The Chromogen, Structure, Inspirations, and Applications of a Photo‑, pH‑, thermal‑, Solvent-, and Mechanical-Response Epoxy Resin

We report the finding of a photochromic phenomenon from a structural epoxy resin, which also has pH-, thermal-, solvent-, and mechanical-response property. Through designing model compounds and doing confirmatory experiments, we find out that one kind of diarylmethane dye (Michler’s hydrol blue) is the chromogen of this epoxy resin. Additionally, we propose and successfully verify the mechanism of this novel color-change phenomenon that it is an oxidation-heterolysis mechanism. Further, the Fourier transform infrared (FTIR) spectroscopy and gel permeation chromatography (GPC) data show that the chromogen can be used as a photoinitiator to initiate free radical polymerization. Additionally, the discovery process is inspiring, which can lead to many applications.