In situ visible spectroscopy of a gadolinium bisphthalocyanine LB film exposed to chlorine gas

We report the preparation of Langmuir-Blodgett (LB) films of a gadolinium phthalocyanine, doubledecker, molecular sandwich-type complex [Gd(Pc)₂] and its ultraviolet-visible spectroscopic characterisation. We have studied the changes in the optical absorbance spectra that occur upon exposure to very low concentrations (~10 ppm) of chlorine gas. The main absorption band in the visible region occurs at ~690 nm. Upon exposure to chlorine gas, the intensity of this band decreases with the simultaneous introduction of a new peak at ~734 nm, an isosbestic point occurring at 721 nm. These spectral changes are indicative of oxidation of the complex by chlorine to form the [Gd(Pc)₂]⁺ species. The kinetics of this response suggest that the adsorption of chlorine by the LB film is a complex process, possibly involving up to three independent mechanisms. The LB film recovers almost fully (> 95%) upon switching off the chlorine supply.     

Reactions of cyclo-octatetraene and its derivatives—VII: Reactions of cyclo-octatetraene tetramer and of the dimer heptacyclo[8.6.0.02,6.03,9.07,15.08,12.011,16]hexadeca-4,13-diene

Supplementary evidence has been obtained for the formulation of the cyclo-octatetraene tetramer as 1. Thus tetracyano-ethylene gives a 2:1 adduct 7, and at ca 310° the tetramer fragments cleanly to afford the cyclo-octatetraene dimer 9. Additions to dimer 9 may be effected selectively at the 4,5-double bond, and occur in the exo-mode. The generation of tetrachlorobenzyne from 3,4,5,6-tetrachlorobenzenediazonium carboxylate in tetrahydrofuran results in the ether-ester 22.     

Synthesis,crystal structure,and electronic structure of a copper(II) chloride complex with 9(E)-phenanthrene-9,10-dione[(1Z)-3,3-dimethyl-3,4-dihydroisoquinolin-1(2H)-ylidene]hydrazone [Cu2(L-H)2Cl2]

The [Cu₂(L-H)₂Cl₂] compound (I) has been obtained by the reaction of 9(E)-phenanthrene-9,10-dione[(1Z)-3,3-dimethyl-3,4-dihydroisoquinolin-1(2H)-ylidene]hydrazone with copper(II) chloride. The crystal and molecular structure of I has been determined by X-ray crystallography. The L-H anion acts as a tridentate chelating ligand and is coordinated to the Cu atom through the O(1) atoms of the phenanthrenequinone moiety, the N(1) atom of the dihydroisoquinoline moiety, and the N(3) atom of the azo group to form two five-membered chelate rings. Complex I is a dimer with a double chloride bridge. The coordination polyhedron of the Cu atom is completed to a distorted pyramid by two chlorine atoms. The molecular and electronic structures of the L molecule and the model [Cu(L-H)Cl] complex have been determined by the density functional theory method. Spectroscopic characteristics of I have been determined.     

Transformations thermiques des photooxydes meso des acenes—III: Dimeres de l'o-quinodimethane issu du photooxyde d'anthracene

Thermolysis of the anthracene photooxide 1a, in solution, can afford successively three dimers (I→II→III) the structures of which have been established by NMR and X-ray analysis for the first one. Their origin is the unstable o-quinodimethane diether 3a, coming from 1a by isomenzation, which at 80° dimerizes to 8a (dimer I) by an unusual [_π8_s+_π6_s] concerted cycloaddition. Above 110°, 8a isomerizes into 9a (dimer II) by a concerted [1,5] suprafacial sigmatropic migration. Finally, at higher temperature (~200°), both dimers are partly converted into the symetrical dimer 10a (dimer III), probably by a radical pathway. Thermolysis runned in presence of N-methylmaleimide show the non-reversibility of these reactions, giving two adducts, 15a and 16a, derived from 9a, the structures of which are deduced from NMR data. An explanation of the nature and high selectivity of the proceeding processes is given by considering orbital factors.     

