Solvatochromic Studies Research Articles

Fe3O4 Nanoparticles Catalyzed Tandem Synthesis of Fluorescent 3‐(4,5‐diaryl‐1H‐imidazol‐2‐yl) quinoline‐2‐amines: Solvatochromic, DFT and Biological Studies

AbstractIn the present work, Fe3O4 nanoparticles were prepared by the co‐precipitation method and employed as effective nanocatalysts in the tandem synthesis of 3‐(4,5‐diaryl‐1H‐imidazol‐2‐yl)quinolin‐2‐amines. An effective multicomponent reaction is plighted for 2‐chloroquinoline‐3‐carbaldehydes and substituted benzils to obtain novel heterocycles 3‐(4,5‐diaryl‐1H‐imidazol‐2‐yl)quinolin‐2‐amines. These molecules are fluorescent and hence for proper understanding of optical behaviour, solvatochromic and DFT studies were carried out. Also, the optical and energy bandgaps were calculated. Molecular docking studies manifested the strong binding affinities by these compounds at the active site of the Candida albicans dihydrofolate reductase enzyme (PDB ID: 1AI9) and Novobiocin (PDB ID: 4URO) with excellent C‐score values. Antimicrobial activity screening results have shown remarkable activity against Escherichia coli with appreciable MIC values and hence noteworthy action has been demonstrated against this bacterium. The zones of inhibition for some of the target compounds are also good against gram positive Staphylococcus aureus exhibiting excellent activity.

Design and Synthesis of Novel Fluorescent 2-(aryloxy)-3-(4,5-diaryl)-1H-imidazol-2-yl)quinolines: Solvatochromic, DFT, TD-DFT Studies, COX-1 and COX-2 Inhibition and Antioxidant Properties.

The present work focuses on the synthesis of novel heterocycles 2-(aryloxy)-3-(4,5-diaryl-1H-imidazol-2-yl)quinolines (6k-v) by an effective condensation reaction. These molecules exhibited fluorescent properties and hence for the proper understanding of their optical behavior and quantum yields, solvatochromic studies have been carried out. Further, frontier molecular orbitals,molecular electrostatic potential (MEP), and geometrical structure optimization have been investigated using the B3LYP/6-311G ++ (d, p) method. The energy gap between the HOMO, LUMO of the optical and energy band gap is determined by DFT and UV-visible spectra for TD-DFT studies are done. The screening of these compounds for in vitro COX-1 and COX-2inhibitionand DPPH free radical scavenging ability assays produced promising results. The binding interactions of these molecules against the COX-2 enzyme (PDB: 5IKR) were validated by docking studies.

Synthesis and Studies of Pyridoneimine-Functionalized PETIM Dendrimers.

Pyridinoimine-functionalized poly(ether imine) (PETIM) dendrimers of 1-3 generations, possessing 4-16 moieties at the peripheries, are synthesized. Chloride-functionalized dendrimers are reacted with N-methylamino pyridine, under basic conditions, which led to functionalization of the peripheries of a dendrimer with pyridoneimine moieties. Variable-temperature 1H NMR studies are performed to assess the contributing resonance forms of pyridoneimine in the dendrimers. Solvatochromism and 15N NMR studies aid further the assessment of the contributing resonance forms. Comparison with derivatives that possess 1 and 2 pyridoneimines illustrates the contributing resonance forms between nonaromatic pyridoneimine and zwitter ionic aromatic imidopyridinium species.

Insights into the electronic properties of 6-substituted quinolone derivatives: A solvatochromic study

Solvent dependent photophysical properties of 6 -substituted N-methyl quinolone molecules namely 6-amino-1-methylquinolin-2(1H)-one (AMQ), 1-methyl-6-(methylamino)quinolin-2(1H)-one (MAMQ), 1-methyl-6-nitroquinolin-2(1H)-one (NMQ) have been studied using steady state UV–Visible absorption, fluorescence emission spectroscopy, fluorescence lifetime measurements and quantum mechanical calculations. It was found that amine and methylamine substitution at 6-position of quinolone moiety enhanced the fluorescent property whereas nitro substitution rendered it non-fluorescent in all the experimental solvent systems. Maximum redshifted spectra were found in dimethyl sulfoxide (DMSO) compared to both alcoholic solvents and pure water. Significant charge transfer in HOMO to LUMO transition was revealed by quantum mechanical calculations but the direction was different depending on the nature of substitution. The pH response of the molecules were also investigated in pure water and the pKa values were found to be 3.70 and 3.90 for AMQ and MAMQ respectively. Analysis of radiative and non-radiative rate constants in all the solvents showed that the deactivation process may be different depending on hydrogen bond donation ability of the solvent. The spectral shift was rationalised by grouping the solvents based on their hydrogen bonding ability.

