New class of light-absorbing materials & uses thereof

Abstract

The invention relates to new light-absorbing materials, in particular polymeric carbon nitrides and covalent organic frameworks applicable in photocatalytic systems and uses thereof.

Description

[0001]NEW CLASS OF LIGHT-ABSORBING MATERIALS & USES THEREOFField of the InventionThe present invention pertains generally to the field of light-absorbing materials, in particularpolymeric carbon nitrides and covalent organic frameworks applicable in photocatalyticsystems and uses thereof. Background of the Invention Photocatalysis refers to processes that use the energy of light to directly drive chemical transformations. The most important, and perhaps the simplest, among them is photocatalytic water splitting, i.e. the process of converting the energy of light into the chemically stored energy of hydrogen H2, a clean fuel. There are, however, many other photocatalytic processes that may play a pivotal role in mitigating climate change and threats to human health, but only if made scalable and economically feasible. This includes, but not limited to, photocatalytic CO2 reduction, nitrogen fixation, pollutant degradation, bacterial and viral disinfection. Photocatalysis comprises of three general steps: (1) light absorption, (2) dissociation and diffusion of photoexcited charge carriers, and (3) their utilization to drive the target reaction at the catalytic active sites. Photocatalytic systems can consist of many distinct compounds and phases, but all include a semiconducting light-absorbing material responsible for step (1). The basic requirement to this material is that its band gap must enclose potentials of the half- reactions of the corresponding chemical reaction. Numerous semiconductors capable of supporting photocatalytic water splitting are known to date. These are mostly inorganic materials, while the discovery of photocatalytic activity ingraphitic (polymeric) carbon nitrides g-C3N4 (Wang et al. 2009, Nat. Mater. 8, 76–80),materials known for almost two centuries, gave a new twist on progress in this direction (Wang et al., 2012, Angew. Chem. Int. Ed.51, 68–89; Kessler et al., 2017, Nat. Rev. Mater. 2, 17030; Barrio et al., 2020, J. Mater. Chem. A 8, 11075–11116). The first step of any photocatalytic process is the generation of photoexcited charge carriers, and the semiconducting nature of g-C3N4 plays a crucial role here. These materials are characterized by band gaps of ca. 2.7 eV—small enough to absorb a significant fraction of visible light photons, yet sufficient to oppose the endothermic character of the water splittingreaction (1.23 eV). More importantly, the potentials of both half-reactions of the watersplitting process are positioned within the band gap of g-C3N4, at energies higher than in most semiconductors, which makes g-C3N4rather unique materials (Ong et al., 2016, Chem. Rev. 116, 7159–7329; Marschall et al., 2014, Adv. Funct. Mater.24, 2421–2440). Bringing photocatalytic systems to practical applications requires increasing their efficiency expressed by numerous parameters, with solar-to-hydrogen (STH) conversion efficiency being the ultimate characteristic. Several techno-economical analyses conducted to date identified 5-10% STH conversion efficiency as the threshold that needs to be surpassed inorder to assure economic feasibility of photocatalytic water splitting (Pinaud et al., 2013,Energy Environ. Sci., 6, 1983–2002; Hisatomi et al., 2019, Nat. Catal., 2, 387–399).The highest STH conversion efficiency for photocatalytic systems based on g-C3N4achieved to date is ca.2% (Liu et al., 2015, Science 347, 970–974). More importantly, the undisputed advantage of g-C3N4materials is their low cost, environmental friendliness and the presenceof only Earth abundant elements in their composition. While small-scale pilot facilitiesutilizing photocatalytic systems of modest STH conversion efficiency based on transition metal oxides have been demonstrated (Nishiyama et al., 2021, Nature 598, 304–307), carbonnitrides, or organic and light-element photocatalytic systems in general, promise to becomeenabling materials for transitioning to large scales. One approach towards achieving higher STH conversion efficiencies consists in developing new classes of light-absorbing materials that transform a larger fraction of visible light photons into charge carriers capable of driving the water splitting reaction.Therefore, the development of new classes of light-absorbing materials for photocatalyticsystems, in particular for water-splitting is highly desirable.Summary of the InventionThe present invention is based on the finding of a physical mechanism, hereby referred to asthe Intermediate Band Reservoir (IBR) mechanism, that underlies stability and photocatalyticactivity of graphitic carbon nitrides g-C3N4. This scientific advance enables the design of anew class of light-absorbing materials, structurally and compositionally distinct from theknown g-C3N4, with superior stability and positions of band edges favorable for highperformance in a broad range of photocatalytic processes, including photocatalytic watersplitting, due to higher light conversion efficiencies.A general object of this invention is to provide new polymeric light-absorbing materials.One of the specific objects of this invention is to provide light-absorbing materials havinghigh solar-to-hydrogen conversions efficiencies in photocatalytic water splitting.It is advantageous to provide light-absorbing materials suitable for photocatalytic applicationsand uses in optoelectronics.It is advantageous to provide light-absorbing materials with band gaps and band edge energiesspanning broad ranges.It is advantageous to provide light-absorbing materials having chemical stability equivalentto or surpassing that of g-C3N4.It is advantageous to provide light-absorbing materials suitable for water splitting having lowproduction costs and are environment-friendly.It is advantageous to provide light-absorbing materials composed of only Earth-abundantchemical elements.Objects of this invention have been achieved by ^-conjugated polymeric materials accordingto claim 1.Disclosed herein are ^-conjugated polymeric materials wherein the atoms of said materialsparticipate into a bipartite (alternant^^^-conjugated polymeric network and are distributed among two distinct sublattices characterized by the following structural characteristics:a) the said bipartite (alternant) ^-conjugated network comprises Carbon (C) atoms, Nitrogen(N) atoms and optionally other atoms distinct from carbon and nitrogen, in which the numberof atoms in one sublattice (dominant sublattice) (nd) is larger than that in the other sublattice(minor sublattice) (nm);b) the said dominant sublattice contains graphitic (tertiary, that is, bonded to three otheratoms) nitrogen (N) atoms, the number of which (NgD) is equal to the difference in numbersof atoms between the two sublattices (nd minus nm);c) the number of tertiary nitrogen (N) atoms in the dominant sublattice (NgD) is smaller thanthe total number of tertiary atoms of any type in this sublattice.Also disclosed herein are uses of ^-conjugated polymeric materials in photocatalyticprocesses, e.g. water splitting, CO2 reduction, N2 fixation, pollutant degradation and bacterialand viral disinfection by virtue of the similarity of half-reaction potentials involved in theseprocesses as compared to the water splitting process.Also disclosed herein are methods of preparation of materials of