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The optical properties of Malachite green (Mg) dye were examined experimentally, including absorption, optical energy gab, refractive index, dielectric constant, optical conductivity and emission spectra in various solvents. Additionally, several significant photophysical parameters were evaluated, including the extinction coefficient (ε), the energy yield of fluorescence (Ef), the length of attenuation Λ (λ), oscillator strength (f), quantum yield (Øf), fluorescence lifetime ( τ f ), decay rate radiative constant (kr), and the dipole moment (μ) in addition to absorption and emission cross-sections (σa) and (σe) respectively. Time Dependent Density function theory (TD-DFT) computations were used to generate the theoretical absorption spectra of the (Mg) compound. The energy gap (Eg), electron density, and electrostatic potential were also simulated. [ABSTRACT FROM AUTHOR]

Femtosecond laser-induced fluorescence (FLIF) and femtosecond laser-induced optical breakdown spectroscopy (FIBS) are important tools for remote diagnostics of atmospheric aerosols using LiDAR (Light Identification Detection and Ranging) technology. They are based on light emission excitation in disperse media via multiphoton nonlinear processes in aerosol particles induced by high-power optical pulses. To date, the main challenge restraining the large-scale application of FLIF and FIBS in atmospheric studies is the lack of a valued theory of the stimulated light emission in liquid microparticles with a sufficiently broad range of sizes. In this paper, we fill this gap and present a theoretical model of dye water droplet emission under high intensity laser exposure that adequately simulates the processes of multiphoton excited fluorescence and optical breakdown plasma emission in microparticles and gives quantitative estimates of the angular and power characteristics of nonlinear emission. The model is based on the numerical solution to the inhomogeneous Helmholtz equations for stimulating (primary) and nonlinear (secondary) waves provided by the random nature of molecule emission in particles. We show that droplet fluorescence stimulated by multiphoton absorption generally becomes more intense with increasing particle size. Moreover, far-field plasma emission from liquid particles demonstrates a larger angular diversity when changing the droplet radius in comparison with multiphoton excited fluorescence, which is mainly due to the excitation of the internal optical field resonances in spherical particles. [ABSTRACT FROM AUTHOR]

Herein, we report the synthetic access to a set of π-extended BODIPYs featuring a penta-arylated (phenyl and/or thiophene) dipyrrin framework. We take advantage of the full chemoselective control of 8-methylthio-2,3,5,6-tetrabromoBODIPY when we conduct the Liebeskind–Srogl cross-coupling (LSCC) to functionalize exclusively the meso-position, followed by the tetra-Suzuki reaction to arylate the halogenated sites. All these laser dyes display absorption and emission bands in the red edge of the visible spectrum reaching the near-infrared with thiophene functionalization. The emission efficiency, both fluorescence and laser, of the polyphenylBODIPYs can be enhanced upon decoration of the peripheral phenyls with electron donor/acceptor groups at para positions. Alternatively, the polythiopheneBODIPYs show an astonishing laser performance despite the charge transfer character of the emitting state. Therefore, these BODIPYs are suitable as a palette of stable and bright laser sources covering the spectral region from 610 nm to 750 nm. [ABSTRACT FROM AUTHOR]

Chemical fine‐tuning of fluorophores is a pivotal step towards development of next generation fluorescent dyes for microscopy. With the advent of high‐resolution two‐photon excitation fluorescence imaging, there is a growing demand for very sensitive laser dyes that can be efficiently excited using commercial Ti:sapphire laser sources in the first near‐infrared window (NIR‐I, 780–1020 nm). Using the fluorescent dye Nile Red as the lead structure, we report a robust and concise Suzuki coupling approach for the synthesis of 14 new Nile Red analogues that feature extended π ring systems and diverse functionalities. For this set, we gauged their two‐photon excitation efficiency in NIR‐I as well as evaluated their general fluorescent properties (emission wavelength, Stokes shift, quantum yield and solvatochromism). Several of the new fluorophores were found to display very favorable characteristics. In particular, the derivative featuring a 4‐aminophenyl group in the 2‐position of Nile Red exhibited extreme solvent sensitivity, and the thien‐2‐yl substituted Nile Red derivative showed significantly redshifted emission, large Stokes shift and high two‐photon brightness. [ABSTRACT FROM AUTHOR]