Benzimidazole-based optical probe for selective detection of multiple-cations via dual-channel analysis

A benzimidazole-based optical probe having pendant carboxyl, amine, and imine groups as ionophore has been prepared for screening various metal ions. The 4-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-5-carboxylic acid (1) has been obtained in good yield and characterized by full battery of complementary physico-chemical techniques including ¹H NMR, UV-Vis, fluorescence spectroscopy, and single crystal X-ray crystallography. Metal ion-binding properties of 1 have been studied using ppm level concentration of representative alkali metal (Na⁺, K⁺), alkaline earth metal (Mg²⁺, Ca²⁺), and transition metal (Zn²⁺, Co²⁺, Fe³⁺, Cd²⁺, Hg²⁺, Pb²⁺, Cu²⁺, Ag⁺) ions and the output signal was monitored via two different channels viz chromogenically and fluorogenically. Selective recognition of Hg²⁺ has been explored with absorption spectra whereas emission spectra of 1 display differential response for multiple cations at parts-per-million (ppm) level concentration that allow selective detection of Ca²⁺, Mg²⁺, and Na⁺ ions. The results have been discussed in light of selectivity, sensitivity, response time, mode of binding/interactions, and sensing properties.     

Conformation of some ribofuranosyl imidazole and uracil nucleosides: a 1H and 13C nmr study

100 and 220 MHz ¹H NMR spectra, recorded in DMSO-d₆ solution and including some measurements at 343 K, of three anomeric pairs of novel 2', 3'-O-isopropylidene nucleosides (two ribofuranosyl imidazoles, 1 and 2, and one uridine 3, all related to intermediates in denovo nucleotide biosynthesis) have been analysed, mostly as overlapping ABX spin systems. Chemical shifts and couplings have enabled the α- and β-anomers to be identified; the sugar-ring vicinal H-H coupling constants indicate that the 2',3'-ketal blocking group locks the α and β anomers in predominantly S and approximately 1:1 N/S ribofuranoside conformations, respectively. Among the ¹³C shifts reported for 3 in DMSO-d₆, those of the 2', 3'-O-isopropylidene CH₃ in the α anomer (shift difference 1.4ppm) are around 1.6 ppm upfield of those for the β anomer (which have a shift difference of 1.8 ppm).     

The nuclear magnetic resonance spectra of porphyrins—XI : Self-aggregation of zinc(II) meso-trifluoroacetoxyoctaethylporphyrin

Complex formation in zinc(II) meso-trifluoroacetoxyoctacthylporphyrin (1) and the corresponding acetate (3) has been studied by ¹H and ¹³C NMR spectroscopy. The large concentration dependence of the ¹H chemical shifts of 1 has been analysed in terms of a monomer-dimer equilibrium to give K ～ 3.01 mole^?1 and monomer-dimer shifts of up to 4.2 ppm (for the γ-meso proton). The dimers are immediately dissociated upon addition of methanol. In complete contrast, 3 shows no concentration dependence nor any change upon addition of methanol.The conformations of the model compounds phenyl acetate (4) and phenyl trifluoroacetate (5) were studied by CNDO and solvation calculations and, for 4, by a LIS experiment. Compound 4 exists as the endo conformer in non-polar media, but the exo conformer is preferentially solvated and is also formed when 4 complexes with Eu(fod)₃. In compound 5, the exo-endo energy difference is smaller and is not so affected by solvation; 5 shows no LIS.The large complex shifts found for compound 1 are best explained on the basis of a dimer structure in which the O·CO·CF₃ groups play no part in the association, which is presumably due to a novel metal to porphyrin interaction.     

Nonlinear optical properties of open-shell polychlorotriphenylmethyl radicals

The second-order nonlinear optical (SONLO) response of a series of the highly chemically and thermally stable polychlorotriphenylmethyl monoradicals 1–8 has been studied by Hyper-Rayleigh Scattering. These radicals exhibit relatively high nonlinear optical (NLO) responses with β values ranging from 118×10⁻³⁰ to 755×10⁻³⁰ esu, which may result from an enhancement of the SONLO activities according to their open-shell electronic state. Hyperpolarizability data for radicals 1–8 have also been correlated with their redox potentials, correlation that has turned out to be linearly proportional either with the oxidation or the reduction potentials. These data have been justified in terms of molecular orbital energies. Finally we have successfully explored the capacity of radicals 1–8 to participate in a molecular switching array involving two main steps, an acid/base reaction and a redox process. The presence of open-shell character for this family of compounds makes them attractive candidates to design new multifunctional materials that would simultaneously possess magnetism and NLO.     

Organometallic compound with Lewis base—IV : Dimerization of methyl crotonate by aluminum alkyl-tertiary amine complex

Aluminum alkyl-tertiary amine complex was found to induce the catalytic dimerization of methyl crotonate (MCr) to dimethyl 2-methylpent-4-ene-1,3-dicarboxylate (1) and dimethyl 2-methylpent-cis-3-ene-1,3-dicarboxylate (2). The of the γ-hydrogen of the MCr molecule. Dimer 2 is formed through the isomerization of dimer 1. The complex of AlR₃ with a bidentate ligand, sparteine, produces dimer 1, selectively. The complex of AlR₃ with monodentate ligand NEt₃, on the other hand, induces the isomerization of dimer 1 to the cis-form of dimer 2. The coordination number of aluminum alkyl-tertiary amine complex seems to control the dimerization mechanism of MCr.     

