Logic gate copolymers of cinchona alkaloid-ferrocene derivatives

Abstract

The cinchona alkaloids quinidine, quinine, cinchonine and cinchonidine were derivatised with ferrocene by Steglich-type esterification and subsequently polymerised with acrylamide by free radical polymerization. The copolymers were characterised by ¹H NMR, FT-IR and UV-vis absorbance spectroscopy. The logic-based computing properties in emission mode are consistent with H⁺, X⁻-driven combinatorial OR-INHIBIT logic (where X = Cl⁻, Br⁻ or I⁻). The maximum fluorescence quantum yields are compromised by the presence of the ferrocene moiety due to photoinduced electron transfer from the ferrocene derivative to the quinoline fluorophore. Attempts to revive the fluorescence with a chemical oxidant were constrained due to inner filter effects or collisional anion quenching. In absorbance mode, the copolymers function as rapid naked-eye colorimetric H⁺, I⁻-driven AND logic gates in 4 : 6 (v/v) THF/water. The colour change from colorless to yellow is attributed to a π–anion non-covalent charge transfer interaction between I⁻ and the quinolium fragment of the alkaloids.