Protonation-Gated Dual Photochromism of a Chromene-Styryl Dye Hybrid.

A novel hybrid bisphotochromic system involving a chromene residue and a styryl dye fragment is described. Initially, the compound shows almost no photochromism due to intramolecular energy and electron transfer between the chromophores. Protonation of the hybrid system blocks the transfer processes and unlocks a dual photochromic activity that includes ring opening of the chromene fragment and E-Z-isomerization of the styryl dye residue. Deprotonation of any photoinduced form resets the system to the initial photoinactive form.