In Vitro Photodynamic Therapy of Mononuclear and Dinuclear Iridium(III) Bis(terpyridine) Complexes

Synthesis, X-ray Studies and Photophysical Properties of Iridium(III) Complexes Incorporating Functionalized 2,2':6',2″ Terpyridines and 2,6-Bis(thiazol-2-yl)pyridines

A series of iridium(III) triimine complexes incorporating 2,2':6',2″-terpyridine (terpy) and 2,6-bis(thiazol-2-yl)pyridine (dtpy) derivatives were successfully designed and synthesized to investigate the impact of the peripheral rings (pyridine, thiazole) and substituents (thiophene, bithiophene, EDOT) attached to the triimine skeleton on their photophysical properties. The Ir(III) complexes were fully characterized using IR, 1H, elemental analysis and single crystal X-ray analysis. Their thermal properties were evaluated using TGA measurements. Photoluminescence spectra of [IrCl3L1-6] were investigated in solution at 298 and 77 K. The experimental studies were accompanied by DFT/TDDFT calculations. The photophysical properties of the synthesized triimine ligands and Ir(III) complexes were studied in detail by electronic absorption and emission. In solution, they exhibited photoluminescence quantum yields ranging from 1.27% to 5.30% depending on the chemical structure. The experimental research included DFT/TDDFT calculations. The photophysical properties of the synthesized triimine ligands and Ir(III) complexes were conducted using electronic absorption and emission techniques. In solution, they displayed photoluminescence quantum yields ranging from 1.27% to 5.30% depending on the chemical structure.

A hetero-bimetallic Ru(II)-Ir(III) photosensitizer for effective cancer photodynamic therapy under hypoxia

A hetero-bimetallic Ru(II)-Ir(III) photosensitizer was developed. Upon light exposure, contrary to the homogeneous Ru(II)-Ru(II) and Ir(III)-Ir(III) complexes that can only produce singlet oxygen, Ru(II)-Ir(III) can generate multiple reactive oxygen species and kill hypoxic tumors. This study presents the first example of a hetero-bimetallic type-I and type-II dual photosensitizer.

Exploring a Mitochondria Targeting, Dinuclear Cyclometalated Iridium (III) Complex for Image-Guided Photodynamic Therapy in Triple-Negative Breast Cancer Cells

Photodynamic therapy (PDT) has emerged as an efficient and noninvasive treatment approach utilizing laser-triggered photosensitizers for combating cancer. Within this rapidly advancing field, iridium-based photosensitizers with their dual functionality as both imaging probes and PDT agents exhibit a potential for precise and targeted therapeutic interventions. However, most reported classes of Ir(III)-based photosensitizers comprise mononuclear iridium(III), with very few examples of dinuclear systems. Exploring the full potential of iridium-based dinuclear systems for PDT applications remains a challenge. Herein, we report a dinuclear Ir(III) complex (IRDI) along with a structurally similar monomer complex (IRMO) having 2-(2,4-difluorophenyl)pyridine and 4'-methyl-2,2'-bipyridine ligands. The comparative investigation of the mononuclear and dinuclear Ir(III) complexes showed similar absorption profiles, but the dinuclear derivative IRDI exhibited a higher photoluminescence quantum yield (Φp) of 0.70 compared to that of IRMO (Φp = 0.47). Further, IRDI showed a higher singlet oxygen generation quantum yield (Φs) of 0.49 compared to IRMO (Φs = 0.28), signifying the enhanced potential of the dinuclear derivative for image-guided photodynamic therapy. In vitro assessments indicate that IRDI shows efficient cellular uptake and significant photocytotoxicity in the triple-negative breast cancer cell line MDA-MB-231. In addition, the presence of a dual positive charge on the dinuclear system facilitates the inherent mitochondria-targeting ability without the need for a specific targeting group. Subcellular singlet oxygen generation by IRDI was confirmed using Si-DMA, and light-activated cellular apoptosis via ROS-mediated PDT was verified through various live-dead assays performed in the presence and absence of the singlet oxygen scavenger NaN3. Further, the mechanism of cell death was elucidated by an annexin V-FITC/PI flow cytometric assay and by investigating the cytochrome c release from mitochondria using Western blot analysis. Thus, the dinuclear complex designed to enhance spin-orbit coupling with minimal excitonic coupling represents a promising strategy for efficient image-guided PDT using iridium complexes.

