment of the latter to PFNX-to-PTAK EET. Global spectral analysis subject to sequential kinetic interconversion models was used to determine timescales on which spectral dynamics occur for all donor CPEs and PFNX:PTAK ^^ CPECs. The best fitting agreement was obtained using a four-state sequential kinetic model, as expressed in Equation 5, producing sensible species associated difference spectra (SADS) that reflect the composition of excited species that give rise to TA signals for both donor CPEs and CPECs. 99 98 ;:< ;=> ;?@ (5)SADS obtained from analysis of CPEC TA spectra are presented in Figs.7A-7D, with fitted ^^^ transients at selected wavelengths presented in Figs.37A-37D. SADS obtained from global analysis of TA data obtained with uncomplexed donors and corresponding fitted transients at select wavelengths (slices) are presented in Figs.38A-38D and 39A-39D. Lifetimes corresponding with each SADS are presented in Tables 4 and 5 for complexes and donor CPEs, respectively. ^^^ Table 4. Best-fit lifetimes determined from global analysis of transient absorption (TA) data collected with PFNX:PTAK CPECs subject to a four-state sequential kinetic interconversion model (see Equation 5). Table 5. Best-fit lifetimes determined from global analysis of transient absorption (TA) data Attorney Docket 8883-0013 collected with donor CPEs subject to a four-state sequential kinetic interconversion model (see Equation 5). For F2 and F4, the SADS capture the spectral evolution expected for donor-acceptor EET: ^^ for both donors, SADS A is dominated by the singlet excited-state absorption of the donor in the red (> 550 nm) and stimulated emission below 500 nm; for both donors SADS A crosses ‘0’ at a wavelength similar to that observed in the donor CPE TA data. In contrast, SADS B is dominated by the PTAK bleach (475-625 nm). SADS B for F2 exhibits the PTAK stimulated emission (625-700 nm) observed via direct excitation of PTAK in CPECs (Figs.6B and 35A- ^^^ 35D). Without being bound by theory, the absorption that remains in this region for F4 most likely reflects uncomplexed regions of the donor in the corresponding solution. The transition from SADS B to C may indicate spectral dynamics of PTAK excited by EET and, for F4, contributions from spectral dynamics of uncomplexed regions of the donor. The differences in the PTAK bleach intensities in SADS B, C, and D may indicate a fraction of PTAK excitons that ^^^ deactivate on associated kinetic lifetimes summarized in Table 4. Without being bound by theory, electrical charge separation may be a viable quenching mechanism in PFNB:PTAK complexes probed in ultrafast experiments and is a likely origin of the long-lived bleach observed in these measurements.7,10^^^ The SADS obtained for T1 and T2 are somewhat different. In both cases, the PTAK bleach features dominantly in SADS A; this is consistent with either some direct excitation of the acceptor or very rapid (faster than the time resolution of the experiment) EET from the donor. The former is plausible, given that the excitation wavelength used for these complexes, although close to the peak of the donor absorption feature, is also closer to that of PTAK. The latter is ^^^ feasible, given the predicted rate of energy transfer (e.g., Table 7 below). Nonetheless, a rapid decay of TA (> 600 nm) and stimulated emission (< 500 nm) signatures associated with the donor occurs on a timescale of less than 200 fs. The evolution of SADS B, C, and D is largely similar across all complexes regardless of the donor, indicating that the associated spectral dynamics are largely attributed to excited PTAK. ^^^ Figures 8A-8D compare the measured time-dependence for donor CPEs and PFNX:PTAK complexes at a probe wavelength of 740 nm together with fits generated from global spectral analysis. These comparisons highlight the differences in excited donor CPE lifetimes upon complexation with PTAK that is consistent with rapid inter-CPE EET. Overall, Attorney Docket 8883-0013 the fits are of excellent quality, which allows quantitative extraction of the EET time scales across the donor series. The EET rates (inverse EET times) from global analysis (τ1 from Equation 5, values listed in Table 6) are shown in Table 7 along with EET rates calculated from the F^rster model according to ^^ (6) where I^is the average radiative lifetime of the isolated donor. Table 6. Deconvolved PL lifetimes, component amplitudes, and average PL lifetimes. PFNF4 PFNF2 PFNT1 PFNT2 EET rate (ps-1) 6.41 4.24 10.4 7.46 Förster ET Rate 0.03 0.05 0.06 0.10 (ps-1) ^^^ Table 7. Measured EET rates from global analysis along with estimations using the F^rster model. Attorney Docket 8883-0013 The PL lifetime at room temperature was used for I^, which is a lower bound given the presence of nonradiative relaxation pathways, and ^^was taken to be unity for all CPECs. From global analysis the shortest times (largest rates) were found to be associated with T1 and T2 CPECs, ^^ followed by F4, F2, and B CPECs. Although the overall trend predicted by the Förster model is observed experimentally for F2, T1, and T2, F4 stands out: its rate is comparable to T2 despite the large difference in spectral overlap. Despite some trend agreement between the model and experiment, there is also an apparent disparity between the ratios of the rates. For example, under the assumption of a similar ^^, the ratio of F$for T2 relative to F4 is ~3.0, while the ^^^ measured F^^Mratio is ~1.2. Similarly, the predicted F2 to F4 F$rate ratio is ~1.3, while the measured F^^Mratio is ~0.7. Role of CPEC Conformation Since all donor CPE have similar ionic electrical charge densities, an initial assumption ^^^ may be that the CPEC conformation is similar across the donor series. To evaluate this assumption, the CPEC conformation across the series was interrogated using structural and spectroscopic probes. Since CPECs are not expected to display long-range order, one of the more direct means of comparing the CPEC structure is to do so in reciprocal space by performing small-angle X-ray scattering (SAXS) measurements. SAXS scattering images were collected ^^^ using a synchrotron X-ray source, and the isotropic SAXS intensity was then azimuthally averaged to produce reduced 1-D scattering intensity curves as a function of scattering vector length Q. These results for all CPECs are shown in Fig.9. The scattering intensity for all CPECs is monotonically decreasing, rather featureless, and reasonably similar in appearance. This suggests that the complexes have similar microstructure. ^^^ At low Q, the approximately linear slopes on a log-log plot suggest a Q scaling with a comparable negative power-law exponent. However, closer inspection makes apparent the subtle differences between the curves. There appears to be an intermediate Q value (~0.02 ^-1) at which the slope of the scattering intensity for the F2, F4, and T1 complexes undergoes a small decrease, which is not observed for B and T2 CPECs. This observation gives a first indication ^^^ that the CPEC structures are similar but not identical across the donor series. The spectral characteristics of PTAK within the CPEC were then interrogated, since PTAK is common to each complex and may thus act as a reporter for differences in complex conformation. Using time-correlated single-photon counting, time-resolved PL (TRPL) decays Attorney Docket 8883-0013 for each CPEC while exciting at 600 nm where only PTAK absorbs were collected. These results are shown in Fig. 10. Each decay curve is well-described by a convolution of the instrument response function (IRF) with a sum of two exponential decays, with the relatively short component being dominant. Fitting parameters following deconvolution of the IRF are ^^ shown in Table 6. PTAK in the T2 CPEC gave the shortest average PL lifetime (119 ps), while F4 gave the largest (150 ps). F2, B, and T1 show similar fast components, only showing subtle differences in the low-amplitude long component. Ultrafast ground state bleach (GSB) spectra of CPECs when PTAK is directly and exclusively excited within the complex at 600 nm were then compared. None of the donor CPEs ^^^ absorb at this wavelength; thus, there is no possibility of EET. GSB spectra following 600-nm excitation at a pump-probe delay of 1 ps for all CPECs are shown in Fig.11. All the PTAK GSB spectra within the CPEC across the donor CPE series are qualitatively similar to each other and qualitatively distinct from that of isolated PTAK (Fig.6A). The similarity in PTAK GSB across different CPECs is consistent with PTAK vibronic 0-0 / 0-1 peak ratios in steady-state PL spectra ^^^ of the complexes (Fig.32), showing a J-aggregate-like