Substituent Effects Research Articles

Coordination Behaviors between Aryl Diamide Amine Ligands and Trivalent Lanthanides: A Spectroscopic and Structural Study

Investigating the complexation of organic ligands with trivalent lanthanides (Ln(III)) is crucial in various fields, particularly in the separation of actinides from lanthanides for spent fuel reprocessing. While alkyl diamide amine ligands have been extensively studied, aryl‐functionalized ligands are rarely reported. To understand the effect of substituents on the coordination mode of diamide amine ligands with Ln(III), two aryl‐substituted diamide amine ligands, 2,2'‐(p‐tolylazanediyl)bis(N‐ethyl‐N‐(p‐tolyl)acetamide) (L1) and 2,2'‐((2‐ethylhexyl)azanediyl)bis(N‐ethyl‐N‐(p‐tolyl)acetamide) (L2), were synthesized and systematically studied. 1H NMR titration showed that metal ion coordination affected the electron density of methylene groups near coordinating atoms more than that of aromatic rings, while fluorescence titration and single‐crystal analysis confirmed 1:1 ligand‐Ln(III) complexes. Compared to alkyl diamide amine ligands, aryl groups increased steric hindrance, enhancing torsional strain and preventing amine nitrogen from participating in complexation, leading to weaker coordination as only two carbonyl oxygen atoms coordinated with Ln(III) in a bidentate mode. This work provides insight into how substituents influence the complexation properties of diamide amine ligands with f‐elements, aiding in the design of new ligands with improved performance.

Theoretical Investigation of the Effects of Aldehyde Substitution with Pyran Groups in D-π-A Dye on Performance of DSSCs.

This work investigated the substitution of the aldehyde with a pyran functional group in D-π-aldehyde dye to improve cell performance. This strategy was suggested by recent work that synthesized D-π-aldehyde dye, which achieved a maximum absorption wavelength that was only slightly off the threshold for an ideal sensitizer. Therefore, DFT and TD-DFT were used to investigate the effect of different pyran substituents to replace the aldehyde group. The pyran groups reduced the dye energy gap better than other known anchoring groups. The proposed dyes showed facile intermolecular charge transfer through the localization of HOMO and LUMO orbitals on the donor and acceptor parts, which promoted orbital overlap with the TiO2 surface. The studied dyes have HOMO and LOMO energy levels that could regenerate electrons from redox potential electrodes and inject electrons into the TiO2 conduction band. The lone pairs of oxygen atoms in pyran components act as nucleophile centers, facilitating adsorption on the TiO2 surface through their electrophile atoms. Pyrans increased the efficacy of dye sensitizers by extending their absorbance range and causing the maximum peak to redshift deeper into the visible region. The effects of the pyran groups on photovoltaic properties such as light harvesting efficiency (LHE), free energy change of electron injection, and dye regeneration were investigated and discussed. The adsorption behaviors of the proposed dyes on the TiO2 (1 1 0) surface were investigated by means of Monte Carlo simulations. The calculated adsorption energies indicates that pyran fragments, compared to the aldehyde in the main dye, had a greater ability to induce the adsorption onto the TiO2 substrate.

Dual-response signal under mechanical stimulation: Alkyl substituent effect on the fine-tuning of molecular packing

Mechanical stimulus-responsive materials are generally considered to be closely related to molecular packing in the solid state, underscoring the significance of regulating molecular packing via precise molecular design. In this study, flexible alkyl substituents were employed to adjust the molecular packing. By modifying alkyl substituents, predictable changes in the molecular packing of their derivatives were observed, resulting in adjustable ML properties. The DPA-PYZ-TB with a tert-butyl-side chain exhibited strong ML and MC stimulus response signals. The enhanced ML and MC performance can be attributed to the effective suppression of non-radiation through the helical crystal arrangement and strong intermolecular interactions. The relationship between molecular arrangement and ML/MC properties was validated through analysis of the single crystal structure and corresponding experimental results. This study offers valuable insights into the enigmatic ML process and the development of efficient luminous materials that utilize both MC and ML.