Dye lasers are commonly used in optical investigation because their solutions in organic solvents deliver tunable, coherent emissions. They exhibit intense fluorescence owing to some specific spectroscopic characteristics. One drawback of the laser dyes is that it shows excessive triplet-state losses (TSLs.) The lack of theoretical predictions of fluorescence rates, intersystem crossing (ISC), and phosphorescence in laser dyes prompted us to report on the predicted rates of radiative and nonradiative transitions of some laser dyes. Structural engineering by some substituents influencing the simulated rates of coumarin laser dye derivatives for an efficient operation was investigated. The NH2 functional group renders the coumarin 120 more fluorescents with reduced TLS than the other investigated materials. Tailoring new efficient laser dyes can be achieved guided by the calculated rates of emission and nonradiative processes. [ABSTRACT FROM AUTHOR]

• Quenching, transition probabilities, frequency dependent parameters, thermochromic shift method. • Intercrossing system. • Radiative and non-radiative transition probabilities. • Fluorescence lifetime. • Activation Energy. Steady state method is employed to study the effect of temperature on the absorption and emission characteristics of 3-(1H-benzo[ d ]imidazol-2-yl)-7-(diethylamino)-2H-chromen-2-one(3HBI-7D-2HChromen-2-one) laser dye in glycerol solvent. Temperature induces thermal effect on maxima absorption, emission wavelength, fluorescence intensity etc. Radiative and non-radiative transition probabilities mechanism, fluorescence lifetime, frequency assisted parameters decay rate constants, and activation energy is estimated. Advance thermochromic shift method is adopted to determine the ground and excited state dipole moments. [Display omitted] [ABSTRACT FROM AUTHOR]

Two-photon nonlinear process induced fluorescence of Rhodamine 6G (R6G), Rhodamine B (RB), and their mixed aqueous solutions in mass proportion of 1:1, is experimentally observed by different exciting wavelengths. It shows that, for each sample, the exciting wavelength can influence the fluorescence intensity considerably but only slightly influence the peak wavelength of the spectrum. The optimal exciting wavelengths of R6G and the mixed dyes are around 700 nm. While for RB, the optimal exciting wavelengths can be 700 nm and 620 nm. For each dye sample, the spectral red-shift will occur as increase of the solution concentration. The mixing of the two dyes will cause the spectral red-shift with regard to the single dye under our experimental conditions. Moreover, in comparison, at lower concentrations, the mixed dye has relatively intense fluorescence. This work is of significance for determining the optimal exciting wavelength and developing the tunable two-photon dye lasers. [ABSTRACT FROM AUTHOR]

Featured Application: Organic lasers active in the red–near-infrared spectral regions endowed with efficient and long-lasting emission. The disposal of long-wavelength-emitting sources is of paramount relevance in technology and biophotonics due to the low interference with the surroundings that these kinds of far-red and near-infrared radiations hold. As a result of the continued efforts carried out during the last few years by our research group to design new boron-dipyrromethene (BODIPY) dyes with improved photonic performance, two approaches were tested to develop a new generation of organic dyes able to display efficient and long-lasting laser emission in both target spectral regions. On the one hand, the annulation of aromatic benzofuran at the dipyrrin backbone leads to conformationally restricted dyes yielding photostable and bright laser emission beyond 600 nm at the far-red spectral region. On the other hand, a more pronounced shift to longer wavelengths reaching 725 nm at the near-infrared region is feasible, while keeping a reasonably high laser efficiency and tolerance to prolonged and intense pumping, based on aza-BODIPYs bearing peripheral aryl rings. These two complementary strategies yield a library of laser-emitting compounds comprising the 600–725 nm spectral region. Moreover, their laser performance is better than the commercially available dye lasers active in this spectral window. [ABSTRACT FROM AUTHOR]

Herein, the effects of media on the fluorescence characteristics (mainly quantum yield, lifetime and radiationless deactivation rate of the excited singlet state) of phenylene-1,4-ethylene-bis-(2-quinoxaline) laser dye, BQxVB have been reported. Also, the sensitivity of the dye to the proton has been tested by studying the effect of changing the acidic properties of the medium. As with polarity, the acidity of solution provokes spectral changes. As the acidity of the medium increases (using H2SO4 solutions), the pale yellow color of BQxVB changes to orange then violet and eventually to deep blue in concentrated acid solutions. The effect of metallic and bimetallic nanoparticles on the spectral behavior of BQxVB dye has been investigated. Additionally, the binding of the dye by β-cyclodextrin was investigated. The capped and binding of the dye with CT-DNA were visualized based on the spectral studies. Finally, a molecular docking analysis was carried out on five chosen proteins, which are largely responsible for the formation of CT-DNA, 4ASD-transferase, 3UW9 protein binding, 3DDC–hydrolase/apoptosis, 3L8-transferase/CT-DNA, and 4ICH-transcription. Based on the results, it has been clearly shown that BQxVB shows better docking with the 4ASD-transferase protein than the other selected proteins, with an estimated binding Gibbs energy of − 50.45 kJ·mol−1, a total intermolecular energy of − 55.09 kJ·mol−1, an inhibition constant of 1.48 nmol·dm−3, and a binding efficiency of 80%. [ABSTRACT FROM AUTHOR]

