Theoretical investigations on electronic structures and photophysical properties of novel bridged triphenylamine derivatives

摘要

It has been proved that triphenylamine (TPA) derivatives can be excellent candidates for hole-transporting materials in organic light-emitting diodes (OLEDs). To improve on the thermal and morphological stability, a fully diarymethylene-bridged TPA derivative (FATPA) which has been proven to enhance electroluminescent (EL) efficiency was synthesized. On the basis of FATPA, two series of novel bridged TPA derivatives have been designed by using diarylmethylene (Series A) or dimethyfluorene (Series B) as the linkage between the ortho-positions of the phenyl rings in this work (see Fig. 1). To reveal the relationships between electronic structures and photophysical properties of these novel functional materials, an in-depth theoretical investigation was elaborated via quantum chemical calculations using the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. In addition, the feasibility of using these bridged TPA derivatives as host in the device of ITO/MoO_3/NPB/mCP/host:Ir(ppy)_3/TAZ/LiF/Al was also evaluated, which including the discussion to their energy levels match with adjacent layers and energy transfer from host to guest. These calculated results show that photophysical properties can be easily tuned by the introduction of various substituent groups into the bridged TPA derivatives, such as the highest occupied molecular orbitals (HOMOs), the lowest unoccupied molecular orbitals (LUMOs), the energies difference between the HOMOs and LUMOs (ΔH-L), the lowest singlet (ES) and triplet (ET) excitation energies, ionization potentials (IPs), electron affinities (EAs), reorganization energies (λ) and the absorption and emission spectra, indicating that these bridged TPA derivatives have great potential applications for OLEDs.