Solvatochromic Studies Research Articles

Solvent scales used to study the intermolecular interactions in binary solutions of two p-aryl-pyridazinium methylids

The visible electronic absorption band with intramolecular charge transfer of two pyridazinium ylids having common carbanion and different heterocycles is recorded in solutions and its position is correlated to parameters of some empirical scales of solvents. The nature of the intermolecular interactions in pyridazinium ylid solutions is discussed and the supply of each type of interaction is established based on solvatochromic study.

Synthesis, characterization, X-ray crystal structure, luminescence, electrochemical and solvatochromism studies of new dimer of nickel and palladium complexes containing ferrocenyl imine ligand

The synthesis of a new Schiff base ligand was investigated by the reaction of ferrocenecarboxaldehyde, [(η5(C5H5) (η5(C5H4CHO)], with 2-aminoethanethiol at room temperature. For this product, ring closure was also observed in the crystalline form which thiazolidine was obtained. Furthermore, new homobimetallic complexes of nickel(II) and palladium(II) were synthesized by the reaction of the new Schiff base ligand with nickel chloride and palladium chloride in 1:1 M ratio. In nickel and also palladium complexes the ligands were coordinated to the metals via the imine N atoms and the chlorido-bridged unit for the reported complexes was suggested. The complexes have been found to possess 1:1 metals to ligands stoichiometry. The emission and absorption spectra of the ligand and its complexes were studied in methanol solvent. Electrochemical properties of the ligand and its metal complexes were investigated in CH3CN solvent at the 100 mVs−1 scan rate. The Schiff base ligand and its metal complexes showed both reversible and irreversible processes at this scan rate. These compounds have been characterized by IR, 1H NMR, UV/Vis and elemental analysis. The crystal structure of the thiazolidine has been determined by single crystal X-ray diffraction.

Aryleneethynylene Trimers Bearing Calix[4]arenes: Synthesis, Optical Properties and Self‐Assembling Studies

SummaryNew homoditopic bis‐calix[4]arene‐carbazole conjugates, armed with hydrophilic carboxylic acid functions at their lower rims, are disclosed. Evidence for their self‐association in solution was gathered from solvatochromic and thermochromic studies, as well as from gel‐permeation chromatography analysis. Their ability to function as highly sensitive sensors toward polar electron‐deficient aromatic compounds is demonstrated.

Synthesis, characterization and solvatochromism study of mixed-chelate copper(II) complexes: A combined experimental and density functional theoretical study

The mixed-chelate copper(II) complexes [Cu(Ph-acac)(diamine)]X, where Ph-acac is 1-phenyl-1,3-butanedione, diamine is N,N-dimethyl,N′-benzyl-1,2-diaminoethane and X=ClO4−, PF6− and BF4−) have been synthesized and characterized spectroscopically (by IR and UV–Vis) and structurally (by single-crystal X-ray diffraction). The X-ray structure of [Cu(Ph-acac)(diamine)]ClO4 demonstrated that the central copper atom is placed in a square planar geometry made by Ph-acac and diamine chelates. Solvatochromism behavior of the compounds was studied in 14 organic solvents, which showed a positive trend with increasing donor power of the solvents. Multi-parametric equation has been utilized to explain the solvent effect on the d–d transition of the complexes using SPSS/PC software. The stepwise multiple linear regression (SMLR) method demonstrated that the donor power of the solvent plays the most important role in the solvatochromism of the compounds. To study the electronic structure of the complex and to confirm the mechanism of the observed solvatochromism, a computation analysis was accomplished on [Cu(Ph-acac)(diamine)]+ by the density functional theory (DFT) and time-dependent DFT calculations. DFT computational results buttressed the experimental observations and indicated that the solvatochromism phenomenon is due to coordination of the solvent molecules on the above and below of the molecular plane, which causes change in geometry of the complex from square planer to octahedron. In this process the d–d transition band of the complex moves to the red with increasing the DN of the solvent.

Characterization of amide-alkanediol intermolecular interactions.

