Apolar Solvents Research Articles

Effects of donor and acceptor substituents on the photophysics of 4-ethynyl-2,1,3-benzothiadiazole derivatives.

The present work explores the photophysical, electrochemical, and fluorescence polarization properties of a group of π-conjugated phenylethynyl-2,1,3-benzothiadiazole derivatives (BTDs) bearing different electron-donating (ED) or electron-withdrawing (EW) substituents at the para position of the phenylethynyl moiety. The BTDs were synthesized through the Sonogashira cross-coupling reaction between 4-bromo-2,1,3-benzothiadiazole and the respective para-substituted phenylethynyl derivatives. The BTDs with the EW-substituents show relatively weak solvatochromic behavior, while the BTDs with the strong ED-substituents like methoxy and N,N-dimethylamino-based substituents (BTDPhOMe and BTDPhNMe2) exhibit a pronounced solvatochromic behavior. The change in dipole moments in the excited states of the derivatives was calculated using Lippert-Mataga plots. The conclusions drawn on the spectral behavior of the molecules could be rationalized by TD-DFT calculations involving electron density difference (EDD) maps that correlate with the ICT characteristics of the molecules. The experimental and theoretical calculations reveal that the BTDs with the strong ED-substituents (strong push-pull type BTDs) have a strong ICT character in the excited state. These strong push-pull type BTDs show high fluorescence quantum yield (ΦF) in apolar solvents and low ΦF in polar solvents. In contrast, the BTDs with the weak ED-substituents (weak push-pull type BTDs) and EW-substituents (pull-pull type BTDs) have a weaker ICT character with low ΦF in apolar and high ΦF in polar solvent media. There is good a agreement among the HOMO-LUMO band gaps obtained from absorption spectroscopy and electrochemical studies and theoretical calculations. The fluorescence anisotropy measurement in the glycerol medium shows that the studied BTDs generally exhibit higher sensitivity towards microviscosity than the traditional DPH fluorescence anisotropy probe.

Solvent quality and solvent polarity in polypeptides.

Using molecular dynamics and thermodynamic integration, we report on the solvation process of seven polypeptides (GLY, ALA, ILE, ASN, LYS, ARG, GLU) in water and in cyclohexane. The polypeptides are selected to cover the full hydrophobic scale while varying their chain length from tri- to undeca-homopeptides, providing indications on possible non-additivity effects as well as the role of the peptide backbone in the overall stability of the polypeptides. The use of different solvents and different polypeptides allows us to investigate the relation between solvent quality - the capacity of a given solvent to fold/unfold a given biopolymer often described on a scale ranging from "good" to "poor"; and solvent polarity - related to the specific interactions of any solvent with respect to a reference solvent. Undeca-glycine is found to be the only polypeptide to have a stable collapse in water (polar solvent), with the other hydrophobic polypeptides displaying repeated folding and unfolding events in water, with polar polypeptides presenting even more complex behavior. By contrast, all polypeptides are found to keep an extended conformation in cyclohexane, irrespective of their polarity. All considered polypeptides are also found to have favorable solvation free energy independent of the solvent polarity and their intrinsic hydrophobicity, clearly highlighting the prominent stabilizing role of the peptide backbone - with the solvation process largely enthalpically dominated in polar polypeptides and partially entropically driven for hydrophobic polypeptides. Our study thus reveals the complexity of the solvation process of polypeptides defying the common view "like dissolves like", with the solute polarity playing the most prominent role. The absence of mirror symmetry upon the inversion of polarities of both the solvent and the polypeptides is confirmed.

From microemulsion phase diagrams to hydrophilicity and hydration controlled adsorption: a dissipative particle dynamics modelling study of phospholipid assembly in bio oils.

