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Polyvinylpyrrolidone (PVP) can be used to produce upconversion nanoparticles (UCNPs) in an advantageous manner, i.e. at modest temperatures in open-to-air conditions with simple hotplate and flask apparatus. However, the influence of PVP parameters on the formation of UCNPs has not been previously investigated. In this exploratory study, we establish that PVP molecular weight and relative amount of PVP can greatly influence the morphology and diameter of NaYF4:Yb,Er UCNPs produced via the PVP-assisted route. At nominal amounts of PVP, varying the molecular weight of PVP in synthesis between 10,000 g/mol (PVP10), 40,000 g/mol (PVP40), and 55,000 g/mol (PVP55), had minimal effect on UCNP morphology, whereas reducing the quantity of PVP10 and PVP40 in the reaction to 10% of the nominal amount resulted in two notable effects: (1) the generation of a greater range of UCNP diameters and (2) the production of an unexpected sub-population of rhombus-shaped UCNPs. Bulk and individual nanoparticle analysis indicates that all UCNP morphologies were cubic (α-phase) crystal structure and consisted of NaYF4:Yb,Er. Optical emission properties exhibited only modest green and red luminescence emission ratio when PVP parameters were varied. However, separately produced PVP40 NaYF4:Yb,Tm UCNPs exhibited a much more intense and dual-band blue /red emission. This exploratory work demonstrates that tailoring PVP content in synthesis of UCNPs can greatly alter morphology of UCNPs produced and should be carefully considered in experimental design. However, the underlying mechanisms of action of the role PVP plays in this synthesis remain unclear. Ultimately, significant further work is still required to fully elucidate the relevant chemistry to achieve full control of PVP-UCNP synthesis.

An RNA-based coordination polymer is formed by the aqueous reaction of CuI ions with the thionucleoside enantiomer (−)6-thioguanosine, (6tGH). The resulting polymer, [CuI(μ3-S-thioG)]n1, has a one-dimensional structure based on a [Cu4–S4] core and undergoes extensive hierarchical self-assembly transforming from oligomeric chains → rod → cable → bundle through which a fibrous gel forms, that undergoes syneresis to form a self-supporting mass. The assembly involves the formation of helical cables/bundles and, in combination with the intrinsic photoemission of the polymer, results in the material exhibiting circularly polarised luminescence (CPL).

Since the pioneering report by Selvin, we have been fascinated by the potential of using lanthanide lu-minescence in bioimaging. The uniquely narrow emission lines and long luminescence lifetimes both provide the potential for background free images together with full certainty of probe localization. General use of lanthanide based bioimaging was first challenged by low brightness, and later by the need of UV (

Helically chiral boron-chelated dipyrromethene (BODIPY) dyes are known to exhibit solution phase circularly polarized luminescence (CPL), but examples are limited to a few synthetically accessible molecular architectures. We report a B−N chelation, SNAr, Suzuki cross-coupling, B−O chelation cascade reaction for the synthesis of understudied helically chiral, N,N,O,C-boron chelated, “confused” BODIPYs, from readily accessible 3,5-dibromo-BODIPY starting materials. Using this approach we have prepared a series of helically chiral “confused” BODIPYs with variation of the 3,5-subsitutents. Following resolution by chiral HPLC, absolute stereochemistry was assigned through comparison of the experimental and calculated ECD spectra, and solution phase chiroptical properties including CPL were determined (|glum| from 2.1 to 3.7×10−3; BCPL from 11.3 to 27.2).

This work showcases chiral complementarity in aromatic stacking interactions as an effective tool to optimize the chiroptical and electrochemical properties of perylene diimides (PDIs). PDIs are a notable class of robust dye molecules and their rich photo- and electrochemistry and potential chirality make them ideal organic building blocks for chiral optoelectronic materials. By exploiting the new bay connectivity of twisted PDIs, a dynamic bis-PDI macrocycle (the “Pink Box”) is realized in which homochiral PDI–PDI π–π stacking interactions are switched on exclusively. Using a range of experimental and computational techniques, we uncover three important implications of the macrocycle’s chiral complementarity for PDI optoelectronics. First, the homochiral intramolecular π–π interactions anchor the twisted PDI units, yielding enantiomers with half-lives extended over 400-fold, from minutes to days (in solution) or years (in the solid state). Second, homochiral H-type aggregation affords the macrocycle red-shifted circularly polarized luminescence and one of the highest dissymmetry factors of any small organic molecule in solution (glum = 10–2 at 675 nm). Finally, excellent through-space PDI–PDI π-orbital overlap stabilizes PDI reduced states, akin to covalent functionalization with electron-withdrawing groups.

