Convenient syntheses and preliminary photophysical properties of novel 8-aminoquinoline appended diaza-18-crown-6 ligands

Novel 7,16-bis(8-amino-2-quinolinylmethyl)- and 7,16-bis(8-amino-7-quinolinylmethyl)-diaza-18-crown-6 ligands (12 and 16) have been synthesized by reductive amination of 8-(di-tert-butoxycarbonyl)amino-2-quinolinecarboxaldehyde (followed by removal of the Boc protecting groups) or 8-amino-7-quinolinecarboxaldehyde with diaza-18-crown-6 using triacetoxyborohydride (NaBH(OAc)3) as the reducing agent. The crystal structure of ligand 16 is also given. The absorption spectra of 12 and 16 are dominated by two intense bands at 250±5 and 238±1 nm which are blue shifted upon addition of alkaline earth and heavy metal ions in acetonitrile. In addition, intensities of the fluorescence bands of 12 and 16 are reduced in the presence of metal ions.