Central Phenyl Research Articles

Unique Organic Crystal Skeleton Based on N-Phenyl-Carbazole Derivatives with Adjustable Room Temperature Phosphorescence and Highly Stable Inclusion Ability to Dichloromethane.

Monosubstituted 9-(2-bromophenyl)-carbazole (1Br1CZ) and disubstituted 9,9'-(2,4-dibromo-1,3-phenylene) bis(9H-carbazole) (2Br2CZ) are synthesized by introducing bromine into ortho-phenyl position of 9-phenyl-carbazole (PhCZ). The decomposition temperature with 5% mass loss and melting point of 2Br2CZ crystal are 360 and 230°C. The highest occupied molecular orbital energy level of PhCZ is the highest, and that of 2Br2CZ is the lowest. The crystals of PhCZ, 1Br1CZ, and 2Br2CZ are monoclinic, orthorhombic, and triclinic system, which exhibit room temperature phosphorescence with lifetimes of 171.81, 37.15, and 28.77ms, and their corresponding phosphorescence quantum yields are 0.83%, 0.16%, and 4.58%. It theoretically reveals that six triplet energy levels (T1-T6) exist under S1 in 2Br2CZ crystal, and the spin orbit coupling constants between S1 and Tn in 2Br2CZ are also greater than those in PhCZ and 1Br1CZ, which promotes the intersystem crossing. Meanwhile, through crystal structure and Hirshfeld surface analysis, the torsion angles between the carbazole unit of 2Br2CZ and the central phenyl group reached 85.28°. The 2Br2CZ crystal exhibits the richest intermolecular interactions. A cavity of 4.498Å is formed within the crystal skeleton of 2Br2CZ, which can precisely fixe dichloromethane with a record-high desorption temperature over 145°C.

Synthesis of four-ring unsymmetrical bent-core mesogens and cybotactic cluster formation in their nematic phase

The synthesis and characterization of novel achiral unsymmetrical four-ring bent-core molecules resembling a hockey-stick shape are described. The present compounds bearing a methyl substituent in the central phenyl ring exhibit the skewed cybotactic nematic (NcybC), smectic C (SmC) and additional tilted smectic phase with tilted molecular arrangement. The skewed cybotactic nematic phase is formed by the bent-core molecules with long range orientational ordered clusters possessing local smectic C type order and within a cluster of tilted molecular assembly. The previously reported four-ring compounds without the methyl moiety did not exhibit nematic phase but show polarization modulated B1revtilt phase. The x-ray diffraction pattern clearly indicated the existence of SmC-type cybotactic clusters over a wide N temperature range; the layer reflection peak is weak at a higher temperature region and becomes more conspicuous with decreasing temperature. The lower temperature phase is distinctly the SmC phase, and in addition another tilted smectic phase emerges below SmC.

Regularly Tuning Quantum Interference in Single‐Molecule Junctions through Systematic Substitution of Side Groups with Varied Electron Effects†

Comprehensive SummaryInvestigating the quantum interference effect in single molecules is essential to comprehensively understand the underlying mechanism of single‐molecule charge transport. In this study, we employed the mother molecule m‐OPE and introduced a series of side groups with various electronic effects at the 2‐position of the central phenyl ring, creating four daughter m‐OPE derivatives. The single molecular conductivities of these molecule wires were measured using the scanning tunneling microscope breaking junction technique. Our findings demonstrate that the substitutions regularly modulate the destructive quantum interference occurring within the m‐OPE molecules. By combining optical and electrochemical investigations, along with density functional theory computations, we discover that the conductivity of the molecules corresponds to the electron‐donating/withdrawing ability of the substituents. Specifically, by adjusting the electron structures of the molecular backbone, we can systematically tailor the destructive quantum interference in the m‐OPE molecules.

