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Miyazaki M, Ohara R, Dedonder C, Jouvet C, Fujii M. Electron-Proton Transfer Mechanism of Excited-State Hydrogen Transfer in Phenol-(NH 3 ) n (n=3 and 5). Chemistry 2017; 24:881-890. [PMID: 29032637 DOI: 10.1002/chem.201704129] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2017] [Indexed: 11/11/2022]
Abstract
Excited-state hydrogen transfer (ESHT) is responsible for various photochemical processes of aromatics, including photoprotection of nuclear basis. Its mechanism is explained by internal conversion from the aromatic ππ* to πσ* states via conical intersection. This means that the electron is transferred to a diffuse Rydberg-like σ* orbital apart from proton migration. This picture means the electron and the proton do not move together and the dynamics are different in principle. Here, we have applied picosecond time-resolved near-infrared (NIR) and infrared (IR) spectroscopy to the phenol-(NH3 )5 cluster, the benchmark system of ESHT, and monitored the electron transfer and proton motion independently. The electron transfer monitored by the NIR transition rises within 3 ps, while the overall H transfer detected by the IR absorption of NH vibration appears with a lifetime of about 20 ps. This clearly proves that the electron motion and proton migration are decoupled. Such a difference of the time-evolutions between the NIR absorption and the IR transition has not been detected in a cluster with three ammonia molecules. We will report our full observation together with theoretical calculations of the potential energy surfaces of the ππ* and πσ* states, and will discuss the ESHT mechanism and its cluster size-dependence between n=3 and 5. It is suggested that the presence and absence of a barrier in the proton transfer coordinate cause the different dynamics.
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Affiliation(s)
- Mitsuhiko Miyazaki
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, R1-15, 4259, Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan
| | - Ryuhei Ohara
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, R1-15, 4259, Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan
| | - Claude Dedonder
- CNRS, Physique des Interactions Ioniques et Moleculaires, Aix Marseille Université, (PIIM) UMR 7345, 13397, Marseille cedex, France
| | - Christophe Jouvet
- CNRS, Physique des Interactions Ioniques et Moleculaires, Aix Marseille Université, (PIIM) UMR 7345, 13397, Marseille cedex, France
| | - Masaaki Fujii
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, R1-15, 4259, Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan
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