DENSITY-FUNCTIONAL STUDY ON THE STRUCTURES AND VIBRATIONAL-SPECTRA OFTHE RADICAL-ANION AND CATION OF BIPHENYL

Density functional theory using the 6-31G basis set and two non-local exchange-correlation functionals (B-YLP and B3-LYP) has been applied to the calculations of the structures and vibrational spectra of the r adical anion and cation, of biphenyl. The B3-LYP dihedral angles betwe en the two phenyl rings are 5.8 degrees and 19.5 degrees for the radic al anion and cation, respectively. Upon ionization, structural changes occur in the direction from benzenoid to quinoid. The unsealed vibrat ional frequencies calculated at the B-YLP/6-31G level are mostly in a greement with the frequencies in the Raman spectra of the radical anio n and cation of the normal and perdeuterated species reported in the l iterature. The calculations predict that both the radical anion and ca tion give rise to a very strong infrared band, and that this band aris es from a mode in which the benzenoid-to-quinoid deformation occurs ou t of phase in the two phenyl rings. (C) 1998 Elsevier Science B.V.