Light-induced E-Z Isomerization of Anthracene-Appended P-Methoxyphenyl Acrylonitrile Giving Fluorescent Crystals

Acrylonitrile-based n-conjugated molecules are an important class of molecular materials due to their unique solid-state optical properties. On the other hand, anthracenes are also known as classical structures demonstrated unique reactivities and optical properties. Herein, we report crystal structure and optical properties of 9-(4methoxyphenylacrylonitrile)anthracene, AA. Knoevenagel condensation synthesis yielded Z-AA. Interestingly, we found that Z-E-isomerization was observed under ambient light. Thus, Z-AA and E-AA crystals were obtained by crystallization under ambient light. The ratio of Z-/E-isomers is reached to 2:1 because of higher thermodynamic stability of Z-AA. The twisted molecular system of anthracene-acrylonitrile-phenyl system in Z-AA and E-AA gave intramolecular charge transfer interaction between electron donor-acceptor system. While both isomers showed no fluorescence in dichloromethane, both crystals exhibited fluorescence (Z-AA crystal: lambda = 541 nm, o = 0.04, E-AA crystal: lambda = 531 nm, o = 0.02), indicating that the molecule behaves as an AIE (aggregationinduced emission) luminogen, AIEgen.