Effects of alkyl side chain length of low bandgap naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole‐based copolymers on the optoelectronic properties of polymer solar cells

Two donor‐π‐acceptor (D‐π‐A) type naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole (NT)‐based conjugated copolymers (CPs), namely, PBDT‐TT‐DTNT‐HD and PBDT‐TT‐DTNT‐OD, containing different side chain length (2‐hexyldecyl, HD and 2‐octyldodecyl, OD) anchoring to thiophene π‐bridge between the two‐dimensional (2D) 5‐((2‐butyloctyl)thieno[3,2‐b]thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT‐TT) unit and NT moiety are developed and fully characterized. The resultant two copolymers exhibited broader absorption in wide range of 300–820 nm and obviously deepened E_HOMO of approximately −5.50 eV. The effects of side chain length on film‐forming ability, absorption, energy levels, aggregation, dielectric constant (ɛ_r), mobility, morphology, and photovoltaic properties are further systematically investigated. It was found that the side chain length had little impact on solution‐processability, absorption, energy levels, and aggregation in CB solution of resultant CPs. However, tinily increasing side chain length promoted to form the more ordered structure of neat polymer film even if the corresponding ɛ_r decreased. As a result, the side‐chain‐extended PBDT‐TT‐DTNT‐OD:PC₇₁BM‐based device achieved 32% increased FF than that of PBDT‐TT‐DTNT‐HD:PC₇₁BM and thus the PCE was significantly raised from 3.99% to 5.21%, which were benefited from 2 times higher SCLC hole mobility, more favorable phase separation, and improved exciton dissociation. These findings could provide an important and valuable insight by side chain modulation for achieving efficient PSCs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2059–2071     

Medium band gap conjugated polymers from thienoacene derivatives and pentacyclic aromatic lactam as promising alternatives of poly(3‐hexylthiophene) in photovoltaic application

Two alternating medium band gap conjugated polymers (PBDT‐TPTI and PDTBDT‐TPTI) derived from 4,8‐bis(4,5‐dioctylthien‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT‐T) or 5,10‐bis(4,5‐didecylthien‐2‐yl)dithieno[2,3‐d:2′,3′‐d′]benzo[1,2‐b:4,5‐b′]dithiophene (DTBDT‐T) with pentacyclic aromatic lactam of N,N‐didodecylthieno[2′,3′:5,6]pyrido[3,4‐g]thieno[3,2‐c]‐iso‐quinoline‐5,11‐dione (TPTI), are synthesized and characterized. The comparative investigation of the photostabilities of the copolymers revealed that the PDTBDT‐TPTI film exhibited the comparable photostability in relative to P3HT. Meanwhile, the inverted photovoltaic cells (i‐PVCs) from the blend films of PBDT‐TPTI and/or PDTBDT‐TPTI with PC₇₁BM, in which poly[(9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)] were used as cathode modifying interlayer, presented higher power conversion efficiencies (PCEs) of 5.98% and 6.05% with photocurrent response ranging from 300 nm to 650 nm in contrast with the PCEs of 4.48% for the optimal inverted PVCs from P3HT/PC₇₁BM under AM 1.5 G 100 mW/cm². The PCEs of the i‐PVCs from PBDT‐TPTI and PDTBDT‐TPTI were improved to 7.58% and 6.91% in contrast to that of 0.02% for the P3HT‐based i‐PVCs, and the photocurrent responses of the devices were extended to 300–792 nm, when the ITIC was used as electron acceptor materials. The results indicate that the PBDT‐TPTI and PDTBDT‐TPTI can be used as the promising alternatives of notable P3HT in the photovoltaic application. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 85–95     

Synthesis and photovoltaic properties of copolymers based on benzo[1,2‐b:4,5‐b′]dithiophene and thiophene with electron‐withdrawing side chains

