Evidence for photoinduced electron transfer from the excited state of a conducting polymer onto buckminsterfullerene, C(60), is reported. After photo-excitation of the conjugated polymer with light of energy greater than the pi-pi* gap, an electron transfer to the C(60) molecule is initiated. Photoinduced optical absorption studies demonstrate a different excitation spectrum for the composite as compared to the separate components, consistent with photo-excited charge transfer. A photoinduced electron spin resonance signal exhibits signatures of both the conducting polymer cation and the C(60) anion. Because the photoluminescence in the conducting polymer is quenched by interaction with C(60), the data imply that charge transfer from the excited state occurs on a picosecond time scale. The charge-separated state in composite films is metastable at low temperatures.

https://science.sciencemag.org/content/sci/258/5087/1474.full.pdf

Photoinduced electron transfer from a conducting polymer to buckminsterfullerene.

Preface Acknowledgements Notation Part I. Overview and Background Topics: 1. Introduction 2. Overview 3. Theoretical background 4. Periodic solids and electron bands 5. Uniform electron gas and simple metals Part II. Density Functional Theory: 6. Density functional theory: foundations 7. The Kohn-Sham ansatz 8. Functionals for exchange and correlation 9. Solving the Kohn-Sham equations Part III. Important Preliminaries on Atoms: 10. Electronic structure of atoms 11. Pseudopotentials Part IV. Determination of Electronic Structure, The Three Basic Methods: 12. Plane waves and grids: basics 13. Plane waves and grids: full calculations 14. Localized orbitals: tight binding 15. Localized orbitals: full calculations 16. Augmented functions: APW, KKR, MTO 17. Augmented functions: linear methods Part V. Predicting Properties of Matter from Electronic Structure - Recent Developments: 18. Quantum molecular dynamics (QMD) 19. Response functions: photons, magnons ... 20. Excitation spectra and optical properties 21. Wannier functions 22. Polarization, localization and Berry's phases 23. Locality and linear scaling O (N) methods 24. Where to find more Appendixes References Index.

Electronic Structure: Basic Theory and Practical Methods

THE synthesis of macroscopic amounts of C60 and C70 (fullerenes)1 has stimulated a variety of studies on their chemical and physical properties2,3. We recently demonstrated that C60 and C70 become conductive when doped with alkali metals4. Here we describe low-temperature studies of potassium-doped C60 both as films and bulk samples, and demonstrate that this material becomes superconducting. Superconductivity is demonstrated by microwave, resistivity and Meissner-effect measurements. Both polycrystalline powders and thin-film samples were studied. A thin film showed a resistance transition with an onset temperature of 16 K and essentially zero resistance near 5 K. Bulk samples showed a well-defined Meissner effect and magnetic-field-dependent microwave absorption beginning at 18 K. The onset of superconductivity at 18 K is the highest yet observed for a molecular superconductor.

/pdf/superconductivity-at-18-k-in-potassium-doped-c60-30fq0lzflp.pdf

Superconductivity at 18 K in potassium-doped C60

In this Account we highlight the experimental evidence in favor of our view that carbon nanotubes should be considered as a new macromolecular form of carbon with unique properties and with great potential for practical applications. We show that carbon nanotubes may take on properties that are normally associated with molecular species, such as solubility in organic solvents, solution-based chemical transformations, chromatography, and spectroscopy. It is already clear that the nascent field of nanotube chemistry will rival that of the fullerenes.

Chemistry of single-walled carbon nanotubes.

The properties of an organic molecular ferromagnet [C(60)TDAE(086); TDAE is tetrakis(dimethylamino)ethylene] with a Curie temperature ;T(c) = 161 kelvin are described The ferromagnetic state shows no remanence, and the temperature dependence of the magnetization below ;T(c) does not follow the behavior expected of a conventional ferromagnet These results are interpreted as a reflection of a three-dimensional system leading to a soft ferromagnet

https://science.sciencemag.org/content/sci/253/5017/301.full.pdf

Organic molecular soft ferromagnetism in a fullerene c60.