the invention.Also disclosed herein are photocatalytic systems comprising a ^-conjugated materialaccording to the invention as light-absorbing material. Other features and advantages of the invention will be apparent from the claims, detailed description, and figures. Brief Description of the drawingsFigure 1 illustrates the structures of graphitic carbon nitrides with a: structures of fullypolymerized g-C3N4derived from the triazine (configuration 1) and heptazine(configuration 2) building blocks. The graphitic and pyridinic nitrogen atoms aredistinguished by circles and squares, respectively; b: Schematic illustration explaining thedifferent π-electron count of the two types of nitrogen atoms.Figure 2 illustrates the construction of a fully polymerized structure of single-layer triazineg-C3N4 (configuration 1). a: Atomic structure of fully polymerized single-layer triazine g-C3N4 (configuration 1) is obtained starting from the honeycomb lattice of graphene in twosteps: (i) removal of single carbon atoms from one of the sublattices and (ii) population of theother sublattice with nitrogen atoms. Graphitic and pyridinic nitrogen atoms are distinguishedby different shading; b: Schematic illustration of the evolution of the π-symmetry bands uponthese two steps for each of the structures from Figure 2a; c: Electronic band structure ofsingle-layer g-C3N4 (configuration 1) calculated at the HSE06 hybrid functional level oftheory. The orbital symmetries of the bands are indicated. Weights w(n, k) of the pz atomicorbital are shown by circle sizes, while the absolute value of sublattice polarization η(n, k) iscolor-coded (grey scale).Figure 3 illustrates the construction of the fully polymerized structure of single-layerheptazine g-C3N4 (configuration 2). a: Atomic structure of fully polymerized single-layerheptazine g-C3N4(configuration 2) is obtained starting from the honeycomb lattice of graphene in two steps: (i) introduction of 4-atom vacancies removing 3 atoms from sublatticeA and 1 atom from sublattice B and (ii) population of sublattice B with nitrogen atoms.Graphitic and pyridinic nitrogen atoms are distinguished by different shading; b: Electronicband structure of single-layer g-C3N4 (configuration 2) calculated at the hybrid functional (HSE06) level of theory. The orbital symmetries of the bands are indicated. Weights w(n, k) of the pzatomic orbital are shown by circle sizes, while the absolute value of sublattice polarization η(n, k) is color-coded (grey scale).Figure 4 compares the structures of ^-conjugated polymeric materials as carbon nitridesaccording to the invention (configurations 3-35) with the structures of the known fullypolymerized single-layer triazine g-C3N4 (configuration 1) or fully polymerized single-layerheptazine g-C3N4 (configuration 2) and other comparative materials (configurations 36 and37) not presenting the structure of the ^-conjugated polymeric materials according to theinvention, i.e. not complying with the Intermediate Band Reservoir mechanism detailed below, namely containing equal number of atoms in the two sublattices and only pyridinicnitrogen atoms. The unit cells are shown using dashed lines.Table 1 represents the composition and calculated properties of known g-C3N4 structuresconfigurations 1 and 2, designed carbon nitride materials of the invention (configurations3-35) and two reference “non-IBR” carbon nitrides as described below (configurations 36and 37). nC refers to the total number of carbon atoms in both sublattices, nNg refers to thenumber of graphitic nitrogen atoms and nNp represents the number of pyridinic nitrogen atoms in the unit cell, that is the smallest repeating unit of the considered fully polymerized structures.Figure 5 presents the properties of designed carbon nitride according to the invention. a:Formation energies per atom Ef of the triazine and heptazine configurations of known g-C3N4structures (configurations 1 and 2) and of the designed of ^-conjugated polymeric materialsas carbon nitrides according to the invention (configurations 3-35) and sequences of modelscontaining only pyridinic or only graphitic nitrogen atoms plotted as a function of nitrogencontent. The calculations were performed at the DFT-GGA level of theory. b: Band edgeenergies of g-C3N4, selected configurations of the ^-conjugated polymeric materials as carbonnitrides according to the invention, and two reference carbon nitrides (configurations 36 and37) containing only pyridinic nitrogen calculated at the HSE06 level of theory. The Fermienergy of graphene as well as potentials of the two half-reactions of water splitting (at pH = 0 and pH = 7) are shown for reference.Figure 6 shows the measured x-ray diffraction (XRD) patterns of sample 2 (dashed line) andsample 2-6 (solid line) as described in Example 3.Figure 7 shows the measured Fourier transform infrared (FT-IR) spectra of sample 2 (dashedline) and sample 2-6 (solid line) as described in Example 3.Figure 8 presents the diffuse reflectance spectroscopy data in the ultraviolet-visible (UV-Vis)range for sample 2 (dashed line) and sample 2-6 (solid line) as described in Example 3.Figure 9 presents the Tauc plot analyses of the measured UV-Vis spectra as described inExample 3. a: Tauc plot analysis of sample 2. b: Tauc plot analysis of sample 2-6. The fittedvalues of the distinct absorption edges are indicated.Figure 10 presents the measured hydrogen evolution rates of samples 2 and 2-6 as describedin Example 3. a: Hydrogen evolution rates of sample 2 (dashed line) and sample 2-6 (solidline) as a function of time T. Illumination of samples started at T = 0 h. b: Hydrogen evolutionrates of samples 2 and 2-6 immediately after the start of illumination (T = 0 h) and at T = 12h. Detailed description of embodiments of the inventionThe expression “bipartite (alternant) ^-conjugated polymeric network” refers to a network of^-bonded atoms wherein all atoms can be divided into two sublattices, each atom in onesublattice is bonded to atoms only in the other sublattice (Orchin et al., 2005, The Vocabularyand Concepts of Organic Chemistry, Wiley; Fetter et al., 2023, Quantum Theory of Many-Particle Systems, Dover). It has to be noted that ^-conjugated networks containing odd-membered rings, e.g. pentagons, are not bipartite (alternant). The present invention relatesonly to systems in which the numbers of atoms belonging to the two sublattices is different.The sublattice that has a larger number of atoms is referred to as the dominant, while the other sublattice is referred to as the minor. The distinction between the two sublattices is not related to their elemental composition. The expression “copolymers” refers to polymeric materials composed of two or more distinct structural building blocks of one or more configurations selected from configurations of theinvention, for example configurations 3-35 and optionally further including configurations1,2. For example, Scheme 3 illustrates the structural patterns occurring in the copolymer ofconfigurations 2 and 6.Graphitic carbon nitrides g-C3N4 and the Intermediate Band Reservoir (IBR) mechanism It is broadly accepted that the ideal, fully polymerized g-C3N4represents two-dimensional frameworks composed of either s-triazine (or simply triazine) or heptazine cores(configurations 1 and 2 in Fig. 1, respectively) wherein g-C3N4 structures contain two typesof nitrogen atoms: in pyridinic and graphitic (tertiary) forms (Fig. 1). While the first typecontributes one electron to the π-conjugated system, graphitic