Visible and near-infrared light-induced photoclick reactions

Photoclick reactions combine the advantages offered by light-driven processes, that is, non-invasive and high spatiotemporal control, with classical click chemistry and have found applications ranging from surface functionalization, polymer conjugation, photocrosslinking, protein labelling and bioimaging. Despite these advances, most photoclick reactions typically require near-ultraviolet (UV) and mid-UV light to proceed. UV light can trigger undesirable responses, including cellular apoptosis, and therefore, visible and near-infrared light-induced photoclick reaction systems are highly desirable. Shifting to a longer wavelength can also reduce degradation of the photoclick reagents and products. Several strategies have been used to induce a bathochromic shift in the wavelength of irradiation-initiating photoclick reactions. For instance, the extension of the conjugated π-system, triplet-triplet energy transfer, multi-photon excitation, upconversion technology, photocatalytic and photoinitiation approaches, and designs involving photocages have all been used to achieve this goal. Current design strategies, recent advances and the outlook for long wavelength-driven photoclick reactions are presented.

A Type of Stable Amides Behaves as Acyl Transfer Reagents upon Visible-Light Irradiation through Self-Aromatization

Organic molecules with light-modifiable reactivity are important in many fields because they can serve as the "switch" for light to trigger chemical processes. Herein, we disclose a new type of stable non-twisted amides, the reactivity of which can be turned on by light as acyl transfer reagents. Upon photo-activation, these amides react with various nucleophiles including amines, phenols, hydroxide, thiols, boronic acids, and alkynes either under metal-free or metal-catalysis conditions. This reactivity hinges on the design and synthesis of a photo-activatable reagent (7-nitro-5,6-dihydrophenanthridine), which undergoes self-aromatization enabled by an internal oxidant under light. This masked acyl donor group is anticipated to be useful in scenarios where light is preferred to trigger a chemical process.

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.

Multiconfigurational photodynamics simulations reveal the mechanism of photodecarbonylations of cyclopropenones in explicit aqueous environments

Gas-evolving photochemical reactions use light and mild conditions to access strained organic compounds irreversibly. Cyclopropenones are a class of light-responsive molecules used in bioorthogonal photoclick reactions; their excited-state decarbonylation reaction mechanisms are misunderstood due to their ultrafast (<100 femtosecond) lifetimes. We have combined multiconfigurational quantum mechanical (QM) calculations and non-adiabatic molecular dynamics (NAMD) simulations to uncover the excited-state mechanism of cyclopropenone and a photoprotected cyclooctyne-(COT)-precursor in gaseous and explicit aqueous environments. We explore the role of H-bonding with fully quantum mechanical explicitly solvated NAMD simulations for the decarbonylation reaction. The cyclopropenones pass through asynchronous conical intersections and have dynamically concerted photodecarbonylation mechanisms. The COT-precursor has a higher quantum yield of 55% than cyclopropenone (28%) because these trajectories prefer to break a σCC bond to avoid the strained trans-cyclooctene geometries. Our solvated simulations show an increased quantum yield (58%) for the systems studied here.

Polymerization-Induced Self-Assembly for Efficient Fabrication of Biomedical Nanoplatforms

Amphiphilic copolymers can self-assemble into nano-objects in aqueous solution. However, the self-assembly process is usually performed in a diluted solution (<1 wt%), which greatly limits scale-up production and further biomedical applications. With recent development of controlled polymerization techniques, polymerization-induced self-assembly (PISA) has emerged as an efficient approach for facile fabrication of nano-sized structures with a high concentration as high as 50 wt%. In this review, after the introduction, various polymerization method-mediated PISAs that include nitroxide-mediated polymerization-mediated PISA (NMP-PISA), reversible addition-fragmentation chain transfer polymerization-mediated PISA (RAFT-PISA), atom transfer radical polymerization-mediated PISA (ATRP-PISA), and ring-opening polymerization-mediated PISA (ROP-PISA) are discussed carefully. Afterward, recent biomedical applications of PISA are illustrated from the following aspects, i.e., bioimaging, disease treatment, biocatalysis, and antimicrobial. In the end, current achievements and future perspectives of PISA are given. It is envisioned that PISA strategy can bring great chance for future design and construction of functional nano-vehicles.

