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Ultrafast Excited State Dynamics of 5,6-Dihydroxyindole, A Key Eumelanin Building Block: Nonradiative Decay Mechanism.

Gauden, Magdalena LU ; Pezzella, Alessandro; Panzella, Lucia; Napolitano, Alessandra; d'Ischia, Marco and Sundström, Villy LU (2009) In The Journal of Physical Chemistry Part B 113. p.12575-12580
Abstract
As part of a program designed to elucidate the excited state properties of key eumelanin building blocks, we report herein a study of 5,6-dihydroxyindole (DHI) in phosphate buffer at pH 3 and pH 7 using femtosecond transient absorption spectroscopy. The transient absorption changes following excitation at 266 nm were used to directly monitor relaxation of the excited states. It was found that the initially generated excited state of DHI, exhibiting two main absorption bands at approximately 450 and approximately 550 nm, decays with a time constant of 5-10 ps to the equilibrated singlet excited state characterized by a very similar spectrum. This latter state then decays to the ground state and the triplet state with a characteristic time... (More)
As part of a program designed to elucidate the excited state properties of key eumelanin building blocks, we report herein a study of 5,6-dihydroxyindole (DHI) in phosphate buffer at pH 3 and pH 7 using femtosecond transient absorption spectroscopy. The transient absorption changes following excitation at 266 nm were used to directly monitor relaxation of the excited states. It was found that the initially generated excited state of DHI, exhibiting two main absorption bands at approximately 450 and approximately 550 nm, decays with a time constant of 5-10 ps to the equilibrated singlet excited state characterized by a very similar spectrum. This latter state then decays to the ground state and the triplet state with a characteristic time of approximately 140-180 ps. Concomitant with the singlet excited state decay of DHI, spectral features characteristic of the DHI cation radical (band at approximately 575 nm) and the triplet state (band at 440-450 nm) are detected. These species do not decay further since geminate recombination of the solvated electron and the DHI radical cation, as well as deprotonation of the cation to form the neutral semiquinone radical, occur on a time scale longer than that covered by the present experiments. These results offer novel insights into the mechanisms of nonradiative decay of eumelanin building blocks of possible relevance to the putative photoprotective and phototoxic roles of these biopolymers. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
The Journal of Physical Chemistry Part B
volume
113
pages
12575 - 12580
publisher
The American Chemical Society
external identifiers
  • wos:000269655700017
  • pmid:19691267
  • scopus:70349126360
ISSN
1520-5207
DOI
10.1021/jp903190k
language
English
LU publication?
yes
id
f42f39c2-f9e4-408c-8210-f9b75b17cb43 (old id 1469605)
date added to LUP
2009-09-08 14:14:33
date last changed
2017-08-20 03:55:30
@article{f42f39c2-f9e4-408c-8210-f9b75b17cb43,
  abstract     = {As part of a program designed to elucidate the excited state properties of key eumelanin building blocks, we report herein a study of 5,6-dihydroxyindole (DHI) in phosphate buffer at pH 3 and pH 7 using femtosecond transient absorption spectroscopy. The transient absorption changes following excitation at 266 nm were used to directly monitor relaxation of the excited states. It was found that the initially generated excited state of DHI, exhibiting two main absorption bands at approximately 450 and approximately 550 nm, decays with a time constant of 5-10 ps to the equilibrated singlet excited state characterized by a very similar spectrum. This latter state then decays to the ground state and the triplet state with a characteristic time of approximately 140-180 ps. Concomitant with the singlet excited state decay of DHI, spectral features characteristic of the DHI cation radical (band at approximately 575 nm) and the triplet state (band at 440-450 nm) are detected. These species do not decay further since geminate recombination of the solvated electron and the DHI radical cation, as well as deprotonation of the cation to form the neutral semiquinone radical, occur on a time scale longer than that covered by the present experiments. These results offer novel insights into the mechanisms of nonradiative decay of eumelanin building blocks of possible relevance to the putative photoprotective and phototoxic roles of these biopolymers.},
  author       = {Gauden, Magdalena and Pezzella, Alessandro and Panzella, Lucia and Napolitano, Alessandra and d'Ischia, Marco and Sundström, Villy},
  issn         = {1520-5207},
  language     = {eng},
  pages        = {12575--12580},
  publisher    = {The American Chemical Society},
  series       = {The Journal of Physical Chemistry Part B},
  title        = {Ultrafast Excited State Dynamics of 5,6-Dihydroxyindole, A Key Eumelanin Building Block: Nonradiative Decay Mechanism.},
  url          = {http://dx.doi.org/10.1021/jp903190k},
  volume       = {113},
  year         = {2009},
}