Two-photon luminescent metal complexes for bioimaging and cancer phototherapy

Highly Efficient Far-Red/NIR-Absorbing Neutral Ir(III) Complex Micelles for Potent Photodynamic/Photothermal Therapy

A critical issue in photodynamic therapy (PDT) is inadequate reactive oxygen species (ROS) generation in tumors, causing inevitable survival of tumor cells that usually results in tumor recurrence and metastasis. Existing photosensitizers frequently suffer from relatively low light-to-ROS conversion efficiency with far-red/near-infrared (NIR) light excitation due to low-lying excited states that lead to rapid non-radiative decays. Here, a neutral Ir(III) complex bearing distyryl boron dipyrromethene (BODIPY-Ir) is reported to efficiently produce both ROS and hyperthermia upon far-red light activation for potentiating in vivo tumor suppression through micellization of BODIPY-Ir to form "Micelle-Ir". BODIPY-Ir absorbs strongly at 550-750 nm with a band maximum at 685 nm, and possesses a long-lived triplet excited state with sufficient non-radiative decays. Upon micellization, BODIPY-Ir forms J-type aggregates within Micelle-Ir, which boosts both singlet oxygen generation and the photothermal effect through the high molar extinction coefficient and amplification of light-to-ROS/heat conversion, causing severe cell apoptosis. Bifunctional Micelle-Ir that accumulates in tumors completely destroys orthotopic 4T1 breast tumors via synergistic PDT/photothermal therapy (PTT) damage under light irradiation, and enables remarkable suppression of metastatic nodules in the lungs, together without significant dark cytotoxicity. The present study offers an emerging approach to develop far-red/NIR photosensitizers toward potent cancer therapy.

Photo-induced mitochondrial DNA damage and NADH depletion by -NO2 modified Ru(II) complexes

Two mitochondria-localized Ru(ii) complexes with photo-labile ligands were reported to exert one- and two-photon activatable anticancer activity through a dual-function mechanism, i.e. mitochondrial DNA covalent binding after photo-induced ligand dissociation and photo-catalyzed NADH depletion, thus displaying good activity towards cisplatin-resistant cancer cells under both normoxic and hypoxic conditions.

Photoluminescent Nanoparticles for Chemical and Biological Analysis and Imaging

Research related to the development and application of luminescent nanoparticles (LNPs) for chemical and biological analysis and imaging is flourishing. Novel materials and new applications continue to be reported after two decades of research. This review provides a comprehensive and heuristic overview of this field. It is targeted to both newcomers and experts who are interested in a critical assessment of LNP materials, their properties, strengths and weaknesses, and prospective applications. Numerous LNP materials are cataloged by fundamental descriptions of their chemical identities and physical morphology, quantitative photoluminescence (PL) properties, PL mechanisms, and surface chemistry. These materials include various semiconductor quantum dots, carbon nanotubes, graphene derivatives, carbon dots, nanodiamonds, luminescent metal nanoclusters, lanthanide-doped upconversion nanoparticles and downshifting nanoparticles, triplet-triplet annihilation nanoparticles, persistent-luminescence nanoparticles, conjugated polymer nanoparticles and semiconducting polymer dots, multi-nanoparticle assemblies, and doped and labeled nanoparticles, including but not limited to those based on polymers and silica. As an exercise in the critical assessment of LNP properties, these materials are ranked by several application-related functional criteria. Additional sections highlight recent examples of advances in chemical and biological analysis, point-of-care diagnostics, and cellular, tissue, and in vivo imaging and theranostics. These examples are drawn from the recent literature and organized by both LNP material and the particular properties that are leveraged to an advantage. Finally, a perspective on what comes next for the field is offered.

Anisotropic Two-Photon Absorption and Second Harmonic Generation in Single Crystals of Silver(I) Coordination Complexes

Metal complexes have been gaining attention in recent times over the traditional inorganic materials such as nonlinear optical materials. Here, we report both two-photon absorption (2PA) and second harmonic generation (SHG) from single crystals of two Ag(I) complexes with considerable optical anisotropy. We demonstrate that by controlling the incident light polarization, the tunability between these two nonlinear optical processes can be achieved. The d_eff values of the observed SHG from one complex are determined to be one order of magnitude greater than β-BBO crystals.

Photoinduced DNA Cleavage and Photocytotoxic of Phenanthroline-Based Ligand Ruthenium Compounds

The photophysical and biological properties of two new phenanthroline-based ligand ruthenium complexes were investigated in detail. Their DNA interaction modes were determined to be the intercalation mode using spectra titration and viscosity measurements. Under irradiation, obvious photo-reduced DNA cleavages were observed in the two complexes via singlet oxygen generation. Furthermore, complex 2 showed higher DNA affinity, photocleavage activity, and singlet oxygen quantum yields than complex 1. The two complexes showed no toxicity towards tumor cells (HeLa, A549, and A375) in the dark. However, obvious photocytotoxicities were observed in the two complexes. Complex 2 exhibited large PIs (phototherapeutic indices) (ca. 400) towards HeLa cells. The study suggests that these complexes may act as DNA intercalators, DNA photocleavers, and photocytotoxic agents.

