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Incorporating pyridyl uniquely from its 2-position onto 10-site of acridone ring generated intramolecular hydrogen bond in a group of acridone-carbazole hybrid thermally activated delayed fluorescence emitters, which universally pulled down non-radiative transition rates by three orders and elevated reverse intersystem crossing rates by two orders, and thus boosted PLQYs to almost unity and EQEs of OLEDs to 30+%, representing the state-of-the-art efficiencies of deep-blue TICT-TADF materials and devices with CIEy≤0.10. [Display omitted] • Intramolecular-hydrogen-bond boosts performance of deep blue TADF emitters. • H-bond reduces k nr by 3 orders and increases k RISC by 2 orders. • PLQYs≈100 %, k RISC s ≥ 105 s−1 and horizontal orientation ratios ≥90 % are obtained. • Deep blue OLEDs exhibit record-high EQEs of 31–33 % with CIE y of 0.09–0.12. A group of D-A-D type thermally activated delayed fluorescence (TADF) emitters were developed with 10-(pyridin-2-yl)acridin-9(10 H)-one as acceptor and substituted carbazoles as donors. The design was focused on incorporating pyridyl to the 10-site nitrogen atom of acridin-9(10 H)-one ring, which improved the reverse intersystem crossing rate constant k RISC from 103 s−1 to 105 s−1. More importantly, the linkage of pyridyl uniquely from its 2-position to acridin-9(10 H)-one ring induced intramolecular hydrogen bond, which suppressed nonradiative transition rates by three to four orders of magnitude and universally increased the photoluminescence quantum yields from 54 % to nearly 100 %. In combination with the intrinsic high horizontal orientation ratios over 90 % of acridin-9(10 H)-one based molecules, such pyridyl decoration boosted the external quantum efficiencies of simple-structure deep blue organic light-emitting diodes to 31–33 % with CIE x of 0.15 and CIE y of 0.09 ∼ 0.12, being double of that for hydrogen-bond-free parent emitter and representing the state-of-the-art efficiencies for the deep blue twisted intramolecular charge transfer type TADF materials with CIEy ≤ 0.10 so far. These TADF emitters are comparable with the prevailing multiresonance blue emitters in terms of distinctive efficiencies, but advantageous in much facile syntheses. [ABSTRACT FROM AUTHOR]

Developing deep blue thermally activated delayed fluorescence (TADF) materials with high efficiencies and good color purities is still a formidable challenge. Here, two novel deep blue TADF emitters, namely MePhCz-AD and MePhCz-AD-Py, were synthesized by incorporating two 3,6-diphenyl-9 H -carbazole donors onto the methyl-modified acridin-9(10 H)-one (AD) acceptor, respectively. The high rigidity of AD acceptor effectively suppressed non-radiative transition and vibration relaxation of excited states, which is favorable for a good emitting quantum yield and narrow spectral width. The presence of methyl groups at 2,7-sites of AD ring slightly reduced the acceptor strength and contributed to the deep blue emission color. Incorporation of phenyls at 3,6-sites of carbazole ring delocalized the distribution of the highest occupied molecular orbital (HOMO), promoting the radiative decay process. As a result, these two emitters showed deep blue TADF with fast radiative decay rates k R > 107 s−1. In addition, with the introduction of pyridyl (Py) group at 10-site of AD ring instead of phenyl, both the spin-orbital coupling (SOC) constant between high-lying triplet states and the lowest singlet excited state (S 1) and thus the reverse intersystem crossing rate constant (k RISC) were dramatically promoted for MePhCz-AD-Py. The organic light-emitting diode with MePhCz-AD-Py as doped emitter exhibited a maximum external quantum efficiency (EQE max) of 15.4% with a relatively narrow FWHM of 60 nm and the deep-blue color coordinates of (0.15, 0.15). A deep blue TADF emitter MePhCz-AD-Py based on diphenylcarbazole as donors and acridin-9(10 H)-one as acceptor with methyl at 2,7-sites and pyridyl at 10-site exhibited both fast k RISC of 3.7 × 104 s−1 and k R of 4.1 × 107 s−1 due to a large SOC and an enlarged oscillator strength. The deep blue OLED with MePhCz-AD-Py as doped emitter realizes an EQE max of 15.4% with CIE coordinates of (0.15, 0.15). [Display omitted] • Deep blue TADF emitters are developed with methyl-modified acridin-9(10 H)-one as acceptor. • Pyridyl is introduced to 10-site of acceptor to increase the SOC and RISC rate constant k RISC. • High EQE of 15.4% and CIE (0.15, 0.15) were obtained for deep blue OLED. [ABSTRACT FROM AUTHOR]

