Synthesis, characterization, and photophysical properties of novel 9‑phenyl-9-phosphafluorene oxide derivatives

• Shuxian Qiu,
• Duan Dong,
• Jiahui Li,
• Huiting Wen,
• Jinpeng Li,
• Yu Yang,
• Shengxian Zhai and
• Xingyuan Gao

Beilstein J. Org. Chem. 2024, 20, 3299–3305, doi:10.3762/bjoc.20.274

• acceptor group in TADF emitters, indicating great potential for the development of highly efficient TADF molecules. In 2019, Nishida and co-workers prepared 5 D–A–D-type PhFlOP derivatives with electron-donating diarylamine or carbazole moieties in positions 2 and 8. They conducted optical and

• electrochemical studies, showing that the photophysical properties of PhFlOP depend on the nature of the electron-donating groups [31]. Later, Wu and co-workers introduced various electron donors to the PhFlOP unit to form new TADF emitters with high electroluminescence efficiency [32][33]. Despite this progress

• , TADF emitters containing the PhFlOP unit as an electron acceptor are still scarce. Meanwhile, the syntheses of the TADF emitters by the groups of Nishida and Wu both utilized palladium noble metal as a catalyst [31][32][33]. Therefore, it is of great significance to develop cost-effective synthetic

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

• Johannes Rocker,
• Till J. B. Zähringer,
• Matthias Schmitz,
• Till Opatz and
• Christoph Kerzig

Beilstein J. Org. Chem. 2024, 20, 1236–1245, doi:10.3762/bjoc.20.106

• ]. Prominent examples include: (i) carbonyl compounds such as benzophenone [31][32] and thioxanthone [33][34][35], (ii) TADF emitters with small singlet-triplet energy splitting [8][36], (iii) substitution with heavy atoms such as sulphur [37] and halides [38] for fast ISC, or a combination of the above

Aromatic systems with two and three pyridine-2,6-dicarbazolyl-3,5-dicarbonitrile fragments as electron-transporting organic semiconductors exhibiting long-lived emissions

• Karolis Leitonas,
• Brigita Vigante,
• Dmytro Volyniuk,
• Audrius Bucinskas,
• Pavels Dimitrijevs,
• Sindija Lapcinska,
• Pavel Arsenyan and
• Juozas Vidas Grazulevicius

Beilstein J. Org. Chem. 2023, 19, 1867–1880, doi:10.3762/bjoc.19.139

• groups to achieve optimal charge-transporting and fluorescent properties within one TADF compound (Figure 1) [5]. The obtained TADF emitters (453 to 550 nm) show photoluminescence quantum yields of up to 98% in oxygen-free toluene solutions. These TADF emitters are suitable for OLEDs with brightness of

• 10 000 cd m−2, electroluminescence ranging from blue to yellow, maximum current of 15 cd/A and higher EQE than 7%. Pyridine-3,5-dicarbonitrile-based TADF materials exhibit different visible light emission spectra (Figure 1). Recently, Chen and Lu reported two new orange-red/red TADF emitters composed

• TADF lifetimes of less than 1 µs. TADF-OLEDs based on these materials exhibited EQEmax of up to 25.0% and well-suppressed efficiency roll-offs. Green and orange normal/dual TADF emitters were produced using compounds containing 3,6-di-tert-butylcarbazole and 3,7-dibromophenothiazine moieties. Pyridine

Quinoxaline derivatives as attractive electron-transporting materials

• Zeeshan Abid,
• Liaqat Ali,
• Sughra Gulzar,
• Faiza Wahad,
• Raja Shahid Ashraf and
• Christian B. Nielsen

Beilstein J. Org. Chem. 2023, 19, 1694–1712, doi:10.3762/bjoc.19.124

• high electron mobility and efficient charge transfer. In particular, Qx derivatives find use as non-fullerene acceptors (NFAs) in OSCs and as essential building blocks in sensitizers for DSSCs. The significance of Qx extends beyond to thermally activated delayed fluorescence (TADF) emitters and

• cm2 V−1 s−1 [20]. Figure 6 shows the molecular structures of the prominent compounds exhibiting potential as n-type materials. Table 4 lists OFET device properties of devices employing Qx derivatives. Quinoxalines as ETL and TADF emitters Qx derivatives have garnered substantial attention from the

