Photodriven electron transfer in triad molecules: a two-step charge recombination reaction

Journal Article · Tue Dec 09 23:00:00 EST 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00285a025· OSTI ID:7202412

Gust, D; Moore, T A; Makings, L R; Liddell, P A; Nemeth, G A; Moore, A L

Excitation of carotenoid-porphyrin-quinone (C-P-Q) triad molecules initiates a two-step electron transfer to yield a final charge separated state of the form C/sup .+/-P-Q/sup .-/. This state has a very long lifetime in solution (10/sup -7/-10/sup -6/ s), and the nature of the ultimate charge recombination reaction has not previously been investigated. Nanosecond transient absorption spectroscopic studies have been performed on a series of such triad molecules wherein the nature of the linkages joining the porphyrin to the quinone and/or carotenoid moieties is varied systematically. The results reveal that charge recombination in C/sup .+/-P-Q/sup .-/ does not occur in a single step but rather via an unusual two-step electron transfer involving an intermediate C-P/sup .+/-Q/sup .-/ species. The temperature dependence is consistent with the formation of C-P/sup .+/-Q/sup .-/ via a thermally activated process, and measurements over the range 221-296 K yield ..delta..H double dagger = 2.7 kcal/mol and ..delta..S double dagger = -20 cal/(deg x mol). The transient absorption measurements also reveal that the quantum yield of the C/sup .+/-P-Q/sup .-/ state is a function of three electron transfer rate constants and that it can therefore be maximized by controlling the ratios of these rate constants to one another and to the rates of other pathways which depopulate the relevant excited states.

• Research Organization: Arizona State Univ., Tempe
• OSTI ID: 7202412
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:25; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ABSORPTION SPECTROSCOPY
AROMATICS
CARBOXYLIC ACIDS
CAROTENOIDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
DATA
EFFICIENCY
ELECTRON TRANSFER
ENERGY LEVELS
EXCITED STATES
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROCARBONS
INFORMATION
KINETICS
LIFETIME
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
PHYSICAL PROPERTIES
PIGMENTS
PORPHYRINS
QUANTUM EFFICIENCY
QUINONES
REACTION INTERMEDIATES
REACTION KINETICS
SPECTROSCOPY
TEMPERATURE DEPENDENCE
TERPENES
THERMODYNAMIC PROPERTIES