Optical resolution of single-walled carbon nanotubes through wrapping with chiral metal coordination polymers followed by interlocking with metal-tethered tetragonal nanobrackets

Abstract

Since the optically active carbon nanotubes (CNTs) were first separated in 2007, many CNTs have been optically resolved mostly by use of chiral surfactants, (bio)polymers and host molecules. In this work, simple metal salts consisting of chiral ligands and metal ion successfully discriminate the handedness or helicity of single-walled carbon nanotubes (SWNTs). Actually, optically active SWNTs were separated with sequential addition of copper (R)- and (S)-mandelate ((R)- and (S)-CuL¹₂, respectively) and dipyrrin nanobracket. After removal of the metal salt and nanobracket, a pair of dispersions gave symmetrical CD spectra, indicating that the small chiral molecules or mandelates discriminate the handedness of SWNTs. The following two steps are conceivable in this optical resolution; 1) the helicity of SWNTs was discriminated through selective wrapping with chiral coordination polymers formed by (R)- and (S)-CuL¹₂, and 2) the SWNTs wrapped with the coordination polymers were selectively dispersed through interlocking by dipyrrin nanobracket copper complexes. The experimental results are supported by the theoretical calculations; the van der Waals interaction of (R)-CuL₂ with (P)-(6,5)-SWNTs is stronger than that with (M)-(6,5)-SWNTs.