Synthesis and characterization of poly(tetramethylsilarylenesiloxane) derivatives with oligothiophene based moiety

Abstract

Poly(tetramethylsilarylenesiloxane) derivatives (P1T-P4T, P4TC) that contained thiophene (1T), oligothiophenes such as dithiophene (2T), terthiophene (3T), quaterthiophene (4T), or 2,6-di(2-thienyl)-4,4-diphenylcyclopentadithiophene (4TC) as the main chain components were synthesized via polycondensation reaction of the corresponding disilanol monomers (M1T-M4T, M4TC). The obtained polymers other than P4T that contained quaterthiophene units exhibited the good solubility in common organic solvents, such as toluene, chloroform, tetrahydrofuran and so on. The glass transition temperature (Tg) and melting temperature (Tm) of the obtained polymers regarding P1T-P4T were increased with the extension of the thiophene rings of the monomeric unit as deduced from the results of the differential scanning calorimetry (DSC). On the other hand, the Tm was not observed for P4TC that was composed of 2,6-di(2-thienyl)-4,4-diphenylcyclopentadithiophene units. P2T that was composed of dithiophene units exhibited the highest temperature at 5% weight loss (Td5) of 467 °C in all present polymers. The bathochromic and hyperchromic effects in the absorption spectra as well as the improvement of fluorescence quantum yield were observed by the introduction of dimethylsilyl group onto the present oligothiophene derivatives. These effects became unremarkable accompanying the elongation of the thiophene rings of the monomeric units; however, 4TC exhibited a more significant change by the introduction of the dimethylsilyl group than the other oligothiophenes derivatives, indicating that the introduction of the cardo-structure was effective in the improvement of the optical properties. M4TC and P4TC exhibited the fluorescence wavelength around 500 nm and the highest fluorescence quantum yield of the present series of poly(tetramethylsilarylenesiloxane) derivatives, i.e., 0.40, plausibly because the free rotation between thiophene rings in oligothiophene inhibited by the cardo-structures and the bulky diphenyl groups at 4-position of cyclopentadithiophene moiety suppressed the nonradiative transition.