Enhancement in Sensitivity and Selectivity of Electrochemical Technique with CuO/g-C3N4 Nanocomposite Combined with Molecularly Imprinted Polymer for Melamine Detection.

This study focused on enhancing the sensitivity and selectivity to detect melamine by utilizing a photoelectrochemical method. This was achieved by combining a melamine-imprinted polymer with a CuO/g-C3N4 nanocomposite, which was synthesized through chemical precipitation and calcination. The resulting nanocomposite exhibits improved carrier mobility and photoelectrochemical properties. A molecularly imprinted receptor for selective detection was created through bulk polymerization with methacrylic acid and a melamine template. The characterization of the nanocomposite was performed using X-ray photoelectron spectroscopy for the chemical oxidation state, X-ray diffraction patterns for the crystalline structure, and ultraviolet/visible/near-infrared spectroscopy for optical properties. The CuO/g-C3N4 nanocomposite exhibits photoactivity under visible light. The modified electrode, incorporating the CuO/g-C3N4 nanocomposite and melamine-imprinted polymer, demonstrates a linear detection range of 2.5 to 50 nM, a sensitivity of 4.172 nA/nM for melamine, and a low detection limit of 0.42 nM. It shows good reproducibility and high selectivity to melamine, proving effective against interferences and real samples, showcasing the benefits of the molecularly imprinted polymer.

Stability improvement of UV-filter between methoxy cinnamic acid derivatives and cyclodextrins inclusion complexes based on DFT and TD-DFT investigations.

Structures and UV-vis absorption spectra of the host-guest interaction of the methoxy cinnamic acid (MCA) derivatives and cyclodextrins (CDs) were performed by using the density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. All geometries of MCA derivatives (4-MCA, 245-MCA, 246-MCA), three types of CD (αCD, ßCD, γCD), and five host-guest inclusion complexes between MCA and CD consisting of 4-MCA/αCD (1), 4-MCA/ßCD (2), 245-MCA/ßCD (3), 246-MCA/ßCD (4), and 246-MCA/γCD (5) were fully optimized by using the M06-2X/6-31G (d,p) levels of theory. Two orientations (A and B) of the MCA guest molecule were considered. Upon examining the optimized geometry, five complexes of the methoxy cinnamic acid molecules are located inside the cavity of CD. Orientation B was more stable than orientation A because of the stronger intermolecular hydrogen bonds between the hydroxyl group of CD and the carboxylic group of MCA. The results indicated that the intermolecular hydrogen bond is mainly the driving force of formation between methoxy cinnamic acid and cyclodextrins. To reveal the host-guest interaction that is relevant to UV-filter compounds, the UV-vis absorption spectra were performed using TD-DFT calculations. The obtained results confirmed that orientation B is the most stable orientation and can absorb in both UVB and UVA regions which is similar to the parent MCA. Therefore, this knowledge will bring to understand the host-guest interaction between methoxy cinnamic acid and cyclodextrin complexes. The theoretical results are expected to provide valuable information for improving the stability of further UV-filter compounds.

Defect-Engineered Hydroxylated Mesoporous Spinel Oxides as Bifunctional Electrocatalysts for Oxygen Reduction and Evolution Reactions.

In this work, defect-rich ordered mesoporous spinel oxides, including CoCo2O4, NiCo2O4, and ZnCo2O4, were developed as bifunctional electrocatalysts toward oxygen reduction and evolution reactions (ORR and OER, respectively). The materials are synthesized via nanocasting and modified by chemical treatment with 0.1 M NaBH4 solution to enhance the defect concentration. The synthesized samples have metal and oxygen divacancies (VCo + VO) as the primary defect sites, as indicated by positron annihilation lifetime spectroscopy (PALS). Cation substitution in the spinel structure induces a higher number of oxygen vacancies. The increased number of surface defects and the synergistic effect between two incorporated metals provide a high activity in both the OER and ORR in the case of NiCo2O4 and ZnCo2O4. Especially, ZnCo2O4 exhibits the highest OER/ORR activity. The defect engineering with 0.1 M NaBH4 solution results in a metal-hydroxylated surface (M-OH) and enhanced the catalytic activity for the post-treated metal oxides in the ORR and OER. This fundamental investigation of the defective structure of the mixed metal oxides offers some useful insights into further development of highly active electrocatalysts through defect engineering methods.

