Three conjugated polymers with the dithienobenzimidazole (DTBIm) unit (P1, P3, and P4) and one conjugated polymer with the dithienobenzoxazole unit (P2) were synthesized by the cross-coupling polymerization. The absorption maxima showed a red-shift in the order of P3 (406 nm), P2 (426 nm), P1 (438 nm), and P4 (450 nm), which was studied in detail using the frontier molecular orbital calculation of the model compounds. The energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the DTBIm unit-containing conjugated polymers were estimated by the cyclic voltammetry. The transformation from DTBIm (P4) to dithienobenzimidazolium (P4') was also carried out to shift the absorption maxima of P4' (454 nm) by promoting the intramolecular charge transfer between the DTBIm and thiophene units. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 401–409

Poly[3-(5′-hexylpyridine-2′-yl)thiophene] (P3PT) (M_n = 13900, H-T content = 90%) was prepared by the regioselective Grignard metathesis reaction and the subsequent Kumada coupling polymerization. Likewise, poly(3-hexylthiophene)-b-poly[3-(5′-hexylpyridine-2′-yl)thiophene] (P3HT-b-P3PT) (M_n = 17,300) was synthesized in the one-pot and successive monomer addition protocol, in which the segment ratio was calculated to be 56 (P3HT)/44 (P3PT) base on the ¹H NMR spectrum. The absorption and emission spectra of homopolymer P3PT(H), obtained by the protonation of the pyridine nitrogen, in THF/cyclohexane shifted to the longer wavelength as compared with those collected in THF, suggesting the aggregation in poor solvent. The aggregation of P3PT induced by the addition of Sc(OTf)₃ could be controlled by the molar ratio of pyridine and scandium complex. The protonated block copolymer P3HT-b-P3PT(H) was also subjected to the aggregate formation. The absorption maximum in THF/CH₃OH showed a bathochromic shift and the fluorescence emission was almost quenched. From the ¹H NMR spectra and DLS measurements, P3HT-b-P3PT(H) forms nanometer scale aggregates particularly with the insolubility and stacking of non-ionic P3HT in alcohol as the driving force. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3383–3389

The Grignard metathesis reaction of 2,5-dibromo-3-(5′-hexylpyridine-2′-yl)thiophene (M1) with i-PrMgCl afforded 5-bromo-2-chloromagnesio-3-(5′-hexylpyridine-2′-yl)thiophene (GM1) in the 86% selectivity. The Kumada coupling polymerization by Ni(dppp)Cl₂ gave polyM1 having the roughly controlled molecular weight between 6700 and 23,400. The characterization using the gel permeation chromatographic and matrix-assisted laser desorption/ionization-time of flight mass spectra indicated the diffusion of the nickel catalyst from the propagating end. Based on the GC and ¹H NMR spectra, the head-to-tail content of polyM1 was calculated to be 89%. The regioselective Grignard metathesis reactions of 5,5′-dibromo-4-(5″-hexylpyridine-2″-yl)-2,2′-bithiophene (M2) and 5,5′-dibromo-4-(5″-hexylpyrimidine-2″-yl)-2,2′-bithiophene (M3) also occurred at the ortho-position of the nitrogen heterocycle. The Kumada coupling polymerizations gave polyM2 and polyM3 having the head-to-tail content of 75% and 85%, respectively. The UV–vis spectra of polymers suggested that the polymer conformation becomes more planar in the order of polyM1 < polyM3 < polyM2, which was investigated by the theoretical calculation of the model oligomers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2166–2174

The Suzuki (for O1–O3) and Stille (for O4) coupling polymerization of 2-(phenylazo)imidazole bearing the benzyl protecting group at the 1-position gave conjugated oligomers. The transformation from the neutral imidazole in the conjugated oligomer O2, consisted of the alternating 2,5-didecyl-1,4-phenylene unit, to the cationic imidazolium salt O2S was performed. Depending on the chemical structure of coupling partners, the absorption maximum of conjugated oligomers showed red shift or blue shift from that of the model compound M with the benzene ring at the 4,5-positions. The absorption maximum wavelength of the cationic conjugated oligomer O2S showed a blue shift from that of the neutral conjugated oligomer O2. The trans-to-cis photoisomerization of the azoimidazole unit in conjugated oligomers was observed by irradiating the light at 436 nm, and the conversion degree to the cis structure had a rough correlation with the maximum absorption wavelength of materials. The trans-to-cis photoisomerization in the film state was sluggish. On the other hand, the cis-to-trans thermal isomerization of the azoimidazole unit was confirmed and the absorbance returned to the initial state before the photoisomerization. The trans-to-cis photoisomerization of the cationic conjugated oligomer O2S required large energy, and the prolonged light irradiation might decompose the azoimidazole unit. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.

