Recent advances of anti-tumor nano-strategies via overturning pH gradient: alkalization and acidification

The acidic tumor microenvironment, a hallmark of many solid tumors, is primarily induced by the high glycolytic rate of tumor cells. To avoid acidosis, tumor cells ingeniously maintain an acidic extracellular pH while keeping a relatively alkaline intracellular pH. Overturning the unique pH gradient of tumor cells has exhibited to be a viable approach for cancer therapy. In this review, the formation and regulatory mechanisms of the acidic microenvironment in solid tumors will be firstly outlined. Subsequently, we will comprehensively summarize the latest advancements in anti-tumor therapy via using nanomedicines to manipulate the tumor pH gradient, including acidifying intracellular environment and alkalizing extracellular environment. Following this, we will discuss the future potential of strategies employing nanomedicines to reverse tumor pH gradient. This review aims to foster research on therapeutic approaches targeting the pH regulation of solid tumors and holds an optimistic outlook for the future development of this field.

A dual experimental-theoretical perspective on ESPT photoacids and their challenges ahead

Photoacids undergo an increase in acidity upon electronic excitation, enabling excited-state proton transfer (ESPT) reactions. A multitude of compounds that allow ESPT has been identified and integrated in numerous applications, as is outlined by reviewing the rich history of photoacid research reaching back more than 90 years. In particular, achievements together with ambitions and challenges are highlighted from a combined experimental and theoretical perspective. Besides explicating the spectral signatures, transient ion-pair species, and electronic states involved in an ESPT, special emphasis is put on the diversity of methods used for studying photoacids as well as on the effects of the environment on the ESPT, illustrated in detail for 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) and the naphthols as examples of prototypical photoacids. The development of exceptionally acidic super-photoacids and magic photoacids is subsequently discussed, which opens the way to applications even in aprotic solvents and provides additional insight into the mechanisms underlying ESPT. In the overview of highlights from theory, a comprehensive picture of the scope of studies on HPTS is presented, along with the general conceptualization of the electronic structure of photoacids and approaches for the quantification of excited-state acidity. We conclude with a juxtaposition of established applications of photoacids together with potential open questions and prospective research directions.

Visible-Light-Fueled Polymerizations for 3D Printing

ConspectusLight-driven polymerizations and their application in 3D printing have revolutionized manufacturing across diverse sectors, from healthcare to fine arts. Despite the popularized notion that with 3D printing "imagination is the only limit", we and others in the scientific community have identified fundamental hurdles that restrict our capabilities in this space. Herein, we describe the ZAP group's efforts in developing photochemical systems that respond to nontraditional colors of light to elicit the rapid, spatiotemporally controlled formation of plastics. Our research addresses key limitations in current photopolymerization methods, such as the reliance on high-energy UV light, oxygen sensitivity, and narrow materials scope. We present a comprehensive overview of our advancements in both light-fueled radical and nonradical chemistry and its implementation in vat photopolymerization 3D printing using panchromatic resins. In radical chemistry, we have developed a class of boron dipyrromethene (BODIPY) dye molecules that act as photoradical generators (PRGs). Upon exposure to visible or near-infrared (NIR) light, these molecules induced efficient polymerization of acrylics. Structural modifications, including the installment of halogens, twisted aromatic groups, nitrogen bridgeheads, and thiophenes, have imbued activity across this wide spectral range. Systematic photophysical characterization of these dyes revealed the presence of long-lived excited (high in energy) states, from which we accredited the enhancements in polymerization efficiency. In turn, curing (converting a liquid to solid) with low intensity visible-to-NIR light was possible in mere seconds; a requirement for many light-based 3D printing technologies. Our efforts in nonradical chemistry have been motivated by the need for new materials with properties and functionality currently inaccessible using radical-based 3D printing approaches (e.g., tough and recyclable), while also providing an avenue toward multimaterial fabrication. We have developed photobase generators (PBGs) - dyes that release basic cargo upon light exposure-to catalyze polymerizations beyond acrylic-only resins. These include coumarinylmethyl- and BODIPY-tetramethylguanidine (TMG) derivatives, as well as onium photocages, which enabled photocuring of thiol-ene and thiol-isocyanate resins. Lastly, we have pioneered rapid, high-resolution visible-to-NIR light-based 3D printing. Our work includes the development of reactive photoredox catalyst systems for speed, additives for oxygen-tolerance, NIR-light reactivity for nanoparticle composites, models for streamlined optimization, and triplet fusion for high resolution. These advancements led to build speeds up to 45 mm/h with features <100 μm, rivaling contemporary UV-based technologies. The impact of our research extends beyond academic interest, offering practical solutions for additive manufacturing of (multi)functional materials. By enabling the use of lower-energy light sources, our work paves the way for environmentally friendly, cost-effective, and versatile 3D printing. It opens new possibilities for printing with previously incompatible materials, including UV-sensitive compounds and high-refractive-index nanocomposites. Nascent developments in multimaterial 3D printing via color- and dose-controlled light exposure are enabling the production of objects with precise placement of materials having disparate composition and properties. As we continue to develop photopolymerizations and light-based 3D printing, we anticipate transformative applications in fields ranging from tissue engineering to advanced electronics manufacturing. This will bring the community one step closer to fulfill the dream of creators only being "limited by imagination".