Making Aggregation-Induced Emission Luminogen More Valuable by Gold: Enhancing Anticancer Efficacy by Suppressing Thioredoxin Reductase Activity

Gold complexes have been recognized as potential anticancer agents against various kinds of diseases due to their inherent suppressions of antioxidant thioredoxin reductase (TrxR) activity. Herein, a powerful aggregation-induced emission luminogen (AIEgen), TBP-Au, was designed and synthesized by integrating an anticancer Au(I) moiety with an AIE-active photosensitizer (TBP), in which both the production and consumption routes of reactive oxygen species (ROS) were elaborately considered simultaneously to boost the anticancer efficacy. It has been demonstrated that TBP-Au could realize superior two-photon fluorescence imaging in tumor tissues with high resolution and deep penetration as well as long-term imaging in live animals due to its AIE property. In addition, the introduction of a special Au(I) moiety could tune the organelle specificity and efficiently facilitate the ROS-determined photodynamic therapy (PDT). More impressively, TBP-Au could efficiently eliminate cancer cells under light irradiation through the preconceived synergetic approaches from the PDT and the effective suppression of TrxR, demonstrating that TBP-Au holds great potential for precise cancer theranostics.

Metal Modulation: An Easy-to-Implement Tactic for Tuning Lanthanide Phototheranostics

Phototheranostics constitute an emerging cancer treatment wherein the core diagnostic and therapeutic functions are integrated into a single photosensitizer (PS). Achieving the full potential of this modality requires being able to tune the photosensitizing properties of the PS in question. Structural modification of the organic framework represents a time-honored strategy for tuning the photophysical features of a given PS system. Here we report an easy-to-implement metal selection approach that allows for fine-tuning of excited-state energy dissipation and phototheranostics functions as exemplified by a set of lanthanide (Ln = Gd, Yb, Er) carbazole-containing porphyrinoid complexes. Femto- and nanosecond time-resolved spectroscopic studies, in conjunction with density functional theory calculations, revealed that the energy dissipation pathways for this set of PSs are highly dependent on the energy gap between the lowest triplet excited state of the ligand and the excited states of the coordinated Ln ions. The Yb complex displayed a balance of deactivation mechanisms that made it attractive as a potential combined photoacoustic imaging and photothermal/photodynamic therapy agent. It was encapsulated into mesoporous silica nanoparticles (MSN) to provide a biocompatible construct, YbL@MSN, which displays a high photothermal conversion efficiency (η = 45%) and a decent singlet oxygen quantum yield (Φ_Δ = 31%). Mouse model studies revealed that YbL@MSN allows for both photoacoustic imaging and synergistic photothermal- and photodynamic-therapy-based tumor reduction in vivo. Our results lead us to suggest that metal selection represents a promising approach to fine-tuning the excited state properties and functional features of phototheranostics.

Luminescent Cationic Group 4 Metallocene Complexes Stabilized by Pendant N-Donor Groups

Cationic group 4 metallocene complexes with pendant imine and pyridine donor groups were prepared as stable crystalline [B(C₆F₅)₄]^- salts either by protonation of the intramolecularly bound ketimide moiety in neutral complexes [(η⁵-C₅Me₅){η⁵-C₅H₄CMe₂CMe₂C(R)═N-κN}MCl] (M = Ti, Zr, Hf; R = t-Bu, Ph) by PhNMe₂H⁺[B(C₆F₅)₄]^- to give [(η⁵-C₅Me₅){η⁵-C₅H₄CMe₂CMe₂C(R)═NH-κN}MCl]⁺[B(C₆F₅)₄]^- or by chloride ligand abstraction from the complexes [(η⁵-C₅Me₅)(η⁵-C₅H₄CMe₂CH₂C₅H₄N)MCl₂] (M = Ti, Zr) by Li[B(C₆F₅)₄]·2.5Et₂O to give [(η⁵-C₅Me₅)(η⁵-C₅H₄CMe₂CH₂C₅H₄N-κN)MCl]⁺[B(C₆F₅)₄]^-. Solid state structures of the new compounds were established by X-ray diffraction analysis, and their electrochemical behavior was studied by cyclic voltammetry. The cationic complexes of Zr and Hf, compared to the corresponding neutral species, exhibited significantly enhanced luminescence predominantly from triplet ligand-to-metal (³LMCT) excited states with lifetimes up to 62 μs and quantum yields up to 58% in the solid state. DFT calculations were performed to explain the structural features and optical and electrochemical properties of the complexes.

