After the characterization of the molecular structure of K-1 and K-2, the photophysical properties of the two compounds were investigated by UV-vis absorption spectroscopy and fluorescence emission spectra (Figure ). The absorption spectra of K-1 in THF exhibited an absorption band from 300 to 420 nm with an absorption maximum at around 320 nm (Figure ). In comparison, the maximum absorption wavelength of the K-2 molecule was 335 nm, showing a slight change from that of K-1 (Figure ). For better understanding of the AIE behaviors of K-1 and K-2, their photoluminescence (PL) properties were investigated in THF/H2O mixture with different water fractions (fw). With the fw gradually increasing to 60%, the maximum emission wavelength of K-1 showed an obvious redshift and the fluorescence intensity decreased significantly, which is the representative twisted intramolecular charge transfer (TICT) process (Figure ). As the fw was further increased from 60% to 90%, the fluorescence intensity started to rise significantly, accompanied with a blue-shift of the maximum emission (Figure ). This indicated that K-1 exhibits aggregation-induced emission (AIE), meanwhile the aggregates of K-1 were formed in the THF/H2O mixture. Similarly, as the fw gradually increased to 50%, K-2 also exhibited the TICT effect first with reduced fluorescence and red-shifted emission band. (Figure ). When the fw was further increased, a significant fluorescence enhancement can be observed, which was consistent with the AIE phenomenon (Figure ).