Preparation and Electrochemical Properties of 1,4,8,11,15,18,22,25‐Octalkylphthalocyanines Containing Four Trithiole Rings

Abstract

Abstract1,4,8,11,15,18,22,25‐Octalkyl‐2,3;9,10;16,17;23,24‐tetrakis(o‐xylylenedithio)phthalocyanines 4a–d (alkyl = ethyl, butyl, octyl, and dodecyl) were prepared in moderate yields by treatment of 3,6‐dialkyl‐4,5‐(o‐xylylenedithio)phthalonitriles 3a–d with lithium in n‐pentanol. Reductive removal of the four o‐xylylene groups from 4b and 4c was performed with lithium/THF/ammonia, and the octathiolate anions generated were then treated with elemental sulfur to give the new phthalocyanines 6b and 6c, respectively, each containing four trithiole rings, after partial desulfurization and ring‐contraction reactions of the corresponding phthalocyanines 5b and 5c. The structures of the phthalocyanines were determined by 1H NMR spectroscopy and MALDI‐TOF mass spectrometry. The absorptions of the Q‐bands of 4a–d were observed at λmax ≈ 770 nm in their UV/Vis spectra, while those of 4b‐Ni, 5b, 5c, and 6c were found in a region, blue‐shifted relative to 4a–d. When the UV/Vis spectrum of 6c wasmeasured in concentrated sulfuric acid, the λmax value of its Q‐band was 887 nm (log ϵ = 4.5), which suggests that the positive charge generated on 6c strongly affects the π‐conjugation of the phthalocyanine skeleton. The ESR spectrum was observed as one broadening signal on treatment of 6c with SbCl5. The redox potentials of the phthalocyanines were determined by cyclic voltammetry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)