Fig 7 - uploaded by Vasyl Pivovarenko
Content may be subject to copyright.
Dependence of log(I N* /I T* ) of the dye 1b on the solvent polarity index PPS. The aprotic solvents are toluene, chloroform, THF, DMF and DMSO. The protic solvents are ethyl alcohol and methyl alcohol. For aprotic solvents, data are fitted to log(I N* /I T* ) = 5474 Â PPS À 5289 (r 2 = 0.97).
Source publication
Herein, the fluorescence properties of a series of 2-aryl-3-hydroxyquinolones (3HQs) were investigated and compared with the properties of well-studied 3-hydroxyflavone. All these compounds were found to display dual fluorescence with well-separated bands in organic solvents and aqueous solutions. Using steady-state and time-resolved fluorescence s...
Context in source publication
Context 1
... scale (PPS). 27 This scale is based on the solvatochromic shifts undergone by the long-wavelength ab- sorption maximum of two indicators-DMANF and FNF. This scale excludes specific solvent-solute interactions and thus reflects 'pure' polarity. 27 The I N* /I T* ratios of all N-Me 3HQs are highly sensitive to solvent polarity (Table 2). In Fig. 7, it can be seen that for the representative compound 1b, the logarithm of the I N* /I T* ratio linearly increases with the PPS index in aprotic solvents. In contrast, the I N* /I T* ratio in the two protic solvents (methyl and ethyl alcohol) was much higher than expected from the PPS scale. This indicates that, as in the case of 3HF ...
Citations
... The 2-Aryl 3-Hydroxybenzo[g]quinolone (2Ar3HBQ) molecules constitute a relatively new family of fluorophores that undergo excited state intramolecular proton transfer (ESIPT) [1][2][3][4][5][6][7][8]. As shown in Fig. 1, they might be considered as aza-analogs of 3-Hydroxyflavones (3HFs), which are among the most widely studied ESIPT fluorophores [9][10][11]. ...
The 2-Aryl 3-Hydroxybenzo[g]quinolones (2Ar3HBQ) are a relatively new family of ESIPT fluorophores distinguished by their visible absorption spectra, which makes them potential ratiometric probes for biological media. In the present work, we found that 2Ar3HBQ residing as guest fluorophores inside biomimetic host systems like surfactant supramolecular assemblies like micelles and reverse micelles, exhibit dual emission attributable to ESIPT. Ratiometric analysis of the two emission peaks corresponding to the normal (N*) and tautomer (T*) species indicated that the ESIPT rates depend strongly on the nature of the host supramolecular assembly. For example, the ESIPT rate in reverse micelles containing no water was found to be similar to that in weak H-bonding and low polar solvents like acetonitrile. However, addition of water leads to the formation of water nano-droplets inside the reverse micelles, with concomitant sharp decrease of ESIPT rates. In each of the cases studied, the major factor determining the ESIPT rate appears to be the competition between intramolecular H-bonding within the guest fluorophore on the one hand, and intermolecular H-bonding involving the guest fluorophore and water molecules in its local environment, on the other hand.
... 3-hydroxyquinolones (3HQs) are structural aza-analogs of the 3HFs. They also display a well-expressed dual emission in most tested media [28] due to an ESIPT reaction [28][29][30]. Spectral properties of 3HQs were up to now less investigated since they are a relatively new class of dyes with more complex synthetic pathways. ...
... 3-hydroxyquinolones (3HQs) are structural aza-analogs of the 3HFs. They also display a well-expressed dual emission in most tested media [28] due to an ESIPT reaction [28][29][30]. Spectral properties of 3HQs were up to now less investigated since they are a relatively new class of dyes with more complex synthetic pathways. But importantly, in comparison to 3HFs, most of the synthesized 3HQs are more photostable and have higher fluorescence quantum yields in aqueous solutions [28]. ...
... Spectral properties of 3HQs were up to now less investigated since they are a relatively new class of dyes with more complex synthetic pathways. But importantly, in comparison to 3HFs, most of the synthesized 3HQs are more photostable and have higher fluorescence quantum yields in aqueous solutions [28]. They were shown to be effective in sensing the viscosity of protic solvents [31] as well as both the polarity and basicity of organic media [32]. ...
