Vapour pressures of crystalline 1,2,4,5-tetrachlorobenzene,and crystalline and liquid 1,3,5-trichlorobenzene and 1,2,4,5-tetramethylbenzene

Vapour pressures as a function of temperature for 1,3,5-trichlorobenzene [CA 108-70-3] (crystalline and liquid), 1,2,4,5-tetrachlorobenzene [CA 95-94-3] (crystalline), and 1,2,4,5-tetramethylbenzene [CA 95-93-2] (crystalline and liquid) were determined by means of a diaphragm manometer and simultaneous torsion, mass-loss effusion. An unconventional but simple method is used for the representation and the assessment of the present experimental results, together with results from other authors. The method is physical in nature, and at the same time reveals the quality of the experimental results in terms of random and systematic errors. The thermodynamic properties at p^o =  1 Pa were evaluated, the results being (the uncertainties are standard deviations, and T_tdenotes triple point):     

Low frequency internal modes of 1,2,4,5-tetramethylbenzene, tetramethylpyrazine and tetramethyl-1,4-benzoquinone INS, Raman, infrared and theoretical DFT studies

The results of inelastic neutron scattering (INS), Raman and infrared (IR) studies on 1,2,4,5-tetramethylbenzene (durene), tetramethylpyrazine (TMP) and tetramethyl-1,4-benzoquinone (TMBQ) in the solid state are reported. The observed frequencies are analyzed on the basis of DFT calculations. The low frequency region, below 400 cm(-1), related to the torsional and bending out-of-plane vibrations of the CH(3) groups, is of particular interest. The detailed analysis is possible due to the simulation of the INS spectra by using the auntie-CLIMAX program. It is shown that the observed low frequency INS bands are dramatically shifted, compared to the calculated ones, towards higher frequencies. Although one cannot exclude deficiencies of theoretical methods as applied to low frequency modes, it seems more probable the interpretation based on an existence of non-conventional CH(...)pi, CH(...)N, CH(...)O hydrogen bonds formed by the methyl groups in crystalline phases.     

1,2,4,5-Tetrazines: An intriguing heterocycles family with outstanding characteristics in the field of luminescence and electrochemistry

The 1,2,4,5-Tetrazines, or s-tetrazines, are a particular example of small, high nitrogen content heterocycle with extremely original physico-chemical properties. In this review, we summarize the last 20 years of research on this topic, focusing more on fluorescence and related optical properties on tetrazines, and tetrazine derived materials.     

Solvent extraction of organic molecules of exobiological interest for in situ analysis of the Martian soil

A solid-liquid extraction method able to perform in situ extraction of organic compounds on Mars is proposed. The extraction efficiency of various organic solvents was tested and compared to that of water. The selected key compounds are molecules of exobiological interest: glycine, alanine, serine, glutamic acid, oxalic acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid and 1,3,5-benzenetricarboxylic acid. Among the organic solvents, propanol gives the highest yield of extraction for all the targeted compounds except for benzoic acid. A mixture of propanol and ethyl acetate increases significantly the extraction yield of benzoic acid. The extraction time was considerably reduced (140 h to 15 min) by using sonication. The method is discussed for an easy automation with coupling to an in situ GC-MS space instrument.     

Conformation and luminescence of isolated molecular semiconductor molecules

In this article, we describe, for the first time, direct comparisons of the detailed structures of two small molecule organic semiconductors, oligo(phenylenvinylene) (OPV) molecules with chains of five and six phenyl rings (5R-OC(8)H(17) and 6R-OC(8)H(17)), respectively, and their luminescence properties on a single molecule level. Our data originate from a combination of two powerful diagnostic tools in physical chemistry: ion mobility and single molecule fluorescence spectroscopy. These techniques enable us to precisely determine the shapes of isolated molecules in the gas phase and to correlate these structures to the emission from single molecules supported on bare glass substrates. The principal structural uncertainty in OPVs is the (possible) presence and location of cis-vinylene linkages (cis-defects) in the oligomer. The results show that the structures observed in the gas phase are strongly correlated to the categories of molecules observed in the single molecule polarization anisotropy measurements with nearly identical distributions for the two OPV molecules studied. Each category is also characterized by the luminescence efficiency of the molecules in each class, providing a direct correlation between the luminescence efficiency and the shape of the molecule. This combination of techniques provides a level of information far beyond that obtained via any other analytical technique.     

The pyrolytic identification of organic molecules: I. The pyrolytic behavior of organic molecules

Results of a study on the pyrolysis of about 70 organic compounds of varied composition are presented and discussed. Identification of the volatile products formed was accomplished by mass spectrometry. It is shown how the pyrolytic patterns may be employed to distinguish one molecule from another. Some attention has been given to isomeric compounds and to aromatic structures containing one or more functional groups.     

Morphine,the Proteus of organic molecules

This feature article encapsulates the senior author's longstanding interests in opiate chemistry and attempts to place it within an historical context and against the backdrop of related work by others who have viewed morphine as one of the pinnacles of natural product synthesis. Biomimetic and 'bioanalogous' routes to the morphine skeleton are discussed followed by approaches based on the elaboration of phenanthrene platforms. The latter include an asymmetric synthesis of ent-morphine developed in our laboratory.     

