Publications

Physics and Chemistry of Two-Dimensional Triangulene-Based Lattices

Hongde Yu, Yu Jing, Thomas Heine. Accounts of Chemical Research, 2025, 58(1), 61-72.

Prediction of Metal-Free Stoner and Mott-Hubbard Magnetism in Triangulene-Based Two-Dimensional Polymers

Hongde Yu, Thomas Heine. Science Advances, 2024, 10(40), eadq7954.

We predicted, for the first time, the emergence of Stoner-ferromagnetic half-metals, as well as antiferromagnetic Mott-Hubbard insulators in metal-free 2D polymers.

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Magnetic Coupling Control in Triangulene Dimers

Hongde Yu, Thomas Heine. Journal of the American Chemical Society, 2023, 145(35), 19303-19311.

We present an effective approach to control the magnetic couplings in triangulene dimers. We investigated 24 triangulene dimers and achieved unprecedented strong J values up to -144 meV. Many of our predictions have been experimentally verified. We show the first example of ferromagnetic triangulene dimers that is beyond Lieb's theorem's predictive power.

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Predicting Magnetic Coupling and Spin-Polarization Energy in Triangulene Analogues

Hongde Yu, Jianwei Sun, Thomas Heine. Journal of Chemical Theory and Computation, 2023, 19(12), 3486–3497.

We developed a benchmark dataset comprising 25 magnetic systems with nonlocal spin densities, including triangulene monomers, dimers, and their analogues. This work highlighted the importance of the choice of DFT functional.

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Suppressing the Excitonic Effect in Covalent Organic Frameworks for Metal-Free Hydrogen Generation

Hongde Yu, Dong Wang. JACS Au, 2022, 2(8), 1848–1856.

Abstract Photocatalytic hydrogen generation is a promising solution for renewable energy production and plays a role in achieving carbon neutrality. Covalent organic frameworks (COFs) with highly designable backbones and inherent pores have emerged as novel photocatalysts, yet the strong excitonic effect in COFs can impede the promotion of energy conversion efficiency. Here, we propose a facile approach to suppress the excitonic effect in COFs, which is by narrowing the band gap and increasing the dielectric screening via a rational backbone design and chemical modifications. Based on the GW-BSE method, we uncover a linear relationship between the electronic dielectric constant and the inverse square of the optical band gap of COFs of the Lieb lattice. We further demonstrate that both reduced exciton binding energy and enhanced sunlight absorption can be simultaneously realized in COFs with a narrow band gap. Specifically, we show that one of our designed COFs whose exciton binding energy is nearly half that of g-C3N4 is capable of metal-free hydrogen production under near-infrared light irradiation. Our results showcase an effective method to suppress the excitonic effect in COFs and also pave the way for their applications in photocatalytic, photovoltaic, and other related solar energy conversions.

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Metal-Free Magnetism in Chemically Doped Covalent Organic Frameworks

Hongde Yu, Dong Wang. Journal of the American Chemical Society, 2020, 142(25), 11013–11021.

Abstract Organic and molecule-based magnets are not easily attainable, as introduction of stable paramagnetic centers to pure organic systems is particularly challenging. Crystalline covalent organic frameworks (COFs) with high designability and chemical diversity constitute ideal platforms to access intriguing magnetic phenomena of organic materials. In this work, we proposed a general approach to attain unpaired electron spin and metal-free magnetism in narrow-band COFs by chemical doping. By using density functional theory calculations, we found that dopants with energy-matched frontier orbitals to COFs not only inject charges but also further localize them through orbital hybridization and the formation of a supramolecular charge-transfer complex. The localized electronic states ensure that stable paramagnetic centers can be introduced to nonmagnetic COFs. On the basis of these discoveries, we designed two new COFs with narrow valence bands, which show prospective magnetism after doping with iodine. Further, we unraveled the magnetic anisotropy in two-dimensional COFs and demonstrated that both spin-conduction and magnetic interactions can be effectively modulated by manipulating the building blocks of COFs. Our work highlights a practical route to attain magnetism in COFs and other organic materials, which show great potential for applications in organic spintronic devices.

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cis-C═C Bond and Amide Regulated Oriented Supramolecular Assembly on Two-Dimensional Atomic Crystals

Hongde Yu^#, Jinghui Wang^#, Liying Jiao, Dong Wang. The Journal of Physical Chemistry C, 2019, 123(51), 30996-31002.