nitrogen atoms contribute two. Therefore, graphitic carbon nitrides g-C3N4 can be considered as nominally electron-richmaterials in the sense of having more than one electron per atom populating the π-conjugatedsystem. In order to understand the relation between the structure and properties of g-C3N4,configurations 1 and 2 need to be constructed starting from the honeycomb lattice ofgraphene. This lattice is bipartite (alternant), that is formed by two inter-connected sublattices(A and B), and the compositions of the two sublattices are identical (e.g. same total number of atoms, same number of atoms of each nature). For the triazine-derived g-C3N4structure (configuration 1) this construction is illustrated in Fig.2a. Single carbon atoms are removedfrom one sublattice (open circles) (Fig. 2a (i)), wherein the other sublattice (black circles)contains only nitrogen atoms (Fig. 2a (ii)).The heptazine-derived structure g-C3N4 (configuration 2) (Fig. 3a) is constructed in a similarmanner with the difference being that 4-atom vacancies are introduced: 3 atoms belong to onesublattice and 1 to other sublattice (Fig. 3b (i)), and this other sublattice (black circles)contains only nitrogen atoms (Fig. 3b (ii)). In both configurations, vacancies break thesublattice balance resulting in a different number of atoms populating the two sublattices. Thesublattice imbalance gives rise to zero-modes and their number is equal or greater to the difference in the number of atoms in the two sublattices (Pereira et al., 2006, Phys. Rev. Lett. 96, 036801; Yazyev and Helm, 2007, Phys. Rev. B 75, 125408; Yazyev, 2008, Phys. Rev. Lett. 101, 037203). The zero modes correspond to non-bonding states localized in the dominant sublattice. The introduction of sublattice imbalance thus reorganized the electronic spectrum in such a way that a non-bonding band (π0) is inserted between the bonding (π) and anti- bonding (π∗) bands (Fig. 2b(i)). This intermediate band is capable of accepting excess electrons donated by the graphitic N atoms thus avoiding their placement in the anti-bondingπ∗ band that would inevitably destabilize the system. Thus, this intermediate band acts as areservoir for excess electrons in such nominally electron-rich systems. In order to guaranteethe semiconducting nature of the system, it shall be further assumed that the π0 band is fullypopulated (Fig. 2b(ii)). The triazine and heptazine-triazine forms of g-C3N4 (configurations1 and 2) satisfy both of these conditions. Furthermore, the π0band is situated at higher energy, which is an important prerequisite for photocatalytic applications. From now on, thismechanism is referred to as the intermediate band reservoir (IBR) mechanism. Based onthis finding, it is possible to design new light-absorbing materials according to the inventionthat comply with this mechanism, but are distinct from known materials, that is graphitic carbon nitrides g-C3N4.First-principles calculations methodology and results for graphitic carbon nitrides g-C3N4. First-principles calculations within the framework based on density functional theory(DFT) (Hohenberg, 1964, Phys. Rev. 136, B864–B871; Kohn et al., 1965, Phys. Rev. 140, A1133–A1138). and the projector augmented wave method (Blöchl et al., 1994, Phys. Rev. B50, 17953–17979) as implemented in the Vienna ab initio simulation package (VASP)(Kresse & Joubert, 1999, Phys. Rev. B 59, 1758–1775) were performed in order to verify the proposed physical mechanism and assess the properties of new materials described in this invention. An energy cutoff of 500 eV was used for the plane-wave basis set throughout this work. For structure relaxation and total energy evaluation, we used the generalized gradient approximation (GGA) exchange-correlation functional of Perdew, Burke and Ernzerhof(Perdew et al., 1997, Phys. Rev. Lett. 78, 1396). Γ-centered uniform k-point meshes withsampling densities equivalent to the 36 × 36 mesh for primitive cell of graphene were employed. Periodic images in the out-of-plane direction were separated by a distance of 15 Å. Both the atomic positions and unit cell dimensions were relaxed, with the corresponding convergence criterion for the forces set to 0.001 eV Å−1. The formation energies Ef in units of eV per atom ^ ^ ^ ^^ ^^^^^ ^^^^ per unit cell. In this expression, Etotis the total energy of the configuration under question with stoichiometric ratio nC : nN, while E1 and E2 are the total energies of the chosen references, that is graphene and the heptazine-based modelof g-C3N4 (configuration 2), respectively.Electronic band structures, band gaps and band edge energies were calculated using the HSE06 parameterisation (Krukau et al., 2006, J. Chem. Phys. 125, 224106)of the hybrid exchange-correlation functional of Heyd, Scuseria and Ernzerhof (Heyd et al., 2003, J. Chem.Phys. 118, 8207–8215). In the hybrid functional calculations, the linear density of k-pointmeshes was reduced by a factor of 2, but was at least a 6 × 6 mesh. All band energies aregiven relative to the vacuum potential. The pzatomic orbital weight w(n, k) and sublattice polarization η(n, k) were calculated according to^^(^^, ^^) = ∑^ ^^^(^^, ^^) (2) characters for the pz orbital of atom i and σi thesublattice index of this atom (σi= −1 and +1 for the respective sublattices).Configuration 2 is lower in energy by 0.367 eV per formula unit as compared toconfiguration 1, in accordance with early calculations (Kroke et al., 2002, New J. Chem. 26,508–512). The electronic band gaps of configurations 1 and 2 obtained using the HSE06parameterisation (Krukau et al., 2006, supra) of the hybrid exchange-correlation functionalof Heyd, Scuseria and Ernzerhof (Heyd et al., 2003, supra) are 3.19 eV and 2.78 eV, respectively. It needs to be stressed that not only the band gap, but also the positions of band edges (−6.14 eV and −3.35 eV relative to the vacuum level for the valence and conductionbands, respectively) of the more stable configuration 2 are in remarkably good agreementwith experimental values (Zhang et al., 2010, Chem. Asian J.5, 1307–1311). Due to the planar structure of these models, the π bands do not hybridize with the σ bands, and hence can beclearly distinguished as observed in the band structure for configuration 1 (Fig. 2c). Incontrast to bonding and anti-bonding states, the non-bonding π0states are localized with thedominant sublattice, and therefore have complete sublattice polarization η(n, k) ≈ 1. The π0band is positioned between the π and π∗bands and is fully populated, even though it overlaps in energy with the σ band that has the largest contribution from the lone-pair orbitals ofpyridinic N atoms (labeled σN) at these energies. These results and the ones for configuration2 (Fig. 3) are fully consistent with the intermediate band reservoir mechanism.Disclosed herein are ^-conjugated polymeric materials wherein the atoms of said materialsparticipate into a bipartite (alternant^^^-conjugated polymeric network and are distributed among two distinct sublattices characterized by the following structural characteristics:a) the said bipartite (alternant) ^-conjugated network comprises Carbon (C) atoms, Nitrogen(N) atoms and optionally other atoms distinct from carbon and nitrogen, in which the numberof atoms in one sublattice (dominant lattice) (nd) is larger than that in the other sublattice(minor lattice) (nm);b) the said dominant sublattice contains graphitic (tertiary, that is, bonded to three otheratoms) nitrogen (N) atoms, the number of which (NgD) is equal to