Spectroscopic studies of rhodamine 6G dispersed in polymethylcyanoacrylate

We report here electronic absorption, fluorescence and resonance Raman studies of rhodamine 6G laser dye dispersed in the polymethylcyanoacrylate matrix. In the electronic absorption and fluorescence spectra of dispersed rhodamine 6G, band maxima are red shifted compared to solution. Raman spectra show some new bands. These spectral changes arise due to matrix effect and interaction between rhodamine 6G and the host material involving amine group of rhodamine.     

Influence of the molecular structure and the nature of the solvent on the absorption and fluorescence characteristics of rhodamines

A study of the equilibrium of the molecular forms of rhodamine 19 in aqueous and ethanolic solution is carried out by determining the absorption and fluorescence characteristics of the zwitterionic and the cationic forms of the dye. The optical properties of rhodamine 19 are compared with those obtained for rhodamine 6G and also with those previously reported for rhodamine 3B and for the molecular forms of rhodamine B in water and ethanol. Different aspects of the molecular structure of the rhodamines and solvent effects are discussed, as well as their influence on the photophysical properties of the rhodamines. The aggregation of the molecular forms of rhodamine 19 is also studied in water and ethanol.     

Ab initio study of optical properties of rhodamine 6G molecular dimers

Equilibrium atomic geometries of rhodamine 6G (R6G) dye molecule dimers are studied using density-functional theory. Electron-energy structure and optical properties of R6G H and J dimers are calculated using the generalized gradient approximation method with ab initio pseudopotentials. Our theory predicts substantial redshifts or blueshifts of the optical absorption spectra of R6G dye molecules after aggregation in J or H dimers, respectively. Predicted optical properties of R6G dimers are interpreted in terms of interatomic and intermolecular interactions. Results of the calculations are discussed in comparison with experimental data.     

Spectral luminescent and laser properties of rhodamine 6G in poly(urethane-<Emphasis Type="Italic">co</Emphasis>-siloxanes)

Solid-state active elements based on poly(urethane-co-siloxanes) with the organic dye rhodamine 6G in their pores are studied. The transparency range of polymer samples is determined. The electronic spectra and the spectra of luminescence and lasing of rhodamine 6G in poly(urethane-co-siloxane) samples are measured. When a polymer obtained at a high content of 2,4-toluene diisocyanate is doped with rhodamine 6G, the luminescence spectrum narrows by a factor of 10. It is shown that the polymers doped with rhodamine 6G feature high photostability. The photostability of rhodamine 6G molecules is strongly dependent on the content of the dimethylsiloxane component in the polymer.     

Effect of poly-HEMA hydrophilic gel environment on the photo-physical behavior of rhodamine dyes

The absorption spectra of rhodamine B (RB) chloride, rhodamine 6G (R6G) tetrafluoroborate and rhodamine 6G chloride in poly-2-hydroxyethyl methacrylate hydrogel (PHEMA) matrix were studied using absorption spectroscopy in the visible region. The transport and aggregative properties of these ionic dyes in aqueous solution across the hydrophilic gel were also investigated. The similarities of absorption spectra of RB in aqueous solutions and in hydrogel host suggest that the hydrogel framework has a minor effect in their absorption spectra. In contrast, there is a relatively strong interaction or electrostatic forces between R6G dyes and the hydrogel matrix. The permeability of R6G chloride through hydrogel host is seen to be markedly higher than RB chloride and R6G tetrafluoroborate.     

Aggregation states of rhodamine 6G in electrospun nanofibrous films

Novel fluorescent composite nanofibrous films of rhodamine 6G (Rh6G) and polyacrylonitrile (PAN) are first prepared by electrospinning. The aggregation states of Rh6G in electruspun nanofibrous films are studied as a function of concentrations and characterized by UV–vis absorption spectroscopy and emission and excitation fluorescence spectroscopy. We have also used casting films as reference material to compare the effect of incorporation of Rh6G in electrospun nanofibrous films and casting films. The large specific surface area of the nanofibers and fast evaporation of the solvents in the electrospinning process reduced the aggregation of Rh6G. The appearance of fluorescent J-type dimers, even at higher dye concentration in elctrospun films, demonstrates that the electrospun films are an ideal material for incorporation of fluorescent dyes.     

