Treatment of 2-ethynylanilines with P(OPh)3 gives either 2,2-diphenoxy-2-λ5-phosphaquinolines or 2-phenoxy-2-λ5-phospha-quinolin-2-ones under transition metal-free conditions. This reaction offers unparalleled access to an underexplored heterocycle, which opens study of the fundamental nature of the N=PV double bond and its potential for delocalization within a cyclic π-electron system. This heterocycle can inherently serve as a carbostyril mimic, with application as a bioisostere for pharmaceuticals based on the 2-quinolone scaffold. Additionally, the molecule holds promise as a new fluorophore, as initial screening reveals quantum yields upwards of ~40%, Stokes shifts of 50–150 nm, and emission wavelengths of 380–540 nm. The phosphaquinolin-2-ones possess one of the strongest solution-state dimerization constants for a D-A system (130 M−1) due to the close proximity of a strong acceptor, P=O, and a strong donor, the phosphonamidate N–H, suggesting this class of compounds might hold promise as new hydrogen bonding hosts for optoelectronic sensing of anions and/or small molecules.

We report the synthesis of an inherently fluorescent macrocyclic receptor for chloride. The use of a disulphide tether provides for an excellent yield in the macrocyclization step. This compound binds chloride in the solution and solid state, and while unstable over time in aqueous solution, shows a selective response toward chloride over other anions in the solid state due to intermolecular interactions between fluorophore backbones. Surprisingly, the optoelectronic response to anions differs in solution and the films, with a distinct colorimetric response observed only in the film.

Treatment of 2‐ethynylanilines with P(OPh)3 gives either 2,2‐diphenoxy‐2‐λ5‐phosphaquinolines or 2‐phenoxy‐2‐λ5‐phosphaquinolin‐2‐ones under transition‐metal‐free conditions. This reaction offers access to an underexplored heterocycle, which opens up the study of the fundamental nature of the NPV double bond and its potential for delocalization within a cyclic π‐electron system. This heterocycle can serve as a carbostyril mimic, with application as a bioisostere for pharmaceuticals based on the 2‐quinolinone scaffold. It also holds promise as a new fluorophore, since initial screening reveals quantum yields upwards of 40 %, Stokes shifts of 50–150 nm, and emission wavelengths of 380–540 nm. The phosphaquinolin‐2‐ones possess one of the strongest solution‐state dimerization constants for a D–A system (130 M−1) owing to the close proximity of a strong acceptor (PO) and a strong donor (phosphonamidate NH), which suggests that they might hold promise as new hydrogen‐bonding hosts for optoelectronic sensing.