Selective chemical sensors based on fluorescent organic nanocrystals confined in sol–gel coatings of controlled porosity

We have developed chemical sensors based on strong modifications of rubrene nanocrystals fluorescence decays under different chemical surroundings. These nanocrystals were grown in silicate sol–gel thin films. To improve the nanosensors selectivity, we used alkoxide mixtures of (TMOS: tetramethoxysilane, MTMOS: methyltrimethoxysilane and TMSE: 1,2-bis(trimethoxysilyl)ethane) to modulate the pore size of the sol–gel films. Pore size distributions were determined by ellipsometry coupled to gas adsorption–desorption technique. We showed that matrices prepared with equimolar TMOS/MTMOS mixtures are typically microporous while new matrices obtained from 2TMOS/TMSE mixtures are mesoporous. Time-resolved fluorescence spectroscopy was used to follow the diffusion of typical probe molecules (Methylene Blue and Cibacron Blue) via the porosity of the sol–gel films. The fluorescence quenching of nanocrystals is in good agreement with the pore sizes determined by ellipsometric porosimetry. Finally, we have demonstrated the basic working principles of fluorescent organic nanocrystals as chemical sensors in aqueous solutions, particularly in the case of H2O2.