(Invited) Microenvironment Effects on Photoluminescent Doped Sites of Locally Functionalized Single-Walled Carbon Nanotubes
Authors: Shiraki Tomohiro , Niidome Yoshiaki , Toshimitsu Fumiyuki , Fujigaya Tsuyohiko 
Published: February 2020

Single-walled carbon nanotubes (SWNTs) with semiconducting features emit photoluminescence (PL) in near infrared (NIR) regions. Owing to their unique one dimensional nanostructures, strong quantum confinement and weak dielectric screening affect Coulombic interactions between electron and electron or hole and, therefore, the PL properties are sensitively changed by effects of microenvironments that are composed of surrounding surfactants and solvent molecules. [1]

Recently, defect doping to SWNTs by local chemical functionalization is gathering great attention due to emergence of new PL properties. Namely, in the locally functionalized SWNTs (lf-SWNTs), additional PL (E
11*) appears with redshifted wavelengths and enhanced quantum yields compared to original PL (E
11) of pristine SWNTs.[2-9] Moreover, it is found that chemical structures of the modified molecules on the doped sites play an important role to determine and modulate the E
11* PL wavelengths.[4-9] Thus, their molecularly-tunable properties of the doped sites need to be clarified not only for fundamentals but also for advanced optical applications using the NIR PL.

Here, we examine microenvironment effects on the E
11* PL of lf-SWNTs for characterization of the doped site properties by comparing those of the pristine sites. Nitroaryl-functionalized lf-SWNTs (lf-SWNTs-NO2) were synthesized using diazonium chemistry, which were solubilized in D2O containing sodium dodecylbenzenesulfonate (SDBS). For microenvironment creation using organic solvents[10], water immiscible organics such as o-dichlorobenzene (oDCB) was added and mixed in order to inject the organic solvent into the hydrophobic domains between the lf-SWNTs-NO2 and the coating SDBS micelles. In PL spectrum of lf-SWNTs-NO2 after the treatment using oDCB, PL peaks of E
11* and E
11 were redshifted from 1.085 eV and 1.269 eV to 1.069 eV and 1.257 eV, respectively. Other organic solvents also induced different spectral redshifts depending on their chemical structures. Importantly, the shifted energy values of the E
11* PL were larger than those of the E
11 PL when aromatic solvents were used. The energy shifts were analyzed by using a solvent parameter and a linear correlation was found. Details of these results will be discussed in this presentation together with effects of molecular structure differences in the doped sites of lf-SWNTs.

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Figure 1