Abstract
Metal complexes containing coordination bonds play a prominent role in many essential biological systems in living organisms. Examples of such complexes include hemoglobin containing iron, chlorophyll containing magnesium, and vitamin B-12 containing cobalt. Although the thermodynamic and other collective properties of metal complexes are well established, their mechanical stability remains minimally explored. Single-molecule force spectroscopy has been used to determine the structural and mechanical properties of chemical bonds; however, it has been minimally utilized in the field of coordination chemistry. Thus, here, we select a unique molecule of interest, HA-Ru-II, {HA = hyaluronan and Ru-II = [(bpy)(2)Ru(4-pyNH(2))(2)](PF6)(2)} and subject it to single-molecule force spectroscopy analysis to directly study its bond-rupture process. The molecule is excited by blue-light irradiation, and surprisingly, this whole process could be reversed without applying any external energy, such as heat or solvent exposure. Our results demonstrate the reversibility of the luminescent Ru-II complex to its original state, a phenomenon that can be further applied to other coordination compounds.