Journal of Materials Chemistry C最新文献

Studies of devices of organic mixed ionic-electronic conductors (OMIECs) have unearthed a discrepancy; unlike other organic semiconductors, OMIECs tend to exhibit high charge carrier mobility despite a large energetic disorder. This has been attributed to the dynamic disorder observed in OMIECs, whereby the energy levels of frontier orbitals are not constant but undergo shifts as a function of time due to interactions with the ionic medium. We develop a method to simulate the dynamic energetic disorder as has been observed for OMIECs. We demonstrate that the mobility of a polymer material undergoing hopping transport increases significantly in the presence of dynamic disorder and further extend the model to explore effects of dynamic disorder on the interactions and delocalisation of electronic states. We parametrized the model to match known OMIEC systems and show that incorporating the dynamic disorder in a charge transport model is essential to compute their mobility.

Thin metal-organic framework (MOF) films, known as surface-anchored metal-organic frameworks (SURMOFs), offer convenient handling and a variety of new applications due to the direct immobilization of porous crystalline materials on various substrates. In this study, we demonstrate the feasibility of using luminescent SURMOFs for optical sensing of oxygen both in the gas phase and in organic solvents. Luminescent SURMOFs were prepared from indium(iii) chloride and platinum(ii) tetrakis(4-carboxyphenyl)porphyrin on pre-treated transparent substrates, such as rigid glass or flexible poly(ethylene terephthalate). These SURMOFs have an average thickness of ∼310 nm and exhibit room-temperature phosphorescence (λ _max = 645-676 nm). This phosphorescence is efficiently quenched by molecular oxygen in the gas phase (I ₀/I _air ∼50, Stern-Volmer constant K _SV ∼4-13 kPa^-1). For the SURMOFs fabricated under similar conditions, the sensitivity does not correlate with the morphology (revealed by scanning electron microscopy) or degree of crystallinity (accessed by grazing-incidence wide angle X-ray scattering) of the porous films. Additionally, it has been demonstrated that the SURMOFs exhibit luminescence in toluene, which is quenched by oxygen (I ₀/I _air ∼ 2.5, K _SV ∼ 0.18 kPa^-1). While optical oxygen sensing in organic solvents remains a significant challenge, the presented approach offers a viable solution, provided that future research can mitigate fast photodegradation of the SURMOFs under continuous irradiation.

Hybrid bonding polymers chemically integrate supramolecular assemblies and covalent macromolecules and can therefore exhibit synergistic functionalities that can impact mechanical properties, catalytic activity, and robotic behavior, among others. In these materials, structural units are connected through both covalent and noncovalent bonds, and this hybrid bonding nature can lead to alterations in nanoscale morphology and internal ordering relative to purely supramolecular or purely covalent polymer systems. We report here on a hybrid bonding polymer in which an ionizable covalent polymer was partially functionalized with electron donor-acceptor dyads and co-assembled with similar dyad small molecules that could form supramolecular polymers on their own. Characterization with UV/Vis spectroscopy revealed charge-transfer interactions among the donor-acceptor dyads in the covalent polymer, the hybrids, and the supramolecular polymer, and wide-angle X-ray scattering indicated a gradual loss of internal order as more covalent polymer was incorporated into the hybrid structures. Interestingly, second harmonic generation confocal microscopy revealed the formation of noncentrosymmetric structures in the hybrid materials but not in the supramolecular polymer. Furthermore, measurements of polarization as a function of applied electric field yielded hysteresis loops characteristic of ferroelectric materials for the hybrid materials, but not for the pure covalent polymer or the pure supramolecular polymer. We found evidence of symmetry breaking and ferroelectricity in the hybrid assemblies only when the covalent polymer was moderately ionized, which suggested that electrostatic interactions played a key role in breaking the centrosymmetry of the donor-acceptor assemblies. Coarse-grained simulations further indicated that electrostatic repulsions between charged groups on the covalent polymers and the donor-acceptor dyad small molecules led to symmetry-breaking defects in these materials and that this effect was most prevalent at moderate degrees of covalent polymer ionization. Such defect-induced ferroelectricity has not been previously reported in other supramolecular ferroelectrics, and further investigation of this symmetry-breaking mechanism could enable simpler fabrication of flexible, lightweight ferroelectric materials.

