High Triplet Energy Polymer as Host for Electrophosphorescence with High Efficiency

A Porous Carbazolic Al-MOF for Efficient Aerobic Photo-Oxidation of Sulfides into Sulfoxides under Air

A robust, microporous, and photoactive aluminum-based metal-organic framework (Al-MOF, LCU-600) has been assembled by an in situ-formed [Al3O(CO2)6] trinuclear building unit and a tritopic carbazole ligand. LCU-600 shows a high water stability and permanent porosity for N2 and CO2 adsorption. Notably, the incorporation of photoresponsive carbazole moieties into LCU-600 makes it a highly efficient and recyclable photocatalyst for aerobic photo-oxidation of sulfides into sulfoxides under an air atmosphere at room temperature. Mechanism investigations unveil that photogenerated holes (h+), superoxide radical anion (O2•-), and singlet oxygen (1O2) are critical active spices for the photo-oxidation reaction performed in an air atmosphere.

Poly(acridan-grafted biphenyl germanium) with High Triplet Energy as a Universal Host for High-Efficiency Thermally Activated Delayed Fluorescence Full-Color Devices and Their Hybrid with Phosphor for White Light Electroluminescence

Developing an effective host for highly efficient full-color electroluminescence devices through a solution-process is still a challenge at present. Here, we use the σ-π conjugated polymer, poly(acridan grafted biphenyl germanium) P(DMAC-Ge), having the highest triplet energy (E_T) 2.86 eV among conjugated polymers as the host in sky-blue phosphorescence, TADFs (blue (B), green (G), and red (R)), and hybrid white (W) PLEDs. Upon doping with a sky-blue phosphor-emitter (Firpic), the resulting device gives the high EQE_max 19.7% with B_max 24,918 cd/m². The Ge-containing polymer backbone can provide as a channel for electron transport and charge trap into the guest as manifested by the electroluminescence dynamics. Further introducing the bipolar material DCzPPy as cohost, the devices with a sky-blue phosphor (Firpic) and each of the TADF-guests─B (DMAC-TRZ), G (DACT-II), and R (TPA-DCPP) in the EML─achieve the high maximum EQEs as 19.7%, 19.4%, 21.5% and 3.82% with the emission peaks at 470, 485, 508, and 630 nm, respectively. As the three guests (DMAC-TRZ, Ir-O, Ir-R) are doped together into the emitting layer, we obtain a TADF-phosphor (T-P) hybrid white PLED giving a record-high EQE 22.5% among the solution processed hybrid OLED with CIE (0.34, 0.40) and B_max 28,945 cd/m². These results manifest that P(DMAC-Ge) is a potential polymer host for full-color TADF and hybrid white light PLEDs with high performance.

Carbazole-Equipped Metal-Organic Framework for Stability, Photocatalysis, and Fluorescence Detection

The useful yet underutilized backfolded design is invoked here for functionalizing porous solids with the versatile carbazole function. Specifically, we attach carbazole groups as backfolded side arms onto the backbone of a linear dicarboxyl linker molecule. The bulky carbazole side arms point away from the carboxyl links and do not disrupt the Zr-carboxyl framework formation; namely, the resultant MOF solid ZrL1 features the same net as that of the unfunctionalized dicarboxyl linker, also known as the PCN-111 net or UiO-66 net. The ZrL1 structure features only half linker occupancy (about 6 out of the 12 linkers around the Zr₆O₈ cluster being missing) and partially collapses upon activation (acetone exchange and evacuation). Notably, the stability improves after heating in diphenyl oxide at 260 °C (POP-260 treatment; to form ZrL1-260), as indicated by the higher crystallinity and surface area of the activated ZrL1-260 sample. The ZrL1-260 samples achieve 72% yield in photocatalyzing reductive dehalogenation of phenacyl bromide; ZrL1 can detect nitro-aromatic compounds via fluorescence quenching, with selectivity and sensitivity toward 4-nitroaniline, featuring a limit of detection of 96 ppb.

Chiral phosphoric acid catalyzed atroposelective C–H amination of arenes: mechanisms, origin and influencing factors of enantioselectivity

The amination reaction between azonaphthalene and carbazole catalyzed by chiral phosphoric acid was theoretically investigated, and the mechanism, origin and influencing factors of enantioselectivity were elaborated.

