Cyclometalated Ir(III) Complexes as Lysosome-Targeted Photodynamic Anticancer Agents

We have designed and synthesized two Ir(III) complexes (Ir1 and Ir2) coordinated with an 8-sulfonamidoquinoline derivative ligand as photosensitizers, which exhibit strong red phosphorescence emission and a long phosphorescence lifetime. The Ir(III) complexes exhibit a high population of triplet states, which enable red phosphorescence and efficient singlet oxygen generation. Ir1 and Ir2 rapidly enter the cancer cells and accumulate in lysosomes, producing large amounts of intracellular singlet oxygen when exposed to light irradiation, eventually leading to cancer cell death, and the phototoxic indexes of complexes Ir1 and Ir2 against cancer cells are in the range of 76-228. Overall, our studies indicate that the synthesized Ir(III) complexes with quinoline ligands exhibit photosensitizing properties, effectively inducing cancer cell death when exposed to light. These promising results suggest their potential application in photodynamic therapy.

Ir(III) Complexes with AIE Characteristics for Biological Applications

Both biological process detection and disease diagnosis on the basis of luminescence technology can provide comprehensive insights into the mechanisms of life and disease pathogenesis and also accurately guide therapeutics. As a family of prominent luminescent materials, Ir(III) complexes with aggregation-induced emission (AIE) tendency have been recently explored at a tremendous pace for biological applications, by virtue of their various distinct advantages, such as great stability in biological media, excellent fluorescence properties and distinctive photosensitizing features. Significant breakthroughs of AIE-active Ir(III) complexes have been achieved in the past few years and great progress has been witnessed in the construction of novel AIE-active Ir(III) complexes and their applications in organelle-specific targeting imaging, multiphoton imaging, biomarker-responsive bioimaging, as well as theranostics. This review systematically summarizes the basic concepts, seminal studies, recent trends and perspectives in this area.

AIE-active iridium(III) complex integrated with upconversion nanoparticles for NIR-irradiated photodynamic therapy

The integration of an aggregation induced emission (AIE)-active Ir(III) complex and upconversion nanoparticles (UCNPs) has achieved a NIR-irradiated photosensitizer (PS), UCNPs@Ir-2-N. This PS has satisfactory biocompatibility, excellent phototoxicity, good accumulation in cells and high ¹O₂ generation ability, thereby effectively killing 4T1 mouse cancer cells in vitro. This work has potential for future photodynamic therapy (PDT) applications.

The fast-growing field of photo-driven theranostics based on aggregation-induced emission

Photo-driven theranostics, also known as phototheranostics, relying on the diverse excited-state energy conversions of theranostic agents upon photoexcitation represents a significant branch of theranostics, which ingeniously integrate diagnostic imaging and therapeutic interventions into a single formulation. The combined merits of photoexcitation and theranostics endow photo-driven theranostics with numerous superior features. The applications of aggregation-induced emission luminogens (AIEgens), a particular category of fluorophores, in the field of photo-driven theranostics have been intensively studied by virtue of their versatile advantageous merits of favorable biocompatibility, tuneable photophysical properties, unique aggregation-enhanced theranostic (AET) features, ideal AET-favored on-site activation ability and ready construction of one-for-all multimodal theranostics. This review summarised the significant achievements of photo-driven theranostics based on AIEgens, which were detailedly elaborated and classified by their diverse theranostic modalities into three groups: fluorescence imaging-guided photodynamic therapy, photoacoustic imaging-guided photothermal therapy, and multi-modality theranostics. Particularly, the tremendous advantages and individual design strategies of AIEgens in pursuit of high-performance photosensitizing output, high photothermal conversion and multimodal function capability by adjusting the excited-state energy dissipation pathways are emphasized in each section. In addition to highlighting AIEgens as promising templates for modulating energy dissipation in the application of photo-driven theranostics, current challenges and opportunities in this field are also discussed.

