Photophysical properties of metallic-phthalocyanines dispersed in sonogel optical glasses

Phthalocyanines (Pc) based compounds having central metallic atoms of Ni were successfully embedded in mesoporous silica gels via a catalyst-free sol-gel (sonogel) process in order to fabricate optically active solid-state hybrid glasses in both bulk and thin film formats at different dopant concentrations. The organic-inorganic hybrid composites obtained at room temperature processing showed stable mechanical performance, controllable geometrical shapes, good transparency and homogeneity suitable for linear and nonlinear optical (NLO) characterizations. Hybrid samples were studied via the NLO third-harmonic generation (THG) technique. AFM studies, epi-microscopy surface evaluation, refractive-index measurements and UV-Vis spectroscopy studies were also performed in selected bulk and film samples. The morphological and spectroscopic results showed a homogeneous dispersion of the organometallic compounds within the highly pure SiO ₂-sonogel network. Moreover, Brewster's angle measurements have demonstrated the feasibility of tuning the refractive index of the samples by varying the chromophore dopant concentration. Additionally, the electronic absorption spectra showed band shifts in the two characteristic bands of the organometallic compound within sonogel environment, which evidence the formation of molecular H-aggregates for the developed hybrids and the consequent modifications of their optical properties. Finally, THG measurements in hybrid film samples exhibited an important NLO activity. We conclude that the optical effects of these composites can be tuned as function of the nickel-Pc concentration and that the sonogel matrix mainly acts as an inert protective shell, giving stable mechanical and thermal properties to the guest dopant compounds.