Phenylene Units Research Articles

Pyrrolopyrimidine based CSF1R inhibitors: Attempted departure from Flatland

The colony-stimulating factor 1 receptor (CSF1R) is an attractive target for inflammation disorders and cancers. Based on a series of pyrrolo[2,3-d]pyrimidine containing two carbo-aromatic rings, we have searched for new CSF1R inhibitors having a higher fraction of sp3-atoms. The phenyl unit in the 4-amino group could efficiently be replaced by tetrahydropyran (THP) retaining inhibitor potency. Exchanging the 6-aryl group with cyclohex-2-ene units also resulted in highly potent compounds, while fully saturated ring systems at C-6 led to a loss of activity. The structure-activity relationship study evaluating THP containing pyrrolo[2,3-d]pyrimidine derivates identified several highly active inhibitors by enzymatic studies. A comparison of 11 pairs of THP and aromatic compounds showed that inhibitors containing THP had clear benefits in terms of enzymatic potency, solubility, and cell toxicity. Guided by cellular experiments in Ba/F3 cells, five CSF1R inhibitors were further profiled in ADME assays, indicating the para-aniline derivative 16t as the most attractive compound for further development.

A dodecamethoxy[6]cycloparaphenylene consisting entirely of hydroquinone ethers: unveiling in-plane aromaticity through a rotaxane structure

[n]Cycloparaphenylenes ([n]CPPs, where n is the number of phenylene groups), consisting of 1,4-linked phenylene unit, have attracted much attention due to their cyclic π-conjugated structures and physical properties. However, functionalizing of the benzene rings of smaller [n]CPPs (n < 7) has been a challenge due to ring strain and steric hindrance of the substituents that hampers their synthesis. Here we show successful synthesis of a new [6]CPP derivative with twelve methoxy groups at the 2,5-positions of all benzene rings by utilizing our developed CPP synthesis method via a macrocyclic gold complex. This molecule exhibited a significantly higher oxidation potential caused by the electron-donating ability of the methoxy groups and the tubular molecular conformation, allowing facile oxidation to give dicationic species with in-plane aromaticity. Furthermore, this molecule successfully included with the guest molecules with a flexible alkyl chain in the cavity, enabling the creation of a CPP-based rotaxane, which exploited its mechanically interlocked molecular structure to the first experimental observation that the in-plane aromaticity in the center of the macrocycle.

A Steric-Repulsion-Driven Clutch Stack of Triaryltriazines: Correlated Molecular Rotations and a Thermoresponsive Gearshift in the Crystalline Solid.

We report that a newly developed type of triaryltriazine rotor, which bears bulky silyl moieties on the para position of its peripheral phenylene groups, forms a columnar stacked clutch structure in the crystalline phase. The phenylene units of the crystalline rotors display two different and interconvertible correlated molecular motions. It is possible to switch between these intermolecular geared rotational motions via a thermally induced crystal-to-crystal phase transition. Variable-temperature solid-state 2H NMR measurements and X-ray diffraction studies revealed that the crystalline rotor is characterized by a vertically stacked columnar structure upon introducing a bulky Si moiety with bent geometry as the stator. The structure exhibits correlated flapping motions via a combination of 85° and ca. 95° rotations between 295 and 348 K, concurrent with a negative entropy change (ΔS‡ = -23 ± 0.3 cal mol-1 K-1). Interestingly, heating the crystal beyond 348 K induces an anisotropic expansion of the column and lowers the steric congestion between the adjacent rotators, thus altering the correlated motions from a flapping motion to a correlated 2-fold 180° rotation with a lower entropic penalty (ΔS‡ = -14 ± 0.5 cal mol-1 K-1). The obtained results of our study suggest that the intermolecular stacking of the C3-symmetric rotator driven by the steric repulsion of the bulky stator represents a promising strategy for producing various correlated molecular motions in the crystalline phase. Moreover, direct and reversible modulation of the intermolecularly correlated rotation is achieved via a thermally induced crystal-to-crystal phase transition, which operates as a gearshift function at the molecular level.

