Rigid-cage effects on the optical properties of the dye 3,3′ -diethyloxadicarbocyanine incorporated in silica-gel glasses

We investigated the optical properties of the saturable absorber 3,3′-diethyloxadicarbocyanine iodide incorporated in a matrix of silica-gel glass by the sol-gel technique. Absorption, emission, and fluorescence lifetime were studied as functions of the densification procedures. With respect to the liquid solutions, we observed a strong quenching of the P-isomer luminescence and an increase of the N-isomer fluorescence lifetime. These effects are ascribed to a restriction on the molecular photoisomerization rearrangement caused by the rigidity of the silica cage. Moreover, entrapping reduces intermolecular concentration effects. Finally, different from other glass-embedded dyes, both the absorption and the emission are blue-shifted by about 20 nm. © 1997 American Institute of Physics