After confirming the structure, we investigated their UV-vis absorption and photoluminescence (PL). As shown in Figure , the four compounds displayed similar characteristic absorption spectra with several sharp bands between 240 nm to 330 nm in THF solutions, which could be attributed to their intramolecular n-π* transition and π-π* transition. To explore their AIE feature, PL spectra were measured in THF/water mixtures, respectively (Figure ). For BISX, when the water fraction was below 80%, it was nonemissive. However, when the water fraction reached 90%, an intensified emission peak at 510 nm emerged. And the emission amplified at fw = 99% with a 25-fold increase relative to that in THF solution, displaying a bright green fluorescence (Figure ). The other three compounds (ISX, MISX and MTSX) showed a similar pattern, with their emission intensity in the aggregate state enhanced to about 35, 80, and 35-fold compared to that of the THF solution, respectively (Figure ). The aggregate formation was manifested by the level-off tails in the long-wavelength region of the absorption spectra in the aqueous mixtures due to the Mie effect of the dye nanoparticles (Figure ). Therefore, all four compounds presented typical AIE features, with aggregates formation confirmed by dynamic light scattering analysis (Figure ). For all of the four compounds, their lifetimes in the crystal state are one order of magnitude higher than that in the solution state, which matched their enhanced emission from solution to solid state (Figure -S20).