Influence of hybrid organic–inorganic sol–gel matrices on the photophysics of amino-functionalized UV-sensitizers

Recent interest in photolithographic processes employing single and two-photon absorption processes have afforded advanced opportunities to fabricate both planar and three-dimensional microstructures. The fabrication of such structures is dependent on the local polymerization of the organic moieties using photoinitiating molecules, and a key parameter to consider is the dependency of the photoreactivity of these initiators on the matrices in which they are dispersed. To our knowledge, there has been no comprehensive investigation reported on the photoreactivity dependency of commercially available photoinitiators inserted within hybrid sol–gel materials. The aim of this paper is to highlight and explain the influence of the composition of hybrid organic–inorganic sol–gel materials on the photoreactivity of UV-sensitive initiators. Of particular interest is the understanding of the interactions between photoinitiating molecules and the sol–gel matrix. It is shown that both the nature of the chelating agent as well as the degree of chelation of the inorganic part of the hybrid sol–gel material significantly influence the spectral absorption of the photoinitiator. It is demonstrated that metal–ligand charge transfer processes are the main phenomena responsible for the red shift of the absorption of the amino-functionalized photoinitiators, which is strongly dependent on the condensation of the materials.