Chemiluminescent self-reported unfolding of single-chain nanoparticles.

We demonstrate the light-induced, crosslinker mediated collapse of linear polymer chains into single-chain nanoparticles (SCNPs) capable of self-reporting their unfolding. The crosslinker entails a phenyloxalate motif allowing for the targeted degradation of the SCNPs via addition of hydrogen peroxide that triggers chemiluminescence (CL). The time-dependant CL emission can serve as a guide to follow the time dependent unfolding of the SCNPs, allowing for a qualitative assessment of the underlying mechanism.

Chemiluminescent read-out of para-fluoro-thiol reaction events.

We exploit the fluoride that is released via the para-fluoro-thiol reaction (PFTR) to cleave silyl ethers, turning the PFTR into an effective self-reporting chemiluminescence (CL) probe. The cleavage induces chemiluminescence and hence provides an optical read-out for the conversion of the PFTR. The PFTR chemiluminescence read-out is established on small molecule thiols, and subsequently expanded to polymers and networks.

Light-fueled dynamic covalent crosslinking of single polymer chains in non-equilibrium states.

While polymer synthesis proceeds predominantly towards the thermodynamic minimum, living systems operate on the reverse principle - consuming fuel to maintain a non-equilibrium state. Herein, we report the controlled formation of 3D macromolecular architectures based on light-fueled covalent non-equilibrium chemistry. In the presence of green light (525 nm) and a bivalent triazolinedione (TAD) crosslinker, naphthalene-containing polymers can be folded into single chain nanoparticles (SCNPs). At ambient temperature, the cycloaddition product of TAD with naphthalene reverts and the SCNP unfolds into its linear parent polymer. The reported SCNP is the first example of a reversible light triggered folding of single polymer chains and can readily be repeated for several cycles. The folded state of the SCNP can either be preserved through a constant supply of light fuel, kinetic trapping or through a chemical modification that makes the folded state thermodynamically favored. Whereas small molecule bivalent TAD/naphthalene cycloaddition products largely degraded after 3 days in solution, even in the presence of fuel, the SCNP entities were found to remain intact, thereby indicating the light-fueled stabilization of the SCNP to be an inherent feature of the confined macromolecular environment.

Wavelength-Selective Folding of Single Polymer Chains with Different Colors of Visible Light.

Photochemistry allows chemists to exert control over chemical reactions with spatiotemporal precision. Furthermore, light holds the potential to not only gate when and where but also which reaction takes place. Herein, two photocycloaddition reactions-initiated by different colors of visible light-are utilized to control the intramolecular crosslinking of single polymer chains. Irradiation with blue light (λmax = 470 nm) triggers a [2 + 2] photocycloaddition inducing an initial intramolecular crosslinking reaction, whereas subsequent irradiation with violet light (λmax = 415 nm) induces a [4 + 4] photocycloaddition, fully compacting the dual photoreactive polymer into a single-chain nanoparticle. Importantly, both crosslinked states are accessible under ultra-mild conditions requiring nothing but two different colors of visible light. The reported strategy of wavelength-selective crosslinking degrees provides key potential to be translated into materials applications for the remote control of mechanical properties on the molecular level.

All Eyes on Visible-Light Peroxyoxalate Chemiluminescence Read-Out Systems.

Chemiluminescence (CL) reactions have been widely employed and explored over the past 50 years because they offer unique light emission upon a defined chemical stimulus. In this Minireview, we focus on peroxyoxalate (PO) compounds because they feature very high quantum yields tuneable over the entire visible spectrum, allowing for visible-light detection by the naked eye without the necessity for expensive analytical instruments. Although analytical methods have been extensively described, PO-CL read-out is a strongly emerging field with ample industrial potential. The state-of-the-art PO-CL detection read-out systems for various key analytes is here explored. In particular, structural requirements, recent developments of PO-CL read-out probes and current limitations of selected examples are detailed. Furthermore, innovative approaches and synthetic routes to push the boundaries of PO-CL reactions into biological systems are highlighted. Underpinned by recent contributions, we share perspectives on embedding PO-CL molecules into polymeric materials, which they consider the next step in designing high performance solid-phase read-out systems.

Self-Propagated para-Fluoro-Thiol Reaction.

