Boosting quantum yields and circularly polarized luminescence of penta- and hexahelicenes by doping with two BN-groups

The incorporation of boron-nitrogen (BN) units into polycyclic aromatic hydrocarbons (PAHs) as an isoelectronic replacement of two carbon atoms can significantly improve their optical properties, while the geometries are mostly retained. We report the first non-π-extended penta- and hexahelicenes comprising two aromatic 1,2-azaborinine rings. Comparing them with their all-carbon analogs regarding structural, spectral and (chir)optical properties allowed us to quantify the impact of the heteroatoms. In particular, BN-hexahelicene BN[6] exhibited a crystal structure congruent with its analog CC[6], but displayed a fivefold higher fluorescence quantum yield (φfl = 0.17) and an outstanding luminescence dissymmetry factor (|glum| = 1.33 × 10-2). Such an unusual magnification of both properties at the same time makes BN-helicenes suitable candidates as circularly polarized luminescence emitters for applications in materials science.

Rapid handheld time-resolved circularly polarised luminescence photography camera for life and material sciences

Circularly polarised luminescence (CPL) is gaining a rapidly increasing following and finding new applications in both life and material sciences. Spurred by recent instrumental advancements, the development of CPL active chiral emitters is going through a renaissance, especially the design and synthesis of CPL active luminescent lanthanide complexes owing to their unique and robust photophysical properties. They possess superior circularly polarised brightness (CPB) and can encode vital chiral molecular fingerprints in their long-lived emission spectrum. However, their application as embedded CPL emitters in intelligent security inks has not yet been fully exploited. This major bottleneck is purely hardware related: there is currently no suitable compact CPL instrumentation available, and handheld CPL photography remains an uncharted territory. Here we present a solution: an all solid-state small footprint CPL camera with no moving parts to facilitate ad hoc time-resolved enantioselective differential chiral contrast (EDCC) based one-shot CPL photography (CPLP).

Coordination-Directed Self-Assembly of Functional Polynuclear Lanthanide Supramolecular Architectures

Lanthanide supramolecular chemistry is a fast growing and intriguing research field due to the unique photophysical, magnetic, and coordination properties of lanthanide ions (Ln^III). Compared with the intensively investigated mononuclear Ln-complexes, polymetallic lanthanide supramolecular assemblies offer more structural superiority and functional advantages. In recent decades, significant progress has been made in polynuclear lanthanide supramolecules, varying from structural evolution to luminescent and magnetic functional materials. This review summarizes the design principles in ligand-induced coordination-driven self-assembly of polynuclear Ln-structures and intends to offer guidance for the construction of more elegant Ln-based architectures and optimization of their functional performances. Design principles concerning the water solubility and chirality of the lanthanide-organic assemblies that are vital in extending their applications are emphasized. The strategies for improving the luminescent properties and the applications in up-conversion, host-guest chemistry, luminescent sensing, and catalysis have been summarized. Magnetic materials based on supramolecular assembled lanthanide architectures are given in an individual section and are classified based on their structural features. Challenges remaining and perspective directions in this field are also briefly discussed.

Luminescent polyelectrolytes with antiviral activity

Radical polymerization was used to synthesize and characterize (co)polymers with sodium styrenesulfonate (NaSS), 4-methacryloylamidosalicylic acid (MASA), and N-vinylpyrrolidone, which have a low cytotoxicity and a high antiviral activity against the human respiratory syncytial virus. The interaction of copolymers with Tb³⁺ ions was studied. The complexes formed in dilute aqueous solutions at a concentration of MASA units c ⩽ 1 · 10^-4 mol L^-1 demonstrate a strong luminescence. The luminescence intensity is independent of copolymer composition, but increases when the NaSS units are substituted with uncharged N-vinylpyrrolidone units. The obtained Tb³⁺ polymer complexes are promising luminescent sensors for the visualization of biological objects interacting with copolymers.

Sorting Phenomena and Chirality Transfer in Fluoride-Bridged Macrocyclic Rare Earth Complexes

The reaction of fluoride anions with mononuclear lanthanide(III) and yttrium(III) hexaaza-macrocyclic complexes results in the formation of dinuclear fluoride-bridged complexes. As indicated by X-ray crystal structures, in these complexes two metal ions bound by the macrocycles are linked by two or three bridging fluoride anions, depending on the type of the macrocycle. In the case of the chiral hexaaza-macrocycle L1 derived from trans-1,2-diaminocyclohexane, the formation of these μ2-fluorido dinuclear complexes is accompanied by enantiomeric self-recognition of macrocyclic units. In contrast, this kind of recognition is not observed in the case of complexes of the chiral macrocycle L2 derived from 1,2-diphenylethylenediamine. The reaction of fluoride with a mixture of mononuclear complexes of L1 and L2, containing two different Ln(III) ions, results in narcissistic sorting of macrocyclic units. Conversely, a similar reaction involving mononuclear complexes of L1 and complexes of achiral macrocycle L3 based on ethylenediamine results in sociable sorting of macrocyclic units and preferable formation of heterodinuclear complexes. In addition, formation of these heterodinuclear complexes is accompanied by chirality transfer from the chiral macrocycle L1 to the achiral macrocycle L3 as indicated by CPL and CD spectra.

