Heteroleptic cuprous complexes of a diimine MePBO ligand and their structure influence on phosphorescent color: Syntheses, structure characterizations, properties and TD‐DFT calculations
D. Dai, Li Song, Yu Ting Liang, Jian‐Teng Wang, Yiming Zhou, Hangyan Shen, Wen‐Xiang Chai
Abstract
Abstract Three new heteroleptic [Cu(NN)P 2 ] + type cuprous complexes 1 – 3 were designed and synthesized by utilizing a diimine ligand 5‐methyl‐2‐(2′‐pyridyl)‐benzoxazole (MePBO) and different phosphine ligands PPh 3 ( 1 ), m‐Tol 3 P ( 2 ) and POP ( 3 ), (PPh 3 =triphenylphosphine, m‐Tol 3 P=tris(3‐methylphenyl)phosphine, POP=bis[2‐(diphenylphosphino)phenyl]ether), respectively. All complexes were characterized by single‐crystal X‐ray diffraction, spectroscopic analysis (IR, UV‐Vis), elemental analysis, and photoluminescence study. Single‐crystal X‐ray diffraction revealed that complexes 1 – 3 all adopt discrete cation complex structure with a tetrahedral CuN 2 P 2 coordination geometry with diverse P−Cu−P angles. Their UV‐Vis absorption spectra exhibit a blue‐shift sequence under the enlarging of P−Cu−P angle from 3 to 2 then to 1 . The PL emission peak wavelengths of 1 – 3 also present similar blue‐shift sequence ( 3 → 1 / 2 ). Their microsecond PL lifetime indicates that their PL behavior belongs to phosphorescence. TD‐DFT calculation and wavefunction analysis illuminate that the S 1 and T 1 states of 1 – 3 should all be assigned as (ML+L′L)CT states. Their UV‐Vis absorption and phosphorescence should be attributed to the charge transfer from the P−Cu−P segment to the MePBO ligand. Therefore, as P−Cu−P angle increases (lower HOMO), the energy of S 1 and T 1 states also increase, following the change of PL color. Additionally, the steric hindrance from substituents of phosphine ligand, as well as extra strong intra‐molecular π−π stacking interactions should effectively inhibit nonradiative decay so that an abnormal PL emission blue‐shift is observed from 1 to 2 .