Novel heterogeneous PET fluorescent sensors selective for transition metal ions or protons: Polymers regularly labelled with naphthalimide

4-(N,N-Dimethylaminoethylene)amino-N-allyl-1,8-naphthalimide has been synthesized as a new polymerizable dye in monomeric form, and can increase its fluorescence intensity in the presence of protons or metal cations. Two intensely yellow-green fluorescent co-polymers of the dye with methyl methacrylate (MMA) and styrene (ST) have been obtained. These polymeric fluorophores, which could be used as heterogeneous photoinduced electron transfer (PET) fluorescent sensors, show different fluorescence behaviour in the presence of protons and Cu²⁺ ions, depending on the structures of their main polymer chains. The fluorescence of poly(MMA-co-dye) is not sensitive towards H⁺ ions, but it is to Cu²⁺ ions. That of poly(ST-co-dye) is sensitive to the presence of both H⁺ and Cu²⁺ ions, the signal increasing and decreasing, respectively.