-Thiophenium Porphyrins and Their Zn(II) Complexes: A New Category of Cationic Photosensitizers.

A new category of cationic -thiophenium porphyrins are introduced as possible alternatives to the popular -pyridinium porphyrins. Combinations of cationic porphyrins bearing -2-methylthiophenium and -4-hydroxyphenyl moieties (AB type) and (AB type) along with their zinc(II) complexes and , are reported. The increase in the number of thienyl groups attached to the -positions of the porphyrin derivatives (AB frame) has been shown to impart longer fluorescence lifetimes and stronger photocytotoxicity toward A549 lung cancer cells, as evident with and its corresponding diamagnetic metal complex The photoactivated imparts an early stage reactive oxygen species (ROS) upregulation and antioxidant depletion in A549 cells and contributes to the strongest oxidative stress-induced cell death mechanism in the series. The DFT calculations of the singlet-triplet energy gap (Δ) of all the four hydrophilic thiophenium porphyrin derivatives establish the potential applicability of these cationic photosensitizers as PDT agents.