Photophysics on surfaces: Absorption and luminescence properties of Pheophorbide-a on cellulose

M. GABRIELA LAGORIO, ENRIQUE SAN ROMÁN, ANDRÉ ZEUG, JOERG ZIMMERMANN AND BEATE ROEDER

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

RSCPublishing

Lugar: Cambridge; Año: 2001 vol. 3 p. 1524 - 1529

1463-9076

Solid samples of Pheophorbide-a adsorbed on microcrystalline cellulose were prepared with a wide range of dye concentrations (7.1]10~9 to 8.9]10~6 mol (g cellulose~1) and studied by diÜuse re?ectance and steady-state and time-resolved ?uorescence spectroscopy in the solid state. Absorption spectra obtained by means of re?ectance spectroscopy were compared with those found in diÜerent environments and carrier systems. No aggregation may be inferred from the spectroscopic data. Changes in the ?uorescence spectra with increasing dye concentration are attributed to : (a) reabsorption of luminescence and re-emission and (b) interaction between the excited dye molecule and ground state neighboring molecules. The ?rst eÜect accounts for the observed diÜerences in emission spectra for thin and thick layers of a given sample. Emission decays are non-exponential even at low dye concentrations. A energy transfer mechanism leading to energy Foé rster trapping by molecules of the same type as the excited dye is proposed. steady-state and time-resolved ?uorescence spectroscopy in the solid state. Absorption spectra obtained by means of re?ectance spectroscopy were compared with those found in diÜerent environments and carrier systems. No aggregation may be inferred from the spectroscopic data. Changes in the ?uorescence spectra with increasing dye concentration are attributed to : (a) reabsorption of luminescence and re-emission and (b) interaction between the excited dye molecule and ground state neighboring molecules. The ?rst eÜect accounts for the observed diÜerences in emission spectra for thin and thick layers of a given sample. Emission decays are non-exponential even at low dye concentrations. A energy transfer mechanism leading to energy Foé rster trapping by molecules of the same type as the excited dye is proposed. ]10~9 to 8.9]10~6 mol (g cellulose~1) and studied by diÜuse re?ectance and steady-state and time-resolved ?uorescence spectroscopy in the solid state. Absorption spectra obtained by means of re?ectance spectroscopy were compared with those found in diÜerent environments and carrier systems. No aggregation may be inferred from the spectroscopic data. Changes in the ?uorescence spectra with increasing dye concentration are attributed to : (a) reabsorption of luminescence and re-emission and (b) interaction between the excited dye molecule and ground state neighboring molecules. The ?rst eÜect accounts for the observed diÜerences in emission spectra for thin and thick layers of a given sample. Emission decays are non-exponential even at low dye concentrations. A energy transfer mechanism leading to energy Foé rster trapping by molecules of the same type as the excited dye is proposed.