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1 August 2002 Photodynamics of the Bacteriochlorophyll–Carotenoid System. 2. Influence of Central Metal, Solvent and β-Carotene on Photobleaching of Bacteriochlorophyll Derivatives
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Abstract

Bacteriochlorophyll (BChl) derivatives (with central Mg replaced by metal “M”) ([M]-BChl with M = 2H, Mg, Zn, Pd, Cu) have been investigated for their photodynamic capacity and stability toward photodegradation in organic solvents and aqueous micellar solution. A protocol has been developed for screening new sensitizers. BChl and [Zn]-BChl are efficient sensitizers, but they are also quickly degraded by the reactive oxygen species (ROS) produced by autosensitization, as well as by hetero-sensitization with 174-methyl-132-demethoxycarbonyl-pheophorbide a (MPP). Photostable [Cu]-BChl is a poor sensitizer, whereas [Pd]-BChl and bacteriopheophytin a are not only very efficient sensitizers but are also very stable toward ROS. β-Carotene is no efficient physical quencher of ROS in the system; rather, it acts as a photochemical quencher that competes with [M]-BChl and undergoes photooxygenation at high rates. Photolability seems to depend on the pigment oxidation potential and, in parallel, on the presence of central metals preferring coordination numbers higher than 4, whereas photodynamic capacity depends on long excited state lifetimes of the pigment or efficient intersystem crossing (or both).

Joanna Fiedor, Leszek Fiedor, Nina Kammhuber, Avigdor Scherz, and Hugo Scheer "Photodynamics of the Bacteriochlorophyll–Carotenoid System. 2. Influence of Central Metal, Solvent and β-Carotene on Photobleaching of Bacteriochlorophyll Derivatives," Photochemistry and Photobiology 76(2), 145-152, (1 August 2002). https://doi.org/10.1562/0031-8655(2002)076<0145:POTBCS>2.0.CO;2
Received: 14 December 2001; Accepted: 1 May 2002; Published: 1 August 2002
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