Efficient Singlet Oxygen Generation by Luminescent 2‐(2′‐Thienyl)Pyridyl Cyclometalated Platinum(II) Complexes and Their Calixarene Derivatives

Luminescent cyclometalated platinum(II) complexes, namely [Pt(Thpy)(PPh3)X]n+ (HThpy = 2-(2′-thienyl)pyridine; X = Cl− (1), n = 0; X = CH3CN (2), pyridine (3), n = 1) and [Pt(Thpy)(HThpy)Y]n+ (Y = Cl− (4), n = 0; Y = pyridine (5), n = 1), exhibit structured emission with peak maximum at ∼556 and 598 nm in degassed acetonitrile and with emission quantum yield and lifetime of up to 0.38 and 26 μs, respectively. These complexes are efficient photosensitizers of singlet oxygen with yields up to >90%. Complex 5 exhibited photocytotoxicity towards cancer cells and fluorescence microscopic images of cells incubated with 5 reveal substantial uptake at the nucleus and mitochondria.