Effect Of Terminal Substituents Research Articles

Effect of terminal substituents on anion recognition in bis-urea receptors and tetracycline sensing in water

Three bis-urea receptors (L1–L3) with varying terminal substituents (viz. electron deficient/π-acidic,-NO2, -CF3, and electron rich-hydrophobic naphthyl) with different electronic properties have been investigated for their anion recognition potential in both solid as well as in solution phase. L1 was efficiently crystallised with acetate anion, where it forms 1:2 host-guest assemblies. Only fluorescent receptor, L3 has been employed for tetracycline sensing in aqueous medium and its analytical utility has also been demonstrated via sensing of tetracycline in various biofluids.

Liquid crystal and photophysical properties of laterally fluorinated azo-ester materials

ABSTRACT Some laterally fluorinated three-benzene-ring molecular core of azo-ester compounds bearing 2-methylbutoxy unit as the terminal chain were prepared to investigate the effects of terminal substituents on the liquid crystal properties where different opposite terminal groups are introduced. The opposite terminal side substituent, R, is a polar group that alternatively changes between the electron-donating group (OCH3 or OC4H9) and electron-withdrawing group (Br or NO2), including the terminally unsubstituted compound. The structures of all synthesised compounds were confirmed by Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, and elemental analysis. Their mesomorphic properties were studied by differential scanning calorimetry, polarised optical microscopy, and small- and wide-angle X-ray scattering. Mesomorphic studies revealed that all derivatives were liquid crystalline materials, except for the unsubstituted terminal derivative (F1). When the electron-donating group is attached to the terminal phenyl ester moiety, the analogues (F2 and F3) were enantiotropically nematogenic. Terminal substitution with the electron-withdrawing bromine atom (F4) induced the nematic-to-nematic (N-NX) phase transition upon cooling, while the nitro group (F5) exhibited an enantiotropic nematic phase. The terminally nitro-substituted analogue F5 showed the highest bathochromic shift UV-vis absorption bands due to the stronger electron-withdrawing inductive effect of NO2 terminal group.

Substituent effects on the ultraviolet absorption properties of stilbene compounds-Models for molecular cores of absorbents.

The effects of substituent X and Y on ultraviolet (UV) absorption properties of stilbene compounds XPhCHCHPhY (XSBY) were studied both experimentally and computationally from the viewpoint of UV maximum absorption wavelength (λmax) and the corresponding energy (υmax). In the studies, the contribution of substituents on υmax shift was explored. The results show that with increase of electron withdrawing or electron donating ability of X or Y, there is an enhanced electron delocalization of XSBY that leads to bathochromic shift. Computational analyses based on density functional theory were conducted to elucidate the phenomena. It is disclosed that the υmax values are significantly affected by the excited state, though the electronic effect of ground state cannot be ignored. Finally, on the basis of the respective influences of X and Y, a quantitative model, which was proved reliable by the leave-one-out method, was developed to scale the effects of terminal substituents on υmax. According to the model, the effects of substituents X or Y exhibit almost the same action on υmax owing to the symmetric skeleton of the XSBY compounds. The findings provide deep insight into the effects of terminal substituents on UV absorption properties of stilbene compounds, and the derived model enables practical expression of the relationship between substituents and UV absorption.

The effect of terminal substituents on crystal structure, mesophase behaviour and optical property of azo-ester linked materials

ABSTRACTA series of azo-ester linked mesogen containing liquid crystalline acrylate compounds C1-C6 having different terminal groups (–F, –Cl, –Br, –OCH3, –OC2H5 and –OC3H7) were successfully synthesised and characterised. The chemical structure, purity, thermal stability, mesophase behaviour and optical property of the synthesised compounds were investigated by different instrumental techniques. X-ray crystal structure showed that compounds C1, C4 and C5 exhibited more stable E configuration with two bulky group in the opposite side of the N=N double bond motifs. The fluoro-substituted derivative (C1) is connected by the R12(5) type of C–H…O hydrogen bond motifs whereas the molecules of C4, and C5 are connected to each other by means cyclic R22(8) type of C–H…O hydrogen bond motifs. Thermogravimetric study revealed that the investigated compounds exhibited excellent thermal stability. All the compounds showed enantiotropic liquid crystal (LC) phase behaviour and the mesophase formation was greatly influenced by the terminal substituents. Alkoxy (–OCH3, –OC2H5 and –OC3H7) substituted compounds exhibited greater mesophase stability than those of halogen (–F, –Cl and –Br) terminated derivatives. UV-vis spectroscopic study revealed that the investigated compounds exhibited a broad absorption band around 300–420 nm with absorption maximum (λmax) of nearly 370 nm.

Effect of terminal substituents on self-assembly behavior of porphyrin molecules on Ag(110)

Effect of terminal substituents on self-assembly behavior of porphyrin molecules has been studied with three derivatives modified with distinctly different substituents, 5,15-(di-3,5-di-tert-butylphenyl) porphyrin, 5,15-(dimesityl) porphyrin, and 5,15-(di-4-ethynylphenyl) porphyrin. Scanning tunneling microscopy and density functional calculations reveal that 5,15-(di-3,5-di-tert-butylphenyl) porphyrin, 5,15-(dimesityl) porphyrin, and 5,15-(di-4-ethynylphenyl) porphyrin spontaneously give different ordered structures on Ag(110) surface both at room temperature and after annealing. It is clear that the tert-butylphenyl substituent could increase the intermolecular van der Waals interactions to form stable network structure under condition of thermal activation, whereas the mesityl substituent plays an essential role in the formation of rigid chain structure as a result of the CH–π interactions between the mesityl groups of molecule enantiomers. Moreover, the ethynylphenyl substituent could induce metal atoms to coordinate with ethynyl to form organometallic chains. Copyright © 2016 John Wiley & Sons, Ltd.

