A flexible macrocyclic ligand with two tridentate {CNC} compartments can host two Cu ions in reversibly interconvertible states, CuICuI (1) and mixed-valent Cu1.5Cu1.5 (2). They were characterized by XRD and multiple spectroscopic methods, including EPR, UV-Vis absorption and MCD, in combination with TD-DFT and CASSCF calculations. 2 features a short Cu⋯Cu distance (~2.5 Å; compared to ~4.0 Å in 1) and a very high delocalization energy of 13000 cm-1, comparable to the mixed-valent state of the biological CuA site. Electron self-exchange between 1 and 2 is rapid despite large structural reorganization, and is proposed to proceed via a sequential mechanism involving an active conformer of 1, viz. 1'; the latter has been characterized by XRD. Such electron transfer (ET) process is reminiscent of the conformationally gated ET proposed for biological systems. This redox couple is a unique pair of flexible dicopper complexes, achieving fast electron self-exchange closely related to the function of the CuA site.