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The synthesis of a family of chiral and enantiomerically pure pyridyl‐diamide (pda) ligands that upon complexation with europium [Eu(CF3SO3)3] result in chiral complexes with metal centered luminescence is reported; the sets of enantiomers giving rise to both circular dichroism (CD) and circularly polarized luminescence (CPL) signatures. The solid‐state structures of these chiral metallosupramolecular systems are determined using X‐ray diffraction showing that the ligand chirality is transferred from solution to the solid state. This optically favorable helical packing arrangement is confirmed by recording the CPL spectra from the crystalline assembly by using steady state and enantioselective differential chiral contrast (EDCC) CPL Laser Scanning Confocal Microscopy (CPL‐LSCM) where the two enantiomers can be clearly distinguished. Enantiopure formation of chiral self‐templated lanthanide supramolecular structures gives rise to CPL when probed both in solution and the solid state demonstrating chirality transfer.

To understand the molecular origins of diseases caused by ultraviolet and visible light, and also to develop photodynamic therapy, it is important to resolve the mechanism of photoinduced DNA damage. Damage to DNA bound to a photosensitizer molecule frequently proceeds by one-electron photo-oxidation of guanine, but the precise dynamics of this process are sensitive to the location and the orientation of the photosensitizer, which are very difficult to define in solution. To overcome this, ultrafast time-resolved infrared (TRIR) spectroscopy was performed on photoexcited ruthenium polypyridyl–DNA crystals, the atomic structure of which was determined by X-ray crystallography. By combining the X-ray and TRIR data we are able to define both the geometry of the reaction site and the rates of individual steps in a reversible photoinduced electron-transfer process. This allows us to propose an individual guanine as the reaction site and, intriguingly, reveals that the dynamics in the crystal state are quite similar to those observed in the solvent medium. Uncertainty associated with solution-based electron-transfer studies of DNA–metal-complex systems has now been overcome by combining X-ray and time-resolved infrared data obtained for ruthenium polypyridyl–DNA crystals. Using these methods both the geometry of the reaction site and the kinetics of the reversible photo-induced one-electron oxidation of guanine have been determined.

Four new fluorescent sensors (1–4) based on the 4-amino-1,8-naphthalimide fluorophores (Naps) have been synthesized based on the classical fluorophorespacer-receptor model. These four compounds all gave rise to emission bands centred at ca. 535 nm, which were found to be highly pH dependent, the emission being ‘switched on’ in acidic media, while being quenched due to PET from the amino moieties to the excited state of the Nap at more alkaline pH. The luminescent pH dependence for these probes was found to be highly dependent on the substitution on the imide site, as well as the polyamine chain attached to the position 4-amino moiety. In the case of sensor 2 the presence of the 4-amino-aniline dominated the pH dependent quenching. Nevertheless, at higher pH, PET quenching was also found to occur from the polyamine site. Hence, 2 is better described as a receptor1-spacer1-fluorophore-spacer2-receptor2 system, where the dominant PET process is due to (normally less favourable) ‘directional’ PET quenching from the 4-amino-aniline unit to the Nap site. Similar trends and pH fluorescence dependences were also seen for 3 and 4. These compounds were also tested for their imaging potential and toxicity against HeLa cells (using DRAQ5 as nuclear stain which does now show pH dependent changes in acidic and neutral pH) and the results demonstrated that these compounds have reduced cellular viability at moderately high concentrations (with IC50 values between ca. 8–30 µmol·L−1), but were found to be suitable for intracellular pH determination at 1 µmol ·L−1concentrations, where no real toxicity was observed. This allowed us to employ these as lysosomal probes at sub-toxic concentrations, where the Nap based emission was found to be pH depended, mirroring that seen in aqueous solution for 1–4, with the main fluorescence changes occurring within acidic to neutral pH.

Supramolecular processes are attractive for the generation of functional materials, but managing multiple, competing self-assembly pathways has remained challenging. Now, the self-assembly of a platinum compound into three different aggregates has been elucidated, visualized in real time, and controlled.

