Ultrafast photoinduced dynamics of halogenated cyclopentadienes: observation of geminate charge-transfer complexes in solution

Abstract

The photoinduced dynamics of the fully halogenated cyclopentadienes C₅Cl₆ and C₅Br₆ have been investigated in solution and gas phase by femtosecond time-resolved spectroscopy. Both in solution and in gas phase, homolytic dissociation into a halogen radical and a C₅X₅ (X = Cl, Br) radical was observed. In liquid phase, solvent-dependent formation of charge transfer complexes between geminate radicals was observed for the first time. These complexes were found to be surprisingly stable and offered the opportunity to follow the dynamics of specific radical pairs. In the case of C₅Cl₆ in trichloroethanol, a reaction of the chlorine radical with molecules from the solvent cage was observed.