Abstract The precise control of the molecular position and orientation of its nanoscale assembly on atomic crystals is pivotal for fabricating hybrid organic/inorganic van der Waals heterostructures with targeted functionalities. Recently, we observed the assembly of oleamide into nanoribbons, orienting exclusively along a crystallographic direction on a variety of atomic crystals. Motivated by this observation, we designed a series of long-chain alkanes, alkenes, and their derivatives with −OH, −COOH, and −CONH2 terminal groups to unveil how chemical units regulate the orientation of suparamolecular assembly by density functional theory calculations. We found that the cis-C═C bond can increase the rigidity of long alkyl chains, tailoring angles and van der Waals interactions between them, while the −CONH2 group facilitates intermolecular hydrogen bonds. Either of these two moieties is required for the oriented assembly on both hexagonal and orthorhombic atomic lattices. We predicted that nanoribbons formed by long-chain cis-alkene and derivatives orient along the zigzag direction on graphene and 32° deflected from the armchair direction on black phosphorene, which were supported by the experiment. The fundamental understandings toward the chemical group regulated intermolecular interactions, and their interplay in the oriented supramolecular assembly is expected to substantially expedite the design and controlled synthesis of organic/inorganic van der Waals heterostructures using the bottom-up method.

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Chemical Doping of Organic and Coordination Polymers for Thermoelectric and Spintronic Applications: A Theoretical Understanding

Dong Wang, Hongde Yu, Wen Shi, Chunlin Xu. Accounts of Chemical Research, 2023, 56(16): 2127-2138.

Abstract The controlled doping of organic semiconductors (OSCs) is crucial not only for improving the performance of electronic and optoelectronic devices but also for enabling efficient thermoelectric conversion and spintronic applications. The mechanism of doping for OSCs is fundamentally different from that of their inorganic counterparts. In particular, the interplay between dopants and host materials is complicated considering the low dielectric constant, strong lattice-charge interaction, and flexible nature of materials. Recent experimental breakthroughs in the molecular design of dopants and the precise doping with high spatial resolution call for more profound understandings as to how the dopant interacts with the charge introduced to OSCs and how the admixture of dopants alters the electronic properties of host materials before one can exploit controllable doping to realize desired functionalities.

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A Thiophene Backbone Enables Two-Dimensional Poly(arylene vinylene)s with High Charge Carrier Mobility

Yamei Liu^#, Heng Zhang^#, Hongde Yu^#, Zhongquan Liao, Silvia Paasch, Shunqi Xu, Ruyan Zhao, Eike Brunner, Mischa Bonn, Hai I. Wang, Thomas Heine, Mingchao Wang, Yiyong Mai, Xinliang Feng. Angewandte Chemie International Edition, 2023, 62(35), e202305978.

Abstract Linear conjugated polymers have attracted significant attention in organic electronics in recent decades. However, despite intrachain π-delocalization, interchain hopping is their transport bottleneck. In contrast, two-dimensional (2D) conjugated polymers, as represented by 2D π-conjugated covalent organic frameworks (2D c-COFs), can provide multiple conjugated strands to enhance the delocalization of charge carriers in space. Herein, we demonstrate the first example of thiophene-based 2D poly(arylene vinylene)s (PAVs, 2DPAV-BDT-BT and 2DPAV-BDT-BP, BDT=benzodithiophene, BT=bithiophene, BP=biphenyl) via Knoevenagel polycondensation. Compared with 2DPAV-BDT-BP, the fully thiophene-based 2DPAV-BDT-BT exhibits enhanced planarity and π-delocalization with a small band gap (1.62 eV) and large electronic band dispersion, as revealed by the optical absorption and density functional calculations. Remarkably, temperature-dependent terahertz spectroscopy discloses a unique band-like transport and outstanding room-temperature charge mobility for 2DPAV-BDT-BT (65 cm2 V−1 s−1), which far exceeds that of the linear PAVs, 2DPAV-BDT-BP, and the reported 2D c-COFs in the powder form. This work highlights the great potential of thiophene-based 2D PAVs as candidates for high-performance opto-electronics.

