Small substituent groups as geometric controllers for tridentate platinum(ii) complexes to effectively suppress non-radiative decay processes

• Published in: Physical chemistry chemical physics : PCCP 2019-01, Vol.21 (5), p.2764-277
• Main Authors: Luo, Yafei, Chen, Zhongzhu, Hu, Jianping, Xu, Zhigang, Meng, Qingxi, Tang, Dianyong
• Format: Article
• Language: English
• Subjects: Controllers; Decay rate; Density functional theory; Distortion; Electrons; Emitters; Emitters (electron); Energy gap; Jahn-Teller effect; Mathematical analysis; Molecular orbitals; Nitrogen dioxide; Phosphorescence; Platinum
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c8cp06804f

For phosphorescent emitters, the rigidity of the geometry is a crucial indicator, which can directly determine the non-radiative decay rate. In this article, density functional theory (DFT) calculations were performed to investigate the influence of the small substituent groups on the rigidities of tridentate Pt( ii ) complexes in detail. The calculated results indicate that the small substituent groups can serve as geometric controllers to suppress the structural distortion on going from the ground state (S 0 ) to the lowest-lying triplet excited state (T 1 ) (Jahn-Teller distortion). For instance, when electron-donating substituent groups, including -NH 2 , -N(CH 3 ) 2 and -OCH 3 , were employed, the rigidities of the corresponding Pt( ii ) complexes can be effectively enhanced because the highest occupied molecular orbital (HOMO)-HOMO−1 energy gaps could be increased. Different from the electron-donating substituent groups, electron-withdrawing substituent groups, i.e. , -NO 2 and -COCH 3 , can cause a negligible change in HOMO and HOMO−1 energies during the S 0 → T 1 transition process, and therefore, for Pt-NO 2 and Pt-COCH 3 , no Jahn-Teller distortion occurs. According to the calculated results, the rigidities of tridentate Pt( ii ) complexes could be raised via tuning the energies of the frontier molecular orbital (FMO) with the help of small substituent groups. For phosphorescent emitters, the rigidity of the geometry is a crucial indicator, which can directly determine the non-radiative decay rate. Small substituent groups as geometric controllers can effectively control the rigidities of tridentate platinum( ii ) complexes.