Augmentation of NIR Circularly Polarized Luminescence Activity in Shibasaki-Type Lanthanide Complexes Supported by the Spirane Sphenol.

We report two new circularly polarized luminescence (CPL)-active lanthanide complexes emissive in the near-infrared (NIR) region; using sphenol as a supporting ligand, we provide the first reported example of an NIR-emissive lanthanide complex supported by a chiral spirane. Inclusion of a quaternary carbon to impart axial chirality results in dramatic augmentation of the CPL strength of the resultant sphenolate complexes (glum ≤ 0.77 for [(sphenol)3ErNa3(thf)6]) compared to that of their contemporary biaryl-based axially chiral analogues (glum ≤ 0.47 for [(binol)3ErNa3(thf)6]). Despite similar structural parameters, the rigid spiro carbon of sphenol enables the strongest dissymmetry factors observed to date from Shibasaki-type complexes for both Yb and Er. We also demonstrate the sensitivity of the reported chiroptical measurements to small variations in instrumental parameters, such as bandpass, and suggest a standardized method or at least that additional detail should be included in future reports to allow for direct comparisons between newly published CPL emitters.

High Quantum Yields from Perfluorinated Binolate Erbium Complexes and Their Circularly Polarized Luminescence.

High quantum yield and circularly polarized luminescence (CPL) brightness values are reported from Shibasaki-type erbium complexes supported by a perfluorinated Binol ligand (F12Binol). The total fluorination of the ligand circumvents nonradiative quenching from Csp2-H vibrations and leads to quantum yields of up to 11% and CPL brightness values of up to 317 M-1 cm-1 (a 19- and 6-fold increase, respectively, compared to (Binol)3ErNa3). These values are the highest values for any molecular erbium complex to date, making them comparable to Yb emitters. A series of fluorinated Shibasaki-type complexes are synthesized by varying the alkali metal (K, Na, Li) in the secondary coordination sphere, leading to unexpected structural differences. NMR (19F, 7Li) and chiroptical spectroscopy analyses provide insights into their structural geometry. With much improved quantum yields and CPL brightness values, we provide synthetic design principles toward other practical candidates for use in quantum communication technologies.

Magnetic Assembly of Eu-Doped NaYF4 Nanorods for Field-Responsive Linearly and Circularly Polarized Luminescence.

Colloidal assembly has emerged as an effective avenue for achieving polarized light emission. Here, we showcase the efficacy and versatility of the magnetic colloidal assembly in enabling both linearly and circularly polarized luminescence. Colloidal europium-doped NaYF4 nanorods with surface-bound Fe3O4 nanoparticles are magnetically assembled into linear or chiral superstructures using corresponding fields created in permanent magnets. In a uniform magnetic field generated by opposing poles, the assemblies exhibit photoluminescence with intensity tunable in response to the magnetic field direction, which is higher when the nanorods are perpendicular to light propagation than when they are parallel. The obtained superstructures display strong linearly polarized luminescence when the nanorods are aligned vertically, exhibiting a high degree of polarization up to 0.61. In a quadrupole chiral field generated by permanent magnets, the assemblies emit left-handed or right-handed polarized light depending on the position of the sample placement, attaining a g-factor of 0.04. Furthermore, the superstructures immobilized in a hydrogel film are found to retain their chirality, exhibiting opposite chiroptical responses depending on the sample orientation. The magnetic colloidal assembly approach facilitates the convenient and efficient generation of polarized light emissions from nonmagnetic luminescent materials, thus creating opportunities for tailoring light behavior in developing innovative optoelectronic devices.

Bis-oxazoline derivatives as ancillary ligands for bis-cyclometalated iridium complexes.