Red light-induced conjugation of amines through amide bond formation triggered via photooxidation of 3-acylindolizines

The development of a conjugation method initiated by irradiation of long-wavelength light (>500 nm) to prepare densely functionalized molecules while avoiding undesired photodegradation has attracted considerable attention. Here we show an amide bond formation method based on the photoreaction of 3-acylindolizines in the presence of amines triggered via red-light irradiation. Photooxidation of 3-acylindolizines using a catalytic amount of a photosensitizer and red light-emitting diodes (660 nm) affords the corresponding conjugated amides in nearly quantitative yields within <5 min. This transformation can be performed in aqueous organic solvents and is applicable to diverse aliphatic amines with various functional groups, including the moieties responsive to short-wavelength light.

Dual Function of β-hydroxy Dithiocinnamic Esters: RAFT Agent and Ligand for Metal Complexation

The reversible addition-fragmentation chain-transfer (RAFT) process has become a versatile tool for the preparation of defined polymers tolerating a large variety of functional groups. Several dithioesters, trithiocarbonates, xanthates, or dithiocarbamates have been developed as effective chain transfer agents (CTA), but only few examples have been reported, where the resulting end groups are directly considered for a secondary use besides controlling the polymerization. We here demonstrate that β-hydroxy dithiocinnamic esters represent a hitherto overlooked class of materials, which were originally designed for the complexation of transition metals but might as well act as reversible CTA. Modified with a suitable leaving group (R-group), these vinyl conjugated dithioesters indeed provide reasonable control over the polymerization of acrylates, acrylamides, or styrene via the RAFT process. Kinetic studies revealed linear evolutions of molar mass with conversion, while different substituents on the aromatic unit had only a minor influence. Block extensions prove the livingness of the polymer chains, although extended polymerization times may lead to side reactions. The resulting dithiocinnamic ester end groups are still able to form complexes with platinum, which verifies that the structural integrity of the end group is maintained. These findings open a versatile new route to tailor-made polymer bound metal complexes. This article is protected by copyright. All rights reserved.

End-functionalized polymers by controlled/living radical polymerizations: synthesis and applications

This review focuses on end-functionalized polymers synthesized by controlled/living radical polymerizations and the applications in fields including bioconjugate formation, surface modification, topology construction, and self-assembly.

Photoclick Chemistry: A Bright Idea

At its basic conceptualization, photoclick chemistry embodies a collection of click reactions that are performed via the application of light. The emergence of this concept has had diverse impact over a broad range of chemical and biological research due to the spatiotemporal control, high selectivity, and excellent product yields afforded by the combination of light and click chemistry. While the reactions designated as "photoclick" have many important features in common, each has its own particular combination of advantages and shortcomings. A more extensive realization of the potential of this chemistry requires a broader understanding of the physical and chemical characteristics of the specific reactions. This review discusses the features of the most frequently employed photoclick reactions reported in the literature: photomediated azide-alkyne cycloadditions, other 1,3-dipolarcycloadditions, Diels-Alder and inverse electron demand Diels-Alder additions, radical alternating addition chain transfer additions, and nucleophilic additions. Applications of these reactions in a variety of chemical syntheses, materials chemistry, and biological contexts are surveyed, with particular attention paid to the respective strengths and limitations of each reaction and how that reaction benefits from its combination with light. Finally, challenges to broader employment of these reactions are discussed, along with strategies and opportunities to mitigate such obstacles.

Light-Triggered Click Chemistry

The merging of click chemistry with discrete photochemical processes has led to the creation of a new class of click reactions, collectively known as photoclick chemistry. These light-triggered click reactions allow the synthesis of diverse organic structures in a rapid and precise manner under mild conditions. Because light offers unparalleled spatiotemporal control over the generation of the reactive intermediates, photoclick chemistry has become an indispensable tool for a wide range of spatially addressable applications including surface functionalization, polymer conjugation and cross-linking, and biomolecular labeling in the native cellular environment. Over the past decade, a growing number of photoclick reactions have been developed, especially those based on the 1,3-dipolar cycloadditions and Diels-Alder reactions owing to their excellent reaction kinetics, selectivity, and biocompatibility. This review summarizes the recent advances in the development of photoclick reactions and their applications in chemical biology and materials science. A particular emphasis is placed on the historical contexts and mechanistic insights into each of the selected reactions. The in-depth discussion presented here should stimulate further development of the field, including the design of new photoactivation modalities, the continuous expansion of λ-orthogonal tandem photoclick chemistry, and the innovative use of these unique tools in bioconjugation and nanomaterial synthesis.

