Photoprotective Properties of Eumelanin: Computational Insights into the Photophysics of a Catechol:Quinone Heterodimer Model System

Victoria C Frederick, Thomas A Ashy, Barbara Marchetti, Michael N R Ashfold, Tolga N V Karsili*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

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Abstract

Melanins are skin-centered molecular structures that block harmful UV radiation from the sun and help protect chromosomal DNA from UV damage. Understanding the photodynamics of the chromophores that make up eumelanin is therefore paramount. This manuscript presents a multi-reference computational study of the mechanisms responsible for the experimentally observed photostability of a melanin-relevant model heterodimer comprising a catechol (C)–benzoquinone (Q) pair. The present results validate a recently proposed photoinduced intermolecular transfer of an H atom from an OH moiety of C to a carbonyl-oxygen atom of the Q. Photoexcitation of the ground state C:Q heterodimer (which has a π-stacked “sandwich” structure) results in population of a locally excited ππ* state (on Q), which develops increasing charge-transfer (biradical) character as it evolves to a “hinged” minimum energy geometry and drives proton transfer (i.e., net H atom transfer) from C to Q. The study provides further insights into excited state decay mechanisms that could contribute to the photostability afforded by the bulk polymeric structure of eumelanin.
Original languageEnglish
Pages (from-to)26-37
Number of pages12
JournalPhotochem
Volume1
Issue number1
DOIs
Publication statusPublished - 10 Mar 2021

Keywords

  • photophysics
  • photoprotection
  • photostability
  • eumelanin
  • catechol
  • benzoquinone
  • ultraviolet
  • conical intersection

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