Supramolecular Receptors for Fullerenes

Abstract

Since the extraction of fullerenes from the carbon soot using aromatic solvents [1], the interaction between the convex surface of fullerenes and the flat π surface of aromatic moieties has received increasing attention [2]. Fullerene [3] is a polyenic structure constituted by 12 pentagonal and 20 hexagonal rings, in which each carbon atom possess sp 2,3 hybridization [4]. The existence of pentagonal rings provokes a curvature and, therefore, a weak polarization on its surface between the 5 : 6 ring junctions, which represent centers of positive charge, and the negatively charged 6 : 6 fusions [5, 6]. This anisotropic distribution of the electronic charge is the basis to determine the interactions with other substrates.There are two main driving forces to design supramolecular receptors for fullerenes: on one hand, it would be feasible for an effective purification from their natural extraction sources, mainly carbon soot and fullerite. On the other hand, in combination with electron donor receptors, we could design highly organized architectures that can find application in optoelectronics, where the organization of the active materials plays a crucial role in the improvement and precise operation of the devices.In the design of supramolecular receptors for fullerenes we have to consider the neutral features of fullerenes. Therefore, there are some energetic factors to take into account that will determine the final properties and the nature of the interactions involved in the supramolecular complexes: (i) van der Waals forces, (ii) electrostatic interactions, (iii) induction energy, (iv) charge-transfer, and (v) desolvation [7, 8].Considering the nature of all of these noncovalent forces and the geometry and electronic features of C 60 and its higher congeners, van der Waals and solvophobic interactions should be decisive in the stability of the C 60 -receptor complexes [9]. The large global area of fullerenes, consequence of their spherical geometry, and their nonpolar character make these noncovalent effects key factors to attain highly stabilized complexes. Thus, the direct strategy consists in increasing the aromatic