Two-photon absorption (TPA) fluorescence of biomarkers has been decisive in advancing the fields of biosensing and deep-tissue in vivo imaging of live specimens. However, due to the extremely small TPA cross section and the quadratic dependence on the input photon flux, extremely high peak-intensity pulsed lasers are imperative, which can result in significant photo- and thermal damage. Previous works on entangled TPA with spontaneous parametric downconversion light sources found a linear dependence on the input photon-pair flux, but are limited by low optical powers, along with a very broad spectrum. We report that by using a high-flux squeezed light source for TPA, a fluorescence enhancement of ∼ 47 is achieved in fluorescein biomarkers as compared to classical TPA. Moreover, a polynomial behavior of the TPA rate is observed in the the laser dye 4-dicyanomethylene-2-methyl-6-(p(dimethylamino)styryl)-4H-pyran in dimethyl sulphoxide. [ABSTRACT FROM AUTHOR]

This work demonstrates the spectral and amplified spontaneous emission (ASE) properties of a new chalcone laser dye material of 1-phenyl-3-[4-(1-pyrrolidinyl) phenyl]-(2E)-propen-1-one (4-Pone) for the first time. The absorption, fluorescence, Stokes' shift and quantum yield were obtained using different organic solvents. The energy band gap was calculated and compared with that of 3-[4-(dimethylamino) phenyl]-1-phenyl-(2E)-propen-1-one (DMAPPP). Under suitable concentrations and pump power excitation (Nd: YAG laser 355 nm), 4-Pone produced an intense ASE at 534 nm. Previously, we had reported that DMAPPP showed optical activities that were significantly better than that of coumarin 503. The results revealed that both chalcones had close fluorescence spectra; nevertheless, the absorption spectra were red-shifted for 4-Pone. Under pulsed laser excitation (Nd: YAG laser λex = 355 nm), 4-Pone produced an ASE peak at 535 nm. The most important feature is that 4-Pone has a low concentration threshold for laser action. [ABSTRACT FROM AUTHOR]

Abstract Novel fluorescent 4-alkynyl coumarins were rapidly and efficiently synthesized by Sonogashira coupling of readily accessible coumaryl triflates. The photophysical properties of the predominantly highly fluorescent compounds were experimentally studied by absorption and fluorescence spectroscopy and their electronic structure was rationalized by DFT and TD-DFT calculations using the PBEh1PBE functional. For certain consanguineous series structure-property relationships of the absorption and emission characteristics were established by Hammett-Taft correlations. Most interestingly, the energy levels of the underlying subchromophores can be electronically fine-tuned and addressed upon photonic excitation for placing donor substituents at the remote alkynyl terminus of the dyes. Graphical abstract Image 1 Highlights The urgency and relevance of our contribution for a broad readership of organic, dye and materials chemists is justified by the following aspects: • Coumarin dyes have found wide spread application as modern functional dyes in laser, DSSC and OLED applications. Surprisingly, 4-alkynyl coumarins have somehow been overlooked. • During our studies towards three-component syntheses of coumarin ‐ based merocyanines initiated by Sonogashira coupling, we discovered that the 4-alkynyl coumarin intermediates were intensively fluorescent. • This prompted us to optimize the alkynylation of 4-triflato coumarins furnishing the title compounds in excellent yield with a variable substitution pattern on both the alkynyl moiety and the coumarin part. • The emission is tunable by the substitution pattern and for certain consanguineous series structure-property relationships of the absorption and emission characteristics can be assessed. Three points of diversity are easily addressed, allowing for a comprehensive physical organic treatment of the photophysical properties. • The elucidation of the electronic structure by DFT and TD DFT calculations using the PBEh1PBE functional reveals that the energy levels of the underlying subchromophores can be electronically fine-tuned and addressed upon photonic excitation with donor substituents at the remote alkynyl terminus of the dyes. [ABSTRACT FROM AUTHOR]

