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

Abstract

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^C^N-coordinated cyclometallated platinum(II) complexes PtL¹X (X = Cl, NCS) and PtL²Cl. Both ligands are intensely luminescent in solution (quantum yields > 0.8). PtL¹X complexes display high quantum yields in solution whereas that of PtL²Cl is very low due to the ease with which trans to cis isomerisation of the diphenylaminostyryl CC 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 PtL²Cl in solution, the best electroluminescence quantum efficiencies are obtained with this complex, which emerges as an excellent candidate for the preparation of NIR-OLEDs.