Zirconium Complexes Bearing Methyl/tButyl Salicylate and Their Catalytic Activity on ε-Caprolactone

In this study, methyl/tbutyl salicylate-bearing zirconium complexes (C1–C8) were prepared by the reaction of zirconium (IV) propoxide/butoxide with salicylic acid, 3-methylsalicylic acid, 4-methylsalicylic acid, and 3,5-di-tert-butylsalicylic acid in alcohols, respectively. All these complexes (C1–C8) were characterized by 1H NMR, 13C NMR, FTIR, mass spectroscopy (MS), elemental, and thermogravimetric analyses (TGA). These complexes were utilized as catalysts in the ring-opening polymerization (ROP) of Ɛ-caprolactone and were very effective. Polycaprolactone (PCL) was characterized by 1H-NMR, 13C NMR, and gel permeation chromatography (GPC). In this study, perhaps for the first time, the effects of electron-donating substituents (Me and tBu) on Ɛ-caprolactone polymerization reactions on salicylate ligands linked to zirconium atoms were investigated.

A comparative theoretical study on the structural, spectral, microtopology exploration (ELF, RDG, IRI, TDM), NBO and nonlinear optical properties of Red170 from different solvents and substituents

The effect of solvents and substituents on the C.I. Pigment PR170, the best known member of the naphthol red family, is investigated. Both PR170 and its alkoxy derivatives were analyzed using FTIR, 1H NMR and UV–Vis spectroscopy. The study included the evaluation of the average local ionization energy (ALIE), MEP, HOMO-LUMO analysis. The nature of intra- and intermolecular contacts in the crystal structure was also investigated using crystal packing and Hirshfeld surface analysis. Covalent and non-covalent interactions in PR170 were comprehensively described by IRI, RDG and ELF. In addition, Natural Bonding Orbital (NBO) and Fukui function calculations were performed. An analysis of the UV–Vis electronic transitions for different solvents was carried out, providing insight into the charge transfer processes within both PR170 and its derivatives. In particular, the research indicated a CT-type excitation at the S2 level during the hole-electron transfer analysis. The NLO results showed that PR170 is a promising candidate for nonlinear optical materials.

Substituent Effect in Salicylaldehyde 2-Furoic Acid Hydrazones: Theoretical and Experimental Insights into DNA/BSA Affinity Modulation, Antimicrobial and Antioxidant Activity

The biological properties of five aroylhydrazones derived from salicylaldehyde and its 5-substituted derivatives with 2-furoic acid hydrazide were thoroughly investigated. NMR analysis confirmed the predominant existence of the aroylhydrazones in the keto-amine form in aqueous solution. Geometries of these compounds were optimized using density functional theory (DFT) calculations with the B3LYP hybrid functional, while ADMET analysis predicted their pharmacokinetic and toxicological properties. Substituent effects on the interactions between the salicyl aroylhydrazones and BSA and DNA were elucidated through experimental and molecular docking studies, revealing the bromo-substituted hydrazone as the most potent binder to both biomolecular targets. Experimental results aligned well with theoretical predictions, indicating that salicyl hydrazones predominantly act as DNA groove binders. Thermodynamic analysis suggested that the hydrazones predominantly interact with BSA through hydrogen bonding and van der Waals forces. Moreover, antioxidant potential assessment using DPPH, ABTS, FRAP, and metal chelating assays demonstrated the potent antioxidant power of nitro and hydroxy-substituted derivatives. Additionally, the antimicrobial properties of hydrazone against Gram-positive and Gram-negative bacteria, as well as fungi, were thoroughly explored, highlighting the nitro derivative as the most prominent candidate with broad-spectrum antimicrobial potential.

External electric field induced emission behavior for ESIPT-based 2-(benzo[d]thiazol-2-yl)-4-(pyren-1-yl)phenol towards near-infrared region

Organic light-emitting diodes (OLEDs) for low energy transfer and double emission, but the current methods for regulating ESIPT processes are mostly solvent and substituent effects. Here, utilizing the density theory functional (DFT) and time-dependent density functional theory (TD-DFT) methods, the ESIPT process controlled by an external electric field (EEF) is proposed, and the changes in photophysical properties of 2-(benzo[d]thiazol-2-yl)-4-(pyren-1-yl)phenol (PyHBT) are investigated. Structural parameter variations and IR vibrational spectra measure the prerequisite for the ESIPT process, namely, intramolecular hydrogen bond (IHB) strength, and the scanned potential energy curves (PECs) demonstrate that the ESIPT process of PyHBT is harder to execute as the positive EEF increases, and the opposite is true for the negative EEF. The absorption and fluorescence spectra show shifts under the distinct EEFs, and even the emission wavelength reaches the short-wave near-infrared (SW-NIR) region (780–1100 nm), such as 815.2 nm for a positive EEF of + 30 × 10-4 a.u. in the keto form. Additionally, the fluorescence intensity of PyHBT is strongly influenced by the positive EEF, especially in the enol form, and the investigation of the mechanism by hole-electron analysis demonstrates that under the positive EEF, the twisted intramolecular charge transfer (TICT) process is induced, which triggers the weakening of the fluorescence intensity. In summary, our work not only complements the theoretical approach to modulate the ESIPT process, but also reveals that the photophysical properties of materials affected by the external electric field are even expected to reach the NIR region.

