Fluorescence turn-on detection of Fe3+ in pure water based on a cationic poly(perylene diimide) derivative

Abstract

Polycondensation of perylene diimide (PDI) diamines with a 2,2′:6′,2′′-terpyridine (tpy)-containing dibromide gives a new fluorescent polymeric chemosensor (L) with good water solubility. L exhibits good selectivity for Fe³⁺ ions over a wide range of tested metal ions Ag⁺, K⁺, Na⁺, Fe²⁺, Cu²⁺, Al³⁺, Cr³⁺, Mn²⁺, Mg²⁺, Ni²⁺, Ca²⁺, Hg²⁺, Pd²⁺, Ba²⁺, Cd²⁺, Co²⁺ and Zn²⁺ in aqueous solution. The binding of Fe³⁺ to chemosensor L leads to significant emission bands at 548 nm and 591 nm, respectively, because the complexation of Fe³⁺ with the tpy moiety of L blocks the photoinduced electron transfer (PET) from tpy units to PDI units. A 1 : 2 stoichiometry was found for the complex formed by L and Fe³⁺ by Job's plot. The association constant (K_a) of Fe³⁺ binding in chemosensor L is 1.32 × 10⁸ M⁻². L can be used to detect Fe³⁺ over a wide pH range of 5.0–9.0. Moreover, by taking advantage of its instant fluorescence turn-on specific to Fe³⁺, L is used as a fluorescent probe to monitor the Fe³⁺/Fe²⁺ transition in the presence of reducing agents such as Na₂S₂O₃ or ascorbic acid (Vc) in water. L can also work well in biological samples, which gives access to the detection of Fe³⁺ in an organism.