Structural,photophysical, and electrophosphorescent properties of platinum(II) complexes supported by tetradentate N2O2 chelates |
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Authors: | Lin Yong-Yue Chan Siu-Chung Chan Michael C W Hou Yuan-Jun Zhu Nianyong Che Chi-Ming Liu Yu Wang Yue |
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Institution: | Department of Chemistry, HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China. |
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Abstract: | We present an examination of the structural and photophysical characteristics of Pt(N(2)O(2))] complexes bearing bis(phenoxy)diimine auxiliaries (diimine=4,7-Ph(2)phen (1) and 4,4'-tBu(2)bpy (2)) that are tetradentate relatives of the quinolinolato (q) ligand. These neutral derivatives display high thermal stability (>400 degrees C in N(2)). While the crystal lattice in 1 consists of (head-to-tail)-interacting dimers, molecules of 2 are arranged into infinitely stacked planar sheets with possible pi-pi interactions but no close Pt.Pt contacts. Complexes 1 and 2 exhibit moderately intense low-energy UV/Vis absorptions around lambda=400-500 nm that undergo negative solvatochromic shifts. Both derivatives are highly luminescent in solution at 298 K with emission lifetimes in the micros range, and mixed (3)l-->pi*(diimine)] (l=lone pair/phenoxide) and (3)Pt(d)-->pi*(diimine)] charge-transfer states are tentatively assigned. The excited-state properties of 2 are also investigated by time-resolved absorption spectroscopy and by quenching experiments with pyridinium acceptors to estimate the excited-state redox potential. These emitters have been employed as electrophosphorescent dopants in multilayer OLEDs. Differences between the brightness, color, and overall performance of devices incorporating 1 and 2 are attributed to the influence of the diimine substituents. |
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Keywords: | charge transfer electroluminescence N O ligands phosphorescence platinum |
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