Supplementary material from "A Cu²⁺ triggered reversible photochromic system: the structure photochromic response relationship study and potential applications"

Fifteen rhodamine B hydrazide hydrazone (RhBHH) derivatives (compounds a-o) with various substituent groups at different position and their photochromic property triggered by Cu²⁺ were studied to illustrate the structure photochromic response relationship (SPRR). Three of them (compounds f-h) with a para-position hydroxyl group and two meta-position halogen substituents display Cu²⁺ triggered photochromic which is significantly different from the previous reports. It was found that halogen atoms, which were generally considered to have no remarkable regulation effect, exhibited great influences on the photochromic behaviour of RhBHH derivatives. Detail photochromic properties of the developed photochromic system were revealed by using compound g as the model substrate and only Cu²⁺ displayed high selective trigger effect. Good reversible photochromic phenomenon was observed after stimulated with visible light irradiation and dark (or heat) bleaching consecutively. Furthermore, this photochromic system could be used in the preparation of photochromic glass, special security ink, molecular logic gate and two-dimensional code for security information storage.