Daniel Volz

Organic light-emitting diodes (OLEDs) produced from metal complexes play an important role in modern electroluminescent devices. While OLEDs are being used in display various applications such as TVs, smartphones and wearables already, a drastic increase in the production volume in the next years is being expected as soon as OLED lighting applications and printed OLEDs hit the market. Given that thus far, phosphorescent iridium compounds are required to make these products, sustainability… Mehr anzeigen

Organic light-emitting diodes (OLEDs) produced from metal complexes play an important role in modern electroluminescent devices. While OLEDs are being used in display various applications such as TVs, smartphones and wearables already, a drastic increase in the production volume in the next years is being expected as soon as OLED lighting applications and printed OLEDs hit the market. Given that thus far, phosphorescent iridium compounds are required to make these products, sustainability issues are imminent. To review viable alternatives, we highlight the current status of sustainable metal complexes with a special focus on copper and zinc complexes. Ligand structures and complex preparation were highlighted. We also briefly address features like cooperativity, chirality, and printing. Weniger anzeigen

Understanding subtle aspects of photophysical behavior is the key to design and synthesize new and improved luminescent materials. We contribute to this with an in-depth photophysical characterization of the binuclear copper complex Cu(I)–NHetPHOS-tris-m-tolylphosphine (1), a member of a recently established emitter class for ultra-efficient, printed organic light-emitting diodes (OLEDs). To this end we studied 1 in solution and in solid form, i.e. neat film and KBr-pellet, by means of… Mehr anzeigen

Understanding subtle aspects of photophysical behavior is the key to design and synthesize new and improved luminescent materials. We contribute to this with an in-depth photophysical characterization of the binuclear copper complex Cu(I)–NHetPHOS-tris-m-tolylphosphine (1), a member of a recently established emitter class for ultra-efficient, printed organic light-emitting diodes (OLEDs). To this end we studied 1 in solution and in solid form, i.e. neat film and KBr-pellet, by means of femtosecond time-resolved transient absorption/reflectivity, time-correlated single photon counting (TCSPC), and nanosecond time-resolved step-scan FTIR spectroscopy. Using these methods, we explore the photoinduced dynamics from ultrafast Franck–Condon state deactivation until the decay of the luminescent states. Upon photoexcitation, we observed multiexponential dynamics in both solution (e.g. acetonitrile 0.8 ps, 59 ps, 3 ns, 11–13 ns) and in solid state (e.g. neat film 0.3 ps, 35 ps, 670 ps, 0.5–1 μs, 3.5–4.5 μs) with four to five time-constants that significantly depend on the type of sample. Quantum chemical calculations at the DFT level in combination with step-scan vibrational spectroscopy provided structural information about the electronic ground state S0 and the lowest lying excited state T1, and show that the latter is populated within 1 μs after photoexcitation. We found thermally activated delayed fluorescence (TADF) for this complex, which has been suggested to be the cause for its high efficiency in printed OLED devices. The results suggest that non-radiative processes, lowering the luminescence quantum yield in solution, are active on the ns to μs timescale. Weniger anzeigen

The structure in the ground and excited electronic state of two binuclear CuI N-heterocyclic phosphine complexes that are promising for implementation in organic light-emitting diodes is investigated by a combination of the time-resolved step-scan FTIR technique and quantum chemical calculations at the DFT level of theory. In contrast to the usual application of step-scan FTIR spectroscopy in solution, the herein-presented analyses are performed in a solid phase, that is, the CuI complexes are… Mehr anzeigen

The structure in the ground and excited electronic state of two binuclear CuI N-heterocyclic phosphine complexes that are promising for implementation in organic light-emitting diodes is investigated by a combination of the time-resolved step-scan FTIR technique and quantum chemical calculations at the DFT level of theory. In contrast to the usual application of step-scan FTIR spectroscopy in solution, the herein-presented analyses are performed in a solid phase, that is, the CuI complexes are embedded in a KBr matrix (KBr pellet). The application of solid-state time-resolved step-scan FTIR spectroscopy is of great importance for transition metal complexes, since their photophysical properties often change on moving from solid to dissolved samples. The efficient applicability of the solid-state step-scan technique in a KBr matrix is demonstrated on the chosen CuI reference systems on nano- and microsecond timescales with an excitation wavelength of 355 nm. By comparison with theoretical results, the structure of the complexes in the electronic ground and lowest-lying electronically excited state can be determined. Weniger anzeigen

