Interaction of triplet sensitizers with chlorophyll: Formation of singlet chlorophyll

Journal Article · Wed Mar 29 00:00:00 EST 1989 · Journal of the American Chemical Society; (USA)

DOI:https://doi.org/10.1021/ja00189a006· OSTI ID:5232550

Bohne, C; Scaiano, J C ^[1]

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1. National Research Council of Canada, Ottawa, Ontario (Canada)

The interaction of several triplet sensitizers with chlorophyll a (Chla) has been examined using laser techniques. For the carbonyl sensitizers (with triplet energies > 53 kcal/mol) it was possible to measure the quenching rate constants; these were systematically {>=} 10{sup 10} M{sup {minus}1} s{sup {minus}1}. In the cases of acetone, benzophenone, and p-methoxyacetophenone the quenching process leads to the formation of the fluorescent singlet state of Chla. For benzophenone (k{sub q} = 2.4 {times} 10{sup 10} M{sup {minus}1} s{sup {minus}1}) approximately 3% of the quenching events lead to the formation of excited Chla. Several sensitizers (decafluorobenzophenone, benzil, and fluorenone) do not induce Chla fluorescence (or do it very inefficiently) in spite of having triplet energies above the S{sub 1} level of Chla. In light of their results the most probable mechanism involves energy transfer from the triplet sensitizer to an upper triple state of Chla ({sup 3}Chla**) which can undergo reverse intersystem crossing to the singlet manifold of Chla and thus induce fluorescence. The inefficient sensitizers are those where electron transfer between the excited singlet of Chla or {sup 3}Chla** and ground-state sensitizers is energetically favorable, leading to rapid in-cage quenching of the initially formed excited states of Chla. Formation of radical-ion pair between the triplet sensitizer and Chla followed by the generation of singlet Chla in the recombination of the radical ions could not be completely discarded.

• OSTI ID: 5232550
• Journal Information: Journal of the American Chemical Society; (USA), Vol. 111:7; ISSN 0002-7863
• Country of Publication: United States
• Language: English

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14 SOLAR ENERGY
37 INORGANIC
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BENZOPHENONE
CHLOROPHYLL
FLUORESCENCE
TRIPLETS
ABSORPTION SPECTROSCOPY
CHEMICAL REACTION KINETICS
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RADIATIONLESS DECAY
RADICALS
THERMODYNAMICS
TRANSIENTS
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
DATA
DE-EXCITATION
ENERGY LEVELS
ENERGY TRANSFER
ENERGY-LEVEL TRANSITIONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
KETONES
KINETICS
LUMINESCENCE
MULTIPLETS
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHYTOCHROMES
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140505* - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)
400500 - Photochemistry