Lowering Electrocatalytic CO2 Reduction Overpotential Using N-Annulated Perylene Diimide Rhenium Bipyridine Dyads with Variable Tether Length

Rhenium coordination-induced conformational modulation in nitrogen-doped nanographene

The conformation of nanographene plays a pivotal role in determining its electronic, mechanical, and optical properties. Analyzing the conformation of nanographene is crucial because of its significant implications in various scientific and technological domains. In this work, we examined the changes in the structural conformation of nanographene upon coordination with a metal. We synthesized a series of nitrogen-doped nanographenes (2, 3, and 4) that differed by one C-C bond and their corresponding nanographene-Re complexes (2Re, 3Re, and 4Re). The conformations of the metal complexes were thoroughly analyzed using various spectroscopic techniques. A comparison of the X-ray crystal structures of nanographene before and after rhenium coordination revealed that rhenium coordination induced conformational changes in the nanographene moiety. Additionally, we assessed the catalytic activity of the nanographene-Re complexes toward the electrocatalytic hydrogen evolution reaction (HER). In the presence of a small amount of weak acid (1.5 mM acetic acid), the nanographene-Re complex exhibited hydrogen production at a low overpotential of 133 mV.

S/Se-Annulated Star-Shaped Perylene Diimides (PDIs) with Large Two-Photon Absorption (TPA) Cross-Section in NIR-I Region

Two-photon absorption (TPA) has attracted growing attention over recent years owing to the wide range of applications in organic nonlinear optical (NLO) materials. The quantitative sensitivity of a two-photon molecular entity is determined by its TPA cross-section (δTPA). Perylene diimides (PDIs) are excellent n-type organic semiconductor materials demonstrating distinguished thermal, optical, and chemical stability. Nonetheless, PDIs-based scaffolds exhibit poor δTPA in the NIR-I region (700-900 nm) due to the lack of suitable molecular design. Here, two novel star-shaped PDIs fluorophores, namely PDI-S and PDI-Se, were constructed by four periphery S/Se-fused PDIs connected with bicarbazole core. PDI-S manifested excellent δTPA of 3775 GM, which are among the highest values reported for PDIs excited in the NIR-I region.

Heterobimetallic NiFe Complex for Photocatalytic CO2 Reduction: United Efforts of NiFe Dual Sites

Catalytic CO2 reduction poses a significant challenge for the conversion of CO2 into chemicals and fuels. Ni-Fe carbon monoxide dehydrogenase ([NiFe]-CODH) effectively mediates the reversible conversion of CO2 and CO at a nearly thermodynamic equilibrium potential, highlighting the heterobimetallic cooperation for the design of CO2 reduction catalysts. However, numerous NiFe biomimetic model complexes have realized little success in CO2 reduction catalysis, which underscores the crucial role of precise bimetallic configuration and functionality. Herein, we presented a heterobimetallic NiFe complex for the photocatalytic reduction of CO2 to CO, demonstrating significantly enhanced catalytic performance compared to the homonuclear NiNi catalyst. Photocatalytic and mechanistic investigations revealed that with the assistance of a redox-active phenanthroline ligand, NiFe achieves dual-site activation of CO2 through a pivotal intermediate, NiII(μ-CO22--κC:κO)FeII, where the Lewis acidity of the FeII site plays an important role, as corroborated in the homonuclear FeFe system. This study introduces the first heteronuclear NiFe molecular catalyst capable of efficiently catalyzing the reduction of CO2 to CO, deepening insights into heterobimetallic cooperation and offering a novel strategy for designing highly active and selective CO2 reduction catalysts.

Single Entity Electrocatalysis

Making a measurement over millions of nanoparticles or exposed crystal facets seldom reports on reactivity of a single nanoparticle or facet, which may depart drastically from ensemble measurements. Within the past 30 years, science has moved toward studying the reactivity of single atoms, molecules, and nanoparticles, one at a time. This shift has been fueled by the realization that everything changes at the nanoscale, especially important industrially relevant properties like those important to electrocatalysis. Studying single nanoscale entities, however, is not trivial and has required the development of new measurement tools. This review explores a tale of the clever use of old and new measurement tools to study electrocatalysis at the single entity level. We explore in detail the complex interrelationship between measurement method, electrocatalytic material, and reaction of interest (e.g., carbon dioxide reduction, oxygen reduction, hydrazine oxidation, etc.). We end with our perspective on the future of single entity electrocatalysis with a key focus on what types of measurements present the greatest opportunity for fundamental discovery.

Low Potential CO2 Reduction by Inert Fe(II)-Macrobicyclic Complex: A New Concept of Cavity Assisted CO2 Activation

The advantage of a pre-organized π-cavity of Fe(II) complex of a newly developed macrobicycle cryptand is explored for CO2 reduction by overcoming the problem of high overpotential associated with the inert nature of the cryptate. Thus, a bipyridine-centered tritopic macrobicycle having a molecular π-cavity capable of forming Fe(II) complex as well as potential for CO2 encapsulation is synthesized. The inert Fe(II)-cryptate shows much lower potential in cyclic voltammetry than the Fe(II)-tris-dimethylbipyridine (Fe-MBP) core. Interestingly, this cryptate shows electrochemical CO2 reduction at a considerably lower potential than the Fe-MBP inert core. Therefore, this study represents that a well-structured π-cavity may generate a new series of molecular catalysts for the CO2 reduction reaction (CO2 RR), even with the inert metal complexes.