The previously unobserved B 2Σ+–X 2Πi electronic system of OH is detected by laser-induced fluorescence in a low-pressure flow system. OH is produced in high vibrational levels of the ground electronic state by the H+O3 reaction. Light from a frequency-doubled tunable dye laser excites the radical via the (0,8), (0,9), and (1,8) bands of the B 2Σ+–X 2Πi transistion at 225, 236, and 221 nm, respectively. The fluorescence is detected in the B 2Σ+–A 2Σ+ system in the visible and near ultraviolet. Measured emission intensities in the (0,3) to (0,9) and the (1,3) to (1,9) bands of B–A are in good agreement with previous theoretical calculations. The experimental branching ratio for emission between the B–A (0,3) and B–X (0,10) bands is about three times larger than theoretically predicted. Detection of high-lying vibrational levels in the electronic ground state, v’’=6 through 15, for experiments in collision dynamics and reaction kinetics, is feasible using the B–X system. [ABSTRACT FROM AUTHOR]

When the Cs2 molecule was excited by a dye-laser line of 15 841 cm-1, the fluorescence from the energy-transferred states as well as the resonance fluorescence fromthe optically excited levels, which were assigned to C 1Πu and d 3Πu, were observed. We measured the picosecond time-resolved fluorescence intensity by changing the vapor pressure and the temperature. The decay curves were analyzed by a least-squares curve fitting, and the lifetimes in the collisionless limit and the collision cross sections were determined. From the consideration of the rise and decay rates of fluorescence intensities, the kinetic pathways of the collisional energy transfer were estimated. The intensity of the fluorescence d 3Πu–X 1Σ+g was found to decrease appreciably in the presence of an external magnetic field. The magnetic field effect was estimated to be due to the predissociation induced by an electronic Zeeman interaction between the d 3Πu and c 3Σ+u states. [ABSTRACT FROM AUTHOR]

The effect of temperature on the fluorescence of carbon dot colloidal solution in glycerol has been studied. The dots were prepared by pyrolysis of a Nile Red laser dye using mesoporous silica as a template. It is established that the temperature dependence of the intensity of dominant emission peak is nontrivial: as the temperature of the solution rises, the initial quenching of the fluorescence is then replaced by its enhancement to the initial value. A three-level model of electronic states is considered, within which the observed temperature dependence of fluorescence is quantitatively described and the energies of nonradiative deactivation and activation of the emissive state are estimated. The nature of the electronic state responsible for the nonradiative activation of the emissive state is discussed. The possible influence of hydrogen bonds in the solute-solvent system on the temperature behavior of the CD fluorescence is also considered. A pronounced solvatochromic effect is noted in the fluorescence spectra of Nile Red based carbon dots in different solvents. • Nile Red laser dye is used to synthesize fluorescent C-dots by template method. • Nontrivial PL intensity temperature dependence of C-dot glycerol solution is revealed. • The dependence can be described within a three-level model of electronic states. • H-bond formation in the solute-solvent system influences the PL temperature behavior. [ABSTRACT FROM AUTHOR]

The field of organic chemistry began with 19th century scientists identifying and then expanding upon synthetic dye molecules for textiles. In the 20th century, dye chemistry continued with the aim of developing photographic sensitizers and laser dyes. Now, in the 21st century, the rapid evolution of biological imaging techniques provides a new driving force for dye chemistry. Of the extant collection of synthetic fluorescent dyes for biological imaging, two classes reign supreme: rhodamines and cyanines. Here, we provide an overview of recent examples where modern chemistry is used to build these old-but-venerable classes of optically responsive molecules. These new synthetic methods access new fluorophores, which then enable sophisticated imaging experiments leading to new biological insights. [ABSTRACT FROM AUTHOR]