Stepwise Access of Emissive Ir(III) Complexes Bearing a Multi-Dentate Heteroaromatic Chelate: Fundamentals and Applications.

Three multi-dentate coordinated chelates LnH2 (n = 1, 2, and 3), comprising a linked 1-(pyridin-2-yl)ethylbenzene and one pyrazolyl pyridine unit and showing either tridentate or tetradentate coordination modes, are successfully designed and synthesized. Dinuclear Ir(III) complexes [Ir(κ4-Ln)(µ-Cl)]2 bearing tetradentate coordinated κ4-Ln chelate (2a, n = 1; 2b, n = 2; 2c, n = 3) were next obtained en route from the respective intermediate [Ir(κ3-LnH)Cl(µ-Cl)]2 bearing the tridentate coordinated κ3-LnH chelate (1a, n = 1; 1b, n = 2; 1c, n = 3). Next, mononuclear Ir(III) complexes Ir(κ4-Ln)(thd) (3a, n = 1; 3b, n = 2; 3c, n = 3) with the tetradentate chelate were obtained upon treatment of 2 with 2,2,6,6-tetramethyl-3,5-heptanedione (thd)H in the presence of K2CO3. Concurrently, methylation of 2c in the presence of MeI and nBu4NCl afforded tridentate Ir(κ3-L3HMe)Cl3 (4) and, next, can be converted to tetradentate Ir(κ4-L3Me)Cl2 (5) by further cyclometalation and HCl elimination in refluxing diethylene glycol monoethyl ether solution. The Ir(III) complexes 3a, 4, and 5 were unambiguously identified using spectroscopic methods, together with single-crystal X-ray structural analyses on Ir(III) derivatives 3a, 4, and 5. Their photophysical and ,electrochemical properties and device fabrication properties were also investigated and compared with results from theoretical studies.

Crystal structure, Hirshfeld surface analysis and computational study of a rhodamine B-salicyl-aldehyde Schiff base derivative.

The mol-ecular structure of the title compound {systematic name: 3',6'-bis(di-ethyl-amino)-2-[(2-hy-droxy-benzyl-idene)amino]-spiro-[isoindoline-1,9'-xan-then]-3-one}, C35H36N4O3 or RbSa, can be seen as being composed of two parts sharing a central quaternary carbon atom. Both the xanthene and iso-indole moieties are nearly planar: 14 atoms in the former moiety show an r.m.s. deviation of 0.0411 Šand eleven atoms in the latter moiety show an r.m.s. deviation of 0.0545 Å. These two planes are almost perpendicular to each other, the angle between the mean planes being 87.71 (2)°. The title compound appears to be in its enol form. The corresponding H atom was located and freely refined at a distance of 1.02 (3) Šfrom the O atom and 1.72 (2) Šfrom the N atom. The strong intra-molecular hydrogen bond O-H⋯N bridging the hydroxyl group and its neighboring nitro-gen atom forms an S(6) graph-set motif. Apart from the intra-molecular O-H⋯N hydrogen bond, C-H⋯O inter-actions are observed between two neighbouring RbSa mol-ecules related by an inversion center. The C-O donor-acceptor distance is 3.474 (2) Å. Moreover, C-H⋯π inter-actions are observed between the C-H bond of one of the ethyl groups and the centroid of the benzene ring of the iso-indole moiety. The C⋯centroid distance is 3.8191 (15) Å. No π-π inter-actions are observed in the crystal structure as the shortest distance between ring centroids is more than 4 Å. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H, C⋯H/H⋯C, O⋯H/H⋯O and N⋯H/H⋯N inter-actions. DFT calculations at the CAM-B3LYP/6-31 G(d) level were carried out to gain a better understanding of the relative energies and the tautomerization process between two possible conformers (keto and enol), as well as the transition state of the title compound.

