Theoretical investigation on the phosphorescence quantum yields of cyclometalated (C∧N*) Pt(II) (acac) complexes: The impact of the position of the BMes2 moiety on the radiative and nonradiative decay processes

Abstract

Abstract The radiative and non-radiative decay processes of four cyclometalated (C ∧ N*)Pt(II)(acac) complexes were investigated by using the density functional theory/time dependent density functional theory (DFT/TD-DFT) approach. In order to explore the influence of the BMes 2 moiety on the quantum yields of complex (ppy)Pt(acac) (ppy = 2-phenylpyridine, acac = acetylacetonate), the radiative process was determined by calculating the spin orbital coupling (SOC) as well as zero-field-splitting (ZFS) parameters. In addition, the SOC matrix elements between T 1 and S 0 state, the Huang-Rhys factor, the degree of vibronic coupling between S 0 and T 1 states were also computed to describe the non-radiative decay process. The results show that, the fatal factor to the low phosphorescence quantum yields in complex Pt(ppy)(acac) is a fast non-radiative decay caused by a large Huang-Rhys factor ( S M ) and the maximum reorganization energy appearing in the high frequency range. However, the introduction of the BMes 2 moiety, a bulky and featuring strong electron-withdrawing character and vacant p-orbital of B atom, could decrease the values of Huang-Rhys factor by suppressing the C-C stretching vibrations in the ppy ligand, inhibiting the non-radiative decay process. Besides, for complex 2 , the introduction of the BMes 2 group into the meta -position of the pyridine ring in C ∧ N chelate, added the π (aryl)-p(B) delocalization interaction, resulting in a large ZFS and k r , a small 〈S 0 |H SOC |T 1 〉 2 , the square value of coupling matrix between the ground state S 0 and the lowest triplet state T 1 , thus leading to its quantum yield is superior to the other complexes.