Effect of silver nanoparticles on luminescent and generation properties of rhodamine 6G in aqueous alcohol solutions

The plasmon effect that silver nanoparticles have on the luminiscent and generation properties of rhodamine 6G molecules in aqueous alcohol solutions is studied. It is found that the intensities of absorption and emission increase when silver nanoparticles are added to aqueous solutions of rhodamine 6G. It is shown that upon the laser photoexcitation of aqueous solutions of rhodamine 6G dye, spontaneous fluorescence occurs that is converted into stimulated laser emission as the pump power grows. It is found that an increase in intensity and a drop in the generation threshold of stimulated emission are observed when silver nanoparticles are added to a solution of rhodamine 6G. It is shown that the dependence of absorbance, the intensity of fluorescence, and the dye’s generation of stimulated emission on the concentration of silver nanoparticles in solution falls as the proportion of alcohol grows.     

The optical properties of molecules and chromogenic aggregates of xanthene dyes

The UV absorption spectra of rhodamine B and G molecules isolated from industrial dye samples were obtained. Two procedures were used. In one of them, rhodamine B molecules were displaced with water into a heptane layer from a solution of the dye in an alcohol-heptane mixture. The second procedure involved heating of the dye introduced into cellulose triacetate films. Individual rhodamine molecules (namely, dye cation-chlorine anion ion pairs) prepared by both methods did not absorb visible light. The spectra of individual rhodamine molecules coincided with the spectra of so-called pseudoleucobases of xanthene dyes reported in the literature. The conclusion was drawn that the chromaticity property in the series of xanthene dyes appeared because of the formation of supramolecular dimeric and larger aggregates, as was earlier established for triphenylmethane dyes (TPMDs) and copper phthalocyanine (CuPc). At the same time, individual xanthene dye molecules, like TPMD and CuPc molecules, are not chromogens.     

Emission of Au nanoparticles with and without rhodamine 6G dye

We have observed Stokes and anti-Stokes emission of Au nanoparticles suspended in methanol and rhodamine 6G dye solution. Photoluminescence of Au nanoparticles is a three-step process involving single-photon or three-photon excitation of electron-hole pairs, relaxation of excited electrons and holes, and emission from electron-hole recombination, possibly enhanced by surface plasmons. In the presence of dye, the excitation of anti-Stokes emission of gold involves two-photon absorption in rhodamine 6G molecules followed by the energy transfer to Au nanoparticles with simultaneous absorption of one pumping photon by Au. This mechanism significantly enhances anti-Stokes emission of gold nanoparticles in the presence of dye.     

光波导分光光谱技术研究染料分子在玻璃表面的吸附特性

光波导分光光谱技术利用光波导表面的消逝场敏感地测定有色物质亚单分子吸附层的偏振吸收光谱, 非常适合于研究染料、颜料、荧光分子、量子点、金属纳米粒子、带色基的蛋白质等在固/液界面的吸附行为. 本文使用宽频带卤钨灯、棱镜耦合的薄膜玻璃光波导和基于电荷耦合器件(CCD)的光谱分析仪设计制作了具有时间分辨本领的光波导分光光谱装置, 并利用该装置实时监测了罗丹明6G(R6G)和亚甲基蓝(MB)在玻璃表面的吸附特性. 通过比较在横电(TE)和横磁(TM)偏振模式下的吸收光谱, 发现R6G主要以二聚体和单体的形式吸附在玻璃表面, 而MB主要以多聚体的形式吸附在玻璃表面, 并分别估算了它们的平均取向角.     

Lipophilic derivative of rhodamine 19: characterization and spectroscopic properties

A new octadecylamide derivative of rhodamine 19 was synthesized by reaction of rhodamine 19 ethyl ester (rhodamine 6 G) with octadecylamine. This lipophilic dye exists in two forms: as a cationic species containing a secondary amide group and as an electrically neutral molecule containing an additional ring closed between the oxygen of the amide group and the central carbon of the xanthene part. Both forms were isolated and characterized in detail by means of elemental analysis, mass spectrometry, IR, NMR and UV-VIS spectroscopy. Depending on the hydrogen ion activity in solution and the availability of solvent hydrogen for hydrogen bond formation, the cationic form easily converted into a neutral one and vice versa. On the basis of absorption and emission UV-VIS spectroscopic data, the equilibrium of the two forms was studied in various solvents. An increase in dye concentration in acidified methanol/water mixture (volume fraction of water, ?=80%) led to aggregation of the cationic molecules. Using the UV-VIS absorption data, a corresponding dimerization constant was evaluated.     

