We review the optical properties of the FMO complex as found by spectroscopic studies of the Qy band over the last two decades. This article emphasizes the different methods used, both experimental and theoretical, to elucidate the excitonic structure and dynamics of this pigment–protein complex.Electronic supplementary materialThe online version of this article (doi:10.1007/s11120-010-9540-1) contains supplementary material, which is available to authorized users.

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We report on adaptive feedback control of photoinduced barrierless isomerization of 1,1'-diethyl-2,2'-cyanine in solution. We compare the effect of different fitness parameters and show that optimal control of the absolute yield of isomerization (photoisomer concentration versus excitation photons) can be achieved, while the relative isomerization yield (photoisomer concentration versus number of relaxed excited-state molecules) is unaffected by adaptive feedback control. The temporal structure of the optimized excitation pulses allows one to draw clear mechanistic conclusions showing the critical importance of coherent nuclear motion for the control of isomerization.

Frequency domain spectra of the photosystem I (PS1) of Synechococcus elongatus are measured in a wide temperature range and explained in an exciton model based on the recently determined X-ray crystal structure. Using the known spatial positions and orientations of the chlorophylls (Chls) the dipole-dipole couplings between the chromophores are calculated. In contrast, the Chl Q y site energies are determined by a simultaneous fit of low-temperature absorption, linear dichroism, and circular dichroism spectra. The best fit is achieved by an evolutionary algorithm after assigning some chromophores to the red-most states. Furthermore, a microscopically founded homogeneous line width is included and the influence of inhomogeneous broadening is discussed. To confirm the quality of the resulting PS1 model, time-dependent fluorescence spectra are calculated, showing a good agreement with recent experimental results.