The self-assembly and self-organization of porphyrins and related macrocycles enables the bottom-up fabrication of photonic materials for fundamental studies of the photophysics of these materials and for diverse applications. This rapidly developing field encompasses a broad range of disciplines including molecular design and synthesis, materials formation and characterization, and the design and evaluation of devices. Since the self-assembly of porphyrins by electrostatic interactions in the late 1980s to the present, there has been an ever increasing degree of sophistication in the design of porphyrins that self-assemble into discrete arrays or self-organize into polymeric systems. These strategies exploit ionic interactions, hydrogen bonding, coordination chemistry, and dispersion forces to form supramolecular systems with varying degrees of hierarchical order. This review concentrates on the methods to form supramolecular porphyrinic systems by intermolecular interactions other than coordination chemistry, the characterization and properties of these photonic materials, and the prospects for using these in devices. The review is heuristically organized by the predominant intermolecular interactions used and emphasizes how the organization affects properties and potential performance in devices.

Self-Organized Porphyrinic Materials

Ever since the first experimental evidence of the existence of endohedral metallofullerenes (EMFs) was obtained, the search for carbon cages with encapsulated metals and small molecules has become a very active field of research. EMFs exhibit unique electronic and structural features, with potential applications in many fields. Furthermore, functionalized EMFs offer additional potential applications because of their higher solubility and their ease of characterization by X-ray crystallography and other techniques. Herein we review the general field of EMFs, particularly of functionalized EMFs. We also address their structures and their (electrochemical) properties, as well as applications of these fascinating compounds.

Chemical, electrochemical, and structural properties of endohedral metallofullerenes.

Endohedral metallofullerenes (EMFs), a new class of hybrid molecules formed by encapsulation of metallic species inside fullerene cages, exhibit unique properties that differ distinctly from those of empty fullerenes because of the presence of metals and their hybridization effects via electron transfer. This critical review provides a balanced but not an exhaustive summary regarding almost all aspects of EMFs, including the history, the classification, current progress in the synthesis, extraction, isolation, and characterization of EMFs, as well as their physiochemical properties and applications in fields such as electronics, photovoltaics, biomedicine, and materials science. Emphasis is assigned to experimentally obtained results, especially the X-ray crystallographic characterizations of EMFs and their derivatives, rather than theoretical calculations, although the latter has indeed enhanced our knowledge of metal–cage interactions. Finally, perspectives related to future developments and challenges in the research of EMFs are proposed. (381 references)

Current status and future developments of endohedral metallofullerenes

In this tutorial review taking X-ray crystallographically characterized compounds as a starting point a walk is taken through the electronic and structural properties of endohedral metallofullerenes After classification of the fullerenes according to the encapsulated guest, particular attention is given to identifying factors that determine the selection of a particular carbon cage network by the internal metal cluster Some of the physical rules that determine which particular fullerene cage is formed will be discussed Concepts such as charge transfer between the cage and the guest metal ions, the topology of the cage, the separations between the 12 pentagons on the fullerene surface, and the effect of entropic factors are used to rationalize the selection of a particular cage The roles of electrochemistry and vibrational spectroscopy in combination with theoretical calculations are considered in understanding the structures of the endohedral fullerenes

Endohedral metallofullerenes: a unique host–guest association

Quantum Mechanical Studies of Large Metal, Metal Oxide, and Metal Chalcogenide Nanoparticles and Clusters.

The remarkably large cluster Sc4(μ3-O)2 has been obtained trapped inside an Ih-C80 cage by conducting the vaporization of graphite rods doped with copper(II) nitrate and scandium(III) oxide in an electric arc under a low pressure helium atmosphere with an added flow of air. The product has been isolated by chromatography and identified by high-resolution mass spectrometry. The structure of Sc4(μ3-O)2@Ih-C80 has been determined by X-ray crystallography on a crystal of Sc4(μ3-O)2@Ih-C80·NiII(OEP)·2(C6H6). The Sc4(μ3-O)2 unit consists of a distorted tetrahedron of scandium atoms with oxygen atoms bridging two of its faces. The Sc−Sc distances range from 2.946(7) to 3.379(7) A.

A Distorted Tetrahedral Metal Oxide Cluster inside an Icosahedral Carbon Cage. Synthesis, Isolation, and Structural Characterization of Sc4(μ3-O)2@Ih-C80

Structural characterizations of three new mixed-metal endohedrals, GdSc2N@Ih-C80, Gd2ScN@Ih-C80, and TbSc2@Ih-C80, have been obtained by single-crystal X-ray diffraction on GdSc2N@Ih-C80·NiII(OEP)·2C6H6, Gd2ScN@Ih-C80·NiII(OEP)·2C6H6, and TbSc2N@Ih-C80·NiII(OEP)·2C6H6. All three have Ih-C80 cages and planar MM′2N units. The central nitride ion is positioned further from the larger Gd3+ or Tb3+ ions and closer to the smaller Sc3+ ions. The MM′2N units show a remarkable degree of orientational order in these and related compounds in which the endohedral fullerene is cocrystallized with a metalloporphyrin. The MM′2N units are oriented perpendicularly to the porphyrin plane and aligned along one of the N−Ni−N axes of the porphyrin. The smaller Sc3+ ions show a marked preference to lie near the porphyrin plane. The larger Gd3+ or Tb3+ ions assume positions further from the plane of the porphyrin. The roles of dipole forces and electrostatic forces in ordering these cocrystals of endohedral fullerenes and metal...

Internal and External Factors in the Structural Organization in Cocrystals of the Mixed-Metal Endohedrals (GdSc2N@Ih-C80, Gd2ScN@Ih-C80, and TbSc2N@Ih-C80) and Nickel(II) Octaethylporphyrin

Christopher J. Chancellor

Papers

A Distorted Tetrahedral Metal Oxide Cluster inside an Icosahedral Carbon Cage. Synthesis, Isolation, and Structural Characterization of Sc4(μ3-O)2@Ih-C80

Internal and External Factors in the Structural Organization in Cocrystals of the Mixed-Metal Endohedrals (GdSc2N@Ih-C80, Gd2ScN@Ih-C80, and TbSc2N@Ih-C80) and Nickel(II) Octaethylporphyrin