Naphthyl decorated polyamidoamine (PAMAM) dendrimers, from zeroth- to third-generation (GnN, n＝0～3), have been synthesized and their structures characterized by IR, 1H NMR, 13C NMR and MALDI TOF mass spectra. Steady state photophysical studies indicate that the fluorescence of naphthyl is quenched by the amine units of dendrimers GnN via intramolecular electron transfer, and a naphthyl-amine exciplex is formed with a structureless emission around 450 nm. The protonation of GnN by addition of excess trifluoroacetic acid made the fluorescence intensity of dendrimers increase dramatically due to suppression of the photoinduced electron transfer and the exciplex formation, and a weak naphthyl excimer emission with maximum at ca. 400 nm could be observed indicative of close-packed periphery and stretched conformation of protonated dendrimers.

Key words: PAMAM dendrimer, naphthyl, photophysical process, protonation