Surface Photochemistry: Phloxine B as a probe for adsorption onto microcrystalline cellulose

ISABEL FERREIRA MACHADO; PAULO DUARTE; DIANA P. FERREIRA; LUIS FILIPE VIEIRA FERREIRA; HERNAN B. RODRIGUEZ; ENRIQUE SAN ROMAN

Coimbra

Simposio; XXIV IUPAC Symposium on Photochemistry; 2012

IUPAC

This work reports the photophysical behaviour of phloxine B (a xanthene dye which differs from fluorescein by the presence of four bromine atoms at the xanthene ring and four chlorine atoms in the carboxyphenyl ring) adsorbed onto microcrystalline cellulose, by reflectance spectroscopy and laser induced time-resolved luminescence in the picosecondnanosecond and microsecond-millisecond ranges. The xanthene dyes are a useful class of luminescent and triplet forming dyes for theoretical studies and practical applications. Prompt fluorescence, phosphorescence and delayed fluorescence spectral decays were measured at room temperature and 77 K, without the need of sample degassing because cellulose protects triplet states from oxygen quenching. In the range of the dye concentrations under study, spectral changes with time and lifetime distribution analysis were consistent with the dye coexisting in two different environments: dye molecules tightly entrapped between polymer chains in the crystalline regions of cellulose showed longer fluorescence and phosphorescence lifetimes and more energetic triplet states, while dyes adsorbed in more amorphous regions of the support showed shorter lifetimes and less energetic triplet states. This behaviour is discussed in terms of the different dye-support interactions in both kinds of adsorption sites.. Prompt fluorescence, phosphorescence and delayed fluorescence spectral decays were measured at room temperature and 77 K, without the need of sample degassing because cellulose protects triplet states from oxygen quenching. In the range of the dye concentrations under study, spectral changes with time and lifetime distribution analysis were consistent with the dye coexisting in two different environments: dye molecules tightly entrapped between polymer chains in the crystalline regions of cellulose showed longer fluorescence and phosphorescence lifetimes and more energetic triplet states, while dyes adsorbed in more amorphous regions of the support showed shorter lifetimes and less energetic triplet states. This behaviour is discussed in terms of the different dye-support interactions in both kinds of adsorption sites..