Foreword to the fullerene special issue

The discovery of fullerene in 1985 by Kroto, Smalley and co-workers was spurred by the interest in the nature and the mechanism of formation of interstellar carbon molecules. Although this notion is highly appealing, it is hard to think of a line of research that may have wider prospects of practical and technological impact. Indeed, fullerene and its derivatives show many interesting properties and have been considered for different applications such as the inhibition of HIV protease, superconductivity, ferromagnetism and optical devices.

The electronic spectroscopy of fullerene represents a challenge because of its high symmetry, which implies a wealth of high degeneracy electronic states that are capable of spontaneous symmetry breaking (Jahn–Teller effect) and of multiple vibronic couplings.

From the chemical point of view, the fullerenes form a unique class of spherical molecules containing a conjugated π system based on a network of fused hexagons and pentagons. It has been suggested that they are the three dimensional analogues of benzene and of planar aromatic hydrocarbons. This has spurred a lively debate on the aromaticity of fullerenes. Certainly, it is undisputed that fullerenes are strong electron-attracting compounds and undergo all the reactions associated with poorly conjugated and electron deficient olefins. The chemistry of fullerenes is therefore concerned with addition reactions and with examining the vast number of products. Owing to its relatively low reduction potential, symmetrical shape, large size and extended π-electron system, fullerene is an ideal candidate as the electron-acceptor partner in a dyad or in supramolecular assemblies suitable to give a photo-induced electron/energy transfer process and charge separation. Thus, the electronic properties of fullerenes make them attractive in the design of new photo- and electro-active materials in which photo-induced electron transfer is the key process for the conversion of light into chemical or electric energy. In this respect, it has been fortunate that the discovery of fullerenes occurred at the same time as the beginning of the branch of supramolecular chemistry. The two fields overlap considerably and much work is being done nowadays in supramolecular assemblies containing C₆₀. The research activity in this area, which may lead to important applications, is currently quite intense.

The continued interest in this field and the bright perspectives regarding both basic understanding and important applications motivate this special issue of Photochemical & Photobiological Sciences devoted to the spectroscopy, photochemistry, and photo-induced electron transfer of fullerene or of fullerene containing supramolecular structures. This issue presents the interested reader an up-to date picture of the current research in the above-mentioned subjects by a collection of research papers. Its scope has been largely shaped by the interest of contributing authors and has no claim of completeness. Indeed, many areas of fullerene research have found their place in other special issues.

I would like to express my gratitude to all the authors for their contributions and to Professor Frans De Schryver, the Editor-in-chief of Photochemical & Photobiological Sciences, for his invaluable support.

Giorgio Orlandi

University of Bologna, Italy

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