iTASO: A Novel Photosensitive Probe for High-Throughput and Selective Submetabolomic Analysis via Flow Injection-Mass Spectrometry

Flow injection mass spectrometry (FI-MS) is widely employed for high-throughput metabolome analysis, yet the absence of prior separation leads to significant matrix effects, thereby limiting the metabolome coverage. In this study, we introduce a novel photosensitive MS probe, iTASO-ONH2, integrated with FI-MS to establish a high-throughput strategy for submetabolome analyses. The iTASO probe features a conjugated-imino sulfonate moiety for efficient photolysis under 365 nm irradiation and a reactive group for selective metabolite labeling. The iTASO-ONH2 probe effectively and selectively labels carbonyl compounds, forming highly stable labeled products. Upon UV exposure, the labeled products rapidly release sulfonic acid-containing photolysis products, detectable with high sensitivity in ESI-negative mode and low matrix effect, offering femtomole-level detection sensitivity. The iTASO-ONH2-based FI-MS strategy was applied to fecal samples from chronic sleep-deprived and control mice, revealing 192 potential carbonyl compounds of which 37 exhibited significant alterations. Additionally, three other photosensitive probes─iTASO-NH2, iTASO-NHS, and iTASO-MAL─were synthesized to selectively label carboxyl, amino, and thiol metabolites, respectively, underscoring the versatility of the iTASO-based FI-MS strategy for submetabolomic analysis across diverse metabolite classes.

Furan-Indole-Chromenone-Based Organic Photocatalyst for α-Arylation of Enol Acetate and Free Radical Polymerization Under LED Irradiation

In this study we report on the efficiency of a furane-indole-chromenone-based organic derivative (FIC) as a photocatalyst in the α-arylation of enol acetate upon LED irradiation at 405 nm, and as a photoinitiator/photocatalyst in the free radical polymerization of an acrylate group in the presence of bis-(4-tert-butylphenyl)iodonium hexafluorophosphate (Iod) as an additive, or in the presence of both Iod and ethyl-4-(dimethyl amino) benzoate (EDB) under LED irradiation at 365 nm. The photochemical properties of this new light-sensitive compound are described, and the wide redox window (3.27 eV) and the high excited-state potentials FIC*/FIC●- (+2.64 V vs. SCE) and FIC●+/FIC* (-2.41 V vs. SCE) offered by this photocatalyst are revealed. The chemical mechanisms that govern the radical chemistry are discussed by means of different techniques, including fluorescence-quenching experiments, UV-visible absorption and fluorescence spectroscopy, and cyclic voltammetry analysis.

Recent Applications of Sulfonium Salts in Synthesis and Catalysis

The use of sulfonium salts in organic synthesis has experienced a dramatic increase during the last years that can arguably be attributed to three main factors; the development of more direct and efficient synthetic methods that make easily available sulfonium reagents of a wide structural variety, their intrinsic thermal stability, which facilitates their structural modification, handling and purification even on large scale, and the recognition that their reactivity resembles that of hypervalent iodine compounds and therefore, they can be used as replacement of such reagents for most of their uses. This renewed interest has led to the improvement of already existing reactions, as well as to the discovery of unprecedented transformations; in particular, by the implementation of photocatalytic protocols. This review aims to summarize the most recent advancements on the area focusing on the work published during and after 2020. The scope of the methods developed will be highlighted and their limitations critically evaluated.

