Theoretical insights into the phosphorescent process of a series of 2-(2-trifluoromethyl) pyrimidine-pyridine based heteroleptic iridium(III) compounds: The influence of the ancillary ligand

Abstract

The structure-property relationship is theoretically elucidated for four heteroleptic Ir(III) complexes with different ancillary ligand (see Fig. 1). Besides the ground state geometric parameters, the different triplet states are finally determined by both the density functional theory (DFT) and time-dependent DFT (TDDFT) methods. On the basis of the respective optimized triplet geometry, the emissive wavelength is determined by the ΔSCF-DFT method. For all the experimental reported complexes, the Kasha rule is broken. The emission from the non-Kasha state is possible. To determine the quantum yield, the radiative rate constant (kr) is calculated by two different methods. Moreover, the items related with the kr, such as, Zero-field splitting (ZFS), transition dipole moments μ(Sn), singlet-triplet splitting energies ΔE(Sn−T1), and spin-orbit coupling (SOC) matrix elements 〈T1|HSO|Sn〉 are also calculated to further confirm the kr. The nonradiative rate constant (knr) is qualitatively evaluated by the popularity of the 3MC d-d state by the energy difference between 3MLCT/π-π∗ and 3MC d-d state, the barrier height between 3MLCT/π-π∗ and 3MC d-d state, and the required energy from 3MC d-d state decay to the 1S0 state. The barrier height between 3MLCT/π-π∗ and 3MC d-d state plays an important role to determine the knr. Finally, a novel Ir(III) complex is designed bearing 2-(2-trifluoromethyl) pyrimidine-pyridine (TPP) as primary ligand and amidinate as ancillary ligand. The phosphorescent emissive wavelength is obviously blue-shifted. Moreover, the quantum yield is comparable with that of complex 1.