Molecular Systems Design & Engineering最新文献

An out-of-equilibrium simulation method for tracking the time evolution of glassy systems (or any other systems that can be described by hopping dynamics over a network of discrete states) is presented. Graph theory and complexity concepts are utilised, alongside the method of the dynamical integration of a Markovian web (G. C. Boulougouris and D. N. Theodorou, J. Chem. Phys., 2007, 127, 084903) in order to provide a unified framework for dealing with the long time-scales of non-ergodic systems. Within the developed formalism, the network of states accessible to the system is considered a finite part of the overall universe, communicating with it through well-defined boundary states. The analytical solution of the probability balance equation proceeds without the need for assuming the existence of an equilibrium distribution among the states of the network and the corresponding survival and escape probabilities (as functions of time) are defined. More importantly, the study of the probability flux through the dividing surface separating the system and its environment reveals the relaxation mechanisms of the system. We apply our approach to the network of states obtained by exploring the energy landscape of an atomistically detailed glassy specimen of atactic polystyrene. The rate constants connecting different basins of the landscape are evaluated by multi-dimensional transition-state-theory. We are able to accurately probe the appearance of the δ- and γ-subglass relaxation mechanisms and their relevant time-scales, out of atomistic simulations. The proposed approach can fill a gap in the rational molecular design toolbox, by providing an alternative to molecular dynamics for structural relaxation in glasses and/or other slow molecular processes (e.g., adsorption or desorption) that involve very distant time-scales.

We present a method of enabling photochemical reactions in water by using biomimetic, water-soluble liposomes and a specifically functionalized perylene diimide chromophore. Linking two flexible saturated C4-alkyl chains with terminal positively charged trimethylammonium groups to the rigid perylene diimide core yielded [1]²⁺ allowing for its co-assembly at the lipid bilayer interface of DOPG liposomes (DOPG = 1,2-dioleoyl-sn-glycero-3-phospho-(1′-rac-glycerol)) with a preferred orientation and in close proximity to the water interface. According to molecular dynamics simulations the chromophore aligns preferably parallel to the membrane surface which is supported by confocal microscopy. Irradiation experiments with visible light and in the presence of a negatively charged, water-soluble oxidant were slower in the DOPG-membrane than under acetonitrile–water reaction conditions. The generated radical species was characterized by EPR spectroscopy in an acetonitrile–water mixture and associated to the DOPG-membrane. Time-resolved emission studies revealed a static quenching process for the initial electron transfer from photoexcited [1]²⁺ to the water soluble oxidant. The findings presented in this study yield design principles for the functionalization of lipid bilayer membranes which will be relevant for the molecular engineering of artificial cellular organelles and nano-reactors based on biomimetic vesicles and membranes.

The scrutiny of molecular photoswitches has received utmost attention owing to their plethora of promising applications. A bicyclooctadiene/tetracyclooctane (BOD/TCO) couple has recently been recognized as a suitable photoswitching system for molecular solar thermal energy storage (MOST). However, there is a desirable interest in tuning the properties of the BOD/TCO couple for enhanced performance. In the present report, a systematic attempt has been made to unravel the photoswitching properties of various aza-BOD/TCO systems using density functional theory (DFT) studies. DLPNO-CCSD(T)/def2TZVP calculations were performed to test the reliability of the obtained outcomes. Attention has also been devoted to assess the effect of substitution and solvation on the photoswitching behaviour. The result reveals that the aza-BOD/TCO couples are versatile systems whose properties substantially depend on the position of N. The substitution of N at the bridgehead position (1-aza-BOD/TCO and 1,4-biaza-BOD/TCO) enhances the barrier height for the thermal back isomerization reaction, whereas substituting the unsaturated C with N (2-aza-BOD/TCO) and the bridgehead and closest unsaturated C with N (1,2-biaza-BOD/TCO) improves the storage density and photophysical properties. The 2-aza-BOD/TCO couple has a storage energy of 213.05 kJ mol^?1 (1.99 MJ kg^?1) which is significantly higher than the parent BOD/TCO couple (163.85 kJ mol^?1 (1.54 MJ kg^?1)). Biaza-TCO has the highest barrier of 200.00 kJ mol^?1 for the thermal back conversion reaction. The spectral overlap is reduced, and an 82.79 nm separation is achieved between the first important excitation wavelengths of substituted aza-BOD and aza-TCO. An approximately 32–109 nm red-shift in the first important excitation wavelength is noticed upon substitution of various aza-BODs and aza-TCOs.

Conjugated polyelectrolytes (CPEs) are a rising class of organic mixed ionic-electronic conductors, with applications in bio-interfacing electronics and energy harvesting and storage devices. Here, we employ a quantum mechanically informed coarse-grained model coupled with semiclassical rate theory to generate a first view of semidilute CPE morphologies and their corresponding ionic and electronic transport properties. We observe that the poor solvent quality of CPE backbones drives the formation of electrostatically repulsive fibers capable of forming percolating networks at semi-dilute concentrations. The thickness of the fibers and the degree of intrafiber connectivity are found to strongly influence electronic transport. Calculated structure factors reveal that fiber formation alters the position and scaling of the inter-chain PE peak relative to good solvent predictions and induces a narrower distribution of interchain spacings. We also observe that electrostatic interactions play a significant role in determining CPE morphology, but have only a small impact on the local site energetics. This work presents a significant step forward in the ability to predict CPE morphology and ion-electron transport properties, and provides insights into how morphology influences electronic and ionic transport in conjugated materials.

