Formation of polyelectrolyte microcapsules with chemically bound adsorbed molecules of fluorescein isotiocyanate and their destruction under laser action

Polyelectrolyte capsules with molecules of fluorescein isotiocyanate included in the shell have been obtained. The inclusion of dye molecules in the shell of the capsule allows the photosensibilized destruction of its structure. The measurements of the fluorescence intensity of a dye that was present in the shell revealed effective dissipation of the energy of photoexcited molecules by the surrounding organic matrix. The capsule suspension was irradiated by a laser in the absorption band of fluorescein isotiocyanate molecules. By measuring the size distribution of the capsules before and after irradiation with a laser it was shown that the capsules are destroyed under the effect of laser radiation.     

Photochemical stability of rhodamine 6G in solution

The photochemical stability of Rhodamine 6G under ultraviolet and copper-vapour laser irradiation has been determined. A strong dependence of this reaction on the solvent has been found. The results indicate a free-radical mechanism as a possible reaction pathway for photobleaching.     

Sonocatalytic and sonophotocatalytic degradation of rhodamine 6G containing wastewaters

The present work deals with degradation of aqueous solution of Rhodamine 6G (Rh 6G) using sonocatalytic and sonophotocatalytic treatment schemes based on the use of cupric oxide (CuO) and titanium dioxide (TiO₂) as the solid catalysts. Experiments have been carried out at the operating capacity of 2 L and constant initial pH of 12.5. The effect of catalyst loading on the sonochemical degradation has been investigated by varying the loading over the range of 1.5–4.5 g/L. It has been observed that the maximum degradation of 52.2% was obtained at an optimum concentration of CuO as 1.5 g/L whereas for TiO₂ maximum degradation was observed as 51.2% at a loading of 4 g/L over similar treatment period. Studies with presence of radical scavengers such as methanol (CH₃OH) and n-butanol (C₄H₉OH) indicated lower extents of degradation confirming the dominance of radical mechanism. The combined approach of ultrasound, solid catalyst and scavengers has also been investigated at optimum loadings to simulate real conditions. The optimal solid loading was used for studies involving oxidation using UV irradiations where 26.4% and 28.9% of degradation was achieved at optimal loading of CuO and TiO_2, respectively. Studies using combination of UV and US irradiations have also been carried out using the optimal concentration of the catalysts. It has been observed that maximum degradation of 63.3% is achieved using combined US and UV with TiO₂ (4 g/L) as the photocatalyst. Overall it can be said that the combined processes give higher extent of degradation as compared to the individual processes based on US or UV irradiations.     

Deterioration of rhodamine 6G dye solution in methanol

The mechanism of the deterioration process of a Rhodamine 6G dye solution in methanol is studied. It is found that oxygen plays an important role in the fading of the Rhodamine 6G solution and during this fading oxygen is spent in the photochemical reaction of methanol. The fading of a Rhodamine 6G solution without oxygen becomes 70 ± 20 times as rapid as that of a Rhodamine 6G solution with a sufficient amount of oxygen.     

The picosecond time-resolved fluorescence spectrum of rhodamine 6G

We have observed the spontaneous flourescence spectrum of rhodamine 6G in glycerol with picosecond resolution using a mode-locked Nd:glass laser. The position, width and shape of the fluorescence spectrum are a function of the delay time between excitation and observation of the spectrum. Initially, the spectrum is close to a lorentzian with 12 nm halfwidth centered at 559 nm. The spectrum finally evolves to a skewed gaussian lineshape of 37 nm halfwidth centered at 569 nm. These results imply that the fluorescence spectrum is inhomogeneously broadened.     

Solvent effects on the gain of rhodamine 6G

The effect of solvents on the gain and the peaks of gain spectra is investigated for rhodamine 6G (R6G) under nitrogen laser pumping. The non-specific solute-solvent interaction for R6G is found to be mainly dispersive. Additional shifts produced for R6G in certain solvents are explained as due to hydrogen bonding. The gain characteristics are interpreted on the basis of the position and overlap of absorption and fluorescence spectra, the quantum yield, the absorption at the pumping wavelength and the refractive index of the solvent. For the solvents studied it is found that R6G has high gain in solvents with low refractive index and high polarity. Amongst the solvents studied the alcohols displayed the highest gain with methanol being the most suitable solvent. The lowest gain amongst the alcohols was with capryllic alcohol which gave a gain that was 69% of that obtained with methanol. Amongst all the solvents studied the lowest gain was with chloroform, being only 34% of the gain in methanol.     

On the mechanism of rhodamine 6G fluorescence quenching

The fluorescence of the widely used TPF dye rhodamine 6G is quenched by photons of the ruby as well as the Nd-glass laser. Taking into consideration the polarisation of the ground- and excited-state absorptions of rhodamine 6G a simple model of quenching results. The main process is an S₁ absorption with subsequent leave of the ordinary rhodamine 6G singlet system. For Nd-laser photons the cross section of the concerned transition following from our quenching experiments is σS₁→S₂ = 1.2×10^-16 cm².     

若丹明6G光解过程的顺磁共振研究

本文报道了用顺磁共振研究激光染料若丹明6G的光解过程。实验表明染料三重态分子和溶剂分子间存在着能量转移。     

Association of rhodamine 6G in light and heavy water solutions

The absorption characteristics of rhodamine 6G molecules in light and heavy water solutions are studied. The association efficiencies of dye molecules and the structure and the binding energy of complexes formed are determined in relation to the solvent composition. The structure of H₂O +D₂O solutions is studied using correlation and low-frequency Raman spectroscopy. The distribution of dissolved complex molecules in the water matrix is shown to have inhomogeneities, which are responsible for a high association efficiency. The characteristic size of these inhomogeneities is estimated. The fractal dimension of the structural formations of light and heavy water molecules is determined as a function of their concentration.     

Opto-acoustic study of tinuvin-P and rhodamine 6G in solid polymeric matrices

Laser-induced opto-acoustic calorimetry has been used to examine the thermo-elastic properties of two polymer matrices doped with tinuvin-P and the radiation-less decay processes of rhodamine 6G (Rh6G) in them. The matrices assayed were methyl methacrylate (MMA) homopolymers P(MMA), and methyl methacrylate and 2-hydroxyethyl methacrylate (HEMA) copolymers P(MMA:HEMA). A slight difference in the thermo-elastic properties of the polymers, namely their adiabatic expansion coefficients, has been detected and found to correlate with the long-term stability of the laser material. This suggests a key role of the heat-dissipation processes in the photostability of these polymeric materials. On the other hand, the fluorescence quantum yield of Rh6G is shown to vary with the polymer-matrix composition in a way consistent with its lasing efficiency. The Rh6G absorption and fluorescence quantum yield also change dramatically upon increasing its concentration, which suggests the co-existence of different Rh6G forms with different photophysical properties. Received: 10 February 2000 / Revised version: 12 June 2000 / Published online: 10 January 2001