Aphj Albert Schenning

Fluorescent Nanoparticles Based on Self‐Assembled π‐Conjugated Systems

pi-Conjugated molecules are interesting components to prepare fluorescent nanoparticles. From the use of polymer chains that form small aggregates in water to the self-assembly of small chromophoric segments into highly ordered structures, the preparation of these materials allows to develop systems with applications as sensors or biolabels. The potential functionalization of the nanoparticles can lead to specific probing. This progress report describes the recent advances in the preparation of such emittive organic nanoparticles.

Chiral-nematic liquid crystals as one dimensional photonic materials in optical sensors

Current developments in the field of thermotropic chiral-nematic liquid crystals as sensors are discussed. These one dimensional photonic materials are based on low molecular weight liquid crystals and chiral-nematic polymeric networks. For both low molecular weight LCs and polymer networks, real-time and time integrating sensors have been realized. The response mechanism is either based on a change of helical twisting power of the dopant upon exposure to an analyte, or due to physical swelling, with a change of order in the liquid crystalline phase upon uptake of the analyte, causing the pitch to change. Sensors that respond to organic and water vapour, amines, water CO2, O2, metal ions, pH, strain and temperature have been reported.

Self-Assembled Fluorescent Nanoparticles from π-Conjugated Small Molecules: En Route to Biological Applications

Since the development of supramolecular chemical biology, self-organised nano-architectures have been widely explored in a variety of biomedical applications. Functionalized synthetic molecules with the ability of non-covalent assembly in an aqueous environment are typically able to interact with biological systems and are therefore especially interesting for their use in theranostics. Nanostructures based on π-conjugated oligomers are particularly promising as theranostic platforms as they bear outstanding photophysical properties as well as drug loading capabilities. This Feature Article provides an overview on the recent advances in the self-assembly of intrinsically fluorescent nanoparticles from π-conjugated small molecules such as fluorene or perylene based chromophores for biomedical applications.

Self-assembled fluorescent organic nanoparticles for live cell imaging

Fluorescent, cell-permeable, organic nanoparticles based on self-assembled π-conjugated oligomers with high absorption cross-sections and high quantum yields have been developed. The nanoparticles are generated with a tuneable density of amino groups for charge-mediated cellular uptake by a straightforward self-assembly protocol, which allows for control over size and toxicity. The results show that a single amino group per ten oligomers is sufficient to achieve cellular uptake. The non-toxic nanoparticles are suitable for both one- and two-photon cellular imaging and flow cytometry, and undergo very efficient cellular uptake.

Superior alignment of multi-chromophoric perylenebisimides in nematic liquid crystals and their application in switchable optical waveguides

Linking monomeric perylenebisimide units to form dimers and trimers dramatically increased alignment in a nematic liquid crystalline host. Connecting units via flexible cross-linkers destroyed alignment: a rigid linker is necessary. Applying the fluorescent trimer dye in a switchable window greatly improved the contrast ratio between the ‘on’ and ‘off’ states of this energy generating device.

Light-Responsive Hierarchically Structured Liquid Crystal Polymer Networks for Harnessing Cell Adhesion and Migration

Extracellular microenvironment is highly dynamic where spatiotemporal regulation of cell-instructive cues such as matrix topography tightly regulates cellular behavior. Recapitulating dynamic changes in stimuli-responsive materials has become an important strategy in regenerative medicine to generate biomaterials which closely mimic the natural microenvironment. Here, light responsive liquid crystal polymer networks are used for their adaptive and programmable nature to form hybrid surfaces presenting micrometer scale topographical cues and changes in nanoscale roughness at the same time to direct cell migration. This study shows that the cell speed and migration patterns are strongly dependent on the height of the (light-responsive) micrometer scale topographies and differences in surface nanoroughness. Furthermore, switching cell migration patterns upon in situ temporal changes in surface nanoroughness, points out the ability to dynamically control cell behavior on these surfaces. Finally, the possibility is shown to form photoswitchable topographies, appealing for future studies where topographies can be rendered reversible on demand.

Directed self-assembly of liquid-crystalline molecular building blocks for sub-5 nm nanopatterning

The thin-film directed self-assembly of molecular building blocks into oriented nanostructure arrays enables next-generation lithography at the sub-5 nm scale. Currently, the fabrication of inorganic arrays from molecular building blocks is restricted by the limited long-range order and orientation of the materials, as well as suitable methodologies for creating lithographic templates at sub-5 nm dimensions. In recent years, higher-order liquid crystals have emerged as functional thin films for organic electronics, nanoporous membranes, and templated synthesis, which provide opportunities for their use as lithographic templates. By choosing examples from these fields, recent progress toward the design of molecular building blocks is highlighted, with an emphasis on liquid crystals, to access sub-5 nm features, their directed self-assembly into oriented thin films, and, importantly, the fabrication of inorganic arrays. Finally, future challenges regarding sub-5 nm patterning with liquid crystals are discussed.

Towards racemizable chiral organogelators

Summary A chiral organogelator has been synthesized that can be racemized and self-assembled in apolar solvents whilst at higher concentrations organogels are formed. Field emission scanning and transmission electron microscopy revealed the formation of bundle fibrils that are able to gelate the solvent. 1H NMR studies showed hydrogen-bond interactions between the peptide head groups of neighbouring organogelator molecules. The enantiomerically pure organogelator can be racemized by the base DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) as was evident from chiral high-performance liquid chromatography analysis.

Photonic shape memory polymer with stable multiple colors

A photonic shape memory polymer film that shows large color response (∼155 nm) in a wide temperature range has been fabricated from a semi-interpenetrating network of a cholesteric polymer and poly(benzyl acrylate). The large color response is achieved by mechanical embossing of the photonic film above its broad glass transition temperature. The embossed film, as it recovers to its original shape on heating through the broad thermal transition, exhibits multiple structural colors ranging from blue to orange. The relaxation behavior of the embossed film can be fully described using a Kelvin–Voigt model, which reveals that the influence of temperature on the generation of colors is much stronger than that of time, thereby producing stable multiple colors.

Stimuli-responsive liquid crystalline materials

Stimuli-responsive materials which respond to triggers from the environment by changing their properties are one of the focal points in materials science. For precise functional properties, well-defined hierarchically ordered supramolecular materials are crucial. The self-assembly of liquid crystals has proven to be an extremely useful tool in the development of well-defined nanostructured materials. Liquid crystalline materials are appealing for making responsive materials since microscopic changes in the molecular order and orientation can lead to macroscopic changes in shape, optical properties, or porosity. By using photopolymerizable liquid crystals a wide variety of stimuli-responsive materials can be made from a relatively simple set of building blocks. Upon mixing different (reactive) mesogens, nematic, chiral nematic, and smectic liquid crystalline phases can be formed that can be applied as soft actuators, responsive optical materials and tunable nanoporous materials, respectively.