We explore here the assembly and adsorption response of a ternary bio oil-phospholipid-water system via dissipative particle dynamics (DPD) simulations. The mesoscale, particle-based modelling approach allows the examination of large-scale self-assembly response of dipalmitoylphosphatidylcholine (DPPC) phospholipids in a model bio oil solvent (modelled by triglycerides) in the presence of varying amounts of water. We report the reverse micellar and microemulsion assembly phase diagrams of the ternary mixture, verifying the model against literature data. The results show water content vs phospholipid concentration dependent transitions in reverse micellar to network-like and various lamellar phases in bulk assembly. Examination of the DPPC adsorption to smooth, homogeneous adsorbate surfaces of differing polarity reveals that phospholipid adsorption response transitions between discrete assemblies on polyethylene-like hydrophobic to continuous coating on mica-like hydrophilic substrates as the function of phospholipid and water concentrations. The significance of the work is that the presented model for phospholipid assembly in apolar solvents is capable of predicting accurately large scale assembly response and morphology changes including adsorption response in terms of system variables. The presented parametrization and verification information of the model enable readily extending the approach to other systems. The work provides computational access for tuning lipid-based microemulsion systems and their adsorption.

Equilibrium state model for surfactants in oils: Colloidal assembly and adsorption

An equilibrium state model addressing the aggregation and adsorption of colloidal assemblies in apolar solvents (oils) via monomer exchange is presented. The model is based on the previously reported step-wise aggregation response of fatty acids and monoglycerides in bio-oils, and captures surface crowding via scaled particle theory (SPT). The sensitivity of key observables - mean aggregation number, adsorbed surfactant amount, and free monomer concentration - to model parameters is demonstrated. Fits to molecular modelling based aggregation and adsorption data of oleic acid and monoolein reveal that the model accurately reproduces chemically specific aggregate exponential distributions in both bulk and surface phases, even outside of its parameterization conditions. A biased state model, where the initial bulk aggregation step (dimer formation) differs from other steps results in a notable improvement in accuracy. Fits to various phospholipid adsorption isotherms demonstrate the applicability of the model to isotherm type experimental data. The fits reveal either monolayer or aggregate like adsorption structures, depending on surfactant head group charge. The presented model provides an easily accessible, computationally feasible means to estimate colloidal assembly and adsorption in oil environments, and enables assessment of surfactant aggregation propensity and adsorption energetics.

The electrophilic aromatic bromination of benzenes: mechanistic and regioselective insights from density functional theory.

The HBr-assisted electrophilic aromatic bromination of benzene, anisole and nitrobenzene was investigated using static DFT calculations in gas phase and implicit apolar (CCl4) and polar (acetonitrile) solvent models at the ωB97X-D/cc-pVTZ level of theory. The reaction profiles corresponding to either a direct substitution reaction or an addition-elimination process were constructed and insight into the preferred regioselectivity was provided using a combination of conceptual DFT reactivity indices, aromaticity indices, Wiberg bond indices and the non-covalent interaction index. Our results show that under the considered reaction conditions the bromination reaction preferentially occurs through an addition-elimination mechanism and without formation of a stable charged Wheland intermediate. The ortho/para directing effect of the electron-donating methoxy-group in anisole was ascribed to a synergy between strong electron delocalisation and attractive interactions. In contrast, the preferred meta-addition on nitrobenzene could not be traced back to any of these effects, nor to the intrinsic reactivity property of the reactant. In this case, an electrostatic clash between the ipso-carbon of the ring and the nitrogen atom resulting from the later nature of the rate-determining step, with respect to anisole, appeared to play a crucial role.

Formation of α,β-Unsaturated Imines in Apolar Aprotic Solvent: Effect of Hidden Acid Catalysts Analyzed by Theoretical Calculations

A theoretical investigation of the 1,2-additon and 1,4-addition reactions of benzylamine to crotonaldehyde in toluene solution is reported in this study, including the effect of trace amounts of acetic acid (AcOH) and methanesulfonic acid (CH3SO2OH). We have determined the reaction free energy profile and performed a detailed microkinetic analysis. Our results point out that this reaction system needs catalysis to take place and it was found that CH3SO2OH is a powerful catalyst, outperforming AcOH in lowering the free energy barrier for the 1,2-addition reaction, which leads to the formation of a,b-unsaturated imine. On the other hand, the 1,4-addition reaction has the direct nucleophilic attack of benzylamine to the b-carbon of s-cis conformation of crotonaldehyde as the rate-determining step, corresponding to slow kinetics. Our results suggest that the experimentally observed formation of the imine can be explained by the presence of hidden acid catalysts present in the reaction medium.

