Solvatochromic shifts of single-walled carbon nanotubes in nonpolar microenvironments.

Single-walled carbon nanotubes (SWNTs) are encapsulated with microenvironments of nonpolar solvent, providing a new method to measure the photophysical properties of nanotubes in environments with known properties. Photoluminescence (PL) and absorbance spectra of SWNTs show solvatochromic shifts in 16 nonpolar solvents, which are proportional to the solvent induction polarization. The shifts in the emission energies (DeltaE(11)) range from approximately 25 to 100 meV and the smallest diameter SWNTs have the largest shifts. The PL intensity of SWNTs is very sensitive to changes in polarity. For example, SWNTs encapsulated with chloroform (epsilon approximately 5) show substantial reductions in intensity. The solvatochromic shifts of SWNTs were used to determine the relationship between the longitudinal polarizability, band gap and radius, alpha(11,||) proportional to 1/(R(2)E(11)(3)).