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While the development of chiral molecules displaying circularly polarized luminescence (CPL) has received considerable attention, the corresponding CPL intensity, glum, hardly exceeds 10−2 at the molecular level owing to the difficulty in optimizing the key parameters governing such a luminescence process. To address this challenge, we report here the synthesis and chiroptical properties of a new family of π-helical push–pull systems based on carbo[6]helicene, where the latter acts as either a chiral electron acceptor or a donor unit. This comprehensive experimental and theoretical investigation shows that the magnitude and relative orientation of the electric (μe) and magnetic (μm) dipole transition moments can be tuned efficiently with regard to the molecular chiroptical properties, which results in high glum values, i.e. up to 3–4 × 10−2. Our investigations revealed that the optimized mutual orientation of the electric and magnetic dipoles in the excited state is a crucial parameter to achieve intense helicene-mediated exciton coupling, which is a major contributor to the obtained strong CPL. Finally, top-emission CP-OLEDs were fabricated through vapor deposition, which afforded a promising gEl of around 8 × 10−3. These results bring about further molecular design guidelines to reach high CPL intensity and offer new insights into the development of innovative CP-OLED architectures., A CPL intensity of up to 3 × 10−2 is achieved in π-extended 6-helicene derivatives, owing to an intense helicene-mediated exciton coupling. Corresponding top-emission CP-OLEDs afforded a promising gEl of around 8 × 10−3.

A pair of hole-conducting polymers comprising 3,6-linked carbazole and meta-linked anisole derivatives having solubilizing moieties to enable their solution processability, and complementarily reactive side-groups (azide and alkyne) for cross-linking, are synthesized and characterized. The polymers can be cross-linked either by thermal annealing at relatively low temperatures in the 85–110 °C range, or by UV irradiation. A general applicability of the latter for a photolithographic patterning of the hole conducting polymer is proven. The polymers have an ionization potential (IP) of 5.8 eV, close to the IP of a small molecule hole-conductor tris(4-carbazoyl-9-ylphenyl)amine (TCTA). In combination with a strong dopant hexacyano-trimethylene-cyclopropane (CN6CP), but not with commercial 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), the polymers can be efficiently p-doped to increase their conductivity by 5–6 orders of magnitude, as measured in devices with a lateral setup. Taken together, these characteristics suggest that the synthesized polymers are promising candidates for their use in solution-processable organic light-emitting diodes as hole-injection layer and hole-transporting layer materials, which will be verified in the upcoming work. © 2022 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH. Technische Universität Dresden, TUD; China Scholarship Council, CSC: 201707040070; European Social Fund, ESF: 100382146; Russian Science Foundation, RSF: 18-13-00161 prolongation E.C.-C. thanks financial support provided by the State budget approved by the delegates of the Saxon State Parliament and by the European Social Fund (ESF) within the project “ReLearning” (SAB appl. No. 100382146) and the “Center for Advancing Electronics Dresden” (CfAED) at the Technische Universität Dresden. T.B. is thankful to Russian Science Foundation (Grant # 18-13-00161 prolongation). K.Z. is grateful to China Scholarship Council (CSC, No. 201707040070) for the financial support. Open access funding enabled and organized by Projekt DEAL. E.C.-C. thanks financial support provided by the State budget approved by the delegates of the Saxon State Parliament and by the European Social Fund (ESF) within the project “ReLearning” (SAB appl. No. 100382146) and the “Center for Advancing Electronics Dresden” (CfAED) at the Technische Universität Dresden. T.B. is thankful to Russian Science Foundation (Grant # 18-13-00161 prolongation). K.Z. is grateful to China Scholarship Council (CSC, No. 201707040070) for the financial support.