Understanding the activity of glucose oxidase after exposure to organic solvents.

Long-term stability of enzymes in organic solvents is one of the most challenging problems in modern biotechnology and chemical industries. However, the resistance of enzymes to organic solvents is not very well understood so far. Herein, the effects of apolar, chlorinated, and polar organic solvents on the activity and structure of glucose oxidase from Aspergillus niger were systemically investigated using spectrophotometric activity assay of this enzyme and absorption and chiroptical spectroscopy. Molecular dynamics simulations and correlation of the activity with properties of the organic solvents were employed to understand the effects of organic solvents on the enzyme. The experimental and theoretical results showed that apolar solvents reduce the enzyme activity because they facilitate its aggregation through inter-enzymatic salt bridges. Moreover, polar solvents strongly coordinate with amino acid residues in the glucose binding pocket and prevent binding of the substrates. We found that this enzyme is stable in pure apolar and chlorinated solvents and these solvents can be used for the functionalization of its residues. This work provides an in depth understanding at the molecular level of the impact of various pure organic solvents on the structure and dynamics of glucose oxidase and the regulation of its catalytic activity.

Fructobacillus trapaeoli - A fructophilic lactic acid bacteria isolated from Manilkara zapota

The study was undertaken to isolate and characterize fructophilic lactic acid bacteria from the fruit Manilkara zapota (chikoo). Microscopic, phenotypic, biochemical and molecular characterisation of the isolates was done. The Gram-positive thin rods (5 μm length and 0.25 μm thickness) were catalase and oxidase negative and did not hydrolyze arginine. The carbohydrate fermentation studies showed that the isolate preferred fructose similar to glucose as an energy source. The isolate had an optimum growth at 37ºC and also had grown at 45ºC. 16S rRNA sequencing confirmed the isolate as Fructobacillus tropaeoli DMM03 (NCBI accession number MT158673). There are very few reports of isolation and characterization of Fructobacillus from India. The osmotolerant nature of the isolate was established by its ability to grow in pH 5, 8 per cent NaCl, 35 per cent D-Fructose and 50 per cent D-Glucose. The isolate had also shown growth in the presence of heavy metals with a maximum concentration of 60 ppm cadmium and 2425 ppm lead. An autoaggregation of 46.3 per cent and cell surface hydrophobicity value of 22 per cent with apolar solvent xylene suggested the high adhesion potential. The isolate was found to be non-haemolytic and not liquefying gelatin which implies its safety in use for product preparation. The results point out a prospective area for future research in Fructobacillus tropaeoli DMM03 for tapping its potential in the field of probiotics and bioremediation.

NMR-Based Characterization of Citrus Tacle Juice and Low-Level NMR and UV-Vis Data Fusion for Monitoring Its Fractions from Membrane-Based Operations.

Tacle is a citrus variety which recently gained further interest due to its antioxidant and biological properties. This study suggests using Nuclear Magnetic Resonance (NMR) imaging to characterize Tacle juice's metabolic composition as it is intimately linked to its quality. First, polar and apolar solvent systems were used to identify a significant fraction of the Tacle metabolome. Furthermore, the antioxidant capacity and the total content of flavonoids, polyphenols and β-carotene in the juice were investigated with UV-Visible spectroscopy. Tacle juice was clarified and fractionated by ultrafiltration (UF) and nanofiltration (NF) membranes in order to recover and purify its bioactive principles. Finally, the second part of this work sheds light on the spectrophotometric assays and 1H-NMR spectra of fractions coming from membrane operations coupled with a multivariate data analysis technique, PCA, to explore the impact of UF and NF processes on the metabolic profile of the juice.

The Crucial Role of Solvation Forces in the Steric Stabilization of Nanoplatelets.

The steric stability of inorganic colloidal particles in an apolar solvent is usually described in terms of the balance between three contributions: the van der Waals attraction, the free energy of mixing, and the ligand compression. However, in the case of nanoparticles, the discrete nature of the ligand shell and the solvent has to be taken into account. Cadmium selenide nanoplatelets are a special case. They combine a weak van der Waals attraction and a large facet to particle size ratio. We use coarse grained molecular dynamics simulations of nanoplatelets in octane to demonstrate that solvation forces are strong enough to induce the formation of nanoplatelet stacks and by that have a crucial impact on the steric stability. In particular, we demonstrate that for sufficiently large nanoplatelets, solvation forces are proportional to the interacting facet area, and their strength is intrinsically tied to the softness of the ligand shell.

