Design and synthesis of broadband absorption covalent organic framework for efficient artificial photocatalytic amine coupling.

Developing highly active materials that efficiently utilize solar spectra is crucial for photocatalysis, but still remains a challenge. Here, we report a new donor-acceptor (D-A) covalent organic framework (COF) with a wide absorption range from 200 nm to 900 nm (ultraviolet-visible-near infrared light). We find that the thiophene functional group is accurately introduced into the electron acceptor units of TpDPP-Py (TpDPP: 5,5'-(2,5-bis(2-ethylhexyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo [3,4-c]pyrrole-1,4-diyl)bis(thiophene-2-carbaldehyde), Py: 1,3,6,8-tetrakis(4-aminophenyl)pyrene) COFs not only significantly extends its spectral absorption capacity but also endows them with two-photon and three-photon absorption effects, greatly enhancing the utilization rate of sunlight. The selective coupling of benzylamine as the target reactant is used to assess the photocatalytic activity of TpDPP-Py COFs, showing high photocatalytic conversion of 99% and selectivity of 98% in 20 min. Additionally, the TpDPP-Py COFs also exhibit the universality of photocatalytic selective coupling of other imine derivatives with ~100% conversion efficiency. Overall, this work brings a significant strategy for developing COFs with a wide absorption range to enhance photocatalytic activity.

Biomimetic nanocluster photoreceptors for adaptative circular polarization vision.

Nanoclusters with atomically precise structures and discrete energy levels are considered as nanoscale semiconductors for artificial intelligence. However, nanocluster electronic engineering and optoelectronic behavior have remained obscure and unexplored. Hence, we create nanocluster photoreceptors inspired by mantis shrimp visual systems to satisfy the needs of compact but multi-task vision hardware and explore the photo-induced electronic transport. Wafer-scale arrayed photoreceptors are constructed by a nanocluster-conjugated molecule heterostructure. Nanoclusters perform as an in-sensor charge reservoir to tune the conductance levels of artificial photoreceptors by a light valve mechanism. A ligand-assisted charge transfer process takes place at nanocluster interface and it features an integration of spectral-dependent visual adaptation and circular polarization recognition. This approach is further employed for developing concisely structured, multi-task, and compact artificial visual systems and provides valuable guidelines for nanocluster neuromorphic devices.

A Self-Assembled 3D Penetrating Nanonetwork for High-Performance Intrinsically Stretchable Polymer Light-Emitting Diodes.

The emergence of wearable technology can significantly benefit from electronic displays fabricated using intrinsically stretchable (is-) materials. Typically, an improvement in the stretchability of conventional light-emitting polymers is accompanied by a decrease in charge transportability, thus resulting in a significant decrease in device efficiency. In this study, a self-assembled 3D penetrating nanonetwork is developed to achieve increased stretchability and mobility simultaneously, based on high-molecular-weight phenylenevinylene (L-SY-PPV) and polyacrylonitrile (PAN). The mobility of L-SY-PPV/PAN increases by 5-6 times and the stretchability increases from 20% (pristine L-SY-PPV film) to 100%. A high current efficiency (CE) of 8.13 cd A-1 is observed in polymer light-emitting diodes (PLEDs) fabricated using 40% stretched L-SY-PPV/PAN. Furthermore, using a polyethyleneimine ethoxylated (PEIE), an 1,10-phenanthroline monohydrate (pBphen), and a reduced Triton X-100 (TR) chelated Zn-based is- electron-injection layer of Zn-PEIE-pBphen-TR, an is-PLED is realized with a turn-on voltage of 6.5 V and a high CE of 2.35 cd A-1 . These results demonstrate the effectiveness of using the self-assembled 3D penetrating nanonetwork for the fabrication of is-PLEDs.

Tunable Planar Focusing Based on Hyperbolic Phonon Polaritons in α-MoO3.

