Synthesis, photophysical and electrophosphorescent properties of mononuclear Pt(II) complexes with arylamine functionalized cyclometalating ligands |
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Authors: | Dongfang Qiu Jiang Wu Yanxiang Cheng Lixiang Wang |
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Affiliation: | a State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, Jilin Province 130022, PR China b Graduate School of Chinese Academy of Sciences, Beijing 100039, PR China |
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Abstract: | Four cyclometalated Pt(II) complexes, i.e., [(L2)PtCl] (1b), [(L3)PtCl] (1c), [(L2)PtCCC6H5] (2b) and [(L3)PtCCC6H5] (2c) (HL2 = 4-[p-(N-butyl-N-phenyl)anilino]-6-phenyl-2,2′-bipyridine and HL3 = 4-[p-(N,N′-dibutyl-N′-phenyl)phenylene-diamino]-phenyl-6-phenyl-2,2′-bipyridine), have been synthesized and verified by 1H NMR, 13C NMR and X-ray crystallography. Unlike previously reported complexes [(L1)PtCl] (1a) and [(L1)PtCCC6H5] (2a) (HL1 = 4,6-diphenyl-2,2′-bipyridine), intense and continuous absorption bands in the region of 300-500 nm with strong metal-to-ligand charge transfer (1MLCT) (dπ(Pt) → π∗(L)) transitions (ε ∼ 2 × 104 dm3 mol−1 cm−1) at 449-467 nm were observed in the UV-Vis absorption spectra of complexes 1b, 1c, 2b and 2c. Meanwhile, with the introduction of electron-donating arylamino groups in the ligands of 1a and 2a, complexes 1b and 2b display stronger phosphorescence in CH2Cl2 solutions at room temperature with bathochromically shifted emission maxima at 595 and 600 nm, relatively higher quantum yields of 0.11 and 0.26, and much longer lifetimes of 8.4 and 4.5 μs, respectively. An electrochromic film of 1b-based polymer was obtained on Pt or ITO electrode surface, which suggests an efficient oxidative polymerization behavior. An orange multilayer organic light-emitting diode with 1b as phosphorescent dopant was fabricated, achieving a maximum current efficiency of 11.3 cd A−1 and a maximum external efficiency of 5.7%. The luminescent properties of complexes 1c and 2c are dependent on pH value and solvent polarity, which is attributed to the protonation of arylamino units in the C^N^N cyclometalating ligands. |
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Keywords: | Neutral-charge Platinum Arylamine Phosphorescence Organic light-emitting diode |
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