Tuning the Properties of Donor-Acceptor and Acceptor-Donor-Acceptor Boron Difluoride Hydrazones via Extended π-Conjugation

Ligand protonation leads to highly fluorescent boronium cations

Fluorophores that respond to external stimuli, such as changes in pH, have utility in bio-imaging and sensing applications. Almost all pH-responsive fluorophores rely on complex syntheses and the use of pH-responsive functional groups that are peripheral to the fluorophore framework. In this work, pH-responsive boron-containing heterocycles based on tridentate acyl pyridylhydrazone ligands were prepared. These non-emissive heterocycles were synthesized in three steps from inexpensive, commercially available reagents without the use of chromatography or air-sensitive reagents. Treatment with acid resulted in protonation of the boron-bound methylamine donor and efficient blue photoluminescence. Experimental and computational analysis revealed that protonation changed the geometric structure of the heterocycles and prevented photoluminescence quenching associated with photoinduced electron transfer. This work demonstrates a new approach for the design of fluorophores with potential applications in biological imaging.

Pnictogen-Rich Heterocycles Derived from a Phosphadiazonium Cation

Heterocycles that pair main group elements and nitrogen are extremely important within the π-conjugated heterocycles research community. Compared to the vast number of boron-nitrogen heterocycles, those that include phosphorus are less common. Furthermore, the use of phosphorus-nitrogen triple bonds of any type to prepare such compounds is unprecedented. Here, we pair pyridyl hydrazonide ligands with phosphadiazonium cations and demonstrate that the chelated Mes*NP group is directly implicated in the photophysical and redox properties observed for the resulting heterocycles. In doing so, we introduce a novel building block for the production of phosphorus-containing heterocycles that could find use in small molecule activation and catalysis or as the functional component of emerging organic electronics.

Synthesis, spectroscopic, topological, hirshfeld surface analysis, and anti-covid-19 molecular docking investigation of isopropyl 1-benzoyl-4-(benzoyloxy)-2,6-diphenyl-1,2,5,6-tetrahydropyridine-3-carboxylate

Isopropyl 1-benzoyl-4-(benzoyloxy)-2,6-diphenyl-1,2,5,6-tetrahydropyridine-3-carboxylate (IDPC) was synthesized and characterized via spectroscopic (FT-IR and NMR) techniques. Hirshfeld surface and topological analyses were conducted to study structural and molecular properties. The energy gap (Eg), frontier orbital energies (EHOMO, ELUMO) and reactivity parameters (like chemical hardness and global hardness) were calculated using density functional theory with B3LYP/6-311++G (d,p) level of theory. Molecular docking of IDPC at the active sites of SARS-COVID receptors was investigated. IDPC molecule crystallized in the centrosymmetric triclinic ( P 1 ¯ ) space group. The topological and Hirshfeld surface analysis revealed that covalent, non-covalent and intermolecular H-bonding interactions, and electron delocalization exist in the molecular framework. Higher binding score (-6.966 kcal/mol) of IDPC at the active site of SARS-COVID main protease compared to other proteases suggests that IDPC has the potential of blocking polyprotein maturation. H-bonding and π-cationic and interactions of the phenyl ring and carbonyl oxygen of the ligand indicate the effective inhibiting potential of the compound against the virus.