Unconventional Modulation of Fluorescence Anisotropy of 3-Hydroxyflavone in Cationic Micelles (original) (raw)
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1996
The excited-state proton transfer and dual emission behaviour of 3-hydroxyfiavone (3HF) have been investigated in reverse micelles of sodium bis(2-ethylhexyl) sulphosuccinate (AOT)/n-heptane at different values of water to surfactant molar ratio (Wo). The green tautomet emission (~i .... ~ 524 nm) and blue-violet normal emission (2 ...... 400 nm) originate from two different ground state populations of 3HF molecules, which are located respectively in the apolar phase and at the interphase of the reverse micelles, proximal to the AOT head groups. With increasing Wo the relative yield of the green emission band is enhanced with a concomitant decrease in that of the blue-violet emission. This is interpreted in terms of the population of 3HF molecules which are initially located in the interfacial region proximal to the polar head groups being "pushed" out into the apolar phase, where external hydrogen bonding perturbations are minimized.
Fluorescence Characteristics of some Flavones Probes in Different Micellar Media
Journal of Fluorescence, 2014
The fluorescence characteristics of five hydroxiflavones (HFs) (some typical models of flavonols), (3 -HF, 6 -HF, 7-HF, 3, 6 -diHF and 3, 7-diHF) in the micellar media of non-ionic surfactant (Triton X-100), anionic surfactant (SDS) and the block copolymer Pluronic F127, have been investigated by means of UV-Vis and steadystate and time resolved fluorescence spectroscopies. Attention is paid to both excited-state intra-molecular proton transfer (ESIPT) as well as ground-state intermolecular proton transfer. The influence of the -OH groups as well as the effect of temperature on the dual fluorescence emission, the Normal and Tautomer emissions, are also investigated. The fluorescence quantum yield of the HFs in mentioned micellar media has been also determined. The results are discussed with relevance to the local environment of HFs as sensitive fluorescence probe in biological membrane systems.
Excited state proton transfer fluorescence of 3-hydroxyflavone in model membranes
Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 1997
3-Hydroxyflavone (3HF), the basic structural moiety of an important group of naturally occurring, biologically active flavonoids, has attracted extensive attention for its intramolecular excited-state proton-transfer (ESPT) and dual fluorescence characteristics. We report here, for the first time, its fluorescence (emission, excitation, polarization anisotropy and lifetime) behaviour in model membranes consisting of small, unilamellar liposomes of synthetic phosphatidylcholine (dimyristoyl phosphatidylcholine (DMPC) and dipalmitoyl phosphatidylcholine (DPPC)). The emission spectrum is conspicuously dominated by the ESPT tautomer fluorescence band. This result, along with other relevant data, indicates that the molecules are embedded in the lipid bilayer matrix facing environments where external H-bonding perturbation effects are minimized. The anisotropy (Y) versus temperature (r) profiles dramatically reveal the thermotropic gel-liquid crystalline phase transition properties of the phospholipids. signifying a novel application of the intrinsic (tautomer) fluorescence of 3HF. 0 1997 Elsevier Science B.V.
The Journal of Physical Chemistry A, 2020
Formation of a probe−solvent network resulting in unusually high fluorescence anisotropy (FA) of an excited-state intramolecular proton transfer (ESIPT) probe, 3-hydroxyflavone (3HF), in water prompted us to explore the solvation patterns on its 7-hydroxy (7HF) and 6-hydroxy (6HF) positional analogues. In the present study, it was observed that 7HF exhibits a lower FA than 3HF does in water, implying that the volume of the 7HF−water cluster is less than that of the 3HF−water cluster. Experimental and computational results led us to propose that 7HF forms its water cluster at the molecular periphery in contrast to the projected-out structure in case of the 3HF−water cluster. Density functional theory (DFT)-based quantum chemical calculations provide an approach for the differential solvation patterns of 3HF and 7HF. 6HF, a non-ESIPT probe, exhibits very low FA in water compared with both 3HF and 7HF. This study demonstrates that proper positioning of the hydroxyl group and its participation in the extended π-conjugation within the molecule dictate the formation of the solvated cluster endorsing directed solvation.
