Luminescence properties of rhodamine 6G intercalated in surfactant/clay hybrid thin solid films

To develop the solid-state laser oscillator based on laser dye compounds, the incorporation of rhodamine 6G (R6G, a laser dye) in cetyltrimethylammonium (CTA+) cationic surfactant/montmorillonite clay hybrid (HpC) thin solid films was investigated. The R6G/HpC samples were prepared by immersing the HpC films into a R6G aqueous solution with various concentration. X-ray diffraction patterns of the films of HpC, measured before and after the intercalation of R6G, proved the coexistence of both the dye and surfactant in clay interlayer spaces. All prepared thin films exhibited luminescence. It indicates that CTA+ molecules play a role as a partial suppressor of the aggregation of R6G molecules which prevents fluorescence. Moreover, the luminescence property of the present thin films was observed to be dependent on the co-intercalated degree of R6G molecules, indicating that the R6G intercalating in HpC interlayer space molecules exist as two or more luminescence species in the clay interlayer space.     

Characterization of rhodamine 6G aggregates intercalated in solid thin films of laponite clay. 2 Fluorescence spectroscopy

The photoluminescence response of Rhodamine 6G (R6G) laser dye intercalated into solid thin films of Laponite (Lap) clay is studied as a function of dye loading. Fluorescence spectroscopy (steady-state and time-resolved techniques) was used to characterize the R6G species adsorbed into the solid films. For very diluted R6G loadings (40% CEC), with a reminiscent fluorescence band at around 600 nm.     

Characterization of supported solid thin films of Laponite clay. Intercalation of rhodamine 6G laser dye

The morphology of thin films of Laponite (Lap) clay elaborated by the evaporation method and spin-coating technique was analyzed by atomic force microscopy and scanning electron microscopy, indicating a better quality film for the latter procedure. Rhodamine 6G (R6G) laser dye was intercalated into these films by ion exchange mechanism, performed by immersing the clay film into adequate dye solutions in which the effect of the dye concentration, immersion time, and nature of the solvent on the adsorption process were checked. The adsorption of R6G at the interlayer space of Lap was analyzed by the X-ray diffraction technique, and the presence of several R6G species (monomers and aggregates) was characterized by absorption and fluorescence spectroscopies. Less viscous solvents lead to higher dye loadings, suggesting a diffusional process for the intercalation of the dye in the interlayer spaces of Lap, and polar solvents favor the swellability of the interlayer space giving rise to a more homogeneous distribution of R6G molecules through the film and decreasing the dye aggregation. With the aging of the samples, the dye molecules can migrate through the interlayer spaces, leading to a more expanded distribution of R6G molecules and to the dye deaggregation.     

Spectral properties of TMPyP intercalated in thin films of layered silicates

The objective of this study was to investigate the spectral characteristics of tetracationic porphyrin dye (TMPyP), intercalated into films of three smectites. The smectites represented the specimens of high (Fluorohectorite; FHT), medium (Kunipia F montmorillonite; KF), and low layer charge (Laponite; LAP). Intercalation of TMPyP molecules was proven by XRD measurements. The molecular orientations of the dye cations were studied by means of linearly polarized ultraviolet-visible (UV-vis) and infrared (IR) spectroscopies. Both the UV-vis and the IR spectroscopy proved the anisotropic character of the films. The spectral analysis of the polarized UV-vis spectra and consequent calculations of tilting angles of the transition moments in the region of Soret band transitions were in the range of 25-35 degrees . The determined angles indicated that the molecular orientation of the dye cations was almost parallel to the surface of the silicates. Slightly higher values, determined for a FHT film, indicated either a slightly more tilted orientation of the dye cations or the change of molecular conformation after the intercalation of the dye. Quenching of TMPyP fluorescence was observed, resulting from the formation of bimolecular layer arrangements with sandwich-type assemblies of the dye molecules.     

