Mechanical macrocyclic effects: stimuli-responsive dual emission by self-inclusion and mutual exclusion

A macrocycle divides space into an inside and an outside. This physical boundary allows a guest to reside either within the cavity or outside. When two guests are tethered to one macrocycle, they compete for the same cavity and mutually exclude each other. We exploit this simple principle to design a macrocyclic molecular device with two identical fluorophores. By design, when one fluorophore pendant is sequestered by the nonpolar cavity ("in"), the other is automatically exposed to the polar external environment ("out"), producing two distinct emission bands. This positional asymmetry arises from self-inclusion, mutual exclusion, and rigid-body tilting, all working cooperatively. The resulting dual emission reports the contrasting environments experienced by the two identical fluorophores within the same molecule, with the relative populations of the in- and out-states controlled by conformational switching driven by solvent polarity, temperature, or host-guest interactions.