Origin of the monomer and the excimer fluorescence of acriflavine dye in water and alcohol and the effects of temperature and the concentration on their intensities (MF- Monomer Fluorescence, EF- Excimer Fluorescence). [Display omitted] • The monomer and excimer fluorescence emissions of acriflavine were observed in the ranges 495–528 nm and 549–587 nm respectively. • The excimer emission band around 575 nm was not found to be originated from a triplet excited state. • At equilibrium concentration, i.e., critical concentration, monomer and excimer fluoresced with equal intensities. • The monomer-excimer equilibrium changes with temperature at a fixed concentration of acriflavine in all the solvents. The light emission properties of acriflavine have been extensively utilised in its applications as dye laser active media, as photosensitizer, as fluorescent and FRET (Fluorescence Resonance Energy Transfer) agent for sensing mechanism etc. However, studies on the photochemical and photophysical properties of acriflavine and its aggregates are very limited and little is known about its emission characteristics in different media. The present study was undertaken to acquire a comprehensive understanding of the aggregation process and emission characteristics of the solution of pure acriflavine dye in water and alcohol, namely the propanol, methanol, ethanol and butanol. This study includes confirming the photoexcimerisation of acriflavine by concentration dependent UV–Visible spectroscopy, steady state fluorescence spectroscopy and time resolved fluorescence spectroscopy at room temperature. The present study shows the monomer and excimer fluorescence emission of acriflavine in the range 495–528 nm and 549–587 nm respectively (monomer and excimer emission peak wavelength varies for different solvents). The nature of the excimer emission band of acriflavine around 575 nm for all the solvents has been tested through temperature dependent steady state fluorescence spectroscopy and also from time resolved fluorescence spectra it has been found that the excimer band does not originate from any triplet excited state. The pH dependent emission spectra for fixed concentration of acriflavine in the solvents reveals red shifts in the monomer and the excimer fluorescence maxima. The excimerisation of acriflavine in water, propanol and methanol is found as static process from excited dimers, whereas in ethanol and butanol it is the result of dynamic diffusion process between a photoexcited and a ground state monomer. The excimerisation process of the acriflavine has been quantified by evaluating the monomer-excimer equilibrium concentration i.e., the critical concentration in the cited solvents. At the critical concentration the monomer and the excimer are found to be fluoresced with equal intensity. The acriflavine solutions specifically at the critical concentration in the cited solvents will enhance its photophysical and photochemical applications by extending them up to the new range of excimer emission radiation at the wavelength in-between 549 nm and 587 nm. Hence, this report shows that, by using acriflavine solutions of certain concentrations in any one of the cited solvents as an active medium of a dye laser and thereby obtaining both the monomer and excimer emission band, the wavelength of the laser can be tuned from 495 nm to 587 nm. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of solvents and substituents on the fluorescence behaviour of coumarin derivatives the absorption and fluorescence emission spectra of 4-phenyl substituted coumarins namely: 4-phenyl-7-hydroxy coumarin (1), 4-phenyl-7-methoxy coumarin (2), 4-phenyl-6-hydroxy-7-methoxy coumarin (3), 4-pheny-6,7-dimethoxy coumarin (4) and 4-phenyl-6,7-dihydroxy coumarin (5) have been studied in various organic solvents of varying dipole moment. It was found that in a given solvent the position of the absorption and fluorescence maxima depends on the nature and position of the additional substituent group linked to the 4-phenyl coumarin and the wavelengths shifts obtained are interpreted in terms of the changes in the mobility of π electrons. From the fluorescence emission spectra of the present coumarins it was found that the 4-phenyl coumarins are less fluorescent and show a smaller change in polarity on excitation as compared to the corresponding 3- henyl derivatives. These changes are interpreted in terms of the possible resonance structures of the coumarin derivatives. [ABSTRACT FROM AUTHOR]

In this work, the dyes Rhodamine B and Coumarin 102 containing titanium dioxide nanoparticles were used as scattering centers to fabricate a random gain medium. The laser dye was dissolved in hexanol and methanol solvent respectively. The titanium dioxide nanoparticles were synthesized by DC reaction magnetron spraying technique. The random-gain medium was made by adding 2.5 mg of titanium dioxide nanoparticles to Rhodamine and coumarin 102 dyes by coating the glass cell with two-sided titanium dioxide with high spectral efficiency and low production cost. A narrow line optical emission was detected at 565 nm for Rhodamine B and 534 nm for coumarin 102, where it was found that rhodamine B dye has FWHM 8 nm and coumarin dye 102 has FWHM 9 nm. Through this, it was concluded that by adding titanium dioxide, we increase the random gain of the pigments added to it. This is a very good start toward making high-efficiency and low-cost laser random transfer fabrication in the visible range. [ABSTRACT FROM AUTHOR]

Quantum yield of fluorescence (QYF) of widely used Rhodamine (RhB) dye in ethanol and water was observed to decrease rapidly with increase in temperature of the dye solutions, which was correlated to enhanced torsional motion of its flexible diethylamino groups. This is harmful for its use in high-average power dye lasers, pumped by copper vapour laser (CVL) or diode-pumped solid-state green laser (DPSSGL), in which bulk temperature of the dye solution was found to increase due to the heat generated by circulation pumps and non-radiative decay processes of excited dye molecules. The QYF of RhB dye in water was found to be not sensitive to temperature in the practical operating region 16-25°C of dye laser by adopting supramolecular route to form an inclusion complex of RhB with the container molecule cucurbit[7]uril (CB[7]). [ABSTRACT FROM AUTHOR]

