Redox-triggered reversible modulation of intense near-infrared and visible absorption using a paddlewheel-type diruthenium(III) complex.

A new paddlewheel-type diruthenium complex with 2-amino-3-(trifluoromethyl)pyridine (amtfmp) [Ru2(amtfmp)4Cl2] ([1]), which shows intense and characteristic near-infrared (NIR) and visible absorption, has been developed and structurally characterized by single crystal X-ray diffraction (SCXRD) analyses. This complex exhibits reversible and dramatic NIR and visible electrochromic behavior from deep-blue ([1]) to pink ([1]−) due to the ON–OFF switching of its characteristic ligand-to-metal charge transfer (LMCT) and d–d absorption bands in response to an external voltage or chemical reagent such as decamethylcobaltocene (CoCp*2). The one-electron reduced species of [1], i.e., [CoCp*2][1], was successfully isolated and fully characterized via SCXRD, the temperature dependence of the magnetic susceptibility, and mass spectroscopy, proving that this electrochromic behavior occurs without significant structural reorganization of [1].