The fluorescence properties of various N-carbonyl-substituted indoles (compounds 1-7) are examined. The N-benzoyl-indole derivatives 1 and 3-5 are shown to fluoresce weakly and the effect of solvent polarity upon the energy of the emitting state and upon the quantum yield of fluorescence is described. It is concluded that the initially formed singlet excited state is non-emissive and can relax to an intramolecular charge transfer state which is weakly ...