Porous sol gel silica films doped with crystalline NiO nanoparticles for gas sensing applications

A reliable sol gel route to synthesize NiO doped SiO₂ films with different NiO content is here described. The films showed detectable and reversible changes in both optical and electrical properties when exposed to some reducing/oxidizing gaseous species at temperatures in the 250°C–350°C range. A functional characterization protocol has been designed and some of the sensing properties of the materials have been investigated for detecting NO₂, CH₄, CO and H₂. An optical transmittance increase up to 2% has been detected for 1% CO in dry air atmospheres, while relative resistance response (R _R = R _gas/R _air) values up to 4.97 for 850 ppm H₂/air mixtures have been registered for conductometric gas sensing. Films at all NiO molar concentrations in the 10% NiO - 40% range showed an optical response to the target gas, while only 30% and 40% NiO films provided a detectable gas induced resistance change.     

An unusual example of angular momentum coupling: the dependence of the hyperfine constants of the A state of ICI on internuclear separation

Hyperfine Constants for both the iodine and chlorine atoms have been measured for 17 vibrational levels ranging fromv=7 tov=34 (32 for the chlorine atom) of theA ³ II ₁ electronic excited state of the ICI molecule. This provides sufficient data to allow the vibrational dependence of the constants to be inverted to give the dependence on internuclear separation. The constants for the iodine atom have an especially strong dependence on internuclear separation, but they change in a fairly continuous fashion. In contrast, the chlorine atom magnetic hyperfine constant drops abruptly from ?50 MHz to ?20 MHz atr ≈ 3.5 Å. In general, the hyperfine data shows that theA state electronic configuration is quite different from theB state, even though in molecular orbital theory these are just two spin orbit states of the same electronic configuration. To probe the nature of the electronic wave function in more detail, a separated atom model is used to fit the data. One property that can be extracted from the data using this model is the orientation of the bonding orbital on each atom as a function of internuclear distance. The iodine orbital orientation varies from 50° atr=2.6 Å to 70° atr=5.0 Å. The chlorine orbital orientation values fall mostly in the range 46° ± 4°. The LCAO-MO model for theA state predicts that each of the orbitals would be oriented at 45° independent ofr. Although the values for the orbital orientation forr < 3.5 Å need to be used with caution, the data provides an usually detailed example of how the electronic wave function depends on internuclear distance.     

Tetrathiafulvalene-annulated dipyrrolylquinoxaline: the effect of fluoride on its optical and electrochemical behaviors

A tetrathiafulvalene donor has been annulated to 2,3-di(1H-2-pyrrolyl)quinoxaline affording a new chemosensor 1, which shows a unique optical selectivity and reactivity for the fluoride ion over other anions in CH₂Cl₂ leading to a colorimetric response. Electrochemical polymerization of 1 occurred in the presence of fluoride.     

A novel donor–acceptor molecule containing a cyclic triphenylamine dimer: synthesis,characterization, and application in memory device

A novel highly soluble push–pull molecule containing electron-rich cyclic triphenylamine dimer (TPAD) and electron-poor N-phenyl-N′-octyl-naphthalene-1,4,5,8-tetracarboxylic acid bisimide [NI-(8,PBr)] was synthesized under Suzuki-coupling conditions. The resulting compound exhibited excellent thermal stability (T_d=354.3 °C) and good solubility in common organic solvents. Cyclic voltammogram and optical absorption spectroscopy showed that both the electroactive units preserve their nature, respectively, in the ground state, whereas photophysical investigations showed a strong fluorescence quenching. Interestingly, excellent switching behavior with extremely high ON/OFF current ratio (1.6E8 at +1 V) was observed through memory devices based on thin films of this material.     

