Mechanometallaphotoredox Catalysis: Utilizing Increased Throughput Mechanochemistry to Develop Solvent-Minimized Aryl Amination and C(sp2)-C(sp3) Cross-Coupling Reactions with Increased Tolerance to Aerobic Conditions

Photocatalysis as a tool used in organic synthesis has predominantly relied on the use of solvents, be it under homogeneous or heterogeneous conditions. In particular, metallaphotoredox catalysis reactions commonly use toxic organic solvents such as DMA and DMF. Herein, we demonstrate how mechanophotocatalysis, the synergistic union of mechanochemistry and photocatalysis, is compatible with this class of dual catalysis reactions involving both photocatalyst and nickel(II) cocatalysts. Using ball milling, these mechanistically complex reactions can be conducted in the absence of a bulk solvent and under air, affording high-yielding aryl aminations and C(sp2)-C(sp3) cross-couplings with alkyl carboxylic acids, alkyl trifluoroborate salts, and alkyl bromides. These advances are facilitated by the introduction of a novel reaction vessel design for conducting four mechanophotocatalysis reactions simultaneously. This work highlights the promise of solvent-minimized photocatalysis reactions, demonstrating that in these examples bulk solvent is redundant, thus significantly reducing this waste stream. Through time-resolved photoluminescence studies, we observed that the excited states of five different photocatalysts were quenched by oxygen more significantly in solution than in the solid state, providing evidence for the origin of the increased tolerance to aerobic conditions that these mechanophotocatalysis reactions experience.

Competitive Spatial Donor/Acceptor Interaction toward Efficient Blue Thermally Activated Delayed Fluorescence

Through-space charge-transfer (TSCT) thermally activated delayed fluorescence (TADF) emitters show great promise for blue organic light-emitting diodes (OLEDs) but face challenges such as low efficiency and limited color purity. In this study, we designed and synthesized three asymmetric TSCT-TADF materials─CzTPT-PA, CzTPT-CIA, and CzTPT-IA─based on a dual donor/acceptor (D1/A/D2) architecture. The molecular design strategically leverages dominant donor-acceptor interactions and auxiliary coupling effects within a unique sandwich-like π-stacked structure, enabling precise control over excited-state properties. This design achieves blue-shifted emission while maintaining high photoluminescence quantum yields, addressing efficiency loss and concentration quenching through spatially confined interactions and locked molecular conformations. The resulting OLEDs exhibited blue electroluminescence with color coordinates of (0.16, 0.27), (0.15, 0.18), and (0.15, 0.09) for CzTPT-PA, CzTPT-CIA, and CzTPT-IA, respectively, alongside maximum external quantum efficiencies of 25.0%, 15.5%, and 9.9%. Notably, the CzTPT-IA-based device achieved deep-blue emission with high color purity, representing a significant advancement in the field. This work introduces an effective design strategy for TSCT-TADF emitters, paving the way for high-performance, blue OLEDs with enhanced efficiency and color precision.

Crystallization of L-Cysteine in Heavy Water Induces Intrinsic Fluorescence

Developing noninvasive techniques that can probe how solvents modulate the nucleation pathways of bioorganic molecules in solution remains an active and open area of research. Herein, we investigate the crystallization of the amino acid L-Cysteine and show that both the structure of the crystal and its intrinsic fluorescence can be drastically altered by the solvent. Crystals formed in heavy water exhibit markedly different intermolecular packing as well as strikingly different monomer conformations compared to those in light water. Remarkably, these differences in the supramolecular packing result in significantly elevated intrinsic fluorescence in the crystal that is formed in heavy water. Using a combination of experimental techniques and advanced electronic structure approaches, we elucidate the molecular interactions within the crystals that govern both the electronic origins and the intensity of their emission. These findings demonstrate how tuning the solvent by changing its isotope leads to the emergence of design principles for new intrinsic fluorophores that could serve as novel sensing probes for biomedical applications.

