Spectral Properties of a bis-Azospiropyran Complexed with Europium

Abstract

The complexation of recently synthesized symmetrical bifunctional bis-azospiropyran photochromic dye with europium nitrate and its effect on UV–vis absorption and fluorescent emission was studied. Upon addition of Eu 3+ to colorless spiropyran, a yellow merocyanine europium complex was obtained with an absorption band at 410 nm. Negatively charged phenolic oxygenin zwitterionic ring-open form provides an effective metal binding site for Eu 3+ . Meanwhile, the inherent fluorescence emission of the photochromic dye at 380 nm is switched off due to the Eu 3+ - induced drive of spiro-mero equilibrium to form mero form. The stoichiometry of dye–europium complexation was evaluated by fluorescence emission and UV–vis absorption spectroscopy and a 8:1 ratio was obtained in both cases. The binding constant (K) value of the dye–europium complex was 3 × 106 M −1 . In conclusion, the current molecular switch is a useful sensitive dual measuring tool for solutions containing europium or europium-like elements by evaluation of visible absorption or fluorescent emission spectroscopy.