Ferromagnetic exchange coupling in a new bis(μ-chloro)-bridged copper(II) Schiff base complex: Synthesis,structure, magnetic properties and catalytic oxidation of cycloalkanes

A new (μ-chloro)-bridged complex [Cu(HL)Cl]₂ · H₂O (1) with the Schiff base ligand H₂L, [2-((E)-(2-hydroxyethylimino)methyl)-4-bromophenol], has been synthesized and characterized by elemental analysis, IR, UV–Vis and EPR spectroscopic studies. X-ray diffraction studies show that 1 is a binuclear Cu^II complex with a pair of chlorine atoms bridging the copper atoms in a central Cu₂Cl₂ core. Each copper atom in 1 adopts a distorted square-pyramidal geometry with the imine nitrogen atom, alkoxy and phenoxy oxygen atoms from the Schiff base ligand and a bridging chlorine atom constructing the basal plane, while the apical position of the pyramid is occupied by the other bridging chlorine atom. Variable temperature susceptibility measurements show that complex 1 presents the highest ferromagnetic coupling [J = +43.2(5) cm⁻¹] reported till date in any doubly chloro-bridged Cu^II dimer, and a weak interdimer antiferromagnetic coupling [J′ = -0.276(8) cm⁻¹]. The complex also exhibits high catalytic activity towards the oxidation of hydrocarbons using H₂O₂ as terminal oxidant.     

Asymmetrical nonbridgehead nitrogen—XXIII: Chiral 3,3-bis(trifluoromethyl)diaziridines

By means of the reaction of O-tosyloxime 1a with propargyl amine, esters of glycine and (S)-α-alanine, β-acetoxyethyl amine and β-dimethylaminoethyl amine functionally substituted 3,3-bis(trifluoromethyl)diaziridines 2a–g have been obtained. In the reactions with more bulky amines, (S)-phenylalanine Et ester, (R, S)-α-phenylethyl amine and t-butyl amine, 1a acts as a tosylating reagent. The ester group in diaziridine 2e is readily saponified by alcoholic alkali, whereas diaziridine 2c is rearranged in these conditions with ring-expansion. Complete asymmetric transformation has been found to take place on the formation of the solid phase of diastereomers 2d and 2j, and a closed cycle of diastereomeric transformations has been accomplished. Diaziridine 2g with chiral centres only at the nitrogen atoms has been obtained with the optical purity of 85.5% by resolution via salt 5c with d-(+)-camphor-3-carboxylic acid. The absolute configuration of (+)-2g and its quaternary salt, (+)-2h, has been determined from CD spectra. Optically active (?)-2h salt (optical purity 2.0%) has been also obtained by asymmetric synthesis on the basis of 1–10-camphorsulphonyl oxime 1b. From the kinetics of 2g, h racemization and 2d, e, i, j, k epimerization the energy parameters of the inversion of N atoms in 3,3-bis (trifluoromethyl)diaziridines have been determined.     

Synthesis, chiroptical properties and photoinduced birefringence of optically active methacrylic copolymers bearing side-chain bisazoaromatic moieties

Three series of optically active photochromic copolymers, deriving from methyl methacrylate (MMA) and the chiral bisazoaromatic monomers (S)-3-methacryloyloxy-1-[4′-phenylazo-(4-azobenzene)]-pyrrolidine [(S)-MPAAP], (S)-3-methacryloyloxy-1-[4′-cyanophenylazo-(4-azobenzene)]-pyrrolidine [(S)-MPAAP-C] and (S)-3-methacryloyloxy-1-[4′-nitrophenylazo-(4-azobenzene)]-pyrrolidine [(S)-MPAAP-N], have been prepared and characterized in solution and in the solid state with the aim to evaluate the effect on their chiroptical and thermal properties originated by the insertion of inactive MMA groups along the main chain. The optical activity displayed by the bisazo polymers is discussed in terms of extent of chiral conformation assumed by the macromolecules as a consequence of dipole-dipole interactions between the bisazoaromatic chromophores.The photoinduction of birefringence has been assessed on thin films of the investigated copolymers in order to evaluate their behaviour as materials for optical data storage. The results are interpreted in terms of copolymer composition and conformational stiffness of the bisazoaromatic chromophoric co-units, which are responsible for the optical response rates, and are compared to those of the similar derivatives containing only one azo bond. The observed enhanced thermal properties and the temporal stability appear of interest for a potential use of these materials in nano technologies for all-optical data manipulation and in optoelectronics.     

ClickEnam. 1. Synthesis of novel 1,4-disubsituted-[1,2,3]-triazole-derived β-aminovinyl trifluoromethylated ketones and their copper(II) complexes

The copper(I) catalyzed cycloaddition reaction of N-Boc propargyl amine (dipolarophile) 1 with benzyl azide (1,3-dipole) 2 was found to proceed smoothly in t-BuOH/H₂O at room temperature, to furnish the corresponding 1,4-disubstituted-[1,2,3]-triazole-derived N-Boc amine 3 in good yield. Deprotection of 3 with trifluoroacetic acid and addition of the trifluoroacetate salt 4 in the presence of triethylamine, with a series of methoxyvinyl(trifluoromethyl)ketones 10-14, gave the corresponding β-aminovinyl trifluoromethylated ketones 15-19 in moderate to good yields. Two copper(II) complexes, one monomer and one dimer with chlorine double bridge, 20 and 21, respectively, were also prepared and their crystal structure determined. β-Aminovinyl trifluoromethylated ketones 15-17 and complexes 20 and 21 have been screened as potential antifungal agents and the antimalarial activity of 15 and 16 were tested against two Plasmodium falciparum strains (3D7 and W2).     

