Contact and solvent-separated geminate radical ion pairs in electron-transfer photochemistry

Journal Article · Thu Mar 07 00:00:00 EST 1991 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100158a031· OSTI ID:5530157

Gould, I R; Young, R H; Moody, R E; Farid, S ^[1]

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1. Eastman Kodak Company, Rochester, NY (USA)

The two primary intermediates that play a major role in determining the efficiencies of bimolecular photoinduced electron-transfer reactions are the contact (A{sup {sm bullet}{minus}}D{sup {sm bullet}+}) and the solvent-separated (A{sup {sm bullet}{minus}}(S)D{sup {sm bullet}+}) radical ion pairs, CRIP and SSRIP, respectively. These two species are distinguished by differences in electronic coupling, which is much smaller for the SSRIP compared to the CRIP, and solvation, which is much larger for the SSRIP compared to the CRIP. The present work addresses the quantitative aspects of these and other factors that influence the rates of energy-wasting return electron transfer within the ion-pair intermediates. The electron acceptor tetracyanoanthracene (TCA) forms ground-state charge-transfer complexes with alkyl-substituted benzene donors. By a change of the excitation wavelength and/or donor concentration, either the free TCA or the CT complex can be excited. Quenching of free {sup 1}TCA{sup *} by the alkylbenzene donors that have low oxidation potentials, such as pentamethylbenzene and hexamethylbenzene, in acetonitrile solution leads to the direct formation of geminate SSRIP. Excitation of the corresponding charge-transfer complexes leads to the formation of geminate CRIP. Rates of return electron transfer within the two types of ion pair are determined from quantum yields for formation of free radical ions pairs depend upon the reaction exothermicity in a manner consistent with the Marcus inverted region.

• OSTI ID: 5530157
• Journal Information: Journal of Physical Chemistry; (USA), Vol. 95:5; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ANTHRACENE
ELECTRON TRANSFER
ABSORPTION SPECTROSCOPY
ACETONITRILE
DATA ANALYSIS
EXPERIMENTAL DATA
ION PAIRS
PHOTOCHEMISTRY
AROMATICS
CHEMISTRY
CONDENSED AROMATICS
DATA
HYDROCARBONS
INFORMATION
NITRILES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
SPECTROSCOPY
400500* - Photochemistry