Synthesis and properties of chiral helical polymers based on optically active polybinaphthyls

The chiral polymer P-1 was synthesized by the polymerization of (R)-6,6'-dibutyl-3.3'-diiodo-2,2'-bisoctoxy-1,1'-binaphthyl (R-M-1) with 5,5'-divinyl-2,2'-bipyridine (M-1) via Pd-catalyzed Heck reaction. P-2 and P-2' were prepared by Wittig-Horner reaction of (R)-6,6'-dibutyl-2,2'-bisoctoxy-1,1'-binaphthyl-3,3'-dicarbaldehyde (R-M-2) with 5,5'-bis (diethylphosphonomethyl)-2,2'-bipyridine (M-2) in the presence of EtONa or NaH, respectively. P-3 was synthesized by Wittig-Horner reaction of (R)-6,6'-di(4-trifluoromethylphenyl)-2,2'-bisoctoxy-1,1'-binaphthyl-3,3'-dicarbaldehyde (R-M-3) with M-2 using NaH as a base. The four polymers have strong blue-green fluorescence due to the extended pi-electronic structure between the chiral model compounds (R)-6,6'-dibutyl-/di(4-trifluoromethylphenyl)-2,2'-bisoctoxy-1,1'-binaphthyl (R-1 or R-2) and the conjugated linker 2,2'-bipyridyl group via vinylene bridge. Both monomers and polymers were analyzed by NMR, MS, FT-IR, UV-vis spectroscopy, DSC-TGA, fluorescence spectroscopy, GPC and circular dichroism (CD) spectroscopy. Based on the great differences of specific rotation values and CD spectra, P-1 and P-2 may adopt a zigzag chain configuration, while P-2' and P-3 may adopt a helical configuration. The responsive optical properties of the two chiral helical polymers P-2' and P-3 on transition metal ions were investigated by fluorescence, UV-vis and CD spectra. The results show that Ag+ and Ni2+ lead to nearly complete fluorescence quenching of P-2' and P-3, Cu2+ and Fe2+ can cause obvious fluorescence quenching, but Zn2+ and Cd2+ can only produce slight fluorescence quenching. Ag+, Ni2+, Cu2+ and Fe2+ can also lead to the obvious changes of UV-vis spectra of P-2' and P-3. On the contrary, Zn2+. and Cd2+, cause little changes. Most importantly, the CD intensities and wavelengths of the chiral helical polymers P-2' and P-3 exhibit the pronounced changes upon addition of Ag+ and Ni2+. (C) 2009 Elsevier Ltd. All rights reserved.