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Photodehalogenation of 9,10-Dichloroanthracene Induced by Electron Transfer Fluorescence Quenching with Primary and Tertiary Amines in Acetonitrile and n-Hexane. Salt Effect on Photodechlorination Process

Mac M.

Polish Journal of Chemistry

2003

Vol. 77 / nr 4

427-439

Quenching of 9,10-dichloroanthracene (DCA) fluorescence by primary or tertiary amines in acetonitrile solution results in formation of DCAradical anions, amine radical cations and triplet DCA, which were observed by nanosecond flash photolysis. In n-hexane, only the triplet-triplet absorption of DCA is observed. Rate constants of back electron transfer from the solvent separated radical ion pair (SSRIP), kbet, were calculated from the quantum yields of charge separation and triplet state formation by assuming a rate of 5_108 s-1 for ion separation from the SSRIP. The rate constants kbet follow the trends expected from the electron transfer theory (inverted Marcus region). Proton transfer from radical cation of primary amine to the radical anion of DCA, occurring in the contact radical ion pair (CRIP) has been found to be the decisive step for photodehalogenation in n-hexane. Importance of the heavy atom effect has been discussed on the basis of photophysical scheme, describing the processes occurring in the CRIP (SSRIP). It has been found, that lithium perchlorate catalyses the photodechlorination of DCA in acetonitrile solution, due to acceleration of the charge separation and retardation of the recombination of formed radical ion pair.