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Robust luminescent dyes with efficient two-photon fluorescence are highly desirable for biological imaging applications, but those suitable for organic dots fabrication are still rare because of aggregation-caused quenching. In this work, a red fluorescent silole, 2,5-bis[5-(dimesitylboranyl)thiophen-2-yl]-1-methyl-1,3,4-triphenylsilole ((MesB)2DTTPS), is synthesized and characterized. (MesB)2DTTPS exhibits enhanced fluorescence efficiency in nanoaggregates, indicative of aggregation-enhanced emission (AEE). The organic dots fabricated by encapsulating (MesB)2DTTPS within lipid-PEG show red fluorescence peaking at 598 nm and a high fluorescence quantum yield of 32%. Upon excitation at 820 nm, the dots show a large two-photon absorption cross section of 3.43 × 105 GM, which yields a two-photon action cross section of 1.09 × 105 GM. These (MesB)2DTTPS dots show good biocompatibility and are successfully applied to one-photon and two-photon fluorescence imaging of MCF-7 cells and two-photon in vivo visualization of the blood vascular of mouse muscle in a high-contrast and noninvasive manner. Moreover, the 3D blood vasculature located at the mouse ear skin with a depth of over 100 μm can also be visualized clearly, providing the spatiotemporal information about the whole blood vascular network.

The real-time monitoring of reactive oxygen species (ROS, particularly singlet oxygen) generation during photodynamic therapy is a great challenge due to the extremely short half-life and small radius of action. To tackle this issue, we herein report a bioprobe composed of a red emissive photosensitizer (PS) with aggregation-induced emission (AIE) characteristics and a fluorogenic green emissive rhodol dye conjugated via a singlet oxygen cleavable aminoacrylate (AA) linker. The probe emits red fluorescence in water, and the red emissive PS can be used for probe self-tracking. Upon image-guided light irradiation, the generated singlet oxygen cleaves the AA linker to yield green fluorescence turn-on of rhodol, which offers real-time and in situ monitoring of singlet oxygen generation during photodynamic ablation of cancer cells, providing a strategy for the early evaluation of the therapeutic effect.

The currently available photosensitizers (PSs) for photodynamic therapy (PDT) can easily lead to undesirable normal cell death due to their intrinsic photo-toxicity and lack of selectivity for cancer cells. Activatable PSs with high therapeutic efficiency towards cancer cells but minimized side effects on normal cells are thus highly desirable. In this work, we developed a probe with dual-targeted activatable PSs that can recognize and ablate cancer cells with high selectivity. The probe is composed of a fluorophore with aggregation-induced emission (AIE) characteristics which can be used as an imaging agent as well as a PS, a quencher moiety that can be cleaved upon encountering biothiols, and a cyclic arginine–glycine–aspartic acid (cRGD) tripeptide for targeting cancer cells with overexpressed αvβ3 integrin. The probe itself is non-fluorescent and its ability to generate reactive oxygen species (ROS) is prohibited. However, it could be selectively activated to offer specific fluorescence turn-on with efficient ROS generation in the aggregated state, which was used to ablate cancer cells overexpressing both αvβ3 integrin receptors and glutathione. As compared to conventional activatable PSs which show quenched fluorescence and reduced ROS generation in the aggregated state, the dual-selection process with enhanced fluorescence and efficient ROS generation of the activated AIE probe in aggregated state offers a high signal-to-background ratio for MDA-MB-231 cancer cell imaging and ablation. This strategy thus opens up new opportunities for designing activatable PSs with high selectivity and low intrinsic photo-toxicity for photodynamic cancer cell ablation.

The efficiency of the intersystem crossing process can be improved by reducing the energy gap between the singlet and triplet excited states (ΔEST), which offers the opportunity to improve the yield of the triplet excited state. Herein, we demonstrate that modulation of the excited states is also an effective strategy to regulate the singlet oxygen generation of photosensitizers. Based on our previous studies that photosensitizers with aggregation-induced emission characteristics (AIE) showed enhanced fluorescence and efficient singlet oxygen production in the aggregated state, a series of AIE fluorogens such as TPDC, TPPDC and PPDC were synthesized, which showed ΔEST values of 0.48, 0.35 and 0.27 eV, respectively. A detailed study revealed that PPDC exhibited the highest singlet oxygen efficiency (0.89) as nanoaggregates, while TPDC exhibited the lowest efficiency (0.28), inversely correlated with their ΔEST values. Due to their similar optical properties, TPDC and PPDC were further encapsulated into nanoparticles (NPs). Subsequent surface modification with cell penetrating peptide (TAT) yielded TAT-TPDC NPs and TAT-PPDC NPs. As a result of the stronger singlet oxygen generation, TAT-PPDC NPs showed enhanced cancer cell ablation as compared to TAT-TPDC NPs. Fine-tuning of the singlet-triplet energy gap is thus proven to be an effective new strategy to generate efficient photosensitizers for photodynamic therapy.

