Figure 5.

Isomerization properties of the sequential photoswitch 1. (a) Comprehensive scheme showing the selective and sequential switching behavior of HTI 1. The nature of individual transformations are assigned. (b) Repetitive reversible switching cycles of racemic HTI 1. The depicted steps represent a complete rac-B → rac-D → rac-C → rac-A cycle but without monitoring the photoreaction from rac-B to rac-D (up to 48% formed in the bulk transformation in MeCN-d₃ and up to 80% formed in MeOH) followed by the thermal reaction to rac-C individually (up to 33% formed in the bulk transformation in MeCN-d₃). Minimal loss of performance is observed after 10 full cycles. Refocusing occurs by the same enrichment of isomer rac-A. (c) Propensity for eight- (green trace) or five-step (red trace) sequential switching cycles depending on the ratio of Hula-Twist (x-axis) versus DSBR (black trace) photoreactions of isomers B/B′. (d) Schematic representation of a molecular motor mechanism as opposed to the herein presented sequential switch mechanism.