NO2 Substituents Research Articles

Unusual solvent-dependent photophysical and self-assembly properties of NO2 substituted T-shaped phenazines.

This paper investigates the importance of substituent placement when designing low-molecular mass π-organogelators. The electron-deficient NO2 substituent was systematically added to novel T-shaped phenazines to examine electronic as well as assembly properties. This T-shaped molecular platform promotes selective electronic tuning, which can be theoretically analyzed by examining the system's frontier molecular orbitals. Electronic properties were characterized by UV-vis spectroscopy and cyclic voltammetry, and comparisons were made based on number and placement of the NO2 group. Computational chemistry (B3LYP/6-31G*) was employed for geometry optimizations, and to generate molecular orbital diagrams for all systems. The most noticeable influence of NO2 position was found for two molecules with four NO2 groups placed at different locations about the molecule (T-34dNT and T-35dNT). A 0.13 eV difference in ELUMO was observed while EHOMO was not significantly impacted by this change only in NO2 placement. Interestingly and unexpectedly, the photophysical properties and solvent-dependent gelation properties were considerably different for T-34dNT and T-35dNT. T-34dNT exhibited a unique fluorescence (FL) solvatochromism, with FL intensity and maxima dependent on solvent polarity. This result is indicative of intramolecular charge transfer. In addition, long tailing at the solid-state absorption of T-34dNT suggests the presence of intermolecular charge transfer. The gelation of T-34dNT produced chromism ranging from red to orange to yellow when the solvents changed from acetonitrile to ethyl acetate to cyclohexane, respectively. T-35dNT gels in these solvents did not exhibit any of the same properties. Xerogel morphology characterizations were carried out using three different solvents for both T-34dNT and T-35dNT. In the case of T-34dNT, striking differences in the morphology were detected by field-emission scanning electron microscopy (FE-SEM). We conclude that numbers of substituents are not the only consideration in effective molecular design for organogelators, but that substituent position plays a critical role in certain fundamental properties of these systems.

Conformational study of some 4′-substituted 2-(phenylselanyl)-2-(ethylsulfanyl)-acetophenones

The conformational analysis of some 4′-substituted 2-(phenylselanyl)-2-(ethylsulfanyl)-acetophenones bearing the substituents NO2 (1), Br (2), H (3), Me (4) and OMe (5) was performed by νCO IR analysis, B3LYP/6-31+G(d,p) and single point polarisable continuum model (PCM) calculations, along with NBO analysis for 1, 3 and 5. Calculations for 1–5 indicate the existence of three stable conformations, c1, c2 and c3, whose stability depends on the balance between electrostatic and orbital interactions that are strictly related to the geometrical arrangement. The comparison between the experimental IR spectra in solution and the computed data in gas phase for 1–5 allows the c1 conformer to be assigned to the less intense component at higher frequency of the carbonyl doublet and both the c2 and c3 ones to the more intense lower frequency component. The sum of the calculated molar fraction of c2 and c3 conformers decreases from 95% to 63% on going from 1 to 5 (in gas phase), and this trend compares well with the PCM calculations and the IR experimental data for the majority of the solvents for all compounds 1–5. The NBO analysis for 1, 3 and 5 shows that the sum of the relevant orbital delocalization energies for the c1, c2 and c3 conformers is almost constant and does not match the computed stability order. The lowest stability of the c1 conformer for 1–3 can be related to the small value of the α dihedral angle that enables a strong electrostatic destabilizing repulsion between the OCOδ−…Sδ− atoms. The relative stability of the c1 conformer increases for 4 and 5 as the α dihedral angle enlarges and the repulsion is minimized. Moreover, the strong repulsive field effect between the Cδ+Oδ− and Cδ+Sδ− dipoles exerted to a greater extent on the c1 conformers of 1–3 with respect to 4 and 5, causes a major increase of the corresponding CO bond orders and related carbonyl frequencies. For the c2 conformer, the electrostatic destabilizing repulsion between the Oδ−…Seδ− atoms is weaker than that involving the Oδ−…Sδ− atoms in the c1 conformer and therefore has negligible effects on the conformer stability that is mainly determined by the sum of the orbital interactions. The c3 conformer has the shortest Sδ−…Seδ− contact for all compounds and thus the related electrostatic repulsion seems to be the most important factor that affects its stability. In conclusion, the computed order of stability of the three conformers for 1–5 depends on the electrostatic repulsions between close charged atoms rather than on the sum of the orbital delocalization energies that are quite similar for all the conformers.

