Terminal Benzene Rings Research Articles

Helix-to-Disc Conversion of Thia[6]helicenes into Coronenes Facilitated by Sulfur Oxidation and Fluorination.

Helicenes, with their unique helical structures, have long captured the interest of synthetic chemists, not only as end products, but also as versatile platforms for further chemical transformations. However, transforming [6]helicene into planar coronene typically requires harsh conditions and poses significant challenges. Herein, we demonstrate that replacing the terminal benzene ring of [6]helicene with a thiophene ring enables its photochemical transformation into coronene. Sulfur oxidation of the thiophene ring enables the corresponding thermal transformation, and the terminal tetrafluorination of the opposite benzene ring further accelerates this process, yielding 1,2-difluorocoronene, as confirmed by X-ray crystallography. The transformation begins with an intramolecular Diels-Alder reaction, whose activation energy is significantly lowered by these structural changes. Our findings underscore the utility of strategic modifications such as sulfur oxidation and fluorination in promoting this "helix-to-disc" conversion and opening new avenues for synthesizing functional polycyclic aromatics.

Stereoelectronic Switches of Single-Molecule Junctions through Conformation-Modulated Intramolecular Coupling Approaches.

Stereoelectronic effects in single-molecule junctions have been widely utilized to achieve a molecular switch, but high-efficiency and reproducible switching remain challenging. Here, we demonstrate that there are three stable intramolecular conformations in the 9,10-diphenyl-9,10-methanoanthracen-11-one (DPMAO) systems due to steric effect. Interestingly, different electronic coupling approaches including weak coupling (through-space), decoupling, and strong coupling (through-bond) between two terminal benzene rings are accomplished in the three stable conformations, respectively. Theoretical calculations show that the molecular conductance of three stable conformations differs by more than 1 order of magnitude. Furthermore, the populations of the three stable conformations are highly dependent on the solvent effect and the external electric field. Therefore, an excellent molecular switch can be achieved using the DPMAO molecule junctions and external stimuli. Our findings reveal that modulating intramolecular electronic coupling approaches may be a useful manner to enable molecular switches with high switching ratios. This opens up a new route for building high-efficiency molecular switches in single-molecular junctions.

Synthesis and Characterization of Conjugated Polymers Based on Thieno[3,4‐b]Thiophene Quinoidal Unit

AbstractDriven by the success of quinoidal units for enabling high‐performance polymer semiconductors, herein a new quinoidal building block that terminated by indandione is reported. By introducing Br atoms into the terminal benzene rings of indandione, two CPs, P2TbTI‐DPP and P2TbTI‐TIID, are synthesized through Stille polycondensation. The strong electron‐withdrawing ability of indandione‐terminated quinoidal unit enables P2TbTI‐DPP and P2TbTI‐TIID with low‐lying LUMO energy levels of ≈–3.90 eV. Organic thin‐film transistors based on P2TbTI‐DPP and P2TbTI‐TIID exhibit n‐type transport behavior. Besides, it is found that the electron mobility of these two polymers is weakly dependent on the annealing temperature due to the near‐amorphous of polymer thin‐film.

Preparation of Laterally Chloro-Substituted Schiff Base Ester Liquid Crystals: Mesomorphic and Optical Properties

A new class of Schiff base/ester compounds: ICln, 4-((2′-chlorophenylimino)methyl)phenyl-4″-alkoxy benzoates, were synthesized and their mesophase characteristics and thermal behavior were evaluated. Differential scanning calorimetry (DSC) was used to study mesophase transitions, and polarized optical microscopy was carried out to identify the phases (POM). The results show that all compounds are monomorphic, and enantiotropic nematic (N) phases were seen at all side chains. It was found that lateral Cl atoms in the terminal benzene ring influence both conformation and mesomorphic properties. Comparisons between the present investigated lateral Cl derivatives and their laterally neat, as well as their isomeric, compounds have been briefly discussed. Results revealed that the insertion of lateral Cl substituent in the molecular structure impacts the type and stability of the formed mesophases. The exchanges of the ester-connecting moiety improve their thermal nematic stability than their previously prepared structurally isomeric derivatives. These compounds exhibit a broad absorption in the UV-Visible region, including a peak in UV region and a tail around 550 nm, and there were observed to be absorption tail increases and energy band gap decreases with the increase of the alkoxy side chain length. The photoluminescence (PL) intensity was noted to be quenched for the bulky alkoxy group ascribed to non-radiative recombination through the defect states. Moreover, time resolved fluorescence decay spectra reveal that both the radiative and non-radiative recombination lifetime increases with the increase of alkoxy side chain length.

