Highly fluorescent emitters based on triphenylamine‐π‐triazine (D‐π‐A) system : effect of extended conjugation on singlet‐triplet energy gap

SK acknowledges the financial support from European Union's Horizon 2020 research and innovation programme under Marie Skłodowska Curie Individual Fellowship (MCIF; Agreement No. 748430‐THF‐OLED).Three D‐π‐A type linearly‐extended emitters, based on diphenylamine ( DPA ) as the donor and 2,4,6‐triphenyl‐1,3,5‐triazine ( TRZ ) as the acceptor, were synthesized and their optoelectronic properties characterized. The introduction of an additional phenyl or phenylethynyl π‐spacer results in an enhancement of the molar extinction coefficient and a systematic bathochromic shift of the charge‐transfer transition in the absorption spectra. A mirrored bathochromic shift in the photoluminescence spectra is also observed with increasing conjugation of the bridge moiety. All three compounds show high photoluminescence quantum yields and moderate singlet‐triplet excited state energy gaps, ΔE ST, of 0.26‐0.37 eV were observed in 10 wt% doped films in mCP as the host matrix.Publisher PDFPeer reviewe

High performance non-doped green organic light emitting diode via delayed fluorescence

P. G. thanks the Science & Engineering Research Board (SERB), India, for the Start-up Research Grant (SRG) (Grant No: SRG/2020/000161). E.Z-C. thanks the Engineering and Physical Sciences Research Council (EPSRC) EP/P010482/1 for support. P. R. thanks the Indian Institute of Science (IISc) for generous financial support and the Science & Engineering Research Board (SERB), India, for the SERB-Power Grant (SPG) (Grant No: SPG/2020/000107). B.S. thank IISc for the C. V. Raman Fellowship under the Institute of Eminence (IoE).Non-doped, delayed fluorescence organic light-emitting diodes (OLEDs) provide a route to high performance devices and simplified device fabrication. Here, two ambipolar anthracene derivatives containing a hole-transporting di-p-tolylamine and a carbazole and an electron-transporting phosphine oxide moiety are rationally designed and synthesized. The thermal and optoelectronic properties were investigated and the neat films of these compounds show high photoluminescence quantum yields of 84–87%. Non-doped OLEDs with these luminogens exhibit green emission at ∼545 nm and an EQEmax of over 7.2% due to the delayed fluorescence resulting from triplet–triplet annihilation (TTA). The devices show a high luminance of over 104 400 cd m−2. Power efficiency and current efficiency maxima are up to 23.0 lm W−1 and 28.3 cd A−1, respectively. Moreover, the devices show very low efficiency roll-off and retain 90% of the maximum efficiency even at 20 000 cd m−2. When combined with a thermally activated delayed fluorescent (TADF) assistant dopant, the green-emitting OLEDs show a high EQEmax of 17.8%.PostprintPeer reviewe

Photoluminescence and electrochemiluminescence of thermally activated delayed fluorescence (TADF) emitters containing diphenylphosphine chalcogenide-substituted carbazole donors

SK acknowledges the financial support from European Union's Horizon 2020 research and innovation programme under Marie Skłodowska Curie Individual Fellowship (MCIF; Agreement No. 748430-THF-OLED). P. R acknowledges support from a Marie Skłodowska-Curie Individual Fellowship (No. 749557). The work has been supported in Mons by European Union through the Interreg V initiative France-Wallonie-Vlaanderen project LUMINOPTEX and 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. J. C. is an FNRS research director. Y. O. acknowledges funding by the Fonds de la Recherche Scientifique-FNRS under Grant no F.4534.21 (MIS-IMAGINE). We acknowledge the research support from Natural Sciences and Engineering Research Council Canada (NSERC, DG RGPIN-2013-201697, DG RGPIN-2018-06556, and SPG STPGP-2016-493924), Canada Foundation of Innovation, Ontario Innovation Trust (CFI/OIT, 9040) and Western University. J. R. A. appreciates the Ontario graduate scholarships (2018–2022). EZ-C is a Royal Society Leverhulme Trust Senior Research fellow (SRF\R1\201089).Aiming to develop efficient blue-emitting thermally activated delayed fluorescence (TADF) compounds, we have designed and synthesized derivatives of the well-known sky-blue emitter 2CzPN that contain electron-accepting phosphine chalcogenide groups to stabilize the HOMO level relative to the pristine compound, thus increasing the HOMO–LUMO gap and blue-shifting the emission wavelength. By cyclic voltammetry, photophysical data and quantum-chemical calculations, it was found that polar solvents and matrices validated the proposed concept, but these trends were not recovered in non-polar media. The suitability of these 2CzPN derivatives in polar matrices for optoelectronic applications was explored with electrochemiluminescence (ECL) by measuring emission delays, radical stability, emission stabilities, emission efficiencies and emission spectra. Some of the 2CzPN derivatives showed an unprecedented delayed onset of the ECL, and delayed rising time to the ECL maximum, as well as long ECL emission decay. All of these mentioned delay times suggest that these luminophores primarily emit via organic long-persistent electrochemiluminescence (OLECL) mechanisms. The derivatization of the donor groups of the emitters affected both the radical stability and the predominant emission mechanism, providing important insight into their potential as emitters in solid-state electroluminescent devices.Publisher PDFPeer reviewe

Substitution effects on a new pyridylbenzimidazole acceptor for thermally activated delayed fluorescence and their use in organic light-emitting diodes

The St Andrews team would like to thank the Leverhulme Trust (RPG-2016-047) for financial support. P.R. acknowledges support from a Marie Skłodowska-Curie Individual Fellowship (MCIF; No. 749557). S.M.S acknowledges support from the Marie Skłodowska-Curie Individual Fellowship, grant 27 agreement no. 838885 (NarrowbandSSL). Computational resources have been provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifiques de Belgique (F.R.S.-FNRS) under Grant No. 2.5020.11, as well as the Tier-1 supercomputer of the Fédération Wallonie-Bruxelles, infrastructure funded by the Walloon Region under the grant agreement n1117545. We acknowledge support from the European Union’s Horizon 2020 research and innovation programme under the ITN TADFlife (GA 812872). Y.O. acknowledges funding by the Fonds de la Recherche Scientifique-FNRS under Grant n° F.4534.21 (MIS-IMAGINE). D.B. is a FNRS Research Director.In this work a new acceptor is used for use in thermally activated delayed fluorescence (TADF) emitters, pyridylbenzimidazole, which when coupled with phenoxazine allows efficient TADF to occur. N-functionalization of the benzimidazole using methyl, phenyl, and tert-butyl groups permits color tuning and suppression of aggregation-caused quenching (ACQ) with minimal impact on the TADF efficiency. The functionalized derivatives support a higher doping of 7 wt% before a fall-off in photoluminescence quantum yields is observed, in contrast with the parent compound, which undergoes ACQ at doping concentrations greater than 1 wt%. Complex conformational dynamics, reflected in the time-resolved decay profile, is found. The singlet−triplet energy gap, ΔEST, is modulated by N-substituents of the benzimidazole and ranges of between 0.22 and 0.32 eV in doped films. Vacuum-deposited organic light-emitting diodes, prepared using three of the four analogs, show maximum external quantum efficiencies, EQEmax, of 23.9%, 22.2%, and 18.6% for BIm(Me)PyPXZ , BIm(Ph)PyPXZ , and BImPyPXZ , respectively, with a correlated and modest efficiency roll-off at 100 cd m–2 of 19% 13%, and 24% of the EQEmax, respectively.Publisher PDFPeer reviewe