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Neurological abnormalities identified via neuroimaging are common in patients with Alzheimer’s disease. However, it is not yet possible to easily detect these abnormalities using head computed tomography in the early stages of the disease. In this review, we evaluated the ways in which modern imaging techniques such as positron emission computed tomography, single photon emission tomography, magnetic resonance spectrum imaging, structural magnetic resonance imaging, magnetic resonance diffusion tensor imaging, magnetic resonance perfusion weighted imaging, magnetic resonance sensitive weighted imaging, and functional magnetic resonance imaging have revealed specific changes not only in brain structure, but also in brain function in Alzheimer’s disease patients. The reviewed literature indicated that decreased fluorodeoxyglucose metabolism in the temporal and parietal lobes of Alzheimer’s disease patients is frequently observed via positron emission computed tomography. Furthermore, patients with Alzheimer’s disease often show a decreased N-acetylaspartic acid/creatine ratio and an increased myoinositol/creatine ratio revealed via magnetic resonance imaging. Atrophy of the entorhinal cortex, hippocampus, and posterior cingulate gyrus can be detected early using structural magnetic resonance imaging. Magnetic resonance sensitive weighted imaging can show small bleeds and abnormal iron metabolism. Task-related functional magnetic resonance imaging can display brain function activity through cerebral blood oxygenation. Resting functional magnetic resonance imaging can display the functional connection between brain neural networks. These are helpful for the differential diagnosis and experimental study of Alzheimer’s disease, and are valuable for exploring the pathogenesis of Alzheimer’s disease.

Development of simple chiral materials with tunable circularly polarized photoluminescence (CPPL) and circularly polarized electroluminescence (CPEL) for efficient circularly polarized organic light-emitting diodes (CP-OLEDs) is the key toward future 3D displays. In this study, four pairs of chiral 1,2-diaminocyclohexane-based fluorescence enantiomers were efficiently prepared with high yields (up to 92%) and enantiomeric excesses (ee >99%). By the introduction of N-methyl, carbazole, and diphenylamine-donating groups, these materials showed multicolor CPPL and CPEL from blue (420 nm) to red (610 nm) with good thermal and conformational stability. The multilayer CP-OLEDs based on these enantiomers show high external quantum efficiency of up to 5.5% with low-efficiency roll-off and microimage circularly polarized electroluminescence with a dissymmetry factor (gEL) of up to -1.4 × 10-3/+1.3 × 10-3. These results push forward the development of future multicolor circularly polarized electroluminescent materials.

To obtain dopants owing excellent electron mobility, four novel iridium (III) complexes (Ir(tfmppm)2(acac), Ir(tfmppm)2(tpip), Ir(f-4-tfmppm)2(tpip) and Ir(f-3-tfmppm)2(tpip)) with green emission using 2-(2,6-bis(trifluoromethyl)pyridin-4-yl)pyrimidine (tfmppm), 2-(2,6-bis(trifluoromethyl)pyridin-4-yl)-5-fluoropyrimidine (f-4-tfmppm) and 2-(2,6-bis(trifluoromethyl)pyridin-3-yl)-5-fluoropyrimidine (f-3-tfmppm) as main ligands, acetylacetonate (acac) and tetraphenylimidodiphosphinate (tpip) as ancillary ligands, were investigated, respectively. Due to the variation of the structures among the complexes, the photoluminescence quantum yield (up to 94%) and electron mobility can be regulated gradually, which would broaden the recombination zone, balance the distribution of holes and electrons, leading to excellent electroluminescence (EL) performances. Among four emitters, the organic light-emitting diodes (OLEDs) using Ir(f-3-tfmppm)2(tpip) display the best EL performances with a maximum current efficiency of 92.83 cd A−1 and a maximum external quantum efficiency of 29.5%, suggesting these materials have potential application in OLEDs.

Seven cyclometalated iridium(III) complexes Ir1–Ir7 based on phenylpyrazole derivatives as main ligands and tetraphenylimidodiphosphinate (tpip) as the ancillary ligand were synthesized and fully characterized. The proligands of 1-[4-(trifluoromethyl)phenyl]-1H-pyrazole (cf3ppz, 2a), substituted phenyl-2H-indazole {2-phenyl-2H-indazole (h-1-pidz, 2b), 2-(4-fluorophenyl)-2H-indazole (f-1-pidz, 2c), and 2-[4-(trifluoromethyl)phenyl]-2H-indazole (cf3-1-pidz, 2d)}, and substituted phenyl-1H-indazole {1-phenyl-1H-indazole (h-7-pidz, 2e), 1-(4-fluorophenyl)-1H-indazole (f-7-pidz, 2f), and 1-[4-(trifluoromethyl)phenyl]-1H-indazole (cf3-7-pidz, 2g)} were prepared with good yields. The emission maxima of all Ir(III) complexes can be tuned from 453 to 576 nm with different photoluminescence quantum yields (10.4–70.9%) by varying the type of substituent on the different main ligand frameworks. The organic light-emitting diodes using Ir(III) complexes as the emitters with blue, bluish-green, and yellow colors exhibit...

