Localized optical excitations and two-exciton spectroscopy of phenylacetylene dendrjmers

The one- and two-exciton manifolds of conjugated dendrimers possessing fractal geometries are studied using the Frenkel exciton model. Two-photon spectra can be used to determine both the magnitude and the sign of short-range coupling among segments. Self-similarity and the high degree of symmetry make it possible to compute the one-exciton states and the optical response with reduced numerical effort that scales linearly rather than exponentially with the number of generations. The third-order optical response and exciton scattering matrix are expressed in compact forms using irreducible representation of optical excitations, totally avoiding the expensive explicit calculation of two-exciton eigenstates.