Coumarin Laser Dyes Research Articles

Enhanced fluorescence of coumarin laser dye in the restricted geometry of a porous nanocomposite

We report here the dramatic increase in fluorescence intensity of 7-diethylamino-4-methylcoumarin (coumarin 1) laser dye in the restricted geometry of a pillared clay nanocomposite. The fluorescence intensity of the alumina-pillared fluorphlogopite– coumarin complex is about 6 times greater than that of the fluorphlogopite–coumarin complex. The prevention of dye aggregation and the change of the crystal field surrounding the coumarin dye molecules in the compartments between pillars apparently lead to this fluorescence enhancement. The positive results obtained here may lead to the potential application of dye-intercalated nanocomposite clays in linear and non-linear optics.

Solvation Dynamics of Coumarin 480 in Reverse Micelles. Slow Relaxation of Water Molecules

The picosecond time-resolved Stokes shift of the laser dye coumarin 480 (I) is studied in Aerosol OT-heptane reverse micelles at various concentrations of water. On addition of water to a n-heptane solution of I containing 0.09 M AOT, the emission spectrum of I exhibits a prominent shoulder at 480 nm which is ascribed to the dye molecules in the water pool of the reverse micelles. In n-heptane, the fluorescence decays of I at short and long wavelengths are identical, which rules out any time-resolved Stokes shift. On addition of water to the AOT/heptane system, the decay at long wavelengths exhibit a distinct growth on the nanosecond time scale. This and the time-dependent Stokes shift indicate that the water molecules in the water pool of the AOT reverse micelles undergo slow relaxation on the nanosecond time scale.

Dual ASE from laser dyes with rigidised electron donors

The laser dyes coumarin 102 (C 102) and LD 473 exhibit dual amplified spontaneous emission (ASE) in inert solvents like benzene under nitrogen laser pumping. The results indicate that the twisting of the electron donor group of the dye molecule, as envisaged earlier, is not an essential prerequisite for the presence of dual ASE. Specific solute—solvent interactions such as H-bonding or exciplex also may not be very important.

Dual ASE from 7-diethylamino-4-trifluoromethylcoumarin (C35)

The laser dye coumarin 35 (C35) exhibits a dual ASE band similar to coumarin1 (C1) and does not require specific solute-solvent interaction for the formation of dual ASE.

Microemulsion-gel glasses doped with coumarin laser dyes

Microemulsion-gel glasses doped with 7-amino—4-methyl coumarin (coumarin 120) and 7-dimethylamino—4-methyl coumarin (coumarin 311) were produced to study the luminescent properties of the resultant materials. The values of the fluorescent quantum yields, the emission wavelength maximum, the excitation wavelength maximum and the photostability were obtained as the gels dried and aged. The quantum yield values were observed to fluctuate with time, eventually settling on relatively stable values after 8 weeks. The samples which used only formamide as the initial solvent resulted in the material with the highest quantum yield values. The changing values of the emission wavelength maximum and the quantum yields indicated a hydrogen bond between the dye and the silicate network, i.e., silanols.

Mechanistic aspects of the photochemistry of [CpM(η6-arene)]+ complexes of Fe, Ru and Os

Abstract

Coumarin laser dyes as matrices for matrix assisted UV laser desorption/ionization mass spectrometry

We describe the performance of laser dyes, coumarin 2, coumarin 47, coumarin 120, and coumarin 152, as matrices, for UV laser desorption ionization mass spectrometry and report their use in the analysis of a variety of macromolecules including peptides, proteins, deoxynucleotides and polymers with masses extending up to about 150 000 u. Mass spectra with intense molecular ion signals have been obtained with subpicomole sensitivity and resolutions in the region of M/Δ M ≈ 450 (FWHM; M < 6000 u), in both the positive and the negative ion modes using 337 nm N 2 laser radiation for sample desorption. We have also studied the influence of laser fluence and matrix concentrations on the mass resolutions of the molecular ion signals and the formation of matrix related adduct ions. Scanning electron microscope inspection of the samples reveals a rather non-homogeneous surface structure and the methods adopted for improving the sample homogeneity are discussed.

