Dibenzofuran photobase generators for polyimide formation

Abstract

The present disclosure relates to photobase generators which include a dibenzofuran moiety, a visible light absorbing moiety, and a linker complex. Application of UV-Vis light to the photobase generator may provide a basic entity for manufacturing a polyimide.

Description

[0001] DIBENZOFURAN PHOTOBASE GENERATORS FOR POLYIMIDE FORMATION

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Application No. 63 / 570,229, filed March 26, 2024, which is incorporated by reference in its entirety.

[0004] FIELD

[0005] The present disclosure relates to photobase generator compounds which may be used in polyimide formation.

[0006] BACKGROUND

[0007] Photobase generators (PBGs) typically include three parts: a chromophore, responsible for light absorption and transforming the energy of photons into chemical energy, a latent base, which is the moiety that releases the actual base upon application of light, and a linker that connects the base with the chromophore. PBGs release amine bases upon light irradiation and are being explored in the areas of photoinitiated polymerization, photoinduced crosslinking of polymers, photo-patterning, adhesives, and lithography. However, photobase generators are less developed than photoacid generators. PBGs are based on both non-ionic and ionic types. A wide range of materials has been used as chromophores for the absorption of light, including those limited to absorption in the ultra-violet region. Typical PBG linkers include carbamates, O- acyloximes, ammonium salts, sulfonamides, formamides, nifedipines, and a- aminoketones. By way of example, O-acyloximes require water to release the base so they may not be ideal in polymeric substrates that are sensitive to water. Overall, carbamate linker based PBGs are efficient and synthetically versatile.

[0008] Polyimides have been widely used as protection and insulation layers in microelectronics due to their excellent chemical, mechanical stability, and electrical properties. Photosensitive polyimides (PSPIs) may be attractive for microelectronics because they can be patterned by direct exposure and developed without a photoresist. PSPIs may find applications in various electronic, electro-optic, waveguide, and nonlinear optical materials. A photosensitive polyimide system typically includes a polyimide precursor and a photobase generator as an accelerator to form a polyimide by photoreaction. However, a polyimide precursor with an aromatic ring as a basic skeleton typically has a broad absorption band in the ultraviolet (UV) region of wavelength below 400 nm. Therefore, when ultraviolet light is applied, the photochemical reaction may not proceed effectively in the exposed area because absorption of light is predominantly by the polyimide precursor, which results in low sensitivity and deterioration of the pattern shape.

[0009] Most PBGs have minimal absorption above 400 nm, so the base generation can only be triggered by ultraviolet (UV) light. Compared to visible (VlS)-light initiators, UV responsive catalysts require high photon energy, often achieve reduced curing depths, and may also cause irreversible damage to UV-sensitive materials. Moreover, existing photobase generators also show high thermal residue, and low photolytic base release efficiency, which are undesirable for improving the efficiency of a photosensitive polyimide-based electronic device. Thus, there is a need for additional contributions in this area of technology.

[0010] SUMMARY

[0011] Photobase generator compounds described herein may be used to provide good absorption in the visible spectral region, efficient photolytic base release under photoirradiation, and low thermal residue. In some embodiments, a photobase generator absorbs light of a first wavelength and emits light of a second, higher wavelength than the first wavelength. The photobase generators disclosed herein may be utilized in methods of making a polyimide film for use in microelectronics, printed circuit boards, and / or optical devices, amongst other things. A polyimide film disclosed herein may exhibit high thermal and mechanical stability properties.

[0012] In one embodiment, a photobase generator includes a light absorbing dibenzofuran derivative, a linker group, and a basic moiety. The linker group may covalently link the dibenzofuran derivative and the basic moiety. The dibenzofuran derivative may absorb light energy of a first excitation wavelength and transfer energy to the linker group, and upon heterolytic cleavage the linker group may release the base moiety. In some forms, the photobase generator may be a compound according to formula (1)

[0013] (1).

[0014] In Formula (1), each of R1and R2represents H or alkoxy, R1and R2are connected together in a hetero-cyclic ring; R3represents H, an alkyl, or an aryl; and the Base is an amine. In some forms, the Base may be a secondary or tertiary amine which when released from the photobase generator provides a primary or secondary amine. In some forms, each of R1and R2may alternatively represent a substituted amine or heterocyclic structure or R1and R2are connected together in a substituted carbo and R3may alternatively represent a heteroaryl substitution. In one form, the base has the following

[0015] D general structure:6, where each of Rs and Rs independently represents H or a C3-

[0016] Cs linear alkyl, or Rs and Rs are connected together in an optionally substituted heterocyclic ring. In forms, Rs-Rs are connected together in a substituted heterocyclic ring having one of the following structures:

[0017] In another embodiment, a method for making a polyimide includes providing a photobase generator as described herein and a polyimide precursor dispersion in a dispersant; covering a substrate with the PBG and polyimide precursor; applying ultraviolet to visible (UV-Vis) light to the PBG and polyimide precursor covered substrate; and heating the covered substrate for at least one of removing the dispersant from the covering and curing the covered substrate. In one form, the method may further include masking portions of the covered substrate to selectively apply UV-Vis light to the covered substrate.

[0018] In a further embodiment, a method for measuring the base release efficiency of a photobase generator compound may include dissolving a photobase generator compound as described herein in acetonitrile; measuring the pH of a solution including the photobase generator and acetonitrile; exposing the solution including the photobase generator and acetonitrile to visible light; and measuring the pH of the solution including the photobase generator and acetonitrile after exposure to UV-Vis light.

[0019] In one aspect, a photobase generator compound described herein may exhibit excellent absorption in the visible spectral region, low thermal residue upon heating temperatures up to 450 °C, and / or base moiety separation. In another aspect, a method for manufacturing polyimide films using a photobase generator compound disclosed herein is provided. These and other embodiments are described in greater detail below.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a graphical illustration of polyimidization efficiency. FIG. 2 is a graphical illustration of absorption spectra of different photobase generator compounds.

[0022] DETAILED DESCRIPTION

[0023] The present disclosure relates to photobase generator compounds and their potential use(s) in generating reactive precursors for polyimide generation. The photobase generator compounds disclosed herein may be used for the formation of a polyimide under light irradiation conditions, which in turn may be useful for fabrication of efficient microelectronic devices. In some embodiments, the photobase generator may absorb light in the visible region, e.g., from about 380 nm to about 440 nm, exhibit high photobase release activity, and / or may have a very low thermal residue upon heating above 400 °C.

[0024] The photobase generator compounds described herein may absorb light energy of first excitation wavelength and undergo a heterolytic cleavage. While not wanting to be bound by theory, it is believed that the absorption may be followed by intramolecular hydrogen abstraction by the nitro group which may form an aci-nitro intermediate. The decay rate constant of the aci-nitro intermediate may depend on the substitution of the oNB group. An irreversible cyclization of the aci-nitro intermediate, and subsequent ringopening, may give a hemiacetal intermediate that may hydrolyze to release a carbamate. The carbamate and carbon dioxide may be further cleaved to provide a desired base compound. In addition, the cleaved base compound(s) may act as a catalyst(s) for formation of a polyimide from a polyimide precursor.

[0025] The term “moiety” as used herein refers to a specific segment or functional group of a molecule. Chemical moieties are often recognized as chemical entities embedded in or appended to a molecule.

[0026] The term “dibenzofuran” as used herein, refers to a chemical moiety with the structure:

[0027] The term “piperidine” or “piperidine derivative” as used herein, refers to a chemical moiety with the structure:

[0028] QIH

[0029] In one embodiment, a photobase generator includes a light absorbing benzofuran derivative, a linker group, and a basic moiety. The linker group may covalently link the dibenzofuran derivative and the base moiety, and the dibenzofuran derivative may absorb light energy of a first excitation wavelength and transfer energy to the linker group. Upon heterolytic cleavage, the linker group may release the base moiety. Without being bound to any particular theory, it is believed that the light absorption may be followed by intramolecular hydrogen abstraction by the nitro group to form an aci-nitro intermediate. The decay rate constant of the aci-nitro intermediate may depend on the substitution of the oNB group. An irreversible cyclization of the aci-nitro intermediate, and subsequent ring-opening, may give a hemiacetal intermediate that may hydrolyze to release the carbamate. In one form, the carbamate may include a piperidine derivative or acyclic amine derivative, and an ester linkage, and may undergo photodecarboxylation to release a desired piperidine or acyclic amine base moiety.

