Halogen-bonding boosting the high performance X-ray imaging of organic scintillators.

Organic scintillators with efficient X-ray excited luminescence are essential for medical diagnostics and security screening. However, achieving excellent organic scintillation materials is challenging due to low X-ray absorption coefficients and inferior radioluminescence (RL) intensity. Herein, supramolecular interactions are incorporated, particularly halogen bonding, into organic scintillators to enhance their radioluminescence properties. By introducing heavy atoms (X = Cl, Br, I) into 9,10-bis(4-pyridyl)anthracene (BPA), the formation of halogen bonding (BPA-X) enhances their X-ray absorption coefficient and restricts the molecular vibration and rotation, which boosts their RL intensity. The RL intensity of BPA-Cl and BPA-Br fluorochromes increased by over 2 and 6.3 times compared to BPA, respectively. Especially, BPA-Br exhibits an ultrafast decay time of 8.25 ns and low detection limits of 25.95 ± 2.49 nGy s-1. The flexible film constructed with BPA-Br exhibited excellent X-ray imaging capabilities. Furthermore, this approach is also applicable to organic phosphors. The formation of halogen bonding in bromophenyl-methylpyridinium iodide (PYI) led to a fourfold increase in RL intensity compared to bromophenyl-methyl-pyridinium (PY). It suggests that halogen bonding serves as a promising and effective molecular design strategy for the development of high-performance organic scintillator materials, presenting new opportunities for their applications in radiology and security screening.

Mechanochemical Synthesis of Cuprous Complexes for X-ray Scintillation and Imaging.

Cuprous complex scintillators show promise for X-ray detection with abundant raw materials, diverse luminescent mechanisms, and adjustable structures. However, their synthesis typically requires a significant amount of organic solvents, which conflict with green chemistry principles. Herein, we present the synthesis of two high-performance cuprous complex scintillators using a simple mechanochemical method for the first time, namely [CuI(PPh3)2R] (R = 4-phenylpyridine hydroiodide (PH, Cu-1) and 4-(4-bromophenyl)pyridine hydroiodide (PH-Br, Cu-2). Both materials demonstrated remarkable scintillation performances, exhibiting radioluminescence (RL) intensities 1.52 times (Cu-1) and 2.52 times (Cu-2) greater than those of Bi4Ge3O12 (BGO), respectively. Compared to Cu-1, the enhanced RL performance of Cu-2 can be ascribed to its elevated quantum yield of 51.54%, significantly surpassing that of Cu-1 at 37.75%. This excellent luminescent performance is derived from the introduction of PH-Br, providing a more diverse array of intermolecular interactions that effectively constrain molecular vibration and rotation, further suppressing the nonradiative transition process. Furthermore, Cu-2 powder can be prepared into scintillator film with excellent X-ray imaging capabilities. This work establishes a pathway for the rapid, eco-friendly, and cost-effective synthesis of high-performance cuprous complex scintillators.

Novel Semiconductive Ternary Hybrid Heterostructures for Artificial Optoelectronic Synapses.

Synaptic devices that mimic biological synapses are considered as promising candidates for brain-inspired devices, offering the functionalities in neuromorphic computing. However, modulation of emerging optoelectronic synaptic devices has rarely been reported. Herein, a semiconductive ternary hybrid heterostructure is prepared with a D-D'-A configuration by introducing polyoxometalate (POM) as an additional electroactive donor (D') into a metalloviologen-based D-A framework. The obtained material features an unprecedented porous 8-connected bcu-net that accommodates nanoscale [α-SiW12 O40 ]4- counterions, displaying uncommon optoelectronic responses. Besides, the fabricated synaptic device based on this material can achieve dual-modulation of synaptic plasticity due to the synergetic effect of electron reservoir POM and photoinduced electron transfer. And it can successfully simulate learning and memory processes similar to those in biological systems. The result provides a facile and effective strategy to customize multi-modality artificial synapses in the field of crystal engineering, which opens a new direction for developing high-performance neuromorphic devices.