Photosensitized Gold-Catalyzed Cross-Couplings of Aryl Bromides

Recently, ligand-promoted Au(I)/Au(III)-catalyzed cross-coupling reactions with aryl iodides have garnered considerable attention. Here, we report the first visible-light-driven gold-catalyzed cross-couplings of challenging aryl bromides. In the presence of a (P, N)-gold(I) catalyst and an acridinium photocatalyst under blue LED irradiation, C-O coupling of aryl bromides with carboxylic acids was achieved, and soon it was found that this photoinduced gold-catalyzed cross-coupling of aryl bromides was appliable for other C-C, C-N, and C-S bond formation. Experimental and computational studies suggest that this visible-light-driven gold-catalyzed cross-couplings of aryl bromides involves two discrete photoinduced energy transfer (EnT) events: first, energy transfer (EnT) from a photosensitizer produces an excited-state gold(I) complex that allows the bottleneck oxidative addition of aryl bromides to form an aryl Au(III) complex and second, the reductive elimination of aryl-Au(III) complex to regenerate Au(I). Collectively, the new synergistic catalytic method developed here highlights the tremendous potential of photochemical gold catalysis via excited-state organogold complexes, as well as its potential to facilitate drug discovery due to the biocompatibility and mildness of the reaction conditions.

An Organic EnT Photocatalyst 4CzMeBN and the Application in the Synthesis of cis-Fused Azetidines

A powerful EnT photocatalyst 4CzMeBN has been developed and utilized in the synthesis of cis-fused azetidines via dearomative [2+2] cycloaddition under visible light. The photocatalyst 4CzMeBN is a donor-acceptor cyanoarene and features high triplet state energy and long lifetime of triplet state, which would be an alternative to widely used EnT photocatalyst Ir[dF(CF3)ppy]2(dtbbpy)PF6. The photochemical [2+2] cycloaddition provides a facile method to synthesize valuable dihydroisoquinolone-fused azetidines with high efficiency.

Hyperconjugation Engineering of π-Extended Azaphosphinines for Designing Tunable Thermally Activated Delayed Fluorescence Emitters

Implanting heteroatoms into organic π-conjugated molecules (OCMS) offered a great opportunity to fine-tune the chemical structures and optoelectronic properties. This work describes a new family of 1,4-azaphosphinines with extended σ-π hyperconjugations. The photophysical studies revealed that azaphosphinines exhibited narrow-band thermally activated delayed fluorescence (TADF) ( full width at half-maximum: 26-40 nm). According to the orbital localization analysis and natural bond orbital analysis, the effective σ*-π* hyperconjugation is believed to induce the multiple-resonance (MR) TADF, which is distinct from the p-π conjugation-induced MR-TADF in BN systems. Although having the large ΔES1-T1s (>3.0 ev), the study suggested that σ*-π hyperconjugation endowed the system with the structural vibration favorable for the spin-vibronic-assisted RISC. Having the tunable p-centers (lp, O, S, Se, and Me+), azaphosphinines showed a fine-tuned TADF. Generally, azaphosphinines with strong σ*-π* hyperconjugations showed small ΔES1-T1s, efficient RISCs, and high PLQYs. Leveraging on the efficient hyperconjugations, TADF emission of the system spanned from UV-blue to green. Particularly, extended azaphosphinines exhibited the high photoluminescence quantum yields (74% in toluene and 92% in the 10% doped PMMA). As a proof of concept, two azaphosphinines with a PO center were applied as the light-emitting materials in organic lighting-emitting diodes. The devices showed the narrow-band UV- and deep-blue emission with EQE as high as 10.3%. The current study offered us a new strategy, namely, σ-π hyperconjugation-induced MR-TADF, for designing OCMs with tunable light-emitting properties.

