arXiv subjects

Jin-Chong Tan

Publications and source records attributed to Jin-Chong Tan.

At least 19 recordsLinked to original sources

arXiv2026

Elucidating Guest-Host Mechanisms in ZIF-L for Tuneable Highly Luminescent 2D Materials

3D metal-organic frameworks (MOFs) are well known effective hosts for luminescent guests that improve tuneability, photostability and material fabricability. 2D guest@MOF systems, while less explored, offer competitive advantages over 3D guest@MOF systems due to their optical transparency, inter-layer spacing, and vertical thinness. This work examines luminescent organic dyes@ZIF-L to establish the underlying mechanisms of guest incorporation in ZIF-L and demonstrate the advantages of the 2D ZIF-L architecture for the material's functional luminescence. Analysing a case study system, fluorescein@ZIF-L (F@ZIF-L), using nanoscale FTIR, diffraction, and topology mapping, confirmed that fluorescein (F) resided in the ZIF-L framework cavities. Supported by surface energy simulations, the extent of guest incorporation was found to be indicated by a morphological continuum, from the characteristic leaf-shaped ZIF-L to rectangular F@ZIF-L. By modifying synthesis temperature and solvent ratios, the luminescent properties of F@ZIF-L could be rationally tuned in terms of guest loading (% mol) and arrangement (i.e. guest monomer to aggregate ratio). When optimised, F@ZIF-L exhibited tuneable emission chromaticity, 99.7% photoluminescent quantum yield, minimal guest leaching in solution over 12 months, and high photostability. Perylene@ZIF-L exhibited unique white light emitting properties, with CIE coordinates (0.33, 0.34) arising from a combination of yellow alpha-phase excimer and blue monomeric perylene emission. Finally, oriented luminescent thin films of guest@ZIF-L materials were grown on malleable Zn foils, demonstrating an in situ fabrication technique. Together, the work highlights the potential for luminescent dye@ZIF-L systems in developing tuneable and resilient luminescent components of next-generation optoelectronics, sensors, and lighting systems.

cond-mat.mtrl-sci↗

arXiv2026

Multimodal and Multiscale Interrogation of a Mechanically Tough Glass Forming Copper-Based Metal-Organic Framework

A copper-based metal-organic framework, Cu(Im)2, was synthesized using a sol-gel process and subsequently melt-quenched into glass upon heating above 240 °C. In this paper, we present a multimodal, multiscale interrogation of the MOF nanocrystals and the resulting glasses. Structural characterization using X-ray diffraction, atomic force microscopy, and electron microscopy was performed to understand the morphology and size of the synthesized nanocrystals and glasses. Thermogravimetric analysis and differential scanning calorimetry were employed to understand the melting process of the crystals to form the glass. Synchrotron pair distribution function analysis was performed to verify that the framework structure is maintained upon melting, and nearfield infrared nanospectroscopy provided insight into the local chemical structure of the materials. The mechanical characterization via nanoindentation revealed that the resulting glasses exhibit an appreciably high elastic modulus (~10 GPa) and the highest fracture toughness (K_1c ~ 0.5 MPa m^1/2) yet reported for MOF glasses. This development is central to the emerging field of MOF-based materials processing and shaping, while upholding mechanical robustness and resistance to cracking.

cond-mat.mtrl-sci↗

arXiv2026

Triboelectrification of a dense metal-organic framework for resilient mechanical energy harvesters

Triboelectric nanogenerators (TENGs) incorporating metal-organic frameworks (MOFs) have largely been designed around porous architectures, based on the assumption that high internal surface area is the primary driver for triboelectric enhancement. Herein, we demonstrate that a dense, nominally nonporous MOF called ZIF-zni can instead function as an effective high-loading filler within a tribopositive polyurethane (PU) matrix, offering a design strategy for harnessing interfacial electromechanical effects. A 20 wt% ZIF-zni@PU composite delivers an output voltage of 470+/-15 V and a peak power density of 1.31+/-0.03 W m-2 against polydimethylsiloxane (PDMS). The device exhibits stable performance over ~94,000 cycles under a contact force of ~100 N, and it remains operational under higher impact beyond 500 N. This concept enables the demonstration of a proof-of-concept triboelectric floor tile. Combined experimental and theoretical studies indicate that the performance enhancement arises from favourable interfacial polarization, reduced dielectric screening, and surface accessible ZIF-zni rich domains, rather than porosity alone. These features are accompanied by reduced work of adhesion and modified surface roughness, hence improving contact electrification. These findings establish dense MOFs as an effective triboelectric filler and identify interfacial electronic structure and polarization as key design parameters for engineering mechanical energy harvesters and self-powered sensors.