Synthesis, crystal structure and proton conductive properties of one stable cobalt(II) coordination polymer from thiourea carboxylate

To search for more high-performance crystalline proton conducting materials and to accelerate the related research progress, in this paper, a one-dimensional coordination polymer (CP), [Co(BBOT)2(H2O)3·2H2O]n (1) (H2BBOT = N-benzoyl-N′-(4-benzoxy)thiourea) was firstly prepared by solvent volatilization approach. Subsequently, the thermal, H2O and chemical stabilities of the CP were tested and its high structural stability was confirmed. Furthermore, in 1, a stable solid three-dimensional framework can be constructed by intermolecular H-bonds and stacking interactions between phenyl units. Then, utilizing the AC impedance determination, the dependence of the proton conductivity of this CP on temperature and humidity in the water vapor environment was explored and the positive correlation was verified. Excitingly, the optimized proton conductivity of this compound under specific test conditions (100 °C/98 % relative humidity) can be as high as 10−4 S/cm, being in the forefront of similar crystalline solid materials. Finally, according to the value of activation energy and the characteristics of crystal structure, we speculate on the proton conduction mechanism.

Synthesis of Nonsymmetric NBN-Embedded [6]- and [7]Helicenes with Amplified Activities.

Two C1-symmetric heterohelicenes were constructed by nonsymmetrically extending the ortho-fused structures of a C2v-symmetric NBN-embedded phenalene derivative and featured intense luminescence, large Stokes shifts, and successive reversible redox behaviors. Increasing one fused phenyl unit in such a helical structure led to a 10-fold-enhanced dissymmetry factor. Their strong double hydrogen-bond-donating capability makes them distinctly red-shifted in absorption, emission, and CD and CPL spectra upon the addition of fluoride anion.

Expanding the Structural Diversity at the Phenylene Core of Ligands for the von Hippel-Lindau E3 Ubiquitin Ligase: Development of Highly Potent Hypoxia-Inducible Factor-1α Stabilizers.

Hypoxia-inducible factor-1α (HIF-1α) constitutes the principal mediator of cellular adaptation to hypoxia in humans. The HIF-1α protein level and activity are tightly regulated by the ubiquitin E3 ligase von Hippel-Lindau (VHL). Here, we performed a structure-guided and bioactivity-driven design of new VHL inhibitors. Our iterative and combinatorial strategy focused on chemical variability at the phenylene unit and encompassed further points of diversity. The exploitation of tailored phenylene fragments and the stereoselective installation of the benzylic methyl group provided potent VHL ligands. Three high-resolution structures of VHL-ligand complexes were determined, and bioactive conformations of these ligands were explored. The most potent inhibitor (30) exhibited dissociation constants lower than 40 nM, independently determined by fluorescence polarization and surface plasmon resonance and an enhanced cellular potency, as evidenced by its superior ability to induce HIF-1α transcriptional activity. Our work is anticipated to inspire future efforts toward HIF-1α stabilizers and new ligands for proteolysis-targeting chimera (PROTAC) degraders.

Synthesis of Thiapillar[6]arenes Bearing Redox-Active (Hydro)quinone Groups. Electrochemical and XRD Study.

Pillar[n]arenes are among the newest members of the macrocyclic family. Nevertheless, their conformational behavior and binding properties as well as redox properties of dealkylated pillar[n]arenes are well-studied. At the same time, introducing a heteroatom into a cyclophane macrocycle is already known to alter all the above properties drastically. This study presents a simple synthetic approach based on thia-Michael addition cyclization that readily resulted into hexathiapillar[6]arene with four phenylene units alternated by two redox-active hydroquinone moieties. The straightforward synthesis of the macrocycle enabled a systematic study of its conformation and redox behavior. The modification of hexathiapillar[6]arene afforded five functionalized derivatives, which were studied structurally in detail. The findings revealed interesting redox and structural properties of the macrocycle and its derivatives including the formation of crystal lattices with continuous channels and empty voids.

D-π-A Structured Porphyrin and Organic Dyes with Easily Synthesizable Donor Units for Low-Cost and Efficient Dye-Sensitized Solar Cells.