vibronic ratio (0-0 intensity > 0-1 intensity). However, the wavelength onsets of GSB signals on the red side exhibit minor shifts and some differences in the ratio of the 0-0 and 0-1 peak intensities, consistent with small differences in the onset of PLE and OD spectra of the CPECs. Without being bound by theory, taken together, the SAXS, TRPL, and GSB following selective PTAK excitation all paint a ^^^ similar picture: that the CPEC microstructure is qualitatively similar across the donor CPE series but exhibits quantitative differences as a function of monomer X. Discussion The steady-state PLE and ultrafast pump / probe data show that, although some qualitative ^^^ agreement with the F^rster model is observed, the F^rster model does not account for the relative magnitude of ^^^^and the EET rate for F4 or some of the rate ratios observed. Without being bound by theory, this is not entirely surprising given the core assumption of the model, namely that the Coulombic coupling between the exciton donor and acceptor could be described as a dipole-dipole interaction between point transition dipole moments. This assumption averages ^^^ away details of the spatially extended transition densities of the two EET partners. As such, the F^rster model may become a progressively poorer approximation as the separation between the centers of mass of the two species becomes comparable to the lengths of their respective chromophores, i.e., the spatial extent of the excitonic wavefunctions. Even for pigment Attorney Docket 8883-0013 molecules in natural light-harvesting antenna complexes, such as chlorophyll and carotenoid derivatives, the F^rster approximation cannot always be justified.42Division of ^^^^by the spectral overlap integral further suggests that the excitonic coupling ,^-may differ substantially across the CPEC series. Specifically, it appears to be ^^ largest for F4 and comparable for F2 and T2. In calculating ^^^^it was implicitly assumed that relaxation rate of donor excitons immediately following photoexcitation is faster than the EET rate. Given the relatively large EET rates measured, this assumption can be reasonably questioned. In the extreme case, the EET rate may be comparable or faster than the relaxation rate of the donor exciton. In such a case, division by " may no longer be justified to isolate ,^-. ^^^ However, even in this case, the EET rate should scale like ,^-multiplied by the density of final states at the exciton energy. The latter is expected to still be related to the magnitude of the PTAK absorption spectrum at that energy. The fact that the PTAK OD ratio for 400 nm relative to 360 nm (the wavelengths used to pump T2 and F4, respectively) is ~2 while the ratio of ^^^^and EET rates for T2 relative to F4 are ~1.5 and ~1.2, respectively, suggests that the same ^^^ conclusion about the difference in ,^-for T2 vs. F4 holds qualitatively as when " is divided out. As mentioned above, ^^^^is likely preferentially underestimated for F4 compared to T2 given the deliberately limited PLE integration window. An objective is to understand why ^^^^and the EET rate for F4 are as large as they are given the fact that F4 has the smallest spectral overlap integral (or expectedly smallest density of ^^^ final states at the pump wavelength). Towards understanding this, several useful parameters of isolated donor CPE repeat units at the level of (time-dependent) density functional theory (DFT) were calculated. Although the calculations were performed on a single repeat unit, this still provides a valuable comparison across the donor series treated on an equal footing. That the calculation is carried out in vacuum means that the role of the environment on the repeat unit ^^^ conformation is not taken into account. However, it is expected that, to a good approximation, the intrinsic monomer-monomer interactions will dominate the electronic structure of the repeat unit. The results of these calculations are shown in Table 8. Two primary takeaways stand out. The equilibrium torsion (dihedral) angle between the fluorene monomer and monomer X varies significantly (see Fig.41 for the explicit definition of the torsional angle). F4 has by far the ^^^ largest angle (most twisted monomers), followed by F2 and B, while the thiophene-containing repeat units have the smallest angles. The ordering of the transition dipole moments is opposite, with T2 having the largest value and F4 the smallest. Attorney Docket 8883-0013 PFNF4 PFNF2 PFNB PFNT1 PFNT2 Torsional Angle 61.0° 53.3 ° 43.8 ° 34.5 ° 33.5° Transition Dipole 2.31 2.47 2.63 3.01 3.58 Magnitude Oscillator Strength 0.640 0.728 0.817 1.021 1.378 Table 8. Repeat unit calculations using DFT and TDDFT at the ^B97X-D3 / def2-TZVPD level of theory. Torsional angles along the linkage bonds of copolymer units for PFNX are calculated for the ground-state equilibrium geometries; transition dipole moments along the linkage axis and oscillator strengths are calculated for the lowest excited states.^ ^^ The transition densities of the repeat units are plotted in Fig.12. The transition density on the fluorene monomer is similar for all. However, the thiophene and thienothiophene monomers contain a significantly larger share of the transition density than the F2 and F4 repeat units, leading to a correspondingly larger degree of electrical charge transfer across the two ^^^ monomers (see Figs.42A-42D) for electrical charge difference densities between the ground states and the lowest excited states of PFNF4, PFNF2, PFNT1, and PFNT2). This suggests that over the length of a donor polymer chromophore the transition density for F2 and F4 will display significant position-dependent variations in magnitude, whereas for T1 and T2 the transition density will depend significantly more weakly on position along the chromophore. ^^^ The implications of these calculations for EET within CPECs can be considered. First considered is the influence of the torsion angle. In conjugated polymers, the excitonic wavefunction can be described as a product of (i) a center-of-mass (envelope) wavefunction that dictates the spatial extent of the exciton and (ii) a relative wavefunction that describes the probability to observe the electron and the hole at a given separation.43,44It is reasonable to ^^^ expect that as the torsion angle increases, the center-of-mass excitonic wavefunction will become dynamically more localized, leading to a smaller mean exciton extent. Thus, it is expected that F4 will have the smallest exciton radius. To appreciate the significance of this expectation for EET, it is instructive to consider the line-dipole approximation, which is an improvement on the F^rster model for conjugated polymers. Within this approximation, the electronic coupling ^^^ between two proximal conjugated polymer chains is given by a sum of pairwise interactions Attorney Docket 8883-0013 between transition dipole moments of each monomer on the first chain with that of each monomer on the second chain. The specific monomer-monomer interaction is still described by the dipole term in the multipole expansion of the full Coulomb interaction. This approximation might not be excellent given the relatively small separation between the donor and the acceptor ^^ within the CPEC. The approximate condition for its validity is that the length of the repeat unit be significantly smaller than the center-to-center separation between the two parallel conjugated- polymer chains, which is not expected to be completely fulfilled in the CPECs. A more accurate way of describing the excitonic coupling is the transition-density cube method, but it is computationally taxing and does not readily yield qualitative insight.45In contrast, the line- ^^^ dipole approximation provides significant qualitative insight that can aid interpretation of the results. It has been shown analytically that for parallel conjugated polymer chains within the line- dipole approximation, the excitonic coupling is a decreasing function of chromophore length, i.e., the length over which the excitonic wavefunction is coherently delocalized.46For identical ^^^ chains, ,^-NOP, where O is the chromphore length, and Q ranges from 1 to ~2 depending on the assumptions made about the functional form of the center-of-mass excitonic wavefunction. In other words, as the exciton radius decreases, the excitonic coupling is expected to increase. The analytical results are supported by quantum-chemical calculations, which show that the coupling increases as either the donor or the acceptor chromophore length decreases as soon as the ^^^ chromophore length extends beyond a couple of repeat units.47,48Without being bound by theory, these