Photophysical and Photobiological Properties of Dinuclear Iridium(III) Bis-tridentate Complexes

Abstract

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 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 predominantlyπ,π* for Ir1 (τ = 3.1 μs) and Ir4 (τ = 48 μs) and 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 (O) 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.

Synthesis, characterization, DNA binding, topoisomerase inhibition, and apoptosis induction studies of a novel cobalt(III) complex with a thiosemicarbazone ligand

“…and ctDNA binding studies-The investigation of the binding of metal complexes to DNA is of prime importance in the development of anticancer drugs [196]. From a pharmacological point of view, the primary target of many anticancer drugs is DNA [36][37][38][39][40][41][42][43][44][45]. Consequently, DNA binding activities of metal complexes have often been a key parameter during the development of chemotherapeutic drugs.…”

“…Those results represented the first evidence of an in vivo effect of FcOHTam and ferrocenyl derivatives on xenografted breast tumors [35]. For many years, and more recently, the interaction between a variety of transition metals with polypyridyl ligands and DNA has been extensively studied as part of the efforts to fight cancer [36][37][38][39][40][41][42][43][44][45]. Due to unusual binding properties and general photoactivity, these coordination compounds are suitable candidates as DNA secondary structure probes, photocleaving agents, and anti-cancer drugs [46].…”

Synthesis and crystal structure of (1,10-phenanthroline-κ2 N,N′)[2-(1H-pyrazol-1-yl)phenyl-κ2 N 2,C 1]iridium(III) hexafluoridophosphate with an unknown number of solvent molecules

“…On the other hand, ancillary ligands with strong conjugated system such as 1,10-phenanthroline (phen) can also enhance the degree of delocalized -electrons of cyclometallated ISSN 2056-9890 iridium(III) complex systems through the interaction between the d orbitals of the transition metal and the -electron orbitals of the organic conjugated system (Liu et al, 2018). This way, the high degree of delocalized -electrons can increase the luminescent properties of Ir III complexes (Choy et al, 2014).…”

New Class of Homoleptic and Heteroleptic Bis(terpyridine) Iridium(III) Complexes with Strong Photodynamic Therapy Effects

“…However, the exploration of these Ir(III) bis(terpyridine) complexes for biological applications is undeveloped. 39,43,45,46 To the best of our knowledge, the only report on bisterdentate Ir(III) complexes for PDT is a series of dinuclear Ir(III) complexes with fluorenyl-linked ditopic terpyridine as the bridging ligand and various terdentate ligand as the end-capped ligands, which was reported by us. 39 We demonstrated that these complexes could be used as in vitro PDT agents toward human SK-MEL-28 melanoma cells when activated with visible light.…”