The pheophorbide-a DAB dendrimer P4 in solution: MD-simulations based studies of exciton states

The conformations and collective electronic excitations of the dissolved butanediamine dendrimer to which four pheophorbide-a molecules have been covalently linked are discussed theoretically. Room-temperature MD simulations of the chromophore complex in methanol are carried out, and the exciton states formed along the nuclear trajectories are computed. The fluctuating exciton levels and respective oscillator strengths give rise to an inhomogeneously broadened absorbance which is also presented. The computations are based on an improved exciton model which takes into account the excitonic coupling by ab initio transition charges and considers a shift in chromophore transition energies by inter chromophore charge density couplings.