Exploring the molecular design principles for efficient diarylethene photoacid and photohydride generators based on the photochemical reaction mechanism

Photoacid generators (PAGs) and photohydride generators (PHGs) are specific photolabile protecting groups that release acid and hydride, respectively. Over the past decade, great efforts have been devoted to developing novel PAGs and PHGs with advanced efficiency, among which, two of the promising candidates are diarylethene (DAE)-based PAGs and PHGs, which release acids/hydrides during photochromic electrocyclization. The release quantum yield for PAGs is acceptable, while that of PHGs is only 4.2% even after molecular structure modification. In this work, time-resolved transient absorption spectroscopies with femtosecond and nanosecond resolutions along with DFT/TD-DFT calculations were utilized to unravel the detailed photochemical reaction mechanisms of DAE-based PAGs (1o) and PHGs (2o), respectively. The results show that the different photochemical mechanisms are the key that leads to distinctive release quantum yields between 1o and 2o. The factors affecting the release quantum yield are discussed in detail, and several key design principles are proposed to facilitate future rational design of DAE-based PAGs and PHGs.

Polymerizable Nonionic Perfluorinated Photoacid Generators for High-Resolution Lithography

Advanced photoresists must satisfy stringent sensitivity requirements while maintaining the ability to print ever-shrinking critical dimensions. However, the unavoidable acid diffusion associated with chemically amplified photoresists has led to a trade-off between resolution, line-edge roughness, and sensitivity, which presents a significant challenge for high-resolution lithography. To address this issue, a novel class of alkene-functionalized nonionic perfluorinated photoacid generators (PAGs) is developed. These fluorine-rich compounds significantly enhance the photochemical reactivity due to the introduction of abundant F-elements, thereby improving sensitivity. Upon irradiation by ultraviolet light or electrons, they generate long-chain perfluorinated sulfonic acids with large sizes and minimal diffusion ranges, effectively suppressing acid diffusion. Furthermore, by employing these polymerizable PAG monomers, PAG-bound polymers are synthesized that are likely to achieve higher resolution by minimizing acid diffusion. Lithography performance demonstrated patterning of sub-45 nm lines at an electron beam dose of 29 µC cm-2. Overall, the developed perfluorinated PAGs and PAG-bound polymer photoresists are promising candidates for achieving high-sensitivity and high-resolution nano-patterning.

Toward Polymeric Room Temperature Acid Generators

Although a variety of acid-generating molecules have been developed, the formation of toxic byproducts and the need for light-activation or temperatures that may be incompatible with physiological conditions leave room for the optimization of biocompatible acid-generators. Herein, we report 4-hydroxybenzyl chloride derivatives that generate hydrochloric acid via hydrolysis at the benzylic position at room temperature in the absence of light. Utilizing the acetal protected 4-hydroxybenzyl chloride scaffold, we access a myriad of compounds that generate acid at different rates.

Photomediated Cationic Ring-Opening Polymerization of Cyclosiloxanes with Temporal Control

Precision synthesis of polyorganosiloxanes and temporal control over the polymerization process during ring-opening polymerization (ROP) of cyclosiloxanes remain challenging due to the occurrence of side reactions, e.g., intramolecular transfer (backbiting) and intermolecular chain transfer, and irreversible catalyst transformation. In this study, a merocyanine-based photoacid catalyst is developed for cationic ROP of different cyclosiloxanes. A series of well-defined cyclotrisiloxane polymers with predetermined molar masses and low dispersities (Đ < 1.30) are successfully synthesized under various conditions (i.e., different catalyst loadings, initiator concentrations, solvents, and monomer types). Mechanistic insights by experiments and theoretical calculations suggest that the cationic active species, siloxonium ions, are combined with the catalyst anions to form tight ion pairs, thereby attenuating the reactivity of active species and subsequently minimizing side reactions. An efficient photocatalytic cycle is established among the catalyst, monomer, and polymer chain due to the rapid and reversible isomeric phototransformation of the catalyst, which endows the polymerization process with excellent temporal control. Successful in situ chain extension further confirms the controlled characteristics of photomediated CROP. This as-developed polymerization strategy effectively addresses long-standing challenges in the field of polyorganosiloxane synthesis.

