in the ground state. The PR also makes an appearance in certain analytic theories of exciton transport in organic photovoltaic materials. For example, in a polymer with n repeat units, a simple analytic theory predicts that the effective Huang-Rys parameter (or linear exciton-phonon coupling constant) should be S(n) = S(1)/PR where S(1) is the Huang-Rys parameter for the monomer unit. An example is poly(p-phenylene vinylene) or PPV, which is the electroluminescent chromophore in one of the first organic light-emitting diodes fashioned from a polymeric material. Excited states of a six-unit PPV polymer [(PV) 6 Ph] are considered in Table . Although these states have been computed using a many-body wave function method, they are characterized in Table using the descriptors introduced above, with indices A and B corresponding to PV monomer units. CT indices Ω A→B are arranged in the form of a matrix Ω that is depicted as a grayscale heat map.