A Comparative Study on Luminescent Copolymers of Fluorene and Carbazole with Conjugated or δ-Si Interrupted Structures:  Steric Effects

Light-emitting alternating copolymers of 9,9-dialkylfluorene and N-hexylcarbazole with conjugated (P1 and P2) and δ-Si interrupted (P3 and P4) structures have been synthesized. The linear tetrahedral polymer P3 and hyperbranched tetrahedral polymer P4 were synthesized from two novel tetrahedral dibromo/tetrabromo precursors (2 and 3, respectively). The thermal and optical properties of all polymers in solution and the condensed state were investigated. A comparative study on the optical properties of P1−P4 showed that, in the condensed state, P1 and P2 suffered seriously from concentration quenching (significant red shift in emission maximum, broadening in emission spectrum and tremendous decrease in quantum yield), whereas the two δ-Si interrupted P3 and P4, particularly the latter, were tremendously less or not prone to self-aggregation such that they did not show significant concentration quenching in the condensed state. We represent in this paper an effective approach, a tetrahedral approach, for the synthesis of nonaggregating optoelectronic polymers.