Effect of Solvents on 1-Butyl-1,2,4-Triazolium Trifluoroacetate Triggered Synthesis of 2,3-Dihydroquinazolin

Background: Quinazolinones are a class of heterocyclic compounds that have a wide variety of applications. They are also used in agrochemicals. There are several methodologies reported for the synthesis of 2,3-dihydroquinazolines using various catalysts. Method: Here, by using 1-butyl-1,2,4-triazolium as cation and trifluoroacetate as anion, 2,3-dihydroquinazolin-4(1H)-one has been synthesized. For the synthesis of 2,3-dihydroquinazolin-4(1H)-one condensation of anthranilamide with the corresponding aldehyde in the presence of organocatalyst and solvent is done. Using benzaldehyde as the parent aldehyde, to validate the outcome, the benzaldehydes were selected as follows a) benzaldehyde, b) 4-methoxybenzaldehyde – electron releasing group and c) 4-nitrobenzaldehyde – electronwithdrawing group. Solvent study has been done with solvents varied from polar to apolar. Both polar protic and polar aprotic solvents are used for the reactions. The polar protic solvents used were water, methanol, ethanol, isopropanol, butanol, hexane-1-ol, and glycerol. The polar aprotic solvents used are ethyl acetate, DMF,acetonitrile, and DMSO. The moderately apolar solvents used are DCM, carbon tetrachloride, 1,4 dioxane, and chloroform. Results: The synthesized triazolium salts are found soluble in polar aprotic, polar protic solvents and few moderately apolar solvents such as DCM, chloroform, acetonitrile, water, methanol and ethanol whereas insoluble with apolar solvents like toluene, benzene, and hexane.The yield of 2-phenyl-2,3-dihydroquinazolin-4(1H)-one was low for 1-butyl-1,2,4-triazolium trifluoroacetate based organocatalyst. But for substituted benzaldehyde, the yield was comparatively high. Comparatively, the yield for 2-(4-methoxyphenyl)-2,3-dihydroquinazolin-4(1H)-one, where the aromatic benzaldehyde had electron-donating group, is less than 2-(4-nitrophenyl)-2,3-dihydroquinazolin-4(1H)-one, where the aromatic benzaldehyde had an electron-withdrawing group. Conclusion: Substituted benzaldehyde gave better yields than benzaldehyde. And nitro group which is electrowithdrawing attached to benzaldehyde enhanced the electrophilic nature at carbonyl center showed higher yields than methoxy group which is electron donating attached to benzaldehyde as it deactivates the carbonyl carbon. The polar protic solvents like water, ethanol and methanol stabilizes the ionic intermediates and gave better yield. Even the moderately apolar solvents like DCM, chloroform resulted in good yields, green solvents like water, ethanol and methanol would be a better choice as solvents. The carbon chain on the solvent has got an effect on product yield. As the carbon chain increases in solvent, the yield decreases due to the separation difficulties. The polar aprotic solvents did gave better yields but not as good as polar protic solvents.

Carboxylic acid catalysis on the imine formation versus aza‐Michael reaction in apolar aprotic solvent

AbstractThe reaction between primary amine and α,β‐unsaturated aldehydes and ketones can produce α,β‐unsaturated imines or aza‐Michael products. However, a theoretical reaction mechanism with the corresponding free energy profile compatible with experimental kinetics in aprotic apolar solvents has not been reported yet. In this work, we have used theoretical calculations to investigate the mechanism behind the 1,2‐addition and 1,4‐addition of benzylamine (BnNH2) to methyl vinyl ketone (MVK) in toluene solution. The calculation of the free energy profile was followed by a microkinetic analysis. According to our results, the experimentally observed formation of the aza‐Michael product is due to more favorable kinetics of the nucleophilic attack of the BnNH2 to the β‐carbon of s‐cis conformation of MVK. Furthermore, acetic acid can be present in MVK as a stabilizer. This contaminant catalyzes the transfer of protons for the formation of the aza‐Michael product and can also catalyze the imine formation. The present analysis indicates that catalysts for proton transfer are essential for the reaction to proceed in aprotic solvent and explain the use of carboxylic acids as an additive in aza‐Michael reactions. In the case of acetic acid, this species has a powerful catalytic effect, which explains why even a trace amount is enough for catalysis. A higher concentration of acetic acid could in principle favor the imine mechanism. However, a high concentration of acetic acid leads to the dimerization of this species, producing a low concentration of the free acid and limiting its ability to produce competitive kinetics for imine formation.

