Ladder Bis-Silicon-Bridged Stilbenes as a New Building Unit for Fluorescent π-Conjugated Polymers

Abstract

π-Conjugated polymers containing the bis-silicon-bridged stilbene (5,10-dihydro-5,10-disilaindeno[2,1-a]indene) skeleton in the main chain have been synthesized. Our synthesis uses 3,8-dimethoxy derivatives (2) and 3,8-difluoro derivatives (3) of the bis-silicon-bridged stilbene as the key precursors. Thus, their regioselective ortho-metalation reactions with appropriate bases (sec-butyllithium for 2 and LitBu2ZnTMP for 3) followed by quenching with electrophiles afford various 2,7-difunctionalized bis-silicon-bridged stilbenes. By using the 2,7-difunctionalized derivatives as starting materials, a series of π-conjugated polymers, including homopolymers of the bis-silicon-bridged stilbene skeleton and copolymers between the bis-silicon-bridged stilbene unit and other types of monomer units, such as bithiophene and diethynylbenzene, have been synthesized by cross-coupling methodologies. While all the homopolymers of the bis-silicon-bridged stilbene skeleton exhibit an intense blue to greenish-blue emission, the copolymers with the bithiophene and diethynylbenzene units show green and orange emissions, respectively, suggesting easy tuning of the emission colors over a wide range.