Overcrowded alkene-based artificial rotary molecular motors are one of the most exciting developments of the past two decades in the field of chemistry. This special class of functional molecules is able to undergo unidirectional rotation initiated by the absorption of light. The unidirectional nature of this movement allows these molecules to carry out work in a progressive manner, setting them apart from the more commonly known photochemical switches. For this reason, there is a major interest in employing these compounds for the development of new smart materials whose properties can be controlled by light. However, molecular motors reported previously had to be operated using high energy UV or blue light which is not compatible with most envisioned applications, especially with regard to applications in vivo.
The goal of this action was, therefore, to develop the first examples of artificial molecular motors which could be efficiently driven using low energy near-infrared light. Light from this part of the electromagnetic spectrum does not lead to the tissue damages commonly observed with UV and blue light and penetrates deeper into tissue and soft materials. These two properties are critical for the realization of novel applications of molecular motors in the fields of smart materials, drug delivery and information storage. Upon successful development of a near-infrared light-driven motor, the next goal was to bind the individual molecules to different surfaces to study the operation of individual molecules as well as monolayers of these molecules. Such monolayers would then be used to develop a “molecular crowd surfer” as well as study the influence of a dynamic surface on the adhesion, spreading and migration behaviour of rat mesenchymal stem cells.
Over the past two years we have successfully designed, synthesized and studied a range of novel visible as well as near-infrared light-driven overcrowded alkene-based artificial rotary molecular motors. Among visible light sensitive compounds are motors which can be powered not with blue but lower energy green and even orange light. Furthermore, two concepts for the design of near-infrared light sensitive motors using the principle of two-photon absorption were studied. Our studies also led to the unexpected discovery of a molecule which can behave both as a unidirectional motor as well as a switch depending on the experimental conditions. To the best of our knowledge, this is the first example of its kind. Finally, a Pd complex showing light-triggered coupled motion was discovered, also marking an exciting, unforeseen finding. In total, this work is going to lead to the publication of five major papers. However, due to the aforementioned unpredicted discoveries warranting further study, the remaining scientific objectives laid out in the original proposal could not be addressed during the runtime of this action.