Generating circularly polarized luminescence from clusterization-triggered emission using solid phase molecular self-assembly

Purely-organic clusterization-triggered emission (CTE) has displayed promising abilities in bioimaging, chemical sensing, and multicolor luminescence. However, it remains absent in the field of circularly polarized luminescence (CPL) due to the difficulties in well-aligning the nonconventional luminogens. We report a case of CPL generated with CTE using the solid phase molecular self-assembly (SPMSA) of poly-L-lysine (PLL) and oleate ion (OL), that is, the macroscopic CPL supramolecular film self-assembled by the electrostatic complex of PLL/OL under mechanical pressure. Well-defined interface charge distribution, given by lamellar mesophases of OL ions, forces the PLL chains to fold regularly as a requirement of optimal electrostatic interactions. Further facilitated by hydrogen bonding, the through-space conjugation (TSC) of orderly aligned electron-rich O and N atoms leads to CTE-based CPL, which is capable of transferring energy to an acceptor via a Förster resonance energy transfer (FRET) process, making it possible to develop environmentally friendly and economic CPL from sustainable and renewable materials.

The design of responsive luminescent lanthanide probes and sensors

The principles of the design of responsive luminescent probes and sensors based on lanthanide emission are summarised, based on a mechanistic understanding of their mode of action. Competing kinetic pathways for deactivation of the excited states that occur are described, highlighting the need to consider each of the salient quenching processes. Such an analysis dictates the choice of both the ligand and its integral sensitising moiety for the particular application. The key aspects of quenching involving electron transfer and vibrational and electronic energy transfer are highlighted and exemplified. Responsive systems for pH, pM, pX and pO₂ and selected biochemical analytes are distinguished, according to the nature of the optical signal observed. Signal changes include both simple and ratiometric intensity measurements, emission lifetime variations and the unique features associated with the observation of circularly polarised luminescence (CPL) for chiral systems. A classification of responsive lanthanide probes is introduced. Examples of the operation of probes for reactive oxygen species, citrate, bicarbonate, α₁-AGP and pH are used to illustrate reversible and irreversible transformations of the ligand constitution, as well as the reversible changes to the metal primary and secondary coordination sphere that sensitively perturb the ligand field. Finally, systems that function by modulation of dynamic quenching of the ligand or metal excited states are described, including real time observation of endosomal acidification in living cells, rapid urate analysis in serum, accurate temperature assessment in confined compartments and high throughput screening of drug binding to G-protein coupled receptors.

Isoquinoline-based Eu(iii) luminescent probes for citrate sensing in complex matrix

A neutral Eu(iii) complex containing the S,S enantiomer of isoQC3A^3- ligand (isoQC3A^3- = N-isoquinolyl-N,N',N'-trans-l,2-cyclohexylenediaminetriacetate) was synthesized and characterized. The complex was spectroscopically investigated and the results compared with those obtained for the similar bis-anionic ligand bisoQcd^2- (bisoQcd^2- = N,N'-bis(2-isoquinolinmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate). Both Eu(iii)-complexes show similar binding constants upon titration with the main analytes contained in interstitial extracellular fluid (i.e. hydrogen carbonate, serum albumin and citrate). However, the analyte affinity is accompanied by different enhancements of the Eu(iii) intrinsic quantum yield (QY). Structures and hydration numbers of the complexes are determined by luminescence decay measurements and DFT calculations. The QYs as well as the binding constants of the individual adducts of the complexes with hydrogen carbonate, bovine serum albumin (BSA) and citrate are determined. The study of the Eu(iii) emission upon the systematic variation of one analyte in a complex mixture has been carried out to predict the performance of the luminescent sensor in conditions close to the real extracellular environment. Both Eu(iii) complexes can detect citrate at extracellular concentrations up to 500 μM, even at millimolar concentrations of the other interfering species. In the case of the Eu(bisoQcd)OTf complex, an increase of 23% of the Eu(iii) luminescence intensity at 615 nm upon addition of 0.3 mM of citrate was recorded. This feature makes the latter complex a viable probe for luminescence analysis of citrate in a complex matrix.

