COMPARATIVE PHOTODEGRADATION STUDY BETWEEN SPIRO[INDOLINE OXAZINE] AND SPIRO[INDOLINE PYRAN] DERIVATIVES IN SOLUTION

The photochromic compounds 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3'-[3H]naphth[2,1-b][1,4]oxazine], 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,2'-[3H]naphth[1,2-b]pyran] and 1,3-dihydro-8'-methoxy-6'-nitro-1,3,3-tri-methylspiro[2H-indole-2,2'[3H]benzopyran] were degraded under UV light irradiation in toluene solution. The resulting main photoproducts separated by gas chromatography and high performance liquid chromatography were identified by different couplings with UV-visible diode array detection, mass spectrometry and Fourier transform IR spectroscopy and were compared with synthetic standards. The different nature of the photoproducts involving the chromene part of the molecules could suggest different mechanisms of degradation between the spiropyran and spiro-oxazine series and could explain the better fatigue resistance of the latter.