Isolated Hierarchical\nSuperstructures with Highly\nOriented P3HT Nanofibers

The preparation of supramolecular\nmesoscale structures\nwith high\nintrinsic order and orientation based on π-conjugated systems\nis of fundamental interest for studying their photophysical characteristics\nas well as for potential applications in (nano)photonics. However,\nthe preparation, isolation and transfer of individual structures to\nsubstrates without compromising their structural integrity is challenging.\nHere we report on the controlled formation of hierarchical superstructures\nbased on poly(3-hexylthiophene) (P3HT) comprising highly ordered and\noriented P3HT nanofibers with lengths of up to 20 μm via a two-step\nself-assembly process. In the first step, we prepare defined supramolecular\nribbons of <i>N</i>,<i>N</i>′-1,4-phenylenebis[4-pyridinecarboxamide].\nIn the second step, these ribbons act as efficient nucleation sites\nfor the transcrystallization of P3HT into μm-long nanofibers\nfrom solution. The resulting shish-kebab-like superstructures can\nbe purified and deposited on substrates without compromising their\nstructural integrity. The densely packed and well-arranged P3HT nanofibers\nwithin the isolated superstructures feature a high orientational order\nparameter close to one up to a distance of 15 μm away from the\ninitial nucleation sites. A systematic variation of photoluminescence\nspectra along the P3HT nanofibers in isolated superstructures indicates\nan increasing defect density toward the nanofiber end due to fractionation\nduring growth. We anticipate that these findings can be transferred\nto designing and realizing superstructures as components for nanophotonic\ndevices or light-harvesting antennae.