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Proton‐Coupled Electron‐Transfer Processes in Ultrafast Time Domain: Evidence for Effects of Hydrogen‐Bond Stabilization on Photoinduced Electron Transfer
Author(s) -
Dey Ananta,
Dana Jayanta,
Aute Sunil,
Maity Partha,
Das Amitava,
Ghosh Hirendra N.
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201605594
Subject(s) - electron transfer , chemistry , proton coupled electron transfer , photochemistry , imidazole , intramolecular force , ultrafast laser spectroscopy , protonation , photoinduced electron transfer , moiety , spectroscopy , stereochemistry , organic chemistry , ion , physics , quantum mechanics
The proton‐coupled electron‐transfer (PCET) reaction is investigated for a newly synthesized imidazole‐anthraquinone biomimetic model with a photoactive Ru II ‐polypyridyl moiety that is covalently coupled to the imidazole fragment. Intramolecular H‐bonding interactions between imidazole and anthraquinone moieties favor the PCET process; this can be correlated to an appreciable positive shift in the one‐electron reduction potential of the coordinated anthraquinone moiety functionalized with the imidazole fragment. This can also be attributed to the low luminescence quantum yield of the Ru II ‐polypyridyl complex used. The dynamics of the intramolecular electron‐transfer (ET) and PCET processes are studied by using femtosecond transient absorption spectroscopy. The steady‐state spectroscopic studies and the results of the time‐resolved absorption studies confirm that H‐bonded water molecules play a major role in both ET and PCET dynamics as a proton relay in the excited state. The electron‐transfer process is followed by a change in the H‐bonding equilibrium between AQ and imidazole in acetonitrile solvent, and protonation of AQ .− by water leads to PCET in the presence of water. A slower forward and backward electron‐transfer rate is observed in the presence of D 2 O compared with that in H 2 O. These results provide further experimental support for a detailed understanding of the PCET process.