Hyperbranched conjugated polymers containing 1,3-butadiene units: metal-free catalyzed synthesis and selective chemosensors for Fe3+ ions

Abstract

Hyperbranched conjugated polymers (P1 and P2) containing 1,3-butadiene repeating units appended with carboxylic ester groups were synthesized in good yield by metal-free catalyzed polymerization of diethyl 4,4′-(5-formyl-1,3-phenylene)(2E,2′E)-bis(but-2-enoate) (M1) or dimethyl 4,4′-(5-formyl-1,3-phenylene)(2E,2′E)-bis(but-2-enoate) (M2). The corresponding P1 and P2 polymers were structurally characterized by NMR and IR spectroscopy. The polymers are highly soluble in common organic solvents. The UV-vis absorption bands of P2 along with its emission spectrum was red-shifted compared to that of P1, indicating the extension of conjugated length. The hyperbranched conjugated polymers were used as ratiometric fluorescence chemosensors for the detection of the biologically important metal ion Fe³⁺. The corresponding Stern–Volmer constants (K_sv) of P1 and P2 are 2.90 × 10⁴ M⁻¹ and 3.83 × 10⁴ M⁻¹, respectively. Detection limits of 6.99 × 10⁻⁷ M for P1 and 6.69 × 10⁻⁷ M for P2 were achieved. The neutral polymer P1 or P2 was hydrolyzed to obtain water-soluble hyperbranched conjugated polymer P3. The ability of P3 to detect different Fe³⁺ ions in aqueous solution was investigated. The results demonstrate that these polymers can serve as sensitive and selective sensors for Fe³⁺ ions in organic and aqueous solutions.