Excitation-induced polarization decay in the plant light-harvesting complex LHCII

The energy migration dynamics of the major light-harvesting antenna (LHCII) of plants was experimentally studied in the chlorophyll Qy region (630–700 nm). Using polarized transient absorption (TA) spectroscopy at 77 K we obtain information unaccessible to conventional isotropic TA on the energy transfer dynamics between isoenergetic Chlorophylls (Chls). The data are simultaneously analyzed with a target analysis and interpreted in the context of the exciton model for LHCII. The transients at 652 and 662 nm excitation show that the memory of polarization is completely lost with a (3.3–5.0 ps)−1 rate over the whole Qy range, which is attributed to equilibration within monomers and between the three subunits of the LHCII trimer.