Facile prepared tropinone-based enone dyes with visible-light induced photothermal liquefaction and cold crystallization properties for reusable and switchable adhesive

The solid-liquid phase transition of adhesives triggered by two different wavelength light stimuli enables the switchable and reusable character. The adhesive which could be liquified by photothermal effect by single-wavelength light stimulus and solidified by natural cooling is much easier to operate but little developed. In this work, a class of tropinone-based enone dyes (TPs), prepared by one-pot Claisen-Schmidt condensation, were explored as a novel kind of single-wavelength light-switchable adhesives. TPs could absorption visible light and are non-fluorescent. By changing the length of alkoxy groups, the melting point and crystallization behavior were regulated. Especially, TP6 and TP8 could form overcooled liquid during the cooling process, thus enabling a proper adhesion operation window. Under 405 nm LED irradiation, the rapid solid-liquid transformation was achieved for some of TPs due to the high thermal conversion ability. TPs presented good adhesion strength toward glass plates. Among them, TP8 could work as a reusable and light-switchable adhesive.