• scientific community due to their remarkable characteristics as electron-transporting and hole-blocking layers in organic electronics [60]. Moreover, these derivatives have exhibited promising traits as thermally activated delayed fluorescence (TADF) emitters. This multifaceted nature has spurred ongoing

Organic thermally activated delayed fluorescence material with strained benzoguanidine donor

• Alexander C. Brannan,
• Elvie F. P. Beaumont,
• Nguyen Le Phuoc,
• George F. S. Whitehead,
• Mikko Linnolahti and
• Alexander S. Romanov

Beilstein J. Org. Chem. 2023, 19, 1289–1298, doi:10.3762/bjoc.19.95

• fluorescence [1][2][3]. Organic TADF emitters have gained substantial attention in recent years for their prospective application in organic light-emitting diodes (OLEDs), photocatalysis, bioimaging, and sensors [4][5][6]. The ability to harvest both singlet and triplet excitons enable organic TADF emitters to

• as phosphorescence from a 3CT state. A more than 100-fold increase in radiative lifetime on cooling to 77 K is characteristic for the organic TADF emitters [1]. Upon cooling Zeonex matrices of 4BGIPN from 296 K to 16 K (Figure 5), the excited state lifetime shows an order of magnitude increase down

The effect of dark states on the intersystem crossing and thermally activated delayed fluorescence of naphthalimide-phenothiazine dyads

• Liyuan Cao,
• Xi Liu,
• Xue Zhang,
• Jianzhang Zhao,
• Fabiao Yu and
• Yan Wan

Beilstein J. Org. Chem. 2023, 19, 1028–1046, doi:10.3762/bjoc.19.79

• intersystem crossing (rISC) is slow, without coupling with an approximate 3LE state. These studies are useful for an in-depth understanding of the photophysical mechanisms of the TADF emitters, as well as for molecular structure design of new electron donor–acceptor TADF emitters. Keywords: charge-transfer

• may also enhance the rISC in OLED devices, in which the electron–hole recombination produces mainly the triplet state (the theoretical probability is 75%, by following the spin statistic rule) [1]. Compared to the application studies, the investigation of the photophysical mechanism of TADF emitters

• is far from mature [19][20][21]. Initially a two-state model was used for understanding of the photophysical processes of the electron donor–acceptor TADF emitters [9][22][23][24][25][26]. Soon it was realized this over simplified model is nonsufficient. For instance, the singlet/triplet charge

Ionic multiresonant thermally activated delayed fluorescence emitters for light emitting electrochemical cells

• Merve Karaman,
• Abhishek Kumar Gupta,
• Subeesh Madayanad Suresh,
• Tomas Matulaitis,
• Lorenzo Mardegan,
• Daniel Tordera,
• Henk J. Bolink,
• Sen Wu,
• Stuart Warriner,
• Ifor D. Samuel and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2022, 18, 1311–1321, doi:10.3762/bjoc.18.136

• ), Universidad de Valencia, C/Catedrático J. Beltrán 2, 46980 Paterna (Valencia), Spain School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, UK 10.3762/bjoc.18.136 Abstract We designed and synthesized two new ionic thermally activated delayed fluorescent (TADF) emitters that are charged analogues of

• limited to 25% [13]. Thermally activated delayed fluorescent (TADF) emitters are one class of purely organic materials that can harvest triplet excitons in electroluminescent (EL) devices through a triplet to singlet reverse intersystem crossing (RISC) upconversion process [14]. Indeed, OLEDs using TADF

• emitters can achieve up to 100% IQE, comparable to devices using phosphorescent emitters [15]. Purely organic TADF emitters have not been widely investigated for use in LEECs. We reported the first organic TADF LEEC, I (Figure 1a, original compound 2 in [16]), in 2015 by adapting the structure of the known

Thermally activated delayed fluorescence (TADF) emitters: sensing and boosting spin-flipping by aggregation

• Ashish Kumar Mazumdar,
• Gyana Prakash Nanda,
• Nisha Yadav,
• Upasana Deori,
• Upasha Acharyya,
• Bahadur Sk and
• Pachaiyappan Rajamalli

