Solvent Polarity Probe Research Articles

Molecular rotors of naphthalimide and benzodithiophene as effective solvent polarity probes, temperature sensors, and for g-C3N4 sensitization.

Acceptor-donor-acceptor (A-D-A) molecular rotors have drawn substantial attention for their applications in monitoring temperature variations within cellular microenvironments, biomimetic photocatalysis, and bioimaging. In this study, we have synthesized two novel rotor molecules, NBN1 and NBN2, by incorporating benzodithiophene (BDT) as the donor core and naphthalic anhydride/naphthalimide (NA/NI) moieties as acceptors using Pd-catalyzed Stille coupling reactions. These molecules exhibited distinct charge transfer (CT) behavior in both their absorption and emission spectra and displayed prominent emission solvatochromism. Notably, NBN1 exhibited better CT properties among the two molecules. Moreover, these A-D-A molecular rotors demonstrated remarkable sensitivities of their emission spectra toward solvent polarities and temperatures. Rotors NBN1 and NBN2 showed positive temperature coefficients with internal temperature sensitivities of 0.34% °C-1 and 0.13% °C-1 in chloroform, respectively, and thus hold significant promise for detecting temperature variations in cellular microenvironment. Furthermore, we have modeled these molecules with graphitic carbon nitride (g-C3N4) to form composite systems and performed theoretical calculations to obtain valuable insights into their charge transfer behavior. Theoretical results suggested that these molecules have the potential to efficiently sensitize and modulate the band gap of g-C3N4 and show potential for diverse photocatalytic applications.

Polyynes as Precursors of Photoluminescent Solvent Polarity Probes

A simple and convenient synthesis of substituted thiophenes from pyrrole end-capped polyynes is being reported. The method allows one to obtain a variety of different fluorescent oligo(hetero)aryles from polyyne precursors. The resulting thiophenes exhibit strong emission solvatochromism in a wide scope of different solvents which makes them promising candidates for fluorescent solvent polarity probes.

Enhanced Intramolecular Charge Transfer in New Type Donor–Acceptor Substituted Perylenes

Here we report the facile synthesis and physical characterization of new type N-(2,6-diisopropylphenyl)-3,4-perylenedicarboximides (PMI) with alkyl-substituted quinoline-4(1H)-ylidenemethyl or acridine-9(10H)-ylidenemethyl units as strong donors in the 9-position. When compared to parent PMI, these perylene dyes, 9-((1-methylquinoline-4(1H)-ylidene)methyl)-PMI, 9-((1-benzylquinoline-4(1H)ylidene)methyl)-PMI, 9-((1-heptylquinoline-4(1H)-ylidene)methyl)-PMI, and 9-((10-methylacridine-9(10H)-ylidene)methyl)-PMI, show a pronounced bathochromic shift of their electronic absorption with solvatochromism because of their intramolecular charge transfer. The solvatochromic behavior of these dyes is further confirmed by second-order nonlinear optical experiments. Remarkably high second-order nonlinear optical values (βHRS up to 1300 ± 50 × 10–30 esu at 880 nm in dichloromethane) are obtained by femtosecond hyper-Rayleigh scattering. The one-step synthesis together with the spectroscopic, solvatochromic, and nonlinear optical characteristics qualify these new types of perylene dyes as promising candidates for solvent polarity probes, photovoltaics, or nonlinear optical applications.

Molecular Design of Low Molecular-weight Aqueous Gels Bearing an Azo-hydrazone Tautomeric Group Useful as a Solvent Polarity Probe

Abstract Novel low molecular-weight gelators for aqueous gels were exploited by systematically search varying sugars and adjusting hydrophilic/lipophilic balance. The azonaphthol group was used as a lipophilic group, which was also useful as a measure of the microscopic solvent polarity. From the azo-hydrazone tautomerism the polarity in the gelator aggregates was estimated to be much less polar than that in the gelation media.

Fluorescence properties and staining behavior of monodansylpentane, a structural homologue of the lysosomotropic agent monodansylcadaverine.