Organometallic iridium complexes with two cyclometalated ligands (CN) and one bis-oxazoline derived ancillary ligand (L^X), i.e. (CN)2Ir(L^X), are reported. The CN ligands are 1-phenylpyrazoline (ppz), 2-(4,6-difluorophenyl)pyridine (F2ppy), 2-phenylpyridine (ppy), 1-phenylisoquinoline (piq). The box ligand is (4S)-(+)-phenyl-α-[(4S)-phenyloxazolidin-2-ylidene]-2-oxazoline-2-acetonitrile. The emission of these complexes span across the visible and into the near-ultraviolet region of the electromagnetic spectrum with moderate to high photoluminescence quantum yields (ΦPL = 0.45-1.0). These complexes were found to emit from a metal-ligand to ligand charge transfer (ML'LCT) state and have lifetimes (1.3-2.1 µs), radiative rates (105 s-1), and nonradiative rates (104-105 s-1) comparable to state-of-the-art iridium emitters. The (ppy)2Ir(BOX-CN) complexes were resolved into the Δ- and Λ- diastereomers using differences in their solubility and additionally characterized by x-ray crystallography, stability, and chiroptic studies. The high ΦPL of these isomers results in the best to date brightness for circularly polarized luminescence (CPL) from iridium complexes (7.0 M-1 cm-1), with dissymmetry factors of -0.57 × 10-3 and +1.9 × 10-3 for 3Δ and 3Λ, respectively. The significant difference in CPL magnitude between 3Δ and 3Λ likely arises from interligand interactions (edge-to-face arrangement versus strong π-π interaction) for the pendant phenyl ring of the BOX-CN ligand which differ for the two isomers.

Enhanced circularly polarized luminescence dissymmetry of [Ru(bpy)3]2+ complexes in a 3D chiral framework: a study of transparent thin films.

Circularly polarized luminescence (CPL) plays an important role in the development of advanced optical devices. However, the design of CPL-active materials with a decent dissymmetry factor is still challenging. Here, we report CPL-active transparent thin films made from optically active ruthenium complexes [Ru(bpy)3]2+ embedded in chiral inorganic frameworks. Due to the unique chiral-in-chiral combination, the obtained [Ru(bpy)3][Zn2(C2O4)3] displays CPL activity with a dissymmetry factor of 5 × 10-3. The CPL measurements show that the luminescence dissymmetry factor can be effectively enhanced by one order of magnitude when an optically active [Ru(bpy)3]2+ complex is incorporated into a chiral inorganic framework compared to its solution form. This study not only emphasizes the potential of constructing CPL-active thin films with coordination polymers but also points out the importance of introducing extra chiral environment to improve the CPL effect.

Why surface hydrophobicity promotes CO2 electroreduction: a case study of hydrophobic polymer N-heterocyclic carbenes.

We report the use of polymer N-heterocyclic carbenes (NHCs) to control the microenvironment surrounding metal nanocatalysts, thereby enhancing their catalytic performance in CO2 electroreduction. Three polymer NHC ligands were designed with different hydrophobicity: hydrophilic poly(ethylene oxide) (PEO-NHC), hydrophobic polystyrene (PS-NHC), and amphiphilic block copolymer (BCP) (PEO-b-PS-NHC). All three polymer NHCs exhibited enhanced reactivity of gold nanoparticles (AuNPs) during CO2 electroreduction by suppressing proton reduction. Notably, the incorporation of hydrophobic PS segments in both PS-NHC and PEO-b-PS-NHC led to a twofold increase in the partial current density for CO formation, as compared to the hydrophilic PEO-NHC. While polymer ligands did not hinder ion diffusion, their hydrophobicity altered the localized hydrogen bonding structures of water. This was confirmed experimentally and theoretically through attenuated total reflectance surface-enhanced infrared absorption spectroscopy and molecular dynamics simulation, demonstrating improved CO2 diffusion and subsequent reduction in the presence of hydrophobic polymers. Furthermore, NHCs exhibited reasonable stability under reductive conditions, preserving the structural integrity of AuNPs, unlike thiol-ended polymers. The combination of NHC binding motifs with hydrophobic polymers provides valuable insights into controlling the microenvironment of metal nanocatalysts, offering a bioinspired strategy for the design of artificial metalloenzymes.

Transition-Metal Isocorroles as Singlet Oxygen Sensitizers.

