Two highly efficient red neutral iridium(III) complexes, Ir1 and Ir2, were rationally designed and synthesized by selecting two pyridylimidazole derivatives as the ancillary ligands. Both Ir1 and Ir2 show nearly the same photoluminescence emission with the maximum peak at 595 nm (shoulder band at about 638 nm) and achieve high solution quantum yields of up to 0.47 for Ir1 and 0.57 for Ir2. Employing Ir1 and Ir2 as emitters, the fabricated red organic light-emitting diodes (OLEDs) show outstanding performance with the maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 20.98%, 33.04 cd/A, and 33.08 lm/W for the Ir1-based device and 22.15%, 36.89 cd/A, and 35.85 lm/W for the Ir2-based device, respectively. Furthermore, using Ir2 as red emitter, a trichromatic hybrid white OLED, showing good warm white emission with low correlated color temperature of <2200 K under the voltage of 4–6 V, was fabricated successfully. The white device also realizes excellent device efficiencies with the maximum EQE, CE, and PE reaching 22.74%, 44.77 cd/A, and 46.89 lm/W, respectively. Such high electroluminescence performance for red and white OLEDs indicates that Ir1 and Ir2 as efficient red phosphors have great potential for future OLED displays and lightings applications.Keywords: external quantum efficiency; imidazole derivatives; iridium(III) complexes; organic light-emitting diodes; phosphorescence;

Real-time monitoring of the contents of molecular oxygen (O2) in tumor cells is of great significance in early diagnosis of cancer. At the same time, the photodynamic therapy (PDT) could be realized by highly toxic singlet oxygen (1O2) generated in situ during the O2 sensing, making it one of the most promising methods for cancer therapy. Herein, the iridium(III) complex cored hyperbranched phosphorescent conjugated polymer dots with the negative charges for hypoxia imaging and highly efficient PDT was rationally designed and synthesized. The incomplete energy transfer between the polyfluorene and the iridium(III) complexes realized the ratiometric sensing of O2 for the accurate measurements. Furthermore, the O2-dependent emission lifetimes are also used in photoluminescence lifetime imaging and time-gated luminescence imaging for eliminating the autofluorescence remarkably to enhance the signal-to-noise ratio of imaging. Notably, the polymer dots designed could generate the 1O2 effectively in aqueous solution, and the image-guided PDT of the cancer cells was successfully realized and investigated in detail by confocal laser scanning microscope. To the best of our knowledge, this represents the first example of the iridium(III) complex cored hyperbranched conjugated polymer dots with the negative charges for both hypoxia imaging and PDT of cancer cells simultaneously.Keywords: hyperbranched polymer dots; hypoxia imaging; iridium(III) complexes; phosphorescence; photodynamic therapy;

•Excellent red Ir(III) phosphor with a bulky fluorophenyl moiety have been designed.•Novel phosphor exhibits red emission with broad FWHM and high ΦPL.•High-performance red OLEDs have been successfully fabricated.A novel and highly efficient thiophenquinolone-based red iridium(III) complex bearing a bulky fluorophenyl moiety is designed and synthesized. The complex shows intensive red phosphorescence (596 nm with shoulder at 642 nm), high photoluminescence efficiency (0.62) and broad full width at half maximum (81 nm). The bulky fluorophenyl moiety introduced into the complex could improve the efficiency of electroluminescence with the maximum current efficiency, power efficiency and the external quantum efficiency up to 29.0 cd/A, 30.4 lm/W and 17.6% due to the effective steric hindrance in solid states.High-efficiency red phosphor with the bulky fluorophenyl moiety has been designed and synthesized for high-performance red OLED with the maximum CE, PE and EQE of 29.0 cd/A, 30.4 lm/W and 17.6%.Download high-res image (138KB)Download full-size image

