Quantum chemical study of π–π stacking interactions of the bacteriochlorophyll dimer in the photosynthetic reaction center of Rhodobacter sphaeroides

Intermolecular π–π stacking interactions of the bacteriochlorophyll dimer in the photosynthetic reaction center of the purple bacterium Rhodobacter sphaeroides were analyzed by the second order Møller–Plesset perturbation method using the modified 6-31G*(0.25) basis set with diffuse d-polarization by Hobza and co-workers. MP2/6-31G*(0.25) calculations yield an intermolecular interaction energy of −21.50 kcal/mol for the bacteriochlorophyll dimer. Thus, the attractive nature of the π–π stacking interaction of the bacteriochlorophyll dimer in the photosynthetic reaction center from Rhodobacter sphaeroides is, for the first time, firmly established.