Near-Infrared Photochemistry Harnesses Excitons for Selective Guanine Functionalization of Single-Wall Carbon...

The optical and electronic properties of single-wall carbon nanotubes (SWCNTs) coated by ssDNA strands can be tailored by covalent bonding of guanine nucleobases in the ssDNA to the nanotube side wall. This reaction is induced by the presence of singlet molecular oxygen, which to date has been generated by irradiation of organic dye sensitizers added to the SWCNT suspension. We demonstrate that this guanine functionalization reaction can proceed without organic sensitizers by resonantly irradiating the nanotubes with near-infrared (NIR) light. The excited nanotubes transfer energy to ground-state O₂ to form singlet O₂, which reacts with guanine nucleobases at the excited nanotube to induce covalent functionalization. The nanotubes thus serve as both sensitizer and reaction substrate. Because functionalization shifts the SWCNT absorption peaks to longer wavelengths, samples drift out of resonance with the irradiation light during irradiation. To compensate, we demonstrate that (6,5) SWCNTs can be more efficiently guanine functionalized using sequential irradiation first at 980 nm and then at 1030 nm. Resonant E₂₂ excitation is also effective, as shown by using 590 nm irradiation to functionalize (6,4) and (6,5) SWCNTs. This self-sensitized method yields dye-free guanine-functionalized nanotubes and, most significantly, enables selective functionalization of specific SWCNT structures in unsorted samples.