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Reflection and transmission of an antiplane shear wave by an infinite array of randomly oriented cracks in an isotropic elastic medium are investigated. The problem has been formulated for an averaged scattered field, and a ''periodization'' technique has been developed to derive the governing singular integral equation for the conditionally averaged crack-opening displacement. The singular integral equation has been solved by splitting the kernel into a singular and a regular part. A point scatterer approximation was introduced for the part containing the regular kernel. The approximation has been checked by comparison with exact results for a deterministic periodic system. By using this approximation, the coherent part of the averaged reflection and transmission coefficients of zeroth order has been calculated for normal incidence, a completely random crack orientation, and various values of the wavenumber and the ratio of crack length and crack-center spacing. The problem was formulated in the context of antiplane shear waves. The results are, however, also applicable to reflection and transmission of acoustic or electromagnetic waves by an array of screens. [ABSTRACT FROM AUTHOR]

We report herein the synthesis of an unprecedented isomer of perylene, dicyclohepta[cd,fg]-as-indacene bearing two phenyl groups (1-Ph) by the nickel-mediated intramolecular homocoupling of a 4,4'-biazulene derivative (2). The X-ray crystallographic analysis and theoretical calculations revealed that 1-Ph adopts a unique helically twisted geometry although the local aromaticity of azulene moieties was preserved. The double covalent linkage of the two azulene skeletons imparts significant orbital interaction, which affords near-infrared (NIR) absorption (up to 1720 nm) and remarkable redox behaviors despite its closed-shell electronic structure. The optical band gap of 1-Ph is calculated to be 0.72 eV from its absorption onset, which is one of the narrowest values among the hitherto reported air-stable non-benzenoid PAHs. Furthermore, the thin-film of 1-Ph serves as a p-type semiconductor. Our study offers fundamental insights into not only the aromaticity with the nonalternant topologies of 1-Ph but also its potential application in novel organic electronics., (© 2025 Wiley‐VCH GmbH.)

Rational molecular design afforded fluorescent Cd 2+ sensors based on bisquinoline derivatives. Introduction of three methoxy groups at the 5,6,7-positions of the quinoline rings of BQDMEN ( N , N '-bis(2-quinolylmethyl)- N , N '-dimethylethylenediamine) resulted in the reversal of metal ion selectivity in fluorescence enhancement from zinc to cadmium. Introduction of bulky alkyl groups and an N , N -bis(2-quinolylmethyl)amine structure, as well as replacement of one of the two tertiary amine binding sites with an oxygen atom and the use of a 1,2-phenylene backbone significantly improved the Cd 2+ specificity. The fluorescent cadmium ion selectivity could be explained by the differential binding with Cd 2+ and Zn 2+ , and the formation of a bis(μ-chloro) dinuclear cadmium complex in contrast to the mononuclear zinc complex.

N -Monosubstituted ethylenediamine derivatives with three methylene-tethered aromatic groups ((ArCH 2 ) 2 NCH 2 CH 2 N(R)CH 2 Ar (R-ArArAr), where Ar = 2-pyridyl, 2-quinolyl, 1- and 3-isoquinolyl and 2-quinoxalyl; R = methyl, benzyl and phenyl) were utilized as pentadentate ligands for copper(II) complexation. Fifteen mononuclear copper(II) complexes were synthesized and exhibit differences in cyclic voltammetry, absorption spectroscopy and solid state geometries, depending on the aromatic group (Ar) and the substituent on the aliphatic nitrogen atom (R) of the ligand. Compared with the pyridine and isoquinoline complexes, the quinoline and quinoxaline derivatives exhibit distinct Cu(II)/Cu(I) redox potentials and d-d transition absorption wavelengths. Similarly, the phenyl derivatives are different from their methyl and benzyl counterparts. These characteristic trends are discussed in relation to the square-pyramidal/trigonal-bipyramidal structure of the complexes which is perturbed by the location of quinoline moieties in the penta- or hexacoordinate complexes with Jahn-Teller distortion. In addition, the results are compared to the copper(II) complexes with pyridine/quinoline mixed ligands, Ph-Ar1Ar2Ar 3 ((Ar 1 CH 2 )(Ar 2 CH 2 )NCH 2 CH 2 N(Ph)CH 2 Ar 3 ).