It is essential to manage the alignment of the locally excited (3LE) and charge-transfer triplet (3CT) and singlet (1CT) states of thermally activated delayed fluorescence (TADF) materials to accelerate reverse intersystem crossing (RISC) process. A series of donor-acceptor (D-A) type TADF emitters were developed by attaching acridine (DMAC) or phenoxazine (PXZ) donor at 3-site of acridin-9(10 H)-one (i.e. acridone, AD) acceptor. Regardless of the donor, the lowest triplet excited states (T 1) are always dominated by the 3LE A state with certain contribution from the 3CT state. By introducing methyl (Me) or trifluoromethyl (CF 3) at 6-site of AD acceptor, the energy levels of 1CT, 3CT and 3LE states were tuned in different ways. When the donor is DMAC, incorporating Me on AD ring (3-DMAC-6-Me-AD) destructed the emission performance, while CF 3 (3-DMAC-6-CF 3 -AD) strongly stimulated the TADF by pulling down the 1CT state level and reducing the energy splitting Δ E ST to almost zero. In the case of strong donor PXZ, decorating acceptor with Me (3-PXZ-6-Me-AD) did not bring extinct effect on the TADF property. In particular, 3-DMAC-6-CF 3 -AD and 3-PXZ-6-Me-AD exhibited high rate constants of RISC (k RISC) of 10−6 and of radiation (k R) of 107 S−1, respectively. They achieved the maximum external quantum efficiency (EQE max) of 21.6% and 23.3% in the doped OLEDs, and realized EQE max of 14.7% and 17.6% with low efficiency roll-offs in non-doped devices. Highly rigid acridone is used as acceptor to construct donor-acceptor type thermally activated delayed fluorescence (TADF) emitters. Both incorporating trifluoromethyl on acceptor and adopting stronger donor can realize the energetically favorable 1CT ≈ 3CT ≈ 3LE status, increasing the k RISC from 105 s−1 to 106 s−1. High EQEs of 21.6%/14.7% and 23.3%/17.6% are achieved in doped and non-doped OLEDs. [Display omitted] • A series of thermally activated delayed fluorescence (TADF) emitters were developed using highly rigid acridone as acceptor. • Design strategies were focused on tuning the substituents on acceptor or varying donor strength, not changing twisting angles. • Energy level differences among 1CT, 3CT and 3LE states were reduced to facilitate the RISC to 106 s−1. • High EQEs of 21.6%/14.7% and 23.3%/17.6% were obtained in the doped and non-doped OLEDs. [ABSTRACT FROM AUTHOR]

9,9‐Dimethyl‐9,10‐dihydroacridine (DMAC) is one of the most widely used electron donor for constructing high‐performance thermally activated delayed fluorescence (TADF) emitters. However, DMAC‐based emitters often suffer from the imperfect color purity, particularly in blue emitters, due to its strong electron‐donating capability. To modulate donor strength, 2,7‐F‐Ph‐DMAC and 2,7‐CF3‐Ph‐DMAC were designed by introducing the electron‐withdrawing 2‐fluorophenyl and 2‐(trifluoromethyl)phenyl at the 2,7‐positions of DMAC. These donors were used, in combination with 2,4,6‐triphenyl‐1,3,5‐triazine (TRZ) acceptor, to develop novel TADF emitters 2,7‐F‐Ph‐DMAC‐TRZ and 2,7‐CF3‐Ph‐DMAC‐TRZ. Compared to the F‐ or CF3‐free reference emitter, both two emitters showed hypsochromic effect in fluorescence and comparable photoluminescence quantum yields without sacrificing the reverse intersystem crossing rate constants. In particular, 2,7‐CF3‐Ph‐DMAC‐TRZ based OLED exhibited a blue shift by up to 39 nm and significantly improved Commission International de l′Éclairage (CIE) coordinates from (0.36, 0.55) to (0.22, 0.41), while the external quantum efficiency kept stable at about 22.5 %. This donor engineering strategy should be valid for improving the color purity of large amount of acridine based TADF emitters. It can be predicted that pure blue TADF emitters should be feasible if these F‐ or CF3‐modifed acridine donors are combined with other weaker electron acceptors. [ABSTRACT FROM AUTHOR]

Two novel tricyclometalated heteroleptic iridium complexes, namely Ir(dfbpy) 2 (pt) and Ir(dfbpy) 2 (dfppy), were designed and synthesized for application as blue phosphors in optoelectronic devices. 2′,6′-difluoro-2,3′-bipyridine (dfbpy) was used as the cyclometalating ligand. In comparison with the parent homoleptic Ir(dfbpy) 3 , the newly developed 3-(1-benzyl-1 H -1,2,3-triazol-4-yl)pyridine (pt) with higher triplet energy than dfbpy or 2-(2,4-difluorophenyl)pyridine (dfppy) was used as the ancillary ligands to tune the electronic properties of these heteroleptic complexes. Both complexes emit strong blue phosphorescence with high quantum yields. The incorporation of high-energy ancillary ligand pt in Ir(dfbpy) 2 (pt) makes the highest-energy sub-band intensity in the phosphorescence spectrum increase relative to those of the parent Ir(dfbpy) 3 , and leads to narrower phosphorescence spectrum than the analogue Ir(dfbpy) 2 (dfppy) as well, which may provide a practical method to adjust the phosphorescence spectra and color purity of the complexes. [ABSTRACT FROM AUTHOR]

