Colour-coded photoluminescence and chemiluminescence of fluorene polymer-based organic nanowires in random and organised arrangements

Organic nanowires based on a fluorene homopolymer and a copolymer, i.e., poly(9,9- dioctylfluorene), F8, and poly(9,9-dioctylfluorene-co- benzothiadiazole), F8BT, respectively, were synthesised by solution assisted wetting of porous anodic alumina templates. Nanowires ranged between 3 μm and 50 μm in length, and were ca. 200 nm in diameter. Absorption and photoluminescence studies of F8BT nanowires yielded spectra characteristic of the parent material. By contrast, the well resolved spectra obtained for F8 nanowires indicated that, during synthesis, a fraction of the molecules within the wires underwent intra-chain re-orientation from the more random molecular conformations of the glassy phase to the more planar extended molecular conformation of the β-phase. Importantly, both F8 and F8BT nanowires exhibited a distinct emission anisotropy, consistent with internal alignment of the emissive polymer chains along the long axes of the wires. This property was exploited by forming nanowire crossbar structures in which, by selecting either luminescence wavelength or polarisation state, spatial confinement and colour tuning of polarised light emission could be readily achieved. Finally, nanowire chemiluminescence was demonstrated. Characteristic blue and green-yellow luminescence was observed for F8 and F8BT wires, respectively, confirming that these novel nanostructures may act as nanoscale chemiluminescent light sources.