INVESTIGATION OF THE CHELATION OF A PHOTOCHROMIC SPIROPYRAN WITH CU(II)

The formation of a Cu(lI) chelate from a photochromic spiropyran in acetone in the dark and the decolouration of its coloured form and the Cu(II) chelate in tetrahydrofuran (THF) after UV irradiation were studied by UV-visible absorption spectroscopy. The results indicate that the rate-determining step of chelate formation in acetone is the formation of the coloured form. The concentration of metal ions has no effect. In THF after UV irradiation, the coloured form and its Cu(II) chelate are in equilibrium during thermal decolouration, with an equilibrium constant K of 8.9x10(4) l mol(-1). The decolouration rate constants of the coloured form and its Cu(II) chelate are 1.57x10(-2) s(-1) and 5.7x10(-4) s(-1) respectively. From electron spin resonance (ESR) spectra of the chelate in acetone at 77 K, the structure of the chelate is square or square pyramidal.