Rational Design of Carbazole- and Carboline-Based Polymeric Host Materials for Realizing High-Efficiency Solution-Processed Thermally Activated Delayed Fluorescence Organic Light-Emitting Diode

Recently, various host materials have been developed for solution-processed thermally activated delayed fluorescent organic light-emitting diodes (TADF-OLEDs). Compared with small-molecule hosts, polymeric hosts are advantageous for inducing a uniform distribution and segregation of dopant molecules in the emissive layer without undesired large-scale phase separation. In this study, new polymer hosts were demonstrated, in which a bipolar conjugative moiety consisting of a carbazole (Cz) donor and an α-carboline (α-Cb) acceptor was bound to the polystyrene backbone through a non-conjugated linker. They exhibited high triplet energies of >2.8 eV, and their emission spectra overlapped with the absorption spectrum of a green TADF emitter, which allowed facile energy transfer from the polymeric host to the small-molecule dopants. High device performance was observed, with external quantum efficiencies (EQEs) of 13.65, 17.09, and 17.48% for solution-processed green TADF-OLEDs using PSCzCz, PSCzCb, and PSCbCz, respectively, as hosts for the EML. The EQEs of bipolar host (PSCzCb and PSCbCz)-based devices were higher than those of unipolar host (poly(N-vinylcarbazole) and PSCzCz)-based devices owing to the well-balanced charge-carrier transport. According to these results, the polymeric host bearing a bipolar Cz and α-Cb coupled moiety is a promising material for solution-processable TADF-OLEDs.

Optoelectronic Properties of High Triplet σ-π-Conjugated Poly[(biphenyl group IV-A atom (C, Si, Ge, Sn)] Backbones

A series of σ-π-conjugated polymers composed of biphenyl and X atom as backbone repeat unit (where X is the group IV-A atom: carbon, silicon, germanium, or tin) grafted with two alkoxy-substituted biphenyls at the X atom as side chains are synthesized and their optoelectronic properties are studied systematically. We choose biphenyl rather than alkyl as the side chain because its frontier molecular orbital distributions are close to those of our previously reported σ-π-conjugated polymer grafted with transport moieties. The present σ-π polymers with various X atoms show significant differences in triplet energy (E_T) ranging from 2.58 to 2.83 eV with the sequence Ge > Si > C > Sn and in charge mobilities from 10^-9 to 10^-7 cm²/(V s) with the sequence Si > Ge > Sn > C, indicating that the properties of the σ-π polymers are largely affected by their X atoms. The Ge- and Sn-based σ-π-conjugated polymers show the highest and lowest E_T values, respectively, due to their different levels of π-electron delocalization caused by size effects and (d-p)π orbital interaction. For their charge transport properties, the Si-based conjugated σ-π polymer gives the highest hole and electron mobilities due to the stronger σ-π conjugation and shorter Si-C bond length between the attached carbon atom in biphenyl and Si. On the contrary, the C-based σ-π-conjugated polymer gives the lowest charge mobilities due to a lack of d orbital in the C atom leading to a poor σ-π conjugation characteristic. These σ-π polymers with different E_T levels and charge transport properties show a significant effect on their electroluminescence characteristics. Among them, the Ge-based σ-π-conjugated polymer when used as host shows the best device performance due to its higher E_T and reasonable charge mobility. Such findings of different optoelectronic properties of these σ-π-conjugated polymers provide useful guidelines for the selection of backbone for designing σ-π-conjugated polymer host grafted with charge transport moieties.

