λ 3 -Phosphinino[3,2- d ]oxazoles─Condensed Phosphinines as Potential Fluorophores: Synthesis and Photophysical Study

Abstract λ3-Phosphinino[3,2-d]oxazoles are obtained from 2H-pyran-2-ones by NaOCP annulation/cyclization without intermediate purification. The 21 derivatives exhibit emission at 366–474 nm, Stokes shifts of 1747–6903 cm–1, and absolute fluorescence quantum yields of <0.1–99% in THF. Tungsten coordination gives an estimated ligand Tolman electronic parameter of 2072.3 cm–1. TD-DFT calculations on 3b and 3u illustrate contrasting excited-state structural relaxation. Phosphorus functionalization affords P(V) derivatives with altered emission wavelengths and efficiencies.