Adaptable and Reprogrammable Surfaces

Polystyrene Brush Evolution by Grafting to Reaction on Deglazed and Not-Deglazed Silicon Substrates

Two model substrates for the grafting to reaction are considered: not-deglazed silicon, whose surface is coated by a thin oxide layer with reactive silanol groups on its surface; and deglazed silicon, where the oxide layer is removed by treatment with hydrofluoric acid. The reactive polymers are hydroxy-terminated polystyrenes with molecular weights ranging from 3.9 to 13.9 kg mol⁻1. The grafting to reaction is carried out at different temperatures and for different periods of time on the two different substrates. The thickness and the thermal stability of the resulting brushes are evaluated. Furthermore, the grafting of a highly dispersed system is simulated by blending two polymers with different molecular weights. Although the brush thickness growth is found to be faster on deglazed silicon, the preferential grafting of short chains occurs with equal chain selection propensity on both substrates.

Fluorescence-readout as a powerful macromolecular characterisation tool

The last few decades have witnessed significant progress in synthetic macromolecular chemistry, which can provide access to diverse macromolecules with varying structural complexities, topology and functionalities, bringing us closer to the aim of controlling soft matter material properties with molecular precision. To reach this goal, the development of advanced analytical techniques, allowing for micro-, molecular level and real-time investigation, is essential. Due to their appealing features, including high sensitivity, large contrast, fast and real-time response, as well as non-invasive characteristics, fluorescence-based techniques have emerged as a powerful tool for macromolecular characterisation to provide detailed information and give new and deep insights beyond those offered by commonly applied analytical methods. Herein, we critically examine how fluorescence phenomena, principles and techniques can be effectively exploited to characterise macromolecules and soft matter materials and to further unravel their constitution, by highlighting representative examples of recent advances across major areas of polymer and materials science, ranging from polymer molecular weight and conversion, architecture, conformation to polymer self-assembly to surfaces, gels and 3D printing. Finally, we discuss the opportunities for fluorescence-readout to further advance the development of macromolecules, leading to the design of polymers and soft matter materials with pre-determined and adaptable properties.

Two-colour light activated covalent bond formation

We introduce a photochemical bond forming system, where two colours of light are required to trigger covalent bond formation. Specifically, we exploit a visible light cis/trans isomerization of chlorinated azobenzene, which can only undergo reaction with a photochemically generated ketene in its cis state. Detailed photophysical mapping of the reaction efficiencies at a wide range of monochromatic wavelengths revealed the optimum irradiation conditions. Subsequent small molecule and polymer ligation experiments illustrated that only the application of both colours of light affords the reaction product. We further extend the functionality to a photo reversible ketene moiety and translate the concept into material science. The presented reaction system holds promise to be employed as a two-colour resist.

Dual-wavelength photochemical systems open up new avenues for novel lithographic techniques but currently only few wavelength-orthogonal photoreactive compounds undergoing reversible photoreaction are known. Here, the authors exploit cis/trans photoisomerization of azobenzenes and demonstrate photoligation of the cis state with a photochemically generated ketene.

Action Plots in Action: In-Depth Insights into Photochemical Reactivity

Predicting wavelength-dependent photochemical reactivity is challenging. Herein, we revive the well-established tool of measuring action spectra and adapt the technique to map wavelength-resolved covalent bond formation and cleavage in what we term "photochemical action plots". Underpinned by tunable lasers, which allow excitation of molecules with near-perfect wavelength precision, the photoinduced reactivity of several reaction classes have been mapped in detail. These include photoinduced cycloadditions and bond formation based on photochemically generated o-quinodimethanes and 1,3-dipoles such as nitrile imines as well as radical photoinitiator cleavage. Organized by reaction class, these data demonstrate that UV/vis spectra fail to act as a predictor for photochemical reactivity at a given wavelength in most of the examined reactions, with the photochemical reactivity being strongly red shifted in comparison to the absorption spectrum. We provide an encompassing perspective of the power of photochemical action plots for bond-forming reactions and their emerging applications in the design of wavelength-selective photoresists and photoresponsive soft-matter materials.