We introduce a protecting-group-free concept for the powerful para-fluoro-thiol reaction (PFTR) employing a source of fluoride ions as base. The reaction is shown to be self-propagating, with under-stoichiometric amounts of base, thus effectively foregoing the need for high base concentrations. Careful tuning of the solvent-thiol combination allows for quantitative conversion, in some cases within a short timeframe, when only minimal amounts of base are used, allowing the PFTR reaction to essentially proceed base-free.

Controlling Chain Coupling and Single-Chain Ligation by Two Colours of Visible Light.

While photochemical synthesis offers access to spatiotemporal reaction control, its potential to selectively address specific reactions by the colour of light is usually limited by ubiquitous spectral absorption overlaps of the reactive groups. Herein, a new concept is introduced that actively suppresses one ligation reaction by triggering the cycloreversion of the [2+2] cycloaddition of styrylpyrene. Combination of the photoreversible styrylpyrene chemistry with the [4+4] cycloaddition of 9-triazolylanthracene makes it possible to initially induce chain coupling using UV light and to subsequently ligate the formed single-chain nanoparticle (SCNP) with a second polymer chain using blue light. Seizing upon the first sequence-independent λ-orthogonal reactivity established here, the same macromolecular architecture was obtained in reverse irradiation sequence, by blue and subsequent violet light irradiation-completely foregoing high-energy UV light.

Photochemistry in Confined Environments for Single-Chain Nanoparticle Design.

Emulating nature's protein paradigm, single-chain nanoparticles (SCNP) are an emerging class of nanomaterials. Synthetic access to SCNPs is limited by ultralow concentrations, demanding reaction conditions, and complex isolation procedures after single-chain collapse. Herein, we exploit the visible light photodimerization of styrylpyrene units as chain folding mechanism. Critically, their positioning along the polymer chain creates a confined environment, increasing the photocycloaddition quantum yields dramatically, enabling single-chain folding at unrivaled high concentrations without subsequent purification. Importantly, the enhanced photoreactivity allows for single-chain folding at λ = 445 nm LED-irradiation within minutes as well as via ambient light, enabling an unprecedented folding system. The herein demonstrated enhancement of quantum yields by steric confinement serves as a blueprint for all photochemical ligation systems.

A Combined Photochemical and Multicomponent Reaction Approach to Precision Oligomers.

We introduce the convergent synthesis of linear monodisperse sequence-defined oligomers through a unique approach, combining the Passerini three-component reaction (P-3CR) and a Diels-Alder (DA) reaction based on photocaged dienes. A set of oligomers is prepared resting on a Passerini linker unit carrying an isocyano group for chain extension by P-3CR and a maleimide moiety for photoenol conjugation enabling a modular approach for chain growth. Monodisperse oligomers are accessible in a stepwise fashion by switching between both reaction types. Employing sebacic acid as a core unit allows the synthesis of a library of symmetric sequence-defined oligomers. The oligomers consist of alternating P-3CR and photoblocks with molecular weights up to 3532.16 g mol-1 , demonstrating the successful switching from P-3CR to photoenol conjugation. In-depth characterization was carried out including size-exclusion chromatography (SEC), high-resolution electrospray ionization mass spectrometry (ESI-MS) and NMR spectroscopy, evidencing the monodisperse nature of the precision oligomers.

Polyselenoureas via Multicomponent Polymerizations Using Elemental Selenium as Monomer.

Multicomponent polymerizations (MCPs) have emerged as a powerful tool in the synthesis of advanced, sequence-regulated polymers based on their mild reaction conditions, ease of use, and high atom economy. Herein, we exploit MCP methodology to introduce elemental selenium into a polymer chain, accessing a unique polymer class,i.e., polyselenoureas. These polyselenoureas can be synthesized from a broad range of commercially available starting materials, in a simple ambient temperature one-step procedure. The incorporation of selenium directly into the polymer backbone provides a unique handle for polymer characterization based on the distinctive isotope profiles exposed by high-resolution mass spectrometry, along with diagnostic signals observed in infrared and X-ray photoelectron spectroscopies. In addition, diffusion ordered spectroscopy provides access to hydrodynamic diameter information on the generated unique polymer class.