Phosphorescent systems based on iridium(III) complexes

Phosphorescent iridium(III)-based complexes are experiencing a growing interest in a number of research fields. Aside from lighting and display technologies (i.e. OLEDs and LECs), they find use in various applications such as biolabeling, sensors, solar cells and water splitting. In particular, the opportunity to tune the electro-optical properties by adapting the coordinated ligand sets makes these transition metal complexes very attractive. Emission colors covering the whole spectrum of the visible light can be realized. High luminescence efficiencies and lifetimes in the range of nano- to micro¬seconds are further promissing features. The rich coordination chemistry of the iridium(III) ion provides immense freedom for the design of new systems. Besides the wide scope of options to modify the electro-optical characteristics, the various possibilities to introduce active sites and functionalities are highly appealing. The most common iridium(III) emitters are bis- and tris-cyclometallated species based on 2-phenylpyridine-derived ligands. In particular, facial tris-cyclometallated emitters are considered to be highly efficient. However, a broad spectrum of ancillary ligand structures can be used in the formation of bis-cyclometallated species offering additional options to tune the electro-optical properties and to introduce lateral functionalities. Dimeric µ-chloro-bridged precursor complexes, easily accessible by the reaction of iridium(III) chloride hydrate and the designated cyclometallating ligands, are the basis for most synthetic approaches towards iridium(III) phosphors. In this thesis, a set of precursors based on "classical" ligands (i.e. 2-phenylpyridinato, 2-(4-formylphenyl)-pyridinato and coumarinato-6) have been synthesized and applied in the formation of various bis-cyclometallated emitters. Depending on the ancillary ligand charged and neutral species can be formed. In the first part, several S-shaped terpyridines have been used to synthesize a series of cationic emitters. The characteristics of the new species were investigated by NMR, UV-vis absorption and photoluminescence spectroscopy as well as elemental analysis, MALDI-TOF mass spectrometry, thermogravimetric analysis and cyclic voltammetry. In particular, the emission behavior was found to be influenced by variations of the coordinated ligands. Aside from the selection of the cyclometallating ligands, some of the employed S-terpyridine ligand caused distinct alterations; while modifications at the periphery of the S-terpyridine (i.e. an arylic substituent) led only to marginal changes in the optical properties, the exchange of a central substituent (aryl towards alkyl) and the modification of the conjunction of the terpyridine rings (from ( CH2-)2 to (-CH2-)1) clearly affected the emission. The synthesis of "classical" cyclometallating compounds exhibiting pyridine motifs commonly involves cross-coupling methods such as the Stille and the Suzuki reaction. In the second part of this thesis, an approach towards new cyclometallating ligands was investigated. The highly efficient "click" reaction of acetylene- and azide-functions was utilized to synthesize two isomeric phenyl-1H-[1,2,3]-triazole derivatives, which were employed in the formation of dimeric µ-chloro-bridged precursor complexes. Based on 1 decyl-4-phenyl-1H-[1,2,3]triazole, a whole set of charged and neutral bis-cyclo¬metallated emitters was synthesized and investigated in detail. The properties of the new species were compared with 2-phenylpyridine-based complexes possessing the same ancillary ligands. More insights into the photophysical properties could be gained by theoretical DFT calculations. Aside from expanding the toolbox for the tuning of the electro-optical properties this coordination approach appears suitable to easily introduce further functionalities. A convenient way to introduce functional groups was followed by utilizing acetoacetate derivatives as ancillary ligand. By performing simple transesterification reactions at commercial tert-butyl acetoacetate, a broad variety of functional derivatives is accessible. Butyl acetoacetate, as well as oxetane- and methacrylate-equipped acetoacetate, have been employed in the formation of emissive bis-cyclometallated species. The oxetane- as well as methacrylate functionality were used to incorporate the phosphorescent emitters into polymeric assemblies. There are two main procedures to fabricate organic light emitting devices: vacuum deposition, and solution processing. While the vacuum deposition of small and thermal stable molecules easily allows the realization of elaborated device designs by applying mask techniques, the assembly of multilayer devices by solution processing techniques such as spin-coating and inkjet-printing is often limited. However, the spectrum of materials which can be processed from solution is much broader, and the processing from solution is cost-effective. One approach to overcome the limitations is the crosslinking of the deposited layers, which prevents redissolving in the following steps. In particular, the cationic ring opening polymerization of oxetane-units was demonstrated to be an effective tool to form crosslinked device layers. One part of this thesis was dedicated to the design of oxetane-equipped iridium(III) phosphors, which can be incorporated into oxetane-based crosslinkable matrixes. Thus, the approach could be expanded to the fabrication of crosslinked emissive layers doped with phosphorescent emitters. After synthesis and characterization of the emitters, their incorporation and performance in an oxetane-equipped matrix were investigated. Although the host and the guest were found to be not a good match, employing an optimized multilayered device assembly including a hole-blocking/electron-conducting layer, a fully solution processed, highly efficient OLED could be fabricated. However, considering the restricted stability of the applied complex (in particular under acidic conditions), the adjustment of the emitter design could lead to further improvements. Due to their film-forming abilities, polymeric materials are highly suitable for processing from solution. The doping of phosphors into polymeric hosts became a common approach for the fabrication of emissive layers. However, the efficiency of such systems can suffer from undesired phase separation and crystallization. By combining the different species for charge transport and emission within one polymer, these problems can potentially be overcome. Moreover, a better performance due to improved charged transport and/or energy transfer to the emitter can be expected. The last part of this thesis deals with two approaches to synthesize polymeric chains with attached iridium(III) complexes. The first approach utilizes a reactive µ-hydroxy-bridged dimeric iridium(III) precursor complex to coordinate polymer-bound ligand sites. The defined polymer was obtained by the copolymerization of methylmethacrylate and acetoacetoxyethyl meth¬acrylate under reversible addition fragmentation chain transfer (RAFT) polymerization conditions. The successful formation of a coordinated polymer could be confirmed by size exclusion chromatography (SEC) in combination with a photodiode array detector. Further evidence was obtained by the comparison of NMR, UV-vis and photo¬luminescence spectra with the data of an analogous butyl acetoacetate coordinated model complex. By this synthetic approach, the complex content within a polymer can be defined by the number of ligand sites and the feed of the coordinating species. For the second approach, a complex monomer (methacrylate-functionalized) was synthesized, which could be successfully applied in radical polymerizations with meth¬acrylate-based comonomers. Also here the formation of polymers containing iridium(III) emitters could be demonstrated by PDA-supported SEC-experiments. Investigations by NMR, UV-vis and photoluminescence spectroscopy provided information about their composition. Moreover, indications for highly efficient host-guest behavior were found for a carbazole-based copolymer

