Angular distribution of luminescence from quasi single crystalline organic nanofibers

Light emitting para-hexaphenylene nanofibers (needles) are grown on mica and transferred to an aqueous solution. By inserting them into or onto micro-pipettes we measure the distribution of emitted bright blue light as a function of azimuthal angle phi perpendicular to the long nanotiber axis. The luminescence from the top and bottom of the fibers was found to be about an order of magnitude more intense than the luminescence from the sides. This cosine squared angular distribution reflects the quasi single crystalline nature of the fibers which consist of an array of well ordered dipole emitters. Needles free floating in water allow us to also analyze the angular distribution of light along the long needle axis. An enhancement of nanofiber tip luminescence as compared to the broad-side luminescence by about half an order of magnitude is observed. This is attributed to waveguiding along the long axis of the aggregates. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.