Novel fluorene/carbazole hybrids with steric bulk as host materials for blue organic electrophosphorescent devices

The problem of self-quenching in organic electrophosphorescence devices has been extensively studied and partially solved by using sterically hindered spacers in phosphorescent dopants. This paper attempts to address this problem by using sterically hindered host materials. Novel fluorene/carbazole hybrids with tert-butyl substitutions, namely 9,9-bis[4-(3,6-di-tert-butylcarbazol-9-yl)phenyl]fluorene (TBCPF) and 9,9-bis[4-(carbazol-9-yl)phenyl]-2,7-di-tert-butylfluorene (CPTBF), have been synthesized and characterized. The compounds exhibit not only high triplet energy (>2.8 eV), but also high glass transition temperature (>160 °C) and thermal stability. The substitution of inert tert-butyl groups to the carbazole/fluorene rings of these host molecules has a remarkable effect on the corresponding properties of the host materials, i.e. enhancing the thermal and electrochemical stability, weakening the intermolecular packing, and tuning the solid-state emission. Blue electrophosphorescent devices with enhanced performance were prepared by utilizing the sterically hindered host materials. The devices based on the four tert-butyl substituted material TBCPF exhibit unusual tolerance of high dopant concentration up to 20% and marked reduction of efficiency roll-off at higher current, indicating significant suppression of self-quenching effect in organic electrophosphorescent devices by the substitution of steric bulks.     

New universal bipolar host materials with fluorene as non-conjugated bridge for multi-color electrophosphorescent devices

Two novel bipolar hosts (CzFCN2 and CzDFCN) comprising a hole-transport carbazole donor and electron-transport cyano-substituted fluorene acceptor have been synthesized, and their thermal, photophysical, and electrochemical properties were characterized. The non-conjugated linkage between the carbazole donor and the cyano-substituted fluorene acceptor provides excellent thermal/morphological properties and high triplet energies (E_T=2.86 eV) for both CzFCN2 and CzDFCN. These bipolar hosts also exhibited reversible redox behavior, which makes them good candidates for the host material in efficient phosphorescent organic light-emitting diode (PhOLED) devices. Multi-color PhOLED devices incorporating CzFCN2 and CzDFCN as the universal host achieved maximum external quantum efficiencies (η_ext) as high as 10.7, 17.0, 17.2, and 17.6% for blue, green, yellow, and red devices, respectively. In addition, three-component white PhOLEDs (WOLEDs) based on CzFCN2 and CzDFCN as host materials exhibited high color stabilities with η_ext as high as 10.5 and 12.4% and power efficiencies (η_p) of 20.5 and 26.7 lm W⁻¹, respectively.     

Synthesis of new bipolar materials based on diphenylphosphine oxide and triphenylamine units: efficient host for deep-blue phosphorescent organic light-emitting diodes

This paper reports the synthesis and physical properties of a series of bipolar host materials, using of a hole-transporting triphenylamine (TPA) monomer as a core incorporated with different numbers of diphenylphosphine oxide (PO) as electron-transporting moieties, 4-(diphenylphosphoryl)-N,N-diphenylaniline (DDPA), 4-(diphenylphosphoryl)-N-(4-(diphenylphosphoryl)phenyl)-N-phenylaniline (DDPP), and tris(4-(diphenylphosphoryl)phenyl)amine (TDPA), for solution-processed deep-blue phosphorescent organic light-emitting devices (PhOLEDs). With the increasing numbers of PO units, the glass-transition temperature of those compounds rise gradually. Moreover, the newly synthesized compounds all possess high triplet energies, which can prevent back energy transfer between the host and dopant molecules, and are expected to serve as appropriate hosts for iridium(III) tris(3,5-difluoro-4-cyanophenyl)pyridinato-N,C′ (FCNIrpic). The solution-processed devices using DDPP and TDPA as the hosts for the phosphorescence emitter FCNIrpic showed the maximum luminance efficiencies of 9.7 and 6.6 cd A⁻¹, respectively. The efficiency of TDPA based device shows nearly three times higher than the value of commonly used host material 1,3-bis(9-carbazolyl)benzene (mCP) with the same structure, which is outstanding with respect to other works related to the solution-processed deep-blue PhOLEDs based on small-molecule hosts.     

Synthesis of carbazole-based dendrimer: host material for highly efficient solution-processed blue organic electrophosphorescent diodes

This paper reports the synthesis and physical properties of two novel carbazole-based dendritic host materials Cz-CCP and Cz-mCP for solution-processed blue phosphorescent organic light-emitting devices (PhOLEDs). These dendritic hosts exhibit high triplet energy (≥2.85 eV), excellent film-forming ability (with low root-mean-square (rms) values less than 0.2 nm), high glass-transition temperatures in the range of 242–248 °C, and the appropriate HOMO energy levels (?5.33–?5.35 eV) facilitating the transfer of holes from Poly(3,4-ethylenedioxythiophene):Poly(styrene-4-sulfonate) (PEDOT:PSS) to the emitting layer. The single-layer device using Cz-CCP and Cz-mCP as the host for the phosphorescence emitter iridium(III) bis(4,6-difluorophenylpyridinato)-picolinate (FIrpic) showed the maximum luminance efficiencies of 9.6 and 10.8 cd A^?1, respectively. By introducing a thin 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBI) electron-transporting and exciton-confining layer, the maximum efficiency of the solution-processed double-layer device based on Cz-CCP and Cz-mCP can be further improved to 20.5 and 22.7 cd A^?1, and maximum external quantum efficiencies as high as 10.2% and 11.5%, respectively. These results demonstrated that the newly synthesized, carbazole-based dendritic host materials are advantageous for fabrication of highly efficient blue PhOLEDs.     

