Wavelength Modulation of Defect Photoluminescence from Locally Functionalized Single-Walled Carbon Nanotubes Using Heterocycle-Substituted Aryldiazonium Salts

Local chemical functionalization of single-walled carbon nanotubes has been developed for defect introduction to produce locally functionalized SWCNTs (lf-SWCNTs). Compared with the original PL of unmodified SWCNTs, lf-SWCNTs exhibit defect photoluminescence (PL) in near-infrared (NIR) regions with higher quantum yields and red-shifted wavelengths. Recently, using a few chemical functionalization approaches, considerably red-shifted defect PL (E11*− PL, >1250 nm) of lf-SWCNTs was observed in contrast to typical defect PL (E11* PL, ∼1150 nm), although the E11*− PL wavelength modulation approaches have yet been unexplored. In this study, we synthesized aryldiazonium salts containing heterocycle substituents at the ortho position for the lf-SWCNT synthesis. The resultant lf-SWCNTs selectively emitted E11*− PL and its wavelength variation was observed by modifying the heterocycle structures. Additionally, wavelength switching of E11*− PL was observed through pH variations, in which the protonation/deprotonation of the ortho-pyridine in the lf-SWCNTs induced large spectral shifts in E11*− PL compared to the observed shifts in earlier para-substituent design systems employing E11* PL. The developed E11*− PL wavelength modulation method based on the functionalized molecule designs for the lf-SWCNT synthesis would provide novel NIR PL nanomaterials relevant to advanced bio/medical and telecom application fields.