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Photophysical Deactivation Mechanisms of the Pyrimidine Analogue 1-Cyclohexyluracil

The photophysical relaxation mechanisms of 1-cyclohexyluracil, in vacuum and water, were investigated by employing the Multi-State CASPT2 (MS-CASPT2, Multi-State Complete Active-Space Second-Order Perturbation Theory) quantum chemical method and Dunning’s cc-pVDZ basis sets. In both environments, ou...

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Autores principales: Valverde, Danillo, de Araújo, Adalberto V. S., Borin, Antonio Carlos
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8434193/
https://www.ncbi.nlm.nih.gov/pubmed/34500625
http://dx.doi.org/10.3390/molecules26175191
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author Valverde, Danillo
de Araújo, Adalberto V. S.
Borin, Antonio Carlos
author_facet Valverde, Danillo
de Araújo, Adalberto V. S.
Borin, Antonio Carlos
author_sort Valverde, Danillo
collection PubMed
description The photophysical relaxation mechanisms of 1-cyclohexyluracil, in vacuum and water, were investigated by employing the Multi-State CASPT2 (MS-CASPT2, Multi-State Complete Active-Space Second-Order Perturbation Theory) quantum chemical method and Dunning’s cc-pVDZ basis sets. In both environments, our results suggest that the primary photophysical event is the population of the [Formula: see text] [Formula: see text] bright state. Afterwards, two likely deactivation pathways can take place, which is sustained by linear interpolation in internal coordinates defined via Z-Matrix scans connecting the most important characteristic points. The first one (Route 1) is the same relaxation mechanism observed for uracil, its canonical analogue, i.e., internal conversion to the ground state through an ethylenic-like conical intersection. The other route (Route 2) is the direct population transfer from the [Formula: see text] [Formula: see text] bright state to the [Formula: see text] [Formula: see text] triplet state via an intersystem crossing process involving the ([Formula: see text] [Formula: see text] / [Formula: see text] [Formula: see text]) [Formula: see text] singlet-triplet crossing point. As the spin-orbit coupling is not too large in either environment, we propose that most of the electronic population initially on the [Formula: see text] [Formula: see text] state returns to the ground following the same ultrafast deactivation mechanism observed in uracil (Route 1), while a smaller percentage goes to the triplet manifold. The presence of a minimum on the [Formula: see text] [Formula: see text] potential energy hypersurface in water can help to understand why experimentally it is noticed suppression of the triplet states population in polar protic solvent.
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spelling pubmed-84341932021-09-12 Photophysical Deactivation Mechanisms of the Pyrimidine Analogue 1-Cyclohexyluracil Valverde, Danillo de Araújo, Adalberto V. S. Borin, Antonio Carlos Molecules Article The photophysical relaxation mechanisms of 1-cyclohexyluracil, in vacuum and water, were investigated by employing the Multi-State CASPT2 (MS-CASPT2, Multi-State Complete Active-Space Second-Order Perturbation Theory) quantum chemical method and Dunning’s cc-pVDZ basis sets. In both environments, our results suggest that the primary photophysical event is the population of the [Formula: see text] [Formula: see text] bright state. Afterwards, two likely deactivation pathways can take place, which is sustained by linear interpolation in internal coordinates defined via Z-Matrix scans connecting the most important characteristic points. The first one (Route 1) is the same relaxation mechanism observed for uracil, its canonical analogue, i.e., internal conversion to the ground state through an ethylenic-like conical intersection. The other route (Route 2) is the direct population transfer from the [Formula: see text] [Formula: see text] bright state to the [Formula: see text] [Formula: see text] triplet state via an intersystem crossing process involving the ([Formula: see text] [Formula: see text] / [Formula: see text] [Formula: see text]) [Formula: see text] singlet-triplet crossing point. As the spin-orbit coupling is not too large in either environment, we propose that most of the electronic population initially on the [Formula: see text] [Formula: see text] state returns to the ground following the same ultrafast deactivation mechanism observed in uracil (Route 1), while a smaller percentage goes to the triplet manifold. The presence of a minimum on the [Formula: see text] [Formula: see text] potential energy hypersurface in water can help to understand why experimentally it is noticed suppression of the triplet states population in polar protic solvent. MDPI 2021-08-27 /pmc/articles/PMC8434193/ /pubmed/34500625 http://dx.doi.org/10.3390/molecules26175191 Text en © 2021 by the authors. https://creativecommons.org/licenses/by/4.0/Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Valverde, Danillo
de Araújo, Adalberto V. S.
Borin, Antonio Carlos
Photophysical Deactivation Mechanisms of the Pyrimidine Analogue 1-Cyclohexyluracil
title Photophysical Deactivation Mechanisms of the Pyrimidine Analogue 1-Cyclohexyluracil
title_full Photophysical Deactivation Mechanisms of the Pyrimidine Analogue 1-Cyclohexyluracil
title_fullStr Photophysical Deactivation Mechanisms of the Pyrimidine Analogue 1-Cyclohexyluracil
title_full_unstemmed Photophysical Deactivation Mechanisms of the Pyrimidine Analogue 1-Cyclohexyluracil
title_short Photophysical Deactivation Mechanisms of the Pyrimidine Analogue 1-Cyclohexyluracil
title_sort photophysical deactivation mechanisms of the pyrimidine analogue 1-cyclohexyluracil
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8434193/
https://www.ncbi.nlm.nih.gov/pubmed/34500625
http://dx.doi.org/10.3390/molecules26175191
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