N-ferrocenyl naphthalimides:: Synthesis, structure, and redox chemistry

A family of N-ferrocenyl-1,8- and N-ferrocenyl-2,3-naphthalimide and N,N-diferrocenyl-1,4,5,8-naphthaldiimide complexes has been prepared by reaction of naphthalic anhydrides or naphthalimide anions with a ferrocenylamine. The N-ferrocenyl substituents are 1,8 (Fc, FcCH(2), FcCHMe, Fc(CH2)(11)), 1,4,5,8 (Fc, FcCH(2), FcCHMe, Fc(CH2)(11)), 3-NO2-1,8- (FcCH(2), FcCHMe), 4-NO2-1,8 (Fc, FcCH2, FcCHMe, Fc(CH2)(11), 1,1'-BrFcCH(2)), 4-Br-1,8 (FcCH(2), Fc(CH2)(11)), and 2,3 (Fc, FcCH(2), FcCKMe, Fc(CH2)(11)). A novel stacking aggregation occurs with the 1,4,5,8-Fc and -FcCH(2) derivatives, and intramolecular donor-acceptor charge transfer is evident in the aggregate. Steric hindrance precludes this aggregation in other 1,4,5,8 analogues. An X-ray structure of the 3-NO2-1,8 derivative shows an L-shaped molecule which packs in a columnar array. Micelle formation occurs with long-chain derivatives. The electronic spect ra and electrochemistry show that the N-ferrocenyl substituents do not perturb the energy levels of the fluorophore, although emission is quenched. Coupling of the 4-Br compounds with ethynylferrocene provides direct communication of the redox switch to the fluorophore.