FIGURE 1.

Model of the ground- and excited-state potential surfaces of the B850 ring pigment in the surrounding protein. The potential surface is shown along the conformational coordinate of the protein. In both the ground and excited states, the protein can be in two conformational states denoted 1 and 2, separated by an energy barrier. In the absence of light, excitation transitions between the conformational states are spontaneous and occur in the ground state ( and ). When the pigment is excited, additional light-induced transitions (with rates and ) occur either in the excited state or in the initial moments after the excitation relaxation.