Azaphosphinines and their derivatives.

Six-membered heterocycles containing one phosphorus and one nitrogen atom, known as azaphosphinines, have existed in the shadows of their single heteroatom-containing analogues for almost 150 years. Despite this, recent chemistry has seen a rapid increase in publications concerning this uncommon scaffold. Azaphosphinines exist in one of six isomers-there are three possible orientations of the pnictogen atoms and in each of these, the phosphorus is in one of two valences (P P).

2-λ-Phosphaquinolin-2-ones as Non-cytotoxic, Targetable, and pH-Stable Fluorophores.

Several phosphaquinolinone derivatives have been synthesized and characterized to explore their usefulness in the realm of cell imaging. Solution-state photophysical properties in both aqueous and organic solutions were collected for these derivatives. Additionally, CCK-8 cell viability assays and fluorescent imaging in HeLa cells incubated with the new heterocyclic derivatives show evidence of favorable cell permeability, cell viability, and moderate intracellular localization when appended with the well-known morpholine targeting motif.

Controlling Tautomerization in Pyridine-Fused Phosphorus-Nitrogen Heterocycles.

Inclusion of a second nitrogen atom in the aromatic core of phosphorus-nitrogen (PN) heterocycles results in unexpected tautomerization to a nonaromatic form. This tautomerization, initially observed in the solid state through X-ray crystallography, is also explained by computational analysis. We prepared an electron deficient analogue (2 e) with a fluorine on the pyridine ring and showed that the weakly basic pyridine resisted tautomerization, providing key insights to why the transformation occurs.

Donor-/Acceptor-Substituted Tetrakis(arylethynyl)benzenes: The Influence of Donor Group on Optoelectronic Properties.

We have prepared nine structural isomers of a tetrakis(arylethynyl)benzene chromophore functionalized with 4-butoxyphenyl and pyridyl units as the respective donor and acceptor units and examined their steady-state spectroscopic parameters to study how small structural variations effect the electronic absorption and emission spectra. Unlike their 4-dibutylaminophenyl congeners that exhibited dynamic hypsochromic or bathochromic shifts in response to Lewis and Brønsted acids, the current class of compounds simply showed quenched fluorescence upon protonation; only AlCl elicited a red-shifted fluorescence response. Computational studies of each system were also performed to provide additional insight into the energy levels and electronic transitions present.

Amplification of the Quantum Yields of 2-λ-Phosphaquinolin-2-ones through Phosphorus Center Modification.

We report the synthesis and characterization of P-phenyl modified phosphorus- and nitrogen-containing phosphaquinolinone heterocycles. The change from -OPh to -Ph results in a marked increase in the quantum yield of the scaffold as well as a moderate red-shifting of the emission. While calculations suggest that π to π* transitions are dominant, intramolecular charge transfer (ICT) also contributes in the excited state.

PN-Containing Pyrene Derivatives: Synthesis, Structure, and Photophysical Properties.

A straightforward method for the preparation of non-K region fused phosphorus- and nitrogen-containing (PN)-heterocyclic pyrenes has been accomplished. Their structural, photophysical, and electrochemical properties have been fully investigated. The described compounds exhibit intriguing redox properties and show strong photoluminescence with a wide range of tunable emission colors, with λ ranging from blue at 459 nm to red at 622 nm in CHCl solution.

Naphtho[2,1- e]-1,2-azaphosphorine 2-Oxide Derivatives: Synthesis, Optoelectronic Properties, and Self-Dimerization Phenomena.

A family of naphtho[2,1- e]-fused 1,2-azaphosphorine 2-oxides that contain electron-withdrawing and -donating substituents on the 3-phenyl groups has been prepared and characterized. This new series of phosphorus- and nitrogen-containing heterocycles is brightly fluorescent with tunable emission wavelengths (λ = 441-493 nm, Φ = 0.19-0.

Exploiting the Hydrogen Bond Donor/Acceptor Properties of PN-Heterocycles: Selective Anion Receptors for Hydrogen Sulfate.

We describe two novel hybrid receptors combining a phosphorus-/nitrogen-containing (PN) phosphonamidate heterocycle with urea recognition units in an arylethynyl backbone. Structural, spectroscopic and computational studies reveal that the origin of superior binding for hydrogen sulfate (HSO ) anion is correlated with the formation of strong hetero-complementary hydrogen bonds with the phosphonamidate motif. We further demonstrate that the hybrid host system is capable of capturing/transporting the HSO anion from an aqueous, biphasic system.