Laser lithotripsy: A preliminary study on its application for sialolithiasis

The present study has established that a flashlamp pumped coumarin dye laser is capable of fragmenting salivary calculi. The refinement of spectroscopic feed-back techniques will allow laser lithotripsy to complement ultrasonic lithotripsy in the non surgical management of salivary calculi.

Pressure effects on absorption and fluorescence of polar dyes

Fluorescence spectra of laser dyes coumarin 1 and coumarin 102 in methanol and ethanol were studied at high pressures using diamond anvil cell. These dyes show a large frequency shift with pressure toward the red end. While the fluorescence maxima vary smoothly with pressure up to the glassification pressure followed by an expected change of slope at this pressure for coumarin 102, coumarin 1 exhibits a pressure-independent regime prior to glassification. This is attributed to a conformational change taking place in coumarin 1 at about 1 GPa

Emission characteristics of laser dyes C1 and Rh6G in cross-linked polyvinyl alcohol solutions

The lifetimes and the relative quantum yields for fluorescence of two laser dyes Coumarin 1 and Rhodamine 6G have been determined in cross-linked polyvinyl alcohol matrix. The cross-linking has been achieved using gamma radiation. The relative fluorescence quantum yields of the dyes increased with increasing cross-linking of the polymer, but the fluorescence lifetimes remained unchanged within experimental error. The results have been attributed to a reduction in the loss of the excitation energy via the internal conversion of the excited singlet state due to increase in the viscosity of the medium brought about by the increased cross-linking of the polymer.

Comparative triplet studies of 7-amino 4-methyl coumarin laser dye in nafion membranes and in homogeneous solutions

Abstract The triplets of 7-amino 4-methyl coumarin (Cl20), a laser dye, were studied in benzene as well as in a polymeric membrane, (Nafion-117). The triplet lifetimes and TT absorption spectra were determined. The TT energy transfer studies between biphenyl—C120 and C120—thionine were carried out in the membrane and the results compared with those obtained in benzene. Due to very slow diffusion of the dye, the energy transfer rates are very low and they are not very efficient compared with other deactivation processes. Effect of counter-ion on the fluorescence lifetimes and triplet yields were studied to see heavy atom effect inside the nafion membrane.

Fluorescence energy transfer between coumarin laser dyes co-bound to poly(methacrylic acid) in water

Coumarin laser dyes have been shown to undergo efficient energy transfer when solubilized and co-bound to poly(methacrylic acid (PMAA) in water at pH 3.0. Under these conditions dyes are bound in relative proximity (about 5.0 nm) within microdomains of the polymer in its compact or hypercoloid form. Energy transfer efficiencies as high as 78% (assumed Förster dipole mechanism) have been measured from the fluorescence data for coumarin pairs displaying a good overlap of absorption and emission spectra.

Photophysics and dynamics of coumarin laser dyes and their analytical implications

A comparative study of the fluorescence of selected flexible and rigidized 7-aminocoumarin derivatives (coumarin 6, 138 and its rigidized coumarin 106) has been made in a series of solvents of varied properties. The studies were further augmented by the quantum chemical SCF-CI MO calculations which provide a theoretical basis for interpreting specific interactions and complex formation with the polar solvents in the intramolecular charge transfer singlet state of these dyes. Moreover, rotational relaxation behaviour, as reflected in the fluorescence polarization of these dyes, is correlated with solvent viscosity/free volume. Through measurements of the temperature/viscosity dependence of the fluorescence depolarization (1/P) in glycerol, we are able to establish an Arrhenius-like relationship linking (1/P) to the free-volume fraction of the medium. Furthermore, depolarization data fitted the Perrin equation with a slope proportional to the sensitivity of the molecular structure towards medium fluidity. The results imply the promising utility of these highly fluorescent dyes as fluorescent probes for local fluidity and polarity of the surrounding medium of interest. We demonstrate possible analytical applications of commercially available coumarin 6 as a promising fluorescent probe for medium properties (e.g. fluidity, polarity and for following micellization in the solutions of some ionic surfactants).