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Temperature-Responsive Self-Assembly of Single Polyoxometalates Clusters Driven by Hydrogen Bonds

Qingda Liu^#, Hongde Yu^#, Qinghua Zhang, Dong Wang, Xun Wang. Advanced Functional Materials, 2021, 31(30), 2103561.

Abstract Smart materials that can respond to external stimuli are typically prepared through the coating of specific responsive ligands. Herein, for the first time, thermally reconfigurable single polyoxometalate (POM) cluster assemblies without temperature-responsive surfactants are reported. Based on transmission electron microscopy observation, POM clusters are obtained to arrange into a 2D single cluster superlattice at 25 °C, and transform themselves into a single cluster nanowire below 0 °C, which is caused by the switching of hydrogen bond linkage between clusters. Contributed by the specific coordinative state, the POM assembly exhibits excellent catalytic activity and stability toward olefin epoxidation at room temperature, demonstrating the application potentials of the nanostructures based on single clusters.

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Visible-light-switched electron transfer over single porphyrin-metal atom center for highly selective electroreduction of carbon dioxide

Deren Yang^#, Hongde Yu^#, Ting He, Shouwei Zuo, Xiaozhi Liu, Haozhou Yang, Bing Ni, Haoyi Li, Lin Gu, Dong Wang, Xun Wang. Nature Communications, 2019, 10(1), 3844.

Abstract External fields are introduced to catalytic processes to improve catalytic activities. The light field effect plays an important role in electrocatalytic processes, but is not fully understood. Here we report a series of photo-coupled electrocatalysts for CO2 reduction by mimicking the structure of chlorophyll. The porphyrin-Au catalyst exhibits a high turnover frequency of 37,069 h−1 at −1.1 V and CO Faradaic efficiency (FE) of 94.2% at −0.9 V. Under visible light, the electrocatalyst reaches similar turnover frequency and FE with potential reduced by ~ 130 mV. Interestingly, the light-induced positive shifts of 20, 100, and 130 mV for porphyrin-Co, porphyrin-Cu, and porphyrin-Au electrocatalysts are consistent with their energy gaps of 0, 1.5, and 1.7 eV, respectively, suggesting the porphyrin not only serves as a ligand but also as a photoswitch to regulate electron transfer pathway to the metal center.

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Single molecule–mediated assembly of polyoxometalate single-cluster rings and their three-dimensional superstructures

Qingda Liu^#, Peilei He^#, Hongde Yu^#, Lin Gu, Bing Ni, Dong Wang, Xun Wang. Science Advances, 2019, 5(7), eaax1081.

Abstract The assembly of atomically precise clusters into superstructures has tremendous potential in structural tunability and applications. Here, we report a series of single-cluster nanowires, single-cluster nanorings, and three-dimensional superstructure assemblies built by POM clusters. By stepwise tuning of interactions at molecular levels, the configurations can be varied from single-cluster nanowires to nanorings. A series of single-cluster nanostructures in different configurations can be achieved with up to 15 kinds of POM clusters. The single-cluster nanowires and three-dimensional superstructures perform enhanced activity in the catalytic and electrochemical sensing fields, illustrating the universal functionality of single-cluster assemblies.

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Probing the crystallographic orientation of two-dimensional atomic crystals with supramolecular self-assembly

Jinghui Wang^#, Hongde Yu^#, Xu Zhou, Xiaozhi Liu, Renjie Zhang, Zhixing Lu, Jingying Zheng, Lin Gu, Kaihui Liu, Dong Wang, Liying Jiao. Nature Communications, 2017, 8(1), 377.

Abstract Probing the crystallographic orientation of two-dimensional (2D) materials is essential to understand and engineer their properties. However, the nondestructive identification of the lattice orientations of various 2D materials remains a challenge due to their very thin nature. Here, we identify the crystallographic structures of various 2D atomic crystals using molecules as probes by utilizing orientation-dependent molecule–substrate interactions. We discover that the periodic atomic packing of 2D materials guides oleamide molecules to assemble into quasi-one-dimensional nanoribbons with specific alignments which precisely indicate the lattice orientations of the underlying materials. Using oleamide molecules as probes, we successfully identify the crystallographic orientations of ~12 different 2D materials without degrading their intrinsic properties. Our findings allow for the nondestructive identification of the lattice structure of various 2D atomic crystals and shed light on the functionalization of these 2D materials with supramolecular assembly.