Synthesis, characterization, TD‐DFT, molecular docking, biological applications, and solvatochromic studies of some new metal complexes derived from semicarbazone of pyrano[3,2‐c]quinoline‐3‐carboxaldehyde

New Zn(II), Cd(II), VO(IV), and UO2(VI) solvatochromic complexes derived from 6‐ethyl‐4‐hydroxy‐2,5‐dioxo‐5,6‐dihydro‐2H‐pyrano[3,2‐c]quinoline‐3‐carboxaldehyde‐semicarbazone ligand (H2L) were synthesized and established by elemental analyses, spectral (IR, UV, NMR, mass spectra), molar conductivity measurements, magnetic susceptibility, and thermal gravimetric analysis (TGA). The ligand coordinates with metal ions through ONO chelating sites, forming an octahedral geometry arrangement, except UO2(VI) that showed pentagonal bipyramidal geometry. Using Coats–Redfern methodology, the kinetic parameters (Ea, A, ΔH, ΔS, and ΔG) of the thermal decomposition steps were calculated and discussed. The complexes showed solvatochromic behavior that used to estimate the ground and excited state dipole moments. Optimization and structural parameters were carried out by density function theory (DFT) at B3LYP/GENECP method at 6‐311G(d,p) basis set for C, H, N, and O atoms and SDD (Stuttgart/Dresden) basis set for the metal atoms and interrelated with the experimental results. The complexes were tested for antimicrobial efficiency against Gram‐positive bacteria, Gram‐negative bacteria, yeast, and fungi. Also, antitumor activity was investigated against HepG‐2 cell line. Finally, the new synthesized complexes upon subjecting to molecular docking and distinguishable results showed outstanding inhibition results of VEGFR‐2 via achieving a high stabilization level inside the largest pocket of 1YWN protein.

Solute − solvent repulsion effects on the absorption spectra of anthracene in n-hexane investigated under high pressure

The band positions in the UV–VIS absorption spectra of compressed solution of anthracene in n-hexane significantly depend not only on the dispersive but also on the repulsive solute–solvent interactions, what has so far been omitted. Their strength is determined not only by the solvent polarity but also by Onsager cavity radius changing with pressure. The results obtained for anthracene show that repulsive interactions should be included in the interpretation of barochromic and solvatochromic results of aromatic compounds. We show that the barochromic studies in the liquid solvent can be an alternative to solvatochromic studies, e.g. to determine the polarizability of organic molecules in the electronic excited state. The pressure-induced polarity change in n-hexane exceeds that induced by the exchange of n-alkane solvents between n-pentane and n-hexadecane.

A disparity in solvatochromism of C[dbnd]O and S[dbnd]O vibrational probe: A study of structurally similar acetone and dimethyl sulfoxide

Solvatochromic studies of small IR probes are beneficialto study the structural dynamics of biomolecules as well as measuring the strength of surrounding electric fields in condensed phases.Herein, we have investigated the CO and SO vibrational probes of structurally similar acetone and dimethyl sulfoxide respectively to compare the solvatochromism. Interestingly in water CO formed both one hydrogen bond and two hydrogen bond complexes wherein SO formed only two hydrogen bond complexes.Not only this, but we have also investigated how different solvents alter the IR spectra of the CO and SO vibrating modes during the interaction with α CH of acetone and DMSO respectively.The IR absorption spectra of CO of acetone altered after αdeuteration(acetoned6) in aprotic organic solvents as well as aqueous solvents. But, surprisingly for DMSO and DMSOd6, the IR spectra of SO mode remain intact during α isotopic exchange (CH3to CD3) in organic aprotic solvents but in strong coordinating polar protic solvents (D2O) it is altered remarkably. The equivalent frequency gap of CO of acetone and acetoned6 in organic solvents and water represent the no interaction of α CH/D with solvent molecules. Parallelly unaltered IR spectral signature of SO of both DMSO and DMSOd6 in aprotic organic solvent represents the stationary state of the ‘S’ atom and altered SO IR absorption in water signifies the different α CH and α C-D interaction with the surrounding water molecules. These results are the cautionary of perturbation on IR probe during α CH interaction with solvents as well as guest molecules.

