INVESTIGADORES
RODRIGUEZ Hernan Bernardo
congresos y reuniones científicas
Título:
Fluorescence and Molecular Singlet Oxygen Generation in Thin Films: Phloxine B in Poly(2-Hydroxyethyl Methacrylate)
Autor/es:
YAIR LITMAN; HERNÁN B. RODRÍGUEZ; ENRIQUE SAN ROMÁN
Lugar:
Córdoba
Reunión:
Congreso; 16th International Congress on Photobiology; 2014
Institución organizadora:
International Union of Photobiology
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 mM-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.
Acknowledgments: Financial support was
obtained from UBA, CONICET and ANPCyT. E.S.R. and H.B.R. are research members
of CONICET. Y.L. acknowledges a CIN fellowship.
[1] L. Kulak, C.
Bojarski, Chem. Phys. 1995, 191, 67.
[2] C. M. Cassidy et
al., J. Photochem. Photobiol. B 2009,
95, 71.