A novel luminophor and host polymer from fluorene-carbazole derivatives for preparing solution-processed non-doped blue and closed-white light devices

A novel blue light emitting polymer was designed and synthesized via alternative conjugated 9,9-dioctylfluorene and 9-(6-(9H-carbazol-9-yl)hexyl)-9H-carbazole, named PF2Cz. It exhibited high thermal stability, good film morphology and strong deep-blue emission peaks at 408 and 429?nm in film. The triplet energy level of PF2Cz (E_T?=?2.30?eV) was also improved. Non-doped and doped devices were both prepared by solution process to characterize the electroluminescent (EL) properties of PF2Cz. In non-doped devices, PF2Cz acted as blue emitter which exhibited a Commission Internation de L'Eclairage (CIE) coordinate of (0.164, 0.102) and a external quantum efficiency (EQE) values of 1.28%. Moreover, the doped phosphorescent devices utilized PF2Cz as host material obtained a closed-white light emission with a content of 1?wt% dopant. All these results indicated that the fluorene-carbazole derivatives could be a promising molecular design strategy for the synthesis of blue light and host organic semiconductors.     

Nonconjugated hybrid of carbazole and fluorene: a novel host material for highly efficient green and red phosphorescent OLEDs

[structure: see text] A novel host material for efficient green and red electrophosphorescence devices is obtained by adopting the new molecular strategy of nonconjugated linkage of carbazole and fluorene moieties. The new host combines characteristics of both carbazole and fluorene, giving a large-gap host material suitable for green and red phosphorescent OLEDs. Green and red phosphoresecent OLEDs with external quantum efficiencies up to 10% have been achieved with this new host material.     

Bis(4-diphenylaminophenyl)carbazole end-capped fluorene as solution-processed deep-blue light-emitting and hole-transporting materials for electroluminescent devices

A new highly fluorescent bis(4-diphenylaminophenyl)carbazole end-capped fluorene (TCF) is synthesized and characterized. TCF is an amorphous molecular glass with a high glass transition temperature of 169 °C, is electrochemically stable, and gives strong blue emission both in solution and solid state. It showed greater ability as a solution processed blue emitter and hole-transporter for OLEDs than commonly used NPB. High-efficiency, deep-blue and Alq3-based green devices with luminance efficiencies and CIE coordinates of 0.93 cd/A and (0.16, 0.09), and 3.78 cd/A and (0.29, 0.45) were achieved, respectively.     

Novel bipolar host for highly efficient green,yellow, orange,red and deep-red phosphorescent organic light-emitting devices

A novel bipolar host tris(4-(pyrimidin-5-yl)phenyl)amine (TPMTPA) constructed by incorporating triphenylamine as the electron-donating core and pyrimidine as the electron-accepting peripheries was designed and synthesized. TPMTPA achieves excellent bipolar charge transport properties and has high enough triplet energy level to sensitize green, yellow, orange, red and deep-red phosphors. By using TPMTPA as a host, high performance green, yellow, orange, red and deep-red phosphorescent organic light-emitting devices (PhOLEDs) were demonstrated with maximum external quantum efficiencies of 20.4%, 17.6%, 15.1%, 15.3% and 15.7% respectively. These results suggested that TPMTPA is a versatile high performance host for PhOLEDs of different emission colors.     

An electron-transporting host material compatible with diverse triplet emitters used for highly efficient red- and green-electrophosphorescent devices

A bifluorene analogue, T2N, containing a pyridyl moiety serves as both a host and an efficient electron-transporting material that is compatible with various heavy metal-containing red (Ir, Ru, Os, and Pt) and green (Ir) phosphors for highly efficient phosphorescent OLEDs possessing simple device architectures.     

Nanofibrils in 3D aligned channel arrays with synergistic effect of Ag/NPs for rapid and highly efficient electric field disinfection

The disinfection of waterborne pathogens from drinking water is extremely important for human health. Although countless efforts have been devoted for drinking water inactivation, challenges still exist in terms of relative high energy consumption and complicated to implement and maintain. Here, silver nanoparticles anchoring wood carbon (Ag NPs/WC) membrane is developed as cost-effective, high flux, scalable filter for highly efficient electric field disinfection of water. Under electric field of 4 V voltage, the designed membrane achieved more than 5 log (99.999%) disinfection performance for different model bacteria, including Escherichia coli (E. coli), Enterococcus faecalis (E. faecalis), Salmonella enterica serovar Typhimirium (S. Typhimurium) and Bacillus subtilis (B. subtilis) with a high flux of 3.8 × 10³ L m⁻² h⁻¹, extremely low energy consumption of 2 J L⁻¹ m⁻² and fantastic durability (7 days). The high disinfection performance of Ag NPs/WC membrane is attributed to the synergistic disinfection of carbon nanofibrils, Ag nanoparticles as well as the low tortuous structure of the channels in wood carbon. The Ag NPs/WC membrane presents a promising strategy for point-of-use drinking water electric field disinfection treatment.