Near infrared (NIR) emission from molecular materials is typically targeted by using more extended conjugated systems compared to visible-emitting materials. But efficiencies usually fall off due to the combined effects of increasing non-radiative and lower oscillator strengths as the energy of emissive excited states decreases. Efficient NIR-emitting organic light emitting diodes (OLEDs) are rare compared to the huge progress that has been made for visible-light devices. For organometallic emitters that contain a heavy metal ion to promote phosphorescence through the effect of enhanced spin-orbit coupling (SOC), the problem is typically exacerbated by decreased metal character in the Sn and T1 excited states as the conjugation in a bound ligand increases. Here we show how the use of a dinuclear metal complex with an extended conjugated ligand allows such effects to be mitigated compared to analogous structures with just one metal centre. The complex Pt2(bis-dthpym)(dpm)2 (complex 5) is readily prepared by a double N^C cyclometallation of 4,6-bis(dithienyl)-pyrimidine (H2bis-dthpym), with the coordination sphere of each Pt centre being completed by O^O-coordinating dipivaloylmethane (dpm). This new complex displays intense NIR emission in solution, λmax = 725 nm, with essentially no "contamination"by visible light

Purposely tailored thin film stacks sustaining surface waves have been utilized to create a unique link between emission angle and wavelength of fluorescent dye molecules. The knowledge of the thin film stack’s properties allows us to derive the intrinsically emitted luminescence spectrum as well as to gain information about the orientation of fluorophores from angularly resolved experiments. This corresponds to replacing all the equipment necessary for polarized spectroscopy with a single smart thin film stack, potentially enabling single shot analyses in the future. The experimental results agree well with those from other established techniques, when analyzing the Rubrene derivative in a 2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine (T2T) host used for the fabrication of optimized organic light-emitting diodes. The findings illustrate how resonant layered stacks can be applied to integrated spectroscopic analyses.

Tavasli, Mustafa/0000-0002-9466-1111; BATTAL, AHMET/0000-0003-0208-1564; Cameron, Joseph/0000-0001-8622-8353 Two novel heteroleptic iridium(III) acetylacetonate (acac) complexes K3a and K3b were synthesised from cyclometallating ligands of 2-(4'-formylphenyl)quinoline lla and 2-(5'-formylphenyl)quinoline 11b. Complexes K3a and K3b were fully characterised by NMR spectroscopy, mass spectrometry and FT-IR. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) indicate that both complexes were amorphous solids, stable up to 303 degrees C and 313 degrees C, respectively. Complexes K3a and K3b showed strong, high-energy absorption bands (

In this study, newly substituted carbazole derivatives of S1; (Z)-4-((9-isobutyl-9H-carbazol-3-ylimino) methyl)phenol, S2; (Z)-9-butyl- N-(2,3,4-trimethoxybenzylidine)-9H-carbazol-3-amine, S3; (Z)-4-((9-octyl-9H-carbazol-3-ylimino)methyl)benzene-1,2-diol and S4; (Z)-3-((9-octyl-9H-carbazol-3-ylimino) methyl)benzene-1,2-diol compounds are synthesized by using condensation reaction between carbazole amines and aromatic aldehydes. All synthesized carbazole Schiff bases are purified by crystallizing from chloroform. The structural and optical characterizations of synthesized compounds are investigated by FT-IR (Fourier Transform-Infrared Spectroscopy), H-1 NMR (Proton Nuclear Magnetic Resonance),C-13 NMR (Carbon Nuclear Magnetic Resonance), LC-MS (Liquid Chromatography-Mass Spectrometry) and temperature dependent PL (Photoluminescence) measurements.. The formations of synthesized Schiff bases were confirmed by FF-IR, NMR and microanalysis. Due to stronger pi-conjugation and efficient charge transfer from host material, the broad and complex bands centered at about similar to 2.16 and similar to 1.76 eV are observed in PL spectra for all samples. Their relative intensities depend on functional groups associated with the carbazole. These newly synthesized Schiff bases could be considered as an active emissive layer for organic light emitting diodes. Balıkesir Üniversitesi (BAP.2015.0001) (BAP.2017/181)

In order to protect a flexible OLED on plastic foil against water from the ambient atmosphere a top and bottom thin-film encapsulation (TFE) is necessary. A TFE stack SiN-OCP-SiN with getter in OCP results in excellent shelf lifetime. However, the getter particles result in light scattering that is lost upon water ingress in the stack. As a result spots of reduced electroluminescence are observed during exposure to the ambient atmosphere that limit the practical lifetime of the device drastically. For the bottom emitting OLED we reduced the getter content in the bottom barrier to a level that does not exhibit visible light scattering. The reduced getter capacity with respect to the top barrier does not result in a lower performance of the bottom barrier due to the lower pinhole density in SiN-ITO with respect to Al-SiN. The projected shelf lifetime at ambient conditions is 10 years. © 2018 Elsevier B.V.

