Magnifying the turn-on luminescence and electrical conductivity via the coupling effect of oxidation, metal ion adhesion and pressure within MnII-MOFs

Abstract

A metal–organic framework (MOF), Mn^II₂-BTDB-MOF (Mn1, BTDB = 4,4′-(1,2,5-benzothiadiazole-4,7-diyl)bis-benzoic acid), exhibits enhancement of turn-on luminescence through the restriction of intramolecular vibration (RIV) mechanism, retaining its crystallinity and porosity. As expected, a 1.8-, 3.6-, 45.5-, and 164.4-fold emission enhancement respect to that of Mn1 by suffering from respective pressure, oxidation, the introduction of Hg²⁺, and the above three strategies totally, are observed, indicating their coupling effects on luminescence sensor. The results of density functional theory calculations reveal that the introduced metal ions trigger the RIV of BTDB by reducing the changes of the dihedral angle between the ground and excited states, suppressing nonradiative energy exhaustion, and thus magnifying turn-on luminescence. Furthermore, through stepwise fine-tuning the intricate physical and electronic structure associated with oxidation and the introduction of Zn²⁺ under 20 MPa, the electrical resistivity is dramatically improved from <10⁻¹⁷ S cm to 4.4 × 10⁻⁸ S cm. It is the first time to systematically magnify the luminescence, along with electrical resistivity, by employing the coupling effects of multiple external stimuli on MOFs, thereby highlighting their adaptabilities as sensors and electronics.