Catalyst-On-Hotspot Nanoarchitecture: Plasmonic Focusing of Light onto Co-Photocatalyst for Efficient Light-To-Chemical Transformation.

Plasmon-mediated catalysis utilizing hybrid photocatalytic ensembles promises effective light-to-chemical transformation, but current approaches suffer from weak electromagnetic field enhancements from polycrystalline and isotropic plasmonic nanoparticles as well as poor utilization of precious co-catalyst. Here, efficient plasmon-mediated catalysis is achieved by introducing a unique catalyst-on-hotspot nanoarchitecture obtained through the strategic positioning of co-photocatalyst onto plasmonic hotspots to concentrate light energy directly at the point-of-reaction. Using environmental remediation as a proof-of-concept application, the catalyst-on-hotspot design (edge-AgOcta@Cu2O) enhances photocatalytic advanced oxidation processes to achieve superior organic-pollutant degradation at ≈81% albeit having lesser Cu2O co-photocatalyst than the fully deposited design (full-AgOcta@Cu2O). Mass-normalized rate constants of edge-AgOcta@Cu2O reveal up to 20-fold and 3-fold more efficient utilization of Cu2O and Ag nanoparticles, respectively, compared to full-AgOcta@Cu2O and standalone catalysts. Moreover, this design also exhibits catalytic performance >4-fold better than emerging hybrid photocatalytic platforms. Mechanistic studies unveil that the light-concentrating effect facilitated by the dense electromagnetic hotspots is crucial to promote the generation and utilization of energetic photocarriers for enhanced catalysis. By enabling the plasmonic focusing of light onto co-photocatalyst at the single-particle level, the unprecedented design offers valuable insights in enhancing light-driven chemical reactions and realizing efficient energy/catalyst utilizations for diverse chemical, environmental, and energy applications.

Incorporating Chaotropic/Kosmotropic Chemistries onto Plasmonic Nanoheater to Boost Steam Generation Beyond its Photothermal Property.

Photothermal steam generation promises decentralized water purification, but current methods suffer from slow water evaporation even at high photothermal efficiency of ≈98%. This drawback arises from the high latent heat of vaporization that is required to overcome the strong and extensive hydrogen bonding network in water for steam generation. Here, light-to-vapor conversion is boosted by incorporating chaotropic/kosmotropic chemistries onto plasmonic nanoheater to manipulate water intermolecular network at the point-of-heating. The chaotropic-plasmonic nanoheater affords rapid light-to-vapor conversion (2.79 kg m-2  h-1  kW-1 ) at ≈83% efficiency, with the steam generation rate up to 6-fold better than kosmotropic platforms or emerging photothermal designs. Notably, the chaotropic-plasmonic nanoheater also lowers the enthalpy of water vaporization by 1.6-fold when compared to bulk water, signifying that a correspondingly higher amount of steam can be generated with the same energy input. Simulation studies unveil chaotropic surface chemistry is crucial to disrupt water hydrogen bonding network and suppress the energy barrier for water evaporation. Using the chaotropic-plasmonic nanoheater, organic-polluted water is purified at ≈100% efficiency, a feat otherwise challenging in conventional treatments. This study offers a unique chemistry approach to boost light-driven steam generation beyond a material photothermal property.

Superlattice-based Plasmonic Catalysis: Concentrating Light at the Nanoscale to Drive Efficient Nitrogen-to-Ammonia Fixation at Ambient Conditions.

Plasmonic catalysis promises green ammonia synthesis but is limited by the need for co-catalysts and poor performances due to weak electromagnetic field enhancement. Here, we use two-dimensional plasmonic superlattices with dense electromagnetic hotspots to boost ambient nitrogen-to-ammonia photoconversion without needing co-catalyst. By organizing Ag octahedra into a square superlattice to concentrate light, the ammonia formation is enhanced by ≈15-fold and 4-fold over hexagonal superlattice and disorganized array, respectively. Our unique catalyst achieves superior ammonia formation rate and apparent quantum yield up to ≈15-fold and ≈103 -fold, respectively, better than traditional designs. Mechanistic investigations reveal the abundance of intense plasmonic hotspots is crucial to promote hot electron generation and transfer for nitrogen reduction. Our work offers valuable insights to design electromagnetically hot plasmonic catalysts for diverse chemical and energy applications.

Dynamic Liquid-Liquid Interface: Applying a Spinning Interfacial Microreactor to Actively Converge Biphasic Reactants for the Enhanced Interfacial Reaction.

A liquid-liquid interfacial reaction combines reactants with large polarity disparity to achieve greener and more efficient chemistry that is otherwise challenging in traditional single-phase systems. However, current interfacial approaches suffer from the need for a large amount of solvent/reactant/emulsifier and poor reaction performance arising from intrinsic thermodynamic constraints. Herein, we achieve an efficient interfacial reaction by creating a magnetic-responsive, microscale liquid-liquid interface and exploit its dynamic spinning motion to generate vortex-like hydrodynamic flows that rapidly converge biphasic reactants to the point-of-reaction. Notably, the spinning of this functional interface at 800 rpm boosts the reaction efficiency and its apparent equilibrium constant by > 500-fold and 105-fold, respectively, higher than conventional methods that utilize bulk and/or non-dynamic liquid interfaces, even with external mechanical stirring. By driving reaction equilibrium toward favorable product formation, our unique design offers enormous opportunities to realize efficient multiphasic reactions crucial for diverse applications in chemical synthesis, environmental remediation, and even molecular recycling.

