Aggregation-induced Emission of a Liquid-crystalline Quinolinium Salt Molecule in Aqueous Solution

Aggregation-induced emission has been observed in a tripodal liquid-crystalline (LC) quinolinium salt. The quinolinium salt exhibits a liquid-crystalline columnar phase within the temperature range 56–191 °C. In the bulk LC state, the compound shows yellow emission. The fluorescence quantum yield (Φ) is 12.6% in the solid state at room temperature. In contrast, the compound shows no photoluminescence in the THF solution (Φ = ca. 0.0%). Addition of water to the THF solution results in stronger emission, and it shows yellow photoluminescence in the THF/water mixed solution above a water fraction of 60% (Φ = 5.2% in THF/water = 1:9 solution), presumably because of the formation of molecular aggregates in water.