Article-Journal

Fine-tuning electron acceptors through changing one cyano group to an amide generates a more stable and emissive fluorophore with the character of aggregation-induced emission. Conjugation between the new fluorophore and CFFKDEL generated an excellent ER targeting light-up probe with high specificity and good photostability.

We report an in-depth photophysical investigation of an asymmetric donor–acceptor–donor′ (D–A–D′) thermally activated delayed fluorescence (TADF) molecule (4-(9H-carbazol-9-yl)phenyl)(4-(10H-phenothiazin-10-yl)phenyl)sulfone and compare its photophysical properties to the parent symmetric D–A–D and D′–A–D′ molecules. These D–A–D type small molecules all show strong TADF. The work reveals how the relative orientations of D–A (D′–A) moieties favor reverse intersystem crossing (rISC) by forming stable charge transfer (CT) states. The key requirement for the efficient TADF emitters is to achieve a very small CT-local triplet state energy splitting, which is shown to be complex in the asymmetric molecule. Throughout the investigations, we show that in the asymmetric D–A–D′ system, even though ECT (D–A) > ECT (D′–A), no evidence of energy transfer from D–A to A–D′ is observed, nor from excited D to D′. This is ascribed to the near orthogonality of the D and D′ units and the very strong decoupling of the electrons on the D and A in the CT state. In addition, the possibility of aggregation-induced TADF (AI-TADF) is examined and shown to be a manifestation of solvatochromism in these particular molecules.

We herein report a new strategy to obtain highly efficient photosensitizers (PSs) by reducing the singlet-triplet energy gap (ΔEST) and blocking the non-radiative decay pathways. Through precise molecular design, TP1-8 were synthesized to exhibit predictable properties including moderate to high photosensitizing efficacy, tunable absorption and emission wavelengths and aggregation-induced emission characteristics.

Conjugated polymer nanoparticles (CP NPs) are emerging candidates of “all-in-one” theranostic nanoplatforms with dual photoacoustic imaging (PA) and photothermal therapy (PTT) functions. So far, very limited molecular design guidelines have been developed for achieving CPs with highly efficient PA and PTT performance. Herein, by designing CP1, CP2, and CP3 using different electron acceptors (A) and a planar electron donor (D), we demonstrate how the D–A strength affects their absorption, emission, extinction coefficient, and ultimately PA and PTT performance. The resultant CP NPs have strong PA signals with high photothermal conversion efficiencies and excellent biocompatibility in vitro and in vivo. The CP3 NPs show a high PA signal to background ratio of 47 in U87 tumor-bearing mice, which is superior to other reported PA/PTT theranostic agents. A very small IC50 value of 0.88 μg/mL (CP3 NPs) was obtained for U87 glioma cell ablation under laser irradiation (808 nm, 0.8 W/cm2, 5 min). This study shows that CP NP based theranostic platforms are promising for future personalized nanomedicine.

A series of D–A′–π–A type photosensitizers, AP3 and AP4, were designed and synthesized to show strong aggregation-induced far red and near infrared emission and very effective 1O2 generation simultaneously. In comparison with the most widely used photosensitizer, Ce6 nanoparticles, AP4 nanoparticles showed over 10-fold higher fluorescence quantum yield, and more than 3-fold higher 1O2 generation efficiency, and have been successfully used for image-guided photodynamic anticancer therapy.

Persistent room-temperature phosphorescence (RTP) in pure organic materials has attracted great attention because of their unique optical properties. The design of organic materials with bright red persistent RTP remains challenging. Herein, we report a new design strategy for realizing high brightness and long lifetime of red-emissive RTP molecules, which is based on introducing an alkoxy spacer between the hybrid units in the molecule. The spacer offers easy Br-H bond formation during crystallization, which also facilitates intermolecular electron coupling to favor persistent RTP. As the majority of RTP compounds have to be confined in a rigid environment to quench nonradiative relaxation pathways for bright phosphorescence emission, nanocrystallization is used to not only rigidify the molecules but also offer the desirable size and water-dispersity for biomedical applications.

A signal amplified fluorogenic ELISA based on self-clickable fluorogens with aggregation-induced emission characteristics (AIEgen) as a substrate was developed for ultrasensitive immunoassay.

The development of red fluorophores with efficient solid-state emission is still challenging. Herein, a red fluorophore 1 with aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics is rationally designed and facilely synthesized by attaching an electron-donor diethylamine and an electron-acceptor maleonitrile group to salicyladazine. In contrast to many red fluorophores which undergo serious aggregation-caused quenching (ACQ), compound 1 emits bright red fluorescence (λem = 650 nm, ΦF = 24.3%) in the solid state with a large Stokes shift of 174 nm. Interestingly, control compounds 2 and 3, which have similar structures as 1, exhibit obvious aggregation-caused quenching (ACQ) characteristics. The difference in the crystal structures of 1, 2, and 3 reveals that the interplanar spacing among molecules plays a decisive role in realizing the AIE characteristics of 1. Moreover, when the hydroxyl group of 1 was substituted by an esterase reactive acetoxyl, a fluorescence light-up probe 4 was developed for sensing of esterase based on the selective reaction between 4 and esterase to generate the AIE and ESIPT active molecule 1. The linear range for in vitro quantification of esterase is 0.01–0.15 U/mL with a detection limit of 0.005 U/mL. Probe 4 was also successfully applied to image esterase in mitochondria of living cells.

Photodynamic therapy (PDT), which relies on photosensitizers (PS) and light to generate reactive oxygen species to kill cancer cells or bacteria, has attracted much attention in recent years. PSs with both bright emission and efficient singlet oxygen generation have also been used for image-guided PDT. However, simultaneously achieving effective 1 O2 generation, long wavelength absorption, and stable near-infrared (NIR) emission with low dark toxicity in a single PS remains challenging. In addition, it is well known that when traditional PSs are made into nanoparticles, they encounter quenched fluorescence and reduced 1 O2 production. In this contribution, these challenging issues have been successfully addressed through designing the first photostable photosensitizer with aggregation-induced NIR emission and very effective 1 O2 generation in aggregate state. The yielded nanoparticles show very effective 1 O2 generation, bright NIR fluorescence centered at 820 nm, excellent photostability, good biocompatibility, and negligible dark in vivo toxicity. Both in vitro and in vivo experiments prove that the nanoparticles are excellent candidates for image-guided photodynamic anticancer therapy.

Long-term tracking of bone marrow stromal cells in a rat photothrombotic ischemia model is achieved by organic nanoparticles with aggregation-induced emission. On page 6576, L.-D. Liao, B. Liu, and co-workers demonstrate the design and synthesis of the nanoparticles to realize low phototoxicity and high stability. These nanoparticles show promising potential for monitoring the transplanted stem cells in cell therapy.