Photoreactions and photoelectrochemical effects in supported multilayer assemblies. Mechanisms of interfacial reactions involving reactive supports, metalloporphyrin surface films, and solutions
- Univ. of North Carolina, Chapel Hill
An investigation of photoprocesses occurring in molecular assemblies consisting of monolayers and multilayers of water-insoluble surfactant tin porphyrins supported on tin oxide optically transparent electrodes and other potentially reactive surfaces in contact with aqueous solutions containing potentially reducing solutes is reported. In each case the light-absorbing species is the surface-bound tin porphyrin. While irradiation of glass- or quartz-supported monolayers and multilayers of the tin porphyrins in contact with aqueous reductants such as amines, hydroquinone, of p-dimethoxybenzene leads to net photoreduction and photoaddition processes for the porphyrin to yield chlorin- and isobacteriochlorin-type products, the net reactivity of the porphyrin is totally quenched or sharply reduced when it is contained in assemblies in contact with n-type SnO/sub 2/, PtO/sub 2/, or platinum films. Several experiments were carried out which demonstrate that excited states of the porphyrin are not strongly quenched by the various supports; thus in this case the major effect of the surface is to intercept reduced species formed in the interfacial photoreaction of the porphyrins with the reducing solute. The SnO/sub 2/-supported porphyrin assemblies can serve as photoanodes for the oxidation of solution reductants; in typical experiments slides having areas ca. 3 cm/sup 2/ give photocurrents in the approx.300-nA range with a quantum efficiency of 0.3%. The low quantum efficiency observed is comparable to that measured for interfacial or homogeneous-solution reduction of the tin porphyrin by the same solutes; thus the net reactivity of the porphyrin in solution and at interfaces appears relatively comparable in these cases and is probably limited by net physical quenching of the porphyrin and triplet by the solute reductant.
- DOE Contract Number:
- AS05-81ER10815
- OSTI ID:
- 5613440
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 104:23; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400500* -- Photochemistry
ABSORPTION SPECTRA
CARBOXYLIC ACIDS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COMPLEXES
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PLATINUM COMPOUNDS
PLATINUM OXIDES
PORPHYRINS
REACTION KINETICS
REDOX PROCESS
REPROCESSING
SEPARATION PROCESSES
SPECTRA
TIN COMPLEXES
TIN COMPOUNDS
TIN OXIDES
TRANSITION ELEMENT COMPOUNDS