Excitation of fluorescence decay using a 265nm pulsed light-emitting diode: Evidence for aqueous phenylalanine rotamers

The authors describe the characteristics and application of a 265nm AlGaN light-emitting diode (LED) operated at 1MHz repetition rate, 1.2ns pulse duration, 1.32μW average power, 2.3mW peak power, and ∼12nm bandwidth. The LED enables the fluorescence decay of weakly emitting phenylalanine to be measured routinely, even in dilute solution. For pH of 6–9.2, the authors find evidence for a biexponential rather than monoexponential decay, providing direct evidence for the presence of phenylalanine rotamers with a photophysics closer to the other two fluorescent amino acids tryrosine and tryptophan than has previously been reported.