SynopsisThe emission properties of l-(4dimethylaminophenyl)-3-(9-phenanthryl)propane, Ph(CHJ3 DMA, and 1,3di49-phenanthryl)propane, Ph(CH2)3Ph, were studied in comparison with those of poly(9-vinylphenanthreneco-p"-dimethylaminostyrene).Ph(CHJ,DMA showed an intense intramolecular exciplex fluorescence in dioxane. Ph(CH2)3Ph did not exhibit a clear intramolecular excimer fluorescence. The quenching of the intramolecular exciplex by several electron acceptors was studied. As a result moderate electron acceptors, such as cyanobenzene, methyl benzoate, and acrylonitrile, selectively quenched the intramolecular exciplex, and in the case of cyanobenzene the subsequent formation of another fluorescent exciplex was observed. The results were discussed in terms of the reduction potentials of electron accepting quenchers.