Towards Energy-Efficient Direct Air Capture with Photochemically-Driven CO2 Release and Solvent Regeneration

The intensive energy demands associated with solvent regeneration and CO2 release in current direct air capture (DAC) technologies makes their deployment at the massive scales (GtCO2/year) required to positively impact the climate economically unfeasible. This challenge underscores the critical need to develop new DAC processes with significantly reduced energy costs. Recently, we developed a new approach to photochemically drive efficient release of CO2 through an intermolecular proton transfer reaction by exploiting the unique properties of an indazole metastable-state photoacid (mPAH), opening a new avenue towards energy efficient on-demand CO2 release and solvent regeneration using abundant solar energy instead of heat. In this Concept Article, we will describe the principle of our photochemically-driven CO2 release approach for solvent-based DAC systems, discuss the essential prerequisites and conditions to realize this cyclable CO2 release chemistry under ambient conditions. We outline the key findings of our approach, discuss the latest developments from other research laboratories, detail approaches used to monitor DAC systems in situ, and highlight experimental procedures for validating its feasibility. We conclude with a summary and outlook into the immediate challenges that must be addressed in order to fully exploit this novel photochemically-driven approach to DAC solvent regeneration.

Preparation and Performance Study of Ultraviolet-Responsive Self-Healing Epoxy Asphalt

In this study, a self-healing epoxy asphalt material was developed by incorporating coumarin groups. This material achieved microcrack self-repair under UV irradiation at 50 °C. Fluorescence microscopy observations and mechanical performance tests demonstrated significant advantages in crack filling and mechanical property recovery after repair, with the fracture toughness of the repaired epoxy asphalt reaching 69% of that in its original state. Furthermore, the synergistic effect of temperature and UV irradiation in the self-healing process enhanced the material's durability and service life. This research offers new insights and methods for developing more durable and long-lasting self-healing asphalt materials, showcasing the great potential of smart materials in infrastructure applications.

Optical control of pH via chromoselective photodosimetry

The dynamic regulation of pH via an external stimulus is an attractive technique to gate chemical transformations. Applying photons of different energy, we preferentially address either a photoacid or a photobase donor in the same solutions and thus, present a technique to regulate the pH of a solution through light pulses.

Onium Photocages for Visible-Light-Activated Poly(thiourethane) Synthesis and 3D Printing

The lack of chemical diversity in light-driven reactions for 3D printing poses challenges in the production of structures with long-term ambient stability, recyclability, and breadth in properties (mechanical, optical, etc.). Herein we expand the scope of photochemistries compatible with 3D printing by introducing onium photocages for the rapid formation of poly(thiourethanes) (PTUs). Efficient nonsensitized visible-light photolysis releases organophosphine and -amine derivatives that catalyze thiol-isocyanate polyaddition reactions with excellent temporal control. Two resin formulations comprising commercial isocyanates and thiols were developed for digital light processing (DLP) 3D printing to showcase the fast production of high-resolution PTU objects with disparate mechanical properties. Onium photocages represent valuable tools to advance light-driven manufacturing of next-generation high-performance sustainable materials.

A strategy for the controllable generation of organic superbases from benchtop-stable salts

Organic superbases are a distinct class of strong base that enable numerous modern reaction applications. Despite their great synthetic potential, widespread use and study of superbases are limited by their air sensitivity and difficult preparation. To address this, we report air-stable carboxylate salts of BTPP and P2-t-Bu phosphazene superbases that, when added to solution with an epoxide, spontaneously generate freebase. These systems function as effective precatalysts and stoichiometric prereagents for superbase-promoted addition, substitution and polymerization reactions. In addition to improving the synthesis, shelf stability, handling and recycling of phosphazenes, this approach enables precise regulation of the rate of base generation in situ. The activation strategy effectively mimics manual slow addition techniques, allowing for control over a reaction's rate or induction period and improvement of reactions that require strong base but are also sensitive to its presence, such as Pd-catalyzed coupling reactions.

Wavelength-Dependent Activation of Photoacids and Bases

Photoacids and bases allow remote control over pH in reaction solutions, which is of fundamental importance to an array of applications. Herein, we determine the wavelength-by-wavelength resolved photoreactivity of triarylsulfonium hexafluorophosphate salts as a representative photoacid generator and p-(benzoyl)benzyl triethylammonium tetraphenylborate as a photobase generator, constructing a wavelength-resolved photochemical action plot for each of the compounds. We monitor the pH change of the solution on-line within the cavity of the laser vial and demonstrate a marked mismatch between the absorption spectrum of the photoacid and base with the photochemical action plot, unveiling reactivity at very low absorptivities. Our findings are of critical importance for the use of photoacids and bases, unambiguously demonstrating that absorption is no guide to chemical reactivity with critical consequences for the wavelength employed in applications of photoacids and bases.