Beilstein J. Org. Chem. 2022, 18, 1177–1187, doi:10.3762/bjoc.18.122

• metal-based emitters in organic light-emitting diode (OLED) devices [18]. Nevertheless, many TADF emitters suffer from quenching of the emission due to the aggregation-caused quenching effect [19][20]. The strong π–π-stacking interactions in the solid or aggregated state may lead to emission quenching

• 'H-[9,3':6',9''-tercarbazol]-9'-yl)phenyl)(pyridin-4-yl)methanone (BPy-p3C) were synthesized via Ullmann coupling following the reported protocol [28]. These two TADF emitters have already been synthesized and device fabrication had been demonstrated. However, detailed photophysical investigations in

• , quenching occurs in the presence of acid and regaining of the fluorescence intensity happens under basic conditions (Figure 7). Conclusion In summary, we designed and synthesized two D–A-based TADF emitters, BPy-pTC and BPy-p3C. Both emitters showed excited-state ICT characteristics, leading to positive

Substituent effect on TADF properties of 2-modified 4,6-bis(3,6-di-tert-butyl-9-carbazolyl)-5-methylpyrimidines

• Irina Fiodorova,
• Tomas Serevičius,
• Rokas Skaisgiris,
• Saulius Juršėnas and
• Sigitas Tumkevicius

Beilstein J. Org. Chem. 2022, 18, 497–507, doi:10.3762/bjoc.18.52

• such as triazine, diazines or aromatics containing cyano and sulfone groups are popular acceptor units for the construction of highly efficient TADF emitters [8][9][10][11]. Pyrimidine (1,3-diazine) owing to its aromaticity, significant π-deficiency, strong electron affinity, high luminous efficiency

• ][19][20][21][22][23], and OLEDs [3][7][8][9][24]. In case of TADF emitters, a pyrimidine ring is often connected with a donor unit through a phenylene group as a conjugate π-spacer (s) [25][26][27][28]. As the majority of research describes TADF compounds with D-s–A–s–D layout, reports on TADF

• pyrimidine–carbazole TADF emitters bearing different substituents in position 2 of the pyrimidine moiety were successfully prepared by using Liebeskind–Srogl cross-coupling, hydrogenolysis, oxidation reactions of 4,6-bis(3,6-di-tert-butyl-9-carbazolyl)-5-methyl-2-methylthiopyrimidine and following

Comparative study of thermally activated delayed fluorescent properties of donor–acceptor and donor–acceptor–donor architectures based on phenoxazine and dibenzo[a,j]phenazine

• Saika Izumi,
• Prasannamani Govindharaj,
• Anna Drewniak,
• Paola Zimmermann Crocomo,
• Satoshi Minakata,
• Leonardo Evaristo de Sousa,
• Piotr de Silva,
• Przemyslaw Data and
• Youhei Takeda

Beilstein J. Org. Chem. 2022, 18, 459–468, doi:10.3762/bjoc.18.48

• theoretical calculations, the role of the additional donor unit in the TADF mechanism is boosting the rISC process by balancing the singlet–triplet energy gap and spin–orbit coupling. The results showcased herein would allow for designing efficient TADF emitters more flexibly in the future. Chemical

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

• Ettore Crovini,
• Zhen Zhang,
• Yu Kusakabe,
• Yongxia Ren,
• Yoshimasa Wada,
• Bilal A. Naqvi,
• Prakhar Sahay,
• Tomas Matulaitis,
• Stefan Diesing,
• Ifor D. W. Samuel,
• Wolfgang Brütting,
• Katsuaki Suzuki,
• Hironori Kaji,
• Stefan Bräse and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2021, 17, 2894–2905, doi:10.3762/bjoc.17.197

• %, with Commission Internationale de l’Éclairage coordinate of (0.22, 0.47), at 1 mA cm−2. Keywords: blue emitters; dimer; indolocarbazole; orientation; outcoupling effect; solution-processed OLEDs; TADF emitters; triazine; Introduction Organic thermally activated delayed fluorescence (TADF) materials

• EML. Thus, vacuum deposition of this family of TADF emitters is clearly superior to solution processing. Conclusion Building upon our previously reported emitter, ICzTRZ, here we presented a dual emitter strategy consisting of two ICzTRZ moieties covalently linked together in the form of DICzTRZ. DFT

Exploring the possibility of using fluorine-involved non-conjugated electron-withdrawing groups for thermally activated delayed fluorescence emitters by TD-DFT calculation