Unusual Magnetic Field Responsive Circularly Polarized Luminescence Probes with Highly Emissive Chiral Europium(III) Complexes

Chirality is ubiquitous within biological systems where many of the roles and functions are still undetermined. Given this, there is a clear need to design and develop sensitive chiral optical probes that can function within a biological setting. Here we report the design and synthesis of magnetically responsive Circularly Polarized Luminescence (CPL) complexes displaying exceptional photophysical properties (quantum yield up to 31 % and |glum | up to 0.240) by introducing chiral substituents onto the macrocyclic scaffolds. Magnetic CPL responses are observed in these chiral EuIII complexes, promoting an exciting development to the field of magneto-optics. The |glum | of the 5 D0 → 7 F1 transition increases by 20 % from 0.222 (0 T) to 0.266 (1.4 T) displaying a linear relationship between the Δglum and the magnetic field strength. These EuIII complexes with magnetic CPL responses, provides potential development to be used in CPL imaging applications due to improved sensitivity and resolution.

Rare-Earth Metal Complexes of the Antibacterial Drug Oxolinic Acid: Synthesis, Characterization, DNA/Protein Binding and Cytotoxicity Studies

"Drug repositioning" is a current trend which proved useful in the search for new applications for existing, failed, no longer in use or abandoned drugs, particularly when addressing issues such as bacterial or cancer cells resistance to current therapeutic approaches. In this context, six new complexes of the first-generation quinolone oxolinic acid with rare-earth metal cations (Y³⁺, La³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺) have been synthesized and characterized. The experimental data suggest that the quinolone acts as a bidentate ligand, binding to the metal ion via the keto and carboxylate oxygen atoms; these findings are supported by DFT (density functional theory) calculations for the Sm³⁺ complex. The cytotoxic activity of the complexes, as well as the ligand, has been studied on MDA-MB 231 (human breast adenocarcinoma), LoVo (human colon adenocarcinoma) and HUVEC (normal human umbilical vein endothelial cells) cell lines. UV-Vis spectroscopy and competitive binding studies show that the complexes display binding affinities (K_b) towards double stranded DNA in the range of 9.33 × 10⁴ - 10.72 × 10⁵. Major and minor groove-binding most likely play a significant role in the interactions of the complexes with DNA. Moreover, the complexes bind human serum albumin more avidly than apo-transferrin.

Self-assembled Tetranuclear EuIII Complexes with D2- and C2h-Symmetrical Square Scaffold

Three new tetranuclear europium(III) alternating circular helicates, (2-^PhRRRR/2-^PhSSSS) [(R)- or (S)-Ph-Pybox]₄Eu^III₄(BPP)₆, (2-^iPrRRRR/2-^iPrSSSS) [(R)- or (S)-ⁱPr-Pybox]₄Eu^III₄(BPP)₆, and (3-^PhRRRR/3-^PhSSSS) [(R)- or (S)-Ph-Pybox]₄Eu^III₄(BHP)₆, are presented with their structural and chiroptical characterization (BPP and BHP = bis-β-diketonates; Pybox = chiral bis(oxazolinyl) pyridine ligand). X-ray crystallographic analysis revealed that different extents of interligand-contacting interactions between bis-β-diketonates and Pybox ligands produce different bis-β-diketonates arrangements around four Eu^III ions and, thus, their specific symmetry in the final tetranuclear complexes. 2-^PhRRRR/2-^PhSSSS and 3-^PhRRRR/3-^PhSSSS are recognized as D₂-symmetry, while 2-^iPrRRRR/2-^iPrSSSS self-assemblies possess pseudo C_2h-symmetry. Due to different molecular symmetry, 2-^PhRRRR/2-^PhSSSS and 2-^iPrRRRR/2-^iPrSSSS crystals display different ligands orientation in their Eu^III coordination spheres. The presence of pseudo σ_h-mirror symmetry in 2-^iPrRRRR/2-^iPrSSSS promotes a pair of distinguishable Eu^III geometries. All the chiral self-assemblies exhibit almost identical photoluminescence emission spectra patterns of f-f transitions in the Eu^III core. The Eu^III self-assemblies exhibit intense CPL with different observed |g_lum| values (2-^PhRRRR/2-^PhSSSS ∼ |0.31|, 2-^iPrRRRR/2-^iPrSSSS ∼ |0.08|, 3-^PhRRRR/3-^PhSSSS ∼ |0.31| in chloroform).