•Excellent thienylquinoline-based red phosphorescent iridium(III) complexes have been designed and prepared.•Novel red phosphors not only effectively broaden FWHMs but also greatly increase ΦPL suitable for solid-state lighting.•High-performance red and white OLEDs have been successfully fabricated.•The designed WOLED exhibits excellent color stability under wide operating voltage range.Highly efficient 2-(thiophen-2-yl)quinoline-based phosphorescent iridium(III) complexes bearing 2-(3-(trifluoromethyl)-1H-1,2,4-triazol-5-yl)pyridine or picolinic acid as ancillary ligands are designed and synthetised. The variation of ancillary ligands is attempted to finely tune the photophysical properties of these complexes, especially the solution phosphorescent quantum yields (ΦPL), full width at half maximum (FWHM), etc. The picolinic acid-based complex displays the slightly red-shifted dual-peak emission compared to triazolpyridine-based one. The complexes show bright emission with broad FWHM up to 83 nm, and the emissions are in red region with the very high absolute ΦPL up to 0.76 in solution. Moreover, high-performance red and three-color-based white organic light-emitting diodes (OLEDs) with excellent color stability have been fabricated. The maximum external quantum efficiencies of red and white OLEDs can reach 16.2% and 15.1%, respectively. The maximum current efficiency and power efficiency of white OLED are as high as 35.5 cd A−1 and 34.0 lm W−1, respectively. Especially, the designed white OLED exhibits excellent spectral stability under wide operating voltage range, and the 1931 Commission Internationale de L'Eclairage of white OLED only changes from (0.43, 0.42) to (0.44, 0.44), the color rendering index is in a narrow range of 75–77.Excellent 2-(thiophen-2-yl)quinoline-based red phosphorescent iridium(III) complexes with triazolpyridine or picolinic acid as ancillary ligands have been designed and prepared. Compared to pentane-2,4-dione analogues, these red phosphors not only effectively broaden full width at half maximum (up to 83 nm) but also greatly increase phosphorescent quantum efficiency (up to 0.76) simultaneously, which have been used for fabricating highly efficient red and white OLEDs.Download high-res image (172KB)Download full-size image

•The white-light hyperbranched copolymers with triple emitting units were designed and synthesized.•These copolymers have shown high fluorescence quantum efficiency.•A high color rendering index (CRI) of 87 and a Commission International de l'Eclairage coordinate of (0.31, 0.33) were achieved.A series of hyperbranched copolymer system (P1, P2, P3 and P4) with tris[1-phenylisoquinolinato-C2,N]iridium(III) (Ir(piq)3) as the red emission core, fluorenone (FO) as the green emission unit and poly(9,9-dioctylfluorene) (PFO) as the blue emission branches was designed and synthesized, in which the balanced emission of red-, green- and blue-light was realized by adjusting the contents ratio of Ir(piq)3 and FO. These hyperbranched copolymers showed high fluorescence quantum efficiency (28.1%–47.2% in neat films) and excellent thermal stabilities. Furthermore, triplet-triplet annihilation was effectively suppressed by this hyperbranched structure. As a result, a high color rendering index (CRI) of 87 and a Commission International de l'Eclairage (CIE) coordinate of (0.31, 0.33) were achieved for P2 (0.05 mol% FO and 0.1 mol% Ir(piq)3)-based single-active-layer OLED device, which shows a maximum current efficiency of 3.85 cd A−1 and a maximum brightness of 3354 cd m−2 (at 10.9 mA cm−2).A series of hyperbranched copolymers were designed and synthesized, achieving the white-light emission with a high CRI of 87.Download high-res image (174KB)Download full-size image

White organic light-emitting diodes (WOLEDs) with an ultra-high color rendering index (CRI) (≥90) are considered to be crucial for special lighting applications, such as in hospitals, art galleries, and museums. However, most reported WOLEDs with a CRI of ≥90 almost all use three or more emitters, and usually suffer from a complicated device structure. In this work, an exciplex formed between a 4,4′,4′′-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA) donor and a bis[2-(2-hydroxyphenyl)-pyridine]beryllium (Bepp2) acceptor, exhibiting a broad-spectrum emission, was employed as a yellow emitter. And a thin 4,4′,4′′-tri(9-carbazoyl)triphenylamine (TCTA) layer (2–6 nm) as a carrier adjustment layer was inserted into the Bepp2 layer of the exciplex to block some of the electrons at the TCTA/Bepp2 interface, inducing a blue light emission from Bepp2. A series of ultra-simple di-chromatic WOLEDs, using only three organic materials, were demonstrated. By changing the thickness of TCTA, the proposed WOLEDs achieve an ultra-high CRI of 92, which, to our knowledge, is by far the simplest structure for a complementary WOLED with a CRI over 90. Besides, the optimized WOLED, at a practical luminance of 3000 cd m−2, shows an ultra-high CRI of 90, and also realizes a high maximum current efficiency and power efficiency of 8.7 cd A−1 and 10.1 lmW−1, respectively. This novel design concept provides a new avenue for achieving simple-structured, but ultra-high-CRI WOLEDs.