Recent Advances in AIEgen-Based Photodynamic Therapy and Immunotherapy

Cancer, one of the leading causes of death, has seriously threatened public health. However, there is still a lack of effective treatments. Nowadays, photodynamic therapy (PDT), relying on photosensitizers to trigger the generation of reactive oxygen species (ROS) for killing cancer cells, has been emerging as a noninvasive anti-cancer strategy. To enhance the overall anti-cancer efficacy of PDT, various approaches including molecular design and combination with other therapeutic techniques have been proposed and implemented. Especially, photodynamic immunotherapy that can effectively evoke the body's immune response has attracted much attention. Recently, a class of photosensitizers with aggregation-induced emission (AIE) character have shown unique promises, taking advantage of their profound fluorescence and ROS-generating ability in the aggregation state. Despite the promising results demonstrated by several groups, the associated studies are few and the mechanism of such AIEgen-based photodynamic immunotherapy has not been fully understood. This review discusses the recent advances in the AIEgen-based enhanced PDT with a special focus on the AIE photosensitizers for photodynamic immunotherapy, aiming to inspire more opportunities for in-depth investigation of the working principles in this emerging anti-cancer approach.

Fluorescence Imaging and Photodynamic Inactivation of Bacteria Based on Cationic Cyclometalated Iridium(III) Complexes with Aggregation-Induced Emission Properties

Antibacterial photodynamic therapy (PDT) is one of the emerging methods for curbing multidrug-resistant bacterial infections. Effective fluorescent photosensitizers with dual functions of bacteria imaging and PDT applications are highly desirable. In this study, three cationic and heteroleptic cyclometalated Ir(III) complexes with the formula of [Ir(CˆN)₂ (NˆN)][PF₆ ] are prepared and characterized. These Ir(III) complexes named Ir(ppy)₂ bP, Ir(1-pq)₂ bP, and Ir(2-pq)₂ bP are comprised of three CˆN ligands (i.e., 2-phenylpyridine (ppy), 1-phenylisoquinoline (1-pq), and 2-phenylquinoline (2-pq)) and one NˆN bidentate co-ligand (bP). The photophysical characterizations demonstrate that these Ir(III) complexes are red-emitting, aggregation-induced emission active luminogens. The substitution of phenylpyridine with phenylquinoline isomers in the molecules greatly enhances their UV and visible-light absorbance as well as the photoinduced reactive oxygen species (ROS) generation ability. All three Ir(III) complexes can stain both Gram-positive and Gram-negative bacteria efficiently. Interestingly, even though Ir(1-pq)₂ bP and Ir(2-pq)₂ bP are constitutional isomers with very similar structures and similar ROS generation ability in buffer, the former eradicates bacteria much more effectively than the other through white light-irradiated photodynamic inactivation. This work will provide valuable information on the rational design of Ir(III) complexes for fluorescence imaging and efficient photodynamic inactivation of bacteria.

Metal-Based Aggregation-Induced Emission Theranostic Systems

Efficient theranostic systems can realize better outcomes in disease treatment because of precise diagnosis and the concomitant effective therapy. Aggregation-induced emission luminogens (AIEgens) are a unique type of organic emitters with intriguing photophysical properties in the aggregate state. Among the AIEgens studied for biomedical applications, so far, metal-based AIE systems have shown great potential in theranostics due to the enhanced multimodal bioimaging ability and therapeutic effect. This research field has been growing rapidly, and many rationally designed systems with promising activities to cancer and other diseases have been reported recently. In this review, we summarized the recent progress of metal-based AIE materials in bioimaging and biological theranostics, and deciphered the pertinent design strategies. We hope that this review can offer new insights into the development of this growing field.

Recent Advances of Near-Infrared (NIR) Emissive Metal Complexes Bridged by Ligands with N- and/or O-Donor Sites

Near-infrared (NIR) emissive metal complexes have shown potential applications in optical communication, chemosensors, bioimaging, and laser and organic light-emitting diodes (OLEDs) due to their structural tunability and luminescence stability. Among them, complexes with bridging ligands that exhibit unique emission behavior have attracted extensive interests in recent years. The target performance can be easily achieved by NIR light-emitting metal complexes with bridging ligands through molecular structure design. In this review, the luminescence mechanism and design strategies of NIR luminescent metal complexes with bridging ligands are described firstly, and then summarize the recent advance of NIR luminescent metal complexes with bridging ligands in the fields of electroluminescence and biosensing/bioimaging. Finally, the development trend of NIR luminescent metal complexes with bridging ligands are proposed, which shows an attractive prospect in the field of photophysical and photochemical materials.