Delayed fluorescence from solutions of anthracene and phenanthrene

Delayed fluorescence has been observed in solutions of anthracene or phenanthrene alone, and sensitized delayed fluorescence from anthracene has been observed in solutions of phenanthrene containing traces of anthracene. The intensities of both the delayed fluorescence and the sensitized delayed fluorescence were found to be proportional to the square of the rate of absorption of exciting light. The results can be explained in terms of a mechanism in which trip let-trip let quenching produces a molecular species carrying the energy from two trip let molecules. The proposed process could apply to other photochemical systems and may have a bearing on the mechanism of photosynthesis.