Quinolone Complexes with Lanthanide Ions: An Insight into their Analytical Applications and Biological Activity

Quinolones comprise a series of synthetic bactericidal agents with a broad spectrum of activity and good bioavailability. An important feature of these molecules is their capacity to bind metal ions in complexes with relevant biological and analytical applications. Interestingly, lanthanide ions possess extremely attractive properties that result from the behavior of the internal 4f electrons, behavior which is not lost upon ionization, nor after coordination. Subsequently, a more detailed discussion about metal complexes of quinolones with lanthanide ions in terms of chemical and biological properties is made. These complexes present a series of characteristics, such as narrow and highly structured emission bands; large gaps between absorption and emission wavelengths (Stokes shifts); and long excited-state lifetimes, which render them suitable for highly sensitive and selective analytical methods of quantitation. Moreover, quinolones have been widely prescribed in both human and animal treatments, which has led to an increase in their impact on the environment, and therefore to a growing interest in the development of new methods for their quantitative determination. Therefore, analytical applications for the quantitative determination of quinolones, lanthanide and miscellaneous ions and nucleic acids, along with other applications, are reviewed here.

Supramolecular chirality transformation driven by monodentate ligand binding to a coordinatively unsaturated self-assembly based on C 3-symmetric ligands

Monodentate ligand binding is facilitated by supramolecular chirality transformations from propeller-shaped chirality into single-twist chirality by altering the self-assembly of C 3-symmetric chiral ligands. The C 3-symmetric chiral ligands (Im R 3Bz and Im S 3Bz) contain three chiral imidazole side arms (Im R  and Im S ) at the 1,3,5-positions of a central benzene ring. Upon coordination to zinc ions (Zn2+), which have a tetrahedral coordination preference, the C 3-symmetric chiral ligands assemble, in a stepwise manner, into a propeller-shaped assembly with a general formula (Im( R or S ) 3Bz)4(Zn2+)3. In this structure each Zn2+ ion coordinates to the three individual imidazole side arms. The resulting assembly is formally coordinatively unsaturated (coordination number, n = 3) and capable of accepting monodentate co-ligands (imidazole: ImH2) to afford a coordinatively saturated assembly [(ImH2)3(Im R 3Bz)4(Zn2+)3]. The preformed propeller-shaped chirality is preserved during this transformation. However, an excess of the monodentate co-ligand (ImH2/Zn2+ molar ratio of ∼1.7) alters the propeller-shaped assembly into a stacked dimer assembly [(ImH2) m (Im R 3Bz)2(Zn2+)3] (m = 4-6) with single-twist chirality. This switch alters the degree of enhancement and the circular dichroism (CD) pattern, suggesting a structural transition into a chiral object with a different shape. This architectural chirality transformation presents a new approach to forming dynamic coordination-assemblies, which have transformable geometric chiral structures.

Eu(iii) and Tb(iii) complexes of 6-fold coordinating ligands showing high affinity for the hydrogen carbonate ion: a spectroscopic and thermodynamic study

In the present contribution, four classes of Ln(iii) complexes (Ln = Eu and Tb) have been synthesized and characterized in aqueous solution. They differ by charge, Ln(bpcd)+ [bpcd2- = N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate] and Ln(bQcd)+ (bQcd2- = N,N'-bis(2-quinolinmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate) being positively charged and Ln(PyC3A) (PyC3A3- = N-picolyl-N,N',N'-trans-l,2-cyclohexylenediaminetriacetate) and Ln(QC3A) (QC3A3- = N-quinolyl-N,N',N'-trans-l,2-cyclohexylenediaminetriacetate) being neutral. Combined DFT, spectrophotometric and potentiometric studies reveal the presence, under physiological conditions (pH 7.4), of a couple of equally and highly stable isomers differing by the stereochemistry of the ligands (trans-N,N and trans-O,O for bpcd2- and bQcd2-; trans-O,O and trans-N,O for PyC3A3- and QC3A3-). Their high log β values (9.97 < log β < 15.68), the presence of an efficient antenna effect and the strong increase of the Ln(iii) luminescence intensity as a function of the hydrogen carbonate concentration in physiological solution, render these complexes as very promising optical probes for a selective detection of HCO3-in cellulo or in extracellular fluid. This particularly applies to the cationic Eu(bpcd)+, Tb(bpcd)+ and Eu(bQcd)+ complexes, which are capable of guesting up to two hydrogen carbonate anions in the inner coordination sphere of the metal ion, so that they show an unprecedented affinity towards HCO3- (log K for the formation of the adduct in the 4.6-5.9 range).

