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

Abstract

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 highbrightness solid-state blue and aggregation-induced emissions (AIE) by introducing the bridging structures of a sevenmembered 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 solidstate emission properties of 1 and 2 will improve the applicability of DSBs and functionalities of light-emitting devices/materials.

meta-Fluorophores: an uncharted ocean of opportunities

“…We will now discuss another interesting set of fluorophores in which there are two pairs of D and A moieties in the single benzenic fluorophore. [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] These molecules have been termed as single-benzenic-fluorophores and no naming with respect to the relative orientation of D and A moieties has been proposed. However, these two sets of D and A pairs can be either considered as double-ortho-substituted or double-metasubstituted (Fig.…”

“…However, during the last five years, red emission has been shown to be possible in small p systems having double-ortho or double-meta-substituted fluorophores (Chart 2). [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] These molecules have the -N-alkyl group as the D moiety and the -CHO, -COMe, -CO 2 R, etc., group as the A moiety (Chart 2). Some of these molecules have shown narrow red emission (FWHM B50 nm).…”

“…46 The next group of molecules in this series includes mostly the -OMe, -N-alkyl/phenyl group (both acyclic and cyclic) as the D moiety and -CN, -CQO, etc., functional groups as the A moiety (Chart 3). [36][37][38]40,43,48,51,52,[54][55][56][57][58][59][60][61][62][63][64] One of these molecules (Chart 3, molecule 13l) exhibits interesting polymorphismdependent emission, as well as reversible mechanochromism. 54 Some of these molecules (Chart 3, molecules 16a-i) emit from green to orange both in solution and solid state.…”

“…However, during the last five years, red emission has been shown to be possible in small π systems having double- ortho or double- meta -substituted fluorophores (Chart 2). 36–54 These molecules have the –N-alkyl group as the D moiety and the –CHO, –COMe, –CO 2 R, etc. , group as the A moiety (Chart 2).…”

“…, functional groups as the A moiety (Chart 3). 36–38,40,43,48,51,52,54–64 One of these molecules (Chart 3, molecule 13l ) exhibits interesting polymorphism-dependent emission, as well as reversible mechanochromism. 54 Some of these molecules (Chart 3, molecules 16a–i ) emit from green to orange both in solution and solid state.…”