(Invited, Digital Presentation) Ortho-Substituent Structure Design in Aryldiazonium Salts for Defect Photoluminescence Modulation of Locally Functionalized Single-Walled Carbon Nanotubes

Abstract

Photoluminescence (PL) of single-walled carbon nanotubes (SWCNTs) appears in the near infrared (NIR) region, which is applicable to advanced optical applications such as bioimaging and telecommunication devices. Local chemical functionalization of SWCNTs has been gathering great attention because of the enhancement of their NIR PL properties. Therein, defects such as sp3 carbon are locally doped to the crystalline sp2 carbon network of the tube walls by the chemical functionalization process.[1-4] As a result, the locally functionalized SWCNTs (lf-SWCNTs) emit new PL with red-shifted wavelengths and increased quantum yields from the doped sites (E 11* PL) compared to original E 11 PL of pristine SWCNTs. It is due to the doping effects to change electronic structures for narrower bandgap formation, by which mobile excitons in the tubes are trapped at the doped sites to be localized states for efficient PL conversion.The chemical functionalization approach allows us to use various chemical reactants for the doped site formation in lf-SWCNTs. The molecular effects including structural differences and molecular binding functions have resulted in versatile NIR PL wavelength modulation of lf-SWCNTs.[1-4] We have reported that E 11* PL generation phenomena were significantly varied depending on isomeric structures of substituted aryldiazonium salts (AD) used for lf-SWCNT synthesis.[5] Especially, ortho-substituted ADs (oADs) produced two PL around 1100 and 1250 nm-regions, respectively for the resulting lf-SWCNTs with (6,5) chirality. Here, we apply various substituent design for oADs and examine the substituent structure effects in terms of modulation of the PL emission properties of lf-SWCNTs. For example, oAD having a phenyl substituent resulted in enhancement of the ~1250 nm PL contribution. Other substituent effects are observed depending on substituent structures of oADs, from which interactions between the substituents and the tubes are considered to induce the observed PL spectral changes. The result indicates that local chemical functionalization using oAD has a high potential to largely modulate NIR PL wavelengths of lf-SWCNTs beyond 1000 nm regions.[1] T. Shiraki et al. Acc. Chem. Res., 53, 1846 (2020). [2] S. Tretiak et al., Acc. Chem. Res., 53, 1791(2020) [3] Y. Wang et al. Nat. Rev. Chem., 3, 375 (2019). [4] T. Shiraki, Chem. Lett., 50, 397 (2021). [5] T. Shiraki et al. Chem. Commun., 53, 12544 (2017).