The influence of molecular shape and electronic properties on the formation of the ferroelectric nematic phase

ABSTRACT The synthesis and characterisation of two series of ferroelectric nematogens based on RM734 having an additional methoxy group on the central phenyl ring are reported, the 3-methoxy-4-((4-nitrophenoxy)carbonyl)phenyl 2-alkoxy-4-alkoxybenzoates (7-m-n) and the 3-methoxy-4-((3-fluoro-4-nitrophenoxy)carbonyl)phenyl 2-alkoxy-4-alkoxybenzoates (8-m-n). In order to compare the behaviour of these series to those of the corresponding materials that do not contain the methoxy group on the central phenyl ring, we also report the synthesis and characterisation of 4-[(4-nitrophenoxy)carbonyl]phenyl 4-methoxybenzoate (11-0-1), 4-[(3-fluoro-4-nitrophenoxy)carbonyl]phenyl 4-methoxybenzoate (12-0-1) and 4-[(3-fluoro-4-nitrophenoxy)carbonyl]phenyl 2,4-diethoxybenzoate (12-2-2). Two compounds in which a lateral ethoxy chain is attached to the central ring, 3-ethoxy-4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (18-2-1) and 3-ethoxy-4-[(3-fluoro-4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (19-2-1), are also described. The behaviour of these materials shows that the relative stabilities of the ferroelectric nematic, NF, and conventional nematic, N, phases are governed by a subtle interplay of steric and electronic factors. Furthermore, the electronic factors are better understood in terms of isolated regions of electron density rather than by a single large longitudinal dipole moment. In terms of molecular shape, to observe the NF phase it appears that the molecular structure must include one or more lateral substituents that enhance molecular biaxiality and destabilise the N phase.

A stable 3D Sr-MOF as an efficient heterogeneous catalyst for the cycloadditions of CO2 and knoevenagel condensation reactions

The catalytic activity of MOF is determined not only by its unique structure but also by the active sites from metal sites and functional ligands. A sTable 3D strontium complex, {[Sr2(BTCB)Cl(H2O)2]}n (Sr-BTCB), was synthesized under solvothermal condition. It is assembled with an amide-functionalized tricarboxylic acid and a Sr(II)-based infinite chain, where Sr2 repeating units are arranged sequentially. Two such 3D structures are interwoven to create a two-folded interpenetrated structure. The interpenetrated structure is strengthened by π-π interstacking between the central phenyl rings of ligands from different 3D structures. After solvent exchange and vacuum drying, the surface of nanochannels in desolvated Sr-BTCB is modified by unsaturated Sr2+ions. Complex Sr-BTCB has abundant Lewis acidic metal sites and Lewis basic sites of amide groups, as well as 1D rhombic channels. It exhibits excellent stability and heterogeneous catalysis on CO2 fixation reactions into cyclic carbonates and Knoevenagel condensation reactions of aldehydes and malononitrile.

Dinuclear tricarbonylrhenium(I) complexes: impact of regioisomerism on the photoluminescence properties.

Dinuclear Re(I) complexes have proportionally been much less studied than mononuclear analogues. In particular, very little information is available about their solid-state emission properties. In this work, two structural isomers of dinuclear complexes (Bi-Re-metaPhe and Bi-Re-paraPhe), which differ by the relative position of the coordination spheres on a central phenyl ring, were synthesized and compared with each other and with the parent mononuclear compound (Mono-Re-Phe), from a theoretical and experimental point of view. In solution, the electronic, electrochemical and spectroscopic properties of the dinuclear complexes were almost identical, and rather close to those of the monomer. In the solid state, the photoluminescence (PL) efficiency of dimers was not higher than that of the monomer, but a clear mechanoresponsive luminescence (MRL) effect appeared only for the former ones. The positional isomerism influenced the amplitude of this effect, as well as the aggregation-induced emission (AIE) properties in a water-acetonitrile mixture. This study reveals the importance of positional isomerism to modulate the emission properties in the solid state. It also shows the advantage of dinuclear structures to access new MRL-active materials.

How substituents tune quantum interference in meta-OPE3 molecular junctions to control thermoelectric transport.

