Guest-Responsive Reversible Electron Transfer in a Crystalline Porous Framework Supported by Dynamic Building Node.

Spatial organization of electron donor-acceptor (D-A) supramolecular assembly is critical to the photophysical processes involved in solar energy conversion systems. Subtle variation in geometry, i.e. D-A distance and transition dipole arrangement can influence kinetics and thermodynamics of the electron transfer (ET) process. To acquire an insight into the structure-function correlation, making of modular, crystalline materials is advantageous. In this regard, we demonstrate a redox-active, crystalline D-A assembly, in which ET process can be reversibly switched. This ET process, induced by a guest-responsive structural transformation at room temperature, is realized in a porous, metal-organic framework (MOF), having anthracene (D) - naphthalenediimide (A) as struts. A control MOF structure obtained by solvent-assisted linker exchange (SALE) method, replacing acceptor strut with a neutral one, supported the switchable electronic states in D-A MOF. Combined investigations with X-ray diffraction, spectroscopic and theoretical analyses revealed the dynamic metal paddle-wheel node as a critical unit for controlling structural flexibility and corresponding unprecedented ET process.