Stefano Brenna

A N , N , N ‐tridentate ligand (3,3′‐(2‐(pyridin‐2‐yl)ethane‐1,1‐diyl)bis(1‐methylimidazo[1,5‐ a ]pyridine), L ^CH2Py ) based on the bis(imidazo[1,5‐ a ]pyridine)methane scaffold has been prepared through the introduction of a methylpyridine pendant arm. This functionalization provides an additional donor site, enabling a different coordination mode compared to previously reported bidentate systems. The reaction of this ligand with zinc(II) salts led to the formation of mononuclear complexes ([Zn( L ^CH2Py )X ₂ ], X = Cl, Br, I; [Zn( L ^CH2Py )Br](BF ₄ ); [Zn( L ^CH2Py ) ₂ ](ClO ₄ ) ₂ ), which were fully characterized both in solution (NMR) and in solid state (X‐ray). The tridentate coordination mode generates a rigid and stereochemically defined coordination sphere around the zinc center, resulting in the formation of chiral complexes, as supported by NMR analysis. The photophysical properties of ligand and complexes were investigated, revealing that all the derivatives exhibit intense blue fluorescence ( λ _em = 453 nm for ligand, 419–437 nm for complexes), comparable to that observed for the parent system with unfunctionalized bis(imidazo[1,5‐ a ]pyridine)methane ( λ _em = 450 nm). These results demonstrate that the extension from N , N ‐ to N , N , N ‐coordination enhances the structural rigidity and stereochemical complexity of the system while preserving the favorable emissive properties. This work further expands the scope of bis(imidazo[1,5‐ a ]pyridine)‐based ligands in coordination chemistry and highlights their potential as building blocks for the development of chiral luminescent materials.

The fluorescent behavior of a series of imidazo[1,5-a]pyridine-3-yl phenols was investigated both experimentally (in solution, the solid state, and thin films) and theoretically. Among these compounds, only a subset exhibited excited-state intramolecular proton transfer (ESIPT) emission, identified as a thermodynamically driven process. To understand this behavior, a comprehensive theoretical study was carried out to elucidate the nature of the electronic transitions and to identify the molecular factors governing the occurrence of ESIPT, revealing that fine-tuning the electron-donating and─withdrawing properties is needed for the proton transfer to take place. A structure–property relationship approach was employed, resulting in the development of a numerical descriptor (Ω), dependent on the substituents on the core architecture, capable of predicting whether, upon excitation, the proton “stays” on the oxygen atom or “goes” to the nitrogen atom via the ESIPT mechanism. The same approach also proved to be effective in predicting the frontier orbital energies of the studied systems.

Imidazopyridines are a versatile class of nitrogen-fused heterocycles bridging medicinal chemistry and materials science. Their π-conjugated framework allows broad structural tuning, yielding diverse biological and photophysical properties. The best-known isomers, imidazo[1,2-a]pyridine and imidazo[1,5-a]pyridine, have been widely studied as pharmacophores and luminescent materials, respectively. The less explored imidazo[4,5-b] and imidazo[4,5-c]pyridines are now emerging as alternative scaffolds with distinctive electronic and functional behavior. This review summarizes synthetic strategies, electronic features, and key applications—from kinase inhibition and antiviral activity to fluorescence imaging, down-conversion, Organic Light Emitting Diode (OLED)/Light-emitting Electrochemical Cell (LEC) and hybrid optoelectronic systems—outlining how imidazopyridines can evolve from molecular frameworks into multifunctional platforms for bioimaging and advanced optoelectronic technologies.

Hydrogenated imidazo[1,5- a ]pyridines show intense solid-state deep-blue emission. We propose packing-induced fluorescence enhancement (PIFE) to describe how crystal lattice engineering suppresses non-radiative pathways to boost quantum efficiency.

The development of highly selective, sensitive and recyclable chemosensors for CN⁻ is critical due to the widespread use of cyanide derivatives in industrial processes and its extreme toxicity to environmental and biological systems. Herein, we report the synthesis and characterization of a water-soluble arene ruthenium metalla-assembly specifically designed to operate in aqueous solutions and under environmentally relevant conditions. The arene ruthenium assembly incorporates functionalized building blocks that enable a selective multi-site recognition of cyanide according to pH by either nucleophilic addition or hydrogen bond interactions. The system exhibits a distinct colorimetric response upon cyanide binding, resulting in a rapid “turn-on” color change. An excellent selectivity and reversibility for cyanide recognition is observed over multiple cycles, with a detection limit in the low micromolar range, thus laying the ground for the future development of sensing technology with supramolecular metal-based assemblies.

Five boron-centered spiro compounds with imidazo[1,5-a]pyridin-3-yl phenols as ligands were synthesized and thoroughly characterized through ¹H-NMR, ¹³C-NMR, infrared spectroscopy, and X-ray single crystal analysis. The fluorescence properties of these compounds in solution and in the solid state were investigated, revealing blue emission with wavelengths maxima dependent on the electronic properties of the substituents on the ligands in solution, and an orange-red emission in the solid state. Time-Dependent Density Functional Theory (TD-DFT) calculations were performed to describe the nature of the transitions

Three bis(imidazo[1,5‐a]pyridine)methane derivatives (bis(1‐methylimidazo[1,5‐a]pyridin‐3‐yl)methane, L^H; 3,3’‐(ethane‐1,1‐diyl)bis(1‐methylimidazo[1,5‐a]pyridine) L^Me; 3,3’‐(2‐phenylethane‐1,1‐diyl)bis(1‐methylimidazo[1,5‐a]pyridine), L^Bz) have been synthesized, and fully characterized in solution (¹H and ¹³C NMR spectra) and in the solid state (X‐ray). In particular, L^H has been prepared in high yield (75 %) under very mild conditions (water, 60 °C), offering an alternative route to those reported in the literature. L^Me and L^Bz have been obtained from L^H by functionalization of the methylene bridge. The bis(imidazo[1,5‐a]pyridine)methane compounds have been coordinated to a zinc(II) center, leading to tetrahedral complexes of general formula [Zn(L^R)₂](ClO₄)₂ (R=H, Me, Bz), which showed a bright fluorescent emission with (x,y) color coordinates very close to standard blue. TD‐DFT have been employed to describe the Frontier Molecular Orbitals (FMOs) participating in electronic transitions, highlighting the main transition as ¹(π‐π*) transition in the bis(imidazo[1,5‐a]pyridine)methane and a mixed intra‐ligand (¹ILT) and ligand‐to‐ligand (¹LLT) transition in the complexes.

Herein, we describe high quantum yields of organotin complexes in Me-THF at 77 K ( Φ _F 37 and 67%) due to the rotational fixation of a terephthalohydrazide bridge. PET bottle waste was used as raw material to synthesize ligand and tin complexes.