e.g. Filippa Pettersson or Cancer Res. 75(6) , 1102-12, (2015) or 10.1002/anie.201600521
Journal of the American Chemical Society
Phosphinemethylenes. III. A new class of azo dyes containing phosphorus
F Ramirez, S Levy
Index: Ramirez; Levy Journal of the American Chemical Society, 1957 , vol. 79, p. 67,68, Journal of the American Chemical Society, 1957 , vol. 79, p. 6171
Triphenylphosphoniumcyclopentadienylide (I) couples readily with diazonium salts producing a new class of brightly colored azo dyes. The coupling reaction occurs at a position in the five-membered ring which preserves the stable cyclopentadienide system and which gives rise to the longest of the possible conjugated systems terminating ata phosphorus atom. The ultraviolet and infrared absorption spectra, and the dipole moment ...
[Higham, Lee J.; Kelly, P. Gabriel; Corr, David M.; Mueller-Bunz, Helge; Walker, Brian J.; Gilheany, Declan G. Chemical Communications, 2004 , # 6 p. 684 - 685]