Unsymmetrically Substituted Benzonaphthoporphyrazines: A New Class of Cationic Photosensitizers for the Photodynamic Therapy of Cancer*

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Abstract
— Unsymmetrical zinc(II) complexes of benzonaphthoporphyrazines 5 a-12a bearing between one and eight pyri-dyloxy substituents are synthesized by statistical tetra-merization of 6-(l,l-dimethylethyl)-2,3-naphthalenedi-carbonitrile (1) with 4-(3-pyridyloxy)- or 4,5-bis-(3-pyri-dyloxy)-1,2-benzenedicarbonitrile (2, 3). Methylation of 5a-12a leads to the cationic pyridyloxybenzonaphtho-porphyrazines 5b- 12b having between one to eight positive charges. The Q-band transition in the visible spectra exhibits a bathochromic shift from 680 to 760 nm dependent upon the number of annelated naphthalene rings. The singlet oxygen quantum yields of the benzonaphthoporphyrazines determined by the dye-sensitized photoox-idation of 1,3-diphenylisobenzofurane is surprisingly high (in the range of zinc phthalocyanine). The photoox-idative stabilities of the photosensitizers described quantitatively by first-order kinetics decrease with the number of annelated naphtho groups. A linear correlation between the logarithm of the decomposition rate constant and the position of the highest occupied molecular orbital (HOMO)-level of the photosensitizers is found. Destabi-lization of the HOMO leads to a decrease of the pho-tostability. Due to their adjustable long wavelength absorption, their intramolecular polarity axis and their different hydrophilic/hydrophobic character, these novel compounds may be suitable photosensitizers for the photodynamic therapy of cancer.