The modular approach to acetylenic phthalocyanines and phthalocyanine analogues

The need for new chromophores with intense absorptions at the far red end o r 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 phthalocyan ines, tetrapyrazinoporphyrazines, and tetra-6,7-quinoxalinoporphyrazines. I n order to assemble these chromophores efficiently and in a modular fashion , we have prepared two types of acetylenic building blocks - namely 3,4-dim ethylenehexa-1,5-diynes and hexa-1,5-diyne-3,4-diones - and have successful ly converted them into alkynyl-substituted benzenoid phthalonitriles, the f ormer 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 usi ng magnesium butoxide in butanol. Core physical properties of the new chrom ophores, most notably their solubilities and absorptivities, are markedly i nfluenced by the presence of the eight alkynyl substituents. Further fine-t uning of these characteristics by appropriate choice of terminal acetylene substituents is possible.