Temperature effects on electron transfer within intervalence bis(hydrazine) radical cations

Analyses of the shape of intervalence charge-transfer bands at various temp eratures (similar to 255-325 K in most cases) in acetonitrile are reported for the radical cations of bis(2-tert-butyl-2,3-diazabicyclo[2.2.2]-oct3-yl ) hydrazines that are bridged by 2,5-xylene-1,4-diyl (2(+)), durene-1,4-diy l (3(+)), naphthalene-1,4-diyl (4(+)), biphenyl-4,4'-diyl (5(+)), and 9,9-d imethylfluorene-2,7-diyl (6(+)) aromatic rings, Electron-transfer (ET) rate constants measured by ESR as a function of temperature are reported for 4( +)-6(+). Despite the fact that the ET barriers for these compounds are domi nated by vibrational reorganization, explicit inclusion of vibronic couplin g effects is not necessary for the prediction of their ET rate constants fr om the optical spectra, Rate constants in excellent agreement with the meas ured ones are predicted by a classical analysis of charge-transfer band sha pe, if the diabatic surfaces are changed from the usual assumption that the y are parabolas to ones that fit the shape of the charge-transfer bands.