Fotoquimica e fotofisica de corantes absorvidos em solidos

The photophysical properties of several cyanine and acridine orange adsorbed onto microcrystalline cellulose have been studied. We have shown the importance of combining diffuse reflectance absorption studies (ground state and excited state) with emission studies (steady state and transients), for the study of these probes onto opaque heterogeneous substrates. Concentration studies of cyanine adsorbed onto microcrystalline cellulose have shown H and/or J aggregates; aggregation is humidity sensitive. The selective use of solvents allowed us to control deposition of probes onto the cellulosic substrate; with the use of solvents which swell cellulose, cyanine become entrapped into polymer chains. Cyanine adsorption onto microcrystalline cellulose increases both fluorescence quantum yields and lifetimes; this allowed us to detect emissions which were not previously observed. Pulsed laser excitation revealed the existence of a "new emission" of fluorescence, with its origin in photo isomers produced after exciting the singlet monomers of several cyanine. We also studied the energy transfer process (singlet-singlet and triplet-triplet) from 2-acetonaphthone to acridine orange, both adsorbed onto adsorbed onto microcrystalline celluloseAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga