Ultrafast excited-state dynamics of tryptophan in water observed by transient absorption spectroscopy

The excited-state dynamics of tryptophan in water is resolved by femtosecond transient absorption (TA) experiments covering the near-UV and Vis range of wavelengths. After a 1 ps solvent relaxation time, the excited-state decays non-radiatively, while an absorption band rises simultaneously at 425 nm on the nanosecond time scale. The 425 nm induced absorption appears to be the signature of the primary photoproduct resulting from the quenching of Trp excited-state in water. While time-resolved Trp fluorescence spectroscopy has characterized Trp’s excited-state lifetime in detail, the present TA experiments give first evidence for the spectroscopic signatures of the quenching-induced photoproduct.