Theoretical study of the structures and electronic properties of the dimers of fluorene and carbazole and their derivatives

The intrinsic properties of the ground and excited states of fluorene, carbazole, fluorene-vinylene and fluorene-acetylene dimers and fluorene-carbazole unit are studied. The ground state optimized structures and energies are obtained using the molecular orbital theory and the density functional theory (DFT). The ground state potential energy curves of the dimers are also obtained. All molecules are nonplanar in their electronic ground states. The character and energy of the first 20 singlet-singlet electronic transitions are investigated by applying the time-dependent DFT approximations to the correspondingly optimized ground state geometries. The lowest singlet state is studied with the configuration interaction (singles) approach (CIS). CIS results suggest geometry relaxation in the first singlet excited state.