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.     

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.     

Coherent amplification in fluorescent dye solutions. II. The inverse pre-resonance Raman spectrum of rhodamine 6G

Inverse pre-resonance Raman spectra of rhodamine 6G in solution in methanol have been recorded over the concentration range 10^?1 to 10^?4 mol ?^?1. The solute and solvent transitions are found to display perfectly normal lorentzian profiles over the whole of this concentration range. Intensities and depolarization ratios of the pre-resonance Raman features are recorded. It is shown that the spectra arise from monomeric rhodamine 6G molecules in the singlet electronic ground state and the relative merits of the CARS and inverse Raman methods for recording resonance Raman spectra are discussed.     

Surface-enhanced Raman scattering imaging of single living lymphocytes with multivariate evaluation

This paper is aimed to show the possibility to determine individual organic compounds introduced into single living cells with surface-enhanced Raman spectroscopy (SERS). Surface enhancement was achieved with gold colloids that were allowed to diffuse into lymphocytes. An introduced analyte, rhodamine 6G, could be imaged together with for example nucleotides and amino acids of the cell. Multivariate evaluation of surface-enhanced Raman images proved to be a powerful tool for the separation of spectral information of various intracellular components. The principal component analysis (PCA) enabled identification of spectra containing different chemical information and separation of the spectral contribution of rhodamine 6G from the complex cellular matrix.     

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].     

Silver Nanostructures on Graphene Oxide as the Substrate for Surface-Enhanced Raman Scattering (SERS)

Nanosized surface-enhanced Raman scattering (SERS) substrates fabricated by the controlled growth of metal nanostructures on water-dispersed two-dimensional nanomaterials can open a new avenue for SERS analysis of liquid samples in biological fields. In this work, regular and uniform Ag nanostructures were grown on the surface of graphene oxide (GO) through a microwave-assisted hydrothermal method. Polyamidoamine (PAMAM) dendrimers were assembled on the surface of GO to form GO/PAMAM templates for growing Ag nanostructures, which are primarily comprised of Ag dimers and trimers. The prepared Ag/GO nanocomposites are highly dispersed and stable in aqueous solution and may be used as substrates for enhanced Raman detection of rhodamine 6?G (R6G) in aqueous solution. This special substrate provides high-performance SERS and suppresses R6G fluorescence in aqueous solution and is promising as a nanosized material for the enhanced Raman detection of liquid samples in biological diagnostics.     

Fourier transform Raman and infrared and surface-enhanced Raman spectra for rhodamine 6G

The vibrational spectra of rhodamine 6G (R6G) are discussed on the basis of Fourier transform infrared and Fourier transform Raman spectra obtained far from resonance which are compared with resonance Raman and surface-enhanced resonance Raman spectra obtained with excitation at 457.9 nm. The behaviour of several bands is described and tentative assignments are proposed. Stong resonance Raman effects are observed for bands assignable to xanthene ring stretching modes and also xanthene ring deformation modes. Some of these are sensitive to the complexing of R6G with silver colloids.     

Interaction of plasmon and molecular resonances for rhodamine 6G adsorbed on silver nanoparticles

Localized surface plasmon resonance (LSPR) is a key optical property of metallic nanoparticles. The peak position of the LSPR for noble-metal nanoparticles is highly dependent upon the refractive index of the surrounding media and has therefore been used for chemical and biological sensing. In this work, we explore the influence of resonant adsorbates on the LSPR of bare Ag nanoparticles (lambda(max,bare)). Specifically, we study the effect of rhodamine 6G (R6G) adsorption on the nanoparticle plasmon resonance because of its importance in single-molecule surface-enhanced Raman spectroscopy (SMSERS). Understanding the coupling between the R6G molecular resonances and the nanoparticle plasmon resonances will provide further insights into the role of LSPR and molecular resonance in SMSERS. By tuning lambda(max,bare) through the visible wavelength region, the wavelength-dependent LSPR response of the Ag nanoparticles to R6G binding was monitored. Furthermore, the electronic transitions of R6G on Ag surface were studied by measuring the surface absorption spectrum of R6G on an Ag film. Surprisingly, three LSPR shift maxima are found, whereas the R6G absorption spectrum shows only two absorption features. Deconvolution of the R6G surface absorption spectra at different R6G concentrations indicates that R6G forms dimers on the metal surface. An electromagnetic model based on quasi-static (Gans) theory reveals that the LSPR shift features are associated with the absorption of R6G monomer and dimers. Electronic structure calculations of R6G under various conditions were performed to study the origin of the LSPR shift features. These calculations support the view that the R6G dimer formation is the most plausible cause for the complicated LSPR response. These findings show the extreme sensitivity of LSPR in elucidating the detailed electronic structure of a resonant adsorbate.     

