J-Aggregate Behavior in Poly-3-hexylthiophene Nanofibers

Nanofibers (NFs) of poly-3-hexylthiophene (P3HT) assembled in toluene exhibit single-chain J-aggregate character. Absorption, fluorescence emission, and Raman spectroscopy of dilute NF dispersions demonstrate that P3HT chains possess long-range intrachain order (planarity) that suppresses interchain exciton coupling. We demonstrate that a delicate interplay exists between intrachain order and interchain coupling as revealed through the emission 0-0/0-1 vibronic intensity ratios. Lowering temperature and application of pressure induces minor perturbations in the NF packing, which destroys J-aggregate character and partially restores predominant interchain interactions (i.e., H-aggregate behavior). The fact that pi-pi stacked P3HT chains can exhibit both H- and J-aggregate behavior opens up new possibilities for controlling electronic coupling through noncovalent stacking interactions.