2,3‐Diaryl substituted maleimides as model compounds of conjugated maleimide polymers [poly(RMI‐alt‐Ar) and poly(RMI‐co‐Ar)] were synthesized from 2,3‐dibromo‐N‐substituted maleimide (DBrRMI) [R= cyclohexyl (DBrCHMI) and n‐hexyl (DBrHMI)] and aryl boronic acid using palladium catalysts. To clarify structures of conjugated polymer containing maleimide units at the main chain, 13C NMR spectra of 2‐aryl or 2,3‐diaryl substituted maleimides were compared with those of N‐substituted maleimide polymers. Copolymers obtained with DBrRMI via Suzuki‐Miyaura cross‐coupling polymerizations or Yamamoto coupling polymerizations were dehalogenated structures at the terminal end. This dehalogenation may contribute to the low polymerizability of DBrRMIs. On the other hand, the π‐conjugated compounds showed high solubility in common organic solvents. The N‐substituents of maleimide cannot significantly affect the photoluminescence spectra of 2,3‐diaryl substituted maleimides derivatives. The fluorescence spectra of poly(RMI‐alt‐Ar) and poly(RMI‐co‐Ar) varied with N‐substituents of the maleimide ring. When exposed to ultraviolet light of wavelength 352 nm, a series of 1,4‐phenylene‐ and/or 2,5‐thienylene‐based copolymers containing N‐substituted maleimide derivatives fluoresced in a yellow to blue color. It was found that photoluminescence emissions and electronic state of π‐conjugated maleimide derivatives were controlled by aryl‐ and N‐substituents, and maleimide sequences of copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Yamamoto coupling polymerizations of 2,3-diiodo-N-cyclohexylmaleimide (DICHMI) with dihalide carbazole derivatives (DXRCz) (3,3, and 2,7-dibromo-N-hexylcarbazole (2,7-DBrHCz)) were performed using a nickel complex. The number-average molecular weights (M n ) of poly(Ncyclohexylmaleimide-co-N-substituted carbazole)s (poly(CHMI-co-RCz)) were in the range of 600-7300, as determined by gel permeation chromatography analyses. The fluorescence emissions of the poly(CHMI-co-RCz) solution showed two emission maxima in the 417-426 and 581-595 nm regions. The fluorescence peaks of co-oligomers at long wavelengths (581-595 nm) were attributable to the conjugated neighboring CHMI-RCz units of polymer main chains. The intensities of fluorescence emissions were significantly affected by the polarity of organic solvents such as tetrahydrofuran and N,N-dimethylformamide. The solvatochromic fluorescence phenomenon may be attributable to the twisting of CHMI-RCz bonds in an excited state in polar solvents.

Yamamoto or Suzuki-Miyaura coupling polymerizations of 2,3-diiodo-N-cyclohexylmaleimide with fluorene derivatives (2,7-dibromo-9,9 0 -dihexylfluorene and 9,9 0 -dihexylfluorene-2,7-diboronic acid) were carried out. The numberaverage molecular weights (M n ) of the resulting copolymers were 2600-3500 by gel permeation chromatography analysis. The fluorescence emission of the alternating copolymer showed the emission maxima at 551 nm in THF. On the other hand, the random copolymers showed the bimodal emission peaks at 418-420 and 555-557 nm region, respectively. The fluorescence peaks of the random copolymers on the long wavelength region (555-557 nm) were attributed to the conjugated neighboring N-cyclohexylmaleimide-9,9 0 -dihexylfluorene units in the polymer main chain. Furthermore, the copolymers exhibited the fluorescence solvatochromism by the difference of the polarity of solvents. The alternating and random copolymers showed the different fluorescence solvatochromism, and the emission colors are distinguishable by the naked eye, respectively.

Yamamoto coupling polymerizations of 2,3-dihalido-N-substituted maleimides (DXRMI) were carried out using nickel catalysts. In addition, coupling reactions of 2,3-dihalido-N-cyclohexylmaleimide (DXCHMI) were performed with nickel complexes in the presence of directly coupled chiral bisoxazolines (R′box) to give optically active poly(N-substituted maleimide-2,3-diyl)s [poly(RMI)s] (specific rotation [α]435 = +6.0 to −34.6°). Polymers with number-average molecular weights (Mn) ranging from 270 to 36200 were obtained in 17% to quantitative yields. Poly(N-cyclohexylmaleimide-2,3-diyl) [poly(CHMI)] formed with [Ni(cod)2]–R′box exhibited the largest absolute value, [α]435 = −34.6°.