By linking the carbazole unit to the nitrogen atom of acridone through phenyl or pyridyl, two compounds, named 10‐(4‐(9H‐carbazol‐9‐yl)phenyl)acridin‐9(10H)‐one (AC‐Ph‐Cz) and 10‐(5‐(9H‐carbazol‐9‐yl)pyridin‐2‐yl)acridin‐9(10H)‐one (AC‐Py‐Cz) were designed and synthesized. These two materials, characterized with highly twisted and rigid structure, good thermal stability, and balanced carrier‐transporting properties, were employed as host materials for green phosphorescent and thermally activated delayed fluorescent organic light‐emitting diodes (OLEDs). The carbazole group, despite its small contribution to the highest occupied molecular orbitals (HOMOs) of these two materials, plays an essential role as an intramolecular host in energy delivering and improving the hole transporting ability of these two hosts. The incorporation of the electron‐deficient pyridyl group as a linking group slightly improves the electron transporting capability of AC‐Py‐Cz. The green phosphorescent OLED (PhOLED) based on AC‐Py‐Cz exhibited excellent device performance with a turn‐on voltage of 2.5 V, a maximum power efficiency and an external quantum efficiency (ηext) of 89.8 lm W−1 and 25.2 %, respectively, benefitting from the better charge‐balancing ability of AC‐Py‐Cz host due to the presence of the pyridyl bridge. More importantly, all the devices based on these two hosts showed low efficiency roll‐off at high brightness due to the suppressed non‐radiative transition in the emitting layer. In particular, the AC‐Py‐Cz‐hosted green PhOLED exhibited an efficiency roll‐off of 1.6 % from the maximum next at a high brightness of 1000 cd m−2 and a roll‐off of 15.9 % at an extremely high brightness of 10000 cd m−2. This study manifests that acridone‐based host materials have great potential in fabricating OLEDs with low efficiency roll‐off. [ABSTRACT FROM AUTHOR]

3,6-di- tert -butyl-9H-carbazole and 3,6-diphenyl-9H-carbazole have been widely used to construct blue thermally activated delayed fluorescence (TADF) emitters. However, it is difficult for related emitters to achieve maximum external quantum efficiency (EQE max) above 20 % with the Commission Internationale de l'Eclairage (CIE) y ≤ 0.12. A new type of donor was developed to construct blue TADF molecules, namely CF 3 P-BuCz-TRZ and CF 3 P-PhCz-TRZ. The weak electron-withdrawing trifluoromethylphenyl (CF 3 P) with moderate steric hindrance was introduced into the 1-site of carbazole donor for improving the color purity for blue TADF emitters. More importantly, the introduction of CF 3 P tightly compacts the energy levels for the significant excited states in RISC process. The energy gap between the lowest singlet excited (S 1) state and the lowest triplet (T 1) state (Δ E (S 1 − T 1) ), as well as between T 1 and the higher triplet (T n , n ≥ 2) states (Δ E (T n − T 1) ) were reduced, so that T n (n ≥ 2) could be effectively harvested to further promote reverse intersystem crossing (RISC). As a result, the OLEDs based on CF 3 P-BuCz-TRZ and CF 3 P-PhCz-TRZ displayed blue electroluminescence with CIE coordinates of (0.156, 0.107) and (0.155, 0.115). In particular, the maximum EQEs of the CF 3 P-PhCz-TRZ device reached 20.43 % without employing any light out-coupling enhancement or TADF-sensitized structure. This strategy should be valuable for designing more pure-blue and deep-blue TADF emitters. The weak electron-withdrawing trifluoromethylphenyl (CF 3 P) with moderate steric hindrance was introduced into the 1-site of carbazole donor. The k RISC s were remarkably facilitated with incorporation of CF 3 P group in CF 3 P-PhCz-TRZ. CF 3 P-PhCz-TRZ exhibited both blue-shifted EL in OLED with CIE (0.155, 0.115) and improved maximum EQE of 20.43 %, which are superior to the parent emitter PhCz-TRZ with CIE (0.154, 0.146) and EQE of 15.18 %. [Display omitted] • Trifluoromethylphenyl (CF 3 P) is introduced to 1-site of carbazole as new donors for blue TADF emitters. • The electron withdrawing CF 3 P group weakens donor strength, making hyprochromic shift by 10 nm. • CF 3 P group compacts the excited states energy levels and reduce energy differences Δ E ST and Δ E TT and facilitates RISC. • CF 3 P based TADF emitters exhibit higher EQE = 20 % (vs 15 %) and better CIE y = 0.115 (vs 0.146) in OLEDs. • Modifying carbazole donors with CF 3 P is a universal design strategy for better blue color and higher efficiencies. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials that can exhibit high efficiencies in non‐doped organic light‐emitting diodes (OLEDs) are highly desired. On the base of a reference TADF molecule (4‐(9,9‐dimethylacridin‐10(9H)‐yl)phenyl)(phenyl)methanone (BP‐DMAC) containing benzoyl/acridine as acceptor/donor, 9‐phenyl‐9H‐3,9"‐bicarbazole (PBCz) is incorporated to the benzoyl side to design and develop a novel emitter, (4‐(9,9‐dimethylacridin‐10(9H)‐yl)phenyl)(9‐phenyl‐9H‐[3,9″‐bicarbazol]‐6‐yl)methanone (PBCz‐BP‐DMAC). The introduction of PBCz unit is proved to endow PBCz‐BP‐DMAC the additional self‐host feature, in addition to its original aggregation‐induced emission and TADF characters. As a result, the non‐doped OLED of PBCz‐BP‐DMAC exhibits sky‐blue emission with remarkable external quantum efficiency (EQE) of 23.0% and rather low efficiency roll‐off (6%) at a brightness of 1000 cd m−2, while its doped device reveals a maximum EQE of 27.5%; the spectra and color coordinates of the doped and non‐doped devices are almost identical. It also acts as a host to sensitize green iridium phosphor (fac‐tris(2‐phenylpyridine) iridium(III), Ir(ppy)3) with high EQE of 23.6%. More fascinatingly, the simplified single‐emitting‐layer all‐TADF white OLED utilizing PBCz‐BP‐DMAC as host emitter in combination with an orange TADF emitter (4CzTPN‐Ph) realizes a state‐of‐the‐art EQE of 20.6%. Evidently PBCz‐BP‐DMAC is one of the best sky‐blue TADF materials and exhibits multi‐functional applications in OLEDs with excellent performance. [ABSTRACT FROM AUTHOR]

