Journal of Physical Chemistry A, Vol.101, No.3, 255-258, 1997
A Resonance Raman Spectroelectrochemical Study of the Zn(II) Tetraphenylchlorin Anion
Zinc(II) tetraphenylchlorin (ZnTPC) and its pi-anion radical have been studied by UV-vis absorption and resonance Raman (RR) spectroscopies. Analyses of the RR spectra were aided by data for the pyrrole-d(8), meso-C-13, and phenyl-d(20) isotopomers. Upon formation of the anion, significant frequency shifts are observed in skeletal vibrational modes, while substituent modes remain essentially unshifted. Both frequency upshifts (nu(37), nu(10), and nu(19)) and downshifts (nu(2), nu(11), and nu(3)) occur for the C-alpha C-m and CbetaCbeta stretching modes in the pi-anion. Modes involving significant CalphaCbeta stretching motion, nu(4) and nu(41), upshift in the anion spectrum. The pattern of vibrational frequency shifts for the anion of ZnTPC is similar to what is observed for the anion of vanadyl tetraphenylporphyrin ((VO)TPP) despite the reduction of a pyrrole ring in TPC. This resemblance is due to the Jahn-Teller distortion in (VO)TPP-, which gives its singly occupied molecular orbital the same bonding pattern as in ZnTPC-.
Keywords:NORMAL-MODE ANALYSIS;ZINC(II) OCTAETHYLPORPHYRIN;VIBRATIONAL CHARACTERISTICS;CHLOROPHYLL MODELS;EXCITED-STATES;FORCE-FIELD;FREE-BASE;SPECTRA;TETRAPHENYLPORPHINE;SPECTROSCOPY