A study of 4-(alkylamino)amino substituted 1,8-naphthalimide fluoroionophores

The fluorescence enhancement (FE) of five 4-(alkylamino)amino-1,8-naphthalimide fluoroionophores upon addition of sub-ppm concentrations of transition, post-transition, and lanthanide metal ions is investigated and the results are reported. Changes in (alkylamino)amine ligand chain length result in significantly different fluorescence enhancement behavior. 4-Diamino substituted 1,8-naphthalimides with two, three, and four carbons between amines exhibit fluorescence enhancement, while substituents of five- and six-carbon spacing between amines exhibit no fluorescence enhancement. Metal ion selectivity as measured by complexation coefficients (log β) is observed with the ethylenediamine and propylenediamine substituted compounds for Cu2+, and metal ion selectivity for Pb2+ is observed for the butanediamine derivative. Inhibition of photoinduced electron transfer (PET) between the distal nitrogen and the aromatic system by metal ion coordination to the distal amine is the mechanism of fluorescence enhancement for the ethylenediamine, propylenediamine, and butanediamine derivatives.