Multi-resonance induced by boron and nitrogen atoms in opposite resonance positions endows a thermally activated delayed fluorescence (MR-TADF) emitter with a strikingly small full width at half maximum of only 26 nm and excellent photoluminescence quantum yield of up to 97.48 %. The introduction of a carbazole unit in the para position of the B-substituted phenyl-ring can significantly boost up the resonance effect without compromising the color fidelity, subsequently enhancing the performances of the corresponding pure blue TADF-OLED, with an outstanding external quantum efficiency (EQE) up to 32.1 % and low efficiency roll-off, making it one of the best TADF-OLEDs in the blue region to date. Furthermore, utilizing this material as host for a yellow phosphorescent emitter, the device also shows a significantly reduced turn-on voltage of 3.2 V and an EQEmax of 22.2 %.

We thoroughly investigated four iridium(III) complexes (Ir(tfmphpm)2(acac), Ir(f-tfmphpm)2(acac), Ir(tfmphpm)2(tpip), and Ir(f-tfmphpm)2(tpip)) using 2-(3,5-bis(trifluoromethyl)phenyl)pyrimidine (tfmphpm) and 2-(3,5-bis(trifluoromethyl)phenyl)-5-fluoropyrimidine (f-tfmphpm) as the main ligands and 2,4-pentanedionate (acac) and tetraphenylimidodiphosphinate (tpip) as the ancillary ligands. All complexes showed bluish green emissions peaking at 473–480 nm with very high photoluminescence quantum efficiencies in the range of 85–95%. The organic light-emitting diodes (OLEDs) using these emitters exhibited good performances. Especially, the device using Ir(tfmphpm)2(tpip) with the structure of ITO (indium-tin-oxide)/MoO3 (molybdenum oxide, 3 nm)/TAPC (di-[4-(N,N-ditolyl-amino)phenyl]cyclohexane, 50 nm)/mCP (1,3-bis(9H-carbazol-9-yl) benzene, 5 nm)/Ir(tfmphpm)2(tpip) (6 wt%) : PPO21 (3-(diphenylphosphoryl)-9-(4-(diphenylphosphoryl)phenyl)-9H-carbazole, 10 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl) benzene, 50 nm)/LiF (1 nm)/Al (100 nm) displayed the best performances with a maximum luminance of 28 194 cd m−2, a maximum current efficiency of 74.70 cd A−1, and a maximum external quantum efficiency up to 35.0%, and the efficiency roll-off ratio was small. The current efficiency of the device remained as high as 66.46 cd A−1 at the brightness of 1000 cd m−2, suggesting that they are potential materials for applications in OLEDs.

Thermally activated delayed fluorescence (TADF) materials have been thoroughly developed and have proven to be the most promising means to generate an efficient deep blue emission. In this work, we prepared a series of deep blue TADF emitters based on trifluoromethyl featuring phenyl and N-heterocyclic rings as electron-withdrawing units and carbazole as electron-donating moieties. Efficient organic light-emitting diodes (OLEDs) utilizing these emitters have a deep blue emission and a high external quantum efficiency of up to 20.4%. These blue emitters are among the bluest in the TADF based OLED category. They can also be implemented in OLED as hosts for green phosphorescent iridium(III) complexes, exhibiting high brightness and a decent external quantum yield.