In vitro and in vivo antitumor activities of Ru and Cu complexes with terpyridine derivatives as ligands

Six terpyridine ligands(L1-L6) with chlorophenol or bromophenol moiety were obtained to prepare metal terpyridine derivatives complexes: [Ru(L1)(DMSO)Cl2] (1), [Ru(L2)(DMSO)Cl2] (2), [Ru(L3)(DMSO)Cl2] (3), [Cu(L4)Br2]·DMSO (4), Cu(L5)Br2 (5), and [Cu(L6)Br2]⋅CH3OH (6). The complexes were fully characterized. Ru complexes 1-3 showed low cytotoxicity against the tested cell lines. Cu complexes 4-6 exhibited higher cytotoxicity against several tested cancer cell lines compared to their ligands and cisplatin, and lower toxicity towards normal human cells. Copper(II) complexes 4-6 arrested T-24 cell cycle in G1 phase. The mechanism studies indicated that complexes 4-6 accumulated in mitochondria of T-24 cells and caused significant reduction of the mitochondrial membrane potential, increase of the intracellular ROS levels and the release of Ca2+, and the activation of the Caspase cascade, finally inducing apoptosis. Animal studies showed that complex 6 obviously inhibited the tumor growth in a mouse xenograft model bearing T-24 tumor cells without significant toxicity.

Controlling of Photophysical Behavior of Rhenium(I) Complexes with 2,6-Di(thiazol-2-yl)pyridine-Based Ligands by Pendant π-Conjugated Aryl Groups

The structure–property correlations and control of electronic excited states in transition metal complexes (TMCs) are of high significance for TMC-based functional material development. Within these studies, a series of Re(I) carbonyl complexes with aryl-substituted 2,6-di(thiazol-2-yl)pyridines (Arⁿ-dtpy) was synthesized, and their ground- and excited-state properties were investigated. A number of condensed aromatic rings, which function as the linking mode of the aryl substituent, play a fundamental role in controlling photophysics of the resulting [ReCl(CO)₃(Arⁿ-dtpy-κ²N)]. Photoexcitation of [ReCl(CO)₃(Arⁿ-dtpy-κ²N)] with 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl leads to the population of ³MLCT. The lowest triplet state of Re(I) chromophores bearing 9-anthryl, 2-anthryl, 1-pyrenyl groups is ligand localized. The rhenium(I) complex with appended 1-pyrenyl group features long-lived room temperature emission attributed to the equilibrium between ³MLCT and ³IL/³ILCT. The excited-state dynamics in complexes [ReCl(CO)₃(9-anthryl-dtpy-κ²N)] and [ReCl(CO)₃(2-anthryl-dtpy-κ²N)] is strongly dependent on the electronic coupling between anthracene and {ReCl(CO)₃(dtpy-κ²N)}. Less steric hindrance between the chromophores in [ReCl(CO)₃(2-anthryl-dtpy-κ²N)] is responsible for the faster formation of ³IL/³ILCT and larger contribution of ³ILCT_{anthracene→dtpy} in relation to the isomeric complex [ReCl(CO)₃(9-anthryl-dtpy-κ²N)]. In agreement with stronger electronic communication between the aryl and Re(I) coordination centre, [ReCl(CO)₃(2-anthryl-dtpy-κ²N)] displays room-temperature emission contributed to by ³MLCT and ³IL_anthracene/³ILCT_{anthracene→dtpy} phosphorescence. The latter presents rarely observed phenomena in luminescent metal complexes.

