Template synthesis of highly oriented polyfluorene nanotube arrays

Polyfluorene nanotubes are synthesized by solution assisted wetting of porous anodic alumina membranes. Well aligned arrays of close packed (∼10⁹ tubes/cm_-2) discrete nanotubes are obtained. Individual tubes have diameters of ∼260 nm and wall thicknesses of ∼50 nm. X-ray diffraction measurements carried out on nanotube arrays embedded in host templates indicate a polymer chain alignment along the long axes of the template pores and, as a result, along the long axes of the nanotubes themselves. Optical spectroscopic studies of mats of nanotubes on glass substrates yield well resolved emission spectra reflecting a narrowed distribution of emitting chain segments with increased effective conjugation lengths. The data indicate intrachain reorientation of the amorphous random poly(9,9-dioctylfluorene-2,7-diy1) molecular conformation to the more planar (low energy) extended 2₁ helical β-phase conformation within the tubes. Raman spectra acquired for template embedded tubes are also consistent with β-phase formation. Finally, polarization resolved photoluminescence data demonstrate a pronounced axial orientation of the emissive β-phase chains within the tubes.