Polymer Coupling via Hetero-Disulfide Exchange and Its Applications to Rewritable Polymer Brushes

An iodide-terminated polymer (Polymer-I) is converted to a thiol-terminated polymer (Polymer-SH) using HSCH₂CH₂SH in a remarkably short time (10 min). Polymer-SH is further converted to a pyridyl disulfide-terminated polymer (Polymer-SS-Py). The hetero-coupling of Polymer-SH and Polymer-SS-Py is successfully achieved to quantitatively generate a polymer disulfide (Polymer-SS-Polymer). Exploiting this efficient hetero-coupling technique, Polymer-SH is attached (grafted) on a Py-SS-immobilized surface to generate a polymer brush via a disulfide (-SS-) linkage (writing process). The -SS- linkage is cleaved by the treatment with dithiothreitol (DTT) to detach the polymer from the surface (erasing process). Subsequently, another Polymer-SH is attached on the surface to generate another polymer brush (rewriting process). Thus, a writable, erasable, and rewritable polymer brush surface is achieved. Hydrophilic, hydrophobic, and super-hydrophobic polymers (Polymer-SH) are attached on the surface, tailoring the surface wettability in the writing-erasing-rewriting cycles. Polymer-SH is also attached on a chain-end Py-SS-functionalized polymer brush surface, generating a rewritable block copolymer brush surface. A patterned block copolymer brush surface is also obtained using photo-irradiation and a photo-mask in the erasing process. The metal-free synthetic procedure, accessibility to patterned brushes, and switchable surface properties via the writing-erasing-rewriting process are attractive features of the present approach.

Inside the brush: partition by molecular weight in grafting to reactions from melt

A substantial partition by molecular weight takes place during the grafting to reactions.

Photodynamic Pattern Memory Surfaces with Responsive Wrinkled and Fluorescent Patterns

Reversible pattern systems, namely pattern memory surfaces, possessing tunable morphology play an important role in the development of smart materials; however, the construction of these surfaces is still extensively challenging because of complicated methodologies or chemical reactions. Herein, a functionalized basement is strategically integrated with a multi-responsive supramolecular network based on hydrogen bonding between aggregation-induced emission luminogens (AIEgens) and copolymers containing amidogen (poly(St-co-Dm) to establish a bilayer system for near-infrared (NIR)-driven memory dual-pattern, where both the fluorescence emission and wrinkled structures can be concurrently regulated by a noninvasive NIR input. The motion of the AIEgens and photo-to-thermal expansion of the modified base allow temporal erasing of the fluorescent wrinkling patterns. Meanwhile, when exposed to 365 nm UV radiation, the fluorescent patterns can be independently regulated through photocyclization. The fluorescent wrinkling pattern presented herein is successfully demonstrated to promote the level of information security and capacity. This strategy provides a brand-new approach for the development of smart memory interfaces.

Reconfigurable Surface with Photodefinable Physicochemical Properties for User-Designable Cell Scaffolds

Surfaces with specific topography and chemical composition are quite useful in many applications ranging from functional interfaces to cell incubation scaffolds. Although these surfaces can be easily fabricated by combining topography-construction methods and surface-functionalization strategies, their properties are often static after fabrication or merely switchable between "on" and "off" states. Developing surfaces that can be on-demand regulated are quite important for the generation of smart surfaces for future applications. In this paper, we present a reconfigurable surface with adjustable topography and chemical functionality utilizing the photodynamic feature of the disulfide bond. Structured surfaces, composed of disulfide-cross-linked polymer networks, were prepared by using disulfide-containing methacrylate as the monomer. We show that the topography and chemical functionality of the surface can be on-demand regulated after its fabrication, with 254 and 365 nm UV light, respectively, allowing to "define" the physicochemical properties of the surface using light before the usage. We also demonstrate the application of such surface as a user-designable cell scaffold, that different cell scaffolds can be generated from one original surface with a simple exposure process, to define the desired bioactivity onto every point of the surface and therefore exactly control cell behaviors on the scaffold.

Visible light enabled para-fluoro-thiol ligation

The visible light-trigged para-fluoro-thiol ligation is demonstrated for first time by using the photogeneration of a superbase DBU.