Synthesis of two optically active V-shaped molecules: Investigating the correlation between the stacking angle and chiroptical properties

This study demonstrates the synthesis of two optically active V-shaped molecules using enantiopure pseudo-ortho- and pseudo-meta-disubstituted [2.2]paracyclophane as the chiral building blocks. Both consist of the same π-electron system (p-phenylene-ethynylene containing three benzenes) stacked at the terminal benzene rings with stacking angles of 60° and 120°, respectively. The chiroptical properties, particularly the circularly polarized luminescence behavior, of the molecule with a stacking angle of 60° were better than those of its counterpart, and these results were confirmed via theoretical studies. A correlation exists between the chiroptical properties and stacking angle of emissive π-conjugated molecules.

Crystal structures of 4-(2/3-meth-oxy-phen-oxy)phthalo-nitrile.

The syntheses and crystal structures are reported of 4-phen-oxy-substituted phthalo-nitriles with meth-oxy groups in the ortho- and meta-positions of the terminal benzene rings, respectively, namely, 4-(2-meth-oxy-phen-oxy)phthalo-nitrile and 4-(3-meth-oxy-phen-oxy)phthalo-nitrile, both C15H10N2O2. The https://journals.iucr.org/e/issues/2023/03/00/mol-ecular structure was determined using the single-crystal X-ray diffraction method. It is shown that short contacts play a more decisive role in the mol-ecular packing compared to van der Waals inter-actions.

Discovery and Mechanistic Investigation of Piperazinone Phenylalanine Derivatives with Terminal Indole or Benzene Ring as Novel HIV-1 Capsid Modulators.

HIV-1 capsid (CA) performs multiple roles in the viral life cycle and is a promising target for antiviral development. In this work, we describe the design, synthesis, assessment of antiviral activity, and mechanistic investigation of 20 piperazinone phenylalanine derivatives with a terminal indole or benzene ring. Among them, F2-7f exhibited moderate anti-HIV-1 activity with an EC50 value of 5.89 μM, which was slightly weaker than the lead compound PF74 (EC50 = 0.75 μM). Interestingly, several compounds showed a preference for HIV-2 inhibitory activity, represented by 7f with an HIV-2 EC50 value of 4.52 μM and nearly 5-fold increased potency over anti-HIV-1 (EC50 = 21.81 μM), equivalent to PF74 (EC50 = 4.16 μM). Furthermore, F2-7f preferred to bind to the CA hexamer rather than to the monomer, similar to PF74, according to surface plasmon resonance results. Molecular dynamics simulation indicated that F2-7f and PF74 bound at the same site. Additionally, we computationally analyzed the ADMET properties for 7f and F2-7f. Based on this analysis, 7f and F2-7f were predicted to have improved drug-like properties and metabolic stability over PF74, and no toxicities were predicted based on the chemotype of 7f and F2-7f. Finally, the experimental metabolic stability results of F2-7f in human liver microsomes and human plasma moderately correlated with our computational prediction. Our findings show that F2-7f is a promising small molecule targeting the HIV-1 CA protein with considerable development potential.

Controlling the Emissive, Chiroptical, and Electrochemical Properties of Double [7] Helicenes through Embedded Aromatic Rings.

