Sensitive and photo-triggered transformation of hierarchical helices assembled from achiral bolaamphiphiles.

Chiral nanostructures, normally formed by chiral molecules, play an essential role in natural systems. The helical assemblies constructed by achiral molecular building blocks are still rare and their regulating mechanisms have not been well studied. An achiral cinnamoyl-terminated bolaamphiphile with three methylene unit spacers was found to self-assemble into hierarchically helical nanostructure. The photo-triggered changes in a small number of achiral molecular building blocks would dramatically and reversibly lead to great variations in the helical nanostructures. Thus, the helical supramolecular assemblies can be altered through changing a very small number of achiral molecular building blocks. Moreover, the co-assembly of the achiral bolaamphiphiles with ds-DNA produced uniform left-handed helices, which were also changed upon slight photoirradiation.