Synthesis and characterization of conjugated polymers containing thienylenevinylene units

Abstract

The long alkyl silyl group, that is considered steric hindrance and electronic delocalization as designing a monomer, was introduced on heteroaromatic ring to overcome the problem of the instability of 2,5-bis(halomethyl) thiophene monomers. In result, the stable monomer could be directly used to prepare the low band-gap energy poly(thienylenevinylene) through heteroaromatic dehydrohalogenation polymerization. Poly[3-(1,1-dimethyl-1-silanonadecyl)-2,5-thienylenevinylene] (PSiTV) were completely soluble in common organic aprotic polar solvents, such as chloroform, tetrahydrofuran, and cyclohexanone, and showed good film quality on both quartz and glass substrates. The number and weight average molecular weights of the resulting polymer were determined to be 26,400 and 145,900 Da, respectively. These values are relatively high molecular weight (DP = 63 - 348), and reliable polydispersity (PDI = 5.5). The polymer thin film on solid state showed the maximum wavelength, $λ_{max}$ = 563 nm in UV-visible absorption but didn’t show any photoluminescence (PL) emission. The PSiTV film have very low band-gap energy, $E_g = 1.57 eV$ according to the onset wavelength, $λ_{onset}$ = 788 nm. A series of new light-emitting random copolymers, poly[2-ethylhexyloxy-5-methoxy-1,4-phenylenevinylene-co-2,5-thienylenevinylene]s (PMEHPVTVs), with fully conjugated structure was prepared, for the first time through the facile Gilch polymerization between 1,4-bis(chloromethyl)-2-ethylhexyloxy-5-methoxybenzene and 2,5-bis(bromomethyl)thiophene monomers in different ratios. The resulting polymers were soluble in common organic solvents such as chloroform, tetrahydrofuran, 1,2-dichloroethane, and cyclohexanone. They showed glass transitions at temperature near 150℃ and also showed good thermal stability up to around 380℃ (at 5% weight loss). The weight average molecular weights of the resulting polymers were obtained to be 743,200-268,000 $(M_w /M_n = 15.9-24.6)$ from gel permeation chro...