Spectroscopic characterization of water-soluble cationic porphyrins in sol–gel silica matrices and coatings

Silica aeorogels doped with different concentrations of water-soluble cationic porphyrins were synthesised by the sol–gel polymerisation of tetraethylorthosilicate (TEOS). Porphyrin dimer formation in sol–gel matrices was studied in the function of gelation time, over the porphyrin concentration range up to 10−5 M. The deviation from the linearity of Beer–Lambert law starts with porphyrin concentration about 5×10−6 M. The dimerization constants were estimated. The similar dependence could be observed for the aerogels and the solid thin films.