Effect of substituents on the ¹O₂ production and biological activity of (NNN)Pt(py) complexes

Twelve (N<^>N<^>N)platinum pyridyl complexes, (N<^>N<^>N)Pt(pyF), were synthesised and investigated for their singlet oxygen generation and potential biological activities. They exhibited (IL)-I-1 and (MLCT)-M-1 absorption transitions at approximately 325 and 360 nm, identified through TD-DFT calculations. Luminescence was observed only in the L-1-derived compounds in solution, with a dual emission with the main contribution of phosphorescence under deaerated conditions. Room temperature phosphorescence was detected in all solid-state cases. Electron-withdrawing substituents at specific positions (R1 and X) and the number of fluorine atoms in R2 were found to enhance the photosensitizing capabilities of these compounds. Biological assessments, including cytotoxicity and photocytotoxicity, were conducted to evaluate their potential as chemotherapeutic agents and photosensitizers. Complexes with chloro substitution in the N<^>N<^>N tridentate ligand of the central pyridine ring exhibited promising chemotherapeutic properties. Ancillary pyridine ring substitution became significant under irradiation conditions, with fluoromethylated substituents enhancing cytotoxicity. Complex 2-CF3 was the most efficient singlet oxygen producer and a highly effective photosensitizer. CHF2-substituted complexes also showed improved photosensitizing activity. DNA binding studies indicated moderate interactions with DNA, offering insights into potential biological applications.