the difference in numbersof atoms between the two sublattices (nd minus nm);c) the number of tertiary nitrogen (N) atoms in the dominant sublattice (NgD) is smaller thanthe total number of tertiary atoms of any type in this sublattice.According to a particular embodiment, the ^-conjugated polymeric material only comprisesCarbon (C) atoms and Nitrogen atoms (e.g. carbon nitrides).According to a particular embodiment, the bipartite (alternant) ^-conjugated network onlycomprises Carbon (C) atoms and Nitrogen atoms.According to a particular embodiment, the ^-conjugated polymeric material further comprisesone or more atoms distinct from carbon and nitrogen, but when those are selected from H andhalogens (F, Cl, Br, I), those do not participate in the^^-conjugated network.According to another particular embodiment, the ^-conjugated polymeric material furthercontains one or more atoms other than carbon and nitrogen selected from O, S, Se, Te and B,wherein: -when one or more atoms selected from O, S, Se and Te are present, said one or moreatoms participate in the ^-conjugated network only when bound to at least one other atom and this atom participates in this ^-conjugated network; or- when one or more atoms selected from O, S, Se and Te are present, participate in the^-conjugated network and are bound to two other atoms, per each said O, S, Se and Te atom one less tertiary nitrogen (N) atom to the conditions under b) of the features of the ^-conjugated polymeric material of the invention is present in the said ^-conjugated network; or- when one or more B is present in the ^-conjugated network, an additional tertiarynitrogen (N) atom per each B atom to the conditions under b) of claim 1 is also present in the said ^-conjugated network.According to another particular embodiment, the ^-conjugated polymeric material furthercontains one or more atoms other than carbon and nitrogen selected from O, S, Se, Te and B,wherein: -when one or more atoms selected from O, S, Se and Te, are present, said one or moreatoms participate in the ^-conjugated network only when bound to only one otheratom and this atom participates in this ^-conjugated network;- when one or more B is present in the ^-conjugated network, an additional tertiarynitrogen (N) atom per each B atom to the conditions under b) is also present in thesaid ^-conjugated network.According to a particular embodiment, is provided a ^-conjugated polymeric materialaccording to the invention, wherein nC, the total number of carbon atoms in both sublattices, per unit cell is higher than 6.According to a particular embodiment, is provided a ^-conjugated polymeric materialaccording to the invention, wherein nC per unit cell is from 9 to 27.According to a particular embodiment, is provided a ^-conjugated polymeric materialaccording to the invention, wherein nNg, the number of graphitic nitrogen atoms, per unit cellis from 1 to 3.According to a particular embodiment, is provided a ^-conjugated polymeric materialaccording to the invention, wherein nNp, the number of pyridinic nitrogen atoms in thedominant sublattice, per unit cell is from 3 to 9.According to a particular aspect, is provided a ^-conjugated polymeric material according tothe invention having a nitrogen content lower than 55% of the total number of atoms (e.g. ofany type) (e.g. from about 53% to about 13%).According to a particular aspect, is provided a ^-conjugated polymeric material according tothe invention comprising or consisting in a configuration selected from configurations 3-35.According to a particular aspect, is provided a ^-conjugated polymeric material according tothe invention or consisting in configuration 5 or 13.According to a particular aspect, is provided a ^-conjugated polymeric material according tothe invention comprising or consisting in configuration 6.According to a particular aspect, is provided a ^-conjugated polymeric material according tothe invention comprising or consisting in configuration 14.According to a particular aspect, is provided a ^-conjugated polymeric material according tothe invention which is a copolymer of one or more configurations selected fromconfigurations 3-35 and optionally further including configurations 1 or 2.According to a particular aspect, is provided a ^-conjugated polymeric material according tothe invention comprising a copolymer of configurations 2 and 6.According to a particular aspect, is provided a ^-conjugated polymeric material according tothe invention that relates to one of configurations 3-35, or copolymers of one or moreconfigurations selected from configurations 3-35 and optionally further includingconfigurations 1 or 2, as a product of incomplete condensation.According to a particular aspect, is provided a ^-conjugated polymeric material according tothe invention, wherein said ^-conjugated polymeric material is a product of incompletecondensation of its constitutive configurations.Products of incomplete condensation refer to ^-conjugated polymeric materials in which allor a fraction of tertiary amine nitrogen atoms are replaced by a larger number of secondary orprimary amine groups. Examples are the melon and poly(heptazine imide) forms of g-C3N4, both known and well-studied photocatalysts, that represent the products of incompletecondensation of configuration 2 (Lau and Lotsch, 2022, Adv. Energy Mater. 12, 2101078).These materials are typically characterized by higher nitrogen content than their fullycondensed counterparts and contain hydrogen associated with the secondary and primaryamine groups. As the replacement of nitrogen atoms affects only the dominant sublattice, aproduct of incomplete condensation fulfils the intermediate band reservoir mechanism if the respective fully condensed structure complies with it.According to a particular aspect, is provided a ^-conjugated polymeric material according tothe invention having the configuration 6, described by stoichiometry C3N2 and values nCequal 12 per unit cell, nNg equal 2 per unit cell and nNp equal 6 per unit cell.According to a particular aspect, is provided a ^-conjugated polymeric material according tothe invention having the configuration 14, described by stoichiometry C9N4 and values nCequal 9 per unit cell, nNg equal 1 per unit cell and nNp equal 3 per unit cell. According to a particular embodiment, materials of the invention present energies of valence band maximum and conduction band minimum positioned at higher energies than commonly known light-absorbing materials due to the electron-rich character of the compounds, i.e. the energy of conduction band minimum considerably higher than −4.44 eV relative to the vacuum level, the value that corresponds to potential of H+ / H2half-reaction at pH = 0. According to a particular embodiment, materials of the invention present band gaps in the visible or near infrared range, in particular spanning the range from 1.23 eV necessary for water splitting reaction to 2.35 eV for configuration 3. Those properties are very promising for achieving not only very efficient photocatalytic watersplitting, but also other photocatalytic processes of high environmental and societal relevance,e.g. CO2 reduction (Albero et al., 2020, ACS Catal. 10, 5734–5749), N2 fixation (Wang et al.,2019, ACS Catal. 