Herein, we present a novel upconversion nanoparticle/photocatalyst system for infrared-light-initiated photoredox catalysis. A tailor-made, metal-based photoredox catalyst was immobilized by ligand exchange to stabilize NaYF4 upconversion nanoparticles. The absorption properties of the immobilized photoredox catalyst were only negligibly changed and the particles could excite the photoredox catalyst by energy transfer, determined by extensive luminescence spectroscopy and excited-state lifetime measurements using a 980 nm near-infrared laser excitation source. The system successfully catalyzed a [Ru(bpy)(3)](2+) promoted oxidation reaction, normally performed with visible light, by using 980 nm near-infrared light. Neither the complex nor the particle without immobilized complex was active in this reaction. The presented system enables potential in vivo application of photoredox catalysis, utilizing the biological window of tissues for near-infrared light by combining the mildness of photoredox catalysis and near-infrared light.

The preparation of water-soluble, N-heterocyclic-carbene-stabilized Au-Pd alloy nanoparticles by a straightforward ligand exchange process is presented. Extensive analysis revealed excellent size retention and stability over years in water. The alloy nanoparticles were applied as biomimetic catalysts for aerobic oxidation of d-glucose, for which monometallic Au and Pd nanoparticles showed no or negligible activity. The alloy nanoparticles were further applied as titania-supported heterogeneous catalysts for the mild hydrogenation of nitroarenes and the semihydrogenation of 1,2-diphenylacetylene with a solvent-dependent selectivity switch between E- and Z-stilbene.

A self-assembly approach for the design of multifunctional nanomaterials consisting of different nanoparticles (gold, iron oxide, and lanthanide-doped LiYF4 ) is developed. This modular system takes advantage of the light-responsive supramolecular host-guest chemistry of β-cyclodextrin and arylazopyrazole, which enables the dynamic and reversible self-assembly of particles to spherical nanoparticle aggregates in aqueous solution. Due to the magnetic iron oxide nanoparticles, the aggregates can be manipulated by an external magnetic field leading to the formation of linear structures. As a result of the integration of upconversion nanoparticles, the aggregates are additionally responsive to near-infrared light and can be redispersed by use of the upconversion effect. By varying the nanoparticle and linker concentrations the composition, size, shape, and properties of the multifunctional nanoparticle aggregates can be fine-tuned.

The design of multifunctional nanomaterials that respond to external stimuli and mimic the capacity of biological materials to respond and adapt to their environment has become a focus of interest in nanotechnology. In this Concept, we describe the development of supramolecular nanoparticle assemblies constructed by use of host-guest interactions between cyclodextrins and suitable guest molecules. The nanoparticle assembly is reversible and can be directed by applying different stimuli that act either on the guest molecules or the nanoparticles. This strategy can be extended to mesoscale assembly of microparticles. We highlight the newest research work in this field of nanochemistry and point out future perspectives and opportunities.

The stabilization of high oxidation state nanoparticles by N-heterocyclic carbenes is reported. Such nanoparticles represent an important subset in the field of nanoparticles, with different and more challenging requirements for suitable ligands compared to elemental metal nanoparticles. N-Heterocyclic carbene coated NaYF4 :Yb,Tm upconversion nanoparticles were synthesized by a ligand-exchange reaction from a well-defined precursor. This new photoactive material was characterized in detail and employed in the activation of photoresponsive molecules by low-intensity near-infrared light (λ=980 nm).

AbstractDie Stabilisierung von hochoxidierten Nanopartikeln mit N‐heterocyclischen Carbenen wird beschrieben. Solche Nanopartikel repräsentieren eine wichtige Untergruppe im Feld der Nanopartikel. Sie stellen andere Anforderungen an geeignete Liganden als elementare Metallnanopartikel. Durch die N‐heterocyclischen Carbene stabilisierte NaYF4:Yb,Tm‐Upconversion‐Nanopartikel wurden mittels einer Ligandenaustauschreaktion ausgehend von einer wohldefinierten Vorstufe synthetisiert. Dieses neue photoaktive Material wurde umfassend charakterisiert und in der Aktivierung von photoresponsiven Molekülen durch Nahinfrarot‐Licht (980 nm) mit niedriger Intensität angewendet.

This communication reports a new type of supramolecular cyclodextrin-guest complexes using cyclodextrin coated upconversion nanoparticles as hosts and monovalent and divalent azobenzenes and arylazopyrazoles as guests. A potentially biocompatible photocontrol of the interaction by isomerization of the azobenzene or arylazopyrazole was achieved by laser irradiation at 980 nm and a very low light intensity of 0.22 W cm-2.

A reusable copper-based catalyst system was employed for the direct arylation of electron-rich heteroarenes. Under mild and operationally simple reaction conditions good yields and selectivities were obtained using diaryliodonium salts as coupling partners. A combination of experimental methods including kinetic studies, filtration tests, and a series of analytical tools (TXRF, ICP-MS, SEM, XPS, TEM, EFTEM) provide evidence for catalytically active soluble nanoparticles formed from an amorphous heterogeneous precursor. Mechanistic studies hint at a redox-neutral process which promotes counterion dissociation from the diaryliodonium salt by a copper(II) oxide species.