Naphthoxaphospholes as examples of fluorescent phospha-acenes.

Seven new fluorescent 2-R-naphtho[2,3-d]oxaphospholes (R-NOPs) (4a–g; R = tBu (a), Ad (b), C(6)H(5) (c), 4-MeC(6)H(4) (d), 4-ClC(6)H(4) (e), 4-BrC(6)H(4) (f ), 4-MeOC(6)H(4) (g)), have been synthesized by cyclocondensation reactions of benzimidoyl chlorides with 3-phosphino-2-naphthol (3). The compounds were characterized by multinuclear NMR, UV-vis, and fluorescence spectroscopy. Compounds 4a–d and 4g were characterized by cyclic voltammetry experiments. The solid state structures of compounds 4b and 4d were also determined by single-crystal X-ray diffraction experiments.