9, 10260–10278), pollutant degradation (Mamba et al., 2016, Appl. Catal.B: Environ.198, 347–377), bacterial and viral disinfection (Zhang et al., 2019, Chemosphere 214, 462–479).Beyond the domain of photocatalysis, the materials of the invention are expected to exhibit promising optical and optoelectronic properties, such as tuneable band gaps covering thevisible range (Giusto et al., 2020, J. Am. Chem. Soc. 142, 20883–20891) and high refractiveindices (Giusto et al., 2020, Adv. Mater.32, 1908140). Heterostructures involving the proposed materials offer the opportunity of achieving large band offsets thanks to the elevated positions of band edges compared to other 2D materials. Furthermore, the intrinsic weak dispersion of sublattice-polarized bands opens a new avenue towards engineering novel platform materials for studying correlated phases of quantummatter (Balents et al., 2020, Nat. Phys. 16, 725–733).Therefore, according to a particular aspect, is provided the use of the material of the inventionis the applications and processes disclosed herein.According to another aspect, are also provided an illustration of methods of preparation ofmaterials according to the invention.According to another particular aspect, materials of the invention can be synthesized via bulk-phase condensation from molecular precursors that contain bipartite (alternant^^^-conjugatednetwork functionalized by amino (-NH2) and nitrile (-CN) group, wherein said molecularprecursors have the following structural characteristics: -when one amino group is connected to an atom in the bipartite (alternant^^^-conjugated molecular network, a nitrile functional group is connected to a neighboring atom in the said bipartite (alternant^^^-conjugated molecular network; -all amino groups connect atoms only in one sublattice of the bipartite (alternant^^^-conjugated molecular network, and all nitrile groups connect atoms only in the other sublattice of the said bipartite (alternant^^^-conjugated molecular network. The invention having been described, the following examples are presented by way of illustration, and not limitation. EXAMPLESThe following examples illustrate some of the new ^-conjugated polymeric materialsaccording to the invention and the properties of a collection of examples of materials belonging to the new class are assessed by means of first-principles calculations.Example 1: Design of new ^-conjugated polymeric materials according to the inventionThe structures of carbon nitrides complying with the above mechanism and distinct fromknown graphitic carbon nitrides g-C3N4 were constructed according to the following three- step protocol that directly reflects Fig.2a:1) Define a two-dimensional hexagonal lattice supercell of graphene with a lattice constantnot larger than 10 Å. The considered superlattice vectors in terms of lattice vectors of graphene are (1, 0), (1, 1), (2, 0), (2, 1), (3, 0), (2, 2), (3, 1) and (4, 0). Configurations 1 and2 of g-C3N4 are defined by superlattice vectors (2, 0) and (3, 0), respectively;2) Introduce one single- or multiple-atom vacancy per supercell to break the sublatticesymmetry and replace two-fold coordinated carbon atoms with nitrogen atoms (pyridinicnitrogen). Additionally, the set of compounds was limited to those where these two-foldcoordinated atoms belong to the dominant sublattice only. This is possible only if theintroduced vacancies correspond to the removal of one atom (as in configuration 1 of g-C3N4), four atoms (as in configuration 2 of g-C3N4) and nine atoms. The latter can beintroduced only into the superlattice defined by the largest vector (4, 0);3) Introduce graphitic nitrogen atoms in the dominant sublattice, the number of which is equalto the difference in numbers of atoms between the two sublattices in order to ensure completefilling of the π0 non-bonding band.Exactly 35 configurations can be constructed according to this procedure (Fig. 4), amongwhich completely new, unanticipated configurations 3–35 realizing 9 distinct stoichiometriesof lower N contents, as compared to configuration 1 and 2 of g-C3N4, ranging from 12.9 at.% N to 52.2 at. % N were generated. As a proof of concept, the properties of these newconfigurations in the fully polymerized, single-layer form are studied using first-principles computations as described herein and presented under Fig.4, Table 1. Further configurations of carbon nitrides complying with the above mechanism can beobtained by relaxing the conditions that, first, attribute nitrogen atoms to only one sublattice,and, second, consider only hexagonal superlattices of limited lattice constant. As far as thelatter is concerned, periodicity is not a necessary requirement of the above mechanism. Thisdesign protocol can be applied to configurations containing elements other than carbon and nitrogen, thus extending the scope to the class of covalent organic frameworks.Firstly, the designed carbon nitride structures are assessed for their computed formationenergies. At ambient pressure, no carbon nitride is characterised by a negative formation energy on a conventional convex hull diagram that assumes as references stable elemental phases of carbon and nitrogen, which is a consequence of the overwhelming stability of the N2molecule (Liu et al., 1994, Phys. Rev. B 50, 10362(R)). Instead, it is more instructive todefine formation energy Ef relative to the single-layer form of known configuration 2 of g-C3N4 and graphene. Figure 5a shows that all newly designed carbon nitrides (configurations3-35) have low formation energies Ef under 0.1 eV / atom among which two of them—structures 3 and 5—have negative Ef values. Noteworthy, these formation energies are well below the trends defined by models containing only graphitic (N substitutional impurities) oronly pyridinic (N-decorated 1- and 4-vacancies) forms of nitrogen (Fig. 5a). This observationclearly demonstrates the synergetic effect of the two forms of nitrogen established by the IBR mechanism described above as the underlying cause of the thermodynamic stability of g-C3N4 materials. Then, the energies of band edges of the designed carbon nitrides need to be assessed. Fig.5b presents the calculated positions of the valence band maxima and conduction band minima,indicated by pairs of bars, of known g-C3N4 configurations 1 and 2 as well as a selection ofdesigned carbon nitrides according to the invention. Two pairs of horizontal dashed linecorrespond to potentials, either at pH = 0 or pH = 7, of the mentioned half-reactions of water splitting. These are fixed, widely known values. The band gap, that is energy difference (distance) between the pairs of bars must enclose bothhorizontal lines for one of the conditions, either pH = 0 or pH = 7, in order to be suitable forsingle-stage photocatalytic water splitting. However, smaller band gaps correspond to absorption of a larger fraction of visible light photons, and hence intrinsically favor higher photocatalytic conversion efficiencies. In this sense, all designed materials with band gaps of larger than 1.23 eV, which is the difference between the potentials of the H+ / H2 and O2 / H2O half-reactions of water splitting, are potentially better photocatalysts as compared graphitic carbon nitrides g-C3N4.The results for all studied configurations from Fig. 4 are listed in Table 1. It can be observedthat upon reducing the nitrogen content, the band gap follows a decreasing trend, and the positions of band edges converge to the Fermi energy of semi-metallic graphene. Importantly,the reduced band gaps continue enclosing potentials of both half-reactions of water splitting,either at pH = 0 or pH = 7, down to 28.6 at. % N. It is worth comparing these results with carbon nitrides that do not realize the IBR mechanism: structures with