Elementary Reaction Steps That Precede or Follow a Unimolecular Reaction Step Can Obfuscate Interpretation of the Driving-Force Dependence to Its Rate Constant

Assessing the validity of a driving-force-dependent kinetic theory for a unimolecular elementary reaction step is difficult when the observed reaction rate is strongly influenced by properties of the preceding or following elementary reaction step. A well-known example occurs for bimolecular reactions with weak orbital overlap, such as outer-sphere electron transfer, where bimolecular collisional encounters that precede a fast unimolecular electron-transfer step can limit the observed rate. A lesser-appreciated example occurs for bimolecular reactions with stronger orbital overlap, including many proton-transfer reactions, where equilibration of an endergonic unimolecular proton-transfer step results in a relatively small concentration of reaction products, thus slowing the rate of the following step such that it becomes rate limiting. Incomplete consideration of these points has led to discrepancies in interpretation of data from the literature. Our reanalysis of these data suggests that proton-transfer elementary reaction steps have a nonzero intrinsic free energy barrier, implying, in the parlance of Marcus theory, that there is non-negligible nuclear reorganization. Outcomes from our analyses are generalizable to inner-sphere electron-transfer reactions such as those involved in (photo)electrochemical fuel-forming reactions.

O-nitrobenzyl Caged Molecule Enables Photo-controlled Release of Thiabendazole

Pesticides are essential in agricultural development. Controlled-release pesticides have attracted great attentions. Base on a principle of spatiotemporal selectivity, we extended the photoremovable protective group (PRPG) into agrochemical agents to achieve controllable release of active ingredients. Herein, we obtained NP-TBZ by covalently linking o-nitrobenzyl (NP) with thiabendazole (TBZ). Compound NP-TBZ can be controlled to release TBZ in dependent to light. The irradiated and unirradiated NP-TBZ showed significant differences on fungicidal activities both in vitro and in vivo. In addition, the irradiated NP-TBZ displayed similar antifungal activities to the directly-used TBZ, indicating a factual applicability in controllable release of TBZ. Furthermore, we explored the action mode and microcosmic variations by SEM analysis, and demonstrated that the irradiated NP-TBZ retained a same action mode with TBZ against mycelia growth.

Visible Light-Regulated Ring-Opening Polymerization of Lactones by Employing Indigo as a Photoacid Catalyst

The development of visible light-regulated polymerizations for precision synthesis of polymers has drawn considerable attention in the past years. In this study, an ancient dye, indigo, is successfully identified as a new and efficient photoacid catalyst, which can readily promote the ring-opening polymerization of lactones under visible light irradiation in a well-controlled manner, affording the desired polyester products with predictable molecular weights and narrow dispersity. The enhanced acidity of indigos by excitation is crucial to the H-bonding activation of the lactone monomers. Chain extension and block copolymer synthesis are also demonstrated with this method.

Photoacid Generators for Biomedical Applications

Photoacid generators (PAGs) are compounds capable of producing hydrogen protons (H+ ) upon irradiation, including irreversible and reversible PAGs, which have been widely studied in photoinduced polymerization and degradation for a long time. In recent years, the applications of PAGs in the biomedical field have attracted more attention due to their promising clinical value. So, an increasing number of novel PAGs have been reported. In this review, the recent progresses of PAGs for biomedical applications is systematically summarized, including tumor treatment, antibacterial treatment, regulation of protein folding and unfolding, control of drug release and so on. Furthermore, a concept of water-dependent reversible photoacid (W-RPA) and its antitumor effect are highlighted. Eventually, the challenges of PAGs for clinical applications are discussed.

Recent Advances in Monocomponent Visible Light Photoinitiating Systems Based on Sulfonium Salts

During the last decades, multicomponent photoinitiating systems have been the focus of intense research efforts, especially for the design of visible light photoinitiating systems. Although highly reactive three-component and even four-component photoinitiating systems have been designed, the complexity to elaborate such mixtures has incited researchers to design monocomponent Type II photoinitiators. Using this approach, the photosensitizer and the radical/cation generator can be combined within a unique molecule, greatly simplifying the elaboration of the photocurable resins. In this field, sulfonium salts are remarkable photoinitiators but these structures lack absorption in the visible range. Over the years, various structural modifications have been carried out in order to redshift their absorptions in the visible region. In this work, an overview of the different sulfonium salts activable under visible light and reported to date is proposed.

