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The hybridization of local and charge transfer excited states is proven to accumulate bright excitons for both optically pumped lasing and electroluminescence at high current density.

Synthesis of single-crystalline micro/nanostructures with curved shapes is essential for developing extraordinary types of optoelectronic devices. Here, we use the strategy of liquid-phase nonconfinement growth to controllably synthesize edge-curved molecular microcrystals on a large scale. By varying the molecular substituents on linear organic conjugated molecules, it is found that the steric hindrance effect could minimize the intrinsic anisotropy of molecular stacking, allowing for the exposure of high-index crystal planes. The growth rate of high-index crystal planes can be further regulated by increasing the molecular supersaturation, which is conducive to the cogrowth of these crystal planes to form continuously curved-shape microcrystals. Assisted by nonrotationally symmetric geometry and optically smooth curvature, edge-curved microcrystals can support low-threshold lasing, and self-focusing directional emission. These results contribute to gaining an insightful understanding of the design and growth of functional molecular crystals and promoting the applications of organic active materials in integrated photonic devices and circuits.

The integration of biological components and artificial devices requires a bio-machine interface that can simultaneously trigger and monitor the activities in biosystems. Herein, we use an organically modified silicate (ormosil) composite coating containing a light-responsive nanocapsule and a fluorescent bioprobe for reactive oxygen species (ROS) to decorate ultrathin optical fibers, namely, ormosil-decorated ultrathin fibers (OD-UFs), and demonstrate that these OD-UFs can optically trigger and monitor the intracellular metabolism activities in living cells. The sizes and shapes of UF tips were finely controlled to match the dimension and mechanical properties of living cells. The increased elasticity of the ormosil coating of OD-UFs reduces possible mechanical damage during the cell membrane penetration. The light-responsive nanocapsule was physically absorbed on the surface of the ormosil coating and could release a stimulant to trigger the metabolism activities in cells upon the guided laser through OD-UFs. The fluorescent bioprobe was covalently linked with the ormosil matrix for monitoring the intracellular ROS generation, which was verified by the

Lenticular printing technique provides a promising way to realize stereoscopic displays, especially, when microscopic optical structures are integrated into light-emitting materials/devices. Here, we fabricated large-area periodic structures with a spatial resolution at a wavelength scale from hybrid perovskite materials via a space-confined solution growth method. It takes advantages of both high refractive index contrast and high luminescence brightness, which allows the optical modulation on not only the reflection of illumination, but also the light emission from hybrid perovskites. The distributed feedback within these periodic structures significantly improves the degree of polarization and directionality of laser actions while their threshold is also reduced. These findings enable us to present a prototype of lenticular printing laser displays that vary emission colors at different view angles, which may find applications in creating high-resolution and high-contrast holographical images.

The generation of reactive oxygen species (ROS) in photodynamic therapy (PDT) involves excited-state intermediates with both singlet and triplet spin configurations, which provides possibilities to modulate the ROS production in PDT under an external magnetic field. Here, we present that magnetically modulated ROS production can promote PDT efficacy and develop a magnetic-field-assisted PDT (magneto-PDT) method for effectively and selectively killing cancer cells. The photosensitization reaction between excited-state riboflavin and oxygen molecules is influenced by the applied field, and the overall magnetic field effect (MFE) shows a moderate increase at a low field (1000 G) and then a boost up to the saturation ∼100% at a high field (1000 G). It is found that the spin precession occurring in radical ion pairs (electron transfer from riboflavin to oxygen) facilitates the O

Organic microlasers hold great potentials in fabricating on-chip sensors for integrated photonic circuits due to their chemical versatility and reactivity. However, chemical vapor detection is still challenging for organic microlaser sensors, as it requires not only optical gain and self-assembly capability, but also rapid response to stimuli and long-term stability under high excitation power. In this work, a new laser dye 4,7-bis(9-octyl-7-(4-(octyloxy)phenyl)-9H-carbazol-2-yl)benzo[c][1,2,5]thiadiazole (BPCBT) is designed and synthesized, which self-assembles into microwires showing strong intramolecular charge transfer (ICT) photoluminescence with >80% quantum efficiency. It enables the lasing from BPCBT microwires under a low threshold of 16 μJ·mm−2·pulse−1 with significantly improved stability over conventional organic microlasers. The stimulated emission amplifies the fluorescence change in the BPCBT microwires under chemical vapors including various acid, acetone, and ethanol vapors, indicating high sensitivity and high selectivity of organic microlaser sensors desirable for compact sensor arrays in integrated photonics. Organic microlaser sensors are highly promising for chemical vapor detection due to their chemical versatility, but their poor stabilities are hampering applications. Here the authors report the synthesis and lasing properties of a dye that is self-assembled into microwires exhibiting a strong acid vapor response and good stability.

Binary organic crystals play critical roles in ambipolar transistors, solar cells, and light-emitting devices. However, these crystals are currently limited to a few planar materials and fixed stoichiometric ratios. Here, a new strategy of binary organic crystals was demonstrated by preparing alloy-like organic single crystals. Binary crystals based on nonplanar 8-hydroxyquinoline metallic complexes were successfully self-assembled through a solution pathway at room temperature. Structural analyses exhibit that the samples are rod-shaped homogeneous mixed crystals. We show that the stoichiometric ratio of the crystals can be arbitrarily adjusted by changing the ratio of the component materials. The charge-transfer (CT) interaction and photophysical properties were also studied. Our strategy of organic crystals may facilitate the development of binary or solid-solution organic crystals with precisely adjusted structures and physical properties.

