Fluorescent chromophore functionalized single-wall carbon nanotubes with minimal alteration to their characteristic one-dimensional electronic states

Soluble, chromophore-functionalized SWNTs (SWNT-NA) have been synthesized via covalent bonding with minimal alteration to the characteristic one-dimensional electronic states of SWNTs. The key step in the molecular design includes incorporating a naphthalimide fluorescent moiety onto SWNTs via the amidation of oxidatively etched SWNTs, where the solubility of the product is brought about by N-octadecyl groups that are attached to naphthalimide. SWNT-NA can be fabricated into in-plane aligned thin films by using the Langmuir–Blodgett (LB) method. The surface pressure–area isotherm is characterized by a steep rise in pressure as well as by a high collapse pressure (up to 40 mN m−1), which indicates that SWNT-NA possesses a good surface spreading property at the air/water interface. The polarized UV-Vis-NIR absorption spectrum of an SWNT-NA LB film (40 layers) by vertical dipping indicates a dichroic ratio of 2.42 at 1340 nm and AFM images show that tubes are preferentially aligned in the dipping direction. Electronic properties of the product were investigated by absorption and luminescence (steady-state and transient) spectroscopy. Fluorescence from the naphthalimide moiety is found to be significantly quenched when bonded to the SWNT backbones.