Water-soluble dinuclear iridium(III) and ruthenium(II) bis-terdentate complexes: photophysics and electrochemiluminescence

The synthesis, photophysics, and electrochemiluminescence (ECL) of four water-soluble dinuclear Ir(III) and Ru(II) complexes (1-4) terminally-capped by 4'-phenyl-2,2':6',2''-terpyridine (tpy) or 1,3-di(pyrid-2-yl)-4,6-dimethylbenzene (N^C^N) ligands and linked by a 2,7-bis(2,2':6',2''-terpyridyl)fluorene with oligoether chains on C9 are reported. The impact of the tpy or N^C^N ligands and metal centers on the photophysical properties of 1-4 was assessed by spectroscopic methods including UV-vis absorption, emission, and transient absorption, and by time-dependent density functional theory (TDDFT) calculations. These complexes exhibited distinct singlet and triplet excited-state properties upon variation of the terminal-capping terdentate ligands and the metal centers. The ECL properties of complexes 1-3 with better water solubility were investigated in neutral phosphate buffer solutions (PBS) by adding tripropylamine (TPA) as a co-reactant, and the observed ECL intensity followed the descending order of 3 > 1 > 2. Complex 3 bearing the [Ru(tpy)₂]²⁺ units displayed more pronounced ECL signals, giving its analogues great potential for further ECL study.

Single-Cell Quantification of a Highly Biocompatible Dinuclear Iridium(III) Complex for Photocatalytic Cancer Therapy

Quantifying the content of metal-based anticancer drugs within single cancer cells remains a challenge. Here, we used single-cell inductively coupled plasma mass spectrometry to study the uptake and retention of mononuclear (Ir1) and dinuclear (Ir2) Ir^III photoredox catalysts. This method allowed rapid and precise quantification of the drug in individual cancer cells. Importantly, Ir2 showed a significant synergism but not an additive effect for NAD(P)H photocatalytic oxidation. The lysosome-targeting Ir2 showed low dark toxicity in vitro and in vivo. Ir2 exhibited high photocatalytic therapeutic efficiency at 525 nm with an excellent photo-index in vitro and in tumor-bearing mice model. Interestingly, the photocatalytic anticancer profile of the dinuclear Ir2 was much better than the mononuclear Ir1, indicating for the first time that dinuclear metal-based photocatalysts can be applied for photocatalytic anticancer treatment.

Photophysics and reverse saturable absorption of cationic dinuclear iridium(III) complexes bearing fluorenyl-tethered 2-(quinolin-2-yl)quinoxaline ligands

The synthesis, photophysics and reverse saturable absorption of two cationic dinuclear Ir(III) complexes bearing fluorenyl-tethered 2-(quinolin-2-yl)quinoxaline (quqo) ligands are reported in this paper. The two complexes possess intense and featureless diimine ligand localized ¹ILCT (intraligand charge transfer)/¹π,π* absorption bands at ca. 330 and 430 nm, and a weak ^1,3MLCT (metal-to-ligand charge transfer)/^1,3LLCT (ligand-to-ligand charge transfer) absorption band at >500 nm. Both complexes exhibit weak dual phosphorescence at ca. 590 nm and 710 nm, which are attributed to the ³ILCT/³π,π* and ³MLCT/³LLCT states, respectively. The low-energy ³MLCT/³LLCT state also gives rise to a moderately strong triplet excited-state absorption at 490-800 nm. Because of the stronger triplet excited-state absorption than the ground-state absorption of these complexes at 532 nm, both complexes manifest a moderate reverse saturable absorption (RSA) at 532 nm for ns laser pulses. Expansion of the π-conjugation of the fluorenyl-tethered diimine ligand in Ir-1 causes a slight red-shift of the ¹ILCT/¹π,π* absorption bands in its UV-vis absorption spectrum and the ³MLCT/³LLCT absorption band in the transient absorption spectrum and slightly enhances the RSA at 532 nm compared to that in Ir-2. This work represents the first report on dinuclear Ir(III) complexes that exhibit RSA at 532 nm.

Mono-/Bimetallic Neutral Iridium(III) Complexes Bearing Diketopyrrolopyrrole-Substituted N-Heterocyclic Carbene Ligands: Synthesis and Photophysics

