2,3,9,10,16,17,23,24-Octakis(hexylsulfonyl)phthalocyanines with good n-type semiconducting properties. Synthesis, spectroscopic, and electrochemical characteristics

Abstract

The synthesis of peripherally octa-substituted phthalocyanine compounds with eight strong electron-withdrawing hexylsulfonyl groups was systematically studied. Three new phthalocyanines M[Pc(SO₂C₆H₁₃)₈] [Pc(SO₂C₆H₁₃)₈ = 2,3,9,10,16,17,23,24-octakis(hexylsulfonyl)phthalocyaninate; M = 2H (1), Cu (2), Zn (3)] were synthesized via direct cyclic tetramerization of 4,5-di(hexylsulfonyl)phthalonitrile or through a diiminoisoindoline intermediate. Compounds 1–3 could alternatively be prepared by oxidation of the hexylthio substituents in corresponding 2,3,9,10,16,17,23,24-octakis(hexylthio)phthalocyanine compounds M[Pc(SC₆H₁₃)₈] (M = 2H, Cu, Zn) with m-chloroperbenzoic acid. They were fully characterized by elemental analysis and a series of spectroscopic methods. Their electrochemistry was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Density function theory (DFT) calculations were conducted to study the effect of the strong electron-withdrawing groups on the electronic structure of the phthalocyanine molecules. Particularly, the first reduction potentials in the range −0.30∼−0.04 V vs. the saturated calomel electrode (SCE) for 1–3 reveal their n-type semiconducting nature. The current–voltage characteristics of their aggregates demonstrate the good semiconducting properties especially for 1 and 2 with the conductivity value of 5.24 × 10⁻⁴ and 2.73 × 10⁻⁴ S m⁻¹, respectively.