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"Photo-Generation and Reactions of Benzhydryl Cations and Radicals:
a complex sequence of mechanisms from femtoseconds to microseconds" C. F. Sailer and E.RiedlePure Appl. Chem. 85, 1487 - 1498 (2013). Abstract: Benzhydryl radicals and cations are reactive intermediates central to the understanding of organic reactivity. They can be generated from benzhydryl halides by UV irradiation. We performed transient absorption measurements over the range from femtoseconds to microseconds to unravel the complete reaction scheme. The 290 - 720 nm probe range allows the unambiguous monitoring of all fragments. The appearance of the radical is delayed to the optical excitation, the onset of the cation signal is found even later. Ab-initio calculations show that this non-rate behavior in the 100 fs range is due to wavepacket motion from the Franck-Condon region to two distinct conical intersections. The rise of the optical signal with a quasi-exponential time of 300 fs is assigned to the planarization and solvation of the photoproducts. The bond cleavage predominantly generates radical pairs. A subsequent electron transfer transforms radical pairs into ion pairs. Due to the broad inter-radical distance distribution and the distance dependence the electron transfer is strongly non-exponential. Part of the ion pairs recombine geminately. The electron transfer and the recombination are terminated by the depletion of close pairs and diffusional separation. The remaining free radicals and cations undergo further reactions in the ns to µs regime. BMO authors (in alphabetic order): Eberhard Riedle Christian Sailer Order Hardcopy  WWW-Version |
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Letzte Änderung: 2016-09-14 13:34
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