We present here the synthesis and in-depth physicochemical characterization of a double hetero[7]helicene fused with four triazole rings at both helical ends. The comparison of this triazole-fused double helicene with the previously reported all-carbon and thiadiazole-fused analogs revealed the huge impact of the embedded aromatic rings on the photophysical features. The small structural variation of the terminal rings from thiadiazole to triazole caused a dramatic change of the photoluminescence quantum yields (PLQYs) from <1 % to 96 %, while the replacement of the terminal benzene rings with triazole rings induced a tenfold enhancement of the circularly polarized luminescence dissymmetry factor. These observations were well corroborated with transient absorption analysis and/or theoretic calculations. In addition, the triazole-fused double helicene exhibited ambipolar redox behavior, enabling the generation of radical cation and anion species by electrochemical and chemical methods and showing its potential for spin-related applications.

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

Cation–π interaction of thallium (I) with [7]helicene: an experimental and theoretical study

Electrospray ionisation mass spectrometry was used to investigate the cation–π interaction of Tl+ with [7]helicene. Further, applying quantum mechanical calculations in the frame of the density functional theory, applying B3LYP functional with Def2TZVP basis set, the most probable structure of the [7]helicene–Tl+ complex was derived. In the resulting complex, the ‘central’ cation Tl+ is bounded between two terminal benzene rings of the parent [7]helicene ligand via cation–π interaction. In such conformation, the [7]helicene creates a tweezer for Tl+ ion. The interaction energy, E(int), of this cation–π complex was calculated to be –160 kJ/mol, which is consistent with the formation of the considered cationic complex species. Other structures were also found and generally lie energetically about 19–24 kJ/mol above the tweezer complex. HIGHLIGHTS Cation Tl+–[7]helicene complex has been observed using the ESI-MS method The structure of the resulting complex has been determined by applying quantum chemical DFT calculations Helicene functions as a chiral molecular tweezer for Tl+.

Hockey-Stick Polycatenars: Network formation and transition from one dimensional to three-dimensional liquid crystalline phases

Photo switchable liquid crystalline (LC) materials are of great interest for optical and photonic applications. Herein we report the design, synthesis, and molecular self-assembly of the first examples of photosensitive hockey-stick (HS) polycatenars. Therefore, two new series of HSLCs derived from 4-cyanoresorcinol bent-core unit connected to a short azobenzene-based side arm with one variable alkoxy chain and a long ester-based wing terminated with two alkoxy chains at 3 and 5 positions of the terminal benzene ring are reported. They differ from each other in the length of the terminal chains connected to the long arm. The LC self-assembly of these HSLCs was investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and electro optical investigations. Depending on length of terminal chains a transition from one dimensional (1D) tilted and non-tilted smectic phases to three dimensional (3D) achiral bicontinuous cubic phases with Ia3¯d symmetry (Cubbi/Ia3¯d) upon chain elongation is observed. Moreover, achiral isotropic liquid networks were observed for medium and long chain homologues. Most of mesophases are room temperature LCs phases with wide ranges as observed in the cooling cycles, where once they are formed on heating, no sign of crystallization is detected down to ambient temperature. Finally, UV light irradiation results in fast and reversible photoinduced transformation between different types of LCs phases as well as between LC phase and isotropic liquid.

Crystal structure and Hirshfeld surface analysis of 6-((E)-2-{4-[2-(4-chloro-phen-yl)-2-oxoeth-oxy]phen-yl}ethen-yl)-4,5-di-hydro-pyridazin-3(2H)-one.

The pyridazine ring in the title compound, C20H17ClN2O3, adopts a screw-boat conformation. The whole mol-ecule is flattened, the dihedral angles subtended by the least-squares plane of the central aromatic ring with those of the terminal benzene and pyridazine rings being 15.18 (19) and 11.23 (19)°, respectively. In the crystal, the mol-ecules are linked by pairs of N-H⋯O bonds into centrosymmetric dimers and by C-H⋯π contacts into columns. The results of the Hirshfeld surface analysis show that the most prominent inter-actions are H⋯H, accounting for 36.5% of overall crystal packing, and H⋯O/O⋯H (18.6% contribution) contacts.

Photostability of luminescent tris(2,4,6-trichlorophenyl)methyl radical enhanced by terminal modification of carbazole donor.