Photocaging of Carboxylic Function Bearing Biomolecules by New Thiazole Derived Fluorophore

The design and synthesis of a new fluorophore containing an arylidene thiazole scaffold resulted in a compound with good photophysical characteristics. Furthermore, the thiazole C5-methyl group was easily modified into specific functional groups (CH2 Br and CH2 OH) for the formation of a series of photocourier molecules containing model compounds (benzoic acids), as well as prodrugs, including salicylic acid, caffeic acid, and chlorambucil via a "benzyl" linker. Spectral characteristics (1 H, 13 C NMR, and high-resolution mass spectra) corresponded to the proposed structures. The photocourier molecules demonstrated absorption with high values of coefficient of molar extinction, exhibited contrasting green emission, and showed good dark stability. The mechanism of the photorelease was investigated through spectral analysis, HPLC-HRMS, and supported by TD-DFT calculations. The photoheterolysis and elimination of carboxylic acids were proved to occur in the excited state, yielding a carbocation as an intermediate moiety. The fluorophore structure provided stability to the carbocation through the delocalization of the positive charge via resonance structures. Viability assessment of Vero cells using the MTT-test confirmed the weak cytotoxicity of prodrugs without irradiation and it increase upon UV-light.

Novel BODIPY-Based Photobase Generators for Photoinduced Polymerization

Photobase generators (PBGs) are compounds that utilize light-sensitive chemical-protecting groups to offer spatiotemporal control of releasing organic bases upon targeted light irradiation. PBGs can be implemented as an external control to initiate anionic polymerizations such as thiol-ene Michael addition reactions. However, there are limitations for common PBGs, including a short absorption wavelength and weak base release that lead to poor efficiency in photopolymerization. Therefore, there is a great need for visible-light-triggered PBGs that are capable of releasing strong bases efficiently. Here, we report two novel BODIPY-based visible-light-sensitive PBGs for light-induced activation of the thiol-ene Michael "click" reaction and polymerization. These PBGs were designed by connecting the BODIPY-based light-sensitive protecting group with tetramethylguanidine (TMG), a strong base. Moreover, we exploited the heavy atom effect to increase the efficiency of releasing TMG and the polymerization rate. These BODIPY-based PBGs exhibit extraordinary activity toward thiol-ene Michael addition-based polymerization, and they can be used in surface coating and polymer network formation of different thiol and vinyl monomers.

Light-Promoted Basic Nitrogen Unmasking in Arene Ruthenium Complexes Derived from Z-Configured 2,2'-Azobispyridine

Two novel 2,2'-azobispyridine derivatives bearing N-dialkylamino substituents at position 4,4' were synthesized and their E-Z photoswitching behavior was characterized by combination of 1 H- and 13 C NMR spectroscopy, UV-Vis absorption and DFT calculations. Both isomers act as ligands towards arene-RuII centers, leading either to E-configured 5-membered chelates (involving coordination of nitrogen atoms from N=N bond and pyridine) or to the uncommon Z-configured 7-membered chelates (involving coordination of nitrogen atoms from both pyridines). The latter show good stability in the dark, allowing single crystal X-ray diffraction study to be reported here for the first time. All synthesized Z-configured arene-RuII complexes undergo irreversible photo-isomerization to their corresponding E isomers with rearrangement of their coordination pattern. This property was advantageously exploited for the light-promoted unmasking of a basic nitrogen atom of the ligand.

Photocatalytic Transformation of Biomass and Biomass Derived Compounds-Application to Organic Synthesis

Biomass and biomass-derived compounds have become an important alternative feedstock for chemical industry. They may replace fossil feedstocks such as mineral oil and related platform chemicals. These compounds may also be transformed conveniently into new innovative products for the medicinal or the agrochemical domain. The production of cosmetics or surfactants as well as materials for different applications are examples for other domains where new platform chemicals obtained from biomass can be used. Photochemical and especially photocatalytic reactions have recently been recognized as being important tools of organic chemistry as they make compounds or compound families available that cannot be or are difficultly synthesized with conventional methods of organic synthesis. The present review gives a short overview with selected examples on photocatalytic reactions of biopolymers, carbohydrates, fatty acids and some biomass-derived platform chemicals such as furans or levoglucosenone. In this article, the focus is on application to organic synthesis.

Recent Advances and Challenges in Long Wavelength Sensitive Cationic Photoinitiating Systems

With the advantages offered by cationic photopolymerization (CP) such as broad wavelength activation, tolerance to oxygen, low shrinkage and the possibility of "dark cure", it has attracted extensive attention in photoresist, deep curing and other fields in recent years. The applied photoinitiating systems (PIS) play a crucial role as they can affect the speed and type of the polymerization and properties of the materials formed. In the past few decades, much effort has been invested into developing cationic photoinitiating systems (CPISs) that can be activated at long wavelengths and overcome technical problems and challenges faced. In this article, the latest developments in the long wavelength sensitive CPIS under ultraviolet (UV)/visible light-emitting diodes (LED) lights are reviewed. The objective is, furthermore, to show differences as well as parallels between different PIS and future perspectives.