Design, Vibrational and Fluorescence Spectroscopic Properties, and Molecular Docking Studies of 3‐(5‐Bromobenzofuran‐3‐ylmethyl)‐5‐(4‐methoxyphenyl)‐4H‐[1,2,4]‐triazole by Experimental and Density Functional Theory Methods

AbstractIn this work, we have reported the spectral and several other properties of 3‐(5‐bromobenzofuran‐3‐ylmethyl)‐5‐(4‐methoxy‐phenyl)‐4H‐[1,2,4]triazole (BBT) molecule. Primarily, the experimental and computational analyses have been conducted for this molecule and compared the results. The computational studies have been conducted by Gaussian software with the help of DFT/B3LYP/6‐311++G (d, p) basis set. First, we have optimised BBT molecule to conduct the overall computational studies. The detailed computational and experimental vibrational analyses of BBT have been carried out. The electronic absorption and emission spectra of BBT have been observed in a variety of solvents with different solvent parameters like refractive index n, and dielectric constant ϵ. In solvatochromic studies, bathochromic (red) shift have observed in the absorption and emission spectra as an outcome of solute‐solvent interaction due to π → transition. The solvent correlation methods experimentally investigated for the ground and excited‐state dipole moments. Along with these studies, we have also conducted Frontier Molecular Orbital (FMO) and Molecular Electrostatic Potential (MEP) analyses. Further, Molecular docking and drug likeness studies have also been performed to determine the pharmacological properties of the title molecule.

Exploring solvation behaviour of biocompatible ionic liquid 2-hydroxyethylammonium formate + polyethylene glycols mixtures: Role of oxyethylene and hydroxyl units of PEGs

The favourable modification of the physicochemical properties of the ionic liquid with green co-solvent and their molecular level characterization with spectroscopic techniques is the area of current research. Further, the co-solvent modified ionic liquid mixtures furnishes interesting properties which render the utility of these solvents in several important applications. In the current work, the effects of addition of two polyethylene glycols (PEGs) with average molecular weights of 200, and 600 on solvent properties of IL 2-hydroxyethyl ammonium formate (HEF) has been explored with the help of solvatochromic absorbance probes. The physicochemical characteristics of the ionic liquid mixtures are altered in an unexpectedly positive way when PEGs are added to IL HEF. The absorbance behaviour of the solvatochromic probes Reichardt dye 33 shows interestingly positive non-ideal behaviour, which may be attributed to the high dipolarity/polarizability (π*) and hydrogen bond donor ability (HBD) (α) of the HEF + PEG mixtures. Further, the Kamlet-Taft parameters, including hydrogen bond acceptor ability (HBA) (β), and hydrogen bond donor ability (HBD) (α), and dipolarity/polarizability (π*) of the HEF + PEG binary mixtures display nonideality, which may be because of the strong Hydrogen bond networking of HEF-PEG molecules along with solute-HEF/PEG interaction present in the mixtures. Moreover, the preferential solvation approach has been invoked to explore the solute–solvent/solvent–solvent interactions present in the HEF + PEGs binary mixtures. The Redlich–Kister (CNIBS/R–K) theoretical model predicts the experimental results obtained by solvatochromic probe studies in satisfactory manner. The results of the DFT and FTIR study also predict the possibility of the H-bonding interactions in HEF + PEGs mixtures.