With a direct bandgap and strong photoluminescence (PL) emission, monolayer molybdenum disulfide (1L MoS₂) is a promising material for next-generation optoelectronic technologies. However, the intrinsically low PL quantum yield (PLQY) and the requirement for dielectric integration present significant challenges in the realisation of practical MoS₂-based devices. Chemical treatment with the superacid bis(trifluoromethanesulfonyl)amide (TFSA) is known to enhance dramatically the PL emission of 1L MoS₂ through defect passivation and p-type doping. Conversely, atomic layer deposition (ALD) of a dielectric material can introduce defect states and induce n-type doping, thus degrading the MoS₂ optical performance. Despite the competing effects of these two processing routes, the combined impact of superacid treatment and ALD dielectric growth on 1L MoS₂ has not been thoroughly studied. In this work, we reveal the instability of the TFSA-enhanced MoS₂ PL intensity during subsequent ALD of aluminium oxide (Al₂O₃), due to thermal exposure and precursor interaction. In contrast, we demonstrate that TFSA treatment of thermal Al₂O₃-encapsulated 1L MoS₂ can successfully enhance the PL intensity by up to two orders of magnitude, even for dielectric films of up to ∼96% surface coverage. This enhancement is suppressed only when the Al₂O₃ layer becomes sufficiently thick (>∼40 nm) and approaches complete coalescence, preventing access of TFSA-derived species to the underlying MoS₂. This work establishes an effective encapsulation/passivation strategy for enhancing the optical performance of dielectric-covered 1L MoS₂, offering a practical pathway for integrating chemical passivation into device-relevant architectures.

High-mobility organic molecular crystals such as rubrene are important materials for organic electronics, yet a quantitatively predictive description of their charge transport properties remains challenging. Direct mixed quantum-classical nonadiabatic molecular dynamics simulations provide a promising route by explicitly propagating the charge carrier wavefunction, without assuming a specific transport mechanism. However, previous large-scale simulations of apolar molecular crystals have commonly neglected dynamic electrostatic disorder, since evaluation of electrostatic interactions is computationally demanding and the approximation appears plausible for apolar systems. Here, we use the damped shifted-force (DSF) real-space electrostatic summation method, combined with an efficient addition-subtraction scheme, to include dynamic electrostatic disorder in fragment orbital-based surface hopping (FOB-SH) simulations of room-temperature hole transport in rubrene. We find that electrostatic interactions increase the reorganization energy for (hypothetical) nearest neighbour hopping by 29 and 39 meV along the a and b-directions, respectively, relative to a baseline value of 152 meV obtained without electrostatics. In FOB-SH simulations, electrostatic interactions lead to increased site energy disorder, reducing the spatial extent of the hole wavefunction, as measured by a decrease in the inverse participation ratio from 13 to 9, and lowering the predicted mobility along the high-mobility direction from 35 to 21 cm² V^-1 s^-1, in close agreement with experiment.

A combination of variable temperature X-ray diffraction, thermal analysis, and electrical measurements by fixed frequency dielectric spectroscopy, impedance spectroscopy, and electro-motive force measurements are used to establish the structure-electrical properties of SrNb₂O₆ ceramics prepared by the conventional solid state reaction technique. A polymorphic phase transition from a monoclinic, m, (space group P2₁/c) to an orthorhombic, o, (space group, Pmcn that is isomorphic with Pnma, CaTa₂O₆) cell occurs at ∼420 °C, accompanied by a negative thermal expansion effect (NTE) along the a-axis. The NTE in the monoclinic phase is driven primarily by a buckling of Nb₂O₁₀ dimers linked by corners sharing anions along the b-axis combined with a switch in their canting arrangement along the c-axis across the m- to o-transition. SrNb₂O₆ ceramics show no evidence of ferroelectricity; however, they display dielectric behaviour below ∼300 °C with m-SrNb₂O₆ exhibiting a room temperature permittivity of ∼30 that approximately doubles on transformation to o-SrNb₂O₆. There is significant leakage conductivity associated with adsorption of moisture near room temperature and mixed oxide-ion and p-type electronic conductivity at >300 °C. Both of these space charge related mechanisms are possible origins of the anomalous behaviour in the dielectric spectroscopy measurements that give rise to the apparent ferroelectric behaviour and mask the intrinsic electrical properties of SrNb₂O₆.