Naphthalenediimide/Iodobismuthate Hybrid Heterostructures: Water Resistance and Long-Lived Charge-Separated States.

Organic-inorganic hybrid iodobismuthate perovskites have become promising semiconductive materials for their environmentally friendly and light-harvesting characteristics. However, their low-dimensional bismuth-iodide skeletons result in poor charge-separation efficiency, limiting their application in optoelectronic devices. To address this issue, the donor-acceptor (D-A) heterostructures have been introduced to the iodobismuthate hybrid materials by incorporating an electron-deficient N,N'-bis(4-aminoethyl)-1,4,5,8-naphthalene diimide (NDIEA) as the electron acceptor and organic counterpart. Five naphthalenediimide/iodobismuthate hybrid heterostructures, named (H2NDIEA)1.5·Bi2I9·3DMF (1), H2NDIEA·[Bi2I8(DMF)2]·2DMF (2), (H2NDIEA)2·Bi4I16·2H2O·4MeOH (3), (H2NDIEA)2·Bi4I16·8H2O (4), and [(H2NDIEA)2·Bi6I22]n·4nH2O (5) (DMF = N,N-dimethylformamide), were synthesized. Their crystal structures, water stabilities, charge-separated behaviors, and electrical properties have been studied through experimental and computational investigations. The results revealed that hybrids 3-5 exhibited high water resistance attributed to their tightly packed structures and robust H-bonds between solvent molecules and organic-inorganic supramolecular frameworks. Density functional theory calculations confirmed characteristic type-IIa band alignments of all the five hybrids, facilitating to the photoinduced charge separation. Moreover, the closer contact caused by the strong anion-π interactions between electron donors and acceptors in hybrid 5 leads to the long-lived charge-separated states and improved electrical properties compared to the other hybrids.

Three Semiconductive 1D Naphthalene Diimide/Iodoplumbate Perovskites with High Moisture Tolerance and Long-Lived Charge Separation States.

Low-dimensional inorganic-organic hybrid perovskites with high moisture tolerance and long-lived charge separation states have captured significant attention in the field of optoelectronic devices. To further achieve the relationship between crystal structures and stability, as well as charge separation behaviors, three one-dimensional hybrid perovskites containing electron-deficient naphthalene diimide ammonium (NDIEA) and electron-rich iodoplumbate chains, [(H2NDIEA)Pb2I6]·2DMF (1), [(H2NDIEA)2Pb5I14·(DMF)2]·4DMF (2), and [(HNDIEA)2Pb2I6]·3H2O (3), were synthesized. Crystal structure determinations revealed various synthesis conditions leading to different stacking modes, especially the inorganic lead iodide fraction, which resulted in different water resistances and charge-separated behaviors. The comprehensive analysis found that strong intermolecular interactions (anion-π interactions and π-π interactions), and matching energy levels between protonated NDIEA and iodoplumbate chains, can facilitate the generation of long-lived charge separation states and extraordinary moisture stability, even in the water environment. In addition, the conductivity behavior of 3 was also explored in detail.

Donor-Acceptor Hybrid Heterostructures: An Emerging Class of Photoactive Materials with Inorganic and Organic Semiconductive Components.

Just as the heterojunctions in physics, donor-acceptor (D-A) heterostructures are an emerging class of photoactive materials fabricated from two semiconductive components at the molecular level. Among them, D-A hybrid heterostructures from organic and inorganic semiconductive components have attracted extensive attention in the past decades due to their combined advantages of high stability for the inorganic semiconductors and modifiability for the organic semiconductors, which are particularly beneficial to efficiently achieve photoinduced charge separation and transfer upon irradiations. In this review, by analogy with the heterojunctions in physics, a definition of the D-A heterostructures and their general design and synthetic strategies are given. Meanwhile, the D-A hybrid heterostructures are focused on and their recent advances in potential applications of photochromism, photomodulated luminescence, and photocatalysis summarized.

