Theoretical study and design of highly efficient platinum() complexes bearing tetradentate ligands for OLED

• Published in: RSC advances 2016-01, Vol.6 (14), p.11648-11656
• Main Authors: Feng, Ting-Ting, Bai, Fu-Quan, Xie, Li-Ming, Tang, Yongan, Zhang, Hong-Xing
• Format: Article
• Language: English
• Subjects: Charge transfer; Coordination compounds; Decay; Density functional theory; Imidazole; Mathematical analysis; Phosphorescence; Rigidity
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/c5ra22754b

Density functional theory and time-dependent density functional theory investigations were performed on the geometrical structures, basic photophysical properties, phosphorescence quantum efficiency ( Φ PL ), and reorganization energy ( λ ) calculations of a new potential class of tetradentate Pt( ii ) complexes Pt[ppz-O-Popy] ( 1 ) (where ppz = phenyl-pyrazole; Popy = phenoxyl-pyridine), Pt[pmi-O-Popy] ( 2 ) (where pmi = phenyl-methylimidazole), Pt[pmi-O-Cbpy] ( 3 ) (where Cbpy = carbazolyl-pyridine) and Pt[ppz-O-Cbpy] ( 4 ), which show highly efficient ( Φ PL > 80%) and deep-blue emission. Nonradiative decay processes were investigated in order to obtain a more reliable nonradiative decay rate comparison. The calculated results confirm that tetradentate Pt( ii ) complexes are conducive to maintaining the rigidity of the molecules. The extended conjugation complexes with carbazole groups in 3 and 4 can not only improve the structural rigidity but also enhance the capability and balance of charge transfer. Thereupon, the following two designed derivatives Pt[pmi-O-Cbmi] ( 5 ) and Pt[pmi-O-Cbbm] ( 6 ) which substitute pyridine with imidazole and benzimidazole based on complexes 3 and 4 are also considered for promising materials exploitation and theoretical understanding. The charge transfer balance performance and the radiative decay rate constant ( k r ) of 5 and 6 are greatly improved compared with 1-4 , and the better structural rigidity will weaken nonradiative decay pathways, which may result in a higher phosphorescence quantum efficiency. Therefore, complexes 5 and 6 through judicious molecular design will be promising candidates as highly efficient blue-emitting phosphorescent materials for applications. Theoretical study for improving the efficiency of a novel tetradentate platinum( ii ) complexes in OLED by molecular modification.