A new photoresponsive coumarin-derived Schiff base: Chemosensor selectively for Al³⁺ and Fe³⁺ and fluorescence “turn-on” under room light (Englisch)

A novel coumarin Schiff base compound (L) prepared from 4-(diethylamino)salicylaldehyde and 6-amino-7-hydroxycoumarin was synthesized and evaluated as a chemoselective Fe³⁺ and Al³⁺ sensor utilizing “turn-on” fluorescence enhancement. There were 7-fold and 4-fold fluorescence enhancement of L at λ_em,max  = 488 nm upon the addition of 1 equiv. of Al³⁺ and Fe³⁺, respectively. Other metal ions, such as K⁺, Li⁺, Na⁺, Cu⁺, Mg²⁺, Ca²⁺, Ba²⁺, Cu²⁺, Fe²⁺, Hg²⁺, Ni²⁺, Sb³⁺, Sn²⁺, Zn²⁺, Ce³⁺, Cr³⁺, Pr³⁺, Sm³⁺ and Sn⁴⁺ had no such significant effect on the fluorescence of L, whereas In³⁺ and Ga³⁺ induced slightly fluorescence enhancement of L. In addition, rapid photoresponse through fluorescence “turn-on” signaling displayed L via intramolecular O—H…N==CH interaction in photoisomerized product (L′) has been described, where showed 130-fold and 65-fold fluorescence enhancement at λ_em,max  = 488 and 516 nm, respectively. The results indicated L′ was less reactive or inert toward metal ions.