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"Ultrafast Relaxation Dynamics of Perchlorinated Cycloheptatriene in Solution" O. Schalk, A.-N. UnterreinerJ. Phys. Chem. A, 111, 3231 (2007). Abstract: The photochemistry of perchlorinated cycloheptatriene (CHTCl8) has been studied by means of ultrafast pumpprobe, transient anisotropy and continuous UV-irradiation experiments in various solvents as well as by DFT calculations. After UV-excitation to the 1A¢¢-state, two competing reactions occursa [1,7]-sigmatropic chlorine migration via two ultrafast internal conversions and a [4,5]-electrocyclization forming octachlorobicylo[3.2.0]- hepta-[2,6]-diene. The first reaction has been studied by excitation with a 263 nm femtosecond-laser pulse. Pump-probe experiments reveal a first, solvent-independent time constant, &tau1 CHTCl8 = 140 fs, that can be associated with the electronic relaxation of the 2A'-1A'' transition, while a second one, &tau2 CHTCl8, ranges from 0.9 to 1.8 ps depending on the polarity of the solvent. This finding is consistent with a [1,7]-chlorine migration during the 1A'-2A'' transition where the migrating chlorine atom is partly negatively charged. The charge separation has also been confirmed by DFT calculations. Transient anisotropy measurements result in a time zero value of r(0) = 0.35 after deconvolution and a decay constant of &tau 1a = 120 fs, which can be explained by vibrational motions of CHTCl8 in the electronically excited states, 1A'' and 2A'. After continuous UV-irradiation of CHTCl8, octachlorobicylo[3.2.0]hepta-[2,6]-diene is primarily formed with a solvent-dependent yield. From these investigations, we suggest a relaxation mechanism for CHTCl8 after photoexcitation that is comparable to cycloheptatriene. This publication has not been written at BMO BMO authors (in alphabetic order): Oliver Schalk  WWW-Version |