Quantum interference (QI) can strongly affect electric and thermoelectric properties of molecular junctions (MJs). So far, however, a limited number of experimental studies have explored the influence of QI on thermoelectric transport in MJs. To address this open point, we synthesized derivatives of meta-OPE3 with an electron-withdrawing nitro (-NO2) substituent or an electron-donating N,N-dimethyl amine (-NMe2) substituent, attached at two different positions of the central phenylene ring, and systematically studied the electrical conductance and thermopower of the corresponding gold-molecule-gold junctions. We show that (i) the electrical conductance of MJs depends weakly on the polarity of the substituents but strongly on the substitution position and (ii) MJs with the N,N-dimethyl amine group feature a higher thermopower than MJs with the nitro group. We also present calculations based on first principles, which explain these trends and show that the transport properties are highly sensitive to microscopic details in junctions, exhibiting destructive QI features.

Molecular Conformations of Shape Anisometrically Variant Mesogens in Liquid Crystalline Phase Studied by 13C NMR Spectroscopy.

Mesogens that vary in shape anisometry have been investigated by 13C solid-state NMR in the liquid crystalline phase to inspect the conformations. The molecules examined comprise of (i) rod-like mesogen with three-phenyl ring core and terminal hexyloxy chains, (ii) three-ring core linked to the fourth phenyl ring via a spacer, and (iii) trimesic acid connected to three side arms core units through a spacer. The order parameter (Szz) values for the phenyl rings of the rod-like mesogen are 0.65-0.68, while the mesogen with a three-ring core linked to a phenyl ring via spacer showed dissimilarity. Consequently, for the core unit's phenyl rings, Szz is ~ 0.70, and the terminal phenyl ring showed a low value of 0.12. For the trimesic acid based mesogen, the Szz value for the side arm phenyl rings is ~ 0.53, and for the central phenyl ring, a very low value of 0.11 is witnessed. By considering the ordering of the rod-like mesogen as a yardstick and employing the ratios of Szz values of the phenyl rings, the average conformations of other mesogens are arrived. Accordingly, for the trimesic acid based mesogen, a tripod-like conformation instead of l shape is proposed in the liquid crystalline phase.

3D-VAT printing of nanocomposites by photopolymerisation processes using amino-meta-terphenyls as visible light-absorbing photoinitiators

ABSTRACT In this article, the application of 10 new amino-m-terphenyls in 3D-VAT printing was described. New compounds have specially designed D-π-A structure, where the central phenyl ring with nitrile and amino groups is the acceptor and the modifiable amino group is donor. Such design eliminates problem with acid scavenging and guaranteed desire properties and photoactivity as well as it allows further development of such system for 3D-VAT printing. Efficient excitation with intramolecular charge transfer provides excellent absorption and electrochemical properties, which can be tuned by modification of the amino group. The design allows photoinitiation of free radical, hybrid and especially cationic polymerisation even at 455 nm with more than 70% of monomer conversion. Such properties allow to use the developed compounds as efficient visible light photoinitiators for 3D printing of nanocomposite materials. The terphenyls can efficiently cure resins containing CuO and Al2O3 nano additives leading to high-resolution 3D prints.

Syntheses, Characterization and X-ray Crystal Structure of Trinuclear NiII—NaI—NiII Assembled with Salen-type Schiff Base

The present investigation describes the synthesis and structural study of a metal-zinc ligand [NiL].H2O, which was used to generate a trinuclear complex formulated as {Ni(m-L)Na(m-L)Ni}.(SCN)0.6.(Cl)0.4. The title compound crystallizes in the tetragonal space group I41/acd with the following unit cell parameters: a = 185403(5) Å, c = 51.925(2) Å, V = 17849.0(3) Å3, Z = 16, R1 = 0.074 and wR2 = 0.209. Each organic molecule acts as a hexadentate ligand and bridges Ni(II) and Na(I). For both Ni(II) cations the coordination environment around the metal center can be described as distorted square planar. The Na(I) cation is eight coordinated and the polyhedron around the sodium ions is best described as a distorted square anti-prism. The means planes of the two phenyl rings with a methoxy substituent form a dihedral angle of 3.870(4)°, while the dihedral angle values of these mean planes with the means plane of the central phenyl ring are, respectively, 11.233(4)° and 14.138(3)°. The Zn–Na distance is 3.4285(7) Å. Weak hydrogen bonds involving C—H as donor and Cl, S or O as acceptor are observed.

