Noncovalent Stable Functionalization Makes Carbon Nanotubes Hydrophilic and Biocompatible

Semiconducting single-wall carbon nanotubes possess an intrinsic photoluminescence in the near-infrared region beyond 900 nm, the NIR-II window of biological imaging. Here, we introduce a modular molecule for noncovalent nanotube functionalization which renders carbon nanotubes hydrophilic and fully biocompatible through a one-step process. We demonstrate through electron energy-loss spectroscopy (EELS) spectroscopy that the noncovalent functionalization mechanism relies on tight and extremely robust π–π stacking, which survives an exchange of the solvent as well as drying. Furthermore, the modularity of the molecule design allows for the introduction of functional units into the molecule itself to modify the optical properties of the carbon nanotube, for instance to augment its excitation window through an excitation energy transfer, facilitating the excitation of most carbon nanotube chiralities at one single wavelength.