3-Hydroxyquinolones (3HQs) are a new class of water soluble dual fluorescence probes that can monitor both polarity and basicity (H-bond accepting ability) parameters. Both parameters play an important role in proteins and lipid membranes. Nevertheless, no method exists actually to measure the basicity parameter separately from the polarity. To achieve this aim, we synthesized 2-benzofuryl-3-hydroxy-4(1H)-quinolone (3HQ-Bf) and characterized its photophysical properties by UV, steady-state and time-resolved fluorescence spectroscopy. Due to its extended conjugation and totally planar conformation, 3HQ-Bf is characterized by a high fluorescence quantum yield. In solution, this dye shows an excited state intramolecular proton transfer (ESIPT) reaction resulting in two tautomer bands in the emission spectra. The ESIPT reaction can be considered as irreversible and is governed by rate constants from 0.6 to 8 x 10(9) s(-1), depending on the solvent. The analysis of the spectral properties of 3HQ-Bf in a series of organic solvents revealed a marginal sensitivity to the solvent polarity, but an exquisite sensitivity to solvent basicity, as shown by the linear dependence of the logarithm of the emission bands intensity ratio, log(I(N*)/I(T*)), as well as the absorption or emission maxima wavenumbers as a function of the solvent basicity parameter. This probe may find useful applications through coupling to a protein ligand, for characterizing the H-bond acceptor ability at the ligand binding site as well as for studying the basicity changes of lipid membranes during their chemo- and thermotropic conversions.
Characterizing molecular interactions at the microscopic level remains difficult and, therefore, represents a key target to better understand macromolecule and biomacromolecule behaviors in solution, alone, or in mixtures with others. Therefore, accurate characterization in liquid media, especially in aqueous solutions, without causing any perturbation of the system in which they are studied, is quite difficult. To this purpose, the present paper describes an innovative methodology based on fluorescence spectrophotometry. Two molecular fluorescent probes, namely 8-anilino-1-naphtalenesulfonic acid (ANS) and 2-benzofuryl-3-hydroxy-4(1H)-quinolone (3HQ-Bf), were selected to characterize, respectively, the dipole-dipole interactions and hydrophobic micro-domains, for the first one, and hydrogen bonding, for the second. As a support to study molecular interactions, xanthan, galactomannan, and corresponding mixtures of these substances which are well known to exhibit a synergy of interactions in well-defined mixture conditions were chosen. Once the methodology was set up, the existence of the three types of interactions in these systems was demonstrated, thus allowing the elucidation of the mechanisms of interactions at the molecular scale.
Tetraamino-tetranitro-azacalixarene 5 is at the crossroad of two different families of compounds depending on the conditions and the agent used to reduce the NO2 groups: (1) azacalixphyrin 7 in neutral medium, or (2) phenazinium of type 8 in acidic medium. The key role of the N-substituted amino functions at the periphery is highlighted by investigating octaaminoazacalixarene as a model compound, and by using the corresponding tetrahydroxy-tetranitro-azacalixarene 15 as a precursor, which behaves differently.
Photodynamic therapy (PDT) is recognized as a powerful method to inactivate cells. However, the photosensitizer (PS), a key component of PDT, has suffered from undesired photobleaching. Photobleaching reduces reactive oxygen species (ROS) yields, leading to the compromise of and even the loss of the photodynamic effect of the PS. Therefore, much effort has been devoted to minimizing photobleaching in order to ensure that there is no loss of photodynamic efficacy. Here, we report that a type of PS aggregate showed neither photobleaching nor photodynamic action. Upon direct contact with bacteria, the PS aggregate was found to fall apart into PS monomers and thus possessed photodynamic inactivation against bacteria. Interestingly, the disassembly of the bound PS aggregate in the presence of bacteria was intensified by illumination, generating more PS monomers and leading to an enhanced antibacterial photodynamic effect. This demonstrated that on a bacterial surface, the PS aggregate photo-inactivated bacteria via PS monomer during irradiation, where the photodynamic efficiency was retained without photobleaching. Further mechanistic studies showed that PS monomers disrupted bacterial membranes and affected the expression of genes related to cell wall synthesis, bacterial membrane integrity, and oxidative stress. The results obtained here are applicable to other types of PSs in PDT.
In photochemistry the excited-state intramolecular proton transfer process (ESIPT) is often observed as a highly efficient singlet excited state depletion pathway, which in the presence of a strong intramolecular hydrogen bond may proceed on a subpicosecond time scale. The present work describes the suppression of unwanted transoid-trans isomer formation in photochromic 3 H -naphthopyran derivatives by the introduction of a 5-hydroxy substituent. According to time-resolved spectroscopy experiments and excited-state ab initio calculations, transoid-cis → transoid-trans photoisomerization is reduced by a competitive ESIPT channel in nonpolar solvent (cyclohexane). Upon specific solute–solvent interactions (methanol, acetonitrile) the intramolecular hydrogen bond in the transoid-cis form is perturbed, favoring the internal conversion S 1 → S 0 process as photostabilizing channel.