We have recently shown that monodansylcadaverine labels autophagic vacuoles. Analysis of the mechanism underlying the labeling revealed that monodansylcadaverine acts as a lysosomotropic agent, being concentrated into acidic compartments by an ion-trapping mechanism, and as a solvent polarity probe, increasing its relative fluorescence intensity by interacting with membrane lipids that are highly concentrated in the autophagic vacuoles. In this study, we synthesized three structurally related derivatives of monodansylcadaverine, replacing the primary amino group of monodansylcadaverine with a neutral (dansylamylamine; MDH), a polar (dansylaminopentanol; MDOH), or an acidic group (dansylaminovaleric acid; MDA), to replace the lysosomotropic character of the marker. Whereas MDH showed a specific staining of autophagic vacuoles, the polar and acidic derivatives did not show any staining. We further demonstrate that the MDH staining of autophagic vacuoles is independent on the acidic pH and thus on an ion-trapping mechanism, but it still shows the same preferences for autophagic membrane lipids as monodansylcadaverine. We propose that MDH can specifically interact with lamellar bodies of the autophagic type as a solvent polarity probe. Therefore, dansylated aminopentane can be used as a specific marker for autophagic vacuoles in vivo and in fixed cells.(J Histochem Cytochem 49:177-185, 2001)

Effect of leucinyl-phenylalanyl-valine on DMPC liposome membrane

Leucinyl-phenylalanyl-valine (LFV) is a hydrophobic tripeptide with a flat egg shaped structure with the long axis dimension of about 12 Å. The effect of LFV on dimyristoylphosphatidylcholine (DMPC) liposome membrane has been studied by differential scanning calorimetry (DSC) and fluorescence spectroscopy. Calorimetric studies shows that incorporation of LFV completely abolishes the pretransition temperature with broadening of main transition temperature. Four conceptually different fluorescence probes, 1-naphthol (1-ROH) an excited state proton transfer probe, 8-anilino-1-naphthalenesulphonate (ANS) a solvent polarity probe, 1-6-diphenylhexatriene (DPH) an anisotropy probe and pyrene an excimer-forming probe have been used for fluorescence spectroscopic studies. For 1-ROH, ANS and DPH, a decreased partitioning with increasing mol.% of LFV was observed. Increasing LFV mol.% caused a decrease in the neutral form emission of 1-ROH, and a decrease in fluorescence intensity with red shift in ANS. The excimer formation ability of pyrene also decreased. The phase transition behavior of DMPC membrane in the presence of LFV was similar to the known effect of cholesterol on lipid bilayers. These results suggest that LFV cause an increased compactness of membrane.

Bands separation in fluorescence spectra of ketocyanine dyes: evidence for their complex formation with monohydric alcohols

In the studies of binary solvent systems containing non-polar (toluene) and polar proton-donating components (monohydric alcohols) using ketocyanine dyes of 2,5-di-benzylidene-cyclopentanone-1 type as solvent polarity probes, we found that in addition to common solvent polarity-dependent shifts of fluorescence spectra, at low alcohol concentrations there appear two new well-resolved spectral bands. They are attributed to the emission of hydrogen bonded complexes of 1:1 and 1:2 type. Effective constants for hydrogen bond complex formation were estimated for them from the fluorescence titration data.

The lysosomotropic agent monodansylcadaverine also acts as a solvent polarity probe.

The autofluorescent substance monodansylcadaverine has recently been reported as a specific in vivo marker for autophagic vacuoles. However, the mechanism for this specific labeling remained unclear. Our results reveal that the common model of ion trapping in acidic compartments cannot completely account for the observed autophagic vacuole staining. Because autophagic vacuoles are characterized by myelin-like membrane inclusions, we tested whether this lipid-rich environment is responsible for the staining properties of monodansylcadaverine. In in vitro experiments using either liposomes or solvents of different polarity, monodansylcadaverine showed an increased relative fluorescence intensity in a hydrophobic environment as well as a Stokes shift dependent on the solvent polarity. To test the effect of autophagic vacuoles or autophagic vacuole lipids on monodansylcadaverine fluorescence, we isolated autophagic vacuoles and purified autophagic vacuole lipids depleted of proteins. Entire autophagic vacuoles and autophagic vacuole lipids had the same effect on monodansylcadaverine fluorescence properties, suggesting lipids as the responsible component. Our results suggest that the in vivo fluorescence properties of monodansylcadaverine do not depend exclusively on accumulation in acidic compartments by ion trapping but also on an effective interaction of this molecule with autophagic vacuole membrane lipids. (J Histochem Cytochem 48:251-258, 2000)

