Kinetic analysis of the thermal isomerisation pathways in an asymmetric double azobenzene switch

Here we report a photochemical and kinetic study of the thermal relaxation reaction of a double azobenzene system, in which two azobenzene photochromic units are connected via a phenyl ring. Upon UV irradiation, three thermally unstable isomers are formed. Kinetic studies using arrayed H-1-NMR spectroscopy revealed four distinct barriers for the thermal reversion to the stable isomer. The double isomerised Z,Z-2 can revert thermally to the E,E-2 isomer via either of two isomerisation pathways. The thermal Z to E isomerisations are not significantly affected by the state of the neighbouring azo-switching unit in the meta position. These findings are supported by quantum chemical calculations on the thermal Z to E isomerisation

Photochromic molecular switches: based on azaobenzenes, dithienylethenes and hemithioindigos

Moleculaire schakelaars werken in principe net zoals een gewone schakelaar, dwz. dat ze de mogelijkheid geven om tussen twee standen te schakelen, bijvoorbeeld uit en aan of stand A en B. Vaak worden deze schakelaars bediend met de hand. Er zijn echter ook lichtgevoelige schakelaars. De schakelaars beschreven in dit proefschrift zijn gebaseerd op moleculen die worden geschakeld met behulp van licht. De energie die licht bevat wordt gebruikt om de vorm van het molecuul te veranderen van A naar B. Deze verandering wordt een isomerisatie genoemd. Over het algemeen wordt ultraviolet (UV) licht gebruikt voor de energetisch bergopwaartse isomerisatie (van stand A naar stand B), omdat UV licht veel energie bevat. Zichtbaar licht wordt gebruikt om de moleculen terug te schakelen van B naar A, energetisch bergafwaarts. Als Nano -technologie meer toegepast wordt in het dagelijks leven, moet ons begrip van dergelijke systemen moet worden uitgebreid. In dit proefschrift wordt de moleculaire gereedschapskist die we gebruiken om dergelijke Nano systemen te ontwerpen en te fabriceren uitgebreid. De fotochemische, thermische en elektrochemische gedrag van verschillende nieuwe moleculaire schakelaars wordt hier gepresenteerd. Het ontwerp van deze fotoschakelaars zijn gebaseerd op azobenzeen, dithienylethene en hemithioindigo structuren. Daarnaast, wordt het ontwerp van een nieuwe fluorescente sonde voor het visualiseren van nanodeeltjes in zoogdiercellen beschreven. Dergelijke deeltjes kunnen gewoonlijk alleen worden gevisualiseerd met behulp van elektronenmicroscopie, deze techniek is duur en niet geschikt levende cellen te visualiseren. Deze nieuwe sonde moet het mogelijk maken om Nano deeltjes observeren met optische microscopie

Dynamic control over cell adhesive properties using molecular-based surface engineering strategies

In complex organisms, cells are often dependent on their extracellular matrix (ECM) for structural integrity, the mechanical properties of tissues, and for signaled regulation of cellular processes including adhesion, migration, growth, secretion, gene expression and apoptosis. Achieving dynamic control, i.e. by using an external stimulus, over the interactions between cells and artificial interfaces holds considerable promise in tissue engineering, medicine, cell biology and immunology. For example, improved spatial control over cell–surface interaction is potentially useful in the design of cell-based screening devices. Dynamic control over SAMs for cell adhesion provides an additional handle to direct and study the attachment of cells to surfaces, e.g., in studying cell spreading from a predetermined pattern in order to screen the cytotoxicity of drug candidates. However, ‘reversible’ control of cell adhesion onto substrates is an area that is still in its infancy. In this critical review recent developments in cell adhesion of mammalian cells to SAM-modified surfaces, the physical properties of which can be controlled by an external stimulus, e.g. by light, electrochemistry, etc., are discussed.

Mild Ti-mediated transformation of t-butyl thio-ethers into thio-acetates

We report a straightforward method for the rapid conversion of thio-ethers to thio-acetates using TiCl4, in good to excellent yields. The reaction conditions tolerate a variety of functional groups, including halide, nitro, ether, thiophene and acetylene functionalities. A catalytic variant of this reaction is also described

Molecular Stirrers in Action

A series of first-generation light-driven molecular motors with rigid substituents of varying length was synthesized to act as "molecular stirrers". Their rotary motion was studied by H-1 NMR and UV-vis absorption spectroscopy in a variety of solvents with different polarity and viscosity. Quantitative analyses of kinetic and thermodynamic parameters show that the rotary speed is affected by the rigidity of the substituents and the length of the rigid substituents and that the differences in speed are governed by entropy effects. Most pronounced is the effect of solvent viscosity on the rotary motion when long, rigid substituents are present. The alpha values obtained by the free volume model, supported by DFT calculations, demonstrate that during the rotary process of the motor, as the rigid substituent becomes longer, an increased rearranging volume is needed, which leads to enhanced solvent displacement and retardation of the motor

Molecular Stirrers in Action

A series of first-generation light-driven molecular motors with rigid substituents of varying length was synthesized to act as “molecular stirrers”. Their rotary motion was studied by ¹H NMR and UV–vis absorption spectroscopy in a variety of solvents with different polarity and viscosity. Quantitative analyses of kinetic and thermodynamic parameters show that the rotary speed is affected by the rigidity of the substituents and the length of the rigid substituents and that the differences in speed are governed by entropy effects. Most pronounced is the effect of solvent viscosity on the rotary motion when long, rigid substituents are present. The α values obtained by the <i>free volume</i> model, supported by DFT calculations, demonstrate that during the rotary process of the motor, as the rigid substituent becomes longer, an increased rearranging volume is needed, which leads to enhanced solvent displacement and retardation of the motor

Control of Surface Wettability Using Tripodal Light-Activated Molecular Motors

Monolayers of fluorinated light-driven molecular motors were synthesized and immobilized on gold films in an altitudinal orientation via tripodal stators. In this design the functionalized molecular motors are not interfering and preserve their rotary function on gold. The wettability of the self-assembled monolayers can be modulated by UV irradiation.

Control of Surface Wettability Using Tripodal Light-Activated Molecular Motors

Monolayers of fluorinated light-driven molecular motors were synthesized and immobilized on gold films in an altitudinal orientation <i>via</i> tripodal stators. In this design the functionalized molecular motors are not interfering and preserve their rotary function on gold. The wettability of the self-assembled monolayers can be modulated by UV irradiation