The synthesis and photophysics (UV-vis absorption, emission, and transient absorption) of four neutral heteroleptic cyclometalated iridium(III) complexes (Ir-1-Ir-4) incorporating thiophene/selenophene-diketopyrrolopyrrole (DPP)-substituted N-heterocyclic carbene (NHC) ancillary ligands are reported. The effects of thiophene versus selenophene substitution on DPP and bis- versus monoiridium(III) complexation on the photophysics of these complexes were systematically investigated via spectroscopic techniques and density functional theory calculations. All complexes exhibited strong vibronically resolved absorption in the regions of 500-700 nm and fluorescence at 600-770 nm, and both are predominantly originated from the DPP-NHC ligand. Complexation induced a pronounced red shift of this low-energy absorption band and the fluorescence band with respect to their corresponding ligands due to the improved planarity and extended π-conjugation in the DPP-NHC ligand. Replacing the thiophene units by selenophenes and/or biscomplexation led to the red-shifted absorption and fluorescence spectra, accompanied by the reduced fluorescence lifetime and quantum yield and enhanced population of the triplet excited states, as reflected by the stronger triplet excited-state absorption and singlet oxygen generation.

Dipyrrinato-Iridium(III) Complexes for Application in Photodynamic Therapy and Antimicrobial Photodynamic Inactivation

The generation of bio-targetable photosensitizers is of utmost importance to the emerging field of photodynamic therapy and antimicrobial (photo-)therapy. A synthetic strategy is presented in which chelating dipyrrin moieties are used to enhance the known photoactivity of iridium(III) metal complexes. Formed complexes can thus be functionalized in a facile manner with a range of targeting groups at their chemically active reaction sites. Dipyrrins with N- and O-substituents afforded (dipy)iridium(III) complexes via complexation with the respective Cp*-iridium(III) and ppy-iridium(III) precursors (dipy=dipyrrinato, Cp*=pentamethyl-η5 -cyclopentadienyl, ppy=2-phenylpyridyl). Similarly, electron-deficient [IrIII (dipy)(ppy)2 ] complexes could be used for post-functionalization, forming alkenyl, alkynyl and glyco-appended iridium(III) complexes. The phototoxic activity of these complexes has been assessed in cellular and bacterial assays with and without light; the [IrIII (Cl)(Cp*)(dipy)] complexes and the glyco-substituted iridium(III) complexes showing particular promise as photomedicine candidates. Representative crystal structures of the complexes are also presented.

Multinuclear 2-(Quinolin-2-yl)quinoxaline-Coordinated Iridium(III) Complexes Tethered by Carbazole Derivatives: Synthesis and Photophysics

Five mono/di/trinuclear iridium(III) complexes (1-5) bearing the carbazole-derivative-tethered 2-(quinolin-2-yl)quinoxaline (quqo) diimine (N^N) ligand were synthesized and characterized. The photophysical properties of these complexes and their corresponding diimine ligands were systematically studied via UV-vis absorption, emission, and transient absorption (TA) spectroscopy and simulated by time-dependent density functional theory. All complexes possessed strong well-resolved absorption bands at <400 nm that have predominant ligand-based ¹π,π* transitions and broad structureless charge-transfer (¹CT) absorption bands at 400-700 nm. The energies or intensities of these ¹CT bands varied pronouncedly when the number of tethered Ir(quqo)(piq)₂⁺ (piq refers to 1-phenylisoquinoline) units, π conjugation of the carbazole derivative linker, or attachment positions on the carbazole linker were altered. All complexes were emissive at room temperature, with 1-3 showing near-IR (NIR) ³MLCT (metal-to-ligand charge-transfer)/³LLCT (ligand-to-ligand charge-transfer) emission at ∼710 nm and 4 and 5 exhibiting red or NIR ³ILCT (intraligand charge-transfer)/³LMCT (ligand-to-metal charge-transfer) emission in CH₂Cl₂. In CH₃CN, 1-3 displayed an additional emission band at ca. 590 nm (³ILCT/³LMCT/³MLCT/³π,π* in nature) in addition to the 710 nm band. The different natures of the emitting states of 1-3 versus those of 4 and 5 also gave rise to different spectral features in their triplet TA spectra. It appears that the parentage and characteristics of the lowest triplet excited states in these complexes are mainly impacted by the π systems of the bridging carbazole derivatives and essentially no interactions among the Ir(quqo)(piq)₂⁺ units. In addition, all of the diimine ligands tethered by the carbazole derivatives displayed a dramatic solvatochromic effect in their emission due to the predominant intramolecular charge-transfer nature of their emitting states. Aggregation-enhanced emission was also observed from the mixed CH₂Cl₂/ethyl acetate or CH₂Cl₂/hexane solutions of these ligands.