The first example of micro-adjustments of a metal organic framework (MOF) structure was observed in a new Zn(ii) MOF (Zn-BTDC-M1) derived from a benzothiadiazole-4,7-dicarboxylic acid (HBTDC) ligand using a light-driven decarboxylation process. Interestingly, such decarboxylation occurs at the non-chelated wing of the ligand, which induced a change in the capability of the MOF for physical N adsorption and chemical NH gas adsorption.

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On the basis of the same benzothiadiazole (BTD) ligand 2,1,3-benzothiadiazole-4,7-dicarboxylic acid (HL), two new isomers of three-dimensional (3D) BTD-derived Cd(II) metal-organic frameworks 1-2 {[S@CdL]·xHO} were obtained by the different solvothermal reactions, which were structurally similar. Surprisingly, structural analyses reveal that in 1 or 2, one free sulfur atom was fixed in a Cd(II) cluster cage by strong intermolecular interaction to form the secondary building unit (SBU) S@Cd. Each SBU S@Cd is connected by six L ligands and further extended into the 3D porous framework. In this work, the BTD antidimmer was evidenced by structural analysis and photophysical study. Furthermore, either 1 or 2 showed the uncommon dual emission, while only one emission was observed in the solution of ligand HL. The dual-emission mechanism was also realized by the structural analysis and photophysical study. Interestingly, although there is slight difference in structure (regular octahedral cage in 1 and slightly distorted octahedral cage in 2), the changes in N adsorption capability and photophysical performance between 1 and 2 are obvious, where 2 shows smaller Brunauer-Emmett-Teller surface area, broader absorption of antidimmer, and longer dual-emission lifetimes. Interestingly, either 1 or 2, the dual emission was clearly red-shifted by increasing the solvent polarity or the acidity of ambience, respectively.

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