| Abstract |
The optical spectra of 10 p-phenylene-bridged delocalized intervalence compounds MC6H4Mcenter dot- or center dot+ are analyzed using the Koopmans-based method, which considers only transitions from filled orbitals to the singly occupied orbital (SOMO), called Hoijtink type A transitions, and from the SOMO to unoccupied orbitals, Hoijtink type B transitions, and ignores configuration interaction. The radical ions with quinonoid structures, those that form ring-M double bonds with M = C(CN)(2), NMe2, 3-oxo-9-azabicyclo[3.3.1], NPPh3, and 0 when the odd electron of the intervalence oxidation level is removed, are calculated to have the lowest-allowed type B transition lying mostly above the lowest-allowed A transition, with B-i - A(j) decreasing in the order shown from +14 370 to -1390 cm(-1), and the more intense second-lowest-allowed type B transition Bi - Aj from +14 940 to +7070 cm(-1). The five radical anions with benzenoid structures, which form ring-M single bonds with X = CN, CO2Me, CHO, C3HMeBF2O2, and NO2 when the odd electron of the intervalence oxidation level is removed, have a Bi - Aj value of the opposite sign that increases in magnitude from -2880 to -17 050 cm(-1) in the order shown. Configuration interaction is of course present in the observed spectra, and the predictions ignoring it mostly overestimate transition energies by 1900-2600 cm(-1) for the quinonoid compounds (but by 450 cm(-1) for the M = C(CN)(2) radical anion), and by 10001400 cm(-1) for the benzenoid compounds (2500 cm(-1) for the M = CN radical anion). The very simple Koopmans-based model is useful for considering the optical spectra of these radical ions. |