Tracking spin and charge with spectroscopy in spin-polarised 1D systems

We calculate the spectral function of a one-dimensional strongly interacting chain of fermions, where the response can be well understood in terms of spinon and holon excitations. Upon increasing the spin imbalance between the spin species, we observe the single-electron response of the fully polarised system to emanate from the holon peak while the spinon response vanishes. For experimental setups that probe one-dimensional properties, we propose this method as an additional generic tool to aid the identification of spectral structures, e.g. in ARPES measurements. We show that this applies even to trapped systems having cold atomic gas experiments in mind.Comment: 5 pages, 4 figure

Microscale Modeling of Magnetoactive Composites Undergoing Large Deformations

This paper is concerned with the development of a material model for the constituents of a magnetoactive composite. Special attention is paid to magnetorheological elastomers which are synthesized from a soft polymeric matrix material with embedded magnetizable particles. Because the particles interact under an applied magnetic load, a coupled magneto-mechanical field problem has to be solved. The mechanical properties of the polymer matrix motivate the consideration of large deformations. We present the balance equations with boundary conditions and an appropriate material model. The corresponding boundary value problems are solved by the Finite-Element-Method. A weak numerical coupling scheme enables the staggered solution of two subproblems, the stationary magnetic and mechanical one. The coupling between both is realized by a surrounding iterative loop

Probing modified gravity with magnetically levitated resonators

We present an experimental procedure, based on Meissner effect levitation of neodymium ferromagnets, as a method of measuring the gravitational interactions between milligram masses. The scheme consists of two superconducting lead traps, with a magnet levitating in each trap. The levitating magnets behave as harmonic oscillators and, by carefully driving the motion of one magnet on resonance with the other, we find that it should easily be possible to measure the gravitational field produced by a 4 mg sphere, with the gravitational attraction from masses as small as 30 μg predicted to be measurable within a realistic measurement time frame. We apply this acceleration sensitivity to one concrete example and show the abilities of testing models of modified Newtonian dynamics