Synthetically straightforward pi-extension of helically chiral N,N,O,O-boron chelated borondipyrromethenes (BODIPYs) has been achieved by incorporation of naphthyl rings into the BODIPY 3- and 5-positions. The effect of this extension on the photophysical and chiroptical properties is strongly dependent on the regiochemistry of the naphthyl substituents (4 exo, 4 lin, 4 endo). The most helicene-like regioisomer 4 endo is a near infra-red (NIR) emitter (lambda(em)(max)=751 nm) with an emission band between 675-875 nm, displaying circularly polarised luminescence (CPL) with a luminescence dissymmetry factor, vertical bar g(lum)vertical bar=5.7x10(-3) and CPL brightness, B-CPL=27, rivalling the best NIR CPL-emitting small organic molecules reported to date.

4 pags., 4 figs., 1 tab., BINOL moieties of different electronic demand are useful blocks for enabling the photo-production and modulation of triplet excited states in readily-accesible BINOL-based O-BODIPY dyes from standard F-BODIPY precursors. The rapid and rational development of smarter triplet-enabling BODIPY dyes on the basis of this strategy (e.g., TADF biomarker 4a or room temperature phosphor 4g) paves the way for advancing photonic applications based on organic triplet photosensitizers., Financial support from MICINN (PID2020-114755GB-C32 and C-33, and PID2020-114347RB-C32), Royal Society (URF\R\191002), UE (H2020-MSCA-ITN-859752 and HEL4CHIROLED), BBSRC (BB/S017615/1) and Basque Government (IT1639-22) is gratefully acknowledged. J. J., R. P.-M. and P. S. respectively thank CM/UCM, MICINN (MARSA21/71) and BB/S017615/1 for research contracts.

The aqueous equimolar reaction of Ag(I) ions with the thionucleoside enantiomer (−)6-thioguanosine, ((−)6tGH), yields a one-dimensional coordination polymer {Ag(−)tG}n, the self-assembly of which generates left-handed helical chains. The resulting helicity induces an enhanced chiro-optical response compared to the parent ligand. DFT calculations indicate that this enhancement is due to delocalisation of the excited state along the helical chains, with 7 units being required to converge the calculated CD spectra. At concentrations ≥15 mmol l−1 reactions form a sample-spanning hydrogel which shows self-repair capabilities with instantaneous recovery in which the dynamic reversibility of the coordination chains appears to play a role. The resulting gel exhibits circularly polarised luminescence (CPL) with a large dissymmetry factor of −0.07 ± 0.01 at 735 nm, a phenomenon not previously observed for this class of coordination polymer.

The formation of bio-inspired healable lanthanide luminescent hydrogels is detailed. These materials are composed of K(I)-stabilized guanosine quadruplexes (G4) that were bio-conjugated to mannose-derived picolinic acid ligand 1 using boric acid chemistry (G4-1). The supramolecular self-assembly between G4-1 and europium (Eu(III)) was confirmed, including the use of time-gated luminescence spectroscopy. The most stable hydrogel was formed when the ratio between 1 and Eu(III) was 1:1, and this gel was found to retain a helical column. The obtained gel samples were further characterized using techniques, such as scanning electron microscopy (SEM), circular dichroism (CD), and luminescence spectroscopy. We demonstrate that a Eu(III)-centered circularly polarized luminescence (CPL) signal from guanosine hydrogels can be observed even via long-range interaction, whereas the rheology of these gels exhibits their healable properties.

Examination of total emission and circularly polarised luminescence (CPL) spectra of three 9-coordinate Eu(iii) complexes with well-defined speciation shows that the ligand fields of these C3 symmetric complexes are extremely sensitive to solvent polarity, even when solvent is not present in the first coordination sphere. The energies, intensities, and (for CPL) the sign of some transitions vary with solvent polarity. These observations are rationalised by analysis of the factors that control total and circularly polarised emission, and have important implications for design of responsive luminescent Ln(iii) probes.