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Laser-Driven Modular Precision Chemistry of Graphene Using λ3-Iodanes

Kevin Gerein, Diyan Unmu Dzujah, Hongde Yu, Frank Hauke, Thomas Heine, Andreas Hirsch, Tao Wei. Angewandte Chemie International Edition, 2024, 63(50), e202414090.

Abstract The emerging laser writing represents an efficient and promising strategy for covalent two dimensional (2D)-patterning of graphene yet remains a challenging task due to the lack of applicable reagents. Here, we report a versatile approach for covalent laser patterning of graphene using a family of trivalent organic iodine compounds as effective reagents, allowing for the engraving of a library of functionalities onto the graphene surface. The relatively weak iodine-centered bonds within these compounds can readily undergo laser-induced cleavage to in situ generate radicals localized to the irradiated regions for graphene binding, thus completing the covalent 2D-structuring of this 2D-film. The tailor-made attachment of distinct functional moieties with varying electrical properties as well as their thermally reversible binding manner enables programming the surface properties of graphene. With this delicate strategy the bottleneck of a limited scope of functional groups patterned onto the graphene surface upon laser writing is tackled.

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Increasing the Accessibility of Internal Catalytic Sites in Covalent Organic Frameworks by Introducing a Bicontinuous Mesostructure

Yamei Liu, Qin Zhou, Hongde Yu, Qiqi Yang, Mingchao Wang, Chuanhui Huang, Luoxing Xiang, Chen Li, Thomas Heine, Guoqing Hu, Shengyao Wang, Xinliang Feng, Yiyong Mai. Angewandte Chemie International Edition, 2024, 136(15), e202400985.

Abstract Introducing continuous mesochannels into covalent organic frameworks (COFs) to increase the accessibility of their inner active sites has remained a major challenge. Here, we report the synthesis of COFs with an ordered bicontinuous mesostructure, via a block copolymer self-assembly-guided nanocasting strategy. Three different mesostructured COFs are synthesized, including two covalent triazine frameworks and one vinylene-linked COF. The new materials are endowed with a hierarchical meso/microporous architecture, in which the mesochannels exhibit an ordered shifted double diamond (SDD) topology. The hierarchically porous structure can enable efficient hole-electron separation and smooth mass transport to the deep internal of the COFs and consequently high accessibility of their active catalytic sites. Benefiting from this hierarchical structure, these COFs exhibit excellent performance in visible-light-driven catalytic NO removal with a high conversion percentage of up to 51.4 %, placing them one of the top reported NO-elimination photocatalysts. This study represents the first case of introducing a bicontinuous structure into COFs, which opens a new avenue for the synthesis of hierarchically porous COFs and for increasing the utilization degree of their internal active sites.

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Linkage-engineered donor–acceptor covalent organic frameworks for optimal photosynthesis of hydrogen peroxide from water and air

Ruoyang Liu, Yongzhi Chen, Hongde Yu, Miroslav Položij, Yuanyuan Guo, Tze Chien Sum, Thomas Heine, Donglin Jiang. Nature Catalysis, 2024, 7, 195-206.

Abstract Charge transfer and mass transport to catalytic sites are critical factors in photocatalysis. However, achieving both simultaneously is challenging due to inherent trade-offs and interdependencies. Here we develop a microporous covalent organic framework featuring dense donor–acceptor lattices with engineered linkages. The donor–acceptor columnar π-arrays function as charge supply chains and as abundant water oxidation and oxygen reduction centres, while the one-dimensional microporous channels lined with rationally integrated oxygen atoms function as aligned conduits for instant water and oxygen delivery to the catalytic sites. This porous catalyst promotes photosynthesis with water and air to produce H2O2, combining a high production rate, efficiency and turnover frequency. This framework operates under visible light without the need of metal co-catalysts and sacrificial reagents, exhibits an apparent quantum efficiency of 17.5% at 420 nm in batch reactors and enables continuous, stable and clean H2O2 production in flow reactors.

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A thienyl-benzodithiophene-based two-dimensional conjugated covalent organic framework for fast photothermal conversion

Yamei Liu, Mingchao Wang, Changlin Dong, Hongde Yu, Yang Lu, Xing Huang, Silvia Paasch, Eike Brunner, Thomas Heine, Fang Song, Florian Auras, Fugui Xu, Yiyong Mai, Xinliang Feng. Journal of Polymer Science, 2023, 61(16), 1843-1848.

