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‐(aminophenyl)‐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 to the surface of Pt or In‐SnO2 (ITO) electrodes in acetonitrile containing Bu4NCIO4 by scanning the potential between O and + 1.6V (for 7a and 7b), and −0.8 and +1.6V (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)22+] by visible light, an electron transfer from the excited state [Ru(terpy)2+*2] to MV2+, reduction of Ru(terpy)3+2 at an electrode, and oxidation of MV+* with O2.