Optical Dephasing in the Light-Harvesting Complex II: A Two-Pulse Photon Echo Study

Time-resolved and integrated two-pulse photon echo signals were measured at 5 K in the wavelength range from 640 to 690 nm (with an increment of 5 nm) in samples of solubilized light-harvesting complex II (LHC II) from spinach. Furthermore, the dephasing time was determined at 680 nm in the temperature range 5 ≤ T ≤ 300 K. The following results and conclusions were gathered from these experiments:  (a) the photon echo intensity as a function of the temporal distance between both excitation pulses exhibits a nonexponential decay; (b) data analysis on the basis of a superposition of several dephasing processes leads to three characteristic dephasing time domains (A, B, and C) with markedly different wavelength dependencies of dephasing time and relative amplitude, T2A ≤ 1.7 ps from 640 to 675 nm, T2B = 4−13 ps over the whole wavelength region of 640 to 690 nm, and T2C ≥ 40 ps from 675 to 685 nm; (c) the dephasing times T2A and T2B are attributed to the kinetics of excitation energy transfer and to multiexci...