Fluorescent plasma nanocomposite thin films containing nonaggregated rhodamine 6G laser dye molecules

This letter reports a novel methodology for the synthesis of dye-containing nanocomposite thin films containing fluorescent rhodamine 6G (Rh6G) laser dye molecules. The nanocomposites are deposited in one step at room temperature in a downstream microwave plasma operating at low pressure and power. By controlling the plasma chemistry, it is possible to reduce the formation of dye dimers and higher aggregates that quench the fluorescence of the dye molecules. The films are intensely absorbent and fluorescent, insoluble in water, mechanically stable, and present good adhesion to the substrate. Besides, the method is compatible with the present silicon technology and therefore particularly interesting for the fabrication of integrated optoelectronic devices.     

Spectral properties and structure of the J-aggregates of pseudoisocyanine dye in layered silicate films

Monolayer behavior of an ion pair amphiphile (IPA), hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), with normal long-chain alcohols at the air/water interface was analyzed by the Langmuir trough technique with the Brewster angle microscope (BAM) observations, and the pronounced stability enhancement of a HTMA-DS monolayer with the presence of the alcohol additives was demonstrated. Two normal long-chain alcohols with alkyl chain lengths of C16 and C18, 1-hexadecanol (HD) and 1-octadecanol (OD), were chosen as the additives. The surface pressure-area and surface potential-area isotherms of the monolayers with BAM images of monolayer morphology implied that the addition of either HD or OD with a comparatively small head group in a double-chained HTMA-DS monolayer at the interface led to better molecular packing and attractive interaction between the molecules, showing a similar condensing effect as that observed in mixed phospholipid/cholesterol systems. Moreover, the monolayer hysteresis and relaxation curves indicated that the incorporation of the alcohols into a HTMA-DS monolayer was able to lessen the monolayer hysteresis and to enhance the monolayer stability. In comparison with OD, HD seemed more effective as an additive in stabilizing a HTMA-DS monolayer, most likely due to the relatively better molecular packing of HTMA-DS and HD molecules at the interface. It is inferred that the stability of a monolayer or vesicular bilayer structure composed of IPAs can be improved by adjusting the molecular packing/interaction with a suitable long-chain alcohol as the additive.     

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.     

Time-resolved fluorescence spectroscopic and scanning near-field optical microscopic studies of rhodamine dye adsorbed in cationic Langmuir-Blodgett films

The fluorescence lifetimes decays and picosecond time-resolved fluorescence spectra were measured to investigate the dynamics of the excited state of sulforhodamine B (SRB) molecules adsorbed in the mono- and multilayered Langmuir-Blodgett (LB) films of octadecylamine. Steady-state and time-resolved fluorescence spectroscopy reveals that the fluorescence lifetimes and contents of the monomer and dimers in the molecular organizates depend upon the concentration of the dye in the solution and the adsorption process. SRB dye molecules adsorbed in LB films have been imaged with scanning near-field optical microscopy (SNOM). This information is exploited to map the distribution with molecular spatial resolution. SNOM provide the visual evidence of the monomers and dimers of SRB in cationic LB films.     

Synthesis of polyurethane/clay intercalated nanocomposites

 A kind of polyurethane/organophilic montmorillonite (PU/OMT) nanocomposite based on polyether, OMT, phenylmethane diisocyante and diglycol was synthesized and characterized by X-ray diffraction (XRD) and high-resolution electron microscopy (HREM). A polyether/OMT hybrid was first prepared in a nanocomposite form as confirmed by XRD. It was shown that there is a multilayered structure consisting of alternating PU chains stacked with the layers of the silicate layers in the microstructure of the PU/OMT nanocomposite as confirmed by study of the XRD patterns and the HREM images. The contents of the hard segment of PU and OMT had an effect on the basal spacing of the PU/OMT nanocomposite. Received: 29 August 2000 Accepted: 16 February 2001     

Humidity-dependent reversible aggregation of rhodamine 6G dye immobilized within layered niobate K4Nb6O17