[0030] In some embodiments, the photobase generator may include a compound according to formula (1):

[0031] In formula (1), each of R1and R2represents H or an, alkoxy, or R1and R2are connected together in a heterocyclic ring, R3represents H, an alkyl, or an aryl, and the base is an amine. In some forms, each of R1and R2may alternatively represent a substituted amine or heterocyclic structure or R1and R2are connected together in a substituted carbo and R3may alternatively represent a heteroaryl substitution. In one form, when the base is released from the photobase generator it may provide a primary or secondary amine. In p some forms, the base has the following general structure: 6 , where each R5and R6independently represents H or a Ca-Cs linear alkyl, or Rs and Rs are connected together in an optionally substituted heterocyclic ring. In some forms where Rs and Rs are connected together in an optionally substituted heterocyclic ring having one of the following structures: Non-limiting examples of compounds according to formula (1) include the following:

[0032]

[0033] In one embodiment, a method for making a polyimide includes providing a photobase generator as described herein and a polyimide precursor dispersion in a dispersant; covering a substrate with the PBG and polyimide precursor; applying UV-Vis light to the PBG and polyimide precursor covered substrate; and heating the covered substrate for at least one of removing the dispersant from the covering and curing the covered substrate. In some forms, the method may further include masking portions of the covered substrate to selectively apply the UV-Vis light to the covered substrate.

[0034] In another embodiment, a method for measuring the base release efficiency of a photobase generator compound includes dissolving a photobase generator compound as described herein in a polar solvent such as acetonitrile; measuring the pH of a solution including the photobase generator compound and acetonitrile; exposing the solution including the photobase generator compound and acetonitrile to UV-Vis light; and measuring the pH of the solution including the photobase generator compound and acetonitrile after exposure to the UV-Vis light. The change in pH before and after exposure may be indicative of the amount of basic moiety released and thus the base release efficiency. In one non-limiting form, the UV-Vis light may be about 600 mJ / cm2although other variations are contemplated.

[0035] Photobase generator compounds described herein may exhibit a high photosensitivity or high quantum yield for release of the base moiety upon exposure to radiation of a desired wavelength. The photosensitivity may be demonstrated by a change in pH in a solution including a photobase generator compound before and after exposure of the solution to the radiation. By way of example, the pH change may be greater than about 0.2, about 0.4, about 0.8, about 1.5, and / or about 2.2 By way of example, the quantum yield for release may be greater than about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1.0, about 1.5 and / or about 2.2. Base release efficiency can be measured by dividing the pH of a solution including a photobase generator compound after exposure to light of certain energy by the pH of the same solution before light exposure, which is equivalent to the release efficiency of the base moiety. In various embodiments, the base moiety may have a release efficiency greater than about 2.2. In some embodiments, the base release efficiency can be greater than about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1 .0, about 1 .25, about 1 .5, about 2.0 and / or about 2.2. The change in pH in solution may be measured by mercury lamp, such as a Dymax UV curing conveyor with 5000-EC lamps.

[0036] Photobase generator compounds described herein may have a peak absorption maximum at a wavelength between about 370 nm to about 440 nm. In some forms, the peak absorption can be at a wavelength in the range of about 370 nm, about 375 nm, about 380 nm, about 390 nm, about 395 nm, about 400 nm, about 410 nm, about 420 nm, about 430 nm, and about 440 nm to about 410 nm, about 420 nm, about 430 nm, and about 440 nm, and / or any permutation of the aforementioned values, e.g., about 365 nm, about 405 nm, and / or about 436 nm, just to provide a few examples.

[0037] In one embodiment, a photobase generator compound includes a yellow light absorbing dibenzofuran derivative and a piperidine base derivative, and the spatial distance therebetween is optimized through a linker complex, for formation of a carbamate anion, and then for photo-release of a piperidine base.

[0038] In one embodiment, a photobase generator compound (PBGBF) includes a UV- Vis light absorbing dibenzofuran derivative, a linker complex, and a piperidine base moiety. The linker complex covalently links the UV-Vis light absorbing dibenzofuran derivative and the piperidine base moiety. In some forms, while not wanting to be bound by any particular theory, it is believed that light absorption by the dibenzofuran derivative may be followed by intramolecular hydrogen abstraction by the nitro group which may form an aci-nitro intermediate. The decay rate constant of the aci-nitro intermediate may depend on the substitution of the oNB group. An irreversible cyclization of the aci-nitro intermediate, and subsequent ring-opening may give a hemiacetal intermediate that may hydrolyze to release the carbamate. In such forms, the carbamate that includes a piperidine derivative, and ester linkage, may undergo photodecarboxylation to release a desired piperidine base moiety. In such forms, the released base pH change may be greater than about 2.2. In some forms, the released base compound may act as a catalyst for formation of a polyimide from a polyimide precursor.

[0039] In one aspect, the linker complex may be tuned to optimize the quick release of a piperidine base moiety. By optimizing the linker complex, the efficiency of base release may be tuned. In some forms, the linker complex may include a stabilizing substitution, e.g., a methyl or phenyl. In In some forms, the linker complex may include an unsubstituted ester group. When the linker complex includes an unsubstituted ester group, the linker complex may include one of the following structures:

[0040] In some forms, the linker complex may include an unsubstituted ester or substituted ester. In some forms, the linker complex may include an optionally substituted C2-C7 ester group. When the linker complex includes a substituted ester group, the linker structures: one embodiment, a method for making polyimide may include providing a photobase generator as described herein and a polyimide precursor dispersion. In some forms, the PBG and polyimide precursor can be dispersed within a solvent and / or a dispersant. In some forms, the polyimide precursor may be polyamidic acid. In some forms, the dispersant may be an aprotic / polar / non-polar solvent, such as n-methyl pyrrolidone (NMP). The method may also include covering a substrate with the PBG and polyimide precursor and applying UV-Vis light to the PBG and polyimide precursor covered substrate, e.g., at about 600 mJ / cm2. In some forms, the method may include heating the covered substrate to remove the dispersant from the covering. By way of example, the heating may be conducted at about 120 °C for at least 10 minutes. In some forms, the method further includes heating the covered surface to cure, polymerize, and / or harden the covered substrate surface. Such hearting may be conducted at about 185 °C for about 5 minutes. In some forms, the method may include masking portions of the dispersant covered substrate to restrict, minimize or reduce the exposure of the precursor dispersant to the enabling UV-Vis light.

[0041] EXAMPLES

[0042] It has been discovered that photobase generators described herein have exhibited absorption at wavelengths over 400 nm, and also exhibited improved photobase release performance. These benefits are further demonstrated by the following examples, which are intended to be illustrative of the disclosure but are not intended to limit the scope or underlying principles in any way.

[0043] The following examples are synthesis procedures for various particular, but nonlimiting photobase generators as described herein: Scheme of compound PBGBF1-2 synthesis

[0044] Compound PBGBF1-2.1 synthesis — (4-(2-bromo-5-methoxyphenoxy)-2- nitrobenzaldehyde): A 100 mL flask was fitted with a stir bar. In the flask, 4-fluoro-2- nitrobenzaldehyde (338.2 mg, 2.0 mmol) and 2-bromo-5-methoxyphenol (385.2 mg, 1.9 mmol) were dissolved in anhydrous dimethylformamide (15 mL), followed by the addition of potassium carbonate (792.7 mg, 5.7 mmol). The mixture was purged with Argon and kept at room temperature overnight. Both TLC and LCMS showed the completion of the reaction. Saturated ammonium chloride solution (30 mL) was added, and the mixture was extracted with ethyl acetate (3* by 15 mL). The combined organic phase was washed with water (45 mL) and brine (45 mL) sequentially and was dried over anhydrous sodium sulfate. After filtration and concentration, the crude product was purified by silica gel chromatography to provide PBGBF1-2.1 as a brown solid using 0-40% ethyl acetate in Hexane as the eluants. 5.7 g, 74% yield. MS (APCI): calculated for Chemical Formula: Ci4Hi0BrNO5([M+H]+') = 352 found: 352.1H NMR (400 MHz, CDCI3) 10.32 (d, J = 0.8 Hz,

[0045] 1 H), 7.98 (d, J = 8.4 Hz, 1 H), 7.57 (d, J = 8.8 Hz, 1 H), 7.50 (d, J = 2.4 Hz, 1 H), 7.22 (ddd, J = 8.4 Hz, 2.4 Hz, 0.8 Hz, 1 H), 6.80 (dd, J = 8.8 Hz, 2.8 Hz, 1 H), 6.72 (d, J = 2.8 Hz, 1 H), 3.81 (s, 3H).

