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 <i>N</i>-hexylcarbazole with conjugated (<b>P1</b> and <b>P2</b>) and δ-Si interrupted (<b>P3</b> and <b>P4</b>) structures have been synthesized. The linear tetrahedral polymer <b>P3</b> and hyperbranched tetrahedral polymer <b>P4</b> were synthesized from two novel tetrahedral dibromo/tetrabromo precursors (<b>2</b> and <b>3</b>, 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 <b>P1</b><b>−</b><b>P4</b> showed that, in the condensed state, <b>P1 </b>and <b>P2</b> 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 <b>P3</b> and <b>P4</b>, 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.