Structures and photochromic properties of substituted spiroindolinonaphthoxazines

Six indolinospironaphthoxazines were studied by X-ray diffraction analysis. demonstrated that the electronic nature of the substituents in the naphthoxazine and indoline fragments has no substantial effect on the C-spiro-O and C-spiro-N bond lengths. Photocolorability of the compounds under study depends only slightly on the above-mentioned bond lengths and correlates mainly with the energy of steric strain of the oxazine ring. The stability of the open forms of spiroindolinonaphthoxazines that formed upon photoirradiation is determined to a large extent by the electronic and steric nature of the substituents. The exception is the compound that contains the NO2 group in the indoline fragment. In the last-mentioned case, the cleavage of the ring occurs through a substantially different pathway.