Silver(I)-iodine cluster with efficient thermally activated delayed fluorescence and suppressed concentration quenching

Reports on highly efficient silver(I)-based thermally activated delayed fluorescence (TADF) materials are scarce due to challenges in molecular design, although these materials show great potential for photoluminescent and electroluminescent applications. Herein, a silver(I)-iodine cluster, namely Ag2I2(dppb-Ac)2, is synthesized by employing a donor-acceptor (D-A) type bisphosphine ligand. Due to the introduction of electron-donating iodine ligands, Ag2I2(dppb-Ac)2 exhibits an emissive singlet state characterized by (metal + iodine)-to-ligand charge transfer and intra-ligand charge transfer transitions, as well as a small singlet-triplet energy gap. Additionally, its non-planar, highly distorted D-A structure efficiently separates adjacent molecules in aggregated state. As a result, Ag2I2(dppb-Ac)2 exhibits efficient TADF and suppressed luminescence concentration quenching in thin films. For instance, the 10 wt%-doped PMMA film and neat film of Ag2I2(dppb-Ac)2 display bright bluish-green and green emission, peaking at 506 and 532 nm, with photoluminescence quantum yields (PLQYs) of 70% and 52%, and lifetimes of 18.9 and 7.9 μs, respectively. The high PLQYs and efficiently suppressed emission concentration quenching of Ag2I2(dppb-Ac)2 in films are outstanding among reported Ag(I)-based TADF emitters.

Cross-Coupling Reactions with Nickel, Visible Light, and tert-Butylamine as a Bifunctional Additive

Transition metal catalysis is crucial for the synthesis of complex molecules, with ligands and bases playing a pivotal role in optimizing cross-coupling reactions. Despite advancements in ligand design and base selection, achieving effective synergy between these components remains challenging. We present here a general approach to nickel-catalyzed photoredox reactions employing tert-butylamine as a cost-effective bifunctional additive, acting as the base and ligand. This method proves effective for C-O and C-N bond-forming reactions with a diverse array of nucleophiles, including phenols, aliphatic alcohols, anilines, sulfonamides, sulfoximines, and imines. Notably, the protocol demonstrates significant applicability in biomolecule derivatization and facilitates sequential one-pot functionalizations. Spectroscopic investigations revealed the robustness of the dynamic catalytic system, while elucidation of structure-reactivity relationships demonstrated how computed molecular properties of both the nucleophile and electrophile correlated to reaction performance, providing a foundation for effective reaction outcome prediction.

Individually Tunable Energy Levels of Oligomers Based on N-B←N Units

Opto-electronic properties and device performance of organic semiconductors are mainly determined by energy levels of their frontier molecular orbitals, e.g. lowest unoccupied molecular orbital (ELUMO) and highest occupied molecular orbital (EHOMO) in the ground state, first singlet state (ES1) and first triplet state (ET1) in the excited state. These energy levels are always intricately intertwined. Herein, we report a series of monodisperse oligomers based on double B←N bridged bipyridine (BNBP) units. With the increasing number of repeating units, the oligomers exhibit gradually downshifted ELUMO and nearly unchanged EHOMO due to the different distribution of the frontier molecular orbitals of the oligomers. Moreover, the oligomers exhibit gradually decreasing ES1 and nearly unchanged ET1 because of the different contributions of the charge transfer component in the excited state. This work provides new insight into energy level tuning of organic semiconductors, which is important for high-performance organic opto-electronic devices.

Reversible Nucleophilic Ring-Opening of Tetraoxapentacene Derivatives: Accessing New Materials for Thermally Activated Delayed Fluorescence

We report the unexpected nucleophilic ring-opening reaction of electron deficient dioxins in the presence of carbazole under basic conditions. This nucleophilic ring-opening reaction is reversible under basic conditions in the absence of nucleophiles. Further, we demonstrate that this unexpected reactivity can be used to prepare novel donor-acceptor compounds that are emissive in solution and as thin films and exhibit thermally activated delayed fluorescence (TADF).

Ketonized Carbonitride Assembled Face Mask with Long-Term Light Triggered Antimicrobial Ability for Bioprotective Applications

The worldwide transmission of infectious respiratory pathogens has caused innumerable deaths and suffering, while wearing a face mask is still the most effective way to terminate the respiratory infections spread. However, the frequent mask replacement as a result of the lack of pathogen sterilization ability not only increases the cross-contamination risk but also, even worse, produces a large amount of medical waste. In this work, we report on a ketonized carbonitride functionalized bioprotective face mask with pathogen sterilization activity that can effectively produce biocidal singlet oxygen triggered by light irradiation. Ketonized carbonitride loading on the outer layer of the mask is found to be capable of generating singlet oxygen, enabling the mask with antibacterial ability. Thanks to its high pathogen inactivation activity, the as-prepared mask exhibits long-term light triggered health protection performance, which, in return, reduces medical waste production as a result of the decreased mask replacement frequency. The synthesis of a fascinating bioprotective mask provides a new viewpoint into the development of personal bioprotective devices for health protection.