Two novel iridium(III) complexes (Ir1 and Ir2), synthesized using 2′-(trifluoromethyl)-2,5′-bipyrimidine and 5-fluoro-2′-(trifluoromethyl)-2,5′-bipyrimidine as the main ligands, and tetraphenylimidodiphosphinate (tpip) as an ancillary ligand, were investigated. The introduction of a nitrogen heterocycle and CF3 substituent improves the electron mobility of the Ir(III) complexes, which is beneficial for device performance. Both of the complexes emit bluish green photoluminescence with very high quantum efficiency yields (Ir1: λmax: 485/516 nm, ηPL: 89%; Ir2: λmax: 482/513 nm, ηPL: 95%) and good electron mobility. Organic light-emitting diodes (OLEDs) constructed with an ITO (indium tin oxide)/MoO3 (molybdenum oxide, 3 nm)/TAPC (di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane, 50 nm)/mCP (1,3-bis(9H-carbazol-9-yl)benzene, 5 nm)/Ir complex (6 wt%):PPO21 (3-(diphenylphosphoryl)-9-(4-(diphenyl-phosphoryl)phenyl)-9H-carbazole, 10 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 50 nm)/LiF (1 nm)/Al (100 nm) structure showed good device performances. Device G1 based on Ir1 showed a ηc,max value of 62.99 cd A−1 with an EQEmax value of 23.5%. Owing to the slightly higher PL efficiency and lower LUMO levels of Ir2, which are beneficial for electron injection, the device based on Ir2 displayed a slightly better performance with a ηc,max value of 71.18 cd A−1 and an EQEmax value of 27.7%. Even at a practical brightness of 1000 cd m2, values of 57.39 cd A−1 and 22.3% could still be reached.

Herein, two iridium(III) complexes with yellow emission using 1-(3,5-bis(trifluoromethyl)phenyl)isoquinoline (tfmphiq) and 4-(3,5-bis(trifluoromethyl)phenyl)quinazoline (tfmphqz) as the main ligands and tetraphenylimidodiphosphinate (tpip) as the ancillary ligand were applied in organic light-emitting diodes (OLEDs). The quinazoline moiety greatly influenced the nature of the complexes, and both the quantum yield and the electron mobility of Ir(tfmphqz)2(tpip) were much higher than that of Ir(tfmphiq)2(tpip) (Ir(tfmphiq)2(tpip) (λem: 581 nm and Φ: 0.61) and Ir(tfmphqz)2(tpip) (λem: 566 nm and Φ: 0.97)). Moreover, the device based on Ir(tfmphqz)2(tpip) displayed far better performance than that based on the Ir(tfmphiq)2(tpip) emitter. The device with a structure of ITO/MoO3 (3 nm)/TAPC (50 nm)/Ir(tfmphqz)2(tpip) (6 wt%): 26DCzPPy (10 nm)/TmPyPB (50 nm)/LiF (1 nm)/Al (100 nm) displayed a maximum luminance of 96 377 cd m−2 and a maximum current efficiency and a maximum power efficiency of 106.66 cd A−1 and 64.72 lm W−1, respectively, with low efficiency roll-off. The current efficiency still remains as high as 89.91 cd A−1 at the brightness of 1000 cd m−2 and 79.73 cd A−1 at the brightness of 5000 cd m−2. These results suggest that the Ir(III) complexes with quinazoline units are potential yellow phosphorescent materials for OLEDs.

Four cyclometalated platinum complexes with trifluoromethyl-substituted 2-phenylpyridine at different positions on its phenyl group as the main ligands and tetraphenylimidodiphosphinate as the ancillary ligand, Pt1 - Pt4 ( Pt1 is a trifluoromethyl-free complex), were prepared, and their X-ray crystallography, photoluminescence, thermal stability, electrochemical analyses, theoretical calculation and EL performances were investigated. The positions of trifluoromethyl groups on the phenyl ring affected the emission spectra of platinum complexes greatly, and their corresponding emission peaks at 504/534, 512/545, 495/526 and 510/542 nm were observed at room temperature, respectively. Constructed with complexes Pt1 - Pt4 as the emitters, respectively, the organic light-emitting diodes (OLEDs) with double light emitting layers structure of ITO/TAPC (1,1-bis[4-(di- p -tolylamino)phenyl]cyclohexane, 40 nm /Pt complexes (5 wt%): TCTA (4,4′,4″-tri(9-carbazoyl)-triphenylamine, 10 nm /Pt complexes (5 wt%): 2,6DCzPPy (2,6-bis(3-(carbazol-9-yl)phenyl)pyridine, 10 nm/TmPyPB (1,3,5-tri( m -pyrid-3-yl-phenyl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) showed good performances. Particularly, device G2 based on 2-trifluoromethyl-substituted complex Pt2 obtained a maximum luminance of 39196 cd m -2 , a maximum current efficiency of 40.1 cd A −1 and a maximum power efficiency of 31.0 lm W −1 , respectively, with low efficiency roll-off. The results suggested that these complexes Pt1 - Pt4 would have potential applications in efficient OLEDs.