Photodimerization-induced transition of helixes to vesicles based on coumarin-12-crown-4

Rational construction of fine-tuning and precisely controllable topological nanostructures based on supramolecular self-assembly system remains a challenge. Herein, coumarin-12-crown-4 (1) as a building block was synthesized by one-pot method and showed reversible high stereo-selective photodimerization (anti-head-to-head dimer (anti-HH-1): syn-head-to-head dimer (syn-HH-1) = 10.8:1) and photocleavage. Helical nanobelts were formed by the self-assembly of 1 through asymmetrical H-bonds, which were in concordance with the crystal state superstructure. Upon irradiation with 365 nm light, these nanobelts transformed into nanoballs which were constructed by three building blocks. Further, we investigated the photoreaction of 1 and got two pure covalent dimers (anti-HH-1 and syn-HH-1). The anti-HH-1 self-assembled into hollow micro-vesicles. The transformation of superstructures based on photo-controlled multiple blocks shines a light to the research on the relationship between molecules and superstructures.     

Optical purity determination and 1H NMR spectral simplification with lanthanide shift reagents—VI. Methohexital, α-dl-5-allyl-1-methyl-5-(1-methyl-2-pentynyl) barbituric acid

The 60 MHz ¹H NMR spectra of racemic methohexital, 1, have been studied with the achiral shift reagent, tris(6,6,7,7,8,8,8-heptafluoro-2,2,-dimethyl-3,5-octanedionato) europium(III), 2, and the chiral tris[3-(trifluoromethylhydroxymethylene)-d-camphorato] europium(III), 3. Appreciable values of the enantiomeric shift differences, ΔΔδ, were observed at low molar ratios of 3:1 for the NHC₃ and CH₃CH in CDCl₃ at 28°C for samples about 0.3 molal in 1. Optical purity determinations should easily be carried out using the CH₃CH resonance at 3:1 ratios as low as 0.067 (ΔΔδ = 0.103 ppm) or within a range of 3:1 ratios from about 0.3 to 0.55. Enantiomeric shift differences of 0.43 and 0.25 ppm were found for the NCH₃ and CH₃CH, respectively, with a 3:1 ratio of 0.575. The latter absorption is preferable for quantitative assays because of freedom from overlap with other protons. Parallel studies with 2 as well as coupling constants support proton assignments.     

Theoretical investigation of nonlinear optical behavior for rod and T-Shaped phenothiazine based D-π-A organic compounds and their derivatives

The exploration of novel materials with excellent nonlinear optical (NLO) features is an area of frontline investigation for scientific community from technological point of view. This study reports the novel phenothiazine-based rod-shaped and T-shaped NLO molecules which are quantum chemically designed from synthesized compounds: rod-shaped (CFA and CBA) and T-shaped (CTA, CCA and CPA). Structural tailoring was performed on D-π-π-A centered CPA chromophore and the effect of various π-spacers, as well as solvents on NLO response properties is investigated. Density functional theory (DFT) along with time dependent DFT (TDDFT) calculations have been executed at B3LYP/6-311G(d,p) functional to examine entire analysis. Results showed a smaller energy gap in structurally modified compounds as compared to reference CPA. Global reactivity parameters analysis revealed smaller hardness and larger softness values in T-shaped compounds. UV–Vis analysis of investigated molecules displayed a red shift in absorption maximum value as compared to CPA. Natural bond orbital (NBO) and frontier molecular orbital (FMO) analysis revealed the stability and intra-molecular electron transferring (ICT) process in investigated molecules. ICT showed the effective charge shift from donor to acceptor via π-spacers. Overall, promising NLO response exists in gas phase and different solvents (acetonitrile, ethyl alcohol and water). Interestingly, proposed molecule CPP presented a maximum value of linear polarizability < α > as 1518.23 a.u and first hyperpolarizability (β_tot) as 755322.39 a.u in acetonitrile solvent. In short, entitled chromophores exhibited excellent NLO properties due to their lower charge transport resistance. This NLO study may open a new topic for researchers to discover novel NLO for hi-tech submissions of modern era.