Synthesis and fluorescence properties of new enaminenaphthalimides

The first 4-enamine-N-methyl-1,8-naphthalimides (amine = piperidine, pyrrolidine, morpholine, (Pr2NH)-N-n, (Pr2NH)-N-i) are reported. The X-ray crystal structure of the piperidine derivative confirmed the E-stereochemistry and showed strong pi - pi stacking in the unit cell. The enamines are strongly fluorescent and quantum yields do not vary with the pK(b) of the amine. The solvent dependence of lambda(abs) and lambda(flu) is consistent with significant charge separation in the excited state.