Dual-radical-based molecular anisotropy and synergy effect of semi-conductivity and valence tautomerization in a photoswitchable coordination polymer

Organic radicals are  widely used as linkers or ligands to synthesize molecular magnetic  materials. However, studies regarding the molecular anisotropies of  radical-based magnetic materials and their multifunctionalities are  rare. Herein, a photoisomerizable diarylethene ligand was used to form  {[Co^III(3,5-DTSQ^·–)(3,5-DTCat^2–)]₂(6F-DAE-py₂)}·3CH₃CN·H₂O (o-1·3CH₃CN·H₂O, 6F-DAE-py₂ = 1,2-bis(2-methyl-5-(4-pyridyl)-3-thienyl)perfluorocyclopentene),  a valence tautomeric (VT) coordination polymer. We directly observed  dual radicals for a single crystal using high-field/-frequency (∼13.3 T  and ∼360 GHz) electron paramagnetic resonance (EPR) spectroscopy along  the c axis, which was further confirmed by angle-dependent  Q-band EPR spectroscopy. Moreover, a conductive anomaly close to the VT  transition temperature was observed only when probes were attached at  the ab plane of the single crystal, indicative of synergy  between valence tautomerism and conductivity. Structural anisotropy  studies and density functional theory (DFT) calculations revealed that  this synergy is due to electron transfer associated with valence  tautomerism. This study presents the first example of dual-radical-based  molecular anisotropy and charge-transfer-induced conductive anisotropy  in a photoswitchable coordination polymer.