Uniform Continuous and Segmented Nanofibers Containing a -Conjugated Oligo(p-phenylene ethynylene) Core via "Living" Crystallization-Driven Self-Assembly: Importance of Oligo(p-phenylene ethynylene) Chain Length

pi-Conjugated nanofibers of controlled length and composition show promising potential applications from biomedicine to optoelectronics. However, efficient preparation of uniform nanofibers from pi-conjugated polymers with precise control over length and composition poses an outstanding challenge. Herein, we report the synthesis of a suite of block copolymers (BCPs) containing pi- conjugated crystalline oligo(p-phenylene ethynylene) (OPE) segments of different chain lengths and a poly(N-isopropylacrylamide) (PNIPAM) or a poly(2-vinylpyridine) (P2VP) block (OPE5-b-PNIPAM(47) , OPE7-b-PNIPAM(47), OPE9-b-PNIPAM(47), and OPE9-b-P2VP(56); subscripts indicate the number of repeat units). The length of OPE segment significantly affected the self-assembly OPE-based BCPs. OPE9-b-PNIPAM(47) chains were molecularly dissolved in ethanol. Although OPE7-b-PNIPAM(47) formed fiber-like micelles of uniform width initially, these micelles were not frozen at room temperature (23 degrees C), leading to the transformation from regular fiber-like micelles to irregular spherical aggregates upon aging for 7 days. Polydisperse fiber-like micelles of uniform width with kinetically frozen morphology at 23 degrees C were formed for OPE9-b-PNIPAM(47) in ethanol by a direct heating-cooling cycle. The results were supported by the observations in dynamic light scattering, UV-vis, and fluorescence measurements, which indicated the resistance of OPE-based micelles toward micelle dissolution increased with the rising of OPE chain length. By the self-seeding approach of living crystallization-driven self-assembly (CDSA), uniform continuous micelles of controlled length (similar to 40 nm-1.2 mu m) consisting of an OPE core and PNIPAM or P2VP shell can be obtained although micelles of OPE9-b-PNIPAM(47) and OPE9-bP2VP(56) exhibited different resistance toward micelle dissolution. Significantly, a series of uniform segmented OPE-based fiber-like comicelles and their hybrid nanostructures with excellent length and composition tunability can be achieved by the seeded growth approach of living CDSA. Overall, we provided a facile access to the fabrication of OPE-based nanofibers with precise control over their length and composition along with instructive information about the influence of structure of it-conjugated block on the CDSA of BCPs containing a crystalline it-conjugated segment.