Redox and Photophysical Properties of Four Subphthalocyanines Containing Ferrocenylcarboxylic Acid as Axial Ligands.

Abstract

Four new ferrocenylsubphthalocyanines Y-BSubPc, with ferrocenylcarboxylic acid YH = Fc-CH2-CH2-COOH (1) or Fc-CH═CH-COOH (2) in the axial Y position, were synthesized with a 40% yield. The axial ferrocenylcarboxylic acid moiety did not have a significant influence on the position of the Q bands maxima of the UV/vis spectra of the ferrocenylsubphthalocyanines or on the 1H NMR position of the ring proton peaks of Y-BSubPc(H12) or on the 19F NMR position of the ring F peaks of YSubPc(F12), relative to their respective parent compounds Cl-BSubPc(H12) 3 and Cl-BSubPc(F12) 4, containing axial chlorine. Very weak metal-to-ligand-charge-transfer bands (MLCT) in the near-IR region were observed. An electrochemical study utilizing cyclic voltammetry showed that electronic communication exists between ferrocene on the axial ferrocenylcarboxylic acid and the π-electrons of the macrocycle of the ferrocenylsubphthalocyanine (Fc(CH2)2COO)-BSubPc(H)12,5, (Fc(CH)2COO)-BSubPc(H)12, 6, (Fc(CH2)2COO)-BSubPc(F)12, 7, and (Fc(CH)2COO)-BSubPc(F)12, 8. The Fe group of the ferrocenyl-containing axial ligand is involved in the first reversible oxidation process, followed by a second oxidation localized on the subphthalocyanine ligand. The fluorine ring substituents in SubPcs 7 and 8 caused the ferrocenyl oxidation to shift more positive by ca. 0.1 V, compared to SubPcs 5 and 6 without fluorine. Density functional theory (DFT) calculations provided further insight into the properties of these novel ferrocenylsubphthalocyanines. The neutral species of SubPcs 5-8 have LUMOs with mainly π-ring character and HOMOs with mainly iron-d character, confirming ring-based reduction, metal-based Fe(II) to Fe(III) oxidation, as well as weak MLCT in the near-IR region. Further DFT optimization of the cation (oxidized) species was essential to verify the second ring-based oxidation.