Electropolymerisable ruthenium(ii) phenanthrolines carrying azacrown ether receptors: metal ion recognition in thin film redox sensors

Abstract

The tris(1,10-phenanthroline)ruthenium(II) complexes 1–3 (with 0, 4 and 2 appended azacrown ether units, respectively) linked via alkyl chains to 4H-cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT) were synthesised, characterised and immobilised on Pt and ITO electrodes through electropolymerisation. The electrochemical, UV-vis absorption and metal ion recognition properties of the thus modified electrodes were investigated in detail. Immobilisation of 2 on electrodes was only feasible in a copolymerisation with the parent CPDT. The copolymer film poly(2 + CPDT) exhibited sensitivity for Ba²⁺ and Pb²⁺ in cyclic voltammetry investigations. At milli- and micromolar concentrations of Ba²⁺ and Pb²⁺, respectively, a redox potential shift of more than 200 mV was found in MeCN. 3 was electropolymerised on electrodes directly and the resulting thin film of poly(3) showed similar redox potential shifts for Ba²⁺ and Pb²⁺ (around 150 mV) with a higher sensitivity for Pb²⁺ than Ba²⁺.