Photoactivated Chiral Molecular Clamp Rotated by Selective Anion Binding

Abstract

Developing chiral molecular platforms that response to external fields provides opportunities for designing smart chiroptical materials. Herein, we introduce a molecular clamp whose chiral optics could be turned on by photoactivation, and selective anion binding achieved rational tuning of conformations and chiroptical properties including circular dichrosim and circularly polarized luminescence. Cyanostilbene segments were conjugated to the chiral amines with a rotable axis. The negeligible chiroptical signals were significantly enhanced through a light illumination-induced isomerization. Binding with halide ions (F-, Cl- and Br-) enables the chiroptical inversion, which could be subsequently amplified in an opposite handedness by photo treatment. In contrast, I- and NO3- with notable size failed to achieve chiroptical inversion. Also the handedness inversion shall be rational hampered by conformatioal locked amines. Density functional theory-based computational studies and experimental results reveal the structural transformation from a butterfly-like open geometry to closed V-shaped state initiated by the quadruple hydrogen bonding and the rotable axis. This work illustrates the design protocols in smart chiroptical molecular platforms mediated by photo treatment and anion binding.