Synthesis, Characterization, and In Vitro Cytotoxicity of Unsymmetrical Tetradentate Schiff Base Cu(II) and Fe(III) Complexes

Unsymmetrical tetradentate Schiff base Fe(III) and Cu(II) complexes were prepared by the coordination of some unsymmetrical tetradentate Schiff base ligands with CuCl₂·2H₂O or FeCl₃·6H₂O. The obtained complexes were characterized by ESI-MS, IR, and UV-Vis. The spectroscopic data with typical signals are in agreement with the suggested molecular formulae of the complexes. Their cyclic voltammetric studies in acetonitrile solutions showed that the Cu(II)/Cu(I) and Fe(III)/Fe(II) reduction processes are at (−)1.882–(−) 1.782 V and at (−) 1.317–(−) 1.164 V, respectively. The in vitro cytotoxicity of obtained complexes was screened for KB and Hep-G2 human cancer cell lines. The results showed that almost unsymmetrical tetradentate Schiff base complexes have good cytotoxicity. The synthetic complexes bearing the unsymmetrical tetradentate Schiff base ligands with different substituted groups in the salicyl ring indicate different cytotoxicity. The obtained Fe(III) complexes are more cytotoxic than Cu(II) complexes and relative unsymmetric Schiff base ligands.

Nano-assembly of ruthenium(II) photosensitizers for endogenous glutathione depletion and enhanced two-photon photodynamic therapy

Photodynamic therapy (PDT) is a promising noninvasive cancer treatment. PDT in the clinic faces several hurdles due to the unique tumor environment, a feature of which is high levels of glutathione (GSH). An excess amount of GSH consumes reactive oxygen species (ROS) generated by photosensitizers (PSs), reducing PDT efficiency. Herein, nano-photosensitizers (RuS1 NPs and RuS2 NPs) are reported. These consist of ruthenium complexes joined by disulfide bonds forming GSH sensitive polymer nanoparticles. The NPs achieve enhanced uptake compared to their constituent monomers. Inside cancer cells, high levels of GSH break the S-S bonds releasing PS molecules in the cell. The level of GSH is also then reduced leading to excellent PDT activity. Furthermore, RuS2 NPs functionalized with tumor targeting hyaluronic acid (HA@RuS2 NPs) assessed in vivo were highly effective with minimal side effects. To the best of our knowledge, RuS NPs are the first metal complex-based nano-assembled photosensitizers which exhibit enhanced specificity and consume endogenous GSH simultaneously, thus achieving excellent two-photon PDT efficiency in vitro and in vivo.

syn-Diarylphthalimidoporphyrins: Effects of Symmetry Breaking on Two-Photon Absorption and Linear Photophysical Properties

Aromatically π-extended porphyrins possess exceptionally intense one-photon (1P) and sometimes two-photon (2P) absorption bands, presenting interest for construction of optical imaging probes and photodynamic agents. Here we investigated how breaking the molecular symmetry affects linear and 2PA properties of π-extended porphyrins. First, we developed the synthesis of porphyrins fused with two phthalimide fragments, termed syn-diarylphthalimidoporphyrins (DAPIP). Second, the photophysical properties of H₂, Zn, Pd, and Pt DAPIP were measured and compared to those of fully symmetric tetraarylphthalimidoporphyrins (TAPIP). The data were interpreted using DFT/TDDFT calculations and sum-over-states (SOS) formalism. Overall, the picture of 2PA in DAPIP was found to resemble that in centrosymmetric porphyrins, indicating that symmetry breaking, even as significant as by syn-phthalimido-fusion, induces a relatively small perturbation to the porphyrin electronic structure. Collectively, the compact size, versatile synthesis, high 1PA and 2PA cross sections, and bright luminescence make DAPIP valuable chromophores for construction of imaging probes and other bioapplications.

Recent advances in cancer photo-theranostics: the synergistic combination of transition metal complexes and gold nanostructures

