Luminescent organoplatinum(II) complexes with functionalized cyclometalated C^N^C Ligands: Structures, Photophysical Properties, and Material Applications

Abstract

A series of [(R'-C^N^C-R')Pt(L)] complexes with doubly deprotonated cyclometalated R'-C^N^C-R' ligands (R'-C^N^C-R'=2,6-diphenylpyridine derivatives) functionalized with carbazole, fluorene, or thiophene unit(s) have been synthesized and their photophysical properties studied. The X-ray crystal structures reveal extensive intermolecular π̄π and C-H̄π interactions between the cyclometalated C^N^C ligands. Compared to previously reported cyclometalated platinum(II) complexes [(C^N^C)Pt(L)], which are non-emissive in solution at room temperature, the carbazole-, fluorene-and thiophene-functionalized [(R'-C^N^C-R')Pt(L)] (L=DMSO 1-9, C=N-Ar, 1a-9a) complexes are emissive in solution at room temperature with λ max at 564-619nm and ∥=0.02-0.26. The emissions of the [(R'-C^N^C-R')Pt(L)] complexes are attributed to electronic excited states with mixed 3MLCT and 3IL character. The carbazole/fluorene/ thiophene unit(s) allow the tuning of the electronic properties of the [(R'-C^N^C-R')Pt] moiety, with the emission maxima in a range of 564-619nm. These are the first examples of organoplatinum(II) complexes bearing doubly deprotonated cyclometalated C^N^C ligands that are emissive in solution at room temperature. In non-degassed DMSO, the emission intensities of 6a-9a are enhanced upon exposure to ambient light. This phenomenon is caused by reacting photogenerated 1O 2 with a DMSO molecule to form dimethyl sulfone, leading to the removal of dissolved oxygen in solution. Self-assembled nanowires and nanorods are obtained from precipitation of 3a in THF/H 2O and 8a in DMSO/Et 2O, respectively. The [(R'-C^N^C-R')Pt(L)] complexes are soluble in common organic solvents with a high thermal stability (>300°C), rendering them as phosphorescent dopants for organic light-emitting diode (OLEDs) applications. Red OLEDs with CIE coordinates of (0.65 ±0.01, 0.35 ±0.01) were fabricated from 7a or 8a. A maximum external efficiency (η Ext) of 12.6% was obtained for the device using 8a as emitter. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.