Sm. Aldoshin et al., STRUCTURES AND PHOTOCHROMIC PROPERTIES OF SUBSTITUTED SPIROINDOLINONAPHTHOXAZINES, Russian chemical bulletin, 47(6), 1998, pp. 1089-1097
Six indolinospironaphthoxazines were studied by X-ray diffraction anal
ysis. demonstrated that the electronic nature of the substituents in t
he naphthoxazine and indoline fragments has no substantial effect on t
he C-spiro-O and C-spiro-N bond lengths. Photocolorability of the comp
ounds under study depends only slightly on the above-mentioned bond le
ngths and correlates mainly with the energy of steric strain of the ox
azine ring. The stability of the open forms of spiroindolinonaphthoxaz
ines that formed upon photoirradiation is determined to a large extent
by the electronic and steric nature of the substituents. The exceptio
n 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.