In this mini review, we highlight advances in the last five years in light-activated cancer theranostics by using hybrid systems consisting of transition metal complexes (TMCs) and plasmonic gold nanostructures (AuNPs). TMCs are molecules with attractive properties and high potential in biomedical application. Due to their antiproliferative abilities, platinum-based compounds are currently first-choice drugs for the treatment of several solid tumors. Moreover, ruthenium, iridium and platinum complexes are well-known for their ability to photogenerate singlet oxygen, a highly cytotoxic reactive species with a key role in photodynamic therapy. Their potential is further extended by the unique photophysical properties, which make TMCs particularly suitable for bioimaging. Recently, gold nanoparticles (AuNPs) have been widely investigated as one of the leading nanomaterials in cancer theranostics. AuNPs—being an inert and highly biocompatible material—represent excellent drug delivery systems, overcoming most of the side effects associated with the systemic administration of anticancer drugs. Furthermore, due to the thermoplasmonic properties, AuNPs proved to be efficient nano-sources of heat for photothermal therapy application. Therefore, the hybrid combination TMC/AuNPs could represent a synergistic merger of multiple functionalities for combinatorial cancer therapy strategies. Herein, we report the most recent examples of TMC/AuNPs systems in in-vitro in-vivo cancer tharanostics application whose effects are triggered by light-exposure in the Vis–NIR region, leading to a spatial and temporal control of the TMC/AuNPs activation for light-mediated precision therapeutics.

Supramolecular Assembly of An Organoplatinum(II) Complex with Ratiometric Dual Emission for Two-Photon Bioimaging

The organoplatinum(II) complex [Pt(C^N^N)(Cl)] (C^N^N=5,6-diphenyl-2,2'-bipyridine, Pt1) can assemble into nanoaggregates via π-π stacking and complementary hydrogen bonds, rather than Pt-Pt interactions. Pt1 exhibits ratiometric dual emission, including rare blue emission (λ_em =445 nm) and assembly-induced yellow emission (λ_em =573 nm), under one- and two-photon excitation. Pt1 displays blue emission in cells with an intact membrane due to its low cellular uptake. In cells where the membrane is disrupted, uptake of the complex is increased and at higher concentrations yellow emission is observed. The ratio of yellow to blue emission shows a linear relationship to the loss of cell membrane integrity. Pt1 is, to our knowledge, the first example of an assembly-induced two-photon ratiometric dual emission organoplatinum complex. The excellent and unique characteristics of the complex enabled its use for the tracking of cell apoptosis, necrosis, and the inflammation process in zebrafish.

Photodynamic antitumor activity of Ru(ii) complexes of imidazo-phenanthroline conjugated hydroxybenzoic acid as tumor targeting photosensitizers

Two novel Ru(ii) polypyridyl complexes bearing imidazo-phenanthroline conjugated hydroxybenzoic acid groups were designed to enhance the tumor targeting ability as photosensitizers for photodynamic therapy. [Ru(bpy)2(phcpip)] (ClO4)2 (Ru-1) and [Ru(bpy)2(ohcpip)] (ClO4)2 (Ru-2) (bpy = 2,2'-bipyridine; phcpip = 2-(3-carboxyl-4-hydroxyphenyl) imidazo [4,5-f]phenanthroline; ohcpip = 2-(2-hydroxyl-3-carboxyphenyl) imidazo [4,5-f] [1,10] phenanthroline) were synthesized and their photodynamic antitumor activities were investigated. Both complexes displayed high photocytotoxicity toward cancerous cell lines HepG2, A549, MCF-7, and MDA-MB-231, but low photocytotoxicity toward normal cell lines GES-1 and Huvec. They were mainly localized at the nucleus of HepG2 cells after 24 h incubation, arrested the cell cycle at the G2/M phase and induced cancer cell apoptosis through reactive oxygen species (ROS) mediated pathways. Tumor targeting of the complexes is attributed to stronger molecular binding to DNA.

Recent progress in photosensitizers for overcoming the challenges of photodynamic therapy: from molecular design to application

Photodynamic therapy (PDT), a therapeutic mode involving light triggering, has been recognized as an attractive oncotherapy treatment. However, nonnegligible challenges remain for its further clinical use, including finite tumor suppression, poor tumor targeting, and limited therapeutic depth. The photosensitizer (PS), being the most important element of PDT, plays a decisive role in PDT treatment. This review summarizes recent progress made in the development of PSs for overcoming the above challenges. This progress has included PSs developed to display enhanced tolerance of the tumor microenvironment, improved tumor-specific selectivity, and feasibility of use in deep tissue. Based on their molecular photophysical properties and design directions, the PSs are classified by parent structures, which are discussed in detail from the molecular design to application. Finally, a brief summary of current strategies for designing PSs and future perspectives are also presented. We expect the information provided in this review to spur the further design of PSs and the clinical development of PDT-mediated cancer treatments.

