title: Steric guided change of electron transfer mechanism in benzene.
abstract: In fluorescence quenching study via electron transfer (ET), the quenching rate constant (k(q)) values generally decrease with lowering of quencher concentration, since smaller concentration of quencher always leads to a red shift in the donor-acceptor (D-A) distance in ET [M. Tachiya, S. Murata, J. Phys. Chem. 96 (1992) 8441; S. Murata, M. Tachiya, J. Phys. Chem. 100 (1996) 4064; L. Burel, M. Mastafavi, S. Murata, M. Tachiya, J. Phys. Chem. A 103 (1999) 5882]. However, while doing a comparative study with different carbazole (CZ) derivatives-1,4-dicyanobenzene (DCB) systems in benzene (BZ), we observed a deviation from that normal behaviour. It was found that for all of them with lower quencher (DCB) concentration, k(q) values actually increase instead of the expected reduction. Exceptionally, for simple CZ (C12H9N) with decrease in concentration of DCB, k(q) values can even reach the order of energy transfer (10(11) s(-1)). Interestingly, it is not observed when toluene (TL) or xylene (XY) is used as solvent. To explain this unique observation, a sandwich type of molecular structure is predicted, where BZ sliding in between CZ and DCB brings them closer enough, imparting more through bond character to CZ-DCB interaction and hence a higher rate of ET (k(q)) is observed [L. Burel, M. Mastafavi, S. Murata, M. Tachiya, J. Phys. Chem. A. 103 (1999) 5882].
authors.affiliation: Department of Chemistry, Serampore College, Serampore, Hooghly 712204, India.
authors.forename: Suchandra
authors.initials: S
authors.lastname: Chatterjee
authors.forename: Samita
authors.initials: S
authors.lastname: Basu
authors.forename: Nandita
authors.initials: N
authors.lastname: Ghosh
authors.forename: Manas
authors.initials: M
authors.lastname: Chakrabarty
mesh_terms: D001554:Benzene / Q000737:chemistry*; D004583:Electrons; D004735:Energy Transfer; D006859:Hydrogen / Q000737:chemistry; D007700:Kinetics; D008968:Molecular Conformation; D015394:Molecular Structure; D012997:Solvents; D013053:Spectrophotometry / Q000379:methods*; D013237:Stereoisomerism
chemical_list: D012997:Solvents; D006859:Hydrogen; D001554:Benzene