Controlling Near-Infrared Photoluminescence Properties of Single-Walled Carbon Nanotubes by Substituent Effect in Stepwise Chemical Functionalization

Abstract

Introducing the quantum defects into single-walled carbon nanotubes (SWNTs) enhances their photoluminescence (PL) with red-shifted peaks; however, the precise control of the chemical modification and PL wavelength remains difficult. In this work, the stepwise chemical functionalization of SWNTs was shown to be useful for controlling site-specific functionalization and PL, experimentally and theoretically. Dialkylated and hydroalkylated SWNTs were selectively synthesized using alkyllithium reagents, bromoalkane, and trifluoroacetic acid. The n Bu-SWNT- n Bu and n Bu-SWNT-H adducts of the (6,4), (6,5), (8,3), and (7,5) SWNTs that were separated using gel chromatography showed dominant E11 ** PL and E11* PL, respectively. The systematic assignments of the PL were performed based on the thermodynamic stability and transition energy of 1,2- and 1,4-adducts of SWNTs using density functional theory (DFT) and time-dependent DFT calculations. It was shown that the steric hindrance of the added group and the R value, that is, mod(n – m, 3) in an (n,m) chiral nanotube, are key factors that control the addition site and the magnitude of the local band gap.

Photoluminescence Properties of Single‐Walled Carbon Nanotubes Influenced by the Tether Length of Reagents with Two Reactive Sites

“…These results are similar to those of previous studies on (6,5) SWNTs [22] . In comparison, the selectivity of the PL wavelength of separated SWNTs‐C 4 H 9 M was low, and the observed E 11 * and E 11 ** PL wavelengths were similar to those of the previously reported n Bu‐SWNTs‐H adduct prepared using butyllithium and CF 3 COOH [30] …”

“…Recently, the dialkylation and hydroalkylation of SWNTs were conducted using n BuLi followed by the addition of either n BuBr or trifluoroacetic acid, respectively. [30] The dibutylated and hydrobutylated (6,5) SWNTs produced PL peaks at ~1230 and ~1100 nm, respectively, which were in good agreement with the results of previous studies, indicating that the bulkiness of the reactants influenced the PL wavelengths of the SWNT adducts. (6,4), (6,5), (8,3), (8,4), and (7,5) SWNTs.…”

“…To evaluate the applicability of the functionalization with dibromoalkanes to the selective generation of PL peaks utilizing other chiral indices, gel column chromatography of SWNTs‐C 4 H 9 M , SWNTs‐C 3 H 6 D , SWNTs‐C 4 H 8 D , and SWNTs‐C 5 H 10 D was conducted using a mixed system of three surfactants as the eluent and Sephacryl S‐200 as the gel [30,33–35] . High‐performance liquid chromatograms (HPLCs) obtained by monitoring the absorption at 280 nm show a stepwise elution of components with the increasing sodium deoxycholate (DOC) fraction (Figure S1).…”

“…[22] In comparison, the selectivity of the PL wavelength of separated SWNTs-C 4 H 9 M was low, and the observed E 11 * and E 11 ** PL wavelengths were similar to those of the previously reported n Bu-SWNTs-H adduct prepared using butyllithium and CF 3 COOH. [30] Piao et al reported that the difference in the emission energy between functionalized and non-functionalized SWNTs (ΔE) was inversely proportional to the SWNT diameter, suggesting that new PL peaks originated from the brightening of dark excitons. [12] Figure 7 depicts the emission energy differences of (6,4), (7,3), (6,5), (8,3), (7,5), and (8,4) SWNTs-C n H 2n D (n = 3-5) plotted as functions of the SWNT diameter.…”

“…n Bu-SWNTs-H [30] n Bu-SWNTs-n Bu [30] SWNTs-C 4 H Chemistry-A European Journal evaluated the differences in the stability and transition energies of three 1,2-addition isomers of (6,4), (7,3), (8,3), (7,5), and (8,4) SWNTs (Figures S17-S21). An R value equal to mod(nÀ m,3) for an (n,m) chiral nanotube has been found to play an important role in functionalized SWNTs.…”