Amplified spontaneous emission spectra from the superexciplex of coumarin 138 (original) (raw)
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Dual ASE Spectra from "Superexciplex" TICT States of Dye Molecules
Laser Physics, 2005
We have studied the amplified spontaneous emission (ASE) characteristics of certain coumarin dyes under pulsed laser excitation. Dyes such as coumarin 445 (C 445 ), coumarin 450 (C 450 ), and coumarin 461 (C 461 ) have exhibited two distinct bands of ASE, although they have only one fluorescence emission band under steady-state CW lamp excitation. Such dual bands of ASE were present only for certain solvents and under high-power laser excitation conditions. We have studied this effect in various types of solvents of different polarities and viscosities. The new band is not due to excited-state absorption or two-photon fluorescence but rather stems from the formation of a new molecular complex called a "superexciplex," in which two excited molecules remain associated with a solvent molecule acting as a bridge. These two ASE bands appear to be from two different excited-state species. One is due to intramolecular change transfer (ICT), and the other, most likely, to the twis...
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.
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. #
Optical Materials, 2018
Highly fluorescence, 3-(p-nitrophenyl)-7-diethylamino and 3-cyano-7-diethylaminocoumarin, iminocoumarins derivatives differing by the position of substituents and acceptors groups were investigated and characterized using 1 H, 13 C NMR and FT-IR spectroscopy analysis. These dyes were photophysically characterized and the effects of the substituents investigated. As a result, efficient charge transfer was maintained through the molecule. UV-visible absorption and fluorescence spectra of these dyes became shifted to longer wavelengths upon substitution at 7-position and depend on the attractor group. However, tradeoffs in spectral shifts were observed when two donor attractor electron groups such as N-diethyl substitue at position 7 and nitrophenyl in position 3, respectively. Theoretical calculations were performed using density functional theory (DFT) for studying the molecular structure and optical properties of the investigated molecule.
A new coumarin laser dye 3-(benzothiazol-2-yl)-7-hydroxycoumarin
Optics & Laser Technology, 2005
The electronic absorption, and emission spectra as well as fluorescence quantum yield of 3-(benzothiazol-2-yl)-7hydroxycoumarin (BTHC) were measured in different solvents and are affected by solvent polarity ðDf Þ: The deprotonation of BTHC by triethylamine is a reversible process. BTHC is relatively photostable, the quantum yield of photodecomposition ðf c Þ was found to be 2 Â 10 À4 and 2:7 Â 10 À4 in EtOH and DMF, respectively. The fluorescence lifetimes of BTHC were measured in the absence and in the presence of molecular oxygen and were found to be 2.82 and 2:78 ns; respectively. BTHC acts as good laser dye upon pumping with nitrogen laser ðl ex ¼ 337:1 nmÞ in ethanol and gives laser emission with maxima at 508 and 522 nm: r
Chemical Physics Letters, 2007
We compare the CIS and TD-DFT excited-state structures of several hydroxy coumarin dyes. These calculations have been performed in both gas-phase and water. In addition, the transition energies corresponding to absorption and fluorescence phenomena have been determined within several theoretical approximations. Though the CIS transition energies are strongly overestimated, this scheme reproduces the major chemical features. However, the symmetry of the excited-state geometries and the solvatochromic effects are not always consistently reproduced by CIS.
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.
Revisiting the photophysical properties and excited singlet-state coumarin derivatives
HAL (Le Centre pour la Communication Scientifique Directe), 2011
The solvent effects on the electronic absorption and fluorescence emission spectra of several coumarins derivatives, containing amino, N,N-dimethyl-amino, N,N-diethyl-amino, hydroxyl, methyl, carboxyl, or halogen substituents at the positions 7, 4, or 3, were investigated in eight solvents with various polarities. The first excited singlet-state dipole moments of these coumarins were determined by various solvatochromic methods, using the theoretical ground-state dipole moments which were calculated by the AM1 method. The first excited singlet-state dipole moment values were obtained by the Bakhshiev, Kawski-Chamma-Viallet, Lippert-Mataga, and Reichardt-Dimroth equations, and were compared to the ground-state dipole moments. In all cases, the dipole moments were found to be higher in the excited singlet-state than in the ground state because of the different electron densities in both states. The redshifts of the absorption and fluorescence emission bands, observed for most compounds upon increasing the solvent polarity, indicated that the electronic transitions were of-* nature.