Photophysical properties of cyanine dyes in sol-gel matrices

Planar and twisted cyanine dyes with different pKa values are examined concerning their protonation equilibrium in sol-gel matrices. In the sol-gel matrix the equilibrium between the cation and the dicationic form shifts to the dication pointing to acid-base reactions of sol-gel walls with cyanine dyes. The colorless dicationic species is not found for pseudoisocyanine and in sol-gel bulks prepared with drying control chemical agents (DCCA) indicating the absence of the responsible interaction. The fluorescence lifetimes of cyanine molecules are used to compare the pore size and distribution in sol-gel matrices prepared with and without DCCA. J-aggregation, examined for one dye, depends strongly on environment polarity and pore size.