Synthesis, spectroscopic, and photophysicochemical behavior of Zn(II) and Mg(II) phthalocyanine– chalcone conjugates

Phthalonitrile derivatives (8, 9, and 10) bearing different chalcone groups and their zinc(II) (ZnPcs) (8a, 9a, and 10a) and magnesium(II) (MgPcs) (8b, 9b, and 10b) complexes were prepared. The new compounds (5, 8–10, 8a–10a, and 8b–10b) were characterized by a combination of spectroscopic techniques, such as FT-IR, ¹H NMR, ¹³C NMR (for 5, 8, 9, and 10), UV–Vis (for metallophthalocyanines), and MALDI-TOF mass spectra, and by elemental analysis (5, 8, 9, and 10). The aggregation behavior and photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen and photodegradation quantum yields) properties of different chalcone-substituted peripheral ZnPcs (8a, 9a, and 10a) and MgPcs (8b, 9b, and 10b) were investigated in dimethylsulfoxide (DMSO) to determine whether they are photosensitizers for photodynamic therapy (PDT) applications. The peripheral tetra-substituted MgPc (9b) showed longer lifetime than other compounds and unsubstituted ZnPc. The tetra-substituted ZnPc (9b) produced higher fluorescence quantum yield than the unsubstituted ZnPc and its chalcone-substituted counterparts. The ZnPcs (8a, 9a, and 10a) and MgPcs (8b, 9b, and 10b) showed low singlet oxygen production, but they showed quite high photostability, except MgPc 10b.