Tuning the interaction between carbon nanotubes and dipole switches: the influence of the change of the nanotube-spiropyran distance.

The non-covalent functionalization of carbon nanotubes with spiropyran molecules, serving as optically addressable dipole switches, is reported. Two kinds of pyrene-spiropyran-based dyads with spacers of different lengths resulting in different switch-tube distances were investigated. While both surfactants were able to form stable carbon nanotube suspensions, the different distances between the switch and the tube affected both of the components' optical properties. In the case of the shorter spacer, the nanotubes' luminescence as well as the merocyanine absorption band were red-shifted and furthermore, the rate of the merocyanine → spiropyran thermal back isomerization was decreased.