analytical and computational results provide an explanation for why F4 stands out in the magnitude of its ^^^^and its relatively large EET rate given its relatively large bandgap and, thus, poor spectral overlap with PTAK. Its largest torsion angle likely leads to the smallest extent of the center-of-mass excitonic wavefunction. ^^^ Moreover, the red edge of the OD and the PLE spectra for the F4 CPEC (blue curves in Figs.3A and 3B, respectively) show that the PTAK region is most blue-shifted compared to the rest of the CPECs. Within the particle-in-a-box approximation, this suggests that the spatial extent of the PTAK exciton is also smallest for the F4 CPEC. Taken together, these observations may be responsible for the apparently disproportionately large excitonic coupling in the F4 CPEC. The ^^^ fact that ^45^6is comparable for F2 and T2 may result from the following: although the torsion angle for F2 is larger than that of T2, the transition dipole moment of the T2 repeat unit is larger than that of the F2 repeat unit. It is not entirely clear what the source of the disagreement Attorney Docket 8883-0013 between the relative position of ^45^6for T1 within the donor series compared to its measured EET rate is. In the electronic energy transfer donor conjugated polyelectrolyte (CPE) copolymer, the ^^ ionic donor repeat unit (e.g., 9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7- diyl) and the second donor repeat unit (e.g., 2,3,5,6-tetrafluorophenyl-1,4-diyl for PFNF4 (F4)) are in torsion with respect to each other through (across) the linkage bond covalently joining them. This torsion can be quantified by a torsional angle that is the dihedral angle between the plane defined by C3 (the carbon in the second donor repeat unit on one end of the linkage bond), ^^^ C2 (carbon in the ionic donor repeat unit on the other end of the linkage bond), and C1 (carbon adjacent and bonded to C2 in the ionic donor repeat unit) and the plane defined by C2, C3, and C4 (carbon adjacent and bonded to C3 in the second donor repeat unit). Examples of this are illustrated in Fig.41. For example, across the linkage bond joining the ionic donor repeat unit 9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7-diyl and the second donor ^^^ repeat unit 2,3,5,6-tetrafluorophenyl-1,4-diyl (e.g., in the PFNF4 donor conjugated polyelectrolyte (CPE) copolymer) the torsional angle was calculated to be 61.0°. In each of the PFNF4, PFNF2, PFNT1, PFNT2, and PFNB polymers, a planar aromatic moiety on the ionic donor repeat unit (i.e., a phenyl moiety on the fluorene of the 9,9-di(N,N,N- trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7-diyl) is bonded through the linkage bond to^^^ a planar aromatic moiety on the second donor repeat unit (e.g., phenyl moiety of 2,3,5,6- tetrafluorophenyl-1,4-diyl in PFNF4). If there were no torsion between the ionic donor repeat unit and the second donor repeat unit (i.e., a torsional angle of 0°), then the bonded planar aromatic moiety on the ionic donor repeat unit and the planar aromatic moiety on the second donor repeat unit would be co-planar. Without being bound by theory, the molecular ^-orbital^^^ (pi-orbital) of the planar aromatic moiety on the ionic donor repeat unit and the molecular ^- orbital of the planar aromatic moiety on the second donor repeat unit would then be co-planar, so that the ^-orbitals of the aromatic moieties on either side of the linkage bond would overlap, and conjugation between the aromatic moieties would approach a maximum as the torsional angle approaches 0°. That is, the delocalization of the ^ electrons between the aromatic moiety on the ^^^ ionic donor repeat unit and the aromatic moiety on the second donor repeat unit across the linkage bond would approach a maximum. Otherwise stated, as no (zero) (0°) torsion is approached, the p-orbitals (carbon atomic orbitals) of the aromatic moiety on the ionic donor repeat unit and the p-orbitals of the aromatic moiety on the second donor repeat unit become Attorney Docket 8883-0013 parallel, so that overlap of the p-orbital of the aromatic moiety on the second donor repeat unit at one end of the linkage bond and of the p-orbital of the aromatic moiety on the ionic donor repeat unit at the other end of the linkage bond across the σ-bond of the linkage bond approaches a maximum. ^^ However, without being bound by theory, with torsion between the ionic donor repeat unit and the second donor repeat unit (i.e., a torsional angle of greater than zero (greater than 0°, 0 degrees)), the molecular ^-orbital (pi-orbital) of the planar aromatic moiety on the ionic donor repeat unit and the molecular ^-orbital of the planar aromatic moiety on the second donor repeat unit are not co-planar, so that overlap of the ^-orbitals of the aromatic moieties on either side of ^^^ the linkage bond is reduced. Otherwise stated, with torsion, the p-orbitals (carbon atomic orbitals) of the aromatic moiety on the ionic donor repeat unit and the p-orbitals of the aromatic moiety on the second donor repeat unit are no longer parallel, so that overlap is reduced of the p- orbital of the aromatic moiety on the second donor repeat unit at one end of the linkage bond and of the p-orbital of the aromatic moiety on the ionic donor repeat unit at the other end of the ^^^ linkage bond across the σ-bond of the linkage bond. As a result, conjugation between the aromatic moieties is reduced and delocalization of the ^ electrons between the aromatic moiety on the ionic donor repeat unit and the aromatic moiety on the second donor repeat unit across the linkage bond is reduced as the torsional angle increases. Without being bound by theory, as a torsional angle of 90° is approached, for example, as ^^^ the torsional angle along the linkage bond increases from about 0° to greater than about 40°, greater than about 43.8°, greater than about 44°, at least about 50°, at least about 53°, at least about 60°, or at least about 61°, the p-orbitals of the aromatic moiety on the ionic donor repeat unit and the p-orbitals of the aromatic moiety on the second donor repeat unit become perpendicular to each other, so that overlap of the p-orbital of the aromatic moiety on the second ^^^ donor repeat unit at one end of the linkage bond and of the p-orbital of the aromatic moiety on the ionic donor repeat unit at the other end of the linkage bond across the σ-bond of the linkage bond approaches a minimum. As this minimum overlap of these p-orbitals and corresponding minimum overlap of the molecular ^-orbitals of the aromatic moieties is approached, conjugation between the aromatic moieties and delocalization of the ^ electrons between the aromatic moiety ^^^ on the ionic donor repeat unit and the aromatic moiety on the second donor repeat unit across the linkage bond approaches a minimum. Attorney Docket 8883-0013 Without being bound by theory, with decrease of conjugation and decrease of delocalization of the ^ electrons between the aromatic moiety on the ionic donor repeat unit and the aromatic moiety on the second donor repeat unit across the linkage bond as torsion between the ionic donor repeat unit and the second donor repeat unit increases, the excitonic ^^ wavefunction becomes more localized and the exciton radius decreases in the donor conjugated copolymer. As discussed above, the decrease in exciton radius in the donor conjugated polyelectrolyte (CPE) copolymer results in an increase in the excitonic coupling between the donor conjugated polyelectrolyte (CPE) copolymer and the acceptor conjugated polyelectrolyte (CPE) polymer. The increase in excitonic coupling results in an increase in the rate and in the ^^^ efficiency of electronic energy transfer from the donor conjugated polyelectrolyte (CPE) copolymer to the acceptor conjugated polyelectrolyte (CPE) polymer. In summary, by conducting the experiments of which the surprising and unexpected results are discussed in this application and then analyzing these results, it was found that by controlling the torsion (the torsional angle) along the linkage bond between the ionic donor ^^^ repeat unit and the second donor repeat unit, for example, through selection of substituents on the ionic donor repeat unit and / or the second donor repeat unit, the rate and efficiency of electronic energy transfer (EET) from a donor conjugated polyelectrolyte (CPE) copolymer to an acceptor conjugated polyelectrolyte (CPE) polymer can be controlled. That is, from the results of the experiments presented herein, it was found that by increasing the torsion (the torsional ^^^ angle), the rate and efficiency of electronic energy transfer (EET) from a donor conjugated polyelectrolyte (CPE) copolymer to an acceptor conjugated polyelectrolyte (CPE) polymer can be desirably increased. For example, obtained were the surprising and unexpected results that increasing the number of fluorine atoms on the phenylene of the second donor repeat unit from none (in PFNB) or two (in PFNF2) to four (in PFNF4) induced an increase in the torsion (the^^^ torsional angle) between the second donor repeat unit and the ionic donor repeat unit (9,9- di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7-diyl), with this increase in torsion resulting in an increase in the relative electronic energy transfer (EET ) and electronic energy transfer rate from the PFNF4 donor conjugated polyelectrolyte (CPE) copolymer to the acceptor conjugated polyelectrolyte (CPE) polymer (poly(3-(4-butanoate)thiophene-2,5-diyl), PTAK). ^^^ Without being bound by theory, the substitution of hydrogens on the phenylene of the second donor repeat unit with fluorines may result in steric repulsion (fluorine being bulkier than hydrogen), may result in electrostatic attraction between the (strongly electronegative and electron withdrawing) fluorines on the phenylene of the second donor repeat unit and the out-of- Attorney Docket 8883-0013 plane positively electrically charged (cationic) ammonium groups attached to the fluorene of the ionic donor repeat unit, and may result in hydrogen bonding between the fluorines (as hydrogen bond acceptors) on the phenylene of the second donor repeat unit and the ammonium groups (as hydrogen bond donors) attached to the fluorene of the ionic donor repeat unit, with the result that ^^ the phenylene of the second donor repeat unit is rotated out of the plane of the aromatic moiety of the fluorene of the ionic donor repeat unit on the other side of the linkage bond. From analyzing the results, it was found that the increase in torsion resulted in a decrease in the exciton radius, which in turn resulted in a desirable increase in the rate and efficiency of electronic energy transfer (EET) from the donor conjugated polyelectrolyte (CPE) copolymer ^^^ (e.g., PFNF4) to the acceptor conjugated polyelectrolyte (CPE) polymer (e.g., PTAK). Although the above factors may be responsible for the EET observations, there are two additional considerations. First, it is possible that the larger spatial variation in the transition density magnitude along the chromophore for F2 and F4 compared to T1 and T2 may lead to ^^^ further differences. Two potential effects may be anticipated. (i) The lateral shifts between monomers in parallel chains may lead to variations in the inter-chain excitonic coupling.14,49The somewhat smaller linear electrical charge density of T2 could be one source of an average lateral shift between donor and acceptor excitonic wavefunctions compared to other donor CPEs. (ii) As the degree of electrical charge transfer between the fluorene monomer and the variable ^^^ monomer increases, the relative wavefunction of the exciton may become a mixture of neutral Frenkel-type and electrical charge-transfer-type states.15,50Second, the results show that, although the average CPEC structures appear similar, they are not identical. Differences in structure could lead to subtle variations in the relative orientation between the donor and acceptor chromophores, which would modify the EET rate. ^^^ For example, in addition to electrostatic interactions between the polyanion and the polycation, the fluorinated benzene monomer in F4 may participate in anion-^ interactions with the carboxylate group at the terminus of the PTAK sidechain. Moreover, there may be some degree of ^-stacking between the donor and acceptor backbones, although the extent of such interactions should likely be limited due to the geometry of the electrostatic binding. Nevertheless, ^- ^^^ stacking would lead to a modification of the exciton transfer integral.15That is, a steady increase in EET efficiency of the CPEC for all donor CPEs as measured by PLE spectroscopy on a days to weeks timescale is observed, as shown in Figs.40A-40B. Without being bound be theory, this increase can be attributed primarily to the condensation of Attorney Docket 8883-0013 multiple chains onto the complex, leading to an increase in the local concentration of donor and acceptor chromophores.51This is consistent with the onset of measurable sample turbidity after approximately 1 week, in contrast to fresh CPEC solutions. In the very long-time limit, the onset of macroscopic phase separation may occur. Although EET efficiencies increase for all donor ^^ CPEs, F4 and F2 exhibit a greater increase than the rest of the donor polymers. In summary, two subfamilies of exciton-donor alternating copolymers consisting of ionic fluorene monomers alternating with thiophene-based or fluorine-substituted phenyl-based monomers (donor conjugated polyelectrolytes (CPEs)), with the linear ionic electrical charge ^^^ density fixed within a narrow range, were synthesized. The EET characteristics of these copolymers were interrogated; it was found that, although the F^rster model is qualitatively consistent with some of the EET trends observed, the F^rster model did not qualitatively account for the ordering of the entire donor CPE series and did not quantitatively account for the ratios of relative EET efficiencies and EET rates. The donor CPE containing a tetrafluoro-substituted ^^^ phenyl co-monomer displayed a disproportionately large EET rate and relative EET efficiency. Without being bound by theory, this may be a result of the excitonic coupling scaling with the mean exciton delocalization length. Although the positions of steady-state donor PL and acceptor OD spectra provide a reasonable starting point for a rough expectation of EET efficiency within a CPEC, because of the relatively small donor / acceptor separations, the precise ^^^ chemical structure of the CPE backbone influences the excitonic coupling. Towards maximizing the EET rate in a particular spectral window, this should be considered in choosing a particular donor / acceptor CPE pair. A CPEC can function as an exciton-transferring antenna component in an overarching soft-matter-based, water-based light-harvesting material. In such a material, different rate ^^^ processes may be balanced to optimize energy conversion efficiencies. Effects of subtle modifications to the chemical structure of a CPE backbone on EET should be considered in engineering CPECs as rapid relays for exciton energy transport. An embodiment of the invention pertains to optimizing electronic energy transfer (EET) in oppositely electrically charged conjugated polyelectrolyte complexes. The synthesis of a ^^^ series of conjugated polyelectrolytes (CPEs) and construction through electrostatic self-assembly of their oppositely electrically charged complexes in water shows an approach to optimize rates of electronic energy transfer in aqueous self-assemblies that can function as quasi-panchromatic excited-state energy relays. The efficiency of a photophysical step in artificial, water-based Attorney Docket 8883-0013 photosynthetic systems has been improved. A method for optimizing the use of spatially extended electronic states in water-based light-harvesting systems is provided. This allows for the simultaneous advantages of "through-bond" and "through-space" energy transfer to funnel excited-state energy to an artificial photosynthetic reaction center. ^^ In some embodiments of the invention, the electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer is an alternating copolymer, for example, with the ionic donor repeat unit and the second donor repeat unit alternating. Alternatively, the electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer can be a random copolymer or a statistical copolymer, for example, with the ionic donor repeat unit and the ^^^ second donor repeat unit distributed along the copolymer chain. Alternatively, the electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer can be a block copolymer, for example, including at least one ionic donor repeat unit block and at least one second donor repeat unit block. Alternatively, the electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer can be another type of copolymer. ^^^ The embodiments illustrated and discussed in this specification are intended only to teach those skilled in the art the best way known to the inventors to make and use the invention. Nothing in this specification should be considered as limiting the scope of the invention. All examples presented are representative and non-limiting. The above-described embodiments of ^^^ the invention may be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described.