Chiral Sensing Using Circularly Polarized Luminescence of Bis(phenanthroline dicarboxylic acid) EuIII Complex Induced by Allosteric-type Interaction with Amino Acid Molecules

[Eu(pda)₂ ]^- and [Eu(bda)₂ ]^- (pda=1,10-phenanthroline-2, 9-dicarboxylic acid; bda=2,2' bipyridine 5,5'-dicarboxylic acid) have an achiral D_2d structure in crystals. These complexes exhibit circularly polarized luminescence (CPL) in water containing chiral amino acids. In this work, induced CPL of [Eu(pda)₂ ]^- and [Eu(bda)₂ ]^- in water solutions containing a mixture of d- and l- amino acids were examined. Plots of g_lum values of the induced CPL as a function of mol-fraction of l- and d- arginine reveal that [Eu(pda)₂ ]^- favors homo-association ([Eu(pda)₂ ]^- -(l-arginine)₂ or [Eu(pda)₂ ]^- -(d-arginine)₂ ) over hetero-association {[Eu(pda)₂ ]^- -(l-arginine)⋅(d-arginine)}. This suggests that association of an arginine molecule induces a structural change in [Eu(pda)₂ ]^- to promote chiral selective association to another arginine, i.e., homo-allosteric association. On the other hand, the system of [Eu(pda)₂ ]^- with histidine favors hetero-allosteric association over homo-association. No allosteric effect is recognized in CPL from [Eu(bda)₂ ]^- .

Reaction-based chiroptical sensing of ClO− using circularly polarized luminescence via self-assembly organogel

A chiral amino acid functionalized probe, PTZ-D, could self-assemble into a chiral organogel displaying unprecedented chiroptical monitoring of ClO⁻ with switchable CPL signals.

Monitoring of the ADP/ATP Ratio by Induced Circularly Polarised Europium Luminescence

A series of three europium complexes bearing picolyl amine moieties was found to possess differing binding affinities towards Zn²⁺ and three nucleotides: AMP, ADP, and ATP. A large increase in the total emission intensity was observed upon binding Zn²⁺ , followed by signal amplification upon the addition of nucleotides. The resulting adducts possessed strong induced circularly polarised emission, with ADP and ATP signals of opposite sign. Model DFT geometries of the adducts suggest the Δ diastereoisomer is preferred for ATP and the Λ isomer for ADP/AMP. This change in sign allows the ADP/ATP (or AMP/ATP) ratio to be assessed by monitoring changes in the emission dissymmetry factor, g_em .

Chiral probes for α1-AGP reporting by species-specific induced circularly polarised luminescence

Luminescence spectroscopy has been used to monitor the selective and reversible binding of pH sensitive, macrocyclic lanthanide complexes, [LnL¹], to the serum protein α₁-AGP, whose concentration can vary significantly in response to inflammatory processes.

Luminescence spectroscopy has been used to monitor the selective and reversible binding of pH sensitive, macrocyclic lanthanide complexes, [LnL¹], to the serum protein α₁-AGP, whose concentration can vary significantly in response to inflammatory processes. On binding α₁-AGP, a very strong induced circularly-polarised europium luminescence signal was observed that was of opposite sign for human and bovine variants of α₁-AGP – reflecting the differences in the chiral environment of their drug-binding pockets. A mixture of [EuL¹] and [TbL¹] complexes allowed the ratiometric monitoring of α₁-AGP levels in serum. Moreover, competitive displacement of [EuL¹] from the protein by certain prescription drugs could be monitored, allowing the determination of drug binding constants. Reversible binding of the sulphonamide arm as a function of pH, led to a change of the coordination environment around the lanthanide ion, from twisted square antiprism (TSAP) to a square antiprismatic geometry (SAP), signalled by emission spectral changes and verified by detailed computations and the fitting of NMR pseudocontact shift data in the sulphonamide bound TSAP structure for the Dy and Eu examples. Such analyses allowed a full definition of the magnetic susceptibility tensor for [DyL¹].

Enantioselective cellular localisation of europium(iii) coordination complexes

The selective mitochondrial localisation of the Λ enantiomer of three different emissive europium(iii) complexes in NIH 3T3 and MCF7 cells contrasts with the behaviour of the Δ enantiomer, for which a predominant lysosomal localisation was observed by confocal microscopy. In each case, cell uptake occurs via macropinocytosis.

Introducing Euro-Glo, a rare earth metal chelate with numerous applications for the fluorescent localization of myelin and amyloid plaques in brain tissue sections

The vast majority of fluorochromes are organic in nature and none of the few existing chelates have been applied as histological tracers for localizing brain anatomy and pathology.

NEW METHOD

In this study we have developed and characterized a Europium chelate with the ability to fluorescently label normal and pathological myelin in control and toxicant-exposed rats, as well as the amyloid plaques in aged AD/Tg mice.