Spectrochemical investigations in dendritic media: evaluation of nitromethane as a selective fluorescence quenching agent in aqueous carboxylate-terminated polyamido amine (PAMAM) dendrimers

Alternant and nonalternant polycyclic aromatic hydrocarbons (PAHs) are employed to compare carboxylate-terminated polyamido amine (PAMAM) dendrimers to typical anionic micelles. Nitromethane is a known, selective, quenching agent of alternant PAHs. However, recent studies by Acree and co-workers have found that nitromethane will also quench the fluorescence emission intensity of nonalternant PAHs in the presence of anionic surfactants above the critical micelle concentration. The quenching of alternant and nonalternant PAHs by nitromethane is used to compare dendritic ‘unimolecular micelles’ to traditional micelles. Experimental results indicate that the PAHs’ association with these dendrimers does not appear to occur in the ‘palisade’ region, as seen in traditional micelles, but rather deeper within the dendrimer structure. Solvent polarity probe studies and quenching in the absence of nitromethane also support this conclusion. Due to the fact that the PAHs do not reside near the negatively charged surface groups, the nitromethane selective quenching rule is obeyed in carboxylate-terminated PAMAM dendrimers (10 mM in surface groups).

Polycyclic aromatic hydrocarbon solute probes Part XII: Dissimilar fluorescence excitation/emission behavior between alkylpyrene and alkylcoronene derivatives and the parent pah molecule

Fluorescence excitation and emission behavior are reported for methylcoronene, 1,2-dimethylcoronene, 2-isopropyl-pyrene, 4-isopropylpyrene, 2,4,7,10-tetraisopropylpyrene, 1,3,6,8-tetraisopropylpyrene, 1,3,5,7,9-pentaisopropylpyrene, 2,7-di- tert-butylpyrene, 2,7-di-(dimethylpropyl)pyrene, 1,3,6,8-tetracyclopentylpyrene and 1,3,6,8-tetracyclohexylpyrene dissolved in various organic solvents of varying solvent polarity. Experimental results are used to test a potential screening method for determining whether a given alkyl-substituted polycyclic aromatic hydrocarbon (PAH) solute is likely to exhibit probe character, as evidenced by a systematic variation in the ratios of the fluorescence intensities of select emission bands with solvent polarity. Of the eleven solutes studied, only 4-isopropylpyrene, methylcoronene and 1,2-dimethylcoronene showed useful solvent polarity probe character. 1,3,6,8-Tetraisopropylpyrene, 1,3,5,7,9-pentaisopropylpyrene, 1,3,6,8-tetracyclohexylpyrene and 1,3,6,8-tetracyclopentylpyrene exhibited slight probe behavior; however, the dynamic ranges covered in emission intensity ratios were believed to be too small for many practical applications when compared against the experimental uncertainty associated with the measured values.

Polycyclic Aromatic Hydrocarbon Solute Probes. Part XI: Unusual Solvent-Modulated Fluorescence Emission Behavior of 1-Methylcoronene and Select Dimethylcoronenes in Nonelectrolyte Solvents

Fluorescence emission spectra are reported for 1-methylcoronene, 1,2-dimethylcoronene, 1,4-dimethylcoronene, 1,6-dimethylcoronene, 2,3-dimethylcoronene, and 2,5-dimethylcoronene dissolved in organic nonelectrolyte solvents of varying polarity. Four of the five coronene derivatives were found to exhibit probe character, as evidenced by a systematic variation in emission intensity ratio with solvent poplarity. Mathematical expressions which correlate measured intensity ratios and solvent polarity probe behavior of 1-methylcoronene and 1,2-dimethylcoronene with pyrene in 46 solvents of varying polarity are reported. Also reported is the preferential solvation behavior of both solutes in binary mixtures of n-heptane + tetrahydrofuran and n-heptane + 1,4-dioxane.

