Two-photon mapping of local molecular orientations in hexaphenyl nanofibers

Two-photon microscopy is used to determine with a resolution of 0.7 mum the local orientations of hexaphenyl molecules in individual needle-shaped nanoaggregates, which possess submicron-widths and heights, whereas they extend to several hundred micrometers in a defined crystallographic direction along a mica surface. Polarized femtosecond laser light at two mutually perpendicular orientations excites luminescence in these nanofibers. From the ratio of polarized luminescence intensities two main orientation angles of the molecular long axes with respect to the long needle axes are revealed as a function of position on the needle. (C) 2004 Elsevier B.V. All rights reserved.