Light-Modulated Self-Blockage of a Urea Binding Site in a Stiff-Stilbene Based Anion Receptor

Anion binding to a receptor based on stiff‐stilbene, which is equipped with a urea hydrogen bond donating group and a phosphate or phosphinate hydrogen bond accepting group, can be controlled by light. In one photoaddressable state (E isomer) the urea binding site is available for binding, while in the other (Z isomer) it is blocked because of an intramolecular interaction with its hydrogen bond accepting motif. This intramolecular interaction is supported by DFT calculations and 1H NMR titrations reveal a significantly lower anion binding strength for the state in which anion binding is blocked. Furthermore, the molecular switching processhas been studied in detail by UV/Vis and NMR spectroscopy. The presented approach opens up new opportunities toward the development of photoresponsive anion receptors.Supramolecular & Biomaterials Chemistr

Photocontrol of Anion Binding Affinity to a Bis-urea Receptor Derived from Stiff-Stilbene

Toward the development of photoresponsive anion receptors, a stiff-stilbene photoswitch has been equipped' with two urea anion -binding motifs. Photoinduced E/Z isomerization has been studied in detail by UV-vis and NMR spectroscopy. Titration experiments (H-1 NMR) reveal strong binding of acetate and phosphate to the (Z)-isomer, in which the urea groups are closely together. Isomerization to the (E)-form separates the urea motifs, resulting in much weaker binding. Additionally, geometry optimizations by density functional theory (DFT) illustrate that oxo-anion binding to the (Z)-form involves four hydrogen bonds

Visible-Light-Driven Tunable Molecular Motors Based on Oxindole

Molecular rotary motors based on oxindole which can be driven by visible light are presented. This novel class of motors can be easily synthesized via a Knoevenagel condensation, and the choice of different upper halves allows for the facile tuning of their rotational speed. The four-step rotational cycle was explored using DFT calculations, and the expected photochemical and thermal isomerization behavior was confirmed by NMR, UV/vis, and CD spectroscopy. These oxindole motors offer attractive prospects for functional materials responsive to light

A chiral self-sorting photoresponsive coordination cage based on overcrowded alkenes

In recent years, increasing efforts have been devoted to designing new functional stimuli-responsive supramolecular assemblies. Here, we present three isomeric supramolecular coordination complexes consisting of a Pd2L4 stoichiometry. As shown by NMR, CD and X-ray studies, as well as DFT calculations, these complexes form cage-like structures by chiral self-sorting. Photochromic ligands derived from first generation molecular motors enable light-driven interconversion between the three isomers. Two of the isomers were able to form host–guest complexes opening up new prospects toward stimuli-controlled substrate binding and release.Supramolecular & Biomaterials Chemistr

Controlled Diffusion of Photoswitchable Receptors by Binding Anti-electrostatic Hydrogen-Bonded Phosphate Oligomers

Dihydrogen phosphate anions are found to spontaneously associate into anti-electrostatic oligomers via hydrogen bonding interactions at millimolar concentrations in DMSO. Diffusion NMR measurements supported formation of these oligomers, which can be bound by photoswitchable anion receptors to form large bridged assemblies of approximately three times the volume of the unbound receptor. Photoisomerization of the oligomer-bound receptor causes a decrease in diffusion coefficient of up to 16%, corresponding to a 70% increase in effective volume. This new approach to external control of diffusion opens prospects in controlling molecular transport using light

Tuning of Morphology by Chirality in Self-Assembled Structures of Bis(Urea) Amphiphiles in Water

We present the synthesis and self-assembly of a chiral bis(urea) amphiphile and show that chirality offers a remarkable level of control towards different morphologies. Upon self-assembly in water, the molecular-scale chiral information is translated to the mesoscopic level. Both enantiomers of the amphiphile self-assemble into chiral twisted ribbons with opposite handedness, as supported by Cryo-TEM and circular dichroism (CD) measurements. The system presents thermo-responsive aggregation behavior and combined transmittance measurements, temperature-dependent UV, CD, TEM, and micro-differential scanning calorimetry (DSC) show that a ribbon-to-vesicles transition occurs upon heating. Remarkably, chirality allows easy control of morphology as the self-assembly into distinct aggregates can be tuned by varying the enantiomeric excess of the amphiphile, giving access to flat sheets, helical ribbons, and twisted ribbons.</p

Salen-Based Amphiphiles:Directing Self-Assembly in Water by Metal Complexation

Tuning morphologies of self‐assembled structures in water is a major challenge. Herein we present a salen‐based amphiphile which, using complexation with distinct transition metal ions, allows to control effectively the self‐assembly morphology in water, as observed by Cryo‐TEM and confirmed by DLS measurements. Applying this strategy with various metal ions gives a broad spectrum of self‐assembled structures starting from the same amphiphilic ligand (from cubic structures to vesicles and micelles). Thermogravimetric analysis and electric conductivity measurements reveal a key role for water coordination apparently being responsible for the distinct assembly behavior.Supramolecular & Biomaterials Chemistr

Designing dynamic functional molecular systems

The design and construction of dynamic functional molecular systems, which mimic some of the properties of living systems, pose a huge contemporary challenge. Recent developments in supramo-lecular self-assembly, molecular switches, motors and machines, and chemical reaction networks, offer an excellent basis for integrating dynamic properties in molecular systems. In this perspective, we discuss different approaches towards dynamic functional molecular systems covering areas such as translated motion, dissipative self-assembly, self-regulation and biohybrid systems. The selected examples illustrate the level of control and complexity that can be achieved at present in this rapidly growing and exciting field of research. (C) 2017 Published by Elsevier Ltd.</p