Phenolic constitutents, antioxidant and repellent activities of coriander (Coriandrum sativum L.) fruits using different solvent extracts

ABSTRACT The organic solvent extracts (hexane, chloroform, acetone, methanol and water) of coriander fruits were reported for their antioxidant and repellent activities. The methanol and acetone extracts revealed the highest antiradical activity as compared to the other solvent extracts. HPLC analysis revealed that phenolic acids were the major compounds in chloroform and acetone extracts, whereas flavonoids in methanol and water extracts. The methanol extract of coriander fruits exhibited the highest repellent effect against coleopteran insects. Additionally, the hexane extract of coriander fruits also exhibited potent repellent and toxic activities against rice weevil. It appeared that coriander fruit extract obtained with the apolar solvent had more repellent potential against Sitophilus oryzae as compared to Tribolium castaneum. For Lasioderma serricorne, the methanol extract of coriander fruits reduced in a very significant way the adults followed by the chloroform and hexane extracts.

Solubility analysis of 18 active pharmaceutical ingredients and intermediates in the non-polar solvents dioxane, toluene and cyclopentyl methyl ether

The temperature dependent solubility of 18 organic compounds, of which some are active pharmaceutical ingredients, was measured in 1,4-dioxane, toluene and cyclopentyl methyl ether over a temperature range between 0 and 70 °C using a turbidity method. The solubility of the studied compounds in the three solvents increases with temperature in all binary solute-solvent systems, and all compounds exhibit a higher solubility in 1,4-dioxane than in toluene and cyclopentyl methyl ether. The non-ideal behaviour of the binary systems was evaluated in terms of the activity coefficient. All the compounds in toluene presented a positive deviation from ideal solution, while both positive and negative deviations were observed for the model compounds in the other two apolar solvents. From the solubility and the activity coefficient, a number of thermodynamic models including van’t Hoff, Apelblat, λh, Margules, van Laar, Wilson, and the Non-Randomness Two Liquids (NRTL) were used for the correlation of the experimental data. The NRTL and the van’t Hoff equations present closer overall correlations, while the Margules and the λh models show deviations >5 % for several compounds in the three solvent systems. The mixing thermodynamic properties of the several solute-solvent systems were further analyzed by the van ‘t Hoff and Wilson equations for a better understanding of the solution behaviour. The analysis revealed systems with apparent ideal behaviour where counteracting non-ideality effects cancel each other’s.

Dynamics and Rheology of Supramolecular Assemblies at Elevated Pressures.

A methodology to investigate the linear viscoelastic properties of complex fluids at elevated pressures (up to 120 MPa) is presented. It is based on a dynamic light scattering (DLS) setup coupled with a stainless steel chamber, where the test sample is pressurized by means of an inert gas. The viscoelastic spectra are extracted through passive microrheology. We discuss an application to hydrogen-bonding motif 2,4-bis(2-ethylhexylureido)toluene (EHUT), which self-assembles into supramolecular structures (tubes and filaments) in apolar solvents dodecane and cyclohexane. High levels of pressure (roughly above 20 MPa) are found to slow down the terminal relaxation process; however, the increases in the entanglement plateau modulus and the associated persistence length are not significant. The concentration dependence of the plateau modulus, relaxation times (fast and slow), and correlation length is practically the same for all pressures and exhibits distinct power-law behavior in different regimes. Within the tube phase in dodecane, the relative viscosity increment is weakly enhanced with increasing pressure and reaches a plateau at about 60 MPa. In fact, depending on concentration, the application of pressure in the tube regime may lead to a transition from a viscous (unentangled) to a viscoelastic (partially entangled to well-entangled) solution. For well-entangled, long tubes, the extent of the plateau regime (ratio of high- to low-moduli crossover frequencies) increases with pressure. The collective information from these observations is summarized in a temperature-pressure state diagram. These findings provide ingredients for the formulation of a solid theoretical framework to better understand and exploit the role of pressure in the structure and dynamics of supramolecular polymers.

