Absorption Spectra Of Rhodamine Research Articles

Fluorescent H-aggregates of pure rhodamine B (RhB) in glycerol, ethylene glycol, methanol and butanol under ambient condition

In the present study, we have discovered a hitherto undetected fluorescence emission band of rhodamine B in the spectral range of 675 nm to 717 nm for solvents, namely glycerol, ethylene glycol, methanol and butanol. This band could be attributed to H-aggregates (H-dimer) of rhodamine B and it is confirmed by a blue-shifted band at 515 nm in the absorption spectra of rhodamine B in all the solvents. The formation of fluorescent H-aggregates has been further substantiated by the concentration-dependent intensity variation of the absorption and fluorescence peak. Hence, contrary to the previous conceptions that many H-aggregates are naturally non-fluorescent, the pure rhodamine B forms highly fluorescent H-aggregates in glycerol, ethylene glycol, methanol and butanol under ambient conditions. The pH dependent absorption and emission spectra for fixed concentration of rhodamine B in the solvents reveals a red shift in the respective absorption and emission maxima. The aggregation process of the rhodamine B molecule in the solvents has been characterised in terms of its critical concentration which represents the equilibrium phase between the monomers and dimers. A relationship between the critical concentration and the dielectric constant of the solvents has been established and it provides a unique method to predict the critical concentration or the monomer-dimer equilibrium of any other fluorescent dye in a solvent of known dielectric constant. The discovery of the new H-aggregated fluorescence peak has opened a new window for rhodamine B to use in organic solar cells, light-emitting diodes, photographic technology, tunable lasers, and fluorescent depolarization diagnostic devices and as photomedicine. In the monomer-dimer equilibrium state (at critical concentration) of rhodamine B, these applications may be extended up to the new range of radiation uncovered in this work.

Spectral Dependences of Optical Absorption of Rhodamine B Immobilized in a Film on the Concentration of Copper Ions in Water

We studied the effect of the concentration of copper ions on the absorption spectrum of Rhodamine B in molecular form in an alcohol solution and immobilized in a polymer hydrogel film. The system is sensitive to the presence of copper ions at a concentration of 0.1 mg/L, which is sufficient for practical use. The insolubility of Rhodamine B in water during its immobilization in the volume of a photopolymerizable hydrogel film makes it possible to create a chemosensor that is stable at long exposures and is capable of sensing ultralow concentrations of impurities.

In Russian

This paper summarizes the cycle of authors’ studies devoted to polyamic acid-based Langmuir–Blodgett (LBF) functionalized by organic dyes. Previously reported results are supplemented with new experimental data. The monolayers of the polyamic acid under study, poly(4, 4'-diphenyl oxide)-2-carboxyisophthalamide, on water surface, which contains 110 –5 М Pb 2+ , at pH 5.8–6.0 the limiting area per repeating unit is S m = (0.52±0.02) nm 2 . The character of the compressing isotherms depends on the pH of the subphase because of the presence of the carboxylic group in the polymer unit. The monolayers and corresponding LBF obtained by the Schaefer method on solid support were modified via n-octadecyl alcohol, N-n-octadecylpyridinium bromide, and acid-base indicators and luminophores. For this purpose, n-decyl esters of fluorescein and eosin, rose Bengal B, n-heptadecyl ester of rhodamine B, N,N'-di-n-octadecylrhodamine, bromothymol blue, quinaldine red, and duplex quinaldine red are used. As a rule, the LBF contained 30–60 monolayers and 2 to 23 molar percent of dyes. The character of the emission and absorption spectra of rhodamine and hydroxyxanthene compounds in the mixed LBF as well as in multilayers of N-n-octadecylpyridinium bromide and stearic acid indicates the weakening of the dye dimerization and further aggregation of these dyes by the matrix. The procedure of determination of the apparent ionization constants of the dyes, pK a app , consisted in immersing of the LBF during 1–5 min into the aqueous solutions with different pH, air drying during several min, and measuring the absorption spectra. Experiments are performed as a rule at ionic strength of the subphase 0.05 М maintained by NaCl additives and 20 °С. Analysis of thus obtained pK a app (≡ – lgK a app ) values allows concluding that they are in outline close to the corresponding values obtained in micellar solutions of surfactants. These pK a app values may be divided into three groups. In the LBF consisting of entire N-n-octadecylpyridinium bromide, without polyamic acid, the pK a app values are generally close to those obtained for the same indicators in micelles of cationic surfactants and in droplets of cationic N-cetylpyridinium chloride-based microemulsions. An expressed differentiating action of this kind of BLF pseudophase is observed. The value of the electrostatic potential in the indicator locus is estimated as + 107 mV. The second group is represented by the pK a app values of indicators in polyamic acid-based LBF modified either by N-n-octadecylpyridinium bromide or n-octadecyl alcohol in the acidic region of pH. Under these conditions, the COOH groups of the polyamic acid are non-ionized, and the pK a app values are also close to those in cationic surfactant micelles. Finally, the third group of pK a app values corresponds to the pH region of 4–10. Here, the ionization of carboxylic groups of polyamic acid takes place. As a result, the transition range of indicators is anomalously expanded. It is these indicator equilibria that can be used in pH-sensor devices. The obtained results are compared with those reported by other authors. In addition, the peculiarity of dissociation of four-charged and triple-charged cations of the duplex quinaldine red is considered and compared with the dissociation of double-charged quinaldine red.

