A molecular thread for H-shaped [2]rotaxanes is investigated in aqueous environment.

What is it about?

Our attention has been drawn to a recently released aqueous pH and metal-actuated synthetic molecular shuttle in which the reversible coexistence of translational isomers results finely modulated by acidic conditions or by a gradual ratio of Ag+ cations. In more detail, a cucurbit[7]uril (CB[7]) macrocycle on a Tolyl-Viologen-Phenylene-Imidazole (T-VPI) molecular wire - at neutral or acid pH (T-VPI-H+) or even after Ag+ addition (T-VPI-Ag+) - is able to reversibly complex both T and P functional subunits contrary to what had been observed on similar systems in dilute water solution. The results obtained – only considering the investigated systems in their own electronic ground state – provide useful insights on the overall ensemble of supramolecular interactions driving discretional complexations and pH-responsive translational movements in a not-interlocked molecular shuttle.

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Photo by Igor Miske on Unsplash

Photo by Igor Miske on Unsplash

Why is it important?

Our investigation analytically shows - for the first time - that the most prominent signals in the UV-Vis absorption spectra of T-VPI and T-VPI-H+ in water should be ascribed to valence singlet π→π* electronic excitations also showing in some cases a charge-transfer (C-T) character among different functional groups. Also, we observe an intricate balance between electronic properties and solvation dynamics which should plausibly affect complexation pathways along the investigated synthetic threads.

Perspectives