Photochemical Processes of Superbase Generation in Xanthone Carboxylic Salts

Photobase generators are species that allow the photocatalysis of various reactions, such as thiol-Michael, thiol-isocyanate, and ring-opening polymerization reactions. However, existing compounds have complex syntheses and low quantum yields. To overcome these problems, photobase generators based on the photodecarboxylation reaction were developed. We synthesized and studied the photochemistry and photophysics of two xanthone photobase, their carboxylic acid precursors, and their photoproducts to understand the photobase generation mechanism. We determined accurate quantum yields of triplet states and photobase generation. The effect of the intermediate radical preceding the base release was demonstrated. We characterized the photophysics of the photobase by femtosecond spectroscopy and showed that the photodecarboxylation process occurred from the second excited triplet state with a rate constant of 2.2×10⁹  s^-1 .

Recent Advances on Furan-Based Visible Light Photoinitiators of Polymerization

Photopolymerization is an active research field enabling to polymerize in greener conditions than that performed with traditional thermal polymerization. At present, a great deal of effort is devoted to developing visible light photoinitiating systems. Indeed, the traditional UV photoinitiating systems are currently the focus of numerous safety concerns so alternatives to UV light are being actively researched. However, visible light photons are less energetic than UV photons so the reactivity of the photoinitiating systems should be improved to address this issue. In this field, furane constitutes an interesting candidate for the design of photocatalysts of polymerization due to its low cost and its easy chemical modification. In this review, an overview concerning the design of furane-based photoinitiators is provided. Comparisons with reference systems are also established to demonstrate evidence of the interest of these photoinitiators in innovative structures.

Surface supramolecular assemblies tailored by chemical/physical and synergistic stimuli: a scanning tunneling microscopy study

Supramolecular self-assemblies formed by various non-covalent interactions can produce diverse functional networks on solid surfaces. These networks have recently attracted much interest from both fundamental and application points of view. Unlike covalent organic frameworks (COFs), the properties of the assemblies differ from each other depending on the constituent motifs. These various motifs may find diverse applications such as in crystal engineering, surface modification, and molecular electronics. Significantly, these interactions between/among the molecular tectonics are relatively weak and reversible, which makes them responsive to external stimuli. Moreover, for a liquid-solid-interface environment, the dynamic processes are amenable to in situ observation using scanning tunneling microscopy (STM). In the literature, most review articles focus on supramolecular self-assembly interactions. This review summarizes the recent literature in which stimulation sources, including chemical, physical, and their combined stimuli, cooperatively tailor supramolecular assemblies on surfaces. The appropriate design and synthesis of functional molecules that can be integrated on different surfaces permits the use of nanostructured materials and devices for bottom-up nanotechnology. Finally, we discuss synergic effect on materials science.

High-Performance Photoinitiating Systems for LED-Induced Photopolymerization

Currently, increasing attention has been focused on light-emitting diodes (LEDs)-induced photopolymerization. The common LEDs (e.g., LED at 365 nm and LED at 405 nm) possess narrow emission bands. Due to their light absorption properties, most commercial photoinitiators are sensitive to UV light and cannot be optimally activated under visible LED irradiation. Although many photoinitiators have been designed for LED-induced free radical polymerization and cationic polymerization, there is still the issue of the mating between photoinitiators and LEDs. Therefore, the development of novel photoinitiators, which could be applied under LED irradiation, is significant. Many photoinitiating systems have been reported in the past decade. In this review, some recently developed photoinitiators used in LED-induced photopolymerization, mainly in the past 5 years, are summarized and categorized as Type Ⅰ photoinitiators, Type Ⅱ photoinitiators, and dye-based photoinitiating systems. In addition, their light absorption properties and photoinitiation efficiencies are discussed.

Spotting Trends in Organocatalyzed and Other Organomediated (De)polymerizations and Polymer Functionalizations

Organocatalysis has evolved into an effective complement to metal- or enzyme-based catalysis in polymerization, polymer functionalization, and depolymerization. The ease of removal and greater sustainability of organocatalysts relative to transition-metal-based ones has spurred development in specialty applications, e.g., medical devices, drug delivery, optoelectronics. Despite this, the use of organocatalysis and other organomediated reactions in polymer chemistry is still rapidly developing, and we envisage their rapidly growing application in nascent areas such as controlled radical polymerization, additive manufacturing, and chemical recycling in the coming years. In this Review, we describe ten trending areas where we anticipate paradigm shifts resulting from novel organocatalysts and other transition-metal-free conditions. We highlight opportunities and challenges and detail how new discoveries could lead to previously inaccessible functional materials and a potentially circular plastics economy.

