Effect of E/Z isomerization on the aggregation-induced emission features and mechanochromic performance of dialdehyde-substituted hexaphenyl-1,3-butadiene
E/Z isomers of hexaphenyl-1,3-butadiene (HPB) derivative containing dialdehyde groups, 4,4’-((1E,3E)-1,2,3,4-tetraphenylbuta-1,3-diene-1,4-diyl)dibenzaldehyde (EE-HPB-CHO), 4,4’-((1Z,3E)-1,2,3,4-tetraphenylbuta-1,3-diene-1,4-diyl)-dibenzaldehyde (EZ-HPB-CHO) and 4,4’-((1Z,3Z)-1,2,3,4-tetra-phenylbuta-1,3-diene-1,4-diyl)dibenzaldehyde (ZZ-HPB-CHO), were firstly synthesized in one-pot and readily separated by silica gel column chromatography . The E/Z isomers containing conjugated diene exhibited remarkable differences in the fields of aggregation-induced emission (AIE) or aggregation-enhancement emission (AEE) behavior, thermostability, and mechanochromic performance. Among them, EE-HPB-CHO with dense molecular packing and strong intermolecular interaction was a better AIEgen while the EZ- and ZZ-isomers exhibited AEE behavior. Moreover, EE-HPB-CHO hardly displayed the mechanochromic performance. EZ-HPB-CHO irreversibly exhibited a blue-shift of 23 nm by grinding treatment, which could not be restored by fuming with organic solvents or heating. In contrast, owing to its twisting conformation and relative loose packing, ZZ-HPB-CHO reversibly displayed a red-shift of 20 nm during multiple repeating cycles of grinding and fuming treatments, showing superior mechanochromic performance.
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