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Manning-Oosawa Counterion Condensation. Physical Review Letters 94, 048302, doi:10.1103 / PhysRevLett.94.048302 (2005). Attorney Docket 8883-0013 40 Clark-Winters, T. L. & Bragg, A. E. Energy-Dependent Charge Separation in Conjugated Polymer Electrolyte Complexes. The Journal of Physical Chemistry C 127, 12466-12476, doi:10.1021 / acs.jpcc.3c01868 (2023). 41 Clark-Winters, T. L. & Bragg, A. E. Electron Transfer in Conjugated Polymer Electrolyte ^^ Complexes: Impact of Donor–Acceptor Interactions on Microstructure, Charge Separation, and Charge Recombination. The Journal of Physical Chemistry C 126, 19580-19593, doi:10.1021 / acs.jpcc.2c04497 (2022). 42 Andrews, D. L., Curutchet, C. & Scholes, G. D. Resonance energy transfer: Beyond the limits. Laser & Photonics Reviews 5, 114-123, ^^^ doi:https: / / doi.org / 10.1002 / lpor.201000004 (2011). 43 Barford, W., Bittner, E. R. & Ward, A. Exciton Dynamics in Disordered Poly(p- phenylenevinylene).2. Exciton Diffusion. The Journal of Physical Chemistry A 116, 10319-10327, doi:10.1021 / jp307041n (2012). 44 Barford, W. Excitons in Conjugated Polymers: A Tale of Two Particles. The Journal of ^^^ Physical Chemistry A 117, 2665-2671, doi:10.1021 / jp310110r (2013). 45 Krueger, B. P., Scholes, G. D. & Fleming, G. R. Calculation of Couplings and Energy- Transfer Pathways between the Pigments of LH2 by the ab Initio Transition Density Cube Method. The Journal of Physical Chemistry B 102, 5378-5386, doi:10.1021 / jp9811171 (1998). ^^^ 46 Barford, W. Exciton transfer integrals between polymer chains. The Journal of Chemical Physics 126, 134905, doi:10.1063 / 1.2714516 (2007). 47 Hestand, N. J. & Spano, F. C. Expanded Theory of H- and J-Molecular Aggregates: The Effects of Vibronic Coupling and Intermolecular Charge Transfer. Chemical Reviews 118, 7069-7163, doi:10.1021 / acs.chemrev.7b00581 (2018). ^^^ 48 Brédas, J.-L., Beljonne, D., Coropceanu, V. & Cornil, J. Charge-Transfer and Energy- Transfer Processes in ^-Conjugated Oligomers and Polymers:^ A Molecular Picture. Chemical Reviews 104, 4971-5004, doi:10.1021 / cr040084k (2004). 49 Soos, Z. G., Hayden, G. W., McWilliams, P. C. M. & Etemad, S. Excitation shifts of parallel conjugated polymers due to ^^electron dispersion forces. The Journal of ^^^ Chemical Physics 93, 7439-7448, doi:10.1063 / 1.459715 (1990). 50 Collado-Fregoso, E., Boufflet, P., Fei, Z., Gann, E., Ashraf, S., Li, Z., McNeill, C. R., Durrant, J. R., Heeney, M. Increased Exciton Dipole Moment Translates into Charge- Transfer Excitons in Thiophene-Fluorinated Low-Bandgap Polymers for Organic Attorney Docket 8883-0013 Photovoltaic Applications. Chemistry of Materials 27, 7934-7944, doi:10.1021 / acs.chemmater.5b02948 (2015). 51 Galvanetto, N., Ivanovi^, M. T., Chowdhurt, A., Sottini, A., Nüesch, M. F., Nettels, D., Best, R. B., Schuler, B. Extreme dynamics in a biomolecular condensate. Nature 619, ^^ 876-883, doi:10.1038 / s41586-023-06329-5 (2023).

