THE FLUORESCENCE DECAY OF REDUCED NICOTINAMIDES IN AQUEOUS SOLUTION AFTER EXCITATION WITH A UV‐MODE LOCKED Ar ION LASER

The fluorescence decay kinetics of the reduced nicotinamides NMNH, NADH and NADPH in aqueous solution were investigated using an Ar ion laser, mode locked in the UV, as source of excitation and single photon counting electronics in the detection system allowing for a time resolution in the picosecond range. Analysis of the experimental fluorescence decay showed that the dinucleotides did not follow a single exponential decay law. Good fitting was accomplished with a sum of two exponentials. The mononucleotide fluorescence decay was a single exponential for at least 95% of its amplitude. The heterogeneity in lifetimes of the fluorescence of the dinucleotides was interpreted in terms of an exciplex mechanism.