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STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS—VII. AB INITIO QUANTUM MECHANICAL CHARACTERIZATION OF THE ELECTRONIC STRUCTURE AND SPECTRA OF CHLOROPHYLLIDE a AND BACTERIOCHLOROPHYLLIDE a CATION RADICALS
Author(s) -
Petke J. D.,
Maggiora Gerald M.,
Shipman Lester L.,
Christoffersen Ralph E.
Publication year - 1980
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.1751-1097.1980.tb03714.x
Subject(s) - chemistry , excited state , ab initio , ground state , absorption spectroscopy , spectral line , wave function , absorption (acoustics) , ab initio quantum chemistry methods , radical , molecular electronic transition , atomic physics , physics , molecule , quantum mechanics , organic chemistry , acoustics
Abstract— Ab initio configuration interaction wavefunctions and energies are reported for 29 doublet states and three quartet states of the cation radicals of ethyl chlorophyllide a (Et‐Chl a + ) and ethyl bacteriochlorophyllide a (Et‐BChl a + ). In Et‐Chl a. + I the lowest excited doublet state D 1 is estimated to lie 5220 cm ‐1 above the ground state D 0 , with a negligibly small D 1 ← D 0 transition probability. The lowest quartet state, Q 1 , is estimated to lie 7980 cm ‐1 above D 1 . The absorption spectrum up to 20,000cm ‐1 is shown to consist primarily of numerous low‐intensity ‘background’ transitions, with transitions to D 5 and D 11 accounting for the observed peaks at 12,200cm ‐1 and 17,500cm ‐1 , respectively. The large intense band at 25,000cm ‐1 is due primarily to transitions to D 22 and D 23 , with numerous lower‐intensity transitions to neighboring states. In Et‐BChl a. + D 1 is estimated to lie 7112 cm‐ 1 above D 0 , and Q, is approximately 5725 cm ‐1 above D. A pair of states, D 3 and D 5 , account for the absorption at 11,000 cm ‐1 , while another pair of states, D 13 and D 14 , are associated with the broad, weak absorption near 20,000 cm ‐1 . The two prominent intense peaks at 23,700 cm ‐1 and 27,700 cm ‐1 are assigned to D 23 and D 28 , respectively, while the shoulder located at 25,500cm ‐1 is attributed to transitions to D 24 and D 26 . As in Et‐Chl at, numerous background transitions are found throughout the spectrum. The π spin density distribution in D 0 of both molecules is similar, with spin density found predominantly on the α‐carbon atoms. In both systems, approximately 65% of the π spin density in D 1 is found on the methine carbon atoms, with the remainder found largely on the nitrogen atoms.