Color change of materials by external stimulus has attracted much attention for various applications. We synthesized 1,3-bis(3,3-dimethyl-2-methylene indolenine)squaraine (ISQ), which was a yellow powder with golden luster (ISQ(gold)) and whose color changed to blue (ISQ(blue)) by being ground using mortar and pestle. Scanning electron microscopy indicated that ISQ(gold) consisted of laminated plate-like crystals with a large flat surface, which was attributable to (2 0-2) facets of monoclinic crystals. Measurements of the diffuse reflectance spectra revealed that J- and H-type aggregates of ISQ were formed by increasing the weight percent of ISQ(blue) in the mixture with BaSO 4 . A thin film, which was prepared by a spin-coating of ethanol with dissolved ISQ(blue) on glass substrates, looked blue on a white paper, whereas it looked yellowish on a black paper. By repeating the coating process, the film thickness increased, and the thick film exhibited yellow with golden luster regardless of the background color. These results indicate that the color depends on whether the transmitted light through ISQ or the reflected light on the ISQ surface mainly contributes to color vision. To neglect the effect of the transmitted light and intensify the reflection on the surface, a pellet with a smooth surface was prepared by pressing ISQ(gold) or ISQ(blue) at 20 kg/cm 2 . The ISQ(blue) pellet consisted of the laminated sheets and was dark blue-green. However, under light irradiation, the ISQ(blue) pellet exhibited a yellow color with golden luster, whose specular reflection spectrum was similar to that of the ISQ(gold) pellet. Our results indicate that the color of ISQ is tunable by controlling the transmission and the reflection of the light, including the specular and diffuse reflections.

The N3O1 tetradentate ligand, TriMeOBQMOA ( N , N -bis(5,6,7-trimethoxy-2-quinolylmethyl)-2-methoxyaniline), was developed as a Cd 2+ -specific fluorescent sensor. The structure of TriMeOBQMOA is half of TriMeOBAPTQ ( N , N , N ', N '-tetrakis(5,6,7-trimethoxy-2-quinolylmethyl)-1,2-bis(2-aminophenoxy)ethane), which is a tetrakisquinoline derivative of the well-known calcium chelator BAPTA (1,2-bis(2-aminophenoxy)ethane- N , N , N ', N '-tetraacetic acid). The fluorescent Cd 2+ selectivity of TriMeOBAPTQ ( I Zn / I Cd = 5.3% in the presence of 3 equiv of metal ions in MeOH-HEPES buffer (9:1)) comes from the formation of fluorescent dinuclear cadmium (M 2 L) and nonfluorescent OH-bridged dizinc ((μ-OH)M 2 L) complexes. TriMeOBQMOA also exhibits excellent Cd 2+ specificity in fluorescence enhancement ( I Zn / I Cd = 2.3% in the presence of 5 equiv of metal ions in DMF-HEPES buffer (1:1, HEPES 50 mM, KCl 0.1 M, pH = 7.5)) via substantial formation of a highly fluorescent bis(μ-chloro)dinuclear cadmium complex ([Cd 2 (μ-Cl) 2 L 2 ] 2+ ), which is in equilibrium with the mononuclear Cd 2+ complex ([CdLCl] + ), and extremely poor stability of the TriMeOBQMOA-Zn 2+ complex. The all-nitrogen derivatives of BQMOA and BAPTQ, namely, N , N -BQDMPHEN ( N , N -bis(2-quinolylmethyl)- N ', N '-dimethyl-1,2-phenylenediamine) and BPDTQ ( N , N , N ', N '-tetrakis(2-quinolylmethyl)-2,2'-( N , N '-dimethylethylenediamino)dianiline), respectively, and their methoxy-substituted derivatives were also prepared, and the fluorescent metal ion sensing properties are discussed.

4,4'-Biazulene is a potentially attractive key component of an axially chiral biaryl compound, however, its structure and properties have not been clarified owing to the lack of its efficient synthesis. We report a breakthrough in the reliable synthesis of 4,4'-biazulene, which is achieved by the access to azulen-4-ylboronic acid pinacol ester and 4-iodoazulene as novel key synthetic intermediates for the Suzuki-Miyaura cross-coupling reaction. The X-ray crystallographic analysis of 4,4'-biazulene confirmed its axial chirality. The enantiomers of 4,4'-biazulene were successfully resolved by HPLC on the chiral stationary phase column. The kinetic experiments and DFT calculations indicate that the racemization energy barrier of 4,4'-biazulene is comparable to that of 1,1'-binaphthyl., (© 2024 Wiley-VCH GmbH.)