Six alternating conjugated copolymers ( PL1 – PL6 ) of benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and thiophene, containing electron‐withdrawing oxadiazole (OXD), ester, or alkyl as side chains, were synthesized by Stille coupling reaction. The structures of the polymers were confirmed, and their thermal, optical, electrochemical, and photovoltaic properties were investigated. The introduction of conjugated electron‐withdrawing OXD or formate ester side chain benefits to decrease the bandgaps of the polymers and improve the photovoltaic performance due to the low steric hindrance of BDT. Bulk heterojunction polymer solar cells (PSCs) were fabricated based on the blend of the as‐synthesized polymers and the fullerene derivative [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) in a 1:2 weight ratio. The maximum power conversion efficiency of 2.06% was obtained for PL5 ‐based PSC under the illumination of AM 1.5, 100 mW/cm². © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Highly Fluorescent Conjugated Copolymers Containing Dithieno[3,2‐b:2′,3′‐d]pyrrole

Three copolymers that incorporate dithieno[3,2‐b:2′,3′‐d]pyrrole with fluorene, carbazole, or pyridine have been prepared by Suzuki reaction and characterized by NMR spectroscopy and GPC. A new homopolymer of dithieno[3,2‐b:2′,3′‐d]pyrrole was also synthesized for the comparison of their structure–property relationships. Their thermal, optical, and electrochemical properties have been investigated. All the polymers exhibit good thermal stability with decomposition temperatures around 400 °C. The fluorescence quantum efficiencies of all these polymers in solution are in the range of 33.5–55.5%. The copolymers also show high film fluorescence quantum efficiencies of about 20% while the fluorescence of the homopolymer film is almost quenched.

     

Three‐Component One‐Pot Synthesis of Indeno[2′,1′:5,6]Pyrido[2,3‐d]Pyrazole Derivatives in Aqueous Media

A series of indeno[2′,1′:5,6]pyrido[2,3‐d]pyrazoles was synthesized by the three‐component reaction of aldehyde, 5‐amino‐3‐methyl‐1‐phenylpyrazole and 1,3‐indenedione in the presence of SDS in aqueous media. The structures were characterized by IR, ¹H NMR, high resolution mass spectra and were further confirmed by X‐ray diffraction analysis.     

Efficient organic photovoltaic cells based on thiazolothiazole and benzodithiophene copolymers with π‐conjugated bridges

New donor–π–acceptor (D–π–A) type conjugated copolymers, poly[(4,8‐bis((2‐hexyldecyl)oxy)benzo[1,2‐b:4,5‐b′]dithiophene)‐alt‐(2,5‐bis(4‐octylthiophen‐2‐yl)thiazolo[5,4‐d]thiazole)] (PBDT‐tTz), and poly[(4,8‐bis((2‐hexyldecyl)oxy)benzo[1,2‐b:4,5‐b′]dithiophene)‐alt‐(2,5‐bis(6‐octylthieno[3,2‐b]thiophen‐2‐yl)thiazolo[5,4‐d]thiazole)] (PBDT‐ttTz) were synthesized and characterized with the aim of investigating their potential applicability to organic photovoltaic active materials. While copolymer PBDT‐tTz showed a zigzagged non‐linear structure by thiophene π‐bridges, PBDT‐ttTz had a linear molecular structure with thieno[3,2‐b]thiophene π‐bridges. The optical, electrochemical, morphological, and photovoltaic properties of PBDT‐tTz and PBDT‐ttTz were systematically investigated. Furthermore, bulk heterojunction photovoltaic devices were fabricated by using the synthesized polymers as p‐type donors and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester as an n‐type acceptor. PBDT‐ttTz showed a high power conversion efficiency (PCE) of 5.21% as a result of the extended conjugation arising from the thienothiophene π‐bridges and enhanced molecular ordering in the film state, while PBDT‐tTz showed a relatively lower PCE of 2.92% under AM 1.5 G illumination (100 mW/cm²). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1978–1988     

Effects of donor unit and π‐bridge on photovoltaic properties of D–A copolymers based on benzo[1,2‐b:4,5‐c']‐dithiophene‐4,8‐dione acceptor unit

