Deep Red Emissive Asymmetric D-A-D′ D-A-D^$ AIEgens Exhibiting Substituent-Dependent Tunable Emission and Optical Waveguiding

A series of asymmetric D-A-D′ aggregation-induced emission compounds (AIEgens) were synthesized by linking triphenylamine (TPA, D) and benzofuran (BF, D′) donors with a malononitrile (A) acceptor. Their structures and the influence of various substituents on solid-state fluorescence and optical waveguide properties were investigated. TPA-MN-BF derivatives exhibited deep-red emission in the range of 625 to 670 nm, with fluorescence efficiency (quantum yield, ϕf) ranging from 3.0% to 20.5% in the solid state. Specifically, TPA-MN-BF exhibited a blue-shifted emission at 625 nm, while TPA-MN-NBF showed a red-shifted emission at 670 nm. The nonplanar conformation of TPA inhibited close π···π stacking in solid-state arrangements, leading to distinct molecular conformations and packing arrangements based on subtle changes in substitution. Studies on aggregation-induced emission (AIE) further reinforced that aggregation enhanced the emission across all four molecules. Computational analyses revealed that substitutions in the benzofuran moiety significantly influenced the HOMO–LUMO energy gap. Notably, deep-red-emissive microrods of TPA-MN-BF and TPA-MN-NBF showed good optical waveguiding capabilities. This study provides a structural framework for the development of deep-red-emissive materials and elucidates the structure-dependent optoelectronic properties.