Optical and Electrical Measurements Reveal the Orientation Mechanism of Homoleptic Iridium-Carbene Complexes.

Understanding and controlling the driving forces for molecular alignment in optoelectronic thin-film devices is of crucial importance for improving their performance. In this context, the preferential orientation of organometallic iridium complexes is in the focus of research to benefit from their improved light-outcoupling efficiencies in organic light-emitting diodes (OLEDs). Although there has been great progress concerning the orientation behavior for heteroleptic Ir complexes, the mechanism behind the alignment of homoleptic complexes is still unclear yet. In this work, we present a sky-blue phosphorescent dye that shows variable alignment depending on systematic modifications of the ligands bound to the central iridium atom. From an optical study of the transition dipole moment orientation and the electrically accessible alignment of the permanent dipole moment, we conclude that the film morphology is related to both the aspect ratio of the dye and the local electrostatic interaction of the ligands with the film surface during growth. These results indicate a potential strategy to actively control the orientation of iridium-based emitters for the application in OLEDs.

Manipulating the Transition Dipole Moment of CsPbBr3 Perovskite Nanocrystals for Superior Optical Properties.

Colloidal cesium lead halide perovskite nanocrystals exhibit unique photophysical properties including high quantum yields, tunable emission colors, and narrow photoluminescence spectra that have marked them as promising light emitters for applications in diverse photonic devices. Randomly oriented transition dipole moments have limited the light outcoupling efficiency of all isotropic light sources, including perovskites. In this report we design and synthesize deep blue emitting, quantum confined, perovskite nanoplates and analyze their optical properties by combining angular emission measurements with back focal plane imaging and correlating the results with physical characterization. By reducing the dimensions of the nanocrystals and depositing them face down onto a substrate by spin coating, we orient the average transition dipole moment of films into the plane of the substrate and improve the emission properties for light emitting applications. We then exploit the sensitivity of the perovskite electronic transitions to the dielectric environment at the interface between the crystal and their surroundings to reduce the angle between the average transition dipole moment and the surface to only 14° and maximize potential light emission efficiency. This tunability of the electronic transition that governs light emission in perovskites is unique and, coupled with their excellent photophysical properties, introduces a valuable method to extend the efficiencies and applications of perovskite based photonic devices beyond those based on current materials.

Correlating Optical and Electrical Dipole Moments To Pinpoint Phosphorescent Dye Alignment in Organic Light-Emitting Diodes.

Understanding the morphology of organic materials within optoelectronic thin film devices is of crucial importance for the development of state-of-the-art organic light emitting diodes (OLEDs). In this context, the preferential alignment of organometallic Ir complexes has been in the focus of research to benefit from the improved light-outcoupling efficiencies. Although the emissive dipole orientation has been identified from an optical point of view and molecular dynamic simulations give first insights into film morphologies, new experimental techniques are necessary to pinpoint the exact alignment of phosphorescent dye molecules. In this work, optical characterization of luminescent thin films was combined with electrical measurements on bilayer devices to elucidate the orientation distribution of both, electrical and optical dipole moments of phosphorescent guest-host systems. The results not only confirm previous suggestions for the alignment mechanism of organometallic dyes but also disclose a direct correlation between the degree of electrical and optical dipole alignment, thus opening a roadway for achieving higher light-outcoupling efficiency in OLEDs.

Insulinoma as rare cause of severe post-partum hypoglycemia.

Post-partum hypoglycemia in non-diabetic women is a rare condition. We report the exceptional case of a 38-year-old obese woman who experienced recurrent neuroglycopenia 3 weeks after delivery. Corresponding to severe hypoglycemia with blood glucose levels of <30 mg/dL, there was no suppression of insulin or C-peptide. Through endoscopic ultrasound we detected a hypoechoic lesion of 8 × 9 mm localized in the head of the pancreas. Thus, the diagnosis of insulinoma was most probable. Complete surgical enucleation of the insulinoma resulted in immediate and permanent resolution of hypoglycemia. The postoperative course was complicated by recurrent episodes of pancreatitis requiring endoscopic ultrasound-guided punctures of pseudocysts and temporary stenting of the pancreatic duct. In conclusion, insulinoma is a very rare, nonetheless important, differential diagnosis of post-partum hypoglycemia.