(Invited) Molecular Structure-Based Photoluminescence Modulation of Locally Functionalized Single-Walled Carbon Nanotubes Using Bis-Aryl Functionalization

Abstract

Single-walled carbon nanotubes (SWCNTs) show photoluminescence (PL) in the near infrared (NIR) region, which is applicable to bioimaging and telecommunication devices. Recently, local chemical functionalization of SWCNTs has been developed to enhance their NIR PL properties, in which defects such as sp3 carbon are locally doped to the crystalline sp2 carbon network of the tube walls by the functionalization.[1-3] Actually, E 11* PL of the locally functionalized SWCNTs (lf-SWCNTs) is observed with red-shifted wavelengths and increased quantum yields compared to original E 11 PL of pristine SWCNTs. It is due to formation of new emissive sites with narrower band gaps and exciton trapping features in the tube structures.In the local chemical functionalization, doped site structures of the lf-SWCNTs can be changed depending on modifier molecules, which results in effective modulation of the NIR PL wavelengths of the lf-SWCNTs beyond 1000 nm-region. Previously, we have developed bis-aryldiazonium salts (bAs) that have two reactive aryldiazonium groups connected with a methylene linker and observed E 11 2* PL over 1200 nm regions from the lf-SWCNTs with (6,5) chirality based on its proximal aryl functionalization.[4]Here, we synthesize new modifier molecules with the bis-aryldiazonium motif and modify the geometry of the proximal aryl-functionalized sites of the lf-SWCNTs. As a result, for example, methylene linker positions on the aryldiazonium groups of bAs clearly changed the trend of methylene length-dependent wavelength shifts of E 11 2* PL. [5] Moreover, bAs having rigid linker structures changed peak positions of E 11 2* PL, indicating that the control of the proximal defect configuration would be an effective way for the PL property modulation of lf-SWCNTs. As another aspect of the proximal aryl functionalization, we found that E 11 2* PL showed unique wavelength shift behaviors by microenvironment changes using various organic solvents. The observed trend was different from those of E 11 PL and E 11* PL[6], in which proximal defect distances could be an important factor for their microenvironment responsiveness.Therefore, molecularly designed bis-aryldiazonium modifiers become promising tools to create structurally controlled bis-aryl functionalized sites of lf-SWCNTs and precisely modulate their NIR PL wavelengths (> 1000 nm).[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 et al. Sci. Rep., 6, 28393 (2016). [5] T. Shiraki et al. Chem. Lett., 48, 791 (2019). [6] T. Shiraki et al. Chem. Commun., 55, 3662 (2019). Figure 1