Enhancement of Excimer Formation Ability by Modulating the Length of Side-Chains in Polyhedral Oligomeric Silsesquioxane (POSS) and Application for Fluorescence Sensors for Metal Cations

Polyhedral oligomeric silsesquioxane (POSS) is a molecule with an inorganic cubic structure and organic side-chains and has attracted great attention for its application to luminescent materials by modifying luminophores. In this study, pyrenes-integrated POSSs with various lengths of side-chains were synthesized and the effect of the length on luminescent properties was evaluated. In optical measurements, highly efficient excimer emission was observed under dilute solution conditions. The higher value of the intensity ratio of the excimer emission to the monomer one was detected in the shortest side-chains. It is likely that the shorter side-chains of POSS lead to more efficient intramolecular interaction. Interestingly, we also found that the luminescence color was changed in response to metal cations in the dilute solutions. From the mechanistic study, metal cations such as Cu2+ can accelerate hydrolysis at the linker moiety. As a result, highly-sensitive luminescent sensors were obtained. These data represent that POSS can work as a reaction field where chemical reactions are accelerated through the accumulation of reactive species.