Multiple states of dimeric aggregates formed by (amido-ethynyl)helicene bidomain compound and (amido-ethynyl-amido)helicene tridomain compound.

An (amido-ethynyl)helicene bidomain compound and an (amido-ethynyl-amido)helicene tridomain compound were synthesized. The multidomain compounds were designed on the basis of previous findings that amido and ethynyl oligomers form dimeric aggregates with properties orthogonal to each other. Four aggregate states of multidomain compounds, namely, all-dimer, amido-dimer, ethynyl-dimer, and random-coil states, were obtained in different solvents, which were analyzed by circular dichroism (CD), UV/Vis, (1)H NMR, and IR spectroscopy; vapor pressure osmometry (VPO); dynamic light scattering (DLS); and atomic force microscopy (AFM). The amido and ethynyl domains independently aggregated and disaggregated in a two-state manner. Reversible structural changes occurred for a tridomain compound between the ethynyl-dimer/random-coil state and the all-dimer/amido-dimer state with heating and cooling. Two structural change processes with different properties were obtained using a single compound.