Highly efficient orange-emitting OLEDs based on phosphorescent platinum(II) complexes

Abstract

The syntheses, characterisations, photophysical properties and their applications in organic light emitting devices of a series of 2-phenylbenzothiazolato (bt)/substituted 2-phenylbenzothiazolato (X-bt) platinum(II) based square-planar complexes [(X-bt)Pt(acac); acac = acetylacetonate; X = unsubstituted (1), F (2), OMe (3) and CF3 (4)] are discussed. Reaction of K2PtCl4 with btH/X-btH in glacial acetic acid for a few days results in the dinuclear chloro-bridged Pt(II) complex, (bt/X-bt)Pt(μ-Cl)Pt(bt/X-bt) which is cleaved with acetylacetone to give the corresponding mononuclear (bt/X-bt)Pt(acac) complex. The (MeO-bt)Pt(acac) complex has been characterized by X-ray single crystal structure analysis. The packing diagram shows the Pt–Pt distances and the intermolecular spacings are 3.369 and 3.360 Å, respectively, which is consistent with excimer formation. It has also been supported by time-resolved photoluminescence (PL) measurements. The nature of the lowest emitting states are the triplet MLCT as well as triplet π–π* states and it has been tuned according to the electronic properties of the substituents. The electroluminescent (EL) devices were fabricated by doping platinum complexes 1 and 2 (the corresponding devices denoted as D-1 and D-2, respectively) into the host CBP (4,4′-(N,N′-dicarbazole)biphenyl), in the emitting zone with a doping content of 5%, 7% and 9%. The EL performances for these devices are exceptionally high (14.3 and 16.0 cd A−1 @2 mA cm−2 and luminances 10 550 and 11 320 cd m−2 @100 mA cm−2 for D-1 and D-2, respectively).