
Issue 18, 2019

The full dynamics of energy relaxation in large organic molecules: from photo-excitation to solvent heating

Abstract

In some molecular systems, such as nucleobases, polyenes or the active ingredients of sunscreens, substantial amounts of photo-excitation energy are dissipated on a sub-picosecond time scale, raising questions such as: where does this energy go or among which degrees of freedom it is being distributed at such early times? Here we use transient absorption spectroscopy to track excitation energy dispersing from the optically accessible vibronic subsystem into the remaining vibrational subsystem of the solute and solvent. Monitoring the flow of energy during vibrational redistribution enables quantification of local molecular heating. Subsequent heat dissipation away from the solute molecule is characterized by classical thermodynamics and molecular dynamics simulations. Hence, we present a holistic approach that tracks the internal temperature and vibronic distribution from the act of photo-excitation to the restoration of the global equilibrium. Within this framework internal vibrational redistribution and vibrational cooling are emergent phenomena. We demonstrate the validity of the framework by examining a highly controversial example, carotenoids. We show that correctly accounting for the local temperature unambiguously explains their energetically and temporally congested spectral dynamics without the ad hoc postulation of additional ‘dark’ states. An immediate further application of this approach would be to monitor the excitation and thermal dynamics of pigment–protein systems.

Supplementary files

Article information

Article type
Edge Article
Submitted
24 Jan 2019
Accepted
29 Mar 2019
First published
02 Apr 2019
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2019,10, 4792-4804

The full dynamics of energy relaxation in large organic molecules: from photo-excitation to solvent heating

V. Balevičius Jr, T. Wei, D. Di Tommaso, D. Abramavicius, J. Hauer, T. Polívka and C. D. P. Duffy, Chem. Sci., 2019, 10, 4792 DOI: 10.1039/C9SC00410F

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

Read more about how to correctly acknowledge RSC content.

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