Recently, numerous efforts have been devoted to sky blue or greenish blue organic light-emitting diodes (OLEDs), nevertheless, the deep blue and pure blue OLEDs still remain a formidable challenge. Herein, a series of deep blue and pure blue donor–acceptor–donor (D–A–D) type emitters, namely Cz-DMTD, PhCz-DMTD and TMCz-DMTD, were constructed. For PhCz-DMTD which exhibited no delayed fluorescence component, the extended delocalization of donors and the enhancement of oscillator strength were both observed through theoretical calculation. For methyl-engineered TMCz-DMTD, the degenerate charge transfer singlet excited (1CT) and triplet excited (3CT) states and localized triplet excited (3LE) state endowed a thermally activated delayed fluorescence (TADF) character. Moreover, PhCz-DMTD and TMCz-DMTD based OLEDs displayed emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.164, 0.077) and (0.157, 0.107) and with maximum external quantum efficiencies (EQEmax) of 4.6% and 8.7%, respectively. It is the first time that the electroluminescence wavelength of TMCz based OLEDs reached below 450 nm with a CIEy below 0.11. Molecular engineering of the carbazole moiety is expected to provide a valuable strategy for molecular design of more deep blue emitters. [ABSTRACT FROM AUTHOR]

It is crucial for thermally activated delayed fluorescence (TADF) emitters to have both high photoluminescence quantum yield (PLQY) and high reverse intersystem crossing rate (k RISC). A novel TADF emitter, namely 3,6-bis(3,6-bis(diphenylamino)-9 H -carbazol-9-yl)-10-phenylacridin-9(10 H)-one (3,6-DPCz-AD), was designed by introducing N 3 , N 3 , N 6 , N 6 -tetraphenyl-9 H -carbazole-3,6-diamine (DPCz) at 3,6-sites of the acceptor acridin-9(10 H)-one (AD) by nucleophilic substitution. On the acridin-9(10 H)-one ring, the sp2-hybridization of the 10-site N atom leads to high rigidity, which inhibited conformation relaxation of excited state to reduce non-radiative decay. The introduction of large conjugated diphenylamine groups at the 3,6-sites of carbazole not only facilitated the RISC by increasing intramolecular charge transfer and generating a low S 1 -T 1 energy gap (Δ E ST), but also enhanced the radiative transition by enlarging the highest occupied molecular orbital (HOMO) delocalization. As a result, even without the traditional highly distorted structure, 3,6-DPCz-AD exhibited strong TADF characteristics with high k RISC of 5.8 × 105 s−1, high k r of 3.4 × 107 s−1 and a high PLQY of 99% simultaneously. The green organic light-emitting diode (OLED) of 3,6-DPCz-AD showed both a maximum external quantum efficiency (EQE max) of 30.1% and a power efficiency of 83.3 lm W−1. An EQE of 20.1% was still remained at a high brightness of 1000 cd m−2. This is one of the best performances for acridin-9(10 H)-one based TADF emitters ever reported so far. A novel thermally activated delayed fluorescence emitter 3,6-DPCz-AD based on acridone acceptor and 3,6-bis(diphenylamino)-carbazole donors realizes effective trade-off between reverse intersystem crossing and radiative transition through appropriate design strategy, which results in high k RISC > 5 × 105 s−1, k r > 107 s−1 and PLQY of 99% simultaneously and finally leads to high external quantum efficiency over 30% with good efficiency stability in simple-structured green OLED. [Display omitted] • A novel thermally activated delayed fluorescence (TADF) emitter 3,6-DPCz-AD was developed for OLED application. • Incorporating diphenylamine on carbazole donors enhanced TADF feature despite small donor-acceptor angles. • Combination of DPCz as donors and acridone as acceptor facilitated both RISC and radiative transition processes. • High k RISC of 5.8 × 105 s−1, k r of 3.4 × 107 s−1 and PLQY of 99.2% were realized simultaneously. • 3,6-DPCz-AD exhibited a very high EQE max of 30.1% in green OLED with slow efficiency roll-off. [ABSTRACT FROM AUTHOR]