2,5-Dibromo-3-(6′-hexylpyridine-2′-yl)thiophene (DBPyTh) was synthesized by the Suzuki coupling reaction between two aromatic compounds followed by the bromination. The Grignard metathesis reaction of DBPyTh with isopropylmagnesium chloride proceeded in 85% conversion and the regioselective halogen–metal exchange at the 2-position was confirmed. Namely, 5-bromo-2-chloromagnesio-3-(6′-hexylpyridine-2′-yl)thiophene and 2-bromo-5-chloromagnesio-3-(6′-hexylpyridine-2′-yl)thiophene were generated in 90:10 molar ratio. Subsequently, the Kumada coupling polymerization was carried out using 1,3-bis(diphenylphosphinopropane)nickel(II) dichloride to obtain poly(3-(6′-hexylpyridine-2′-yl)thiophene) (PolyPyTh). The polymer molecular weight could be roughly controlled by the catalyst concentration and the molecular weight distribution ranged from 1.25 to 1.80. The gas chromatograph analysis indicated that 5-bromo-2-chloromagnesio-3-(6′-hexylpyridine-2′-yl)thiophene was preferentially polymerized in 90% conversion and the percentage of the head-to-tail content (regioregularity) was calculated to be 96%. The matrix-assisted laser desorption/ionization time-of-fright mass spectrum indicated that both polymer chain ends were substituted with the hydrogen atom. The absorption maxima of polymer in CHCl₃ and thin film were observed at 447 and 457 nm, respectively, which were blue-shifted compared with poly(3-(4′-octylphenyl)thiophene). From the CV measurement of the polymer thin film, highest occupied molecular orbital (HOMO) (−5.31 eV) and lowest unoccupied molecular orbital (LUMO) (−3.76 eV) energy levels were calculated from the oxidation and reduction onset potentials, respectively, and the electrochemical band gap energy was determined to be 1.62 eV. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Two arylenevinylene compounds bearing the cyano group at α-position (6) and β-position (9) from the dialkoxylphenylene unit were synthesized, in which the molecular termini were functionalized with 3-bromocarbazole. The Suzuki coupling copolymerization of these compounds with 1,4-bis[(3′-bromocarbazole-9′-yl)methylene]-2,5-didecyloxybenzene and 9,9-dihexylfluorene-2,7-bis(boronic acid) was carried out to obtain copolymers (cp67 and cp97) containing the cyano-substituted arylenevinylene fluorophore of 7 mol %. Model compounds (6′ and 9′) corresponding to the arylenevinylene fluorophore were also prepared. The UV spectra of copolymers resembled that of homopolymer hp with no arylenevinylene segment in both CHCl₃ solution and thin film. The emission maxima of copolymers in CHCl₃ (394 nm) agreed with that of homopolymer indicating that the emission bands originated from the carbazole-fluorene-carbazole segment. The emission maximum wavelength of copolymer cp67 in thin film (477 nm) indicated fluorescence from the cyano-substituted arylenevinylene fluorophore because of the occurrence of fluorescence resonance electron transfer. In contrast, copolymer cp97 showed fluorescence at 528 nm to suggest the formation of a new emissive species such as a charge-transfer complex (exciplex). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 91–98, 2010

We have prepared four light-emitting polymers bearing a chromophore composed of carbazole and fluorene by the Suzuki coupling polycondensation. Two nonconjugated polymers (P3CzBFXy and P2CzFXy) had a chromophore tethered by the p-xylylene spacer, whose connection point between carbazole and fluorene in addition to the number of fluorene unit was systematically changed to investigate the emission wavelength and intensity. The red-shifted absorption and emission maximum wavelengths together with the improved fluorescence quantum yield of polymers P3CzBFXy and P2CzFXy indicate that the increment of the number of para-connected benzene rings included in the chromophore effectively extends the conjugation length. The fact that polymer P3CzBFXy has longer wavelength absorption and emission spectra also indicates the interaction of the carbazole nitrogen lone pair with the oligophenylene moiety. Other two polymers P3CzFPy and P3CzFPym having the heterocycle directly bound to the carbazole nitrogen were prepared to know the character of the carbazole nitrogen lone pair and their influence on the fluorescence behavior. The fluorescence spectra of polymer P3CzFPym bearing the pyrimidine ring gradually red-shifted in conjunction with the decrease of fluorescence quantum yield on going from toluene solution to CHCl₃ solution because of the intramolecular charge transfer at the excited state. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3729–3735, 2010

