Multiple Hydrogen Bonds Promoted ESIPT and AIE-active Chiral Salicylaldehyde Hydrazide

The simpler, the better! A series of simple and highly fluorescent salicylaldehyde hydrazide molecules (41 samples) have been designed and prepared. Even though these soft materials contain a very small -conjugated system, they can go through multiple intramolecular and intermolecular hydrogen bonds promoted excited-state intramolecular proton-transfer (ESIPT) to display strong blue, green, yellow, and orange aggregation-induced emission (AIE) with large Stokes shifts (up to 184 nm) and high fluorescence quantum yields (? up to 0.20). Unusual mechanochromic fluorescence enhancements are also found in some solid samples. Through coordination, hydrogen and halogen bonds, these flexible molecules can be used as Mg2+ (? up to 0.46) probes, universal anion (? up to 0.14) and unprotected amino acids (? up to 0.16) probes, and chiral diamine (enantiomeric selectivity and ? up to 0.36 and 0.062, respectively) receptors. Combining their advantages of AIE and biocompatibility, these low cytotoxic dyes have potential application in living cell imaging. Furthermore, the effects of different functional groups on the molecule arrangement, ESIPT, AIE, probe, and chiral recognition properties are also examined, which provide a simple and bright paradigm for the design of multiple-stimuli-responsive smart materials.