Theoretical investigation on rotaxanes containing a pyridyl-acyl hydrazone moiety: chemical Z → E and photochemical E → Z isomerizations

A theoretical calculation toward efficient control of a molecular shuttle of directional chemical Z -> E and photochemical E -> Z isomerization is reported. The fully optimized geometric structures are evaluated using five different functionals and are compared with the corresponding X-ray crystal structures. Frequency analysis is conducted on the basis of the optimized geometries to find the most stable state. The graphical user interface of the free molecular program VMD combined with the Multiwfn program is used to visualize the noncovalent interactions of the molecular shuttle. The time-dependent functional theory is used to calculate the ultraviolet absorption spectra of different isomers, excitation energies, and absorption wavelengths and then visualized them by a multifunctional wavefunction analyzer. The donor-acceptor interactions between the macrocycle and thread that constitute the molecular shuttle are probed through natural bond orbital calculations, and the transition state of the rotaxanes is calculated at the B3LYP-D3/6-311G(d,p) level. These calculations support the experimental observations of a large population ratio for Z ⇆ E.