Supramolecular assemblies showing thermally activated delayed fluorescence

We thank the East of Scotland Industrial Catalysis Centre for Doctoral Training (EaSI-CAT) for financial support [Ph.D. studentship to “T.A.C”].Supramolecular assemblies based on luminescent components can offer significant advantages over their discrete counterparts, including improved quantum yields, stability, and tunability. Following interest as advanced optoelectronic materials, thermally activated delayed fluorescence (TADF) emitters have been incorporated into a range of supramolecular structures. Here we present a summary of the known examples of emissive supramolecular systems that operate via a TADF mechanism with comparisons, where possible, to their discrete counterparts. While the types of supramolecular structures are diverse, there are limited examples shown for each class. With the increase in photophysical performance and/or emergence of new photochemical properties upon going from molecular to supramolecular, the potential that these systems hold becomes apparent.Publisher PDFPeer reviewe

Recent advances in materials for organic light emitting diodes

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Mechanophotocatalysis : a generalizable approach to solvent-minimized photocatalytic reactions for organic synthesis

The authors thank the Leverhulme Trust (RPG-2023-110), the Engineering and Physical Sciences Research Council for funding (EP/W007517, EP/W015137/1) and the European Commission (PhotoReAct ITN: 956324). F. M. thanks the EaSI-CAT CDT at the University of St Andrews for support in the form of a studentship.This proof-of-concept study cements the viability and generality of mechanophotocatalysis, merging mechanochemistry and photocatalysis to enable solvent-minimized photocatalytic reactions. We demonstrate the transmutation of four archetypal solution-state photocatalysis reactions to a solvent-minimized environment driven by the combined actions of milling, light, and photocatalysts. The chlorosulfonylation of alkenes and the pinacol coupling of aldehydes and ketones were conducted under solvent-free conditions with competitive or superior efficiencies to their solution-state analogues. Furthermore, decarboxylative alkylations are shown to function efficiently under solvent-minimized conditions, while the photoinduced energy transfer promoted [2+2] cycloaddition of chalcone experiences a significant initial rate enhancement over its solution-state variant. This work serves as a platform for future discoveries in an underexplored field: validating that solvent-minimized photocatalysis is not only generalizable and competitive with solution-state photocatalysis, but can also offer valuable advantages.Peer reviewe

Luminescent iridium complexes used in Light Emitting Electrochemical Cells (LEECs)

EZ-C acknowledges the University of St Andrews for financial support. The authors would like to thank the Engineering and Physical Sciences Research Council for financial support for Adam Henwood: EPSRC DTG Grants: EP/J500549/1; EP/K503162/1; EP/L505097/1.Cationic iridium(III) complexes represent the single largest class of emitters used in light emitting electrochemical cells (LEECs). In this chapter, we highlight the state-of-the-art emitters in terms of efficiency and stability in LEEC devices, highlighting blue, green, yellow/orange, red and white devices, and provide an outlook to the future of LEECs.Publisher PDFPeer reviewe

Materials for electrochemiluminescence : TADF, hydrogen-bonding, and aggregation- and crystallization-induced emission luminophores

Authors thank the Natural Sciences and Engineering Research Council Canada (NSERC, DG RGPIN-2018- 06556, DG RGPIN-2023-05337 and SPG STPGP-2016-493924), New Frontiers in Research Fund (NFRFR-2021-00272), Canada Foundation of Innovation/Ontario Innovation Trust (CFI/OIT, 9040) and The University of Western Ontario for the support to this research. KC is an Ontario Graduate Scholar.Electrochemiluminescence (ECL) is a rapidly growing discipline with many analytical applications from immunoassays to single-molecule detection. At the forefront of ECL research is materials chemistry, which looks at engineering new materials and compounds exhibiting enhanced ECL efficiencies compared to conventional fluorescent materials. In this review, we summarize recent molecular design strategies that lead to high efficiency ECL. In particular, we feature recent advances in the use of thermally activated delayed fluorescence (TADF) emitters to produce enhanced electrochemiluminescence. We also document how hydrogen bonding, aggregation, and crystallization can each be recruited in the design of materials showing enhanced electrochemiluminescence.Publisher PDFPeer reviewe

Compositional variation in hybrid organic-inorganic lead halide perovskites : kinetically- versus thermodynamically-controlled synthesis

Authors thank the Chinese Scholarship Council and the University of St Andrews for Ph.D. Studentship support (to JT, CSC No. 201603780020).The formation and study of partial solid solutions in Az1-xFAxPbBr3, using reportedly similar sized cations azetidinium (Az+) and formamidinium (FA+), was explored via mechanosynthesis and precipitation synthesis. The composition and lattice parameters of samples from both syntheses were analyzed by 1H NMR and Rietveld refinement of powder X-ray diffraction. A clear mismatch in the composition of the perovskite was found between the precipitated samples and the corresponding solutions. Such a mismatch was not observed for samples obtained via mechanosynthesis. The discrepancy suggests products are kinetically-controlled during precipitation, compared to thermodynamically controlled mechanosynthesis. Furthermore, the cell volume as a function of composition in both hexagonal, 6H (Az-rich) and cubic, 3C (FA-rich) perovskite solid solutions suggests that FA+ is actually smaller than Az+, contradicting the literature. In the 3C (Az-poor) solid solutions, the extent of Az1-xFAxPbBr3 is unexpectedly smaller than in the corresponding methylammonium (MA+) system, Az1-xMAxPbBr3, which suggests that the extent of solid solution formation in these halide perovskites is predominantly dependent on the average A-cation size while the size mismatch plays a lesser role in comparison to oxides.PostprintPeer reviewe

