Theoretical investigation of the structure and the electron-vibrational dynamics of 9,9′-spirobifluorene

The theoretical investigation of 9,9′-spirobifluorene as a simple model for rigid molecules with spiro-carbon linkage in the electronic ground (GS) and lowest excited (ES) state is presented. Molecular dynamics (MD), based upon the semiempirical Austin Model 1 Hamiltonian, where the ES is evaluated using the Multi Electron Configuration Interaction treatment, has been applied for the picosecond time scale. Subsequently, the geometrical and theoretical spectral characteristics have been calculated and compared to available experimental data. Our analysis shows that the optical excitation is confined to a single fluorene fragment of the composite molecule. The averaged quasi-period of oscillations of the evaluated geometry parameters for investigated GS and ES is very fast and practically identical (approx. 10 fs). Finally, density functional theory and ab initio coupled-cluster singles and doubles method, which are computationally much more demanding than the semiempirical method, also have been used as reference methods for the investigation of the electronic GS.