Self-assembly of a white-light emitting polymer with aggregation induced emission enhancement using simplified derivatives of tetraphenylethylene

Abstract

White-light emitting materials and devices have gained a great deal of interest and play an important role in next generation solid-state lighting applications. The unique aggregation-induced emission (AIE) route offers a forthright solution to the bottleneck problem of aggregation caused quenching (ACQ) in the solid state. A significant fluorescence enhancement was realized by tailoring a new luminogen (2Z,2′Z)-3,3′-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis(3,1-phenylene))bis(2-(4-bromophenyl)-3-phenylacrylonitrile) (FBPAN) based on the AIE strategy, which exhibits yellow fluorescence with a high quantum yield of 63.41%. Electroluminescence characteristics with a maximum luminance, current and power efficiency of 16673 cd m⁻², 9.32 cd A⁻¹ and 5.88 lm W⁻¹, respectively, were obtained for FBPAN. The white light emitting polymers were obtained by the copolymerization of a 9,9′-dihexylfluorene host with a FBPAN moiety as a covalent dopant. Bright white light emission with a high quantum yield of 80.2% was obtained from the copolymer FBPAN 0.5, which contained 0.5% FBPAN. Importantly, the copolymers exhibit enhanced emission upon aggregation, even at low compositions of FBPAN. A careful inspection reveals that the enhanced emission in the solid state is due to the formation of “J-aggregates” with ordered supramolecular self-assembly. Interestingly, the copolymer FBPAN 0.5 exhibits a unique ordered flower shaped self-assembly and significantly reduces the charge trapping due to balanced charge transport. As a result, bright and high efficiency white light emission was achieved with Commission Internationale de l'Eclairage (CIE) coordinates of (0.32, 0.31) and a maximum luminance, current and power efficiency of 13455 cd m⁻², 7.56 cd A⁻¹ and 5.32 lm W⁻¹, respectively. The copolymers possess very low turn-on voltage in the range of 1.5 to 3 V.