Bipolar and Unipolar Silylene-Diphenylene σ-π Conjugated Polymer Route for Highly Efficient Electrophosphorescence

σ-π conjugated polymer strategy is proposed for designing electroluminescent host polymers with silylene-diphenylene as the backbone repeat unit giving a high triplet energy (E_T = 2.67 eV). By incorporation of high E_T (3.0 eV) electron (oxadiazole, OXD) and hole (triphenyl amine, TPA) transport moieties, or TPA alone (in this case, the main chain acts as electron transport channel) as side arms on the silylene, the high E_T bipolar and unipolar polymers are formed, allowing a use of iridium green phosphor (Ir(ppy)₂(acac), Ir-G) (E_T = 2.40 eV) as the dopant. The matching of energy levels of the dopant with the hosts, leading to charge trapping into it; and singlets and triplets of the exciplex and excimer can be harvested via energy transfer to the dopant. Using these host-guest systems as the emitting layer, chlorinated indium-tin-oxide (Cl-ITO) as the anode, and benzimidazole derivative (TPBI) as the electron transport layer, this two-layer device gives the high luminance efficiency 80.1 cd/A and external quantum efficiency 21.2%, which is the best among the report values for polymer light emitting diode (PLED) in the literatures. This example manifests that σ-π conjugated polymer strategy is a promising route for designing polymer host for efficient electrophosphorescence.

Bifunctional Heterocyclic Spiro Derivatives for Organic Optoelectronic Devices

A series of heterocyclic spiro derivatives has been successfully synthesized and characterized by photophysical and electrochemical studies. Taking advantage of their excellent hole-transporting properties, highly efficient small-molecular organic photovoltaic devices based on these heterocyclic compounds as donors with very low dopant concentrations have been prepared; particularly, a high open-circuit voltage of up to 1.10 V and a power conversion efficiency of up to 5.12% have been realized. In addition, most of these heterocyclic spiro derivatives are found to be highly emissive in solutions with photoluminescence quantum yields of up to 0.91, and high-performance deep-blue-emitting organic light-emitting diodes (OLEDs) have been achieved. Such devices exhibit a stable deep blue emission with CIE coordinates of (0.16, 0.04) and high external quantum efficiencies of up to 4.7%, which is one of the best values among the reported OLEDs with CIEy < 0.08.

Linkage and donor–acceptor effects on resistive switching memory devices of 4-(N-carbazolyl)triphenylamine-based polymers

In order to gain deeper insight about the linkage effect and donor–acceptor effect on memory behavior (from DRAM to WORM), 4-(N-carbazolyl)triphenylamine-based polyimides and polyamides were synthesized and their memory behaviours were investigated.

One-pot two-step synthesis of N-arylcarbazole-based skeleton

A highly site-selective, one-pot, sequential C–N and C–C bond forming process was developed, affording a carbazole-based skeleton that contains biphenyl and diarylacetylene cores.

Theoretical investigations of the electronic structures of carbazole-based triphenylphosphine oxide derivatives, potential bipolar host materials in blue-phosphorescent devices

Density functional theory calculations were performed to investigate the electronic structures of bipolar host materials comprising a backbone of linked acceptor moieties where each acceptor was also linked to a pendant donor moiety. The acceptor was triphenylphosphine oxide with two of its phenyls substituted with fluorine atoms or nitrile groups (CN). The donor was carbazole (CZ) substituted, or not, with t-butyl groups. The HOMO and LUMO energy levels of these host molecules were mainly influenced by their respective hole- and electron-transport units. The t-butyl substituents on the CZ moieties had an adverse effect on the triplet energies (E T) of the host molecules, especially for molecules where the phenyls of the backbone chain were substituted with CN groups. While introducing CN substituents onto the backbone chain decreased the energy difference between the lowest singlet and triplet excited states (ΔE ST), it also caused the energy gap between the HOMO and LUMO to narrow. Among the host molecules investigated, that in which one of the phenyls in the acceptor moiety was linked to the donor while the other two phenyls in the acceptor were substituted with CN substituents exhibited the highest E T, balanced charge transport, a low charge-injection barrier, and a small ΔE ST, and is therefore a promising candidate host material for use in blue-phosphorescent devices. Graphical Abstract Density functional theory calculations were performed to explore the electronic properties of bipolar host materials comprising a backbone of linked acceptor moieties where each acceptor was also linked to a pendant donor moiety. All of the designed molecules with high triplet energies were found to be suitable for use as host materials when matched with a blue-light guest material. The results demonstrate that the host molecule in which one of the phenyls in the triphenylphosphine oxide acceptor moiety was linked to the carbazole donor while the other two phenyls in the acceptor moiety were substituted with CN substituents yields the highest blue-phosphorescent device performance, as this host molecule has interesting features such as a high E T, balanced charge transport, a low charge-injection barrier, and a small ΔE ST.

