Theoretical Design of Blue-Color Phosphorescent Complexes for Organic Light-Emitting Diodes: Emission Intensities and Nonradiative Transition Rate Constants in Ir(ppy) 2 (acac) Derivatives.

Theoretical calculations of phosphorescent spectra and nonradiative transition (NRT) rate constants for S 1 ⇝ T 1 , T 1 ⇝ S 0 , and S 1 ⇝ S 0 were carried out to determine the best candidate for a blue-color phosphorescent complex among several derivatives of bis(2-phenylpyridine)(acetylacetonate)iridium(III). The geometries of the ground state (S 0 ), the lowest triplet state (T 1 ), and the lowest excited singlet state (S 1 ) were optimized at the levels of density functional theory, in which B3LYP functionals and SBKJC+p basis sets were used. The NRT rate constants were derived by using a generating function method within the displaced harmonic oscillator model. The results of the calculation for phosphorescence showed that the introduction of F and/or CN substituents at the 4'/6'-th and 5'-th sites in 2-phenylpyridinate (ppy) ligands, respectively, causes a blue shift of the emission spectra. They also suggest that Ir(5-CN,6-F-ppy) 2 (acac), denoted 3 (56) in the text, is a good candidate for a blue-color phosphorescent complex because a blue shift of emission spectra and a moderate intensity are obtained for phosphorescence and, furthermore, this complex is calculated to have a large rate constant for S 1 ⇝ T 1 and relatively smaller rate constants for T 1 ⇝ S 0 and S 1 ⇝ S 0 based on the calculations of spin-orbit coupling and nonadiabatic coupling constants.