Syntheses and properties of core-substituted naphthalene bisimides with aryl ethynyl or cyano groups

This paper reports the synthesis, the absorption and the emission spectra and the electrochemical and spectroelectrochemical properties of new naphthalene bisimides substituted in positions 2 and 6 of the napthyl core by cyano, pyrrolidino, 4-phenylethynyl, 4-ethynyl-N,N-dihexylaniline or 4-cyanophenyl groups. The synthesis of these five new compounds shares the common precursor: 2,6-dibromonaphthalene tetracarboxylic dianhydride. We show that the aryl ethynyl substituent red-shifts the absorbance and enhances the fluorescence quantum yield of the naphthalene bisimide, making these new compounds potential useful dyes. The cyano groups directly connected to the naphthyl core significantly decrease the two first reduction potentials of the molecule. The large electron affinity and the stability of the radical anion of the latter compound make it ideally suited to transport electrons or to act as an electron acceptor.