Tetrazole and Oxadiazole Derivatives as Thermally Activated Delayed Fluorescence Emitters.

Organic light-emitting diodes (OLEDs) are promising lighting solutions for sustainability and energy efficiency. Incorporating thermally activated delayed fluorescence (TADF) molecules enables OLEDs to achieve internal quantum efficiency (IQE), in principle, up to 100 %; therefore, new classes of promising TADF emitters and modifications of existing ones are sought after. This study explores the TADF emission properties of six designed TADF emitters, examining their photophysical responses using experimental and theoretical methods. The design strategy involves creating six distinct types of a donor-acceptor (D-A) system, where tert-butylcarbazoles are used as donors, while the acceptor component incorporates three different functional groups: nitrile, tetrazole and oxadiazole, with varying electron-withdrawing character. Additionally, the donor-acceptor distance is adjusted using a phenylene spacer, and its influence on TADF functionality is examined. The clear dependency of an additional spacer, inhibiting TADF, could be revealed. Emitters with a direct donor-acceptor connection are demonstrated to exhibit TADF moderate emissive behavior. The analysis emphasizes the impact of charge transfer, singlet-triplet energy gaps (ΔEST), and other microscopic parameters on photophysical rates, permitting TADF. Among the emitters, TCz-CN shows optimal performance as a blue-green emitter with an 88 % photoluminescence quantum yield (PLQY) and fast rate of reversible intersystem crossing of 2×106 s-1 and 1×107 s-1, obtained from time-resolved photoluminescence (TRPL) experiment in PMMA matrix and quantum mechanical calculations, respectively. This comprehensive exploration identifies molecular bases of superior TADF emitters and provides insights for future designs, advancing the optimization of TADF properties in OLEDs.

Multiscale Model of CVD Growth of Graphene on Cu(111) Surface.

Due to its outstanding properties, graphene has emerged as one of the most promising 2D materials in a large variety of research fields. Among the available fabrication protocols, chemical vapor deposition (CVD) enables the production of high quality single-layered large area graphene. To better understand the kinetics of CVD graphene growth, multiscale modeling approaches are sought after. Although a variety of models have been developed to study the growth mechanism, prior studies are either limited to very small systems, are forced to simplify the model to eliminate the fast process, or they simplify reactions. While it is possible to rationalize these approximations, it is important to note that they have non-trivial consequences on the overall growth of graphene. Therefore, a comprehensive understanding of the kinetics of graphene growth in CVD remains a challenge. Here, we introduce a kinetic Monte Carlo protocol that permits, for the first time, the representation of relevant reactions on the atomic scale, without additional approximations, while still reaching very long time and length scales of the simulation of graphene growth. The quantum-mechanics-based multiscale model, which links kinetic Monte Carlo growth processes with the rates of occurring chemical reactions, calculated from first principles makes it possible to investigate the contributions of the most important species in graphene growth. It permits the proper investigation of the role of carbon and its dimer in the growth process, thus indicating the carbon dimer to be the dominant species. The consideration of hydrogenation and dehydrogenation reactions enables us to correlate the quality of the material grown within the CVD control parameters and to demonstrate an important role of these reactions in the quality of the grown graphene in terms of its surface roughness, hydrogenation sites, and vacancy defects. The model developed is capable of providing additional insights to control the graphene growth mechanism on Cu(111), which may guide further experimental and theoretical developments.

Twisting of Porphyrin by Assembly in a Metal-Organic Framework yielding Chiral Photoconducting Films for Circularly-Polarized-Light Detection.

While materials based on organic molecules usually have either superior optoelectronic or superior chiral properties, the combination of both is scarce. Here, a crystalline chiroptical film based on porphyrin with homochiral side groups is presented. While the dissolved molecule has a planar, thus, achiral porphyrin core, upon assembly in a metal-organic framework (MOF) film, the porphyrin core is twisted and chiral. The close packing and the crystalline order of the porphyrin cores in the MOF film also results in excellent optoelectronic properties. By exciting the Soret band of porphyrin, efficient photoconduction with a high On-Off-ratio is realized. More important, handedness-dependent circularly-polarized-light photoconduction with a dissymmetry factor g of 4.3×10-4 is obtained. We foresee the combination of such assembly-induced chirality with the rich porphyrin chemistry will enable a plethora of organic materials with exceptional chiral and optoelectronic properties.

