Axially chiral propeller-shaped spiroborates with aggregation-modulated circularly polarized luminescence

Abstract

Modulating CPL with large luminescent dissymmetry factors and reversal signals is a great challenge in developing chiroptical small organic molecules (SOMs) materials. We herein report a series of axially chiral propeller-shaped pyridyl-/benzothiazolyl-enolato-naphtholate spiroborates ((R)-/(S)-2a-2d). Of these spiroborates, the CPL signals of (R)-/(S)-2c-2d could be effectively modulated by increasing water fraction (fw) from 50% to 90% in the THF-H2O solution. (R)-/(S)-2c exhibit aggregation-amplified CPL with the dissymmetry factor (glum) up to 2.38 × 10−2 and (R)-/(S)-2d show aggregation-induced CPL. In addition, the CPL signals of (R)-/(S)-2c exhibit reversible inversion with the fw increasing from 50% to 90%. The amplification and inversion of the CPL signals are revealed via the helical self-assemblies observed by scanning electron microscopy (SEM) images and the promotion of the population of emissive intramolecular charge transfer (ICT) state.