Retrieving the original appearance of polyhedral oligomeric silsesquioxane-based porous polymers

Abstract

A class of polyhedral oligomeric silsesquioxane (POSS)-based porous polymers containing typical π-conjugated units, including biphenyl, tetrahedral silicon-centered units and tetraphenylethene, have been prepared by Heck reactions of octavinylsilsesquioxane (OVS) with the corresponding brominated monomers. Two sets of reaction conditions were employed to retrieve their original appearance. These materials exhibit tunable appearance with the colors from dark colors to various colors and the physical forms from coarse powders with irregular shape particles to fine powders with relatively uniform solid spheres by altering the reaction conditions from method A to method B. It is found that the variation of appearance leads to the alteration of the fluorescence from nearly no fluorescence to bright fluorescence. Considering the conjugated feature of these polymers, we speculate that these polymers were afforded as their original appearance by method B. This finding could explain the unexpected phenomenon that many conjugated porous polymers exhibit no or very low fluorescence despite of their π-conjugated structures, that is, their real appearance may be covered by the residuals in the networks. Thus, researchers should deliberately consider the material's appearance when preparing fluorescent porous polymers. Additionally, samples with fine powders show excellent dispersion stability in solvents, which is beneficial for the use of these materials in solution processable methodologies such as spin-coating. Furthermore, these materials show efficient fluorescence quenching for nitrobenzene vapour in thin films, thereby indicating their potential application as sensing agents for the detection of explosives.