[0046] Compound PBGBF1-2.2 synthesis — (2-(4-(2-bromo-5-methoxyphenoxy)-2- nitrophenyl)-1,3-dioxolane): A 100 mL flask was fitted with a stir bar and set up with a Dean-Stark apparatus. To the flask, compound PBGBF1-2.1 (500.0 mg, 1.4 mmol) and benzene (30 mL) were added, followed by the addition of ethylene glycol (0.5 mL) and p- toluenesulfonic acid monohydrate (50.0 mg, 0.3 mmol). The mixture was purged with Argon and warmed up to 110 °C and has been kept at this temperature for 20 hours. Both TLC and LCMS showed completion of the reaction. The mixture was cooled down to room temperature and then poured into saturated sodium bicarbonate solution (20 mL). The mixture was extracted with ethyl acetate (3* by 15 mL). The combined organic phase was washed with water (10 mL) and brine (10 mL) sequentially and dried over anhydrous sodium sulfate. After filtration and concentration, the crude was purified by silica gel chromatography to PBGBF1-2.2 provide a light-yellow liquid using 0-40% ethyl acetate in Hexane as the eluants. Quantitative yield. MS (APCI): calculated for Chemical Formula: Ci6Hi4BrNO6([M+HD = 398 found: 398.1H NMR (400 MHz, CDCI3) 7.74 (d, J = 8.4 Hz, 1 H), 7.54 (d, J = 8.8 Hz, 1 H), 7.41 (d, J = 2.4 Hz, 1 H), 7.15 (dd, J = 8.4 Hz, 2.4 Hz, 1 H), 6.72 (dd, J = 8.8 Hz, 2.8 Hz, 1 H), 6.64 (d, J = 2.8 Hz, 1 H), 6.40 (s, 1 H), 4.07-4.02 (m, 4H), 3.78 (s, 3H).

[0047] Compound PBGBF1-2.3 synthesis — (2-(1,3-dioxolan-2-yl)-7-methoxy-3- nitrodibenzo[b,d]furan): A 100 mL flask was fitted with a stir bar. Compound PBGBF1- 2.2 (396.2 mg, 1.0 mmol) and dimethylacetamide (8 mL) were added to the flask, followed by the addition of palladium on carbon (31.9 mg, 0.03 mmol) and sodium acetate (123.0 mg, 1.5 mmol). The mixture was degassed at room temperature using Argon bubbling for 1 hour. The reaction was heated up to 115 °C and kept at this temperature for 2 days. Neither TLC nor LCMS could be used to track the progress of the reaction. The mixture was cooled down to room temperature and then filtered through celite pad. The pad was extracted with dichloromethane. The filtrate was extracted with ethyl acetate (3* by 15 mL). The combined organic phase was washed with water (20 mL) and brine (20 mL) sequentially and was dried over anhydrous sodium sulfate. The crude was purified by recrystallization with ethyl acetate in Hexane to provide compound PBGBF1-2.3 as a white cotton-like solid. 110 mg, 35% yield. MS (APCI): calculated for Chemical Formula: Ci6Hi3NO6([M+HD = 316 found: 316.1H NMR (400 MHz, CDCI3) 8.26 (s, 1 H), 8.16 (s, 1 H), 7.88 (d, J = 8.4 Hz, 1 H), 7.13 (d, J = 2.0 Hz, 1 H), 7.03 (dd, J = 8.4 Hz, 2.0 Hz, 1 H), 6.63 (s, 1 H), 4.12 (s, 4H), 3.93 (s, 3H). Compound PBGBF1-2.4 synthesis — (7-methoxy-3-nitrodibenzo[b,d]furan- 2-carbaldehyde): Compound PBGBF1-2.3 (700.0 g, 2.2 mmol) was suspended in tetrahydrofuran / water (18mL / 6mL), while p-toluene sulfonic acid monohydrate (211.2 mg, 1.1 mmol) was added. The reaction was heated up to 60 °C and kept at this temperature for 24 hours. After LCMS showed the completion of the reaction, it was cooled down to room temperature. After removing the THF by rotavapor, the product was precipitated out and it was collected via vacuum filtration to provide PBGBF1-2.4 as a red solid. 593.0 mg, 98% yield. MS (APCI): calculated for Chemical Formula: C14H9NO5 ([M-H] *) = 271 found: 271.1H NMR (400 MHz, CDCI3) 10.51 (s, 1 H), 8.42 (s, 1 H), 8.29 (s, 1 H), 7.93 (d, J = 8.8 Hz, 1 H), 7.16 (d, J = 2.0 Hz, 1 H), 7.08 (dd, J = 8.8 Hz, 2.0 Hz, 1 H), 3.95 (s, 3H).

[0048] Compound PBGBF1-2.5 synthesis — (1-(7-methoxy-3- nitrodibenzo[b,d]furan-2-yl)ethan-1-ol): A 100 mL flask was fitted with a stir bar. In the flask, compound PBGBF1-2.4 (593.0 mg, 2.2 mmol) was dissolved in anhydrous dichloromethane (5 mL). The solution was cooled down to 0 °C with an ice-water bath. Trimethylaluminium (2.0 in Hexane, 2.2 mL) was added dropwise to the solution. The reaction was slowly warmed up to room temperature after the completion of the addition. The reaction was kept at room temperature overnight. Both TLC and LCMS showed completion of the reaction. It was cooled down to 0 °C and worked-up by the addition of water and sodium hydroxide (1 N) solution, 5 mL for each. The mixture was extracted with dichloromethane (3* by 10 mL). The combined organic phase was dried over anhydrous sodium sulfate. After filtration and concentration, the crude was purified by silica gel chromatography to provide PBGBF1-2.5 as an orange-yellow solid using 0-40% ethyl acetate in Hexane as the eluants. 235.0 mg, 37% yield. MS (APCI): calculated for Chemical Formula: C15H13NO5 ([M+H]+') = 288 found: 288.1H NMR (400 MHz, CDCI3) 8.27 (s, 1 H), 8.12 (s, 1 H), 7.87 (d, J = 8.8 Hz, 1 H), 7.10 (d, J = 2.0 Hz, 1 H), 7.01 (dd, J = 8.8 Hz, 2.0 Hz, 1 H), 5.64-5.54 (m, 1 H), 3.93 (s, 3H), 2.46 (d, J = 3.6 Hz, 1 H), 1.66 (d, J =

[0049] 6.4 Hz, 3H).

[0050] Compound PBGBF1-2.6 synthesis — )1-(7-methoxy-3- nitrodibenzo[b,d]furan-2-yl)ethyl (4-nitrophenyl) carbonate): A solution of PBGBF1-

[0051] 2.5 (235.0 mg, 0.8 mmol) in dimethylacetamide (5 mL) was cooled down to 0 °C. Triethylamine (0.23 mL) was added, followed by degassing of the solution. 10 minutes later, 4-nitrophenyl chloroformate (181.4 mg, 0.9 mmol) was added, and the reaction solution was warmed up gradually to room temperature. It was kept at room temperature overnight. LCMS showed completion of the reaction. The reaction solution was then poured into water (60 mL). The product was collected as a precipitate by vacuum filtration. The crude was re-dissolved in dichloromethane and purified by silica gel flash chromatography to provide PBGBF1-2.6 as a pale-yellow solid using 40%-100% dichloromethane in Hexane, then 0-20%-40% ethyl acetate in dichloromethane as the eluants. 345.0 mg, 93% yield. MS (APCI): calculated for Chemical Formula: C22H16N2O9 ([M-CO2-H]-) = 408 found: 408.1H NMR (400 MHz, CDCI3) 8.26-8.20 (m, 2H), 8.20 (s, 1 H), 8.17 (s, 1 H), 7.92 (d, J = 8.8 Hz, 1 H), 7.38-7.31 (m, 2H), 7.12 (d, J = 2.0 Hz, 1 H), 7.05 (dd, J = 8.8 Hz, 2.0 Hz, 1 H), 6.58 (q, J = 6.4 Hz, 1 H), 3.94 (s, 3H), 1.89 (d, J = 6.4 Hz, 3H).