A series of donor‐π‐acceptor (D‐π‐A) conjugated copolymers ( PBDT‐AT, PDTS‐AT, PBDT‐TT , and PDTS‐TT ), based on benzo[1,2‐b:4,5‐c']dithiophene‐4,8‐dione (BDD) acceptor unit with benzodithiophene (BDT) or dithienosilole (DTS) as donor unit, alkylthiophene (AT) or thieno[3,2‐b]thiophene (TT) as conjugated π‐bridge, were designed and synthesized for application as donor materials in polymer solar cells (PSCs). Effects of the donor unit and π‐bridge on the optical and electrochemical properties, hole mobilities, and photovoltaic performance of the D‐π‐A copolymers were investigated. PSCs with the polymers as donor and PC₇₀BM as acceptor exhibit an initial power conversion efficiency (PCE) of 5.46% for PBDT‐AT , 2.62% for PDTS‐AT , 0.82% for PBDT‐TT , and 2.38% for PDTS‐TT . After methanol treatment, the PCE was increased up to 5.91%, 3.06%, 1.45%, and 2.45% for PBDT‐AT, PDTS‐AT, PBDT‐TT , and PDTS‐TT , respectively, with significantly increased FF. The effects of methanol treatment on the photovoltaic performance of the PSCs can be ascribed to the increased and balanced carrier transport and the formation of better nanoscaled interpenetrating network in the active layer. The results indicate that both donor unit and π‐bridge are crucial in designing a D‐π‐A copolymer for high‐performance photovoltaic materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1929–1940     

One‐pot Sequential Reactions Featuring a Copper‐catalyzed Amination Leading to Pyrido[2′,1′:2,3]imidazo[4,5‐c]quinolines and Dihydropyrido[2′,1′:2,3]imidazo[4,5‐c]quinolines

Tetracyclic skeletons combining an imidazo[1,2‐a]pyridine moiety with a quinoline framework such as pyrido[2′,1′:2,3]imidazo[4,5‐b]quinoline are stimulating increasing interests since they are close isosteres of a series of powerful antiproliferative compounds. In this paper, we report a novel methodology for the synthesis of pyrido[2′,1′:2,3]imidazo[4,5‐c]quinolines through one‐pot sequential reactions of commercially available or readily obtainable 2‐aminopyridines, 2‐bromophenacyl bromides, aqueous ammonia, and aldehydes. Moreover, dihydropyrido[2′,1′:2,3]imidazo[4,5‐c]quinolines could also be obtained in a similar manner by using various ketones as the substrates in place of aldehydes. Notably, the whole procedure combines condensation/amination/cyclization reactions in one pot to give complex compounds in a simple and practical manner. Compared with literature methods, the synthetic strategy reported herein has the advantages of readily available starting materials, structural diversity of products, good functional group tolerance, and obviation of step‐by‐step operations.     

Synthesis and photovoltaic properties of thieno[3,4‐b]pyrazine or dithieno[3′,2′:3,4;2″,3″:5,6]benzo[1,2‐d]imidazole‐containing conjugated polymers

Novel conjugated polymers composed of benzo[1,2‐b:4,5‐b′]dithiophene and thieno[3,4‐b]pyrazine or dithieno[3′,2′:3,4;2″,3″:5,6]benzo[1,2‐d]imidazole units are synthesized by Stille polycondensation. The resulting polymers display a longer wavelength absorption and well‐defined redox activities. The effective intramolecular charge‐transfer and energy levels of all polymers are elucidated by computational calculations. Bulk‐heterojunction solar cells based on these polymers as p‐type semiconductors and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) as an n‐type semiconductor are fabricated, and their photovoltaic performances are for the first time evaluated. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1067–1075     

Synthesis and Properties of N,N′‐Bis(difuroxano [3,4‐b:3′,4′‐d]phenyl)oxalic Amide

