Factors affecting the luminescence of tryptophan at 77 K

The effects of solvent polarity, heavy atoms and sulphur-containing compounds on the fluorescence and phosphorescence of indole and tryptophan have been investigated. The low-temperature luminescence of a group of dipeptides containing tryptophan is also reported. The phosphorescence to fluorescence quantum yield ratio and the phosphorescence lifetime are shown to be particularly sensitive to environmental factors. The relevance of these results to the interpretation of protein luminescence spectra is briefly discussed.