A Solvent Free Neutral Cobalt Complex Exhibiting Macroscopic Polarization Switching Induced by Directional Charge Transfer

Materials with polarization switching induced by directional charge transfer under the external stimuli are of great interest due to their fast swicthing rate and potential applications. Nonetheless, most of these crystals contain solvents or counter ions, and their effects during measurement or calculations are far from trivial. Therefore, synthesizing a solvent-free and neutral complex exhibiting polarization switching is highly desirable. Herein, we successfully observe directional charge transfer-induced electronic pyroelectricity in a solvent-free neutral cobalt complex, namely Co(teeda)(3,6-dbq)2 (teeda = N,N,N’,N’-tetraethylethane-1,2-diamine and 3,6-dbq = 3,6-di-tert-butylcatecholate or 3,6-di-tert-butylsemiquinonate). The charge transfer property is confirmed by magnetometry, infrared and UV-vis-NIR spectroscopy, and single-crystal X-ray diffraction (SCXRD) measurements. Furthermore, pyroelectric current is observed during the valence tautomerism (VT) process. Theoretical calculations demonstrate that the origin of polarization switching is mainly ascribed to the charge transfer. These results indicate that Co(teeda)(3,6-dbq)2 is a promising candidate for exploring new VT compounds that exhibit polarization switching.