title: Quantum yields lower than unity in photo- induced dissociative electron transfers: the reductive cleavage of carbon tetrachloride.
abstract: It has been shown recently that the electrochemical reduction of carbon tetrachloride in N,N'-dimethylformamide follows a mechanism in which electron transfer and bond cleavage are concerted. We report here results concerning photoinduced electron transfer from the singlet excited state of two aromatic molecules, 2-ethyl-9,10-dimethoxyanthracene and perylene, to CCl4 , which is characterised by a quantum yield of complete quenching fragmentation ranging from 0.7 to 0.8. It is shown that a quantum yield below unity is compatible with a dissociative mechanism and arises from partitioning of the system at the intersection of the product- and ground-state potential energy surfaces. This phenomenon predominates over back electron transfer from the clustered fragments state. The photoinduced reductive cleavage of CCl4 thus provides a clear illustration of the recent theoretical prediction, that photoinduced dissociative electron transfers are not necessarily endowed with a unity quantum yield. This offers an opportunity to estimate the magnitude of the electronic matrix element that couples the fragmented product state and the ground reactant state.
authors.affiliation: Laboratoire d'Electrochimie Moléculaire, Unité Mixte de Recherche Université, CNRS No 7591 Université de Paris 7, Denis Diderot 2 place Jussieu, 75251 Paris Cedex 05, France.
authors.forename: L
authors.initials: L
authors.lastname: Pause
authors.forename: M
authors.initials: M
authors.lastname: Robert
authors.forename: J M
authors.initials: JM
authors.lastname: Savéant
mesh_terms: D000873:Anthracenes / Q000737:chemistry; D002251:Carbon Tetrachloride / Q000737:chemistry*; D004126:Dimethylformamide / Q000737:chemistry; D004579:Electron Transport; D007834:Lasers; D010084:Oxidation-Reduction; D010569:Perylene / Q000737:chemistry; D010782:Photolysis; D011789:Quantum Theory
chemical_list: C512082:2-ethyl-9,10-dimethoxyanthracene; D000873:Anthracenes; D010569:Perylene; D004126:Dimethylformamide; D002251:Carbon Tetrachloride