This study investigates the synthesis and characterization new peripherally (beta) tetra-substituted 4-(2-mercaptoquinoline phthalocyaninato) Co(II) (CoPcSHQn, 3), and 4-(2-phenoxy-4-trifluoromethylpyridine phthalocyaninato) Co(II) (CoPcOHPy, 4). These complexes were characterized by elemental analysis, IR, mass and electronic spectroscopies and electrochemical methods. Both complexes show well resolved redox peaks attributed to both ring and metal based processes. Spectroelectrochemistry was used to confirm the assignments of the redox processes. For CoPcSHQn (3): (CoPc-2)-Pc-I/(CoPc-3)-Pc-I (E-1/2 = -1.25 V, I), (CoPc-2)-Pc-II/(CoPc-2)-Pc-I (E-1/2 = -0.57 V, II), (CoPc-2)-Pc-III/(CoPc-2)-Pc-II (E-1/2 = +0.45 V, IV) and an irreversible process at E-p = +1.05 V vs Ag vertical bar AgCl for (CoPc-1)-Pc-III/(CoPc-2)-Pc-III (V). Redox couple III at E-1/2 = -0.15 V was ascribed to aggregation. In the case of CoPcOHPy (4): (CoPc-2)-Pc-I/(CoPc-3)-Pc-I (E-1/2 = 1.13V, I), (CoPc-2)-Pc-II/(CoPc-2)-Pc-I (E-1/2 = -0.45V, II), (CoPc-2)-Pc-III/(CoPc-2)-Pc-II at E-1/2 = +0.21 V (IV), and (CoPc-I)-Pc-III/(CoPc-2)-Pc-III (E-1/2 = +1.01 V vs Ag vertical bar AgCl, V). Again III is associated with the aggregated species. Both complexes were electrodeposited on a glassy carbon electrode (GCE). For complex 3 self-assembled monolayers was also formed. The modified (CoPc-GCE) electrodes electrocatalytically detected L-cysteine at E-p = 0.62 V (3-GCE) and 0.59V (4-GCE) vs Ag vertical bar AgCl. (C) 2010 Elsevier B.V. All rights reserved.