Turn-On Fluorescence and Unprecedented Encapsulation of Large Aromatic Molecules within a Manganese(II)–Triazole Metal–Organic Confined Space

For the purpose of investigating the coordination behavior of sterically congested alkenes and exploring the possibility of cofacial complexation in the polycyclic aromatic system for the formation of extended polymeric networks, a new tetradentate ligand, 1,1,2,2-tetrakis[4-(1H-1,2,4-triazol-1-yl)phenyl]ethylene (TTPE), has been designed and synthesized. By using TTPE as a building block with regard to the self-assembly with MnCl2⋅4 H2O, a novel two-dimensional coordination framework {[Mn(TTPE)Cl2]⋅4 CHCl3}n (1) can be isolated. Anion-exchange and organic-group-functionalized aromatic guest TTPE-loaded host–guest complex experimental results indicate that coordinated Cl− anions in the 2D framework of 1 can be completely replaced with dissociative ClO4− groups in an irreversible single-crystal-to-single-crystal transformation fashion, as evidenced by the anion-exchange products of {[Mn(TTPE)(H2O)2](ClO4)2⋅0.5 TTPE⋅5.25 H2O}n (2). Interestingly, TTPE, acting as an organic template, was encapsulated in the confined space of the 2D grid of 2. To the best of our knowledge, such large organic molecules encapsulated in the reactive organic-group-functionalized aromatic-guest-loaded host–guest complex are unprecedented up to now. Luminescence measurements illustrate that 1 and 2 represent novel examples of sensing materials based on triazole derivatives. Further, 2 has been demonstrated by tuning the fluorescence response of porous metal–organic frameworks as a function of adsorbed small analytes.