Achieving Tunable Monomeric TADF and Aggregated RTP via Molecular Stacking

Organic emitters with both thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) have attracted widespread interest for their intriguing luminescent properties. Herein, a series of triphenylamine-substituted isoquinoline derivatives possessing monomeric TADF and aggregated RTP properties are reported. As the molecules exhibited various forms of π-π and charge transfer (CT) stacking with different intensities, inter/intramolecular CT can be meticulously modulated to achieve tunable TADF-RTP. Aggregated phosphorescence originates from intermolecular CT initiated by CT dimers, whereas monomeric TADF is facilitated by intramolecular CT enhanced by π-π dimers. Leveraging the properties of these molecules, luminescent materials with tunable TADF-RTP properties in multistates are obtained by molecular substitution position alignment, dealing with different solvents, grinding, adjusting concentration, changing polymer matrix, photoactivation, and heat treatment. This work is critical for a deeper understanding of construction and regulation of the TADF-RTP dual-channel emission, enabling the development of advanced optoelectronic devices with tailored emission properties.

Light-Induced 1,3-Thiosulfonylation of β,γ-Unsaturated Ketones with Thiosulfonates

Sulfur-containing compounds exhibit potent significance in drug molecules. Thiosulfonates as 1,3-thiosulfonylation reactants to olefins have yet to be investigated. Herein, we report photoinduced 1,3-difunctionalization of β,γ-unsaturated ketones with thiosulfonates, which undergo a radical 1,2-acyl shift. The protocol features mild conditions, high regioselectivity, and 100% atom economy.

Exciplex, Not Heavy-Atom Effect, Controls the Triplet Dynamics of a Series of Sulfur-Containing Thermally Activated Delayed Fluorescence Molecules

The efficiency of thermally activated delayed fluorescence (TADF) in organic materials relies on rapid intersystem crossing rates and fast conversion of triplet (T) excitons into a singlet (S) state. Heavy atoms such as sulfur or selenium are now frequently incorporated into TADF molecular structures to enhance these properties by increased spin-orbit coupling [spin orbit coupling (SOC)] between the T and S states. Here a series of donor-acceptor (D-A) molecules based on 12H-benzo[4,5]thieno[2,3-a]carbazole and dicyanopyridine is compared with their nonsulfur control molecules designed to probe such SOC effects. We reveal that unexpected intermolecular interactions of the D-A molecules with carbazole-containing host materials instead serve as the dominant pathway for triplet decay kinetics in these materials. In-depth photophysical and computational studies combined with organic light emitting diode measurements demonstrate that the anticipated heavy-atom effect from sulfur is overshadowed by exciplex formation. Indeed, even the unsubstituted acceptor fragments exhibit pronounced TADF exciplex emission in appropriate carbazole hosts. The intermolecular charge transfer and TADF in these systems are further confirmed by detailed time-dependent density functional theory studies. This work demonstrates that anticipated heavy-atom effects in TADF emitters do not always control or even impact the photophysical and electroluminescence properties.

Unraveling the Photocatalytic Mechanism of N2 Fixation on Single Ruthenium Sites

Photocatalytic N2 fixation offers promise for ammonia synthesis, yet traditional photocatalysts encounter challenges such as low efficiency and short carrier lifetimes. Atomically precise ligand-metal nanoclusters emerge as a solution to address these issues, but the photophysical mechanism remains elusive. Inspired by the synthesis of Au4Ru2 NCs, we investigate the mechanism behind N2 activation on Au4Ru2, focusing on photoactivity and carrier dynamics. Our results reveal that vibration of the Ru-N bond in the low-frequency domain suppresses the deactivation process leading to a long lifetime of the excited N2. By the strategy of isoelectronic substitution, we identify the single Ru sites as the active sites for N2 activation. Furthermore, these ligand-protected M4Ru2 (M = Au, Ag, Cu) NCs show robust thermal stability in explicit solvation and decent photochemical activity for N2 activation and NH3 production. These findings have significant implications for the optimization of catalysts for sustainable ammonia synthesis.