Blue iridium phosphors are always precious and desirable for both fundamental research and industrial applications in organic light-emitting diodes (OLEDs). Three heteroleptic cyclometalated iridium(III) complexes, namely, Ir1, Ir2 and Ir3, incorporating 2-(3,5-bis(trifluoromethyl)phenyl)-pyrimidine (tfmphpm) or 2-(2,4-difluorophenyl)-pyrimidine (dfppm) as the main ligand, and 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine (fppz) or 2-(5-(4-(trifluoromethyl)phenyl)-2H-1,2,4-triazol-3-yl)pyridine (Htaz) as the ancillary ligand, were developed for application in OLEDs. Owing to the introduction of the strong-field CF3-containing ancillary ligand and the incorporation of electron-withdrawing F or CF3 groups on the HOMO-lying C-related aromatic rings of the C^N cyclometalating ligands, the phosphorescence of these Ir(III) complexes peaked at 457–459 nm. In comparison with the well-known commercial sky-blue iridium complex FIrpic (bis(4′,6′-difluorophenylpyridinato) iridium(III) picolinate, 475 nm), the phosphorescence of these complexes is hypsochromically shifted by 16–18 nm, more closely approaching standard blue light. They have high phosphorescence quantum yields in solution. The phosphorescent OLEDs employing these complexes as doped emitters display impressive performance. In particular, the PhOLED based on Ir3 achieves an outstanding maximum external quantum efficiency of 21.23% with Commission Internationale de l'Eclairage (CIE) coordinates of (0.15, 0.26), which is about 27% higher than that of the control device using FIrpic as a dopant (16.63%). [ABSTRACT FROM AUTHOR]

Multiresonance thermally activated delayed fluorescence (MR-TADF) materials have attracted wide attention due to their large radiation rate constant (k r) and high color purity. Attaching additional electron donor or acceptor was established as an effective strategy to optimize the optoelectronic parameters of MR-TADF emitters, such as the reverse intersystem crossing rate constant (k RISC). However, these is no report that both the MR and twisted intramolecular charge transfer (TICT) excited states can be detected simultaneously from a single molecule yet. Herein, a group of MR-TADF emitters BNCz-SAF, BNCz-DMAC and BNCz-PXZ are designed and synthesized through introducing different donor, spiroacridine (SAF), acridine (DMAC) and phenoxazine (PXZ), at the para-site of the boron atom of a famous MR core BNCz. All these three emitters maintained intrinsically excellent properties of MR-TADF molecules with high k r over 108 s−1 and high k RISC over 105 s−1. Interestingly, with gradually increasing the donor strength to PXZ, dual emissions from the MR core and the CT excited state between PXZ and BNCz moieties are detected simultaneously for BNCz-PXZ in either strong polar solvents or doped film in highly polar host, both of which are confirmed as the TADF with the lifetimes of about 4 μs. Independent of the host, the organic light-emitting diodes (OLEDs) of BNCz-SAF and BNCz-DMAC exhibited sky-blue electroluminescence with high external quantum efficiencies (EQE max) of 25.3% and 23.8% and narrow full widths at half maximum (FWHM) of 23–25 nm. In contrast, BNCz-PXZ exhibited a single-band (482 nm) sky-blue EL in mCBP host with EQE max of 20.9%, while exhibited dual-band EL at 484 and 548 nm from MR and CT states in higher polar host DPEPO, realizing a warm white emission with CIE (0.31, 0.48) and EQE max of 16.4%. For the first time both the short-range CT (i.e. MR) and long-range CT (i.e. TICT) excited states are experimently detected and confirmed simultaneously from a donor-modified B,N-based polycyclic hydrocarbon skeleton, which may be a potential strategy to bulid up broad-spectra or white emission. Dual TADF was experimentally confirmed from the donor modified multiresonance TADF framework through tuning the donor strength, from the coexistent short-range charge transfer (CT) state of the MR core and the long-range twisted intramolecular CT state between MR core and the PXZ donor. Warm white OLED was realized with CIE (0.31, 0.48) and EQE of 16.4% when BNCz-PXZ was doped in polar host. [Display omitted] • Three MR-TADF emitters were developed by introducing different donors into the BNCz framework. • Both high k r over 108 s−1 and high k RISC over 105 s−1 were achieved for all these emitters. • Weak donor modified emitters exhibited single-band blue emission, resulting in EQE of 25.3% and 23.8% in OLEDs. • Dual TADF was detected for strong donor based BNCz-PXZ, from SRCT state of the MR core and the long-range TICT state. • When DPEPO was used as host for BNCz-PXZ, single-molecule warm white emission was achieved in its OLED with EQE of 16.4%. [ABSTRACT FROM AUTHOR]

