Photodynamic therapy is arising as a noninvasive treatment modality for cancer and other diseases. One of the key factors to determine the therapeutic function is the efficiency of photosensitizers (PSs). Opposed to traditional PSs, which show quenched fluorescence and reduced singlet oxygen production in the aggregate state, PSs with aggregation-induced emission (AIE) exhibit enhanced fluorescence and strong photosensitization ability in nanoparticles. Here, the design principles of AIE PSs and their biomedical applications are discussed in detail, starting with a summary of traditional PSs, followed by a comparison between traditional and AIE PSs to highlight the various design strategies and unique features of the latter. Subsequently, the applications of AIE PSs in photodynamic cancer cell ablation, bacteria killing, and image-guided therapy are discussed using charged AIE PSs, AIE PS molecular probes, and AIE PS nanoparticles as examples. These studies have demonstrated the great potential of AIE PSs as effective theranostic agents to treat tumor or bacterial infection. This review hopefully will spur more research interest in AIE PSs for future translational research.

Photosensitizers with Aggregation-Induced Emission: Materials and Biomedical Applications

In this work, we describe the synthesis, structural and photophysical characterization of four novel Pd(II) and Pt(II) complexes bearing tetradentate luminophoric ligands with high photoluminescence quantum yields (ΦL) and long excited state lifetimes (τ) at room temperature, where the results were interpreted by means of DFT calculations. Incorporation of fluorine atoms into the tetradentate ligand favors aggregation and thereby, a shortened average distance between the metal centers, which provides accessibility to metal–metal-to-ligand charge-transfer (3MMLCT) excimers acting as red-shifted energy traps if compared with the monomeric entities. This supramolecular approach provides an elegant way to enable room-temperature phosphorescence from Pd(II) complexes, which are otherwise quenched by a thermal population of dissociative states due to a lower ligand field splitting. Encapsulation of these complexes in 100 nm-sized aminated polystyrene nanoparticles enables concentration-controlled aggregation-enhanced dual emission. This phenomenon facilitates the tunability of the absorption and emission colors while providing a rigidified environment supporting an enhanced ΦL up to about 80% and extended τ exceeding 100 μs. Additionally, these nanoarrays constitute rare examples for self-referenced oxygen reporters, since the phosphorescence of the aggregates is insensitive to external influences, whereas the monomeric species drop in luminescence lifetime and intensity with increasing triplet molecular dioxygen concentrations (diffusion-controlled quenching).

/pdf/ligand-controlled-and-nanoconfinement-boosted-luminescence-2d7vw7rsh7.pdf

Ligand-controlled and nanoconfinement-boosted luminescence employing Pt(II) and Pd(II) complexes: from color-tunable aggregation-enhanced dual emitters towards self-referenced oxygen reporters

A series of four-coordinated PtII(C^N)(N-donor ligand)Cl-type complexes have been synthesized through combination between C^N-type and N-donor ligands with different sizes. Photophysical features, electrochemical behaviors and electroluminescent (EL) performances have been investigated in detail. Critically, the relationship between the size of organic ligands and aggregation-induced phosphorescence emission (AIPE) behaviors for these PtII(C^N)(N-donor ligand)Cl-type complexes has been characterized. With extending the dimensions of the C^N-type and/or N-donor ligands, the AIPE of these PtII(C^N)(N-donor ligand)Cl-type complexes is more likely to show up with lower H2O volumetric fractions (fw) in the THF solution of these complexes. These unique AIPE experimental results have clearly revealed a new AIE mechanism called restrained D2d deformation of the coordinating skeleton of these PtII(C^N)(N-donor ligand)Cl-type complexes from square-planar (D4h) in the ground states to the tetrahedron (Td) skeleton in the excited states. In addition, solution-processed organic light-emitting diodes (OLEDs) based on these AIPE emitters have been fabricated to characterize their EL potential. Impressive EL efficiencies with the maximum external quantum efficiency (ηext) of 25.2%, current efficiency (ηL) of 53.9 cd A−1 and power efficiency (ηP) of 43.5 lm W−1 can be achieved, indicating great potential of these PtII(C^N)(N-donor ligand)Cl-type AIPE emitters in the field of OLEDs. Importantly, this research has proposed a new AIE mechanism to promote the development of new phosphorescent AIPE complexes with great potential in the field of OLEDs.