The properties of formamide + 1,2-alkanediol binary liquid systems were studied both at the macro- and microscopic levels using a combined experimental and computational methodology. Physicochemical properties, infrared spectroscopy, and solvatochromic studies together with classic molecular dynamics and quantum chemistry calculations allowed the main characteristics of these binary fluids to be inferred with regard to the variations of hydrogen bonding with formamide and 1,2-alkanediol molecular structures, mixture composition, and temperature. The complexity of these liquid systems arising from the presence of three different functional groups, which may act as hydrogen bond donors and acceptors, is analyzed, allowing a detailed picture to be inferred of the studied systems which is of relevance both for basic liquid state theory and for industrial purposes.

Emerging ground and excited state dipole moments and external electric field effect on electronic structure. A solvatochromism and theoretical study on 2-((phenylimino)methyl)phenol derivatives

The absorption and fluorescence spectra of three 2-((phenylimino)methyl)phenol derivatives have been evaluated in a series of organic solvents. The ground state (μg) and excited state (μe) dipole moments are determined by means of Lippert–Mataga, Bakhshiev, Kaski–Chamma–Viallet and Reichardt solvatochromic shift methods based on the solvent polarity parameters. Excited state dipole moments are found as larger than the ground state dipole moment due to substantial redistribution of the π-electron density in more polar excited state and thus resonance structures of 2-((phenylimino)methyl)phenol derivatives are analyzed. Solute–solvent interactions are analyzed by means of linear solvation energy relationships (LSER) using dielectric constant function f(ε), refractive index function f(n) and Kamlet–Taft parameters (H-bond donor ability, α and H-bond acceptor ability, β). External electric field (EF) effect on HOMO–LUMO gap (HLG) and dipole moment are investigated by B3LYP, LDA and GGA methods. Density of states (DOS) and HOMO, LUMO plots are also investigated by the same methods.

Synthesis, characterization, crystal structure, solvatochromism, fluorescence and electrochemical studies of new organometallic platinum complexes, kinetic investigation of oxidative addition reaction

A new organoplatinum(II) complex containing 2,2′-biquinoline ligand (biq) was synthesized by the reaction of [Pt(p-MeC6H4)2(SMe2)2] with 2,2′-biquinoline in a 1:1 molar ratio. In this complex the ligand was coordinated to metal via the chelating nitrogen donor atoms. Also, platinum(IV) complex was obtained by the oxidative addition reaction of the methyl iodide with the platinum(II) complex in acetone. The platinum complexes have been found to possess 1:1 metal to ligand stoichiometry and the molar conductance data revealed that the metal complexes were non-electrolytes. The platinum(II) and platinum(IV) complexes exhibited square planar and octahedral coordination geometry, respectively. The emission spectra of the platinum(II) and platinum(IV) complexes were studied in dichloromethane. Furthermore, electrochemical properties of the metal complexes were investigated in dimethylformamide (DMF) solvent at 150 mV s−1 scan rate. The ligand and metal complexes showed both reversible and irreversible processes at this scan rate. The complexes have been characterized by IR, 1H NMR, UV/Vis, elemental analysis and conductometry. The crystal structure of the platinum(II) complex containing 2,2′-biquinoline has been determined by single crystal X-ray diffraction. Moreover, kinetic studies of the oxidative addition reaction of methyl iodide with the platinum(II) complex in different temperatures were investigated. It was indicated that the reaction occurred by the SN2 mechanism. The rate of reaction in two different solvents was compared and the activation parameters were determined.

Solvatochromic studies of biologically active iodinated 4-aryloxymethyl coumarins and estimation of dipole moments

The steady state absorption and emission spectra of biologically active iodinated 4-aryloxymethyl coumarins 4-(4-iodo-phenoxymethyl)-benzo[h]coumarin (4IPMBC) and 4-(4-iodo-phenoxymethyl)-6-methoxy coumarin (4IPMMC) are studied at room temperature in a series of solvents and 1,4-dioxane–acetonitrile solvent mixture. The effect of pure solvents upon the spectral properties are analyzed using Lippert–Mataga polarity function, Reichardt's microscopic solvent polarity parameter, Kamlet's and Catalan's multiple linear regression approaches. General solute–solvent interactions and hydrogen bonding interactions are operative in these systems. However, the contribution of later interaction is less. The solvatochromic data is used to estimate excited state dipole moment using experimentally determined ground state dipole moment. The bathochromic shift of emission spectra and increase in dipole moment after excitation indicate the intramolecular charge transfer (ICT) character in the emitting singlet state. The solvation studies in 1,4-dioxane–acetonitrile solvent mixture suggest that these dyes are preferentially solvated by 1,4-dioxane.