In the last few years, the development of new materials has had a significant impact on the advancement of organic light-emitting diodes (OLEDs). Thanks to these advanced materials, OLED displays are now being used in smartwatches, smartphones, and TVs. However, there is still room for improvement in areas like display resolution and energy efficiency. Thermally activated delayed fluorescence (TADF) is a relatively new technology that has been developed to tackle these issues. This article… Mehr anzeigen

In the last few years, the development of new materials has had a significant impact on the advancement of organic light-emitting diodes (OLEDs). Thanks to these advanced materials, OLED displays are now being used in smartwatches, smartphones, and TVs. However, there is still room for improvement in areas like display resolution and energy efficiency. Thermally activated delayed fluorescence (TADF) is a relatively new technology that has been developed to tackle these issues. This article describes the crucial role of emitter materials in OLED technology, and introduces the TADF concept. Weniger anzeigen

The substitution of rare metals such as iridium and platinum in light-emitting materials is a key step to enable low-cost mass-production of organic light-emitting diodes (OLEDs). Here, we demonstrate that using a solution-processed, fully bridged dinuclear Cu(I)-complex can yield very high efficiencies. An optimized device gave a maximum external quantum efficiency of 23 ± 1% (73 ± 2 cd A−1).

Organische Leuchtdioden (OLEDs) sind Flächenstrahler und lassen sich auf flexible sowie semitransparente Substrate aufbringen, wodurch visionäre neue Produkte wie selbstleuchtende Fenster und rollbare Bildschirme in den Bereich des Machbaren gelangen. Dennoch beschränkt sich die Verwendung von OLEDs heute nur auf kleinformatige Anwendungen wie Smartphone-Displays. Ein Grund hierfür ist die momentan noch vorherrschende, schwer skalierbare Herstellungsmethode aus der Gasphase und die häufig… Mehr anzeigen

Organische Leuchtdioden (OLEDs) sind Flächenstrahler und lassen sich auf flexible sowie semitransparente Substrate aufbringen, wodurch visionäre neue Produkte wie selbstleuchtende Fenster und rollbare Bildschirme in den Bereich des Machbaren gelangen. Dennoch beschränkt sich die Verwendung von OLEDs heute nur auf kleinformatige Anwendungen wie Smartphone-Displays. Ein Grund hierfür ist die momentan noch vorherrschende, schwer skalierbare Herstellungsmethode aus der Gasphase und die häufig verwendeten, seltenen und teuren Metalle wie Iridium.

In der vorliegenden Arbeit wurden durch die Weiterentwicklung einer flüssigprozessierbaren Materialklasse von elektrolumineszenten Kupfer(I)komplexen sowie der Entwicklung neuer Konzepte zur Realisierung von effizienten Mehrschicht-OLEDs diese beiden Punkte adressiert. Bekannte Materialklassen wurden entscheidend verbessert; im grünen Spektralbereich zeigen die neuen Verbindungen eine Emissionsquantenausbeute von nahezu 100%, wodurch eine Anwendung in OLEDs sehr attraktiv erscheint. Die Grundlage für nasschemisch hergestellte Mehrschicht-OLEDs wurde gelegt, indem durch Modifikation der Komplexe thermisch- und selbst-vernetzte Emissionsschichten hergestellt wurden. Als Highlight wird ein grün leuchtendes OLED-Bauteil mit einer extrem hohen Effizienz von 73 cd A-1 (externe Quanteneffizienz: 23.2%) präsentiert, wobei keine Auskopplungstechnologien verwendet wurden. Damit gehören die hier entwickelten Kupferkomplexe zu den effizientesten derzeit bekannten OLED-Leuchtstoffen. Weniger anzeigen

The emission color of Cu(I) complexes is often not the same when comparing bulk samples with thin films, e.g., for organic light-emitting diodes. We investigated if the reason for this is a result of destruction or rather structural distortion for three exemplary complexes with (diphenylphosphino)pyridine derivatives (PyrPHOS)-type ligands.

