The role of molecular size in the excited state behavior of aminocoumarin dyes in restricted media — 2: study of BC I in AOT-formamide reversed micelles (original) (raw)
Related papers
Photophysical features of coumarin 120 in reverse micelles
Journal of Molecular Structure, 2018
The photophysical properties of 7-amino 4-methyl coumarin (C120) were investigated in the reverse micelle systems by using molecular UV-Vis absorption, steady-state and timeresolved fluorescence spectroscopy techniques. For this purpose, the fluorescence spectra of C120 dye in reverse micelle systems with different values of W 0 (from 0 to 45) were examined. The bathochromic shift from 400 nm to 439 nm was observed for the fluorescence maxima of C120. It was found that intramolecular arrangements occurred in the structure of C120 molecule due to specific solute-solvent interactions. Fluorescence lifetime measurements were carried out and quantum yield values, radiative (k r) and non-radiative rate constants (k nr) were calculated. The data compared with the values reported in the literature. Steady-state anisotropy (r) studies were done to explain the microenvironment around the C120 molecules. Anisotropy data varying 0.048 to 0.030 with varying W 0 displayed that the microenvironment for the C120 dye in water pools of reverse micelles was different than C120 dye in pure water which is 0.009. The microviscosity and rotational relaxation time values were calculated as a function of W 0. We have determined that C120 dye is a useful probe for the definition the microviscosity of reverse micelles with different water pool sizes.
Photochemistry and Photobiology, 2009
Photophysical studies on coumarin-7 (C7) dye in different protic solvents reveal interesting changes in the properties of the dye on increasing the solvent polarity (Df; Lippert-Mataga solvent polarity parameter) beyond a critical value. Up to Df 0.31,thephotophysicalpropertiesofthedyefollowgoodlinearcorrelationswithDf.ForDf>0.31, the photophysical properties of the dye follow good linear correlations with Df. For Df >0.31,thephotophysicalpropertiesofthedyefollowgoodlinearcorrelationswithDf.ForDf>0.31, however, the photophysical properties, especially the fluorescence quantum yields (F f), fluorescence lifetimes (s f) and nonradiative rate constants (k nr), undergo large deviations from the above linearity, suggesting an unusual enhancement in the nonradiative decay rate for the excited dye in these high polarity protic solvents. The effect of temperature on the s f values of the dye has also been investigated to reveal the mechanistic details of the deexcitation mechanism for the excited dye. Studies have also been carried out in deuterated solvents to understand the role of solute-solvent hydrogen bonding interactions on the photophysical properties of the dye. Observed results suggest that the fluorescence of the dye originates from the planar intramolecular charge transfer (ICT) state in all the solvents studied and the deviations in the properties in high polarity solvents (Df >$0.31) arise due to the participation of a new deexcitation channel associated with the formation of a nonfluorescent twisted intramolecular charge transfer (TICT) state of the dye. Comparing present results with those of a homologous dye coumarin 30 (C30; Photochem. Photobiol., 2004, 80, 104), it is indicated that unlike in C30, the TICT state of the C7 dye does not experience any extra stability in protic solvents compared to that in aprotic solvents. This has been attributed to the presence of intramolecular hydrogen bonding between the NH group (in the 3-benzimidazole substituent) of the C7 dye and its carbonyl group, which renders an extra stability to the planar ICT state, making the TICT state formation relatively difficult. Qualitative potential energy diagrams have been proposed to rationalize the differences observed in the results with C7 and C30 dyes in high polarity protic solvents.
Substituent and solvent effects on the photo-physical properties of some coumarin dyes
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2010
Absorption and fluorescence spectra of three coumarin dyes with various substituents and alkyl groups have been recorded in solvents in the range of 200-730 nm. The photo-physical behavior of dissolved dye depends on the nature of its environment, i.e. the solvatochromic behaviors of coumarin dyes and solvent/solute hydrogen bonding interactions can be analyzed by means of linear solvation energy relationships concept proposed by Kamlet and Taft. The intensity, shape, and maximum wavelength of the absorption and fluorescence band of these dyes in solution depend strongly on the solvent-solute interactions and solvent nature. Hydrogen bonding interactions (specific solute-solvent interactions) between these dye-solvent complex and dipolarity/polarizability (non-specific solute-solvent interactions) control reorientation of solvent molecules around the dye.
Photophysical Properties of Coumarin-30 Dye in Aprotic and Protic Solvents of Varying Polarities¶
Photochemistry and Photobiology, 2004
Experimental results on various photophysical properties of coumarin-30 (C30) dye, namely, Stokes' shift (Av), fluorescence quantum yield (Qf), fluorescence lifetime (q), radiative rate constant (kf) and nonradiative rate constant (knr), as obtained using absorption and fluorescence measurements have been reported. Though in most of the solvents the properties of C30 show more or less linear correlation with the v o s t e d on the website on 28 May 2004 *To whom conespondence should be addressed Radiation Chemistry and
Photophysics and dynamics of rigidized coumarin laser dyes
Journal of Photochemistry and Photobiology A: Chemistry, 1989
This paper describes some photophysical properties, the results of CNDO molecular orbital (MO) calculations and excited state complex formation for two solvatochromic coumarin laser dyes of the rigidized multichromophoric electron donor-acceptor type (coumarins 314 and 337). Light absorption results in the population of an almost fully fluorescent polar charge transfer singlet state characterized by non-alternate electron density distributions and a remarkable sensitivity to solvent properties. Useful nonlinear, linear and multiparameter relationships between the quantum yield of fluorescence, the emission and absorption maxima and the Stokes shift and some solvent parameters are established. Hydrogen-bonding solvents such as ethanol cause quenching and a bathochromic shift of fluorescence due to ground state complexation. Excited state equilibrium studies reveal the formation of weak (with equilibrium constant of 2 -19 1 mol-') hydrogenbonding complexes with a stoichiometry of 2: 1 (dye:ethanol). The fluorescence polarization behaviour in glycerol at various temperatures shows that the molecular rotational diffusion is controlled by the free volume of the medium. The results point to a possible use of these highly fluorescent dyes as bifunctional fluorescent probes for determining the rigidity and polarity of the surrounding medium of interest. lOlO-6030/89/$3.50 @ Elsevier Sequoia/Printed in*The Netherlands 260 interest to predict and control the properties of fluorescent dyes. In recent years many investigations have focused on the role of the solvent in controlling the intramolecular charge transfer (ICT) process for electron donoracceptor (EDA) dye molecules in solution [4, 6, 7, 15,21 -311, as well as in the gas phase using supersonic jet expansion techniques [32]. Certain dye families of the EDA type are good fluorescers (e.g. the oxazines, rhodamines and coumarins) [4, 331 and they have been used as laser dyes and solar energy concentrators.
