Motor on dating
On the other side of the double bond, the two methyl substituents of the five-membered aliphatic ring are bisected by the carbonyl oxygen atom of the thioindigo fragment.The helical twist is clearly a result of steric repulsion between the substituents on the stilbene and the thioindigo fragment, which leads to a SC=CC(Ar) dihedral angle of 12.8°.Direct assignment of the two separated species to the corresponding diastereomers was straightforward in solution, as NOESY NMR spectra showed specific cross-signals between the thioindigo and the stilbene part of the molecule (Supplementary Figs 6 and 11).In addition, crystal structure analysis unambiguously confirmed our assignment of the species and their solution spectra.2a–c), as well as for both Z and E isomers of the corresponding unoxidized HTI (CCDC 1408096 and CCDC 1408097, see Supplementary Figs 37 and 38 and Supplementary Tables 2 and 3).(a) Crystal structure of racemic Z-(S)-(P)/Z-(R)-(M) isomers, only the Z-(S)-(P) isomer is shown (CCDC 1061969).(b) Crystal structure of racemic E-(S)-(P)/E-(R)-(M) isomers, only the E-(S)-(P) isomer is shown (CCDC 1061970).We were able to grow crystals suitable for structure analysis from the second fraction obtained after chromatographic separation, which could be assigned to the Z-(S)-(P)/Z-(R)-(M) isomers (CCDC 1061969).The H NMR and ultraviolet/visible (ultraviolet/vis) spectra of the same crystal batch were recorded, showing only one single species to be present in solution.
For the following spectroscopic studies however, the racemic mixture was analysed for convenience reasons.We describe here a hemithioindigo-based molecular motor, which is powered exclusively by nondestructive visible light (up to 500 nm) and rotates completely directionally with k Hz frequency at 20 °C.This is the fastest directional motion of a synthetic system driven by visible light to date permitting materials and biocompatible irradiation conditions to establish similarly high speeds as natural molecular motors..When a solution of 1 in xylene-d is heated to 130 °C for 12 h, 73% of the Z-(S)-(P)/Z-(R)-(M) isomers and 27% of the E-(S)-(P)/E-(R)-(M) isomers are obtained (Supplementary Fig. This thermal behaviour translates into an energy difference of 0.81 kcal mol between the Z and E diastereomeric pairs according to the relation of the change of Gibbs free energy and the equilibrium constant–ΔG=RTln K.
First-order kinetic analysis of thermal conversion from the E-(S)-(P)/E-(R)-(M) to the Z-(S)-(P)/Z-(R)-(M) isomers provided an energy barrier of 29.54 kcal mol for the process (Supplementary Fig. With such high thermal stability, that is, a half-life of 16 years for the metastable E-(S)-(P)/E-(R)-(M) isomers at 25 °C, the two Z and E diastereomers could conveniently be separated by conventional chromatography and studied individually.
Brook Crompton has a long history in electric motor development, dating back to 1878.