Unlocking the potential of 2,1,3-benzoxadiazole-based luminescent liquid crystals

ABSTRACT Here, we report the synthesis and characterisation of 2,1,3-benzoxadiazole-based (BOX) luminescent liquid crystals with a π-conjugated core and different elongated donor units connected by triple bonds. These molecules exhibited calamitic thermotropic mesomorphism with nematic and smectic phases and intense photoluminescence under UV–vis light excitation in solutions and films. In solution, the emission revealed a maximum in the yellow region (502 to 590 nm), similar to that of benzothiadiazoles (BTD) homologous, but with fluorescence quantum, it yields significantly higher (ΦPL = 0.30–54). The nature of donor unit substantially influenced the quantum yields and excited state lifetimes. Solvatochromism studies showed a dependence of the emission, quantum yield and lifetimes with the polarity of the solvent. This work demonstrates that 2,1,3-benzoxadiazole core derivatives have thermal and photophysical properties similar to BTDs but with superior quantum efficiency.

Vibrational Solvatochromism Study of the C-H···O Improper Hydrogen Bond.

The improper C-H···O hydrogen bond is an important weak interaction, with broad implications for protein and nucleic acid structure, molecular recognition, enzyme catalysis, and drug interaction. Despite its wide identification in crystal structures, the general existence of C-H···O hydrogen bonds remains elusive especially for natural C-H groups in bulk aqueous solutions at room temperature. Vibrational spectroscopy is a promising methodology to tackle this challenge, as formation of C-H···O hydrogen bonds usually causes shifts of the C-H stretch frequency. Yet, prior observations are inconclusive, as they are all based on a simple blue-shift in aqueous solution and cannot distinguish if it is an effect caused by solvent reorganization or a specific hydrogen-bonding interaction. In this work, we used vibrational solvatochromism as a calibration of the solvent reorganization effect and identified a specific H-bonding interaction. We performed vibrational solvatochromism study of C-H(D) of multiple alcohol molecules including the CH mode of CD3CH(OH)CD3 and the CD3 modes of CD3OH, CD3CH2OH, and CD3CH(OH)CD3 in a series of solvents. We found an abnormal blue-shift of the Raman frequency of the C-H and C-D bonds at both the Cα and Cβ positions of alcohols in water, which lies in an opposite direction to the expected trend due to vibrational solvatochromism. This experimental evidence supports that the improper C-H···O hydrogen bonds might generally exist between nonpolarized C-H and water in liquid solutions at room temperature.

New heterocyclic azo-disperse dyes; their synthesis, characterization, application, photo physical properties and solvatochromic studies

In current research exploration, novel heterocyclic disperse dyes were synthesized, using 8-aminonaphthalen-2-ol as a coupling component and different heterocyclic aromatic amines e.g. sulfadiazine, sulfamethazine, sulfathiazole sodium salt, 2-aminobenzothiazole and 2-amino-6-methoxybenzothiazol as a diazonium component. Different analytical techniques including FT-IR, 1H-NMR, UV-Visible, FAB-LRMS and FAB-HRMS were used for the structural elucidation of the synthesized disperse dyes. The melting point of the synthesized compounds were also determined. The solvatochromism of these dyes was examined in six organic solvents possessing different polarity and the sensitivity of the absorption maxima (λmax) to acidic and basic pH were evaluated in methanol. Bathochromic shift was observed with increase in solvent polarity and under acidic pH. The fluorescence studies all the dyes were performed in four different solvents. The obtained chromophores were applied on polyester fabric observing different parameters like build-up profile, perspiration fastness, rubbing fastness, wash fastness, light fastness and sublimation fastness. All the dyes exhibited good to very good color yield and excellent fastness properties.

Photophysical Behavior of Self-Organizing Derivatives of 10- and 12-Vertex p-Carboranes, and their Bicyclo[2.2.2]octane and Benzene Analogues.

