Nanooptics using organic nanofibers

The possibility to separate nanofibers from each other by distances that are larger than the wavelength of the emitted light allows one to investigate in detail the influence of morphological changes in the nanometer-range on the optical properties. As an example we show in Fig. 9.1 spectra obtained from a single para-hexaphenylene (p6P) nanofiber (circles) and from an ensemble of p6P nanofibers (solid line). The spectrum from the single nanofiber has been obtained by illuminating the nanofiber inside a microscope with UV light and sampling the emitted light also inside the microscope with an optical fiber, connected to a miniature spectrometer. The well-separated spectral lines are due to a vibronic progression of the exciton emission (perpendicular lines on top of the graph). In the case of the single nanofiber spectrum the highest energy (0,0) band is not visible due to a cut-off filter in the microscope. Nevertheless, comparison with the spectra from the needle ensembles reveals that the light emission becomes more focussed to a narrow color range (namely 420±5 nm) if an individual nanoaggregate is considered. More extended spectroscopic measurements along a nanofiber show that the spectral width of this residual line depends on the morphology of the aggregate and that it becomes narrower if the nanofiber width decreases, e.g., at the tip of the nanofiber [1].