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.

C–H Metalation of Terpyridine Stereoisomers with Ni(II), Pd(II), and Pt(II)

Ni(II), Pd(II), and Pt(II) complexes [M(Y-terpy)X] (X = Cl or Br) containing the tridentate N^C^N-cyclometalating 2,3′:5′,2″and 2,2′:4′,2″ stereoisomers of the well-known tridentate N^N^N ligand 2,2′:6′,2″-terpyridine (terpy) were synthesised in moderate to good yields through C–H activation. For the Pt complexes, the phenyl ethynide derivatives [Pt(Y-terpy)(C≡CPh)] were also obtained under Sonogashira conditions. In contrast to this, C^N^N cyclometalated complexes using the 2,2′:6′,3″- and 2,2′:6′4″-terpy isomers were not obtained. Comparison of the N^C^N complexes of the cyclometalated 2,3′:5′,2″- and 2,2′:4′,2″-terpy ligands with complexes [M(dpb)Cl] of the prototypical N^C^N cyclometalating ligand dpb− (Hdpb = 2,6-diphenyl-pyridine) showed higher potentials for the terpy complexes for the ligand-centred reductions in line with the superior π-accepting properties of the terpy ligands compared with dpb. Metal-centred oxidations were facilitated by the dpb ligand carrying a central σ-donating phenyl group instead of a metalated pyridine moiety. The same trends were found for the long-wavelength absorptions and the derived electrochemical and optical band gaps. The lower σ-donating capacities of the cyclometalated terpy derivatives is also confirmed by a reduced trans influence in the structure of [Ni(2,3′:5′,2″-terpy)Br0.14/OAc0.86]. Attempts to re-crystallise some poorly soluble Pd(II) and Pt(II) complexes of this series under solvothermal conditions (HOAc) gave two structures with N-protonated cyclometalated pyridine moieties, [Pt(2,3′:5′,2″-terpyH)Cl].Cl and [Pd(2,3′:5′,2″-terpyH)Cl2].

Molecular Shape, Electronic Factors, and the Ferroelectric Nematic Phase: Investigating the Impact of Structural Modifications.

The synthesis and characterisation of two series of low molar mass mesogens, the (4-nitrophenyl) 2-alkoxy-4-(4-methoxybenzoyl)oxybenzoates (NT3.m) and the (3-fluoro-4-nitrophenyl) 2-alkoxy-4-(4-methoxybenzoyl)oxybenzoates (NT3F.m), are reported in order to investigate the effect of changing the position of a lateral alkoxy chain from the methoxy-substituted terminal ring to the central phenyl ring in these two series of materials based on RM734. All members of the NT3.m series exhibited a conventional nematic phase, N, which preceded the ferroelectric nematic phase, NF , whereas all the members of the NT3F.m series exhibited direct NF -I transitions except for NT3F.1 which also exhibited an N phase. These materials cannot be described as wedge-shaped, yet their values of the ferroelectric nematic-nematic transition temperature, T , exceed those of the corresponding materials with the lateral alkoxy chain located on the methoxy-substituted terminal ring. In part, this may be attributed to the effect that changing the position of the lateral alkoxy chain has on the electronic properties of these materials, specifically on the electron density associated with the methoxy-substituted terminal aromatic ring. The value of TNI decreased with the addition of a fluorine atom ortho to the nitro group in NT3F.1, however, the opposite behaviour was found when the transition temperatures of the NF phase were compared which are higher for the NT3F.m series. This may reflect a change in the polarity and polarizability of the NT3F.m series compared to the NT3.m series. Therefore, it is suggested that, rather than simply promoting a tapered shape, the role of the lateral chain in inhibiting anti-parallel associations and its effect on the electronic properties of the molecules are the key factors in driving the formation of the NF phase.

