title: Dynamic localization of electronic excitation in photosynthetic complexes revealed with chiral two-dimensional spectroscopy.
abstract: Time-resolved ultrafast optical probes of chiral dynamics provide a new window allowing us to explore how interactions with such structured environments drive electronic dynamics. Incorporating optical activity into time-resolved spectroscopies has proven challenging because of the small signal and large achiral background. Here we demonstrate that two-dimensional electronic spectroscopy can be adapted to detect chiral signals and that these signals reveal how excitations delocalize and contract following excitation. We dynamically probe the evolution of chiral electronic structure in the light-harvesting complex 2 of purple bacteria following photoexcitation by creating a chiral two-dimensional mapping. The dynamics of the chiral two-dimensional signal directly reports on changes in the degree of delocalization of the excitonic states following photoexcitation. The mechanism of energy transfer in this system may enhance transfer probability because of the coherent coupling among chromophores while suppressing fluorescence that arises from populating delocalized states. This generally applicable spectroscopy will provide an incisive tool to probe ultrafast transient molecular fluctuations that are obscured in non-chiral experiments.
authors: Department of Chemistry, Institute for Biophysical Dynamics, James Franck Institute, University of Chicago, 929 East 57th Street, Chicago, Illinois 60637, USA.
authors: Andrew F
authors: AF
authors: Fidler
authors: Department of Chemistry, Institute for Biophysical Dynamics, James Franck Institute, University of Chicago, 929 East 57th Street, Chicago, Illinois 60637, USA.
authors: Ved P
authors: VP
authors: Singh
authors: Program in the Biophysical Sciences, Institute for Biophysical Dynamics, University of Chicago, 929 East 57th Street, Chicago, Illinois 60637, USA.
authors: Phillip D
authors: PD
authors: Long
authors: Program in the Biophysical Sciences, Institute for Biophysical Dynamics, University of Chicago, 929 East 57th Street, Chicago, Illinois 60637, USA.
authors: Peter D
authors: PD
authors: Dahlberg
authors: Department of Chemistry, Institute for Biophysical Dynamics, James Franck Institute, University of Chicago, 929 East 57th Street, Chicago, Illinois 60637, USA.
authors: Gregory S
authors: GS
authors: Engel
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D010788:Photosynthesis; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013057:Spectrum Analysis / Q000379:methods
chemical_list: C081521:B800-850 light-harvesting complex, bacteria; D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes