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Highlights: The single-atom Cu species with S = 0 spin ground state in CuIII-HHTP have been fabricated. The CuIII-HHTP exhibits remarkable performance with a high urea yield of 7.780 mmol h−1 g−1 with the corresponding Faradaic efficiency of 23.09% at − 0.6 V (vs. RHE). Low spin state and empty ( d x 2 -y 2 0 ) orbitals are favorable to enhance the production urea of C–N coupling process. The catalytic activities are generally believed to be relevant to the electronic states of their active center, but understanding this relationship is usually difficult. Here, we design two types of catalysts for electrocatalytic urea via a coordination strategy in a metal–organic frameworks: CuIII-HHTP and CuII-HHTP. CuIII-HHTP exhibits an improved urea production rate of 7.78 mmol h−1 g−1 and an enhanced Faradaic efficiency of 23.09% at − 0.6 V vs. reversible hydrogen electrode, in sharp contrast to CuII-HHTP. Isolated CuIII species with S = 0 spin ground state are demonstrated as the active center in CuIII-HHTP, different from CuII with S = 1/2 in CuII-HHTP. We further demonstrate that isolated CuIII with an empty d x 2 -y 2 0 orbital in CuIII-HHTP experiences a single-electron migration path with a lower energy barrier in the C–N coupling process, while CuII with a single-spin state ( d x 2 -y 2 1 ) in CuII-HHTP undergoes a two-electron migration pathway. [ABSTRACT FROM AUTHOR]

Circularly polarized (CP) electroluminescence from organic light-emitting diodes (OLEDs) has aroused considerable attention for their potential in future display and photonic technologies. The development of CP-OLEDs relies largely on chiral-emitters, which not only remain rare owing to difficulties in design and synthesis but also limit the performance of electroluminescence. When the polarization (pseudospin) degrees of freedom of a photon interact with its orbital angular momentum, photonic spin-orbit interaction (SOI) emerges such as Rashba-Dresselhaus (RD) effect. Here, we demonstrate a chiral-emitter-free microcavity CP-OLED with a high dissymmetry factor (gEL) and high luminance by embedding a thin two-dimensional organic single crystal (2D-OSC) between two silver layers which serve as two metallic mirrors forming a microcavity and meanwhile also as two electrodes in an OLED architecture. In the presence of the RD effect, the SOIs in the birefringent 2D-OSC microcavity result in a controllable spin-splitting with CP dispersions. Thanks to the high emission efficiency and high carrier mobility of the OSC, chiral-emitter-free CP-OLEDs have been demonstrated exhibiting a high gEL of 1.1 and a maximum luminance of about 60000 cd/m2, which places our device among the best performing CP-OLEDs. This strategy opens an avenue for practical applications towards on-chip microcavity CP-OLEDs. Nanoscale circularly polarized light sources are an important building block for future integrated photonics. Here the authors demonstrate circularly polarized light emission from a thin organic single crystal light-emitting diode. [ABSTRACT FROM AUTHOR]

Exciton–polariton Bose–Einstein condensation (EP BEC) is of crucial importance for the development of coherent light sources and optical logic elements, as it creates a new state of matter with coherent nature and nonlinear behaviors. The demand for room temperature EP BEC has driven the development of organic polaritons because of the large binding energies of Frenkel excitons in organic materials. However, the reliance on external high-finesse microcavities for organic EP BEC results in poor compactness and integrability of devices, which restricts their practical applications in on-chip integration. Here, we demonstrate room temperature EP BEC in organic single-crystal microribbon natural cavities. The regularly shaped microribbons serve as waveguide Fabry–Pérot microcavities, in which efficient strong coupling between Frenkel excitons and photons leads to the generation of EPs at room temperature. The large exciton–photon coupling strength due to high exciton densities facilitates the achievement of EP BEC. Taking advantages of interactions in EP condensates and dimension confinement effects, we demonstrate the realization of controllable output of coherent light from the microribbons. We hope that the results will provide a useful enlightenment for using organic single crystals to construct miniaturized polaritonic devices. The use of room temperature exciton–polariton Bose–Einstein condensation is limited by the need for external high-finesse microcavities. The authors generate room temperature EPs with single-crystal microribbons as waveguide Fabry–Pérot microcavities, and demonstrate controllable output of coherent light. [ABSTRACT FROM AUTHOR]