Manipulation of the propagation and energy-transport characteristics of subwavelength infrared (IR) light fields is critical for the application of nanophotonic devices in photocatalysis, biosensing, and thermal management. In this context, metamaterials are useful composite materials, although traditional metal-based structures are constrained by their weak mid-IR response, while their associated capabilities for optical propagation and focusing are limited by the size of attainable artificial optical structures and the poor performance of the available active means of control. Herein, a tunable planar focusing device operating in the mid-IR region is reported by exploiting highly oriented in-plane hyperbolic phonon polaritons in α-MoO3 . Specifically, an unprecedented change of effective focal length of polariton waves from 0.7 to 7.4 µm is demonstrated by the following three different means of control: the dimension of the device, the employed light frequency, and engineering of phonon-plasmon hybridization. The high confinement characteristics of phonon polaritons in α-MoO3 permit the focal length and focal spot size to be reduced to 1/15 and 1/33 of the incident wavelength, respectively. In particular, the anisotropic phonon polaritons supported in α-MoO3 are combined with tunable surface-plasmon polaritons in graphene to realize in situ and dynamical control of the focusing performance, thus paving the way for phonon-polariton-based planar nanophotonic applications.

Doping-driven topological polaritons in graphene/α-MoO3 heterostructures.

Control over charge carrier density provides an efficient way to trigger phase transitions and modulate the optoelectronic properties of materials. This approach can also be used to induce topological transitions in the optical response of photonic systems. Here we report a topological transition in the isofrequency dispersion contours of hybrid polaritons supported by a two-dimensional heterostructure consisting of graphene and α-phase molybdenum trioxide. By chemically changing the doping level of graphene, we observed that the topology of polariton isofrequency surfaces transforms from open to closed shapes as a result of doping-dependent polariton hybridization. Moreover, when the substrate was changed, the dispersion contour became dominated by flat profiles at the topological transition, thus supporting tunable diffractionless polariton propagation and providing local control over the optical contour topology. We achieved subwavelength focusing of polaritons down to 4.8% of the free-space light wavelength by using a 1.5-µm-wide silica substrate as an in-plane lens. Our findings could lead to on-chip applications in nanoimaging, optical sensing and manipulation of energy transfer at the nanoscale.

Multifunctional Theranostic Agent of Cu2(OH)PO4 Quantum Dots for Photoacoustic Image-Guided Photothermal/Photodynamic Combination Cancer Therapy.

Image-guided phototherapy is considered to be a prospective technique for cancer treatment because it can provide both oncotherapy and bioimaging, thus achieving an optimized therapeutic efficacy and higher treatment accuracy. Compared to complicated systems with multiple components, using a single material for this multifunctional purpose is preferable. In this work, we strategically fabricated poly(acrylic acid)- (PAA-) coated Cu2(OH)PO4 quantum dots [denoted as Cu2(OH)PO4@PAA QDs], which exhibit a strong near-infrared photoabsorption ability. As a result, an excellent photothermal conversion ability and the photoactivated formation of reactive oxygen species could be realized upon NIR irradiation, concurrently meeting the basic requirements for photothermal and photodynamic therapies. Moreover, phototherapeutic investigations on both cervical cancer cells in vitro and solid tumors of an in vivo mice model illustrated the effective antitumor effects of Cu2(OH)PO4@PAA upon 1064-nm laser irradiation, with no detectable lesions in major organs during treatment. Meanwhile, Cu2(OH)PO4@PAA is also an exogenous contrast for photoacoustic tomography (PAT) imaging to depict tumors under NIR irradiation. In brief, the Cu2(OH)PO4@PAA QDs prepared in this work are expected to serve as a multifunctional theranostic platform.

MoO3-x quantum dots for photoacoustic imaging guided photothermal/photodynamic cancer treatment.

A theranostic system of image-guided phototherapy is considered as a potential technique for cancer treatment because of the ability to integrate diagnostics and therapies together, thus enhancing accuracy and visualization during the treatment. In this work, we realized photoacoustic (PA) imaging-guided photothermal (PT)/photodynamic (PD) combined cancer treatment just via a single material, MoO3-x quantum dots (QDs). Due to their strong NIR harvesting ability, MoO3-x QDs can convert incident light into hyperthermia and sensitize the formation of singlet oxygen synchronously as evidenced by in vitro assay, hence, they can behave as both PT and PD agents effectively and act as a "dual-punch" to cancer cells. In a further study, elimination of solid tumors from HeLa-tumor bearing mice could be achieved in a MoO3-x QD mediated phototherapeutic group without obvious lesions to the major organs. In addition, the desired PT effect also makes MoO3-x QDs an exogenous PA contrast agent for in vivo live-imaging to depict tumors. Compared with previously reported theranostic systems that put several components into one system, our multifunctional agent of MoO3-x QDs is exempt from unpredictable mutual interference between components and ease of leakage of virtual components from the composited system.