Organoboron-Conjugated Homopolymers with Bright Narrowband Near-Infrared Emission

Near-infrared (NIR) light-emitting polymers are important because of their many civilian and military applications. The general strategy to design NIR-emissive conjugated polymers is to copolymerize an electron-donating unit and electron-accepting unit to design donor-acceptor-type copolymers. The resulting NIR-emissive copolymers suffer from low fluorescence efficiencies and wide fluorescence spectra. In this work, we report a series of organoboron-conjugated homopolymers with high quality NIR light emission. The repeating unit of these homopolymers is a double B <- N-bridged bipyridine (BNBP) unit bearing diphenylether as a large steric hindrance. Because of the rigid backbone and small reorganization energy of BNBP, the organoboron homopolymers emit high-quality NIR light with the emission peak wavelength of ca. 750 nm, fluorescence quantum efficiency of ca. 0.7, and full width at half-maximum of ca. 50 nm. The application of these homopolymers as visible to NIR light converters in NIR organic light-emitting diodes has been demonstrated. This work indicates a new strategy of organoboron chemistry to develop narrow-band and bright NIR-emissive polymers for practical applications.