The spectroscopic behavior of rhodamine 6G (R6G) dye intercalated in layered hexaniobate K4Nb6O17 was investigated. R6G cations were intercalated into the niobate through displacement of preintercalated alkylammonium ions. Powder X-ray diffraction and elemental analysis indicated that the dye molecules were densely accommodated in the interlayer spaces of niobate. The spectroscopic behavior of intercalated R6G was characterized by humidity-dependent aggregation at room temperature. The dye molecules were present dominantly as monomers under humid conditions (93% relative humidity (RH)), while they formed dimers under relatively dry conditions (20% RH). The aggregation-deaggregation of dye occurred reversibly depending on the humidity. The reversible aggregation was not accompanied by a large alteration of the interlayer structure of the sample, because only a small amount of water was adsorbed/desorbed with a small change in the basal spacing of the intercalation compound during the humidity change.     

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.     

Synthesis of transparent and ordered mesoporous silica monolithic films embedded with monomeric zinc phthalocyanine dye

Monolithic transparent mesoporous silica films embedded with zinc phthalocyanine (ZnPc) have been synthesized and it is shown that the encapsulated ZnPc dye molecules exist predominantly in monomeric form.     

On-line micellar-enhanced spectrofluorimetric determination of rhodamine dye in cosmetics

A simple FI-fluorimetric analytical methodology for the continuous and sequential determination of rhodamine B (RhB) in cosmetic products has been developed and evaluated in terms of sensibility and selectivity. The influence of several surfactant solutions on RhB fluorescence signal has been studied; particular attention was paid in the aggregation behavior of RhB-SDS system. Linear response has been obtained in the range of 1.6 x 10(-9) and 1 x 10(-6) mol L(-1), with a detection limit of 5 x 10(-10) mol L(-1). The novel technique provides a simple dissolution of sample, on-line filtration with sampling rate higher than 100 samples h(-1) and has been satisfactorily applied to the RhB determination in commercial lipsticks.     

Magnetic-field-assisted assembly of CoFe layered double hydroxide ultrathin films with enhanced electrochemical behavior and magnetic anisotropy

Magnetic films based on CoFe LDH nanoplatelets and porphyrin anions were fabricated by the layer-by-layer assembly technique with an assistance of an external magnetic field, which show enhanced electrochemical behavior and magnetic anisotropy.     

Optical-activity anisotropy of ordered phases in cellulose acetates

The optical activity of anisotropic solutions of cellulose diacetate in nitromethane and dimethyl sulfoxide and of diand triacetate films with vitrified ordered structure has been studied. The systems under study are characterized by high specific optical rotation [α], suggesting formation of a cholesteric mesophase. The value of [α] is found to depend on the angle of rotation of the samples relative to the direction of the polarization vector of an incident light beam in the plane perpendicular to this beam (the anisotropy of optical activity). This dependence (indicatrix) shows an irregular pattern and, when plotted in Cartesian coordinates, can be described with a distorted sinusoid. The data on the resolution of indicatrices into harmonic constituents and isolation of contributions due to isotropic components and anisotropic components, each of which is determined by the structural element with the corresponding asymmetry, are analyzed.     

Benzocarbazole anions intercalated layered double hydroxide and its tunable fluorescence

Luminescent benzocarbazole anions (BCZC) intercalated into the interlayer region of Mg-Al-layered double hydroxides (BCZC/LDH) with different layered charge densities (LCD) were prepared. The structure and chemical composition of the composites were characterized by X-ray diffraction, elemental analysis, thermogravimetry and differential thermal analysis (TG-DTA), infrared spectra (FT-IR), UV-vis absorption and fluorescence spectroscopy. The photoemission behavior of BCZC in the LDH matrix with high (Mg/Al ratio = 1.801) and low (Mg/Al ratio = 3.132) LCD is similar to that of BCZC solid and aqueous solution states respectively, indicating that the luminescence performances of the intercalated dye anions can be tuned by adjusting the LCD of the LDH layer. Moreover, the thermal stability and stacking order of BCZC are largely improved upon intercalation, and the BCZC/LDH thin film exhibits well polarized luminescence with the luminescent anisotropy of 0.15-0.20. In addition, molecular dynamics (MD) simulation was employed to calculate the basal spacing and molecular arrangement of the intercalated BCZC within the LDH matrix. The simulation results show that the distribution of BCZC anions is much broader in the gallery of Mg-Al-LDH with high LCD, while BCZC anions exhibit a more ordered arrangement in LDH with low LCD. Furthermore, the radial distribution functions of interlayer water molecules were also studied. Based on the combination of experiment and theoretical simulation, this work provides a detailed understanding of the tunable photoluminescence, orientation and diffusion behavior of the luminescent molecules confined within the gallery of a 2D inorganic matrix.     