Polycyclic Aromatic Hydrocarbon Solute Probes. Part X: Evaluation of Select Hydrogenated Pyrene, Benzo[ghi]perylene, and Naphthacene Derivatives as Possible Solvent Polarity Probes

Fluorescence emission spectra are reported for 3,4,5-trihydrobenzo[cd]pyrene, 3,4-dihydrobenzo[ghi]perylene, 5,6,7,8,9,10-hexahydrobenzo[ghi]perylene, trans-10b,10c-dihydro-10b,10c-dimethylpyrene, trans-12b,12c-dihydro-12b,12c-dimethylbenzo[a]pyrene, and trans-14b,14c-dihydro-14b,14c-dimethylnaphtho[2,1,8-qra]naphthacene dissolved in organic nonelectrolyte solvents of varying polarity. Dihydrobenzo|ghi]perylene was found to exhibit probe character, as evidenced by a systematic variation in emission intensity ratio with solvent polarity. It has a dynamic range of 0.98 and a high fluorescence quantum yield and is thought to be noncarcinogenic. Also reported are mathematical expressions which correlate measured intensity ratios and solvent polarity probe behavior of dihydrobenzo[ghi]perylene, pyrene, benzo[ghi]perylene, coronene, and ovalene in 48 solvents of varying polarity.

Dynamic solvent effects on electron transfer rates in the inverted regime: Ultrafast studies on the betaines

Transient pump–probe measurements have been made on betaine-30, the solvent polarity probe. Betaine-30 is composed of organic donor and acceptor groups, D+A−⇄kethνDA (excited state). The transient data has been analyzed to measure ket, the electron transfer (et) rate constant, in polar solvents for this inverted regime et. The observed rate constant ket,obs in various polar solvents is as much as a factor of 108 larger than is predicted by the standard, classical, implementation of the theory of Sumi and Marcus, using Kjaer and Ulstrup’s estimates for necessary parameters. In contrast, a quantum treatment of the vibrational modes by Jortner and Bixon, which includes the dynamic solvent effect, predicts that the rate should be approximately ket,JB≂1/〈τs〉. This is close to the experimental results (≂1012 s−1) in typical polar aprotic solvents. However, in highly viscous, slowly relaxing solvents, ket,JB≪ket,obs. This is taken as evidence that the efficient coupling modes for the et in these environments is not the ‘‘conventional solvent coordinate.’’ It is shown that a hybrid of the Jortner/Bixon and Sumi/Marcus theories can physically account for the results. The kinetic behavior of betaine-30 in slowly relaxing solvents is shown to be in the ‘‘diffusionless limit’’ of the hybrid, generalized Sumi–Marcus/Jortner–Bixon picture.

Optical sensor for on-line determination of solvent mixtures based on a fluorescent solvent polarity probe

A new optical sensor for determination of solvent mixtures (such as water in organic solvent) is based on a fluorescent solvent polarity (SP) probe immobilized on an ion-exchange membrane. The fluorescent probe responds to changes in SP by both a shift in the fluorescence emission maximum and a change in fluorescence quantum yield. In this sensor, the analytical information is the relative fluorescence intensity measured at 620 nm (500 nm excitation). The sensor can be applied over a wide range of solvents. The response time ( t 90) is of the order of 15 s. Given the unique applications of fibre optic sensors (e.g., for remote sensing and sensing in explosive areas), the new sensor is expected to be applicable in process control.

Polycyclic Aromatic Hydrocarbon Solute Probes. Part IX: Evaluation of Additional Pentaphene, Pentacene, and Pyranthrene Compounds as Possible Solvent Polarity Probes

Fluorescence emission spectra are reported for benzo[rst]dinaphtho[2,1,-8,7defg;2′1′8′,7′ijkl]pentaphene, dibenzo[a,rst]naphtho[8,l,2cde]pentaphene, dibenzo[fg,ij]pentaphene (also called dibenzo[b,n]perylene), dibenzo[de,kl]naphtho[l,2,3,4rst]pentaphene, dibenzo[h,rst]pentaphene, pyranthrene, tetrabenzo[de,hi,op,st]pentacene, and dinaphtho[2,l,8,7de fg;2′,l′,8′,7′opqr]pentacene dissolved in various organic solvents. Results of these measurements are used to screen PAHs for potential solvent polarity behavior. Of the eight PAHs examined, only dibenzo-[h,rst]pentaphene exhibited probe behavior as evidenced by selective, systematic emission intensity enhancement of band I with increasing solvent polarity.