Bithiophene monomers (5HBTh and 5HBThO) were prepared by the Suzuki coupling reaction of 3-thienylboronic acid with 2-bromo-5-hexylthiophene and 2-bromo-5-hexylthiophene-1,1-dioxide. The oxidation polymerization mediated by vanadium catalyst gave poly(5HBTh) and oligo(5HBThO). 5HBThO bearing thiophene-1,1-dioxide had an absorption maximum at longer wavelength region than 5HBTh due to the intramolecular charge transfer interaction, while peak maxima blue shifted and their difference became small after the polymerization. Terthiophene monomers (5″HTTh, 3,5″DHTTh, and 4,5″DHTTh) were subsequently prepared by the mono-bromination of 5HBTh followed by the Suzuki coupling reaction with boronic acid derivatives. The vanadium-catalyzed oxidation polymerization of 5″HTTh and 4,5″DHTTh afforded soluble polymers and the absorption maximum wavelengths red shifted after the polymerization in contrast to bithiophene monomers and 3,5″DHTTh. The absorption and emission spectra of poly(5″DHTTh) red shifted when compared with those of poly(4,5″DHTTh). Thus the presence and position of n-hexyl chain influenced the monomer polymerizability and optoelectronic properties of branched polythiophenes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3034–3044, 2009

Dibromobenzimidazole and dibromoimidazole bearing hydroxyl group-protected phenol unit (1 and 2) were prepared and they showed an intramolecular hydrogen bonding between ether oxygen and amino proton of imidazole. The palladium-catalyzed Suzuki coupling polymerization of 1 and 2 with benzene bis(boronic acid) derivatives gave soluble polymers (3 and 4), where the molecular weights were limited probably due to the coordination ability of imidazole to palladium metal. The phenol hydroxyl groups were subsequently deprotected using BBr₃ to obtain 3′ and 4′. From the ¹H NMR spectra, the complete conversion to the hydroxyl group and the formation of another type of intramolecular hydrogen bonding between hydroxyl proton and imine nitrogen were confirmed. In the UV and PL spectra of 3′ and 4′, the excited state intramolecular proton transfer (ESIPT) occurred to shift the emission spectra toward lower energy region compared to 3 and 4. Especially, the PL spectrum of 3′ demonstrated large stokes shift (145 nm) in THF solution. The ESIPT-mediated fluorescence was influenced by the addition of methanol and trifluoroacetic acid, which inhibited the formation of intramolecular hydrogen bonding. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4822–4829, 2009

The Suzuki coupling polymerization between bis(carbazole) monomer (CzDB) and 9,9-dihexylfluorene-2,7-diboronic acid was carried out to obtain PFCz-PEDA0 having the number-averaged molecular weight of 7000. The absorption and emission maximum wavelengths were observed at 344 and 408 nm, respectively. The quantum yield (QY) was relatively low (0.12) because of the photo-induced electron transfer. Subsequently, CzPEDA-bearing 2,5-bis(phenylethenyl)-4-decyloxyanisole (PEDA) segment sandwiched with 3-bromocarbazole units was copolymerized to give PFCz-PEDAn (n = 05, 10, 20, 35, and 50). The content of PEDA segment in polymer could be controlled by the monomer feed ratio. In CHCl₃ solution, the absorbance at around 400 nm became larger with one isosbestic point at 370 nm, and the emission peak at 448 nm became prominent with increasing the PEDA content. The QY of polymer was increased as the PEDA content, which was a consequence of the fluorescence resonance energy transfer from carbazole-containing chromophore (energy donor) to PEDA fluorophore (energy acceptor). In spin-coated film, the maximum QY was obtained in PFCz-PEDA05 having the most appropriate molar balance of energy donor and acceptor units. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8141–8148, 2008