Photochromism of spironaphthooxazines having electron-donor substituents

Spectral and photochromic properties of spironaphthooxazines (SNOs) with piperidine and morpholine substituents have been studied at different temperatures in various solvents. It has been recognized that introduction of these substituents in naphthooxazine fragment leads to fluorescence of the initial form of SNO molecules at low temperatures, which disappears with temperature rise. The dependences of the photoinduced form of spectral characteristics on temperature and concentration make it possible to assume the aggregation of the molecules of photoinduced form in non-polar solvents. It is proposed that the coloured form of substituted SNOs has a bipolar structure with a positive charge on piperidine or morpholine nitrogen atom contrary to the quinonoic form of unsubstituted SNO.