Article-Journal

In article number 1800766, Hairong Zheng, Bin Liu, and co-workers develop aggregation-induced-emission (AIE) dots with super-bright NIR-II emission and strong photoacoustic characteristics for clear visualization of brain tumors. The dual-modal AIE dots hold great promise for intraoperative image-guided surgery.

Photodynamic therapy (PDT) employs accumulation of photosensitizers (PSs) in malignant tumor tissue followed by the light-induced generation of cytotoxic reactive oxygen species to kill the tumor cells. The success of PDT depends on optimal PS dosage that is matched with the ideal power of light. This in turn depends on PS accumulation in target tissue and light administration time and period. As theranostic nanomedicine is driven by multifunctional therapeutics that aim to achieve targeted tissue delivery and image-guided therapy, fluorescent PS nanoparticle (NP) accumulation in target tissues can be ascertained through fluorescence imaging to optimize the light dose and administration parameters. In this regard, zebrafish larvae provide a unique transparent in vivo platform to monitor fluorescent PS bio-distribution and their therapeutic efficiency. Using fluorescent PS NPs with unique aggregation-induced emission characteristics, we demonstrate for the first time the real-time visualization of polymeric NP accumulation in tumor tissue and, more importantly, the best time to conduct PDT using transgenic zebrafish larvae with inducible liver hyperplasia as an example.

Precise diagnostics are of significant importance to the optimal treatment outcomes of patients bearing brain tumors. NIR-II fluorescence imaging holds great promise for brain-tumor diagnostics with deep penetration and high sensitivity. This requires the development of organic NIR-II fluorescent agents with high quantum yield (QY), which is difficult to achieve. Herein, the design and synthesis of a new NIR-II fluorescent molecule with aggregation-induced-emission (AIE) characteristics is reported for orthotopic brain-tumor imaging. Encapsulation of the molecule in a polymer matrix yields AIE dots showing a very high QY of 6.2% with a large absorptivity of 10.2 L g−1 cm−1 at 740 nm and an emission maximum near 1000 nm. Further decoration of the AIE dots with c-RGD yields targeted AIE dots, which afford specific and selective tumor uptake, with a high signal/background ratio of 4.4 and resolution up to 38 µm. The large NIR absorptivity of the AIE dots facilitates NIR-I photoacoustic imaging with intrinsically deeper penetration than NIR-II fluorescence imaging and, more importantly, precise tumor-depth detection through intact scalp and skull. This research demonstrates the promise of NIR-II AIE molecules and their dots in dual NIR-II fluorescence and NIR-I photoacoustic imaging for precise brain cancer diagnostics.

A new second near-infrared (NIR II) conjugated polymer (CP) was designed and synthesized. The CP nanoparticles have good biocompatibility, excellent photostability and high imaging contrast, and have been successfully used to demonstrate the first example of NIR II photoacoustic imaging of orthotopic brain tumors. In comparison with existing contrast agents for photoacoustic imaging, the NIR II CP nanoparticles showed more efficient skull penetration and a much higher signal/background ratio using a 1064 nm laser.

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.