Synthesis and properties of an AIE fluorescent probe for Cu2+ detection based on ESIPT system

ESIPT‐based AIE luminogens: Design strategies, applications, and mechanisms

“…[ 40 ] The addition of Cu 2+ will induce a remarkable fluorescence quenching, whereas the other metal ions do not interfere with the binding of compound 4 to Cu 2+ (see Figure 4C). [ 40 ] The fluorescence quenching by Cu 2+ has also been observed for other ESIPT‐based AIEgens [ 29, 34, 35, 37, 41, 44, 47, 48, 50, 52, 54, 56 ] and may result from ligand‐to‐metal charge transfer, as has been demonstrated by density functional theory calculations. [ 50 ] The computed highest occupied molecular orbital and lowest unoccupied molecular orbital of a ligand–Cu 2+ complex are localized on ligand and metal center, respectively.…”

“…Akin to Schiff base, azine can also act as an AIE unit and proton acceptor to form intramolecular hydrogen bonding with the o ‐hydroxyl group on benzene (Scheme 2D,E), [ 40, 41, 48, 54, 61, 67, 75, 79, 82, 84, 85, 87, 91, 92, 94, 95, 97, 98, 104– 106, 111, 115, 117, 173–178 ] naphthalene (Scheme 2F), [ 49, 80, 174 ] and coumarin rings (Scheme 2H). [ 93, 179 ] Among these compounds, symmetric salicylaldehyde azine derivatives (SAA, Scheme 2E) [ 41, 61, 75, 79, 87, 91, 92, 94, 95, 97, 98, 104–106, 111, 115 , 117, 175–178 ] have gained the most popularity in construction of ESIPT‐based AIEgens because they are easily synthesized from salicylaldehyde derivatives and hydrazine hydrate even in one step.…”

“…A significant advantage of symmetric SAA is that the hydroxyl group can be easily modified by various protecting and targeting groups, making it suitable in the detection of small and biological molecules. [ 61, 75, 79, 91, 92, 84, 95, 97, 98, 104–106, 111, 115, 117, 175–178 ] Moreover, a series of asymmetric SAA derivatives, [ 40, 54, 67, 84, 85, 173, 174 ] including keto‐salicylaldehyde azine (KSA), [ 48, 82 ] have also been developed as ESIPT‐based AIEgens and applied in different fields. The emergence of KSA makes the synthesization of asymmetric SAA become easier, thus opening the avenues for further development of asymmetric SAA as ESIPT‐based AIEgens.…”

“…Therefore, almost all the reported ESIPT‐based AIEgens for detection of metal cations involve SSB or SAA scaffolds, or at least, involve Schiff base or azine bearing an intramolecular hydrogen bond O─H···N. [ 28–57 ]…”

“…The development of ESIPT‐based AIEgens has attracted great attention in the fields of physics, chemistry, and biology science. A growing number of ESIPT‐based AIEgens have been developed and applied in the detection of cations, [ 28–57 ] anions, [ 34, 35, 41, 43, 58–68 ] and small molecules, [ 69–76 ] bioimaging in the living cell and in vivo, [ 77–116 ] drug delivery systems (DDS), [ 44, 117–119 ] liquid crystal, [ 120–122 ] white light emitters, [ 123–127 ] and latent fingerprinting. [ 56, 128–131 ]…”