A 3D view on free-floating, space-fixed and surface-bound para-phenylene nanofibres.

Nanofibres from para-hexaphenylene and functionalized quaterphenylene molecules are grown on mica surfaces and are thereafter transferred into solution, where they either freely rotate in water or are space-fixed in sucrose. From freely rotating aggregates highly anisotropic angular intensity distributions of emitted light for individual aggregates are determined. Luminescence is enhanced at the nanofibre tip as compared to the broad side by about an order of magnitude probably due to waveguiding along the long axis of the aggregates. For dense arrays of nanofibres on mica the increase of emitted intensity towards the substrate plane in the direction of the long axes of the nanofibres is smaller and it depends on the effective thickness of the nanofibre films. The difference between individual aggregates and aggregate arrays is interpreted in terms of light scattering at surface roughness inside the nanofibre film and on the border of the underlying mica substrate. Aggregates fixed in solution, with the help of femtosecond laser scanning microscopy, allow us to obtain two-photon absorption spectra of functionalized nanofibres between 720 and 900 nm as well as morphological features from three-dimensional optical images. The lateral resolution is about 400 nm.