Tracking Conical Intersection Dynamics of Tryptophan with Sub-20-fs UV Pulses

Tryptophan is one of the three natural aromatic amino acids and can serve as local probe of photoreactions of proteins irradiated with UV light. However, the photophysics of tryptophan are complex, especially when the interaction with solvent is considered. The excited state evolution of tryptophan in condensed phase has been reported previously on picosecond and nanosecond time scales, using transient absorption (TA) spectroscopy [1]. Here we track the primary photoinduced processes in tryptophan using TA spectroscopy with unprecedented sub-30-fs temporal resolution [2] and compare them with state-of-the-art quantum mechanics/molecular mechanics computations [3]