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

Shiro Koseki; Masaki Yoshii; Toshio Asada; Yuichi Fujimura; Takeshi Matsushita; Shigeyuki Yagi

doi:10.1021/acs.jpca.1c08261

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

J Phys Chem A. 2021 Dec 23;125(50):10604-10614. doi: 10.1021/acs.jpca.1c08261. Epub 2021 Dec 14.

Authors

Shiro Koseki^{1

2}, Masaki Yoshii¹, Toshio Asada^{1

2}, Yuichi Fujimura³, Takeshi Matsushita^{2

4}, Shigeyuki Yagi^{2

5}

Affiliations

¹ Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Sakai 599-8531, Japan.
² The Research Institute for Molecular Electronic Devices (RIMED), Osaka Prefecture University, Sakai 599-8531, Japan.
³ Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
⁴ JNC Corporation, 5-1 Goikaigan, Ichihara, Chiba 290-8551, Japan.
⁵ Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan.

PMID: 34905372
DOI: 10.1021/acs.jpca.1c08261

Abstract

Theoretical calculations of phosphorescent spectra and nonradiative transition (NRT) rate constants for S₁ ⇝ T₁, T₁ ⇝ S₀, and S₁ ⇝ S₀ 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 (S₀), the lowest triplet state (T₁), and the lowest excited singlet state (S₁) 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 S₁ ⇝ T₁ and relatively smaller rate constants for T₁ ⇝ S₀ and S₁ ⇝ S₀ based on the calculations of spin-orbit coupling and nonadiabatic coupling constants.