Preparation and thermal decomposition study of pyridinedicarboxylate intercalated layered double hydroxides

Supramolecular 2,3- and 2,5-pyridinedicarboxylate (PDC) intercalated ZnAl-layered double hydroxides (2,3- and 2,5-PDC–ZnAl–LDHs) have been prepared by ion exchange method. The structure and composition of the intercalated materials have been studied by X-ray diffraction (XRD) and inductively coupled plasma emission spectroscopy (ICP). The study indicates that the 2,3-PDC and 2,5-PDC anions are accommodated as interdigitated bilayer and monolayer arrangement respectively between the sheets of LDHs. Furthermore, their thermal decomposition processes were studied by the use of in situ high temperature X-ray diffraction (HT-XRD), and the combined technique of thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS) under N2 atmosphere. Based on the comparison study on the temperatures of both decarboxylation and complete decomposition of interlayer PDC, it can be concluded that 2,5-PDC–ZnAl–LDHs has higher thermal stability than that of 2,3-PDC–ZnAl–LDHs.     

Synthesis and characterization of 5-fluorocytosine intercalated Zn-Al layered double hydroxide

In this paper, the intercalation of 5-fluorocytosine (5-FC) into a layered inorganic host, Zn-Al layered double hydroxide (LDH), has been carried out using coprecipitation method to obtain 5-FC/LDH nanohybrids. The intercalated amount (A_In) of 5-FC into the LDH is remarkably dependent on the molar ratio (R_F/M) of 5-FC to metal ions and the pH of coprecipitation system. The morphology of 5-FC molecules in 5-FC/LDH nanohybrids is dependent on the A_In. It is interestingly found that the morphology of the nanohybrid particles may be changed with the increase of R_F/M from hexagonal plate particles to threadlike particles. The in vitro drug release from the nanohybrids is remarkably lower than that from the corresponding physical mixture and pristine 5-FC at either pH 4.8 or pH 7.5. In addition, the release rate of 5-FC from the nanohybrid at pH 7.5 is remarkably lower than that at pH 4.8, this is due to a possible difference in the release mechanism. The obtained results show these drug-inorganic nanohybrids can be used as a potential drug delivery system.     

Thiuram disulfide intercalated hybrid materials of layered lead and cadmium iodides

Thiuram disulfide intercalates of lead(II) and cadmium(II) were prepared by the reaction of binary layered metal iodides with five dithiocarbamates in air. The intercalates were characterized by elemental analysis, Powder X-ray diffraction (XRD), infrared (IR), ultraviolet–visible spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM) techniques. IR showed increased contribution of the thioureide bond and the presence of weak disulfide stretching frequency. Powder XRD showed the characteristic intermediate 2θ signal confirming the intercalation. Powder XRD clearly differentiated intercalates from the iodinated product of dithiocarbamate. As the bulkiness of substituents on disulfide increased, “d” also increased. The higher thermal stability associated with intercalates clearly suggests a strong ionic interaction and a difficult de-intercalation. SEM images of lead intercalates indicated crystalline nature. The intercalates appeared as rods or spheres. The diallyl-intercalate, [PbI₂](H₅C₃)₂NCSS-SSCN(C₃H₅)₂ (where (H₅C₃)₂NCSS-SSCN(C₃H₅)₂ is diallylthiuram disulfide), shows “net like structures.” Intercalation of oxidized dithiocarbamates in the “galleries” of layered PbI₂/CdI₂ is observed. HRTEM and AFM analysis of intercalates showed the particles to be nano-rods.