Toward Fabrication of Bioactive Papers: Covalent Immobilization of Peptides and Proteins

Herein, we report a novel two-step method for the covalent, site-directed, and efficient immobilization of proteins on lab-made paper sheets. First, paper fibers were modified with a peptidic anchor comprising enzyme recognition motifs. Four different conjugation strategies for peptide immobilization were evaluated with respect to reproducibility and fiber loading efficiency. After manufacturing of the peptide-preconditioned paper, oriented conjugation of the model protein tGFP containing a C-terminal recognition sequence for either sortase A or microbial transglutaminase was assessed semiquantitatively by fluorescence measurement and inspected by confocal laser scanning microscopy (CLSM). The two enzymes utilized for protein conjugation used the same oligoglycine peptide anchor, and both proved to be suitable for controlled oriented linkage of substrate proteins at physiological conditions.

Hetero-Diels-Alder Cycloaddition with RAFT Polymers as Bioconjugation Platform

We introduce the bioconjugation of polymers synthesized by RAFT polymerization, bearing no specific functional end group, by means of hetero-Diels-Alder cycloaddition through their inherent terminal thiocarbonylthio moiety with a diene-modified model protein. Quantitative conjugation occurs over the course of a few hours, at ambient temperature and neutral pH, and in the absence of any catalyst. Our technology platform affords thermoresponsive bioconjugates, whose aggregation is solely controlled by the polymer chains.

Mass spectrometry as a tool to advance polymer science

In contrast to natural polymers, which have existed for billions of years, the first well-understood synthetic polymers date back to just over one century ago. Nevertheless, this relatively short period has seen vast progress in synthetic polymer chemistry, which can now afford diverse macromolecules with varying structural complexities. To keep pace with this synthetic progress, there have been commensurate developments in analytical chemistry, where mass spectrometry has emerged as the pre-eminent technique for polymer analysis. This Perspective describes present challenges associated with the mass-spectrometric analysis of synthetic polymers, in particular the desorption, ionization and structural interrogation of high-molar-mass macromolecules, as well as strategies to lower spectral complexity. We critically evaluate recent advances in technology in the context of these challenges and suggest how to push the field beyond its current limitations. In this context, the increasingly important role of high-resolution mass spectrometry is emphasized because of its unrivalled ability to describe unique species within polymer ensembles, rather than to report the average properties of the ensemble.

Photochemical Reactions in the Synthesis of Protein-Drug Conjugates

The ability to modify biologically active molecules such as antibodies with drug molecules, fluorophores or radionuclides is crucial in drug discovery and target identification. Classic chemistry used for protein functionalisation relies almost exclusively on thermochemically mediated reactions. Our recent experiments have begun to explore the use of photochemistry to effect rapid and efficient protein functionalisation. This article introduces some of the principles and objectives of using photochemically activated reagents for protein ligation. The concept of simultaneous photoradiosynthesis of radiolabelled antibodies for use in molecular imaging is introduced as a working example. Notably, the goal of producing functionalised proteins in the absence of pre-association (non-covalent ligand-protein binding) introduces requirements that are distinct from the more regular use of photoactive groups in photoaffinity labelling. With this in mind, the chemistry of thirteen different classes of photoactivatable reagents that react through the formation of intermediate carbenes, electrophiles, dienes, or radicals, is assessed.

Light-Driven Intramolecular C-N Cross-Coupling via a Long-Lived Photoactive Photoisomer Complex

Reported herein is a visible-light-driven intramolecular C-N cross-coupling reaction under mild reaction conditions (metal- and photocatalyst-free, at room temperature) via a long-lived photoactive photoisomer complex. This strategy was used to rapidly prepare the N-substituted polycyclic quinazolinone derivatives with a broad substrate scope (>50 examples) and further exploited to synthesize the natural products tryptanthrin, rutaecarpine, and their analogues. The success of gram-scale synthesis and solar-driven transformation, as well as promising tumor-suppressing biological activity, proves the potential of this strategy for practical applications. Mechanistic investigations, including control experiments, DFT calculations, UV-vis spectroscopy, EPR, and X-ray single-crystal structure of the key intermediate, provides insight into the mechanism.

