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

The formation of a Cu(lI) chelate from a photochromic spiropyran in ac etone in the dark and the decolouration of its coloured form and the C u(II) chelate in tetrahydrofuran (THF) after UV irradiation were studi ed by UV-visible absorption spectroscopy. The results indicate that th e rate-determining step of chelate formation in acetone is the formati on of the coloured form. The concentration of metal ions has no effect . In THF after UV irradiation, the coloured form and its Cu(II) chelat e are in equilibrium during thermal decolouration, with an equilibrium constant K of 8.9x10(4) l mol(-1). The decolouration rate constants o f 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) spect ra of the chelate in acetone at 77 K, the structure of the chelate is square or square pyramidal.