SENSITIZATION OF SPIROOXAZINES PHOTOCHROMISM BY TRIPLET-TRIPLET ENERGY-TRANSFER

The present publication describes sensitized photocoloration by triplet-triplet energy transfer of some photochromic spirooxazines. The dominant reaction leading to the colored dye product B in the direct photolysis of the spirooxazine (SPO) in toluene involves the singlet excited state but the results obtained in this work show that both triplet and singlet states are involved in the color-forming reaction. We employed sensitizers of decreasing triplet energy in an attempt to locate the triplet level in the SPO. From the triplet energies of the sensitizers of the SPO color formation it can be concluded that the energy of the spirooxazine triplet state is about 212 kJ.mol-1. The camphorquinone (CQ) sensitizes the formation of B. This compound is particularly suitable for investigation of sensitized photocoloration of spirooxazines since it absorbs in a region of the spectrum where SPO does not absorb (lambda-max = 471 nm). Then, it is possible to extend the photochromic properties of the SPO to the visible region (lambda less-than-or-equal-to 500 nm) for industrial applications. The absorption spectra of the colored form were determined for the direct and sensitized photolysis in toluene solutions.