The Journal of Physical Chemistry B, 2019
Based on the unusually high fluorescence anisotropy (FA) of 3-hydroxyflavone (3HF) in water medium in contrast to the very low FA of its methoxy counterpart (3MF), our proposition invoked formation of intermolecular hydrogen bonded cage-like probe−solvent cluster of 3HF in water. In the present work ab-initio DFT-based quantum chemical calculations have been exploited to provide a foundation for our interpretation. Ground state optimization of 3HF with varying number of water molecules leads to the formation of cage-like or loop-like probe−water cluster. Our calculations reveal that the structures with 4-5 water molecules are stabilized to the maximum extent. Classical molecular dynamics (MD) simulations reveal that the rotational dynamics of 3HF is much slower in water compared to that in alkane medium which also goes in favor of the probe−solvent cluster formation in water medium. Apart from the theoretical studies, an indirect experimental approach has been adopted to substantiate formation of the probe−water cluster. The atypical observation of reduced FA of 3HF entrapped in micelles relative to that of the fluorophore in water, implies disruption of the probe−water cluster with the addition of micelles, corroborating our original proposition of formation of intermolecularly hydrogen bonded 3HF−water cluster.
Proton transfer reactions in nanoscopic polar domains: 3-hydroxyflavone in AOT reverse micelles
The Journal of Chemical Physics, 2010
A dramatic reduction in the excited-state intramolecular proton transfer ͑ESIPT͒ rate is observed for 3-hydroxyflavone ͑3-HF͒ within the nanoscopic polar domains of Aerosol-OT ͑AOT͒/n-heptane reverse micelle solutions. It is attributed to the formation of intermolecularly hydrogen-bonded 3-HF:AOT complexes, which cause a significant disruption of intramolecular hydrogen bonding within the complex-bound 3-HF molecules, thereby limiting the overall rate of the ESIPT process. Introduction of strong hydrogen-bonding polar solvents like water or methanol into the reverse micelles causes extensive solvation of the AOT head groups, leading to the collapse of the 3-HF:AOT complex and eventual release of intramolecularly hydrogen-bonded 3-HF molecules which are then able to undergo ultrafast ESIPT. With increasing W-value ͑W = ͓polar solvent͔ : ͓AOT͔͒, a larger number of 3-HF:AOT complexes are decimated, thus accelerating the overall ESIPT process. In contrast, in presence of solvents like acetonitrile, whose hydrogen-bonding power is inherently weak, the AOT head groups are poorly solvated, so that the 3-HF:AOT complexes are hardly affected at any W-value. Consequently the ESIPT dynamics of 3-HF in acetonitrile-containing AOT reverse micelles is nearly independent of the W-value, and always slower compared to that in water-or methanol-containing AOT reverse micelles. The results highlight the importance of hydrogen-bonding property of the polar solvent on the ESIPT of 3-HF within a nanoscopic domain.
Elimination of the Hydrogen Bonding Effect on the Solvatochromism of 3-Hydroxyflavones
The Journal of Physical Chemistry A, 2003
We address the important, frequently discussed, and still unresolved question of the role of solute-solvent hydrogen bonding in modulating the excited-state intramolecular proton transfer (ESIPT) reaction in 3-hydroxyflavone (3HF) derivatives, which provides a dramatic variation of the relative intensities of normal (N*) and phototautomer (T*) emissive species. We synthesized a new 3HF derivative, 5,6-benzo-4′diethylamino-3-hydroxyflavone (BFE), in which the additional benzene ring protects the 4-carbonyl from H-bonding with the protic solvents but allows the intramolecular bond with the 3-hydroxyl group, which is the pathway of ESIPT, to be maintained. The absorption and fluorescence properties of BFE and its parent analogue 4′-diethylamino-3-hydroxyflavone (FE) were studied in a set of 20 representative solvents. In aprotic media, these dyes in absorption and fluorescence spectra show similar solvatochromism, whereas in protic solvents dramatic differences are observed, which demonstrate that for BFE the effects of intermolecular H-bonding are eliminated. The elimination of the specific interaction of BFE with protic media in the ground state is shown by thin-layer chromatography. The most dramatic differences in spectroscopic properties between BFE and FE are observed for the intensity ratio of the two emission bands, I N* /I T* . Whereas for FE a linear correlation of log(I N* /I T* ) with the solvent polarity function f( ) exists only in aprotic media and in protic solvents strong systematic deviations are observed, for BFE this linear correlation extends to all of the studied solvents. Therefore, we suggest that the protic solvents modulate ESIPT in 3-hydroxyflavone derivatives exclusively by proton-donor intermolecular H-bonding with 4-carbonyl, which occurs with the preservation of the intramolecular H-bond. Our results show how molecular design allows the elimination of the strong intermolecular H-bonding perturbation of the solvent polarity-dependent ESIPT reaction, which provides the means for constructing fluorescent probes with strong selectivity to universal solvent effects.
