Chem. Rev. 2000, 100, 1075−1120 Discrete Fulleride Anions and Fullerenium Cations Christopher A. Reed* and Robert D. Bolskar Department of Chemistry, University of CaliforniasRiverside, Riverside, California 92521-0403 Received June 22, 1999 Contents I. Introduction, Scope, and Nomenclature II. Electrochemistry A. Reductive Voltammetry B. Oxidative Voltammetry III. Synthesis A. Chemical Reduction of Fullerenes to Fullerides i. Metals as Reducing Agents ii. Coordination and Organometallic Compounds as Reducing Agents iii. Organic/Other Reducing Agents B. Electrosynthesis of Fullerides C. Chemical Oxidation of Fullerenes to Fullerenium Cations IV. Electronic (NIR) Spectroscopy A. Introduction B. C 60 n- Fullerides C. C 70 and Higher Fullerenes D. Fullerenium Cations E. Diffuse Interstellar Bands V. Vibrational Spectroscopy A. Infrared Spectroscopy B. Raman Spectroscopy VI. X-ray Crystallography A. Introduction B. [PPN] 2 [C 60 ] and Related C 602- Structures C. C 60 - Structures D. C 603- Structures E. Comparison of Discrete and Extended Structures VII. Magnetic Susceptibility and Spin States VIII. NMR Spectroscopy A. Introduction B. 13 C NMR Data in Solution C. Interpretation of Solution NMR Data D. 13 C NMR Data in the Solid State E. Knight Shift in A 3 C 60 F. 3 He NMR of Endohedral Fullerides G. 13 C NMR of Derivatized Fullerenes H. 13 C NMR of Fullerenium Cations IX. EPR Spectroscopy A. Introduction B. Features of the C 60 - Spectrum i. The Low g Value ii. Temperature Dependence of the Line Width (∆H pp ) X. XI. XII. XIII. iii. Anisotropy iv. Problem of the Sharp Signals v. Origins of Sharp Signals vi. The C 120 O Impurity Postulate vii. The Dimer Postulate C. Features of the C 602- EPR Spectrum D. Features of the C 603- EPR Spectrum E. Features of C 604- and C 605- EPR Spectra F. EPR Spectra of Higher Fullerides G. EPR Spectra of Fullerenium Cations Chemical Reactivity A. Introduction B. Fulleride Basicity C. Fulleride Nucleophilicity/Electron Transfer D. Fullerides as Intermediates E. Fullerides as Catalysts F. Fullerides as Ligands G. Fullerenium Cations Conclusions and Future Directions Acknowledgments References I. Introduction, Scope, and Nomenclature The electron-accepting ability of C 60 , the archetypal fullerene, is its most characteristic chemical property. It is a natural consequence of electronic structure and was anticipated in early molecular orbital calcula- tions 1 which place a low-lying unoccupied t 1u level about 2 eV above the h u HOMO: 2-4 Early in the gas-phase investigations of fullerenes, the electron affinity of C 60 was measured and found to be high (2.69 eV). 5-7 When the macroscopic era of C 60 chemistry began in 1990, this property was soon found to translate into the solution phase. 8 In a rather remarkable cyclic voltammogram (see Figure 1), the reversible stepwise addition of up to six electrons was soon demonstrated electrochemically. 9,10 10.1021/cr980017o CCC: $35.00 © 2000 American Chemical Society Published on Web 02/16/2000

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Discrete fulleride anions and fullerenium cations.

Applying the method of density functional theory calculations, we examine the Raman and surface-enhanced Raman spectra (SERS) of crystal violet. The resulting optimized structure is of point symmetry D3, and the calculated Raman spectrum provides an excellent match with the observed normal Raman spectrum. This provides a reliable assignment of the symmetry and normal modes of the observed spectrum, which consists of bands assigned to modes of either a1 or e symmetry. The e modes are not split, showing that D3 symmetry remains, even on the surface. The SERS spectra, both normal and single-molecule, are dominated by the nontotally symmetric e vibrations, which are preferentially enhanced in accord with the Herzberg−Teller-surface selection rules. The mechanism involves intensity borrowing through vibronic coupling between a charge-transfer state and the lowest-lying π → π* transition. A quantitative measure of the degree of charge transfer is obtained by analyzing the potential dependence of SERS intensitie...

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Electrofluorochromism deals with electrochemical monitoring of luminescence features There are several reasons to be interested in that field The first one is the design of displays working in a similar way to electrochromic devices, substituting colors due to absorption with colors due to emission, thus producing much higher brilliance This requires designing smart molecules and materials, which are likely to exhibit reversible switch of emission by controlling their redox state There are also a lot of analytical applications, especially in biochemical issues, where in situ dual detection of electrochemical and fluorescence signals can lead to very sensitive and selective biosensors To achieve this goal, instrumental developments are necessary, involving, among others, beyond diffraction limit and single molecule detection optical techniques This paper reviews the most recent developments in the above mentioned fields of fluorescence spectroelectrochemistry, coupled detection of fluorescence and electrochemical signals and design of molecules and materials exhibiting electrofluorochromic properties The first part describes the required features for molecular systems to exhibit a reversible switch in their luminescence properties according to a change in their redox state Examples among organic and organometallic dyes and redox labelled fluorophores are listed The second part focuses on the instrumental development in fluorescence spectroelectrochemistry and recent coupling of electrochemical techniques with fluorescence microscopy Finally, some applications and devices are presented in the last part of this review This should give an overview of this emerging research field at the interface between physics, chemistry and biology

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R. Geoffrey Wellington

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