Helicity Control of Triphenylamine-Based Supramolecular Polymers: Correlation between Solvent Properties and Helicity in Supramolecular Gels

We describe the role of amide groups formed by achiral and chiral moieties to study supramolecular helicity at the molecular level and the correlation between helicity and solvent properties at the supramolecular level. Using circular dichroism (CD) spectroscopy, we observed the CD spectra of supramolecular gel 1, which comprised a triphenylamine (TPA) core, terpyridine, and alanine moieties, formed in various solvents. The strong positive CD signals of supramolecular gel 1 formed in organic solvents, such as chloroform, tetrahydrofuran (THF), and dichloromethane, which have low polarity and a low acceptor number, were observed at 350 nm, indicating right-handed helicity. In contrast, the negative CD signals of supramolecular gel 1 formed in mixed DMSO/water (5:1 v/v), methanol, ethanol, and n-propanol were obtained at 350 nm, indicating left-handed helicity. These findings suggest that the helicity of supramolecular gel 1 was strongly influenced by the solvent properties. Indeed, atomic force spectroscopy images showed the right- and left-handed helicity of supramolecular gel 1 formed in various organic solvents, which was pure helicity.