N,N′‐Bis(difuroxano[3,4‐b:3′,4′‐d]phenyl)oxalic amide was synthesized via acylation, nitration, azidation, and pyrolysis‐denitrogenation from the starting materials of oxalyl chloride and 3,5‐dichloroaniline, under mild reaction conditions, with the yields of 81.0%, 82.0%, 86.0% and 81.7% respectively. The title compound and its precursors were characterized by ¹H NMR, IR, MS, and elemental analysis. The title compound has a density of 1.92 g·cm^?3 by a suspension method, a standard formation enthalpy of 979 kJ·mol^?1 calculated by Gaussian programs, a detonation velocity of 8.17 km·s^?1, and a detonation pressure of 31 GPa obtained by Kamlet Equation. The thermal decomposition reactions of the title compound at different heating rates were tested by differential scanning calorimetry (DSC). The kinetics parameters of the pyrolysis of the compound were calculated by Kissinger's method. The values of apparent activation energy (E_a) and pre‐exponential constant (A) were 226.7 kJ·mol^?1 and 10^23.17 s^?1 respectively. It was presupposed that N,N′‐bis(difuroxano[3,4‐b:3′,4′‐d]phenyl)oxalic amide would be a promising high energetic explosive with low sensitivity.     

Synthesis of Certain 3-Aminopyrazolo[5,4-b]pyridine and 3,4-Substituted Pyrido[2′,3′：3,4]pyrazolo[5,1-c][1,2,4]triazine Derivatives

2-Thioxo-1,2-dihydropyridine derivatives 2a, 2b were reacted with methyl iodide to give 2-methylthiopyridines 3a, 3b, which were reacted with hydrazine hydrate to produce 3-aminopyrazolo[5,4-b]pyridines 4a, 4b. Compounds 4a, 4b were diazotized to afford the corresponding diazonium salts 5a, 5b, which were reacted with some active methylene compounds 6a-6h to give the corresponding pyrido[2′,3′ ： 3,4]pyrazole[5,1-c][1,2,4]triazines 7-14.     

One‐Pot Synthesis of 5,7,8,9,9a,10‐Hexahydro‐8‐thioxotetrahydropyrido[2,3‐d : 6,5‐d′]dipyrimidine‐2,4,6(1H,3H,5aH)‐triones via a Four‐Component Coupling Reaction of Aldehydes,Amines, Barbituric Acids,and Thiouracil

An efficient one‐pot approach to the synthesis of 5,7,8,9,9a,10‐hexahydro‐8‐thioxopyrido[2,3‐d : 6,5‐d′]dipyrimidine‐2,4,6(1H,3H,5aH)‐triones 5 via a four‐component reaction of an aldehyde 1 , an amine 2 , a barbituric acid 3 , and thiouracil ( 4 ) is reported for the first time. This new multicomponent reaction is accomplished in refluxing EtOH in the presence of tungstophosphoric acid (H₃PW₁₂O₄₀) as a catalyst. A variety of hexahydropyrido[2,3‐d : 6,5‐d′]dipyrimidinetrione derivatives were successfully synthesized in excellent yields with this protocol (Table 2).     

Ionic Liquid as an Efficient Promoting Medium for Synthesis of Bis‐Pyrazolo[3,4‐b:4′,3′‐e]Pyridines

The preparation of a series of bis‐pyrazolo[3,4‐b:4′,3′‐e]pyridines by the reaction of 5‐aminopyrazole with aldehydes in ionic liquid [bmim]Br is described. This new method has the advantages of easier work‐up, milder reaction conditions, high yields and environmental friendliness compared with other methods.     