Organic Photoredox-Catalyzed S-Trifluoromethylation of Aromatic and Heteroaromatic Thiols

A visible-light-mediated trifluoromethylation protocol was developed for the conversion of (hetero)aromatic thiols to their respective S-trifluoromethylated derivatives employing trifluoromethanesulfonyl chloride (CF3SO2Cl) as a cost-effective source of trifluoromethyl radical (CF3·) and a highly reducing organophotocatalyst, 3DPA2FBN. The developed methodology is operationally simple, providing access to a diverse range of products in up to 92% yield. A plausible mechanism has been postulated based on preliminary mechanistic studies, including irradiation on/off, UV-vis studies, and radical trapping experiments.

Mechanisms of Photoredox Catalysis Featuring Nickel-Bipyridine Complexes

Metallaphotoredox catalysis can unlock useful pathways for transforming organic reactants into desirable products, largely due to the conversion of photon energy into chemical potential to drive redox and bond transformation processes. Despite the importance of these processes for cross-coupling reactions and other transformations, their mechanistic details are only superficially understood. In this review, we have provided a detailed summary of various photoredox mechanisms that have been proposed to date for Ni-bipyridine (bpy) complexes, focusing separately on photosensitized and direct excitation reaction processes. By highlighting multiple bond transformation pathways and key findings, we depict how photoredox reaction mechanisms, which ultimately define substrate scope, are themselves defined by the ground- and excited-state geometric and electronic structures of key Ni-based intermediates. We further identify knowledge gaps to motivate future mechanistic studies and the development of synergistic research approaches spanning the physical, organic, and inorganic chemistry communities.

Photocatalytic α-arylation of cyclic ketones by a thermally activated delayed fluorescence molecule

α-Arylation of cyclic ketones via an organophotocatalytic route has been described utilizing PXZ-TRZ, a molecule displaying thermally activated delayed fluorescence (TADF). Using this route, a plethora of cyclic ketones including cyclohexanone, cyclopentanone and even cyclooctanone can be effectively arylated with many aryl iodides or bromides under mild conditions.

Photocatalyzed C3-H Nitrosylation of Imidazo[1,2-a]pyridine under Continuous Flow and External Photocatalyst-, Oxidant-, and Additive-Free Conditions

This study reports a protocol for the highly regioselective photocatalyzed C-H nitrosylation of imidazo[1,2-a]pyridine scaffolds at the C3 position under a combination of visible-light irradiation and continuous flow without any external photocatalyst. This protocol involves mild and safe conditions and shows good tolerance to air and water along with excellent functional group compatibility and site selectivity, generating various 3-nitrosoimidazo[1,2-a]pyridines in excellent yields under photocatalyst-, oxidant-, and additive-free conditions.Notably, the proposed nitrosylation reaction, which introduces the chromophore NO into imidazo[1,2-a]pyridine scaffolds, occurs efficiently under visible-light irradiation without any additional photocatalyst owing to the intense light-absorption characteristics of the nitrosylation products. This study could guide future studies on the development of green organic-synthesis strategies with a wide variety of potential applications.

Role of Bridging Groups in Regulating the Luminescence and Charge Transfer Properties of Thermally Activated Delayed Fluorescence Molecules: A Theoretical Perspective