stoichiometries CN (configuration 36) and C2N (configuration 37) (comparative structures, not from the invention) that contain only pyridinic nitrogen (no graphitic nitrogen), have equal number of atoms in their two sublattices and consequently do not feature any non-bonding π0band having sufficiently large band gaps of 3.19 eV and 2.47 eV, respectively.Compared to g-C3N4 and structures 3-35 according to the invention, in these comparativecarbon nitrides the conduction band minimum, and especially the valence band maximum, are positioned at significantly lower energies. While this arrangement is more common for semiconductors, it implies that the electron charge carries may not possess sufficient driving force for the H+ / H2half-reaction of the water splitting process, while the energy of hole chargecarriers is not optimally utilized in the complementary O2 / H2O half-reaction. This supportsthe fact that those comparative structures with energies of band edges significantly lower are unsuitable for photocatalysis or at best will present low efficiency in photocatalysis. A separate remark has to be made in relation to small predicted band gaps of configurations24–27 (Fig. 4, Table 1). These configurations are generated by superlattice vectors (3, 0)(configurations 24, 25) and (2, 2) (configurations 26, 27) and contain one-atom vacanciesthat remove sites from only one sublattice. For graphene superlattices defined by vectors (n,m) with n − m mod 3 = 0 both Dirac cones fold onto the Γ point. In this situation, strongperturbation in one of the sublattices gaps only one of the two Dirac cones due to the valley- momentum locking (Ren et al., 2015, Phys. Rev. B 91, 245415, Gamayun et al., 2018, New J.Phys., 20, 023016). In the case of considered carbon nitrides, the dominant sublattice is alsoperturbed, but this perturbation opens only a relatively small band gap.Therefore, based on those unexpected findings, it can be derived that ^-conjugated polymericmaterials having the following features would have improved properties, namely highstability, tunable band gaps in the visible range and systematically higher band edges energies,useful for applications in the field of photocatalysis and optoelectronics:- the atoms of said materials participate into a bipartite (alternant^^^-conjugated polymericnetwork and are distributed among two distinct sublattices characterized by the following structural characteristics:- the said bipartite (alternant) ^-conjugated network comprises Carbon (C) atoms, Nitrogen(N) atoms and optionally other atoms distinct from carbon and nitrogen, in which the numberof atoms in one sublattice (dominant lattice) (nd) is larger than that in the other sublattice(minor lattice) (nm);- the said dominant sublattice contains graphitic (tertiary, that is, bonded to three other atoms)nitrogen (N) atoms, the number of which (NgD) is equal to the difference in numbers of atomsbetween the two sublattices (nd minus nm);- the number of tertiary nitrogen (N) atoms in the dominant sublattice (NgD) is smaller thanthe total number of tertiary atoms of any type in this sublattice.The above considerations focus only on light absorption as the first step of any photocatalytic process leaving aside dissociation and diffusion of photoexcited charge carriers as well as the subsequent chemical reactions at the catalytic active sites. A general strategy for designing materials with increased STH conversion efficiency would be to consider structures withoptimized positions of band edges such as configurations 3-35 according to the invention toensure a more complete coverage of solar light spectrum, yet leaving a sufficient thermodynamic driving force to overcome charge-carrier dissociation and reaction overpotentials that need to be addressed separately.Example 2: Exemplary synthetic strategies leading to ^-conjugated polymeric materialsof the inventionMaterials of the invention can be prepared according to bulk-phase condensation or on-surface self-assembly approach as described herein. The following examples are provided below for the sake of illustration.Bulk-phase synthesis of several carbon nitrides from the proposed configurations 3-35 canbe performed using the ionothermal protocol from aminonitrile precursors as introduced inBuyukcakir et al., 2019, Angew. Chem. Int. Ed. 58, 872–876. This condensation approachresults in tricycloquinazoline linkages that include graphitic nitrogen atoms in the resultingpolymer and trigger local sublattice imbalance. In order to assure global sublattice imbalanceof the ^-conjugated polymeric network, as required by the IBR mechanism, amine functional groups have to be connected to one sublattice of the bipartite (alternant) precursor molecule, while the nitrile functional groups have to be connected to the other sublattice. It has to benoted that the latter condition is not satisfied by the aminonitrile precursor used in Buyukcakiret al., 2019, supra, and the resulting covalent organic framework is not consistent with theIBR mechanism.Configuration 6 can be obtained from (diaminomethylene)malononitrile 6’, a commerciallyavailable compound, by means of bulk-phase condensation at ca. 350^C that uses ZnCl2 as both the solvent and the catalyst, as illustrated under Scheme 1 below: Scheme 1Configuration 6 structure features N-decorated 4-atom vacancies similar to the heptazine structure of g-C3N4 (configuration 2).However, unlike configuration 2, it contains in its structure 4-atom aggregates containingonly carbon atoms. According to the performed first-principles calculations, the predictedband gap of this material is 2.182 eV, which makes it a more efficient light absorber ascompared to, for example, g-C3N4 materials. The positions of the valence band maximum andconduction band minimum relative to the vacuum level are −5.934 eV and −3.753 eV,respectively. These energies enclose the potentials of both half-reactions of the water splittingprocess at both neutral and acidic conditions.Configuration 14 can be obtained from an aromatic aminonitrile precursor 14’, acommercially available compound, by means of bulk-phase condensation at ca. 350^C thatuses ZnCl2 as both the solvent and catalyst producing tricycloquinazoline linkages asillustrated under Scheme 2 below: Scheme 2 Synthesis from lower molecular weight precursors, for example aminocyanoacetylene, canalso be envisaged. Configuration 14 corresponds to carbon nitride of C9N4 composition. Itsstructure features N-decorated single-atom vacancies similar to the triazine structure of g- C3N4 (configuration 1). However, unlike configuration 1, it contains in its structure hexagonal rings containing only carbon atoms. According to the performed first-principles calculations, the predicted band gap of this material is 1.799 eV, which makes it a more efficient light absorber as compared to, for example, g-C3N4materials. The positions of the valence band maximum and conduction band minimum relative to the vacuum level are−5.454 eV and −3.655 eV, respectively. These energies enclose the potentials of both half-reactions of the water splitting process at all values of pH except for strongly acidic conditions.