Fully zwitterionic diaminobenzoquinonediimines promoted by cyanoaromatic N-substituents

2,5-Diamino-1,4-benzoquinonediimine (DABQDI) derivatives possessing two electron-withdrawing aromatic N-substituents can potentially exhibit a zwitterionic ground state in lieu of the expected canonical structure. It was previously shown that the use of nitroaromatics electron-withdrawing groups (EWG) could yield the quantitative formation of zwitterionic tautomer of DABQDI in polar solvents, while a mixture of canonical and zwitterionic forms was present in low polarity solvents. In this work, we report that the replacement of nitro-containing EWG by weaker nitrile ones prevents the formation of canonical species in apolar solvents for the benefit of the zwitterionic tautomer. This counterintuitive observation is rationalized with theoretical calculations, which points out that the fully zwitterionic electronic structure of the nitrile-containing DABQDI arises from the absence of possible intramolecular hydrogen bonding between the cyanoaromatic N-substituent and the N–H proton of the bridge in the canonical form.

Carbon Nanodots with Solvatochromic Photoluminescence for the Electrochemical Determination of Estrogenic Steroids

Herein, we utilized carbon nanodots (R-CNDs) for the electrochemical detection of estrogens in tap and natural water samples and simulated effluents from Swedish waste water treatment plants (WWTPs). R-CNDs were prepared from 2-aminophenol by solvothermal synthesis and used as a modifier for chitosan-based selective membranes. The data obtained from atomic force microscopy and transmission electron microscopy suggest a spherical morphology of the R-CNDs with lateral size in the range of 3–8 nm and the height of 1–8 nm. In contrast to most other known carbon nanodots, R-CNDs are soluble in various organic solvents, including apolar, and less soluble in water. Small nanodots (3 nm) are more hydrophilic than large ones (6–8 nm) and can be separated from the bulk suspension of R-CNDs in heptane by their extraction into a water/ethanol mixture. Suspensions of large R-CNDs in apolar solvents exhibit green photoluminescence, while small R-CNDs in polar solvents have orange. This phenomenon was attributed to a solvatochromic rather than to a quantum effect. The R-CNDs were embedded on a chitosan-modified pencil electrode and the electrode was applied for voltammetric determination of four abandoned estrogens: estrone, estradiol, estriol, and ethynyl estradiol. The sensor demonstrates a group-selective response to the estrogens with a detection limit of 17.0 nmol L–1. It can be applied to determine the estrogens in the range of 0.05–4.6 μmol L–1 in the presence of typical interfering bioactive compounds, such as paracetamol, uric acid, progesterone, sulfamethoxazole, trimethoprim, ibuprofen, and caffeine. The developed sensors show repeatability and reproducibility values of 1.8–3.4% and 4.3%, respectively. The efficiency was proved by application for tap and lake water samples, where the recovery range was found to be 93–100%. The low cost, stability, and high sensitivity and selectivity of fabricated sensors make R-CNDs a perspective modifier for electrochemical sensors for the detection of estrogen microquantities in variable water samples.

New insights into the Van Krevelen diagram: Automated molecular formula determination from HRMS for a large chemical profiling of lichen extracts.

