Exciton Dynamics in LH1 and LH2 of Rhodopseudomonas Acidophila and Rhodobium Marinum Probed with Accumulated Photon Echo and Pump−Probe Measurements

Abstract

Exciton dynamics in the B850 and B875 bands of isolated complexes of Rhodopseudomonas acidophila (strain 10 050 and 7050) and in the B875 band of isolated complexes of Rhodobium marinum were investigated by means of accumulated photon echo and pump-probe techniques at different temperatures and wavelengths. For all three systems, the optical dephasing time T 2 was found to be very similar: at 4.2 K, T 2 is 116 and 106 ps for the B850 and B875 bands of Rhodopseudomonas acidophila, respectively, and 93 ps for the B875 band of Rhodobium marinum. The rapid dephasing, which displays glassy character, is a consequence of the strong pigment-protein interactions that arise through the rather short distances in these complexes. The observed dephasing time at the red edge of the B850 band of Rhodopseudomonas acidophila at 4.2 K reveals the existence of spectral diffusion in this system. From the wavelength dependence of the pump-probe signal in the B875 LH1 band of Rhodopseudomonas acidophila at 3 K it is concluded that energy transfer between energetically inequivalent LH1 rings occurs on a time scale of several tens picoseconds, while energy trapping takes place in about 250 ps.

The Optical Dynamics of Excitons in Cylindrical J-Aggregates

“…A 16 cm focal length lens was employed to focus and cross the two collinear beams in the sample, which was located in an Oxford Research Instruments Variox variable-temperature optical cryostat. Pumpprobe and accumulated photon echo experiments were performed in the wavelength range of 588-610 nm in the same way as described in ref 13.…”

“…The use of stochastic excitation allows discrimination between both contributions because the APE signals grow with the field correlation of the pulses, while the pump-probe signal grows with the much broader intensity correlation. 13 Unequivocal identification of the signals can be made by scrambling the optical phase difference between consecutive pulse pairs. In that case, no accumulation of the signal can occur, leaving only the pumpprobe signal.…”

“…1 Much theoretical and experimental work has been done on these circular structures. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] Especially, the efficiency of the excitonic energy transport in these antenna systems has attracted much attention. [16][17][18][19][20][21][22][23][24] Studies on the optical dynamics of excitons in these natural aggregates provide inspiration for the search for artificial antenna systems.…”

Optical dephasing in red fluorescent protein

“…In other words, in the general expression G 0 ¼ 1 2 p ð1=t fl þ 1=t ET Þ; the second term 1/t ET vanishes for these excitation wavelengths. A T 1.3 power law, which was observed for many organic amorphous systems [19][20][21][22] and a few biological complexes [23,24,[26][27][28][29], suggests that two-level systems (TLSs) [20,30,31] are responsible for the dephasing in DsRed.…”

Single complex line shapes of the B850 band of LH2

“…Different experiments support different delocalization lengths, 3,4,39,40 and no consensus exists on the type and degree of disorder in the Hamiltonian. 34 B850 was the subject of various nonlinear spectroscopic experiments, which provide information on the long-lived lowest excitonic state 5,10 and the relaxation time scale of the higher excitonic states. 9,12,13,23 However, the subensembles involved in different experimental measurements are not always simple to identify.…”