Electronic spectroscopy of highly-polar aromatics. V. The polar excimer of N,N-dialkyl-p-cyanoaniline

The fluorescence spectra of N, N-dialkyl-p-cyanoanilines in fluid media have been re-examined. The long-wavelength fluorescence, previously attributed to a solvated ¹L_a → ¹A₁ fluorescence, is interpreted as an excimer fluorescence, an assignment which is supported by concentration dependence studies and quenching experiments. The temperature dependence of the excimer/ monomer fluorescence intensity ratio indicates that excimer formation is a diffusion controlled process. The binding energy of the excimer is found to be independent of the nature of the solvent and to be smaller than those values estimated for excimers of polycyclic aromatic hydrocarbons. Solvent viscosity, solvent polarity and specific solvent-solute interactions affect the excimer/monomer fluorescence intensity and these effects are interpreted. The geometry of the excimer is also discussed.     

High-load, oligomeric dichlorotriazine: a versatile ROMP-derived reagent and scavenger

A new high-load, soluble oligomeric dichlorotriazine (ODCT) reagent derived from ring-opening metathesis polymerization (ROMP) is reported as an effective coupling reagent, scavenger of nucleophilic species, and activator of DMSO for the classic Swern oxidations. Two variants of this reagent (2G)ODCT 4 and (1G)ODCT 16, possessing theoretical loads of 5.3 and 7.3 mmol/g, respectively, have been synthesized. Preparation was accomplished via simple synthetic protocols affording free flowing powders, amenable for large-scale production. Removal of the spent oligomeric reagent was achieved via either precipitation of the spent reagent or simple filtration utilizing a silica SPE, followed by solvent removal, to deliver products in excellent yield and purity. In addition, the corresponding norbornenyl monomer 3 was successfully demonstrated in a couple-ROMP-filter protocol utilizing in situ polymerization, achieving comparable results versus the corresponding oligomeric variant.     

Zinc(II), nickel(II) and cadmium(II) coordination polymers based on the ligand oxamide <Emphasis Type="Italic">N,N</Emphasis>-bis(4-phthalic acid): synthesis,structural characterization and magnetic properties

Three coordination polymers based on the new ligand oxamide N,N-bis(4-phthalic acid), namely [Zn(L)_0.5-(2,2′-bpy)] _n (1), [Ni₂(2,2′-bpy)₄(µ ²-Ox)]L·3H₂O (2) and [Cd(L)(1,10-phen)] (3) [L = oxamide N,N-bis(4-phthalic acid)], (2,2′-bpy = 2,2′-bipyridine), (1,10-phen = 1,10-phenanthroline), have been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction: compound 1 is one-dimensional ladder-like coordination polymer, compound 2 exhibits a three-dimensional structure resulting in extensive hydrogen bonds built with the help of lattice water molecules, compound 3 also exhibits a three-dimensional supramolecular structure. All compounds were also characterized by elemental analysis, IR spectra and thermogravimetric analysis; furthermore, the magnetic measurements for 2 reveal antiferromagnetic coupling between the nickel(II) ions.     

The Influence of Divalent Anions on the Rectification Properties of Nanofluidic Diodes: Insights from Experiments and Theoretical Simulations

During the last decade, the possibility of generating synthetic nanoarchitectures with functionalities comparable to biological entities has sparked the interest of the scientific community related to diverse research fields. In this context, gaining fundamental understanding of the central features that determine the rectifying characteristics of the conical nanopores is of mandatory importance. In this work, we analyze the influence of mono‐ and divalent salts in the ionic current transported by asymmetric nanopores and focus on the delicate interplay between ion exclusion and charge screening effects that govern the functional response of the nanofluidic device. Experiments were performed using KCl and K₂SO₄ as representative species of singly and doubly charged species. Results showed that higher currents and rectification efficiencies are achieved by doubly charged salts. In order to understand the physicochemical processes underlying these effects simulations using the Poisson‐Nernst‐Planck formalism were performed. We consider that our theoretical and experimental account of the effect of divalent anions in the functional response of nanofluidic diodes provides further insights into the critical role of electrostatic interactions (ion exclusion versus charge screening effects) in presetting the ionic selectivity to anions as well as the observed rectification properties of these chemical nanodevices.     