The influence of solvent polarity on the self‐assembly processes and its effect on the morphological outcome of self‐assembled aggregates is another domain that requires a comprehensive study. The present investigation aims to address these issues by employing a unique “V‐shaped” luminogen (TBNap, N‐(3‐pyridyl)‐4‐amino‐1,8‐naphthalimide Tröger's base), where the two 1,8‐naphthalimide units are nearly orthogonal to each other. The TBNap is synthesized in high yield and fully characterized using standard characterization methods, including X‐ray diffraction analysis, which reveals distinctly different structural arrangements of TBNap crystallized as different solvates in various solvent media. Furthermore, due to its internal charge transfer nature, the TBNap exhibits positive solvatochromism and solvent‐guided morphogenesis. Given the unique structure, TBNap displays aggregation‐induced emission enhancement in THF‐H2O medium and forms self‐assembled fluorescent nanoaggregates as imaged using different microscopic imaging techniques such as scanning electron microscopy (SEM) and confocal fluorescence microscopy. Furthermore, the latter is employed to demonstrate the in situ real‐time visualization of these fluorescent nanoaggregates formations in native conditions and correlate the morphological outcome with SEM imaging. It is demonstrated that the self‐assembly process of the 3‐pyridyl‐based TBNap structure is highly solvent deepened. X‐ray diffraction analysis confirms that the TBNap structure possesses solvent‐depended packing arrangements in the crystalized form. This packing is translated into aggregation‐induced emission enhancement where fluorescent nanoaggregates are formed in THF‐H2O solution as imaged in real‐time using confocal fluorescence microscopy.

This mini review highlights the synthesis and photophysical evaluation of anion sensors, for nonaqueous solutions, that have been developed in our laboratories over the last few years. We have focused our research mainly on developing fluorescent photoinduced electron transfer (PET) sensors based on the fluorophore-spacer-anion receptor principle using several anthracene (emitting in the blue) and 1,8-naphthalimide (emitting in the green) fluorophores, with the aim of targeting biologically and industrially relevant anions such as acetates, phosphate and amino acids, as well as halides such as fluoride. The receptors and the fluorophore are separated by a short methyl or ethyl spacer, where the charge neutral anion receptors are either aliphatic or aromatic urea (or thiourea) moieties. For these, the anion recognition is through hydrogen bonding, yielding anion:receptor complexes. Such bonding gives rise to enhanced reduction potential in the receptor moieties which causes enhancement in the rate of PET quenching of the fluorophore excited state from the anion:receptor moiety. This design can be further elaborated on by incorporating either two fluorophores, or urea/thiourea receptors into the sensor structures, using anthracene as a fluorophore. For the latter design, the sensors were designed to achieve sensing of bis-anions, such as di-carboxylates or pyrophosphate, where the anion bridged the anthracene moiety. In the case of the naphthalimide based mono-receptor based PET sensors, it was discovered that in DMSO the sensors were also susceptible to deprotonation by anions such as F− at high concentrations. This led to substantial changes in the absorption spectra of these sensors, where the solution changed colour from yellow/green to deep blue, which was clearly visible to the naked eye. Hence, some of the examples presented can act as dual fluorescent-colorimetric sensors for anions. Further investigations into this phenomenon led to the development of simple colorimetric sensors for fluorides, which upon exposure to air, were shown to fix carbon dioxide as bicarbonate.

This mini review gives some highlights of the work recently carried out in our research group in Dublin on the developments of lanthanide luminescent devices, where the future goal is to produce devices that can operate as sensors. A few examples demonstrate our design principles for targeting both anion and cations that are of biological or pharmaceutical relevance, where the recognition occurs in aqueous competitive media. We also discuss the possibility of developing mixed f-d metal complexes and conjugates that can be employed as novel supramolecular architectures.

The synthesis and characterisation of two novel self‐assembled amphiphiles (SSAs) SQS‐1 and SQS‐2 are reported. Both compounds, based on the squaramide motif, were fully soluble in a range of solvents and were shown to undergo self‐assembly through a range of physical techniques. Self‐assembly was shown to favour the formation of crystalline domains on the nanoscale but also fibrillar film formation, as suggested by SEM analysis. Moreover, both SQS‐1 and SQS‐2 were capable of anion recognition in DMSO solution as demonstrated using 1H NMR and UV/Vis absorption spectroscopy, but displayed lower binding affinities for various anions when compared against other squaramide based receptors. In more competitive solvent mixtures SQS‐1 gave rise to a colourimetric response in the presence of HPO42− that was clearly visible to the naked eye. We anticipate that the observed response is due to the basic nature of the HPO42− anion when compared against other biologically relevant anions. Sticky squaramides: Two squaramide‐based self‐assembled amphiphiles (SSAs) are reported that are capable of colorimetric anion recognition in both organic and aqueous solution. Although these SSAs displayed lower binding affinities for anions than other squaramide‐based receptors, in competitive aqueous mixtures, they are fully soluble and capable of selective recognition of HPO42− in comparison with other biologically relevant anions.