Quantification of Excited-State Brønsted-Lowry Acidity of Weak Photoacids Using Steady-State Photoluminescence Spectroscopy and a Driving-Force-Dependent Kinetic Theory

Photoacids and photobases constitute a class of molecules that upon absorption of light undergoes a reversible change in acidity, i.e. pK_a. Knowledge of the excited-state pK_a value, pK_a*, is critical for predicting excited-state proton-transfer behavior. A reasonable approximation of pK_a* is possible using the Förster cycle analysis, but only when the ground-state pK_a is known. This poses a challenge for the study of weak photoacids (photobases) with less acidic (basic) excited states (pK_a* (pK_b*) > 7), because ground-state pK_a (pK_b) values are >14, making it difficult to quantify them accurately in water. Another method to determine pK_a* relies on acid-base titrations with photoluminescence detection and Henderson-Hasselbalch analysis. This method requires that the acid dissociation reaction involving the thermally equilibrated electronic excited state reaches chemical quasi-equilibrium, which does not occur for weak photoacids (photobases) due to slow rates of excited-state proton transfer. Herein, we report a method to overcome these limitations. We demonstrate that liquid water and aqueous hydroxide are unique proton-accepting quenchers of excited-state photoacids. We determine that Stern-Volmer quenching analysis is appropriate to extract rate constants for excited-state proton transfer in aqueous solutions from a weak photoacid, 5-aminonaphthalene-1-sulfonate, to a series of proton-accepting quenchers. Analysis of these data by Marcus-Cohen bond-energy-bond-order theory yields an accurate value for pK_a* of 5-aminonaphthalene-1-sulfonate. Our method is broadly accessible because it only requires readily available steady-state photoluminescence spectroscopy. Moreover, our results for weak photoacids are consistent with those from previous studies of strong photoacids, each showing the applicability of kinetic theories to interpret driving-force-dependent rate constants for proton-transfer reactions.

Arylazo Sulfones as Nonionic Visible-Light Photoacid Generators

The selective visible-light-driven generation of a weak acid (sulfinic acid, in nitrogen-purged solutions) or a strong acid (sulfonic acid, in oxygen-purged solutions) by using shelf-stable arylazo sulfones was developed. These sulfones were then used for the green, smooth, and efficient photochemical catalytic protection of several (substituted) alcohols (and phenols) as tetrahydropyranyl ethers or acetals.

Visible-Light-Initiated Palladium-Catalyzed Cross-coupling by PPh3 Uncaging from an Azobenzene Ruthenium-Arene Complex

Photo-release of triphenylphosphine from a sulfonamide azobenzene ruthenium-arene complex was exploited to activate PdII Cl2 into Pd0 catalyst, for the photo-initiation of Sonogashira cross-coupling. The transformation was initiated on demand - by using simple white LED strip lights - with a high temporal response and the ability to control reaction rate by changing the irradiation time. Various substrates were successfully applied to this photo-initiated cross-coupling, thus illustrating the wide functional-group tolerance of our photo-caged catalyst activator, without any need for sophisticated photochemistry apparatus.

Synthesis and Characterization of Multifunctional Secondary Thiol Hardeners Using 3-Mercaptobutanoic Acid and Their Thiol-Epoxy Curing Behavior

3-Mercaptobutanoic acid (3-MBA) was synthesized by the less odorous Michael addition pathway using an isothiouronium salt intermediate. Using the synthesized 3-MBA, multifunctional secondary thiol (sec-thiol) compounds were obtained and applied to thiol-epoxy curing systems as hardeners. As the functionality of the sec-thiol hardeners increased, the purity of the product obtained after distillation decreased. The equivalent epoxy mixtures with multifunctional sec-thiol hardeners were evaluated based on their impact on the curing behavior in thiol-epoxy click reactions by differential scanning calorimetry. The thermal features of sec-thiol-epoxy click reactions in the presence of a base catalyst were assessed according to the functionality of the sec-thiol hardeners. Our results showed that sec-thiol hardeners with less reactivity to the epoxy group provide long-term storage stability for the formulated epoxy resin, promising for industrial applications.