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Time-Resolved and Pulse EPR Study of Triplet States of Alkylketones in beta-Cyclodextrin

Abstract : The triplet states of deoxybenzoin (DOB) and benzophenone (BP) molecules in randomly methylated beta-cyclodextrin (CD) cavity are studied by time-resolved (TR) and pulse electron paramagnetic resonance (EPR). The observed TR EPR spectrum of DOB in beta-CD at 30 K is close to the spectrum measured in polar solvent trifluoroethanol, revealing strong hydration by water molecules. At the same time, TR EPR spectrum of BP in beta-CD corresponds to nonpolar surrounding of the CO-group. The electron spin relaxation times T (1) and T (2) of triplet BP at 30 K measured by pulse EPR are found to be different in beta-CD compared to nonpolar toluene glass. The observed increase of T (2) by up to a factor of four in beta-CD is caused by the lower vibration amplitude of CO-bond of BP due to the confinement in beta-CD. The influence of beta-CD with covalently attached nitroxide on the triplet states of DOB and BP is principally different: the excited triplet states could not be observed by TR EPR due to the efficient quenching of the excited states by nitroxide.
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Submitted on : Tuesday, February 7, 2017 - 4:35:19 PM
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O. Krumkacheva, M. Tanabe, S. Yamauchi, M. Fedin, S. R. A. Marque, et al.. Time-Resolved and Pulse EPR Study of Triplet States of Alkylketones in beta-Cyclodextrin. Applied Magnetic Resonance, Springer Verlag, 2012, 42 (1), pp.29--40. ⟨10.1007/s00723-011-0289-2⟩. ⟨hal-01460358⟩

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