Rigid biimidazole ancillary ligands as an avenue to bright deep blue cationic iridium(III) complexes

EZ-C acknowledges the University of St Andrews for financial support. Date of Acceptance: 03/06/2014Herein we report the synthesis and optoelectronic characterisation of three deep blue-emitting cationic iridium complexes, of the form [Ir(dFppy)2(N^N)]PF6, bearing biimidazole-type N^N ancillary ligands (dFppyH = 2-(2,4-difluorophenyl)pyridine). Complex 1 contains the parent biimidazole, biim, while 2 contains a dimethylated analog, dMebiim, and 3 contains an ortho-xylyl-tethered biimidzole, o-xylbiim. We explore a strategy of tethering the biimidazole in order to rigidify the complex and increase the photoluminescent quantum yield, culminating in deep blue (λmax: 457 nm in MeOH at 298 K) ligand-centered emission with a very high photoluminescent quantum yield of 68% and microsecond emission lifetime. Density functional theory calculations elucidate the origin of such disparate excited state kinetics across this series, especially in light of virtually identical optoelectronic properties observed for these compounds.PostprintPeer reviewe

Pyridine-functionalized carbazole donor and benzophenone acceptor design for thermally activated delayed fluorescence emitters in blue organic light emitting diodes

The authors thank the Marie Skłodowska-Curie Individual Fellowship (MCIF, no 749557), the Leverhulme Trust (RPG-2016-047) and EPSRC (EP/P010482/1) for financial support.In this paper we report a new molecular design approach for blue emitting thermally activated delayed fluorescence (TADF) molecules. The two novel TADF emitters, (4-(3,6-di(pyridin-3-yl)-9H-carbazol-9- yl)phenyl)(phenyl)methanone ( 3PyCzBP ), and (4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl)(phenyl)methanone ( 4PyCzBP ) possess a pyridine-functionalized carbazole donor and a benzophenone acceptor. Both compounds shows broad charge-transfer emission in DCM with a λmax at 497 nm and a photoluminescence quantum yield, ΦPL of 56% for 3PyCzBP and a λmax at 477 nm and a ΦPL of 52% for 4PyCzBP . The ΦPL decreased to 18% and 10%, respectively for 3PyCzBP and 4PyCzBP in the presence of O2 confirming that triplet states involved in emission. The PMMA doped (10 wt%) films show blue-shifted emission with λmax at 450 and 449 nm for 3PyCzBP and 4PyCzBP , respectively. The maximum ΦPL of 23.4% is achieved for these compounds in PMMA doped film. Difference in energy between the singlet and triplet excited states (ΔEST) is very small at 0.06 eV and 0.07 eV for 3PyCzBP and 4PyCzBP , respectively. Multilayer organic light emitting diode devices fabricated using these molecules as emitters show that the maximum efficiency (EQEmax) of the blue devices is 5.0%.PostprintPeer reviewe

Design of multi-resonance thermally activated delayed fluorescence materials for organic light-emitting diodes

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska Curie grant agreement no. 891606 (TADFNIR). We are also grateful for financial support from the University of St Andrews Restarting Research Funding Scheme (SARRF), which is funded through the Scottish Funding Council grant reference SFC/AN/08/020. J.W. thanks the China Scholarship Council (202006250026). We thank the Engineering and Physical Sciences Research Council for support (EP/P010482/1, EP/R511778/1 and EP/L017008/1).Two strategies to improve the performance of multiresonant thermally activated delayed fluorescence (MR-TADF) compounds are explored. These include incorporation of units to turn on aggregation-induced emission so as to permit use of MR-TADF compounds at high doping concentrations, and the use of heavy atoms to increase spin-orbit coupling to enhance reverse intersystem crossing rates. Preliminary photophysical investigations are presented.Postprin

Thermally activated delayed fluorescence and high-contrast mechanochromism of anthrone-based donor-acceptor systems

Funding: This project was funded by the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie grant agreement no. 891606 (TADFNIR). The authors thank the Engineering and Physical Sciences Research Council for funding (EP/P010482/1).The development of materials that emit in the deep red to near-infrared region of the spectrum has attracted significant attention on account of their potential as optical sensing and imaging reagents in biology. We report herein the synthesis and optoelectronic characterization of four anthraquinone-based emitters T-tBuCz-AQ, T-MeOCz-AQ, C-tBuCz-AQ, and C-MeOCz-AQ, and two pyrazoloanthrone-based emitters tBuCz-PA and DMAC-PA. Depending on the donor, these compounds emit between 640-750 nm in the neat film, while the emission of the 10 wt% doped films in PMMA are blue-shifted to between 600-700 nm and have low photoluminescence quantum yields of between 2.6-6.6%. Of these compounds, T-tBuCz-AQ, T-MeOCz-AQ, and C-tBuCz-AQ exhibited thermally activated delayed fluorescence in 10 wt% doped films in PMMA, while the crystals of T-tBuCz-AQ also showed TADF. Compound tBuCz-PA showed highcontrast and reversible PL response upon mechanical grinding and hexane fuming.Publisher PDFPeer reviewe