Synthesis of Pyrazolo‐[4́,3́:5,6]pyrido[2,3‐d]pyrimidine‐diones Catalyzed by a Nano‐sized Surface‐Grafted Neodymium Complex of the Tungstosilicate via Multicomponent Reaction

An inorganic–organic hybrid based on lanthanide clusters and Keggin type polyoxometalates (POMs) (Na[Nd (pydc‐OH)(H₂O)₄]₃}[SiW₁₂O₄₀]) was used the first time as trinuclear catalyst for one pot synthesis of pyrazolo[4??,3?:5,6]pyrido[2,3‐d]pyrimidine‐diones, via two different four and five‐component reactions involving hydrazine hydrate, ethyl acetoacetate, aryl aldehydes, and 6‐amino‐1,3‐dimethyl uracil or barbituric acid with ammonium acetate as alternative materials in green condition. To evaluate potential application of the as‐made hybrid in adsorption and separation processes, nitrogen adsorption was performed at 77 K through simulation study. The hybrid catalyst was further characterized via powder X‐ray diffraction (PXRD) at room temperature which indicated the good phase purity of the catalyst. The results show that the catalytic activity of the hybrid catalyst has increased relative to each parent component due to the special interaction between Keggin anions and pydc‐OH ligands.     

One‐pot Combinatorial Synthesis of Benzo[4,5]imidazo‐[1,2‐a]thiopyrano[3,4‐d]pyrimidin‐4(3H)‐one Derivatives

A series of novel fused tetracyclic benzo[4,5]imidazo[1,2‐a]thiopyrano[3,4‐d]pyrimidin‐4(3H)‐one derivatives were synthesized via the reaction of aryl aldehyde, 2H‐thiopyran‐3,5(4H,6H)‐dione, and 1H‐benzo[d]imidazol‐2‐amine in glacial acetic acid. This protocol features mild reaction conditions, high yields and short reaction time.     

Tuning the π‐π stacking distance and J‐aggregation of DPP‐based conjugated polymer via introducing insulating polymer

The close π–π stacking and the high J‐aggregation during the formation of fibrillar morphology in films of the poly[[2,5‐bis(2‐octyldodecyl)?2,3,5,6‐tetrahydro‐3,6‐dioxopyrrolo[3,4‐c]pyrrole‐1,4‐diyl]‐alt–[[2,2′‐(2,5‐thiophene)bis‐thieno[3,2‐b]thiophen]‐5,5′‐diyl]] (PDPPTT‐T) are demonstrated via blending with polystyrene (PS). The hydrodynamic radius (R_h) of PDPPTT‐T is decreased from 16.7 nm in the neat solution to 12.7 nm in the blend solution at the ratio of 1/20(PDPPTT‐T/PS). This phenomenon suggests that blending PS is beneficial for the disentanglement of PDPPTT‐T. The disentanglement of PDPPTT‐T facilitates the formation of fibrillar morphology. The growth of the fibrils occurs along the molecular backbones and the width of the fibrils is parallel to the π–π stacking direction. The disentanglement of PDPPTT‐T helps the molecules adjust conformation to improve J‐aggregation and decrease the π–π stacking distance. The maximum absorption is red‐shifted from 825 nm to 849 nm and the relative intensity of J‐aggregation (the 0‐0/0‐1 ratio) is increased from 1.19 to 1.60. The π–π stacking distance decreases from 3.57 to 3.52 Å. The charge‐carrier mobility will be improved in the fibrillar morphology with close π–π stacking and high J‐aggregation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 838–847     

Novel pendent thiophene side‐chained benzodithiophene for polymer solar cells

In this article, pendent thiophene (2‐butyl‐5‐octylthiophene) side chain is used to modify the backbone of the polymers containing benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and thieno[3,4‐c]pyrrole‐4,6‐dione (TPD). Compared with the dodecyloxy side‐chained polymer (P1), pendent thiophene‐based polymers (P2 and P3) show similar number‐average molecular weight (M_n), polydispersity index, thermal stability (T_d ～ 334–337 °C), and optical band gaps ( ) (～1.8 eV). Polymer (P2)‐based BDT with pendent thiophene and ethylhexyl‐modified TPD shows relatively low‐lying HOMO energy level (?5.52 eV) and nearly 1 V high open circuit voltage (V_OC). The polymer solar cell devices based on three copolymers show power conversion efficiencies from 2.01% to 4.13%. The hole mobility of these polymers tested by space charge limited current method range from 3.4 × 10^?4 to 9.2 × 10^?4 cm²V^?1s^?1. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1558–1566     

