Coherent exciton pulse propagation in disordered transmission lines

Coherent exciton transport is investigated in the presence of several different forms of disorder. We consider linear dye assemblies capable of functioning as exciton transmission lines and focus on the degrading effects of static disorder on exciton coherence in several scenarios, whether introduced through lattice imperfections or in the optical response of the constituent dyes. Impurities are ascribed to sections of consecutive dyes in the line in which incident ballistic excitons can propagate in and scatter, reflecting and transmitting as conditions permit. Single- and few-site impurities are first considered, and then static disorder is introduced in the scattering sections in two ways: as random transition energies or as altered transfer couplings between dyes. These cases are compared, and some intriguing dynamics result: reflection (attenuation) is more significant with disorder in the transfer couplings, some conditions have an even-odd pattern in reflections, and midband exciton encounters with this type of disorder acquire no phase alteration. Lastly, these two cases of static disorder are compared with the dynamic noise arising from molecular vibrations, and both are found to be comparably modest. With applications in mind, several phenomenological and quantitative relations for coherent exciton transport are obtained as simple functions of the introduced disorder.