ChemInform Abstract: Palladium‐Catalyzed Synthesis of 2‐Aminobenzoxazinones by Aerobic Oxidative Coupling of Anthranilic Acids and Isocyanides.

AbstractThe presented scalable reaction does not work for anthranilic acids bearing NO2, I, OH, or COOH substituents.

Anti‐Tuberculosis Evaluation and Conformational Study of N‐Acylhydrazones Containing the Thiophene Nucleus

A series of N-acylhydrazonyl-thienyl derivatives (compounds 2 and 3), mainly of the type 2-(aryl-CH=N-NHCOCH2 )-thiene (2: aryl = substituted-phenyl; 3: aryl = heteroaryl) were evaluated against Mycobacterium tuberculosis. Particularly active compound was 3 (heteroaryl = 5-nitrothien-2-yl or 5-nitrofuran-2-yl) with MIC values of 8.5 and 9.0 μM, respectively. Moderately active compounds were compound 3 (heteroaryl = pyridin-2-yl) and compound 2 containing aryl = 2- or 4-hydroxyphenyl groups, with MIC values between 170 and 408 μM. Compound 2 containing OMe, H, F, Cl, Br, CN, and NO2 substituents and compound 3 (heteroaryl = furan-2-yl, thien-2-yl, pyrrol-2-yl, imidazol-2-yl, pyridin-3-yl, and pyridin-4-yl) were all inactive. Clearly, there is no correlation of activity with the electronic effects of the substituents. The activities suggest different modes of biological action of the compounds having nitro-heteroaryl groups, on the one hand, and the 2-hydroxyphenyl or pyridin-2-yl substituents, on the other hand. Compounds having 2- or 4-hydroxyphenyl, 2-hydroxy-5-nitrophenyl, or 4-hydroxy-3-chlorophenyl were less cytotoxic than ethambutol. It is important to notice that compound 3 (aryl = 5-NO2 -furan-2-yl) exhibited a promising therapeutic index (TI = 1093.90), with a value 4.4 less than that of ethambutol. Compounds 2 and 3 exist in DMSO or MeOD solutions as mixtures of EC(O)N /EC=N and ZC(O)N /EC=N conformers.

Some interesting aspects of N-oxides

N-oxides feature a coordinate covalent N+→O− bond, in which both electrons formally come from the nitrogen. Such compounds are important in organic and biological chemistry, and increasingly in the area of energetic materials. The N+→O− linkage has the interesting property that it can be either a donor or an acceptor of electronic charge through resonance delocalisation. It will be shown that the relative reactivities toward N-oxide formation of nonequivalent nitrogens in a given polyazine molecule can be predicted by computing the respective local ionisation energies. Charge delocalisation plays a reinforcing role. However, it can be used to rationalise the remarkable range of N+→O− bond lengths in polyazine N-oxides, as well as the opposite effects of NO2 and NH2 substituents. It is pointed out that, at least for some N-oxides, there are surprisingly large differences between the N+→O− bond lengths in the crystalline and the gas phases. While the approaches being used to explain and/or rationalise N-oxide properties are able to achieve considerable success, it is important to recognise and keep in mind their limitations – examples of which are given.

Structural analysis of 2‐arylidene‐1‐indanone derivatives by electrospray ionization tandem mass spectrometry

2-arylidene-4-methoxy (or hydroxy)-7-methyl-1-indanone derivatives inspired from donepezil, the current drug used for the treatment of Alzheimer's disease as inhibitor of acetylcholinesterase (AChE), were studied for the first time by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). Structurally, these arylidene-indanone compounds are considered as cyclic analogues of chalcones. ESI-MS and tandem mass spectra were acquired using a Q-TOF 2 instrument. Fragmentation patterns were analyzed by CID-MS(2-3) spectra acquired in a Q-TOF and in LXQ linear ion trap mass spectrometers using standard isolation and excitation procedures. All the 2-arylidene indanones have shown a common fragmentation pathway leading to a (2(1), 1')A(+) product ion at m/z 187 and the retro-aldol product ion [(2, 2(1))B(+)] that allow to establish the substitution in the B ring. The effect of electron-donating and -withdrawing substituents on these fragmentation pathways was noticed. The presence of the OCH3, OH, NO2 and Br substituents gave typical fragmentation processes that allowed their unequivocal fingerprinting. The combined loss of the ortho substituent in the B-ring plus hydrogen (H, OCH3, Br and F) is proposed to form a stable cyclic ring product. Arylidene indanones with different substituents on the B ring are associated with a specific fragmentation pattern. In addition, differentiation between isomers with substituents in B ring at ortho and para positions were achieved using ESI-MS/MS. These fragmentation pathways can be used to further identify and determine the fate of these molecules in all stages of drug discovery.

