Functional alcohol-soluble double-decker phthalocyanines: Synthesis, characterization, electrochemistry and peripheral metal ion binding

In this study we report the preparation, physical characterization and electrochemistry of peripherally functionalized substituted ionophore double-decker lanthanide phthalocyanines, lanthanide bis-[(4,4′,4″, 4‴)-tetrakis-(6-hydroxyhexylthio)phthalocyaninates], {M[Pc(S-C ₆H₁₃OH)₄]₂} (M = Pr^III, Yb^III, and Lu^III). All benzenes on the double-decker phthalocyanines are functionalized with hydroxyhexylsulfanyl moieties for potential use as metal ion binding and surface anchors. The double-decker phthalocyanines synthesized from the anhydrous metal salts {Ln(acac) ₃} and the corresponding 4-(6-hydroxyhexylthio)-1,2-dicyanobenzene exhibit ion-specific optical changes in the presence of Ag⁺ and Pd²⁺. Thio donors of the complexes coordinate to Ag⁺ and Pd²⁺ to give 4:1 metal-phthalocyanine complexes. Newly synthesized lanthanide double-decker phthalocyanines are soluble in methanol (MeOH), ethanol (EtOH), tetrahydrofuran (THF), dimethylformamide (DMF), dimethylsulfoxide (DMSO), chloronapthalene, quinoline and less soluble in i-PrOH and acetonitrile. Electrochemical studies reveal that all lanthanide-base complexes undergo ligand-based redox processes. The smaller HOMO-LUMO gaps of the complexes indicate the existence of strong it-orbital interactions between the rings of the sandwich. The newly synthesized compounds have been characterized by elemental analysis, FTIR, ¹H and ¹³C NMR, MS (ESI and MALDI-TOF), UV-vis and EPR spectral data.