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 (E-11* PL) and exhibit sensitive and remarkable E-11* PL energy shifts in response to changes in their surrounding dielectric environment. In this study, we exploited the E-11* PL responsiveness of lf-SWCNTs to investigate polymer wrapping structures around nanotubes by analyzing four vinyl polymers. The observed E-11* 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 E-11* PL wavelength shift responses, which would contribute to development of advanced lf-SWCNT sensors.