Organic emitters with a simultaneous combination of aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF) characteristics are in great demand due to their excellent comprehensive performances toward efficient organic light-emitting diodes (OLEDs), biomedical imaging, and the telecommunications field. However, the development of efficient AIE-TADF materials remains a substantial challenge. In this work, light-emitting properties of two AIE-TADF molecules with different bridging groups ICz-BP and ICz-DPS are theoretically investigated in the solid state with the combined quantum mechanics/molecular mechanics (QM/MM) method and the thermal vibration correlation function (TVCF) theory. The research indicates that the C═O bridging bond in ICz-BP is more favorable than the S═O bridging bond in ICz-DPS for enhancing the planarity of the acceptor, increasing conjugation, and thereby elevating the transition dipole moment density. Simultaneously, the stacking pattern of ICz-BP in the solid facilitates a reduction in energy gap between S1 and T1 (ΔEST), achieving rapid reverse intersystem crossing rate (kRISC). Furthermore, compared to toluene, the stacking patterns of ICz-BP and ICz-DPS in the solid effectively suppress the out-of-plane wagging vibration of the acceptor, thereby inhibiting the loss of nonradiative energy in the excited state and realizing aggregation-induced emission. Moreover, the charge transport properties of both electrons and holes in ICz-BP are found to be higher than the corresponding rates in ICz-DPS, attributed to the smaller internal reorganization energy of ICz-BP in the solid state. Additionally, the calculations reveal a more balanced charge transport characteristic in ICz-BP, contributing to efficient exciton recombination and emission and ultimately mitigating efficiency roll-off. Based on these computational results, we aim to unveil the relationship between molecular structure and light-emitting properties, aiding in the design and development of efficient AIE-TADF devices.

Strategic Insertion of Heavy Atom to Tailor TADF OLED Material for the Development of Type I Photosensitizing Catalytic Red Emissive Assemblies

The work presented in the manuscript describes a simple strategy for transforming thermally activated delayed fluorescent organic light-emitting diodes (TADF OLEDs) compound 10-(dibenzo[a,c]phenazin-11-yl)-10H-phenoxazine (DPZ-PXZ) into type I photosensitizer 10-(dibenzo[a,c]phenazin-11-yl)-10H-phenothiazine (DPZ-PHZ) by strategically introducing sulfur atom in the photosensitizing core. The synthesized compound DPZ-PHZ exhibits aggregation-induced enhancement (AIE) and through-space charge transfer (TSCT) characteristics and generates red emissive assemblies in mixed aqueous media. The original compound DPZ-PXZ exhibits well-separated HOMO and LUMO levels and is reported to have highly efficient reverse intersystem crossing (RISC). In comparison, the incorporation of sulfur atom in the phenothiazine donor regulates the electronic communication between donor and acceptor units and promotes the intersystem crossing (ISC) in DPZ-PHZ molecules. Interestingly, compound DPZ-PHZ exhibits rapid activation of aerial oxygen for instant generation of superoxide radical anion. Backed by excellent type I photosensitizing activity, DPZ-PHZ assemblies have high catalytic potential for the synthesis of benzimidazoles, benzothiazoles and quinazolines derivatives under mild reaction conditions. The work presented in the manuscript provides an insight into the combination of heavy atom approach and TSCT for achieving adequate electronic communication between donor and acceptor units, balanced RISC/ISC, and stabilized-charge separated state for the development of efficient type I photosensitizing assemblies.

Red Light-Blue Light Chromoselective C(sp2)-X Bond Activation by Organic Helicenium-Based Photocatalysis

Chromoselective bond activation has been achieved in organic helicenium (nPr-DMQA+)-based photoredox catalysis. Consequently, control over chromoselective C(sp2)-X bond activation in multihalogenated aromatics has been demonstrated. nPr-DMQA+ can only initiate the halogen atom transfer (XAT) pathway under red light irradiation to activate low-energy-accessible C(sp2)-I bonds. In contrast, blue light irradiation initiates consecutive photoinduced electron transfer (conPET) to activate more challenging C(sp2)-Br bonds. Comparative reaction outcomes have been demonstrated in the α-arylation of cyclic ketones with red and blue lights. Furthermore, red-light-mediated selective C(sp2)-I bonds have been activated in iodobromoarenes to keep the bromo functional handle untouched. Finally, the strength of the chromoselective catalysis has been highlighted with two-fold functionalization using both photo-to-transition metal and photo-to-photocatalyzed transformations.