Integrated systems that offer traceable cancer therapy are highly desirable for personalized medicine. Herein, a probe is reported that is composed of a red-emissive photosensitizer (PS) with aggregation-induced emission characteristics and a built-in apoptosis sensor with activatable green emission for targeted cancer cell ablation and real-time monitoring of PS activation and therapeutic response. The probe is nonemissive in aqueous media and can be selectively uptaken by alpha(v)beta(3) integrin overexpressed cancer cells. Cleavage of the probe by intracellular glutathione leads to release of the apoptosis sensor and red fluorescence turn-on to report the PS activation. Upon light irradiation, the PS can generate reactive oxygen species to induce cell apoptosis and activate caspase-3/-7, which will cleave the apoptosis sensor to yield intense green fluorescence. Both the red and green emission can be obtained through a single wavelength excitation, which makes the probe very convenient for therapeutic protocol development.

A novel white-light-emitting organic molecule, which consists of carbazolyl- and phenothiazinyl-substituted benzophenone (OPC) and exhibits aggregation-induced emission-delayed fluorescence (AIE-DF) and mechanofluorochromic properties was synthesized. The CIE color coordinates of OPC were directly measured with a non-doped powder, which presented white-emission coordinates (0.33, 0.33) at 244 K to 252 K and (0.35, 0.35) at 298 K. The asymmetric donor-acceptor-donor’ (D-A-D’) type of OPC exhibits an accurate inherited relationship from dicarbazolyl-substituted benzophenone (O2C, D-A-D) and diphenothiazinyl-substituted benzophenone (O2P, D’-A-D’). By purposefully selecting the two parent molecules, that is, O2C (blue) and O2P (yellow), the white-light emission of OPC can be achieved in a single molecule. This finding provides a feasible molecular strategy to design new AIE-DF white-light-emitting organic molecules.

Compounds displaying delayed fluorescence (DF), from severe concentration quenching, have limited applications as nondoped organic light-emitting diodes and material sciences. As a nondoped fluorescent emitter, aggregation-induced emission (AIE) materials show high emission efficiency in their aggregated states. Reported herein is an AIE-active, DF compound in which the molecular interaction is modulated, thereby promoting triplet harvesting in the solid state with a high photoluminescence quantum yield of 93.3%, which is the highest quantum yield, to the best of our knowledge, for long-lifetime emitters. Simultaneously, the compound with asymmetric molecular structure exhibited strong mechanoluminescence (ML) without pretreatment in the solid state, thus exploiting a design and synthetic strategy to integrate the features of DF, AIE, and ML into one compound.

Piezochromic (machanochromic) luminescent materials are a class of “smart” materials with luminescent properties that change in response to external force stimuli. These materials are widely used in many fields such as mechanosensors, memory chips, security inks and optoelectronic devices, and have attracted considerable interest in recent years. However, the piezochromic luminescent materials that are dependent on changes in physical molecular packing modes are extremely rare. This rarity may be attributed to two major issues. First, a common method for piezochromic luminescent compound synthesis is not to be realized. Each identified compound is an isolated event, rendering difficulty in the identification of a general characteristic. Second, the fluorescence efficiency of organic luminescent materials often becomes very weak while in solid state because of the aggregation-caused quenching effect. Consequently, the piezochromic luminescent phenomenon becomes difficult to observe. Until the last two years, we recognized the existence of a structural relationship between the aggregation-induced emission compound and the piezochromic luminescent nature, and put forward the concept of “piezochromic aggregation-induced emission materials”, many piezochromic aggregation-induced emission materials have been reported one after another. Aggregation-induced emission compounds can be expected to become an important source of piezochromic luminescent materials, and in other words piezochromic luminescent materials would no longer be rare in the future. In this review, recent progress in the area of piezochromic aggregation-induced emission materials is summarized, and majority of the reported piezochromic aggregation-induced emission systems are discussed, including concept, mechanism, structure-property relationship, application, and so on.

A series of new homopolymers with various degrees of polymerization derived from vinyl tetraphenylethene, that is, poly[2-(4-vinylphenyl)ethene-1,1,2-triyl)tribenzene] homopolymers, is synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The homopolymers exhibit a significant aggregation-induced emission (AIE) effect and an ability to assemble themselves into AIE polymer nanoparticles (NPs) during precipitation in a water/tetrahydrofuran (THF) mixture. The NPs also exhibit good dispersibility, stability, and biocompatibility. The AIE polymer NPs are used in imaging studies of HeLa cells.

The homogeneous and mediated oxidation of guanine by [Ru(bpy)3]2+ (2,2′-bipypyridine) in the presence of surfactants and single-walled carbon nanotubes (SWCNTs) has been investigated using cyclic voltammetry, repetitive differential pulse voltammetry and rotating electrode method. In acidic medium, the oxidation of guanine was controlled by mass transport process of [Ru(bpy)3]2+ in solution, leading to a homogeneous electrocatalysis. In neutral medium, the result from emission spectroscopy suggested the formation of the aggregates containing [Ru(bpy)3]2+, dihexadecyl phosphate (DHP) and guanine. The electrocatalysis of [Ru(bpy)3]2+ toward guanine oxidation was promoted by anionic surfactant DHP and, however, hindered by an excess amount of hexadecyl trismethyl ammonium chloride (HTAC) or SWCNTs added to solutions. The electrocatalytic mechanism of [Ru(bpy)3]2+ for guanine oxidation becomes evident, strongly depending on the presence of anionic or cationic surfactants and SWCNTs.