Synthesis and properties of cyclopentadithiophene-based poly(silarylenesiloxane) derivatives

Poly(silarylenesiloxane) derivatives with 4,4-dimethylcyclopenta2,1-b:3,4-b′]dithiophene moiety, bearing dimethyl- (P1), methylphenyl- (P2) and diphenyl- (P3) substituents on silyl moieties, were prepared via polycondensation of the corresponding disilanol monomers, that is, 2,6-bis(dimethylhydroxysilyl)-4,4-dimethylcyclopenta2,1-b:3,4-b′]dithiophene (M1), 2,6-bis(methylphenylhydroxysilyl)-4,4-dimethylcyclopenta2,1-b:3,4-b′]dithiophene (M2), and 2,6-bis(diphenylhydroxysilyl)-4,4-dimethylcyclopenta2,1-b:3,4-b′]dithiophene (M3), respectively. P1-P3 exhibited the good solubility in common organic solvents, such as benzene, toluene, chloroform, dichloromethane, THF, and so on. The glass transition temperatures (T_gs) of P1, P2 and P3 were determined by differential scanning calorimetry to be 56, 97 and 137 °C, respectively, depending on the substituent on the silyl moieties. No melting temperatures (T_ms) of P1, P2 and P3 were observed, suggesting the obtained P1-P3 are amorphous polymers. The temperatures at 5% weight loss (T_d5s) of P1, P2 and P3 were 460, 459 and 479 °C, respectively, indicating that the larger number of phenyl group on the silyl moieties resulted in the better thermostability. Bathochromic and hyperchromic effects were observed in the absorption and fluorescence spectra by introducing silyl substituents onto 4,4-dimethylcyclopenta2,1-b:3,4-b′]dithiophene moiety. In addition, the bathochromic shift of the maximum absorption (λ_abs) and the increase in the fluorescence quantum yield (Φ_F) were observed by the introduction of phenyl group onto the silyl moieties.