In recent years, LC-MS has become the golden standard for metabolomic studies. Indeed, LC is relatively easy to couple with the soft electrospray ionization. As a consequence, many tools have been developed for the structural annotation of tandem mass spectra. However, it is sometimes difficult to do data-dependent acquisition (DDA), especially when developing new methods that stray from the classical LC-MS workflow. An old tool from petroleomics that has recently gained popularity in metabolomics, the Van Krevelen diagram, is adapted for an overview of the molecular diversity profile in lichens through high-resolution mass spectrometry (HRMS). A new method is benchmarked against the state-of-the-art classification tool ClassyFire using a database containing most known lichen metabolites (n ≈2,000). Four lichens known for their contrasted chemical composition were selected, and extractions with apolar, aprotic polar, and protic polar solvents were performed to cover a wide range of polarities. Extracts were analyzed with direct infusion electrospray ionization mass spectrometry (DI-ESI-MS) and atmospheric solids analysis probe mass spectrometry (ASAP-MS) techniques to be compared with the chemical composition described in the literature. The most common lichen metabolites were efficiently classified, with more than 90% of the molecules in some classes being matched with ClassyFire. Results from this method are consistent with the various extraction protocols in the present case study. This approach is a rapid and efficient tool to gain structural insight regarding lichen metabolites analyzed by HRMS without relying on DDA by LC-MS/MS analysis. It may notably be of use during the development phase of novel MS-based metabolomic approaches.

Solvato-, thermo- and photochromism in a new diazo diaromatic dye: 2-(p-tolyldiazenyl)naphthalen-1-amine

The novel azo dye 2-(p-tolyldiazenyl)naphthalen-1-amine (2tona) was synthesized and structurally characterized by infrared, 1H- and 13C NMR spectroscopies, complemented by density functional theory (DFT) calculations on the different possible isomeric species of the compound. The solvatochromism exhibited by 2tona in several solvents with different characteristics, as well as its thermo- and photochromic properties, were then investigated using UV–vis absorption spectroscopy, complemented by time-dependent DFT calculations.Solvatochromism was evaluated using the Kamlet-Taft model, highlighting the relevance of dipolarity/polarizability of the solvent, but also of its hydrogen bonding acceptor and donor abilities, in determining the optical properties of 2tona in the different solutions studied. In apolar solvents and polar solvents with no ability to participate in H-bonds as donors, the solutions show yellow tones, and only the azo-trans isomeric form of the compound exists (two conformers in equilibrium). Solvents with higher polarity and H-bond acceptor character red shift the bands of the azo-trans conformers observed in the visible region, with all probability by stabilizing their LUMO and LUMO+1 orbitals. The red tones of the solutions of the solvents with high ability to participate in H-bonds as donors reveal the presence in these media also of the hydrazone-trans tautomer of the compound.Thermo- and phochromic (induced by UV light; λ = 311 nm) behaviors observed in methanol and chloroform solutions were also evaluated, and interpreted in terms of azo-hydrazone tautomerism and cis-trans isomerism.The studied compound appears as a versatile solvato-, thermo- and photochromic system, which is sensitive to different types of intermolecular interactions with the solvent, thus being a good candidate for practical applications in materials sciences.

Rigid Bay-Conjugated Perylene Bisimide Rotors: Solvent-Induced Excited-State Symmetry Breaking and Resonance-Enhanced Two-Photon Absorption

Intramolecular charge transfer and excited-state symmetry breaking have a significant effect on the nonlinear optical properties of multipolar chromophores. Rigid and nonplanar perylene bisimide derivatives (PBIs) functionalized at bay positions were comparatively and comprehensively investigated. In apolar solvents, two quadrupolar molecular rotors showed an obvious decrease of the A0-0/A0-1 ratios, suggesting strong exciton coupling with the adjacent PBI units initiated by the π-π stacking. The vanishment of the preferable dimer emission in polar solvents supported the plausible phenomena of excited-state symmetry breaking, thanks to the facile rotation around the rigid linkers. Comparative femtosecond transition absorption studies confirmed their notable differences in relaxation dynamics and the generation of radical anions (PBI•-) and cations (PBI•+). The maxima two-photon absorption (2PA) wavelengths obtained for the molecular rotors were slightly red-shifted to 670 nm with intrinsic resonance-enhanced characteristics, reflecting the synergistic effect of functional positions and molecular architectures. Meanwhile, the obvious increase of significant 2PA cross-section values in polar solvents illustrated the stabilization of the symmetry-broken dipolar states. Further femtosecond Z-scan also manifested the contribution of excited-state dynamics on the nonlinear optical properties of multipolar chromophores.