•The red tandem organic light-emitting diode based on an organic photovoltaic-type charge generation layer of carbon 60/copper (Ⅱ) phthalocyanine.•We considered both optical and electrical properties to decide the optimized structure of OPV-type CGL.•A comparison of tandem OLED with bulk heterojunction structure was fabricated, which is not better than the tandem OLED with OPV-type CGL.In this paper, a significant enhancement in current efficiency of a red tandem organic light-emitting diode (OLED), which is based on an organic photovoltaic-type charge generation layer (CGL) of fullerene carbon 60/copper (Ⅱ) phthalocyanine, is introduced. The CGL can absorb a part of photons, radiated from emission zone, then form excitons, which are dissociated into free charges. It induces in lower driven voltage and better efficiency of tandem OLED. Compared with single emitter-unit OLED and tandem OLED with bulk heterojunction CGL, the luminous efficiency boosts remarkably with increasing current density and shows rather slower roll-off. Our results demonstrate that the organic photovoltaic heterojunction, consists of two matched n- and p-type organic semiconductors, is a promising CGL for tandem OLEDs with high efficiency.

•Achieving highly efficient fluorescent OLEDs of 8.1% EQE with rubrene as the emitter.•Utilizing the energy transfer from simple bilayer interface TADF exciplex.•Up-conversion of exciplex triplet excitons and efficient energy transfer play the key role in this system.We demonstrated highly efficient traditional orange emission fluorescent OLEDs with simple device structure by utilizing energy transfer from bilayer interface TADF exciplex to dopant. With rubrene as the dopant, under the optimized concentration of 1.5%, the device achieved maximum current efficiency, power efficiency and EQE of 25.3 cd/A, 22.6 lm/W and 8.1%, respectively. Even at the luminance of 1000 cd/m2, the EQE also remained 6.9%. The obtainment of so high efficiency could be attributed to highly efficient RISC efficiency of triplet excitons and energy transfer efficiency from TADF exciplex to dopant. The more detailed working mechanism was also argued.

A novel orange fluorescence probe based on efficient fluorescence resonance energy transfer from poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-fluorenone] nanoparticles to Rhodamine B dye molecules was developed. This novel probe exhibited a larger Stokes shift, enhanced photostability and longer lifetime comparing to Rhodamine B dye molecules. Meanwhile, it demonstrated the characteristics that especially useful in live cell or in vivo studies, such as narrow full width at half-maximum emission, excitation bands in the visible range and the sensitivity of its fluorescence to temperature. Confocal fluorescence images of the fluorescent probe proved that it could effectively label HeLa cells.A novel orange fluorescence probe with narrow emission, large Stokes shift and high photostability.

Simplified phosphorescent light-emitting devices with the structure ITO/MoO3 (3 nm)/4,4′-bis(9H-carbazol-9-yl)biphenyl (CBP): x wt% tris(2-phenylpyridine)iridium(III) [Ir(ppy)3] (30 nm)/3-(biphenyl-4-yl)-4-phenyl-5-(4-tert-butylphenyl)-4H-1,2,4-triazole (50 nm)/LiF (1 nm)/Al (100 nm) are demonstrated. The optimized organic light-emitting diode with CBP: 25 wt% Ir(ppy)3 as a light-emitting layer showed a peak current efficiency of 46.8 cd A−1, which is 1.64 times that of the reference device with the structure ITO/N,N′'-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (30 nm)/CBP: 8 wt% Ir(ppy)3 (30 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (10 nm)/(4,7-diphenyl-1,10-phenanthroline) (40 nm)/LiF (1 nm)/Al (100 nm). The improvement in efficiency is attributed to the charge-trapping effect of the heavy doping of Ir(ppy)3 and the excellent hole-transporting ability of the CBP layer doped with Ir(ppy)3. When we incorporated bis(4,6-difluorophenyl-pyridine)(picolinate)iridium(III) into the CBP: 25 wt% Ir(ppy)3 layer, the device showed a higher efficiency of 71.2 cd A−1, which is superior to that of previously reported simplified organic light-emitting diodes.

