Resonance Raman, infrared, and normal coordinate analysis of free-base tetraphenylbacteriochlorin: A model for bacteriopheophytins
- Princeton Univ., NJ (United States)
Resonance Raman (RR) and FT-IR spectra are reported for free-base tetraphenylbacteriochlorin and its pyrrole-{sup 15}N{sub 4}, {beta}-D{sub 8}, meso-{sup 13}C{sub 4}, and phenyl-D{sub 20} isotopomers. A normal mode analysis is carried out in order to assign observed RR and IR modes, using a NiTPP-based force field, with bond-distance scaling of force constants and the introduction of long-range interaction constants. The modes correlate well with those of NiTPP, once due allowance is made for direct effects of pyrrole ring reduction: inequivalent C{sub {beta}}-C{sub {beta}} and C{sub {alpha}}-C{sub {beta}} bonds and extra C{sub {beta}}-H bending modes. Although the C{sub {alpha}}-C{sub m} and C{sub {alpha}}-N bonds of the 16-membered inner ring are not strictly equivalent, there is little tendency for mode localization with respect to these bonds. The absence of a central metal lowers the frequencies of C{sub {alpha}}-C{sub m} stretching and pyrrole translational modes. The RR enhancement pattern is quite different than for porphyrins. Totally symmetric modes dominate spectra in resonance with the Q{sub x} band, due to a larger transition moment than in porphyrins, while non-totally symmetric modes are strongly enhanced in the region of the close-lying B{sub x} and B{sub y} transitions, reflecting vibronic coupling between them. 38 refs., 11 figs., 7 tabs.
- DOE Contract Number:
- FG02-93ER14403
- OSTI ID:
- 501884
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 101, Issue 3; Other Information: PBD: 16 Jan 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
Resonance Raman studies and vibrational analysis of Ni(II) porphyrins
Synthesis, vibrational spectra, and normal mode analysis of nickel(II) 1,5-dihydroxy-1,5-dimethyloctaethylbacteriochlorin. A model for bacteriochlorophylls