Mechanochemical Synthesis of Tripodal Tris[4-(1,2,3-triazol-5-ylidene)methyl]amine Mesoionic Carbene Ligands and Their Complexation with Silver(I).

The conjugate acids of 1,2,3-triazolylidene mesoionic carbenes can be prepared in a straightforward fashion by alkylation of 1-substituted 1,2,3-triazoles. However, this becomes a much more challenging proposition when other nucleophilic centers are present, which has curtailed the development of ligands containing multiple 1,2,3-triazolylidene donors. Herein, methylation of a series of tris[(1-aryl-1,2,3-triazol-4-yl)methyl]amines possessing both electron-rich and electron-deficient aromatic substituents, using Me3OBF4, is shown to proceed with much higher chemoselectivity under mechanochemical conditions than when conducted in solution. This provides a means to reliably access a series of tricationic tris[4-(1,2,3-triazolium)methyl]amines in good yields. DFT calculations suggest that a potential reason for this change in regioselectivity is the difference between the background dielectric of the DCM solution versus the solid state, which is predicted to have a large effect on the relative thermodynamic driving force for alkylation of the tertiary amine center versus the triazole rings. Homoleptic silver complexes of the triazolylidene ligands derived therefrom, of formulas [Ag3(1a-d)2](X)3 (X- = BF4-, TfO-), have been isolated and fully characterized. In the case of the ligand bearing the smallest aryl substituents, 1b, argentophilic interactions yield a triangular Ag3 core. The [Ag3(1a-d)2](X)3 silver salts are viable agents for transmetalation to other transition metals, demonstrated here for cobalt. In the case of 1a, the complex [CoII(1a)(NCMe)](OTf)2 was obtained. Therein, the bulky mesityl substituents enforce a tetrahedral geometry, in which only the triazolylidene donors of 1a coordinate (i.e., it acts as a tridentate ligand). Transmetalation of the less sterically encumbered ligand 1b yields six-coordinate cobalt(III) complexes, [CoIII(1b)(Cl)(NCMe)](OTf)2 and [CoIII(1b)(NCMe)2](OTf)3, in which the ligand coordinates in a tetradentate fashion. These are the first examples of tris(1,2,3-triazolylidene) ligands containing an additional coordinating heteroatom and, more generally, of tetradentate 1,2,3-triazolylidene ligands. Crucially, we believe that the divergent chemoselectivity under mechanochemical conditions (vs conventional solution-based chemistry) demonstrated herein offers a pathway by which other challenging synthetic targets, including further multidentate carbene ligands, can be prepared in superior yields.

Carbodicarbene Ligand Redox Noninnocence in Highly Oxidized Chromium and Cobalt Complexes.

Carbodicarbenes (CDCs) possess two lone pairs of electrons on their central carbone C atom (Ccarbone). Coordination to a transition metal via a σ bond leaves one pair of electrons with appropriate symmetry for π donation to the metal. However, the high energy of the latter also renders the CDC ligand potentially redox-active. Herein, we explore these alternatives in the redox series [Cr(L)2]n+ and [Co(L)2]n+ (n = 2-5), where L is a tridentate ligand comprised of a central CDC and two flanking pyridine donors. To this end, all members of both redox series were synthesized and their electronic structures were investigated by using a combination of 1H NMR, Evans' NMR, IR, UV-vis, and EPR spectroscopies, SQUID magnetometry, X-ray crystallography, and density functional theory studies. Whereas [CoII(L)2]2+ is a straightforward low-spin (S = 1/2) cobalt(II) complex, the corresponding chromium complex was found to feature an electronic structure that is intermediate between the two limiting resonance forms [CrIII(L•-)(L)]2+ and [CrII(L)2]2+. In the case of the tri-, tetra-, and pentacationic complexes, the qualitatively identical electronic structures [MIII(L)2]3+, [MIII(L•+)(L)]4+, and [MIII(L•+)2]5+ were observed for both metals. Thus, the metal ions retain a 3+ oxidation state throughout, and the higher redox states contain oxidized ligands. The majority of the unpaired spin on the cation radical ligands was calculated to be localized in π-symmetry orbitals on the coordinated Ccarbone atoms. Analogous behavior was previously reported for the corresponding iron redox series and, as such, redox noninnocence in oxidized CDC and, more broadly, carbone complexes is likely widely accessible.

Observation of Carbodicarbene Ligand Redox Noninnocence in Highly Oxidized Iron Complexes.

To probe the possibility that carbodicarbenes (CDCs) are redox active ligands, all four members of the redox series [Fe(1)2 ]n+ (n=2-5) were synthesized, where 1 is a neutral tridentate CDC. Through a combination of spectroscopy and DFT calculations, the electronic structure of the pentacation is shown to be [FeIII (1.+ )2 ]5+ (S= 1 / 2 ). That of [Fe(1)2 ]4+ is more ambiguous, but it has significant contributions from the open-shell singlet [FeIII (1)(1.+ )]4+ (S=0). The observed spin states derive from antiferromagnetic coupling of their constituent low-spin iron(III) centres and cation radical ligands. This marks the first time redox activity has been observed for carbones and expands the diverse chemical behaviour known for these ligands.