RESULTS

This study demonstrates how Euro-Glo can be used for the detailed labeling of both normal myelination in the control rat as well as myelin pathology in the kainic acid exposed rat. In addition, this study demonstrates how E-G will label the shell of amyloid plaques in an AD/Tg mouse model of Alzheimer's disease a red color, while the plaque core appears blue in color. The observed E-G staining pattern is compared with that of well characterized tracers specific for the localization of myelin (Black-Gold II), degenerating neurons (Fluoro-Jade C), A-beta aggregates (Amylo-Glo) and glycolipids (PAS).

COMPARISONS WITH EXISTING METHODS

This study represents the first time a rare earth metal (REM) chelate has been used as a histochemical tracer in the brain. This novel tracer, Euro-Glo (E-G), exhibits numerous advantages over conventional organic fluorophores including high intensity emission, high resistance to fading, compatibility with multiple labeling protocols, high Stoke's shift value and an absence of bleed-through of the signal through other filters.

CONCLUSIONS

Euro-Glo represents the first fluorescent metal chelate to be used as a histochemical tracer, specifically to localize normal and pathological myelin as well as amyloid plaques.

Circularly-Polarized Luminescence (CPL) from Chiral AIE Molecules and Macrostructures

Circularly-polarized luminescence (CPL) has received new attention on the rise of applications to generate devices and biologically active probes. These applications require fluorophores that are not only chiral but also provide strong fluorescence intensity in aggregated state. Thus, a new research branch has opened up a few years ago, which allows CPL-active fluorophores to be emissive in aggregated-state. As a result, reports on the combination of the CPL property with the aggregation-induced emission (AIE) phenomenon have emerged. Herein the early design principles that have been reported until now to generate CPL-active AIE-active fluorophores (AIEgens) are summarized. In this regard the alignment of monomeric emitters in a chiral fashion, either in supramolecules, polymers or liquid crystals has been proven to be a successful approach. Additionally, first reports have appeared that demonstrate how to tackle the daunting task to furnish individual CPL-active AIEgens.

A colour-tunable chiral AIEgen: reversible coordination, enantiomer discrimination and morphology visualization

We present a conceptually new approach to synthesise a boron-containing Aggregation-Induced Emissive Luminogen (AIEgen) with a chiral chromophore. An intramolecular N-B coordinating bond results in a low-energy transition that renders the material red-emissive in a solid state. By competitive binding of nucleophiles to the boron atom, this bond is replaced in favour of an intermolecular coordinating bond, which results in a tremendous blue-shift in both the absorption and emission. A supportive DFT computation elucidates that a breakage of the intramolecular N-B coordinating bond causes a tremendous loss of conjugation in the LUMO, resulting in a larger energy gap. Owing to the fact that our scaffold is intrinsically chiral and Lewis-acidic, we demonstrate how our AIEgen discriminates between two pairs of enantiomers in a simple UV-vis measurement. Furthermore, the binding capabilities are exploited to stain polymer blends that comprised a non-coordinating and a Lewis-basic polymer. The red fluorescence that originates only from domains of the non-coordinating polymer is conveniently detected by a fluorescence microscope. Thus, compared to current analytical methods, we present a cheaper and faster methodology to study the micro-morphologies of certain polymer blends.

Chiral metal-macrocycle frameworks: supramolecular chirality induction and helicity inversion of the helical macrocyclic structures

Porous molecular solids composed of discrete macrocycles/cages have great potential for catalysis, separation and sensing techniques. Dynamic structural transformation of the host building blocks, especially a helicity inversion responsive to chemical triggers, is central to upgrading the spatial functions. Here we have achieved the syntheses of homochiral porous molecular solids composed of helical metal macrocycles through supramolecular chirality induction to both enantiomorphic forms with the aid of two different enantiopure sugar-derived lactones in the crystallization process. Moreover, we found that the helicity of the macrocyclic skeletons can be inverted in the crystalline state only by changing the type of solvent. This finding would lead to dynamic control of space chirality in connection with optical resolution, chiral amplification and asymmetric reactions.

A luminescent europium(iii)–platinum(ii) heterometallic complex as a theranostic agent: a proof-of-concept study

We present a luminescent heterometallic multifunctional theranostic Eu–Pt₂ complex, [{cis-PtCl₂(DMSO)}₂Eu(L)(H₂O)], possessing two cytotoxic Pt-centers with four DNA-binding sites, which shows intracellular Eu-based red luminescence sensitized by platinum based MLCT excited states.

