AN INVESTIGATION OF THE ELECTRONIC SPECTRAL PROPERTIES OF THE MEROCYANINES DERIVED FROM PHOTOCHROMIC SPIROINDOLINONAPHTH[2,1-B][1,4]OXAZINES

Spiroindolinonaphth[2,1-b][1,4]oxazines are of considerable current interest as photochromic dyes with good colouring power and fatigue resistance. The results of PPP molecular orbital calculations, after refinement by parameter optimisation, were found to provide a reasonable account of the experimental lambda(max) values for the ring-opened merocyanine forms of a range of spirooxazines, although precise interpretation is complicated by the possible presence of a number of geometrical isomers. The electronic structure of the photomerocyanine derived from the parent compound and the nature of the electronic excitation process are discussed in terms of the calculated pi-electron charge densities.