The reproducing kernel algorithm for handling differential algebraic systems of ordinary differential equations

The aim of the present analysis is to implement a relatively recent computational method, reproducing kernel Hilbert space, for obtaining the solutions of differential algebraic systems for ordinary differential equations. The reproducing kernel Hilbert space is constructed in which the initial conditions of the systems are satisfied. While, two smooth kernel functions are used throughout the evolution of the algorithm in order to obtain the required grid points. An efficient construction is given to obtain the numerical solutions for the systems together with an existence proof of the exact solutions based upon the reproducing kernel theory. In this approach, computational results of some numerical examples are presented to illustrate the viability, simplicity, and applicability of the algorithm developed. Finally, the utilized results show that the present algorithm and simulated annealing provide a good scheduling methodology to such systems. Copyright © 2016 John Wiley & Sons, Ltd.     

Electronic states and “Geometric Isomerism” of p-disubstituted cyanoanilines

Computations of CNDO/s CI type show that the two lowest energy ¹Γ

states of p-disubstituted cyanobenzenes are 1¹B₁(ππ^*) and 2¹A₁(ππ^*), in order of increasing energy. If the (CH₃)₂N-group of N,N-dimethyl-p-cyanoaniline (NNDMPCA or dimethylaminobenzonitrile) is twisted out of the plane of the benzenoid ring, the two transitions 1¹B₁ ← 1¹A₁ and 2¹A₁ ← 1¹A₁ undergo an increase of energy and a decrease of intensity. The postulated state in which an electron is promoted from the twisted (90°) (CH₃)₂N-group to a vacant in-plane π_χ^* orbital of the cyano group is predicted to lie ≈35409 cm^?1 above the 1¹B₁(ππ^*) state. This prediction contradicts an essential postulate of the excited state isomerization model which has been used to interpret the anomalous fluorescence behavior of NNDMPCA.     

Novel 2′-substituted amino-3-methoxy-16α-bromo-17-oxoestra-3,5(10)-dieno[1,2-b]thiazoles

A novel series of steroidal[1,2-b]thiazoles was synthesized by cyclization of several thiourea derivatives with bromine according to Hugerschoff synthesis. The H-nmr spectral analyses elucidating the structure of the products and the orientation of ring closure are reported.     

Studies on quinones. Part 40: Synthesis and cytotoxicity evaluation of anthraquinone epoxides and isomerization products

Aerobic oxidation of 1,4,4a,10a-tetrahydro-1,4-alkano-5,10-anthraquinones and thiophene-analogues in dichloromethane-DBU yielded the corresponding dihydroalkanoquinones which, depending on their structures, react with in situ generated hydroperoxide anion to give quinone epoxides and/or hydroperoxides. The calcium hydroxide-induced rearrangement of quinone epoxides yielded furan-containing angular quinones. The cytotoxic activities of quinone epoxides and their isomerization products were evaluated in vitro against normal human lung fibroblasts (MRC-5) and human cancer gastric epithelial cells (AGS).     

Computation of aromatic C3N4 networks and synthesis of the molecular precursor N(C3N3)3Cl6

The successful synthesis and structural characterization of molecules that represent segments of extended solids is a valuable strategy for learning metric and stereochemical characteristics of those solids. This approach has been useful in cases in which the solids are particularly difficult to crystallize and thus their atomic connectivity and overall structures become difficult to deduce with X-ray diffraction techniques. One such class of materials is the covalently linked C(x)N(y) extended solids, where molecular analogues remain largely absent. In particular, structures of C(3)N(4) solids are controversial. This report illustrates the utility of a simple molecule, N(C(3)N(3))(3)Cl(6), in answering the question of whether triazine based C(3)N(4) phases are layered or instead they adopt 3D structures. Here, we present density functional calculations that clearly demonstrate the lower stability of graphitic C(3)N(4) relative to 3D analogues.     

Solvent-dependent photoacidity state of pyranine monitored by transient mid-infrared spectroscopy.

We investigate with femtosecond mid-infrared spectroscopy the vibrational-mode characteristics of the electronic states involved in the excited-state dynamics of pyranine (HPTS) that ultimately lead to efficient proton (deuteron) transfer in H2O (D2O). We also study the methoxy derivative of pyranine (MPTS), which is similar in electronic structure but does not have the photoacidity property. We compare the observed vibrational band patterns of MPTS and HPTS after electronic excitation in the solvents: deuterated dimethylsulfoxide, deuterated methanol and H2O/D2O, from which we conclude that for MPTS and HPTS photoacids the first excited singlet state appears to have charge-transfer (CT) properties in water within our time resolution (150 fs), whereas in aprotic dimethylsulfoxide the photoacid appears to be in a non-polar electronic excited state, and in methanol (less polar and less acidic than water) the behaviour is intermediate between these two extremes. For the fingerprint vibrations we do not observe dynamics on a time scale of a few picoseconds, and with our results obtained on the O-H stretching vibration we argue that the dynamic behaviour observed in previous UV/Vis pump-probe studies is likely to be related to solvation dynamics.