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Spectroscopic Properties of Nanotube–Chromophore Hybrids

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Changshui Huang†, Randy K. Wang‡, Bryan M. Wong

, David J. McGee

, François Léonard

, Yun Jun Kim†, Kirsten F. Johnson†, Michael S. Arnold†, Mark A. Eriksson‡*, and Padma Gopalan†§*

^†Department of Materials Science & Engineering, ^‡Department of Physics, and ^§Department of Chemistry, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States

Sandia National Laboratories, Livermore, California 94551, United States

Department of Physics, The College of New Jersey, Ewing, New Jersey 08628, United States

ACS Nano, 2011, 5 (10), pp 7767–7774

DOI: 10.1021/nn202725g

Publication Date (Web): September 15, 2011

Address correspondence to pgopalan@cae.wisc.edu, maeriksson@wisc.edu.

Section:

Optical, Electron, and Mass Spectroscopy and Other Related Properties

Abstract

Recently, individual single-walled carbon nanotubes (SWNTs) functionalized with azo-benzene chromophores were shown to form a new class of hybrid nanomaterials for optoelectronics applications. Here we use a number of experimental and computational techniques to understand the binding, orientation, and nature of coupling between chromophores and the nanotubes, all of which are relevant to future optimization of these hybrid materials. We find that the binding energy between chromophores and nanotubes depends strongly on the type of tether that is used to bind the chromophores to the nanotubes. The pyrene tethers form a much stronger attachment to nanotubes compared to anthracene or benzene rings, resulting in more than 80% retention of bound chromophores post-processing. Density functional theory (DFT) calculations show that the binding energy of the chromophores to the nanotubes is maximized for chromophores parallel to the nanotube sidewall, even with the use of tethers; optical second harmonic generation measurements show that there is nonetheless a partial radial orientation of the chromophores on the nanotubes. We find weak electronic coupling between the chromophores and the SWNTs, consistent with noncovalent binding. This weak coupling is still sufficient to quench the chromophore fluorescence through a combination of static and dynamic processes. Photoluminescence measurements show a lack of significant energy transfer from the chromophores to isolated semiconducting nanotubes.