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STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS. XI. AB INITIO QUANTUM MECHANICAL CHARACTERIZATION OF THE ELECTRONIC STRUCTURE AND SPECTRA OF THE CHLOROPHYLLIDE a AND PHEOPHORBIDE a ANION RADICALS
Author(s) -
Petke J. D.,
Maggiora G. M.,
Shipman Lester L.,
Christoffersen Ralph E.
Publication year - 1982
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1982.tb04391.x
Subject(s) - chemistry , excited state , ab initio , molecule , pheophorbide a , absorption spectroscopy , ab initio quantum chemistry methods , density functional theory , ion , spectral line , resonance (particle physics) , computational chemistry , atomic physics , organic chemistry , physics , photodynamic therapy , quantum mechanics , astronomy
Ab initio configuration interaction wavefunctions and energies are reported for the ground and low‐lying excited doublet states of the anion radicals of ethyl chlorophyllide a (Et‐Chl a ‐ ) and ethyl pheophorbide a (Et‐Pheo a ‐ ), and are employed in a comparative analysis of their respective electronic absorption spectra. Strong similarities exist between the first five computed excited states of both molecules, providing no distinguishing features in the electronic absorption spectra below 20000 cm ‐ . Their ground state charge and spin density distributions are also very similar, and there is negligible spin density predicted on the magnesium atom in Et‐Chl a ‐ . The Soret bands of both molecules are predicted to arise from intense transitions to several closely‐spaced higher excited states, and the calculations indicate that there are significant differences in the number and composition of these states in the two molecules. It is suggested that these differences may provide a means of distinguishing between the two molecules using resonance Raman spectroscopy.