Precise control of solid-state fluorescence through molecular design is central to the development of advanced functional materials for sensing, imaging, and optical information storage. In particular, aggregation-induced emission (AIE) and mechanochromic luminogens have emerged as promising platforms for stimuli-responsive photonic applications. Herein, four constitutional isomers of carbonyl-bridged tetraphenylethylene (TPE)-carbazole derivatives were synthesised to systematically investigate how molecular connectivity governs their optoelectronic, aggregation, and mechanoresponsive properties. Distinct structure-property relationships were established, demonstrating that subtle variations in connectivity produce significant differences in electronic structure, molecular packing, aggregation-induced emission, and mechanochromic behaviour. Compounds 1, 3, and 4 exhibit AIE characteristics, whereas compound 2 displays aggregation-caused quenching-like behaviour arising from differences in accessible conformational and solid-state packing states. Among the four isomers, compounds 1 and 2 exhibit mechanochromism, with compound 1 showing highly reversible fluorescence switching, while compound 2 undergoes an irreversible pressure-induced transition associated with a metastable amorphous phase. Fluorescence microscopy revealed an exceptionally low pressure-sensing threshold of 0.2 MPa for compound 1 deposited on paper substrates, enabling sensitive detection of gentle mechanical stimuli and reversible invisible-ink write-erase cycles. These findings establish constitutional isomerism as an effective strategy for controlling aggregation, solid-state organisation, pressure sensitivity, and mechanochromic reversibility, providing molecular design principles for next-generation low-force pressure sensors and stimulus-responsive organic materials.

Controlling the topology of curved transition-metal dichalcogenides remains challenging because shell formation, precursor conversion and hollowing occur simultaneously during growth. Here, we show that the thickness of sputtered tungsten (W) films provides a direct handle for selecting WS₂ nanotube topology during charcoal-assisted oxide-template sulfurization. Varying the initial W thickness from 1 to 100 nm drives a transition from laterally extended WS₂-like domains to hollow nanotubes and, finally, to retained-core nanotubes exhibiting shell-front mismatch and spiral-like shell wrapping. Sulfur-free controls, Raman spectroscopy, grazing-incidence X-ray diffraction, transmission electron microscopy and elemental mapping reveal that this transition is governed by the continuity, accessibility, and recession of WO _x -derived precursor structures. As an initial test of functionality, multiphoton microscopy further shows that the oxide-core nanotube assemblies are optically active nonlinear emitters, generating second-harmonic, sum-frequency and four-wave-mixing signals that are readily detected under conditions where a WS₂ monolayer reference is near the detection limit. These results establish film thickness as a synthetic handle for curved transition-metal dichalcogenide architectures and identify these self-formed nanostructures as a promising platform for nonlinear nanophotonics.

We report here the structural and magnetic characterisation of the high-pressure double perovskite Pb₂MgReO₆. Our analysis using neutron diffraction demonstrates that the second-order Jahn-Teller Pb²⁺ cation plays the dominant structural role, preventing the proposed delicate quadrupolar order from emerging. We explore the relationship between related polar and antipolar structural phases in the context of other complex double perovskites. Muon-spin relaxation (µSR) measurements suggest that a short-range ordered state occurs for 11.3 K < T < 30 K, before a collinear AFM state sets in for T < 11.3 K. These findings add to our understanding of the structural behaviour of lead-based perovskites, as well as the sensitivity of multipolar order to site symmetry.

MAX phases (M _n+1AX _n ), precursors to MXenes, span a vast compositional space, motivating efficient computational screening for synthesisable candidates. We employ CrystaLLM-π, a large language model fine-tuned on 6179 double transition-metal MAX phases, and demonstrate its ability to generate novel structures consistent with known experimental trends. Using a conditioning vector with two dimensions (a statistically derived MXene derivative count and a surrogate for A-site binding energy), the model was able to target MXene-favourable regions of phase space for generation. Specific condition vectors double novel stable structure generation rates versus unconditioned baselines. Of ten compositionally novel candidates, five exhibit DFT-validated (meta)stability (E _hull < 0.050 eV per atom). This work showcases the potential for autoregressive generative models to explore targeted materials' spaces, offering a scalable framework for accelerated discovery in compositionally complex systems.