2013
Department of Chemistry, West Bengal State University, Barasat, Kolkata-700 126, India <em>E-mail:</em> ranjan.das68@gmail.com Fax : 91-33-25241977 <em>Manuscript received online 19 July 2012, revised 21 August 2012, accepted 22 August 2012</em> The photo physics of 2-(2<em>' </em>-furyl)-3-hydroxychromone (FHC) was explored in three different non-ionic micelles of Triton X-100, Brij-58 and Tween-20. FHC exhibits a dual emission, attributable to the excited normal (<strong>N*</strong>) and tautomer (<strong>T*</strong>) forms resulting from an excited state intramolecular proton transfer (ESIPT) reaction (<strong>N*→T*</strong>). The ESIPT dynamics of FHC in the non-ionic micelles demonstrates a dependence on the hydrophile-lipophile balance (HLB) parameter of the surfactants by an increase in the kinetic constant of ESIPT reaction (<em><sup>k</sup></em>PT) with a decrease in HLB. A c...
The Journal of Physical Chemistry A, 2003
Picosecond time-resolved fluorescence spectroscopy has been applied to the studies of excited-state intramolecular proton transfer (ESIPT) dynamics in two 4′-(dialkylamino)-3-hydroxyflavone derivatives (unsubstituted and substituted at the 6-position) in ethyl acetate and dichloromethane. In all the studied cases, the fluorescence decay kinetics of both short-wavelength normal (N*) and long-wavelength tautomer (T*) bands can be characterized by the same two lifetime components, which are constant over the all wavelength range of the emission. In the meantime, the preexponential factor of the short-lifetime component changes its sign, being positive for the N* and negative for the T* emission band. Moreover, the two preexponential factors of the T* emission decay are the same in magnitude but opposite in sign. These features are characteristic of a fast reversible two-state ESIPT reaction. Reconstruction of time-resolved spectra allows observing the evolution of these spectra with the appearance, rapid growth, and stabilization (in less than 200 ps) of the relative intensities of the two emission bands. A detailed kinetic model was applied for the analysis of these data, which involved the determination of radiative and nonradiative decay rate constants of both N* and T* forms and of forward and reverse rate constants for transitions between them. We show that ESIPT reaction in the studied conditions occurs on the scale of tens of picoseconds and thus is uncoupled with dielectric relaxations in the solvent occurring at subpicosecond times. Moreover, the radiative and nonradiative deactivation processes were found to be much slower than the ESIPT reaction, suggesting that the relative intensities of the two emission bands are mainly governed by the ESIPT equilibrium. Therefore, both electrochromic and solvatochromic effects on the relative intensities of the two emission bands in 4′-(dialkylamino)-3-hydroxyflavones result from the shifts in the ESIPT equilibrium.
Unprecedented high fluorescence anisotropy in protic solvents: Hydrogen bond induced solvent caging?
Chemical Physics Letters, 2016
Atypical high fluorescence anisotropy has been revealed in protic solvents for excited state intramolecular proton transfer (ESIPT) prone 3-hydroxyflavone and some of its hydroxy derivatives. In non-protic solvents, however, the anisotropy values are low. The low and alike anisotropy values of 3-methoxyflavone in all the studied solvents and other experimental evidences ascribe the formation of hydrogen bond induced cage-like structures in case of the hydroxy compounds involving the probe and the solvent molecules to be responsible for the high values of fluorescence anisotropy in protic media.