Спектральные зависимости оптического поглощения иммобилизованного в пленке Родамина Б от концентрации ионов меди в воде

The influence of copper ion concentration on the absorption spectrum of Rhodamine B in molecular form in an alcohol solution and immobilized in a polymer hydrogel film was studied. The sensitivity of the system to the presence of copper ions at a concentration of 0.1 mg/l, sufficient for practical use, is shown. The insolubility of Rhodamine B in water when it is immobilized in the volume of a photopolymerizing hydrogel film makes it possible to create a chemosensor that is stable at long exposures and can sense ultra-small concentrations of the analyzed impurity.

Smartphone-based spectrometer with high spectral accuracy for mHealth application

Utilizing its integrated camera, smartphone transforms to a burgeoning spectrometer which is promising for mHealth. However, this type of device suffers from the nonlinear sensitivity of camera which result in the imprecision of spectra. Here, we report a smartphone spectrometer with special designed calibration method to improve the spectral accuracy. Both wavelength calibration and intensity correction are adopted to eliminate the influence of nonlinear sensitivity from CMOS camera. The calibrated smartphone spectrometer is tested via comparing the fluorescence and absorption spectra of Rhodamine B with a standard commercial spectrometer. Meanwhile, the feasibility of this device in mHealth application is demonstrated via quantitative detection of creatinine. We argue that the high spectral accuracy and multimode-supporting ability enable the proposed smartphone spectrometer a powerful tool for mHealth with time and cost saving.

Light scattering and optic studies of Rhodamine B-comprising cylindrical-like AOT reversed micelles

In this study, we report photo-physical properties of Rhodamine B–comprising AOT reversed micelles in oil of decane at W=[H2O]∕[AOT]=7 and different mass fraction of water nano-droplet (MFD) values. Dynamic light scattering (DLS) measurement of AOT reversed micelles (RMs) showed that the diffusion coefficient of nano-droplets increased as concentration of Rhodamine B increased as a function of MFD and interaction between AOT reversed micelles remained attractive for all Rhodamine B concentrations due to transition in shape of micelles. Absorption spectrum of Rhodamine B (RB) at the high concentration (0.001), was deviated from linear trend at the larger MFD. Fluorescence emission intensity of Rhodamine B at 0.001 concentration increased from MFD=0.01 to MFD=0.04, and then decreased with MFD in AOT reversed micelles. Furthermore, blue shift in λmax of fluorescence of Rhodamine B in AOT reversed micelles was observed with MFD by decreasing concentration of RB in the system.

Dynamic and spectroscopic studies of nano-micelles comprising dye in water/ dioctyl sodium sulfosuccinate /decane droplet microemulsion at constant water content

In the present work, the dynamic and spectroscopic properties of water-in-decane dioctyl sodium sulfosuccinate (AOT) microemulsions comprising dye, Rhodamine B (RB), were studied by varying content of decane at the constant water content (W = 20), by using dynamic light scattering (DLS), UV/visible, and fluorescence techniques. The characterization results of DLS of AOT micelles showed that by decreasing concentration of Rhodamine B in the water/AOT/decane microemulsion, the inter-droplet interactions changed from attractive to repulsive as the mass fraction of nano-droplets (MFD) increased. A deviation in the absorption spectra of Rhodamine B from the Beer's law at the high Rhodamine B concentration (0.001) was observed in the AOT reversed micelles. The Quenching in the emission intensity of AOT droplets comprising Rhodamine B and red shift in λmax of fluorescence of dye was observed as a function of concentration of RB in AOT RMs. The Stokes shift of AOT droplets containing the high concentration of RB, increased with mass fraction of nano-droplet (MFD), whereas at the low Rhodamine B concentration, its variation remained constant up to MFD = 0.07, and then increased.

