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Proton‐Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution

Photoacids attract increasing scientific attention, as they are valuable tools to spatiotemporally control proton‐release reactions and pH values of solutions. We present the first time‐resolved spectroscopic study of the excited state and proton‐release dynamics of prominent merocyanine representat...

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Autores principales: Kaiser, Christoph, Halbritter, Thomas, Heckel, Alexander, Wachtveitl, Josef
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8361770/
https://www.ncbi.nlm.nih.gov/pubmed/33929051
http://dx.doi.org/10.1002/chem.202100168
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author Kaiser, Christoph
Halbritter, Thomas
Heckel, Alexander
Wachtveitl, Josef
author_facet Kaiser, Christoph
Halbritter, Thomas
Heckel, Alexander
Wachtveitl, Josef
author_sort Kaiser, Christoph
collection PubMed
description Photoacids attract increasing scientific attention, as they are valuable tools to spatiotemporally control proton‐release reactions and pH values of solutions. We present the first time‐resolved spectroscopic study of the excited state and proton‐release dynamics of prominent merocyanine representatives. Femtosecond transient absorption measurements of a pyridine merocyanine with two distinct protonation sites revealed dissimilar proton‐release mechanisms: one site acts as a photoacid generator as its pK(a) value is modulated in the ground state after photoisomerization, while the other functions as an excited state photoacid which releases its proton within 1.1 ps. With a pK(a) drop of 8.7 units to −5.5 upon excitation, the latter phenolic site is regarded a super‐photoacid. The 6‐nitro derivative exhibits only a phenolic site with similar, yet slightly less photoacidic characteristics and both compounds transfer their proton to methanol and ethanol. In contrast, for the related 6,8‐dinitro compound an intramolecular proton transfer to the ortho‐nitro group is suggested that is involved in a rapid relaxation into the ground state.
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spelling pubmed-83617702021-08-17 Proton‐Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution Kaiser, Christoph Halbritter, Thomas Heckel, Alexander Wachtveitl, Josef Chemistry Full Papers Photoacids attract increasing scientific attention, as they are valuable tools to spatiotemporally control proton‐release reactions and pH values of solutions. We present the first time‐resolved spectroscopic study of the excited state and proton‐release dynamics of prominent merocyanine representatives. Femtosecond transient absorption measurements of a pyridine merocyanine with two distinct protonation sites revealed dissimilar proton‐release mechanisms: one site acts as a photoacid generator as its pK(a) value is modulated in the ground state after photoisomerization, while the other functions as an excited state photoacid which releases its proton within 1.1 ps. With a pK(a) drop of 8.7 units to −5.5 upon excitation, the latter phenolic site is regarded a super‐photoacid. The 6‐nitro derivative exhibits only a phenolic site with similar, yet slightly less photoacidic characteristics and both compounds transfer their proton to methanol and ethanol. In contrast, for the related 6,8‐dinitro compound an intramolecular proton transfer to the ortho‐nitro group is suggested that is involved in a rapid relaxation into the ground state. John Wiley and Sons Inc. 2021-06-01 2021-06-21 /pmc/articles/PMC8361770/ /pubmed/33929051 http://dx.doi.org/10.1002/chem.202100168 Text en © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH https://creativecommons.org/licenses/by-nc/4.0/This is an open access article under the terms of the http://creativecommons.org/licenses/by-nc/4.0/ (https://creativecommons.org/licenses/by-nc/4.0/) License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
spellingShingle Full Papers
Kaiser, Christoph
Halbritter, Thomas
Heckel, Alexander
Wachtveitl, Josef
Proton‐Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution
title Proton‐Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution
title_full Proton‐Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution
title_fullStr Proton‐Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution
title_full_unstemmed Proton‐Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution
title_short Proton‐Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution
title_sort proton‐transfer dynamics of photoacidic merocyanines in aqueous solution
topic Full Papers
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8361770/
https://www.ncbi.nlm.nih.gov/pubmed/33929051
http://dx.doi.org/10.1002/chem.202100168
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