9-Diphenylphosphinophenanthrene in solutions at 298 K gives a broad ICT fluorescence spectrum centered at 5 10 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 sp(3) orbital of the P atom and the n 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. (c) 2006 Elsevier B.V. All rights reserved.