Poly(tetramethylsilarylenesiloxane) derivatives having diphenylfluorene (P1) or diphenyldibenzosilole (P2) moieties were prepared via polycondensation of the corresponding disilanol monomers, that is, 2,7-bis(dimethylhydroxysilyl)-9,9-diphenylfluorene (M1) and 2,7-bis(dimethylhydroxysilyl)-9,9-diphenyldibenzosilole (M2), respectively. P1 and P2 exhibited good solubility in common organic solvents. The glass transition temperatures (T(g)s) of P1 and P2 were determined by differential scanning calorimetry to be 125 and 119 degrees C, respectively. The melting temperature (T(m)) of P1 was observed at 276 degrees C; however, the T(m) of P2 was not observed, indicating that the introduction of a dibenzosilole moiety decreased the crystallization tendency. The temperatures at 5% weight loss (T(d5)s) of P1 and P2 were 539 and 520 degrees C, respectively, suggesting good thermostability of P1 and P2. Bathochromic and hyperchromic effects were observed in the absorption and fluorescence spectra by introducing a dimethylsilyl substituent onto diphenylfluorene and diphenyldibenzosilole skeletons. The replacement of diphenylfluorene by the corresponding diphenyldibenzosilole also led to bathochromic shifts. The fluorescence quantum yield (Phi(F)) of P1 was lower than that of M1, probably because of the formation of aggregates; however, the Phi(F) of P2 was higher than that of M2, indicating a decrease in the tendency toward aggregation using a dibenzosilole skeleton. Polymer Journal (2011) 43, 58-65; doi:10.1038/pj.2010.104; published online 3 November 2010