Abstract
Cycloaddition reactions have widely been used for surface functionalization of single walled carbon nanotubes (SWNTs). Here, 1,3-dipolar cycloaddition (1,3-DC) of two new pyridinium ylides, generated in-situ via the addition of triethylamine (NEt3) to the Kröhnke salts N-(4-methyl sodium benzene sulfonate)-pyridinium bromide and N-(4-nitrobenzyl)-pyridinium bromide, to SWNTs under microwave conditions are assessed both theoretically using PM3 (RHF) type calculations and experimentally. Evidence of covalent surface modification is provided by FTIR, UV–vis–NIR and resonance Raman spectroscopy. Solubility of the modified SWNTs increases when compared to as-received SWNTs. Quantification of surface groups is performed via TGA-MS and XPS. 1,3-DC of pyridinium ylides with smaller HOMO–LUMO energy gap is found to be more selective to large diameter SWNTs. Theoretically predicted smaller energy gaps between HOMOylides and LUMO(8,8) SWNT suggest that the charges are probably transferred from pyridinium ylides to SWNTs indicating HOMOylide–LUMO(8,8) SWNT controlled 1,3-DC. Regioselectivity of second ylide addition as addendum to ylide–SWNT adduct is also discussed.
Highlights
Carbon nanotubes (CNTs) have gained increasingly more scientific attention in nanoscience due to their exceptional electrical, M.K
We have shown that pyridinium ylides generated from simple Kröhnke salts undergo a 1,3-DC to single walled carbon nanotubes (SWNTs) to afford indolizine functionalized fluorescent SWNTs [5]
HOMOeLUMO energies of corresponding ylides and (8,8) SWNT segments were estimated via semi-empirical PM3 method at the level of restricted HartreeeFock (RHF) approach [25]
Summary
Carbon nanotubes (CNTs) have gained increasingly more scientific attention in nanoscience due to their exceptional electrical, M.K. Covalent surface modification of CNTs enhances the solubility and processability of them together with offering possible reactive functional side groups for further applications and separation [3e8]. Functionalized SWNTs showed one pyrrolidine ring correspond to about 95 carbon atoms of the SWNT and solubility values closer to 50 mg mLÀ1 in chloroform. Microwave induced functionalization of carbon nanotubes has been described showing that 1,3-DC of nitrile imines to SWNT sidewall under microwave conditions was faster than conventional heating [18]. Brunetti et al reported the microwave-assisted rapid cycloaddition to pristine nanotubes in solvent free conditions using octyl substituted aziridines [19]. It was shown that the microwave assisted cycloaddition of aziridines were much more efficient than the classical thermal conditions for azomethine ylides [6]
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