Effect of Specific Solute-Solvent Interaction and Electron Donor-Acceptor Substituents of Novel Pyrazolo Naphthyridines on Fluorescence

Heterocyclic orthoaminoaldehyde such as 4-amino-3-(4-phenyl)-1-phenyl-1H-Pyrazolo[3,4-b]pyridine-5-carbaldehyde was synthesized by multistep reactions involving reduction of azido derivative 2 with LAH to yield aminoalcohol 3 and oxidation of it with MnO(2) to aminoaldehyde 4.The pyridine ring annulated on to 4 by Friedl?nder condensation using acetophenones in presence of base to obtained pyrazolo[3,4-h][1,6]naphthyridine 5 in excellent yield. Study of photophysical properties of 5 revealed that the absorption and emission of them depends up on the substituents present on benzene ring in newly annulated pyridine ring.     

Polarized naphthalimide CH donors enhance Cl- binding within an aryl-triazole receptor

The dipolar character of 1,8-naphthalimide together with polarization of the C(4)-H and C(5)-H donors has been utilized in receptor 1 to effectively bind chloride alongside triazole and phenylene units. The Cl(-) binding strength of 1 shows that the naphthalimide provides greater anion stabilization than an unactivated phenylene, and DFT calculations show that its collinear donor array can be a "urea-like" analog for CH···anion interactions.     

Synthesis of nicotinonitrile derivatives and study of their photophysical properties

Abstract  

A convenient route was developed for the synthesis of novel nicotinonitrile derivatives by a three-component Dimroth reaction of chalcones, malononitrile, and secondary heterocyclic amines or sodium alcoholate. Nicotinonitrile derivatives are obtained in fair to good yields. The structures of all new compounds were established by spectroscopic characteristics and their photophysical properties were studied.     

Aromatic and aliphatic CH hydrogen bonds fight for chloride while competing alongside ion pairing within triazolophanes

Triazolophanes are used as the venue to compete an aliphatic propylene CH hydrogen‐bond donor against an aromatic phenylene one. Longer aliphatic C? H ??? Cl^? hydrogen bonds were calculated from the location of the chloride within the propylene‐based triazolophane. The gas‐phase energetics of chloride binding (ΔG_bind, ΔH_bind, ΔS_bind) and the configurational entropy (ΔS_config) were computed by taking all low‐energy conformations into account. Comparison between the phenylene‐ and propylene‐based triazolophanes shows the computed gas‐phase free energy of binding decreased from ΔG_bind=?194 to ?182 kJ mol^?1, respectively, with a modest enthalpy–entropy compensation. These differences were investigated experimentally. An ¹H NMR spectroscopy study on the structure of the propylene triazolophane’s 1:1 chloride complex is consistent with a weaker propylene CH hydrogen bond. To quantify the affinity differences between the two triazolophanes in dichloromethane, it was critical to obtain an accurate binding model. Four equilibria were identified. In addition to 1:1 complexation and 2:1 sandwich formation, ion pairing of the tetrabutylammonium chloride salt (TBA⁺ ? Cl^?) and cation pairing of TBA⁺ with the 1:1 triazolophane–chloride complex were observed and quantified. Each complex was independently verified by ESI‐MS or diffusion NMR spectroscopy. With ion pairing deconvoluted from the chloride–receptor binding, equilibrium constants were determined by using ¹H NMR (500 μM ) and UV/Vis (50 μM ) spectroscopy titrations. The stabilities of the 1:1 complexes for the phenylene and propylene triazolophanes did not differ within experimental error, ΔG=(?38±2) and (?39±1) kJ mol^?1, respectively, as verified by an NMR spectroscopy competition experiment. Thus, the aliphatic CH donor only revealed its weaker character when competing with aromatic CH donors within the propylene‐based triazolophane.     

Synthesis of Polysubstituted Pyrazolo[3,4‐b]pyridine‐3‐Carbohydrazide and Pyrazolo[3,4‐d]pyridazine Derivatives

5‐Amino‐4‐formyl pyrazole carboxylate gave facile reactions with malononitrile, hydrazine, and ketones in the presence of piperidine furnished substituted pyrazolo[3,4‐b]pyridines and pyrazolo[3,4‐b]quinolones. The pyridazine sulfonamides were obtained by the reaction of 5‐chloro 4‐formyl pyrazole carboxylate with sulfonamide derivatives.     

Michael addition of dimedone with α,β‐unsaturated ketones: Synthesis of quinoline and chromene derivatives

A series of quinoline and chromene derivatives has been synthesized by Michael addition of dimedone 1 with 2‐aroyl‐3‐arylacrylonitrile 2 and study of absorption and fluorescence maxima of quinolines.     

Dendrimer analogues of linear molecules to evaluate energy and charge-transfer properties

[reaction: see text] We have designed and synthesized difunctionalized dendrimers containing two donors in the periphery and an acceptor at the core to serve as scaffolds for comparison with linear analogues to investigate the advantage of dendritic scaffolds for energy and charge transfer. Comparison of these dendrimers with the fully decorated dendrimers provides information on the advantage of chromophore density in energy/charge transfer from periphery to the core.     

Synthesis of novel benzo[h][1,6]naphthyridine derivatives from 4-aminoquinoline and cyclic β-ketoester

This paper describes the synthesis of 2,8-dichloroquinolin-4-amine 4 and 4,5,7-trichloro-3-(2-chloroethyl)-2-methylbenzo[h][1,6]naphthyridine 8 as novel class of building blocks. Also describes the regioselective S_NAr reactions of 2,4,8-trichloroquinoline 2 on C₂ and C₄ positions with azide, similarly S_NAr reactions of benzo[h][1,6]naphthyridine 8 at C₄, C₅ positions, and S_N2 reactions on C₃-(2-chloroethyl) side chain with nucleophiles such as primary aromatic amines, methoxide/ethoxide, and azide at different temperatures.     

Finite element simulation of deformation behaviour of cellular rubber components

This paper presents a new prospect of investigating the mechanical behaviour of cellular rubber using porous hyperelastic material model. There are number of hyperelastic material models to describe the behaviour of homogeneous elastomer, but very few to characterise the complex properties of cellular rubber. The analysis of dependence of material behaviour on pore density using the new material model is supported with experiments to characterise the actual material behaviour. The new material model which is based on Danielsson et al [1] decouples the influence of porosity from the mechanical properties of the solid material by introducing volume fraction of the pores as an explicit scalar variable. The finite element simulations are then followed by experiments on complex model to validate the material model. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of Pyrazolopyridine Annulated Heterocycles and Study the Effect of Substituents on Photophysical Properties

Pyrazolo[3,4-b]pyridines having 4-chloro-5-chloroethyl side chain are synthesized by the reaction of 5-aminopyrazole and cyclic β-formylester gave aminopyrazolodihydrofuranone intermediate, which on cyclization in phosphorous oxychloride exclusively converted in to 4-chloro-5-chloroethyl pyrazolo[3,4-b]pyridines 4(a-b) in major amount. The side chain with acetic acid, thiourea and aromatic amines are used to form angular ring leads to formation of tricyclic Furo[2,3-d]pyrazolo[2,3-b]pyridines 5(a-b), pyrazolo[3,4-b]thieno[2,3-d]pyridines 6(a-b) and pyrazolo[3,4-b]pyrrolo[2,3-d]pyridines 7(a-n) respectively. The substituents effect at C₄ position on fluorescence properties of pyrazolopyridines has been studied. Moreover the effect of electron donor and halogen substituents on fluorescence properties of pyrazolopyrrolopyridines 7(a-n) has been investigated along with their fluorescent quantum yield.