^-conjugated polymeric material according to the invention can be also obtained ascopolymers involving structural fragments inherited from two or more configurationsdiscussed above using a high-temperature bulk condensation route. For example, precursors6’ and 14’ can be used in combination with typical precursors for synthesizing configuration2 (e.g. urea, dicyandiamide, melamine) of different degrees of condensation (e.g. melon,poly(heptazine imide)) to produce copolymers with configurations 6 and 14. Such synthesisis commonly performed at higher temperatures around ca. 550^C, either without anyadditional components or via the ionothermal route, e.g. in LiCl / KCl eutectic melts (Pelicanoand Antonietti, 2024, Angew. Chem. Int. Ed.63, e202406290). Such copolymers satisfy both the IBR mechanism and the claims of this patent. Scheme 3 below illustrates the structuralfragments of copolymers obtained upon condensation of precursor 6’ with dicyandiamide 2’.The resulting copolymer contains both the structural fragments inherent to configuration 2 at its realistic degree of polymerization (top) and the fragments related to configuration 6(bottom) as illustrated below.Scheme 3 Respectively, obtainedupon condensation of dicyandiamide 2’ with precursor 14’.Scheme 4 The emerging on-surface self-assembly approach (Clair et al., 2019, Chem. Rev.119, 4717–4776), however, provides a flexibility for the synthesis of highly ordered graphenenanostructures with high contents of pyridinic and graphitic nitrogen substitutions (Cai et al., 2014, Nat. Nanotechnol, 9, 896–900; Wang et al., 2022, J. Am. Chem. Soc.144, 4522–4529; Vilas-Varela et al., 2023, Chem. Int. Ed.62, e202307884; Wen et al., 2023, J. Am. Chem. Soc. 145, 19338–19346). Some illustrations of possible routes of synthesis are provided below.Configuration 5 can be obtained from a molecular precursor 5’ by means of an on-surfacecondensation with HHal (Hal = Cl, Br, I) release followed by on-surface dehydrogenation ata higher temperature (ca. 400^C) as illustrated in Scheme 5 below:Scheme 5A positions of graphitic N atoms. For example, configuration 6 can be synthesized frommolecular precursor 6’’ as illustrated under Scheme 6 below:Scheme 6 depict the same structure, and are equivalent to the presentation shown in Figure 4.Configuration 13 can be synthesized by on-surface synthesis on substrates such as Au (111)involving Ullmann coupling at ca. 200^C followed by a dehydrogenation on the same substrate at a higher temperature (ca. 400^C). Several different precursors are possible,Scheme 7 provides an example from precursor 13’:Scheme 7 Example 3: Synthesis, characterization and photocatalytic activity of a copolymer ofconfigurations 2 and 6As an experimental proof of principle of the invention, a copolymer of configurations 2 and6 is synthesized according to Scheme 3. It is demonstrated that the activity of this copolymertowards photocatalytic hydrogen evolution is significantly higher than that of configuration2 synthesized under equivalent conditions.Materials synthesis0.8408 g (10 mmol) of dicyandiamide 2' (99%, Thermo Fisher Scientific) and 0.0541 g (0.5mmol) of (diaminomethylene)malononitrile 6’ were ground in an agate mortar in a gloveboxunder Ar atmosphere. The mixture was placed in an alumina crucible with a lid and heated to500^C for 1h with a ramping rate of 10^C / min. The resulting product was ground with 1 g ofLiCl / KCl eutectic mixture, placed in an alumina crucible with a lid and heated to 550^C for3h with a ramping rate of 10^C / min. The content of the crucible was dispersed in hot water,filtered, thoroughly washed with deionized water and dried in vacuum. The resulting solidlabelled sample 2-6 had an amber-yellow color. The control experiment repeated the samesteps, but without the addition of precursor 6’. The resulting solid of luminous yellow color was labelled sample 2. Materials characterization and photocatalytic activity measurements Powder x-ray diffraction (XRD) measurements of the samples were performed using a Malvern Panalytical Empyrean instrument. FT-IR spectroscopy measurements were performed using a PerkinElmer Spectrum 3 spectrometer equipped with an ATR top plate accessory containing an uncoated diamond crystal. Diffuse reflectance UV-Vis spectroscopy data was obtained using a Shimadzu UV-3600TMspectrometer. Photocatalytic hydrogenevolution measurements were performed on suspensions of 1 mg of each of the two samplesin 2 ml of aqueous solution containing 10 vol. % of triethanolamine (TEOA) as a sacrificialelectron donor and 0.06 g of KCl. In addition, in situ photodeposited Pt of 3 wt. % relative tothe sample mass was used as the hydrogen evolution reaction cocatalyst. The suspensionswere loaded into 4 ml vials containing small magnetic stirrers and purged with N2at a constant gas flow rate of 3 ml / min. The samples were bottom-illuminated in a setup (Firth et al., 2024, Adv. Energy Mater., 2403372) equipped with a 500 W Xe lamp fitted with a KG2 Colored Glass Bandpass Filter (304–785 nm) from ThorLabs and adjusted to 1 sun equivalentirradiance (100 mW cm-2). The illumination area of each vial was 1.3 cm2. The hydrogenevolution rate was quantified every 20 mins using a Shimadzu Nexis GC-2030 gaschromatograph fitted with a BID detector, the response of which was calibrated using a Ptelectrode electrolysis cell.Figure 6 shows the powder XRD patterns of samples 2 and 2-6 revealing the presence ofboth the layered structure and the in-plane order characteristic to the poly(heptazine imide)form of configuration 2 (Schlomberg at al., 2019, Chem. Mater. 31, 7478–7486). Namely,the 001 reflections at 2^ ^ 28^ correspond to 3.2 Å interlayer distance, while the 1^ 10reflections at 2^ ^ 8^ correspond to the ca. 13 Å in-plane lattice constant of poly(heptazineimide). Fourier-transform infrared (FT-IR) spectra of samples 2 and 2-6 are shown in Figure7. Both spectra show a clear peak at ca. 800 cm-1 that can be attributed to the vibrationalmodels of the heptazine cores (Liu et al., 2020, ACS Omega 21, 12557–12567). The FT-IRspectrum of sample 2-6 contains two absorption peaks not present in the spectrum of sample2, namely, at 847 cm-1 tentatively assigned to the larger used cores shown in Scheme 3 andat 1576 cm-1, which corresponds to the C-C stretching modes. The UV-Vis spectrum ofsample 2 measured in the diffuse reflectance mode (Figure 8) shows a very sharp band edgeat 450 nm, in agreement with previous reports (Pelicano and Antonietti, 2024, Angew. Chem.Int. Ed. 63, e202406290). The Tauc plot fit (Tauc, 1968, Mat. Res. Bull. 3, 37–46; Makuła etal., 2018, J. Phys. Chem. Lett. 9, 6814–6817) of this spectrum shown in Figure 9a yields aband gap of 2.73 eV. The same band edge is recognized in the spectrum of sample 2-6, whichalso shows enhanced absorption down to 2 eV, consistent with the predictions forconfiguration 6. The Tauc plot fits for sample 2-6 resolve three different absorption edgesat 2.71 eV, 1.99 eV and 1.53 eV (Figure 9b).During the photocatalytic activity measurements, hydrogen was detected immediately afterstarting illumination (Figures 10a). The initial H2 evolution rates of 21.7 mmol h-1 g-1 and27.3 mmol h-1g-1 were observed for samples 2 and 2-6, respectively. The hydrogen evolutionrates decayed to lower values, stabilizing at 2.70 mmol h-1 g-1 and 6.66 mmol h-1 g-1,respectively, after 12 h of continuous illumination (Figures 10a and 10b). The latter pair ofvalues corresponds to a factor of 2.5 increase in photocatalytic activity of sample 2-6 ascompared to sample 2. The values of photochemical conversion efficiency of sample 2-6 atT = 0 h and T = 12 h are 1.67% and 0.41%, respectively.Altogether, those data support that the ^-conjugated polymeric materials presentphotocatalytic activities which are promising for use in water splitting and any otherindustrially relevant photocatalytic processes.

