Coumarin-functionalized zinc(II) phthalocyanines: Photophysical properties, BSA/DNA affinity, and DFT calculations

This study presents the synthesis and characterization of three novel coumarin-functionalized zinc(II) phthalocyanine (ZnPc) derivatives (2a, 2b, and 2c), aimed at overcoming the inherent limitations of traditional ZnPcs in photodynamic therapy (PDT), such as aggregation and poor solubility. Detailed investigations have demonstrated that these compounds possess enhanced photophysical properties, including favorable Q-band absorption (677-690 nm), low aggregation tendencies, and extended fluorescence lifetimes. Most importantly, these complexes exhibited high singlet oxygen quantum yields, with the Φ_Δ value for 2a reaching an impressive 0.80, and demonstrated superior photostability compared to unsubstituted ZnPc. Moreover, the binding experiments revealed significant interactions with biological macromolecules, indicating an intercalative mode of binding to DNA with binding constants (K_b) in the range of 2.72 × 10⁵ M^-1 to 3.18 × 10⁵ M^-1, and notable affinity toward BSA, exhibiting magnitude of K_b values reaching up to 10⁷-10⁸ M^-1. All experimental findings were supported by density functional theory (DFT) and molecular docking studies. These results clearly indicate the potential of these coumarin-functionalized ZnPcs as next-generation photosensitizers for advanced PDT applications.