A Three-Component Donor-Acceptor Hybrid Framework with Low-Power X-ray-Induced Photochromism.

Donor-acceptor (D-A) hybrid frameworks with visual X-ray photochromism at room temperature are fascinating because of their promising applications as X-ray detectors. Herein, a 3-fold interpenetrated D-A hybrid framework, [Eu(bcbp)1.5(DMF)(H2O)2][Co(CN)6]·4H2O·CH3OH (1), has been obtained by incorporating electron-rich Co(CN)63- into the electron-deficient europium viologen framework, which interestingly exhibits ultraviolet and low-power X-ray dual photochromism with a remarkable color change from brown to green. Experimental and theoretical studies revealed that the X-ray photochromic behavior of hybrid 1 could be attributed to its D-A hybrid structural feature increasing the extent of photoinduced electron transfer and thus photogenerated radical species upon X-ray irradiation. Meanwhile, due to the introduction of emissive lanthanide cations in the D-A system, hybrid 1 exhibits photomodulated luminescence properties.

Photochromic Polyoxometalate/Perylenediimide Donor-Acceptor Hybrid Crystals with Interesting Luminescent Properties.

The self-assembly of electron-deficient protonated N, N'-dipyridyltetrachloroperylenediimide (4Cl-DPPDI) and electron-rich polyoxometalate acids HnXM12O40 (POMs; X = P or Si; M = W or Mo) resulted in four isomorphous donor-acceptor hybrid crystals 1-4 with segregated POM anions and one-dimensional racemic hydrogen-bonded 4Cl-DPPDI networks as electron-donor and -acceptor components, respectively. Because of the compact contacts between the POM anions and 4Cl-DPPDI tectons induced by anion-π interactions, besides enhanced photochromism, these four unique isostructural hybrids exhibited unusual room-temperature phosphorescence (RTP) emissions. More interestingly, owing to the facial compact contacts of two racemic 4Cl-DPPDI tectons induced by lone pair-π-assisted π-π interactions, they also showed unprecedented photon upconversion by triplet-triplet annihilation (TTA).

Intramolecular Energy and Solvent-Dependent Chirality Transfer within a BINOL-Perylene Hetero-Cyclophane.

Multichromophoric macrocycles and cyclophanes are important supramolecular architectures for the elucidation of interchromophoric interactions originating from precise spatial organization. Herein, by combining an axially chiral binaphthol bisimide (BBI) and a bay-substituted conformationally labile twisted perylene bisimide (PBI) within a cyclophane of well-defined geometry, we report a chiral PBI hetero-cyclophane (BBI-PBI) that shows intramolecular energy and solvent-regulated chirality transfer from the BBI to the PBI subunit. Excellent spectral overlap and spatial arrangement of BBI and PBI lead to efficient excitation energy transfer and subsequent PBI emission with high quantum yield (80-98 %) in various solvents. In contrast, chirality transfer is strongly dependent on the respective solvent as revealed by circular dichroism (CD) spectroscopy. The combination of energy and chirality transfer affords a bright red circularly polarized luminescence (CPL) from the PBI chromophore by excitation of BBI.

Enantioselective Recognition of Helicenes by a Tailored Chiral Benzo[ghi]perylene Trisimide π-Scaffold.

