Highly Red Emissive Conjugated Homopolymers Based on Double B←N Bridged Bipyridine Unit

Conjugated homopolymers based on six-member rings, e.g., polyfluorene, always exhibit blue emission and conjugated homopolymers based on five-member rings, e.g., polythiophene, can give red emission with low efficiency. In this work, we report a series of new conjugated homopolymers based on six-member rings with high-efficiency deep-red emission. The repeating units of the red light emitting homopolymers are double B←N bridged bipyridine (BNBP) with the boron atoms functionalized with diphenyl, borafluorene, and 2,7-di-tert-butyl-borafluorene groups, respectively. The relationship between the chemical structures and the opto-electronic properties of the monomers and the homopolymers has been systematically studied. The three polymers emit pure red light (λ_max=656 nm) or deep red light (λ_max=693 nm) with fluorescence quantum efficiency in solution higher than 60%. The polymers can be used as the emitters in solution-processed organic light-emitting diodes with red emission and decent device performance. This work indicates a new strategy to design highly efficient light emitting conjugated polymers.