Thermodynamics study of the dimerization equilibria of rhodamine B and 6G in different ionic strengths by photometric titration and chemometrics method

The dimerization constants of rhodamine B and 6G have been determined by studying the dependence of their absorption spectra on the temperature in the range 20-80 degrees C at different total concentrations of rhodamine B (5.89 x 10(-6) to 2.36 x 10(-4)M) and rhodamine 6G (2.34 x 10(-5) to 5.89 x 10(-4)M) and in different concentrations of LiCl, NaCl and KCl salts as supporting electrolytes. The monomer-dimer equilibrium of rhodamine B and 6G have been determined by chemometrics refinement of the absorption spectra obtained by thermometric titrations performed at different ionic strengths. The quantitative analysis of the data of undefined mixtures, was carried out by simultaneous resolution of the overlapping spectral bands in the whole set of absorption spectra. The dimerization constants are varied by changing the ionic strength and the degree of dimerization are decreased by increasing of the ionic strength of the medium. The enthalpy and entropy of the dimerization reactions were determined from the dependence of the equilibrium constants on the temperature (van't Hoff equation). From the thermodynamic results the TDeltaS degrees -DeltaH degrees plot was sketched. It shows a fairly good positive correlation which indicates the enthalpy-entropy compensation in the dimerization reactions (compensation effect).     

Molecular aggregation of rhodamine dyes in dispersions of layered silicates: influence of dye molecular structure and silicate properties

The molecular aggregation of six rhodamine dyes (rhodamine 560, B, 3B, 19, 6G, 123) in layered silicate (saponite and fluorohectorite) dispersions was investigated by using visible (vis) spectroscopy. The dye molecular aggregation was influenced by the properties of both the silicates and the dyes themselves. The layer charge of the silicates enhanced the molecular aggregation of the hydrophilic, cationic dyes. The presence of a carboxyl acid group in the dye molecules inhibited adsorption of the dyes on the surface of fluorohectorite, a silicate with a high charge density. A lower or no adsorption could be observed by vis spectroscopy. Strong association of the dyes to the silicate surface led to remarkable changes in the dye spectra, mainly due to the molecular aggregation. Dye assemblies initially formed after mixing the dye solutions with silicate dispersions were unstable. Decomposition of the dye molecular assemblies, and the formation of new species or molecular aggregate rearrangements, were studied on the bases of time-difference spectra. The reaction pathways were specific, not only for the dyes, depending upon their molecular structure and properties, but also on the silicate substrates.     

新型双发色团固体激光染料薄膜的光稳定性研究

利用UV-Vis吸收光谱仪和光化学反应器研究了新型双发色团固体激光染料薄膜的光降解动力学.研究结果表明:双发色团固体激光染料薄膜的光褪色反应遵循假一级动力学衰减.在PRNAM系列共聚物(N-烯丙基-若丹明1、N-[(2-丙烯酸基)乙基]-1,8-萘酰亚胺和甲基丙烯酸甲酯的共聚物)中萘酰亚胺基团通过聚合物碳链与若丹明基团的氮原子相连;而在PRNM系列共聚物(若丹明1的烯丙基酯、N-[(2-丙烯酸基)乙基]-1,8-萘酰亚胺和甲基丙烯酸甲酯的共聚物)中则是与若丹明基团的酯基相连.PRNAM系列共聚物的光稳定性优于PRNM和PRM(若丹明1的烯丙基酯和甲基丙烯酸甲酯的共聚物)系列的光稳定性.     

A Transparent Thin Film with Hexagonal Mesostructure Containing Rhodamine 6G

A transparent this film was prepared by depositing the sol-gel mixture for the synthesis of MCM-41 mesoporous molecular sieve doped with rhodamine 6G(R6G) dye on glass substrates. The film of silica-surfactant-R6G materials, which was identified to possess hexagonally ordered mesostructure,was composed of nanocrystallites about 35 nm in diameter and 1-10μm in thickness. Cleanness of the substrates, concentration of the sol-gel mixture and rate of evaporation of the solvent were the key factors affecting transparency and homogeneity of the film. Moreover,optical change and lack in dye aggregation were observed to the R6G-functionalized MCM-41 thin film in contrast with that in ethanol solution.     

Density functional calculations of 9-diphenylaminoacridine fluorescent indicator and its interactions with analyte molecules: I. Structures of complexes in the ground electronic states and absorption spectra

The interaction of 9-diphenylaminoacridine dye (indicator) with several small analyte molecules (methanol, acetonitrile, acetone, tetrahydrofuran, benzene, ammonia, formaldehyde, and acetaldehyde) has been theoretically studied in relation to the problem of the development of optical chemosensors based on organic dyes. The structures of the resulting complexes and the absorption spectra of 9-diphenylaminoacridine and its complexes with analytes were calculated using density functional theory (DFT) with the PBE0 functional and the 6-31G(d,p) basis set. It was demonstrated that complexes of two types with different mutual arrangements of molecules corresponding to the lateral and stacking structures can be formed for each analyte. The calculated absorption spectrum only weakly changes upon complex formation, which is in agreement with experimental data on the absorption spectra of 2,7-dimethyl-9-ditolylaminoacridine in solutions of corresponding solvents. The method for the calculation of excited states that was used in this work can be applied to the calculation of the fluorescence spectra of 9-diphenylaminoacridine complexes.     

