The synthesis of arylalkyne-substituted tetrapyrazinoporphyrazines and an evaluation of their potential as photosensitisers for photodynamic therapy

New aryl-terminated octaalkynyl tetrapyrazinoporphyrazines were prepared in three steps starting from functionalised bisarylalkynyl 1,2-diones. While the tert-butylphenyl substituents were shown to aid solubility in organic solvents and to reduce chromophore aggregation efficiently, more hydrophilic tetrapyrazinoporphyrazines were obtained through the use of polyethylene glycol-substituted (PEG-substituted) phenyl groups. The absorption profiles and the singlet oxygen quantum yields of the acetylenic tetrapyrazinoporphyrazines were determined with a view to assess their suitability for PDT applications. In all cases the presence of the terminal aryl moieties resulted in noticeable bathochromic and hyperchromic shifts of the lowest-energy absorption maxima to 680 nm and of the extinction coefficients to beyond 320000. If magnesium is coordinated in the centre of the acetylenic tetrapyrazinoporphyrazines the compounds have singlet oxygen quantum yields of 0.40 in THE. With zinc as the central metal ion, the singlet oxygen quantum yields in the same solvent increase to 0.70. The absorption characteristics of the newly prepared chromophores, as well as their ability to generate singlet oxygen, suggest that these phthalocyanine analogues are interesting candidates as PDT-sensitisers. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.