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.
Highlights
Phthalocyanines represent a class of chromophores, which consist of four isoindole subunits, tethered together by aza-bridges, resulting in an 18 π-electron aromatic configuration [1]
The difference in dodecyl substitution pattern had an effect on the 1 H NMR resonance position of the “benzylic” methylene protons
Non-peripherally and peripherally octakis(dodecyl)-substituted phthalocyanines 3, 4, 6, 7, and 8 may be synthesized utilizing the same experimental techniques, but poorer solubility of the peripherally substituted derivatives complicate workup procedures, to the extent that columns cannot be run with the metal-free derivative 8
Summary
Phthalocyanines represent a class of chromophores, which consist of four isoindole subunits (red fragment highlighted in Figure 1), tethered together by aza-bridges, resulting in an 18 π-electron aromatic configuration [1]. Protons situated on peripheral positions (positions 2, 3, 9, 10, 16, 17, 23, and 24 of structure 1a in Figure 1) are simultaneously meta and para relative to the pyrrolic fragment of the phthalocyanine. The properties of these protons differ from those of non-peripheral phthalocyanine protons (positions 1, 4, 8, 11, 15, 18, 22, and 25 of phthalocyanine 1b in Figure 1), and this positioning is always ortho relative to the pyrrolic fragment of the phthalocyanine. Peripheral and non-peripheral protons in 1a and 1b exist in chemically inequivalent environments They are aromatic protons because of the aromaticity of the 18 π-electron phthalocyanine macrocycle
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