Photoisomerization mechanism of iminoguanidinium receptors from spectroscopic methods and quantum chemical calculations

Duy Khoi Dang; Jeffrey D. Einkauf; Xinyou Ma; Radu Custelcean; Ying Zhong Ma; Paul M. Zimmerman; Vyacheslav S. Bryantsev

doi:10.1039/d4cp02747g

Photoisomerization mechanism of iminoguanidinium receptors from spectroscopic methods and quantum chemical calculations

Duy Khoi Dang, Jeffrey D. Einkauf, Xinyou Ma, Radu Custelcean, Ying Zhong Ma, Paul M. Zimmerman, Vyacheslav S. Bryantsev

Chemical Separations Group

Research output: Contribution to journal › Article › peer-review

Abstract

The hydrazone functional group, when coupled with a pyridyl substituent, offers a unique class of widely tunable photoswitches, whose E-to-Z photoisomerization equilibria can be controlled through intramolecular hydrogen bonding between the N-H hydrazone donor and the pyridyl acceptor. However, little is known about the photoisomerization mechanism in this class of compounds. To address this issue, we report a pyridine-appended iminoguanidinium photoswitch that is functionally related to acylhydrazones and provides insight into the photoisomerization processes between the E and Z configurations. The E-to-Z photoisomerization of the E-2-pyridyl-iminoguanidinium cation (2PyMIG) in DMSO, prepared as the bromide salt, was quantified by ¹H NMR, and probed in real time with ultrafast laser spectroscopy. The photoisomerization process occurs on a picosecond timescale, resulting in low fluorescence yields. The multiconfigurational reaction path found with the growing string method features a small barrier (4.3 or 6.5 kcal mol⁻¹) that the E isomer in the π-π* state must overcome to reach the minimum energy conical intersection (MECI) connecting the E and Z isomers of 2PyMIG. While two possible pathways exist depending on the orientation of the pyridine ring, both exhibit the same qualitative features along the path and at their MECIs, involving simultaneous changes in the CCNN and CNNC dihedral angles. Furthermore, the ground state barrier for pyridine ring rotation is readily accessible, thus a low barrier pathway to the experimentally observed Z isomer exists for both MECIs leading to a transition from the E isomer to photoproduct. Combining multiconfigurational reaction path calculations using growing string method with time-resolved fluorescence spectroscopy provided crucial insights into the photoisomerization process of 2PyMIG, resulting in both the computational and experimental results pointing to rapid photoisomerization via a surface crossing between the singlet π-π* and the ground states.

Original language	English
Journal	Physical Chemistry Chemical Physics
DOIs	https://doi.org/10.1039/d4cp02747g
State	Accepted/In press - 2024

Funding

This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. The manuscript was produced by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. D.-K. D. and P. M. Z. are additionally supported by NSF CHE-1551994 and NSF 2246764. D.-K. D. also acknowledges the National Science Foundation for providing a Graduate Research Fellowship under grant number DGE 1841052. This research used resources of the Compute and Data Environment for Science (CADES) at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725 and the National Energy Research Scientific Computing Center (NERSC), a Department of Energy Office of Science User Facility using NERSC award BES-ERCAP0020739. The publisher acknowledges the U.S. Government license to provide public access under the DOE Public Access Plan ( https://energy.gov/downloads/doe-public-access-plan ). This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( https://energy.gov/downloads/doe-public-access-plan ).

Funders	Funder number
Basic Energy Sciences
Data Environment for Science
U.S. Department of Energy
CADES
National Science Foundation	DGE 1841052, 2246764, CHE-1551994
Chemical Sciences, Geosciences, and Biosciences Division	DE-AC05-00OR22725
Office of Science	BES-ERCAP0020739

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10.1039/d4cp02747g

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title = "Photoisomerization mechanism of iminoguanidinium receptors from spectroscopic methods and quantum chemical calculations",

abstract = "The hydrazone functional group, when coupled with a pyridyl substituent, offers a unique class of widely tunable photoswitches, whose E-to-Z photoisomerization equilibria can be controlled through intramolecular hydrogen bonding between the N-H hydrazone donor and the pyridyl acceptor. However, little is known about the photoisomerization mechanism in this class of compounds. To address this issue, we report a pyridine-appended iminoguanidinium photoswitch that is functionally related to acylhydrazones and provides insight into the photoisomerization processes between the E and Z configurations. The E-to-Z photoisomerization of the E-2-pyridyl-iminoguanidinium cation (2PyMIG) in DMSO, prepared as the bromide salt, was quantified by 1H NMR, and probed in real time with ultrafast laser spectroscopy. The photoisomerization process occurs on a picosecond timescale, resulting in low fluorescence yields. The multiconfigurational reaction path found with the growing string method features a small barrier (4.3 or 6.5 kcal mol−1) that the E isomer in the π-π* state must overcome to reach the minimum energy conical intersection (MECI) connecting the E and Z isomers of 2PyMIG. While two possible pathways exist depending on the orientation of the pyridine ring, both exhibit the same qualitative features along the path and at their MECIs, involving simultaneous changes in the CCNN and CNNC dihedral angles. Furthermore, the ground state barrier for pyridine ring rotation is readily accessible, thus a low barrier pathway to the experimentally observed Z isomer exists for both MECIs leading to a transition from the E isomer to photoproduct. Combining multiconfigurational reaction path calculations using growing string method with time-resolved fluorescence spectroscopy provided crucial insights into the photoisomerization process of 2PyMIG, resulting in both the computational and experimental results pointing to rapid photoisomerization via a surface crossing between the singlet π-π* and the ground states.",