cond-mat.mtrl-sci↗

arXiv2026

A MOF-reinforced self-foaming sponge for mechanically robust triboelectric membranes with improved resistance to humidity

Porous triboelectric materials offer significant potential for enhancing the performance of triboelectric nanogenerators, yet their practical application is limited by structural instability and humidity-induced performance degradation. In this work, a bio-derived, sustainable polyamide containing disulfide linkages was developed to enable spontaneous formation of a porous dielectric without external templating. Hydrophilic MOF fillers comprising HKUST-1 crystals are incorporated within the porous matrix to reinforce the membrane structure and regulate moisture effects. Mechanical characterization demonstrates that HKUST-1 suppresses pore collapse and improves structural robustness under repeated deformation, while analysis of stress-strain behaviour reveals the critical role of pore stability in achieving stable triboelectric output. In addition, HKUST-1 mitigates humidity-induced charge dissipation by confining water molecules within its framework, giving enhanced triboelectric output stability and reduced performance degradation under increasing relative humidity compared to the neat porous system. This work demonstrates a strategy that integrates self-foamed porous structures, sustainable polymer design, and functional filler reinforcement to engineer mechanically robust and environmentally stable triboelectric systems.

cond-mat.mtrl-sci↗

arXiv2026

Topology-Controlled Phonon Dielectric Response Beyond Density Scaling in Metal-Organic Frameworks

Effective-medium theory treats material porosity as passive dilution. Using ab initio density functional theory and high-resolution synchrotron terahertz (THz) spectroscopy on isochemical zeolitic-imidazolate frameworks, we show that while the electronic permittivity obeys Clausius-Mossotti density scaling, the phonon contribution violates the conventional density scaling rules. Identical Born charges rule out the role of local chemistry. Instead, the framework connectivity localizes the THz response, where the coherency of phonon eigenvectors determines the mode-effective charges. Long-range architecture of framework topology ubiquitous in metal-organic frameworks is therefore a dielectric degree of freedom beyond the density scaling of conventional solids.

cond-mat.mtrl-sci↗

arXiv2026

An Efficient Approach for Calculating Free Energy in Molecular Dynamics: Demineralization of Hydroxyapatite as a Case Study

Despite the strength of Molecular Dynamics simulations in providing insights into the microscopic details of phenomenon in many fields in materials science, physics and biology, the biggest barrier is its limited timescale which is several orders of magnitude lower than the timescale of the real-world processes and phenomena being modeled. Free energy calculations are designed as a remedy to this problem that in theory can overcome this barrier. This is particularly relevant for biomineralisation processes such as tooth mineral formation and dissolution, while reflecting a broader challenge in accurately modelling rare events and long-timescale phenomena across complex molecular systems. However, due to the novelty of the field, a number of questions remain outstanding pertaining to the best practice of applying this method. The non-equilibrium work approach based on the Jarzynski equation is one of the most promising free energy calculation methods. However, the biggest challenge for the broader use of this method is the question of how many simulations are required for an accurate free energy estimation. Comparing the free energy results with very long reversible pulling simulations of atom clusters from the surface, each taking 75 days on the 48-core Intel Xeon Platinum 8268 CPUs, in this study we showed that this question is irrelevant and higher quality and better equilibrated initial structures is the proper approach than simply based on the number of simulations. We designed a new adaptive free energy calculation methodology which combines high quality, high computational cost free energy values with lower quality, lower cost values to build up the entire free energy profile. In the best case scenario this method lowers manifold the computational cost required for the non-equilibrium work free energy calculations compared to both the regular method and the reversible simulation.

cond-mat.mtrl-sci↗

arXiv2026

Uncovering the role of ionic doping in hydroxyapatite: The building blocks of tooth enamel and bones

Hydroxyapatite (HAp) is the primary mineral component of various mineralized tissues in the human body, including bone and teeth, where it performs critical roles of structural support and load transmission. In the context of dental health, the two most crucial properties of HAp are mechanical stability, which ensures resistance to forces, and chemical stability, which preserves surface integrity in acidic environments. During early stages of human evolution, e.g. when teeth were used to crush uncooked food, mechanical stability was of paramount importance. However, with changes in diet and lifestyle, the principal origins of tooth damage and loss shifted towards bacterially mediated chemical attack, known as tooth decay, or caries. To enhance the chemical stability, ion doping has emerged as a particularly significant approach, and it lies at the focus of the present study. A Molecular Dynamics (MD) framework was developed to investigate the effects of ion doping on the chemical and mechanical stability of HAp and to identify optimal doping candidates. The framework combines conventional MD with Steered Molecular Dynamics (SMD), Thermodynamic Integration (TI) and uniaxial compression test simulations to provide comprehensive insights into the doping process. The findings revealed surface atoms as the most viable candidates for doping, as demonstrated by SMD and conventional MD simulations. Notably, TI calculations have identified magnesium ions as a better candidate among the ions considered here for enhancing the chemical stability of HAp. The results presented in this study offer valuable guidelines for synthesizing HAp-based substituent materials with properties tailored to meet the demands of modern dental applications such as implant coatings, enamel remineralization agents and restorative materials.