Four series of isostructural derivatives of 3-ring liquid crystalline derivatives containing p-carboranes (12-vertex A, and 10-vertex B), bicyclo[2.2.2]octane (C), or benzene (D) as the variable structural element were investigated for their mesogenic behavior and electronic interactions. Comparative studies demonstrated that the effectiveness of elements A-D in stabilization of the mesophase typically increases in the order: B<A<C<D. Absorption and emission spectroscopy for the four series and reference compounds augmented with DFT computational results revealed that the degree of electronic interactions with the connected benzene π system increases in the order C<A<B<D. Emission spectra exhibit large Stokes' shifts for 10-vertex derivatives (B) in solutions and in the solid state. Spectroscopic characterization was supplemented with polarization electronic spectroscopy and solvatochromic studies of selected series. Overall, 12-vertex p-carborane A acts as an electron withdrawing auxochromic substituent with interactions similar to those of bicyclo[2.2.2]octane, although capable of accepting some electron density in the excited state. In contrast, 10-vertex p-carborane B is much more interactive with the π-aromatic electron manifold and exhibits greater ability to participate in photo-induced CT processes. Absorption and emission energies and quantum yields (1-51 %) for carborane derivatives, representing the D-A-D system, were compared to those of their isoelectronic zwitterionic analogues (the A-D-A system). The analysis is supplemented with four single-crystal XRD structures.

Synthesis, Solvatochromism and Fluorescence Quenching Studies of Naphthalene Diimide Dye by Nano graphene oxide.

A naphthalene diimide dye with two side amine arm was prepared. Uv-Vis and fluorescence spectroscopic techniques are used for their photophysical and solvatochromic characteristics in different solvents. The Lippert-Mataga plot for naphthalene diimide demonstrated a negative linear dependence by increasing polarity. Results showed naphthalene diimide is more polar in the ground than in the excited state. A quenching study was conducted for interacting the naphthalene diimide as a fluorophore and graphene oxide as a quencher. Fluorescence quenching-based platforms in nanoscale have been used in sensing systems. Raman, FTIR, Uv-Vis and fluorescence spectroscopic techniques were used to study the quenching mechanism. The results indicated that graphene plays an effective quencher against the naphthalene diimide, with a quenching efficiency 91%. The Stern-Volmer analysis results show a mix of static and dynamic quenching mechanisms. The binding constant of the quencher-fluorophore and the number of binding sites have been reported. Thermodynamic parameters of their interaction were evaluated. The negative values of the Gibbs free energy confirm that the complexation process is spontaneous. Meanwhile, the positive entropy value confirms that the favorable pathway process.

Synthesis, computational study, solvatochromism and biological studies of thiazole-owing hydrazone derivatives

In the present work, we have synthesized thiazole-hydrazone conjugates 5(a–h) and characterized them using various analytical techniques such as UV, IR, NMR, and mass spectrometry. Solvatochromic properties were evaluated in ten solvents with different polarity and quantum chemical parameters using a DFT study. The antibacterial activity results revealed that compounds 5c, 5d and 5g exhibited good efficacy and that the remaining compounds displayed significant activity. The synthesized compounds were screened for their cytotoxic activity against HepG2 and MCF-7 cell lines, and all the synthesized compounds exhibited significant potency towards the screened cancer cell lines. The anti-inflammatory efficacy of the synthesized thiazole derivatives was determined against MMP-2 and MMP-9, and some of the compounds showed significant activity. Furthermore, the in silico molecular docking was performed with the COX-2 receptor.

Intermolecular Interactions in Binary and Ternary Solutions of a Zwitterionic Compound Studied by Solvatochromism

The 1-dithiocarboxy-2-ethoxy-1-(isoquinolin-2-yl)-2-oxoethan-1-ylid (iQTCY) zwitterionic molecule has been studied by computational and spectral means in order to establish some of its structural parameters in the ground electronic state as well as the nature and the strength of its universal and specific interactions with different solvents. The prevalence of the orientation–induction interactions in the diluted solutions of iQTCY in aprotic solvents and the additional specific interactions by hydrogen bonds (HB) in the protic solvents were demonstrated. Three theoretical models were comparatively used to estimate the composition of the first solvation shell of the iQTCY molecule in ternary solutions. The difference between the interaction energies in molecular pairs solute–solvent was computed based on the statistical cell model of ternary solutions of iQTCY in mixtures of water–ethanol and water–methanol. Using the electro-optical parameters computed by the quantum-mechanical technique and the results of the solvatochromic study, the excited state dipole moment of iQTCY was estimated within the limit of the variational method applicable to molecules that show only an absorption electronic spectrum.

