Unravelling the Role of an Aqueous Environment on the Electronic Structure and Ionization of Phenol Using Photoelectron Spectroscopy.

Jamie W Riley,Graham A Worth,Joanne L Woodhouse,Helen H Fielding,Bingxing Wang,Mariana Assmann

doi:10.1021/acs.jpclett.7b03310

Jamie W Riley, Graham A Worth + Show 4 more

Open Access

https://doi.org/10.1021/acs.jpclett.7b03310

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Abstract

Water is the predominant medium for chemistry and biology, yet its role in determining how molecules respond to ultraviolet light is not well understood at the molecular level. Here, we combine gas-phase and liquid-microjet photoelectron spectroscopy to investigate how an aqueous environment influences the electronic structure and relaxation dynamics of phenol, a ubiquitous motif in many biologically relevant chromophores. The vertical ionization energies of electronically excited states are important quantities that govern the rates of charge-transfer reactions, and, in phenol, the vertical ionization energy of the first electronically excited state is found to be lowered by around 0.8 eV in aqueous solution. The initial relaxation dynamics following photoexcitation with ultraviolet light appear to be remarkably similar in the gas-phase and aqueous solution; however, in aqueous solution, we find evidence to suggest that solvated electrons are formed on an ultrafast time scale following photoexcitation just above the conical intersection between the first two excited electronic states.

Highlights

M uch of our detailed understanding of the intrinsic electronic relaxation dynamics of photoexcited molecules has come from gas-phase experiments and calculations involving isolated molecules, free from interactions with solvent or protein environments
Electronically excited states can be very sensitive to their microenvironment, and the extent to which dynamical insights obtained from gas-phase studies can be used to inform our understanding of the dynamics in chemically and biologically relevant environments is a subject of considerable discussion.[1]
Phenol is ubiquitous as a molecular motif in large biologically relevant chromophores; important examples include the amino acid tyrosine, which plays a prominent role in the catalysis of a wide range of enzymes that includes photosystem II, and the chromophore of green fluorescent protein, the most widely used fluorescent probe for in vivo monitoring of biological and biochemical processes

Summary

Introduction

M uch of our detailed understanding of the intrinsic electronic relaxation dynamics of photoexcited molecules has come from gas-phase experiments and calculations involving isolated molecules, free from interactions with solvent or protein environments.

Results

Conclusion