THE recent syntheses1,2 of macroscopic quantities of C60 have suggested possible applications in host–guest and organic chemistry, tribology, electrochemistry and semiconductor tech-nology. Here we report the preparation of alkali-metal-doped films of C60 and C70 which have electrical conductivities at room temperature that are comparable to those attained by n-type doped polyacetylene. The highest conductivities observed in the doped films are: 4Scm−1 (Cs/C60), 100 (Rb/C60), 500 (K/C60), 20 (Na/C60), 10 (Li/C60), 2 (K/C70). The doping process is reversed on exposure of the films to the atmosphere. At high doping levels, the films become more resistive. We attribute the conductivity induced in these films to the formation of energy bands from the π orbitals of C60 or C70, which become partially filled with carriers on doping. The smaller alkali metal ions should be able to fit into the interstices in the lattice without disrupting the network of contacts between the carbon spheroids. In the case of C60, this would allow the development of an isotropic band structure, and we therefore propose that these materials may constitute the first three-dimensional 'organic' conductors.

Conducting films of C60 and C70 by alkali-metal doping

BULK C60 (fullerite) is a solid composed of extremely hard pseudospherical molecules bonded by weak van der Waals interactions. We expect that pressurization will probe this diversity as the intermolecular distance is reduced. Here we present experimental measurements of the room-temperature pressure–volume equation of state of C60 fullerite to pressures of 20 GPa. The face-centred cubic phase remains stable under hydrostatic compression to this pressure, with an atmospheric-pressure isothermal bulk modulus of K0 = 18.1 ± 1.8 GPa and dK0/dP = 5.7 ± 0.6, characteristic of isotropic van der Waals intermolecular bonding. X-ray diffraction intensity changes are consistent with the compressibility of the C60 molecule being significantly lower than that of the bulk fullerite solid. Under non-hydrostatic compression, a transition to a crystallographic structure of lower symmetry is observed at 16±1 GPa.

Effects of pressure and stress on C60 fullerite to 20 GPa

The room temperature Raman spectra of the intramolecular modes between 100 cm–1 and 2000 cm–1 are reported for alkali-metal doped AxC60 films. For A = K, Rb, and Cs, phase separation is observed with the spectra of C60, K3C60, K6C60, Rb3C60, Rb6C60, and Cs6C60 phases reported. The x = 3 phases show only three Raman active modes: two of Ag symmetry and only the lowest frequency Hg mode. The other Hg modes regain intensity in the x = 6 films, with several mode splittings observed. For A = Na, such phase separation is not clearly observed, and reduced mode shifts are interpreted as due to incomplete charge transfer in these films.

https://science.sciencemag.org/content/sci/254/5038/1625.full.pdf

Raman Studies of Alkali-Metal Doped AxC60 Films (A = Na, K, Rb, and Cs; x = 0, 3, and 6).

Measurements of the superconducting ${\mathit{T}}_{\mathit{c}}$ and Raman spectra in isotopically modified ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$ are reported. A decrease in ${\mathit{T}}_{\mathit{c}}$ of 0.65\ifmmode\pm\else\textpm\fi{}0.10 K in samples with (75\ifmmode\pm\else\textpm\fi{}5)% substitution of $^{13}\mathrm{C}$ for $^{12}\mathrm{C}$ yields an exponent of \ensuremath{\alpha}=0.37\ifmmode\pm\else\textpm\fi{}0.05. This interpreted as evidence for phonon-mediated pairing.

S. J. Duclos

Papers

Conducting films of C60 and C70 by alkali-metal doping

Effects of pressure and stress on C60 fullerite to 20 GPa

Raman Studies of Alkali-Metal Doped AxC60 Films (A = Na, K, Rb, and Cs; x = 0, 3, and 6).

Isotope effect in superconducting Rb3C60.

The influence of oxygen on the Raman spectrum of C60 films