Easy come, easy go: the great structural diversity of Cu(I) complexes is an ambivalent trait. Apart from the well-known catalytic properties of Cu(I), a great number of potent luminescent complexes have been found in the last ten years featuring a plethora of structural motifs. The downside of this variety is the undesired formation of other species upon processing. In here, strategies to avoid this behavior are presented: Only one favorable structural unit often exists for multinuclear Cu(I)… Mehr anzeigen

Easy come, easy go: the great structural diversity of Cu(I) complexes is an ambivalent trait. Apart from the well-known catalytic properties of Cu(I), a great number of potent luminescent complexes have been found in the last ten years featuring a plethora of structural motifs. The downside of this variety is the undesired formation of other species upon processing. In here, strategies to avoid this behavior are presented: Only one favorable structural unit often exists for multinuclear Cu(I) complexes with bridging ligands. In addition, these complexes exhibit favorable photophysical properties due to cooperative effects of the metal halide core. Furthermore, we demonstrate the broad range of applications of emitting Cu(I) compounds. Weniger anzeigen

Imaging is – even these days – still restricted to of a few classes of robust dyes. A demand for switchable tags led us to the design of a new class of pre-fluorophores. We achieved this by using a non-fluorescent N-(4-azidophenyl)-carbazole tag which turns fluorescent by click reaction with alkynes and cyclooctynes. The spectral properties of the labelled dyes were investigated. Our results suggest that a twisted internal charge transfer (TICT) transition is responsible for the emission. DFT… Mehr anzeigen

Imaging is – even these days – still restricted to of a few classes of robust dyes. A demand for switchable tags led us to the design of a new class of pre-fluorophores. We achieved this by using a non-fluorescent N-(4-azidophenyl)-carbazole tag which turns fluorescent by click reaction with alkynes and cyclooctynes. The spectral properties of the labelled dyes were investigated. Our results suggest that a twisted internal charge transfer (TICT) transition is responsible for the emission. DFT calculations and single-crystal X-ray diffraction of selected examples support this explanation. The feasibility of the new dyes for biological application has also been tested via confocal microscopy. Weniger anzeigen

The photoluminescence quantum efficiency as well as the processing properties of a series of brightly luminescent Cu(I)-metallopolymers strongly depended on the chosen synthetic approach. A monomeric, substituted styrenic complex features a photoluminescence quantum efficiency (PLQY) of only 4%, while its metallopolymeric thin film is over one order of magnitude more efficient.

A series of highly luminescent, heteroleptic copper(I) complexes has been synthesized using a modular approach based on easily accessible P^N ligands, triphenylphosphine, and copper(I) halides, allowing for an independent tuning of the emission wavelength with low synthetic efforts. The molecular structure has been investigated via X-ray analysis, confirming a dinuclear copper(I) complex consisting of a butterfly shaped metal-halide cluster and two different sets of ligands. The bidentate P^N… Mehr anzeigen

A series of highly luminescent, heteroleptic copper(I) complexes has been synthesized using a modular approach based on easily accessible P^N ligands, triphenylphosphine, and copper(I) halides, allowing for an independent tuning of the emission wavelength with low synthetic efforts. The molecular structure has been investigated via X-ray analysis, confirming a dinuclear copper(I) complex consisting of a butterfly shaped metal-halide cluster and two different sets of ligands. The bidentate P^N ligand bridges the two metal centers and can be used to tune the energy of the frontier orbitals and therefore the photophysical characteristics, as confirmed by emission spectroscopy and theoretical investigations, whereas the two monodentate triphenylphosphine ligands on the periphery of the cluster core mainly influence the solubility of the complex. By using electron-rich or electron-poor heterocycles as part of the bridging ligand, emission colors can be adjusted, respectively, between yellow (581 nm) and deep blue (451 nm). These complexes have been further investigated in particular with regard to their photophysical properties in thin films and polymer matrix as well as in solution. Furthermore, the suitability of this class of materials for being applied in organic light-emitting diodes (OLEDs) has been demonstrated in a solution-processed device with a maximum current efficiency of 9 cd/A and a low turn-on voltage of 4.1 V using a representative complex as an emitting compound. Weniger anzeigen

Organic light-emitting diodes (OLEDs) are currently being commercialized for lighting and display applications, but more work has to be done. Beside the ongoing optimization of materials and devices in terms of efficiency and lifetime, the substitution of processing steps involving vacuum deposition for solution processing techniques is favourable. To reach this aim, well-soluble materials are required. A modular family of highly emissive PyrPHOS-copperiodide complexes featuring various… Mehr anzeigen

Organic light-emitting diodes (OLEDs) are currently being commercialized for lighting and display applications, but more work has to be done. Beside the ongoing optimization of materials and devices in terms of efficiency and lifetime, the substitution of processing steps involving vacuum deposition for solution processing techniques is favourable. To reach this aim, well-soluble materials are required. A modular family of highly emissive PyrPHOS-copperiodide complexes featuring various ancillary phosphine ligands has been synthesized. Photoluminescence spectroscopy, TDSPC (time-correlated single photon counting), cyclic voltammetry, X-ray diffraction and DFT-calculations were performed to gain a broad understanding of the complexes. While the photophysical properties are consistent within the family, thermal stability and solubility depend on the ligands. The materials showed very high photoluminescence quantum efficiencies up to 99% in powders and 85% in thin films. Selected examples were tested in devices, confirming the suitability of heteroleptic PyrPHOS-complexes for OLEDs. Weniger anzeigen