Perturbative multireference configuration interaction (CI-MRPT2) calculations in a focused dynamical approach: a computational study of solvatochromism in pyrimidine.

We have investigated solvatochromic effects over a solvent series of increasing polarity on the prototype molecule pyrimidine as a solute species. The line shape profiles, obtained by a time-dependent approach based on quantum mechanical calculations performed over frames sampled from classical molecular dynamics trajectories, were directly compared to the available experimental bands. The multireference configuration interaction second-order perturbation (CI-MRPT2) calculations are in quantitative agreement with the experiment. The results also confirm how nonprotic solvents can be confidently modeled by continuous solvation models as the polarizable continuum model, whereas protic solvents, as water, require the inclusion of explicit solvent molecules to account for the effects of hydrogen bonds.

Halochromism, ionochromism, solvatochromism and density functional study of a synthesized copper(II) complex containing hemilabile amide derivative ligand

This study investigates chromotropism of newly synthesized 3,3′-(ethane-1,2-diylbis(benzylazanediyl))dipropanamide copper(II) perchlorate complex. The compound was structurally characterized by physico-chemical and spectroscopic methods. X-ray crystallography of the complex showed that the copper atom achieved a distorted square pyramidal environment through coordination of two amine N atoms and two O atoms of the amide moieties. The pH effect on the visible absorption spectrum of the complex was studied which functions as pH-induced “off–on–off” switches through protonation and deprotonation of amide moieties along with the CuO to CuN bond rearrangement at room temperature. The complex was also observed to show solvatochromism and ionochromism. The distinct solution color changes mainly associated with hemilability of the amide groups. The solvatochromism of the complex was investigated with different solvent parameter models using stepwise multiple linear regression method. The results suggested that the basicity power of the solvent has a dominant contribution to the shift of the d–d absorption band of the complex. Density functional theory, DFT calculations were performed in order to study the electronic structure of the complex, the relative stabilities of the CuN/CuO isomers, and to understand the nature of the halochromism processes taking place. DFT computational results buttressed the experimental observations indicating that in the natural pH (5.8) the CuO isomer is more stable than its linkage isomer and conversely in alkaline aqueous solution.

Synthesis, characterization, spectroscopic and electrochemical studies of donor–acceptor ruthenium(II) polypyridine ligand derivatives with potential NLO applications

In this work we report the preparation of six new donor–metal–acceptor (D–M–A) type complexes of ruthenium(II) with the highly absorbing “chromophoric” ligand 4,4′-bis(2-(4-methoxyphenyl)styryl)-2,2′-bipyridine, (L-OCH3, donor moiety) and substituted polypyridinic ligands with electron acceptor character (NN-A). The NN-A studied ligands were pyrazino[2,3-f][1,10]phenanthroline (ppl), 11-R-dipyrido[2,3-a:2′,3′-c]phenazine (dppz-R; R is H, NO2, or CN) and 10,11-[1,4-naphtalenedione]dipyrido[3,2-a:2′,3′-c]phenazine (Aqphen). The complexes were characterized by IR, NMR, UV–Vis spectroscopy and cyclic voltammetry. The potential NLO response of the complexes was evaluated by solvatochromic studies. Although the communication between D and A exists, the effect of the change of the acceptor moiety on the properties of the complexes is small and the behavior of the complexes is governed mainly by the donor ligand. The Metal to Ligand Charge Transfer bands (MLCT) exhibited by all complexes in the visible region have dominant electronic density transfer character from the metal to the chromophoric L-OCH3 ligand. The hypsochromic shift of this low energy absorption band on going from a less polar (benzene) to a more polar solvent (acetonitrile) indicated that a redistribution of the electronic density among the metal and the donor ligand is observed. This behavior permits to predict a NLO response for these types of complexes. The combination of high molar absorptivity with intraligand charge transfer (ILCT) mixing into the MLCT bands are encouraging for the generation of new materials with interesting NLO properties.

Size vs surface: tuning the photoluminescence of freestanding silicon nanocrystals across the visible spectrum via surface groups.

