The fluorescence of a large set of tryptophan analogues, including several that are conformationally constrained, was studied. The constrained analogues include tetrahydrocarboline-3-carboxylic acid and 3-amino-3-carboxytetrahydrocarbazole. Steady state and time-resolved fluorescence measurements were made as a function of pH. The fluorescence quantum yields of the constrained analogues are higher than those for the ...