In order to protect a flexible OLED on plastic foil against water from the ambient atmosphere a top and bottom thin-film encapsulation (TFE) is necessary. A TFE stack SiN-OCP-SiN with getter in OCP results in excellent shelf lifetime. However, the getter particles result in light scattering that is lost upon water ingress in the stack. As a result spots of reduced electroluminescence are observed during exposure to the ambient atmosphere that limit the practical lifetime of the device drastically. For the bottom emitting OLED we reduced the getter content in the bottom barrier to a level that does not exhibit visible light scattering. The reduced getter capacity with respect to the top barrier does not result in a lower performance of the bottom barrier due to the lower pinhole density in SiN-ITO with respect to Al-SiN. The projected shelf lifetime at ambient conditions is 10 years. © 2018 Elsevier B.V.

Highly-functional photonic sensor networks integrated in thin polymer foils offer great potential for versatile applications in the life sciences, medicine, environmental analytics or production technology. For their realization, suitable low-cost and high-throughput production techniques need to be developed. Here, we describe work towards this goal, i.e. the fabrication of multimode polymer waveguides through a combination of thermal imprint and doctor blading. For imprint master stamp fabrication, a combined Bosch and O2 plasma etching process in silicon is utilized. We also demonstrate stamp fabrication by an additive manufacturing method, i.e. by employing maskless UV lithography, to enhance the flexibility and cost-effectiveness of our approach. We, thus, realize various all-polymer waveguide arrays, beam splitters, and grating couplers which serve as basic elements to create more complex photonic circuits. We also demonstrate polymer based transmission lines comprising semiconductor as well as organic light sources and detectors. We discuss both the integration of semiconductor light sources and detectors such as verticalcavity surface-emitting lasers (VCSEL) and photo detectors as well as organic light emitting diodes (OLEDs) and organic photo detectors. In first applications, we combine these elements to create sensor arrays for measuring temperature, strain or refractive index. We show results of various sensor types utilizing different measurement principles implemented in laboratory environments so far. For example, a waveguide array containing a linear discontinuity which serves as elongation zone for displacement, strain or tilt measurement by detecting the intensity variation of the transmitted light propagating inside the structure is presented. In future, we plan to create more powerful sensor photonics networks for reliable and robust applications in real life, e.g. for point-of-care testing or production monitoring.

© 2018, Blackwell Publishing Ltd. All rights reserved. We present a 350°C self-aligned dual-gate a-IGZO backplane technology with a monolithically integrated multi-layer high-temperature thin-film barrier for flexible AMOLED. Thin-film barrier properties and TFT technology are optimized on 320 x 352mm substrates, and demonstrated in a flexible QQVGA 100 ppi AMOLED display prototype. ispartof: pages:1577-1580 ispartof: Digest of Technical Papers - SID International Symposium vol:49 issue:1 pages:1577-1580 status: published

In this paper, a color- and brightness-tunable organic light-emitting diode (OLED) is reported. This OLED was realized by inserting a charge generation layer into an electron only device to form an n-i-p-i-n structure. It is shown that, by changing the polarity of applied voltage, only the p-i-n junction operated under positive bias can emit light and, by applying an AC voltage, emission from both junctions was realized. It is also shown that, by using a combination of blue- and red-emiting layers in two p-i-n junctions, both the color and brightness of the resulting white OLED can be tuned independently by changing the positive and negative amplitudes of the AC voltage. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore)

