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Kao YT, Guo X, Yang Y, Liu Z, Hassanali A, Song QH, Wang L, Zhong D. Ultrafast dynamics of nonequilibrium electron transfer in photoinduced redox cycle: solvent mediation and conformation flexibility. J Phys Chem B 2012; 116:9130-40. [PMID: 22735101 DOI: 10.1021/jp304518f] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
We report here our systematic characterization of a photoinduced electron-transfer (ET) redox cycle in a covalently linked donor-spacer-acceptor flexible system, consisting of N-acetyl-tryptophan methylester as an electron donor and thymine as an electron acceptor in three distinct solvents of water, acetonitrile, and dioxane. With femtosecond resolution, we determined all the ET time scales, forward and backward, by following the complete reaction evolution from reactants to intermediates and finally to products. Surprisingly, we observed two distinct ET dynamics in water, corresponding to a stacked configuration with ultrafast ET in 0.7 ps and back ET in 4.5 ps and a partially folded C-clamp conformation with ET in 322 ps but back ET in 17 ps. In acetonitrile and dioxane, only the C-clamp conformations were observed with ET in 470 and 1068 ps and back ET in 110 and 94 ps, respectively. These relatively slow ET dynamics in hundreds of picoseconds all showed significant conformation heterogeneity and followed a stretched decay behavior. With both forward and back ET rates determined, we derived solvent reorganization energies and coupling constants. Significantly, we found that solvent molecules intercalated in the cleft of the C-clamp structure mediate electron transfer with a tunneling parameter (β) of 1.0-1.4 Å(-1) and the high-frequency vibration modes in the product(s) couple with the back ET process, leading to the ultrafast back ET dynamics in tens of picoseconds. These findings provide mechanistic insights of nonequilibrium ET dynamics modulated by conformation flexibility, mediated by unique solvent configuration, and accelerated by vibrational coupling.
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Affiliation(s)
- Ya-Ting Kao
- Department of Physics, and Programs of Biophysics, Chemical Physics, and Biochemistry, 191 West Woodruff Avenue, The Ohio State University, Columbus, Ohio 43210, USA
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Saleh N, Al-Soud YA, Nau WM. Novel fluorescent pH sensor based on coumarin with piperazine and imidazole substituents. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2008; 71:818-822. [PMID: 18343715 DOI: 10.1016/j.saa.2008.02.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2007] [Revised: 01/28/2008] [Accepted: 02/01/2008] [Indexed: 05/26/2023]
Abstract
A new coumarin derivative containing piperazine and imidazole moieties is reported as a fluorophore for hydrogen ions sensing. The fluorescence enhancement of the studied sensor with an increase in hydrogen ions concentration is based on the hindering of photoinduced electron transfer from the piperazinyl amine and the imidazolyl amine to the coumarin fluorophore by protonation. The presented sensor has a novel design of fluorophore-spacer-receptor(1)-receptor(2) format, which is proposed to sense two ranges of pH (from 2.5 to 5.5) and (from 10 to 12) instead of sensing one pH range. A model compound, in which the piperazinyl ring is absent, was synthesized as well to confirm the novel pH sensing of the proposed sensor.
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Affiliation(s)
- Na'il Saleh
- Department of Chemistry, Yarmouk University, 21163 Irbid, Jordan.
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Schmidhammer U, Megerle U, Lochbrunner S, Riedle E, Karpiuk J. The Key Role of Solvation Dynamics in Intramolecular Electron Transfer: Time-Resolved Photophysics of Crystal Violet Lactone. J Phys Chem A 2008; 112:8487-96. [DOI: 10.1021/jp800863u] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Uli Schmidhammer
- Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität (LMU), Oettingenstr. 67, 80538 München, Germany, and Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Uwe Megerle
- Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität (LMU), Oettingenstr. 67, 80538 München, Germany, and Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Stefan Lochbrunner
- Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität (LMU), Oettingenstr. 67, 80538 München, Germany, and Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Eberhard Riedle
- Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität (LMU), Oettingenstr. 67, 80538 München, Germany, and Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Jerzy Karpiuk
- Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität (LMU), Oettingenstr. 67, 80538 München, Germany, and Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
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Zhou J, Lukin LV, Braun CL. Charge Separation Distance for Flexible Donor−Bridge−Acceptor Systems after Electron-Transfer Quenching. J Phys Chem A 2008; 112:7507-13. [DOI: 10.1021/jp800396d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Jinwei Zhou
- Department of Chemistry, 6128 Burke Laboratory, Dartmouth
College, Hanover, New Hampshire 03755, and Institute for Energy Problems
of Chemical Physics, Russian Academy of Sciences, Chernogolovka, P.O.