Two series of chiral cyclometalated iridium(III) complexes based on sulfur atom containing enantiopure BINOL derivatives were rapidly synthesized, which are endowed with varied chiroptical properties. Moreover, the circularly polarized OLEDs using enantiomers show a maximum luminance of above 40 000 cd m−2 and an external quantum efficiency of 23.6% with low efficiency roll-off as well as obvious CPEL properties.

Two iridium complexes with 1-(2,6-bis(trifluoromethyl)pyridin-4-yl)isoquinoline (tfmpiq) and 4-(2,6-bis(trifluoromethyl)pyridin-4-yl)quinazoline (tfmpqz) main ligands and a tetraphenylimidodiphosphinate (tpip) ancillary ligand were applied in organic light-emitting diodes (OLEDs). The introduction of quinazoline greatly influences the nature of the complex. The quantum yield and the electron mobility of Ir(tfmpqz)2(tpip) are much higher than those of Ir(tfmpiq)2(tpip) (Ir(tfmpiq)2(tpip): Φ: 0.47, μe: 8.93–9.47 × 10−6 cm2 V−1 s−1 under an electric field from 1040 (V cm−1)1/2 to 1300 (V cm−1)1/2; Ir(tfmpqz)2(tpip): Φ: 0.98, μe: 6.44–7.20 × 10−6 cm2 V−1 s−1 under an electric field from 1040 (V cm−1)1/2 to 1300 (V cm−1)1/2). In addition, the Ir(tfmpqz)2(tpip)-based device also displayed better performance than that using Ir(tfmpiq)2(tpip). Furthermore, with a europium complex, Eu(DBM)3phen (DBM = dibenzoylmethide; phen = 1,10-phenanthroline) as a sensitizer, the device based on Ir(tfmpqz)2(tpip) with a double emissive layer structure of ITO/MoO3 (3 nm)/TAPC (50 nm)/Ir(tfmpqz)2(tpip) (5 wt%):TcTa (10 nm)/Eu(DBM)3phen (0.2 wt%):Ir(tfmpqz)2(tpip) (5 wt%):26DCzPPy (10 nm)/TmPyPB (50 nm)/LiF (1 nm)/Al (100 nm) displayed the best performance with a maximum luminance of 129 466 cd m−2, and a maximum current efficiency and a maximum power efficiency of 62.96 cd A−1 and 53.43 lm W−1, respectively, with low efficiency roll-off. The current efficiency still remains as high as 58.84 cd A−1 at a brightness of 1000 cd m−2 and 53.27 cd A−1 at a brightness of 5000 cd m−2. These results suggest that Ir(III) complexes with quinazoline units are potential orange-red phosphorescent materials for OLEDs.

Two novel iridium(iii) complexes, Ir(tfmpiq)2(acac) (tfmpiq = 1-(2,6-bis(trifluoromethyl)pyridin-4-yl)isoquinoline, acac = acetylacetone) and Ir(tfmpqz)2(acac) (tfmpqz = 4-(2,6-bis(trifluoromethyl)pyridin-4-yl)quinazoline), were synthesized and thoroughly investigated. Both complexes emit orange-red photoluminescence with high quantum yields (Ir(tfmpiq)2(acac): λmax: 587 nm, ηPL: 42%; Ir(tfmpqz)2(acac): λmax: 588 nm, ηPL: 91%). Furthermore, the complex containing quinazoline shows higher electron mobility than that with isoquinoline. The organic light-emitting diodes (OLEDs) with single- or double-emitting layers (EML) were fabricated using two new emitters. The double-EML device using Ir(tfmpqz)2(acac) with the structure of ITO (indium-tin-oxide)/MoO3 (molybdenum oxide, 3 nm)/TAPC (di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane, 50 nm)/Ir(tfmpqz)2(acac) (1 wt%):TcTa (4,4',4''-tris(carbazole-9-yl)triphenylamine, 10 nm)/Ir(tfmpqz)2(acac) (1 wt%):2,6DCzPPy (2,6-bis(3-(carbazol-9-yl)phenyl)pyridine, 10 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 50 nm)/LiF (1 nm)/Al (100 nm) displays good electroluminescence performances with a maximum luminance of 96 609 cd m-2, a maximum current efficiency of 59.09 cd A-1, a maximum external quantum efficiency of 20.2%, a maximum power efficiency of 53.61 lm W-1, and the efficiency roll-off ratio is mild.

