Substituent and solvent effect on the photochromic properties of a series of spiroindolinonaphthooxazines

The photochromic reactions of six recently synthesised spiroindolinonaphthooxazines bearing different substituents on the basic skeleton are studied under continuous UV irradiation in solvents of different polarity. A comparison of these results with the data obtained for the unsubstituted parent compound provides the examination of the specific effect of substituents on their photochromic properties and relaxation kinetics. The photomerocyanines of all substituted compounds show positive solvatochromism indicating that their excited state is more polar than the ground state. High colourabilities (up to 8.5×104) of photomerocyanines are calculated from the absorbance values obtained by extrapolation to t=0 of their room temperature linearly descending kinetic curves ln A/t. The relaxation time at 25 °C ranges from 2 to 130 s the actual value depending on the compound and solvent.