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 N-methylimidazole groups as metal-binding
units. Reaction of the ligand 1,2-bis­[2-methyl-5-(1-methyl-1H-imidazol-2-yl)-3-thienyl]-cyclopentene (L2H) with cis-dichlorobis­(dimethylsulfoxido)­platinum­(II)
generated the bimetallic complex trans-[Pt2Cl4(DMSO)2(L2H)] (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 L2H or of the metal
complex. Computational studies were performed and revealed significant
differences in the electronic structure of L2H compared with L1H (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 L2H toward photocyclization.