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Substituent Effects on the Redox States of Locally Functionalized Single-Walled Carbon Nanotubes Revealed by in situ Photoluminescence Spectroelectrochemistry

Abstract

Single-walled carbon nanotubes (SWNTs) with local chemical modification have been recognized as a novel near infrared (NIR) photoluminescent nanomaterial due to the emergence of a new red-shifted photoluminescence (PL) with enhanced quantum yields. As a characteristic feature of the locally functionalized SWNTs (lf-SWNTs), PL wavelength changes occur with structural dependence of the substituent structures in the modified aryl groups, showing up to a 60-nm peak shift according to an electronic property difference of the aryl groups. Up to now, however, the structural effect on the electronic states of the lf-SWNTs has been discussed on the basis of theoretical calculations due to the very limited amount of modifications. Here we describe the successfully-determined electronic states of the aryl modified lf-SWNTs with different substituents (Ar-X SWNTs) using an in situ PL spectroelectrochemical method based on electrochemical quenching of the PL intensities analyzed by the Nernst equation. In particular, we reveal that the local functionalization of the (6,5)SWNTs induces potential changes in energy level of the HOMO and the LUMO by 23~38 meV and +20~+22 meV, respectively, compared to those of the pristine SWNTs, which generates exciton trapping sites with narrower band gaps. Moreover, the HOMO levels of the Ar-X SWNTs specifically shift in a negative potential direction by 15 meV according to an enhancement of the electron-accepting property of the substituents in the aryl groups that corresponds to increase in the Hammet substituent constants, suggesting the importance of the dipole effect from the aryl groups on the lf-SWNTs to the level shift of the frontier orbitals. Our method is a promising way to characterize the electronic features of lf-SWNTs.

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Publication details

The article was received on 26 Jul 2017, accepted on 12 Oct 2017 and first published on 12 Oct 2017


Article type: Paper
DOI: 10.1039/C7NR05480G
Citation: Nanoscale, 2017, Accepted Manuscript
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    Substituent Effects on the Redox States of Locally Functionalized Single-Walled Carbon Nanotubes Revealed by in situ Photoluminescence Spectroelectrochemistry

    T. Shiraishi, T. Shiraki and N. Nakashima, Nanoscale, 2017, Accepted Manuscript , DOI: 10.1039/C7NR05480G

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