Organic donor-acceptor thermally activated delayed fluorescence photocatalysts in the photoinduced dehalogenation of aryl halides

We are grateful to the University of St Andrews, Syngenta, and the EPSRC Centre for Doctoral Training in Critical Resource Catalysis (CRITICAT) for financial support [Ph.D. studentship to “M.A.B.”; Grant code: EP/L016419/1]. E.Z.-C. acknowledges EPSRC for support (EP/W007517/1). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska Curie grant agreement No 812872 (TADFlife). We are thankful to the SFC Saltire Emerging Researcher Scheme for funding the placement of M.A.B to the A.S. lab.We report a family of donor-acceptor thermally activated delayed fluorescent (TADF) compounds based on derivatives of DMAC-TRZ, that are strongly photoreducing. Both Eox and thus E*ox could be tuned via substitution of the DMAC donor with a Hammett series of p-substituted phenyl moieties while Ered remained effectively constant. These compounds were assessed in the photoinduced dehalogenation of aryl halides, and analogues bearing electron withdrawing groups were found to produce the highest yields. Substrates of up to Ered = -2.72 V could be dehalogenated at low PC loading (1 mol%) and under air, conditions much milder than previously reported for this reaction. Spectroscopic and chemical studies demonstrate that all PCs, including literature reference PCs, photodegrade, and that it is these photodegradation products that are responsible for the reactivity.Peer reviewe

Identification of the key parameters for horizontal transition dipole orientation in fluorescent and TADF organic light-emitting diodes

This research was financially supported by the Volkswagen Foundation (No. 93404), the European Commission under EU Horizon 2020 Grant Agreement No. 812872 (TADFlife), the European Research Council under the European Union's Horizon 2020 Framework Programme (FP/2014-2020)/ERC grant agreement no. 640012 (ABLASE), and The Leverhulme Trust (RPG-2016047). M.C.G. acknowledges support from the Alexander von Humboldt Stiftung through the Humboldt-Professorship. All computations were performed using resources kindly provided by the University of Mons (UMONS), supported by the Belgian National Fund for Scientific Research (FRS-FNRS). Computational resources were provided by the Consortium des Équipements de Calcul Intensif (CÉCI) funded by F.R.S.-FNRS under Grant 2.5020.11. Y.O. acknowledges funding from the FRS-FNRS under the grant F.4534.21 (MIS-IMAGINE).In organic light-emitting diodes (OLEDs), horizontal orientation of the emissive transition dipole moment (TDM) can improve light outcoupling efficiency by up to 50% relative to random orientation. Therefore, there have been extensive efforts to identify drivers of horizontal orientation. The aspect ratio of the emitter molecule and the glass-transition temperature (Tg) of the films are currently regarded as particularly important. However, there remains a paucity of systematic studies that establish the extent to which these and other parameters control orientation in the wide range of emitter systems relevant for state-of-the-art OLEDs. Here, recent work on molecular orientation of fluorescent and thermally activated delayed fluorescent emitters in vacuum-processed OLEDs is reviewed. Additionally, to identify parameters linked to TDM orientation, a meta-analysis of 203 published emitter systems is conducted and combined with density-functional theory calculations. Molecular weight (MW) and linearity are identified as key parameters in neat systems. In host–guest systems with low-MW emitters, orientation is mostly influenced by the host Tg, whereas the length and MW of the emitter become more relevant for systems involving higher-MW emitters. To close, a perspective of where the field must advance to establish a comprehensive model of molecular orientation is given.Publisher PDFPeer reviewe

Molecular Design and Synthesis of Dicarbazolophane-Based Centrosymmetric Through-Space Donors for Solution-Processed Thermally Activated Delayed Fluorescence OLEDs

Conjugation-extended carbazolophane donors, dicarbazolophanes (DCzp), were designed and synthesized using a multifold stepwise Pd-catalyzed Buchwald-Hartwig amination/ring cyclization process. Furthermore, elaboration of the DCzp core is possible with the introduction of pendant carbazole derivative groups. This provides a way to tune the optoelectronic properties of the thermally activated delayed fluorescence (TADF) compounds DCzpTRZtBu, dtBuCzDCzpTRZtBu, and dMeOCzDCzpTRZtBu. Solution-processed organic light-emitting diodes (OLEDs) were fabricated and achieved a maximum external quantum efficiency (EQE(max)) of 8.2% and an EQE of 7.9% at 100 cd/m(2).Peer reviewe

Molecular Design and Synthesis of Dicarbazolophane-Based Centrosymmetric Through-Space Donors for Solution-Processed Thermally Activated Delayed Fluorescence OLEDs

Conjugation-extended carbazolophane donors, dicarbazolophanes (DCzp), were designed and synthesized using a multifold stepwise Pd-catalyzed Buchwald-Hartwig amination/ring cyclization process. Furthermore, elaboration of the DCzp core is possible with the introduction of pendant carbazole derivative groups. This provides a way to tune the optoelectronic properties of the thermally activated delayed fluorescence (TADF) compounds DCzpTRZtBu, dtBuCzDCzpTRZtBu, and dMeOCzDCzpTRZtBu. Solution-processed organic light-emitting diodes (OLEDs) were fabricated and achieved a maximum external quantum efficiency (EQE(max)) of 8.2% and an EQE of 7.9% at 100 cd/m(2).Peer reviewe

Effect of a twin-emitter design strategy on a previously reported thermally activated delayed fluorescence organic light-emitting diode

