Supramolecular Functionalization of SWNTs
Supramolecular functionalization of nanotubes is advantageous in that it avoids the formation of covalent bonds to the nanotube surface and therefore avoids the introduction of defects. This preserves the superior conductivity and strength properties of nanotubes. Planar aromatic molecules, such as pyrene and porphyrins, are known to pi-stack to the nanotube surface. We have prepared a series of pyrene-functionalized block copolymers that bind to the nanotube surface and render the resulting complexes soluble (see below). In addition we have begun to explore the interactions of conjugated polymers with carbon nanotubes. This has included the investigation of a conjugated poly(porphyrin) polymer that binds with high strength to SWNT surfaces, as well as polyfluorene and polythiophene derivatives. This work is now being extended to other conjugated polymers with interesting photophysical properties. In all cases, we have observed highly soluble materials that open the door to device fabrication and the investigation of photovoltaic effects within these complexes.
Polyfluorene and poly(fluorene-co-thiophene) derivatives strongly interact with SWNTs and impart solubility in organic solvents, enabling the formation of stable complexes with interesting photophysical properties.
Key References: Cheng, F.; Imin, P.; Maunders, C.; Botton, G. A.; Adronov, A., Macromolecules, 2008, 41, 2304-2308; Cheng, F.; Adronov, A. J. Porphyrins Phthalocyanines, 2007, 11, 198-204; Cheng, F.; Adronov, A. "Noncovalent Functionalization and Solubilization of Carbon Nanotubes Using a Conjugated Zn-Porphyrin Polymer" Chem. Eur. J., 2006, 12, 5053-5059.
The strong interactions between conjugated polymers and carbon nanotubes can be extended to aqueous solution by using conjugated polyelectrolytes as the polymeric adsorbent. This enables not only the formation of strong complexes in water, but also allows for manipulation of nanotubes for surface patterning, electrophoretic deposition, and the formation of intimate mixtures with biological molecules (i.e., enzymes) for the production of highly efficient biosensors.
An anionic polyphenylene complex with SWNTs enabled patterning on surfaces (left) and a cationic polyfluorene allowed for electrophoretic deposition on transparent ITO electrode surfaces (right). Key references: Cheng, F.; Imin, P.; Lazar, S.; Botton, G. A.; de Silveira, G.; Marinov, O.; Deen, J.; Adronov, A. "Supramolecular Functionalization of Single-Walled Carbon Nanotubes (SWNTs) with Conjugated Polyelectrolytes and their Patterning on Surfaces" Macromolecules, 2008, 41, 9869-9874; Casagrande, T.; Imin, P.; Cheng, F.; Botton, G. A.; Zhitomirsky, I.; Adronov, A. Chem. Mater. 2010, 22, 2741-2749.
A cationic polythiophene derivative also produces soluble nanotube complexes in water and can be mixed with glucose oxidase, followed by deposition on an electrode, to produce an electrochemical biosensor that is extremely sensitive to glucose addition. Response to glucose addition in 0.2 mM aliquots is shown in the plot on the right (a - without nanotubes, b - with nanotubes). Key reference: Xin, P.; Imin, P.; Zhitomirsky, I.; Adronov, A. Macromolecules, 2010, 43, 10376-10381.
Pyrene-Functionalized Polymers - We have prepared a series of block copolymers in which one block contains specific amounts of a pyrene-decorated monomer. Incorporation of pyrene within these block copolymers gives them the ability to bind to the nanotube surface and render the resulting complexes soluble. We have investigated the effect of distributing pyrene in a block as opposed to randomly along the entire polymer backbone, as well as the effect of changing pyrene concentration and block length (see figure below). We have also extended this work to investigate the effect of polymer architecture with a series of linear-dendritic block copolymers, where the dendrons are peripherally functionalized with pyrene units.
Key References: J. Polym. Sci. A: Polym. Chem., 2006, 44, 1941-1951; J. Polym. Sci. A: Polym. Chem., 2010, 48, 1016-1028.

© 2011 Alex Adronov