Amplifying the sensitivity of zinc(II) responsive MRI contrast agents by altering water exchange rates

Given the known water exchange rate limitations of a previously reported Zn(II)-sensitive MRI contrast agent, GdDOTA-diBPEN, new structural targets were rationally designed to increase the rate of water exchange to improve MRI detection sensitivity. These new sensors exhibit fine-tuned water exchange properties and, depending on the individual structure, demonstrate significantly improved longitudinal relaxivities (r1). Two sensors in particular demonstrate optimized parameters and, therefore, show exceptionally high longitudinal relaxivities of about 50 mM(-1) s(-1) upon binding to Zn(II) and human serum albumin (HSA). This value demonstrates a 3-fold increase in r1 compared to that displayed by the original sensor, GdDOTA-diBPEN. In addition, this study provides important insights into the interplay between structural modifications, water exchange rate, and kinetic stability properties of the sensors. The new high relaxivity agents were used to successfully image Zn(II) release from the mouse pancreas in vivo during glucose stimulated insulin secretion.

Circularly polarized luminescence of AIE-active chiral O-BODIPYs induced via intramolecular energy transfer

Two AIE-active chiral BINOL-based O-BODIPY enantiomers (R/S-5) were synthesized and showed mirror-image red-color CPL induced via intramolecular energy transfer. The chiroptical properties of the molecules indicate that the chirality of electronic ground and excited states is stable and independent of aggregation.

Ratiometric luminescence thermometry based on crystal-field alternation at the extremely narrow ⁵D₀ → ⁷F₂ transition band of europium(III)

A dinuclear europium(III) complex with a structure of [BP-(Eu(III))2-(ODA)3] (BP = 2,2'-bipyridine-6,6'-dicarboxylic acid bis(N-hydroxy-succinimide) ester, ODA = diglycolic acid) shows a fully reversible emission spectral change at the extremely narrow (5)D0 → (7)F2 transition band in response to temperature changes ranging from 283 K to 333 K.

Lanthanide(iii) and lead(ii) complexes of a chiral nonaaza macrocyclic amine based on 1,2-diaminocyclopentane

We report the synthesis, spectroscopic characterization and X-ray crystal structures of a series of helical complexes of a new chiral macrocycle based on diaminocyclopentane fragments. In the case of a Pb(ii) derivative the NMR data indicate a dynamic process corresponding to partial wrapping and unwrapping of the macrocycle resulting in the switching of the helix axis.

EuroTracker® dyes: design, synthesis, structure and photophysical properties of very bright europium complexes and their use in bioassays and cellular optical imaging

The creation of the most emissive series of europium complexes is traced and examples given of their use in imaging.

Anion and solvent induced chirality inversion in macrocyclic lanthanide complexes

A series of the lanthanide(III) or yttrium(III) complexes of the type [LnL(NO3)(H2O)2](NO3)2, [LnL(NO3)(H2O)](NO3)2, [LnL(H2O)2](NO3)3, and [LnLCl(H2O)2]Cl2 where L is an all-R or all-S enantiomer (L(R) or L(S)) of the chiral hexaaza macrocycle, 2(R),7(R),18(R),23(R)- or 2(S),7(S),18(S),23(S)-1,8,15,17,24,31-hexaazatricyclo[25.3.1.1.0.0]-dotriaconta-10,12,14,26,28,30-hexaene, and Ln(III) = Sm(III), Tb(III), Ho(III), Er(III), Tm(III), Yb(III), Lu(III), or Y(III), have been synthesized and structurally characterized. The crystal structure of the free macrocycle shows a highly twisted molecule, preorganized for the formation of helical complexes. The crystal structures of the lanthanide(III) complexes show two different diastereomeric forms of the macrocycle with different configurations at the stereogenic amine nitrogen atoms: (RRRR) or (RSRS) (denoted as L(RI) and L(RII), respectively). The L(RI) diastereomeric form of the nitrate derivatives [LnL(NO3)(H2O)](NO3)2 (Ln = Ho, Er) and [LnL(H2O)2](NO3)3 (Ln = Tm, Yb, Lu) convert slowly to the L(RII) form in methanol or acetonitrile solutions, while this process is not observed for the L(RI) diastereomers of analogous chloride derivatives [LnL(H2O)2]Cl3 (Ln = Tm, Yb, Lu). On the other hand, the L(RI) → L(RII) conversion for these Tm(III), Yb(III), and Lu(III) chloride derivatives can be triggered by the addition of external nitrate anions. The circular dichroism (CD) and (1)H NMR data indicate initial fast exchange of axial chloride for axial nitrate ligand, followed by slow chirality inversion of the equatorial macrocyclic ligand.

