Highly Luminescent Ladderized Fluorene Copolymers Based on B-N Lewis Pair Functionalization

A new B-N functionalized polyaromatic building block for conjugated hybrid polymers is developed. Bromine-functionalized dipyridylfluorene is first subjected to Lewis-base-directed electrophilic borylation and subsequently incorporated into conjugated polymers via transition-metal-catalyzed cross-coupling reactions. The borane monomer exhibits bright blue luminescence in solution, as a result of the rigid ladder-type structure generated upon electrophilic borylation. Yamamoto coupling gives rise to a homopolymer and Stille coupling to a vinylene-bridged copolymer. Polymerization of the BN-fused ladder molecules leads to large bathochromic shifts in absorption and emission, which are most pronounced for the vinylene-bridged copolymer. The polymers display strong luminescence in solution with quantum yields of 55% and 78% and sub-ns fluorescence lifetimes; the copolymer also exhibits bright yellow luminescence in the solid state when precipitated from solution.