Influence of Wallach’s Rule on Chiral AIE Systems and Its Application in Cryptographic Information Storage

Abstract

Aggregation-induced emission luminogens (AIEgens) exhibit excellent luminescence properties in the aggregated state. For chiral AIEgens, a combination of right- and left-handed objects can be packed more tightly than homochiral objects due to Wallach’s rule. However, the manner in which Wallach’s rule can affect the luminescence properties of chiral AIEgens remains unclear. We report that, in contrast to their homochiral counterparts, racemic AIEgens obtained using binaphthyl-2,2′-diamine salicylaldehyde Schiff-bases (BINAPAS) exhibit racemism-enhanced emission. It was found that the intramolecular motion of racemic BINAPAS is more restricted than that of chiral BINAPAS due to its denser packing mode, which significantly enhances the emission intensity of racemic BINAPAS. Based on this finding, a novel single-molecule cryptographic information storage system was constructed. This work offers a new perspective for understanding the influence of Wallach’s rule on the aggregation-induced emission properties of organic molecules, and more importantly, extends Wallach’s rule to the fundamental difference in chiral-photophysics.