Valine-containing silole: Synthesis, aggregation-induced chirality, luminescence enhancement, chiral-polarized luminescence and self-assembled structures

The synthesis of valine-containing silole is reported. The introduction of a chiral valine pendant to silole endows the new compound (1 in Scheme 1) with not only circular dichroism (CD) and chiral-polarized luminescence (CPL), but also an aggregation-induced emission (AIE) property. The AIE effect boosts the fluorescence quantum efficiency, Φ_F, from 0.33% in pure THF to a maximum of 18.9% when water is added, which is 57 times higher than that in pure THF. In the thin film state, the Φ_F value measured by a calibrated integrating sphere can reach 80.3%, which is 243 times higher than that in the solution state. The amphiphilic valine attachments enable the compound to aggregate into complex architectures by a self-assembling process as revealed by AFM images. This compound self-assembles into helical fibers on the evaporation of its THF solution, which corresponds well with its CD and CPL properties. The addition of a poor solvent such as water or hexane to the THF solution also leads to the formation of aggregated structures, which exhibit helical enhancement or inversion in handedness to different extents.