ELECTROPOLYMERIZATION AND CHARACTERIZATION OF TERPYRIDINYL IRON(II) AND RUTHENIUM(II) COMPLEXES

Electroactive 2,2':6',2''-terpyridinyl ligands (3, 5, 6) and their iron(II) (7a-9a) and ruthenium(II) complexes (7b-9b) were synthesized. Bis[3-amino-phenyl)-2,2':6'2''-terpyridinyl]metal(II) complexes (7a, 7b) and bis[2-(hydroxyphenyl)-2,2':6'2''-terpyridinyl]metal(II) complexes (8a, 8b) were electropolymerized on the surface of Pt or In-SnO2 (ITO) electrodes in acetonitrile containing Bu4NClO4 by scanning the potential between 0 and + 1.6 V (for 7a and 7b), and -0.8 and + 1.6 V (for 8a and 8b) versus saturated calomel electrode. The electrodes obtained by electropolymerization exhibited reversible electrochromism based on Fe(II)/Fe(III) or Ru(II)/Ru(III) redox couple. Photoresponses to visible light were found in the modified electrode obtained by electropolymerization of ruthenium complex 7b in an aqueous LiClO4 solution containing methylviologen (cation MV2+) under an O2 atmosphere. The mechanism for the photoresponded cathodic current was explained in terms of an excitation of bis(terpyridinyl)ruthenium(II) complex [Ru(terpy)2(2+)] by visible light, an electron transfer from the excited state [Ru(terpy)2(2+)] to MV2+, reduction of Ru(terpy)2(3+) at an electrode, and oxidation of MV+. with O2.