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Using phosphotungstic acid, tetraethyl ethylenebisphosphonate (L) and rare earth chloride as raw materials, a series of Keggin-type POM-based rare earth complexes were synthesized by a heating and stirring method: [LnL3(H2O)]PW12O40·CH3CN (1–6) (Ln = Dy, Ho, Er, Tm, Yb, Lu). The molecular structures of the complexes were determined by X-ray single-crystal diffraction, and the influence of weak forces on the molecular packing structures were studied by calculating the presence of hydrogen bonds inside the complexes using PLATON. By analyzing the experimental results, it is concluded that tetraethyl ethylenebisphosphonate is coordinated with rare earth ions through bidentate chelation, and POMs which are not involved in coordination exist as anions. Complexes 1–6 are three-dimensional supramolecular structures constructed by hydrogen bonds. Powder X-ray diffraction proved that the structures of the synthesized complexes are consistent with the results of single-crystal analysis, and the purity is high. Thermogravimetric analysis showed that the series of complexes have good thermal stability above 200 °C. Notably, the complexes 1–6 showed good photocatalytic degradation ability to methyl orange (MO) solution under UV irradiation; their degradation rate reached more than 95% within 15 min. The membrane material of complex 1 was successfully prepared by combining complex 1 with polyvinylidene fluoride (PVDF). Scanning electron microscopy (SEM) showed that complex 1 was supported on the surface of the PVDF film. For photocatalytic degradation of MO solution, the MO degradation rate reached 97.4% within 50 min. Compared with the powder-type catalyst, the degradation efficiency is lower, but the membrane material catalysis solves the problem of catalyst recovery and has better recyclable performance. Using the method of adding different active species scavengers, the mechanism of the photocatalytic reaction was studied. Finally, terahertz time-domain spectroscopy (THz-TDS) was performed, which provided a spectroscopic basis for the rapid detection of the weak forces contained in the complexes. [ABSTRACT FROM AUTHOR]

Organic donor–acceptor (D–A) cocrystals have recently attracted widespread attention owing to the synergetic electron donor–acceptor blending properties via non-covalent interactions, becoming good candidate materials for optoelectronic applications. However, the rational design and selection of donor/acceptor components in organic cocrystals with the desired morphology, size, and function remains a key synthetic objective. As the single components possess inherent individual properties, including optical, electronic, and crystalline lattice features, co-crystalline engineering is a powerful but challenging strategy for obtaining new materials with combined physical and chemical properties. In this review, we mainly focus on the organic donor acceptor cocrystal molecular design, synthetic approaches, and their photophysical and photochemical properties as well as optical function application devices. Finally, an outlook is provided for the future development of organic D–A cocrystals toward next-generation organic crystal materials. [ABSTRACT FROM AUTHOR]

Geometrically well-defined microcrystals with polymorphic tailorability are in high demand for multi-directional photon flow at the microscale. Herein, diphenylamine (DPA) substituted 5,6,12,13-tetraazaperopyrene c-TAPP-DPA is synthesized and explored as a versatile fluorophore to fabricate polymorphic microcrystals for photonic applications. The flexibly twisted and electron rich DPA groups are verified as a crucial structure element to tune the intermolecular interactions and packing modes of c-TAPP-DPA, resulting in three kinds of crystals, including microrods, and rhomboid and hexagonal microplates. These microcrystals display geometry-dependent fluorescence properties and 1D or 2D waveguide properties with low optical loss. Impressively, the micro-rhomboids show a unique 2D asymmetric waveguide character. Our work enriches the diversity of polymorphic microcrystals, and sheds more light on the structure–property relationship of organic crystals for multi-directional optical waveguide applications. [ABSTRACT FROM AUTHOR]

Organic homostructures with tunable physiochemical properties were fabricated by simply changing the isomer molecules via the "cocrystal engineering" approach. The morphology of the cocrystals can be changed into rod-like or branched, with superior waveguide and multi-directional waveguide performance, respectively, which contributes to the realization of optical waveguide modules with integrated functions. [ABSTRACT FROM AUTHOR]

A suitable energy level system of organic laser gain material is vital for the realization of organic solid-state lasers (OSSLs). In this work, it is experimentally demonstrated that the excited state intramolecular proton transfer (ESIPT) occurred within ∼1.4 ps in the singlet excited state (S1*) of the organic dye 1,5-dihydroxyanthraquinone (1,5-DHAQ). An optimized energy level system is thereby constructed via the ESIPT process for efficient optical gain, and a deep red laser emission at ∼672 nm with a low threshold of 0.39 μJ is achieved based on the self-assembled square microdisks of 1,5-DHAQ, which simultaneously function as the high quality (Q ∼ 2033) whispering-gallery mode (WGM) cavity and efficient laser gain medium. Our work realizes the efficient WGM OSSL with a favored energy level system based on the ESIPT process, providing insight into the ESIPT lasing mechanism. The results would ultimately contribute to the development of organic coherent light sources. [ABSTRACT FROM AUTHOR]

The self-assembled organic microspheres of (E)-3-(4-(dip-tolylamino)phenyl)-1-(4-fluoro-2-hydroxyphenyl)prop-2-en-1-one (DTPHP) are fabricated, which serve as active WGM resonators. In addition, a dispersion relationship between the group refractive index (ng) and wavelength (λ) is revealed to demonstrate the strong light–matter interaction inside the WGM microcavity with a maximum ng to be 7.7. [ABSTRACT FROM AUTHOR]