•Nanoplatforms patterning structure is introduced into multiple emissive layers WOLED.•Nanoplatforms pattering structure can suppress the optical waveguide mode.•WOLEDs with nanoplatforms exhibit improved current efficiency.•WOLEDs with nanoplatforms at NPB/EML interface exhibit improved color balance.•The implanting process of nanoplatforms is very simple and low-cost.In this paper, white organic light-emitting device (WOLED) with the structure of ITO/NPB/EML (blue)/CBP/EML (red)/CBP/EML (blue)/TPBi/LiF/Al was selected as reference. Then, the reference device was modified by nanoplatforms patterning structure at the TPBi/LiF or NPB/EML interface. The electroluminescence performance of above two kinds of devices was carefully investigated. The results indicate that WOLED with nanoplatforms at TPBi/LiF interface exhibits an enhanced current efficiency relative to reference device, and the enhancement factor is 1.52, which is due to improved light extraction efficiency. When nanoplatforms are located at the NPB/EML interface, WOLED shows more significantly improved current efficiency relative to reference device, and the enhancement factor is 1.80. Here, the improvement in current efficiency is attributed to increased light extraction efficiency and broadened carrier recombination zone. In addition, it is also found that WOLED with nanoplatforms located at the NPB/EML interface exhibits remarkably strengthened red light intensity in electroluminescence spectrum and good color balance, in which the intensity ratio of red-light to blue-light (Ired/Iblue) is 0.68, higher than that of reference WOLED (Ired/Iblue = 0.5). The implanting process of nanoplatforms patterning structure introduced in this paper is very simple and low-cost, which can be scaled up to large area WOLED manufacturing.

A new bipolar host material based on carbazole and dimesitylboron moieties, 3,6-bis(dimesitylboryl)-9-(4-(dimesitylboryl)phenyl) carbazole (BDDPC), has been successfully synthesised and characterised by elemental analysis, nuclear magnetic resonance spectroscopy, mass spectrometry and thermogravimetric analysis. The electrochemical and photophysical properties of BDDPC are studied by both experimental and theoretical methods. BDDPC exhibits excellent thermal stability (Td = 234 °C), electrochemical stability, high fluorescence quantum yield (0.95) and high triplet energy (2.83 eV). A red phosphorescent organic light-emitting diode (PhOLED) device comprising BDDPC as the host material and Os(bpftz)2(PPh2Me)2 as the dopant is fabricated and displays promising electrophosphorescence properties with a turn-on voltage of 3.0 V, a maximum brightness of 12337 cd m−2 and a maximum current efficiency of 11.04 cd A−1. Similarly, BDDPC is used to fabricate a green PhOLED device with Ir(ppy)2(acac) as the dopant, possessing a turn-on voltage of 2.5 V, a maximum brightness of 26473 cd m−2 and a maximum current efficiency of 38.60 cd A−1. Furthermore, a blue PhOLED device with BDDPC as the host material and FIrpic as the dopant is fabricated with a turn-on voltage of 3.0 V, a maximum brightness of 7622 cd m−2 and a maximum current efficiency of 7.39 cd A−1. It is anticipated that BDDPC has great potential in manufacturing PhOLED devices for display or lighting applications.

•White light emission achieved using the monomer and excimer emission from single Pt-4 dopant.•Extremely low efficiency roll-off even at luminance exceeding 6000 cd/m2.•Device efficiency has been improved by at least two times with further doping of Ir(ppy)3.•By utilization of TPBi as space layer, the device performance was further improved.Phosphorescent white organic light-emitting diodes (WOLEDs) based on single doped platinum(II) [1,3-difluoro-4,6-di(2-pyridinyl)benzene] chloride (Pt-4) emission layers were investigated in this paper. The devices exhibited electroluminescence spectra composed of bluish (λmax = 480 nm) and reddish (λmax = 660 nm) emission bands, which corresponding to monomer and excimer emission originated from Pt-4 dopants. With optimized device structures, a maximum current efficiency of 11.5 cd/A was obtained and remained above 10 cd/A even the brightness was over 6000 cd/m2. Furthermore, by integrating the fac-tris(2-phenylpyridine) iridium(III) as a complementary emitter and an additional 2,2′,2″-(1,3,5-phenylene)-tris(1-phenyl-1H-benzimidazole) space layer, the device efficiency was further improved, which exhibited a maximum current efficiency of 20.4 cd/A at the luminance of 100 cd/m2, and maintained the mild efficiency roll-off that similar to its single Pt-4 doped counterpart.

