Resonance Raman studies of phenylcyclopropane radical cations

Resonance Raman spectra of the radical cations of phenylcyclopropane and tr ans-1-phenyl-2-methylcyclopropane are reported. A near-UV pump pulse excite s a photosensitizer which oxidizes the species of interest, and a visible p robe pulse delayed by 35 ns obtains the spectrum of the radical. ion. The t ransient 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 r esonant excited state and comparison between the unsubstituted and methyl-s ubstituted compounds. The transient spectra are consistent with the large e ffect of methyl substitution on the geometry of the radical cation predicte d by DFT. The resonance Raman spectrum of the electron donor-acceptor compl ex between phenylcyclopropane and tetracyanoethylene is also obtained on re sonance with the visible charge-transfer absorption band, but the spectra a re very weak and only a few resonance enhanced lines are observed. These re sults are compared with previously published data on the p-methoxybenzyltri methylsilane charge-transfer complex and radical cation, Copyright (C) 2000 John Wiley & Sons, Ltd.