Volume 212, 2018

The influence of aqueous solvent on the electronic structure and non-adiabatic dynamics of indole explored by liquid-jet photoelectron spectroscopy

Abstract

Understanding how the electronic structure of an aqueous solute is intricately bound up with the arrangement of a host liquid provides insight into how non-adiabatic photochemistry takes place in the condensed phase. For example, the presence of water provides additional solute–solvent interactions compared to non-polar solvents: changing the stability of ionized products and modifying the energies of low-lying excited valence states, as well as moving the point of intersection between potential surfaces. Thus, the locations and topography of conical intersections between these surfaces also change. The overall impact of the aqueous environment can be to modify the intricate photochemical and non-radiative pathways taking place after photoexcitation. Time-resolved photoelectron spectroscopy (TRPES) in a liquid micro-jet is implemented here to investigate the influence of water on the electronic structure and dynamics of indole, the chromophore of the amino acid tryptophan. TRPES is used to establish ultrafast relaxation pathways that vary as a function of excitation wavelength. In our experiment, aqueous indole was excited with femtosecond pulses centered at 292 nm and 266 nm. The vertical excitation energy of aqueous indole is extracted and found to be lowered by 0.5 eV in water relative to the gas phase. In the TRPES study, the spectral signature of 1La and evidence of solvated electron formation on an ultrafast timescale are observed. Our data also points to a possible contribution of the dissociative πσ* state, which can be accessed by a conical intersection (CI) with the 1La state.

Graphical abstract: The influence of aqueous solvent on the electronic structure and non-adiabatic dynamics of indole explored by liquid-jet photoelectron spectroscopy

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
15 jun 2018
Accepted
18 jun 2018
First published
20 jun 2018

Faraday Discuss., 2018,212, 359-381

Author version available

The influence of aqueous solvent on the electronic structure and non-adiabatic dynamics of indole explored by liquid-jet photoelectron spectroscopy

G. Kumar, A. Roy, R. S. McMullen, S. Kutagulla and S. E. Bradforth, Faraday Discuss., 2018, 212, 359 DOI: 10.1039/C8FD00123E

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