Synthesis, Photophysical and Electrochemical Properties of Spiro-Phosphonium Compounds.

A series of spiro-phosphonium compounds have been synthesized by copper-mediated coupling reaction of phosphacyclic compounds with alkynes. Their photophysical properties are tuned by varying substituents and exhibit different luminescent colors from blue to green, and finally, yellow. The fluorescence quantum efficiency of diethyl spiro-xanthenebenzophosphole 3aa in solid and liquid states reached 31% and 76%, respectively. Diphenyl spiro-xanthenebenzophosphole 3ad displayed relatively low cytotoxicity toward lung cancer cells A549 and was able to effectively penetrate the cell membrane and maintain strong staining. Moreover, density functional theory (DFT) and time-dependent DFT calculations have been performed to explore the origin of their photophysical properties.