Photosensitized singlet oxygen production upon two-photon excitation of single-walled carbon nanotubes and their functionalized analogues

Single-walled carbon nanotubes (SWNTs) functionalized with -COOH (along with some sulfonation and nitration) and/or modified with chitosan were prepared and tested for their singlet oxygen ( ¹O ₂) production. The emission from ¹O ₂ observed upon SWNT irradiation at 532 nm was due to a two-photon process, while 1O2 production via excitation at 355 nm occurred through a conventional one-photon pathway. The relative quantum yield of ¹O ₂ production at excitation wavelength of 532 nm was found to be 0.00, 0.07-0.13, and 0.24-0.53 for highly functionalized, partially functionalized, and nonfunctionalized SWNT samples, respectively. The nanotube-mediated generation of ¹O ₂ may find applications in both targeted destruction of tumor cells and selective degradation of drug molecules. Our research provides a practical approach to modulate the production of reactive oxygen species from SWNTs via surface functionalization/ modification.