Stable organic luminescent radicals have attracted much attention, but their stability under light irradiation is not yet satisfactory. New luminescent radicals (TTMs) based on terminal benzene ring modified carbazole donors were synthesized and evaluated. Their photostability (half-life under continuous laser irradiation) has improved by 1 order of magnitude compared to simple carbazole donors. This is a new molecular design strategy to improve the photostability of luminescent radicals without reducing other photophysical properties.

Syntheses, crystal structures and properties of three compounds based on the dicarboxylate ligand with S-S flexible linkage

Three new compounds, [MnL(2, 2΄-bipy)2]n·1.5nH2O (1), Co(4, 4ˊ-bipy)(H2O)4·2HL (2) and 2HL·(4, 4ˊ-bipyH)·2H2O (3) (H2L = 2,2΄-dithiosalicylic acid, 2, 2΄-bipy = 2, 2΄-bipyridine, 4, 4΄-bipy = 4, 4΄-bipyridine), have been synthesized by hydrothermal and evaporation methods. Structural determination reveals that compound 1 shows a one-dimensional chain structure with L2- ligands adopting bridging coordination modes, compound 2 features a mononuclear structure with uncoordinated HL- anions, balancing the charges, compound 3 is a new inclusion compound of HL- anions and 4, 4ˊ-bipyH cation with π-π stacking interactions. In compounds 1-3, the flexible S-S linkages can make H2L ligands present different conformations of dihedral angles between the terminal benzene rings. The S-O hypervalent bonds can stabilize the conformations. Thermogravimetric analyses and fluorescent measurements of compounds 1 and 2 have been performed. Compounds 1 and 2 exhibit broad blue fluorescent emission bands at 420 nm and 424 nm, respectively.

Amino Alcohols from Eugenol as Potential Semisynthetic Insecticides: Chemical, Biological, and Computational Insights.

A series of β-amino alcohols were prepared by the reaction of eugenol epoxide with aliphatic and aromatic amine nucleophiles. The synthesized compounds were fully characterized and evaluated as potential insecticides through the assessment of their biological activity against Sf9 insect cells, compared with a commercial synthetic pesticide (chlorpyrifos, CHPY). Three derivatives bearing a terminal benzene ring, either substituted or unsubstituted, were identified as the most potent molecules, two of them displaying higher toxicity to insect cells than CHPY. In addition, the most promising molecules were able to increase the activity of serine proteases (caspases) pivotal to apoptosis and were more toxic to insect cells than human cells. Structure-based inverted virtual screening and molecular dynamics simulations demonstrate that these molecules likely target acetylcholinesterase and/or the insect odorant-binding proteins and are able to form stable complexes with these proteins. Encapsulation assays in liposomes of DMPG and DPPC/DMPG (1:1) were performed for the most active compound, and high encapsulation efficiencies were obtained. A thermosensitive formulation was achieved with the compound release being more efficient at higher temperatures.

Antibacterial Activity and Mesophase Identification of Azomethnine and Azo derivatives

A new mesogenic homologous series of liquid crystalline azomethnine and azo derivatives of 4ꞌ-nalkoxybenzylidiene- 4-aminoazobenzene has been synthesized and characterized by a combination of elemental analysis and standard spectroscopic methods. In the present series, nematic mesophase commences from n-propyloxy derivative as enantiotropic and persists up to the last member synthesized except in derivative C10. The smectic A (SmA) mesophases commences from n-pentyloxy derivative as enantiotropic and also persists up to ntetradecyloxy synthesized. Imine linkage (-CH═N-) between central and terminal benzene rings helping to understand the polarizability effect as well as nature of mesophase as stability gets reduced due to the presence of nitrogen in the ring. The mesomorphic properties of present series are of great importance to evaluate the effects of central linkage on mesomorphism. The mesomorphic properties of present series were compared with other structurally related mesogenic homologous series to evaluate the effects of central linkage on mesomorphism.