Colorless polyimides derived from rigid trifluoromethyl-substituted triphenylenediamines

Colorless polyimides (CPIs) have wide applications in flexible photoelectric devices, thanks to their high transparency and heat-resistance. Herein, three rigid aromatic triphenylenediamine monomers containing varied number and position of trifluoromethyl (-CF3) substituents, i.e., c-3FTP, c-6FTP, and s-6FTP, were designed. The corresponding CPI films were fabricated by polycondensation with the commercial 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) or 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA). Due to the steric hindrance of –CF3 groups, three diamines all exhibit large torsion angles within 46.1°–87.1° between benzene rings determined via single crystal analysis. The structure-property analysis reveals that –CF3 substitution located on the central phenyl ring facilitates the high glass transition temperature (Tg), while more –CF3 substitutions are beneficial for high optical transparency. Among all the CPIs, the 6FDA/c-6FTP film exhibits the most remarkable balance in thermal, optical, and dielectric properties, including high thermal resistance (Tg = 385 °C, Td5% = 537 °C), excellent optical transparency (λcutoff = 350 nm, T450 = 84.5%, and b* = 1.44), low dielectric nature (Dk = 2.84, Df = 0.0053) at 10 GHz, and high surface hydrophobicity (θ = 100°, WH2O = 0.25%). This systematic study would complement the basic structure-property relationship of aromatic CPIs and inspire rational development of high-performance aromatic CPI materials toward applications in flexible display or 5G technology.

Substituent-Guided Cluster Nuclearity for Tetranuclear Iron(III) Compounds with Flat {Fe4(μ3-O)2} Butterfly Core

The tetranuclear iron(III) compounds [Fe4(μ3-O)2(μ-LZ)4] (1-3) were obtained by reaction of FeCl3 with the shortened salen-type N2O2 tetradentate Schiff bases N,N'-bis(salicylidene)-o-Z-phenylmethanediamine H2LZ (Z = NO2, Cl and OMe, respectively), where the one-carbon bridge between the two iminic nitrogen donor atoms guide preferentially to the formation of oligonuclear species, and the ortho position of the substituent Z on the central phenyl ring selectively drives towards Fe4 bis-oxido clusters. All compounds show a flat almost-symmetric butterfly-like conformation of the {Fe4(μ3-O)2} core, surrounded by the four Schiff base ligands, as depicted by both the X-ray molecular structures of 1 and 2 and the optimized geometries of all derivatives as obtained by UM06/6-311G(d) DFT calculations. The strength of the antiferromagnetic exchange coupling constants between the iron(III) ions varies among the three derivatives, despite their magnetic cores remain structurally almost unvaried, as well as the coordination of the metal ions, with a distorted octahedral environment for the two-body iron ions, Feb, and a pentacoordination with trigonal bipyramidal geometry for the two-wing iron ions, Few. The different magnetic behavior within the series of examined compounds may be ascribed to the influence of the electronic features of Z on the electron density distribution (EDD) of the central {Fe4(μ3-O)2} core, substantiated by a Quantum Theory of Atoms In Molecules (QTAIM) topological analysis of the EDD, as obtained by UM06 calculations 1-3.

