Noncovalent attachment of CdSe quantum dots to single wall carbon nanotubes

Noncovalent attachment of CdSe quantum dots (QDs) to single wall carbon nanotubes (SWNTs) through an intermediary 1-pyrenebutyric acid N-hydroxy-succinimide ester (PBASE) molecule has been performed. The ligand exchange process from trioctylphosphine oxide (TOPO)-capped CdSe to the 4-aminothiophenol (ATP) ligand is supported by solvent solubility, NMR spectroscopy, and IR spectroscopy, with an estimated molecular efficiency > 50:1. Noncovalent coupling of the PBASE molecule causes a redshift in the SWNT interband electronic transitions, consistent with a π–π interaction that promotes electron delocalization. TEM analysis after chemical coupling of the CdSe–ATP QDs to the PBASE–SWNTs shows an abundant coverage of QDs along the SWNT bundles. Raman spectra (1.96 eV excitation) of PBASE–SWNTs and the noncovalent product demonstrate that each of the major Raman modes (RBM, D-, G-, or G′-bands) is unaltered by the noncovalent interaction with PBASE or attachment of CdSe QDs, indicating that the structural integrity of the SWNTs is maintained. However, upshifts in the Raman modes are observed, the largest being for the G′-band, indicating charge transfer between the SWNTs and attached CdSe QDs.