Box 56, Moscow Region 142432, Russian Federation
| | - Leonid V. Lukin
- Department of Chemistry, 6128 Burke Laboratory, Dartmouth
College, Hanover, New Hampshire 03755, and Institute for Energy Problems
of Chemical Physics, Russian Academy of Sciences, Chernogolovka, P.O.
Box 56, Moscow Region 142432, Russian Federation
| | - Charles L. Braun
- Department of Chemistry, 6128 Burke Laboratory, Dartmouth
College, Hanover, New Hampshire 03755, and Institute for Energy Problems
of Chemical Physics, Russian Academy of Sciences, Chernogolovka, P.O.
Box 56, Moscow Region 142432, Russian Federation
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Bassil DB, Dalgarno SJ, Cave GWV, Atwood JL, Tucker SA. Spectroscopic investigations of ADMA encapsulated in pyrogallol[4]arene nanocapsules. J Phys Chem B 2007; 111:9088-92. [PMID: 17602580 DOI: 10.1021/jp0707642] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Pyrogallol[4]arenes form stable hydrogen-bonded nanocapsules that have unique properties that may make them suitable for diverse applications, such as catalysts and molecular transporters. Little is known about the behavior of the interior of these new materials in solution, and by using the solvent-dependent properties of 1-(9-anthryl)-3-(4-dimethylaniline) propane (ADMA), the inner phase properties of the hexamers are investigated. Steady-state and dynamic spectrofluorometric results are in agreement, are consistent with solid-state studies, and indicate that the majority of ADMA is sequestered in an extended conformation with the crystallization solvent. The conformational flexibility of ADMA is attributed to lower capsule occupancies ( approximately 50%, i.e., 1 molecule per 2 capsules, one occupied and one empty) relative to our previous study with pyrene butyric acid (occupancy of 150%, i.e., 1.5 molecules per capsule) in which the probe was restricted within a nanocapsule. The nature of the encapsulated ADMA complexes are found to change with time, as there is either fluorophore leaching from the capsule or endo-exo-capsule solvent exchange. However, the choice of crystallizing solvent (ethyl acetate or acetonitrile) and PgC(n) alkyl tail (C(6) or C(10)) does not influence experimental outcomes. These research findings give a better understanding of the encapsulation versatility of these unique supramolecular assemblies and the protective nanopockets that can exist for guest molecules.
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Affiliation(s)
- Daniel B Bassil
- Department of Chemistry, University of Missouri-Columbia, 601 South College Avenue, Columbia, Missouri 65211, USA
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Benniston AC, Harriman A, Rostron JP. The effect of solvent polarity on the photophysical properties of 4-cyano-(4′-methylthio)diphenylacetylene: A prototypic donor–acceptor system. Phys Chem Chem Phys 2005; 7:3041-7. [PMID: 16186908 DOI: 10.1039/b506776f] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The photophysical properties of the target compound are extremely sensitive to changes in solvent polarity since the lowest-energy excited states possess considerable charge-transfer character. Excitation results in a greatly increased dipole moment, with the resultant excited singlet state retaining a lifetime of ca. 1 ns in all solvents. Radiative decay involves coupling between the lowest-energy excited singlet state and both the ground state and an upper excited singlet state. The level of coupling to the upper singlet decreases in non-polar solvents, presumably due to symmetry factors. The radiative rate constant decreases smoothly with increasing solvent polarity function as the molecule acquires an ever increasing dipolar character. Non-radiative decay includes both intersystem crossing and internal conversion, but the former process dominates in polar solvents. The excited singlet state lifetime is very weakly dependent upon temperature in the solid state. However, in polar solutions where the Stokes' shift decreases with decreasing temperature, there is clear evidence for an activated process. This is believed to involve coupling to the upper-lying singlet excited state.
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Affiliation(s)
- Andrew C Benniston
- Molecular Photonics Laboratory, School of Natural Sciences, University of Newcastle, Newcastle upon Tyne, NE1 7RU, UK
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