This study aimed to develop low-cost D-π-A structured porphyrin and organic dyes with easily synthesizable donor units instead of the conventional complex multistep synthetic donor unit of Hexyloxy-BPFA [bis(7-(2,4-bis(hexyloxy)phenyl)-9,9-dimethyl-9H-fluoren-2-yl)amine] used in SGT-021 and SGT-149 as well-known record cosensitizers with an extremely high power conversion efficiency (PCE). The design strategy concerned the easier synthesis of low-cost donor units with inversion structures in donor groups via donor structural engineering, particularly by changing the position of the fluorene and phenylene units in the donor moiety while keeping the π-bridge and acceptor unit unchanged, leading to the synthesis of two D-π-A structured porphyrins [SGT-021(D0) and SGT-021(D)] and one D-π-A structured organic sensitizer [SGT-149(D)] for dye-sensitized solar cells (DSSCs). Specifically, porphyrin SGT-021(D0) incorporated two hexyl chains into the 9-position of each fluorene, while SGT-021(D) and SGT-149(D) substituted two hexyloxy chain units to the terminal position of each fluorene in the donor groups of porphyrin dyes. The effect of the position of the fluorene and phenylene units in the donor moiety on the photochemical and electrochemical properties, as well as the photovoltaic performance, was compared with the reference dyes of SGT-021 and SGT-149, previously reported by the research group. After optimizing the DSSC devices, SGT-021(D) and SGT-021(D0) achieved a high PCE of 11.6 and 10.5%, respectively, while SGT-149(D) exhibited a little lower PCE of 10.3% under the standard AM 1.5G light intensity. The cell performance of DSSC devices based on SGT-021(D) and SGT-149(D) was inferior to the corresponding reference dyes of SGT-021 and SGT-149 due to their lower donating ability of Hexyloxy-BPFA than Hexyloxy-BFPA.

A π‐Extension Process from 9‐Phosphaanthracene Leading to Phosphatetraphenes and Phosphatetracenes

AbstractExtension of π‐system with phosphinine (phosphorine, phosphabenzene) has been of interest because of the expected higher HOMO and lower LUMO levels compared with the corresponding carbon congeners. In this paper, a π‐extension process based on the 9‐phosphaanthracene skeleton was demonstrated by synthesizing 12‐phosphatetraphene and 9‐phosphabenzo[f]tetraphene by utilizing the deaminative aromatization pathway. Starting from 3,5‐bis(trifluoromethyl)aniline, we developed the dibromotriarylmethane precursors containing the 3,5‐bis(trifluoromethyl)‐2‐bromophenyl unit, which would be slightly effective to increase the steric congestion around the fragile P=C bonds incorporated in the fused polyaromatic skeletons. The bis‐trifluoromethyl 12‐phosphatetraphenes have been synthesized together with the mono‐trifluoromethyl derivative, and the planar 12‐phosphatetraphene skeleton was confirmed. On the other hand, the CF3‐substituted 9‐phosphabenzo[f]tetraphene displayed a remarkably twisted fused five ring system leading to the wavy structures incorporating phosphinine. Also, synthetic study of 5‐phosphatetracene using the bis(trifluoromethyl)phenyl unit was attempted and the incomplete elimination of the amine indicated labile characters of the observed phosphorus congener of tetracene. The findings of this study would be informative for developing heavier congeners of polyaromatic hydrocarbons (PAHs) as well as the trifluromethyl effects.

Excited state electronic structure and dynamics in diblock π-conjugated oligomers

The excited state electronic structure and ultrafast energy transfer in two diblock oligomers F3-TBT and F3-mP-TBT was explored (F3 = tri-(9,9-dioctylfluorene), TBT = 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole, mP = meta-phenylene). These diblock oligomers feature strongly coupled, π-conjugated F3 and TBT segments that have different bandgaps. F3-TBT is a fully π-conjugated chromophore in which the two conjugated segments are directly linked. By contrast, in F3-mP-TBT the chromophores are separated by a meta-linked phenylene unit. The objective of this study was to discern whether the Franck-Condon excited state produced by selective excitation of the F3 moiety in fully conjugated F3-TBT gives rise to a localized or fully delocalized excited state. The oligomers’ excited state dynamics were probed by steady-state UV–visible absorption, fluorescence and excitation wavelength dependent ultrafast time resolved transient absorption (TA) spectroscopy. Density functional theory (DFT) calculations were applied to provide insight concerning the electronic structure of the oligomers. The diblock oligomers feature distinct absorption bands due to transitions mainly localized on the F3 (high energy, 3.5 eV) and TBT (low energy, 2.75 eV) segments. Ultrafast TA spectroscopy with excitation corresponding to the low energy TBT unit reveals that the initial excitation is localized on TBT and does not vary with time. By contrast, in both oligomers excitation corresponding to high energy F3 produces an excited state that evolves rapidly (200–300 fs) into the lower energy state that is localized on the TBT chromophore. The ultrafast process is attributed to relaxation of an excited state that is predominantly localized on F3 into a lower energy state that is localized on TBT. The observation of an F3-localized excited state is unexpected for F3-TBT, given that the molecule is fully π-conjugated.