Enantioselective molecular recognition of chiral molecules that lack specific interaction sites for hydrogen bonding or Lewis acid-base interactions remains challenging. Here we introduce the concept of tailored chiral π-surfaces toward the maximization of shape complementarity. As we demonstrate for helicenes it is indeed possible by pure van-der-Waals interactions (π-π interactions and CH-π interactions) to accomplish enantioselective binding. This is shown for a novel benzo[ghi]perylene trisimide (BPTI) receptor whose π-scaffold is contorted into a chiral plane by functionalization with 1,1'-bi-2-naphthol (BINOL). Complexation experiments of enantiopure (P)-BPTI with (P)- and (M)-[6]helicene afforded binding constants of 10 700 M-1 and 550 M-1 , respectively, thereby demonstrating the pronounced enantiodifferentiation by the homochiral π-scaffold of the BPTI host. The enantioselective recognition is even observable by the naked eye due to a specific exciplex-type emission originating from the interacting homochiral π-scaffolds of electron-rich [6]helicene and electron-poor BPTI.

Photochromic and Room Temperature Phosphorescent Donor-Acceptor Hybrid Crystals Regulated by Core-Substituted Naphthalenediimides.

Donor-acceptor (D-A) hybrid crystals are an emerging kind of crystalline hybrid material composed of semiconductive inorganic donors and organic acceptors. Except for the intrinsic photochromism, recently we have reported that the anion-π polyoxometalate (POM)/naphthalenediimide (NDI) hybrid crystals could produce an interesting room temperature phosphorescence (RTP) quantum yield up to 7.2%. Herein, we extended into core-substituted NDIs and anticipated the regulation of their photochromic and RTP properties. Thus, two hybrid crystals, namely (H4BDMPy-Br2NDI)·(NMP)4·(HPW12O40) (1) and (H4BDMPy-I2NDI)·(HPW12O40) (2) (H2BDMPy-Br2NDI: N,N'-bis(3,5-dimethylpyrazolyl)-2,6-dibromo-1,4,5,8-naphthalenediimide and H2BDMPy-I2NDI: N,N'-bis(3,5-dimethylpyrazolyl)-2,6-diiodide-1,4,5,8-naphthalenediimide), have been synthesized from phosphotungstic anions (PW12O403-) and Br or I core-substituted NDIs. Compared to the core-unsubstituted analogues (H4BDMPy-NDI)·(NMP)4·(HPW12O40) (3), 2 with photosensitive iodine substituents is more sensitive to light, which can become discolored under natural light. As a result of the heavy-atom effect, hybrid 1 exhibits remarkable RTP with the quantum yield up to 10.2% and a lifetime of 1.14 ms.

Donor-Acceptor Conjugated Heptazine Polymers with Highly Efficient Photocatalytic Degradations towards Tetracyclines.

Photocatalysis is an efficient and green technology in the environmental protection. Due to the high charge separation and transfer, donor-acceptor (D-A) conjugated polymers attract much attention for their photocatalytic degradations towards organic pollutants. Herein, the authors reported three novel D-A conjugated polymers, named as HPBP, HPTP, and HPF, with heptazine moieties as electron acceptors, while biphenyl, terphenyl, or fluorene moieties as electron donors, respectively, which indeed exhibit a highly efficient photocatalytic degradation towards tetracyclines upon the visible-light irradiation. Among them, the photocatalytic performance of HPF is especially noticeable with the degradation rate up to 87% within 30 min, almost 11 times in comparison to those of pristine g-C3 N4 , which is mainly attributed to its high crystallinity and conjugation. For their photocatalytic mechanism, the •O2 - radical anions are regarded as the active species.

Stable Bifunctional Perylene Imide Radicals for High-Performance Organic-Lithium Redox-Flow Batteries.

The search for high-performance organic redox-active materials for non-aqueous redox-flow batteries remains a key challenge. Organic radicals and aromatic imides are two promising classes of redox-active materials with complementary advantages, such as the specific capacity, operating voltage, and stability, etc. Herein, this work reports two stable bifunctional radicals synthesized by the C-C coupling of redox-active phenoxyl radicals and perylene diimides (PDIs, 1. ) or benzo[ghi]perylene triimides (BPTIs, 2. ). The incorporation of electron-deficient PDIs or BPTIs into phenoxyl radicals is desired, to not only increase the number of redox-active groups per molecule and, thus, improve their specific capacities, but also to increase the redox potential and the stability of the phenoxyl radicals and, thus, enhances their battery voltages and cycle lives. When serving as the redox-active species in the catholyte of a non-aqueous static redox-flow battery, both radicals 1. and 2. exhibited a cooperatively enhanced performance with an unprecedented initial discharge voltage up to 3.12 V versus Li+ /Li, which is the hitherto most presentable potential for imide- and radical-based energy storage materials in redox-flow batteries.