Synthesis and molecular structure of V-shaped liquid crystalline compounds: Spectroscopic, mesomorphic, DFT investigations, electrochemical and fluorescence studies

A series of V-shaped compounds consisting of a central phenyl core connected by two identical mesogenic units which possess the imine (C=N) and ester (COO) bonds along with the terminal alkoxy chain (-OCnH2n+1) where n = 6-12. The ultimate compounds were synthesised and characterized by CHN elemental analysis, Fourier-Transform Infrared (FT-IR), nuclear magnetic resonance (1H-NMR), and UV-Visible (UV-Vis) spectroscopic techniques. The mesomorphic properties, thermal behaviour and conformation of compounds were studied by using polarised optical microscopy (POM), and differential scanning calorimetry (DSC). It can be generalized from present study that the V-shaped compounds with odd n carbon number in alkoxy chains were non-mesogenic. Whilst the compounds with shorter alkoxy chains of n = 6 and 8 were monotropic nematic, the compounds which possess longer alkoxy chains (n = 10 and 12) exhibited enantiotropic nematic phase. The computational method Chem3D Pro suggests the molecular structures of all the compounds with even n carbon number in the alkoxy chain. The Gaussian calculation with B3LYP/6-31G+(d,p) condition was employed to further demonstrate the chemical reactivity for all target compounds based on HOMO-LUMO analysis, the energy difference between HOMO-LUMO and surface charges. The target molecules of which the member containing the even n parity along the mesogenic arms have shown the same trend of electrocatalytic behaviour particularly toward the detection of hydrogen peroxide via the cyclic voltammetry study. Furthermore, the member with n=12 has been validated as a remarkable fluorogenic probe for the detection of Zn2+ ion.

Partner effect in accelerating pincer-co catalyzed nitrile hydroboration reactions.

The pincer-Co catalyzed nitrile hydroboration of nitrile has been presented as an elegant strategy to afford amine synthesis; however, ligand engineering is required. We show here a strategy to tune the catalytic behavior of the organometallic catalyst, as an alternative approach to ligand engineering, by means of computational investigations to understand the effect of partners such as (18-crown-6)K+, W(CO)3 and W(PMe3)3 on the reactivity of the pincer-Co catalyzed nitrile hydroboration reaction through π-coordination to the ligand aromatic ring. The extra additives bind the central phenyl ring of the ligand by either dispersion or chemical bonding. The electron-richness of the cobalt center is tuned by the partner, and follows the order (18-crown-6)K+ > W(PMe3)3 > no partner > W(CO)3. While the influence of the covalent W-containing partners parallels the electron-richness of the W, the non-covalent partner, (18-crown-6)K+, surprisingly increases the donor ability of the pincer ligand through the polarization effect. All the elementary steps involved in the nitrile hydroboration reaction are influenced by the partner, and the overall barrier is lowered by a surprisingly large amount of 4.9 kcal mol-1 in the presence of (18-crown-6)K+, suggesting a notable partner effect to be explored by experimentalists so that the reactivity of a catalyst can be tuned without ligand modification.

Molecular Design Principles to Elongate the Metal-to-Ligand Charge Transfer Excited-State Lifetimes of Square-Planar Nickel(II) Complexes.

Square-planar NiII complexes and their electronically excited states play key roles in cross-coupling catalysis and could offer new opportunities to complement well-known isoelectronic PtII luminophores. Metal-to-ligand charge transfer (MLCT) excited states and their deactivation pathways are particularly relevant in these contexts. We sought to extend the lifetimes of 3MLCT states in square-planar NiII complexes by creating coordination environments that seemed particularly well adapted to the 3d8 valence electron configuration. Using a rigid tridentate chelate ligand, in which a central cyclometalated phenyl unit is flanked by two coordinating N-heterocyclic carbenes, along with a monodentate isocyanide ligand, a very strong ligand field is created. Bulky substituents at the isocyanide backbone furthermore protect the NiII center from nucleophilic attack in the axial directions. UV-Vis transient absorption spectroscopies reveal that upon excitation into 1MLCT absorption bands and ultrafast intersystem crossing to the 3MLCT excited state, the latter relaxes onward into a metal-centered triplet state (3MC). A torsional motion of the tridentate ligand and a NiII-carbon bond elongation facilitate 3MLCT relaxation to the 3MC state. The 3MLCT lifetime gets longer with increasing ligand field strength and improved steric protection, thereby revealing clear design guidelines for square-planar NiII complexes with enhanced photophysical properties. The longest 3MLCT lifetime reached in solution at room temperature is 48 ps, which is longer by a factor of 5-10 compared to previously investigated square-planar NiII complexes. Our study contributes to making first-row transition metal complexes with partially filled d-orbitals more amenable to applications in photophysics and photochemistry.

