New Nitro-Laterally Substituted Azomethine Derivatives; Synthesis, Mesomorphic and Computational Characterizations.

Mohamed A El-Atawy,Hoda A Ahmed,Salma A Al-Zahrani,Magdi M Naoum

doi:10.3390/molecules26071927

Abstract

Two new homologues series, based on two rings of the azomethine central group bearing the terminal alkoxy group of various chain lengths, were prepared. The alkoxy chain length varied between 6 and 16 carbons. The other terminal wing in the first series was the F atom, and the compound is named N-4-florobenzylidene-4-(alkoxy)benzenamine (In). The second group of compounds included a lateral NO2 substituent in addition to the terminal F atom, named N-(4-fluoro-3-nitrobenzylidene)-4-(alkyloxy)aniline (IIn). Mesomorphic and optical properties were carried out via differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Elemental analyses, FT-IR, and NMR spectroscopy were carried out to elucidate the molecular structures of the synthesized groups. Mesomorphic investigations indicated that all the synthesized homologues (In) were monomorphic, possessing the smectic A (SmA) phase monotropically, while the second group (IIn) members were non-mesomorphic. The experimental data indicated that the formation of the mesophase is affected by the protrusion of the lateral nitro group. The disruption of the mesophase in the second group was attributed to the increase of its molecular width, which affects its lateral intermolecular interactions. The computational simulations were in agreement with the experimental data. On the other hand, the location of NO2 group within the molecular geometry increased the melting temperature of the molecule, and thus, affected their thermal and physical properties. By discussing the estimated parameters, it was found that the molecular architecture, the dipole moment, and the polarizability of the investigated compounds are highly affected by the electronic nature and position of the terminal and lateral substituents as well as their volumes.

Highlights

Today, liquid crystalline (LC) materials prove to have wide area of technological applications as optical displays, emitting-diodes, and photoconductors based on organic compounds [1–3]
SSiimmuullaattiioonnss ooff the thheeoorretical calculations for predicting the molecular geometry are mmore interesting for the estimation of the tthhermal properties, and we correlated them with tthhee eexxpperimental ffiindings data [8,9,48–52]
Members of the nitro-free, terminal fluoro-substituted homologues exhibited only one transition peak upon heating and two transition peaks on the cooling cycles, as indicated by their differential scanning calorimetry (DSC) thermograms, which were assigned to Cr-to-isotropic liquid phase in addition to the smectic A (SmA)-to-Cr phase

Summary

Introduction

Liquid crystalline (LC) materials prove to have wide area of technological applications as optical displays, emitting-diodes, and photoconductors based on organic compounds [1–3]. Geometric characteristic relationships are important tools to synthesize a suitable structural shape to achieve the desired properties for specific industrial applications [4–7]. The choices of the laterally attached groups, terminal wings, as well as the mesogenic linkages are important criteria in the formation of thermotropic LC for proper characteristic applications. The incorporation of a nitro substituent into a molecular structure significantly increases. The incorporation of a nitro substituent into a molecular structure significantly incttmhhreeoeaiNeseletOeysc2ittnrhmodenoueiecelgeetaycsttairivnopidntoyuesgcioteafistvtivaheiecptyhmoasooriftglieetvcheouenclemhta[ho1rel7ge–Nec2uo4aln]et.ot[Tmh1he7,e–aN2sn4tdar]o.ttonThmguh,esm,asientnsrdcoormtnehgaeusrmsei,sceitpnshocreormepeaeleesrriectctsyrpotohrnfoeetpgheelaeerttcNiyvtrOiooty2-f noefgtahteivgitryouopf t[h1e7,1g8ro].upTh[1e7r,e1s8o].nTahnecereaspopnraonacceh ahpapsrobaecehn hsuasppboeertnedsubpypodritpeodlebmy odmipeonlet minovmesetnigtaitniovnesst[i2g5a]t,ioNnMs [R2,5a],nNdMthRe,cahnedmtihcael cehleecmtriocnal-weliethctdroranw-winitghdchraawraicntgercohfatrhaectneritroof tghreonuiptr, owghriocuhpa,fwfehcitcshthafefemctesatshueremmeeansutsre[m26e–n2t8s].[2F6o–2r8t]h.eFodretvheelodpemveelnotpmofetnhteomf tehseommeosr-opmhiocrrpahnigceraanngdemanedsomphesaospehsatasbeislittaibeisliotifetshoefpthreepparreepdamreadtemriaatlesr,iaalns,eaffnecetfifvecetsivtreastetrgaytefgoyr fmorodmifiodcaiftiicoantioofnthoef tahrechairtcehctiutercetsuorefscoomf cpoomupnodusnisdsneiscensescaersys. SSiimmuullaattiioonnss ooff the thheeoorretical calculations for predicting the molecular geometry are mmore interesting for the estimation of the tthhermal properties, and we correlated them with tthhee eexxpperimental ffiindings data [8,9,48–52].

Results and Discussion

Geometrical Simulations and Thermal Parameters

Conclusions