Resonance Raman studies of phenylcyclopropane radical cations

Abstract

Resonance Raman spectra of the radical cations of phenylcyclopropane and trans-1-phenyl-2-methylcyclopropane are reported. A near-UV pump pulse excites a photosensitizer which oxidizes the species of interest, and a visible probe pulse delayed by 35 ns obtains the spectrum of the radical ion. The transient Raman spectra of the phenylcyclopropane radical cations show nine or ten enhanced modes for which assignments are suggested based on density functional theory (DFT) results, previously published calculations on the resonant excited state and comparison between the unsubstituted and methyl-substituted compounds. The transient spectra are consistent with the large effect of methyl substitution on the geometry of the radical cation predicted by DFT. The resonance Raman spectrum of the electron donor-acceptor complex between phenylcyclopropane and tetracyanoethylene is also obtained on resonance with the visible charge-transfer absorption band, but the spectra are very weak and only a few resonance enhanced lines are observed. These results are compared with previously published data on the p-methoxybenzyltrimethylsilane charge-transfer complex and radical cation.