Attachment of 4-methoxy benzyl units to a tripodal fluoroionophore shows reversal of output functionality with Cu(II) input

Abstract

Syntheses of three tris-(2-aminoethyl)amine, tren based tripodal fluoroionophores (L₂, L₃, and L₅), are reported. These fluoroionophores are designed based on the fluorophore–spacer–receptor format (choice of fluorophore in all three cases is anthryl unit). In L₂, three anthracene moieties are attached to the three arms of tren via –CH₂-spacer whereas L₃ and L₅ have p-nitro benzyl and p-methoxy benzyl substitutions, respectively, on L₂, which are in close proximity to the photoinduced electron transfer (PET) center. All three fluoroionophores show appreciably lower fluorescence compared to anthracene due to effective PET process in these systems but the quantum yield varies depending upon the nature of substitution at the PET center. In the cases of L₂ and L₅ different amounts of fluorescence recovery are observed in the presence of different cation inputs whereas L₃ is almost inactive toward cation sensing. Detailed fluorescence emission studies on L₂ and L₅ in the presence of different cation inputs showed that L₅ having N4 donor sets bearing three p-methoxy benzyl units attached to the three nitrogen centers involving photoinduced electron transfer process is a viable candidate for enhancement of fluorescence with Cu(II) input. In the absence of p-methoxy benzyl units at the nitrogen centers' resulting system, L₂ shows quenching of fluorescence with the Cu(II) under same experimental conditions.