M. J. Tapia Estevez

Spectroscopic study of the adsorption of rhodamine 6G on clay minerals in aqueous suspensions

Abstract Absorption and fluorescence spectroscopies were applied to study the adsorption of rhodamine 6G on several smectite-type clays in aqueous suspension. The dye can be adsorbed as the monomeric and the dimeric forms on both the external and the interlamellar surfaces of the clay. The presence of these species and their evolution with the stirring time of the sample and the relative dye/ clay concentration depend on the nature of the smectite, the clay concentration and the particle size, factors that also affect the dispersion degree of the clay particles in water.

Binary solvent effects on the absorption and emission of 7-aminocoumarins

Abstract The photophysical properties of di-, mono- and non-ethyl 7-aminocoumarins have been investigated in different water/ethanol mixtures. The effect of the solvent composition on the spectral shifts and on the radiationless deactivation process depends on the molecular structure of the dye. The solvent effect is analyzed in terms of hydrogen bondings between the dye and protic solvents. The mechanism for internal conversion is discussed by two models: via a twisted intramolecular charge transfer (TICT) state, and by an hybridational change of the amino group (open-close umbrella-like motion, ULM model). Both models can explain the experimental results if solute-solvent hydrogen bonds are considered.

Luminescence properties of rhodamines in water/ethanol mixtures

Abstract The absorption and the emission (fluorescence spectra and radiative decay curves) characteristics of rhodamine R3B and R6G and of the molecular forms of RB and R19 are determined in different water/ethanol mixtures. The influences of molecular structure (alkylation of the amino groups and photonation or esterification of the carboxyphenyl group) and the nature of the solvent (specific solute-solvent interactions) on these properties are investigated. The internal conversion mechanism of rhodamines is discussed.

TICT and ULM models for the radiationless deactivation of rhodamines

The formation of a twisted intramolecular charge transfer state (TICT model) and changing of the amino group from a planar to a pyramidal structure (ULM model) are applied to explain the radiationless deactivation of rhodamines with different molecular structures in water and in ethanol. Both theories offer valid interpretation for the photophysics of rhodamines if intramolecular xanthene-carboxyphenyl and specific solutesolvent interactions are considered.