Photo-induced synthesis of polymeric nanoparticles and chemiluminescent degradable materials via flow chemistry.

We report the photo-induced, additive-free, continuous synthesis of polymeric particles using flow chemistry. Not only can these particles be formed under ambient conditions in a solely light-induced precipitation polymerisation, they can be prepared via continuous flow techniques to up-scale the synthetic process. We carefully assess the flow chemical parameters and analyse the resulting particles quantitatively using scanning electron microscopy (SEM). Particle formation is a direct result of the step-growth polymerisation via a photochemically induced AA + BB Diels-Alder reaction, which we herein base on the dialdehyde monomer (AA) derived from the sustainable precursor, thymol. By employing a peroxyoxalate bismaleimide (BB), we introduce particles that can be selectively degraded on-demand, self-reported by light emission through chemiluminescence.

The Power of Action Plots: Unveiling Reaction Selectivity of Light-Stabilized Dynamic Covalent Chemistry.

Exploiting the optimum wavelength of reactivity for efficient photochemical reactions has been well-established based on the development of photochemical action plots. We herein demonstrate the power of such action plots by a remarkable example of the wavelength-resolved photochemistry of two triazolinedione (TAD) substrates, i.e., aliphatic and aromatic substituted, that exhibit near identical absorption spectra yet possess vastly disparate photoreactivity. We present our findings in carefully recorded action plots, from which reaction selectivity is identified. The profound difference in photoreactivity is exploited by designing a 'hybrid' bisfunctional TAD molecule, enabling the formation of a dual-gated reaction manifold that demonstrates the exceptional and site-selective (photo)chemical behavior of both TAD substrates within a single small molecule.

Ferrocene-driven single-chain polymer compaction.

We introduce single-chain nanoparticles (SCNPs) exclusively folded by covalently bonded ferrocene units. Specifially, we demonstrate the ability of 2-ferrocenyl-1,10-phenanthroline to fuse single-chain collapse with the concomitant introduction of a donor functionality allowing the installation of a Pd-catalytic site, affording the first heterobimetallic ferrocene-functionalized SCNP.

Fluorescence turn-on by photoligation - bright opportunities for soft matter materials.

Photochemical ligation has become an indispensable tool for applications that require spatially addressable functionalisation, both in biology and materials science. Interestingly, a number of photochemical ligations result in fluorescent products, enabling a self-reporting function that provides almost instantaneous visual feedback of the reaction's progress and efficiency. Perhaps no other chemical reaction system allows control in space and time to the same extent, while concomitantly providing inherent feedback with regard to reaction success and location. While photoactivable fluorescent properties have been widely used in biology for imaging purposes, the expansion of the array of photochemical reactions has further enabled its utility in soft matter materials. Herein, we concisely summarise the key developments of fluorogenic-forming photoligation systems and their emerging applications in both biology and materials science. We further summarise the current challenges and future opportunities of exploiting fluorescent self-reporting reactions in a wide array of chemical disciplines.

Internal catalysis for dynamic covalent chemistry applications and polymer science.

Strong covalent chemical bonds that can also be reversed, cleaved or exchanged are the subject of so-called dynamic covalent chemistry (DCC). Applications range from classical protective groups in organic chemistry and cleavable linkers for solid phase synthesis, to more modern applications in dynamic compound libraries and adaptive materials. Interest in dynamic, reversible or responsive chemistries has risen in particular in the last few decades for the design and synthesis of new DCC-based polymer materials. Implementation of DCC in polymers yields materials with unique combinations of properties and in some cases even unprecedented properties for covalent materials, such as self-healing materials, covalent adaptable networks (CANs) and vitrimers. In particular, the incorporation of DCC in polymer materials aims to find a balance between a swift and triggerable reactivity, combined with a high degree of intrinsic robustness and stability. Applying harsh conditions, highly active catalysts or highly reactive bonding groups, as is done in classical DCC, is often not feasible or desirable, as it can damage the polymer's integrity, leading to loss of function and properties. In this context, so-called internally catalysed DCC platforms have started to receive more interest in this area. This approach relies on the relative proximity and orientation of common functional groups, which can influence a chemical exchange reaction in a subtle but significant way. This approach mimicks the strategies found in enzymic reactions, and is known in classical organic chemistry as neighbouring group participation (NGP). The use of internal catalysis or NGP within polymer material science has proven to be a highly attractive strategy. This tutorial review will outline examples showing the scope, advantages and pitfalls of using internal catalysis within different DCC applications, ranging from small molecules to dynamic polymer materials.

