Studies on metal-ion complex formation of crown ether derivatives incorporating a photoionizable spirobenzopyran moiety by electrospray ionization mass spectrometry

Metal-ion complexation of crown ether derivatives incorporating one and two spirobenzopyran units was investigated by electrospray ionization mass spectrometry. The crowned spirobenzopyran derivatives exhibited very different metal ion-complexing behavior from their corresponding parent crown ether rings, preferring multivalent to monovalent metal ions owing to the additional ionic interaction with the nitrophenolate anion of the merocyanine moiety. The on-line photochemical reaction for mass spectrometry indicated that the metal ion-complexing ability and ion selectivities of the crowned spirobenzopyrans can be switched photochemically, taking advantage of the difference between the spiropyran and merocyanine isomers.