A Green Environmental Protection Photocatalytic Molecular Reactor for Aerobic Oxidation of Sulfide to Sulfoxide

The design and synthesis of metal-organic frameworks (MOFs) as photocatalytic molecular reactors for varied reactions have drawn great attention. In this work, we designed a novel photoactive perylenediimides-based (PDI) carboxylate ligand N,N'-di(3',3",5',5"-tetrakis(4-carboxyphenyl))-1,2,6,7-tetrachloroperylene-3,4,9,10-tetracarboxylic acid diimide (Cl-PDI-TA) and use it to successfully synthesize a novel Zr(IV)-based MOF 1 constructed from [Zr6 O8 (H2 O)8 ]8+ clusters bridged by Cl-PDI-TA ligands. Structural analysis revealed that Zr-MOF 1 manifests a 3D framework with (4,8)-connected csq topology and possesses triangular channels of ~17 Å and mesoporous hexagonal channels of ~26 Å along c-axis. Moreover, the synthesized Zr-MOF 1 exhibits visible-light absorption and efficient photoinduced free radical generation property, making it a promising photocatalytic molecular reactor. When Zr-MOF 1 was used as a photocatalyst for the aerobic oxidation of sulfides under irradiation of visible light, it could afford the corresponding sulfoxides with high yield and selectivity. Experimental results demonstrated that the substrate sulfides could be fixed in the pores of 1 and directly transformed to the products sulfoxides in the solid state. Furthermore, the mechanism for the photocatalytic transformation was also investigated and the results revealed that the singlet oxygen (1 O2 ) and superoxide radical (O2 ⋅- ) generated by the energy transfer and electron transfer from the photoexcited Zr-MOF to oxidants were the main active species for the catalytic reactions. This work offers a perceptive comprehension of the mechanism in PDI-based MOFs for further study on photocatalytic reactions.

Post-Functionalization of Organometallic Complexes via Click-Reaction

CuAAC (Cu catalyzed azide-alkyne cycloaddition) click-reaction is a simple and powerful method for the post-synthetic modification of organometallic complexes of transition metals. This approach allows the selective introduction of additional donor sites or functional groups to the periphery of the ligand environment. This is especially important if a metalloligand with free donor sites, which are of the same nature as the primary site for the coordination of the primary metal, has to be created. The concept of post-synthetic modification of organometallic complexes by click-reaction is relatively recent and the currently available experimental material does not yet allow us to identify trends and formulate recommendations to address specific problems. In the present study, we have applied the CuAAC reaction for the post-synthetic modification of diimine mononuclear complexes Re(I), Pt(II) and Ir(III) with C≡C bonds at the periphery of the ligand environment and demonstrated that click-chemistry is a powerful tool for the tunable chemical post-synthetic modification of coordination compounds.

Modular Regiodivergent Synthesis of Benzo-Fused Isocoumarins by a Cyclopropane Aromatization Strategy

Reported herein is an electrophile-modulated aromatization reaction of highly functionalized cyclopropanes to structurally diverse benzoisocoumarins featuring concurrent formation of the benzenoid and α-pyrone rings under mild conditions. An aromatization reaction of the proposed benzonorcaradiene intermediates prepared independently revealed a crucial role of the neighboring olefinic substituents in determining whether the cyclopropane ring expansion is followed by a 1,2-shift of the ester group.

Co-facial π-π Interaction Expedites Sensitizer-to-Catalyst Electron Transfer for High-Performance CO2 Photoreduction

The sunlight-driven reduction of CO₂ into carbonaceous fuels can lower the atmospheric CO₂ concentration and provide renewable energy simultaneously, attracting scientists to design photocatalytic systems for facilitating this process. Significant progress has been made in designing high-performance photosensitizers and catalysts in this regard, and further improvement can be realized by installing additional interactions between the abovementioned two components, however, the design strategies and mechanistic investigations on such interactions remain challenging. Here, we present the construction of molecular models for intermolecular π-π interactions between the photosensitizer and the catalyst, via the introduction of pyrene groups into both molecular components. The presence, types, and strengths of diverse π-π interactions, as well as their roles in the photocatalytic mechanism, have been examined by ¹H NMR titration, fluorescence quenching measurements, transient absorption spectroscopy, and quantum chemical simulations. We have also explored the rare dual emission behavior of the pyrene-appended iridium photosensitizer, of which the excited state can deliver the photo-excited electron to the pyrene-decorated cobalt catalyst at a fast rate of 2.60 × 10⁶ s^-1 via co-facial π-π interaction, enabling a remarkable apparent quantum efficiency of 14.3 ± 0.8% at 425 nm and a high selectivity of 98% for the photocatalytic CO₂-to-CO conversion. This research demonstrates non-covalent interaction construction as an effective strategy to achieve rapid CO₂ photoreduction besides a conventional photosensitizer/catalyst design.

