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)).

Long-term improvements to photoluminescence and dispersion stability by flowing SDS-SWNT suspensions through microfluidic channels.

Shearing single-walled carbon nanotubes (SWNTs) coated with sodium dodecyl sulfate in microfluidic channels significantly increases the photoluminescence (PL) intensity and dispersion stability of SWNTs. The PL quantum yield (QY) of SWNTs improves by a factor of 3 for initially bright suspensions; on the other hand, SWNT QYs in a "poor" suspension improve by 2 orders of magnitude. In both cases, the QYs of the sheared suspensions are approximately 1%. The increases in PL intensity persist for months and are most prominent in larger diameter SWNTs. These improvements are attributed to surfactant reorganization rather than disaggregation of SWNTs bundles or shear-induced alignment. The results also highlight potential opportunities to eliminate discrepancies in the PL intensity of different suspensions and further improve the PL of SWNTs by tailoring the surfactant structure around SWNTs.