A novel sensitive sensor for Cu2+ and multi-switch based on a diarylethene with a 2-(2′-hydroxyphenyl)benzothiazole unit

A new asymmetrical photochromic diarylethene with a 2-(2′-hydroxyphenyl)benzothiazole unit has been synthesized. It underwent reversible cyclization and cycloreversion reactions upon alternating irradiation with lower energy UV (297 nm, 25 μW/cm2) and visible light, while it could induce intramolecular proton transfer reaction upon irradiation with higher energy UV light (254 nm, 92 μW/cm2) with distinct color change. The absorption maximum of the closed-ring isomer was redshifted from 539 nm to 660 nm and the color changed from purple to cyan when the diarylethene was stimulated with base. Furthermore, addition of acid enhanced its fluorescence intensity by 5.5 fold and the emission peak was blueshifted from 596 nm to 570 nm with a concomitant color change from light orange to bright green, while base could efficiently quench its fluorescence intensity. Finally, the diarylethene was highly selective towards Cu2+ with significant absorption and fluorescence changes, which makes the 'naked-eye' detection of Cu2+ possible.