Modular activatable bioorthogonal reagents

The bioorthogonal reaction toolbox contains approximately two-dozen unique chemistries that permit selective tagging and probing of biomolecules. Over the past two decades, significant effort has been devoted to optimizing and discovering bioorthogonal reagents that are faster, fluorogenic, and orthogonal to the already existing bioorthogonal repertoire. Conversely, efforts to explore bioorthogonal reagents whose reactivity can be controlled in space and/or time are limited. The "activatable" bioorthogonal reagents that do exist are often unimodal, meaning that their reagent's activation method cannot be easily modified to enable activation with red-shifted wavelengths, enzymes, or metabolic-byproducts and ions like H₂O₂ or Fe³⁺. Here, we summarize the available activatable bioorthogonal reagents with a focus on our recent addition: modular caged cyclopropenes. We designed caged cyclopropenes to be unreactive to their bioorthogonal partner until they are activated through the removal of the cage by light, an enzyme, or another reaction partner. To accomplish this, their structure includes a nitrogen atom at the cyclopropene C3 position that is decorated with the desired caging group through a carbamate linkage. This 3-N cyclopropene system can allow control of cyclopropene reactivity using a multitude of already available photo- and enzyme-caging groups. Additionally, this cyclopropene scaffold can enable metabolic-byproduct or ion activation of bioorthogonal reactions.

Visible light controlled aqueous RAFT continuous flow polymerization with oxygen tolerance

A fast visible light controlled RAFT polymerization system without the prior removal of oxygen was successfully carried out in a continuous tubular reactor with water as a green solvent.

Hyphenation of size-exclusion chromatography to mass spectrometry for precision polymer analysis – a tutorial review

Herein we demonstrate how SEC-ESI-MS can be used to analyze complex polymers, a significant challenge in contemporary polymer chemistry.

Spatially-Resolved Multiple Metallopolymer Surfaces by Photolithography

A tetrazole-based photoligation protocol for the spatially-resolved encoding of various defined metallopolymers onto solid surfaces is introduced. By using this approach, fabrication of bi- and trifunctional metallopolymer surfaces with different metal combinations were achieved. Specifically, α-ω-functional copolymers containing bipyridine as well as triphenylphosphine ligands were synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization, and subsequently metal loaded to afford metallopolymers of the widely-used metals gold, palladium, and platinum. Spatially-resolved surface attachment was achieved by means of a nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) based photoligation protocol, exploiting tethered tetrazoles and metallopolymers equipped with a maleimide chain terminus. Metallopolymer coated surfaces with three different metals were prepared and characterized by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and spatially-resolved X-ray photoelectron spectroscopy (XPS) mapping, supporting the preserved chemical composition of the surface-bound metallopolymers. The established photochemical technology platform for arbitrary spatially-resolved metallopolymer surface designs enables the patterning of multiple metallopolymers onto solid substrates. This allows for the assembly of designer metallopolymer substrates.

Reversible Surface Engineering via Nitrone-Mediated Radical Coupling

Efficient and simple polymer conjugation reactions are critical for introducing functionalities on surfaces. For polymer surface grafting, postpolymerization modifications are often required, which can impose a significant synthetic hurdle. Here, we report two strategies that allow for reversible surface engineering via nitrone-mediated radical coupling (NMRC). Macroradicals stemming from the activation of polymers generated by copper-mediated radical polymerization are grafted via radical trapping with a surface-immobilized nitrone or a solution-borne nitrone. Since the product of NMRC coupling features an alkoxyamine linker, the grafting reactions can be reversed or chain insertions can be performed via nitroxide-mediated polymerization (NMP). Poly( n-butyl acrylate) ( M_n = 1570 g·mol^-1, D̵ = 1.12) with a bromine terminus was reversibly grafted to planar silicon substrates or silica nanoparticles as successfully evidenced via X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry, and grazing angle attenuated total reflection Fourier-transform infrared spectroscopy (GAATR-FTIR). NMP chain insertions of styrene are evidenced via GAATR-FTIR. On silica nanoparticles, an NMRC grafting density of close to 0.21 chains per nm² was determined by dynamic light scattering and thermogravimetric analysis. Concomitantly, a simple way to decorate particles with nitroxide radicals with precise control over the radical concentration is introduced. Silica microparticles and zinc oxide, barium titanate, and silicon nanoparticles were successfully functionalized.