Fluoranthene-terminated terpyridine ensemble for fluorescence light up and ratiometric chemical sensor for multi toxic metals

A novel π-electron rich fluoranthene embellished with a phenyl spacer and coupled with terpyridine (TS1) was developed through Diels-Alder reaction. Single crystal X-ray structure evidences the variations in dihedral angles between the fluoranthene and the phenyl unit responsible for development of non-coplanar interactions and stabilized by a wave-like molecular packing in the crystal lattice with weak π-π interaction of 4.125 Å. The peripheral terpyridine of TS1 endows an efficient binding with multiple metal ions by colorimetric and fluorometric methods. TS1 exhibits a ratiometric fluorescence response from sky blue to yellow colour upon the addition of Zn2+ ions with a limit of detection (LOD) of 0.05 ppm. The other metal ions such as Cu2+, Co2+ and Fe2+ demonstrate fluorescence quenching behaviour with LODs of 0.1, 0.3 and 0.7 ppm, respectively. The intramolecular charge transfer (ICT) shows the variation in TS1 emission behaviour upon metal ions interaction and quantitatively discriminates the metal ion concentrations. TS1 conferred a visual colorimetric change from colourless to magenta, enabling naked-eye detection of Fe2+ and showing clear discrimination between Fe2+ and Fe3+ ions for the real-time water samples. Furthermore, we have investigated the effect of TS1 in Zebrafish larvae/embryos and cytotoxicity in human urinary tract transitional cell carcinoma cells (UM-UC-3).

A symmetrical carbazole/benzonitrile-based high triplet energy bipolar host designed by a para-linkage strategy for efficient blue and green phosphorescent organic light-emitting diodes

Based on a para-linkage concept, a symmetrical carbazole-benzonitrile derivative of 4-(9H-carbazol-9-yl)-3,5-diphenyl-2,6-difluoronitrile (CzPhFBN) was designed and prepared as a host for phosphorescent organic light-emitting diodes (PhOLEDs). In the CzPhFBN molecular, a cyano (CN) unit and a carbazole (Cz) unit were attached to the central phenyl ring at the para positions. Simultaneously, the Cz group was surrounded by two phenyl units to increase structure distortion for high triplet energy and CN unit was surrounded by two F units to improve electron transporting behavior. The photophysical properties and carrier transport behavior of CzPhFBN were investigated. The results demonstrated that CzPhFBN offered a high triplet energy of exceeding 3.0 eV and bipolar carrier transporting property. By incorporating CzPhFBN as the host, the blue FIrpic- and green Ir(ppy)3-based PhOLEDs with a common device configuration delivered the maximum efficiencies of 11.1%/19.7 cd A−1/12.1 lm W−1 and/13.1%/43.6 cd A−1/28.6 lm W−1, respectively. These results indicate that this study provides a potential design strategy of high triplet energy bipolar host materials with a simple and elegant structure.

Well‐Designed Highly Conjugated Covalent Organic Frameworks as Light Responsive Oxidase Mimic for Effective Detection of Uric Acid

Covalent organic frameworks (COFs) are widely used in photocatalysis due to their periodic π–π arrays, high crystallinity, and adjustable bandgap. Herein, a new strategy for integrating polyphenyl building blocks in COFs is presented to improve the photocatalytic efficiency. To implement this strategy, a series of COFs with different numbers of phenyl groups are successfully designed and synthesized. By varying the number of phenyl units in the precursor, the COFs exhibit different bandgaps, band‐edge positions, carrier mobilities, and interfacial transfer resistances. The corresponding characterization reveals that the photocatalytic capacity of COFs increases with the number of phenyls in the basic structural unit. Further, under visible light irradiation, the COFs prepared from 1,3,5‐tris [4‐amino(1,1‐biphenyl‐4‐yl)] benzene (TABB) and 1,4‐benzenedicarboxaldehyde (BDB) (named TABB‐BDB COF) exhibit superior light‐responsive oxidase‐mimicking characteristic, which can catalyze the oxidation of 2,2′‐azino‐bis (3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS). Based on the aforementioned characteristics, TABB‐BDB COF is designed as a robust colorimetric probe for the inexpensive, highly sensitive, and rapid detection of uric acid (UA) with a linear range of 5–160 mg L−1. This study not only demonstrates COFs‐based light‐response oxidase mimicking for efficient UA detection but also provides an intelligent tactic for boosting the photocatalytic competence of COFs.