Tracking mesenchymal stem cells with Ir(III) complex-encapsulated nanospheres in cranium defect with postmenopausal osteoporosis

Osteoporosis (OP) is a significant public health problem with associated fragility fractures, thereby causing large bone defects and difficulty in self-repair. The introduction of human mesenchymal stem cells (hMSCs) is the most promising platform in bone tissue engineering for OP therapy, which induces less side effects than conventional medication. However, the safety and efficiency of the cell-based OP therapy requires the ability to monitor the cell's outcome and biodistribution after cell transplantation. Therefore, we designed an in vivo system to track hMSCs in real time and simultaneously attempted to obtain a significant therapeutic effect during the bone repair process. In this study, we synthesized Ir(III) complex, followed by encapsulation with biodegradable methoxy-poly(ethylene glycol) poly(lactic-co-glycolic acid) nanospheres through double emulsions strategy. The Ir(III) complex nanospheres did not affect hMSC proliferation, stemness, and differentiation and realized highly efficient and long-term cellular labeling for at least 25 days in vivo. The optimal transplantation conditions were also determined first by injecting a gradient number of labeled hMSCs percutaneously into the cranial defect of the nude mouse model. Next, we applied this method to ovariectomy-induced OP mice. Results showed long-term optical imaging with high fluorescence intensity and computed tomography (CT) scanning with significantly increased bone formation between the osteoporotic and sham-operated bones. During the tracking process, two mice from each group were sacrificed at two representative time points to examine the bony defect bridging via micro-CT morphometric analyses. Our data showed remarkable promise for efficient hMSC tracking and encouraging treatment in bioimaging-guided OP stem cell therapy.

Self-assembled heterometallic complexes showing enhanced two-photon absorption and their distribution in living cells

Heterometallic complexes were prepared via self-assembly, showing enhanced TPA ability and preferable localization into lysosomes.

The modification of a pyrene group makes a Ru(ii) complex versatile

A versatile Ru(ii) complex with self-reporting ligand photo-dissociation and efficient two-photon excited synergistic PACT and PDT abilities was designed and studied.

A mitochondrial-targeting iridium(iii) complex for H2O2-responsive and oxidative stress amplified two-photon photodynamic therapy

The mitochondrial-targeting iridium(iii) complex Ir–B(OH)2 is activated in the presence of endogenous H2O2 to release the two-photon photosensitizer Ir–OH and the GSH scavenger methylquinone for amplified two-photon photodynamic therapy.

The impact of cyclometalated and phosphine ligands on the luminescence properties of cycloplatinated(ii) complexes: photophysical and theoretical investigations

The effects of various C^N cyclometalated and phosphine ligands on the photophysical properties of cycloplatinated(ii) complexes were investigated experimentally and theoretically.

Photofunctional transition metal complexes as cellular probes, bioimaging reagents and phototherapeutics

This critical review summarises the recent biological applications of transition metal complexes as cellular probes, bioimaging reagents and phototherapeutics.

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.

Metallodrugs are unique: opportunities and challenges of discovery and development

Metals play vital roles in nutrients and medicines and provide chemical functionalities that are not accessible to purely organic compounds. At least 10 metals are essential for human life and about 46 other non-essential metals (including radionuclides) are also used in drug therapies and diagnostic agents. These include platinum drugs (in 50% of cancer chemotherapies), lithium (bipolar disorders), silver (antimicrobials), and bismuth (broad-spectrum antibiotics). While the quest for novel and better drugs is now as urgent as ever, drug discovery and development pipelines established for organic drugs and based on target identification and high-throughput screening of compound libraries are less effective when applied to metallodrugs. Metallodrugs are often prodrugs which undergo activation by ligand substitution or redox reactions, and are multi-targeting, all of which need to be considered when establishing structure-activity relationships. We focus on early-stage in vitro drug discovery, highlighting the challenges of evaluating anticancer, antimicrobial and antiviral metallo-pharmacophores in cultured cells, and identifying their targets. We highlight advances in the application of metal-specific techniques that can assist the preclinical development, including synchrotron X-ray spectro(micro)scopy, luminescence, and mass spectrometry-based methods, combined with proteomic and genomic (metallomic) approaches. A deeper understanding of the behavior of metals and metallodrugs in biological systems is not only key to the design of novel agents with unique mechanisms of action, but also to new understanding of clinically-established drugs.

Dinuclear Rhenium Complexes with a Bridging Helicene-bis-bipyridine Ligand: Synthesis, Structure, and Photophysical and Chiroptical Properties

By attaching pyridine groups to a diaza[6]helicene, a helical, bis-ditopic, bis-N N-coordinating ligand can be accessed. Dinuclear rhenium complexes featuring this bridging ligand, of the form [{Re(CO)3 Cl}2 (N N-N N)], have been prepared and resolved to give enantiopure complexes. These complexes are phosphorescent in solution at room temperature under one- and two-photon excitation. Their experimental chiroptical properties (optical rotation, electronic circular dichroism and circularly polarized emission) have been measured. They show, for instance, emission dissymmetry factors of c.a. ±3x10-3 . Quantum-chemical calculations indicate the importance of stereochemistry on the optical activity, pointing towards further design improvements in such types of complexes.

