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Vázquez SR, Rodríguez MCR, Mosquera M, Rodríguez-Prieto F. Excited-State Intramolecular Proton Transfer in 2-(3‘-Hydroxy-2‘-pyridyl)benzoxazole. Evidence of Coupled Proton and Charge Transfer in the Excited State of Some o-Hydroxyarylbenzazoles. J Phys Chem A 2007; 111:1814-26. [PMID: 17309239 DOI: 10.1021/jp0653813] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The influence of solvent, temperature, and viscosity on the phototautomerization processes of a series of o-hydroxyarylbenzazoles was studied by means of ultraviolet-visible (UV-vis) absorption spectroscopy and steady-state and time-resolved fluorescence spectroscopy. The compounds studied were 2-(2'-hydroxyphenyl)benzimidazole (HBI), 2-(2'-hydroxyphenyl)benzoxazole (HBO), 2-(2'-hydroxyphenyl)benzothiazole (HBT), 2-(3'-hydroxy-2'-pyridyl)benzimidazole (HPyBI), and the new derivative 2-(3'-hydroxy-2'-pyridyl)benzoxazole (HPyBO), this one studied in neutral and acid media. All of these compounds undergo an excited-state intramolecular proton transfer (ESIPT) from the hydroxyl group to the benzazole N3 to yield an excited tautomer in syn conformation. A temperature- and viscosity-dependent radiationless deactivation of the tautomer has been detected for all compounds except HBI and HPyBI. We show that this radiationless decay also takes place for 2-(3-methyl-1,3-benzothiazol-3-ium-2-yl)benzenolate (NMeOBT), the N-methylated analog of the tautomer, whose ground-state structure has anti conformation. In ethanol, the radiationless decay shows intrinsic activation energy for HPyBO and HBO; however, it is barrierless for HBT and NMeOBT and controlled instead by the solvent dynamics. The relative efficiency of the radiationless decay in the series of molecules studied supports the hypothesis that this transition is connected with a charge-transfer process taking place in the tautomer, its efficiency being related to the strength of the electron donor (dissociated phenol or pyridinol moiety) and electron acceptor (protonated benzazole). We propose that the charge transfer is associated with a large-amplitude conformational change of the tautomer, the process leading to a nonfluorescent charge-transfer intermediate. The previous ESIPT step generates the structure with the suitable redox pair to undergo the charge-transfer process; therefore, an excited-state intramolecular coupled proton and charge transfer takes place for these compounds.
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Affiliation(s)
- Sonia Ríos Vázquez
- Departamento de Química Física, Facultade de Química, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
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Stein M, Keck J, Waiblinger F, Fluegge AP, Kramer HEA, Hartschuh A, Port H, Leppard D, Rytz G. Influence of Polymer Matrixes on the Photophysical Properties of UV Absorbers. J Phys Chem A 2001. [DOI: 10.1021/jp012134k] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Martin Stein
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, 3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany, and Ciba Specialty Chemicals, Inc., Additives Division, Rosental R 1059, CH-4002 Basle, Switzerland
| | - Juergen Keck
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, 3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany, and Ciba Specialty Chemicals, Inc., Additives Division, Rosental R 1059, CH-4002 Basle, Switzerland
| | - Frank Waiblinger
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, 3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany, and Ciba Specialty Chemicals, Inc., Additives Division, Rosental R 1059, CH-4002 Basle, Switzerland
| | - Anja P. Fluegge
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, 3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany, and Ciba Specialty Chemicals, Inc., Additives Division, Rosental R 1059, CH-4002 Basle, Switzerland
| | - Horst E. A. Kramer
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, 3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany, and Ciba Specialty Chemicals, Inc., Additives Division, Rosental R 1059, CH-4002 Basle, Switzerland
| | - Achim Hartschuh
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, 3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany, and Ciba Specialty Chemicals, Inc., Additives Division, Rosental R 1059, CH-4002 Basle, Switzerland
| | - Helmut Port
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, 3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany, and Ciba Specialty Chemicals, Inc., Additives Division, Rosental R 1059, CH-4002 Basle, Switzerland
| | - David Leppard
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, 3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany, and Ciba Specialty Chemicals, Inc., Additives Division, Rosental R 1059, CH-4002 Basle, Switzerland
| | - Gerhard Rytz
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, 3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany, and Ciba Specialty Chemicals, Inc., Additives Division, Rosental R 1059, CH-4002 Basle, Switzerland
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