Photophysics of Rhodamine 101 linked to Cellulose

HERNÁN B. RODRÍGUEZ; ENRIQUE SAN ROMÁN

La Plata, Argentina

Otro; VIII Encuentro Latinoamericano de Fotoquímica y Fotobiología (VIII ELAFOT); 2004

Rhodamine 101 (R101, fluorescence quantum yield of 1.0 in ethanol) has advantages as a fluorescence standard in solution over Rhodamine B, a classical fluorescence standard. As it lacks from groups undergoing torsional movements, its fluorescence quantum yield is expected to be independent of the environment. However, experiments carried out on R101 adsorbed on microgranular cellulose showed that fluorescence quantum yield decreases as the dye penetrates into the solid matrix. To observe the effect of chemical binding on the photophysical properties of the dye, R101 was attached to the surface of microcrystalline cellulose. Anchoring was achieved by esterification in heterogeneous conditions in pyridine, using dicyclohexylcarbodiimide for "in situ" activation of the dye carboxyl group. Chemical binding was assayed by desorption tests in ethanol and compared with similar samples containing R101 adsorbed on the same material. Solid samples were studied by diffuse and total reflectance and by steady state fluorescence spectroscopy. Reflectance spectra were corrected for the emission of the dye, emission spectra were corrected for reabsorption and reemission, and absolute fluorescence quantum yields were calculated. For this sake, methods and models previously developed in our laboratory were applied. Remission function and emission spectra show a bathochromic shift of 10 nm, as compared with adsorbed R101, with no noticeable change in their shape. Absolute fluorescence quantum yields are lower than one, 0,82, remaining essentially constant between 500 and 600 nm. This material has potential utility as fluorescence reference in heterogeneous media as well as in energy transfer studies.