Light-Induced Step-Growth Polymerization of AB-Type Photo-Monomers at Ambient Temperature

We introduce two AB-type monomers able to undergo a facile catalyst-free photoinduced polycycloaddition of photocaged dienes, enabling rapid Diels-Alder ligations under UV-irradiation (λ_max = 350 nm) at ambient temperature, closely adhering to Carother's equation established by a careful kinetic study (17800 g mol^-1 < M_w < 24700 g mol^-1). The resulting macromolecules were in-depth analyzed via size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. Additionally, SEC hyphenated to high resolution-electrospray ionization-mass spectrometry (HR-ESI-MS) enabled the careful mapping of the end group structure of the generated polymers. Furthermore, we demonstrate that both monomer systems can be readily copolymerized. The study thus demonstrates that Diels-Alder ligation resting upon photocaged dienes is a powerful tool for accessing step-growth polymers.

A microfluidic photoreactor enables 2-methylbenzophenone light-driven reactions with superior performance

A general and scalable microfluidic photoreactor for light-driven reaction of 2-methylbenzophenones was successfully developed.

Spatially resolved photochemical coding of reversibly anchored cysteine-rich domains

We present a novel methodology to generate recodable surfaces using cysteine-rich domains (CRD) via a combination of photolithography and reversible covalently peptide-driven disulfide formation. Therefore, two 21mer CRD peptide derivatives were synthesized, one bearing an electron deficient fumarate group for immobilization via nitrile imine-ene mediated cycloaddition (NITEC) to a tetrazole-functional surface. Secondly, a bromine moiety is introduced to the CRD for analytic labelling purposes to detect surface encoding. The photolithography is conducted by selectively passivating the surface with a polyethylene glycol (PEG)-fumarate via NITEC using a photomask in a dotted pattern. Consecutively, the CRD-fumarate is immobilized via NITEC adjacent to the PEG-functional areas to the unaffected tetrazole covered surface layer. Subsequently, the CRD-bromide is covalently linked to the CRD-fumarate by forming disulfide bonds under mild reoxidative conditions in a buffer solution. The CRD-bromide is released from the surface upon reduction to recover the prior state of the surface without the bromine marker. The analysis of the CRD precursors is based on electrospray ionization mass spectrometry (ESI-MS). The surface analytics were carried out via time-of-flight secondary ion mass spectrometry (ToF-SIMS), unambiguously verifying the successful immobilization as well as coding and decoding of the CRD-bromide on the surface based on dynamically reversible disulfide bond formation.

Photochemically Driven Polymeric Network Formation: Synthesis and Applications

Polymeric networks have been intensely investigated and a large number of applications have been found in areas ranging from biomedicine to materials science. Network fabrication via light-induced reactions is a particularly powerful tool, since light provides ready access to temporal and spatial control, opening an array of synthetic access routes for structuring the network geometry as well as functionality. Herein, the most recent light-induced modular reactions and their use in the formation of precision polymeric networks are collated. The synthetic strategies including photoinduced thiol-based reactions, Diels-Alder systems, and photogenerated reactive dipoles, as well as photodimerizations, are discussed in detail. Importantly, applications of the fabricated networks via the aforementioned reactions are highlighted with selected examples. Concomitantly, we provide future directions for the field, emphasizing the most critically required advances.

Photo-induced ring-closure via a looped flow reactor

Looped flow processes are an efficient and versatile tool to synthesize cyclic macromolecular materials.

Natural RAFT Polymerization: Recyclable-Catalyst-Aided, Opened-to-Air, and Sunlight-Photolyzed RAFT Polymerizations

The successful sunlight-photolyzed reversible addition-fragmentation chain transfer (RAFT) photopolymerization can be reversibly activated and deactivated by irradiation with sunlight in the absence of photocatalyst and photoinitiator. In the present work, the thiocarbonylthio compounds (dithiobenzoate, trithiocarbonate, and xanthate) can all be employed to carry out the polymerization under sunlight irradiation acting as an initiator, chain transfer agent, and termination agent. Moreover, it was demonstrated that the recyclable-catalyst-aided, opened-to-air, and sunlight-photolyzed RAFT (ROS-RAFT) polymerizations can be successfully carried out to fabricate precise and predictable polymers in the presence of the recyclable magnetic semiconductor nanoparticles (NPs). The oxygen tolerance is likely attributed to a specific interaction between NPs and oxygen.

