Functionalised Fullerenes in Carbon Nanotubes: Controlled Assembly of Molecular Chains

Thomas W. Chamberlain1, Rudolf Pfeiffer2, Herwig Peterlik2, Hans Kuzmany2, Francesco Zerbetto3, Manuel Melle-Franco3, Luke Staddon1, Neil R. Champness1, G. Andrew D. Briggs4, and Andrei N. Khlobystov1.
1 School of Chemistry, University of Nottingham, Nottingham NG7 2RD, .UK.
2 Fakultat fur Physik, Universitat Wien, Austria.
3 Dipartimento di Chimica 4Department of Materials, University of Oxford, Oxford OX1 3PH, UK.

Due to their tubular nature, carbon nanotubes (NTs) have been demonstrated to en¬capsulate different molecules, thus forming quasi one-dimensional molecular systems. Provided that the mechanisms of interactions between the molecules and nanotubes are understood, nanotubes could be used to template formation of molecular chains of desired structure and properties. Previously it has been demonstrated that the most important parameter defining the efficiency of the NT-molecule interaction is the nano¬tube internal diameter. For example, for spheroidal molecules, such as C60, the nano¬tube diameter controls the packing arrangement of the molecules. For ellipsoidal C70 or other higher fullerenes the nanotube diameter also controls the orientations of mo¬lecules.

An alternative mechanism for controlling the assembly of molecular arrays in NTs is via the size and geometry of functional groups of the molecules inserted in nanotubes. We have synthesised a series of fullerenes functionalised with alkyl- or aryl-groups of various length, width and confor mat ional rigidity to explore this effect systematical¬ly. We have inserted these molecules into nanotubes under mild conditions to prevent decomposition of the molecules and to form C60X@NT structures (where X is a func¬tional group). The molecular chains thus formed have been studied by high resolution TEM, XRD, and Raman spectroscopy revealing that the functional groups increase the inter-fullerene separation proportionally with the size of X. However, the functio¬nal groups themselves appear to adopt various conformations (as in the case of X = alkyl) or different orientations with respect of each other (as in the case of X = aryl). All these effects create a distribution of inter-fullerene separations in NTs. Our experi¬mental observations are discussed in terms of molecular geometries and inter-molecular interactions and compared with theoretical simulations carried out for these systems. Acknowledgement: this work is supported by a EURO CORES Programme on Fun¬damentals of Nanoelectronics (IMPRESS project).