Leveraging long-lived arenium ions in superacid for meta-selective methylation

Electrophilic aromatic substitution is one of the most mechanistically studied reactions in organic chemistry. However, precluded by innate substituent effects, the access to certain substitution patterns remains elusive. While selective C–H alkylation of biorelevant molecules is eagerly awaited, especially for the insertion of a methyl group whose magic effect can boost lead molecules potency, one of the most obvious strategies would rely on electrophilic aromatic substitution. Yet, the historical Friedel-Crafts methylation remains to date poorly selective and limited to activated simple aromatics. Here, we report the development of a selective electrophilic methylation enabling the direct access to highly desirable 1,3-disubstituted arenes. This study demonstrates that this reaction is driven by the generation of long-lived arenium intermediates generated by protonation in superacid and can be applied to a large variety of functionalized (hetero)aromatics going from standard building blocks to active pharmaceutical ingredients.

The Substituent Effects of Suzuki Coupling in Aqueous Micelles.

The Suzuki coupling in aqueous micelles has received much attention, but few attempts focus on its substituent effects. In view of the significant substituent effects on this reaction, it is necessary and practical to investigate its substituent effects. Herein, the substituent effects of Suzuki coupling in aqueous micelles are well established through Hammett plots and kinetic studies. In the cases of aryl halides, the rate-determining step of the reaction will shift from the oxidation addition step to the transmetalation step as the substituents' electron withdrawing ability increases, so aryl halides with weak electron-withdrawing groups exhibit better reactivity than ones containing strong electron-withdrawing or electron-donating groups. For arylboronic acids, the electron donating groups are beneficial to the Suzuki reaction, while the electron withdrawing group is unfavorable for the reaction. The Suzuki reactions of substituent exchange between arylboronic acids and aryl halides further confirm these substituent effects.

Insights into the adsorption of thiophene and fluorinated-thiophenes on the Mg4O4 cluster: a quantum chemical investigation

In this work, the adsorption of thiophene on the Mg4O4 cluster was examined at the LC-ωPBE/6-311G(d,p) level of theory. The influence of replacing hydrogen atoms of thiophene with fluorine atoms was considered. The comparison of relative stabilities of possible isomers indicated most stable isomers were 3-FT … Mg4O4, 3,4-DFT … Mg4O4, 2,3,4-TFT … Mg4O4 structures in the mono, di and tri-fluorinated thiophenes, respectively. Corrected adsorption energy and thermodynamic parameter values of these systems were evaluated and the substituent effect on the adsorption was explored. 2-FT … Mg4O4, 3,4-DFT … Mg4O4, 2,3,4-TFT … Mg4O4 structures indicated the most significant adsorptions in the mono, di and tri-fluorinated thiophenes, respectively. Electrophilicity-based charge transfer (ECT) was employed to illustrate charge transfer between aromatic systems and the Mg4O4 cluster. Quantum theory of atoms in molecule (QTAIM) and interaction region indicator (IRI) were used to deeply investigate two fragments.

Effect of Alkyl Substituents on Molecular Packing and Luminescence Properties of Crystalline Thioxanthone Derivatives

Effect of Alkyl Substituents on Molecular Packing and Luminescence Properties of Crystalline Thioxanthone Derivatives

Substituent effect induced circularly polarized luminescence enhancement of Eu(III) enantiomers

Circularly polarized luminescence (CPL) has received much attention in optical displays, information storage, and biological probes. Designing effective strategy to improve the CPL activities is significant for complex materials. Structural modification is a rational way which is seldom reported. In this work, three chiral binuclear Eu(III) complexes coordinated with different chiral Schiff base ligands were designed and synthesized. CPL performances of these Eu(III) complexes were substantially improved by polarity of substituents at the chiral carbon sites of the ligands, leading to a five-fold increase in the luminescence dissymmetry factor (glum). Additionally, three complexes exhibited similar luminescence properties with the characteristic peaks of Eu(III) ion, which can be rapidly quenched by Co(II) ion, allowing their further applications in anti-counterfeiting and sensors. Therefore, this work not only uncovers the relationship between the substituents of chiral ligand and the corresponding CPL properties of Eu(III) complexes to some extent, but also creates opportunities for design and synthesis of Eu(III) complexes with excellent CPL activity.

