Structure Dependence of Photoluminescence Solvatochromic Energy Shifts Based on Exciton Localization in Locally Functionalized Single-Walled Carbon Nanotubes

Defect doping of single-walled carbon nanotubes (SWCNTs) by local chemical functionalization produces locally functionalized SWCNTs (lf-SWCNTs) that emit red-shifted and bright photoluminescence (PL) in near-infrared regions beyond 1000 nm (E11* PL) from localized excitons trapped at doped sites in the tubes. In this study, we use lf-SWCNTs with different doped sites such as proximal aryl-doped sites and oxygen-doped sites (ether-type and epoxide-type) showing largely red-shifted PL than typical E11* PL, which allow us to elucidate the structural effects on PL solvatochromism (via organic solvent injection) and reveal the excitonic property variations of the localized excitons. We correlate PL solvatochromic energy shifts of the lf-SWCNTs with solvent orientation polarization parameters. The proximal aryl-doped sites of bisaryl-modified lf-SWCNTs emit E112* PL (∼1253 nm), and the observed solvatochromic energy shifts appeared between those of the E11 PL (∼980 nm) and E11* PL (∼1125 nm). The epoxide-type doped sites of the oxygen-doped lf-SWCNTs emit E11*b PL (∼1250 nm), with almost no solvatochromism; this was totally different from the trends seen for other PL, including E11*a PL from the ether-type doped sites. The unique structure-dependent solvatochromism is correlated with the (1) localization-induced polarizability or dipole moment changes and (2) different degrees of exciton localization at doped sites.