Theoretical Studies of the Structure, Absorption and Emission Properties of Terfluorene and Ter(9,9-diarylfluorene) Derivatives

The structures, ionization potentials (IP), electron affinities (EA) and HOMO-LUMO gaps (ΔEH-L) of the terfluorene oligomers were studied by the density functional theory with B3LYP functional. The characters of the front orbitals were analyzed on the basis of the ground structure. The vertical excitation energies EV and the maximal absorption wavelengths λ abs of a series of ter(9,9-diarylfluorene) compounds were studied employing the time dependent density functional theory (TD-DFT) and ZINDO. The calculated maximal absorption wavelengths by both methods are in good agreement with the experimental data. The results show that the differences between terfluorene hh and ter(9,9-diarylfluorene) derivatives are slight in the structures and the electronic states except that there is the spiroconjugation in the latter. The spiroconjugation made these derivatives far from optimization in terms of stability. Excited structure of hh was calculated to be compared with the ground structure, which indicats that it has strong coplanar tendency of aromatic ring with the neighbour in the excited state. Consequently, they are good blue emitting materials with promising thermal stability.