Crystal structure, Hirshfeld surface analysis and computational study of 2-chloro-N-[4-(methyl-sulfan-yl)phen-yl]acetamide.

In the title compound, C9H10ClNOS, the amide functional group -C(=O)NH- adopts a trans conformation with the four atoms nearly coplanar. This conformation promotes the formation of a C(4) hydrogen-bonded chain propagating along the [010] direction. The central part of the mol-ecule, including the six-membered ring, the S and N atoms, is fairly planar (r.m.s. deviation of 0.014). The terminal methyl group and the C(=O)CH2 group are slightly deviating out-of-plane while the terminal Cl atom is almost in-plane. Hirshfeld surface analysis of the title compound suggests that the most significant contacts in the crystal are H⋯H, H⋯Cl/Cl⋯H, H⋯C/C⋯H, H⋯O/O⋯H and H⋯S/S⋯H. π-π inter-actions between inversion-related mol-ecules also contribute to the crystal packing. DFT calculations have been performed to optimize the structure of the title compound using the CAM-B3LYP functional and the 6-311 G(d,p) basis set. The theoretical absorption spectrum of the title compound was calculated using the TD-DFT method. The analysis of frontier orbitals revealed that the π-π* electronic transition was the major contributor to the absorption peak in the electronic spectrum.

5-Methyl-1,3-phenyl-ene bis-[5-(di-methyl-amino)-naphthalene-1-sulfonate]: crystal structure and DFT calculations.

The title compound, C31H30N2S2O6, possesses crystallographically imposed twofold symmetry with the two C atoms of the central benzene ring and the C atom of its methyl substituent lying on the twofold rotation axis. The two dansyl groups are twisted away from the plane of methyl-phenyl bridging unit in opposite directions. The three-dimensional arrangement in the crystal is mainly stabilized by weak hydrogen bonds between the sulfonyl oxygen atoms and the hydrogen atoms from the N-methyl groups. Stacking of the dansyl group is not observed. From the DFT calculations, the HOMO-LUMO energy gap was found to be 2.99 eV and indicates n→π* and π→π* transitions within the mol-ecule.

Photophysical properties for excited-state intramolecular proton transfer (ESIPT) reaction of N-salicylidene-o-aminophenol: Experimental and DFT based approaches.

Photophysical properties for excited-state intramolecular proton transfer (ESIPT) reaction of N-salicylidene-o-aminophenol (SA) Schiff base were comprehensively studied based on experimental methods combined with theoretical calculations. The results revealed that the SA was mainly presented in enol form in acidic solutions while it was predominantly existed in keto form in basic solutions. From UV-vis absorption and fluorescence emission studies, it showed that the ESIPT could effectively take place in non-polar and aprotic polar solvents. By using the CAM-B3LYP/6-311G(d,p) level of theory, it was found that the intramolecular proton transfer could preferably occur through six-membered ring transition rather than through five-membered ring transition. The dynamics of the ESIPT reactions of enol and keto tautomers were studied using TD-CAM-B3LYP with 6-311G(d,p) basis set. The potential energy curves for the intramolecular proton transfer in the ground (GSIPT) and excited state (ESIPT) exhibited that the GSIPT could occur through a low activation barrier, whereas in the case of ESIPT, the process could arise via low energy barrier.

Density functional theory study of adsorption geometries and electronic structures of azo-dye-based molecules on anatase TiO2 surface for dye-sensitized solar cell applications.

