Spin density distribution of the excited triplet state of bacteriochlorophylls. Pulsed ENDOR and DFT studies.
The photoexcited triplet states of bacteriochlorophyll a and bacteriochlorophyll b have been investigated by ENDOR spectroscopy at 34 GHz in frozen solution and by DFT calculations. The spin density distributions in the triplet state were found to be similar for bacteriochlorophyll a and bacteriochlorophyll b except for the presence of spin density on carbon 8(1) in bacteriochlorophyll b. Judging from a comparison with ENDOR experiments for the radical cation and anion, the triplet state in bacteriochlorophylls cannot be explained as being a simple HOMO-->LUMO excitation of Gouterman orbitals. Rather, it must be described as a mixture of HOMO-->LUMO and HOMO-1-->LUMO excitations for a satisfactory explanation of the observed hyperfine interactions. The observed hyperfine couplings in the ENDOR spectra were assigned, and the field dependence of the signals was found to be fully compatible with the orientation of the zero-field splitting tensor determined from magnetophotoselection studies.
Marchanka
Aliaksandr
A
Max Planck Institut fur Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mulheim an der Ruhr, Germany.
Lubitz
Wolfgang
W
van Gastel
Maurice
M
D001429:Bacteriochlorophylls / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory
D001429:Bacteriochlorophylls