Claims

Attorney Docket 8883-0013 CLAIMS:

1. A conjugated polyelectrolyte complex (CPEC), comprising: an electronic energy transfer (EET) acceptor conjugated polyelectrolyte (CPE) polymer; and ^^ an electronic energy transfer (EET) donor conjugated polyelectrolyte (CPE) copolymer, wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer comprises an acceptor repeat unit, wherein the acceptor repeat unit comprises aryl or heteroaryl functionalized with an acceptor ionic group comprising an acceptor electrical charge, ^^^ wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer comprises an ionic donor repeat unit and a second donor repeat unit, wherein the ionic donor repeat unit comprises an aryl or heteroaryl group functionalized with a donor ionic group comprising a donor electrical charge, wherein the donor electrical charge is opposite to the acceptor electrical charge, ^^^ wherein the second donor repeat unit comprises aryl or heteroaryl, and wherein the ionic donor repeat unit is bonded to the second donor repeat unit through a linkage bond, such as a covalent linkage bond.

2. The conjugated polyelectrolyte complex of claim 1, wherein the ionic donor repeat unit and ^^^ the second donor repeat unit are in an induced torsion about the linkage bond.

3. The conjugated polyelectrolyte complex of claim 2, wherein the torsion reduces an exciton radius. ^^^ 4. The conjugated polyelectrolyte complex of claim 2, wherein the torsion reduces overlap of an ionic donor repeat unit aryl or heteroaryl group ^-orbital with a second donor repeat unit aryl or heteroaryl ^-orbital.

5. The conjugated polyelectrolyte complex of claim 4, wherein the reduced overlap reduces an ^^^ exciton radius.

6. The conjugated polyelectrolyte complex of claim 3 or 5, wherein the reduced exciton radius increases excitonic coupling between the electronic energy transfer donor conjugatedAttorney Docket 8883-0013 polyelectrolyte polymer and the electronic energy transfer acceptor conjugated polyelectrolyte copolymer.

7. The conjugated polyelectrolyte complex of claim 6, wherein the increased excitonic coupling ^^ increases the rate of electronic energy transfer from the electronic energy transfer donor conjugated polyelectrolyte copolymer to the electronic energy transfer acceptor conjugated polyelectrolyte polymer.

8. The conjugated polyelectrolyte complex of any one of claims 1 through 7, wherein a ratio of a ^^^ number of the ionic donor repeat units : a number of the second donor repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer is in the range of from about 1:5, 1:3, 1:2, 1:1.5, 1:1, 1.5:1, 2:1, or 3:1 to about 1:3, 1:2, 1:1.5, 1:1, 1.5:1, 2:1, 3:1, or 5:

1. ^^^ 9. The conjugated polyelectrolyte complex of any one of claims 1 through 7, wherein the ratio of the number of the ionic donor repeat units : the number of the second donor repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer is in the range of from about 1:2 to about 2:

1. ^^^ 10. The conjugated polyelectrolyte complex of any one of claims 1 through 7, wherein the ratio of the number of the ionic donor repeat units : the number of the second donor repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer is about 1:

1.

11. The conjugated polyelectrolyte complex of any one of claims 1 through 10, wherein the ^^^ electronic energy transfer donor conjugated polyelectrolyte copolymer is a random copolymer.

12. The conjugated polyelectrolyte complex of any one of claims 1 through 10, wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer is a statistical copolymer. ^^^ 13. The conjugated polyelectrolyte complex of any one of claims 1 through 10, wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer is a block copolymer comprising at least one ionic donor repeat unit block and at least one second donor repeat unit block.Attorney Docket 8883-0013 14. The conjugated polyelectrolyte complex of any one of claims 1 through 7, wherein the ionic donor repeat unit and the second donor repeat unit alternate in the electronic energy transfer donor conjugated polyelectrolyte copolymer. ^^ 15. The conjugated polyelectrolyte complex of any one of claims 1 through 14, wherein the acceptor repeat unit comprises thiophene functionalized with the acceptor ionic group.

16. The conjugated polyelectrolyte complex of any one of claims 1 through 14, wherein the ^^^ acceptor repeat unit comprises benzothiadiazole, thienothiophene, dithiophene, or dithienothiophene functionalized with the acceptor ionic group.

17. The conjugated polyelectrolyte complex of any one of claims 1 through 14, wherein the acceptor repeat unit comprises phenylene functionalized with the acceptor ionic group. ^^^ 18. The conjugated polyelectrolyte complex of any one of claims 1 through 14, wherein the acceptor repeat unit comprises 3,4-ethylenedioxythiophene, pyrrole, or furan functionalized with the acceptor ionic group. ^^^ 19. The conjugated polyelectrolyte complex of any one of claims 1 through 18, wherein the acceptor ionic group is an anionic group.