Structure of flavones and flavonols. Part I: Role of substituents on the planarity of the system

In this first part of our investigation the effect of –OH, –NH2, –NO2 and other substituents on the planarity (and the level of delocalization) of a series of flavones and flavonols is assessed. This feature is particularly important with respect to the biological activity of flavonoids. The values of the dihedral angles were obtained from the optimized in gas phase and in water geometries at the density functional theory B3LYP/6-31G(d,p) level.

RETRACTED: Aerobic degradation of 4-nitroaniline (4-NA) via novel degradation intermediates by Rhodococcus sp. strain FK48

An aerobic strain, Rhodococcus sp. strain FK48, capable of growing on 4-nitroaniline (4-NA) as the sole source of carbon, nitrogen, and energy has been isolated from enrichment cultures originating from contaminated soil samples. During growth studies with non- induced cells of FK48 catalyzed sequential denitrification (release of NO₂ substituent) and deamination (release of NH₂ substituent) of 4-NA. However, none of the degradation intermediates could be identified with growth studies. During resting cell studies, 4-NA-induced cells of strain FK48 transformed 4-NA via a previously unknown pathway which involved oxidative hydroxylation leading to formation of 4-aminophenol (4-AP). Subsequent degradation involved oxidated deamination of 4-AP and formation of 1,2,4-benzenetriol (BT) as the major identified terminal aromatic intermediate. Identification of these intermediates was ascertained by HPLC, and GC-MS analyses of the culture supernatants. 4-NA-induced cells of strain FK48 showed positive activity for 1,2,4-benzenetriol dioxygenase in spectrophotometric assay. This is the first conclusive study on aerobic microbial degradation of 4-NA and elucidation of corresponding metabolic pathway.

Effect of length on the position of negative differential resistance and realization of multifunction in fused oligothiophenes based molecular device

The length modulation of electron transport properties for molecular devices based on fused oligothiophenes has been investigated theoretically using a combination of non-equilibrium Green's functions and first-principles density functional theory. The results show that the lengths of the molecules have a distinct influence on the position of negative differential resistance (NDR) of the molecular devices. By exploring the effect on transmission properties of substituent groups, hexathieno[3,2-b:2',3'-d]thiophene with -NH2 and -NO2 substituents (model L) can be regard as a good candidate of multifunctional molecular device, which shows excellent rectifying performance (the largest rectification ration is 14.3 at 1.2 V) and clear NDR behavior (at 1.4 V).

Can the substituent in the para position of anilide ion influence the N−···H–F → N–H···F− switching: a quantum chemical study

The effect of substituents in the para position of anilide ion (An) on the N−···H–F → N–H···F− switching in X–An–HF (X = H, Me, CHO, CN, NO, F, NO2, OH and OMe) complexes was investigated by means of B3LYP and MP2 quantum chemical methods. To delve into the mechanistic details of the proton transfer process, potential energy curve and further geometrical parameters involved in H-bonding during the course of the proton transfer process were evaluated at the MP2/6-311++G(2d,2p) level of theory. The changes in H-bond strength because of variation of substituents were well accompanied by changes in formation energy of complexes, structural parameter, electron density, natural charge and charge transfer between subunits. For X = H, Me, CHO, CN, NO, F and NO2 substituents, our results at MP2/6-311++G(2d,2p) level showed that the minimum energy structures correspond to the N···HF H-bonded complexes without proton transfer occurring. On the other hand, for electron-donating substituents OH and OMe, proton is transferred from HF to anilide ion and the minimum energy structures are HNH···F− H-bonded complexes. The nature of HN−···HF and HN–H···F− interactions in complexes was characterized by means of atoms in molecules and natural bond orbital analyses.

