Photoinduced electron transfer from higher excited singlet states of tryprophan: 1. Effects of the excitation wavelength, pH, and temperature on quenching of Tryptophan fluorescence by europium(III) ions

Effects of the excitation energy, temperature, and pH on the quantum yield and the Stern-Volmer quenching constant for tryptophan fluorescence quenching by europium(III) chloride were studied. Competition between intracomplex reversible photoinduced electron transfer from tryptophan to Eu(III) ions and the processes of internal conversion and vibrational relaxation of higher excited singlet states Sn(n > 1) of tryptophan was revealed.