Quantum Mechanical and Absorption Spectral Characterization of Rhodamine B in Ternary Solution

ABSTRACTGeometrically optimized structure and quantum mechanical properties of rhodamine B were calculated. Electronic absorption spectra of rhodamine B were studied in a ternary solution of methanol and water. Kamlet–Taft empirical scales were utilized to characterize intermolecular interactions and their contributions to total spectral shifts.

Two-photon-excited fluorescence resonance energy transfer in an aqueous system of CdTe quantum dots and Rhodamine B

Two-photon excited fluorescence resonance energy transfer (FRET) between CdTe quantum dots with different emission peaks and Rhodamine B in aqueous solution are investigated both experimentally and theoretically. The photoluminescence and lifetime are measured using a time-resolved fluorescence test system. The two-photon excited FRET efficiency is found to increase as the degree of spectral overlap of the emission spectrum of CdTe and the absorption spectrum of Rhodamine B increases, which is due to the increase of Forster radius of the sample. Moreover, FRET efficiency increases when the ratio of acceptor/donor concentration increases. The two-photon excited FRET efficiency was found to reach 40%.

Hydrophilic gel composition effect on the molecular association and spectroscopic behavior of rhodamine B

Electronic absorption spectra of rhodamine B dye in aqueous solutions and in a polyacrylamide hydrogel matrix with different structural compositions were studied at room temperature. The transport and the solute–solute interactions of rhodamine B in aqueous solutions across the hydrophilic gels were investigated via exploration of the spectral properties of the dye-loaded hydrogel. The nature of the dye pair interactions in these media was discussed using the Kasha exciton theory. In addition, the monomer–dimer equilibrium of rhodamine B molecules in hydrogels with different compositional percentages was studied by means of UV–vis spectroscopy and least-squares fitting methods.

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.

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-hydoxyethyl 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.

Interferometric measurement of fluorescence excitation spectra

A Michelson interferometer has been adapted as an excitation source for fluorescence spectroscopy. A moving fringe pattern was generated by linear displacement of the movable mirror of the Michelson interferometer coupled to a xenon-arc lamp. This spectrally modulated source was monitored by a reference photomultiplier and used for exciting a Rhodamine B solution. The fluorescence emission at >645 nm was detected by a second photomultiplier. The two interferograms were acquired by a dual-channel digital oscilloscope, and their discrete Fourier transforms and corresponding power spectra were generated in a computer. The power spectrum of the emission signal represented the excitation spectrum, as was confirmed by comparison with the absorption spectrum of Rhodamine B. Thisoptical arrangement is well suited for acquiring fluorescence excitation spectra in the optical microscopy of biological specimens.

Absorption spectra of rhodamine B dimers in dip-coated thin films prepared by the sol-gel method

Thin films including rhodamine B (RB) which were dip-coated using the sol-gel reaction of tetraethyl orthosilicate (TEOS) have been prepared as a function of time and their absorption spectra observed 72 h after preparation of the thin films. One monomer and two dimers (H- and J-types) are clearly and simultaneously resolved both for RB in the thin films and the water-ethanol mixed solvent. Just after mixing the reaction system, the proportion of the dimers for RB was significant, and the H and J dimer amounts were nearly equal. As the sol-gel reaction proceeded, the relative contribution from the monomer species increased. The relative contribution of the monomer to that of the dimers reached a constant value long before the gelation time. This behavior indicates that the dye molecules are encapsulated in a certain structural region (pores) long before the gelation point of the sol-gel reaction of TEOS.

Difference Spectrophotometry of Rhodamine B in Aqueous Solution

The effect of concentration on absorption spectrum of Rhodamine B (RB) has been investigated by difference spectrophotometry.