title: Symmetry-Breaking Charge Transfer of Visible Light Absorbing Systems: Zinc Dipyrrins.
abstract: Zinc dipyrrin complexes with two identical dipyrrin ligands absorb strongly at 450-550 nm and exhibit high fluorescence quantum yields in nonpolar solvents (e.g., 0.16-0.66 in cyclohexane) and weak to nonexistent emission in polar solvents (i.e., <10-3, in acetonitrile). The low quantum efficiencies in polar solvents are attributed to the formation of a nonemissive symmetry-breaking charge transfer (SBCT) state, which is not formed in nonpolar solvents. Analysis using ultrafast spectroscopy shows that in polar solvents the singlet excited state relaxes to the SBCT state in 1.0-5.5 ps and then decays via recombination to the triplet or ground states in 0.9-3.3 ns. In the weakly polar solvent toluene, the equilibrium between a localized excited state and the charge transfer state is established in 11-22 ps.
authors.affiliation: Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Cong
authors.initials: C
authors.lastname: Trinh
authors.affiliation: Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Kent
authors.initials: K
authors.lastname: Kirlikovali
authors.affiliation: Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Saptaparna
authors.initials: S
authors.lastname: Das
authors.affiliation: California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States.
authors.forename: Maraia E
authors.initials: ME
authors.lastname: Ener
authors.affiliation: California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States.
authors.forename: Harry B
authors.initials: HB
authors.lastname: Gray
authors.affiliation: Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Peter
authors.initials: P
authors.lastname: Djurovich
authors.affiliation: Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Bradforth
authors.affiliation: Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Thompson