Efficient and tunable phosphorescence of new platinum(II) complexes based on the donor–π–acceptor Schiff bases

• Donor–π–acceptor type platinum(II) Schiff base complexes were developed.
• Their photophysical properties and electrochemical behaviors were investigated.
• The HOMO and LUMO energy levels can be adjusted by the structure optimization.
• The complexes emit in the range of yellow to red.
• Their photophysical properties were investigated by density functional theory.

The condensation of 4-(diethylamino)-2-hydroxybenzaldehyde with 2,3-diaminomaleonitrile and benzene-1,2-diamine, respectively, afforded two donor–π–acceptor Schiff base ligands H2L1 and H2L2. For comparison, the condensation of 3,5-di-tert-butyl-2-hydroxybenzaldehyde with 4-(trifluoromethyl)benzene-1,2-diamine produced the ligand H2L3. Subsequently, their corresponding platinum(II) complexes PtL1, PtL2 and PtL3 were prepared through the metallation of ligands with K2PtCl4. All the ligands and complexes were characterized by 1H NMR, infrared spectroscopy and mass spectrometry. And their thermal stabilities, photophysical properties, and electrochemical behaviors were investigated in detail. These complexes show yellow to red emissions with the highest quantum yield of 8.6% for PtL1. The decay times in microsecond scale (1.97–2.35 μs) indicate their phosphorescence characteristics arising from the triplet state. The B3LYP density functional theory calculations shows that the HOMO–LUMO gaps of PtL1, PtL2 and PtL3 are 2.53, 3.07 and 2.78 eV, respectively, which are well consistent with their photophysical properties. With the advantages of preparative accessibility and high thermal stability, these new phosphorescent platinum(II) complexes are attractive as emissive layer in organic light-emitting diodes.

The condensation of 4-(diethylamino)-2-hydroxybenzaldehyde with 2,3-diaminomaleonitrile and benzene-1,2-diamine, respectively, afforded two donor–π–acceptor Schiff base ligands H2L1 and H2L2. And their corresponding platinum(II) complexes PtL1, PtL2 show yellow to red emissions with the highest quantum yield of 8.6% for PtL1.Figure optionsDownload as PowerPoint slide