Platinum(II) complexes with cyclometallated 5-pi-delocalized-donor-1,3-di(2-pyridyl)benzene ligands as efficient phosphors for NIR-OLEDs

Two new pincer proligands, namely 5-(p-(N, N-diphenylamino) phenylethynyl)-1,3-di(2-pyridyl) benzene (HL1) and trans-5-(p-(N, N-diphenylamino) styryl-1,3-di(2-pyridyl) benzene (HL2) were prepared together with their N boolean AND C boolean AND N-coordinated cyclometallated platinum(II) complexes (PtLX)-X-1 (X = Cl, NCS) and (PtLCl)-Cl-2. Both ligands are intensely luminescent in solution (quantum yields > 0.8). (PtLX)-X-1 complexes display high quantum yields in solution whereas that of (PtLCl)-Cl-2 is very low due to the ease with which trans to cis isomerisation of the diphenylaminostyryl C=C bond occurs. Distinct sets of emission bands attributable to the cis and trans forms are observable in glass at 77 K, the assignments being supported by TD-DFT calculations. Organic light-emitting diodes (OLEDs) have been prepared using the new compounds as phosphorescent emitters. Remarkably, despite the inferior quantum yield of (PtLCl)-Cl-2 in solution, the best electroluminescence quantum efficiencies are obtained with this complex, which emerges as an excellent candidate for the preparation of NIR-OLEDs.