Off-Equilibrium Speed Control of a Multistage Molecular Rotor: 2-Fold Chemical Fueling by Acid or Silver(I)

Driving conformational motion in defined off-equilibrium oscillations can be achieved using chemical fuels. When the ultrafast turnstile 1 (k(298)> 10(12) Hz) was fueled with 2-cyano-2-phenylpropanoic acid (Fuel 1), the diprotonated rotor [H-2(1)](2+) (k(298) = 84.0 kHz) formed as a transient regaining the dynamics of the initial turnstile after consumption of the fuel (135 min). Upon addition of silver(I) (Fuel 2) to turnstile 1, the metastable rotor [Ag-2(1)](2+) (k(298) = 1.57 Hz) was initially furnished, but due to a consequentially triggered S(N)2 reaction, the Ag+ ions were consumed as insoluble AgBr along with regeneration of 1 (within 3 h). The off-equilibrium fast reversible arrow slow rotor conversions fueled by acid and silver(I) were directly monitored by fluorescence and H-1 NMR. In addition, metal ion exchange was fueled enabling off-equilibrium oscillations between rotors [Li-2(1)](2+) reversible arrow [Ag-2(1)](2+). In the end, both sustainability and efficiency of the process were increased in unison by using the interfering proton waste in the formation of a [2]pseudorotaxane.

Automated summary

The study demonstrates that driving conformational motion in defined off-equilibrium oscillations can be achieved using chemical fuels. Different rotors can be formed in ultrafast timescales by adding different fuels to the turnstile, and rotor conversions can be facilitated by consequentially triggered reactions, which can be monitored by fluorescence and NMR techniques. Additionally, metal ion exchange can be fueled to enable off-equilibrium oscillations between different rotors, ultimately increasing sustainability and efficiency of the process.