Polymorphism is often linked to the choice of processing solvents. Packing effects or the preference of one certain conformer as possible causes of this phenomenon are strongly dependent on solvents and especially on their polarity. Polymorphs or amorphous solids featuring different packing densities can exhibit different properties in terms of stability or optical effects. The influence of these effects on a binuclear, strongly luminescent copper(I) complex was investigated. Many possible… Mehr anzeigen

Polymorphism is often linked to the choice of processing solvents. Packing effects or the preference of one certain conformer as possible causes of this phenomenon are strongly dependent on solvents and especially on their polarity. Polymorphs or amorphous solids featuring different packing densities can exhibit different properties in terms of stability or optical effects. The influence of these effects on a binuclear, strongly luminescent copper(I) complex was investigated. Many possible applications for luminescent, amorphous coordination compounds, such as organic light-emitting diodes, sensors, and organic lasers, rely on photophysical properties like quantum efficiency to be repeatable. The effect of processing solvents in this context is often underestimated, but very relevant for utilization in device manufacturing and should therefore be understood more deeply. In this work, theoretical derivations, DFT calculations, X-ray-diffraction, photoluminescence spectroscopy, and the time-dependent single-photon-counting-technique (TDSPC) were used to understand this phenomenon more deeply. The influence of five different solvents on Cu2I2(MePyrPHOS)3 was probed. This resulted in a modulation of the photoluminescence quantum yield between 0.5 and 0.9 in amorphous solid state. The reduced efficiency could be correlated with a higher porosity and a reduced packing density. Dense packing reduces nonradiative decay by geometrical fixation and thus increases the quantum efficiency. The existence of similar effects on aluminum and iridium compounds has been confirmed by application of different processing solvents on Alq3 and Ir(ppy)3. These results show that a tuning of the efficiency of a emissive metal complexes by choosing a proper processing solvent is possible. If highly efficient materials for practical applications are desired, an evaluation of multiple solvents has to be considered. Weniger anzeigen

The production of solution-processed OLEDs requires materials suitable for subsequent multilayer deposition. In the current study, we present an autocatalytic method to crosslink a luminescent copper(I)-complex with a polymeric backbone, in which the emitter itself acts as catalyst. In a showcase reaction demonstrating this concept for the first time, we combined a highly luminescent binuclear copper(I)-complex with a polystyrene derivative in order to prove the potential of the protocol. The… Mehr anzeigen

The production of solution-processed OLEDs requires materials suitable for subsequent multilayer deposition. In the current study, we present an autocatalytic method to crosslink a luminescent copper(I)-complex with a polymeric backbone, in which the emitter itself acts as catalyst. In a showcase reaction demonstrating this concept for the first time, we combined a highly luminescent binuclear copper(I)-complex with a polystyrene derivative in order to prove the potential of the protocol. The luminescence properties were only slightly affected by the crosslinking, while the general stability increased drastically, as proven by thermogravimetric analysis (TGA). OLED tests confirmed the fundamental suitability of the concept for device applications as well as for subsequent solution-based multilayer deposition. Weniger anzeigen

The production of solution-processed OLEDs requires materials suitable for subsequent multilayer deposition. In the current study, we present an autocatalytic method to crosslink a luminescent copper(I)-complex with a polymeric backbone, in which the emitter itself acts as catalyst. In a showcase reaction demonstrating this concept for the first time, we combined a highly luminescent binuclear copper(I)-complex with a polystyrene derivative in order to prove the potential of the protocol. The… Mehr anzeigen

The production of solution-processed OLEDs requires materials suitable for subsequent multilayer deposition. In the current study, we present an autocatalytic method to crosslink a luminescent copper(I)-complex with a polymeric backbone, in which the emitter itself acts as catalyst. In a showcase reaction demonstrating this concept for the first time, we combined a highly luminescent binuclear copper(I)-complex with a polystyrene derivative in order to prove the potential of the protocol. The luminescence properties were only slightly affected by the crosslinking, while the general stability increased drastically, as proven by thermogravimetric analysis (TGA). OLED tests confirmed the fundamental suitability of the concept for device applications as well as for subsequent solution-based multilayer deposition. Weniger anzeigen