The 2-Phenyl,3-Hydroxybenzo[g]quinolone (2P3HBQ) fluorophore and its derivative, 2-(4’-hydroxyphenyl)-3-hydroxybenzo[g]quinolone (2HP3HBQ),exhibit well-separated dual emission peaks attributable to Excited State Intramolecular Proton Transfer (ESIPT), thus offering promise as useful visible-absorbing ratiometric fluorescence probes. Time-resolved emission measurements in polar and H-bonding solvents reveal very long time-constants extending up to ∼2 ns, ostensibly associated with the ESIPT process, although the latter has traditionally been known to be ultra-fast for ordinary ESIPT molecules. These unusually long time-constants suggest that ESIPT of 2P3HBQ and 2HP3HBQ involves a large activation barrier, resulting from intermolecular H-bonding with the solvent. This is supported by temperature-dependent fluorescence studies, which show that the ESIPT rates in a polar solvent differ significantly over a range of temperatures, implying that solvent‧‧‧fluorophore intermolecular H-bonding is prevalent at lower temperatures but get disrupted at higher temperatures. Our studies were extended up to 2P3HBQ molecules incorporated inside G4 Supramolecular hydrogels via host-guest type non-covalent binding. ESIPT observed in the gels differ from that in solution state on several counts, reflecting the effect of confinement on the photophysics of the gel-bound fluorophores.
Excited state intramolecular proton transfer (ESIPT) core containing, two series of benzothiazole and benzimidazole based fluorescent acid azo dyes were synthesized. These dyes analyzed and confirmed by ¹H NMR, ¹³C NMR, FT-IR and elemental analysis. Spectral characteristics of these dyes studied in different polarity solvents showed Stokes shift 2888–4678 cm–1 and 2167–4837 cm–1 for benzimidazole and benzothiazole series, respectively. Wool and silk fabric dyed with these dyes, shows 92.1–94.4% (benzimidazole) and 92.4–95.1% (benzothiazole) percentage exhaustion on wool. The dyed substrate evaluated for UV rays protective properties, antibacterial activity light, wash and rubbing fastness. Synthesized dyes show significant antibacterial activity when tested by Agar-well diffusion test against Staphylococcus aureus (Gram positive), Klebsiella pneumonia (Gram negative) bacteria.
Photochemical stability is one of the most important parameters that determine the usefulness of organic dyes in different applications. This Review addresses key factors that determine the dye photostability. It is shown that photodegradation can follow different oxygen-dependent and oxygen-independent mechanisms and may involve both 1S1 - 3T1 and higher-energy 1Sn - 3Tn excited states. Their involvement and contribution depends on dye structure, medium conditions, irradiation power. Fluorescein, rhodamine, BODIPY and cyanine dyes, as well as conjugated polymers are discussed as selected examples illustrating photobleaching mechanisms. The strategies for modulating and improving the photostability are overviewed. They include the improvement of fluorophore design, particularly by attaching protective and anti-fading groups, creating proper medium conditions in liquid, solid and nanoscale environments. The special conditions for biological labeling, sensing and imaging are outlined.
Aza-flavonols are compounds containing the 3-hydroxy-4(1H)-quinolone moiety, a unique scaffold with applications expanding from fluorescent probes and bioimaging to potential metal-related pharmaceutical drugs. Compositions and stability constants of metal complexes of an aza-flavonol 1-methyl-2-phenyl-3-hydroxy-4(1H)-quinolone (LH) in aqueous micellar medium of hexadecyltrimethylammonium bromide were established by fluorescence and spectrophotometric titrations of LH in the presence of metal ions of different type at variable pH. Strong binding with quenching of ligand fluorescence was observed for Cu²⁺, Fe2+/3+ and Pb²⁺ cations. The complexation with Zn²⁺ induced strong fluorescence enhancement in ZnL⁺ complex and smaller enhancement in ZnL2 complex. Al³⁺, Ga³⁺ and Me2Sn²⁺ cations induced strong fluorescence enhancement in 1:1 ML complexes, but quenching in ML2 complexes. Together with the relevant literature data these results indicate that the quenching effect in 1:2 complexes along with strong fluorescence enhancement in respective 1:1 complexes is a general phenomenon for 3-hydroxypyranone and 3-hydroxypyridinone ligands. The quantum mechanical Natural Transition Orbital analysis of ground and excited states of LH, AlL²⁺ and AlL2⁺ species reveals that the fluorescence of AlL2⁺ complex is quenched by an internal electron transfer process, which is absent in the 1:1 AlL²⁺ complex. The results emphasize strong dependence of the coordination induced fluorescence changes on the complex composition.