[0052] Compound PBGBF1-2 synthesis: (1-(7-methoxy-3-nitrodibenzo[b,d]furan-2- yl)ethyl (2R,6S)-2,6-dimethylpiperidine-1-carboxylate): A mixture of PBGBF1-2.6 (345.0 mg, 0.8 mmol) and 1 -hydroxybenzotriazole hydrate (35.0 mg, 0.2 mmol) in dimethylacetamide (5 mL) was stirred at room temperature, and then it was degassed. To the solution, 4-(dimethylamino)pyridine (0.3 mL, 2.1 mmol) was injected. The reaction solution was degassed again and then heated up 90 °C and kept at this temperature for 2 hours. TLC and LCMS showed completion of the reaction. The reaction mixture was poured into 1% sodium bicarbonate (100 mL) and the precipitate was collected via vacuum filtration. The crude was re-dissolved in dichloromethane and purified by silica gel flash chromatography to provide PBGBF1-2 as a light-yellow solid using ethyl acetate in Hexane (0-40%) as the eluants, followed by another silica gel flash chromatography 40%-100% dichloromethane in Hexane, then 0-20%-40% ethyl acetate in dichloromethane as the eluants. 223.0 mg, 74% yield. MS (APCI): calculated for Chemical Formula: C23H26N2O6 ([M+H]+') = 427 found: 427.1H NMR (400 MHz, CDCI3) 8.16 (s, 1 H), 8.01 (s, 1 H), 7.83 (d, J = 8.8 Hz, 1 H), 7.12 (d, J = 2.0 Hz, 1 H), 7.01 (dd, J = 8.8 Hz, 2.0 Hz, 1 H), 6.46 (q, J = 6.4 Hz, 1 H), 4.46-4.42 (m, 2H), 3.93 (s, 3H), 1.83-1.56 (m, 5H), 1.73 (d, J = 8.4 Hz, 3H), 1.51-1.44 (m, 1 H), 1.26 (d, J = 7.2 Hz, 3H), 1.21 (d, J = 7.2 Hz, 3H).

[0053] Scheme of compound PBGBF1-5 synthesis

[0054] Compound PBGBF1-5 synthesis — (1-(7-methoxy-3-nitrodibenzo[b,d]furan- 2-yl)ethyl dihexylcarbamate): A mixture of PBGBF1-2.5 (554.0 mg, 1.9 mmol) and 1,1’- carbonyldiimidazole (591.5 mg, 3.6 mmol) was degassed at room temperature. Then dichloromethane (14 mL) and triethylamine (0.3 mL, 2.1 mmol) were added sequentially. The solution was heated up to 50 °C and kept at this temperature for 4 hours. LCMS showed the consumption of the starting material. Then dihexylamine (1.3 mL, 5.7mmol) was added, followed by the addition of dimethylacetamide (10 mL) and 1- hydroxybenzotriazole hydrate (87.0 mg, 0.6 mmol). The reaction was kept refluxing overnight. LCMS showed completion of the reaction. After cooling down to room temperature, the reaction was washed with brine. The aqueous phase was further extracted by dichloromethane (100 mL*3). The combined organic phase was concentrated under rotavapor and purified by silica gel flash chromatography to provide PBGBF1-5 as a yellow solid using 0-20%-40% ethyl acetate in Hexane as the eluants. The fraction was further purified by another column using 40%-50%-100% dichloromethane in Hexane as the eluants. 615.0 mg, 89% yield. MS (APCI): calculated for Chemical Formula: C28H38N2O6 ([M-H]”) = 498 found: 498.1H NMR (400 MHz, CDCI3) 8.16 (s, 1 H), 7.99 (s, 1 H), 7.82 (d, J = 8.4 Hz, 1 H), 7.12 (d, J = 2.0 Hz, 1 H), 7.00 (dd, J = 8.4 Hz, 2.0 Hz, 1 H), 6.41 (dd, J = 6.4 Hz, 6.4 Hz, 1 H), 3.93 (s, 3H), 3.38-3.07 (m, 4H), 1.72 (d, J = 6.4 Hz, 3H), 1.67-1.57 (m, 2H), 1.51-1.11 (m, 14H), 0.95-0.75 (m, 6H).

[0055] Scheme of compound PBGBF1-3synthesis

[0056] Compound PBGBF1-2.4 synthesis — (7-methoxy-3-nitrodibenzo[b,d]furan-

[0057] 2-carbaldehyde): PBGBF1-2.4 was made as described above in Example synthesis of

[0058] PBGBF1-2 (PBGBF1-2.1 through 1.2-4 described above).

[0059] Compound PBGBF1-3.1 synthesis — ((7-methoxy-3-nitrodibenzo[b,d]furan- 2-yl)methanol): A 100 mL flask was fitted with a stir bar and a Dean-Stark apparatus. To the flask, compound PBGBF1.2.4 (1.0 g, 3.7 mmol) was dissolved in isopropyl alcohol (10 mL). The solution was degassed at room temperature. Aluminium isopropoxide (187.9 mg, 0.92 mmol) was added. The reaction was heated up to 110 °C and kept at this temperature for 1 hour. Both TLC and LCMS showed completion of the reaction. It was then cooled down to room temperature and worked-up by the addition of 0.2 N hydrochloric acid (200 mL). The mixture was diluted by water (500 mL). The precipitate was collected via vacuum filtration. The crude product was dried over vacuum oven at 105 °C for 3 hours to deliver the product PBGBF1-3.1 as a gray solid, which was used for the next step without further purification. 947.0 mg, 94% yield. MS (APCI): calculated for Chemical Formula: C14H11NO5 ([M-H]”) = 273 found: 273.1H NMR (400 MHz, CDCI3) 8.33 (s, 1 H), 8.15 (s, 1 H), 7.89 (d, J = 8.4 Hz, 1 H), 7.13 (d, J = 2.4 Hz, 1 H), 7.03 (dd, J = 8.4 Hz, 2.4 Hz, 1 H), 5.09 (d, J = 6.4 Hz, 2H), 4.74-4.69 (m, 1 H), 3.94 (s, 3H).

[0060] Compound PBGBF1-3 synthesis — ((7-methoxy-3-nitrodibenzo[b,d]furan-2- yl)methyl dihexylcarbamate): A mixture of PBGBF1-3.1 (1.0 g, 3.7 mmol) and 1,1’- carbonyldiimidazole (1.2 g, 4.4 mmol) was degassed at room temperature. Dichloromethane (24 mL) and triethylamine (0.6 mL, 4.1 mmol) were then added sequentially. The solution was heated up to 50 °C and kept at this temperature for 4 hours. LCMS showed consumption of the starting material. Dihexylamine (3.4 mL, 15 mmol) was then added. The reaction was kept refluxing overnight. LCMS showed completion of the reaction. After cooling down to room temperature, the reaction was washed by brine. The aqueous phase was further extracted by dichloromethane (100 mL*3). The combined organic phase was concentrated under rotavapor and purified by silica gel flash chromatography to provide PBGBF1-3 as a yellow solid using 0-20% ethyl acetate in hexane as the eluants. The collected fraction was concentrated under rotavapor and purified by another column using 40%-100% dichloromethane in Hexane, then 0-10% ethyl acetate in dichloromethane. 1.7 mg, 97% yield. MS (APCI): calculated for Chemical Formula: C27H36N2O6 ([M-H]”) = 484 found: 484.1H NMR (400 MHz, CDCh) 8.29 (s, 1 H), 7.98 (s, 1 H), 7.83 (d, J = 8.4 Hz, 1 H), 7.13 (d, J = 2.4 Hz, 1 H), 7.01 (dd, J = 8.4 Hz, 2.4 Hz, 1 H), 5.64 (s, 2H), 3.93 (s, 3H), 3.30-3.22 (m, 4H), 1.61-1.50 (m, 4H), 1.31-1.26 (m, 12H), 0.89-0.85 (m, 6H).

[0061] Scheme of compound PBGBF1-1 synthesis:

[0062] HOBt, DMA 90 °C, 2 hrs

[0063] Compound PBGBF1-1.1 synthesis — ((7-methoxy-3-nitrodibenzo[b,d]furan- 2-yl)methyl (4-nitrophenyl) carbonate): A solution of PBGBF1-3.1 (947.0 mg, 3.5 mmol) in dimethylacetamide (14 mL) was cooled down to 0 °C. Triethylamine (0.97 mL) was added, followed by degassing of the solution. 10 minutes later, 4-nitrophenyl chloroformate (0.77 g, 3.8 mmol) was added, and the reaction solution was warmed up gradually to room temperature, followed by addition of another portion of 4-nitrophenyl chloroformate (0.35 g, 1.8 mmol). The reaction mixture was kept at room temperature overnight. LCMS showed completion of the reaction, and reaction was poured into water (250 mL). The product was collected as a precipitate by vacuum filtration. The crude was re-dissolved in dichloromethane and purified by silica gel flash chromatography to provide PBGBF1-3.2 as a yellow solid using 0-10% ethyl acetate in dichloromethane as the eluants. 1.1 g, 72% yield. MS (APCI): calculated for Chemical Formula: C21H14N2O9 ([M- CO2-H]-) = 394 found: 394.1H NMR (400 MHz, CDCI3) 8.41 (s, 1 H), 8.32-8.28 (m, 2H), 8.11 (s, 1 H), 7.91 (d, J = 8.8 Hz, 1 H), 7.47-7.41 (m, 2H), 7.16 (d, J = 2.0 Hz, 1 H), 7.05 (dd, J = 8.8 Hz, 2.0 Hz, 1 H), 2.04 (d, J = 0.8 Hz, 2H), 3.95 (s, 3H).