Claims

Claims1. A ^-conjugated polymeric material wherein the atoms of said material participate in abipartite (alternant^^^-conjugated polymeric network and are distributed among two distinct sublattices characterized by the following structural characteristics: a) the said bipartite (alternant) ^-conjugated network comprises Carbon (C) atoms, Nitrogen (N) atoms and optionally other atoms distinct from carbon and nitrogen, in which the number of atoms in one sublattice (dominant lattice) (nd) is larger than that in the other sublattice (minor lattice) (nm); b) the said dominant sublattice contains tertiary (graphitic) nitrogen (N) atoms, thenumber of which (NgD) is equal to the difference in numbers of atoms between the two sublattices (ndminus nm); c) the number of tertiary nitrogen (N) atoms in the dominant sublattice (NgD) is smaller than the total number of tertiary atoms of any type in this sublattice.

2. A ^-conjugated polymeric material according to claim 1 further comprising one or moreatoms distinct from carbon and nitrogen, but when those atoms distinct from carbon andnitrogen are selected from H and halogens (F, Cl, Br, I), those do not participate in the^^- conjugated network.

3. A ^-conjugated polymeric material according to claim 1 or 2, wherein the bipartite(alternant) ^-conjugated network only comprises Carbon (C) atoms and Nitrogen atoms.

4. A ^-conjugated material according to claim 1 or 2, further containing one or more atomsother than carbon and nitrogen selected from O, S, Se, Te and B, wherein: -when one or more atoms selected from O, S, Se and Te are present, said one or moreatoms participate in the ^-conjugated network only when bound to at least one otheratom and this atom participates in this ^-conjugated network; or- when one or more atoms selected from O, S, Se and Te are present, said one or moreatoms participate in the ^-conjugated network and are bound to two other atoms, pereach said O, S, Se and Te atom one less tertiary nitrogen (N) atom to the conditionsunder b) of claim 1 is also present in the said ^-conjugated network; or- when one or more B is present in the ^-conjugated network, an additional tertiarynitrogen (N) atom per each B atom to the conditions under b) of claim 1 is also present in the said ^-conjugated network.

5. A ^-conjugated polymeric material according to claim 1, wherein said material onlycomprises Carbon (C) atoms and Nitrogen atoms (e.g. carbon nitrides).

6. A ^-conjugated material according to claim 1 or 5, wherein nC, the total number ofgraphitic carbon atoms in both sublattices, is higher than 6.

7. A ^-conjugated material according to claim 1 or 5 to 6, wherein nC is from 9 to 27.

8. A ^-conjugated material according to claim 1 or 5 to 7, wherein nNg is from 1 to 3.

9. A ^-conjugated material according to claim 1 or 5 to 8, wherein nNp is from 3 to 9.

10. A ^-conjugated material according to claim 1 or 5 to 9 having a nitrogen content lowerthan 55% of the total number of atoms (e.g. from about 53% to about 13%).

11. A ^-conjugated material according to claim 1 or 5 to 10, comprising or consisting in aconfiguration selected from configurations 3-35.

12. A ^-conjugated material according to claim 1 or 5 to 11, which is a copolymer of one ormore configurations selected from configurations 3-35 and optionally further includingconfigurations 1,2.

13. A ^-conjugated material according to claim 11, comprising or consisting in theconfiguration 6 or 14.

14. A ^-conjugated material according to claim 11, comprising or consisting in theconfiguration 5 or 13.

15. A ^-conjugated material according to claim 12 comprising a copolymer of configurations2 and 6.

16. A ^-conjugated material according to any one of claims 11 to 12, wherein said ^-conjugated material is a product of incomplete condensation of its constitutiveconfigurations.

17. Use of a ^-conjugated material according to claim any one of claims 1 to 16 in aphotocatalytic process, in particular water splitting.

18. Use of a ^-conjugated material according to claim any one of claims 1 to 16 inphotocatalytic processes for CO2 reduction, N2 fixation, pollutant degradation andbacterial and viral disinfection.

19. A photocatalytic system comprising a ^-conjugated material according to any one ofclaims 1 to 16 as light-absorbing material.

Images