A tunable charge-transfer-state rotaxane gated by solvent, anions, and aggregation

Precise multi-stimuli regulation of intramolecular charge-transfer (CT) states in mechanically interlocked systems is challenging due to the complexities of synergistic control and unresolved ultrafast dynamics. We report a triple-stimuli strategy to modulate CT states in a [3]rotaxane by controlling solvent polarity, anion-induced macrocycle translocation, and aggregation, thereby regulating the vibrational freedom of the central 9,10-distyrylanthracene (DSA) chromophore. Spectroscopy studies show that increased solvent polarity shortens the CT-state lifetime and enhances non-radiative decay, thereby quenching fluorescence. In contrast, aggregation induces a blue-shift in emission, enhances intensity, and prolongs the CT-state lifetime, consistent with aggregation-induced emission (AIE). Anion binding triggers macrocycle movement, releasing steric constraints to tune the lifetime to an intermediate value. This work elucidates a supramolecular steric-electronic regulatory mechanism and offers design principles for stimuli-responsive optical materials.