Enhanced Fluorescence in Tetraylnitrilomethylidyne–Hexaphenyl Derivative-Functionalized Periodic Mesoporous Organosilicas for Sensitive Detection of Copper(II)

Highly fluorescent and copper­(II)-responsive periodic mesoporous organosilicas (TH-PMOs) were successfully obtained by using a (tetrayl­nitrilo­methylidyne–hexaphenyl (TH))-derived tetrasiloxane (TH-Si₄) as the organosilica precursor. The TH unit was embedded within the framework of PMOs by four silyl groups without forming associated species, and high fluorescence quantum yields were achieved even for the PMOs prepared from 100% organosilane precursor. The optical studies indicated that the intramolecular rotation of TH was restricted by the framework of TH-PMOs, resulting in the decline of the nonradiative decay process and enhanced monomeric fluorescence emission. The unique structure of the TH groups not only assured their aggregation-induced enhanced emission (AIEE) characteristics but also provided potential coordinating sites for metal ions. Therefore, the enhanced fluorescence of PMOs showed a highly selective response to copper ions in aqueous solution with the detection sensitivity up to the 10^–8 M level. Moreover, the diffusion process of Cu²⁺ and the competitive effect between Cu²⁺ and Fe²⁺ on TH-PMOs were measured by STXM; the results reveal that the specific binding between TH and Cu²⁺ brings about a relatively high adsorption capacity of the hybrid material toward Cu²⁺.