One of the most important characteristics of polymethine dyes is their strong absorption in the ultraviolet, visible and near infrared regions. These properties also enable their use in many areas other than colouring. In this study, the preparation of chloro heptamethine cyanine as a type of polymethine dye was prepared. The preparation was carried out in the solution of quaternary ammonium salt and bisaldehyde in a controlled manner through heating under reflux. The product was characterized by determinations of its molecular weight, melting point, fluorescence, excitation and absorption properties. After wards, the suitability of the product on dye laser was investigated. Dye laser system was performed and, as expected, it was shown that the dye could produce laser light in the intervals where it shows its fluorescence property. [ABSTRACT FROM AUTHOR]

A hydride generation laser induced fluorescence (HG LIF) approach has been investigated for trace level measurements of bismuth. The technique uses a tunable dye laser operating at 306.7 nm as the excitation source and bismuth fluorescence is measured at 472 nm. The optimized HCl and NaBH4concentrations for bismuth measurements were 1.2 M and 2.0%, respectively. The current technique has a limit of detection of 0.03 ppb and 0.01 ppb for blank measurements performed with the laser tuned on and off the bismuth excitation wavelength, respectively. Measurements of bismuth in different sample matrices have demonstrated the effectiveness of thiourea and ascorbic acid as masking agents for measuring samples containing interfering ions. Measurements of bismuth have been performed in reference materials, a bismuth-containing medication, and tea leaves. The results demonstrate that the HG LIF approach has feasibility for measuring bismuth in various samples at environmentally relevant concentrations. [ABSTRACT FROM AUTHOR]

Many cationic cyanine dyes show strong fluorescence enhancement when they interact with DNA double strand. In this paper, we studied a hemicyanine dye, 4-[4-(dimethylamino)stylyl]-1-dococylpyridnium bromide (DMASDPB), which is a typical nonlinear optical compound but has not been attracted as a light emitter because of its low fluorescence efficiency. We fabricated DNA-CTMA-DMASDPB complex thin films by spin coating from chloroform/ethanol solution, and demonstrated laser emissions from the films. Their wavelength tuning (600-630 nm) was achieved by changing the angle between two pumping beams interfering on the samples. We also made a durability test under continuous excitation of 3 mJ/Cm²- with 10 Hz about an hour, showing that the degradation of the emission was about 20%. [ABSTRACT FROM AUTHOR]

A fluorescent microdroplet was created in an elastomer by using a glycerol, polyethylene-glycol, or polysorbate solution of rhodamine 6G. Droplets exhibited a whispering gallery mode emission at a specific spectral band (yellow-green to orange), which shifted to a longer wavelength range (redshift) as the droplet diameter increased. The TE mode emission was stronger than the TM mode emission. As the elastomer was pressed in one direction, the droplet expanded in the perpendicular directions. Consequently, the resonant emission disappeared in the pressure direction, while the emission in the perpendicular direction exhibited the redshift of the resonance peaks. [ABSTRACT FROM AUTHOR]

Molecules of the coumarin family have fluorescence characteristicsthat are highly sensitive to their environment, and thus, they havebeen used as fluorescent sensors in chemical and biological systems.However, the very poor fluorescence yield of most coumarin dyes inaqueous media limits their applications. We have adopted a supramolecularstrategy to improve the fluorescence intensity of coumarin dye throughits interaction with the relatively new host cucurbit[7]uril (CB[7]).The virtually nonfluorescent coumarin 1 (Φf= 0.04)was converted into a highly fluorescent (Φf= 0.52)entity in water upon addition of the nonfluorescent host CB[7]. Variousspectroscopy techniques, namely, UV–vis absorption and steady-stateand time-resolved fluorescence spectroscopies, established the formationof a strong 1:1 dye–CB[7] inclusion complex with a high bindingconstant of (1.2 ± 0.1) × 105M–1for the dye. The stable inclusion complex of the neutral moleculewas supported by density-functional-theory- (DFT-) based quantum chemicalcalculations. Energy decomposition analysis of various interactionfactors in the host–guest complex revealed that key componentsproviding stability to the complex were electrostatic, polarization,and charge-transfer energies. These new results on the formation ofa strong inclusion complex of the versatile fluorophore coumarin 1with the nontoxic host CB[7] could lead to the design of efficientmolecular-scale biological probes, sensors, and photostable aqueousUV dye lasers. [ABSTRACT FROM AUTHOR]

ABSTRACT Radiative lifetimes of 94 high-lying even-parity levels from 29 717.231 to 41 692.155 cm−1 of Gd i and 10 high-lying even-parity levels from 38 057.954 to 49 291.082 cm−1 of Gd ii, have been measured using time-resolved laser-induced fluorescence method. The lifetime values range from 7.1 to 220 ns for Gd i and from 5.2 to 47.4 ns for Gd ii. Most results reported here lie within the uncertainty of ±5 per cent. Free neutral and singly ionized gadolinium atoms were generated by laser ablation. The second harmonic of different dye lasers was employed as the tunable UV exciting source (242-337 nm) to excite the investigated levels. A good agreement between our results and the previous ones was achieved. [ABSTRACT FROM AUTHOR]

