On the fluorescence of æsculin

Abstract In a paper published in 1918, describing observations on thin films of fluorescent solutions, Perrin presented an extremely interesting explanation of fluorescence. According to him, organic substances when fluorescing are in the process of being destroyed. This destruction he considers to be the cause of the fluorescence. The molecule of the fluorescent substance is supposed not to possess a permanent ability to emit light under stimulation, but to have the power to give out light at the moment of its transformation. On being transformed it is rendered incapable of further fluorescence. Since the molecules of all the fluorescent substances studied by him contained one or more benzene rings, he made the suggestion that fluorescence in the cases investigated was probably due to the rupture of these rings. R. W. Wood has also published recently an account of an investigation on the destruction of the fluorescent powers of certain solutions by exposure to sunlight. He found that the fluorescent solutions studied by him could be transformed into coloured non-fluorescent liquids that gave absorption spectra decidedly different from the original solutions. Prolonged exposure to sunlight, moreover, rendered his solutions colourless. In particular, he found that solutions of rhodamine could be bleached without the emission of fluorescent light by maintaining them at a temperature of 100°C., a result which would indicate that the transformation of the molecules of fluorescent solutions may not be as intimately connected with the phenomenon of fluorescence as Perrin has supposed.