Post-Chemical Modification of Doped Sites of Locally Functionalized Single-Walled Carbon Nanotubes for Multistep Photoluminescence Modulation

Abstract

Locally functionalized single-walled carbon nanotubes (lf-SWNTs) have local defects on the sp2 carbon networks of the tube structures through chemical modification using ozonization and diazonium chemistry.[1-8] They emit redshifted photoluminescence (PL) with high efficiency compared to original PL (E 11) of pristine SWNTs. The newly generated PL (E 11*) of lf-SWNTs shows PL wavelength variation and selective wavelength shifts based on the modified molecule structures. For example, protonation of amino groups[1] and molecular recognition[6, 7] at the doped sites effectively induced wavelength shifting of E 11* PL. Such external stimuli responsiveness, therefore, is expected to develop advanced sensing and imaging materials and optical devices using the near infrared (NIR) PL functions. In this study, the doped sites are newly designed as a chemical reaction platform for versatile modulation of the E 11* PL.[8] We employ imine chemistry at the doped sites of lf-SWNTs. Imine bond is formed by a condensation reaction between aldehyde and amine groups. The dynamic bonding feature also allows reversible bond formation and exchange reactions of the bound molecules. Firstly, aromatic aldehyde-modified lf-SWNTs (lf-SWNTs-CHO) were synthesized. Chemical reactions for imine formation using lf-SWNTs-CHO were examined by mixing various aniline derivatives. The lf-SWNTs-CHO showed a PL peak at 1140 nm (E 11*) which was redshifted than the E 11 PL (980 nm). When p-methylaniline, p-bromoaniline or p-nitroaniline was mixed with the lf-SWNTs-CHO, wavelength shifts of the E 11* PL occurred, which provided different wavelength shift values Dl (= λ(E 11*) − λ(E 11)) of 154, 163, and 165 nm, respectively. The result indicates that the observed wavelength shifts of E 11* depend on the chemical structures of the bound aniline derivatives in the imine bond. Moreover, additional chemical reactions including exchange reactions of the bound aniline derivatives and the Kabachnik-Fields reaction realized further wavelength changes in the E 11* PL of the lf-SWNTs. Thus, the present approach using post-modification of the doped sites achieves multistep PL modulation based on the local chemical reactions.