Abstract Two tris-cyclometalated heteroleptic iridium complexes incorporating 2-(2,4-difluorophenyl)pyridine (dfppy) as the main cyclometalating ligand, 2′,6′-Difluoro-2,3′-bipyridine (dfbpy) or 3-(1-benzyl-1 H -1,2,3-triazol-4-yl)pyridine (pt) as the second cyclometalating ligand, namely Ir(dfppy) 2 (pt) (M 1) and Ir(dfppy) 2 (dfbpy) (M 2), were developed for application as blue phosphors in organic light-emitting diodes (OLEDs). The spectroscopic behavior of the complex phosphors was correlated with the ligand properties. With incorporation of the high-triplet-energy pt as the second cyclometalating ligand in Ir(dfppy) 2 (pt), the phosphorescence spectrum was slightly hypsochromatically shifted and narrowed with reduced intensity in long-wavelength vibration band, resulting in improved blue color purity in comparison with the traditional sky-blue iridium complex FIrpic. In simple-structure phosphorescence OLEDs, Ir(dfppy) 2 (pt) exhibited a current efficiency of 19.1 cd A−1 (EQE of 10.7%), while Ir(dfppy) 2 (dfbpy) exhibited an efficiency of 24.2 cd A−1 (EQE of 11.2%). Graphical abstract Incorporation of high-triplet-energy ancillary cyclometalating ligand brings about hypsochromic shift, narrowed spectrum, and reduced intensity at long-wavelength vibronic band, resulting in improved color purity for sky-blue iridium complex phosphor. Image 1 Highlights • Two tris-cyclometalated heteroleptic iridium complexes were designed and synthesized as sky-blue phosphors. • Iridium complex with high-triplet-energy ligand exhibited better color purity in both photoluminescence and electroluminescence. • Organic light-emitting diodes were fabricated using these iridium phosphors to realize improved color purity than the famous FIrpic. [ABSTRACT FROM AUTHOR]

A series of thermally activated delayed fluorescence (TADF) materials, namely o -Ac2BBP, o -Px2BBP, D-BP-DMAC and D-BP-PXZ, were designed with double acridine (DMAC) or phenoxazine (PXZ) donors and double carbonyl acceptors. Phenylene and biphenylene were selected as the central bridges for these emitters, and each benzene ring on the central bridge was substituted at ortho-sites. The biphenylene bridge based D-BP-DMAC and D-BP-PXZ show 3D dimensional non-planar conformations and multi-fold layout, which result in multiple intramolecular interactions including C–H⋯O hydrogen bonds and C–H···π interactions and finally strongly stabilized and rigidified the whole molecular structures by locking the molecular geometry. As a result, the nonradiative transition rates (k nr) were effectively suppressed by 5 times in comparison with the corresponding phenylene bridged analogues, and the photoluminescence quantum yields were increased to over 95%. The green and yellow OLEDs with D-BP-DMAC and D-BP-PXZ as doped emitters exhibited the maximum external quantum efficiencies (EQE) of 24.3% and 17.3%, which are almost double of the corresponding values (13.1% and 9.3%) of the phenylene bridged analogues o -Ac2BBP and o -Px2BBP. These results indicate that to increase molecular rigidity by multi-fold-layout is an effective design strategy to enhance the performance of TADF materials and OLEDs. By incorporating a biphenylene as central linking bridge in thermally activated delayed fluorescence emitters, a multi-fold layout is generated, which enables multiple intramolecular interactions, strongly increases molecular rigidity, and thus suppresses non-radiative decays and increases PLQY to 95%. The OLEDs exhibit high EQEs of 24.3%, being twice of those for the less-folded reference analogues. [Display omitted] • A group of TADF emitters are designed with phenylene or biphenylene as central linking bridge. • The biphenylene bridge endows D-BP-DMAC and D-BP-PXZ with 3D non-planar conformations and unique multi-fold layout. • The multi-fold layout enables multiple interactions, increases molecular rigidity, and suppresses non-radiative decays. • The k nr of D-BP-DMAC and D-BP-PXZ are suppressed by 5 times, and the PLQYs are increased to over 95%. • OLEDs of D-BP-DMAC and D-BP-PXZ exhibit maximum EQEs of 24.3% and 17.3%, being twice of the phenylene bridged analogues. [ABSTRACT FROM AUTHOR]

