Fig. 1

Chiral substrate induced unidirectional rotation in a photoswitchable receptor. a Scheme of photochemical and thermal isomerization steps showing that when starting from the planar (E)-isomer, e.g. bis-thiourea receptor (E)-2, irradiation with light produces a racemic mixture of helical (P)-(Z)-2 and (M)-(Z)-2. Binding of a chiral guest molecule to the receptor, e.g. phosphate (S)-3 favours formation of one of these helical (Z)-isomers. As a consequence, the backward photochemical isomerisation process, affording the (E)-isomer, takes place predominantly from the most favoured (Z)-isomer, i.e. (P)-(Z)-2@(S)-3 resulting in a net unidirectional rotation. b Illustrative energy profile describing a full rotation. Note that (P)-(Z)-2 and (M)-(Z)-2 are produced with equal probability and that only formation of the first isomer gives rise to a rotation, while formation of the latter results in an oscillation