[0064] Compound PBGBF1-1 synthesis — ((7-methoxy-3-nitrodibenzo[b,d]furan-2- yl)methyl (2R,6S)-2,6-dimethylpiperidine-1-carboxylate): A mixture of PBGBF1-1.1 (1.1 g, 2.5 mmol) and 1 -hydroxybenzotriazole hydrate (114.8 mg, 0.8 mmol) in dimethylacetamide (17 mL) was stirred at room temperature. It was then degassed at room temperature. To the solution, 4-(dimethylamino)pyridine (0.9 mL, 6.8 mmol) was injected. The reaction solution was degassed again and then heated up 90 °C and kept at this temperature for 2 hours. TLC and LCMS showed completion of the reaction. The reaction mixture was poured into 1 % sodium bicarbonate (100 mL) and the precipitate was collected via vacuum filtration. The crude was re-dissolved in dichloromethane and purified by silica gel flash chromatography to provide PBGBF1-3 as a yellow solid using ethyl acetate in Hexane (0-20%-40%) as the eluants. 0.8 g, 74% yield. MS (APCI): calculated for Chemical Formula: C22H24N2O6 ([M-H]”) = 412 found: 412.1H NMR (400 MHz, CDCh) 8.26 (s, 1 H), 7.97 (s, 1 H), 7.81 (d, J = 8.4 Hz, 1 H), 7.11 (d, J = 2.4 Hz, 1 H), 7.01 (dd, J = 8.4 Hz, 2.4 Hz, 1 H), 5.64 (s, 2H), 4.43-4.33 (m, 2H), 3.93 (s, 3H), 1.83-1.73 (m, 1 H), 1 .70-1 .55 (m, 4H), 1.52-1.44 (m, 1 H), 1.26 (s, 3H), 1 .25 (s, 3H).

[0065] Scheme of compound PBGBF1-4 synthesis benzaldehyde PBGBFI-4.I C, NaOAc, DM °C, 48 hrs

[0066] 50 °C, overnight

[0067] Compound PBGBF1-4.1synthesis — (4-(2-bromo-4-methoxyphenoxy)-2- nitrobenzaldehyde): A 500 mL flask was fitted with a stir bar. In the flask, 4-fluoro-2- nitrobenzaldehyde (3.38 g, 20.0 mmol) and 2-bromo-4-methoxyphenol (3.85 g, 19.0 mmol) were dissolved in anhydrous dimethylformamide (150 mL), followed by the addition of potassium carbonate (7.93 g, 57.0 mmol). The mixture was purged with Argon and kept at room temperature for 6 hours. It was then heated up to 50 °C and kept at this temperature overnight. Both TLC and LCMS showed completion of the reaction. Saturated ammonium chloride solution (300 mL) was then added. The mixture was extracted with ethyl acetate (3* by 150 mL). The combined organic phase was washed with water (450 mL) and brine (450 mL) sequentially and dried over anhydrous sodium sulfate. After filtration and concentration, the crude was purified by silica gel chromatography to provide PBGBF1-4.1 as a yellow solid using 0-20% ethyl acetate in Hexane as the eluants. 5.0 g, 74% yield. MS (APCI): calculated for Chemical Formula: Ci4Hi0BrNO5([M+HD = 353 found: 353.1H NMR (400 MHz, CDCI3) 10.31 (s, 1 H), 7.97 (d, J = 8.4 Hz, 1 H), 7.45 (d, J = 2.4 Hz, 1 H), 7.22 (d, J = 3.2 Hz, 1 H), 7.19 (dd, J = 8.4 Hz, 2.4 Hz, 1 H), 7.11 (d, J = 8.8 Hz, 1 H), 6.94 (dd, J = 8.8 Hz, 2.4 Hz, 1 H), 3.85 (s, 3H).

[0068] Compound PBGBF1-4.2 synthesis — )2-(4-(2-bromo-4-methoxyphenoxy)-2- nitrophenyl)-1,3-dioxolane): A 1 L flask was fitted with a stir bar and set up with a Dean- Stark apparatus. To the flask, compound PBGBF1-4.1 (5.0 g, 14.1 mmol) and benzene (300 mL) were added, followed by the addition of ethylene glycol (5.0 mL) and p- toluenesulfonic acid (500.0 mg, 3.0 mmol). The mixture was purged with Argon and warmed up to 110 °C and kept at this temperature for 20 hours. Both TLC and LCMS showed completion of the reaction. The mixture was cooled down to room temperature and then poured into a saturated sodium bicarbonate solution (200 mL). The mixture was extracted with ethyl acetate (3* by 150 mL). The combined organic phase was washed with water (100 mL) and brine (100 mL) sequentially and dried over anhydrous sodium sulfate. After filtration and concentration, the crude was purified by silica gel chromatography to provide PBGBF1-4.2 as a pale-yellow liquid using 0-20%-40% ethyl acetate in Hexane as the eluants. Quantitative yield. MS (APCI): calculated for Chemical Formula: Ci6Hi4BrNO6([M-H]”) = 396, 398 found: 396, 398.1H NMR (400 MHz, CDCI3) 7.72 (d, J = 8.8 Hz, 1 H), 7.34 (d, J = 2.4 Hz, 1 H), 7.20 (d, J = 2.8 Hz, 1 H), 7.11 (dd, J = 8.8 Hz, 2.8 Hz, 1 H), 7.05 (dd, J = 8.8 Hz, 1 H), 6.90 (dd, J = 8.8 Hz, 2.8 Hz, 1 H), 6.34 (s, 1 H), 4.06-4.02 (m, 4H), 3.84 (s, 3H).

[0069] Compound PBGBF1-4.3 synthesis — (2-(1,3-dioxolan-2-yl)-8-methoxy-3- nitrodibenzo[b,d]furan): A 500 mL flask was fitted with a stir bar. To the flask, compound PBGBF1-4.2 (5.6 mg, 14.1 mmol) and dimethylacetamide (120 mL) were added, followed by the addition of palladium on carbon (450.2 mg, 0.4 mmol) and sodium acetate (1.74 g, 21.2 mmol). The mixture was degassed at room temperature using Argon bubbling for 1 hour. The reaction was heated to 115 °C and kept at this temperature for 2 days. Neither TLC nor LCMS could be used to track the progress of the reaction. The mixture was cooled down to room temperature and then filtered through celite pad. The pad was extracted with dichloromethane. The filtrate was extracted with ethyl acetate (3* by 210 mL). The combined organic phase was washed with water (280 mL) and brine (280 mL) sequentially and dried over anhydrous sodium sulfate. The crude was purified by recrystallization with ethyl acetate-Hexane to provide PBGBF1-4.3 as a yellow crystalline solid. 3.08 g, 62% yield. MS (APCI): calculated for Chemical Formula: C16H13NO6 ([M-H]’ •) = 315 found: 315.1H NMR (400 MHz, CDCI3) 8.34 (s, 1 H), 8.15 (s, 1 H), 7.54 (d, J = 8.8 Hz, 1 H), 7.46 (d, J = 2.4 Hz, 1 H), 7.17 (dd, J = 8.8 Hz, 2.4 Hz, 1 H), 6.62 (d, J = 0.4 Hz, 1 H), 4.15-4.09 (m, 4H), 3.93 (s, 3H).

[0070] Compound PBGBF1-4.4 synthesis — (8-methoxy-3-nitrodibenzo[b,d]furan- 2-carbaldehyde): PBGBF1-4.3 (2.8 g, 8.8 mmol) was suspended in tetrahydrofuran / water (75mL / 25mL), while p-toluene sulfonic acid monohydrate (835.6 mg, 4.4 mmol) was added. The reaction was heated up to 60 °C and kept at this temperature for 48 hours. After LCMS showed completion of the reaction, it was cooled down to room temperature. After removing the tetrahydrofuran by rotavapor, the product was precipitated out and it was collected via vacuum filtration to provide PBGBF1-4.4 as a yellow-orange solid. 2.35 g, 98% yield. MS (APCI): calculated for Chemical Formula: C14H9NO5 ([M-H]-) = 271 found: 271.1H NMR (400 MHz, CDCI3) 10.50 (s, 1 H), 8.54 (s, 1 H), 8.30 (s, 1 H), 7.59 (d, J = 8.8 Hz, 1 H), 7.49 (d, J = 2.8 Hz, 1 H), 7.23 (dd, J = 8.8 Hz, 2.8 Hz, 1 H), 3.94 (s, 3H).

