Synthesis of pyrene and pyrrole-appended fluorescent turn-off sensor toward Cr(VI) detection: Chemical oxidative and electrochemical polymerization of carboxamide

Abstract

A carboxylic amide compound containing pyrrole and pyrene groups, referred to as PP, was synthesized and characterized for its structural, optical, and electrochemical properties. Upon excitation with 320 nm light, PP displayed blue emission at 387 nm, which was found to be quenched due to chelate formation in the presence of Cr(VI). Conducted competition experiments involving chloride salts of Ag+, Al3+, Cd2+, Co2+, Cr3+, Fe3+, Hg2+, K+, Mn2+, Ni2+, Pb2+, Sn2+, and Zn2+ demonstrated the notable selectivity of compound PP towards Cr(VI) ions. This selectivity was evidenced by a pronounced turn-off fluorescent effect, attributed to a chelation-enhanced quenching (CHEQ) mechanism by the formation of 1:2 chelation between Cr(VI) and the ligand PP. Moreover, addition of EDTA to PP– Cr(VI) chelation recovered the fluorescence offering receptor PP as a reversible sensor. The PP probe demonstrated remarkable selectivity in detection Cr(VI) ions among various metallic ions, displaying a limit of detection (LOD) value of 0.106 µM. Chemical oxidative and electropolymerization methods were employed to synthesize two distinct polymers, namely Poly(PP)-O and Poly(PP)-E, respectively. The electropolymerization of PP was carried out in 0.1 M TBAF6P serving as a supporting electrolyte solution, while oxidative polymerization was conducted in the presence of FeCl3. Mass average molecular weight of the oxidative polymerization product was 5200 Da, as determined by GPC analysis. Thermal characterization was performed via TG-DTA-DTG curves. The electropolymerization product of PP coated on the ITO surface was further characterized by SEM.