Open AccessPhotophysical and Photobiological Properties of Dinuclear Iridium(III) Bis-tridentate Complexes
Author(s) -
Bingqing Liu,
Susan Monro,
Levi Lystrom,
Colin G. Cameron,
Katsuya L. Colón,
Huimin Yin,
Svetlana Kilina,
Sherri A. McFarland,
Wenfang Sun
Publication year - 2018
Publication title -
inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.348
H-Index - 233
eISSN - 1520-510X
pISSN - 0020-1669
DOI - 10.1021/acs.inorgchem.8b00789
Subject(s) - chemistry , iridium , phosphorescence , photochemistry , photosensitizer , singlet oxygen , cationic polymerization , photodynamic therapy , visible spectrum , bridging ligand , time dependent density functional theory , fluorescence , excited state , absorption (acoustics) , molecule , polymer chemistry , organic chemistry , oxygen , physics , optoelectronics , quantum mechanics , nuclear physics , acoustics , catalysis
A series of cationic dinuclear iridium(III) complexes (Ir1-Ir5) bearing terpyridine-capped fluorenyl bridging ligands and different polypyridyl or cyclometalating terminal tridentate ligands were synthesized, characterized, and evaluated for their photophysical and photobiological activities. The influence of the bridging and terminal ligands on the photophysical properties of the complexes was investigated by UV-vis absorption, emission, and transient absorption spectroscopy and simulated by TDDFT calculations. All of the complexes displayed strong bridging-ligand localized visible 1 π,π* absorption and red- or near-infrared phosphorescence as well as broad triplet excited-state absorption across both visible and NIR wavelengths. These triplet states were assigned as predominantly 3 π,π* for Ir1 (τ = 3.1 μs) and Ir4 (τ = 48 μs) and 3 CT (charge transfer) for Ir2, Ir3, and Ir5 (τ = 1.7-2.7 μs). Complexes Ir1-Ir5 acted as in vitro photodynamic therapy (PDT) agents toward human SK-MEL-28 melanoma cells when activated with visible light, with submicromolar photocytotoxicity and phototherapeutic indices ranging from 20 to almost 300. The in vitro PDT effects with visible light did not correlate with singlet oxygen ( 1 O 2 ) quantum yields or DNA photocleaving capacity probed under cell-free conditions. All of the Ir(III) complexes phosphoresced brightly when associated with compromised cells (with or without light treatment) and exhibited photoactivated cellular uptake, highlighting the theranostic potential of this new class of Ir(III) complex photosensitizers.