On electronic structure of neutral and monocharged 9,9′-spirobifluorene

The geometries of neutral 9,9′-spirobifluorene and of its single charged cation and anion are optimized at B3LYP/6-31G∗ level of theory. Their electronic structure is described in terms of Mulliken and QTAIM (Quantum-Theory-of-Atoms-in-Molecule) population analysis. Whereas neutral and cationic species belong to D2d symmetry group, the fluorene units in their anionic counterpart are non-equivalent (C2v symmetry group) due to Jahn-Teller effect. The oxidation of the neutral molecule is less advantageous than its reduction. Both these processes decrease the aromaticity of hexagonal carbon rings. The geometry and electron structure changes during the oxidation of the neutral molecule are symmetrically distributed within both fluorene units, analogous changes related to the reduction are concentrated to one of these units only.