Fullerene-Containing Supramolecular Polymers

More recently, intense research efforts have been devoted to developing [60] fullerene-polymer hybrids in which [60]fuUerene molecules are incorporated onto polymer main chains or side chains [23-25]. These [60]fullerene-polymer hybrids have proven to be innovative materials, functioning as organic solar cells, magnets, photoconductors, optical-limiting devices and semiconductors [26-28]. Synthetically, the 30 highly reactive double bonds of a [60]fullerene molecule limit the possible polymerization reactions [24, 28-31]. However, supramolecular methods of incorporating [60]fullerene onto a polymer main chain can overcome this Umitation. 

A supramolecular polymer is any type of self-assembly that creates polymer-Uke a egates via reversible interactions of one or more types of components [32-34]. The reversible interactions can allow supramolecular polymers to thermally equilibrate with their monomers, whereas conventional polymers never show such reversibility [35]. For instance, classes of supramolecular polymers include micelles, colloids, hquid crystals, gels, aromatic stacks and hydrogen-bonded polymers. One characteristic they share is the ability to reversibly change their structures at the supramolecular level in response to external stimuli [36, 37], which offers a new way to engineer functional systems at the nano-scale [38]. Thus, 

Fullerene Polymers. Synthesis, Properties and Applications. Edited by Nazario Martin and Francesco Giacalone Copyright 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32282-4 

This chapter focuses on recent developments in the construction of supramo-lecular polymer-like ensembles incorporating [60]fullerene, including supramo-lecular polymers, nano-arrays and discrete assemblies of [60]fuUerene derivatives. These ensembles have been constmcted in various phases solid state, meso, solution and solid-liquid and liquid-liquid interfaces. 

Calix[5]arenes encapsulate groups of fullerenes into their cone-shaped cavity [48-59]. Atwood, Barbour, Raston and coworkers have reported that calix[5]arene 3, toluene and the [60]fullerene molecule form co-crystals one with a 1 1 1 composition with the [60]fullerene molecules arranged in a supramolecular zigzag and the other with a 4 2 5 composition, giving rise to a Z-array of the [60]fullerene 

---

This section discusses the scope of [60]fullerene-based polymer chemistry. These approaches may allow for the development, on a supramolecular level, of unprecedented architectures. Previous sections have dealt primarily with the self-assembly of the [60]fullerene and its derivatives as a result of microphase separation and subsequent formahon of huge [60]fullerene clusters driven by the weak noncovalent forces in the solid state, mesophase and water. To avoid microphase separation, the introduction of functionalized [60]fullerene derivatives into polymer main chains through noncovalent interactions is a very promising approach. The construction of fullerene-containing supramolecular polymers in organic solution is now presented. 

Fullerene-containing supramolecular polymers based on DNA templating have been reported by Chu and coworkers [96]. Cationic [60]fullerene derivahves bind onto the DNA main chain through Coulombic interachons, which gives rise to the polymeric nano-array of [60]fullerene. Shinkai and coworkers have reported photocurrent generation in a supramolecular fullerene polymer [97]. A [60]fullerene/ porphyrin/DNA ternary complex is deposited on an ITO (indium tin oxide) electrode by oxidative polymerization of E DOT. The effechve photocurrent generation is observed by light excitation of the porphyrin. 

Although the supramolecular chemistry of fullerene derivatives is a well explored and established field [53], surprisingly, fuUerene-containing supramolecular polymer systems have been scarcely studied. In fact, this family can be considered as the most recently explored among the other polyfullerenes, and it is now experiencing growing interest... 

---