Mixed Quantum Classical Simulations of Electronic Excitation Energy Transfer and Related Optical Spectra: Supramolecular Pheophorbide-a Complexes in Solution

Abstract

Photoinduced electronic excitation energy transfer in chromophore complexes is studied by utilizing a mixed quantum classical methodology. In order to describe the electronic excitations a Frenkel–exciton model is used and treated quantum mechanically while all nuclear coordinates are described classically, finally by carrying out room-temperature MD simulations. The theory is applied to chromophore complexes dissolved in ethanol, with the single complex formed by a butanediamine dendrimer to which pheophorbide–a molecules are covalently linked. The improved exciton model introduced for the description of the chromophore complex accounts for charge distributions in the chromophores electronic ground and excited state. It also includes a correct description of the excitonic coupling among different chromophores by introducing atomic centered transition charges. Excitation energy transfer, linear absorbance, and time and frequency resolved luminescence are computed and a good agreement with measured data is found.