Acid-, mechano- and photochromic molecular switches based on a spiropyran derivative for rewritable papers

Abstract

In this work, we report a novel acid-, photo- and mechanochromic material based on a spiropyran (SP) derivative. Multiple stimuli-responsive discolouration was noted with the photochromism, halochromism, and mechanochromism of the molecule C based on two moieties, Rh-NH₂ and SP-COOH, which present good acidichromism, mechanochromism and photochromism. Particularly, both in solution and in the solid state, the molecule exhibits efficient photochromic properties. Remarkably, this new molecule also exhibited mechanochromic properties under mechanical force. Compared with the spiropyran chromophore, this new molecule showed a better reversible photochromic property and the film containing molecule C and polymethyl methacrylate (PMMA) after ultraviolet light irradiation could maintain its colour for at least 2–3 days without fading. However, it could easily turn back to the original colour with heating at 70 °C for 5 min and after use for 100 cycles, with no obvious fatigue. These attributes of molecule C make it a promising candidate in UV printing and rewritable papers.