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1 January 2006 Energy Transfer Among Dyes on Particulate Solids
Hernán B. Rodríguez, Analía Iriel, Enrique San Román
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Abstract

Absorption and fluorescence properties of methylene blue (MB), a well-known singlet molecular oxygen photosensitizer, and its mixtures with pheophorbide-a (Pheo) sorbed on microgranular cellulose are studied, with emphasis on radiative and nonradiative energy transfer from Pheo to MB. Although pure MB builds up dimeric species on cellulose even at 2 × 10−8 mol g−1, addition of 2.05 × 10−7 mol g−1 Pheo largely inhibits aggregation up to nearly 10−6 mol g−1 MB. At the same time, the absorption spectrum of monomeric MB in the presence of Pheo differs from the spectrum in pure cellulose. Both effects reveal a strong influence of Pheo on the medium properties. A model relying entirely on experimental data is developed, through which energy transfer efficiencies can be calculated for thin and thick layers of dye-loaded cellulose. At the largest concentration of MB assuring no dye aggregation, nonradiative energy transfer efficiencies reach a maximum value of nearly 40%. This value is quite high, taking into account the low fluorescence quantum yield of Pheo, Φ = 0.21, and results from the existence of high local concentrations of the acceptor within the supporting material. These results show that large energy transfer rates can exist in a system devoid of any special molecular organization.

Hernán B. Rodríguez, Analía Iriel, and Enrique San Román "Energy Transfer Among Dyes on Particulate Solids," Photochemistry and Photobiology 82(1), 200-207, (1 January 2006). https://doi.org/10.1562/2005-07-08-RA-609
Received: 12 July 2005; Accepted: 22 August 2005; Published: 1 January 2006
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