Structural and electronic properties of eight isolated azo dyes (ArNNAr', where Ar and Ar' denote the aryl groups containing benzene and naphthalene skeletons, respectively) were investigated by density functional theory (DFT) based on the B3LYP/6-31G(d,p) and TD-B3LYP/6-311G(d,p) methods The effect of methanol solvent on the structural and electronic properties of the azo dyes was elucidated by employing a polarizable continuum model (PCM). Then, the azo dyes adsorbed onto the anatase TiO2 (101) slab surface through a carboxyl group. The geometries and electronic structures of the adsorption complexes were determined using periodic DFT based on the PWC/DNP method. The calculated adsorption energies indicate that the adsorbed dyes preferentially take configuration of the bidentate bridging rather than chelating or monodentate ester-type geometries. Furthermore, the azo compounds having two carboxyl groups are coordinated to the TiO2 surface more preferentially through the carboxyl group connecting to the benzene skeleton than through that connecting to the naphthalene skeleton. The dihedral angles (ΦB-N) between the benzene- and naphthalene-skeleton moieties are smaller than 10° for the adsorbed azo compounds containing one carboxyl group. In contrast, ΦB-N>30° are obtained for the adsorbed azo compounds containing two carboxyl groups. The almost planar conformations of the former appear to strengthen both π-electrons conjugation and electronic coupling between low-lying unoccupied molecular orbitals of the azo dyes and the conduction band of TiO2. On the other hand, such coupling is very weak for the latter, leading to a shift of the Fermi level of TiO2 in the lower-energy direction. The obtained results are useful to the design and synthesize novel azo-dye-based molecules that give rise to higher photovoltaic performances of the dye-sensitized solar cells.

Bis(phenothiazyl-ethynylene)-Based Organic Dyes Containing Di-Anchoring Groups with Efficiency Comparable to N719 for Dye-Sensitized Solar Cells.

A new series of acetylene-bridged phenothiazine-based di-anchoring dyes have been synthesized, fully characterized, and used as the photoactive layer for the fabrication of conventional dye-sensitized solar cells (DSSCs). Tuning of their photophysical and electrochemical properties using different π-conjugated aromatic rings as the central bridges has been demonstrated. This molecular design strategy successfully inhibits the undesirable charge recombination and prolongs the electron lifetime significantly to improve the power conversion efficiency (η), which was proven by the detailed studies of electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD). Under a standard air mass (AM) 1.5 irradiation (100 mW cm-2 ), the DSSC based on the dye with phenyl bridging unit exhibits the highest η of 7.44 % with open-circuit photovoltage (Voc ) of 0.796 V, short-circuit photocurrent density (Jsc ) of 12.49 mA cm-2 and fill factor (ff) of 0.748. This η value is comparable to that of the benchmark N719 under the same conditions.

Elucidation of hydroxyl groups-antioxidant relationship in mono- and dihydroxyflavones based on O-H bond dissociation enthalpies.

Radical scavenging potential is the key to anti-oxidation of hydroxyflavones which generally found in fruits and vegetables. The objective of this work was to investigate the influence of hydroxyl group on the O-H bond dissociation enthalpies (BDE) from a series of mono- and dihydroxyflavones. Calculation at the B3LYP/6-31G(d,p) level reveals the important roles of an additional one hydroxyl group to boost the BDE of hydroxyflavones that were a stabilization of the generated radicals through attractive H-bond interactions, an ortho- and para-dihydroxyl effect, and a presence of the 3-OH in dihydroxyflavones. On the other hand, the meta-dihydroxyl effect and range-hydroxyl effect especially associated with the either 5-OH or 8-OH promoted greater BDE. Results did not only confirm that dihydroxyflavones had lower BDE than monohydroxyflavones but also suggest the selective potent hydroxyflavone molecules that are the 6'-hydroxyflavone (for monohydroxyflavone) and the 5',6'-, 7,8- and 3',4'-dihydroxyflavone which the corresponding radical preferable generated at C6'-O•, C8-O• and C4'-O•, respectively. Electron distribution was limited only over the two connected rings of hydroxyflavones while the expansion distribution into C-ring could be enhanced if the radical was formed especially for the 2',3'- and 5',6'dihydroxyflavone radicals. The delocalized bonds were strengthened after radical was generated. However the 5-O• in 5,6-dihydroxyflavone and the 3-O• in 3,6'-dihydroxyflavone increased the bond order at C4-O11 which might interrupt the conjugated delocalized bonds at the keto group.

