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Intramolecular interaction of synthetic chlorophyll heterodyads with different π-skeletons

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Abstract

Two heterodyads were prepared from the chemical modification of naturally occurring (bacterio)chlorophyll-a and composed of a chlorin π-skeleton linked to a porphyrin or bacteriochlorin π-system. Zinc methyl pyropheophorbide-a, one of the chlorophyll-a derivatives, was covalently linked with its 17,18-didehydrogenated species (zinc methyl pyroprotopheophorbide-a) or its trans-7,8-dihydrogenated analog (zinc methyl pyrobacteriopheophorbide-a as one of the bacteriochlorophyll-a derivatives) through ethylene glycol diester at their 17-propionate residues. In benzene, the central zinc atoms of the synthetic conjugates were coordinated by two methanol molecules which were hydrogen-bonded with the 13-keto-carbonyl groups in a dyad molecule. The methanol locked, y-axis aligned, and slipped cofacial conformers showed two apparent Qy bands at longer wavelengths than those of the composite zinc complex monomers. The red-shifted Qy bands are ascribable to the exciton coupling of the two different π-systems in the folded heterodyad conformers. The synthetic heterodyads could be models of chlorophyll-a/c dimers in the light-harvesting antennas of chromophytes including fucoxanthin–chlorophyll proteins in diatoms and also chlorophyll-a species interacting with bacteriochlorophyll-a or g species in the charge-separating reaction centers of green sulfur bacteria or heliobacteria, respectively.

Graphical abstract: Intramolecular interaction of synthetic chlorophyll heterodyads with different π-skeletons

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Article information


Submitted
06 Sep 2019
Accepted
13 Jan 2020
First published
14 Jan 2020

Photochem. Photobiol. Sci., 2020, Advance Article
Article type
Paper

Intramolecular interaction of synthetic chlorophyll heterodyads with different π-skeletons

H. Tamiaki, K. Fukai and S. Nakamura, Photochem. Photobiol. Sci., 2020, Advance Article , DOI: 10.1039/C9PP00373H

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