Analysis of electron-molecular vibration interactions in π-electron conjugated radical ion species

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(1) By using a transmission probe combined with bundles of mid-infrared optical fibers, high-quality infrared spectra have been observed for the radical anion of naphthalene in deuterated tetrahydrofuran and the radical cation of 4,4'-dimethylbiphenyl in deuterated dichloromethane. The transmission probe can be inserted into a glass-tube cell with O-rings under vacuum. Organic radical ions prepared separately in a vacuum system are transferred into the cell for infrared absorption measurements. Observed infrared spectra are in good agreement with calculated spectra based on density functional theory..(2) The molecular structures and infrared absorption and Raman spectra of the neutral species and radical cation of 2,5""-dimethylquinquethiophene and the neutral species and dication of [2.2]quinquethiophenophane were obtained by density functional theory calculations. Strong infrared absorptions characteristic of the dication of [2.2]quinquethiophenophane were calculated. The vibrational modes of these strong infrared absorptions are out-of-phase in the two quinquethiophene parts. The corresponding vibrational modes of the radical cation of 2,5""-dimethyIquinquethiophene have weak infrared absorption intensities.