Absorption spectroscopic investigation of rhodamine dye vapors

The dyes rhodamine 6G and rhodamine 19 are investigated. The dye stability versus temperature and time is studied. Bulk dye stuff is found to be less stable than dye adsorbed to the stainless steel cell walls and in the vapor phase. Rhodamine 6G converts to rhodamine 19 before evaporation. Adsorbed rhodamine 19 and rhodamine 19 vapor disintegrate most likely into 2,7-dimethylrhodamine 110 at elevated temperatures (> 320°C). For rhodamine 19 vapor the absorption spectrum, the saturated vapor density and the latent heat of evaporation are determined. The vapor absorption spectra of rhodamine 19 and 2,7-dimethylrhodamine 110 are compared with solution spectra.     

Donor fluorescence decay in the rhodamine 6G-malachite green system in the presence of energy migration

The decay of rhodamine 6G fluorescence in the presence of malachite green was investigated. For the systems subject to investigations the electronic excitation energy migration among rhodamine 6G molecules plays an essential role in the process of energy transfer to malachite green. The epxerimental results were compared with a theoretical formula for the fluorescence decay function.     

THE PHOTOREACTION OF A RHODAMINE 6G MONOLAYER ADSORBED ON QUARTZ STUDIED BY SURFACE SECOND HARMONIC GENERATION

Abstract— A monolayer of rhodamine 6G on quartz in air exhibited photochemistry upon laser irradiation in the first absorption band. The course of the reaction was followed in real time by the surface second harmonic generation method. It was observed that the photoproduct had an enhanced non-linear coefficient, relative to rhodamine 6G. Absorption spectra showed that this was not a result of a stronger resonance enhancement of the signal by the photoproduct. Consideration of the factors to which the surface second harmonic signal is sensitive suggested that the enhancement arose from an increased charge transfer character of the photoproduct's electronic transitions, and a reorientation of its transition dipole.     

Pre-resonance Raman intensity studies of TCNQ and TCNQ−

Pre-resonance Raman spectra have been obtained for TCNQ and LiTCNQ in acetonitrile solution using an Ar⁺—Kr⁺ laser and a tunable rhodamine 6G dye laser. Using the theory of Albrecht and Hutley, we have calculated frequency factors for the intensity variations for several symmetric vibrational modes of each molecule. The observed spectra for TCNQ and LiTCNQ with violet, blue, and green excitation give evidence for B-type resonance enhancement due to vibronic mixing between at least two violet and ultraviolet transitions. The Raman spectra for LiTCNQ with yellow, orange, and red excitation show A-type enhancement due to a single electronic excitation in the near infrared.     

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.     

Aminorhodamine (ARh): A Bichromophore with Three Emission Bands in Low Temperature Glasses

At first glance, aminorhodamine (ARh) is a typical pH responsive fluorescent, rhodamine‐type dye. However, hidden under the typical rhodamine absorption band, ARh has another electronic transition of similar energy, but polarized orthogonal to that of the rhodamine chromophore. This transition—assigned to an arylpyrylium type chromophore contained in the system—is responsible for the sensor action of the dye. ARh is non‐fluorescent, while protonation of a donor amino group turn on a strong rhodamine‐type emission. At low temperature in frozen solution emission from both electronic subsystems of ARh are observed. In order to achieve more complete understanding of the photophysical mechanisms in this type of fluorescent probes, ARh and its protonated counterpart HARh were studied by absorption and fluorescence spectroscopy, computational chemistry, and at low temperatures in solid solution. Results from fluorescence anisotropy and time‐resolved fluorescence spectra establish a bichromophore model and suggest that a remarkable weak coupling between the two nearly isoenergetic excited states in ARh enables the dual emission. All the complicated properties observed for ARh was accounted for by a bichromophore model describing the electronic system of ARh as a bichromophore constituted by a rhodamine and an arylpyrylium subsystem.     

