Electronic properties of charged fullerenes characterized by EPR and Vis-NIR spectroscopy

EPR and Vis-NIR absorption spectra have both been measured for clarification of contradictory statements about the para-and diamagnetic states of fullerenes. Thereby identification of one sharp EPR signal in solution at room temperature to C ₆₀ ^? (g=2.000±4.0001; ΔB=0.07±0.01 mT) could be made upon using different fullerene sources (TechnoCarbo, Hoechst) and methods of anion generation (chemically, electrochemically, and photochemically). This fact is also supported by the similar observation for a monosubstituted derivative (g=1.9999; ΔB=0.10 mT), in which a small broadening of this sharp signal is found originating from additional¹H hyperfine interactions. Furthermore theg-values of the radical anions of C₆₀ increase with charge (g(C ₆₀ ^? <g(C ₆₀ ^2? ) < <g(C ₆₀ ^3? ) <g(C ₆₀ ^5? )) indicating largest contributions from spin-orbit coupling for the monoanion. No diamagnetic states for the dianions of [60]- and [70]- fullerenes could be found so far but biradical species with largest zero field splittingsD=2.7 mT (C ₆₀ ^2? ), andD=3.1 mT (C ₇₀ ^2? ), respectively. The cation formation of C₆₀ (g=2.0023-2.0029; ΔB=0.15-0.20 mT) with antimony pentachloride was controlled by mass spectrometry. Stable cations were found only in methylenechloride. In other solvents like toluene addition reactions seem to occur.     

Pyrolysis in the mesophase: a chemist's approach toward preparing carbon nano- and microparticles

A mild pyrolytic method is proposed for the generation of different carbon micro- and nanoparticles that are either unprecedented or have never been reported under the present experimental conditions. A hexa-alkyl-substituted hexa-peri-hexabenzocoronene serves as a graphite-like starting compound that melts into a discotic liquid crystalline phase prior to heat-induced cross-linking and dehydrogenation. An essential feature of the process is that the liquid crystalline order persists even above 400 degrees C, i.e., during alkyl chain cleavage. The present approach bears a resemblance to carbomesophase formation during graphitization starting from pitch. The pyrolysis products are characterized by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, optical microscopy, selected area electron diffraction (SAED), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM).     

Nanosized molecular propellers by cyclodehydrogenation of polyphenylene dendrimers

In a polymer analogous approach, large dendritic oligophenylenes containing benzene and tetraphenylmethane cores are transformed via oxidative cyclodehydrogenation to novel propeller-shaped molecules with large polycyclic aromatic hydrocarbon units as "blades". Structure analysis is performed by a combination of MALDI-TOF mass spectrometry, UV/vis, fluorescence, and Raman spectroscopy using solid-state sample preparation methods. These methods are also utilized to determine the degree of the cyclodehydrogenation reaction.