Octakis(dodecyl)phthalocyanines: Influence of Peripheral versus Non-Peripheral Substitution on Synthetic Routes, Spectroscopy and Electrochemical Behaviour

Abstract

Non-peripherally octakis-substituted phthalocyanines (npPc’s), MPc(C12H25)8 with M = 2H (3) or Zn (4), as well as peripherally octakis-substituted phthalocyanines (pPc’s) with M = Zn (6), Mg (7) and 2H (8), were synthesized by cyclotetramerization of 3,6- (2) or 4,5-bis(dodecyl)phthalonitrile (5), template cyclotetramerization of precursor phthalonitriles in the presence of Zn or Mg, metal insertion into metal-free phthalocyanines, and removal of Mg or Zn from the phthalocyaninato coordination cavity. The more effective synthetic route towards pPc 8 was demetalation of 7. npPc’s were more soluble than pPc’s. The Q-band λmax of npPc’s was red-shifted with ca. 18 nm, compared to that of pPc’s. X-ray photoelectron spectroscopy (XPS) differentiated between N–H, Nmeso and Ncore nitrogen atoms for metal-free phthalocyanines. Binding energies were ca. 399.6, 398.2 and 397.7 eV respectively. X-ray photoelectron spectroscopy (XPS) also showed zinc phthalocyanines 4 and 6 have four equivalent Nmeso and four equivalent N–Zn core nitrogens. In contrast, the Mg phthalocyanine 7 has two sets of core N atoms. One set involves two Ncore atoms strongly coordinated to Mg, while the other encompasses the two remaining Ncore atoms that are weakly associated with Mg. pPc’s 6, 7, and 8 have cyclic voltammetry features consistent with dimerization to form [Pc][Pc+] intermediates upon oxidation but npPc’s 3 and 4 do not. Metalation of metal-free pPc’s and npPc’s shifted all redox potentials to lower values.

Keywords

• phthalocyanine
• metal-free
• zinc
• magnesium
• UV–vis
• FTIR