Aggregation-induced phosphorescence emission (AIPE) behaviors in PtII(C^N)(N-donor ligand)Cl-type complexes through restrained D2d deformation of the coordinating skeleton and their optoelectronic properties

A new ABW-type luminescent metal–organic framework (MOF) namely (H3O)[Zn2L(H2O)]·3NMP·6H2O (1), constructed with eco-friendly Zn2+ and the multicarboxylate intraligand (LH5) was designed, synthesized and fully characterized by X-ray single-crystal diffraction, steady-state absorption and emission spectroscopy, and SEM observations. The MOF-based suspension sensor 1 (NMP) demonstrated high sensitivity to low-concentration pesticides of chlorothalonil (CTL), nitrofen (NF), trifluralin (TFL), and 2,6-dichloro-4-nitroaniline (DCN), which was assigned to the synergistic effect of the photoinduced electron transfer and the fluorescence resonance energy transfer. With the highest luminescent detection efficiency (KSV up to 11.194 μmol−1 and LOD down to 2.93 ppm) to DCN, 1 (NMP) was successfully applied for the selective sensing of DCN. The MOF-based film sensor 1 (film) illustrated the selective visualization sensing of trace amounts of DCN. In addition, based on the high saturated vapor pressure of TFL and the unique bathochromic shift effect to the emission maxima of 1, the MOF-based luminescent vapor sensing device 1 (LED) successfully exhibited operability for sensing of TFL vapor. The results illustrated a feasible approach to construct new MOF-based luminescent sensors for selective sensing and visualization of pesticides.

/pdf/selective-sensing-and-visualization-of-pesticides-by-abw-4l6yh494j7.pdf

Selective sensing and visualization of pesticides by ABW-type metal─organic framework based luminescent sensors

AIE-active luminogens are attractive for bioimaging, sensors, and optical detections. However, controllably switching and adjusting the AIE activity of luminogens in aqueous media to perform the best of AIE performance under appropriate water fraction remains a challenge. Herein, we report the first case of switchable and adjustable AIE activity based on Pt(II) complexes. The AIE activity of Pt(II) complexes in aqueous media can be flexibly switched and adjusted via finely tuning the rotation activity of the substituents. And the rotation activity of the substituents have been experimentally confirmed by the luminescent lifetimes and theoretically verified by the dipole moments of Pt(II) complexes. Furthermore, luminescent oxygen sensing films were constructed by combining the AIE-active Pt(II) complexes with commercially available, low-cost ethyl cellulose (EC). With the attenuation of EC film thickness, swift-responding quenching/recovering cycles (7.7 s) of the PtTPA-EC(N10) oxygen sensing film were demonstrated. And the controllable AIE property of Pt(II) complexes can effectively improve the oxygen sensitivity and the homogeneity of oxygen sensing films.

Switchable and adjustable AIE activity of Pt(II) complexes achieving swift-responding and highly sensitive oxygen sensing

Three Ir(III) complexes IrC1, IrC2, and IrC3 substituted with 4-(diphenylamino)phenyl (TPA), 4-(9H-carbazol-9-yl)phenyl (Cz1), and 9-phenyl-9H-carbazol-3-yl (Cz2) moieties were prepared and fully characterized as phosphorescent emitters. In comparison with Ir(ppy)3, introduction of TPA, Cz1, and Cz2 moieties strongly improved the oxygen sensitivities of IrC1–IrC3. Short-decayed IrC1 with I0/I100 of 168.6 and KappSV of 202.2 bar−1 in THF exhibited the highest sensitivity for oxygen. TPA and Cz moieties caused remarkable collision radius variations of the Ir(III) complexes with 2.13 ± 0.08 for σIrC1/σIr(ppy)3, 1.24 ± 0.06 for σIrC2/σIr(ppy)3, and 1.54 ± 0.08 for σIrC3/σIr(ppy)3. For demonstrating the dependence of oxygen sensitivity on the molecular structure of the oxygen-sensitive probes (OSPs), the delocalization of spin populations (DSPs) has been applied for the first time to confirm the collision radius variations of Ir(III) complexes. Remarkable DSPs were found on the TPA, Cz1, and Cz2 moieties with the spin population (percentage of the spin population) of 0.23210 (11.61%), 0.08862 (4.43%), and 0.13201 (6.60%), respectively. And strong linear correlations (R2 = 0.997) between the collision radius variations and spin population on TPA and Cz moieties were apparent. The DSPs could be used to describe the dependence of oxygen sensitivity on the molecular structure of the OSPs. For achieving real-time oxygen sensing, the photostability, oxygen sensing performance, and operational stability of IrC1–IrC3 and Ir(ppy)3 immobilized in ethyl cellulose (EC) were investigated. The IrC1-EC film demonstrated outstanding photostability after 60 min of irradiation and excellent operational stability for continuous oxygen monitoring with no attenuation of the original emission intensity in 4000 s. This study quantified and analyzed the dependence of oxygen sensitivity on the molecular structure of Ir(III) complexes for the first time and illustrated a feasible approach to achieve high-efficiency sensors for real-time monitoring of oxygen.

/pdf/the-dependence-of-oxygen-sensitivity-on-the-molecular-g1b521mtaw.pdf

The dependence of oxygen sensitivity on the molecular structures of Ir(iii) complexes and their application for photostable and reversible luminescent oxygen sensing

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Switchable and adjustable AIE activity of Pt(II) complexes achieving swift-responding and highly sensitive oxygen sensing

The dependence of oxygen sensitivity on the molecular structures of Ir(iii) complexes and their application for photostable and reversible luminescent oxygen sensing