Experimental and theoretical study of the intramolecular charge transfer on the derivatives 4-methoxy and 4-acetamide 1,8-naphthalimide N-substituted

The photo-physical properties of the 4-methoxy and 4-acetamide 1,8-naphthalimide N-substituted with the ethyldialkylamino groups, show a photo-induced charge transfer effect (PCT). The addition of protons to the solution blocked this effect and the molecules have an intense laser emission in polar solvents such as acetonitrile and ethylene glycol. We present here the photo-physical properties of the 1,8-naphthalimide and three of these derivatives in neutral and acidified 1,4-dioxane solutions. We observed that the fluorescence quenching is minor because of the PCT effect, in this solvent of lower polarity. We also present the theoretical calculation at semi-empirical level PM3, about these neutral molecules and with a proton in the amino group R1, to elucidate the experimental behaviour.