The development of fluorescent Cd 2+ sensors requires strict selectivity over Zn 2+ because of the high availability of Zn 2+ in the natural environment. In this paper, bisquinoline-based fluorescent sensors with a 2-aminoethanol backbone were investigated. The weak coordination ability of quinoline compared to well-studied pyridine is suitable for Cd 2+ selectivity rather than Zn 2+ . In the presence of 3 equiv. of metal ions, TriMeO- N,O -BQMAE ( N,O -bis(5,6,7-trimethoxy-2-quinolylmethyl)-2-methylaminoethanol ( 3 )), as well as its N,N -isomer TriMeO- N,N -BQMAE ( N,N -bis(5,6,7-trimethoxy-2-quinolylmethyl)-2-methoxyethylamine ( 6 )), exhibits Cd 2+ -selective fluorescence enhancement over Zn 2+ in DMF-HEPES buffer (1:1, 50 mM HEPES, 0.1 M KCl, pH = 7.5) ( I Zn / I Cd = 26-34%), which has similar selectivity in comparison to the corresponding ethylenediamine derivative TriMeOBQDMEN ( N,N' -bis(5,6,7-trimethoxy-2-quinolylmethyl)- N,N' -dimethylethylenediamine) under the same experimental condition ( I Zn / I Cd = 24%). The fluorescence mechanisms of N,O - and N,N -isomers of BQMAE are quite different, judging from the fluorescence lifetimes of their metal complexes. The Cd 2+ complex with TriMeO- N,O -BQMAE ( 3 ) exhibits a long fluorescence lifetime similar to that of TriMeOBQDMEN via intramolecular excimer emission, whereas the Cd 2+ complex with TriMeO- N,N -BQMAE ( 6 ) exhibits a short lifetime from monomer emission.

Eighteen mononuclear copper(II) complexes with oxygen-containing N4O1 pentadentate ligands were prepared. The ligand library consists of 2-aminoethanol derivatives ((Ar 1 CH 2 )(Ar 2 CH 2 )NCH 2 CH 2 OCH 2 Ar 3 ) bearing three nitrogen-containing heteroaromatics (Ars) including pyridine, quinoline and isoquinoline via a methylene linker. Systematic replacements of pyridine binding sites with quinolines and isoquinolines reveal the general trends in the perturbation of bond distances and angles, the redox potential and the absorption maximum wavelength of the copper(II) complexes, depending on the position and number of (iso)quinoline heteroaromatics. The small effect on the redox potentials resulting from quinoline substitution at the Ar 3 position (near oxygen) of the ligand comes from the steric hindrance of the peri hydrogen atom in the quinoline moiety at this position, which removes the counter anion to enhance the coordination of quinoline nitrogen and ether oxygen atoms to the metal centre. In the absorption spectra of copper(II) complexes in the d-d transition region, the quinoline substitution at this site (Ar 3 ) exhibits an opposite effect to those at the Ar 1 and Ar 2 sites. The electronic and steric contributions of the heteroaromatic binding sites to the ligand properties are comprehensively discussed.

BQDMEN ( N , N '-bis(2-quinolylmethyl)- N , N '-dimethylethylenediamine) and its 6-methoxyquinoline derivative (6-MeOBQDMEN) are fluorescent Zn 2+ sensors with minor response to Cd 2+ ( I Zn / I Cd = 3.9 for BQDMEN and I Zn / I Cd = 2.2 for 6-MeOBQDMEN in the presence of 1 equiv. of metal ion). Nevertheless, the introduction of three methoxy substituents at the 5,6,7-position of both quinoline rings of BQDMEN reversed the fluorescent metal ion selectivity to favor Cd 2+ ( I Zn / I Cd = 0.22 for TriMeOBQDMEN in the presence of 1 equiv. of metal ion). This reversal of Zn 2+ /Cd 2+ preference in fluorescence enhancement by trimethoxy substitution was also valid for 1,3-propanediamine derivatives. The X-ray crystallography, ESI-MS, fluorescence lifetime and pH profile of the fluorescence intensity suggest that the dinuclear cadmium complex is a key component of the fluorescent Cd 2+ selectivity in TriMeOBQDMEN.

