Non-Switching 1,2-Dithienylethene-based Diplatinum(II) Complex Showing High Cytotoxicity

A diplatinum­(II) complex was prepared from a new 1,2-dithienylethene-based ligand containing <i>N</i>-methylimidazole groups as metal-binding units. Reaction of the ligand 1,2-bis­[2-methyl-5-(1-methyl-1<i>H</i>-imidazol-2-yl)-3-thienyl]-cyclopentene (<b>L2</b>^<b>H</b>) with <i>cis</i>-dichlorobis­(dimethylsulfoxido)­platinum­(II) generated the bimetallic complex <i>trans</i>-[Pt₂Cl₄(DMSO)₂(<b>L2</b>^<b>H</b>)] (DMSO = dimethyl sulfoxide), whose DNA-interacting properties were investigated using different techniques. Cytotoxicity assays with various cancer cell lines showed that this compound is active, with IC₅₀ values in the micromolar range. Surprisingly, the diplatinum­(II) complex does not exhibit the anticipated photoswitching properties; indeed, UV irradiation does not lead to the photocyclization of the ligand <b>L2</b>^<b>H</b> or of the metal complex. Computational studies were performed and revealed significant differences in the electronic structure of <b>L2</b>^<b>H</b> compared with <b>L1</b>^<b>H</b> (i.e., 1,2-bis­[2-methyl-5-(4-pyridyl)-3-thienyl]-cyclopentene, which exhibits photoswitching properties), in terms of the relevant molecular orbitals involved in the UV–vis absorption features, which ultimately is responsible for the inertia of <b>L2</b>^<b>H</b> toward photocyclization