From Sequence-Defined Macromolecules to Macromolecular Pin Codes.

Dynamic sequence-defined oligomers carrying a chemically written pin code are obtained through a strategy combining multicomponent reactions with the thermoreversible addition of 1,2,4-triazoline-3,5-diones (TADs) to indole substrates. The precision oligomers are specifically designed to be encrypted upon heating as a result of the random reshuffling of the TAD-indole covalent bonds within the backbone, thereby resulting in the scrambling of the encoded information. The encrypted pin code can eventually be decrypted following a second heating step that enables the macromolecular pin code to be deciphered using 1D electrospray ionization-mass spectrometry (ESI-MS). The herein introduced concept of encryption/decryption represents a key advancement compared with current strategies that typically use uncontrolled degradation to erase and tandem mass spectrometry (MS/MS) to analyze, decipher, and read-out chemically encrypted information. Additionally, the synthesized macromolecules are coated onto a high-value polymer material, which demonstrates their potential application as coded product tags for anti-counterfeiting purposes.

Automated Synthesis Protocol of Sequence-Defined Oligo-Urethane-Amides Using Thiolactone Chemistry.

An automated, iterative protocol for the synthesis of multifunctional, sequence-defined oligo-urethane-amides using thiolactone chemistry is reported. Here, sequenced functionalization of the backbone is easily introduced using commercially available primary amines. The chemistry is carried out on solid phase using different supports for better optimization of the synthetic protocol and in order to demonstrate the versatility of the approach. This technique is very effective for iterative synthesis and solid-phase chemistry and enables the exploration of full automation of this approach using a robotic peptide synthesizer. As a result, this automated protocol allows for the synthesis of a sequence-defined nonamer of high purity.

Tailored Modification of Thioacrylates in a Versatile, Sequence-Defined Procedure.

A strategy for the synthesis of sequence-defined oligomers using a selective side-group insertion approach making use of thiophenol-catalyzed amidation reactions is herein reported. In this context, a new thiolactone-based, multistep, iterative protocol is designed, utilizing thioacrylates in combination with solid-phase synthesis for step-by-step growth, resulting in sequence-defined oligomers. Sequence definition and structure variation are introduced by substituting the thioacrylate side groups with a wide variety of amines. The step-by-step growth of the oligomers is followed by liquid chromatography-mass spectrometry and high-resolution mass spectroscopy to determine both conversion and purity.

Click and Click-Inspired Chemistry for the Design of Sequence-Controlled Polymers.

During the previous decade, many popular chemical reactions used in the area of "click" chemistry and similarly efficient "click-inspired" reactions have been applied for the design of sequence-defined and, more generally, sequence-controlled structures. This combination of topics has already made quite a significant impact on scientific research to date and has enabled the synthesis of highly functionalized and complex oligomeric and polymeric structures, which offer the prospect of many exciting further developments and applications in the near future. This minireview highlights the fruitful combination of these two topics for the preparation of sequence-controlled oligomeric and macromolecular structures and showcases the vast number of publications in this field within a relatively short span of time. It is divided into three sections according to the click-(inspired) reaction that has been applied: copper-catalyzed azide-alkyne cycloaddition, thiol-X, and related thiolactone-based reactions, and finally Diels-Alder-chemistry-based routes are outlined, respectively.