Complexation between Rhodamine 101 and single-walled carbon nanotubes indicative of solvent-nanotube interaction strength

Single walled carbon nanotubes (SWNT) have excellent mechanical, electrical, and thermal properties but their manipulation is hampered since they do not readily dissolve in most organic solvents. In particular, the interaction of nanotubes and organics is not universally understood. Using UV-vis absorption and visible fluorescence spectroscopy we show that, in chloroform, the laser dye Rhodamine 101 (R101) forms ground-state complexes with CoMoCAT SWNT, but that in N,N-dimethylacetamide (DMA), no such complexes exist. We suggest a strong interaction between zwitterionic R101 and nanotube in chloroform where the interaction between nanotube and solvent is weak. We describe how this interaction is solvent specific and how R101 and its analogs may be used as an indicator of strength of interaction of solvent. We also suggest that charge transfer/dipole stabilization should be investigated further in the search for more stable and long lasting SWNT dispersions for improved nanotube manipulation.