Highly Twisted Isomers of Triphenylacrylonitrile Derivatives with High Emission Efficiency and Mechanochromic Behavior

Abstract

Two novel triphenylacrylonitrile derivatives (TPAN-C2 and TPAN-C3) with highly twisted conformations have been successfully prepared by Suzuki coupling reaction. Both of them show mechanochromic (MC) fluorescent behaviour and exhibit remarkable fluorescence redshifts from sky-blue to light green upon fully grinding them. Interestingly, the ground powders recover their original states upon heating at 100 °C for 1 min or fuming with solvents vapour. Such intriguing MC properties of TPAN-C2 and TPAN-C3 are attributed to their phase transitions between crystalline and amorphous states, which are confirmed by powder X-ray diffraction (XRD) data. Moreover, the behaviour of both TPAN-C2 and TPAN-C3 indicates that the aggregation-induced emission (AIE) gives rise to rather high fluorescence quantum efficiencies (Φf) of 0.78 and 0.97, respectively. The influences of stacking mode and molecular conformation on MC properties and the high Φf of TPAN-C2 and TPAN-C3 are discussed.