Authors thank EU Horizon 2020 Grant Agreement No. 812872 (TADFlife) for funding this project. Further support was obtained by the Helmholtz Association Program at the Karlsruhe Institute of Technology (KIT). The German Research Foundation (formally Deutsche Forschungsgemeinschaft DFG) in the framework of SFB1176 Cooperative Research Centre "Molecular Structuring of Soft Matter" (CRC1176, A4, B3, C2, C6) and the cluster 3D Matter Made To Order all funded under Germany’s Excellence Strategy 2082/1--390761711 are greatly acknowledged for financial contributions. We acknowledge support from the Engineering and Physical Sciences Research Council of the UK (grant EP/P010482/1), from the International Collaborative Research Program of Institute for Chemical Research, Kyoto University (grant # 2020-37 and 2021-37), and from JSPS KAKENHI Grant Number JP20H05840 (Grant-in-Aid for Transformative Research Areas, “Dynamic Exciton”). ZZ acknowledges the financial support from the China Scholarship Council (CSC, 201606890009) for his PhD studies. EZ-C is a Royal Society Leverhulme Trust Senior Research fellow (SRF\R1\201089).In this work we showcase the emitter DICzTRZ in which we employed a twin-emitter design of our previously reported material, ICzTRZ . This new system presented a redshifted emission at 488 nm compared to that of ICzTRZ at 475 nm and showed a comparable photoluminescence quantum yield of 57.1% in a 20 wt% CzSi film versus 63.3% for ICzTRZ . The emitter was then incorporated within a solution-processed organic light-emitting diode that showed a maximum external quantum efficiency of 8.4%, with Commission Internationale de l’Éclairage coordinate of (0.22, 0.47), at 1 mA cm−2.Publisher PDFPeer reviewe

Design and synthesis of triazine-based blue and oriented TADF emitters for high-efficiency OLEDs

This thesis focuses on the design, synthesis, characterization and OLED fabrication and testing of TADF emitters, with a particular emphasis on trying to achieve high horizontal orientation of their TDM. Chapter 1 explains the basic concepts behind light-matter interaction, photoluminescence, and electroluminescence, focusing on TADF materials and their use in OLEDs. An in-depth explanation of the outcoupling effect will be given, with a discussion of several literature-known strategies to achieve optimal orientation of the emitter in the OLED stack. Chapter 2 focuses on a highly oriented TADF emitter, ICzTRZ. The theoretical and optoelectronic properties and TDM orientation of the material were studied, with its most interesting feature being the nearly completely horizontal orientation of the TDM in the film. OLED performance is then discussed. Chapter 3 describes a study to try and enhance the efficiency of ICzTRZ by adopting a twin-emitter design strategy, with DICzTRZ. Due to its high molecular weight, we hypothesize that DICzTRZ could also maintain horizontal orientation in solution-processed films. Chapter 4 concludes the work on the ICz family, with a study on how the horizontal orientation of ICzTRZ derivates changes when the position and the number of tert-butyl groups on the material are modified. In Chapter 5, the knowledge gathered from the previous study on the ICz series is applied to the known randomly oriented emitter DMAC-TRZ, to try in achieving horizontal orientation of the material and therefore generate an improvement in the device efficiency. Chapter 6 continues the work on DMAC-TRZ by investigating the effect that a heteroaromatic bridge has on the photophysics of the emitter. Chapter 7 summarizes and compares the results from Chapters 2-6. A discussion of the future work and outlooks of these projects is also presented."This work was supported by the EU Horizon 2020 Grant Agreement No. 812872 (TADFlife)." --Fundin

Organic donor-acceptor thermally activated delayed fluorescence photocatalysts in the photoinduced dehalogenation of aryl halides

We report a family of donor-acceptor thermally activated delayed fluorescent (TADF) compounds based on derivatives of DMAC-TRZ, that are strongly photoreducing. Both Eox and thus E*ox could be tuned via substitution of the DMAC donor with a Hammett series of p-substituted phenyl moieties while Ered remained effectively constant. These compounds were assessed in the photoinduced dehalogenation of aryl halides, and analogues bearing electron withdrawing groups were found to produce the highest yields. Substrates of up to Ered = -2.72 V could be dehalogenated at low PC loading (1 mol%) and under air, conditions much milder than previously reported for this reaction. Spectroscopic and chemical studies demonstrate that all PCs, including literature reference PCs, photodegrade, and that it is these photodegradation products that are responsible for the reactivity

Organic donor-acceptor thermally activated delayed fluorescence photocatalysts in the photoinduced dehalogenation of aryl halides

We report a family of donor-acceptor thermally activated delayed fluorescent (TADF) compounds based on derivatives of DMAC-TRZ, that are strongly photoreducing. Both Eox and thus E*ox could be tuned via substitution of the DMAC donor with a Hammett series of p-substituted phenyl moieties while Ered remained effectively constant. These compounds were assessed in the photoinduced dehalogenation of aryl halides, and analogues bearing electron withdrawing groups were found to produce the highest yields. Substrates of up to Ered = -2.72 V could be dehalogenated at low PC loading (1 mol%) and under air, conditions much milder than previously reported for this reaction. Spectroscopic and chemical studies demonstrate that all PCs, including literature reference PCs, photodegrade, and that it is these photodegradation products that are responsible for the reactivity

Design and Synthesis of Triazine-based Blue and Oriented TADF Emitters for High-Efficiency OLEDs (thesis data)

X-Rays and XYZ files of the molecules discussed in the thesis The data files are embargoed until 16/09/202