Polymer Wrapping State Changes at Defect Sites of Locally Functionalized Single-Walled Carbon Nanotubes

Polymer wrapping techniques of single-walled carbon nanotubes (SWCNTs) are used for not only their solubilization in solvents but also tube structure separation and biosensor fabrication. Locally functionalized SWCNTs (lf-SWCNTs) contain defect sites that show bright defect photoluminescence (E₁₁* PL) and exhibit sensitive and remarkable E₁₁* PL energy shifts in response to changes in their surrounding dielectric environment. In this study, we exploited the E₁₁* PL responsiveness of lf-SWCNTs to investigate polymer wrapping structures around nanotubes by analyzing four vinyl polymers. The observed E₁₁* PL energy shifts clarify the unique microenvironment formation at the defect sites based on the polymer wrapping fashion differences: Namely, the side chains of the used polymers modulate the polymer wrapping tightness that change the amounts of D₂O molecules accessing to the nanotube surfaces for local polarity variation near the defect sites, which induces the polymer-dependent PL shifts. Moreover, the substituents of the modified aryl groups in lf-SWCNTs contribute to the defect site polarity and hydrophobicity, by which a clear correlation between the substituent structures and the induced PL shifts is found. Therefore, the lf-SWCNT defect sites can produce unique molecular interaction fields showing E₁₁* PL wavelength shift responses, which would contribute to development of advanced lf-SWCNT sensors.