Modulation of photochromic properties of spirooxazine bearing sulfobutyl substituent by metal ions

Abstract A novel spirooxazine bearing sulfobutyl substituent on the indoline part of the molecule has been synthesized and its photochromic properties and complex formation with metal ions have been studied. Under UV light irradiation of colorless acetonitrile solution of spirooxazine the open merocyanine form having an absorption band in visible region of the spectrum with λ max  = 625 nm is generated. Thermal back reaction of merocyanine form to spirooxazine with the rate constant 1.10 s −1 at 298 K has been observed. Interaction of spirooxazine with Mg 2+ , Ca 2+ , Cd 2+ , Zn 2+ or Pb 2+ ions in the dark leads to the formation of complexes of merocyanine form demonstrating a visible absorption band shifted from 20 to 8 nm relative to the uncomplexed merocyanine form. The activation energy of metal-induced coloration process in the dark is in the range of 84–88 kJ mol −1 and does not depend on the nature of the metal ions. This suggests that the process of thermal ring opening of the spiro form is the rate limiting step of complex formation. The degree of conversion of spirooxazine to complexed merocyanine form strongly depends on metal ions nature and irradiation wavelength.