The solid-to-solid crystallization processes of organic molecules have been poorly understood in view of the complexity and the instability of organic crystals. Here, we studied the crystallization of a π-conjugated small molecular semiconductor, bis-(8-hydroxyquinoline) copper (CuQ2), by annealing the thin films at different temperatures. We observed a classical film-to-nanorods crystallization at 80 °C, a coexistence of classical and nonclassical nucleation and particle growth at 120 °C, and a nonclassical crystal growth at 150 °C. We found that the growth of the crystals followed the following processes: particle nucleation, particle growth, particle migration, nondirectional particle attachment, and structure reconstruction. We notice that the growth of CuQ2 particles follows an outside-to-inside process. More interestingly, our experiments suggest that the submicron CuQ2 particles are able to migrate dozens of micrometers at 150 °C.

The development of room temperature organic magnets is long viewed as great challenge in chemistry, physics, materials science, and spintronics. Here, room temperature ferromagnetic properties of rare earth Sm-doped tris(8-hydroxyquinoline) gallium (GaQ3) molecular thin films prepared by thermally co-evaporating Sm metals and GaQ3 powders were reported. X-ray photoelectron spectrometer, Fourier transform infrared spectroscopy and density functional theory analysis suggest that the doped Sm atom bonds with N atoms on different hydroxyquinoline ligands. The room temperature ferromagnetism is attributed to the extremely large energy difference (594 meV) between the ferromagnetic ground state and the antiferromagnetic state. Furthermore, photoluminescence experiments show that the films emit green light at room temperature. Our experiments may be helpful for the development of molecular ferromagnetic optoelectronic materials for the use of novel multifunctional optoelectronic and spintronic devices.

The construction of “photonic molecules” with controlled sizes and shapes is of particular interest for the integration of miniaturized devices into optoelectronic chips. Here, a general approach is reported that allows the assembly of colloidal microspheres into coupled microcavities with high yield and large scale, utilizing magnetostatic interactions between diamagnetic building blocks dispersed in a ferrofluid under an external field. By precisely designing the local field gradient around diamagnetic microspheres, “virtual templates” can be formed to produce various coupled photonic structures, including diatomic heterogeneous molecules and polyatomic chain molecules. The diatomic structures can modulate the optical resonance modes upon the coherent coupling between microsphere cavities and serve as single-mode wavelength-tunable microlasers. The chain photonic molecules, as coupled resonator optical waveguides, could modulate the light propagation and store photons up to tens of picoseconds. The magnetically controlled assembly method is demonstrated, which provides a promising way for the facile and efficient fabrication of coupled microstructures for fascinating photonic and optoelectronic applications.

Exciplex-based thermally activated delayed fluorescence (TADF) materials show long luminescence lifetimes and high quantum efficiency by converting the non-radiative triplets into the radiative singlets. Here, strong upconverted fluorescence from the amorphous thin films of TADF donor-acceptor (D-A) exciplexes is observed under near-infrared excitation. The spectroscopic studies demonstrate that the enhanced upconversion in exciplex emission combines a series of excited state processes including the two-photon absorption (TPA) of donors and the TADF of D-A pairs. The comparison between donor-only and D-A systems indicates that the upconversion is greatly facilitated by the energy harvesting mechanisms existing in the exciplex-based TADF materials. The results reveal the formation mechanism of exciplex excited-states following the two-photon excitation in D-A blends, and consequently the potentials of exciplex materials in nonlinear optics applications. Moreover, a maximum D-A distance of ~6.9 nm for two-photon excited exciplex formation is obtained.

The solid-to-solid crystallization processes of organic molecules have been poorly understood in view of the complexity and the instability of organic crystals. Here, we studied the crystallization of a π-conjugated small molecular semiconductor, bis-(8-hydroxyquinoline) copper (CuQ2), by annealing the thin films at different temperatures. We observed a classical film-to-nanorods crystallization at 80 °C, a coexistence of classical and nonclassical nucleation and particle growth at 120 °C, and a nonclassical crystal growth at 150 °C. We found that the growth of the crystals followed the following processes: particle nucleation, particle growth, particle migration, nondirectional particle attachment, and structure reconstruction. We notice that the growth of CuQ2 particles follows an outside-to-inside process. More interestingly, our experiments suggest that the submicron CuQ2 particles are able to migrate dozens of micrometers at 150 °C.

High quality single crystals of bis-(8-hydroxyquinoline) zinc (ZnQ2), a π-conjugated molecular semiconductor with high thermal stability, good electron transport ability and excellent electroluminescence properties, were prepared by physical vapor deposition (PVD) method in a double zone tube furnace. X-ray single crystal diffraction (XSCD) indicates that the sample was ZnO2 tetramer, (ZnQ2)4, with the triclinic unit cell parameters: a = 10.8537(15) A, b = 11.8814(16) A, c = 13.0532(18) A, α = 74.119(2)°, β = 73.449(2)°, γ = 70.999(2)°, volume = 1494.9(4) A3 and Z = 1. The crystallization mechanism analysis suggests a classical crystal growth process at low temperatures (300 and 320 °C) and an existence of non-classical particle-attachment crystal growth pathway at high temperature (340 °C). The (ZnQ2)4 crystals also show enhanced photoluminescence (PL) intensities and narrower full width at half maximum (FWHM) compared with that of the ZnQ2 thin film.