Separation and identification of the products of the photodegradation of 7-amino-4-methylcoumarin and the mechanism of its photodegradation

The separation of the products of the photodegradation of 7-amino-4-methylcoumarin (C120), a laser dye, has been achieved by a reverse phase high performance liquid chromatography method. Two reverse phase columns (C6 and ODS) were used to optimize the separation conditions and various mixtures of methanol and water served as the mobile phase. The chromatograms representing the separation of the photolyte from the photoproducts under various experimental conditions are also shown. The fluorescent photodegradation product in an oxygenated methanolic solution of the dye has been separated by column chromatography assisted by thin layer chromatography and high performance liquid chromatography. The structure of the compound has been ascertained by mass spectrometric and IR spectroscopic analysis and found to be 7-amino-3-hydroxy-4-methyl-coumarin. A mechanism is suggested for the formation of this product by the interaction of singlet oxygen and the dye. On the basis of the behaviour of the dye in degassed solutions, a general scheme is postulated to represent the photobleaching of C120.