Synthesis of Unsymmetrical Alkyloxy/Aryloxy-azaphthalocyanines Based on a Transetherification Reaction

An approach leading to unsymmetrical azaphthalocyanines (AzaPcs) bearing one aryloxy and seven butoxy substituents on the periphery is described. Several cyclotetramerization methods were tested, including the template effect of a metal salt in a melt/solution and the Linstead method, but only one was found to be suitable for the isolation of unsymmetrical alkyloxy/aryloxy-AzaPcs. Undesired transetherification with alkoxides, which is common with these types of compounds, was considered to be an advantage in this approach, and an unsymmetrical AzaPc was isolated in 10 % yield. An analysis of the transetherification process is also described. Unsymmetrical zinc(II) and magnesium(II) AzaPcs showed excellent spectral properties (λmax = 620 nm; ϵ = 1.5–2.2 × 105 dm3mol–1 cm–1) as well as promising singlet oxygen (ΦΔ = 0.44 and 0.26, respectively) and fluorescence quantum yields (ΦF = 0.50 and 0.65, respectively). The metal-free derivative (λmax = 603 and 640 nm; ϵ = 0.80 and 1.2 × 105 dm3 mol–1 cm–1) dissipated energy in a different way, and the ΦΔ and ΦF values were one order of magnitude smaller (0.030 and 0.053, respectively). All the parameters were comparable to the corresponding symmetrical AzaPcs containing eight butoxy substituents, which suggests that an unsymmetrical composition of AzaPc on the periphery has no negative effect on the photophysical or photochemical properties.