Configurable photochromism of an unsymmetrical dithienylethene derivative by Cu²⁺ ions or water

We describe a gated photochromic behavior of an unsymmetrical dithienylethene derivative, which is intrinsically inert to photoisomerization in organic solvents and which is activated by addition of Cu²⁺ ions or water. The mechanism behind the gated photochromic property is interpreted by theoretical simulations, suggesting that the energy levels of frontier molecular orbitals are altered by the interaction of the Schiff base moiety with Cu²⁺ ions or water molecules. Potential applications of such gated photochromic materials have been exemplified not only by the reversible interchange between the photoactive and photoinactive states triggered by Cu²⁺ ions and EDTA, but also by the construction of a keypad with sequence-dependent input signals at the molecular level.