Solvation and Rotational Dynamics of Coumarin 153 in Ionic Liquids: Comparisons to Conventional Solvents (original) (raw)
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Fluorescence Dynamics of Monocyclodextrin– and Bis(thiol‐cyclodextrin)–Coumarin C153 Complexes
ChemPhysChem, 2015
The solvation and confinement of coumarin C153 within supramolecular host/guest complexes based on β‐cyclodextrin (β‐CD) and 6‐deoxy‐6‐thio‐β‐cyclodextrin (β‐CD‐SH) in water are studied by fluorescence spectroscopy. For β‐CD/C153, the 1:1 complex is proposed, and for β‐CD‐SH/C153 both the 1:1 and 2:1 complexes are believed to be formed. The 2:1 β‐CD‐SH/C153 complex has an association constant of 4.2×105 M−1 and a C153 population of 82 %, which are interestingly high values, indicating that the proposed β‐CD‐SH dimers structure are connected by covalent disulfide bonds; this is supported by mass spectrometry. Solvation related to fast hydrogen‐bond rearrangement as a part of fluorescence relaxation is determined by the ultrafast components of time‐resolved spectroscopy to be 3 and 7 ps for the 1:1 β‐CD/C153 and 2:1 β‐CD‐SH/C153 complexes, respectively.
The Journal of Physical Chemistry B, 2020
Deep eutectic solvents (DESs) are novel environment-friendly media for a variety of applications. In order to obtain insight into the structure and dynamics of some less-explored DESs comprising ethylene glycol and tetraalkylammonium bromide salts with variable alkyl chain length, we have captured complete dynamics occurring in these solvents in a timescale of few femtoseconds to several nanoseconds by monitoring the time-dependent fluorescence Stokes shift of coumarin 153 (C153) employing a combination of time-correlated single-photon counting (TCSPC) and fluorescence upconversion (UPC) techniques. The solvent response function constructed from the measured data reveals a sub-picosecond component (~ 0.8 ps, 2035%) in addition to a slow component (180475 ps) with a distribution of relaxation time. The slow time component is found to be strongly dependent on the viscosity of the medium, indicating that it arises from the diffusive motions of the solvent constituents into and out of the solvation shell, whereas the ultrafast time component, which is nearly independent of the solvent viscosity, arises from fast local motions of the constituents in the immediate vicinity of the solute molecule.
Journal of Molecular Liquids, 2017
Using picosecond time-correlated single photon counting (TCSPC) technique, C-153 fluorescent probe solvation and orientational dynamics in [BMIM][TFSI]/PC mixtures have been investigated. The bi-exponential fit of the solvation response gives tens and hundreds of picoseconds time-components, respectively. Both components are dependent on mixture composition. A characteristic power-law relation between integral solvation times and mixture viscosity has been extracted. As the solvation dynamics is controlled by translational motion, we chose to confront integral solvation times of C-153 in [BMIM][TFSI]/PC with the translational diffusion coefficients of BMIM + cations and propylene carbonate molecules, as well as with average rotational times , obtained measuring time-resolved fluorescence anisotropy. Our results allow to make the hypothesis that the solvation dynamics of C-153 in this mixture is mainly influenced by the cation. Highlights. Solvation responses of [BMIM][TFSI]/propylene carbonate mixtures.. Time-resolved anisotropies. A characteristic power-law relation between solvation times and mixture viscosity. The solvation dynamics of C153 is mainly influenced by the BMIM + cation entity
Solvation dynamics of coumarin 153 in mixtures of carbon dioxide and room temperature ionic liquids
Chemical Physics Letters, 2011
Effects of dissolved carbon dioxide (CO 2 ) on the solvation dynamics of coumarin 153 were studied in 1butyl-3-methylimidazolium hexafluorophosphate, and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide by the time resolved fluorescence spectroscopy. The solvation dynamics showed an ultrafast response less than 1 ps and a slower response extended to a half of ns under ambient condition. With increasing the CO 2 pressure, the slower component became fast, although no significant change was observed for the faster component. The CO 2 effect on the average solvation time was compared with that on the translational diffusion of the solute molecule dissolved in the mixture.