Dinuclear ReI complex based on 1,2,4,5-tetrakis(diphenylphosphino)- pyridine: synthesis and luminescence properties

The reaction of 1,2,4,5-tetrakis(diphenylphosphino)pyridine (L) with Re(CO)₅Br (in a molar ratio of 1:2) leads to the bis-chelated complex [Re₂(CO)₆(L)Br₂] in 95% yield. At ambient temperature, the solid complex exhibits green phosphorescence (λ_max = 535 nm) with a quantum yield of 12% and a lifetime of 90 μs.     

Dinuclear Cu(I) complexes of 1,2,4,5-tetra(7-azaindolyl)benzene: persistent 3-coordinate geometry, luminescence, and reactivity

Five Cu(I) complexes [Cu2(ttab)(CH3CN)2][BF4]2 (1), [Cu(2)(ttab)(PPh3)2][BF4]2 (2), [Cu2(ttab)I2] (3), [Cu2(ttab)(I3)2] (4), and [Cu2(ttab)(I)BF4]n (5) with 1,2,4,5-tetra(7-azaindolyl)benzene (ttab) have been synthesized and characterized. The structures of compound 1, 2, 4, and 5 have been determined by single-crystal X-ray diffraction analyses, which established that 1, 2, and 4 are discrete dinuclear Cu2 compounds while compound 5 is a 1D coordination polymer with the I- ligand bridging two dinuclear Cu2 units. The ttab ligand in all four complexes adopts a 1,3-chelation mode. The Cu(I) center in all complexes is three-coordinate. Close contact between the Cu(I) center and the benzene ring in the ttab ligand was observed in all four structures, which is believed to play a role in stabilizing the three-coordinate geometry of the Cu(I) center. The crystals of 1, 2, and 5 contain channels in the lattice that host solvent molecules such as CH2Cl2 and toluene. Fluorescent measurements established that, in solution, compounds 1-3 display weak blue luminescence which originates from the ttab but is significantly red-shifted and has a much lower emission intensity, compared to the free ttab ligand. The application of compound 1 in C-N cross-coupling reactions was examined by using the reaction of phenyl halides with imidazole as a model system. For the reaction with phenyl iodide, 1 was found to be as effective a catalyst as the CuI/1,10-phenanthroline system. For the reaction with phenyl bromide, 1 is less effective than the CuI/1,10-phenanthroline system. Compound 1 reacts with O2 gas, as established by UV-vis spectra, but the oxidized products have not been characterized.     

In situ analysis of the Martian soil by gas chromatography: decoding of complex chromatograms of organic molecules of exobiological interest

Gas chromatography-mass spectrometry (GC-MS) will be used in future space exploration missions, in order to seek organic molecules at the surface of Mars, and especially potential chemical indicators of life. Carboxylic acids are among the most expected organic species at the surface of Mars, and they could be numerous in the analysed samples. For this reason, a chemometric method was applied to support the interpretation of chromatograms of carboxylic acid mixtures. The method is based on AutoCovariance Function (ACVF) in order to extract information on the sample--number and chemical structure of the components--and on separation performance. The procedure was applied to standard samples containing targeted compounds which are among the most expected to be present in the Martian soil: n-alkanoic and benzene dicarboxylic acids. ACVF was computed on the obtained chromatograms and plotted versus retention time: peaks of the ACVF plot can be related to specific molecular structures and are diagnostic for chemical identification of compounds.     

Quintet states of organic molecules: magnetic energies,spin-states and ESR-selection rules

For a pure quintet state (S = 2) consisting of four electrons interacting via magnetic dipole interaction the following magnetic properties are calculated: zero field splitting, selection rules for magnetic dipole transition in zero field, anisotropy of the ESR resonance fields, ESR selection rules and effective spin. The comparison with experimental ESR spectra on intermediate states during the photopolymerisation of diacetylene crystals shows that these states are quintet states.     

Water-soluble organic dppz analogues--tuning DNA binding affinities, luminescence, and photo-redox properties

Three new water-soluble dppz derivatives are reported, one of which binds to DNA with an affinity comparable to any mononuclear metal complex and also displays a high selectivity for GC sites.     

Microwave-assisted solvent-free catalyzed synthesis and luminescence properties of 1,2,4,5-tetrasubstituted imidazoles bearing a 4-aminophenyl substituent

A solvent-free microwave-assisted four-component synthesis of 1,2,4,5-tetrasubstituted imidazoles bearing a 4-aminophenyl substituent was studied by condensation of p-phenylenediamine, aryl diketone, benzaldehyde derivatives and ammonium acetate in the presence of solid support silica gel and catalyst Keggin-H₃[PW₁₂O₄₀]. The effects of four components molar ratio along with catalyst loading, irradiation time on the yields were investigated. Also, the structures of synthesized compounds were characterized by FT-IR, HRMS, ¹H NMR and ¹³C NMR spectroscopy. Furthermore, their ultraviolet–visible maximum absorption, liquid fluorescence emission maximum and quantum yields were, respectively, measured in 0.05 M H₂SO₄ aqueous solution and in dichloromethane. Simultaneously, solid fluorescence spectra were determined in the powder state. The relationships between the optical behavior and the polarity of the solvents for some compounds were assessed. The results showed that the fluorescence quantum efficiency was increased by introducing amino phenyl in comparison with benzyl on 1-position of trisubstitued imidazoles. The compounds synthesized were sensitive to the polarity of the solvents.     

