A highly selective fluorescence "turn-on" sensor for Ca²⁺ based on diarylethene with a triazozoyl hydrazine unit

A new photochromic diarylethene derivative with a triazozoyl hydrazine unit has been designed and synthesized. Its photochromism and photoswitchable fluorescence behaviors were studied systematically by the stimuli of lights and chemical substances in acetonitrile solution. With the addition of Ca²⁺, the emission intensity enhanced 6.7 fold, accompanied by an obvious fluorescent color change from dark to light blue. The complexation between the derivative and Ca²⁺ is reversible with the 1 : 1 stoichiometry, which was verified by Job's plot and MS. The limit of detection (LOD) for Ca²⁺ was determined to be 2.49 × 10^-8 mol L^-1. Based on this unimolecular platform, a logic circuit was designed with fluorescence intensity at 482 nm as the output and the combined stimuli of UV/vis and Ca²⁺/EDTA as four inputs.