Two new platinum(II) cyclometalated complexes with 2-phenylpyridine (Pt1) and 2-(4-trifluoromethyl)phenylpyridine (Pt2) as the main ligands and 2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenol (pop) as the electron-transporting ancillary ligand were developed. The photoluminescence quantum efficiency yields of both green Pt1 and Pt2 phosphors (λmax 490 and 496 nm) are 20.0% and 31.0% in CH2Cl2 solutions, respectively. Efficient OLEDs (organic light emitting diodes) of ITO/TAPC (bis[4-(N,N-ditolylamino)phenyl]cyclohexane, 40 nm)/Pt1 or Pt2 (5 wt %):TCTA (4,4′,4″-tri(carbazoyl-9-yl)triphenylamine, 10 nm)/Pt1 or Pt2 (5 wt %):2,6DCzPPy (2,6-bis(3-(carbazol-9-yl)phenyl)pyridine, 10 nm)/TmPyPB (1,3,5-tris(m-pyrid-3-ylphenyl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) were fabricated. Particularly, device G1 based on complex Pt1 with 5 wt % doped concentration showed superior performance with a maximum current efficiency (ηmax,c) of 55.6 cd A–1, a maximum power efficiency (ηmax,p) of 52.2 lm W–1, and a maximum external quantu...

Two new iridium complexes, (dfppy) 2 Ir( l -alanine) (dfppy = 2-(2,4-difluorophenyl)pyridine) and (piq) 2 Ir( l -alanine) (piq = 1-phenylisoquinoline) were prepared with l -alanine as ancillary ligand. The two complexes show bright greenish-blue and red emission respectively. Theoretic study demonstrated that the emission nature of these complexes is mainly determined by the main ligand. And their improved aqueous solubility and the retained quantum yield favor their application in cell imaging. Intracellular imaging suggested that these two complexes have fine cell membrane permeability and is mainly distributed in cytoplasm. This study displayed a new strategy to design aqueous soluble phosphorescent cyclometallated Ir(III) complex via introducing amino acid as ancillary ligand.

Circularly polarized organic light-emitting diodes (CP-OLEDs) are particularly favorable for the direct generation of CP light, and they demonstrate a promising application in 3D display. However, up to now, such CP devices have suffered from low brightness, insufficient efficiency, and serious efficiency roll-off. In this study, a pair of octahydro-binaphthol (OBN)-based chiral emitting enantiomers, (R/S)-OBN-Cz, are developed by ingeniously merging a chiral source and a luminophore skeleton. These chirality-acceptor-donor (C-A-D)-type and rod-like compounds concurrently generate thermally activated delayed fluorescence with a small ΔEST of 0.037 eV, as well as a high photoluminescence quantum yield of 92% and intense circularly polarized photoluminescence with dissymmetry factors (|gPL |) of ≈2.0 × 10-3 in thin films. The CP-OLEDs based on (R/S)-OBN-Cz enantiomers not only display obvious circularly polarized electroluminescence signals with a |gEL | of ≈2.0 × 10-3 , but also exhibit superior efficiencies with maximum external quantum efficiency (EQEmax ) up to 32.6% and extremely low efficiency roll-off with an EQE of 30.6% at 5000 cd m-2 , which are the best performances among the reported CP devices to date.

Aiming to balance the injection and transport of electrons and holes, nitrogen heterocycle and 1,3,4-oxadiazole derivatives were introduced in iridium(III) complexes to obtain organic light-emitting diodes (OLEDs) with high performances. Thus, two novel Ir(III) complexes (Ir(tfmphpm)2(pop) and Ir(tfmppm)2(pop)) with green emissions using 2-(3,5-bis(trifluoromethyl)phenyl)pyrimidine (tfmphpm) and 2-(2,6-bis(trifluoromethyl)pyridin-4-yl)pyrimidine (tfmppm) as cyclometalating ligands, and 2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenol (pop) as an ancillary ligand were synthesized. Both emitters show high photoluminescence efficiencies up to 94% and good electron mobility. The devices using two emitters with the structure of ITO (indium-tin-oxide)/MoO3 (molybdenum oxide, 5 nm)/TAPC (di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane, 30 nm)/mCP (1,3-bis(9H-carbazol-9-yl)benzene, 5 nm)/Ir(III) complexes (6 wt%) : PPO21 (3-(diphenylphosphoryl)-9-(4-(diphenylphosphoryl)phenyl)-9H-carbazole, 10 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl) benzene, 40 nm)/LiF (1 nm)/Al (100 nm) display good electroluminescence performances with a maximum luminance of 48 981 cd m−2, a maximum current efficiency of 92.79 cd A−1 and a maximum external quantum efficiency up to 31.8%, respectively, and the efficiency roll-off ratio is low, suggesting that they have potential application in OLEDs.