[0071] Compound PBGBF1-4.5 synthesis — ((8-methoxy-3-nitrodibenzo[b,d]furan- 2-yl)methanol): A 100 mL flask was fitted with a stir bar and a Dean-Stark apparatus. In the flask, compound PBGBF1-4.4 (1.5 g, 5.5 mmol) was dissolved in isopropyl alcohol (15 mL). The solution was degassed at room temperature. Aluminium isopropoxide (282.4 mg, 1 .4 mmol) was then added. The reaction was heated up to 110 °C and kept at this temperature for 1 hour. Both TLC and LCMS showed completion of the reaction. It was then cooled down to room temperature and worked-up by the addition of 0.2 N hydrochloric acid (300 mL). The mixture was diluted by water (750 mL). The precipitate was collected via vacuum filtration. The crude product was dried over vacuum oven at 105 °C for 3 hours to deliver the product PBGBF1-4.5 as a gray solid, which was used for the next step without further purification. 1.4 g, 95% yield. MS (APCI): calculated for Chemical Formula: C14H11NO5 ([M-H]-) = 273 found: 273.1H NMR (400 MHz, CDCI3) 8.33 (s, 1 H), 8.24 (s, 1 H), 7.54 (d, J = 8.8 Hz, 1 H), 7.46 (d, J = 2.4 Hz, 1 H), 7.19 (dd, J = 8.8 Hz, 2.4 Hz, 1 H), 5.11 (d, J = 6.4 Hz, 2H), 3.93 (s, 3H), 2.69-2.64 (m, 1 H).

[0072] Compound PBGBF1-4 synthesis — ((8-methoxy-3-nitrodibenzo[b,d]furan-2- yl)methyl dihexanoylcarbamate): A mixture of PBGBF1 -4.5 (1 .0 g, 3.7 mmol) and 1,1’- carbonyldiimidazole (1.2 g, 4.4 mmol) was degassed at room temperature. Dichloromethane (24 mL) and triethylamine (0.6 mL, 4.1 mmol) were then added sequentially. The solution was heated up to 50 °C and kept at this temperature for 4 hours. LCMS showed consumption of the starting material. Dihexylamine (3.4 mL, 15 mmol) was then added. The reaction was kept refluxing overnight. LCMS showed completion of the reaction. After cooling down to room temperature, the reaction was washed by brine. The aqueous phase was further extracted by dichloromethane (100 mL*3). The combined organic phase was concentrated under rotavapor and purified by silica gel flash chromatography to provide PBGBF1-4 as a yellow solid using 0-20% ethyl acetate in hexane as the eluants. The collected fraction was concentrated under rotavapor and purified by another column using 40%-100% dichloromethane in Hexane, then 0-10% ethyl acetate in dichloromethane. 1.5 g, 89% yield. MS (APCI): calculated for Chemical Formula: C27H36N2O6 ([M-H] *) = 484 found: 484.1H NMR (400 MHz, CDCh) 8.28 (s, 1 H), 8.08 (s, 1 H), 7.54 (d, J = 8.8 Hz, 1 H), 7.41 (d, J = 2.4 Hz, 1 H), 7.18 (dd, J = 8.8 Hz, 2.4 Hz, 1 H), 5.63 (s, 2H), 3.92 (s, 3H), 3.28-3.21 (m, 4H), 1.59-1.50 (m, 4H), 1.31-1.24 (m, 12H), 0.90-0.83 (m, 6H).

[0073] Scheme of compound - PBGBF2-1 synthesis

[0074] Compound PBGBF2-1.1 synthesis — (4-(benzo[d][1,3]dioxol-5-yloxy)-2- nitrobenzaldehyde): A 100 mL flask was fitted with a stir bar. In the flask, 4-fluoro-2- nitrobenzaldehyde (644.4 mg, 3.8 mmol) and benzodioxol-5-ol (500.0 mg, 3.6 mmol) were dissolved in anhydrous dimethylformamide (21 mL), followed by the addition of potassium carbonate (1.5 g, 11.1 mmol). The mixture was purged with Argon and kept at room temperature for 3 hours. Both TLC and LCMS showed completion of the reaction. Saturated ammonium chloride solution (100 mL) was then added. The mixture was extracted with ethyl acetate (3* by 100 mL). The combined organic phase was washed with water (150 mL) and brine (150 mL) sequentially and dried over anhydrous sodium sulfate. After filtration and concentration, the crude was purified by silica gel chromatography to provide PBGBF2-1.1 as a yellow solid using 0-20% ethyl acetate in Hexane as the eluants. 753.0 mg, 73% yield. MS (APCI): calculated for Chemical Formula: CI4H9NO6([M-H] *) = 287 found: 287.1H NMR (400 MHz, CDCI3) 10.30 (d, J = 0.4 Hz, 1 H), 7.96 (d, J = 4.8 Hz, 1 H), 7.51 (d, J = 2.4 Hz, 1 H), 7.26 (ddd, J = 8.4 Hz, 2.8 Hz, 0.8 Hz, 1 H), 6.85 (d, J = 8.4 Hz, 1 H), 6.61 (d, J = 2.8 Hz, 1 H), 6.57 (dd, J = 8.4 Hz, 2.4 Hz, 1 H), 6.05 (s, 2H).

[0075] Compound PBGBF2-1.2 synthesis — (4-((6-bromobenzo[d][1,3]dioxol-5- yl)oxy)-2-nitrobenzaldehyde): A 100 mL flask was fitted with a stir bar. In the flask, PBGBF2-1.1 (753.0 mg, 2.6 mmol) was dissolved in anhydrous dichloromethane (13 mL), followed by the addition of N-bromosuccinimide (513.3 mg, 2.9 mmol). The mixture was heated up to 35 °C and kept at this temperature overnight. Both TLC and LCMS showed completion of the reaction. The solution was concentrated and purified by silica gel chromatography to provide PBGBF2.1.2 as a yellow solid using 0-20% ethyl acetate in Hexane as the eluants. 834.0 mg, 88% yield. MS (APCI): calculated for Chemical Formula: Ci4H8BrNO6([M-H]”) = 366, 368 found: 366, 368.1H NMR (400 MHz, CDCI3) 10.32 (d, J = 0.8 Hz, 1 H), 7.98 (d, J = 8.8 Hz, 1 H), 7.47 (d, J = 2.4 Hz, 1 H), 7.22 (ddd, J = 8.8 Hz, 2.4 Hz, 0.8 Hz, 1 H), 7.01 (s, 1 H), 6.89 (s, 1 H), 6.08 (s, 2H).

[0076] Compound PBGBF2-1.3 synthesis — (5-(4-(1,3-dioxolan-2-yl)-3- nitrophenoxy)-6-bromobenzo[d][1,3]dioxole): A 500 mL flask was fitted with a stir bar and set up with a Dean-Stark apparatus. Compound PBGBF2-1.2 (4.3 g, 11.7 mmol) and benzene (250 mL) were added to the flask, followed by the addition of ethylene glycol (4.1 mL) and p-toluenesulfonic acid monohydrate (402.0 mg, 2.3 mmol). The mixture was purged with Argon and was warmed to 110 °C and kept at this temperature for 20 hours. Both TLC and LCMS showed completion of the reaction. The mixture was cooled down to room temperature and then poured into a saturated sodium bicarbonate solution (180 mL). The mixture was extracted with ethyl acetate (3* by 150 mL). The combined organic phase was washed with water (100 mL) and brine (100 mL) sequentially and dried over anhydrous sodium sulfate. After filtration and concentration, the crude was purified by silica gel chromatography to provide PBGBF2-1.3 as a yellow liquid using 0-40% ethyl acetate in Hexane as the eluants. 97% yield. MS (APCI): calculated for Chemical Formula: Ci6Hi2BrNO7([M-H]-) = 410, 412 found: 410, 412.1H NMR (400 MHz, CDCI3) 7.73 (d, J = 8.8 Hz, 1 H), 7.35 (d, J = 2.4 Hz, 1 H), 7.13 (dd, J = 8.8 Hz, 2.4 Hz, 1 H), 7.07 (s, 1 H), 6.64 (s, 1 H), 6.39 (s, 1 H), 6.05 (s, 2H), 4.06-4.02 (m, 4H).

