title: Proton-Coupled Electron-Transfer Processes in Ultrafast Time Domain: Evidence for Effects of Hydrogen-Bond Stabilization on Photoinduced Electron Transfer.
abstract: The proton-coupled electron-transfer (PCET) reaction is investigated for a newly synthesized imidazole-anthraquinone biomimetic model with a photoactive RuII-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 RuII-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 D2O compared with that in H2O. These results provide further experimental support for a detailed understanding of the PCET process.
authors.affiliation: Organic Chemistry Division CSIR, National Chemical Laboratory, Pune, Maharashtra, 411008, India.
authors.forename: Ananta
authors.initials: A
authors.lastname: Dey
authors.affiliation: Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.
authors.forename: Jayanta
authors.initials: J
authors.lastname: Dana
authors.affiliation: Organic Chemistry Division CSIR, National Chemical Laboratory, Pune, Maharashtra, 411008, India.
authors.forename: Sunil
authors.initials: S
authors.lastname: Aute
authors.affiliation: Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.
authors.forename: Partha
authors.initials: P
authors.lastname: Maity
authors.affiliation: Organic Chemistry Division CSIR, National Chemical Laboratory, Pune, Maharashtra, 411008, India.|CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar, 364002, Gujarat, India.
authors.forename: Amitava
authors.initials: A
authors.lastname: Das
authors.affiliation: Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.|Institute of Nano Science and Technology, Mohali, Punjab, 160062, India.
authors.forename: Hirendra N
authors.initials: HN
authors.lastname: Ghosh
keywords: electron transfer; hydrogen bonds; intramolecular electron transfer; proton-coupled electron transfer; ruthenium