20. The conjugated polyelectrolyte complex of any one of claims 1 through 18, wherein the acceptor ionic group comprises an alkyl carboxylate. ^^^ 21. The conjugated polyelectrolyte complex of any one of claims 1 through 18, wherein the acceptor ionic group comprises butylcarboxylate.

22. The conjugated polyelectrolyte complex of any one of claims 1 through 18, wherein the ^^^ acceptor ionic group comprises ethylcarboxylate, propylcarboxylate, or pentylcarboxylate.

23. The conjugated polyelectrolyte complex of any one of claims 1 through 18 wherein the acceptor ionic group comprises an alkyl sulfonate.Attorney Docket 8883-0013 24. The conjugated polyelectrolyte complex of any one of claims 1 through 18, wherein the acceptor ionic group is a cationic group. ^^ 25. The conjugated polyelectrolyte complex of any one of claims 1 through 18 and 24, wherein the acceptor ionic group comprises a quaternary alkyl ammonium.

26. The conjugated polyelectrolyte complex of any one of claims 1 through 18 and 24 through 25, wherein the acceptor ionic group comprises a trimethyl alkyl ammonium. ^^^ 27. The conjugated polyelectrolyte complex of any one of claims 1 through 18 and 24 through 26, wherein the acceptor ionic group comprises a quaternary alkyl phosphonium.

28. The conjugated polyelectrolyte complex of any one of claims 1 through 27, wherein the ^^^ electronic energy transfer acceptor conjugated polyelectrolyte polymer is regioregular.

29. The conjugated polyelectrolyte complex of any one of claims 1 through 14, wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer is poly(3-(4- butanoate)thiophene-2,5-diyl). ^^^ 30. The conjugated polyelectrolyte complex of any one of claims 1 through 29, wherein the ionic donor repeat unit comprises a phenylene functionalized with the donor ionic group.

31. The conjugated polyelectrolyte complex of any one of claims 1 through 29, wherein the ^^^ ionic donor repeat unit comprises a biphenylene functionalized with the donor ionic group.

32. The conjugated polyelectrolyte complex of any one of claims 1 through 29, wherein the ionic donor repeat unit comprises fluorene functionalized with the donor ionic group. ^^^ 33. The conjugated polyelectrolyte complex of any one of claims 1 through 29, wherein the ionic donor repeat unit comprises carbazole functionalized with the donor ionic group.Attorney Docket 8883-0013 34. The conjugated polyelectrolyte complex of any one of claims 1 through 29, wherein the ionic donor repeat unit is fluorene functionalized at the 9-carbon with the donor ionic group.

35. The conjugated polyelectrolyte complex of any one of claims 1 through 23 and 28 through ^^ 34, wherein the donor ionic group is a cationic group.

36. The conjugated polyelectrolyte complex of any one of claims 1 through 23 and 28 through 35, wherein the donor ionic group comprises a quaternary alkyl ammonium. ^^^ 37. The conjugated polyelectrolyte complex of any one of claims 1 through 23 and 28 through 36, wherein the donor ionic group comprises a trimethyl alkyl ammonium.

38. The conjugated polyelectrolyte complex of any one of claims 1 through 23 and 28 through 37, wherein the donor ionic group comprises a gem-di(trimethyl alkyl ammonium). ^^^ 39. The conjugated polyelectrolyte complex of any one of claims 1 through 23 and 28 through 38, wherein the donor ionic group comprises a quaternary phosphonium alkyl.

40. The conjugated polyelectrolyte complex of any one of claims 1 through 18, 24 through 28, ^^^ and 30 through 34, wherein the donor ionic group is an anionic group.

41. The conjugated polyelectrolyte complex of any one of claims 1 through 18, 24 through 28, 30 through 34, and 40, wherein the donor ionic group comprises an alkyl carboxylate. ^^^ 42. The conjugated polyelectrolyte complex of any one of claims 1 through 18, 24 through 28, 30 through 34, and 40 through 41, wherein the donor ionic group comprises an alkyl sulfonate.

43. The conjugated polyelectrolyte complex of any one of claims 1 through 23 and 28 through 34, wherein the donor ionic group is gem-di(N,N,N-trimethylpropan-1-ammonium-3-yl). ^^^ 44. The conjugated polyelectrolyte complex of any one of claims 1 through 23 and 28 through 29, wherein the ionic donor repeat unit is 9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H- fluorene-2,7-diyl.Attorney Docket 8883-0013 45. The conjugated polyelectrolyte complex of any one of claims 1 through 44, wherein the second donor repeat unit is nonionic. ^^ 46. The conjugated polyelectrolyte complex of any one of claims 1 through 45, wherein the second donor repeat unit is functionalized with an electron-withdrawing group.

47. The conjugated polyelectrolyte complex of any one of claims 1 through 45, wherein the second donor repeat unit comprises a phenylene functionalized with an electron-withdrawing ^^^ group.

48. The conjugated polyelectrolyte complex of any one of claims 1 through 45, wherein the second donor repeat unit comprises a phenylene functionalized with a halogen. ^^^ 49. The conjugated polyelectrolyte complex of any one of claims 1 through 45, wherein the second donor repeat unit comprises a phenylene functionalized with a fluorine.

50. The conjugated polyelectrolyte complex of any one of claims 1 through 45, wherein the second donor repeat unit comprises a phenylene functionalized with two or three fluorines. ^^^ 51. The conjugated polyelectrolyte complex of any one of claims 1 through 45, wherein the second donor repeat unit is 2,3-difluorophenyl-1,4-diyl.

52. The conjugated polyelectrolyte complex of any one of claims 1 through 45, wherein the ^^^ second donor repeat unit comprises a phenylene functionalized with four fluorines.

53. The conjugated polyelectrolyte complex of any one of claims 1 through 45, wherein the second donor repeat unit is 2,3,5,6-tetrafluorophenyl-1,4-diyl. ^^^ 54. The conjugated polyelectrolyte complex of any one of claims 1 through 53, wherein a torsional angle about the linkage bond is greater than about 40 degrees.Attorney Docket 8883-0013 55. The conjugated polyelectrolyte complex of any one of claims 1 through 53, wherein a torsional angle about the linkage bond is greater than about 43.8 degrees.

56. The conjugated polyelectrolyte complex of any one of claims 1 through 53, wherein a ^^ torsional angle about the linkage bond is greater than about 44 degrees.

