Studies on Preparation and Characterization of Phthalocyanines with the Trithiole Rings

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1,4,8,11,15,18,22,25-Octalkyl-2,3,9,10,16,17,23,24-tetrakis(o-xylylene-dithio)phthalocyanines (1a,b) [alkyl=butyl and octyl] were prepared in moderate yields on treatment of 3,6-dialkyl-4,5-(o-xylylenedithio)-phthalonitriles with lithium in n-pentanol. Reductive removal of four o-xylylene groups from 1a,b was performed with Li/THF/NH_3,and octathiolate anions generated were then reacted with elemental sulfur to give new phthalocyanines (3a,b) with four trithiole rings, respectively, after partial desulfurization and ring contraction reactions of corresponding phthalocyanines (2a,b). The structures of phthalocyanines were determined with ^1H NMR and MALDI-TOF MS. The absorption of the Q-band of 1a,b was observed at around λ_<max>=770 nm in the UV-vis spectra, while that of 3a,b was found at around a relatively blueshifted region. When the UV-vis spectrum for 3b was measured in concentrated sulfuric acid, the λ_<max> value of the Q-band was 887 nm (log ε=4.5), which suggests that the positive charge generated on 3b strongly affects the π-conjugation of the phthalocyanine skeleton. The ESR spectrum was observed as one broadening signal on treatment of 3b with SbCl_5.