Gas-Phase Fluorescence Excitation and Emission Spectroscopy of Three Xanthene Dyes (Rhodamine 575, Rhodamine 590 and Rhodamine 6G) in a Quadrupole Ion Trap Mass Spectrometer

The gas-phase fluorescence excitation, emission and photodissociation characteristics of three xanthene dyes (rhodamine 575, rhodamine 590, and rhodamine 6G) have been investigated in a quadrupole ion trap mass spectrometer. Measured gas-phase excitation and dispersed emission spectra are compared with solution-phase spectra and computations. The excitation and emission maxima for all three protonated dyes lie at higher energy in the gas phase than in solution. The measured Stokes shifts are significantly smaller for the isolated gaseous ions than the solvated ions. Laser power-dependence measurements indicate that absorption of multiple photons is required for photodissociation. Redshifts and broadening of the dispersed fluorescence spectra at high excitation laser power provide evidence of gradual heating of the ion population, pointing to a mechanism of sequential multiple-photon activation through absorption/emission cycling. The relative brightness in the gas phase follows the order R575(1.00) < R590(1.15) < R6G(1.29). Fluorescence emission from several mass-selected product ions has been measured.     

Consecutive Photoinduced Electron Transfer (conPET): The Mechanism of the Photocatalyst Rhodamine 6G

The dye rhodamine 6G can act as a photocatalyst through photoinduced electron transfer. After electronic excitation with green light, rhodamine 6G takes an electron from an electron donor, such as N,N-diisopropylethylamine, and forms the rhodamine 6G radical. This radical has a reduction potential of around −0.90 V and can split phenyl iodide into iodine anions and phenyl radicals. Recently, it has been reported that photoexcitation of the radical at 420 nm splits aryl bromides into bromide anions and aryl radicals. This requires an increase in reduction potential, hence the electronically excited rhodamine 6G radical was proposed as the reducing agent. Here, we present a study of the mechanism of the formation and photoreactions of the rhodamine 6G radical by transient absorption spectroscopy in the time range from femtoseconds to minutes in combination with quantum chemical calculations. We conclude that one photon of 540 nm light produces two rhodamine 6G radicals. The lifetime of the photoexcited radicals of around 350 fs is too short to allow diffusion-controlled interaction with a substrate. A fraction of the excited radicals ionize spontaneously, presumably producing solvated electrons. This decay produces hot rhodamine 6G and hot rhodamine 6G radicals, which cool with a time constant of around 10 ps. In the absence of a substrate, the ejected electrons recombine with rhodamine 6G and recover the radical on a timescale of nanoseconds. Photocatalytic reactions occur only upon excitation of the rhodamine 6G radical, and due to its short excited-state lifetime, the electron transfer to the substrate probably takes place through the generation of solvated electrons as an additional step in the proposed photochemical mechanism.     

Self-association of rhodamine dyes in different host materials

The aggregation of rhodamine 6G in liquid crystalline solution (anisotropic host) was studied using polarised spectroscopy and in a guest-host system. The self-association of rhodamine B was investigated in molecular sieves of type AlPO(4)-5 (microporous host) using diffuse reflectance spectroscopy. Also, the molecular interaction of rhodamines in normal solvents (isotropic hosts) was studied using visible spectroscopy for comparison. Therefore, the role of the host nature in the different phases on the self-association of the guest molecules has been investigated and compared. The absorption spectrum of the rhodamine dye in liquid crystalline host is affected by a specific interaction related to the alignment by the liquid crystal property as well as solvent polarity. Due to the existence of a large amount of water molecules absorbed into channels and cavities of aluminophosphate molecular sieve, the maximum absorption wavelengths of the dye loaded AlPO(4)-5 is affected by aqueous environment of the aluminophosphate pores.     

新型双发色团染料荧光光谱及其寿命的研究

有效的染料激光操作需要较高的荧光量子效率,若丹明是在500~700 nm光谱区中一类最重要的激光染料.然而,染料的基态分子和三线态对辐射能量的吸收将会大大降低激光输出效率,再者,由于若丹明类染料在紫外区的吸收系数较小,为了有效吸收泵浦能量(如用XeCI准分子激光,308 nm),就必须使用高浓度染料溶液,在这种情况下,若丹明类染料较小的Stokes位移就势必造成基态分子更大的重复吸收,即造成更大的谐振腔损耗^[1].