The effect of oxygen bleaching on reactivity of syringyl and guaiacyl units of Eucalyptus tereticornis pulps lignin

Dioxin lignin of Eucalyptus tereticornis kraft pulps and its oxygen-treated pulps with kappa number 21.32, 12.84; 13.03, 12.18 were isolated and subjected to alkaline nitrobenzene oxidation studies to determine the structural changes during oxygen bleaching. HPLC quantitatively identified eight compounds during nitrobenzene oxidation of dioxin lignin in alkaline media. Lignin obtained from E. tereticornis has syringyl and guaiacyl units. Residual lignin composition in pulps was studied and found that during oxygen delignification, the syringyl unit was degraded more in comparison to guaiacyl and p-hydroxy phenyl unit, i.e., the molar ratio of syringyl unit is lower than guaiacyl and p-hydroxy phenyl unit. The results are adequately described in the research.

Substituent Effect on Stimuli-Responsive Donor–Acceptor Framework-Based 2-Thiohydantoins for Monitoring Nonanal Vapors

Tuning the π-conjugation and varying the functional units can improve the response behavior with superior sensitivity and selectivity. Herein, we report on five novel donor–acceptor (D–A) molecular ensembles developed through C5 substitution on 2-thiohydantoin (2TH) with π-conjugation having different electron-donating groups. The structure–property relationships were investigated by single-crystal X-ray diffraction (SC-XRD) analysis, photophysical, electrochemical, and computational studies. The structural influence of 2TH derivatives on surface interactions with volatile organic compounds (VOCs) were analyzed by binding affinities, kinetics, and other intrinsic parameters (work function, surface photovoltages (SPVs), and response and recovery times). N,N-diMeAPh-2TH exhibits mechanochromic and vapochromic behavior, shows red-shifted emission at ∼554 nm upon exposure to nonanal vapors with a visual color change from orange-red to brown, and shows vivid color variations with different VOCs. N,N-diMeAPh-2TH shows reversible vapochromic behavior as well. Ph-2TH, 4-OMePh-2TH, and 2,4-diOMePh-2TH exhibit n-type behavior with the greater SPV response achieved for Ph-2TH (90%), but good recovery (58%) in SPV in 439 s is observed in the case of 2,4-diOMePh-2TH. In contrast, 3,4-diOMePh-2TH and N,N-diMeAPh-2TH exhibit p-type behavior toward nonanal vapors with a high SPV response obtained for N,N-diMeAPh-2TH (94%) within 293 s as well as recovery (87%) in surface PVT in 692 s. The results demonstrate that electron-donating substituents −N(CH3)2 can improve sensing performance by increasing electron density, whereas steric hindrance on the phenyl unit can modulate sensing performance.

Difluoroborate-based bichromophores: Symmetry relaxation and two-photon absorption

Given potential applications of multiphoton absorbers, in the present work we have studied the symmetry-relaxation effects in one- and two-photon absorption spectra in two bichromophore systems based on difluoroborate core linked by biphenylene or bianthracene moieties. We have employed a palette of experimental methods (synthesis, one- and two-photon spectroscopy, X-ray crystallography) and state-of-the-art computational methods to shed light on how symmetry relaxation, a result of twisting of building blocks, affects one- and two-photon absorption of the two studied fluorescent dyes. Electronic-structure calculations revealed that the planarity of central biphenyl moiety, as well as deviations from planarity up to 30–40 deg., ensure maximum values of two-photon transition strengths. Perpendicular arrangement of phenylene units in biphenylene moiety leads to 20% drop in the two-photon transition strengths. More detailed studies demonstrated that equilibrium structures of both compounds in chloroform solution show very different values of two-photon absorption cross sections at absorption band maxima, i.e. 224 GM for and 134 GM for biphenyle and bianthracene linkers, respectively. The latter value is in good agreement with experimental value obtained using Z-scan method. The difference in two-photon absorption cross section between both compounds can be rationalized based on equilibrium geometry differences, i.e. interplanar angle is 35 deg and 91 deg in the case of biphenylene and bianthracene moiety, respectively. It is thus not beneficial to introduce conformationally locked central linker based on bianthracene moiety.

Near-Infrared Acceptors with Imide-Containing End Groups for Organic Solar Cells.

Near-infrared electron acceptors for organic solar cells (OSCs) mostly contain electron-withdrawing 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC) end groups, which can be modified by but limited to phenyl, thienyl, and naphthyl units with halogenated, methyl, and methyloxy substitution. In this work, we employed an imide-containing unit to construct a new IC end group, based on which a series of new electron acceptors were synthesized. The strong electron-deficient nature of imide units enables the new acceptors to show efficient intramolecular charge transfer and hence red-shifted absorption spectra compared to their IC counterparts. These new electron acceptors were applied to OSCs, providing efficiencies of over 17% with a low voltage loss of 0.52 eV. These results demonstrate that the new imide-containing end groups are promising fragments for the construction of near-infrared electron acceptors for high-performance OSCs.