Intramolecular perturbations and the quenching of luminescence in small molecules

We consider the problem of interpreting quenching kinetics in small molecules [e.g., CN, CH₂, NO₂ and SO₂] which show significant intrinsic interactions, and argue the importance of analyzing these data in terms of collisional transitions between perturbed (mixed electronic parentage) as opposed to pure (non-spectroscopic) vibronic states. Time resolved experiments are discussed which could determine more unambiguous deactivation cross sections and spectral assignments.     

Bicyclo[2.2.2]octene-based "crab-like" molecules: synthesis, complexation, luminescence properties, and solid-state structures

[structure, reaction: see text] The U-shaped, multifunctionalized tetraetheno-bridged dicyclopenta[b,i]anthracenediol 10 was synthesized to serve as a platform molecule. The molecule was prepared from the Diels-Alder adduct 5a of tricycloundecatriene 3 and bicyclo[2.2.2]octene-fused p-benzoquinone 4. Functionalization of 10 to construct crab-like molecules was achieved via the base-promoted bis-O-alkylation of two endo-oriented hydroxyl groups at termini in 10 with the following alkyl halides: allyl, propagyl, and benzyl bromides; 1-bromo- and 1-iodo-4-(bromomethyl)benzene; 9-(bromomethyl)anthracene; 1-(bromomethyl)pyrene; and isomeric bromomethylpyridines. Single-crystal X-ray structures were obtained for bis-phenyl (21) and bis-pyrenyl (25) crabs, and for the silver(I) complex (32 and 33) crabs. The silver(I) complex 32 from bis-o-pyridyl crab 30 is a [2+2] dimeric dimetallocyclophane, and 33 from bis-m-pyridyl crab 29 is a [1+1] metallo-bridged cyclophane. The self-assembled intramolecular pi-stacking of pyrenyl rings in 25 with an interplanar distance of 3.40 A and the consequent pi-pi interactions were revealed by the X-ray crystal structure and its luminescence property.     

两种新型有机激光染料的合成、结构和上转换 发光性质

合成了两个新的有机晶体：反式-4-[4'-(N-羟乙基-N-甲基胺基)苯乙烯基]-N-甲基吡啶对甲苯磺酸盐trans-4-[4'-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridiniumtoluene-p-sulfonate(简称HMASPS)和反式-4-[4'-(N-羟乙基-N-乙基胺基)苯乙烯基]-N-甲基吡啶对甲苯磺酸盐trans-4-[4'-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridiniumtoluene-p-sulfonate(简称HEASPS)。用X射线衍射方法对这两个单晶进行了结构测定。测试了它们频率上转换荧光及激光性质。在1064nm的ps脉冲激光的激发下,HMASPS和HEASPS在溶液中均发出～625nm的上转荧光和激光,并且有可观的激光效率。     

Dielectric studies on some mesogenic,non-mesogenic and organic molecules

Two important molecular parameters, namely, the dielectric relaxation time τ and electric dipole moment are highly useful in having insight into the molecular structure, size, shape, apart from the inter- and intra-molecular forces, etc. With these in view dielectric measurements in benzene at room temperature on the pure samples of o-ethyl phenol, 2-n-butylphenol, 4-n-butylphenol, 2,6-dimethoxyphenol and 3,4-difluorophenol were carried out at a frequency of 9.98 GHz by employing concentration variation method. Similar measurements, on a single weight fraction of each of them at 9.98 GHz and also at 8.74 GHz are carried out. Measurements on a single weight fraction in benzene of each of the liquid crystal samples, namely, EPCP.car (Butyl-p-(p-ethoxy phenoxy corbonyl)-phenyl carbonate), PPPB (p-pentylphenyl-p-propyl benzonate), EPAP.Hp (p-(p-ethoxyphenyl azo) phenyl heptenate) and EPAP. Und (p-(p-ethoxyphenyl azo) phenyl undecylenate were also carried out at the said two frequencies. Using the obtained values of ε′, ε′′ relaxation time and dipole moment were determined using different methods. The obtained results are compared with earlier results wherever available.     

Determining and reporting purity of organic molecules: why qNMR

Although NMR has been routinely used to determine/estimate relative number of protons for structure elucidation, it has been rarely used to determine and report the purity of organic compounds. Through this paper, we want to emphasize on routine use of quantitative NMR (qNMR) for this purpose. The results of qNMR can be routinely considered as documentation of purity much like other established methods (HPLC, elemental analysis and differential scanning calorimetry). qNMR is a fast, easy, accurate and non‐destructive alternate to speed up the whole analytical process and serves the purpose of both identification and purity determination of compounds using single technique. Copyright © 2012 John Wiley & Sons, Ltd.