The effect of terminal substituents on the electronic properties of rod-shaped [HGaNH]n oligomers.

The effect of electron-donating and electron-withdrawing terminal groups on the electronic structure of the rod-shaped X3[HGaNH]nY3 or needle-shaped XGa[HGaNH]nNY oligomers (X, Y = H, CH3, F, CF3; n = 9, 30 and 114) was computationally studied at the B3LYP/SVP level of density functional theory. While the needle-shaped oligomers exhibit moderate variability in the electronic structure upon changing the terminal substituents X and Y, the energy gap of long rod-shaped oligomers varies within 2 eV. For oligomers with n = 114, F3[HGaNH]n(CH3)3 exhibits the largest HOMO-LUMO gap of 2.91 eV, while (CH3)3[HGaNH]nF3 has the smallest gap of 0.94 eV.

Conformational state of benzilidene aniline derivatives from ab initio calculation and NMR spectroscopy data

Quantum chemical calculations of the structure and conformational state of a number of Shiff bases have been performed. 13C NMR spectra of investigated molecules were calculated and compared with experimental data to test verification of the used calculation model. The effect of terminal substituents on the conformation of azomethines and a relation between the conformation and 13C NMR chemical shift were examined.

Effects of Terminal Substituents on Mesomorphic Properties: Phenyl 444-X-Substituted phenyliminomethyl)benzoate and its Isomeric Compounds

Abstract The nematic-isotropic transition temperature of phenyl 4-(4-X-substituted phenyliminomethy1)benzoate and its seven isomeric compounds carrying only one terminal substituent; i.e., methoxyl, ethoxyl, nitro, or cyano group, has been compared. The temperature is influenced not only by the terminal substituent but also by the arrangement of the linking groups and the effects of these two features are mutually dependent. The efficiency order of substituents for nematic thermal stability was found to be CN < NO2 < C2H5O < CH3O. The difference in the temperature is as large as 31 to 54°C between the cyano and methoxy derivatives and 23 to 44°C between the nitro and methoxy derivatives. The latter finding is in sharp contrast with the order CH3O < NO2, which has been generally quoted. In order to find some clue to the relationship between molecular features and mesomorphic behavior, the compounds were classified into four pairs of the isomeric compounds with the same molecular skeleton, those with a carb...

Steric effect of terminal substituents in azomethins and thermal stability of the nematic phase

The paper studies the steric eflect of terminal substituents on the temperature Tc of the phase transition “nematic liquid crystal-isotropic liquid” in mesogenic azomethins with one or two noninteracting or strongly interacting conformation degrees of freedom. The linear dependence Tc(Q) has been confirmed, where Q=(cos2 ϕN) is the conformation paramefer of the molecular ensemble; ϕN is the angle between the planes of the bridging group CH=N and the aniline ring in the benzylideneaniline fragment. Direct and indirect steric eflects of lateral substituents are shown to take place, which explain an anomalous variation of Tc in some compounds upon substitutions in them.

Influence of molecular structure on the liquid-crystalline properties of 1,5-dihetero-spiro[5.5]undecane- and -dispiro[5.2.5.2]hexadecane derivatives

Abstract The synthesis and liquid-crystalline properties of 1,5-dioxa- and 1,5-dithiaspiro[5.5]undecane, 7,16-dioxa-dispiro[5.2.5.2]hexadecane and 1,5,10,14-tetraoxa-dispiro[5.2.5.2]hexadecane derivatives are described. The effects of terminal sub-stituents and molecular structure on the liquid-crystalline properties of these materials are discussed.

Molecular Structure and Nematic Liquid Crystalline Behaviour

Abstract In this review some experimental results on the variation of the nematic-isotropic transition temperature TN1 with molecular structure will be evaluated with the aid of expressions for TN1 from molecular-statistical theories. The effect of terminal substituents on TN1 and some typical trends in the values of TN1 for the members of homologous series can be understood from changes in the anisotropic dispersion forces as discussed in Maier and Saupe's theory. The effects of some other structural changes in the molecules on TN1, as for example the variation of central groups, cannot be explained on this basis. Probably it is necessary to take into account as well the molecular repulsions due to the excluded volume.

Terminal groups in the nematic and cholesteric phases: a thermodynamic study

The effects of terminal substituents in the nematic and cholesteric phases have been investigated by examination of the enthalpy and entropy changes of the mesophase–isotropic transition by calorimetric differential thermal analysis. A series of nematic, unsymmetrical p-phenylene bis-(para-substituted benzoates) were chosen in which one substituent was varied among small, compact groups, and a series of cholesteryl para-substituted benzoates were also studied. The nematic series showed that the transition temperature and the transition heat are not directly proportional as is quite commonly assumed; ΔHN→I was found to be strongly related to the electron donating character of the substituent. The cholesteric series showed ΔHch→I which were not correlatable with substituent polarity or electronic donating character; Tch→I and ΔHCh→I were also not directly related. The heats and entropies were intimately related along both series suggesting that as intermolecular order increases so does intermolecular binding for these compounds. The nematic and cholesteric phases have very similar terminal group efficiencies when the transition temperature is taken as the criterion for mesophase stability, but they show no such similarities with regard to heats and entropies of the mesophase–isotropic transition.

Liquid crystals. IV. Effects of terminal substituents on the nematic mesomorphism of p-phenylene dibenzoates

Liquid crystals. IV. Effects of terminal substituents on the nematic mesomorphism of p-phenylene dibenzoates