Silver nanowire mesh electrodes represent a possible mass-manufacturable route toward transparent and flexible electrodes for plastic-based electronics such as organic photovoltaics (OPVs), organic light emitting diodes (OLEDs), and others. Here we describe a route that is based upon spray-coated silver nanowire meshes on polyethylene terephthalate (PET) sheets that are treated with a straightforward combination of heat and pressure to generate electrodes that have low sheet resistance, good optical transmission, that are topologically flat, and adhere well to the PET substrate. The silver nanowire meshes were prepared by spray-coating a solution of silver nanowires onto PET, in air at slightly elevated temperatures. The as-prepared silver nanowire electrodes are highly resistive due to the poor contact between the individual silver nanowires. Light pressure applied with a stainless steel rod, rolled over the as-sprayed silver nanowire meshes on PET with a speed of 10 cm s-1 and a pressure of 50 psi, results in silver nanowire mesh arrays with sheet resistances of less than 20 Ω/□. Bending of these rolled nanowire meshes on PET with different radii of curvature, from 50 to 0.625 mm, showed no degradation of the conductivity of the electrodes, as shown by the constant sheet resistance before and after bending. Repeated bending (100 times) around a rod with a radius of curvature of 1 mm also showed no increase in the sheet resistance, demonstrating good adherence and no signs of delamination of the nanowire mesh array. The diffuse and direct transmittance of the silver nanowires (both rolled and as-sprayed) was measured for wavelengths from 350 to 1200 nm, and the diffuse transmission was similar to that of the PET substrate; the direct transmission decreases by about 7-8%. The silver nanowires were then incorporated into OPV devices with the following architecture: transparent electrode/PEDOT:PSS/P3HT:PC61BM/LiF/Al. While slightly lower in efficiency than the standard indium tin oxide substrate (ITO), the rolled silver nanowire electrodes had a very good device yield, showing that short circuits resulting from the silver nanowire electrodes can be successfully avoided by this rolling approach. © 2013 American Chemical Society.

A design strategy is presented for the development of Ag(I)-based materials for thermally activated delayed fluorescence (TADF). Although Ag(I) complexes usually do not show TADF, the designed material, Ag(dbp)(P2-nCB) (with dbp = 2,9-di-n-butyl-1,10-phenanthroline and P2-nCB = nido-carborane-bis-(diphenylphosphine)), shows a TADF efficiency breakthrough exhibiting an emission decay time of τ(TADF) = 1.4 µs at a quantum yield of ΦPL = 100 %. This is a consequence of three optimized parameters: (i) The strongly electron-donating negatively charged P2-nCB ligand destabilizes the 4d-orbitals and leads to low lying charge (CT) states of MLL’CT character, with L and L’ being the two different ligands, thus, giving a small energy separation between the lowest singlet S1 and triplet T1 state of ∆E(S1-T1) = 650 cm-1 (80 meV). (ii) The allowedness of the S1→S0 transition is more than one order of magnitude higher than found for other TADF metal complexes, as shown experimentally and by TD-DFT calculations. Both parameters favor short TADF decay time. (iii) The high quantum efficiency is dominantly related to the rigid molecular structure of Ag(dbp)(P2-nCB), resulting from the design strategy of introducing n-butyl substitutions at the 2,9-positions of phenanthroline which sterically interact with the phenyl groups of the P2-nCB ligand. In particular, the shortest TADF decay time of τ(TADF) = 1.4 µs at ΦPL = 100 % reported so far suggests the use of this outstanding material for OLEDs. Importantly, the emission of Ag(dbp)(P2-nCB) is not subject to concentration quenching. Therefore, it may be applied even as a 100% emission layer.

17th International Conference on Numerical Simulation of Optoelectronic Devices (2017 : Copenhagen), The effects of the structural parameters of the photonic crystal (PC) placed between glass and indium tin oxide (ITC) for an efficient organic light-emitting diode (OLED) design is studied. It is shown that the light extraction efficiency of OLEDs varies with the PC height and period. The maximum relative extraction efficiency (EEr) value is obtained at 0.4 ?m PC height and 0.36 ?m period. © 2017 IEEE., D.Y. acknowledges the partial support from the Scientific and Technical Research Council (TUBITAK) BIDEB-2211 Grant. H.K. acknowledges the partial support of the Turkish Academy of Sciences.