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

Three mononuclear or dinuclear bis(terpyridine) (tpy) iridium(III) complexes bearing pyren-1-yl (pyr) group(s) were synthesized. Their photophysical properties in water and in vitro photodynamic therapy (PDT) effects toward the human lung epithelial cancer cell line A549 and the human epidermal skin cancer cell line A431 were investigated to evaluate the effects of dinuclear versus mononuclear complexes and the impact of the oligoether substituent at the ligand. All complexes possessed pyr-tpy ligand-associated charge transfer (¹CT)/¹π,π* absorption bands at 350-550 nm, with the dinuclear complex Ir3 showing the much enhanced absorptivity of this band. These complexes exhibited dual emission upon excitation at >430 nm in most cases, with the emitting states being ascribed to ¹ILCT (intraligand charge transfer) and ³π,π*/³CT states, respectively. All complexes exhibited relatively weak to moderate cytotoxicity in the dark but high photocytotoxicity upon broadband visible light irradiation. Among them, the dinuclear complex Ir3 showed the highest intracellular reactive oxygen species (ROS) generation and PDT efficiency compared to its mononuclear counterpart Ir1. Introducing an oligoether substituent on one of the tpy ligands in Ir2 also improved its intracellular ROS generation and PDT efficacy compared to those induced by Ir1. Ir3 induced both mitochondrial dysfunction and lysosomal damage upon light activation toward both cell lines, whereas Ir1 and Ir2 caused both mitochondrial dysfunction and lysosomal damage in A431 cells but only lysosomal damage in A549 cells. The dominant cell death pathway induced by Ir1-Ir3 PDT is apoptosis.

A Mitochondrion-Localized Two-Photon Photosensitizer Generating Carbon Radicals Against Hypoxic Tumors

The efficacy of photodynamic therapy is typically reliant on the local concentration and diffusion of oxygen. Due to the hypoxic microenvironment found in solid tumors, oxygen-independent photosensitizers are in great demand for cancer therapy. We herein report an iridium(III) anthraquinone complex as a mitochondrion-localized carbon-radical initiator. Its emission is turned on under hypoxic conditions after reduction by reductase. Furthermore, its two-photon excitation properties (λ_ex =730 nm) are highly desirable for imaging. Upon irradiation, the reduced form of the complex generates carbon radicals, leading to a loss of mitochondrial membrane potential and cell death (IC₅₀ ^light =2.1 μm, IC₅₀ ^dark =58.2 μm, PI=27.7). The efficacy of the complex as a PDT agent was also demonstrated under hypoxic conditions in vivo. To the best of our knowledge, it is the first metal-complex-based theranostic agent which can generate carbon radicals for oxygen-independent two-photon photodynamic therapy.

Deep-Red Luminescence from Platinum(II) Complexes of N^N-^N-Amido Ligands with Benzannulated N-Heterocyclic Donor Arms

A synthetic methodology for accessing narrow-band, deep-red phosphorescence from mononuclear Pt(II) complexes is presented. These charge-neutral complexes have the general structure (N^N^-^N)PtCl, in which the Pt(II) centers are supported by benzannulated diarylamido ligand scaffolds bearing substituted quinolinyl and/or phenanthridinyl arms. Emission maxima ranging from 683 to 745 nm are observed, with lifetimes spanning from 850 to 4500 ns. In contrast to the corresponding proligands, benzannulation is found to counterintuitively but markedly blue-shift emission from metal complexes with differing degrees of ligand benzannulation but similar substitution patterns. This effect can be further tuned by incorporation of electron-releasing (Me, tBu) or electron-withdrawing (CF₃) substituents in either the phenanthridine 2-position or quinoline 6-position. Compared with symmetric bis(quinoline) and bis(phenanthridine) architectures, "mixed" ligands incorporating one quinoline and one phenanthridine unit present a degree of charge transfer between the N-heterocyclic arms that is more pronounced in the proligands than in the Pt(II) complexes. The impact of benzannulation and ring-substitution on the structure and photophysical properties of both the proligands and their deep-red emitting Pt(II) complexes is discussed.

Photosensitive properties, synergistic antibacterial abilities of intelligent response-type self-assembled nanoparticle TiO2@V2O5

Representative pathogenic bacteria such as Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) are widespread in nature and pose a threat to human health. To control the propagation of these pathogens from the source, the key is to design broad-spectrum antibacterial materials to reduce the serious damage of pathogenic bacteria. At present, more and more nanoparticles are widely researched and applied due to their multi-pathway antibacterial properties, such as regulating physiology, biochemistry and physical chemistry. In this work, we synthesized a uniformly dispersed and stable spherical nanoparticle (TiO₂@V₂O₅) synthesized by self-assembly of tianium dioxide and vanadium pentoxide. Based on its excellent photosensitive properties, TiO₂@V₂O₅ nanoparticles have showed excellent antibacterial properties under the light irradiation due to the production of hydroxyl radicals in antibacterial and mechanism tests. In addtion, related cell and plant experiments have showed that TiO₂@V₂O₅ nanoparticles are excellent biocompatible materials, it could be widely used in environmental pollution control, limiting the serious damage caused by pathogens.