Using a facile solution-evaporation method, we controllably fabricated DPEpe–F4DIB single-crystalline microrods and microtubes by tuning the solvent-system. Due to the thin tubular wall acting as an annular cavity, the organic microtubes demonstrated a lower optical loss of 0.0145 dB μm−1, and are promising building blocks for various optoelectronic devices. [ABSTRACT FROM AUTHOR]

Organic molecules of DIDB can inherently assemble into fluorescent green-emissive microwires with a low photoluminescence quantum efficiency (PLQY) of 1.0%. Impressively, by doping DIDB into the nonluminous 4-iodobenzonitrile crystal matrix with a molar ratio of 1 : 100, phosphorescent yellow-emissive microwires with a much higher PLQY of 50.5% are obtained. [ABSTRACT FROM AUTHOR]

Through a facile solid-state mechanochemical method, we have prepared WO3 nanobelts with a length of ∼80 nm and a width of ∼10 nm, which were doped into PEDOT:PSS as a hybrid hole-injecting layer (HIL) for conventional red quantum dot light-emitting diodes (QLEDs). The work function (WF) of the hybrid HIL was enhanced from 4.91 to 5.25 eV and the hole-injecting barrier was decreased from 0.89 to 0.55 eV. Notably, an optimal red QLED based on the hybrid HIL PEDOT:PSS:WO3 (4.0 wt%) achieved a satisfactory reduction in the driving voltage at the luminance of 100 cd A−1 from 5.18 V (pristine PEDOT:PSS) to 2.97 V. Moreover, the optimal device exhibits a maximal current efficiency of 15.5 cd A−1 and a high external quantum efficiency (EQE) of 10.60%, which are nearly two-folds higher than those (8.0 cd A−1 and 5.82%) of the reference device based on pristine PEDOT:PSS. It was demonstrated that doping these as-prepared WO3 nanobelts into the PEDOT:PSS could be an effective route toward high-performance QLEDs. [ABSTRACT FROM AUTHOR]

Organic nano/microcrystals with desirable optical/electrical properties and a regular morphology are extensively applied in various optoelectronic devices at the microscale, but the morphology/luminescence-modulation of organic microstructures remains to be a great challenge. Herein, we utilize a protonation/de-protonation process to simultaneously modulate both the luminescence and the morphology of blue-emissive two-dimensional (2D) organic microcrystals, which are self-assembled from 1,4-bis((E)-2-(3-methylpyridin-4-yl)vinyl)benzene (MSP) by a facile solution-exchange method. Impressively, 1D color-tunable MSP·nHCl (n is an integer) organic microwires can be obtained by the protonation process activated by the addition of an acid (such as hydrochloric acid). When n = 2 or n ＞ 2, these obtained MSP·2HCl or MSP·nHCl microcrystals with a 1D wire-morphology emitted yellow light and red light, respectively. [ABSTRACT FROM AUTHOR]

For the purpose of fabricating solution-processed quantum-dot light-emitting diodes (QLEDs) with high performance, the efficient hole–electron recombination at low current density is particularly pivotal. Herein, to enhance the charge balance of the QLED device, we employed lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI) as a p-type dopant into the hole-transporting material (HTM) of poly(9-vinlycarbazole) (PVK). In the experiment, the increased conductivity and the enhanced charge mobility of the Li-TFSI-doped PVK layer were confirmed by the J–V curves of the hole-only devices and conductive atomic force microscopy (c-AFM). Furthermore, on combining ultraviolet photoelectron spectroscopy (UPS) and the absorption spectra, it was found that the highest occupied molecular orbital (HOMO) of the Li-TFSI-doped PVK layers gradually shifted closer to the Fermi level upon increasing the doping ratios from 0 to 4.5 wt%. Therefore, the hole-injecting barrier decreases from 1.17 eV to 0.64 eV. As a result, the maximum current efficiency and the highest external quantum efficiency (EQE) of our fabricated QLED devices can reach as high as 15.5 cd A−1 and 11.46%, respectively. It was demonstrated that the p-type dopant Li-TFSI in the HTM can contribute to the fabrication of high-performance solution-processed light-emitting diodes. [ABSTRACT FROM AUTHOR]

Small organic dyes with large two-photon absorption (TPA) cross sections ( δ ) are more desirable in many applications compared with large molecules. Herein, we proposed a facile theoretical method for the fast screening of small organic molecules as potential TPA dyes. This method is based on a theoretical analysis to the natural transition orbitals (NTOs) directly associated with the TPA transition. Experimental results on the small indolic squaraine dyes (ISD) confirmed that their TPA cross sections is strongly correlated to the delocalization degree of the NTOs of the S 2 excited states. Aided by this simple and intuitive method, we have successfully designed and synthesized a small indolic squaraine dye (ISD) with a remarkable δ value above 8000 GM at 780 nm. The ISD dye also exhibits a high singlet oxygen generation quantum yield about 0.90. The rationally designed TPA dye was successfully applied in both two-photon excited fluorescence cell imaging and in vivo cerebrovascular blood fluid tracing.