A Theoretical Investigation of the Ring Strain Energy, Destabilization Energy, and Heat of Formation of CL-20

The cage compound CL-20 (a.k.a., 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, HNIW, or 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.03,11.05,9]dodecane) is a well-studied high-energy-density material (HEDM). The high positive gas- (ΔfHg°) and solid- (ΔfHs°) phase heat of formation values for CL-20 conformers have often been attributed to the strain energy of this cage compound and, by implication, to the conventional ring strain energy (CRSE) inherent in isowurtzitane which may be viewed as a “parent compound” (although not the synthetic precursor) of CL-20. ΔfHg° values and destabilization energies (DSEs), which include the contribution from CRSE, were determined by computation using a relatively new multilevel ab intio model chemistry. Compared to cubane, isowurtzitane does not have an exceptionally high CRSE. It is about the same as that of cyclopropane and cyclobutane. These investigations demonstrate that instead of the CRSE inherent in the isowurtzitane parent compound, the relatively high ΔfHg° and DSE values of CL-20 conformers must be due, primarily, to torsional strain (Pitzer strain), transannular strain (Prelog strain), and van der Waals interactions that occur due to the presence of the six >N–NO2 substituents that replace the six methylene (–CH2–) groups in the isowurtzitane parent compound. These conclusions are even more pronounced when 2,4,6,8,10,12-hexaazaisowurtzitane is viewed as the “parent compound.”

Semicarbazone – a versatile therapeutic pharmacophore for fragment based anticonvulsant drug design

During the last fifteen years, semicarbazones have been extensively investigated for their anticonvulsant properties. 4-(4-Flurophenoxy) benzaldehyde semicarbazone (C0102862, V102862) was discovered as a lead molecule and is being developed as a potent antiepileptic drug, with maximal electroshock (MES) ED₅₀ of i.p. 12.9 mg kg⁻¹. In MES (oral screen), this compound has a protective index (PI = TD₅₀/ED₅₀ > 315) higher than carbamazepine (PI 101), phenytoin (PI > 21.6) and valproate (PI 2.17). The compound is a potent sodium channel blocker. Other semicarbazones have demonstrated activity in various chemoshock screens, like subcutaneous pentylenetetrazole, subcutaneous strychnine, subcutaneous picrotoxin and subcutaneous bicculine. Semicarbazones are also GABA-transaminase inhibitors. Extensive structure- -activity relationship has demonstrated that F, Cl, Br and NO₂ substituents in the arylhydrophobic pocket and a hydrogen bonding domain (HBD) are generally found in active anticonvulsant agents.

Simulating Adsorption of Organic Pollutants on Finite (8,0) Single-Walled Carbon Nanotubes in Water

Understanding the mechanism and thermodynamics of the adsorption of chemicals on carbon nanotubes (CNTs) is important to risk assessment and pollution control of both CNTs and chemicals. We computed the adsorption of cyclohexane, benzene derivatives, and polycyclic aromatic hydrocarbons (PAHs) on (8,0) single-walled carbon nanotubes by the M05-2X of density functional theory. The computed adsorption energies (E(a)) in the aqueous phase are lower than those in the gaseous phase, indicating that the adsorption in the aqueous phase is more favorable. The contribution of π-π interactions and the enhancing effect of a -NO(2) substituent on the adsorption were quantified. For a hypothetical aromatic with the same hydrophobicity (logK(OW)) to cyclohexane, π-π interactions contribute ca. 24% of the total interactions as indicated by E(a). -NO(2) enhances the π-π interactions due to its electron withdrawing effects, and contributes 24% to the value of E(a). Simple linear regression showed the computed Gibbs free energy changes for the adsorption correlate significantly with the experimental values (r = 0.97, p < 0.01). The correlation together with the computed thermodynamic parameters may be employed to predict the adsorption affinity of other chemicals. The study may pave a new way for evaluating/predicting the adsorption affinity of organic compounds on SWNTs and probing the adsorption mechanisms.

Sensitizers in inelastic electron tunneling spectroscopy: a first-principles study of functional aromatics on Cu(111)

Low sensitivity is a key problem in inelastic electron tunneling spectroscopy (IETS) with the scanning tunneling microscope. Using first-principles simulations, we predict different means to tune the IETS sensitivity of symmetrical functional aromatics on a Cu(111) surface. We show how the IET-spectra of phenyl-NO2 compounds can be greatly enhanced as compared to pristine phenyl. More precisely, the NO2 substituent qualifies as a sensitizer of low-frequency wagging modes, but also as a quencher of high-frequency stretching modes. At variance, the CO2 substituent is found to suppress the whole IET-activity. The head-up (non-anchoring) and head-down (anchoring) configurations of the functional group lead to minor changes in the signals, nevertheless allowing access to discriminate configurational features. It is shown how to disentangle the electronic and steric effects of the substituent in the STM junction.