Moderate Zn 2+ selectivity over Cd 2+ ( I Zn / I Cd = 1.6) in the fluorescence enhancement of TQEN ( N , N , N ', N '-tetrakis(2-quinolylmethyl)ethylenediamine) was changed to Cd 2+ preference via the introduction of a methoxymethyloxy (MOMO) substituent at the 8-position of one of the four quinoline rings ( I Zn / I Cd = 0.2). Thus, 8-MOMOTQEN ( N -(8-methoxymethyloxy-2-quinolylmethyl)- N , N ', N '-tris(2-quinolylmethyl)ethylenediamine) showed not only high Cd 2+ -selectivity but also an enhanced fluorescence quantum yield upon Cd 2+ binding and high sensitivity for Cd 2+ detection as shown by ϕ Cd = 0.065 and LOD (limit of detection) = 19 nM. The two oxygen atoms of the MOMO group in 8-MOMOTQEN play a crucial role in the fluorescent metal-ion selectivity because the corresponding hydroxy (8-OHTQEN) and methoxy (8-MeOTQEN) derivatives resulted in a poor fluorescent response and metal selectivity, respectively. Another N6O2 ligand, N , N '-bis(8-methoxy-2-quinolylethyl)- N , N '-bis(2-quinolylmethyl)ethylenediamine ((8-MeO) 2 TQEN) exhibited a Zn 2+ -selective fluorescence enhancement ( I Zn / I Cd = 2.2), indicating the superiority of the MOMO group for the selective sensing of Cd 2+ .

Intramolecular cycloaddition reactions of α-bromostyrene-functionalized amides of monomethyl fumarate were investigated. The reaction of the amides with Et 3 N in toluene at 110 °C gave 1,4-dihydronaphthalenes. The 1,4-dihydronaphthalenes may be produced via the intramolecular Diels-Alder reaction, proton transfer, and dehydrobromination by a base, along with C═C bond isomerization by proton transfer. The reaction of amide derivatives with halogen on a benzene ring and alkali metal carbonates in toluene at 110 °C gave naphthalene derivatives directly. Dehydrogenation of various 1,4-dihydronaphthalenes with cesium or rubidium carbonate in toluene at 110 °C gave naphthalene derivatives. The retardation by TEMPO, acceleration by air for some substrates, and density functional theory calculations suggest a radical mechanism caused by intervention of molecular oxygen.

A bis(μ-oxo)diiron(IV,IV) complex as a model for intermediate Q in the methane monooxygenase reaction cycle has been prepared. The precursor complex with a [Fe III Fe IV (μ-O) 2 ] core was fully characterized by X-ray crystallography and other spectroscopic analyses and was converted to the [Fe IV 2 (μ-O) 2 ] complex via electrochemical oxidation at 1000 mV (vs Ag/Ag + ) in acetone at 193 K. The UV-vis spectral features, Mössbauer parameters (Δ E Q = 2.079 mm/s and δ = -0.027 mm/s), and EXAFS analysis (Fe-O/N = 1.73/1.96 Å and Fe···Fe = 2.76 Å) support the structure of the low-spin ( S = 1, for each Fe) [Fe IV 2 (μ-O) 2 ] core. The rate constants of the hydrogen abstraction reaction from 9,10-dihydroanthracene at 243 K suggest the high reactivity of these synthetic bis(μ-oxo)diiron complexes supported by simple N4 tripodal ligand.

Mechanistic understanding of the asymmetric autocatalysis of pyrimidyl alkanol is a highly attractive and challenging topic due to its unique feature of amplification of enantiomeric excess. Circular dichroism spectroscopic analysis of this reaction allows monitoring of the structual changes of possible catalyst precursors in the solution state and shows characteristic temperature and solvent dependence. TD-DFT calculations suggest that these spectral changes are induced by a dimer-tetramer equilibrium of zinc alkoxides.

