Isolated Hierarchical Superstructures with Highly Oriented P3HT Nanofibers

The preparation of supramolecular mesoscale structures with high intrinsic order and orientation based on pi-conjugated systems is of fundamental interest for studying their photophysical characteristics as well as for potential applications in (nano)photonics. However, the preparation, isolation and transfer of individual structures to substrates without compromising their structural integrity is challenging. Here we report on the controlled formation of hierarchical superstructures based on poly(3-hexylthiophene) (P3HT) comprising highly ordered and oriented P3HT nanofibers with lengths of up to 20 mu m via a two-step self-assembly process. In the first step, we prepare defined supramolecular ribbons of N,N '-1,4-phenylenebis[4-pyridinecarboxamide]. In the second step, these ribbons act as efficient nucleation sites for the transcrystallization of P3HT into mu m-long nanofibers from solution. The resulting shish-kebab-like superstructures can be purified and deposited on substrates without compromising their structural integrity. The densely packed and well-arranged P3HT nanofibers within the isolated superstructures feature a high orientational order parameter close to one up to a distance of 15 mu m away from the initial nucleation sites. A systematic variation of photoluminescence spectra along the P3HT nanofibers in isolated superstructures indicates an increasing defect density toward the nanofiber end due to fractionation during growth. We anticipate that these findings can be transferred to designing and realizing superstructures as components for nanophotonic devices or light-harvesting antennae.