Luminescence properties of a type of polyfluorene copolymer (PFO–DBT5) used for white-light organic light emitting device (OLED) were studied and discussed, in which a very low concentration of 0.05 mol% 4,7-bithienyl-2,1,3-benzothiadiazole (DBT) molecules were inserted in polyfluorene chain as orange-light unit. From the spectroscopic analysis of PFO–DBT5 in solution and nanoparticles, it is concluded that inter-chain Förster energy transfer from polyfluorene segments to DBT units play major role in process of white-light emission of PFO–DBT5. By measurement of electroluminescent properties, it is found that annealing of PFO–DBT5 film in vacuum is favorable for improving white-light emission owing to enhancement in inter-chain Förster energy transfer. CIE coordinates (0.38, 0.33) were obtained under the annealing temperature of 140 °C. It was found that the annealing temperature affects the luminance and efficiency of white-light OLED. The optimum annealing temperature was 100 °C.Graphical abstractHighlights► Inter-chain Förster energy transfer is dominant during white-light emission of PFO–DBT5. ► Vacuum annealing of PFO–DBT5 film is favorable for improving white-light emission. ► The optimum annealing temperature is 100 °C.

•The photovoltaic effect on the performance of OLEDs was studied.•The device performance with different planar heterojunctions was investigated.•The mechanism relies on the overlap of electroluminescence and absorption spectrum.Organic light-emitting diodes (OLEDs) with planar heterojunction (PHJ) architecture consisting of photovoltaic organic materials of fullerene carbon 60 (C60) and copper (II) phthalocyanine (CuPc) inserted between emitting unit and cathode were constructed, and the photovoltaic effect on OLEDs performance was studied. The electroluminescent (EL) characteristics and mechanism of device performance variation without and with different PHJs (herein including C60/CuPc, CuPc/C60 and CuPc) were systematically investigated in red, green and blue OLEDs. Of the three combinations, OLEDs with C60/CuPc showed the highest efficiency. It is revealed that the photovoltaic C60/CuPc PHJ can absorb part of photons, which are radiated from emission zone, then form excitons, and dissociated into free charges. Consequently, the high device efficiency of OLEDs performance improvement was acquired. This research demonstrates that PHJ consisting of two n- and p-type photovoltaic organic materials could be a promising methodology for high performance OLEDs.

A new bipolar host material based on carbazole and dimesitylboron moieties, 3,6-bis(dimesitylboryl)-9-(4-(dimesitylboryl)phenyl) carbazole (BDDPC), has been successfully synthesised and characterised by elemental analysis, nuclear magnetic resonance spectroscopy, mass spectrometry and thermogravimetric analysis. The electrochemical and photophysical properties of BDDPC are studied by both experimental and theoretical methods. BDDPC exhibits excellent thermal stability (Td = 234 °C), electrochemical stability, high fluorescence quantum yield (0.95) and high triplet energy (2.83 eV). A red phosphorescent organic light-emitting diode (PhOLED) device comprising BDDPC as the host material and Os(bpftz)2(PPh2Me)2 as the dopant is fabricated and displays promising electrophosphorescence properties with a turn-on voltage of 3.0 V, a maximum brightness of 12337 cd m−2 and a maximum current efficiency of 11.04 cd A−1. Similarly, BDDPC is used to fabricate a green PhOLED device with Ir(ppy)2(acac) as the dopant, possessing a turn-on voltage of 2.5 V, a maximum brightness of 26473 cd m−2 and a maximum current efficiency of 38.60 cd A−1. Furthermore, a blue PhOLED device with BDDPC as the host material and FIrpic as the dopant is fabricated with a turn-on voltage of 3.0 V, a maximum brightness of 7622 cd m−2 and a maximum current efficiency of 7.39 cd A−1. It is anticipated that BDDPC has great potential in manufacturing PhOLED devices for display or lighting applications.