Our aim is to doubly confine a molecule of coumarin C522 in a host–guest supramolecular complex with b-cyclodextrin in a reverse sodium dioctyl sulfosuccinate (AOT) micelle using nonpolar n-heptane and polar water solvents. Varying the volumes of coumarin C522 and b-cyclodextrin dissolved in water allows us to control the water-pool diameters of the reverse micelle in n-heptane with values of w=3, 5, 10, 20, and 40, where w is the ratio of water concentration to AOT concentration in n-heptane. To study the fluorescence dynamics of coumarin C522, the spectral steady-state and time-resolved dependences are compared for the two systems coumarin C522- (water)/AOT(n-heptane), denoted C522/micelle, and coumarin C522/b-cyclodextrin(water)/AOT(n-heptane), referred to as C522/CD/micelle. The formation of the supramolecular host– guest complex CD–C522 is indicated by a blue shift, but in the micelle, the shift is red. However, the values of the fluorescence maxima at 520 and 515 nm are still way below the value of 535 nm representing bulk water. The interpretation of the red shift is based on two complementary processes. The first one is the confinement of CD and C522 by the micelle water pool and the second is the perturbation of the micelle by CD and C522, resulting in an increase of the water polarity. The fluorescence spectra of the C522/micelle and C522/CD/micelle systems have maxima and shoulders. The shoulder intensities at 440 nm, representing the C522 at n-heptane/AOT interface, decrease as the w values decrease. This intensity shift suggests that the small micelle provides a stronger confinement, and the presence of CD shifts the equilibrium from n-heptane towards the water pool even more. The fluorescence emission maxima of the C522/micelle and C522/CD/micelle systems for all w values clearly differentiate two trends for w=3–5, and w=10–40, suggesting different interaction in the small and large micelles. Moreover, these fluorescence maxima result in 7 and 13 nm differences for w=3 and w=5, respectively, and provide the spectral evidence to differentiate the C522 confinement in the C522/micelle and C522/CD/micelle systems as an effect of the CD molecule, which might be interpreted as a double confinement of C522 in CD within the micelle. The ultrafast decay in the case of w=3 ranges from 9.5 to 16 ps, with an average of 12.6 ps, in the case of the C522/micelle system. For C522/CD/micelle, the ultrafast decay at w=3 ranges from 9 to 14.5 ps, with an average of 11.8 ps. Increasing w values (from 10 to 40) result in a decrease of the ultrafast decay values in both cases to an average value of about 6.5 ps. The ultrafast decays of 12.6 and 11.8 ps for C522/micelle and C522/CD/micelle, respectively, are in the agreement with the observed red shift, supporting a double confinement in the C522/CD/micelle(w=3) system. The dynamics in the small and large micelles clearly show two different trends. Two slopes in the data are observed for w values of 3–5 and 10–40 in the steady-state and time-resolved data. The average ultrafast lifetimes are determined to be 12.6 and 6.5 ps for the small (w=3) and the large (w=40) micelles, respectively. To interpret the experimental solvation dynamics, a simplified model is proposed, and although the model involves a number of parameters, it satisfactory fits the dynamics and provides the gradient of permittivity in the ideal micelle for free water located in the centre (60–80) and for bound water (25–60). An attempt to map the fluorescence dynamics of the doubly confined C522/CD/micelle system is presented for the first time.
Journal of the Physical Society of Japan, 2012
The solvent effect on the steady-state and time-resolved fluorescence spectra of coumarin 120 in water was studied utilizing a molecular dynamics simulation with combined quantum mechanical/molecular mechanical method. The constructed steady-state fluorescence spectra reproduced the Stokes shift of the experimental data. The solvent effects on the spectra were examined by constructing three different spectra: spectra using the entire system, spectra including water molecules only in the first solvent shell, and spectra excluding all water molecules. We found that the variation in C-C bond length makes the largest contribution to the solvent shift in the fluorescence spectrum, which indicates the importance of the electronic structure variation.
Supramolecular host-guest complexes between coumarin 460 and cyclodextrins: a matter of size
The role of the host size on stoichiometry, structure and strength of supramolecular association between a fluorescent probe, coumarin 460 (C460), and the three natural cyclodextrins (CDs) with increasing cavity sizes (α, β fluorescent probe, coumarin 460 (C460), and the three natural cyclodextrins (C s) with increasing cavity si es (α, β and γ-cyclodextrin) is analyzed, using fluorescence spectroscopy. The variations of the fluorescence emission spectra of C460 with CD concentration can be explained with a 1:1 complexation equilibrium model for α-CD and β-CD, but also a 1:2 complex has to be included in the case of γ-CD. Nevertheless, the photophysical properties and the stability of the complexes do not correlate in a simple way with the cavity size. For instance, the association between y p p y y , C460 and β-CD, which is the CD with medium cavity size, is much stronger than with the other CDs but it does not provoke fluorescence enhancement as in those cases. Detailed analysis o...
Luminescence : the journal of biological and chemical luminescence, 2017
The UV/Vis absorption and fluorescence characteristics of 3-cyano-7-hydroxycoumarin [CHC] and 7-amino-4-methyl-3-coumarinylacetic acid [AMCA-H] were studied at room temperature in several neat solvents and binary solvent mixtures of 1,4-dioxane/acetonitrile. The effects of solvent on the spectral properties are analyzed using single and multi-parameter solvent polarity scales. Both general solute/solvent interactions and hydrogen bond interactions are operative in these systems. The solvation of CHC and AMCA-H dyes in 1,4-dioxane/acetonitrile solvent mixtures has been studied. The solutes CHC and AMCA-H are preferentially solvated by acetonitrile and a synergistic effect is observed for both molecules in dioxane/acetonitrile solvent mixtures. In addition, using the solvatochromic method the ground- and the excited-state dipole moments of both the dyes were calculated. The ground- and excited-state dipole moments, absorption and emission maxima and HOMO-LUMO gap were also estimated t...