• Dongyang Chen and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2021, 17, 210–223, doi:10.3762/bjoc.17.21

• thermally activated delayed fluorescence (TADF) emitters. In the present study, we investigate computationally the potential of other fluorine-containing acceptors, trifluoromethoxy (OCF3), trifluoromethylthio (SCF3), and pentafluorosulfanyl (SF5), within two families of donor–acceptor TADF emitters. Time

• , respectively. The compounds 2CzCF3, 2CzSCF3, and 2CzSF5, from Type I molecules, show significant promise as deep blue TADF emitters, possessing high calculated singlet energies in the gas phase (3.62 eV, 3.66 eV, and 3.51 eV, respectively) and small, ΔESTs, of 0.17 eV, 0.22 eV, and 0.07 eV, respectively. For

• compounds 5CzSCF3 and 5CzSF5, from Type II molecules, the singlet energies are stabilized to 3.24 eV and 3.00 eV, respectively, while ΔESTs are 0.27 eV and 0.12 eV, respectively, thus both show promise as blue or sky-blue TADF emitters. All these six molecules possess a dense number of intermediate excited

Aryl-substituted acridanes as hosts for TADF-based OLEDs

• Naveen Masimukku,
• Dalius Gudeika,
• Oleksandr Bezvikonnyi,
• Ihor Syvorotka,
• Rasa Keruckiene,
• Dmytro Volyniuk and
• Juozas V. Grazulevicius

Beilstein J. Org. Chem. 2020, 16, 989–1000, doi:10.3762/bjoc.16.88

• devices [1]. Nowadays, organic compounds exhibiting thermally activated delayed fluorescence (TADF) are widely used as emitters for OLEDs [2]. The great interest in TADF emitters is mainly explained by their heavy-atoms-free molecular structure and 100% theoretical limit of internal quantum efficiency

• splitting (∆EST) between the lowest singlet and triplet excited states [5]. Various TADF derivatives have been developed with the aim to obtain highly efficient OLEDs by combining diverse donor and electron-acceptor moieties [6][7]. To successfully exploit TADF emitters in OLED structures, appropriate hosts

• are required [8]. Since the selection of suitable hosts is very important for achieving high OLED efficiencies, there was considerable interest in host compounds for TADF emitters in recent years [9][10]. The host compounds for TADF-based OLEDs must match a number of censorious requests. For example

Synthesis and optoelectronic properties of benzoquinone-based donor–acceptor compounds

• Daniel R. Sutherland,
• Nidhi Sharma,
• Georgina M. Rosair,
• Ifor D. W. Samuel,
• Ai-Lan Lee and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2019, 15, 2914–2921, doi:10.3762/bjoc.15.285

• is difficult to realize highly efficient TADF emitters, which is especially the case for red emitters where nonradiative rates are high due to the well-known energy gap law [28]. While anthraquinone-based charge-transfer compounds have recently been shown to exhibit TADF that then translated to their

• behavior of the four compounds was disappointing, especially compared to the high ΦPL values and deep red emission reported for anthraquinone-based TADF emitters [29]. For the nonemissive complexes, it is possible that this was due to ISC being much faster than RISC. For benzoquinone, ISC occurs within 10

Recent advances on organic blue thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs)

• Thanh-Tuân Bui,
• Fabrice Goubard,
• Malika Ibrahim-Ouali,
• Didier Gigmes and
• Frédéric Dumur

Beilstein J. Org. Chem. 2018, 14, 282–308, doi:10.3762/bjoc.14.18

• popularized by Chihaya Adachi since 2012. In this review, we proposed to focus on the recent advances in the molecular design of blue TADF emitters for OLEDs during the last few years. Keywords: blue; electroluminescence; emitter; OLED; TADF; Introduction Since the pioneering works of Tang and VanSlyke in

• delayed fluorescence (TADF) emitters. As specificity, these materials can thermally repopulate the singlet state from the triplet state by reverse intersystem crossing (RISC), leading to an increase of the luminescence intensity. From the OLEDs viewpoint, TADF emitters behave by harvesting both singlet

• ). TADF materials can also be metal-free, addressing the fabrication cost and environmental issues. Therefore, TADF emitters retain the high efficiency of the second generation of emitters (triplet emitters), the stability of the first generation of fluorescent materials while eliminating the different