UV-vis absorption spectroscopy was used to monitor the isomerization
processes for the three different diastereomers of Zn3 (Figure
4A–C). Irradiation of solutions containing either one of the isomers ofZn3 with UV light (λmax = 365 nm) to the
photostationary state (PSS) resulted in an increase in absorption around
λ = 460 nm, and a concomitant decrease in absorption around λ = 380 nm.
The thermal helix inversion (THI) of the metastable motors to the stable
motors restored the original UV-vis spectra. The processes of
photochemical isomerization and subsequent thermal helix inversion were
monitored at five different temperatures. The Eyring equation was used
to determine the activation parameters for the thermal helix inversion
steps (Table 2, Supporting Information, Figure S39, Table S20). UV-vis
absorption spectroscopy did not allow the determination of the rate
constants for the THI step of each individual motor moiety attached to
the host, i.e. the reported k THI-values
are apparent values (See Supporting Information, Equations 7–38).
Nevertheless, double-motorized isomers Zn3a (two loose motors)
and Zn3c (two bound motors) rotate with similar rates as the
corresponding single-motorized isomers Zn2a (one loose motor)
and Zn2b (one bound motor), respectively. Furthermore, the
apparent rotation rate of the non-symmetric isomer Zn3b is in
between the rotation rates of the other two diastereomers Zn3aand Zn3c . UV-vis absorption spectroscopy