Solid-state photochromic molecular switches based on axially chiral and helical spiropyrans

Solid-state photochromic switches with reversible luminescence modulation property have wide applications in optical data storage, anticounterfeiting, sensing, and bioimaging, however, it is a significant challenge to design and prepare such materials. In the present work, a novel class of chiral and helical binaphthyl-substituted spiropyrans has been synthesized and characterized. The introduction of binaphthyl can not only promote the solid-state luminescence but also achieve the interesting chimptical switching properties for the potential applications in chiral recognition and circularly polarized luminescence. The single-crystal structures and density functional theory calculations reveal that the presence of strong electron-withdrawing nitro groups can promote photo-switch efficiency by stabilizing the electron-rich conjugated memcyanine with the lower electron cloud density and LUMO/HOMO levels. For charge transfer in excited states, pi -> pi* transition would enhance emission, but n -> pi* transition and intramolecular charge transfer show the opposite effect. Therefore, these photochromic switches provide a novel paradigm in the design of multiple-responsive, chiral, and luminescent materials.