Modelling and control of a water jet cutting probe for flexible surgical robot

Surgical removal of cancerous tissue from the spine is limited by the inability of hand held drills and cutting tools to reach small crevices present in complex bones such as the spinal column, especially on the anterior side. In addition, the high speed rotating mechanisms used presently are subject to stability issues when manoeuvring around tortuous bone forms. We report on the design and experimental testing of a novel flexible robotic surgical system which addresses these issues. The robot consists of a flexible probe, a water jet cutting system, and a haptic feedback controller. The water jet cutting system consists of a flexible end effector capable of bending around the anterior of the spinal column for tissue removal. A new experimental method of controlling the depth of water jet cut is described. The haptic feedback controller is based on a constraint set approach to define 3D boundaries, based on five key types of constraints. Experimental outcomes of measuring the depth of water jet cut were combined with haptic regional constraints with the aim of improving the safety of surgical procedures. The reliability, accuracy and performance of the prototype robot were tested in a mock surgical procedure on the lower lumbar vertebrae. Results show promise for the implementation of water jet cutting for robotic surgical spinal procedures

Testing Dissipative Collapse Models with a Levitated Micromagnet

We present experimental tests of dissipative extensions of spontaneous wave function collapse models based on a levitated micromagnet with ultralow dissipation. The spherical micromagnet, with radius $R=27$ $\mu$m, is levitated by Meissner effect in a lead trap at $4.2$ K and its motion is detected by a SQUID. We perform accurate ringdown measurements on the vertical translational mode with frequency $57$ Hz, and infer the residual damping at vanishing pressure $\gamma/2\pi<9$ $\mu$Hz. From this upper limit we derive improved bounds on the dissipative versions of the CSL (continuous spontaneous localization) and the DP (Di\'{o}si-Penrose) models with proper choices of the reference mass. In particular, dissipative models give rise to an intrinsic damping of an isolated system with the effect parameterized by a temperature constant; the dissipative CSL model with temperatures below 1 nK is ruled out, while the dissipative DP model is excluded for temperatures below $10^{-13}$ K. Furthermore, we present the first bounds on dissipative effects in a more recent model, which relates the wave function collapse to fluctuations of a generalized complex-valued spacetime metric.Comment: 10 pages, 7 figure

Body composition evaluated by skinfolds, bioimpedance and body mass index in adults

El objetivo de este estudio fue comparar la composición corporal por pliegues cutáneos (DC) por bioimpedancia eléctrica(BIA) y el índice de masa corporal(IMC). Se hizo un trabajo de campo con 153 militares usando los siguientes equipos: balanza Wiso; estadiómetro WCS; adipómetro Cescorf científico y Malton BF-900 para bioimpedancia eléctrica. La densidad corporal se consiguió por la ecuación de Jackson&Pollock y la clasificación delporcentaje de grasa corporal siguiendo Pollock&Wilmore. Para verificar la correlación se usó el test de Spearman. Los resultados promedios (± desviación estándar) hallados para edad, peso, estatura e IMC, fueron: 19 años (±1,8 años), 70,9Kg (±9,55), 1,74 metros (±0.06) y 23,9 kg/m² (±2,76) respectivamente. El porcentaje de grasa corporal por DC y BIA fueron respectivamente 12,78 (±5,45); 16,29 (±4,02). Concluí que la composición corporal por el método de DC, BIA e IMC presentó datos que se correlacionan, siendo que el uso de la bioimpedancia fue más indicada en grupos cuyo porcentaje de grasa corporal variaba entre 18-20%.The aim of this study was to compare body composition by skinfold thickness (DC) by bioelectrical impedance analysis (BIA) and body mass index (BMI). Research was carried out with 153 soldiers with the equipment: balance Wiso; WCS stadiometer; adipometer Cescorf Malton scientific and BF-900 to bioelectrical impedance analysis. Body density was obtained by the equation of Jackson&Pollock and classification of the percentage of fat by following Pollock&Wilmore. To check the correlation was used Spearman's test. The average results (±standard deviation) found for age, weight, height and BMI were: 19 years (±1.8years), 70.9 kg (±9.55), 1.74 meters (±0.06) and 23.9 kg/m² (±2.76), respectively. The fat percentage by BIA and DC were respectively 12.78 (±5.45) and 16.29 (±4.02). Concluded that body composition by the method of DC, BIA and BMI have data that correlate, and the use of bioimpedance was indicated in most groups whose fat percentage ranged around 18-20%.Gracias CAPES para la inversión financiera en forma de beca en el Programa de Posgrado en Ingeniería Eléctrica e Informática Industrial (CPGEI) de la Universidad Tecnológica Federal de Paraná (UTFPR)

Wie investiert man richtig in Bildung?

Durch das Konjunkturpaket und den Hochschulpakt fließen in den nächsten Jahren große Investitionsbeträge in die Bildung. Fraglich bleibt allerdings, ob es im Bildungsbereich auf mehr Finanzmittel ankommt. Reformbedarf besteht wohl eher bei den Strukturen des Bildungswesens und der Qualität der Angebote