Self-Assembly of Thienopyrrole-Fused Thiadiazoles Containing an Amide Linker: Control of Supramolecular Polymerization Mechanism and Chiroptical Properties by Trialkoxy Side Chains.

Three thienopyrrole-fused thiadiazole (TPT) fluorescent dyes featuring a common amide linker and different alkoxy substituents on peripheral trialkoxybenzene moieties were synthesized, and their self-assembly behavior in solution was investigated. The obtained results revealed a substantial steric effect of the alkoxy substituents on the supramolecular polymerization mechanism, which results from a combination of π-stacking and hydrogen (H)-bonding interactions. Detailed spectroscopic measurements revealed that with increasing steric demand of the substituents, the supramolecular polymerization processes in pure methylcyclohexane (MCH) or a mixture of MCH and toluene become temperature-sensitive and enthalpically favorable, resulting in a change from the isodesmic assembly mechanism to the cooperative mechanism. Theoretical calculations suggested that in TPTs with bulky substituents, steric hindrance causes the H-bonding array of the amide moieties to be aligned along the stacking axis of the π-systems; thus, the H-bonding interactions are strengthened compared to those in TPTs with less bulky substituents, compensating for the weakened π-stacking interactions. A chiral TPT derivative with (S) stereogenic centers was found to form homochiral helical supramolecular assemblies that generate discernible circularly polarized luminescence. Achiral TPTs also generate helical assemblies to which preferential helicity can be imparted through the external chiral bias of the solvents (R)- and (S)-limonene.

Substituent effects on first generation photochemical molecular motors probed by femtosecond stimulated Raman.

Unidirectional photochemical molecular motors can act as a power source for molecular machines. The motors operate by successive excited state isomerization and ground state helix inversion reactions, attaining unidirectionality from an interplay of steric strain and stereochemistry. Optimizing the yield of the excited state isomerization reaction is an important goal that requires detailed knowledge of excited state dynamics. Here, we investigate the effect of electron withdrawing and donating substituents on excited state structure and ultrafast dynamics in a series of newly synthesized first generation photochemical molecular motors. All substituents red-shift the absorption spectra, while some modify the Stokes shift and render the fluorescence quantum yield solvent polarity dependent. Raman spectra and density functional theory calculations reveal that the stretching mode of the C=C "axle" in the electronic ground state shows a small red-shift when conjugated with electron withdrawing substituents. Ultrafast fluorescence measurements reveal substituent and solvent polarity effects, with the excited state decay being accelerated by both polar solvent environment and electron withdrawing substituents. Excited state structural dynamics are investigated by fluorescence coherence spectroscopy and femtosecond stimulated Raman spectroscopy. The time resolved Raman measurements are shown to provide structural data specifically on the Franck-Condon excited state. The C=C localized modes have a different substituent dependence compared to the ground state, with the unsubstituted motor having the most red-shifted mode. Such measurements provide valuable new insights into pathways to optimize photochemical molecular motor performance, especially if they can be coupled with high-quality quantum molecular dynamics calculations.

Reduction and Hydrocyanation of Aziridines with C−C Bond Cleavage

AbstractThe carbon‐carbon bond in three‐membered ring of 2,3‐diaryl aziridines was reductively cleaved to give the corresponding dibenzylamine derivatives by electrocyclic ring opening of N‐Li or N‐Na aziridines followed by reduction of the 2‐azaallyl anion formed with sodium borohydride in ethanol. Hydrocyanation of the 2‐azaallyl anion with trimethylsilyl cyanide gave a secondary amine bearing a cyano group at the benzylic position. The effects of substituents on the electrocyclic ring opening of N‐Li aziridines were also clarified.

Achieving ultrahigh electrochromic stability of triarylamine-based polymers by the design of five electroactive nitrogen centers

A shortage of long-term stability of electrochromic materials has been hindering their practical application. A series of novel polyamides (PAs) (4) with five electroactive nitrogen atoms within triphenylamine (TPA)-containing structures was synthesized via phosphorylation polyamidation. Polyamide 4b exhibited highly integrated electrochromic performances, including multiple color changes, high contrast of optical transmittance change, and the highest electrochromic stability (only 11.2 and 9.6 % decay of its coloration efficiency (CE) at 450 nm after 50000 and 16000 switching cycles, respectively) compared to all other triarylamine-based polymers to date. This record-high electrochromic cycling is attributed to the enhanced stability of polaron, which was studied through the electron-donating or electron-withdrawing effect of substituents and the resonance effect of electron delocalization over the electroactive nitrogen centers. Importantly, our core design of five electroactive nitrogen centers with electron-donating methoxy groups is the key factor to increase stability of polaron in the resulting polymers 4. More electroactive nitrogen centers are able to create a weaker electronic coupling due to a charge of cation radical dispersed by resonance successfully in-between the different redox states, which is evidenced clearly by the observed longer wavelength absorption in the NIR region. Our research confirms that the key to determining polaron stability is the resonance by the electrons delocalized over all the redox centers, rather than the electronic coupling between the different redox centers. And the resonance leads to increasing electrochromic stability of the polymer.