Polycyclic Aromatic Hydrocarbon Solute Probes. Part VIII: Evaluation of Additional Naphthacene and Perylene Derivatives as Possible Solvent Polarity Probe Molecules

Fluorescence emission spectra are reported for phenanthro[5,4,3,2efghi]perylene, dibenzo[cd,k]naphtho[8,1,2fghi]perylene, benzo[b]peryiene, dibenzo[e,ghi]perylene, and benzo[a]naphtho[8,1,2cde]-naphthacene dissolved in various organic solvents. Results of these measurements are used to screen PAHs for potential solvent polarity behavior. Of the five PAHs studied, only phenanthro[5,4,3,2efghi]perylene exhibited probe behavior, as evidenced by selective emission intensity enhancement of band I with increasing solvent polarity.

Polycyclic Aromatic Nitrogen Heterocycles. Part II: Effect of Solvent Polarity on the Fluorescence Emission Fine Structure of Three Azapyrene Compounds

Fluorescence emission spectra are reported for 1-azapyrene, 2-azapyrene, and 4-azapyrene dissolved in several nonelectrolyte solvents of varying polarity. Results of these measurements show that all three solutes are unsuitable for solvent polarity probes, as the calculated emission intensity ratios remain nearly constant, irrespective of solvent polarity. Abnormal fluorescence behavior was also noted for 1-azapyrene and 2-azapyrene dissolved in several chlorinated solvents. Time-dependent fluorescence spectra for 1-azapyrene in dichloromethane suggest a possible photochemical reaction between the PANH solute and chlorinated solvent molecule.

New highly fluorescent ketocyanine polarity probes

The syntheses and spectral properties of three new and highly fluorescent solvent polarity probes are described. They are found to be extremely sensitive to solvent polarity in that spectral red shifts in both absorption and fluorescence spectra occur upon increasing solvent polarity. Excitation and emission data of the dyes in a set of different polar solvents are given. The emission data are compared with the standard ET N values of solvent polarity and a linear correlation is obtained over a wide range. The origin of the unusual solvatochromic properties is discussed in terms of the resonance structures of this new group of molecular probes. Their outstanding features include high spectral sensitivity to polarity, high molar absorptivities, high fluorescence quantum yields, longwave excitation and emission, insignificant quenching by oxygen, and a sufficient stability in aqueous solution. Therefore, the new probes are considered to be advantageous over other polarity probes used so far in probing biochemical and biological systems.

Polycyclic Aromatic Hydrocarbons and Polycyclic Aromatic Sulfur Heterocycles: Examination of Molecular Structure-Fluorescence Probe Character Correlations

Fluorescence emission spectra are reported for 1,6-dithiapyrene, 3,10-dithiaperylene, 1,7-dithiaperylene, thianthrene, benz[4,10]anthra-[1,9,8abcd]coronene, and benzo[cd]chryseno [4,5,6,7fghijk] perylene dissolved in several nonelectrolyte solvents of varying polarity. Emission spectra of the four polycyclic aromatic sulfur heterocycles (PASHs) contained very little fine structure. Severe spectral distortion, along with significant band broadening, was often observed in the case of PASHs dissolved in polar solvents. Benz[4,10]anthra[1,9,8abcd]coronene showed some probe-like character as evidenced by selective emission intensity enhancement of band I in dimethyl sulfoxide as compared to n-hexadecane solvent. The ratio of emission intensities for benz[4,10]anthra-(1,9,8abcd]coronene, however, failed to vary systematically with solvent polarity. Results of these fluorescence measurements indicate that all six solutes are unsuitable for solvent polarity probes.

ChemInform Abstract: Sextett Rearrangements as Solvent Polarity Probes.

AbstractThe rate constant of the Chapman variant of the Beckmann rearrangement of the anti‐ketoximpicrates (I) is used as a solvent polarity probe and is mainly influenced by the polarizability of the solvent.