Molecular Motors for Surface Applications

Project Information

MMSA

Grant agreement ID: 793082

DOI

10.3030/793082

Project closed

EC signature date 9 March 2018

Start date 1 April 2018

End date 31 March 2020

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 165 598,80

EU contribution

€ 165 598,80

Coordinated by

RIJKSUNIVERSITEIT GRONINGEN
Netherlands

Periodic Reporting for period 1 - MMSA (Molecular Motors for Surface Applications)

Reporting period: 2018-04-01 to 2020-03-31

Summary of the context and overall objectives of the project

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.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Over the course of this action, several new molecular motors driven by visible as well as near-infrared light have been developed.
Our first paper on molecular motors functionalized with both electron donating as well as withdrawing substituents, so-called push-pull motors, was published in Chemical Science, in 2019. This kind of substitution pattern was found to red-shift the absorption spectrum of molecular motors and the most red-shifted example in this paper could be operated with light up to 530 nm, the longest wavelength to directly excite a molecular motor at the point of publication. A follow-up paper describing a push-pull motor showing the highly unusual behaviour of functioning both as a unidirectional motor as well as a switch depending on the experimental conditions is currently being prepared.
This kind of substituted molecular motor also formed the basis for our first design of a near-infrared light-driven compound where the motor component was covalently bound to a separate two-photon absorption dye. Upon irradiation with 780 nm light, the dye gets excited initially before transferring the energy to the motor unit which subsequently undergoes rotation. A manuscript describing our results is currently under review in Science Advances. A significantly simplified system, not requiring a separate dye to absorb the incident near-infrared light while preserving the high sensitivity towards two-photon absorption has also been developed with the manuscript being prepared for submission at the moment.
In a separate attempt, Pd complexation was explored as a means for red-shifting the absorption spectrum of a bis-phosphine substituted molecular motor. The absorption spectrum of the studied compound was indeed shifted to longer wavelengths upon complexation of Pd but it was furthermore found that the Pd complex is undergoing coupled motion of the motor backbone and the Pd centre following excitation. This was a highly unexpected result which warranted further study and a publication disclosing our findings is currently being prepared.
Finally, a third approach using energy transfer from near-infrared light sensitive upconverting nanoparticles to a molecular motor ligand was explored. Both the molecular motor and a batch of the required nanoparticles were prepared but due to time constraints the binding of the motor to these nanoparticles as well as the energy transfer could not be studied so far.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The development of the first artificial rotary molecular motors which can be efficiently operated using near-infrared light represents a significant step beyond the state of the art prior to the onset of this action. Furthermore, our unexpected discovery of a molecule whose mode of operation can be altered between that of a unidirectional motor and a switch is, to the best of our knowledge, in this form unprecedented and marks an exciting step forward. Finally, our novel example of a molecule displaying light-triggered coupled motion was an exciting discovery due to the limited precedent for molecules displaying similar behaviour.
The impact of this action on the scientific community is therefore significant, given its two-year duration. The obtained results are set to be the basis for exciting future research in the host group but also in the wider community, opening up new avenues for the design and application of molecular machines. Especially our newly developed strategies for obtaining near-infrared light sensitive motors will form a basis for the development of molecular motors suitable for in vivo applications. Coupled motion is a central aspect for the creation of more advanced molecular machines, and our new compound displaying this kind of behaviour which can furthermore be conveniently operated using visible light is an ideal candidate to apply in future studies towards this goal. Finally, being able to switch the mode of operation of a nanoscale light-driven machine by alternating its environment is an interesting basis for the creation of materials whose properties can be controlled by multiple orthogonal stimuli.
Society at large benefits from this action due to the advancement of fundamental research into molecular machines which hold great promise for future applications in smart materials, drug delivery and information storage. Especially in vivo applications are set to profit significantly from our studies into near-infrared light-driven motors due to the benign nature and improved penetration depth of near-infrared light compared to UV and visible light.

Impact of this action on the state of the art.