European Journal of Chemistry, 2012
In the present work, the effect of solvents on absorption and fluorescence spectra and dipole moments (μg, μe) of 7-diethylamino coumarin (7DEAC) and 7-diethylamino-4-methyl coumarin (7DEA4MC) have been studied in different solvents of various polarity at room temperature. The solvents have been selected in a way to cover the full range of intermolecular interactions from non-polar hexane to strongly polar formamide. Using the methods of solvatochromism, the difference in the first excited singlet-state (μe) and ground state (μg) dipole moments was estimated from Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet and McRae equations. The Onsager's cavity radius of the probes has been calculated by AM1 and PM3 quantum chemical calculations and also by a direct relation. The change in dipole moment value (Δμ) was also calculated by using the variation of Stoke's shift with microscopic solvent polarity parameter (ET N ). The calculated dipole moments represent new results, as well as some of the solvatochromic results that were not studied earlier in such large number of solvents. It is observed that the values of excited singlet-state dipole moments are higher than the ground state ones in both the molecules, which shows that excited states are more polar than the ground states.
Influence of solvents and temperature on the excited state characteristics of coumarin laser dyes
Acta Physica Hungarica, 1991
The present work deals with the effect of solvents and temperature on the photophysical propertJes of 4-methyl-7-aminocoumarin (I), and 4-methyl-7-dimethylaminocoumaxin (II). Change of solvent gives rise to Stokes' shift but due to specific interactions, the excited state dipole moments cannot be calcu]ated. Experimental values of percentage po_ ]axization in different polar solvents indicate the formation of 1:1 solute-solvent exciplexes/intermolecular hydrogen bonding. Further, it is observe(] that the fluorescence intensity decreases with increase in temperature for the compound II, but remains constant for compound I. Tkis difference in behaviour is examined in terms of intramolecular charge transfer (ICT) and twisted intraraolecular charge transfer (TICT) states of the cournarin molecu]e.
International journal of scientific research in computer science, engineering and information technology, 2019
Coumarin derivatives are extensively investigated in terms of their photo physical properties to understand excited state in regard to understand and innovate molecules. In this article we study steady state quenching of fluorescence of a coumarin derivative namely 3-Hydroxy-3-[2-oxo-2-(3-oxo-3H-benzo[f]chromen-2-yl)ethyl]-1,3-dihydro-indol-2-one (3HBCD) in binary mixture of acetonitrile and 1,4 dioxane. Dimethylaniline is used as quencher. A negative deviation is seen with modest quencher concentration in the Stern-Volmer (S-V) plots. The quenching ability of Dimethylaniline in reference to aniline is more due to its higher ionization energies.
The Journal of Physical Chemistry A, 2012
Photophysical properties of coumarin-481 (C481) dye in aqueous solution show intriguing presence of multiple emitting species. Concentration and wavelength dependent fluorescence decays and timeresolved emission spectra and area-normalized emission spectra suggest the coexistence of dye monomers, dimers, and higher aggregates (mostly trimers) in the solution. Because of the efficient intramolecular charge transfer (ICT) state to twisted intramolecular charge transfer (TICT) state conversion, the dye monomers show very short fluorescence lifetime of ∼0.2 ns. Fluorescence lifetimes of dimers (∼4.1 ns) and higher aggregates (∼1.4 ns) are relatively longer due to steric constrain toward ICT to TICT conversion. Observed results indicate that the emission spectra of the aggregates are substantially blueshifted compared to monomers, suggesting H-aggregation of the dye in the solution. Temperature-dependent fluorescence decays in water and timeresolved fluorescence results in water−acetonitrile solvent mixtures are also in support of the dye aggregation in the solution. Though dynamic light scattering studies could not recognize the dye aggregates in the solution due to their small size and low concentration, fluorescence up-conversion measurements show a relatively higher decay tail in water than in water−acetonitrile solvent mixture, in agreement with higher dye aggregation in aqueous solution. Time-resolved fluorescence results with structurally related non-TICT dyes, especially those of coumarin-153 dye, are also in accordance with the aggregation behavior of these dyes in aqueous solution. To the best of our knowledge, this is the first report on the aggregation of coumarin dyes in aqueous solution. Present results are important because coumarin dyes are widely used as fluorescent probes in various microheterogeneous systems where water is always a solvent component, and the dye aggregation in these systems, if overlooked, can easily lead to a misinterpretation of the observed results.