Reversible Bond/Cation-Coupled Electron Transfer on Phenylenediamine-Based Rhodamine B and Its Application on Electrochromism

A biomimetic system on reversible bond-coupled electron transfer (BCET) has been proposed and investigated in a switchable Rh–N molecule with redox active subunits. We discover that energy barrier of C–N bond breaking is reduced dramatically to less than 1/7 (from 40.4 to 5.5 kcal/mol), and 1/3 of the oxidation potential is simultaneously lowered (from 0.67 to 0.43 V) with the oxidation of Rh–N. The concept, cation-coupled electron transfer (CCET), is highly recommended by analyzing existing proton coupled electron transfer (PCET) and metal coupled electron transfer (MCET) along with aforementioned BCET, which have same characteristic of transferring positive charges, such as proton, metal ion, and organic cation. Molecular switch can be controlled directly by electricity through BCET process. Solid electrochromic device was fabricated with extremely high coloration efficiency (720 cm2/C), great reversibility (no degradation for 600 cycles), and quick respond time (30 ms).