The syntheses of colloidal silicon nanocrystals (Si-NCs) with dimensions in the 3-4 nm size regime as well as effective methodologies for their functionalization with alkyl, amine, phosphine, and acetal functional groups are reported. Through rational variation in the surface moieties we demonstrate that the photoluminescence of Si-NCs can be effectively tuned across the entire visible spectral region without changing particle size. The surface-state dependent emission exhibited short-lived excited-states and higher relative photoluminescence quantum yields compared to Si-NCs of equivalent size exhibiting emission originating from the band gap transition. The Si-NCs were exhaustively characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformed infrared spectroscopy (FTIR), and their optical properties were thoroughly investigated using fluorescence spectroscopy, excited-state lifetime measurements, photobleaching experiments, and solvatochromism studies.

Solvatochromic study of highly fluorescent alkylated isocyanonaphthalenes, their π-stacking, hydrogen-bonding complexation, and quenching with pyridine.

Mono- and dialkylated derivatives of 1-amino-5-isocyanonaphthalene (ICAN) were studied as new members of a multifunctional, easy-to-prepare fluorophore family, which showed excellent solvatochromic properties. The monoallyl derivative and the starting ICAN exhibited strong fluorescence quenching in the presence of small amounts of pyridine. The formation of a hydrogen-bonded ground-state pyridine complex was detected; however, analysis of quantum chemical calculations suggested the presence of an additional π-stacked pyridine complex. The Stern-Volmer plot of the quenching process exhibited a downward curvature and after reaching a minimum the fluorescence intensity increased back to a significant level at high pyridine concentrations. Significant fluorescence was observed even in pure pyridine. A new mechanism and a simple mathematical equation were derived to explain the downward curvature and the remaining fluorescence by the formation of a fluorescent π-stacked complex.

Click chemistry to fluorescent hyperbranched polymers. 1 – Synthesis, characterization and spectroscopic properties

The synthesis of two new fluorescent hyperbranched polymers with low molecular weight macromolecular skeleton is presented. An experimental approach to obtain fluorescent dansyl derivatives of commercial hydroxyl-terminated hyperbranched polymers (HBPs) have been obtained through click chemistry reactions. Photophysical characterization of the HBP probes compared with their low molecular weight reference compounds shows that the fluorophore in the polymer skeleton behaves as an individual molecule, showing similar emission properties in terms of absorption extinction coefficient, fluorescence quantum yields and position of the fluorescent band. Solvatochromic study of the HBPs in several solvents using ET30, π* and SPP scales demonstrates that there is not a loss of sensitivity towards polarity when the sensor moiety is included in the HBP structure. The absence of quenching deactivation processes in these multifunctional sensors has been attributed to their irregular hyperbranched skeleton, in contrast to what occurs in highly regular dendrimeric analogues. The advantage of the oligomeric probes versus the monomeric ones has been checked preparing transparent and sensitive films using the fluorophores as dopants. The swelling kinetics of the films has been monitored by fluorescence and the diffusion coefficient estimated. Negligible extraction of the hyperbranched probes was found for long time immersions of the films in acetonitrile, whereas low molecular weight derivatives showed continuous extraction.

Short-conjugated zwitterionic cyanopyridinium chromophores: Synthesis, crystal structure, and linear/nonlinear optical properties

A new class of short-conjugated zwitterionic cyanopyridinium chromophores with the absorption maxima less than 550 nm were designed and synthesized. These chromophores display a good solubility in organic solvents and exist in a charge-separated ground state, as confirmed by IR, X-ray crystallography, negative solvatochromism and fluorescence studies. They can be doped up to 10% by weight into poly(ether sulfone) and attached onto a methacrylate polymer by grafting. Without optimization of the poling conditions, a high electro-optic coefficient can be readily achieved using the chromophore-grafted nonlinear optical polymers.