author = "Dang, {Duy Khoi} and Einkauf, {Jeffrey D.} and Xinyou Ma and Radu Custelcean and Ma, {Ying Zhong} and Zimmerman, {Paul M.} and Bryantsev, {Vyacheslav S.}",

note = "Publisher Copyright: {\textcopyright} 2024 The Royal Society of Chemistry",

year = "2024",

doi = "10.1039/d4cp02747g",

language = "English",

journal = "Physical Chemistry Chemical Physics",

issn = "1463-9076",

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T1 - Photoisomerization mechanism of iminoguanidinium receptors from spectroscopic methods and quantum chemical calculations

AU - Dang, Duy Khoi

AU - Einkauf, Jeffrey D.

AU - Ma, Xinyou

AU - Custelcean, Radu

AU - Ma, Ying Zhong

AU - Zimmerman, Paul M.

AU - Bryantsev, Vyacheslav S.

PY - 2024

Y1 - 2024

N2 - The hydrazone functional group, when coupled with a pyridyl substituent, offers a unique class of widely tunable photoswitches, whose E-to-Z photoisomerization equilibria can be controlled through intramolecular hydrogen bonding between the N-H hydrazone donor and the pyridyl acceptor. However, little is known about the photoisomerization mechanism in this class of compounds. To address this issue, we report a pyridine-appended iminoguanidinium photoswitch that is functionally related to acylhydrazones and provides insight into the photoisomerization processes between the E and Z configurations. The E-to-Z photoisomerization of the E-2-pyridyl-iminoguanidinium cation (2PyMIG) in DMSO, prepared as the bromide salt, was quantified by 1H NMR, and probed in real time with ultrafast laser spectroscopy. The photoisomerization process occurs on a picosecond timescale, resulting in low fluorescence yields. The multiconfigurational reaction path found with the growing string method features a small barrier (4.3 or 6.5 kcal mol−1) that the E isomer in the π-π* state must overcome to reach the minimum energy conical intersection (MECI) connecting the E and Z isomers of 2PyMIG. While two possible pathways exist depending on the orientation of the pyridine ring, both exhibit the same qualitative features along the path and at their MECIs, involving simultaneous changes in the CCNN and CNNC dihedral angles. Furthermore, the ground state barrier for pyridine ring rotation is readily accessible, thus a low barrier pathway to the experimentally observed Z isomer exists for both MECIs leading to a transition from the E isomer to photoproduct. Combining multiconfigurational reaction path calculations using growing string method with time-resolved fluorescence spectroscopy provided crucial insights into the photoisomerization process of 2PyMIG, resulting in both the computational and experimental results pointing to rapid photoisomerization via a surface crossing between the singlet π-π* and the ground states.

AB - The hydrazone functional group, when coupled with a pyridyl substituent, offers a unique class of widely tunable photoswitches, whose E-to-Z photoisomerization equilibria can be controlled through intramolecular hydrogen bonding between the N-H hydrazone donor and the pyridyl acceptor. However, little is known about the photoisomerization mechanism in this class of compounds. To address this issue, we report a pyridine-appended iminoguanidinium photoswitch that is functionally related to acylhydrazones and provides insight into the photoisomerization processes between the E and Z configurations. The E-to-Z photoisomerization of the E-2-pyridyl-iminoguanidinium cation (2PyMIG) in DMSO, prepared as the bromide salt, was quantified by 1H NMR, and probed in real time with ultrafast laser spectroscopy. The photoisomerization process occurs on a picosecond timescale, resulting in low fluorescence yields. The multiconfigurational reaction path found with the growing string method features a small barrier (4.3 or 6.5 kcal mol−1) that the E isomer in the π-π* state must overcome to reach the minimum energy conical intersection (MECI) connecting the E and Z isomers of 2PyMIG. While two possible pathways exist depending on the orientation of the pyridine ring, both exhibit the same qualitative features along the path and at their MECIs, involving simultaneous changes in the CCNN and CNNC dihedral angles. Furthermore, the ground state barrier for pyridine ring rotation is readily accessible, thus a low barrier pathway to the experimentally observed Z isomer exists for both MECIs leading to a transition from the E isomer to photoproduct. Combining multiconfigurational reaction path calculations using growing string method with time-resolved fluorescence spectroscopy provided crucial insights into the photoisomerization process of 2PyMIG, resulting in both the computational and experimental results pointing to rapid photoisomerization via a surface crossing between the singlet π-π* and the ground states.

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U2 - 10.1039/d4cp02747g

DO - 10.1039/d4cp02747g

M3 - Article

AN - SCOPUS:85203416338

SN - 1463-9076

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

ER -

Photoisomerization mechanism of iminoguanidinium receptors from spectroscopic methods and quantum chemical calculations

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