Alumina Supported Au–Ni: Surface Synergism in the Gas Phase Hydrogenation of Nitro-Compounds

The catalytic gas phase hydrogenation of 1,3-dinitrobenzene over Au/Al2O3 delivered exclusive reduction of a single −NO2 substituent to generate 1,3-nitroaniline (Ea = 131 kJ mol–1), reaction over Ni/Al2O3 resulted in full hydrogenation to 1,3-phenylenediamine (Ea = 38 kJ mol–1), whereas both products were isolated over Au–Ni/Al2O3. In the hydrogenation of 1,3,5-trinitrobenzene, Au/Al2O3 promoted preferential partial hydrogenation (3,5-dinitroaniline), Ni/Al2O3 generated 1,3,5-triaminobenzene as the predominant product, while Au–Ni/Al2O3 exhibited an intermediate catalytic response. The catalysts have been characterized in terms of temperature programmed reduction (TPR), H2 chemisorption, powder XRD, high-resolution TEM, XPS, and XANES/EXAFS measurements. Post-TPR, there was evidence of a metal particle redispersion resulting from the introduction of Au to Ni/Al2O3 where HRTEM-EDX mapping has established close proximity of Au and Ni on Au–Ni/Al2O3 with electron transfer from Ni to Au (from XPS analysis). Hydrogen chemisorption on Au–Ni/Al2O3 was 3 times lower than that recorded for Ni/Al2O3, suggesting Au–Ni interaction that inhibits H2 uptake. Simulation of the XANES/EXAFS response provided a better fit when incorporating Au–Ni interaction. The results demonstrate control of selectivity in poly nitroarene hydrogenation through the use of mono- (Au and Ni) and bi- (Au–Ni) metallic catalysts, where catalytic response is governed by surface composition.

Effect of Axially Projected Oligothiophene Pendants and Nitro-Functionalized Diimine Ligands on the Lowest Excited State in Cationic Ir(III) bis-Cyclometalates

The novel terthiophene (3T) oligomer 6 and a series of cationic Ir(III) bis-cyclometalates [Ir(C^N)(2)(N^N)]PF(6) 9-12 were prepared. The synthesis, characterization, electrochemical, and photophysical properties are reported. The cyclometalating ligands (C^N) are 2-phenylpyridinato (ppy) or the 3T oligomer (3T-ppy), asymmetrically capped in the 5 and 5" positions with the ppy and mesityl groups. The diimine ligands (N^N) are 2,2'-bipyridine (bpy) or 4-NO(2)-bipyridine (4-NO(2)-bpy). Hybrid metal-organic complexes 11 and 12 bear 3T-pendants ligated through the ppy cap, 10 and 12 contain NO(2) functionalized diimines, whereas 9 contains neither. Structural characterization of 10 by single crystal X-ray diffraction confirms the presence of the NO(2) substituent and pseudo-octahedral coordination geometry about the Ir(III) ion. Cyclic voltammetry highlights the large electron withdrawing effect of the NO(2) substituent, providing an 850 mV shift toward lower potentials for the first diimine centered reduction of 10 and 12. Strong overlap of the intense π → π* absorptions of the 3T-pendants with Ir(III) charge transfer bands is evident in complexes of 11 and 12, precluding the possibility for selective excitation of either chromophore. Photoexcitation (λ(ex) = 400 nm) of the series affords strong luminescence from the 3T oligomer 6 and the unsubstituted 9, with φ(em) = 0.11. In stark contrast the NO(2) and 3T functionalized complexes 10-12 display near total quenching of luminescence. Computations of the ground and excited state electronic structure using density functional theory (DFT) and time-dependent DFT (TD-DFT) indicate that both the NO(2) and 3T substituents play an important role in excited state deactivation of complexes 10-12. A substantial electronic contribution of the NO(2) substituent results in stabilization of the diimine based molecular orbital (MO) and offers an efficient nonradiative decay pathway for the excited state. Spin-orbit coupling effects of the Ir(III) ion lead to efficient population of the low lying, nonluminescent, triplet states centered on the 3T-pendants.

