Optical excitations in diphenylacetylene based dendrimers studied by a coupled exciton model with off-diagonal disorder

A phenomenological coupled exciton model is proposed in order to characteri ze optical excitations in extended dendrimers. An onsite exciton state is a ssigned at each phenyl rings and a nearest neighbor hopping integral which obeys the Gaussian distribution is considered between the exciton states. T he decreasing optical excitation energy with respect to the dendrimer size indicates the presence of exciton funnels along the backbone of the dendrim ers. Therefore, the extended dendrimers can work as artificial fractal ante nna systems which capture energy of light. Dynamics of an exciton is also i nvestigated by solving time development of a wavefunction of optical excita tions. It is shown that a damping term with a certain magnitude is necessar y in order that optical excitations captured at the outer edge of the super molecule move to the central areas of the molecule.