A general supramolecular strategy for fabricating full-color-tunable thermally activated delayed fluorescence materials

Developing a facile and feasible strategy to fabricate thermally activated delayed fluorescence materials exhibiting full-color tunability remains an appealing yet challenging task. In this work, a general supramolecular strategy for fabricating thermally activated delayed fluorescence materials is proposed. Consequently, a series of host-guest cocrystals are prepared by electron-donating calix[3]acridan and various electron-withdrawing guests. Owing to the through-space charge transfer mediated by multiple noncovalent interactions, these cocrystals all display efficient thermally activated delayed fluorescence. Especially, by delicately modulating the electron-withdrawing ability of the guest molecules, the emission colors of these cocrystals can be continuously tuned from blue (440 nm) to red (610 nm). Meanwhile, high photoluminescence quantum yields of up to 87% is achieved. This research not only provides an alternative and general strategy for the fabrication of thermally activated delayed fluorescence materials, but also establishes a reliable supramolecular protocol toward the design of advanced luminescent materials.

Organic Photothermal Materials Obtained Using Thermally Activated Delayed Fluorescence Design Principles

Organic small molecules with high photothermal conversion efficiencies that absorb near-infrared light are desirable for photothermal therapy due to their improved biocompatibility compared to inorganic materials and their ability to absorb light in the biological transparency window (650-1350 nm). Here we report three donor-acceptor organic materials DM-ANDI, O-ANDI, and S-ANDI that show high photothermal conversion efficiencies of 46-68 % with near-infrared absorption. The design of these molecules is based on the rational modification of a thermally activated delayed fluorescence material to favour a low photoluminescence quantum yield by reducing HOMO-LUMO overlap. Encapsulating these materials into either neat nanoparticles or aggregated organic dots modulates their photothermal conversion efficiencies, and also facilitates dispersion in water.

A Paradigm Shift in Catalysis: Electro- and Photomediated Nickel-Catalyzed Cross-Coupling Reactions

ConspectusTransition-metal catalyzed cross-coupling reactions are fundamental reactions in organic chemistry, facilitating strategic bond formations for accessing natural products, organic materials, agrochemicals, and pharmaceuticals. Redox chemistry enables access to elusive cross-coupling mechanisms through single-electron processes as an alternative to classical two-electron strategies predominated by palladium catalysis. The seminal reports of Baran, MacMillan, Doyle, Molander, Weix, Lin, Fu, Reisman, and others in merging redox perturbation (photochemical, electrochemical, and purely chemical) with catalysis are pivotal to the current resurgence and mechanistic understanding of first-row transition metal-based catalysis. The hallmark of this redox platform is the systematic modulation of transition-metal oxidation states by a photoredox catalyst or at a heterogeneous electrode surface. Electrocatalysis and photocatalysis enhance transition metal catalysis' capacity for bond formation through electron- or energy-transfer processes that promote otherwise challenging elementary steps or elusive mechanisms. Cross-coupling conditions promoted by electrocatalysis and photocatalysis are mild, and bond formation proceeds with exceptionally high chemoselectivity and wide functional group tolerance. The interfacing of abundant first-row transition-metal catalysis with electrocatalysis and photocatalysis has brought about a paradigm shift in cross-coupling technology as practitioners are quickly applying these tools in synthesizing fine chemicals and pharmaceutically relevant motifs. In particular, the merger of Ni catalysis with electro- and photochemistry ushered in a new era for carbon-carbon and carbon-heteroatom cross-couplings with expanded generality compared to their thermally driven counterparts. Over the past decade, we have developed enabling photo- and electrochemical methods throughout our combined research experience in industry (BMS, AstraZeneca) and academia (Professor Baran, Scripps Research) in cross-disciplinary collaborative environments. In this Account, we will outline recent progress from our past and present laboratories in photo- and electrochemically mediated Ni-catalyzed cross-couplings. By highlighting these cross-coupling methodologies, we will also compare mechanistic features of both electro- and photochemical strategies for forging C(sp2)-C(sp3), C(sp3)-C(sp3), C-O, C-N, and C-S bonds. Through these side-by-side comparisons, we hope to demystify the subtle differences between the two complementary tools to enact redox control over transition metal catalysis. Finally, building off the collective experience of ourselves and the rest of the community, we propose a tactical user guide to photo- and electrochemically driven cross-coupling reactions to aid the practitioner in rapidly applying such tools in their synthetic designs.