Abstract: The optical properties including electronic absorption spectrum, emission spectrum, fluorescence quantum yield, and dipole moment of electronic transition of 7-diethylaminocoumarin (DEAC) laser dye have been measured in different solvents. Both electronic absorption and fluorescence spectra are red shifted as the polarity of the medium increases, indicating that the dipole moment of molecule increases on excitation. The fluorescence quantum yield of DEAC decreases as the polarity of solvent increases, a result of the role of solvent polarity in stabilization of the twisting of the intramolecular charge transfer (TICT) in excited state, which is a non-emissive state, as well as hydrogen bonding with the hetero-atom of dye. The emission spectrum of DEAC has also been measured in cationic (CTAC) and anionic (SDS) micelles, the intensity increases as the concentration of surfactant increases, and an abrupt change in emission intensity is observed at critical micelle concentration (CMC) of surfactant. 2×10−3 moldm−3 of DEAC gives laser emission in the blue region on pumping with nitrogen laser (λ ex=337.1nm). The laser parameters such as tuning range, gain coefficient (α), emission cross section (σ e), and half-life energy have been calculated in different solvents, namely acetone, dioxane , ethanol, and dimethyforamide (DMF). The photoreactivity of DEAC has been studied in CCl4 at a wavelength of 366nm. The values of photochemical yield (ϕ c) and rate constant (k) are determined. The interaction of organic acceptors such as picric acid (PA), tetracyanoethylene (TCNE), and 7,7,8,8-tetracynoquinonedimethane (TCNQ) with DEAC is also studied using fluorescence measurements in acetonitrile (CH3CN); from fluorescence quenching study we assume the possible electron transfer from excited donor DEAC to organic acceptor forming non-emissive exciplex. [Copyright &y& Elsevier]

ABSTRACT Natural radiative lifetimes of 53 odd-parity highly excited levels of singly ionized samarium in the energy range 26 599.08-36 107.66 cm−1 have been measured by the time-resolved laser-induced fluorescence technique in an ionic plume produced by laser ablation. The fundamental frequency and second harmonic of a dye laser have been adopted as the tunable exciting source (308-650 nm), and a fast detection system has been used to record fluorescence signals. The lifetime values obtained in this paper are in the range 10.5-271 ns. A good agreement between the present results and the previously published values was achieved. This work will be useful for investigating the composition of chemically peculiar stars. [ABSTRACT FROM AUTHOR]

combined experimental and theoretical study of the photo-physical, laser properties and molecular structures of three relatively recent Pyrromethene (PM) class dyes, PM597, PM580 and PM567, have been carried out. Laser characteristics of these three PM dyes were compared with three other widely used Rhodamine (RH) class dyes, RH6G, RHB and KRS, using a narrow-band dye laser setup, transversely pumped by the second harmonic (532 nm) of a Q-switched Nd-YAG laser. In addition to generating comparative data of these dyes for optimal use in dye lasers, we observed that unlike the RH dyes, the PM dyes show high efficiencies and wide tunability, despite the low fluorescence yield and high rate of non-radiative decay. Particularly, PM597 dye, in spite of a very low quantum yield of fluorescence (Φ=0.42), high non-radiative decay rate, and a large distortion from planarity in its excited state, when used in a laser cavity it exhibited similar laser efficiency and a beneficially wider tuning curve in comparison to other two PM dyes. Theoretical studies were carried out applying density functional theory and time-dependent density functional theory (DFT/TDDFT) to obtain new information on ground and the first excited state geometrical parameters of the PM dyes. Good correlation between calculated molecular properties and experimental results was observed for the evolution of the longest wavelength absorption maximum. [ABSTRACT FROM AUTHOR]

For cholesteric liquid crystals (CLC) based on azoxy nematic ZhK-440 and cholesterol esters, variation of selective reflection band maximum with temperature and under irradiation by light of different wavelengths were studied. In these materials, lasing is hindered because fluorescence quantum yield of most lasing dyes falls sharply at concentrations 0.3-0.5 wt.%. We have shown that for some phenolenone and pyrromethene dyes the fluorescence quantum yield in such systems reaches 50% and more. Lasing has been obtained in CLC on the basis of azoxy nematic ZhK-440, with reversible phototuning by 30 nm towards shorter, and by 20 nm - towards longer wavelengths. [ABSTRACT FROM AUTHOR]

