Excitonic versus electronic couplings in molecular assemblies: The importance of non-nearest neighbor interactions.

We demonstrate that for a range of phenylene- and thiophene-based conjugated polymers of practical relevance for optoelectronic applications, exciton couplings in one-dimensional stacks deviate significantly from the nearest neighbor approximation. Instead, long-range interactions with non-nearest neighbors have to be included, which become increasingly important with growing oligomer size. While the exciton coupling vanishes for infinitely long ideal polymer chains and provides a sensitive measure of the actual conjugation length, the electronic coupling mediating charge transport shows rapid convergence with molecular size. Similar results have been obtained for very different molecular backbones, thus highlighting the general character of these findings.