From visible to far-red excitable chromophores derivatives of vitamin B6. Evaluation as pH-responsive probes and solvatochromic study

Owing to the great potential and application of pH probes in biological and environmental sciences, four aqueous soluble vitamin B6 derivatives 1–4 bearing visible excitable chromophores as coumarin, fluorescein, cresyl violet and nile blue were successfully synthetized and characterized. Compounds 2–4 are highly pH dependent revealed significant spectral changes in the ground and excited states, with exception of 1 whereas no changes in the excited state were visualized. In the same way, at pH 6–7 probes 1 and 3 exhibited the highest fluorescent quantum yield, with values of 0.65 and 0.51. Concerning the solvatochromic behaviour, a positive effect was witnessed for compound 4. Moreover, in the excited state were observed different colours ranging from red (CH2Cl2) to orange (CHCl3, CH3CN), to pink (EtOH), to green (DMSO) and to blue (H2O). The dipole moments in the ground and excited states were determined for compound 4, whereas values of μg.imineE = 3.62 D, μe.imineE = 12.35 D (Δμ = 8.73 D), μg.iminez = 3.38 D and μe.iminez = 11.54 D, (Δμ = 8.16 D), revealing that 4 is more polar in the excited state.

Solvent Swelling Activation of a Mechanophore in a Polymer Network

A spiropyran mechanophore (force-sensitive molecule), which is fluorescent in its mechanically activated state, is used to investigate swelling-induced mechanochemistry in cross-linked poly(methyl methacrylate). The spiropyran is incorporated as a cross-linker. A correlation is observed between solvent-induced polymer swelling and fluorescence intensity, suggesting that the forces during swelling are sufficient to drive the electrocyclic ring-opening of spiropyran to its colored and fluorescent merocyanine form. Control experiments and solvatochromic studies validate that activation is indeed due to swelling-induced mechanical forces and not solvent effects. Systematic studies varying solvents and cross-linking densities provide insight into how altering swelling parameters influences the mechanophore response at the molecular level.

Synthesis and solvatochromism studies of novel bis(indolyl)methanes bearing functionalized arylthiophene groups as new colored materials

The demand for dyes with solvatochromic properties has increased in the last few years, mainly due to their wide range of applications in the analytical and industrial fields, such as in the textile industry. The phenomenon of solvatochromism is associated with the differential solvation of the ground and excited states of the solvatochromic compounds, leading to an important tool for the study of the nature of solute-solvent interactions. In this paper we report the synthesis of new bis(indolyl)methane derivatives bearing arylthiophene spacers (2a-d) functionalized with electron-donating and electron-withdrawing groups, and the photophysical studies in different solvents, such as ethanol, acetonitrile, dichloromethane, trichloromethane, dimethylsulfoxide, diethylether and 1,4-dioxane. Aiming to explore their solvatochromic behaviour in the ground and excited states, all solvents employed have different hydrogen-bond donor abilities. The largest colour modifications were visualized for compound 2b, the solution colours of which are orange in DMSO, blue in trichloromethane, green in dichloromethane and purple in 1,4-dioxane. A negative solvatochromism was observed in 2b and a positive one in 2a, 2c and 2d.

Spectroscopy and solvatochromism studies along with antioxidant and antibacterial activities investigation of azo–azomethine compounds 2-(2-hydroxyphenylimino)methyl)-4-phenyldiazenyl)phenol

The azo–azomethine compounds 2-(2-hydroxyphenylimino)methyl)-4-phenyldiazenyl)phenol (2a–d) were prepared from the reaction of 2-aminophenol with 2-hydroxy-5-(aryldiazenyl)benzaldehyde (1a–d). The structures of all compounds were then characterized by elemental analysis, mass, infrared, UV–vis, 1H and 13C NMR spectroscopy. The electronic absorption spectra indicated enol–keto tautomeric and positive solvatochromism in compounds (2a–d), which is dependent on the substitution, nature of solvent, pH and environment temperature. The compounds (2a–d) were also evaluated for antibiotic activities by disc diffusion method. Compounds 2a and 2b exhibited antibacterial activities against Staphylococcus aureus and Bacillus cereus, but 2c and 2d were found to have no remarkable antibacterial activity. All the compounds (2a–d) also showed antioxidant activity as determined by 1,1-diphenyl-2-picryl-hydrazyl (DPPH) method.

Solvatochromic studies of pull–push molecules containing dimethylaniline and aromatic hydrocarbon linked by an acetylene unit

Pull–push molecules containing dimethylaniline and aromatic hydrocarbon linked by an acetylene unit were studied using spectroscopic methods and DFT theoretical calculations.