2,1,3-Benzothiadiazole-based bis-silylated compounds: Synthesis and use in the preparation of highly fluorescent low-contend organic–inorganic hybrid materials

Herein, we report the synthesis of bis-silylated 2,1,3-benzothiadiazole derivatives and their use in the preparation of photoactive organic–inorganic hybrid materials with extremely low fluorophore/tetraethylorthosilicate molar ratios. The organic compounds were synthesized in good to excellent yields (55 %-94 %) using Pd-catalyzed Sonogashira cross-coupling as the key step. The bis-silylated benzothiadiazoles exhibited absorption in the UV-A region (∼376 nm), attributed to fully spin- and symmetry-allowed π-π* electronic transitions. An emission located in the blue-cyan region with a high quantum yield and large Stokes shift was observed, most likely due to a charge-transfer mechanism in the excited state. BTD-containing hybrid materials were obtained through a sol–gel process, for which the dye loading and aging time were studied. Optimal reproducibility of the photophysical results was achieved when the sol–gel reaction was conducted for 10 d at 60 °C. In the solid state, the obtained hybrid materials exhibited fluorescence emission in the blue-cyan-green regions, with relatively high quantum yields (∼ 30 %). The protocol allows for the preparation of analogous photoactive hybrid materials containing very low amounts of BTD, behaving as fluorescent fumed silica.