On the relation of protein dynamics and exciton relaxation in pigment-protein complexes: An estimation of the spectral density and a theory for the calculation of optical spectra

A theory for calculating time- and frequency-domain optical spectra of pigment-protein complexes is presented using a density matrix approach. Non-Markovian effects in the exciton-vibrational coupling are included. A correlation function is deduced from the simulation of 1.6 K fluorescence line narrowing spectra of a monomer pigment-protein complex (B777), and then used to calculate fluorescence line narrowing spectra of a dimer complex (B820). A vibrational sideband of an excitonic transition is obtained, a distinct non-Markovian feature, and agrees well with experiment on B820 complexes. The theory and the above correlation function are used elsewhere to make predictions and compare with data on time-domain pump-probe spectra and frequency-domain linear absorption, circular dichroism and fluorescence spectra of Photosystem II reaction centers. (C) 2002 American Institute of Physics.