Synthesis, luminescence properties of Eu(III) and Tb(III) complexes with a novel aromatic carboxylic acid and their interactions with bovine serum albumin

A novel aromatic carboxylic acid ligand (L) was synthesized and its corresponding Eu(III) and Tb(III) complexes, Na(3)EuLCl(3)·2H(2)O (EuL) and Na(3)TbLCl(3)·3H(2)O (TbL), were successfully prepared. L and its corresponding complexes were characterized by means of MS, elemental analysis, IR, (1)H NMR and TG. The luminescence spectra of Eu(III) and Tb(III) complexes were investigated and the results showed that L was an efficient sensitizer for Eu(III) and Tb(III) luminescence. The interactions of L, EuL and TbL with bovine serum albumin (BSA) have been investigated through fluorescence spectroscopy under physiological conditions. The Stern-Volmer analysis indicated that the fluorescence quenching of BSA by L, EuL and TbL was resulted from static mechanism, and the binding constants (K(a)) were 2.22×10(4), 1.33×10(5) and 4.27×10(5) at 300 K, respectively. The binding sites (n) and the corresponding thermodynamic parameters ΔH, ΔS, and ΔG were calculated at different temperatures. According to the theoretical and experimental results, van der Waals interactions and hydrogen bonds were found to play major roles in the binding reaction. Furthermore, UV-Vis absorption spectroscopy and synchronous fluorescence spectra indicated that the conformation of BSA was changed. The results obtained in the work can help understand the action mode between L and its corresponding Eu(III) and Tb(III) complexes with BSA, and they are also expected to provide important information of designs of new inspired drugs based on Eu and Tb.

Chiroptical spectra of tetrakis (+)-3-heptafluorobutylrylcamphorate Ln(III) complexes with an encapsulated alkali metal ion: solution structures as revealed by chiroptical spectra

The preparation of tetrakis((+)-hfbc) lanthanide(III) complexes with an encapsulated alkali metal and ammonium ions M[Ln((+)-hfbc)(4)] (hereafter abbreviated as M-Ln : (+)-hfbc, (+)-heptafluorobutyrylcamphorate; M, ammonium or benzyl ammonium ions as well as alkali metal ions) was reported and discussed. The electronic circular dichroism (CD) spectra in the intraligand π-π* transition of M-Ln were examined in view of the solvent effect. Here, the concentration, alkali metal, and ammonium ion dependences are compared with the solid CD, (5)D(0)←(7)F(0) (Eu(III)) excitation spectra, circularly polarized luminescence, and vibrational circular dichroism. It has been revealed that the dodecahedral eight coordinate DD-8-M-Ln complexes in crystals are equilibrated between the diastereoselectively formed square antiprism eight coordinate SAPR-8-M-Ln and [Ln((+)-hfbc)(3)] in EtOH and CH(3) CN solutions or between the SAPR-8-M-Ln and DD-D(2d) (mmmm)-8-M-Ln complexes in CHCl(3) solution. The observed CD couplets are found to reflect the exciton CD couplets which are useful to determine the four-bladed SAPR-(llll) absolute configuration around the lanthanide(III) ion.

Coordination chemistry strategies for dynamic helicates: time-programmable chirality switching with labile and inert metal helicates

'Chirality switching' is one of the most important chemical processes controlling many biological systems. DNAs and proteins often work as time-programmed functional helices, in which specific external stimuli alter the helical direction and tune the time scale of subsequent events. Although a variety of organic foldamers and their hybrids with natural helices have been developed, we highlight coordination chemistry strategies for development of structurally and functionally defined metal helicates. These metal helicates have characteristic coordination geometries, redox reactivities and spectroscopic/magnetic properties as well as complex chiralities. Several kinds of inert metal helicates maintain rigid helical structures and their stereoisomers are separable by optical resolution techniques, while labile metal helicates offer dynamic inversion of their helical structures via non-covalent interactions with external chemical signals. The latter particularly have dynamically ordered helical structures, which are controlled by the combinations of metal centres and chiral ligands. They further function as time-programmable switches of chirality-derived dynamic rotations, translations, stretching and shape flipping, which are useful applications in nanoscience and related technology.

Metal-controlled diastereoselective self-assembly and circularly polarized luminescence of a chiral heptanuclear europium wheel

The chiral dissymmetric tetradentate ligand (S)-6'-(4-phenyloxazolin-2-yl)-2,2'-bipyridine-6-carboxylate (S-Phbipox) leads to the diastereoselective assembly of a homochiral Eu(3+) triangle and a highly emissive (quantum yield = 27%) heptanuclear wheel that is the largest example of a chiral luminescent complex of Eu(3+) reported to date. The nuclearity of the assembly is controlled by the solvent and the Eu(3+) cation. All of the compounds show large circularly polarized luminescence with an activity that varies with the nature of the assembly (highest for the homochiral trimer).