Multicolor mechanochromism of a phenothiazine derivative through molecular interaction and conformational modulations

Mechanochromic luminescent (MCL) materials have attracted great attention in the fields of sensing, memory chips, and anti-counterfeiting. However, most MCL materials only display a two-color change and it is challenging to achieve multicolor mechanochromism with a single molecule. Herein, we reported a twisted D-π-A type molecule (PZ-BZ) composed of a phenothiazine (donor), 1,4-phenylene unit (π), and benzothiazole (acceptor). PZ-BZ exhibits intramolecular charge transfer and aggregation-induced emission enhancement properties. Additionally, the multicolor mechanochromic behaviour of PZ-BZ single crystal is observed. The original crystal of PZ-BZ emits cyan fluorescence (470 nm). When crushed, it exhibits blue-shifted emission (455 nm) due to the destruction of intermolecular interactions. Further grinding induces conformation planarization, resulting in large red-shifted fluorescence (503 nm). This study provides a deep insight into the molecular mechanism of multicolor mechanochromism through molecular interaction and conformation modulations.