Molecular Engineering of Perylene Imides for High-Performance Lithium Batteries: Diels-Alder Extension and Chiral Dimerization.

The search for high-performance electrode materials in organic rechargeable batteries remains a key challenge. Reported herein is a molecular structural modification of perylene imides, a promising class of redox-active electrode materials, for improved battery performance. The Diels-Alder extension of perylene imides at the lateral position led to the simultaneous incorporation of two electron-withdrawing carbonyl groups and extension of the π system, which is supposed to favor high specific capacity, operating voltage, and electronic conductivity. After the chiral dimerization of the extended species with 1,2-diaminocyclohexane, it was anticipated that the porosity and coulombic interactions with lithium ions would be promoted, which would be beneficial for fast reaction kinetics and long cycling life. As expected, in lithium batteries, the obtained chiral and π-extended tweezer, which features six imide groups and a porous solid-state network of 42.2 % accessible cell volume, was found to deliver a reversible capacity of 92.1 mA h g-1 at a charge/discharge rate of 1 C within an operating voltage window of 1.60-2.80 V versus Li+ /Li, around 75 and 50 % of which was maintained after 100 and 300 galvanostatic cycles, respectively, much better than those of unmodified species.

Encapsulating Naphthalene in an Electron-Deficient MOF to Enhance Fluorescence for Organic Amines Sensing.

Host-guest encapsulation of electron-rich naphthalene molecules into a weakly emissive porous metal-organic framework based on π-electron-deficient (π-acidic) naphthalene diimide tectons leads to orange-emissive crystals, which can be used to sense strongly basic organic amines in a fast response, high photostability, and tunable sensitivity. Moreover, such host-guest inclusion crystals are also a good photochromic probe for the detection of weakly basic N-methyl-2-pyrrolidone and N,N-dimethylformamide molecules.

Perylene Bisimide Radicals and Biradicals: Synthesis and Molecular Properties.

Unprecedented neutral perylene-3,4:9,10-tetracarboxylic acid bisimide (PBI) radicals and biradicals were synthesized by facile chemical oxidation of 4-hydroxyaryl-substituted PBIs. Subsequent characterization by optical and magnetic spectroscopic techniques, as well as quantum chemical calculations, revealed an open-shell singlet biradical ground state for the PBI biradical OS-2(..) (〈s(2)〉=1.2191) with a relatively small singlet-triplet energy gap of 0.041 eV and a large singlet biradical character of y=0.72.

Two-dimensional J-resolved LASER and semi-LASER spectroscopy of human brain.

PURPOSE: Two-dimensional J-resolved localized and semi-localized by adiabatic selective refocusing (LASER and semi-LASER) spectroscopy, named "J-resolved LASER" and "J-resolved semi-LASER", were introduced to suppress chemical shift artifacts, additional J-refocused artifactual peaks from spatially dependent J-coupling evolution, and sensitivity to radiofrequency (RF) field inhomogeneity. METHODS: Three pairs of adiabatic pulses were employed for voxel localization in J-resolved LASER and two pairs in J-resolved semi-LASER. The first half of t1 period was inserted between the last pair of adiabatic pulses, which was proposed in this work to obtain two-dimensional adiabatic J-resolved spectra of human brain for the first time. Phantom and human experiments were performed to demonstrate their feasibility and advantages over conventional J-resolved spectroscopy (JPRESS). RESULTS: Compared to JPRESS, J-resolved LASER or J-resolved semi-LASER exhibited significant suppression of chemical shift artifacts and additional J-refocused peaks from spatially dependent J-coupling evolution, and demonstrated insensitivity to the change of RF frequency offset over large bandwidth. CONCLUSION: Experiments on phantoms and human brains verified the feasibility and strengths of two-dimensional adiabatic J-resolved spectroscopy at 3T. This technique is expected to advance the application of in vivo two-dimensional MR spectroscopy at 3T and higher field strengths for more reliable and accurate quantification of metabolites.