Abstract Two-dimensional conjugated covalent organic frameworks (2D c-COFs) are emerging semiconductor materials for optoelectronic and photothermal applications. In particular, the highly tailorable, semiconducting thiophene-based 2D c-COFs have attracted considerable interest due to their nontrivial physicochemical properties such as photo-activity, broad optical absorption, tunable electronic structures, and so forth. Herein, we demonstrate a novel, crystalline 2D c-COF based on thienyl-functionalized benzodithiophene (BDT) and biphenyl (BP) via the Schiff-base polycondensation reaction. The resultant BDT-BP-COF exhibits a broad optical absorption up to ca. 600 nm and decent π-conjugation along the 2D polymer skeleton, as revealed by the optical absorption and theoretical calculations. The favorable π-conjugation and the abundant electron-rich thiophene units confer excellent photo-activity to BDT-BP-COF towards the usage of solar energy. As a proof-of-concept application, we explore BDT-BP-COF in photothermal conversion, in which it shows a fast surface-temperature increase upon light irradiation for seconds.

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Hydrogen Bonding-Induced Morphology Dependence of Long-Lived Organic Room-Temperature Phosphorescence: A Computational Study

Huili Ma, Hongde Yu, Qian Peng, Zhongfu An, Dong Wang, Zhigang Shuai. The Journal of Physical Chemistry Letters, 2019, 10(21), 6948-6954.

Abstract Organic room-temperature phosphorescence (RTP) is generally only exhibited in aggregate with strong dependence on morphology, which is highly sensitive to the intermolecular hydrogen bonding interaction. Here, 4,4′-bis(9H-carbazol-9-yl)methanone (Cz2BP), emitting RTP in a cocrystal consisting of chloroform but not in the amorphous nor in the crystal phase, was investigated to disclose the morphology dependence through molecular dynamics simulations and first-principles calculations. We find that the strong intermolecular C═O···H–C hydrogen bonds between Cz2BP and chloroform in cocrystals decrease the nonradiative decay rate of T1 → S0 by 3–6 orders of magnitude due to the vibronic decoupling effect on the C═O stretching motion and the increase of (π,π*) composition in the T1 state. The former is responsible for high efficiency and the latter for long-lived RTP with a calculated lifetime of 208 ms (exp. 353 ms). Nevertheless, the weak hydrogen bonds cannot cause any appreciable RTP in amorphous and crystal phases. This novel understanding opens a way to design organic RTP materials.

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Layer-Dependent Chemically Induced Phase Transition of Two-Dimensional MoS2

Lifei Sun, Xingxu Yan, Jingying Zheng, Hongde Yu, Zhixing Lu, Shang-Peng Gao, Lina Liu, Xiaoqing Pan, Dong Wang, Zhiguo Wang, Peng Wang, Liying Jiao. Nano letters, 18(6), pp.3435-3440.

Abstract Two-dimensional (2D) transition metal dichalcogenides (TMDCs) with layered structures provide a unique platform for exploring the effect of number of layers on their fundamental properties. However, the thickness scaling effect on the chemical properties of these materials remains unexplored. Here, we explored the chemically induced phase transition of 2D molybdenum disulfide (MoS2) from both experimental and theoretical aspects and observed that the critical electron injection concentration and the duration required for the phase transition of 2D MoS2 increased with decreasing number of layers. We further revealed that the observed dependence originated from the layer-dependent density of states of 2H-MoS2, which results in decreasing phase stability for 2H-MoS2 with increasing number of layers upon electron doping. Also, the much larger energy barrier for the phase transition of monolayer MoS2 induces the longer reaction time required for monolayer MoS2 as compared to multilayer MoS2. The layer-dependent phase transition of 2D MoS2 allows for the chemical construction of semiconducting-metallic heterophase junctions and, subsequently, the fabrications of rectifying diodes and all 2D field effect transistors and thus opens a new avenue for building ultrathin electronic devices. In addition, these new findings elucidate how electronic structures affect the chemical properties of 2D TMDCs and, therefore, shed new light on the controllable chemical modulations of these emerging materials.

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