Olivier Siri

This article reports the synthesis and characterization of cross‐conjugated donor–acceptor dyes based on a N , N , N ’, N ’‐tetraphenyl‐1,4‐phenylenediamine core, substituted at the 2,5‐positions with various electron‐withdrawing groups (carbonyl, imines, nitriles, or electron‐poor heterocycles). Electrochemical studies reveal electronic communication between para ‐substituted donor groups and, in some cases, between acceptor groups. Photophysical studies show tunable absorption and emission properties based on the strength of the electron‐withdrawing groups, a trend that is rationalized through computational analysis. Notably, some compounds exhibit long emission lifetimes in solution, whereas all dyes emit in the solid state, with emission extending into the near‐infrared (up to > 1000 nm).

Fluorescence imaging has become an indispensable tool for the rapid, simple and minimally invasive visualization of the cellular structures and processes. Among the diverse families of emissive probes, triamino-phenazinium dyes, closely related to rhodamines, have recently emerged as promising candidates thanks to their significant theranostic potential. In this study, we report a facile synthetic route that enables direct access to diamino-phenazinium dyes directly from their triamino-phenazinium precursors. The resulting dyes display bathochromically shifted optical bands with absorption of red light and emission bands spanning up to the near-infrared region. Theoretical calculations reveal that this spectral shift originates from an enhanced intramolecular charge transfer character in the diamino derivative. Quantitative colocalization analysis further demonstrates that the diamino-substituted dye exhibit improved mitochondrial targeting efficiency, achieving a Pearson’s correlation coefficient of 0.8. These findings highlight the potential of rationally modified diamino-phenazinium fluorophores as next-generation tools for high-performance mitochondrial biolabeling.

Tetraureido tetranitro-azacalix[4]arene architectures are substitution-tunable supramolecular systems representing promising anion receptors, with potential to form self-assemblies, both modulated by the nature of the aryl substituents.

A series of twenty-two acceptor–donor–acceptor chromophores, comprising both dicationic and neutral dyes, were synthesized and characterized. These compounds were designed with a wide range of electron-withdrawing end groups to explore the balance between acceptor–donor–acceptor aromatic structures and hypothetical nonaromatic coupled polymethine electronic structures within the central six-membered ring. Structural, electrochemical, photophysical, and computational investigations were conducted to gain insights into the structure–property relationships of these systems. The experimental data revealed that the redox and optical properties were most consistent with acceptor–donor–acceptor aromatic structures, significantly impacted by the nature of the end groups. Solvatochromic studies further indicated that the dyes were unlikely to lose their aromatic character in favor of a coupled polymethine structure. Theoretical calculations suggested that a few dicationic derivatives exhibited a slightly reduced aromatic character, hinting at minor coupled polymethine contributions. However, the majority of the chromophores retained a predominantly aromatic central ring.

The reaction of tetranitropolyamino carriers with 4-tert-butylphenyl isocyanate gives rise to ureido-based receptors. These receptors vary in the acidity of their bridging NH groups on supporting skeletons, significantly affecting their complexation ability. While introducing nonbasic anions leads to the independent action of ureido-binding sites, accomplished with low binding efficiency for all studied compounds, the results for basic anions depend on the system used. Here, due to a different electron density distribution on supporting skeletons, the interaction with basic anions may cause unwanted deprotonation (acyclic systems 5) or lead to anion complexation (macrocycles 6 and 7). Moreover, in the case of tetraureido azacalix[4]arene 6, the addition of carboxylates and phosphate induces system cooperativity, which changes the complex stoichiometry from 1:4 to a 1:2 ratio (receptor: anion) and positively improves binding efficiency.

We report a lower thermal conductance of benzo-bis(imidazole) molecular junctions connected in meta conformation. The effects of the protonation/deprotonation on the electrical and thermal conductances are also investigated.

Gabriel Canard and Olivier Siri introduce this themed issue on Nitrogen Ligands, initiated at the 8 ^th EuCheMS Conference on Nitrogen Ligands which was held in June 2024.

An electron‐deficient tetranitroazacalixarene is shown to undergo reversible cyanide capture via nucleophilic aromatic substitution, yielding an unprecedented class of metastable dianionic macrocycle incorporating two Meisenheimer units, fully characterized by single‐crystal X‐ray diffraction, NMR, and electronic absorption spectroscopies. Acting as a chemical fuel, cyanide transiently drives the formation of this adduct, which can spontaneously regenerate the parent macrocycle under mild conditions, representing a rare demonstration of metastability in a Meisenheimer complex. The dynamic behavior of this system, reminiscent of out‐of‐equilibrium assemblies, is finely tunable through macrocycle concentration, counterion nature, solvent, and temperature. Detailed crystallographic, spectroscopic, and computational analyses reveal that intramolecular hydrogen bonding plays a key role in stabilizing the adduct. Comparative studies with simpler analogues further highlight the importance of macrocyclic preorganization and non‐covalent interactions in governing this reversible reactivity.