(Invited) Different Fluorescent Modifications of Carbon Nanotubes with Aromatic Reactants

Abstract

Covalent functionalization of single-wall carbon nanotubes (SWCNTs) can produce a stable material with electronic and optical properties enhanced purposely as compare to original species. In the present report we describe a new category of reactions between photoexcited aromatic compounds and SWCNTs, creating different fluorescent trapping states in SWCNTs. The reactions take place in aqueous suspensions of SWCNTs with small addition of soluble or even very-slightly soluble organic aromatic compounds excited by UV light. The reaction rate depends on the aromatic compound structure and proportional to its concentration, and in some cases, as with aniline or iodoaniline, these strong spectral sidebands appear within one minute. Total SWCNT photoluminescence intensity can be increased by a factor as large as 5. Shifted emission bands and the trapping nature of them may be interesting for a variety of optical and electronic applications.Most notably, in most cases of these photochemical reactions, the emission spectra of altered SWCNTs become different, never observed previously, upon removal of molecular oxygen from the solution, thus indicating different chemical products of the reactions. For instance, for (6,5) SWCNTs, treatment in oxygen presence gives a new emission band red-shifted by 160 meV from the pristine position, which is similar to many previously studied reactions starting with oxygen doping. However, same UV treatments after dissolved molecular oxygen removal will lead to two new emission bands red-shifted by 140 and 270 meV, growing with different rate under UV illumination. Variance spectroscopy shows the presence of individual “multicolor” nanotubes with three distinct emission bands, original plus two shifted. The reaction demonstrates new possibilities for creation different trapping states on individual nanotubes, and opens new options for tuning electronic and optical properties of nanotubes for possible applications.