A set of four luminescent EuIII complexes bearing an extended aryl‐alkynylpyridine chromophore has been studied, showing very different pH‐dependent behaviour in their absorption and emission spectral response. For two complexes with pK a values of 6.45 and 6.20 in protein‐containing solution, the emission lifetime increases very significantly following protonation. By varying the gate time during signal acquisition, the ‘switch‐on’ intensity ratio could be optimised, and enhancement factors of between 250 to 1330 were measured between pH 8 and 4. The best‐behaved probe showed no significant emission dependence on the concentration of endogenous cations, reductants, and serum albumin. It was examined in live‐cell imaging studies to monitor time‐dependent lysosomal acidification, for which the increase in observed image brightness due to acidification was a factor of 50 in NIH‐3T3 cells., Watching lysosomes age with a ‘switch‐on’ optical sensor is shown to be possible by using four europium complexes with extended aryl‐alkylnyl pyridine antennae that show very different pH‐dependent behaviour. A ‘switch‐on’ of europium luminescence occurs at low pH, allowing confocal microscopy to reveal increases in image brightness of ageing lysosomes in live‐cell imaging studies.

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 5D0 → 7F1 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., A series of chiral, water‐soluble, DO3A‐based EuIII complexes was designed and synthesized. The chiral substituents introduced onto the macrocyclic scaffolds enhanced the photophysical properties with quantum yields up to 31 % and |glum| up to 0.240. The |glum| value increased by 20 % from 0.222 to 0.267 under external magnetic field showing a linear response.

Organ and tissue development are highly coordinated processes; lens growth and functional integration into the eye (emmetropia) is a robust example. An epithelial monolayer covers the anterior hemisphere of the lens, and its organization is the key to lens formation and its optical properties throughout all life stages. To better understand how the epithelium supports lens function, we have developed a novel whole tissue imaging system using conventional confocal light microscopy and a specialized analysis software to produce three-dimensional maps for the epithelium of intact mouse lenses. The open source software package geometrically determines the anterior pole position, the equatorial diameter, and three-dimensional coordinates for each detected cell in the epithelium. The user-friendly cell maps, which retain global lens geometry, allow us to document age-dependent changes in the C57/BL6J mouse lens cell distribution characteristics. We evidence changes in epithelial cell density and distribution in C57/BL6J mice during the establishment of emmetropia between postnatal weeks 4–6. These epithelial changes accompany a previously unknown spheroid to lentoid shape transition of the lens as detected by our analyses. When combined with key findings from previous mouse genetic and cell biological studies, we suggest a cytoskeleton-based mechanism likely underpins these observations.

Super resolution microscopy has become a staple in optical microscopy with applications ranging from imaging sub-cellular features to monitoring the stages of chemical reactions. In this chapter we present a brief background on the origin of the diffraction limit, a summary of the key techniques and their individual strengths and weaknesses.

In summing up, we have asked each of our authors to provide their view of what the future holds in this exciting and rapidly developing field.

A new method for facilitating the delivery, uptake and intracellular localisation of thermally activated delayed fluorescence (TADF) complexes was developed. First, confinement of TADF complexes in liposomes was demonstrated, which were subsequently used as the delivery vehicle for cellular uptake. Confocal fluorescence microscopy showed TADF complexes subsequently localise in the cytoplasm of HepG2 cells. The procedures developed in this work included the removal of molecular oxygen in the liposome preparation without disrupting the liposome structures. Time-resolved fluorescence microscopy (point scanning) showed initial prompt fluorescence followed by a weak, but detectable, delayed fluorescence component for liposomal TADF internalised in HepG2 cells. By demonstrating that it is possible to deliver un-functionalised and/or unshielded TADF complexes, a sensing function for TADFs, such as molecular oxygen, can be envisaged.

Multidrug resistance in pathogenic bacteria is an increasing problem in patient care and public health. Molecular nanomachines (MNMs) have the ability to open cell membranes using nanomechanical action. We hypothesized that MNMs could be used as antibacterial agents by drilling into bacterial cell walls and increasing susceptibility of drug-resistant bacteria to recently ineffective antibiotics. We exposed extensively drug-resistant Klebsiella pneumoniae to light-activated MNMs and found that MNMs increase the susceptibility to Meropenem. MNMs with Meropenem can effectively kill K. pneumoniae that are considered Meropenem-resistant. We examined the mechanisms of MNM action using permeability assays and transmission electron microscopy, finding that MNMs disrupt the cell wall of extensively drug-resistant K. pneumoniae, exposing the bacteria to Meropenem. These observations suggest that MNMs could be used to make conventional antibiotics more efficacious against multi-drug-resistant pathogens.

