A cyclometallated fluorenyl Ir(iii) complex as a potential sensitiser for two-photon excited photodynamic therapy (2PE-PDT)

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 44; no. 36; pp. 16127 - 16135
• Main Authors: Boreham, Elizabeth M, Jones, Lucy, Swinburne, Adam N, Blanchard-Desce, Mireille, Hugues, Vincent, Terryn, Christine, Miomandre, Fabien, Lemercier, Gilles, Natrajan, Louise S
• Format: Journal Article
• Language: English
• Published: England 28.09.2015
• Subjects: Absorption cross sections; Capture cross sections; Constants; Energy management; Excitation; Morphology; Oxygen; Singlet oxygen
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c5dt01855b

A new Ir(iii) cyclometallated complex bearing a fluorenyl 5-substituted-1,10-phenanthroline ligand ([Ir(ppy)2()][PF6], ppy = 2-phenylpyridine) is presented which exhibits enhanced triplet oxygen sensing properties. The efficacy of this complex to act as a photosensitiser for altering the morphology of C6 Glioma cells that represent malignant nervous tumours has been evaluated. The increased heavy metal effect and related spin-orbit coupling parameters on the photophysical properties of this complex are evidenced by comparison with Ru(ii) analogues. The complex [Ir(ppy)2()][PF6] is shown to exhibit relatively high two-photon absorption efficiencies for the lowest energy MLCT electronic transitions with two-photon absorption cross sections that range from 50 to 80 Goeppert-Mayer units between 750 to 800 nm. Quantum yields for the complex were measured up to 23% and the Stern-Volmer quenching constant, KSV was determined to be 40 bar(-1) in acetonitrile solution, confirming the high efficiency of the complex as a triplet oxygen sensitiser. Preliminary in vitro experiments with C6 Glioma cells treated with [Ir(ppy)2()][PF6], show that the complex is an efficient sensitizer for triplet oxygen, producing cytotoxic singlet oxygen ((1)O2) by two-photon excitation at 740 nm resulting in photodynamic effects that lead to localised cell damage and death.