Substituent effects on the ESIPT process of H2O2 sensing product 1,3-bis(bispyridin-2-ylimino) isoindolin-4-ol: A theoretical study

H2O2 plays an important role in a variety of physiological processes, but its overproduction or accumulation can lead to oxidative damage and related diseases, so it is crucial to establish accurate H2O2 detection methods. Fluorescence sensing as a potential method, the design and modulation of its luminescent properties are crucial to the detection results. In this work, we investigated the sensing mechanism of a novel H2O2 fluorescent probe (P1) and examined the role of substituent effects in modulating the fluorescence properties of its reaction products. The results show that the non-fluorescence property of the probe is due to twisted intramolecular charge transfer (TICT) mechanism resulting from a torsion of the excited state molecular conformation, and the fluorescence turn-on upon recognition of H2O2 by the probe is due to the reaction product (BBYI1) following the excited state intramolecular proton transfer (ESIPT) process. When the substituent is an electron-donating group, the energy barrier of the ESIPT reaction is lowered, promoting luminescence, while the electron-withdrawing group has the opposite effect. In summary, the present work may offer a theoretical foundation for the development of more sensitive fluorescent probes for ESIPT-based H2O2 detection.

Mild and Stereoselective Synthesis of (1E,3E)-Dienes through Silver(I)-Catalyzed β-Hydride Migration from Allylic α-Diazo Esters

AbstractA mild procedure for the diastereoselective preparation of functionalized 1,3-dienes and their synthetic versatility are described herein. The silver-catalyzed decomposition of α-diazo-γ,δ-unsaturated esters through β-hydride migration at room temperature resulted in the stereoselective formation of 12 conjugated (1E,3E)-dienes. Further synthetic post-modifications included intramolecular Heck reaction and hydrogenation, leading to a novel substituted indene and an aliphatic diester, respectively. To rationalize the observed reaction outcome, a computational investigation of the mechanisms was conducted, emphasizing the importance of factors such as metallocarbenoid stability, substituent effects, and microkinetics simulations to better understand the reaction intricacies.

Computational Study of the Kinetics and Mechanisms of Gas-Phase Decomposition of N-Diacetamides Using Density Functional Theory.

In this research work, we examined the decomposition mechanisms of N-substituted diacetamides. We focused on the substituent effect on the nitrogen lone-pair electron delocalization, with electron-withdrawing and electron donor groups. DFT functionals used the following: B1LYP, B3PW91, CAMB3LYP, LC-BLYP, and X3LYP. Dispersion corrections (d3bj) with Becke-Johnson damping were applied when necessary to improve non-covalent interactions in the transition state. Pople basis sets with higher angular moments and def2-TZVP basis sets were also applied and were crucial for obtaining consistent thermodynamic parameters. The proposed mechanism involves a six-membered transition state with the extraction of an α hydrogen. Several conformers of N-diacetamides were used to account for the decrease in entropy in the transition state in the rate-determining state. All calculations, including natural bond orbital (NBO) analyses, were performed using the Gaussian16 computational package and its GaussView 6.0 visualizer, along with VMD and GNUPLOT software. The isosurfaces and IBSIs were calculated using MultiWFN and IGMPlot, respectively.

BIOLOGICAL ACTIVITY CALCULATED BY THE PASS METHOD AND EXPERIMENTAL ASSESSMENT OF THE ACIDITY OF NH GROUPS IN SULPHONAMIDE POLYCHLOROETHYLATED ARENES AND GLYCINE DERIVATIVES IN DIMETHYL SULPHOXIDE MEDIUM

The acidity of NH-groups of a number of sulphonamides and glycine derivatives in a dimethyl sulphoxide medium has been investigated using the potentiometric method. Dissociation constants of these compounds are determined from titration curves. It is shown that the acidity of NH groups in the studied sulphonamides is controlled by the polar effect of substituents. The possibility of quantitative potentiometric analysis of glycine derivatives has been established for the first time. Biological activity has been predicted with the help of PASS software. The correlation of NH group acidity with the biological potential of the compounds has been established.