Disordered Exciton Analysis of Linear and Nonlinear Absorption Spectra of Antenna Bacteriochlorophyll Aggregates: LH2−Only Mutant Chromatophores of Rhodobacter sphaeroides at 8 K under Spectrally Selective Excitation

Abstract

The objective of this work is two-fold. First, the effects of static diagonal disorder on the linear and nonlinear absorption spectra of excitons in circular molecular aggregates are studied by computer modeling. Second, it is demonstrated that this simplified model successfully reproduces the main features of both the ground-state absorption and initial pump−probe absorption difference spectra of LH2 antenna proteins from photosynthetic bacteria measured upon spectrally selective population of excitons at low temperature. Of the usual first-order approximations in the Frenkel exciton theory, our model exploits only two: the two-state and the zero electron−vibrational coupling approximations. In our model, the molecules of the aggregate are allowed to have different site energies. The coupling between all aggregate molecules is taken into account. An important difference between our study and previous work is that the exciton state selective spectra are calculated corresponding to the recently performed ...