Abstract: Dual fluorescence at ca. 447 nm and 545 nm was observed from the aqueous 1-naphthylamine (NA) solutions at pHhigher than 13.6. Similar dual fluorescence was also found with sodium 1-naphthylaminoacetate(NAA), but not with N, N-disubstituted 1-aminonaphthalenes such as sodium 1-naphthylaminodiacetate(NADA) and 1-dimethylaminonaphthalene(DMAN). No change in absorption spectra of NAand NAAwas observed in this pHregion.It was proposed that the dual fluorescence observed with NAand NAAwas due to the excited state dissociation of the primary and secondary amines at high pH. From the dual fluorescence intensity ratio pHtitration curve, the p K_a^*' s of NAand NAAwere estimated to be between 14 and 15 which are much lower than the ground state p K_a. The novel approatch is such a simple, convenient and frequent analysis technique that it can be widely used in detecting the substitutional derivatives of aminonaphthalene.

Key words: 1-Naphthylamines, Excited state ionization of amino group, Dual fluorescence