Copper/β-diketone-catalysed N-arylation of carbazoles

A copper/β-diketone-catalysedN-arylation of carbazoles with aryl iodides is developed with broad substrate applicability and moderate to good yields.

Photo- and electro-luminescence of four cuprous complexes with sterically demanding and hole transmitting diimine ligands

The steric methyl group at emissive cuprous complexes largely increases both the PL and EL efficiency, while the carbazole appendage modestly improves the EL efficiency. So, 4 shows the highest efficiency with a CE_max of 27.1 cd A⁻¹ and an EQE_max of 8.7%.

Wide bandgap materials design toward tunable bandgap and increased carries injection property: silane interrupting π-conjugation together with peripheralcarbazolyl substituents

Universal host for blue, green and red phosphorescent dopants is achieved by rational molecule design with silane interrupting π-conjugation and non-conjugated peripheralcarbazolyl substituents.

Violet-blue- or pure-blue-emitting triphenylamine derivatives: synthesis and properties

We report the synthesis and optoelectronic properties of a series of nine triphenylamine derivatives. They were synthesized by Suzuki cross-coupling reactions and characterized by elemental analysis, nuclear magnetic resonance, ultraviolet visible absorption spectra, fluorescence spectra, and cyclic voltammetry. All compounds exhibit reversibly electrochemical behavior. In solid state, compounds 5 and 9 emit near violet blue and compounds 1, 2, 4, 6, 7, and 8 emit deep blue or pure blue and compound 3 emits green. Of all of these compounds, compounds 1, 3, 4, and 8 exhibit high fluorescence quantum yields (44%–68%) with the best coplanarity. Compared with them, compounds 5 and 9 have the lowest fluorescence quantum yields due to the least coplanarity. With the similarity in structure with those reported in literature, these compounds can be potentially useful for blue-emitting, host, and up-converting materials.

A blue emission polymer: synthesis, photophysical and electrochemical properties

A novel π-conjugated polymer (PCPyrene) containing N-benzylcarbazole and pyrene units has been synthesized and characterized. The polymer possesses high thermal stability with the decomposition temperature of 440 °C. It shows higher fluorescence quantum yields of in solution and solid state, respectively. PCPyrene can emit bright blue-lights both in different organic solutions (440-460 nm) and in the solid state (492 nm). Compared the emission spectra of PCPyrene in solutions with in solid state, the solid state emission of PCPyrene is significantly red-shifted. Additionally, it is not obvious changes of the solid emission spectra even after being annealed at 150 °C under nitrogen for 24 h. The electrochemical properties and energy levels of PCPyrene were also investigated by cyclic voltammetry. Furthermore, in order to provide a basis forecasting the structure-physical property relationships, the photophysical properties of PCPyrene have been carefully investigated by fluorescence emission and UV-vis absorption spectra.

Singlet Generation from Triplet Excitons in Fluorescent Organic Light-Emitting Diodes

A potential major drawback with organic light-emitting devices, (OLEDs) is the limit of 25% singlet exciton production through spin-dependent charge recombination. Recent device results, however, show that this limit does not hold and far higher efficiencies can be achieved in purely fluorescent-based systems (Wohlgenannt et al. (2001), Dhoot et al. (2002), Lin et al. (2003), Wilson et al. (2001), Cao et al. (1999), Baldo et al. (1999), and Kim et al. (2000)). Thus, the question arises; is recombination spin dependent (Tandon et al. (2003)) or are singlet excitons generated in secondary processes? Direct measurement of the singlet generation rate in working devices of 44% has been shown (Rothe et al. (2006)), which have been verified as being part due to direct singlets formed on recombination and part from triplet fusion, singlets produced during triplet annihilation (Kondakov et al. (2009), King et al. (2011), and Zhang and Forrest (2012)). Here, the various routes by which triplet excitons can generate singlet states are discussed and their relative contributions to the overall electroluminescence yield are given. The materials requirements to obtain maximum singlet production from triplet states are discussed. These triplet contributions can give very high device yields for fluorescent emitters, which in the case of blue devices can be highly advantageous. Further, new devices architectures open up which are simple and have intrinsically low turn on voltages, ideal for large-area OLED lighting applications.