Building on a highly efficient synthesis of pyrrole-appended isocorroles, we have worked out conditions for manganese, palladium, and platinum insertion into free-base 5/10-(2-pyrrolyl)-5,10,15-tris(4-methylphenyl)isocorrole, H2[5/10-(2-py)TpMePiC]. Platinum insertion proved exceedingly challenging but was finally accomplished with cis-Pt(PhCN)2Cl2. All the complexes proved weakly phosphorescent in the near-infrared under ambient conditions, with a maximum phosphorescence quantum yield of 0.1% observed for Pd[5-(2-py)TpMePiC]. The emission maximum was found to exhibit a strong metal ion dependence for the 5-regioisomeric complexes but not for the 10-regioisomers. Despite the low phosphorescence quantum yields, all the complexes were found to sensitize singlet oxygen formation with moderate to good efficiency, with singlet oxygen quantum yields ranging over 21-52%. With significant absorption in the near-infrared and good singlet oxygen-sensitizing ability, metalloisocorroles deserve examination as photosensitizers in the photodynamic therapy of cancer and other diseases.

Vanol-Supported Lanthanide Complexes for Strong Circularly Polarized Luminescence at 1550†nm.

Strong circularly polarized luminescence (CPL) at 1550 nm is reported for lanthanide complexes supported by Vanol; these are the first examples of coordination of Vanol to lanthanides. A change in the ligand design from a 1,1'-bi-2-naphthol (in Binol) to a 2,2'-bi-1-naphthol (in Vanol) results in significantly improved dissymmetry factors for (Vanol)3 ErNa3 (|glum |=0.64) at 1550 nm. This is among the highest reported dissymmetry factors to date in the telecom C-band region, and among the highest for any lanthanide complexes. Comparative solid-state structural analysis of (Vanol)3 ErNa3 and (Binol)3 ErNa3 suggests that a less distorted geometry around the metal center is in part responsible for the high chiroptical metrics of (Vanol)3 ErNa3 . This phenomenon was further evidenced in the analogous ytterbium complex (Vanol)3 YbNa3 that also exhibit a significantly improved dissymmetry factor (|glum |=0.21). This confirms and generalizes the same observation that was made in other visibly emitting, six-coordinate lanthanide complexes. Due to their strong CPL at 1550 nm, the reported complexes are potential candidates for applications in quantum communication technologies. More importantly, our structure-CPL activity relationship study provides guidance towards the generation of even better near-infrared CPL emitters.

Anionic ligand-induced chirality in perovskite nanoplatelets.

Perovskite materials passivated by chiral ligands have recently shown unique chiroptical activity with promising optoelectronic applications. However, the ligands have been limited to chiral amines. Here, chiral phosphate molecules have been exploited to synthesize CsPbBr3 nanoplatelets. The nanoplatelets showed a distinct circular dichroism signal and maintained their chiroptical properties after purification with anti-solvent.

Spinolate Lanthanide Complexes for High Circularly Polarized Luminescence Metrics in the Visible and Near-Infrared.

Analogues of Shibasaki's complexes supported by enantiopure Spinol are synthesized and characterized. The tris(Spinol) LnIII complexes are generated either by ligand deprotonation followed by complexation with lanthanide triflate salts or by in situ deprotonation by Ln(N(SiMe3)2)3 salts in the presence of additional base. The resulting complexes are found to be luminescent and chiroptically active for both circular dichroism and circularly polarized luminescence (CPL), notably producing strong CPL with dissymmetry factors (glum) of up to 0.50, 0.53, and 0.53 for Sm, Tb, and Dy, respectively. The Sm complex is found to be CPL-active in the near-infrared (NIR) region at 980 nm, representing the first report of NIR CPL from Sm. Additionally, the Tb complex, due to efficient sensitization (Φ = 0.846 in tetrahydrofuran) coupled with strong dissymmetry factors, achieves a CPL brightness (BCPL) of 3760 M-1 cm-1, the highest reported for any CPL-active compound to date. These are rare examples of compounds that show simultaneous improvement of both CPL metrics (glum and BCPL). Solid-state structural analysis of the Spinolate complexes and comparisons to other CPL-active analogues of Shibasaki's complexes also suggest that nondistorted geometries should generate even stronger metrics.