Poly(p-phenylenevinylene), or PPV, is a polymer of great technological relevance due to its electroluminescence properties, which have been exploited in organic light emitting diodes, flexible displays and other optoelectronic devices. Although PPV is a material of foremost importance for many applications, its synthesis on the nano/microscale cannot be achieved through the standard method that uses heating of a precursor polymer. This paper shows how direct laser writing with femtosecond pulses can be employed for the synthesis of PPV in pre-determined regions, allowing a novel approach towards the precise fabrication of complex polymeric microcircuits. The physical-chemical phenomena involved in the conversion of the precursor into PPV are shown to be related to a two-photon induced thermal process, which is confined to the focal volume, resulting in the controlled synthesis of PPV.

New well-defined bulky anthracene derivatives with side groups having electron donating or withdrawing properties 8a-d were synthesized. The compounds contain substituted anthracene as the central core attaching 2-(4-(2-pyridinyl)- phenyl)vinyl and 4-R-phenyl [R: H (a), OMe (b) and CF3 (c), N(Ph)2 (d)] groups at 9- and 10- positions. The impact of electron donating, withdrawing and neutral groups and their influence on the molecules photophysical, charge transfer (CT), triplet transfer (TT) and triplet-triplet annihilation (TTA) properties has been investigated. Based on the photophysical studies the most promising molecule (8d) has been selected and high efficiency fluorescent OLEDs with EQE at very low current efficiency reaching 7% were obtained. The value at low current density implies a Triplet Fusion (TF) contribution of 45%, very close to the maximum theoretical value of 50% when only the singlet decay channel is open to TTA, however we believe that in this case both TTA and TADF contribute to the triplet harvesting to yield high EQE values, and this mixed triplet harvesting arises through the heterogeneity of the films. At high current density a brightness of 20000 cd/m2 was achieved and it is assigned partially to the material crystallisation. © 2015 Elsevier B.V. Devlet Planlama Örgütü Engineering and Physical Sciences Research Council F.T. gratefully acknowledge the (Turkish) State Planning Organization (DPT) for Financial support. G.H. also thanks Turkish DPT for financial support for her MSc. The authors are grateful to Dr. Serife Sarioglan for her initial help in electrochemistry measurements. OEM group at Physics Department/Durham University would like to thank EPSRC for partial financial support of this project. Appendix A

We present a quantitative analysis of the loss of electroluminescence in light-emitting diodes (LEDs) based on poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) due to the combination of non-radiative trap-assisted recombination and exciton quenching at the metallic cathode. It is demonstrated that for an MEH-PPV LED the biggest efficiency loss, up to 45%, arises from extrinsic non-radiative recombination via electron traps. The loss caused by exciton quenching at the cathode proves only to be significant for devices thinner than 100 nm. Removal of electron traps by purification is expected to enhance the efficiency of polymer LEDs by more than a factor of two. (C) 2012 Elsevier B.V. All rights reserved.

A new family of highly soluble electrophosphorescent dopants based on a series of tris-cyclometalated iridium(III) complexes (1-4) of 2-(carbazol-3-yl)-4/5-R-pyridine ligands with varying molecular dipole strengths have been synthesized. Highly efficient, solution-processed, single-layer, electrophosphorescent diodes utilizing these complexes have been prepared and characterized. The high triplet energy poly(9-vinylcarbazole) PVK is used as a host polymer doped with 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) for electron transport. Devices with a current efficiency of 40 cd A(-1) corresponding to an EQE of 12% can thus be achieved. The effect of the type and position of the substituent (electron-withdrawing group (CF3) and electron-donating group (OMe)) on the molecular dipole moment of the complexes has been investigated. A correlation between the absorption strength of the singlet metal-to-ligand charge-transfer ((MLCT)-M-1) transition and the luminance spectral red shift as a function of solvent polarity is observed. The strength of the transition dipole moments for complexes 1-4 has also been obtained from TD-DFT computations, and is found to be consistent with the observed molecular dipole moments of these complexes. The relatively long lifetime of the excitons of the phosphorescence (microseconds) compared to the charge-carrier scattering time (less than nanoseconds), allows the transition dipole moment to be considered as a "quasi permanent dipole". Therefore, the carrier mobility is sufficiently affected by the long-lived transition dipole moments of the phosphorescent molecules, which are randomly oriented in the medium. The dopant dipoles cause positional and energetic disorder because of the locally modified polarization energy. Furthermore, the electron-withdrawing group CF3 induces strong carrier dispersion that enhances the electron mobility. Therefore, the strong transition dipole moment in complexes 3 and 4 perturbs both electron and hole mobilities, yielding a reduction in exciton formation and an increase in the device dark current, thereby decreasing the device efficiency. UK Research & Innovation (UKRI) Engineering & Physical Sciences Research Council (EPSRC) (EP/I013695/1)

