2006 Volume 74 Issue 1 Pages 49-52
Fluorenyl anions were successfully accumulated in the cathode compartment of a two-compartment cell by electrochemical reduction of fluorene in various solvents. Examination of the anions by UV-visible absorption spectroscopy and NMR spectroscopy revealed that all the obtained fluorenyl anions with tetraalkylammonium counter cations were contact ion pairs. Their electronic states were close to those of solvent-separated ion pairs. These observations were understood as that, in the contact ion pairs with tetraalkylammonium counter cations, anion and cation centers were far apart, for the alkyl chains of the cations prevented the cation centers to get closer to the anion centers. Among the contact ion pairs, those in dimethyl sulfoxide (solvent with the largest dielectric constant) showed their electronic states closest to those of the solvent-separated ion pairs. The influence of alkyl chain length and that of temperature on the electronic state of the anions were both small.
