The Modular Approach to Acetylenic Phthalocyanines and Phthalocyanine Analogues

Abstract

The need for new chromophores with intense absorptions at the far red end or the near infrared region of the electromagnetic spectrum is evident from recent developments in materials science and medicinal chemistry. This has prompted us to explore the potential of octaalkynyl-substituted phthalocyanines, tetrapyrazinoporphyrazines, and tetra-6,7-quinoxalinoporphyrazines. In order to assemble these chromophores efficiently and in a modular fashion, we have prepared two types of acetylenic building blocks − namely 3,4-dimethylenehexa-1,5-diynes and hexa-1,5-diyne-3,4-diones − and have successfully converted them into alkynyl-substituted benzenoid phthalonitriles, the former by means of cycloadditions with dicyanoacetylene, the latter through condensation reactions with vicinal diamines such as diaminomaleodinitrile and 4,5-diaminophthalonitrile. The dinitriles were cyclotetramerised to the corresponding octaalkynyl phthalocyanines and phthalocyanine analogues using magnesium butoxide in butanol. Core physical properties of the new chromophores, most notably their solubilities and absorptivities, are markedly influenced by the presence of the eight alkynyl substituents. Further fine-tuning of these characteristics by appropriate choice of terminal acetylene substituents is possible.