Time resolved resonance raman, ab initio Hartree-Fock, and density functional theoretical studies on the transients states of perfluoro-p-benzoquinone

In recent times, perfluorinated organic compounds have been investigated ex tensively to understand the influence of perfluorination on structure-react ivity correlations. Here, we report the time-resolved resonance Raman (TR3) , ab initio Hartree-Fock (HF), and density functional theoretical (DFT) stu dies on the photogenerated transient states of perfluoro-p-benzoquinone (Fl uoranil, FA). In particular, for the triplet excited states, radical anion and ketyl radical Raman spectra have been recorded. The observed Raman exci tation profiles and the decay rate constants of triplet excited states of F A satisfactorily reproduce, respectively, the absorption spectra and decay rate constants reported previously from transient absorption studies. The s tructure and vibrational spectra of all these intermediates of FA have been calculated using both ab initio unrestricted Hartree-Fock (UHF) and densit y functional (UBP86) methods with standard 6-31G(d) basis set. The assignme nts for all the experimentally observed resonance Raman bands are made usin g the calculated frequencies and the normal coordinate analysis. Potential energy distributions (PEDs) are also presented. Perfluoro, effect is found to be more pronounced in the triplet excited state than in the ground state or the radical anion, whereas the effect in the ground state seems to be h igher than that in the radical anion. The lowest triplet excited state of F A has been identified as the pi pi* state (B-3(3G)) in nonpolar solvents an d the n pi* state (B-3(1G)) in polar solvents. The solvent polarity appears to play a major role in the nature of the lowest triplet excited states, s ince these two states are very close to each other.