Infrared absorption spectroscopic studies of alpha,omega-diphenylpolyenyl anions with odd numbered polyene molecules

Infrared absorption spectra of alpha,omega -diphenylpolyenyl anions Ph(CH)( n)Ph- (DPn-, n=7, 9, and 13) in the tetrahydrofuran-d(6) solutions was meas ured in the range of 1700 and 1200 cm(-1). The infrared spectra obtained fr om anions (DPn) showed considerable difference from their neutral species ( DPn); their intensities were enhanced at least two orders of magnitude stro nger than their neutral species. The in-plane CH bending modes at 1464 and 1375 cm(-1) are correspondingly strengthened with the chain length increase d, but the C=C stretching at 1541 cm(-1) is weakened and frequencies are no t changed. We provide an IR evidence for the first time that the bond order or bond alternations of the anions (soliton) are different from those of r adical anions (polaron) as well as neutral species.