Electromagnetic and chemical interaction between Ag nanoparticles and adsorbed rhodamine molecules in surface-enhanced Raman scattering

The critical importance of the junction between touching or closely adjacent Ag nanoparticles associated with single-molecule sensitivity (SMS) in surface-enhanced Raman scattering (SERS) was confirmed via the following observations: (1) an additional peak is observed in elastic scattering only for the SERS-active state, which originated from absorption of adsorbates, (2) local- and far-field evaluation using a finite difference time domain method could reproduce this extra peak and anticipate the significantly enhanced field even inside the adsorbates sitting at the junction through an increased coupling of the localized surface plasmons, and (3) in addition to enhanced fluorescence of adsorbed dye, an inelastic scattering peak was observed and attributed to the metal surface electron. Concerning the chemical enhancement in SERS, Cl⁻ anions activate the Ag-Cl-R6G (rhodamine) samples by inducing intrinsic electronic interaction between Ag and R6G molecules. This electronic interaction is irreversibly quenched by the addition of thiosulfate anions which dissolve Ag⁺ cations while the electromagnetic (EM) effect remains intact.     

Spectral properties of (5-phenyl-1,3,4-oxadiazol-2-yl)-7-hydroxycoumarin (POHC)

The electronic absorption, emission and excitation spectra of POHC were measured in different solvents and are affected by solvent polarity. The fluorescence quantum yield of POHC decreases with increasing Richardt and Dimorth solvent parameter (E(T)) value of the solvent. In dilute solutions POHC is almost totally present in its protonated nitrogen tautomer form. The deprotonation is a reversible process. A shoulder in the absorption spectra at approximately 473 nm indicates the presence of a portion of the tautomer (s) that disappears on lowering the temperature. Molecular oxygen acts as a quencher with quenching rate constant of 1.8 x 10(10) M(-1) s(-1) in DMF. Energy transfer from POHC to rhodamine 6G in ethanol was also studied. POHC is relatively photostable in ethanol (phic approximately 1.7 x 10(-4)). Quantum chemical calculations were carried out and correlated to experimental observations.     

三元若丹明激光染料荧光寿命研究

利用单光子计数技术测试了新型三元若丹明激光染料在不同溶剂中的荧光寿命、荧光光谱及其寿命的实验数据.实验表明,所研究的三元若丹明染料存在着有效的分子内能量传递过程,这些过程使得激光染料的荧光量子效率及光稳定性明显改善.     

A reinvestigation of the molecular structures, vibrations and rotation of methyl group in o-methylaniline in S0 and S1 states studied by laser induced fluorescence spectroscopy and ab initio calculations

The UV fluorescence excitation and dispersed fluorescence spectra of a jet-cooled o-methylaniline have been obtained for the S1 <-- S0 transition, in which some of the bands have been observed and assigned for the first time. The origin of the electronic transition appears at 34,328.4 cm(-1). It was found that the spectra exhibit an important feature corresponding to the internal rotation of the methyl group in the electronic ground and excited states. Ab initio calculations at MP2/6-31 + G* and CIS/6-31 + G* show that the optimised structure of o-methylaniline in the ground state is not planar with the amino group having sp3 hybridation-like character due to the existence of lone paired electrons on the N atom. Upon electronic excitation, the C-N bond exhibits a partial double character, as in the case of other aniline derivatives.     

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.     

Resonance Raman scattering of rhodamine 6G as calculated using time-dependent density functional theory

In this work, we present the first calculation of the resonance Raman scattering (RRS) spectrum of rhodamine 6G (R6G) which is a prototype molecule in surface-enhanced Raman scattering (SERS). The calculation is done using a recently developed time-dependent density functional theory (TDDFT) method, which uses a short-time approximation to evaluate the Raman scattering cross section. The normal Raman spectrum calculated with this method is in good agreement with experimental results. The calculated RRS spectrum shows qualitative agreement with SERS results at a wavelength that corresponds to excitation of the S(1) state, but there are significant differences with the measured RRS spectrum at wavelengths that correspond to excitation of the vibronic sideband of S(1). Although the agreement with the experiments is not perfect, the results provide insight into the RRS spectrum of R6G at wavelengths close to the absorption maximum where experiments are hindered due to strong fluorescence. The calculated resonance enhancements are found to be on the order of 10(5). This indicates that a surface enhancement factor of about 10(10) would be required in SERS in order to achieve single-molecule detection of R6G.