A Tri‐state Fluorescent Switch with “Gated” Solid‐state Photochromism Induced by an External Force

Abstract

In this article, we report a newly designed molecule composed of a dihydroazulene (DHA) group and a phenothiazine (PTZ) moiety, which achieves AIEE, mechanochromism and “gated” solid-state photochromism by external force. Grinding loosens intermolecular interactions in crystal and causes the red shift of fluorescence from 570 nm to 600 nm. Meanwhile, the ring-opening reaction of DHA unit is activated by grinding and the remarkable photochromism could be observed from grinded powder. The reddish emission of the grinded powder peaked at 600 nm weakened gradually and finally became dark, and a new absorption band at 470 nm emerged in the absorption spectra. TD-DFT result reveals that the intramolecular ICT process is replaced by LE emission on the DHA group, which leads to the quenching of fluorescence. Its impressive photochromic property inspires a simple but effective way to develop an encryption system which can let the correct information be displayed under external stimulation.