Octasubstituted zinc tetrapyrazinoporphyrazines with four N,N-dimethylaminophenyls and four phenyl or pyridin-3-yl substituents were synthesized and fully characterized. Their fluorescence quantum yields in DMF or pyridine were very low, almost undetectable, as a consequence of ultrafast intramolecular charge transfer. Titration of their DMF solutions with sulfuric acid led to increase of the fluorescence quantum yields by two orders of magnitude when the full protonation of peripheral substituents was achieved. Intramolecular charge transfer is no longer a favorable way of excited-state relaxation at full protonation of N,N-dimethylaminophenyl substituents because of loss of donor centers (free electron pair on its nitrogen). Similarly, singlet oxygen quantum yields also increased by two orders of magnitude when sulfuric acid was added to tetrapyrazinoporphyrazine solutions in DMF. Protonation at azomethine nitrogens of tetrapyrazinoporphyrazine macrocycle was observed at higher acid concentrations and it led to considerable decrease of fluorescence quantum yields. Octaphenyl zinc tetrapyrazinoporphyrazine and octa(pyridin-3-yl) zinc tetrapyrazinoporphyrazine were used as controls without intramolecular charge transfer. Their fluorescence and singlet oxygen quantum yields were high in DMF and decreased at higher concentrations of sulfuric acid due to protonation of azomethine nitrogens. The results suggest that the photophysical and photochemical properties of studied compounds may be controlled by changes of pH of medium.
我们合成了具有四个 N,N-二甲基氨基苯基和四个苯基或吡啶-3-基取代基的八代四吡嗪卟啉锌,并对其进行了全面表征。由于超快的分子内电荷转移,它们在 DMF 或吡啶中的荧光量子产率非常低,几乎检测不到。当外围取代基完全质子化时,用硫酸滴定它们的 DMF 溶液可使荧光量子产率提高两个数量级。在 N,N-二甲氨基苯基取代基完全质子化时,分子内电荷转移不再是激发态弛豫的有利方式,因为供体中心(其氮上的自由电子对)已经丧失。同样,在 DMF 中的四吡嗪卟嗪溶液中加入硫酸后,单线态氧量子产率也增加了两个数量级。在酸浓度较高时,四吡嗪卟啉大环的偶氮甲基硝基会发生质子化,从而导致荧光量子产率大幅下降。八苯基四吡嗪卟嗪锌和八(吡啶-3-基)四吡嗪卟嗪锌被用作没有分子内电荷转移的对照组。在 DMF 中,它们的荧光和单线态氧量子产率较高,而在较高浓度的硫酸中,它们的荧光和单线态氧量子产率会因偶氮甲基硝基的质子化而降低。结果表明,所研究化合物的光物理和光化学性质可能受介质 pH 值变化的控制。