INQUIMAE   12526
INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Fluorescence and Molecular Singlet Oxygen Generation in Thin Films: Phloxine B in Poly(2-Hydroxyethyl Methacrylate)
Autor/es:
Y. LITMAN; H. B. RODRÍGUEZ; E. SAN ROMÁN
Lugar:
Córdoba
Reunión:
Congreso; 16th International Congress on Photobiology; 2014
Resumen:
Phloxine B (PhB) is a hydrophilic dye used in drugs and cosmetics. It has low toxicity in the dark but it is currently used as photoinsecticide because it generates singlet molecular oxygen (1O2) on illumination. Poly(2-hydroxyethyl methacrylate) (PHEMA) is a bio-compatible polymer that forms hydrogels in water and, conveniently crosslinked, builds up hardly hydrolizable materials. Preliminary experiments are described, based on PhB incorporated in 100300 nm thick 20 kDa PHEMA films obtained by spin coating on glass substrates. Samples were characterized by absorption and emission spectroscopies. Fluorescence quantum yields were obtained using PhB in ethanol as a reference (ΦF = 0.76 ± 0.02). 1O2 formation was evaluated using 1,3-diphenylisobenzofuran as chemical quencher in dichloromethane. Absorption spectra do not change with dye concentration (200 M0.1 M) and resemble the spectrum in ethanol, showing that dye aggregation does not take place. In spite of that, fluorescence quenching occurs at [PhB] > 0.005 M. Results are interpreted in terms of a quenching-radius model with randomly distributed molecules, computing excitation energy migration and trapping (FRET) through LAF theory calculations [1]. The best fit is obtained with a quenching radius of 12 Å, compatible with quenching centers formed by slightly interacting molecules in close contact (statistical traps). Relative 1O2 quantum yields follow a similar trend. Generation of 1O2 is limited only by the formation of statistical traps at high dye concentrations. The maximum rate for a given illumination is obtained around [PhB] = 0.010 M, where the product between absorptance and quantum yield attains its maximum. Potential applications in photodynamic antimicrobial chemotherapy and other fields [2] are discussed.