Synthesis of novel phenothiazine, phenoxazine and carbazole derivatives via Suzuki-Miyaura reaction

The Suzuki-Miyaura cross-coupling reaction was utilized for the synthesis of 15 new compounds containing phenothiazine (PTZ), phenoxazine (POZ), carbazole (Cz), and triphenylamine (TPA) as good electron donors. The synthesized compounds were furnished with active carbaldehyde groups and decorated with phenyl, thienyl, furyl, imidazolyl, or oxadiazolyl units linked to either one or two sides of the central cores (PTZ, POZ, and Cz). A simple catalytic systems based on Pd(PPh3)4 were tried and the results showed better CC coupling efficiencies of the electron-rich phenothiazine halides over phenoxazine and carbazole analogues when coupled with either electron-rich or electron-deficient boronic acid precursors. Besides, the coupling process of substituted phenothiazine halides with different boronic acids precursors, based on phenyl (Ph), furyl (Fu) and thienyl (Th) units, was found to be dependent on the electronic nature of both PTZ-halide and boronic acid precursors. Coupling efficiency of Ph, Fu, and Th rings with the skeleton of imidazolyl-PTZ-Br coupler to bring up compounds 6a-c showed the order: Ph>Fu>Th (with the yield of 86, 85, and 80%, respectively), while coupling efficiency of the brominated PTZ-oxadiazolyl-phenyl coupler with different arylboronic acids showed the order of Th>Ph>Fu to obtain compounds 8a-c. Additionally, the TPA derivative 11b was obtained with an excellent yield of 96% using Pd(PPh3)4 . The successful activation of the synthesized derivatives with carbaldehyde groups and the integration of different spacers made them substantially suitable to be exploited as promising intermediates for the future synthesis of versatile π-conjugated systems.

A silane-based host material with improved electron transport properties for phosphorescent OLEDs with high efficiency and low efficiency roll-off

A dibenzosilole-based host material was designed and characterized. The host material, 9,9′-(5,5-diphenyl-5H-dibenzo[b, d]silole-2,8-diyl)bis(9H-carbazole) (S-SiCz), was designed to enhance the electron transport properties and rigidity by coupling two phenyl units of the tetraphenyl silane of a strong hole transport type bis(4-(9H-carbazol-9-yl)phenyl)diphenylsilane host. The device efficiency roll-off was improved considerably by balancing the carriers in the phosphorescent organic light-emitting diodes (PhOLEDs), and the driving voltage at high luminance was reduced. The red and green PhOLEDs exhibited high external quantum efficiencies (EQEs) of 23.8% and 24.9%, respectively, and a relieved efficiency roll-off. In addition, S-SiCz was used as an electron transport type host with a hole transport type 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl host. The maximum EQEs of the red and green PhOLEDs using the mixed host were 26.0% and 25.5%, respectively, and EQE roll-off values were 18% and 6%, respectively. Therefore, the planarization design strategy of the host is effective for better device performance.

Understanding the electronic pi-system of 2D covalent organic frameworks with Wannier functions

We investigate a family of hexagonal 2D covalent organic frameworks (COFs) with phenyl and biphenyl spacer units and different chemical linker species. Chemical trends are elucidated and attributed to microscopic properties of the pi-electron-system spanned by atomic p_z-orbitals. We systematically investigate the electronic structure, delocalization of electronic states, effects of disorder, bond torsion, and doping, and correlate these with variable pi-conjugation and nucleus-independent chemical shift (NICS) aromaticity. Molecular orbitals are obtained from maximally localized Wannier functions that have sigma- and pi-character, forming distinct sigma- and pi-bands for all valence states. The Wannier-orbital description goes beyond simple tight-binding models and enables a detailed understanding of the electronic topology, effective electronic coupling and delocalization. It is shown that a meaningful comparison between COFs with different chemical elements can only be made by examining the entire pi-electron system, while a comparison of individual bands (e.g., bands near the Fermi energy) can be a insufficient to derive general design rules for linker and spacer monomer selection. We further identify delocalized states that are spread across tens or hundreds of pores of the 2D COFs and analyze their robustness against structural and energetic disorders like out-of-plane rotations of molecular fragments, different strength of energetic disorder and energetic shifts due to chemical doping.