title: Heterogeneous exciton dynamics revealed by two-dimensional optical spectroscopy.
abstract: We show that optical two-dimensional (2D) spectroscopy can recover ultrafast heterogeneous dynamics of closely spaced delocalized exciton states from a molecular exciton manifold characterized by a single absorption band. The complete experimental third-order nonlinear optical response from room-temperature J-aggregates in liquid phase is reproduced for the first time with self-consistent Frenkel exciton theory combined with modified Redfield theory. We show that exciton relaxation between the exciton states and nuclear-motion-induced exchange-narrowed energy fluctuations of individual delocalized exciton states can be distinguished because these two processes lead to a distinctively different evolution of the absolute 2D spectrum. Our technique also allows recovery of the variation of the exciton relaxation rates as well as the degree of exciton delocalization across the absorption band.
authors.affiliation: Department of Chemistry and QB3 Institute University of California, Berkeley, Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-1460, USA.
authors.forename: Igor
authors.initials: I
authors.lastname: Stiopkin
authors.forename: Tobias
authors.initials: T
authors.lastname: Brixner
authors.forename: Mino
authors.initials: M
authors.lastname: Yang
authors.forename: Graham R
authors.initials: GR
authors.lastname: Fleming
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D005456:Fluorescent Dyes / Q000737:chemistry*; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry; D013057:Spectrum Analysis / Q000379:methods*; D013816:Thermodynamics
chemical_list: D005456:Fluorescent Dyes; D045342:Light-Harvesting Protein Complexes