Photophysical properties and photochemistry of substituted cinnamates and cinnamic acids for UVB blocking: effect of hydroxy, nitro, and fluoro substitutions at ortho, meta, and para positions.

Photophysical properties and photochemistry of various substituted cinnamates and cinnamic acids for ultraviolet B blocking were investigated experimentally and theoretically. This series includes monohydroxy, -nitro, and -fluoro derivatives. The absorption spectra were satisfactorily reproduced by the direct SAC-CI method with respect to the peak position and intensity. The transition character of the low-lying two ππ* and σπ* states for these 18 derivatives was analyzed. The para derivatives have a different transition character of the ππ* transitions compared with those of the ortho and meta derivatives. To elucidate the relaxation mechanism, the emission spectra were observed with oxygen quenching and the photostability was examined experimentally. The calculated radiative lifetimes indicate that the ortho- and meta-substituted derivatives have longer lifetimes for emission than the para derivatives. The potential energy curves of the first and second singlet excited states of the hydroxy derivatives as well as the vertical singlet and triplet transitions were examined to investigate the relaxation qualitatively. The ortho and meta derivatives have an energy barrier or flat surface in S1 resulting in fluorescence, whereas the para derivatives show nonradiative decay without an energy barrier. The para-hydroxy derivative was found to be an excellent UV absorber based on its broad absorption in the UVB/UVA regions, less emission, and higher photostability.

The effect of alkali and Ce(III) ions on the response properties of benzoxazine supramolecules prepared via molecular assembly.

A series of benzoxazine monomer supramolecules with different substituted groups on their benzene ring was prepared with a Mannich reaction and characterized by FTIR, 1H-NMR and MS. The obtained products were 3,4-dihydro-3-(2'-hydroxyethylene)-6-methyl-2H-benzoxazine (BM1), 3,4-dihydro-3-(2'-hydroxyethylene)-6-ethyl-2H-benz-oxazine (BM2), and 3,4-dihydro-3-(2'-hydroxyethylene)-6-methoxy-2H-benzoxazine (BM3). The efficiency of alkali metal ion extraction from the products was determined with Pedersen's technique, while the complexation of the Ce(III) ion was confirmed by the Job's and the mole ratio methods. The evidence of complex formation between benzoxazine monomers and Ce(III) ions was obtained with FTIR and a computational simulation. Single phase ceria (CeO2) as observed with XRD was successfully prepared by calcinating the Ce(III)-benzoxazine monomer complexes at 600 °C for 2 h. In addition, the geometry of the ceria nanoparticles confirmed by TEM is spherical, with an average diameter of 10-20 nm.

Photophysical properties and photochemistry of EE-, EZ-, and ZZ-1,4-dimethoxy-2,5-bis[2-(thien-2-yl)ethenyl] benzene in solution: theory and experiment.

Photophysical properties and photoisomerization of 1,4-dimethoxy-2,5-bis[2-(thien-2-yl)ethenyl] benzene (DMTB) have been investigated for the EE-, EZ-, and ZZ- stereoisomers. The EE-DMTB was prepared, and the absorption/fluorescence spectra of EE- isomer as well as transient spectra in photoisomerization among three isomers were observed. Absorption and fluorescence spectra of three isomers were analyzed by the symmetry-adapted cluster-configuration interaction (SAC-CI) and time-dependent density functional theory (TDDFT) methods. The characteristics of the absorption spectra of three isomers were satisfactorily reproduced by the direct SAC-CI and TDDFT methods in both peak position and intensity. The relative stability of three isomers and the photoisomerization among these isomers were also examined theoretically. The ground (S(0)) and first excited state (S(1)) geometries were calculated by the DFT/TDDFT method with the M06HF functional, and the calculated S(0) structures of EE- and ZZ- isomers agreed well with those of the X-ray structures. The geometry relaxation in the S(1) state was interpreted with regard to the excitation character. The solvent effect in the absorption and fluorescence spectra was examined by the polarizable continuum model (PCM) and was found to be 0.05-0.20 eV, reflecting the charge polarization. The results show that the photophysical properties of DMTB can be controlled with the conformation constraint and also indicate the possibility of a photofunctional molecular device such as a switching function.