Optical activity, also called circular birefringence, is known for two hundred years, but its applications for topological photonics remain unexplored. Unlike the Faraday effect, the optical activity provokes rotation of the linear polarization of light without magnetic effects, thus preserving the time-reversal symmetry. In this work, we report a direct measurement of the Berry curvature and quantum metric of the photonic modes of a planar cavity, containing a birefringent organic microcrystal (perylene) and exhibiting emergent optical activity. This experiment, performed at room temperature and at visible wavelength, establishes the potential of organic materials for implementing non-magnetic and low-cost topological photonic devices. Most work in topological photonics is performed in periodically structured systems. Here, the authors directly measure the nontrivial Berry curvature of the photonic modes of a birefringent continuous organic system exhibiting emergent optical activity. [ABSTRACT FROM AUTHOR]

Photon upconversion in lanthanide-doped upconversion nanoparticles offers a wide variety of applications including deep-tissue biophotonics. However, the upconversion luminescence and efficiency, especially involving multiple photons, is still limited by the concentration quenching effect. Here, we demonstrate a multilayered core-shell-shell structure for lanthanide doped NaYF4, where Er3+ activators and Yb3+ sensitizers are spatially separated, which can enhance the multiphoton emission from Er3+ by 100-fold compared with the multiphoton emission from canonical core-shell nanocrystals. This difference is due to the excitation energy transfer at the interface between activator core and sensitizer shell being unexpectedly efficient, as revealed by the structural and temperature dependence of the multiphoton upconversion luminescence. Therefore, the concentration quenching is suppressed via alleviation of cross-relaxation between the activator and the sensitizer, resulting in a high quantum yield of up to 6.34% for this layered structure. These findings will enable versatile design of multiphoton upconverting nanoparticles overcoming the conventional limitation. Photon upconversion in nanoparticles is often limited by concentration quenching. The authors present a multi-layered particle approach that enables increased upconversion efficiency by reducing cross-relaxation, through spatial separation of activator and sensitizer. [ABSTRACT FROM AUTHOR]

Host−guest interactions are of central importance in many biological and chemical processes. However, the investigation of the formation and decomplexation of host−guest systems at the single-molecule level has been a challenging task. Here we show that the single-molecule conductance of organoplatinum(II) metallocycle hosts can be enhanced by an order of magnitude by the incorporation of a C60 guest molecule. Mechanically stretching the metallocycle-C60 junction with a scanning tunneling microscopy break junction technique causes the release of the C60 guest from the metallocycle, and consequently the conductance switches back to the free-host level. Metallocycle hosts with different shapes and cavity sizes show different degrees of flexibility to accommodate the C60 guest in response to mechanical stretching. DFT calculations provide further insights into the electronic structures and charge transport properties of the molecular junctions based on metallocycles and the metallocycle-C60 complexes. Studying the single-molecule behavior of host-guest complexes can provide fundamental insights into their supramolecular interactions. Here, the authors use the scanning tunneling microscopy break junction technique to show that encapsulation of a C60 molecule significantly enhances the conductance of an organoplatinum metallocycle; mechanical stretching of the junction releases the guest, returning the conductance to free-host level. [ABSTRACT FROM AUTHOR]

Laser displays, which exploit characteristic advantages of lasers, represent a promising next-generation display technology based on the ultimate visual experience they provide. However, the inability to obtain pixelated laser arrays as self-emissive full-color panels hinders the application of laser displays in the flat-panel sector. Due to their excellent optoelectronic properties and processability, organic materials have great potential for the production of periodically patterned multi-color microlaser arrays. Here, we demonstrate for the first time full-color laser displays on precisely patterned organic red-green-blue (RGB) microlaser matrices through inkjet printing. Individual RGB laser pixels are realized by doping respective luminescent dyes into the ink materials, resulting in a wide achievable color gamut 45% larger than the standard RGB space. Using as-prepared microlaser arrays as full-color panels, we achieve dynamic laser displays for video playing through consecutive beam scanning. These results represent a major step towards full-color laser displays with outstanding color expression. In the next generation of display technology for portable devices, lasers could replace LEDs to achieve more vibrant colours. Here, Zhao et al. demonstrate a dynamic full-color display in which each pixel is made up of three printed organic microlasers to cover the RGB space. [ABSTRACT FROM AUTHOR]