Highly Reversible Electrofluorochromism from Electrochemically Decoupled but Electronically Coupled Molecular Dyads

Although electrofluorochromism enables unique optoelectronic applications, its utility has been limited by poor reversibility. It is demonstrated that high reversibility in electrofluorochromism is obtainable from molecular dyads having a redox-stable acceptor and an aromatic or antiaromatic donor. The structural control aims to generate excited-state conjugation that produces twisted intramolecular charge-transfer fluorescence, while suppressing the ground-state conjugation in order to confine electrochemical processes exclusively within the acceptor unit. Overpotential-free electrofluorochromism can be achieved with a high fatigue resistance against repeated electrochemical cycles. The electrofluorochromism is investigated using structural, spectroscopic, electrochemical, spectroelectrochemical, and quantum chemical techniques. The studies reveal that electrochemical gating of intramolecular charge transfer is the key mechanism underlying the improved electrofluorochromism performance. The study will provide novel insights into the future development and applications of electrofluorochromic devices.