Towards General Guidelines for Aligned, Nanoscale Assemblies of Hairy-Rod Polyfluorene

This account highlights recent progress towards understanding the complex hierarchical levels of solid-state structure in a prototypical helical hairy-rod polyfluorene, poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (or PF2/6). This branched-side-chain containing polyfluorene undergoes a systematic intermolecular self-assembly and liquid-crystalline phase behavior in combination with uniaxial and biaxial alignment. The latter processes yield full three-dimensional orientation of the crystallites and polymer chains. Also reviewed are the impact of the molecular structure and phase behavior on surface morphology, anisotropic film formation, and, ultimately, the overall impact of these physical attributes on optical constants. This particular polyfluorene also represents a model system for demonstrating the applicability of mean-field theory in detailing the self-organization of aligned hairy-rod block-copolymer systems. These results of PF2/6 are compared to those of other archetypical -conjugated hairy-rod polymers. General guidelines of how molecular weight influences nanostructure, phase behavior, alignment, and surface morphology are given.