Push-Pull Bridged Distyrylbenzene with Highly Bright Solid-State Red-Orange Aggregation-Induced Emission

Multiple emission colors in solid-state organic fluorophores with the same main skeleton are essential for improving the performance of light-emitting devices/materials. Specifically, emission in the red/near-infrared region is of great importance in the biological field. Previously, we developed di-bridged-distyrylbenzene DBDB[7] with high-brightness solid-state blue and aggregation-induced emissions (AIE) by introducing the bridging structures of a seven-membered ring into the vinylene groups of distyrylbenzene (DSB). Herein, we synthesize MNDBDMeODB[7] (1), which features substituted methoxy and malononitrile groups as donor and acceptor groups, respectively, in DBDB[7]. In solvents more polar than THF, MNDSDMeOB (3), which has the same main skeleton as 1 but without bridges, shows no emission in the solid state, whereas 1 exhibits highly bright red-orange emission in the solid state owing to the suppression of intermolecular electronic interactions by the bridges and the AIE property. We also synthesize MNDSD(EHO)B (2) in which the methoxy groups of 3 are replaced by ethylhexyloxy groups, thus disrupting the crystallinity of the molecule. 2 exhibits positive fluorescence solvatochromism and has a high fluorescence quantum yield in the solid state as a red-emitting DSB derivative. The solid-state emission properties of 1 and 2 will improve the applicability of DSBs and functionalities of light-emitting devices/materials.