Selective Protonation of Unbounded Sodium Cholates for Reversible Blue-Shift Absorption Spectra of Single-Chirality Single-Walled Carbon Nanotube in Solution

In contradiction to the long-standing optical depletion of single-walled carbon nanotubes (SWCNT) by acid doping, this work reports the blue-shifted and optical density-increased S11 (the first Van Hove singularity transition) peak absorption spectra of single-chirality (6,5) SWCNT dispersed in specific surfactant compositions such as 1% SDS (sodium dodecyl sulfate) /1% SC (sodium cholate) and 2% SDS/0.5% SC, which were caused by addition of acid. These anomalous optical changes can be reversed by adding base, and they are discussed on the basis of surfactant arrangements on SWCNT sidewalls, which arose from the selective protonation of unbounded SC to shift the thermodynamic equilibrium of SC adsorbed SWCNT to the desorption of SC from SWCNT surface. The spectroscopic interpretation obeys the dipole moment transition related energy level variation and oscillator strength change.