Central condensed ring changes for manipulating the self-assembly and photophysical behaviors of cyanostilbene-based hexacatenars

Two series of condensed ring hexacatenars consisting of a central naphthalene/anthracene and two cyanostilbene units as the π-conjugated rigid core were reported. The thermodynamics behaviors and liquid crystalline structures of these mesogens were investigated by the combination of POM, DSC and XRD. It is indicated that only higher naphthalene-based homologues exhibit hexagonal columnar phases, the other lower naphthalene-based homologues and all the anthracene-based homologues are non-mesogens. The results demonstrated that the steric effect provided by the larger central aromatic group hinders the ordered molecular stacking. The temperature-dependent fluorescence demonstrated that the fluorescence stability of these hexacatenars increased from central phenyl via naphthyl to anthryl due to the increased degree of molecular distortions induced by the central larger aromatic group. The solvatochromism and AIEE behaviors were also studied by UV–vis absorption, fluorescence emission and density functional theory (DFT) demonstrating that the anthracene-based compounds exhibit more distinct solvatochromism, higher fluorescence quantum yield than those of naphthalene-based compounds and more distinct ICT effect, and both series of compounds exhibited strong fluorescence in both solutions and aggregated state due to ICT effect and the long π-conjugated aromatic core with twisted conformations. Additionally, photoisomerization behaviors demonstrated both cis and trans conformations showed high stability in condensed and solution states.

Intrinsically-ionic donor-acceptor molecules featuring thermally-activated delayed fluorescence for high-performance host-guest blue light-emitting electrochemical cells

High-performance blue light-emitting electrochemical cells (LECs) have remained a formidable challenge. Ionic donor–acceptor molecules, especially those featuring thermally-activated delayed fluorescence (TADF), are promising hosts for developing high-performance blue LECs, but such hosts have remained undeveloped. Here, we report two intrinsically-ionic donor–acceptor molecules, 1-(3-(4-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)-6-phenylpyrimidin-2-yl)phenyl)-3-ethyl-1H-imidazol-3-ium hexafluorophosphate (H1) and 1-(3-(4-(2-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)-6-phenylpyrimidin-2-yl)phenyl)-3-ethyl-1H-imidazol-3-ium hexafluorophosphate (H2), and their use as hosts for high-performance blue LECs. 3,6-di-tert-butylcabazole and imidazolium-substituted 2,4-diphenylpyrimidine are used as the donor and acceptor, respectively, which are located para (for H1) or ortho (for H2) to each other on the central phenyl linker. While H1 shows a low triplet energy (<2.6 eV), a large singlet–triplet energy gap (ΔEST) (>0.4 eV) and no TADF, H2 exhibits a high triplet energy (>2.8 eV), a small ΔEST (∼0.2 eV) and distinct TADF, due to its twisted donor–acceptor conformation. Both H1 and H2 show excellent electrochemical stability. Host-guest blue LECs using H2 as the host and a phosphorescent cationic Ir(III) complex as the guest afford sky-blue electroluminescence with high blue-color stability and peak brightness/peak external quantum efficiency/half-lifetime at 1078 cd m−2/8.6%/66 min under a constant-current driving. Upon adding LiPF6 into the active layer, a half-lifetime of ∼ 2 h is achieved at 918 cd m−2. These performances are the highest for host–guest blue LECs reported so far. The efficiencies and operational stability achieved at the high brightness are also the highest for blue LECs with inert-metal cathodes reported so far.