Synthesis of emissive water-soluble network polymers based on polyhedral oligomeric silsesquioxane and their application as optical sensors for discriminating the particle size

Abstract

We report organic–inorganic hybrid gels composed of polyhedral oligomeric silsesquioxane (POSS)-based network polymers and their variable emission properties depending on the size of coexisting silica particles (SPs). The POSS networks were constructed from octaammonium POSS by connecting with bithiophene dicarboxylic acid. By modulating the feed ratio of the bithiophene linker, a series of POSS networks were obtained with various cross-linking ratios among the POSS units. The POSS networks showed good water-solubility and emissions originating from the bithiophene linkers in water. Initially, it was observed that the POSS networks with relatively low cross-linking ratio showed higher affinity to SPs. An increase of the affinity was observed from all POSS networks to small-sized SPs. Interestingly, it was found that the emission properties were varied simply by adding silica particles into the sample. In the presence of nanoparticles dispersed in the sample, the red-shifted emission of the POSS network was induced. On the other hand, the blue-shifted emission was observed from the samples containing microparticles. These peak shifts depending on the size of coexisting particles should originate from the polarity changes around the bithiophene cross-linkers induced by the adsorption of the POSS networks onto the particle surfaces. These emission characteristics could be applicable for developing a facile optical chemosensor for discriminating the size of nanomaterials.