Narrow-band laser performance of alcohol solutions of pyrromethene 567 (PM567) and rhodamine 6G (RH6G) dye was investigated using a home-made GIG-configured dye laser, excited by the second-harmonic radiation (at 532 nm) of a pulsed Nd:YAG laser. Higher laser efficiency was observed with PM567 dye (∼23% peak) in comparison to the commonly used RH6G dye (16.5%), in spite of much lower fluorescence quantum efficiency of the PM567 (0.83) vis-à-vis RH6G (0.98) dye solutions in ethanol. First principle-based electronic structure calculations were performed on PM567 dye in the ground ( S) and excited states ( S) using density functional theory to elucidate the structure and photophysical properties of the dye. [ABSTRACT FROM AUTHOR]

Abstract: The photo-physical properties of Xanthene dyes: Basic Rhodamine Yellow (BRY), Rhodamine590perchlorate (R590p), SulforhodamineB (SRB) doped in tetramethylorthosilicate (TMOS) and poly-methylmethacrylate (PMMA) are observed. The various parameters viz. full-width at half-maxima (FWHM), peak emission wavelength, quantum yield and excited state lifetime at different concentrations ranging from ∼0.05 to ∼1mM of the dye under excitation by Copper Vapor Laser (CVL) of high repetition rate (∼5.6kHz) of are investigated. In order to identify photostability in dyes, normalized photostability has been studied and found that silica gel samples containing dye are more stable than that of polymeric samples. This has been further understood in terms of number density of unbleached dye molecules that infers that photobleaching of dye molecules is not prominent at higher concentrations in glassy solid matrices. Pump intensity dependent optical gain of the samples has also been reported and efforts have been made to study the efficiency of solid-state laser samples in a cavity for the performance of the dye laser. [Copyright &y& Elsevier]

Spontaneous emission of laser dye molecules (rhodamine 6G and pironin G) embedded into pores of synthetic opal photonic crystals is studied in the spectral region of 520-650 nm. It is ascertained that the emission spectra are greatly dependent on the photonic stop-band position and the spectral distribution of photon density of states. A dependence of spectral position of the emission band from the dielectric contrast is found. [ABSTRACT FROM AUTHOR]

Abstract: The field of laser dyes-active solid polymer materials is a promising field and quite competitive with liquid dye lasers. This paper investigates some photo-physical parameters of pyromethene (PM-567, PM-597) and Rhodamine B dyes incorporated into glycidyl methacrylate (GMA) promising polymeric host matrix. These parameters are: absorption and emission cross-sections, fluorescence lifetime and quantum yield, in addition to FT-Raman spectra as an indication for binding the dye molecules with the backbones of GMA polymeric chain. [Copyright &y& Elsevier]

Spectra of spin-forbidden and spin-allowed transitions in the mixed b 3Πu∼A 1Σu+ state of Na2 are measured separately by two-photon excitation using a single tunable dye laser. The two-photon excitation produces Na*(3p) by photodissociation, which is easily and sensitively detected by atomic fluorescence. At low laser power, only the A 1Σu+ state is excited, completely free of triplet excitation. At high laser power, photodissociation via the intermediate b 3Πu triplet state becomes much more likely, effectively “switching” the observations from singlet spectroscopy to triplet spectroscopy with only minor apparatus changes. This technique of perturbation-assisted laser-induced atomic fragment fluorescence may therefore be especially useful as a general vehicle for investigating perturbation-related physics pertinent to the spin-forbidden states, as well as for studying allowed and forbidden states of other molecules. [ABSTRACT FROM AUTHOR]

The rapid internal conversion dynamics at room temperature is determined by using the femtosecond time-resolved fluorescence depletion measurements of a complex solvated molecule of LD 700 (rhodamine 700) combined with steady-state absorption and fluorescence spectroscopy, as well as quantum chemical calculation. The molecule is excited by a 50 fs laser pulse at 400 nm which directly populated the highly excited singlet state, the rapid internal conversions (ICs) are observed, which leads to the directional changes of the emission transition moment following photoexcitation to the highly excited singlet state S5 of LD 700. [ABSTRACT FROM AUTHOR]

Sodium photoejection from a paraffin coated cell has been observed and analyzed in detail. The effect has been detected by observing the fluorescence induced by a cw dye laser. A maximum Na density of about 2.9 ×108 atoms/cm3 was obtained by shining the cell with 1.05 W Ar+ laser green light. A progressive slowing of the dynamics of the process is reported, probably due to a change in the chemical rearrangement of the Na atoms in the coating under intense light exposure. This aging effect represents a limitation in the practical application of this kind of materials. [ABSTRACT FROM AUTHOR]