Linear and non-linear optical properties of 2,5-disubstituted pyrroles supported by a catalyst-free SiO2 sonogel network

The preparation and optical characterization of pyrrole based sol–gel hybrid materials generated by ultrasonic irradiation (Sonogel composites) are presented in this work. Pyrrole compounds were recently synthesized in our group by a modification of the Schulte–Reisch reaction; these molecular systems were dissolved at different concentrations in tetrahydrofuran (THF) and optimally embedded into a catalyst-free SiO2 sonogel network. For this purpose, we exploited the novel catalyst-free (CF) sonolysis route to produce highly pure sol–gel glasses, generated via sonochemical reactions. This approach has been recently developed in our research group and has been successfully implemented to develop several hybrid composites for optical applications. By this method, homogeneous and stable solid-state hybrid samples suitable for optical characterization can be produced. The high porosity exhibited by the sonogel matrix allowed us to prepare several pyrrole doped composites with variable dopant concentration. The linear and nonlinear optical (NLO) properties of these amorphous hybrid structures were determined by absorption- and photoluminescent (PL)-spectroscopies, and by the optical third harmonic generation (THG) techniques, respectively. The implemented catalyst-free sonolysis route produced SiO2-host networks of high chemical and optical purity, suitable for optical and photonic applications.