N-Heteroaryl-1,8-naphthalimide fluorescent sensor for water: Molecular design, synthesis and properties

A series of N-heteroaryl-1,8-naphthalimides with good sensitivity to solvent polarity were prepared. Empirical and quantum calculations showed that the electron withdrawing effect of the heteroaryl group increases the change in dipole moment on excitation which results in the fluorescence quantum yield dramatically falling as the solvent polarity increases. A typical compound 4-(1-piperidyl)-N-(2-pyrimidinyl)-1,8-naphthalimide was chosen to determine the water content in six common solvents (p-dioxane, tetrahydrofuran, acetone, dimethylformamide, acetonitrile and methanol). Fluorescence intensity changes as a function of water content correlated well with a modified Stern–Volmer equation over a wide range, with detection limits being 0.016% and 0.020% for acetone and tetrahydrofuran, respectively.