Two new fluorescent second generation poly(propyleneimine) dendrimers, peripherally modified with 1,8-naphthalimide, have been synthesized for the first time and characterized. The photophysical characteristics of the new dendrimers have been studied in organic solvents of different polarity. The effect of the chemical nature of the 1,8-naphthalimide C-4 substituent on the photophysical properties of new dendrimers is discussed. The complexes formed between the dendrimers and the metal cations in solution have been studied, with regard to potential applications as fluorescent sensors for metal ion contamination. The results show that the C-4 substituent determines both the response to the presence of metal cations and the selectivity of the sensors. (c) 2007 Elsevier Ltd. All rights reserved.