Charge-transfer Excitons in Strongly Coupled Organic Semiconductors

The physics of organic semiconductor materials attracts enormous multidisciplinary interest due to emerging applications in optoelectronics. Their electronic properties depend sensitively upon supramolecular structure. A promising strategy to enhance carrier mobilities, for example, is to induce supramolecular order in configurationally disordered systems such as solution-processable conjugated polymers. Here, we investigate the fate of electronic excitations in sexithiophene nanostructures that demonstrate strong supramolecular excitonic coupling. Time-resolved and temperature-dependent photoluminescence measurements on one-dimensional sexithiophene lattices reveal intrinsic branching of photoexcitations to two distinct species: self-trapped excitons and dark charge-transfer excitons (CTX; ~ 5% yield), with radii spanning 2–3 sites. The signi?cant CTX yield results from the strong charge-transfer character of the Frenkel exciton band due to the large free exciton bandwidth (~ 400 meV) in these supramolular nanostructures.