Dendritic luminescent gold(III) complexes for highly efficient solution-processable organic light-emitting devices

Emission control: carbazole-based dendritic alkynylgold(III) complexes have been evaluated as phosphorescent emitters in organic light-emitting devices. The energy as well as the bathochromic shift of the emissions can be tuned effectively through a control of the dendrimer generation. The optimized devices show high current and external quantum efficiencies of up to 24.0 cd A(-1) and 7.8 %, respectively.

Highly luminescent lanthanide complexes with novel bis-β-diketone ligand: synthesis, characterization and photoluminescent properties

A biphenyl-linked bis-β-diketone ligand, 3,3'-bis(3-phenyl-3-oxopropanol)biphenyl (BPB) has been prepared for the syntheses of a series of dinuclear lanthanide complexes. The ligand bears two benzoyl β-diketonate sites linked by a 3,3'-biphenyl spacer. Reaction of the doubly negatively charged bis-bidenate ligand with lanthanide ions forms triple-stranded dinuclear complexes Ln(2)(BPB)(3) (Ln=Nd (1), Sm (2), Eu (3), Yb (4) and Gd (5)). Electrospray mass spectrometry is used to identify the formation of the triple-stranded dinuclear complexes 1-5, which have been further characterized by various spectroscopic techniques. The complexes display strong visible and NIR luminescence upon excitation at ligands bands around 360 nm, depending on the choice of the lanthanides, and the emission quantum yields and luminescence lifetimes of 2-3 have been determined. It shows that the biphenyl-linked ligand BPB is a more efficient sensitizer than the monodiketone ligand DBM (dibenzoylmethane), through the comparisons of Ln(2)(BPB)(3) and Ln(DBM)(3) on their photoluminescent properties.

Efficient phosphorescent polymer light-emitting diodes by suppressing triplet energy back transfer

Phosphorescent polymer light-emitting diodes (PhPLEDs) are promising devices in flat panel displays and solid state lighting sources since they can combine the advantages of the high efficiency of electrophosphorescence and low-cost, large-scale manufacture by using a solution process. However, their efficiencies are generally much lower than those of small-molecule-based devices fabricated by using a thermal deposition approach. One of the major reasons for their low efficiency is that energy is lost by back transfer to a polymer host. This tutorial review gives a brief introduction to the fundamentals of PhPLEDs, and then highlights recent progress in the main approaches to suppress triplet energy back transfer from the phosphor to the polymer host towards realizing highly efficient PhPLEDs. The suppressing mechanisms are discussed, and the achievement of high device efficiencies are demonstrated. Emphasis is placed on the relationships between molecular structure, the extent of suppressing triplet energy back transfer, and device performance.

Highly luminescent bis-diketone lanthanide complexes with triple-stranded dinuclear structure

A new bis-β-diketone, 3,3'-bis(4,4,4-trifluoro-1,3-dioxobutyl)biphenyl (BTB), has been designed and prepared for the synthesis of a series of dinuclear lanthanide complexes [Ln(2)(BTB)(3)(C(2)H(5)OH)(2)(H(2)O)(2)] [Ln = Eu (1), Gd (2)], [Ln(2)(BTB)(3)(DME)(2)] [Ln = Nd (3), Yb (4); DME = ethylene glycol dimethyl ether] and [Eu(2)(BTB)(3)(L)(2)] [L = 2,2-bipydine (5); 1,10-phenanthroline (6); 4,7-diphenyl-1,10-phenanthroline (7)]. Complexes 1-7 have been characterized by various spectroscopic techniques and their photophysical properties are investigated. X-ray crystallographical analysis reveals that complexes 1, 3 and 4 adopt triple-stranded dinuclear structures which are formed by three bis-bidentate ligands with two lanthanide ions. The complexes 1 and 3-7 display strong visible red or NIR luminescence upon irradiation at ligand band around 372 nm, depending on the choice of the lanthanide. The solid-state photoluminescence quantum yields and the lifetimes of Eu(3+) complexes are determined and described.