The incorporation of organic semiconducting materials within solid-state electronic devices provides a potential route to highly efficient photovoltaics, transistors, and light emitting diodes. Key to the realisation of such devices is efficient intramolecular charge transport within molecular species, as well as intermolecular/interdomain transport, which necessitates highly ordered supramolecular domains. The on-surface synthesis of polymeric organic materials (incorporating donor and/or acceptor moieties) is one pathway towards the production of highly ordered molecular domains. Here we study the formation of a polymer based upon a diketopyrrolopyrrole (DPP) monomer unit, possessing aryl-halide groups to facilitate on-surface covalent coupling and functionalised with alkyl chains which drive the self-assembly of both the monomer material prior to reaction and the domains of polymeric material following on-surface synthesis. The self-assembled structure of close-packed domains of the monomer units, and the ordered polymers, are investigated and characterised using scanning tunnelling microscopy and X-ray photoelectron spectroscopy.

Due to growing environmental concerns and increasing energy needs, hydrogen, one of the key options as a future energy carrier, has lately gained more interest. In this study, we have reported nanohybrid electrocatalyst materials based on peripherally and non-peripherally carboxylic acid substituted copper phthalocyanines (CuPcs) and reduced graphene oxide (rGO) constructed via π–π interactions between CuPcs and rGO. Prepared nanocomposites were coated onto the surface of a glassy carbon electrode and their electrocatalytic activity for the hydrogen evolution reaction (HER) was studied. Structural, electrochemical, and surface morphological properties of the produced electrodes were investigated using Fourier transform infrared (FT-IR) and Raman spectroscopy, X-ray diffraction (XRD), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) analyses. Electrochemical measurements indicated that the peripherally substituted rGO/CuPc electrodes have more efficiency and activity compared to the non-peripherally substituted ones. In addition, the EIS results show that peripherally carboxylic substituted rGO/CuPc electrodes become more conductive due to the position and content of the carboxyl groups. This increasing performance of the HER implied by a smaller impedance together with more facile electron transfer kinetics indicates a pronounced enhancement of the electrocatalytic hydrogen activity of peripherally carboxylic substituted rGO/CuPc electrodes.

To realize lanthanide metal–organic frameworks (Ln-MOFs) with white light emission, it is necessary to adjust their RGB composition. We adopted the Bayesian optimization technique to optimize the stoichiometric ratio of metal-salts in Ln-MOFs. We successfully synthesized MIL-103 (Ln(BTB)(H₂O), H₃BTB = 1,3,5-tris(4-carboxyphenyl)benzene), which emits white light.

Fragrance precursors are an assorted class of pro-fragrances that could realize the controlled release of aromatic compounds. Herein, nicotinoylhydrazone-based pH-triggered fragrance precursors (NTA1–NTA4) have been prepared by reacting nicotinoylhydrazine with a series of aromatic benzaldehydes bearing different electron-donating groups. The chemical structures and substituent effects have been confirmed by FT-IR, NMR, mass and ultraviolet-visible (UV-vis) spectroscopies. Controlled release studies in an acidic environment revealed that a strong electron-donating substituent accelerates the release rate, while weak electron donor groups favor the deceleration of fragrance release. Surprisingly, intramolecular hydrogen bond formation (–OH?NC–) has a positive impact upon the stability of the hydrazone bridge in precursor NTA4, consistent with the simulation of the molecular electrostatic potential (MEP) results. In addition, the release kinetics were also investigated and the release rate constant could be estimated with a first-order kinetic model (R² > 0.98). Furthermore, it was demonstrated that fragrance precursors on cotton fabrics could be an efficient controlled release strategy for fragrant aldehydes after exposure to an ambient atmosphere for several days, compared to a reference sample containing the raw aroma chemicals.

With the application of new materials and the optimization of device structure, binary bulk heterojunction organic solar cells (OSCs) have exhibited the outstanding performance in recent years. However, the open-circuit voltage (V_oc) of binary OSCs is normally below 1 V and the matched energy levels of the donor, acceptor and transport materials with high V_oc in binary OSCs have been rarely proposed. Herein, four different machine learning (ML) algorithms are applied to investigate V_oc in binary?OSCs according to the energy level of donor, acceptor and transport materials. Among them, the eXtreme Gradient Boosting (XGBoost) model provides the best prediction ability. Its prediction accuracy and root mean square error reach 0.94 and 0.04, respectively. Therefore, SHapley Additive exPlanations of XGBoost is selected and showed that the highest occupied molecular orbital (HOMO) of the donor plays the most important role for the improvement of V_oc in all the energy level of donor, acceptor and transport materials. More importantly the energy level matching strategy of binary OSC materials for high V_oc is delivered by machine learning, where the HOMO of the donor is about ?5.45 ± 0.1 eV, the lowest unoccupied molecular orbital (LUMO) of the acceptor is about ?3.80 ± 0.1 eV, and the work functions of the matched electron and hole transport materials are about ?3.6 ± 0.2 eV and ?5.1 ± 0.1 eV, respectively. In addition, the experimental verification results display that the measured V_oc just has a relatively low error compared with the predicted V_oc. Likewise, the predicted V_oc based on the XGBoost model of PTB7:PC₇₁BM is 0.79 V, and the experimental value is 0.76 V. The relative error is only 3.95%, which indicates the reliability of the ML prediction for high V_oc in binary OSCs.

Zr-containing UiO-66 and UiO-66-NH₂ are good heterogeneous catalysts for the acetalization of phenylacetaldehyde with glycerol, producing the corresponding hyacinth fragrance in high yields after short (2 h) reaction times. Mixtures of 1,3-dioxolanes and 1,3-dioxanes are obtained, whose ratios can be modified between 2.8 and 4.6 depending on the catalyst used, the amount of missing linker defects of the solid, and the reaction time. The catalysts are stable under the reaction conditions used, and they can be reused without loss of activity or selectivity. The scope of UiO-66 materials is demonstrated for the formation of other glyceryl acetals of interest for the flavoring industry, which represents an interesting route for glycerol valorization.