  We report the functionalization of carbon nanotubes with two azobenzene-based
chromophores with large internal dipole moments and opposite dipole
orientations. The molecules are attached to the nanotubes non-covalently via a
pyrene tether. A combination of characterization techniques shows uniform
molecular coverage on the nanotubes, with minimal aggregation of excess
chromophores on the substrate. The large on/off ratios and the sub-threshold
swings of the nanotube-based field-effect transistors (FETs) are preserved
after functionalization, and different shifts in threshold voltage are observed
for each chromophore. Ab initio calculations verify the properties of the
synthesized chromophores and indicate very small charge transfer, confirming a
strong, non-covalent functionalization.
