Photomodulation of Charge Transfer through Excited‐State Processes: Directing Donor‐Acceptor Binding Dynamics

Modulating charge transfer (CT) interactions between donor and acceptor molecules may give rise to unique dynamic changes in physicochemical properties, exhibiting great importance in supramolecular chemistry and materials science. In this work, we demonstrate the first instance of reversible photomodulation of donor-acceptor (D-A) CT interaction in the solid state. Pyridinium-based chromophore featuring π-conjugated D-A structures can not only function as a good electron acceptor to undergo photoinduced electron transfer (ET) or engage in intermolecular CT interaction, but also exhibit unique dual emission depending on the excitation wavelengths. The rotatable C-C single bonds within D-A pairs enhance the tunability of molecular structure. Through the synergy of a photoinduced ET and an excited-state conformational change, the intermolecular CT interaction can be switched on and off by alternate light irradiation to enable reversibly modulation of the affinity between donor and acceptor molecules, accompanied by visual color switching and fluorescence on-off as feedback signals.