Computational Design of Host Materials Suitable for Green-(Deep) Blue Phosphors through Effectively Tuning the Triplet Energy While Maintaining the Ambipolar Property

We theoretically designed a series of ambipolar host materials ( 1 – 8 ) which incorporate phosphine oxide and carbazole groups to the two ends of diphenyl (DP)-like bridges by para- and meta-connections, respectively. Density functional theory calculations were performed to investigate the influence of altering the DP-like bridges of these molecules on electronic structures and properties, and further to predict their performances as host materials in organic light-emitting diodes. The investigated results show the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of 1 – 8, distributed at the phenylcarbazole and the DP-like bridge, are responsible for hole and electron injection properties, respectively. The difference in the energies of HOMOs or LUMOs for 1 – 8 may be derived from different degrees of conjugation effect and electrostatic induction with altering the DP-like bridges of 1 – 8 . The singlet states (S 1 ), arising from the HOMO → LUMO transition, have intramolecular charge transfer character, which determines the small and different values of S 1 energies. On the other hand, altering the DP-like bridges brings a great effect on triplet exciton distributions, and consequently different triplet energies. The different singlet/triplet energies for 1 – 8 make hosts 1 – 8 suitable for four reference guests with green/deep-blue light when scientists consider the matching of host and guest in singlet/triplet energies for efficient energy transfer.