A group of heteroleptic cyclometalated iridium complexes Ir1–Ir4 were designed with 2-phenylpyridine (ppy) derivatives as cyclometalating ligands and 2-(3-(trifluoromethyl)-1 H -pyrazol-5-yl)pyridine (fppz) or 2-(5-(4-(trifluoromethyl)phenyl)-2 H -1,2,4-triazol-3-yl)pyridine (Htaz) as ancillary ligands. The incorporation of electro-donating group into ppy ligands to elevate ligands-centered 3π-π* energy level and utilization of fppz or Htaz ancillary ligands combined to tune the intrinsic electronic properties. These complexes showed greenish-blue or green phosphorescence and are characterized by high photoluminescence quantum yields of up to 70% and short lifetimes below 1 μs. The organic light-emitting diodes (OLEDs) with Ir1–Ir4 as doped emitters all exhibited high efficiencies with low efficiency roll-off. Particularly, the Ir3 device exhibited distinguished performances with the maximum current efficiency of 86.9 cd A−1 and an external quantum efficiency (EQE) of 33.5%. Even at high brightness of 1000 cd m−2, the EQE still remained at 24.6%. Evidently the EQE of 33.5% of Ir3 device is one of the highest efficiencies ever reported for greenish-blue phosphorescence OLEDs. By selecting dimethylamino or ethoxyl decorated 2-phenylpyridine as cyclometalating ligands and fppz and Htaz as ancillary ligands, a group of heteroleptic iridium complexes were developed with characters of high photoluminescence quantum yields up to 70% and short lifetimes below 1 μs. All complexes exhibited good efficiencies over 20% in OLEDs, and the Ir3 device gave the highest EQE max of 33.5% and low efficiency roll-off, being one of the highest EQEs for greenish-blue phosphorescence OLEDs so far. [Display omitted] • Highly efficient iridium complexes are developed with decorated phenylpyridine as cyclometalating ligands. • Rich-nitrogen heterocyclic ligands were utilized as the ancillary ligands. • These complexes are characterized by high PLQY, short excited state lifetimes below 1 μs, and high EQEs over 20% in OLEDs. • The Ir3 based OLED gave a maximum EQE of 33.5%, being among the highest efficiencies for greenish-blue OLEDs so far. • Fluorine-free feature of the cyclometalating ligands was attributed to be one reason for extra efficiency stability. [ABSTRACT FROM AUTHOR]

Carbazole is a weak electron donor suitable to construct blue thermally activated delayed fluorescence (TADF) emitters, but the less repulsion effect of its five-member-ring structure can't guarantee the frontier molecular orbital separation and TADF feature. A group of carbazole-π-triazine based blue fluorescence emitters is designed by introducing the steric hindrance groups with different electronic properties at the donor or π-bridge. When electron-withdrawing pyridyl with moderate steric hindrance is introduced to the 1-site of 3,6-Di-tert-butyl-9H-carbazole, PyBuCz-TRZ and PyBuCz-MeTRZ gain the blue-shifted TADF. The observed charge transfer triplet excited state within the donor (3CT D) between carbazole and pyridyl units has different spatial orbital angular momentum and allowed spin-orbit coupling (SOC) with the charge transfer singlet excited state (1CT) of the whole molecule from carbazole donor to triazine acceptor, thus, acting as the media state to facilitate efficient multi-channel reverse intersystem crossing (RISC) process. This is the first time to introduce an electron-withdrawing group into the 1-position of carbazole donors to construct TADF molecules, not only achieving the blue-shifted TADF at 455 nm but also improving the external quantum efficiency to 15.3% in organic light-emitting diodes. This donor strategy should be valid to design more blue TADF materials. A donor design strategy for blue TADF is developed by incorporating electron-withdrawing and bulky pyridyl at 1-site of carbazole, not only leading to blue-shift of TADF but also facilitating multi-channel reverse intersystem crossing via the participation of the charge transfer triplet state of the donor (3CT D). An EQE of 15.3% is achieved in pure blue OLED of these TADF emitters. [Display omitted] • Electron-withdrawing pyridyl was introduced at 1-site of carbazole to construct thermally activated delayed fluorescence (TADF) emitters. • Blue shifted emission and improved EQE were simultaneously achieved in the pure blue OLEDs. • A new triplet state 3CT D was detected within the donor and facilitated multi-channel RISC process. • Too strong electron-withdrawing substituent on carbazole like cyano was proved to make TADF feature disappear. • This is the first report to incorporate electron-withdrawing substituent at 1-site of carbazole for blue TADF materials. [ABSTRACT FROM AUTHOR]

The non-doped organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) materials are attracting increasing attentions due to the excellent performance and simple fabrication. We report an effective design strategy of TADF emitters to improve the non-doped performance by adjusting the valence state of the S atom in TADF molecules and utilizing the steric hindrance effect. Two novel TADF materials PT-BZ-DMAC and PS-BZ-DMAC were designed and synthesized with benzophenone acceptor and acridine donor. In particular, the thioether or sulfone group was attached to benzophenone. Remarkably, the bluish-green TADF-OLED with non-doped PT-BZ-DMAC turned on at 2.5 V and realized a maximum external quantum efficiency (EQE) of 17.34%, which was comparable with its doped OLED (17.71%) but showed much slower roll-off. At 100 and 1000 cd m−2, the non-doped PT-BZ-DMAC device still maintained acceptable efficiencies at 14.65% and 12.59%. In contrast, sulfone-modified PS-BZ-DMAC exhibited good efficiency of 20.55% only in doped OLED. The single crystal analysis and DFT calculation revealed that the phenyl thioether unit in PT-BZ-DMAC hardly contributes to the LUMO or the electronic transitions, instead determines the highly twisted geometry and acts as the barrier group, finally improving the performance of PT-BZ-DMAC in neat film device. Two TADF emitters are developed by attaching thioether or sulfone groups to the benzophenone acceptor. Unlike the strong electron withdrawing sulfone group that contributes to the electronic transition and TADF, the phenyl thioether blocked the conjugation of molecular backbone. The steric hindrance effect of phenyl thioether moiety along with the intermolecular hydrogen bondings can effectively prevents exciton quenching, thus further raising the EQE of non-doped TADF-OLED to 17.34% with low efficiency roll-off. [Display omitted] • Thioether and sulfone were incorporated as substituents to design TADF molecules PT-BZ-DMAC and PS-BZ-DMAC. • Thioether was found to strongly suppress intermolecular interactions and prevent exciton quenching via steric hindrance effect. • Non-doped OLED of thioether based PT-BZ-DMAC exhibited comparably high efficiency (17.34%) to its doped device (17.71%), but with much slower roll-off. • Sulfone based PS-BZ-DMAC exhibited high efficiency of 20.55% only in doped OLED, while non-doped device did not work. [ABSTRACT FROM AUTHOR]

