Phosphorous atom induced intramolecular charge transfer fluorescence in 9-diphenylphosphinophenanthrene

9-Diphenylphosphinophenanthrene in solutions at 298 K gives a broad ICT fluorescence spectrum centered at 510 nm in n-hexane. The origin of the ICT fluorescence is discussed on the basis of X-ray structure analysis, solvent effects on fluorescence, and MO calculations by contrast with 9-diphenylaminophenanthrene. The weak interaction between the non-bonding sp³ orbital of the P atom and the π orbital of the phenanthrene moiety in the ground state is considered to promote the intramolecular charge transfer in the excited singlet state, leading to the ICT fluorescence.