Two-dimensional semi-LASER correlation spectroscopy with well-maintained cross peaks.

PURPOSE: To demonstrate that the limited bandwidth of the second 90° radiofrequency (RF) pulse in two-dimensional (2D) localized correlation spectroscopy (L-COSY) induces spatially dependent magnetization transfer that results in attenuated cross-peaks, and to propose a new 2D semi-adiabatically localized COSY sequence to solve this problem. METHODS AND THEORY: A semi-localization by adiabatic selective refocusing (semi-LASER or sLASER) method was incorporated into the COSY sequence with the slice-selective first 90° RF pulse and the non-slice-selective second 90° RF pulse to form a new 2D sLASER localized COSY sequence, named "sLASER-first-COSY," to solve the problem of spatially dependent magnetization transfer. Experiments were performed to verify the feasibility and advantages of sLASER-first-COSY sequence over a recently reported other sLASER COSY sequence with a slice-selective second 90° RF pulse, named "sLASER-last-COSY". RESULTS: Phantom, ex vivo, and in vivo human brain experiments demonstrated that sLASER-first-COSY yielded stronger cross peaks and higher ratios of cross peak volumes to diagonal peak volumes than sLASER-last-COSY. CONCLUSION: As COSY relies on the cross peaks to obtain larger dispersion of peaks for quantification, the new sLASER-first-COSY sequence yielding well-maintained cross peaks will facilitate more reliable and accurate quantification of metabolites with coupled spin systems.

Polyoxometalate/s-triazine hybrid heterostructures with ultrafast photochromic properties.

As an emerging class of hybrid complexes, donor-acceptor (D-A) hybrid heterostructures, which combine the advantages of both organic and inorganic photoactive components, provide excellent platforms for the fabrication of photochromic materials with enhanced photo-responsive performances. Herein, four novel hybrid heterostructures, namely H3TPT·(PW12O40)·2NMP (1), (H1.5TPT)2·(PW12O40) (2), (H3TPT)2·(SiW12O40)·2Cl·2MeCN (3), and H3TPT·(HPMo12O40)·Cl·3NMP (4) (TPT is tri(4-pyridyl)-s-triazine, NMP is N-methylpyrrolidone), have been synthesized and characterized. Benefitting from the strong interactions (anion-π interactions) and matching electron energy levels between the donors and acceptors, some of them exhibited ultrafast photochromic behaviour even up to 1 second. Furthermore, based on experimental and theoretical calculations, the plausible PIET process and structure-activity relationship have been discussed in detail.

Radial magnetic resonance image reconstruction with a deep unrolled projected fast iterative soft-thresholding network.

Radially sampling of magnetic resonance imaging (MRI) is an effective way to accelerate the imaging. How to preserve the image details in reconstruction is always challenging. In this work, a deep unrolled neural network is designed to emulate the iterative sparse image reconstruction process of a projected fast soft-threshold algorithm (pFISTA). The proposed method, an unrolled pFISTA network for Deep Radial MRI (pFISTA-DR), include the preprocessing module to refine coil sensitivity maps and initial reconstructed image, the learnable convolution filters to extract image feature maps, and adaptive threshold to robustly remove image artifacts. Experimental results show that, among the compared methods, pFISTA-DR provides the best reconstruction and achieved the highest PSNR, the highest SSIM and the lowest reconstruction errors.