Ultrafast relaxation dynamics of perchlorinated cycloheptatriene in solution.
J Phys Chem A
; 111(17): 3231-40, 2007 May 03.
Article
em En
| MEDLINE
| ID: mdl-17428037
ABSTRACT
The photochemistry of perchlorinated cycloheptatriene (CHTCl(8)) has been studied by means of ultrafast pump-probe, 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 occur--a [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(CHTCl(8)) = 140 fs, that can be associated with the electronic relaxation of the 2A'-1A' ' transition, while a second one, tau2(CHTCl(8)), 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 tau1(a) = 120 fs, which can be explained by vibrational motions of CHTCl(8) in the electronically excited states, 1A' ' and 2A'. After continuous UV-irradiation of CHTCl(8), 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 CHTCl(8) after photoexcitation that is comparable to cycloheptatriene.
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01-internacional
Base de dados:
MEDLINE
Assunto principal:
Cloro
/
Cicloeptanos
Tipo de estudo:
Prognostic_studies
Idioma:
En
Revista:
J Phys Chem A
Assunto da revista:
QUIMICA
Ano de publicação:
2007
Tipo de documento:
Article
País de afiliação:
Alemanha