Diphenylether based derivatives as Fe(iii) chemosensors: spectrofluorimetry, electrochemical and theoretical studies

Abstract

4-(2,4-Dinitrophenoxy)-3-methoxybenzaldehyde (DPE-I) and (4-(2,4-dinitrophenoxy)-3-methoxyphenyl)methanol (DPE-II) were synthesized with high yield and characterized by spectroscopic techniques. The complexation behaviours of DPE-I and DPE-II for various cationic species (Na⁺, K⁺, Mg²⁺, Cu²⁺, Ba²⁺, Cr³⁺, Fe³⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, and Pb²⁺) in HEPES buffered CH₃CN : H₂O system were investigated and compared by spectroscopic and voltammetric techniques. Both receptors showed high degree of selectivity for Fe³⁺ over other cations. Receptors showed 1 : 1 complexation with Fe³⁺. DPE-I showed fluorescence quenching on complexation with Fe³⁺ ion at 350 nm due to PET (photon induced transfer) mechanism between Fe³⁺ and the large π electron conjugate system of ligand, while DPE-II displayed emission band at 314 nm which underwent fluorescence quenching selectively on gradual addition of Fe³⁺ at 314 nm and simultaneously a new band at 424 nm emerged with isosbestic point at 355 nm which increases with increase in Fe³⁺ conc. Electrochemically, DPE-I due to presence of electron withdrawing (aldehydic group) facilitates reduction of nitro group on benzene ring of the molecule so, peak potentials of the two curves obtained for DPE-I appear at −1.16 V (E_pc1) and −1.39 V (E_pc2) respectively, while in DPE-II (methanolic group) due to its electron donating character makes the reduction of nitro group a little difficult due to which peak potentials occur at higher potential as compared to DPE-I i.e. at −1.30 V (E_pc1) and −1.43 V (E_pc2) respectively.