Circularly Polarized Luminescence from Uranyl Improves Resolution of Electronic Transitions.

The first reported example of circularly polarized luminescence from a chiral, molecular uranyl (UO22+) complex in solution is presented. This uranyl chiroptical activity is enabled by complexation with ibuprofen, an enantiopure chiral carboxylate ligand. Salt metathesis between [UO2Cl2(thf)2]2 and the sodium ibuprofenate salts results in the formation of the anionic tris complexes; these complexes are found to be luminescent in solution, both under visible excitation, directly targeting the metal, and through sensitization by UV absorption and energy transfer from the ligand. Each enantiomer displays both circular dichroism and circularly polarized luminescence (CPL) with |gabs| ≤ 8.1 × 10-2 and |glum| ≤ 8.0 × 10-3 under UV excitation, comparable to chiral transition metal complexes or purely organic emitters. The strength of the CPL emission is found to be comparable following excitation of either the ligand or metal directly. Further, use of CPL allows for resolution of subcomponents of the emission spectrum not previously possible at room temperature using standard fluorescence techniques. Observation of CPL following direct uranyl excitation presents a new tool for probing speciation of uranyl complexes when chiral ligands are used, without the need for synthetic modification to incorporate a suitable chromophore, and could enable the design of improved ligands for uranyl extraction from wastewater.

Strong Circularly Polarized Luminescence at 1550 nm from Enantiopure Molecular Erbium Complexes.

Circularly polarized luminescence (CPL) in two subregions of the near-infrared (NIR) has been achieved. By leveraging the rigidity and diminishing detrimental vibrations of the heterobimetallic binolate complexes of erbium [(Binol)3ErNa3], species exhibiting an exceptionally high dissymmetry factor (|glum |) of 0.47 at 1550 nm were obtained. These erbium complexes are the first reported examples of CPL observed beyond 1200 nm. Analogous complexes of ytterbium and neodymium also exhibited strong CPL (|glum| = 0.17, 0.05, respectively) in a higher energy NIR window (800-1200 nm). All complexes exhibit high quantum yields (Er: 0.58%, Yb: 17%, Nd: 9.3%) and high BCPL values (Er: 57 M-1 cm-1, Yb: 379 M-1 cm-1, Nd: 29 M-1 cm-1). Because of their strong CPL emission in the telecom band (1550 nm), biologically relevant NIR emission window (800-1100 nm), and synthetic versatility, the complexes reported here could permit further promising developments in quantum communication technologies and biologically relevant sensors.

High circularly polarized luminescence brightness from analogues of Shibasaki's lanthanide complexes.

To reach the promising potential of circularly polarized luminescence (CPL) emitters, high CPL brightness must be achieved. We describe the synthesis of analogues of the C3-symmetrical Shibasaki's lanthanide complexes (Sm, Tb, Dy) supported by enantiopure 5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol (H8-Binol). The complexes exhibit visible luminescence in solution with exceptionally high quantum yields for Sm (4%) and Dy (17%), and strong circularly polarized luminescence for Sm, Tb, and Dy (|glum| up to 0.44, 0.32, 0.33, respectively). Altogether, these complexes possess amongst the strongest CPL brightness reported to date in lanthanide molecular complexes (up to 782 M-1 cm-1 for Tb).

Circularly Polarized Luminescence from Enantiopure C2-Symmetrical Tetrakis(2-pyridylmethyl)-1,2-diaminocyclohexane Lanthanide Complexes.

We report the synthesis and characterization of C2-symmetrical lanthanide complexes supported by enantiopure hexadentate ligands derived from 1,2-diaminocyclohexane. Coordination of (R,R)- or (S,S)-N,N,N',N'-tetrakis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane (tpdac) to samarium, europium, terbium, and dysprosium generates the corresponding C2-symmetrical (tpdac)Ln(OTf)3 complexes in high yields. The tpdac ligands are competent sensitizers for lanthanide luminescence, yielding modest emissions (Φ of ≤28%). Additionally, the complexes exhibit strong circularly polarized luminescence (|glum| values of up to 0.13, 0.09, 0.22, and 0.15 for Sm, Eu, Tb, and Dy, respectively) in solution. We also observed that some transitions typically associated with small dissymmetry factors exhibit unusually high |glum| values and, therefore, should not be overlooked in future studies.

