Luminescent Organoplatinum(II) Complexes with Functionalized Cyclometalated C∧N∧C Ligands: Structures, Photophysical Properties, and Material Applications

A series of [(R'-C boolean AND N boolean AND C-R'')Pt(L)] complexes with doubly deprotonated cyclometalated R'-C boolean AND N boolean AND C-R'' ligands (R'-C boolean AND N boolean AND 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 pi center dot center dot center dot pi and C-H center dot center dot center dot pi interactions between the cyclometalated C boolean AND N boolean AND C ligands. Compared to previously reported cyclometalated platinum(II) complexes [(C boolean AND N boolean AND C)Pt(L)], which are non-emissive in solution at room temperature, the carbazole-, fluorene- and thiophene-functionalized [(R'-C boolean AND N boolean AND C-R'')Pt(L)] (L=DMSO 19, C?N?Ar, 1?a9?a) complexes are emissive in solution at room temperature with ?max at 564619 nm and F=0.020.26. The emissions of the [(R'-C boolean AND N boolean AND 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 boolean AND N boolean AND C-R'')Pt] moiety, with the emission maxima in a range of 564619 nm. These are the first examples of organoplatinum(II) complexes bearing doubly deprotonated cyclometalated C boolean AND N boolean AND 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 1O2 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/H2O and 8a in DMSO/Et2O, respectively. The [(R'-C boolean AND N boolean AND C-R'')Pt(L)] complexes are soluble in common organic solvents with a high thermal stability (>300 degrees 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 7?a or 8a. A maximum external efficiency (eta Ext) of 12.6% was obtained for the device using 8a as emitter.