Effect of ligand substituents on supramolecular self-assembly and electrochemical properties of copper(II) complexes with benzoylhydrazones: X-ray crystal structures and cyclic voltammetry

Complexation of copper(II) with a series of hetero-donor chelating Schiff bases (HLLR) of para-substituted benzhydrazides (with R=OH, NO2, CH3O, Cl and tert-butyl substituents) and acetone affords mononuclear [Cu(LLR)2] molecules: 1 [Cu(anbhz)2] (R=NO2); 2 [Cu(ahbhz)2] (R=OH) 3 [Cu(ambhz)2] (R=CH3O); 4 [Cu(acbhz)2] (R=Cl); and 5 [Cu(atbhz)2] (R=tert-butyl). Single-crystal X-ray diffraction results for 2–5 reveal their various supramolecular architectures including 1D and 2D dimensionalities. A detailed analysis of crystal structures allows to gain insight into intermolecular interactions accountable for self-assembly into different networks as well as for various physicochemical properties of the compounds. The major interactions include O–H⋯N hydrogen bonds (2) as well as CH⋯N and axial Cu⋯O (3); π⋯π stacking (4) and van der Waals CH⋯C interactions (5). All compounds are characterized by elemental analyses; IR and UV–Vis spectroscopy as well as magnetic susceptibility and cyclic voltammetry measurements. Electrochemical studies reveal the dependence of [Cu(LLR)2]/[Cu(LLR)2]− reduction potentials on substituents of benzoylhydrazonoate ligands.

Quantitative structure–activity relationship analysis of perfluoroiso-propyldinitrobenzene derivatives known as photosystem II electron transfer inhibitors

Quantitative structure–activity relationship (QSAR) analysis of the twenty-six perfluoroisopropyl-dinitrobenzene (PFIPDNB) derivatives was performed to explain their ability to suppress photochemical activity of the plants photosystem II using chloroplasts and subchloroplast thylakoid membranes enriched in photosystem II, called DT-20. Compounds were optimized by semi-empirical PM3 and DFT/B3LYP/6-31G methods. The Heuristic and the Best Multi-Linear Regression (BMLR) method in CODESSA were used to select the most appropriate molecular descriptors and to develop a linear QSAR model between experimental pI50 values and the most significant set of the descriptors. The obtained models were validated by cross-validation (R2cv) and internal validation to confirm the stability and good predictive ability. The obtained eight models with five-parameter show that: (a) coefficient (R2) value of the chloroplast samples are slightly higher than that of the DT-20 samples both of Heuristic and BMLR models; (b) the coefficients of the BMLR models are slightly higher than that of Heuristic models both of chloroplasts and DT-20 samples; (c) The YZ shadow parameter and the indicator parameter, for presence of NO2 substituent in the ring, are the most important descriptor at PM3-based and DFT-based QSAR models, respectively. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

Synthesis, antimycobacterial, antiviral, antimicrobial activities, and QSAR studies of nicotinic acid benzylidene hydrazide derivatives

A series of nicotinic acid benzylidene hydrazide derivatives (1–18) was synthesized and tested in vitro for biological evaluations. The antimycobacterial activity results indicated that the presence of electron-withdrawing halogen groups at para position of the phenyl ring improved their activity. The results of antiviral evaluation depicted that none of the synthesized derivatives inhibited the replication of viruses at subtoxic concentration. Further, the antimicrobial screening results indicated that compounds having OCH3 and NO2 substituents were the most active ones. QSAR investigations revealed that multi-target QSAR models were effective in describing the antimicrobial activity.

Substituent effects on thermal and photo‐alignment behavior of poly(ethylene imine)s carrying azobenzene side groups

AbstractA new class of liquid‐crystalline poly(ethylene imine)s (PEIs) having four differently substituted (CN,C4H9,OCH3 andNO2) azobenzene side‐chain groups attached through alkyl spacer groups were successfully synthesized using a solution polycondensation reaction. The synthesized polymers were characterized using differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. The photochemical, thermo‐optical and photo‐orientational behavior of the polymers were investigated in detail. Spin‐coated films of PEIs with azobenzene groups havingC4H9,OCH3 andNO2 substituents showed out‐of‐plane molecular orientation on annealing. Except for the PEI with an azobenzene group having NO2 substituent, all polymers exhibited good photoresponsive properties upon irradiation with UV and visible light. Films of PEIs with azobenzene side groups havingCN,C4H9 andOCH3 substituents showed reversible alignment behavior from random state to out‐of‐plane and from out‐of‐plane to random state on annealing and on irradiation with UV and non‐polarized visible light. The reversibility of the molecular orientation of PEIs from random state to out‐of‐plane and from out‐of‐plane to random state greatly depended on the substituent attached to the azobenzene side‐chain group. Copyright © 2010 Society of Chemical Industry