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Issue 18, 2019
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The full dynamics of energy relaxation in large organic molecules: from photo-excitation to solvent heating

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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.

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

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Publication details

The article was received on 24 Jan 2019, accepted on 29 Mar 2019 and first published on 02 Apr 2019


Article type: Edge Article
DOI: 10.1039/C9SC00410F
Chem. Sci., 2019,10, 4792-4804
  • Open access: Creative Commons BY license
    All publication charges for this article have been paid for by the Royal Society of Chemistry

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    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

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