THERMALLY REVERSIBLE PHOTOCONVERSION OF SPIROINDOLINE-NAPHTHO-OXAZINES TO PHOTOMEROCYANINES - A PHOTOCHEMICAL AND KINETIC-STUDY

In this paper, a treatment of the spectroscopic data from thermoreversible photochromic systems is described which allows the molar absorption coefficient of the metastable photomerocyanine, the quantum yield of the colour-forming reaction and the kinetic parameters of the thermal bleaching to be determined. The results obtained for five spiroindoline-oxazines indicate that ''colourability'' on steady state irradiation depends on the photomerocyanine molar absorption coefficient, quantum yield and bleaching rate coefficient. For the molecules investigated, the ''colourability'' markedly depends on temperature, due to the temperature dependence of the bleaching reaction. The results obtained are compared with literature ''colourability scales'', determined empirically by comparison of different systems excited by pulsed light.