Universal mass spectrometric analysis of poly(ionic liquid)s

We introduce a universal high resolution mass spectrometric method for the analysis of poly(ionic liquid)s (PILs), which belong to the most challenging polyelectrolytes from an analytical perspective, by fusing high resolution collision-induced dissociation (CID)-Orbitrap mass spectrometry (MS) with supercharging agents as well as quadrupole time-of-flight (QToF) MS. The study includes a wide array of hydrophilic halide-containing PILs, which were analyzed in negative mode. The influence of the core structures (based on imidazolium, triazolium, ammonium, phosphonium and pyridinium moieties), and variable styrene-, acrylate- and vinyl-type IL polymers on the ionization behavior is mapped in detail. Variable end group functionalities were introduced via functional chain transfer agents (CTA) in reversible addition-fragmentation chain transfer (RAFT) polymerization to study their behavior during the MS analysis. Furthermore, the demanding class of vinylimidazolium halide IL polymers was investigated. The current contribution thus introduces a new analytical technology platform for an entire polymer class.

A Light-Activated Reaction Manifold

We introduce an efficient reaction manifold where the rate of a thermally induced ligation can be controlled by a photonic field via two competing reaction channels. The effectiveness of the reaction manifold is evidenced by following the transformations of macromolecular chain termini via high-resolution mass spectrometry and subsequently by selective block copolymer formation. The light-controlled reaction manifold consists of a so-called o-quinodimethane species, a photocaged diene, that reacts in the presence of light with suitable enes in a Diels-Alder reaction and undergoes a transformation into imines with amines in the absence of light. The chemical selectivity of the manifold is controlled by the amount of ene present in the reaction and can be adjusted from 100% imine formation (0% photo product) to 5% imine formation (95% photo product). The reported light-controlled reaction manifold is highly attractive because a simple external field is used to switch the selectivity of specific reaction channels.

α,ω-Reactive Building Blocks Based on a Dual Functional RAFT Agent for Thermal and Light-Induced Ligation

A dual functional chain transfer agent (CTA) capable of highly efficient sequential thermal and photoinduced ligation, generating α,ω-functional polymers, is introduced. The newly designed CTA (1-(4-((2-formyl-3-methyl phenoxy)methyl)phenyl)ethyl (diethoxyphosphoryl)methane dithioate) fuses thermally triggered hetero Diels-Alder chemistry with rapid light-induced photoenol chemistry. The versatility of the CTA is exemplarily demonstrated via the preparation of an amphiphilic triblock quaterpolymer poly(isoprene-co-styrene)-block-poly(ethyl acrylate)-block-poly(ethylene oxide) (P(I-co-S)-b-PEA-b-PEO). Subsequent to the homopolymerization of ethyl acrylate (PEA), a Cp-functional poly(isoprene-co-styrene) (P(I-co-S)) is conjugated with the electron-deficient C═S double bond (dienophile) of the CTA end group, generating a P(I-co-S)-b-PEA diblock terpolymer. The triblock quaterpolymer P(I-co-S)-b-PEA-b-PEO is generated by photoligation of a macromolecular dienophile, i.e., the fumarate-terminated poly(ethylene oxide) (PEO-fum) to the photoenol-functional P(I-co-S)-b-PEA. The new dual functional ligation RAFT agent constitutes a technology platform for generating α,ω-reactive building blocks from one single chain transfer agent.

Light-driven nitrile imine-mediated tetrazole-ene cycloaddition as a versatile platform for fullerene conjugation

An efficient methodology for modular fullerene functionalization via the photo-induced nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) is introduced. The versatility and platform character of the method is illustrated by the light-driven reaction of fullerenes with small molecule, polymeric and surface-immobilized tetrazoles. The efficient fullerene conjugation is evidenced via mass spectrometric techniques.