Femtosecond Extreme Ultraviolet Photoelectron Spectroscopy of Organic Molecules in Aqueous Solution.

Time-resolved valence photoelectron spectroscopy is an established tool for studies of ultrafast molecular dynamics in the gas phase. Here we demonstrate time-resolved XUV photoelectron spectroscopy from dilute aqueous solutions of organic molecules, paving the way to application of this method to photodynamics studies of organic molecules in natural environments, which so far have only been accessible to all-optical transient spectroscopies. We record static and time-resolved photoelectron spectra of a sample molecule, quinoline yellow WS, analyze its electronic structure, and follow the relaxation dynamics upon excitation with 400 nm pulses. The dynamics exhibit three time scales, of which a 250 ± 70 fs time scale is attributed to solvent rearrangement. The two longer time scales of 1.3 ± 0.4 and 90 ± 20 ps can be correlated to the recently proposed ultrafast excited-state intramolecular proton transfer in a closely related molecule, quinophthalone.