Photo-dynamic and fluorescent zinc complex based on spiropyran ligand

Spiropyrans are among a class of organic molecules widely studied as molecular photoswitches. A photochromic and solvatochromic spiropyran-containing Zinc (II) complex (ZnMC) was successfully synthesized and characterized, and its chromic properties were studied. A solid complex was isolated through a precipitation process induced by UV radiation. The binding specificities were studied by FTIR-ATR spectroscopy and DFT calculations, demonstrating that phenolate and carboxylic acid are the binding sites of merocyanine. Mass spectrometry and computational methods revealed the possibility of two complexes with different geometries, tetrahedral and octahedral; the complex with tetrahedral characteristics proved to be more stable and abundant. ZnMC solvatochromic properties were analyzed, presenting a wide variation in its absorption band in the visible region. We addressed the issue of ZnMC photodegradation in different solvents, and the observed absorbance did not vary after the first cycles for acetonitrile, while, in tetrahydrofuran, the absorbance decayed throughout the 48 cycles of switching between UV and visible light irradiation. [Display omitted] •The Zinc complex displayed fluorescent properties in solution and solid state.•Stability of ZnMC was verified in both solid state and acetonitrile solution.•Computational data shows that tetrahedral is more stable than octahedral geometry.