The synthesis, photophysical properties and application as emitters in solution-processed multi-layer organic light-emitting diodes (OLEDs) of a series of blue-green to red light-emitting phosphorescent platinum(II) complexes are reported. These complexes consist of phenylisoquinoline, substituted phenylpyridines or tetrahydroquinolines as C^N cyclometalating ligands and dipivaloylmethane as an ancillary ligand. Depending on both the structure of the C^N cyclometalating ligands and the dopant concentration in the matrix, these platinum(II) complexes exhibit different aggregation tendencies. This property affects the photoluminescence spectra of the investigated compounds and colour-stability of the fabricated OLEDs. Using the blue-green to yellow-green emitting complexes, the best results were obtained with the 2-(4-trifluoromethylphenyl)-5,6,7,8-tetrahydroquinoline based platinum(II) complex. A maximum luminous efficiency of 4.88 cd A⁻¹ and a power efficiency of 4.65 lm W⁻¹, respectively, were achieved. Employing the red emitting phenylisoquinoline based complex as an emitter, colour-stable and efficient (4.71 cd A⁻¹, 5.12 lm W⁻¹) devices were obtained.

In this study, multilayer organic light-emitting diodes (OLEDs) consisting of three solution-processed layers are fabricated using slot die coating, gravure printing, and inkjet printing, techniques that are commonly used in the industry. Different technique combinations are investigated to successively deposit a hole injection layer (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)), a cross-linkable hole transport layer (N,N′-bis(4-(6-((3-ethyloxetan-3-yl)methoxy)-hexyloxy)phenyl)-N,N′-bis(4-methoxyphenyl)biphenyl-4,4′-diamin (QUPD)), and a green emissive layer (TSG-M) on top of each other. In order to compare the application techniques, the ink formulations have to be adapted to the respective process requirements. First, the influence of the application technique on the layer homogeneity of the different materials is investigated. Large area thickness measurements of the layers based on imaging color reflectometry (ICR) are used to compare the application techniques regarding the layer homogeneity and reproducible film thickness. The total stack thickness of all solution-processed layers of 32 OLEDs could be reproduced homogeneously in a process window of 30 nm for the technique combination of slot die coating and inkjet printing. The best efficiency of 13.3 cd A⁻¹ is reached for a process combination of slot die coating and gravure printing. In order to enable a statistically significant evaluation, in total, 96 OLEDs were analyzed and the corresponding 288 layers were measured successively to determine the influence of layer homogeneity on device performance.

The structure–property correlations of a set of heteroleptic red- and green-emitting Ir(III) complexes with different temperature sensitivities and charge trapping capabilities are described, revealing superb performance in multi-layer phosphorescent organic light-emitting diodes (PhOLEDs) expressed by very high maximum luminous efficiencies up to 36.8 cd A⁻¹. Using 2-phenylpyridine and with 2-(naphthalen-1-yl)pyridine as the C⁁N ligand, the resulting red emitting complex featured a maximum luminous efficiency of 10.8 cd A⁻¹; one of the most excellent device performances within this class of red Ir(III) emitters.

Bis‐cyclometalated Pt^II complexes of dianionic 2,5‐bis(aryl)‐pyridine ligands (L^1–6)^2–, carrying various cyclometalating or pending aryl groups, are synthesised in two steps. The reactions of H₂L protoligands with K₂[PtCl₄] in acetic acid give the mono‐cyclometalated complexes [Pt(HL)Cl]₂. Heating these complexes in hot DMSO (dimethyl sulfoxide) yields the double‐cyclometalated DMSO complexes [Pt(L^1–6)(DMSO)]. The reaction of [Pt(L⁴)(DMSO)] with N,N‐dimethylimidazolium iodide in the presence of KOtBu as the base gives the carbene complex [Pt(L⁴)(Me₂Imd)]. Detailed photophysical studies reveal the intense orange luminescence of these complexes in CH₂Cl₂ solution, with quantum yields up to 0.22, and increased quantum yields of up to 1.00 in glassy frozen CH₂Cl₂/MeOH (1:1) and up to 0.44 in PMMA matrices. Detailed electrochemistry (including spectroelectrochemistry) reveals reversible ligand‐based first reductions at –2.1 to –2.3 V, irreversible Pt‐centred oxidations at around 0.8 V and electrochemical band gaps of 2.8–3.0 eV. Further reduction waves at very negative potentials interfere with the solvent (THF with traces of water) discharge and can be traced, with UV/Vis spectroelectrochemistry, to Pt‐centred reductions for the DMSO complexes and to a second ligand‐centred reduction for the Me₂Imd complex from. The photo/electrochemical properties can be roughly correlated with the ligand pattern and suggest their use in optoelectronic applications.