Insight from the old: mechanochromism and mechanoluminescence of two amine-containing tetraphenylethylene isomers

Abstract

Herein, we investigated the mechanochromism (MC) and mechanoluminescence (ML) properties of an “old” tetraphenylethylene derivative p-NH₂ and its isomer m-NH₂ and provided important insights into the mechanism of these two properties. Both compounds possess aggregation induced emission (AIE) properties inherited from their TPE skeleton. However, their fluorescence differs in the aggregation state due to their different conjugation degrees. Molecule p-NH₂ is both MC- and ML-active, while m-NH₂ is only ML-active. The single-crystal structures and related experimental results suggest that the ML/MC properties are closely related to intermolecular interactions and molecular conformation. There are abundant intermolecular interactions in their single crystals, endowing both isomers with ML properties, while too strong intermolecular interactions and planar conformation on the other hand inhibit a reversible transition between different molecular packing modes and disable the MC activity of m-NH₂.