Modelling of formation processes of inclusion complexes of coumarin laser dyes and ?-cyclodextrin by the MM2 force field method. I. 7-Amino-4-methylcoumarins

In order to improve the generating and photochemical properties of coumarin laser dyes, the following active media were synthesized: inclusion complexes of β-cyclodextrin (β-CD) and 7-amino-4-methylcoumarins (COU1, COU102, COU120). Complex formation processes were studied, and the structure of the inclusion complexes was estimated using the method of MM2 molecular mechanics. The data obtained suggest the reasons underlying the complex structure effects on their spectral, luminescent and generating characteristics.

Borohydride anion exchange resin stabilization of flash-lamp-pumped coumarin dye lasers

The operation of flash-lamp-pumped Coumarin 460 and 480 dye laser with ethanol solvent produced acetaldehyde; its production paralleled the increase in the optical density of the dye solution at the dye lasing wavelength and the decrease in the output intensity of the dye laser. The yield of acetaldehyde was shown to be higher with higher light intensity and with the presence of molecular oxygen. Acetaldehyde formation was further enhanced by simultaneous excitation of the singlet-singlet and triplet-triplet absorption bands of Coumarin 460. The formation of acetaldehyde and other material which interferes with stimulated emission is discussed in terms of upper triplet state energy transfer from the dye to the solvent. The concentrations of acetaldehyde and material absorbing at the lasing wavelength of the dye were controlled in real time by introducing a cartridge containing a borohydride anion exchange resin in the dye steam to reduce carbonyl functional groups to less absorbing alcohol functional groups as they were formed photochemically. The presence of the resin increased the initial output power of the dye laser and substantially improved its output stability.

A new laser dye

The various molecular parameters of singlet and triplet states of a new dye belonging to coumarin series, i.e. 7-dimethylaminocyclopenta [c] coumarin (coumarin 138), have been determined. Evaluation of these parameters showed the potentiality of its lasing. For the first time, coumarin 138 (C138) lasing was observed by pumping with a nitrogen laser. The lasing performance of C138 when compared with the known standard laser dye coumarin 1 (C1), the new dye (C138) was found to be more efficient.

Influence of solvents and temperature on the excited state characteristics of coumarin laser dyes

The present work deals with the effect of solvents and temperature on the photophysical properties of 4-methyl-7-aminocoumarin (I), and 4-methyl-7-dimethylaminocoumarin (II). Change of solvent gives rise to Stokes’ shift but due to specific interactions, the excited state dipole moments cannot be calculated. Experimental values of percentage polarization in different polar solvents indicate the formation of 1∶1 solute-solvent exciplexes/intermolecular hydrogen bonding. Further, it is observed that the fluorescence intensity decreases with increase in temperature for the compound II, but remains constant for compound I. This difference in behaviour is examined in terms of intramolecular charge transfer (ICT) and twisted intramolecular charge transfer (TICT) states of the coumarin molecule.

Common emissive intermediates in the thermal and photochemical reactions of nonemissive cyclopentadienylruthenium(II) complexes of coumarin laser dyes

Fluorescent intermediates are observed in the reaction of [CpRu(CH 3 CN) 3 ] + (Cp=η 5 -C 5 H 5 ) with five highly emissive 7-aminocoumarin laser dyes

A study of the triplet state of 7-amino coumarin laser dyes by the nanosecond pulse radiolysis technique

The triplet characteristics of two 7-amino coumarin laser dyes (7-diethylamino 4-methyl coumarin (C 1) and 7-diethylamino 4-trifluoromethyl coumarin (C 1F)) were studied in benzene solution using the nanosecond pulse radiolysis technique. Their T—T absorption spectra, rate constants for triplet to ground state transition and triplet—triplet annihilation and G values were determined. The energy transfers from coumarin triplets to various acceptor molecules such as pyrene, t-stilbene and anthracene and from benzene, biphenyl and naphthalene triplets to these dyes as acceptors were studied. Estimates of their energy levels were made.

Dramatic fluorescence effects for coumarin laser dyes coincluded with organic solvents in cyclodextrins

Small amounts of organic cosolvents produce dramatic enhancements of fluorescence quantum yield with coumarins C6F and Cl in aqueous β- and γ-cyclodextrin solutions. We interpret these results to mean that the small molecules are included in the cyclodextrin cavity and displace water which has a pronounced fluorescence quenching capacity. With coumarin ClF, fluorescence is further reduced under these conditions, an observation reflecting the unusual characteristics of this closely related structure