FLUORESCENCE OF PYRANINE IN SOL-GEL BASED SILICA AND HYBRID THIN-FILMS

The sensitivity of the pyranine fluorescence to protonation/deprotonat ion is used to follow modifications in cured sol-gel thin films. The a cid concentration in the sol-gel solution is varied for TEOS-based coa tings and a series of organically modified silanes Si(OR)(3)R' are add ed to the TEOS solution. The concentration of the organically modified silane is varied as well as the chain length of the alkylgroup (R'). The stationary fluorescence measurements show that the equilibrium bet ween the protonated and the deprotonated form of pyranine changes depe nding on the type of silica matrix. The deprotonated form is dominant in the cured SiO2 films and the protonation/deprotonation ratio of pyr anine is constant for the different acid concentrations used. The prot onated form becomes dominant as the concentration of Si(OR)3R' is incr eased and as the alkyl chain length (R') of the organically modified s ilanes is augmented. Emission anisotropy measurements of pyranine in t he same coatings show that the rotational freedom of the molecule chan ges due to modifications in the cages for the TEOS-based coatings. The se modifications are produced by the acid concentration used to prepar e the coatings. An increase in the rotational freedom of pyranine is o bserved in the TEOS-Si(OR)(3)R' systems.