57. The conjugated polyelectrolyte complex of any one of claims 1 through 53, wherein a torsional angle about the linkage bond is at least about 50 degrees. ^^^ 58. The conjugated polyelectrolyte complex of any one of claims 1 through 53, wherein a torsional angle about the linkage bond at least about 53 degrees.

59. The conjugated polyelectrolyte complex of any one of claims 1 through 49 and 52 through 53, wherein a torsional angle about the linkage bond is at least about 60 degrees. ^^^ 60. The conjugated polyelectrolyte complex of any one of claims 1 through 49 and 52 through 53, wherein a torsional angle about the linkage bond is at least about 61 degrees.

61. The conjugated polyelectrolyte complex of any one of claims 1 through 23 and 28 through ^^^ 29, wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer is poly(9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7-diyl)-alt-(2,3- difluorophenyl-1,4-diyl)) (PFNF2).

62. The conjugated polyelectrolyte complex of any one of claims 1 through 23 and 28 through ^^^ 29, wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer is poly(9,9-di(N,N,N-trimethylpropan-1-ammonium-3-yl)-9H-fluorene-2,7-diyl)-alt-(2,3,5,6- tetrafluorophenyl-1,4-diyl)) (PFNF4).

63. The conjugated polyelectrolyte complex of any one of claims 1 through 62, wherein a ratio ^^^ of a sum of the donor electrical charges : a sum of the acceptor electrical charges is in a range of from about 20:80 to about 80:20.Attorney Docket 8883-0013 64. The conjugated polyelectrolyte complex of any one of claims 1 through 62, wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is in a range of from about 40:60 to about 95:5, in a range of from about 50:50 to about 90:10, in a range of from about 60:40 to about 80:20, or in a range of from about 65:35 to about 75:

25. ^^ 65. The conjugated polyelectrolyte complex of any one of claims 1 through 62, wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is at least about 70:

30. ^^^ 66. The conjugated polyelectrolyte complex of any one of claims 1 through 62, wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is about 70:

30.

67. The conjugated polyelectrolyte complex of any one of claims 1 through 66, wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy ^^^ transfer donor conjugated polyelectrolyte copolymer are in solution.

68. The conjugated polyelectrolyte complex of any one of claims 1 through 66, wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in aqueous solution. ^^^ 69. The conjugated polyelectrolyte complex of any one of claims 1 through 66, wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in solution in water. ^^^ 70. The conjugated polyelectrolyte complex of any one of claims 67 through 69, wherein the solution has a predetermined ionic strength.

71. The conjugated polyelectrolyte complex of any one of claims 1 through 69, further comprising a salt. ^^^ 72. The conjugated polyelectrolyte complex of any one of claims 67 through 69 further comprising a salt at a concentration of at most about 5 M in the solution.Attorney Docket 8883-0013 73. The conjugated polyelectrolyte complex of claim 1, comprising: the electronic energy transfer acceptor conjugated polyelectrolyte polymer; and the electronic energy transfer donor conjugated polyelectrolyte copolymer, wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer ^^ comprises the acceptor repeat unit, wherein the acceptor repeat unit comprises a poly(3-(4-butanoate)thiophene-2,5-diyl) of the acceptor electrical charge of -1 e (1 electron), wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer comprises the ionic donor repeat unit and the second donor repeat unit, ^^^ wherein the ionic donor repeat unit comprises 9,9-di(N,N,N-trimethylpropan-1- ammonium-3-yl)-9H-fluorene-2,7-diyl of the donor electrical charge of +2 e (-2 electrons), and wherein the second donor repeat unit comprises phenyl.

74. The conjugated polyelectrolyte complex of claim 73, wherein a ratio of a number of the ^^^ ionic donor repeat units : a number of the second donor repeat units in the electronic energy transfer donor conjugated polyelectrolyte copolymer is in a range of from about 1:2 to about 2:

1.

75. The conjugated polyelectrolyte complex of claim 73, wherein a ratio of a number of the ionic donor repeat units : a number of the second donor repeat units in the electronic energy ^^^ transfer donor conjugated polyelectrolyte copolymer is about 1:

1.

76. The conjugated polyelectrolyte complex of any one of claims 73 through 75, wherein the electronic energy transfer donor conjugated polyelectrolyte copolymer is a random copolymer. ^^^ 77. The conjugated polyelectrolyte complex of any one of claims 73 through 75, wherein the ionic donor repeat unit and the second donor repeat unit alternate.

78. The conjugated polyelectrolyte complex of any one of claims 73 through 77, wherein the second donor repeat unit comprises 2,3-difluorophenyl-1,4-diyl. ^^^ 79. The conjugated polyelectrolyte complex of any one of claims 73 through 78, wherein the second donor repeat unit comprises 2,3,5,6-tetrafluorophenyl-1,4-diyl.Attorney Docket 8883-0013 80. The conjugated polyelectrolyte complex of any one of claims 73 through 79, wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is in the range of from about 80:20 to about 20:

80. ^^ 81. The conjugated polyelectrolyte complex of any one of claims 73 through 79, wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is in a range of from about 40:60 to about 95:5, in a range of from about 50:50 to about 90:10, in a range of from about 60:40 to about 80:20, or in a range of from about 65:35 to about 75:

25. ^^^ 82. The conjugated polyelectrolyte complex of any one of claims 73 through 79, wherein a ratio of a sum of the donor electrical charges : a sum of the acceptor electrical charges is at least about 70:

30.

83. The conjugated polyelectrolyte complex of any one of claims 73 through 79, wherein a ratio ^^^ of a sum of the donor electrical charges : a sum of the acceptor electrical charges is about 70:

30.

84. The conjugated polyelectrolyte complex of any one of claims 73 through 83, wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in a solution. ^^^ 85. The conjugated polyelectrolyte complex of any one of claims 73 through 83, wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in an aqueous solution. ^^^ 86. The conjugated polyelectrolyte complex of any one of claims 73 through 83, wherein the electronic energy transfer acceptor conjugated polyelectrolyte polymer and the electronic energy transfer donor conjugated polyelectrolyte copolymer are in a solution in water.

87. The conjugated polyelectrolyte complex of any of claims 85 through 86, wherein the ^^^ solution has a predetermined ionic strength.

88. The conjugated polyelectrolyte complex of any of claims 84 through 87, wherein the solution further comprises a salt.Attorney Docket 8883-0013 89. The conjugated polyelectrolyte complex of claim 85, further comprising a salt at a concentration of at most about 5 M in the aqueous solution.

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