Anthony J. Fitzpatrick

The development of robust, scalable materials for next-generation anti-counterfeiting technologies requires the integration of unique optical signatures with practical processability.

The development of robust, scalable materials for next-generation anti-counterfeiting technologies requires the integration of unique optical signatures with practical processability. Here, we report a modular platform of room-temperature luminescent ionic liquids based on trihexyl(tetradecyl)phosphonium salts of lanthanide tris(dipicolinate) complexes (Ln = Eu, Tb, Dy, Sm). These materials combine the sharp, line-like f–f emission characteristics of lanthanides with the inherent advantages of ionic liquids, including negligible vapor pressure, high miscibility, and facile formulation. Crucially, the liquid nature enables direct volumetric mixing of discrete emitters, allowing rapid generation of binary, ternary, and quaternary systems with dense, information-rich emission spectra. The intrinsic emission signatures of each lanthanide are retained in the liquid state, while mixture systems exhibit enhanced spectral complexity without requiring additional synthetic steps. Thermal and calorimetric analyses confirm the preservation of stable room-temperature liquid behaviour, supporting compatibility with established processing and printing technologies. This approach decouples spectral complexity from synthetic complexity, establishing a scalable route to tailorable photonic security materials. The concept of “complexity through simplicity” introduced here offers significant potential for advanced optical tagging, secure identification, and functional soft-material design.

The coordination chemistry of a hydrazinylpyrazine-derived Schiff base ligand (L1), formed in situ from salicylaldehyde and 2-hydrazinopyrazine, with Fe(III) salts has been systematically investigated under varied synthetic conditions. Six discrete Fe(III) complexes (1a–1e and 2) were isolated and structurally characterised via single-crystal X-ray diffraction, revealing diverse coordination geometries ranging from five-coordinate pseudo-trigonal bipyramidal to six-coordinate pseudo-octahedral environments. The supramolecular architectures are governed by a rich interplay of non-covalent interactions, including hydrogen bonding, halogen bonding, and π–π stacking, which significantly influence the crystallisation pathways and final solid-state structures. Continuous shape measure (CShM) analysis highlights substantial geometric distortion in the bis-tridentate complexes, attributed to the steric and electronic constraints imposed by the ligand. Powder X-ray diffraction and infrared spectroscopy confirm the presence of multiple phases in bulk samples, underscoring the kinetic competition between crystallisation and coordination. The results demonstrate that supramolecular stabilisation of monoligated species can kinetically inhibit bis-ligation, with ligand excess and solvent polarity serving as key parameters to direct complex speciation. These findings provide insight into the delicate balance between coordination geometry, ligand strain, and supramolecular assembly in Fe(III) Schiff base complexes.

Direct environmental control of the spin state is observed in alkyl sulfate Fe(III) complexes of 5-OMeSal2trien. High spin, low spin and mixed spin state responses are controlled by the aggregation properties of the dodecyl and octadecyl sulfate anions. Smaller particles favour the LS state due to size constraints, while larger aggregate formation favours the HS state allowing it to take up more space in a larger, relaxed particle.

Graphical Characterizing the proteomic profile of the Escherichia coli strain, BW2513, exposed to two novel iron-halide complexes: iron tetrachloride and iron tetrabromide.

Four Zn(II) Schiff base complexes that exhibit crystallisation-induced emission enhancement (CIEE) are presented. There is an intermolecular dimerisation through the hydrogen bonding of the mixed phenol/phenolate donors. The choice of ligand also determines the emission wavelength. The complexes have been investigated using experimental and theoretical techniques.

A neutral octahedral mononuclear iron(II) tetrabromide complex, [Fe(Hampy)2Br4], that consists of equatorial bromide and protonated aminopyrazinium axial ligands is successfully synthesised through redox chemistry and analysed using X-ray crystallography. The iron(II) oxidation state is balanced by the protonated pyrazinium nitrogen just outside the coordination sphere. The biological properties of this and two other related complexes are investigated using both Gram-negative and Gram-positive bacteria as well as methicillin resistant strains. They all exhibit some antimicrobial properties albeit at moderate to poor concentrations. However, the tetrahalide complexes analysed exhibit excellent anti biofilm properties well below cytotoxic levels.

Antimicrobial resistance (AMR) has become one of the more serious threats to the global health. The emergence of bacteria resistant to antimicrobial substances decreases the potencies of current antibiotics. Consequently, there is an urgent and growing need for the developing of new classes of antibiotics. Three prepared novel iron complexes have a broad-spectrum antimicrobial activity with minimum bactericidal concentration (MBC) values ranging from 3.5 to 10 mM and 3.5 to 40 mM against Gram-positive and Gram-negative bacteria with antimicrobial resistance phenotype, respectively. Time-kill studies and quantification of the extracellular DNA confirmed the bacteriolytic mode of action of the iron-halide compounds. Additionally, the novel complexes showed significant antibiofilm activity against the tested pathogenic bacterial strains at concentrations lower than the MBC. The cytotoxic effect of the complexes on different mammalian cell lines show sub-cytotoxic values at concentrations lower than the minimum bactericidal concentrations.