Influence of primary and auxiliary ligand on spectroscopic properties and luminescent efficiency of organoplatinum(ii) complexes bearing functionalized cyclometalated C^N^C ligands

Abstract

A theoretical investigation into eighteen recently synthesized Pt(II) complexes [(R1ⁿ–C^N^C–R2ⁿ)Pt(L)] with doubly deprotonated cyclometalated R1ⁿ–C^N^C–R2ⁿ ligands (n = 1–9, R1ⁿ–C^N^C–R2ⁿ = 2,6-diphenylpyridine derivatives) and L ligands (L = DMSO, 1–9; L = –CN–Ar, 1a–9a), which are used as emitters in orange-red emitting diodes, is reported in this paper. Geometric and electronic structures, absorption and emission spectra, phosphorescence quantum yields, and electroluminescence (EL) efficiency were investigated by DFT and TDDFT methods. We focused on the influence of the primary ligand (R1ⁿ–C^N^C–R2ⁿ) and auxiliary ligand (L) on the optical and electronic properties of Pt(II) complexes by introducing carbazole, fluorene, and thiophene group in the primary ligand and/or the replacement of DMSO by –CN–Ar as an ancillary ligand. The incorporation of carbazole, fluorene, and thiophene into the primary ligand caused the red-shift of absorption and emission spectra. The metal–ligand bond length is contracted where –CN–Ar was employed as the secondary ligand, which facilitate the metal to ligand charge transfer (MLCT). The larger involvement of MLCT character in emission process is beneficial for improving the quantum yields of 2a–9a. For EL efficiency, all the complexes have a good balance of reorganization energy as potential systems for fabricating effective OLEDs devices except for 1 and 1a. In addition, two new molecules were designed with comparable or better EL efficiency.