Complex formation and microheterogeneity in water–alcohol binary mixtures investigated by solvatochromic study

Complex formation and microheterogeneity in water–alcohol binary mixtures investigated by solvatochromic study

Synthesis and Fluorescent Properties of Alkynyl- and Alkenyl-Fused Benzotriazole-Derived α-Amino Acids.

Fluorescent unnatural α-amino acids are widely used as probes in chemical biology and medicinal chemistry. While a variety of structural classes have been developed, there is still a requirement for new environmentally sensitive analogues that can closely mimic proteinogenic α-amino acids. Here, we report the synthesis and fluorescent properties of highly conjugated, benzotriazole-derived α-amino acids designed to mimic l-tryptophan. Alkynyl-substituted analogues were prepared using three key steps, nucleophilic aromatic substitution with a 3-aminoalanine derivative, benzotriazole formation via a one-pot diazotization and cyclization process, and a Sonogashira cross-coupling reaction. E-Alkenyl-substituted benzotriazoles were accessed by stereoselective partial hydrogenation of the alkynes using zinc iodide and palladium catalysis. The alkynyl analogues were found to possess higher quantum yields and stronger brightness and, a solvatochromic study with the most fluorogenic α-amino acids demonstrated sensitivity to polarity.

Cyanopyridone-cored fluorophores with triphenylamine peripheries: From molecular design to OLED fabrication studies

• Seven novel cyanopyridone-based D-A-D type molecules with a fixed triphenylamine donor, were synthesized. • Theoretical, optical, solvatochromic, thermal, electrochemical, electrical, and EL studies were performed to evaluate structure-property relationships. • Doped OLEDs using novel fluorophores as dopants outperform non-doped devices. • OLEDs emit yellow light with maximum efficiencies of 10.72 cd/A, 7.87 lm/W, and 5.32%. Amongst many types of fluorescent organic materials, compounds with π-conjugation between an electron donor (D) and electron acceptor (A) have been intensively investigated as effective organic electroluminescence (EL) device components. Herein, we report the synthesis and structural characterization of a new series of D-A-D configured small molecule-based fluorophores ( TPA-CyP1-7 ) having triphenylamine ( TPA ) as a donor unit and 3-cyanopyridine-2-one ( CyP ) as an acceptor core with different architects for use as efficient yellow light emitters in fluorescent organic light-emitting diodes (OLED). The detailed photophysical, solvatochromic, thermal, electrochemical, and EL properties, including quantum chemical calculations, were systematically investigated to study their relation between structure and properties. All the fluorophores show high fluorescent quantum yields in the solid film state and display high thermal stability with decomposition temperatures above 350 o C. The study reveals that they possess appropriate HOMO and LUMO energies level for effective charge injection. Finally, these yellow luminogens were employed to fabricate new OLED devices as sole emitters and dopants with CBP host materials. Interestingly, the host-guest devices doped with CBP host emitters show a remarkable improvement in the overall device performance. Among them, the TPA-CyP3 -based doped device has achieved a maximum current efficiency ( η c ), high power efficiency ( η p ), and good external quantum efficiency ( η EQE ) of 10.72 cd/A, 7.87 lm/W, and 5.32%, respectively.

4-Cyanotryptophan as a Sensitive Fluorescence Probe of Local Electric Field of Proteins.

Electrostatic interactions are key determinants of protein structure, dynamics, and function. Since protein electrostatics are nonuniform, assessment of the internal electric fields (EFs) of proteins requires spatial resolution at the amino acid residue level. In this regard, vibrational Stark spectroscopy, in conjunction with various unnatural amino acid-based vibrational probes, has become a common method for site-specific interrogation of protein EFs. However, application of this method is often limited to proteins with relatively high solubility, due to the intrinsically low oscillator strength of vibrational transitions. Therefore, it would be useful to develop an alternative method that can overcome this limitation. To this end, we show that, using solvatochromic study and molecular dynamics simulations, the frequency of maximum emission intensity of the fluorophore of 4-cyanotryptophan (4CN-Trp), 3-methyl-1H-indole-4-carbonitrile, exhibits a linear dependence on the local EF. Since the absorption and emission spectra of 4CN-Trp are easily distinguishable from those of naturally occurring aromatic amino acids, we believe that this linear relationship provides an easier and more sensitive means to determine the local EF of proteins.