The expression of cutaneous fatty acid-binding protein (C-FABP) in prostate tissues was examined by immunohistochemistry. Among the 76 cases, all seven (100%) normal tissues were unstained. Of the 35 benign prostatic hyperplasia (BPH), 25 (71.4%) specimens were unstained and 10 (28.6%) were stained positively. For the 34 prostatic carcinomas, the C-FABP expression was remarkably increased: 25 (73.5%) samples stained positively, and only nine (26.5%) were unstained. Transfection of a vector expressing an antisense C-FABP transcript into the PC-3M prostatic cancer cells yielded two transfectant lines: PC-3M-CFABP-1 and PC-3M-CFABP-3, producing, respectively, a 3.8- and a 6.9-fold reduction in C-FABP levels. Comparing with the control transfectants, the in vitro invasiveness of both PC-3M-CFABP-1 and PC-3M-CFABP-3 was significantly reduced. When tested in nude mouse, the average size of tumours produced by PC-3M-CFABP-1 and by PC-3M-CFABP-3 was reduced by 2.9- and 4.2-fold respectively, in comparison with that of tumours produced by the control transfectants. Analysis showed that the decreased vascular endothelial growth factor (VEGF) and microvessel densities in the tumours were associated with the reduced C-FABP. These data show that C-FABP is increased in prostatic carcinoma cells and suppression of its expression can significantly inhibit the tumorigenicity, probably by reducing the expression of VEGF.Oncogene (2003) 22, 2739-2749. doi:10.1038/sj.onc.1206341 [ABSTRACT FROM AUTHOR]

A group of D-π-A type emitters were designed and synthesized by using triazine (Trz) as electron acceptor (A), carbazole (Cz), 10-dimethylacridine (DMAC) or 10H-phenoxazine (PXZ) as electron donors (D), and phenylene as π-bridge between D and A. The electron withdrawing ability of A unit and thus the intramolecular charge transfer (ICT) strength play the most essential role to determine the luminescence mechanism and the emission color. By gradually enhancing the ICT extent through selecting strong electron donating D and/or replacing methyl with electron withdrawing cyano group on the π-bridge, the luminescence is tuned from normal fluorescence to thermally activated delayed fluorescence (TADF) and the emission color is successfully tuned from pure-blue (434 nm) to orange-red (616 nm). Organic light-emitting diodes (OLEDs) based on these emitters exhibit bright electroluminescence covering the major visible-light range. An external quantum efficiency (η ext) of 4.8% with excellent color coordinate of (0.16, 0.08) is obtained for pure blue fluorescent OLED of TrzCz-Me. TrzCz-CN, TrzDMAC-Me, and TrzPXZ-Me exhibited higher η ext values of 14.40% (19.73 cd A−1), 19.01% (41.12 cd A−1), 16.50% (51.17 cd A−1) in their blue, sky-blue, and green TADF OLEDs. This study provides a practical strategy related to ICT strength to facilitate generation of TADF emitters and tune the emission colors over the visible light range. A group of D-π-A emitters were developed by combining triazine acceptor with different donors and incorporating either cyano or methyl on phenylene bridge. The triazine/carbaozle based blue emitter was tuned from normal fluorescence to thermally activated delayed fluorescence (TADF) by incorporating cyano group, and the emission color was tuned from deep blue to orange-red. It was proved the intramolecular charge-transfer strength played the most important role to facilitate both the emission mechanism evolution and color tuning. The TADF emitters exhibited high quantum efficiencies of 14–19% in organic light-emitting diodes. Image 1 • A series of D-p-A type emitters were developed with various donors. • Cyano or methyl was grafted on phenylene bridge to tune the acceptor strength and molecular steric conformation. • The triazine/carbazole compound was tuned from normal fluorescence to TADF by incorporating cyano group. • The emission color was continuously tuned from deep blue to orange-red by tuning the intramolecular charge-transfer strength. [ABSTRACT FROM AUTHOR]