Synthesis and photovoltaic performances of benzo[1,2‐b:4,5‐b']dithiophene‐alt‐2,3‐diphenylquinoxaline copolymers pending functional groups in phenyl rings

Two donor/acceptor (D/A)‐based benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐2,3‐biphenyl quinoxaline copolymers of P 1 and P 2 were synthesized pending different functional groups (thiophene or triphenylamine) in the 4‐positions of phenyl rings. Their thermal, photophysical, electrochemical, and photovoltaic properties, as well as morphology of their blending films were investigated. The poly(4,8‐bis((2‐ethyl‐hexyl)oxy)benzo[1,2‐b:4,5‐b'] dithiophene)‐alt‐(2,3‐bis(4′‐bis(N,N‐bis(4‐(octyloxy) phenylamino)‐ 1,1′‐biphen‐4‐yl)quinoxaline) ( P 2) exhibited better photovoltaic performance than poly(4,8‐bis((2‐ethylhexyl)oxy)benzo[1,2‐b:4,5‐b'] dithiophene)‐alt‐(2,3‐bis(4‐(5‐octylthiophen‐2‐yl)phenyl)quinoxaline) ( P 1) in the bulk‐heterojunction polymer solar cells with a configuration of ITO/PEDOT:PSS/polymers: [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM)/LiF/Al. A power conversion efficiency of 3.43%, an open‐circuit voltage of 0.80 V, and a short‐circuit current of 9.20 mA cm^?2 were achieved in the P 2‐based cell under the illumination of AM 1.5, 100 mW cm^?2. Importantly, this power conversion efficiency level is 2.29 times higher than that in the P 1‐based cell. Our work indicated that incorporating triphenylamine pendant in the D/A‐based polymers can greatly improved the photovoltaic properties for its resulting polymers.     

Synthesis and photovoltaic behaviors of narrow‐band‐gap π‐conjugated polymers composed of dialkoxybenzodithiophene‐ and thiophene‐based fused aromatic rings

π‐Conjugated polymers, PBDT‐CNETT and PBDT‐CNECPDT , were prepared by the Stille cross‐coupling polymerization. Optical and thermal properties of the obtained polymers were investigated by UV–vis spectroscopy and thermogravimetric analysis. PBDT‐CNETT and PBDT‐CNECPDT exhibited very narrow band gaps of 1.39 and 1.13 eV, respectively. Highest occupied molecular orbital energy levels estimated by surface analyzer were ?5.17 and ?5.11 eV for PBDT‐CNETT and PBDT‐CNECPDT , respectively. The solar cells based on these polymers were evaluated with the cell configuration of ITO/PEDOT‐PSS/polymer:PC₆₁BH/LiF/Al. The power conversion efficiencies of the solar cells were estimated to be 1.57 and 0.16% for PBDT‐CNETT and PBDT‐CNECPDT , respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Molecular Tuning in Diaryl-Capped Pyrrolo[2,3-d:5,4-d′]bisthiazoles: Effects of Terminal Aryl Unit and Comparison to Dithieno[3,2-b:2′,3′-d]pyrrole Analogues

A series of six conjugated oligomers consisting of a central pyrrolo[2,3-d:5,4-d′]bisthiazole (PBTz) end-capped with either thienyl, furyl, or phenyl groups have been prepared from N-alkyl-and N-aryl-pyrrolo[2,3-d:5,4-d′]bisthiazoles via Stille and Negishi cross-coupling. The full oligomeric series was thoroughly investigated via photophysical and electrochemical studies, in parallel with density functional theory (DFT) calculations, in order to correlate the cumulative effects of both aryl end-groups and N-functionalization on the resulting optical and electronic properties. Through comparison with the analogous dithieno[3,2-b:2′,3′-d]pyrrole (DTP) materials, the effect of replacing DTP with PBTz on the material HOMO energy and visible light absorption is quantified.