title: Disorder-Induced Quantum Beats in Two-Dimensional Spectra of Excitonically Coupled Molecules.
abstract: Quantum superposition of molecular electronic states is very fragile because of thermal energy fluctuations and the static conformational disorder induced by the intimate surrounding of constituent molecules of the system. However, the nature of the long-lived quantum beats, observed in time-resolved spectra of molecular aggregates at physiological conditions, is still being debated. We present our study of the conditions when long-lived electronic quantum coherences originating from recently proposed inhomogeneous broadening mechanism are enhanced and reflected in the two-dimensional electronic spectra of the excitonically coupled molecular dimer. We show that depending on the amount of inhomogeneous broadening, the excitonically coupled molecular system can establish long-lived electronic coherences, caused by a disordered subensemble, for which the dephasing due to static energy disorder becomes significantly reduced. On the basis of these considerations, we present explanations for why the electronic or vibrational coherences were or were not observed in a range of recent experiments.
authors.affiliation: Department of Theoretical Physics, Faculty of Physics, Vilnius University , Sauletekio 9-III, 10222 Vilnius, Lithuania.|Center for Physical Sciences and Technology, Gostauto 9, 01108 Vilnius, Lithuania.
authors.forename: Vytautas
authors.initials: V
authors.lastname: Butkus
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Physical Biosciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Hui
authors.initials: H
authors.lastname: Dong
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Physical Biosciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Graham R
authors.initials: GR
authors.lastname: Fleming
authors.affiliation: Department of Theoretical Physics, Faculty of Physics, Vilnius University , Sauletekio 9-III, 10222 Vilnius, Lithuania.
authors.forename: Darius
authors.initials: D
authors.lastname: Abramavicius
authors.affiliation: Department of Theoretical Physics, Faculty of Physics, Vilnius University , Sauletekio 9-III, 10222 Vilnius, Lithuania.|Center for Physical Sciences and Technology, Gostauto 9, 01108 Vilnius, Lithuania.
authors.forename: Leonas
authors.initials: L
authors.lastname: Valkunas