Colour tuning of white polymer light emitting diode (LED) light sources can be attained by various methods at various stages in the production process of the lamps and/or by the design of the active material incorporated in the LEDs. In this contribution we will describe the methods and discuss the physical background of colour tuning. Furthermore, the material design has led to polymers which are more stable during electrical stress, so that colour shift during lifetime can be excluded for white polymer LEDs. © 2010 Elsevier B.V.

Micro-optical sensors based on optical waveguides are widely used to measure temperature, force and strain but also to detect biological and chemical substances such as explosives or toxins. While optical micro-sensors based on silicon technology require complex and expensive process technologies, a new generation of sensors based completely on polymers offer advantages especially in terms of low-cost and fast production techniques. We have developed a process to integrate micro-optical components such as embedded waveguides and optical interconnects into polymer foils with a thickness well below one millimeter. To enable high throughput production, we employ hot embossing technology, which is capable of reel-to-reel fabrication with a surface roughness in the optical range. For the waveguide fabrication, we used the thermoplastic polymethylmethacrylate (PMMA) as cladding and several optical adhesives as core materials. The waveguides are characterized with respect to refractive indices and propagation losses. We achieved propagation losses are as low as 0.3 dB/cm. Furthermore, we demonstrate coupling structures and their fabrication especially suited to integrate various light sources such as vertical-cavity surface-emitting lasers (VCSEL) and organic light emitting diodes (OLED) into thin polymer foils. Also, we present a concept of an all-polymer and waveguide based deformation sensor based on intensity modulation, which can be fabricated by utilizing our process. For future application, we aim at a low-cost and high-throughput reel-to-reel production process enabling the fabrication of large sensor arrays or disposable single-use sensing structures, which will open optical sensing to a large variety of application fields ranging from medical diagnosis to automotive sensing. © 2016 SPIE. DFG/CRC/PlanOS

An organic light emitting diode (OLED) emitting reddish-orange light has been constructed using a Sm 3+ complex, composed of 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 1,10-phenanthroline, as emitting layer and poly(vinylcarbazole) (PVK) and 2-(4-biphenylyl)-5-(4- tert -butylphenyl)-1,3,4-oxadiazole (PBD) as hole and electron transporters, respectively. Photoluminescence (PL) spectra suggest that energy pumping is made through both Sm 3+ -complexed ligands and poly(vinylcarbazole) providing an efficient electroluminescent system.

We report the self-aligned passivation of a current distribution grid for an organic light emitting diode (OLED) anode using a pulsed Joule heating method to align the passivation layer accurately on the metal grid. This method involves passing an electric current through the grid to cure a polymer dielectric. Uncured polymer is then rinsed away, leaving a patterned dielectric layer that conforms to the shape of the grid lines. To enhance the accuracy of the alignment, heat conduction into the substrate and the transparent electrode is limited by using short current pulses instead of a constant current. Excellent alignment accuracy of the dielectric layer on printed metal grid lines has been achieved, with a typical 4-μm dielectric overhang. In addition to good accuracy, pulsed Joule heating significantly cuts down process time and energy consumption compared to heating with a constant current. The feasibility of using a printed current distribution grid and Joule heating was demonstrated in an OLED device. cop. 2015 Author(s).