cond-mat.mtrl-sci↗

arXiv2022

Quantifiably Tuneable Luminescence by Ultra-Thin Metal-Organic Nanosheets via Dual-Guest Energy Transfer

Luminescent metal-organic frameworks (LMOFs) are promising materials for organic light-emitting diode (OLED) alternatives to silicate-based LEDs due to their tuneable structure and programmability. Yet, the 3D nature of LMOFs creates challenges for stability, optical transparency, and device integration. Metal-organic nanosheets (MONs) potentially overcome these limitations by combining the benefits of MOFs with an atomically thin morphology of large planar dimensions. Here, we report the bottom-up synthesis of atomically thin ZIF-7-III MONs via facile low-energy salt-templating. Employing guest@MOF design, the fluorophores Rhodamine B and Fluorescein were intercalated into ZIF-7 nanosheets (Z7-NS) to form light emissive systems exhibiting intense and highly photostable fluorescence. Aggregation and Förster resonance energy transfer, enabled by the MON framework, were revealed as the mechanisms behind fluorescence. By varying guest concentration, these mechanisms provided predictable quantified control over emission chromaticity of a dual-guest Z7-NS material and the definition of an 'emission chromaticity fingerprint' - a unique subset of the visible spectrum which a material can emit by fluorescence.

physics.app-ph↗

arXiv2022

In situ micropillar compression of an anisotropic metal-organic framework single crystal

Understanding of the complex mechanical behavior of metal-organic frameworks (MOF) beyond their elastic limit will allow the design of real-world applications in chemical engineering, optoelectronics, energy conversion apparatus, and sensing devices. Through in situ compression of micropillars, the uniaxial stress-strain curves of a copper paddlewheel MOF (HKUST-1) were determined along two unique crystallographic directions, namely the (100) and (111) facets. We show strongly anisotropic elastic response where the ratio of the Young's moduli are E(111) ~ 3.6 x E(100), followed by extensive plastic flows. Likewise, the yield strengths are considerably different, in which Y(111) ~ 2 x Y(100) because of the underlying framework anisotropy. We measure the fracture toughness using micropillar splitting. While in situ tests revealed differential cracking behavior, the resultant toughness values of the two facets are comparable, yielding Kc ~ 0.5 MPa m^1/2. This work provides new insights of porous framework ductility at the micron scale and failure by bonds breakage.

cond-mat.mtrl-sci↗

arXiv2022

Fracture behavior of MOF monoliths revealed by nanoindentation and nanoscratch

Monolithic metal-organic frameworks (MOFs) represent a promising solution for the industrial implementation of this emerging class of multifunctional materials, due to their structural stability. When compared to MOF powders, monoliths exhibit other intriguing properties like hierarchical porosity, that significantly improves volumetric adsorption capacity. The mechanical characterization of MOF monoliths plays a pivotal role in their industrial expansion, but so far, several key aspects remain unclear. In particular, the fracture behavior of MOF monoliths has not been explored. In this work, we studied the initiation and propagation of cracks in four prototypical MOF monoliths, namely ZIF-8, HKUST-1, MIL-68 and MOF-808. We observed that shear faults inside the contact area represent the main failure mechanism of MOF monoliths and are the source of radial cracks. MIL-68 and MOF-808 showed a remarkably high resistance to cracking, which can be ascribed to their consolidated nanostructure.

cond-mat.mtrl-sci↗

arXiv2022

Surface modulation of metal-organic frameworks for on-demand photochromism in the solid state

