Influence of weak vibrational-electronic couplings on 2D electronic spectra and inter-site coherence in weakly coupled photosynthetic complexes.
Coherence oscillations measured in two-dimensional (2D) electronic spectra of pigment-protein complexes may have electronic, vibrational, or mixed-character vibronic origins, which depend on the degree of electronic-vibrational mixing. Oscillations from intrapigment vibrations can obscure the inter-site coherence lifetime of interest in elucidating the mechanisms of energy transfer in photosynthetic light-harvesting. Huang-Rhys factors (S) for low-frequency vibrations in Chlorophyll and Bacteriochlorophyll are quite small (S ≤ 0.05), so it is often assumed that these vibrations influence neither 2D spectra nor inter-site coherence dynamics. In this work, we explore the influence of S within this range on the oscillatory signatures in simulated 2D spectra of a pigment heterodimer. To visualize the inter-site coherence dynamics underlying the 2D spectra, we introduce a formalism which we call the "site-probe response." By comparing the calculated 2D spectra with the site-probe response, we show that an on-resonance vibration with Huang-Rhys factor as small as S = 0.005 and the most strongly coupled off-resonance vibrations (S = 0.05) give rise to long-lived, purely vibrational coherences at 77 K. We moreover calculate the correlation between optical pump interactions and subsequent entanglement between sites, as measured by the concurrence. At 77 K, greater long-lived inter-site coherence and entanglement appear with increasing S. This dependence all but vanishes at physiological temperature, as environmentally induced fluctuations destroy the vibronic mixing.
Department of Chemistry, University of California, Berkeley, California 94720, USA.
Daniele M
DM
Monahan
Department of Chemistry, University of California, Berkeley, California 94720, USA.
Lukas
L
Whaley-Mayda
Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki 444-8585, Japan.
Akihito
A
Ishizaki
Department of Chemistry, University of California, Berkeley, California 94720, USA.
Graham R
GR
Fleming
D003198:Computer Simulation; D019281:Dimerization; D005583:Fourier Analysis; D008956:Models, Chemical; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D013057:Spectrum Analysis; D014732:Vibration
D045322:Photosynthetic Reaction Center Complex Proteins