The construction of sophisticated molecular machines requires not only precise control of energy fueled motions but their integration into larger functional architectures. Macrocyclization of molecular motors is a way to harness the intrinsic directionality of their rotation and use them to actively power different processes at the nano-scale. An effective concept in this regard uses a defined fragment of the molecular motor as a revolving door within the macrocycle. In this way, motor motions can be transmitted to distant structural entities, other rotations can be actively accelerated, or mechanical molecular threading events can be realized. In this work, a dual macrocyclization approach is presented, which not only allows to supersize the revolving door element but also structurally reconfigure the macrocycle in which the revolving door rotates. Unique possibilities for a multi-level precision control over integrated directional motions are thus opened up without deteriorating the functionality of the molecular machine.

Light driven synthetic molecular motors represent crucial building blocks for advanced molecular machines and their applications. A standing challenge is the development of very fast molecular motors able to perform rotations with kHz, MHz or even faster frequencies. Central to this challenge is the direct experimental evidence of directionality because analytical methods able to follow very fast motions rarely deliver precise geometrical insights. Here, a general photochemical method for elucidation of directional motions is presented. In a macrocyclization approach the molecular motor rotations are restricted and forced to proceed in two separate ~180° rotation-photoequilibria. Therefore, all four possible photoinduced rotation steps (clockwise and counterclockwise directions) can be quantified. Comparison of the corresponding quantum yields to the unrestricted motor delivers direct evidence for unidirectionality. This method can be used for any ultrafast molecular motor even in cases where no high energy intermediates are present during the rotation cycle.