[0077] Compound PBGBF2-1.4 synthesis — (8-(1,3-dioxolan-2-yl)-7- nitrobenzo[b][1,3]dioxolo[4,5-f]benzofuran): A 250 mL flask was fitted with a stir bar. To the flask, compound PBGBF2-1.3 (4.6 g, 11.3 mmol) and dimethylacetamide (100 mL) were added, followed by the addition of palladium on carbon (360.8 mg, 0.3 mmol) and sodium acetate (1.4 g, 17.0 mmol). The mixture was degassed at room temperature using Argon bubbling for 1 hour. The reaction was heated up to 115 °C and kept at this temperature for 2 days. Neither TLC nor LCMS could be used to track the progress of the reaction. The mixture was cooled down to room temperature and then filtered through celite pad. The filtrate was extracted with ethyl acetate (3* 220 mL) after the addition of ammonium chloride (saturated, 330 mL). The combined organic phase was washed with water (200 mL) and brine (200 mL) sequentially and was dried over anhydrous sodium sulfate. The crude was purified by recrystallization with ethyl acetate-Hexane to provide PBGBF2-1.4 as a yellow solid 2.2 g, 60% yield. MS (APCI): calculated for Chemical Formula: Ci6HnNO7([M+H]+’) = 330 found: 330.1H NMR (400 MHz, CDCI3) 8.21 (s, 1 H), 8.15 (s, 1 H), 7.35 (s, 1 H), 7.11 (s, 1 H), 6.63 (s, 1H), 6.11 (s, 2H), 4.11 (s, 4H).

[0078] Compound PBGBF2-1.5 synthesis — (7-nitrobenzo[b][1,3]dioxolo[4,5- f]benzofuran-8-carbaldehyde): PBGBF2-1.4 (561.0 mg, 1.7 mmol) was suspended in tetrahydrofuran / water (15 mL / 5 mL), while p-toluene sulfonic acid monohydrate (162.0 mg, 0.85 mmol) was added. The reaction was heated to 60 °C and kept at this temperature for 48 hours. After LCMS showed completion of the reaction, it was cooled down to room temperature. After removing the THF by rotavapor, the product was precipitated out and collected via vacuum filtration to provide PBGBF2-1.5 as a brown solid. 481.0 mg, quantitative yield. MS (APCI): calculated for Chemical Formula: C14H7NO6 ([M-H] *) = 285 found: 285.1H NMR (400 MHz, CDCI3) 10.51 (s, 1 H), 8.38 (s, 1 H), 8.28 (s, 1 H), 7.37 (s, 1 H), 7.15 (s, 1 H), 6.14 (s, 2H).

[0079] Compound PBGBF2-1.6 synthesis — ((7-nitrobenzo[b][1,3]dioxolo[4,5- f]benzofuran-8-yl)(phenyl)methanol): A two-neck round bottle flask was charged with palladium(ll) chloride (15.0 mg, 0.09 mmol), ligand tri-1-naphthylphosphine (35.0 mg, 0.09 mmol), phenylboronic acid (514.0 mg, 4.2 mmol), potassium carbonate (469.2 mg, 3.4 mmol) and PBGBF2-1.5 (481.0 mg, 1.7 mmol) in tetra hydrofuran (8.5 mL). The mixture was stirred at refluxing for 12 hours. It was then cooled down to room temperature, and the mixture was filtered through a celite pad. Ethyl acetate (10 ml) was used to rinse the celite pad. The filtrate was concentrated and purified by silica gel chromatography to provide PBGBF2-1.6 as a yellow solid using 0-20%-40% ethyl acetate in Hexane as the eluants. 358.0 mg, 58% yield. MS (APCI): calculated for Chemical Formula: C20H13NO6 ([M-H]”) = 363 found: 363.1H NMR (400 MHz, CDCI3) 8.18 (s, 1 H), 8.14 (s, 1 H), 7.40- 7.28 (m, 6H), 7.10 (s, 1 H), 6.60 (d, J = 4.8 Hz, 1 H), 6.10 (s, 2H), 2.89 (d, J = 4.8 Hz, 1 H). Compound PBGBF2-1 synthesis ((7-nitrobenzo[b][1,3]dioxolo[4,5- f]benzofuran-8-yl)(phenyl)methyl dihexylcarbamate): A mixture of PBGBF2-1.6 (358.0 mg, 1.0 mmol) and 1 ,1’-carbonyldiimidazole (306.8 mg, 1.9 mmol) was degassed at room temperature. Dimethylacetamide (10 mL) and triethylamine (0.15 mL, 1.1 mmol) were then added sequentially. The solution was heated to 50 °C and kept at this temperature for 4 hours. LCMS showed consumption of the starting material. Dihexylamine (1.4 mL, 5.9 mmol) and 1 -hydroxybenzotriazole hydrate (75.8 mg, 0.5 mmol) were then added. The reaction was kept at 90 °C overnight. LCMS showed completion of the reaction. After cooling down to room temperature, the reaction was poured into 1 % sodium bicarbonate to precipitate out the crude product, which was redissolved in dichloromethane and purified by silica gel flash chromatography to provide PBGBF2-1 as a yellow solid using 0-20%-40% ethyl acetate in hexane as the eluants. 306.0 mg, 54% yield. MS (APCI): calculated for Chemical Formula: C33H38N2O7 ([M-H] *) = 574 found: 574.1H NMR (400 MHz, CDCI3) 8.19 (s, 1 H), 7.96 (s, 1 H), 7.58 (s, 1 H), 7.42- 7.38 (m, 2H), 7.36-7.28 (m, 3H), 7.25 (s, 1 H), 7.10 (s, 1 H), 6.10 (dd, J = 2.4 Hz, 1.2 Hz, 2H), 3.36-3.14 (m, 4H), 1.52-1.46 (m, 2H), 1.33-1.22 (m, 14H), 0.87-0.81 (m, 6H).

[0080] Scheme of compound PBGBF2-2 synthesis

[0081] Compound PBGBF2-2.1 synthesis — (1-(7-nitrobenzo[b][1,3]dioxolo[4,5- f]benzofuran-8-yl)ethan-1-ol): A 100 mL flask was fitted with a stir bar. In the flask, compound PBGBF2-1.5 (967.0 mg, 3.4 mmol) was suspended in anhydrous dichloromethane (40 mL). The solution was cooled down to 0 °C with an ice-water bath. Trimethylaluminium (2.0 in Hexane, 3.6 mL) was added dropwise to the solution. The reaction was slowly warmed up to room temperature after the completion of the addition. The reaction was kept at room temperature for 2 hours. Both TLC and LCMS showed completion of the reaction. It was then cooled down to 0 °C and worked-up by the addition of water and sodium hydroxide (1 N) solution, 20 mL for each. The mixture was extracted with dichloromethane (3* by 100 mL). The combined organic phase was dried over anhydrous sodium sulfate. After filtration and concentration, the crude was purified by silica gel chromatography to provide PBGBF2-2.1 as an orange-yellow solid using 0-10% ethyl acetate in dichloromethane as the eluants. 318.0 mg, 31% yield. MS (APCI): calculated for Chemical Formula: Ci5HnNO6([M+H]+') = 302 found: 302.1H NMR (400 MHz, CDCI3) 8.24 (s, 1 H), 8.14 (s, 1 H), 7.35 (s, 1 H), 7.10 (s, 1 H), 6.11 (s, 2H), 5.64-5.56 (m, 1 H), 2.39 (d, J = 4.0 Hz, 1 H), 1.66 (d, J = 6.4 Hz, 3H).

[0082] Compound PBGBF2-2 synthesis — (1-(7-nitrobenzo[b][1,3]dioxolo[4,5- f]benzofuran-8-yl)ethyl dihexylcarbamate): A mixture of PBGBF2-2.1 (254.0 mg, 0.8 mmol) and 1 ,1’-carbonyldiimidazole (262.3 mg, 1.6 mmol) was degassed at room temperature. Dimethylacetamide (8.5 mL) and triethylamine (0.13 mL, 0.9 mmol) were then added sequentially. The solution was heated up 50 °C and kept at this temperature for 4 hours. LCMS showed consumption of the starting material. Dihexylamine (1.2 mL, 5.0 mmol) and 1 -hydroxybenzotriazole hydrate (64.3 mg, 0.4 mmol) were then added. The reaction was kept at 90 °C overnight. LCMS showed completion of the reaction. After cooling down to room temperature, the reaction was poured into 1% sodium bicarbonate to precipitate out the crude product, which was re-dissolved in dichloromethane and purified by silica gel flash chromatography to provide PBGBF2-2 as a yellow solid using 0-20%-40% ethyl acetate in hexane as the eluants. 166.0 mg, 39% yield. MS (APCI): calculated for Chemical Formula: C28H36N2O7 ([M-H]”) = 512 found: 512.1H NMR (400 MHz, CDCI3) 8.13 (s, 1 H), 7.93 (s, 1 H), 7.26 (s, 1 H), 7.08 (s, 1 H), 6.41 (dd, J = 12.8 Hz, 6.4 Hz, 1 H), 6.10 (d, J = 2.8 Hz, 2H), 3.37-3.10 (m, 4H), 1.71 (d, J = 6.4 Hz, 3H), 1.54- 1.13 (m, 16H), 0.94-0.77 (m, 6H).

