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Discovering a rotational barrier within a charge-transfer state of a photoexcited chromophore in solution

Methylation occurs in a myriad of systems with protective and regulatory functions. 8-methoxypyrene-1,3,6-trisulfonate (MPTS), a methoxy derivative of a photoacid, serves as a model system to study effects of methylation on the excited state potential energy landscape. A suite of spectroscopic techn...

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Autores principales: Krueger, Taylor D., Boulanger, Sean A., Zhu, Liangdong, Tang, Longteng, Fang, Chong
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Crystallographic Association 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7056454/
https://www.ncbi.nlm.nih.gov/pubmed/32161777
http://dx.doi.org/10.1063/1.5143441
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author Krueger, Taylor D.
Boulanger, Sean A.
Zhu, Liangdong
Tang, Longteng
Fang, Chong
author_facet Krueger, Taylor D.
Boulanger, Sean A.
Zhu, Liangdong
Tang, Longteng
Fang, Chong
author_sort Krueger, Taylor D.
collection PubMed
description Methylation occurs in a myriad of systems with protective and regulatory functions. 8-methoxypyrene-1,3,6-trisulfonate (MPTS), a methoxy derivative of a photoacid, serves as a model system to study effects of methylation on the excited state potential energy landscape. A suite of spectroscopic techniques including transient absorption, wavelength-tunable femtosecond stimulated Raman spectroscopy (FSRS), and fluorescence quantum yield measurements via steady-state electronic spectroscopy reveal the energy dissipation pathways of MPTS following photoexcitation. Various solvents enable a systematic characterization of the H-bonding interaction, viscosity, and dynamic solvation that influence the ensuing relaxation pathways. The formation of a charge-transfer state out of the Franck–Condon region occurs on the femtosecond-to-picosecond solvation timescale before encountering a rotational barrier. The rotational relaxation correlates with the H-bond donating strength of solvent, while the rotational time constant lengthens as solvent viscosity increases. Time-resolved excited-state FSRS, aided by quantum calculations, provides crucial structural dynamics knowledge and reveals the sulfonate groups playing a dominant role during solvation. Several prominent vibrational motions of the pyrene ring backbone help maneuver the population toward the more fluorescent state. These ultrafast correlated electronic and nuclear motions ultimately govern the fate of the photoexcited chromophore in solution. Overall, MPTS in water displays the highest probability to fluoresce, while the aprotic and more viscous dimethyl sulfoxide enhances the nonradiative pathways. These mechanistic insights may apply robustly to other photoexcited chromophores that do not undergo excited-state proton transfer or remain trapped in a broad electronic state and also provide design principles to control molecular optical responses with site-specific atomic substitution.
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spelling pubmed-70564542020-03-11 Discovering a rotational barrier within a charge-transfer state of a photoexcited chromophore in solution Krueger, Taylor D. Boulanger, Sean A. Zhu, Liangdong Tang, Longteng Fang, Chong Struct Dyn ARTICLES Methylation occurs in a myriad of systems with protective and regulatory functions. 8-methoxypyrene-1,3,6-trisulfonate (MPTS), a methoxy derivative of a photoacid, serves as a model system to study effects of methylation on the excited state potential energy landscape. A suite of spectroscopic techniques including transient absorption, wavelength-tunable femtosecond stimulated Raman spectroscopy (FSRS), and fluorescence quantum yield measurements via steady-state electronic spectroscopy reveal the energy dissipation pathways of MPTS following photoexcitation. Various solvents enable a systematic characterization of the H-bonding interaction, viscosity, and dynamic solvation that influence the ensuing relaxation pathways. The formation of a charge-transfer state out of the Franck–Condon region occurs on the femtosecond-to-picosecond solvation timescale before encountering a rotational barrier. The rotational relaxation correlates with the H-bond donating strength of solvent, while the rotational time constant lengthens as solvent viscosity increases. Time-resolved excited-state FSRS, aided by quantum calculations, provides crucial structural dynamics knowledge and reveals the sulfonate groups playing a dominant role during solvation. Several prominent vibrational motions of the pyrene ring backbone help maneuver the population toward the more fluorescent state. These ultrafast correlated electronic and nuclear motions ultimately govern the fate of the photoexcited chromophore in solution. Overall, MPTS in water displays the highest probability to fluoresce, while the aprotic and more viscous dimethyl sulfoxide enhances the nonradiative pathways. These mechanistic insights may apply robustly to other photoexcited chromophores that do not undergo excited-state proton transfer or remain trapped in a broad electronic state and also provide design principles to control molecular optical responses with site-specific atomic substitution. American Crystallographic Association 2020-03-04 /pmc/articles/PMC7056454/ /pubmed/32161777 http://dx.doi.org/10.1063/1.5143441 Text en © 2020 Author(s). 2329-7778/2020/7(2)/024901/11 All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle ARTICLES
Krueger, Taylor D.
Boulanger, Sean A.
Zhu, Liangdong
Tang, Longteng
Fang, Chong
Discovering a rotational barrier within a charge-transfer state of a photoexcited chromophore in solution
title Discovering a rotational barrier within a charge-transfer state of a photoexcited chromophore in solution
title_full Discovering a rotational barrier within a charge-transfer state of a photoexcited chromophore in solution
title_fullStr Discovering a rotational barrier within a charge-transfer state of a photoexcited chromophore in solution
title_full_unstemmed Discovering a rotational barrier within a charge-transfer state of a photoexcited chromophore in solution
title_short Discovering a rotational barrier within a charge-transfer state of a photoexcited chromophore in solution
title_sort discovering a rotational barrier within a charge-transfer state of a photoexcited chromophore in solution
topic ARTICLES
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7056454/
https://www.ncbi.nlm.nih.gov/pubmed/32161777
http://dx.doi.org/10.1063/1.5143441
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