The syntheses and photophysical behaviour of nine, strongly luminescent nonadentate Eu(III) complexes are reported. Each complex is based on N-functionalised 1,4,7- triazacyclononane, and linkage to other groups or targeting vectors can occur either via amide bond formation to a coordinated pyridine p-aminopropyl group or via a nucleophilic substitution reaction involving thiol attack on a metal coordinated p-nitropyridyl moiety. Evidence is presented in favour of the latter conjugation strategy, as parallel work with maleimide conjugates was complicated or compromised by the propensity to undergo postconjugation thiol exchange or succinimide ring hydrolysis reactions. Confocal microscopy and spectral imaging studies revealed that the peptide conjugate of AcCFFKDEL was found to localise selectively in the endoplasmic reticulum of mouse fibroblast cells, whereas the related maleimide conjugate was only observed in cellular lysosomes

One-step cyclization of a tetraazamacrocycle 5 with 70% yield in a 25-g scale was performed. Its chiral DOTA derivatives, L4, has ∼93% of TSAP coordination isomer in its Eu(III) and Yb(III) complexes in aqueous solution. [GdL4]5– exhibits a high relaxivity, making it a promising and efficient MRI contrast agent. High luminescence dissymmetry factor (glum) values of 0.285 (ΔJ = 1) for [TbL3]– and 0.241 (ΔJ = 1) for [TbL4]5– in buffer solutions were recorded.

Peroxynitrite (ONOO−) is a powerful and short-lived oxidant formed in vivo, which can react with most biomolecules directly. To fully understand the roles of ONOO− in cell biology, improved methods for the selective detection and real-time analysis of ONOO− are needed. We present a water-soluble, luminescent europium(iii) probe for the rapid and sensitive detection of peroxynitrite in human serum, living cells and biological matrices. We have utilised the long luminescence lifetime of the probe to measure ONOO− in a time-resolved manner, effectively avoiding the influence of autofluorescence in biological samples. To demonstrate the utility of the Eu(iii) probe, we monitored the production of ONOO− in different cell lines, following treatment with a cold atmospheric plasma device commonly used in the clinic for skin wound treatment., Reactivity-based europium(iii) probe displays excellent selectivity for peroxynitrite (ONOO−), enabling its time-resolved luminescence detection in living cells.

Authenticating products and documents with security inks is vital to global commerce, security and health. Lanthanide complexes are widely used in luminescent security inks owing to their unique and robust photophysical properties. Lanthanide complexes can also be engineered to undergo circularly polarized luminescence (CPL), which encodes chiral molecular fingerprints in luminescence spectra that cannot be decoded by conventional optical measurements. However, chiral CPL signals have not yet been exploited as an extra security layer in advanced security inks. This Review introduces CPL and related concepts that are necessary to appreciate the challenges and potential of lanthanide-based, CPL-active security inks. We describe recent advances in CPL analysis and read-out technologies that have expedited CPL-active security ink applications. Further, we provide a systematic meta-analysis of strongly CPL-active Euiii, Tbiii, Smiii, Ybiii, Cmiii, Dyiii and Criii complexes, discussing the suitability of their photophysical properties and highlighting promising candidates. We conclude by providing key recommendations for the development and advancement of the field. Several transition-metal and lanthanide complexes undergo circularly polarized luminescence. This Review describes design principles for the complexes and instruments used to measure them, including in the context of security inks.

Light-activated molecular nanomachines (MNMs) can be used to drill holes into prokaryotic (bacterial) cell walls and the membrane of eukaryotic cells, including mammalian cancer cells, by their fast rotational movement, leading to cell death. We examined how these MNMs function in multicellular organisms and investigated their use for treatment and eradication of specific diseases by causing damage to certain tissues and small organisms. Three model eukaryotic species, Caenorhabditis elegans, Daphnia pulex, and Mus musculus (mouse), were evaluated. These organisms were exposed to light-activated fast-rotating MNMs and their physiological and pathological changes were studied in detail. Slow rotating MNMs were used to control for the effects of rotation rate. We demonstrate that fast-rotating MNMs caused depigmentation and 70% mortality in C. elegans while reducing the movement as well as heart rate and causing tissue damage in Daphnia. Topically applied light-activated MNMs on mouse skin caused ulceration and microlesions in the epithelial tissue, allowing MNMs to localize into deeper epidermal tissue. Overall, this study shows that the nanomechanical action of light-activated MNMs is effective against multicellular organisms, disrupting cell membranes and damaging tissue in vivo. Customized MNMs that target specific tissues for therapy combined with spatial and temporal control could have broad clinical applications in a variety of benign and malignant disease states including treatment of cancer, parasites, bacteria, and diseased tissues., Graphical Abstract

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.