Reversible mechanofluorochromic properties of phenothiazine-based D-A-D′ aza-N,O-chelated boron difluoride complexes

Two new phenothiazine-based D-A-D' aza- N,O-Chelated boron difluoride complexes (E)-5-(4-(dimethylamino)phenyl)-3-((10-ethyl-10H-phenothiazin-3-yl)methylene)-2,2-difluoro-2,3-dihydro-1,3,4,2-oxadiazaborol-3-ium-2-uide (DPDFB) and (E)-3-((10-ethyl-10H-phenothiazin-3-yl)methylene)-2,2-difluoro-5-phenyl-2,3-dihydro-1,3,4,2-oxadiazaborol-3-ium-2-uide (PDDFB) were designed and synthesized. The two BF2 chelating donor–acceptor type aza-N,O-chelated five-membered-ring organoboron complexes displayed large Stokes shifts and remarkable solvatofluorochromism in solutions, as well as good thermal stability in the solid state. Strikingly, the attachment of N,N-dimethyl groups to the terminal benzene ring unit induced significant reversible mechanofluorochromic (MFC) properties (with emission wavelength changes from 617 nm to 660 nm). And the MFC mechanism was ascribed to the phase transformation between crystalline and amorphous state, which was revealed by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and field emission scanning electron microscopy (FESEM) analyses. The introduction of the N,N-dimethyl group demonstrated in this work would be of great help in understanding and designing new MFC materials.

Magnetic polyamidoamine dendrimer grafted with 4-mercaptobenzoic acid as an adsorbent for preconcentration and sensitive determination of polycyclic aromatic hydrocarbons from environmental water samples

Polyamidoamine dendrimer decorated Fe3O4 magnetic nanoparticles was synthesized and grafted with 4-mercaptobenzoic acid (4-MBA). The resulting material was utilized to develop an effective magnetic solid phase extraction method in combination with high performance liquid chromatography for trace determination of polycyclic aromatic hydrocarbons including phenanthrene (PHE), anthracene (ANT), fluoranthene (FLT), pyrene (PYR) and benzo(a)pyrene (BaP). The MNPs@G3.0@4-MBA exhibited to be an efficient extracting medium due to the existence of terminal benzene ring groups, the internal pores, and strong hydrophobic interactions and π-π interactions. The experiments demonstrated that the proposed method possessed excellent linearity in the concentration range of 0.1–300 μg L−1 with correlation coefficients (R) larger than 0.997, and the limits of detection (LODs, S/N = 3) according to the ratio of signal to noise equal to three of PHE, ANT, FLT, PYR and BaP were 0.014 μg L−1, 0.032 μg L−1, 0.055 μg L−1, 0.027 μg L−1 and 0.039 μg L−1, respectively. The proposed method was applied to real water samples and the spiked recoveries were over the range of 92–99%. The results showed that the method earned good repeatability and high sensitivity, and the as-prepared materials were stable and reusable, which displayed that the proposed method would have a wonderful application prospect.

Mol-ecular and crystal structure, optical properties and DFT studies of 1,4-dimeth-oxy-2,5-bis-[2-(4-nitro-phen-yl)ethen-yl]benzene.

The title compound DBNB, C24H20N2O6, has been crystallized and studied by X-ray diffraction, spectroscopic and computational methods. In the title mol-ecule, which is based on a 1,4-distyryl-2,5-di-meth-oxy-benzene core with p-nitro-substituted terminal benzene rings, the dihedral angle between mean planes of the central fragment and the terminal phenyl ring is 16.46 (6)°. The crystal packing is stabilized by π-π inter-actions. DFT calculations at the B3LYP/6-311 G(d,p) level of theory were used to compare the optimized structures with the experimental data. Energy parameters, including HOMO and LUMO energies, their difference, and vertical excitation and emission energies were obtained.

2,4,6-Triphenyl-N-{(3E)-3-[(2,4,6-tri-phenyl-phen-yl)imino]-butan-2-yl-idene}aniline.

The title compound, C52H40N2, is disposed about a centre of inversion and the conformation about the imine bond [1.268 (3) Å] is E. The terminal benzene ring is approximately perpendicular to the central 1,4-di-aza-butadiene mean plane, forming a dihedral angle of 81.2 (3)°. Weak C-H⋯π and π-π [inter-centroid distance = 4.021 (5) Å] inter-actions help to consolidate the packing.