Synthesis of Enantiopure Lanthanide Complexes Supported by Hexadentate N,N'-Bis(methylbipyridyl)bipyrrolidine and Their Circularly Polarized Luminescence.

We report the synthesis of lanthanide complexes supported by enantiopure N,N'-bis(methylbipyridyl)bipyrrolidine and subsequent characterization through luminescence studies. Complexes of this ligand with the visibly emissive lanthanides Sm, Eu, Tb, and Dy are luminescent (ϕf of ≤0.32) and demonstrate strong preferential emission of circularly polarized light in all four cases (|glum| of ≤0.26). Notably, all four possess at least one transition with a |glum| of >0.2, and the strongest preferential emission is measured from the complexes of Sm and Dy.

Alkali-metal- and halide-free dinuclear mixed-valent samarium and europium complexes.

We describe the synthesis of mixed-valent (Ln(ii)/Ln(iii)) dilanthanide complexes supported by a calix[4]pyrrole ligand. The complexes are obtained by one-electron reduction of Ln(iii)/Ln(iii) complexes and are alkali-metal- and halide-free. The complexes are designed to activate small molecules by taking advantage of both the base and the one-electron reductant contained in their structure. We demonstrate a proof-of-principle concept of this mechanism by activating water and silanol.

Yellow Circularly Polarized Luminescence from C1 -Symmetrical Copper(I) Complexes.

The synthesis of chiral C1 -symmetrical copper(I) complexes supported by chiral carbene ligands is described. These complexes are yellow emitters with modest quantum yields. Circularly polarized luminescence (CPL) spectra show a polarized emission band with dissymmetry factors |glum |=1.2×10-3 . These complexes are the first reported examples of molecular copper(I) complexes exhibiting circularly polarized luminescence. In contrast with most CPL-emitting molecules, which possess either helical or axial chirality, the results presented show that simple chiral architectures are suitable for CPL emission and unlock new synthetic possibilities.

A Polymer Solution To Prevent Nanoclustering and Improve the Selectivity of Metal Nanoparticles for Electrocatalytic CO2 Reduction.

The stability of metal nanocatalysts for electrocatalytic CO2 reduction is of key importance for practical application. We report the use of two polymeric N-heterocyclic carbenes (NHC) (polydentate and monodentate) to stabilize metal nanocatalysts (Au and Pd) for efficient CO2 electroreduction. Compared with other conventional ligands including thiols and amines, metal-carbene bonds that are stable under reductive potentials prevent the nanoclustering of nanoparticles. Au nanocatalysts modified by polymeric NHC ligands show an activity retention of 86 % after CO2 reduction at -0.9 V for 11 h, while it is less than 10 % for unmodified Au. We demonstrate that the hydrophobicity of polymer ligands and the enriched surface electron density of metal NPs through σ-donation of NHCs substantially improve the selectivity for CO2 reduction over proton.

Monometallic lanthanide salicylhydrazone complexes exhibiting strong near-infrared luminescence.

We report the synthesis of monometallic lanthanide complexes supported by one salicylhydrazone ligand. Complexes of neodymium, erbium, and ytterbium have been synthesized, and exhibit near infrared luminescence with modest to high quantum yields. The luminescence of ytterbium is increased by a factor of five when comparing our complex to other salicylhydrazone-supported complexes.

Catalytic hydrazine disproportionation mediated by a thiolate-bridged VFe complex.

A heterobimetallic VFe complex is demonstrated to catalyse hydrazine disproportionation with yields of up to 1073 equivalents of NH3 per catalyst, comparable to the highest turnover known for any molecular catalyst. Notably, the heterobimetallic complex is appreciably more active than monometallic analogues of the V and Fe sites, suggesting that bimetallic cooperativity may facilitate the observed catalysis.