Enhanced yet Inverted Effects of π-Extension in Self-Assembly of Curved π-Systems with Helicity.

A sextuple helix molecule possessing four cove regions of helicene and two axes of biaryls was synthesized. The entropy-driven self-assembly in solution was determined by concentration- and temperature-dependent NMR spectra, which also revealed unique dynamics of isomerization involving structural changes at the cove regions. Unexpectedly, the assembly retarded the isomerization in solution, and the sextuple helix structure was rigidified.