Synthesis, Photophysics, and Reverse Saturable Absorption of trans-Bis-cyclometalated Iridium(III) Complexes (C^N^C)Ir(R-tpy)+ (tpy = 2,2':6',2″-Terpyridine) with Broadband Excited-State Absorption

Extending the bandwidth of triplet excited-state absorption in transition-metal complexes is appealing for developing broadband reverse saturable absorbers. Targeting this goal, five bis-terdentate iridium(III) complexes (Ir1-Ir5) bearing trans-bis-cyclometalating (C^N^C) and 4'-R-2,2':6',2″-terpyridine (4'-R-tpy) ligands were synthesized. The effects of the structural variation in cyclometalating ligands and substituents at the tpy ligand on the photophysics of these complexes have been systematically explored using spectroscopic methods (i.e., UV-vis absorption, emission, and transient absorption spectroscopy) and time-dependent density functional theory (TDDFT) calculations. All complexes exhibited intensely structured ¹π,π* absorption bands at <400 nm and broad charge transfer (¹CT)/¹π,π* transitions at 400-600 nm. Ligand structural variations exerted a very small effect on the energies of the ¹CT/¹π,π* transitions; however, they had a significant effect on the molar extinction coefficients of these absorption bands. All complexes emitted featureless deep red phosphorescence in solutions at room temperature and gave broad-band and strong triplet excited-state absorption ranging from the visible to the near-infrared (NIR) spectral regions, with both originating from the ³π,π*/³CT states. Although alteration of the ligand structures influenced the emission energies slightly, these changes significantly affected the emission lifetimes and quantum yields, transient absorption spectral features, and the triplet excited-state quantum yields of the complexes. Except for Ir3, the other four complexes all manifested reverse saturable absorption (RSA) upon nanosecond laser pulse excitation at 532 nm, with the decreasing trend of RSA following Ir2 ≈ Ir4 > Ir1 > Ir5 > Ir3. The RSA trend corresponded well with the strength of the excited-state and ground-state absorption differences (ΔOD) at 532 nm for these complexes.

A mitochondria-targeting magnetothermogenic nanozyme for magnet-induced synergistic cancer therapy

Magnetic hyperthermia therapy (MHT) and chemodynamic therapy (CDT) are non-invasive in situ treatments without depth limitations and with minimum adverse effects on surrounding healthy tissue. We herein report a mitochondria-targeting magnetothermogenic nanozyme (Ir@MnFe2O4 NPs) for highly efficient cancer therapy. An iridium(III) complex (Ir) acts as a mitochondria-targeting agent on the surface of MnFe2O4 NPs. On exposure to an alternating magnetic field (AMF), the Ir@MnFe2O4 NPs induce a localized increase in temperature causing mitochondrial damage (MHT effect). Meanwhile glutathione (GSH) reduces Fe(III) to Fe(II) on the NPs surface, which in turn catalyzes the conversion of H2O2 to cytotoxic •OH (CDT effect). The depletion of GSH (a •OH scavenger) increases CDT efficacy, while the localized increase in temperature increases the rate of conversion of both Fe(III) to Fe(II) and H2O2 to •OH further enhancing the CDT effect. In addition, the disruption of cellular redox homeostasis due to CDT, leads to greater sensitivity of the cell towards MHT. This nanoplatform integrates these excellent therapeutic properties, with two-photon microscopy (TPM) (demonstrated in vitro) and magnetic resonance imaging (MRI) (demonstrated in vivo) to enable the precise and effective treatment of cancer.

Boosting two-photon photodynamic therapy with mitochondria-targeting ruthenium-glucose conjugates

Herein, we present a series of dual-targeted ruthenium-glucose conjugates that can function as two-photon absorption (TPA) PDT agents to effectively destroy tumors by preferentially targeting both tumor cells and mitochondria. The in vivo experiments revealed an excellent tumor inhibitory efficiency of the dual-targeted TPA PSs.