Sequential Knoevenagel condensation/cyclization leading to indene and benzofulvene derivatives has been developed. The reaction of 2-(1-phenylvinyl)benzaldehyde with malonates gave benzylidene malonates, cyclized indenes, and dehydrogenated benzofulvenes. The product selectivity depends on the reaction conditions. The reaction with piperidine, AcOH in benzene at 80 °C for 1.5 h gave a benzylidene malonate in 75% yield as a major product. The reactions with piperidine, AcOH in benzene at 80 °C for 17 h and with TiCl 4 -pyridine at room temperature gave an indene derivative in 56 and 79% yields, respectively, as a major product. The reaction with TiCl 4 -Et 3 N gave a benzofulvene in 40% yield selectively. Indene was transformed to a benzofulvene derivative using the reagents TiCl 4 -Et 3 N and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The reaction of variously substituted aryl derivatives with dimethyl malonate gave indene and benzofulvene derivatives. The reactions of 2-(1-phenylvinyl)benzaldehyde with Meldrum's acid or malononitrile also gave cyclized compounds in the suitable sequential or stepwise conditions. Furthermore, the reaction of 2-arylbenzaldehydes has been investigated. The limitation and scope have been described. The reaction mechanism of the cyclization steps has been examined by DFT calculations., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Seven new bis(μ-oxo)dimanganese complexes with Mn 2 (iii,iii) or Mn 2 (iii,iv) oxidation states were prepared using quinoline- and isoquinoline-based tetraamine ligands. The structures of the ligands include ethylenediamine, trans-1,2-cyclohexanediamine and tripodal amine, bearing two or three nitrogen-containing heteroaromatics. Regardless of the skeleton and number of aliphatic nitrogen atoms in the ligands, quinoline complexes stabilize the Mn 2 (iii,iii) oxidation state, whereas, isoquinoline ligands afford Mn 2 (iii,iv) complexes. A systematic comparison of the differences in structural parameters and redox potentials of a total of 14 complexes with a (μ-O) 2 Mn 2 diamond core, which includes corresponding pyridine and quinoxaline derivatives as supporting ligands, highlights the distinct deviation of quinoline and tripodal amine motifs in this ligand series.

Rational molecular structure alterations of TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine) produced variable fluorescent sensors for specific metal ions and phosphate species. Utilization of methoxy-substituted quinoline and isoquinoline chromophores, conformational restriction and multidentate coordination structure allow discrimination between Zn2+ and Cd2+. Pyrophosphate (P2O74-, PPi) and phosphate (PO43-) also are selectively detected with dinuclear Zn2+ complexes of tetrakisquinoline-based ligands. Differential stability and structure of the metal complexes, as well as resulting fluorescence enhancement mechanism, such as intramolecular excimer formation via change in coordination geometry, play key roles in the discrimination of target ions.

A quinoline-based hexadentate ligand, ( S , S )- N , N , N' , N' -tetrakis(6-methoxy-2-quinolylmethyl)-1,2-diphenylethylenediamine (( S , S )-6-MeOTQPh 2 EN), exhibits fluorescence enhancement at 498 nm upon addition of 1 equiv of Zn 2+ ( I Zn / I 0 = 12, φ Zn = 0.047) in aqueous DMF solution (DMF/H 2 O = 2:1). Addition of 1 equiv of Cd 2+ affords a much smaller fluorescence increase at the same wavelength ( I Cd / I 0 = 2.5, I Cd / I Zn = 21%). The trivalent metal ions such as Al 3+ , Cr 3+ , and Fe 3+ also exhibit fluorescence enhancement at 395 nm ( I Al / I 0 = 22, I Cr / I 0 = 6 and I Fe3+ / I 0 = 13). In contrast, meso -6-MeOTQPh 2 EN exhibits a Cd 2+ -selective fluorescence increase at 405 nm in the presence of 1 equiv of metal ion ( I Cd / I 0 = 11.5, φ Cd = 0.022), while Zn 2+ induces a smaller fluorescent response under the same experimental conditions ( I Zn / I 0 = 3.3, I Zn / I Cd = 29%). In this case, the fluorescence intensities of meso -6-MeOTQPh 2 EN in the presence of a large amount of Zn 2+ and Cd 2+ become similar. This diastereomer-dependent, fluorescent metal ion specificity is derived from the Zn 2+ -specific intramolecular excimer formation in ( S , S )-6-MeOTQPh 2 EN-Zn 2+ complex and higher binding affinity of meso -6-MeOTQPh 2 EN with Cd 2+ in comparison to Zn 2+ . The more conformationally restricted diastereomeric pair, namely, cis- and trans -TQDACHs ( cis- and trans - N , N , N' , N' -tetrakis(2-quinolylmethyl)-1,2-diaminocyclohexanes), both exhibit Zn 2+ -specific fluorescence enhancement because of the high metal binding affinity and intramolecular excimer forming property derived from the rigid DACH backbone.