Organic photoswitchable molecules have struggled in solid state form to fulfill their remarkable potential, in terms of photoswitching performance and long-term stability when compared to their inorganic counterparts. We report the concept of non-electron deficient host's surface with optimal porosity and hydrophobicity, as a priori strategy to design photoefficient organic solid-state photochromic materials with outstanding mechanical robustness. When exposed to a light stimulus including natural sunlight, the photoswitchable nanocomposite changes color promptly and reversibly, in a matter of seconds along with excellent photo-fatigue resistance, which are on a par with inorganic photochromes. Exemplars of commercially viable prototypes that are optically clear, comprising smart windows, complex photochromic sculptures, and self-erasing rewritable devices, were engineered by direct blending with resilient polymers; particularly, the use of high-stiffness polymer (> 2 GPa) is no longer an insurmountable challenge. Finally, photochromic films with anticounterfeiting features could be manufactured through precision inkjet printing of nanocrystals.

physics.app-ph↗

arXiv2022

Nano-Trap Engineering in MOF Microenvironment for Ultratrace Iodine Sensors

Ultra-sensitive and highly selective iodine gas sensors play a crucial role during the nuclear radiation leak for a timely detection and mitigation of pollution, ensuring the safety of a vast number of operators and subsequent integrity of the facility. Herein, we rationally designed a metal-organic framework (MOF) that exhibits an outstanding performance with an almost billion-fold enhancement in the electrical response due to its optimized hydrophobicity, which allows the easy migration of iodine molecules though the channels and the presence of suitable interaction sites, temporarily anchoring the target molecule for ultra-trace sensing. The prototype sensor tested in demanding environments demonstrates its high selectivity, ultra-trace parts per billion (ppb)-level sensitivity, good reversibility, and a very fast response time even at high frequencies compared to existing adsorbents, including commercially available materials. Further, the iodine sensing at the atomic level was studied in detail by measuring the electrical response of a single crystal and, the optimal thickness of the MOF layer was identified for an industrially-viable prototype sensor by using inkjet printing. In a wider perspective, we propose a general strategy towards electrically efficient sensing materials with hybrid functionalities for engineering high-sensitivity iodine sensors for a safe and sustainable future.

physics.ins-det↗

arXiv2021

Vibrational Modes and Terahertz Physical Phenomena Underpinning ZIF-71 Metal-Organic Framework

The zeolitic imidazole framework ZIF-71 has the potential to outperform other well-studied metal-organic frameworks due to its intrinsic hydrophobicity and large pore size. However, a detailed description of its complex physical phenomena and structural dynamics has been lacking thus far. Herein, we elucidated all vibrational modes of ZIF-71 using high-resolution inelastic neutron scattering and synchrotron radiation infrared spectroscopy in conjunction with density functional theory calculations. We discover low-energy collective modes, such as gate-opening and shearing mechanisms that may affect the functions and framework stability of ZIF-71. Its single-crystal mechanical properties are further unraveled by nanoscale analytics.

cond-mat.mtrl-sci↗

arXiv2021

Nanoconfinement of Tetraphenylethylene in Zeolitic Metal-Organic Framework for Turn-on Mechanofluorochromic Stress Sensing

Mechanofluorochromic materials are of great significance for the fabrication of innovative sensors and optoelectronics. However, efficient mechanofluorochromic materials are rarely explored due to the deficiency of existing design strategies. Here, we demonstrate the incarceration of aggregation-induced emission (AIE) materials within metal-organic framework (MOF) single crystals to construct a composite system with turn-on mechanofluorochromism. A new type of AIE@MOF material was designed: integrating a zeolitic MOF (ZIF-71) and tetraphenylethylene (TPE, a topical AIE material) to generate a TPE@ZIF-71 system with exceptional turn-on type mechanofluorochromism. Using terahertz vibrational spectroscopy, we show the unique fluorochromism emanates from the enhanced nanoconfinement effect exerted by ZIF-71 host on TPE guest under pressure and its permanent fluorescence after stress release. Compared with pure TPE, we demonstrate the nanoconfinement in AIE@MOF not only changes the TPE's turn-off type sensing behavior to a turn-on type, but boosts the original sensitivity markedly by tenfold. Significantly, because ZIF-71 prevents the spontaneous recrystallization of TPE upon unloading, this allows TPE@ZIF-71 to record the stress history. This is the first demonstration of the Guest@MOF system combining the concepts of AIE and MOF; its promising properties and potential engineering applications will stimulate new directions pertaining to luminescent stress sensors and smart optics.

physics.app-ph↗

arXiv2021

Long-Lived Highly Emissive MOFs as Potential Candidates for Multiphotonic Applications