Iridium(iii) complexes with the dithieno[3,2-b:2',3'-d]phosphole oxide group and their high optical power limiting performances

A new 2-phenylpyridine-type (ppy-type) ligand with the dithieno[3,2-b:2',3'-d]phosphole oxide (DTPO) group has been successfully synthesized. Based on this novel ligand, three cyclometalated iridium(iii) complexes (P-Ir-P, P-Ir-T and P-Ir-C) are synthesized with symmetrical and unsymmetrical structures. Photophysical results reveal that these cyclometalated iridium(iii) complexes can show weak near-infrared (NIR) phosphorescence emission with wavelengths of 739 nm for P-Ir-P, 750 nm for P-Ir-T and 746 nm for P-Ir-C. Importantly, transient absorption characterization shows that these cyclometalated iridium(iii) complexes can exhibit strong excited state absorption in the range of ca. 520 to 700 nm, indicating their optical power limiting (OPL) potential in this wavelength range. Open-aperture Z-scan against a 532 nm laser shows their OPL ability in the order of P-Ir-P > P-Ir-C > P-Ir-T. Complex P-Ir-P shows an even better OPL ability than the state-of-the-art OPL material C60, indicating the important potential application of these cyclometalated iridium(iii) complexes as new OPL materials.

Imidazole and Benzimidazole Modified Half-Sandwich IridiumIII N-Heterocyclic Carbene Complexes: Synthesis, Anticancer Application, and Organelle Targeting

Herein, we report the synthesis, characterization and anticancer activity of a series of half-sandwich iridium^III imidazole and benzimidazole N-heterocyclic carbene (NHC) anticancer complexes, and the general formula of which can be expressed as [(η⁵-Cp^x)Ir(C^∧N)Cl]Cl (Cp^x: pentamethylcyclopentadienyl (Cp^*) or biphenyl derivatives (Cp^xbiph); C^∧N: imidazole and benzimidazole NHC chelating ligands). Compared with cis-platin, these complexes showed interesting antitumor activity against A549 cells. Complexes could bind to bovine serum albumin (BSA) by means of static quenching mode, catalyze the oxidation of nicotinamide adenine dinucleotide (NADH) and increase the levels of reactive oxygen species (ROS). Meanwhile, these complexes could arrest the cell cycles of A549 cells and influence the mitochondrial membrane potential significantly. Due to the inherent luminescence property, laser confocal test show that complexes could enter cells followed an energy-dependent mechanism and effectively accumulate in lysosome (the value of Pearson's co-localization coefficient is 0.70 after 1 h), further destroy lysosome integrity and induce apoptosis.

Molecular Design of Bioorthogonal Probes and Imaging Reagents Derived from Photofunctional Transition Metal Complexes

For more than 15 years, bioorthogonal chemistry has received increasing attention due to its successful applications in the detection and imaging of biomolecules in their native biological environments. The method typically proceeds with the incorporation of a biological substrate appended with a bioorthogonal functional group (chemical reporter), followed by the introduction of the substrate to biological systems. Biomolecules containing the substrate are then recognized by an exogenously delivered bioorthogonal probe. Despite the fact that many useful chemical reporters and bioorthogonal reactions have been developed, most of the bioorthogonal probes reported thus far are fluorescent dyes. A limitation is that stringent washing is required due to the interference caused by the background fluorescence of unreacted probes. Thus, fluorogenic probes with turn-on emission properties upon bioorthogonal labeling have been designed as an alternative strategy. These probes are highly appealing because excellent images can be obtained without the need for washing steps. Nearly all fluorogenic bioorthogonal probes designed are essentially organic dyes, their emission is limited to fluorescence, and the utilization of the probes is confined to bioimaging applications. Recently, there has been a growing interest in the bioimaging and therapeutic applications of luminescent inorganic and organometallic transition metal complexes due to their intriguing photophysical and photochemical properties, high membrane permeability, controllable cellular uptake, intracellular localization, and cytotoxicity. We anticipate that photofunctional transition metal complexes can be exploited as valuable bioorthogonal probes due to these appealing advantages. In this Account, we introduce the molecular design, photophysical and photochemical properties, and biological applications of various bioorthogonal probes and imaging reagents based on photofunctional transition metal complexes. The presence of a cationic metal center significantly enhances the bioorthogonal reactivity of the probes, yet their stability in aqueous solutions can be maintained. Interestingly, some of these metal complexes are strategically modified to display phosphorogenic properties, that is, phosphorescence turn-on upon bioorthogonal labeling reactions. Importantly, these probes not only exhibit favorable photophysical properties after bioorthogonal labeling, but also efficient photoinduced singlet oxygen (¹O₂) generation. This interesting bioorthogonal reaction-triggered photosensitization capability allows the modulation of ¹O₂ generation efficiency and contributes to the development of controllable photocytotoxic agents. The exploration of transition metal complex-based probes not only significantly widens the scope of bioorthogonal labeling but also further highlights the unique advantages of these complexes in the design of theranostic reagents. The development of these innovative reagents is expected to contribute to the basic understanding of biological processes in living systems and provide exciting opportunities for new diagnostic and therapeutic applications.