[0083] 1.1. PBG base release efficiency measurements pH Change studies of dibenzofuran based PBGs were performed in acetonitrile solvent with a 1 mg / mL concentration. In an amber vial, weighed ~6 mg of corresponding PBG compound and then ~6 mL acetonitrile was added to dissolve it. Initial pH (before exposure) was measured using a pH meter (after 3 pH Calibrations at pH 4.0, 7.0 and 10.0). Then, the solution containing the dibenzofuran based PBGs was exposed to -600 mJ / cm2mercury lamp using a Dymax UV curing conveyor. pH after exposure was then measured using the same pH meter. pH Change was calculated by subtracting the pH after exposure with the initial pH. The pH Change results are shown in Table 1. Solution base release experiments of dibenzofuran based PBGs were performed in MeCN solvent with a 1 mg / mL concentration. In a transparent glass vial, -1 mg of the corresponding PBG compound was added and then -1 mL acetonitrile was added to dissolve it. Then, the solution containing the dibenzofuran based PBGs was exposed to 5 a -600 mJ / cm2mercury lamp using a Dymax UV curing conveyor. Analysis of photo products and efficiency was carried out using Shimadzu LC / MS.

[0084] 1.2. TGA Data of dibenzofuran based PBGs

[0085] TGA measurements were taken from 25°C to 590°C under nitrogen with a flow rate of 250 mL / min using the method with the ramp rate of 10°C / min by TA instrument TGA550. The TGA data of dibenzofuran based PBGs are presented in Table 1.

[0086] Table 1. Efficiency of base-release under light, and TGA of PBG compounds

[0087] 1.3. Standard Polyimide formation method

[0088] First, a selected PBG (i.e. PBGBF1-5) and polyimide precursor (polyamidic acid) were weighed into a container / jar (j.e. 30 mg of PBG in 3 g PI Varnish), then mixed by using

[0089] 5 Thinky (2000 rpm for 3 min, added more mixing time as needed until all fully dissolved). Next, the mixed solution was spin-coated on Steel Use Stainless (SUS) 304 substrates taped on rigid glass plate (main spin-coating rate: 1100 rpm for 30 sec). (SUS304 is a Japanese JIS Standard and one of the most frequently used stainless steels, comprising 18% Cr and 8% Ni). Then, it was baked at 120 °C for 10 min to remove N-methyl-2-0 pyrrolidone (NMP) solvent. After that, 600 mJ / cm2of mercury lamp was exposed on the sample with a mask on (using a Dymax UV curing conveyor). Afterwards, the postexposure baking was conducted at 200 °C for 5 min. As the final step, FT-IR (Thermo Nicolet iS50) measurements of the exposed and the unexposed area of the sample were performed to obtain imidization contrast ratio. (Imidization rate%= Corrected height of5 imide peak (1777cm'1) / Corrected height of benzene peak (1489 cm-1) x 100). The imidization contrast ratio is the ratio of the imidization rate% of exposed area to the imidization rate% of the unexposed area. PBGF1-5 showed good imidization contrast ratio of 1.50 and 2.0 in U-Varnish-S and PAA-55, respectively. Related results are illustrated in FIG. 1. 0

[0090] 1.4. Optical Measurements of PBGs

[0091] Additional optical properties of PBGBF1-1, PBGBF1-2, PBGBF1-3, PBGBF1-4, PBGBF1- 5, PBGBF2-1, and PBGBF2-2 are graphically illustrated in FIG. 2. Absorbance spectra of the PBGs were measured in N-methylpyrrolidone (NMP) solvent (~ 0.001 mmol / ml5 concentration) using Shimadzu UV3600 spectrometer. The normalized absorption spectra of the PBGs are graphically illustrated in FIG. 2. Unless otherwise indicated, all numbers expressing quantities of ingredients, properties, such as, molecular weight, reaction conditions, and so forth used in the specifications and embodiments are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached embodiments are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents, to the scope of the embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying conventional and ordinary rounding techniques.

[0092] For the processes and / or methods disclosed, the functions performed in the process and methods may be implemented in differing order, as may be indicated by context. Furthermore, the outlined steps and operations are only provided as examples and some of the steps and operations may be optional, combined into fewer steps and operations, or expanded into additional steps and operations.

[0093] This disclosure may sometimes illustrate different components contained within, or connected with, other different components. Such depicted architectures are merely examples, and many other architectures can be implemented to achieve the same or similar functionality.

[0094] The terms used in this disclosure and in the appended embodiment, (e.g., bodies of the appended embodiments) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including, but not limited to,” the term “having” should be interpreted to “having at least”, the term “includes” should be interpreted as “includes, but not limited to,” etc. in addition, if a specific number of elements is introduced, this may be interpreted to mean at least the recited number, as may be indicated by context (e.g., the bare recitation of “two recitations”, without other modifiers, means at least two recitations or two or more recitations). As used in this disclosure, any disjunctive word and / or phrase presenting two or more alternative terms should be understood to contemplate the possibilities of including one of those terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of A” or “B” or “A and B”. Similarly, the phrase “A and / or B” will be understood to include the possibilities of A” or “B” or “A and B”.

[0095] The terms “a”, “an”, “the”, and similar referents used in the context of describing the present disclosure (especially in the context of the following embodiments) are to construe to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples, or representative language (e.g., “such as” or “for instance”) provided herein is intended merely to better illustrate the present disclosure and does not pose a limitation on the scope of any embodiments. No language in this specification herein shall be construed as indicating any non-embodied element essential to the practice of the present disclosure.

[0096] Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and embodied individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and / or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified, thus fulfilling the written description of all Markush groups used in the appended embodiments.

[0097] Certain embodiments are described herein, including the best mode known to the inventors for carrying out the present disclosure. Of course, variations on these described embodiments, will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the present disclosure to be practiced otherwise than specifically described herein. Accordingly, the embodiments are permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context. In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the embodiments. Therefore, by way of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Henceforth, the embodiments are not limited to the embodiments precisely as shown and described herein.

Claims

CLAIMSWhat is claimed is:

1. A photobase generator, comprising: a light absorbing dibenzofuran derivative; a linker group; and a basic moiety; wherein the linker group covalently links the dibenzofuran derivative and the base moiety, wherein light energy of a first excitation wavelength is absorbable by the dibenzofuran derivative and energy is transferable from the dibenzofuran derivative to the linker group, and wherein upon heterolytic cleavage the base moiety is releasable from the linker group.

2. The photobase generator of claim 1 , wherein the light absorbing dibenzofuran derivative is a compound according to formula (1):wherein each of R1and R2represents H or an alkoxy, or R1and R2are connected together in a heterocyclic ring;R3represents H, an alkyl, or an aryl; andBase is an amine.

3. The photobase generator of claim 2, wherein the Base has the followingD general structure:6, wherein each of Rs and Rs represents a Ca-Cs linear alkyl, orRs and Rs are connected together in an optionally substituted heterocyclic ring.

4. The photobase generator of claim 3, wherein Rs and Rs are connected together in a substituted heterocyclic ring having one of the following structures:

5. The photobase generator of claim 1, comprising one of the following structures:

6. A method for making a polyimide, comprising: providing a photobase generator (PBG) according to any one of claims 1-5 and a polyimide precursor dispersion in a dispersant; covering a substrate with the PBG and polyimide precursor; applying UV-Vis light to the PBG and polyimide precursor covered substrate; and heating the covered substrate for at least one of removing the dispersant and curing the covered substrate.

7. The method of claim 6, further comprising masking portions of the covered substrate to selectively apply UV-Vis light to the covered substrate.

8. A method for measuring the base release efficiency of a photobase generator compound, comprising: dissolving a photobase generator compound of one of claims 1-5 in acetonitrile; measuring the pH of a solution including the photobase generator and acetonitrile;exposing the solution including the photobase generator and acetonitrile to UV- Vis light; and measuring the pH of the solution including the photobase generator and acetonitrile after exposure to the UV-Vis light.

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