Development of Tetrameric N-Annulated Perylene Diimides Using "Click" Chemistry

Herein, we report the design, synthesis, and characterization of two novel N-annulated perylene diimide (NPDI) tetramer arrays that were developed using copper catalyzed alkyne-azide cycloaddition. Despite the optoelectronic properties of both tetramers being nearly identical, the two tetramers exhibited very different molecular geometries. The twisted spirobifluorene NPDI tetramer (sbfNPDI₄ ) was found to have an extended and flexible geometry, while the planar pyrene NPDI tetramer (pyrNPDI₄ ) exhibited a highly congested and conformationally locked geometry. Organic photovoltaic devices were constructed to demonstrate the use of both new compounds as electron acceptor materials, where slightly higher power conversion efficiencies were achieved with pyrNPDI₄ than sbfNPDI₄ . This study highlights the viability of using "click" chemistry as a facile synthetic strategy towards the development of new multicomponent perylene diimide materials for organic electronic applications.

Nanoscale Double-Heterojunctional Electrocatalyst for Hydrogen Evolution

The active sites and charge/mass transfer properties in electrocatalysts play vital roles in kinetics and thermodynamics of electrocatalysis, and impose direct impacts on electrocatalytic performance, which cannot be achieved by a simplex structure. As a prototype, the authors propose a double-heterojunctional nanostructure of NiS2 /Ni3 C@C containing NiS2 /Ni3 C and Ni3 C/C heterojunctions as a general model to optimize the above issues and boost electrocatalytic performance. During the thermal reorganization, the in situ reaction between NiS2 nanoparticles and carbon induces the formation of Ni3 C between them and constructs tightly contacted two kinds of interfaces among the three components. The TEM and XPS reveal the intimately contacted three components and the as-constructed interacted dual interfaces, further confirming the formation of a porous double-heterojunctional nanostructure. Theoretical calculations uncover that the electron density redistribution occurs at Ni3 C/C interface by spontaneous electron transfer from defected carbon to Ni3 C and lower ΔGH* achieves at NiS2 /Ni3 C interface by the concentrated interfacial charge density, which favors the simultaneous realization of high catalytic activity and rapid charge/mass transfer. When applied for hydrogen evolution reaction (HER), the porous double-heterojunctional NiS2 /Ni3 C@C exhibits excellent HER activity and durability among all pH values. Profoundly, this special double-heterojunctional structure can provide a new model for high-performance electrocatalysts and beyond.

Boosting CO2-to-CO evolution using a bimetallic diketopyrrolopyrrole tethered rhenium bipyridine catalyst

The use of homogeneous electro- and photo-catalysis involving molecular catalysts offers valuable insight into reaction mechanisms as it relates to the structure–function of these tunable systems.

Electrocatalyst decomposition pathways: torsional strain in a second sphere proton relay shuts off CO2RR in a Re(2,2′-bipyridyl)(CO)3X type electrocatalyst

Group 7 tris(carbonyl) bipyridine complexes have been well explored as important CO2 reduction reaction (CO2RR) electrocatalysts and now represent an excellent platform for catalyst design.

Promoting photocatalytic CO2 reduction through facile electronic modification of N-annulated perylene diimide rhenium bipyridine dyads

The development of CO₂ conversion catalysts has become paramount in the effort to close the carbon loop. Herein, we report the synthesis, characterization, and photocatalytic CO₂ reduction performance for a series of N-annulated perylene diimide (NPDI) tethered Re(bpy) supramolecular dyads [Re(bpy-C2-NPDI-R)], where R = –H, –Br, –CN, –NO₂, –OPh, –NH₂, or pyrrolidine (–NR₂). The optoelectronic properties of these Re(bpy-C2-NPDI-R) dyads were heavily influenced by the nature of the R-group, resulting in significant differences in photocatalytic CO₂ reduction performance. Although some R-groups (i.e. –Br and –OPh) did not influence the performance of CO₂ photocatalysis (relative to –H; TON_co ∼60), the use of an electron-withdrawing –CN was found to completely deactivate the catalyst (TON_co < 1) while the use of an electron-donating –NH₂ improved CO₂ photocatalysis four-fold (TON_co = 234). Despite being the strongest EWG, the –NO₂ derivative exhibited good photocatalytic CO₂ reduction abilities (TON_co = 137). Using a combination of CV and UV-vis-nIR SEC, it was elucidated that the –NO₂ derivative undergoes an in situ transformation to –NH₂ under reducing conditions, thereby generating a more active catalyst that would account for the unexpected activity. A photocatalytic CO₂ mechanism was proposed for these Re(bpy-C2-NPDI-R) dyads (based on molecular orbital descriptions), where it is rationalized that the photoexcitation pathway, as well as the electronic driving-force for NPDI²⁻ to Re(bpy) electron-transfer both significantly influence photocatalytic CO₂ reduction. These results help provide rational design principles for the future development of related supramolecular dyads.

Seven N-annulated perylene diimide tethered rhenium (2,2′-bipyridine) supramolecular dyads are evaluated as photocatalysts for the reduction for carbon dioxide, highlighting the importance of photoexcitation pathway and electronic driving-force.