Long-lived emissive materials based on room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) are considered as the cornerstone of the development of optical sensors, security systems and solid-state lighting. Nevertheless, molecular systems with these properties are scarce because most of them suffer from aggregation caused quenching emission (ACQ). One approach to address this shortcoming is by inhibiting the molecular motions/vibrations by employing a fixed matrix as afforded by a metal-organic framework (MOF). There, the organic chromophores are confined in a crystalline framework, and the structure-property relationship can be designed to get RTP/TADF. Inspired by this, the present work explores the relation between the linker arrangement and the physicochemical properties of two isochemical MOFs with different crystalline structures. The denser MOF exhibits a long-lived green RTP due to a hyperfine coupling of the linkers. On the other hand, the more porous MOF presents a long-lived temperature-dependent turquoise emission, reflecting the influence of the TADF. Hence, this study provides a huge advance about the potential of MOFs to undergo RTP and TADF emission, and at the same time, demonstrates their potential applicability in a wide range of photonic technologies, including physical and chemical sensing and the first example of a MOF-LED based on RTP-MOFs.

cond-mat.mtrl-sci↗

arXiv2021

Mechanical Properties and Nanostructure of Monolithic Zeolitic Imidazolate Frameworks: A Nanoindentation, Nanospectroscopy and Finite-Element Study

The synthesis of metal-organic frameworks (MOFs) in a monolithic morphology is a promising way to achieve the transition of this class of materials from academia to industrial applications. The sol-gel process has been widely employed to produce MOF monoliths. It is relatively cheap and simple compared to other techniques (e.g., mechanical densification) and moreover it allows to produce "pure" monoliths, i.e., without the need of using binders or templates that could affect the functional properties of the MOF. Understanding the mechanical properties of these monoliths is crucial for their transit to practical applications. We studied the mechanical behavior of two zeolitic imidazolate frameworks (ZIF-8 and ZIF-71) by means of instrumented nanoindentation and atomic force microscopy (AFM). Tip Force Microscopy (TFM), an extension of AFM, was used to reveal the surface nanostructure of the monoliths. We employed finite-element (FE) simulations alongside the experiments, to establish a suitable constitutive model and determine an improved estimate of the yield stress of ZIF monoliths. NanoFTIR was subsequently used to pinpoint local structural alteration of the framework in the contact area. The combination of TFM, FE simulations, and nanoFTIR enabled us to identify the mechanical deformation mechanisms in monolithic ZIF materials: grain boundaries sliding is dominating at low stresses, then breakage of chemical bonds and a partial failure of the framework occurs, eventually leading to a densification of porous framework at the contact zone. Finally, we measured the fracture toughness using a cube corner indenter to study the resistance of monoliths against cracking failure.

cond-mat.mtrl-sci↗

arXiv2021

Tunable Fluorescein-Encapsulated Zeolitic Imidazolate Framework-8 Nanoparticles for Solid-State Lighting

A series of fluorescein-encapsulated zeolitic imidazolate framework-8 (fluorescein@ZIF-8) luminescent nanoparticles with a scalable guest loading has been fabricated and characterized. The successful encapsulation of the organic dye (fluorescein) is supported by both experimental evidence and theoretical simulations. The measured optical band gap is found to be comparable with the computed values of a hypothetical guest-host system. Isolated monomers and aggregates species of fluorescein confined in ZIF-8 nanocrystals have been systematically investigated through fluorescence lifetime spectroscopy. The quantum yield (QY) of the obtained solid-state materials is particularly high (QY~98%), especially when the concentration of the fluorescein guest is low. Combining a blue LED chip and a thin photoactive film of fluorescein@ZIF-8, we demonstrate a device with good optical tunability for multicolor and white light emissions. Additionally, we show that the fluorescein@ZIF-8 nanoparticles exhibit an improved photostability due to the shielding effect conferred by the nanoconfinement of host framework, making them promising candidates for practical applications such as solid-state lighting, photonics, and optical communications.

cond-mat.mtrl-sci↗

arXiv2021

Defects in ZIF-8 crystallization and their impact on mechanical properties

The growth process of metal-organic frameworks (MOFs) defines their properties for functional applications. However, it is very plausible that defects may occur during the crystallization of even seemingly perfect MOFs, such as ZIF-8, and yet, direct probing of such structural defects has been challenging due to the lack of techniques to locally examine individual nanocrystals. Now, we directly study local defects - such as missing linkers or metal vacancies - in ZIF-8 nano- and microcrystals with near-field infrared nanospectroscopy combined with density function theory calculations. We have tracked the chemical changes during crystallization and found that structural defects like zinc-rich regions gradually disappear with the ripening of the crystals, while missing linker defects prevail. The resulting open metal sites reduce the Young's modulus, as measured with tip force microscopy and supported by theoretical modelling, but also open the door for defect engineering to tune the adsorption and catalytic performance of ZIF-8.

cond-mat.mtrl-sci↗