pH-Responsive Cotton Effects in the d–d Transition Band of Self-Assembling Copper(II) Complexes with a Cholesteryl-Armed Ligand

New amphiphilic transition metal complexes with helical structures self-assembled to form disk-like units in 20 wt % EtOH/water. d–d transition bands in the visible-near IR region were used to probe conformational changes during the assembly process. Self-assembly resulted in dynamic conformational changes and considerable enhancement of circular dichroism (CD) in the d–d transition bands due to steric interaction among neighboring complexes. A copper(II) complex showed the most dramatic CD changes upon self-assembly, including sign inversion of the CD signal. The self-assembled Cu(II) complexes also showed pH-responsive Cotton effects between pH 6 and pH 7 due to deprotonation. The Cotton effects of the Cu(II) complex could be finely tuned by varying the pH and ethanol content of the aqueous solvent.