Novel recovery of nano-structured ceria (CeO(2)) from Ce(III)-benzoxazine dimer complexes via thermal decomposition.

N,N-bis(2-hydroxybenzyl)alkylamines, benzoxazine dimers, are the major product produced from benzoxazine monomers on mono-functional phenol by the one step ring opening reaction. Due to the metal responsive property of benzoxazine dimers, in this present work, N,N-bis(5-methyl-2-hydroxybenzyl)methylamine (MMD), N,N-bis (5-ethyl-2-hydroxybenzyl)methylamine (EMD), and N,N-bis(5-methoxy-2-hydroxybenzyl) methyl amine (MeMD), are considered as novel ligands for rare earth metal ion, such as cerium(III) ion. The complex formed when the clear and colorless solutions of cerium nitrate and benzoxazine dimers were mixed, results in a brown colored solution. The metal-ligand ratios determined by the molar ratio and the Job's methods were found to be in a ratio of 1:6. To clarify the evidence of the complex formation mechanism, the interactions among protons in benzoxazine dimers both prior to and after the formation of complexes were determined by means of (1)H-NMR, 2D-NMR and a computational simulation. The single phase ceria (CeO(2)) was successfully prepared by thermal decomposition of the Ce(III)-benzoxazine dimer complexes at 600 °C for 2 h, was then characterized using XRD. In addition, the ceria powder investigated by TEM is spherical with an average diameter of 20 nm.

Absorption and emission spectra of ultraviolet B blocking methoxy substituted cinnamates investigated using the symmetry-adapted cluster configuration interaction method.

The absorption and emission spectra of ultraviolet B (UVB) blocking cinnamate derivatives with five different substituted positions were investigated using the symmetry-adapted cluster configuration interaction (SAC-CI) method. This series included cis- and trans-isomers of ortho-, meta-, and para-monomethoxy substituted compounds and 2,4,5-(ortho-, meta-, para-) and 2,4,6-(ortho-, para-) trimethoxy substituted compounds. The ground and excited state geometries were obtained at the B3LYP/6-311G(d) and CIS/D95(d) levels of theory. All the compounds were stable as cis- and trans-isomers in the planar structure in both the S(0) and S(1) states, except the 2,4,6-trimethoxy substituted compound. The SAC-CI/D95(d) calculations reproduced the recently observed absorption and emission spectra satisfactorily. Three low-lying excited states were found to be relevant for the absorption in the UV blocking energy region. The calculated oscillator strengths of the trans-isomers were larger than the respective cis-isomers, which is in good agreement with the experimental data. In the ortho- and meta-monomethoxy compounds, the most intense peak was assigned as the transition from next highest occupied molecular orbital (next HOMO) to lowest unoccupied molecular orbital (LUMO), whereas in the para-monomethoxy compound, it was assigned to the HOMO to LUMO transition. This feature was interpreted as being from the variation of the molecular orbitals (MOs) due to the different substituted positions, and was used to explain the behavior of the excited states of the trimethoxy compounds. The emission from the local minimum in the planar structure was calculated for the cis- and trans-isomers of the five compounds. The relaxation paths which lead to the nonradiative decay were also investigated briefly. Our SAC-CI calculations provide reliable results and a useful insight into the optical properties of these molecules, and therefore, provide a useful tool for developing UVB blocking compounds with regard to the tuning of the photoabsorption.