Caging interactions between a dopant chromophore and the sol–gel matrix

The successful incorporation of chromophores in a sol–gel matrix requires a careful study of their interaction with the gel environment. Photoacoustic spectroscopy is used to probe chemical changes in the direct neighborhood of dopant molecules in a silica-based sol–gel during times of evolution up to 100 times the gelation time. Studies of different chromophores such as β-carotene (β-Car.) and copper phthalocyanine (Cu-Pht.) show a size dependent steric hindrance effect as well as chromophore relaxation phenomena within the gel pores. Three main phases of evolution of the medium are distinguished. The stability of the chromophores is discussed and the results compared to FTIR spectra over time.