Control of translational and rotational movement at nanoscale
Stacko, Peter
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Publication date: 2017
Link to publication in University of Groningen/UMCG research database
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Stacko, P. (2017). Control of translational and rotational movement at nanoscale. University of Groningen.
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English Summary
The goal of this thesis was to develop and investigate photochemically driven molecular motors with the idea of harnessing the unidirectional motion in a more advanced machinery.
Chapter 1 briefly describes the importance and examples of molecular motors, starting from installments in biological settings, continuing with chemically and electrochemically powered motors, finally concluding with photochemically driven unidirectional motors. The most recent examples of applications of such molecular motors in materials and more advanced machines are presented. Chapter 2 focuses on preparation of photochemically driven molecular dragsters for the purpose of directional movement on surfaces and potential cargo release (Figure 8.1). The two motor units embedded in the carbazole part act as wheels rotating in the same direction from the external observer point of view facilitating directional movement. The molecules were shown that the rotary movement is preserved in a solution, however, no movement on a surface has been observed so far.
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Chapter 3 discusses quaternarization of the stereogenic centre of the second generation motors with a fluorine atom (Figure 8.2). A large increase in the barrier
for the thermal helix inversion has been observed (20‒25 kJ.mol-1) in all cases. The
unidirectional motor function was shown to be fully preserved providing a motor with sufficiently low steric hindrance in the fjord region was used as a starting scaffold for derivatization.
Figure 8.2. Derivatives with quaternary stereogenic centre.
Chapter 4 introduces a novel class of achiral autonomous unidirectional molecular motors (Figure 8.3). The pseudoasymmetric center installed in the core of the molecule ensures sufficient bias required for unidirectionality of the photochemical driven rotary movement. The synthesis and photochemical studies of the molecules are included. This case demonstrates that a chiral element is not required for autonomous directionality.
In chapter 5, a concept of “tidal-locking” of a naphthyl unit is described (Scheme 8.4). The naphthyl unit precesses around rotating molecular motor in a synchronous fashion resulting in the same face of the naphthalene always facing the motor during the rotation of the molecular motor. This demonstrates that the rotational behavior of the molecular motor can be further expanded to influence systems coupled to the motor, thus opening additional venues for more elaborate molecular machinery
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Figure 8.3. Third generation molecular motor.
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Scheme 8.4. Molecular motor featuring a tidally-locked naphthyl unit.
Chapter 6 describes preparation of a series of bisthioxanthylidene based amphiphiles (Scheme 8.5). The study examines influence of various hydrophilic
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and lipophilic tails, and polar groups on the ability to self-assembly into uniform long nanotubes. It has been shown that the self-assembly process remains undisturbed in most cases, moreover the ability to undergo photochemical disassembly is also preserved. Other applications, such as osmosis induced loading of vesicles into the nanotubes, photocontrol of surface pressure and chiral amplification using chiral amphiphiles are also presented.
Scheme 8.5. Various derivatives of photoresponsive amphiphile.
Chapter 7 investigates the influence of solvent viscosity on the dynamics of the singlet excited state of molecular motors. A homologous series with increasing lengths of the arms has been prepared and studied by transient absorption spectroscopy (Figure 8.6). It was anticipated that increase in the length of the arms would translate into increased interaction with the solvent, thereby affecting the dynamics of the excited state. Unfortunately, no influence of the increasing arm size on the dynamics of the excited state was observed, besides from the initial change upon introduction of the substituents.
