Dual ASE Spectra from "Superexciplex" TICT States of Dye Molecules (original) (raw)
Related papers
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.
Influence of solvent and substituent on excited state characterstics of laser grade coumarin dyes
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2003
Absorption and fluorescence emission of 4 and 7 substituted coumarins viz. C 440, C 490, C 485 and C 311 have been studied in various polar and non-polar organic solvents. These coumarin dyes are substituted with alkyl, amine and fluorine groups at 4-and 7-positions. They give different absorption and emission spectra in different solvents. The study leads to a possible assignment of energy level scheme for such coumarins including the effect on ground state and excited state dipole moments due to substitutions. Excited state dipole moments of these dyes are calculated by solvetochromic data experimentally and theoretically these are calculated by PM 3 method. The dipole moments in excited state, for all molecules investigated here, are higher than the corresponding values in the ground state. The increase in dipole moment has been explained in terms of the nature of excited state and resonance structure. #
Amplified spontaneous emission spectra from the superexciplex of coumarin 138
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, 2012
In this report the dual amplified spontaneous emission (ASE) characteristics of coumarin 138 (C(138)) had been studied, under different solvent environments. The results obtained were compared with coumarin 461 (C(461)) and coumarin 450 (C(450)), which have closely related structure. The results showed that all these dyes could produce ASE from superexciplex - a new molecular species - formed only under high inversion densities, obtainable by pulsed laser excitation. We have strong indication that a superexciplex with TICT conformation is capable of producing strong ASE.
Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2008
The effect of solvents on the absorption and emission spectra of ergone has been studied in various solvents at 298 K. The bathochromic shift was observed in absorption and fluorescence spectra with the increase of solvents polarity, which implied that transition involved was → *. And the normalized transition energy value E N T showed some scattering when plotted versus . The ground state and excited state dipole moments were calculated by quantum-mechanical second-order perturbation method as a function of the dielectric constant (ε) and refractive index (n). The result was found to be 1.435 D and 2.520 D in ground state and excited state respectively. And also, the density functional calculations were used to obtain the ground state and excited state dipole moments for it has proven to be suitable for calculating electronic excitation energy. And the result is consistent with the experimental.
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.
Amplified Spontaneous Emission Characteristics of LD 473 and Coumarin 102 Laser Dyes
1998
The amplified spontaneous emission spectrum (ASE) of the laser dyes LD 473 and coumarin 102 in certain solvents is largely red shifted from the fluorescence band maximum. The emission characteristics of these dyes have been studied in various solvents using spectrofluorimeter measurements and laser pumping to understand the above behaviour. The study shows that the photophysical properties of LD 473 and coumarin 102 observed under laser pumping may be different from those observed under conventional spectrofluorimeter measurements.
2000
Out of thousands of organic dyes synthesized over the last hundred years only a few show laser action when excited by Q-switched laser or a pulsed nitrogen laser and still fewer under flash lamp excitation. Organic dyes that show laser action are selected by trial and error. For an efficient working of a laser material it is important to select dyes which have high quantum yield and low lasing threshold. Coumarins or -benzopyrones are known for their strong lasing effect. It is a class of laser dyes emitting in the blue green region of the spectrum and derived from coumarin-the parent molecule on substitution with auxochromic (OH, NH2, CH3, etc.) groups at various carbon positions. Depending on the location and direction of the singlet-singlet (S-S) relative to triplet-triplet (T-T) oscillators within the molecular frame, substitution by the hydroxy auxochromic group may cause T-T absorption bands to move in or out of fluorescence region, or they may be left unchanged. An attempt is made to study the spectroscopic characteristics of 4hydroxycoumarin molecule. Electronic absorption spectra of 4-hydroxycoumarin are measured in the wavelength region 200 700 nm in liquid solvents and solgel. Fluorescence spectrum is measured on exciting 4-hydroxycoumarin doped in solgel by varying the excitation wavelengths. Electronic transitions observed experimentally, are interpreted using the optimized geometries and CNDO/S-CI method. Assignments of observed electronic transitions are made on the basis of singlet-triplet electronic transitions. Further, effect of hydroxy substituent on the spectral properties of the parent aromatic molecule are investigated on the basis of molecular structure and spectral predictions for 4-hydroxycoumarin as a potential dye laser material are made. These predictions supported by theoretical results are presented graphically with possible arrangements of low energy S-S oscillators relative to T-T oscillators located in the fluorescence region. Depending on short or long axis substitution, the redshifts of the S-S and T-T absorption bands are observed and the importance of these red shifts, as related to the laser action properties are discussed. We found a good agreement between the experimental and calculated results. Further more, 4-hydroxy coumarin doped in solgel is found to be a potential dye laser material.
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.