A series of four emissive europium complexes has been evaluated for the binding of glyphosate in various aqueous media, including river water and grain extracts. Binding selectivity toward inorganic phosphate and bicarbonate was enhanced by measuring samples at pH 5.9, above the pKa of glyphosate itself. The highest affinity was shown with [Eu·L1], which creates an exocyclic tripicolylamine moiety when one pyridine group dissociates from Eu. Glyphosate was bound selectively over dihydrogenphosphate, glycinate, aminomethylphosphonate and the related herbicide glufosinate. The complex was used to measure glyphosate over the range 5 to 50 μM, in river water and grain extracts.

For almost a century, the resolution of optical microscopy was thought to be limited by Abbe's law describing the diffraction limit of light. At the turn of the millennium, aided by new technologies and fluorophores, the field of optical microscopy finally surpassed the diffraction barrier: a milestone achievement that has been recognized by the 2014 Nobel Prize in Chemistry. Many super-resolution methods rely on the unique photophysical properties of the fluorophores to improve resolution, posing significant limitations on biological imaging, such as multicoloured staining, live-cell imaging and imaging thick specimens. Structured Illumination Microscopy (SIM) is one branch of super-resolution microscopy that requires no such special properties of the applied fluorophores, making it more versatile than other techniques. Since its introduction in biological imaging, SIM has proven to be a popular tool in the biologist's arsenal for following biological interaction and probing structures of nanometre scale. SIM continues to see much advancement in design and implementation, including the development of Image Scanning Microscopy (ISM), which uses patterned excitation via either predefined arrays or raster-scanned single point-spread functions (PSF). This review aims to give a brief overview of the SIM and ISM processes and subsequent developments in the image reconstruction process. Drawing from this, and incorporating more recent achievements in light shaping (i.e. pattern scanning and super-resolution beam shaping), this study also intends to suggest potential future directions for this ever-expanding field.

Invited for this month's cover are the collaborating groups of Dr. Thomas Just Sørensen at the University of Copenhagen, Denmark and Dr. Robert Pal at Durham University, United Kingdom. The front cover shows the clouds parting for a cell imaged using a thioxanthone-appended Eu

Recently, synthetic molecular nanomachines (MNMs) that rotate unidirectionally in response to UV light excitation have been used to produce nanomechanical action on live cells to kill them through the drilling of holes in their cell membranes. In the work here, visible-light-absorbing MNMs are designed and synthesized to enable nanomechanical activation by 405 nm light, thereby using a wavelength of light that is less phototoxic than the previously employed UV wavelengths. Visible-light-absorbing MNMs that kill pancreatic cancer cells upon response to light activation are demonstrated. Evidence is presented to support the conclusion that MNMs do not kill cancer cells by the photothermal effect when used at low optical density. In addition, MNMs suppress the formation of reactive oxygen species, leaving nanomechanical action as the most plausible working mechanism for cell killing under the experimental conditions.

Bright lanthanide based probes for optical bioimaging must rely on the antenna principle, where the lanthanide-centred excited state is formed by a complex sensitization process. Efficient sensitization of lanthanide-centred emission occurs via triplet states centred on the sensitizing chromophore. Here, the triplet state of thioxanthone chromophores is modulated by extending the π-system. Three thioxanthone chromophores-thioxanthone, benzo[c]thioxanthone, and naphtho[2,3-c]thioxanthone were synthesised and characterised. The triplet state energies and lifetimes is found to change as expected, and two dyes are found to be suitable sensitizers for europium(iii) luminescence. Reactive derivatives of thioxanthone and benzo[c]thioxanthone were prepared and coupled to a 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) lanthanide binding pocket. The photophysics and the performance in optical bioimaging of the resulting europium(iii) complexes were investigated. It is concluded that while the energetics favour efficient sensitization, the solution structure does not. While it was found that the complexes are too lipophilic to be efficient luminescent probes for optical bioimaging, we successfully demonstrated bioimaging using europium(iii) luminescence following 405 nm excitation.