Hierarchical Coarse-Grained Strategy for Macromolecular Self-Assembly: Application to Hepatitis B Virus-Like Particles.

Macromolecular self-assembly is at the basis of many phenomena in material and life sciences that find diverse applications in technology. One example is the formation of virus-like particles (VLPs) that act as stable empty capsids used for drug delivery or vaccine fabrication. Similarly to the capsid of a virus, VLPs are protein assemblies, but their structural formation, stability, and properties are not fully understood, especially as a function of the protein modifications. In this work, we present a data-driven modeling approach for capturing macromolecular self-assembly on scales beyond traditional molecular dynamics (MD), while preserving the chemical specificity. Each macromolecule is abstracted as an anisotropic object and high-dimensional models are formulated to describe interactions between molecules and with the solvent. For this, data-driven protein-protein interaction potentials are derived using a Kriging-based strategy, built on high-throughput MD simulations. Semi-automatic supervised learning is employed in a high performance computing environment and the resulting specialized force-fields enable a significant speed-up to the micrometer and millisecond scale, while maintaining high intermolecular detail. The reported generic framework is applied for the first time to capture the formation of hepatitis B VLPs from the smallest building unit, i.e., the dimer of the core protein HBcAg. Assembly pathways and kinetics are analyzed and compared to the available experimental observations. We demonstrate that VLP self-assembly phenomena and dependencies are now possible to be simulated. The method developed can be used for the parameterization of other macromolecules, enabling a molecular understanding of processes impossible to be attained with other theoretical models.

A coarse-grained xDLVO model for colloidal protein-protein interactions.

Colloidal protein-protein interactions (PPIs) of attractive and repulsive nature modulate the solubility of proteins, their aggregation, precipitation and crystallization. Such interactions are very important for many biotechnological processes, but are complex and hard to control, therefore, difficult to be understood in terms of measurements alone. In diluted protein solutions, PPIs can be estimated from the osmotic second virial coefficient, B22, which has been calculated using different methods and levels of theory. The most popular approach is based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and its extended versions, i.e. xDLVO. Despite much efforts, these models are not fully quantitative and must be fitted to experiments, which limits their predictive value. Here, we report an extended xDLVO-CG model, which extends existing models by a coarse-grained representation of proteins and the inclusion of an additional ion-protein dispersion interaction term. We demonstrate for four proteins, i.e. lysozyme (LYZ), subtilisin (Subs), bovine serum albumin (BSA) and immunoglobulin (IgG1), that semi-quantitative agreement with experimental values without the need to fit to experimental B22 values. While most likely not the final step in the nearly hundred years of research in PPIs, xDLVO-CG is a step towards predictive PPIs calculations that are transferable to different proteins.

Tuning Optical Properties by Controlled Aggregation: Electroluminescence Assisted by Thermally-Activated Delayed Fluorescence from Thin Films of Crystalline Chromophores.

Several photophysical properties of chromophores depend crucially on intermolecular interactions. Thermally-activated delayed fluorescence (TADF) is often influenced by close packing of the chromophore assembly. In this context, the metal-organic framework (MOF) approach has several advantages: it can be used to steer aggregation such that the orientation within aggregated structures can be predicted using rational approaches. We demonstrate this design concept for a DPA-TPE (diphenylamine-tetraphenylethylene) chromophore, which is non-emissive in its solvated state due to vibrational quenching. Turning this DPA-TPE into a ditopic linker makes it possible to grow oriented MOF thin films exhibiting pronounced green electroluminescence with low onset voltages. Measurements at different temperatures clearly demonstrate the presence of TADF. Finally, this work reports that the layer-by-layer process used for MOF thin film deposition allows the integration of the TADF-DPA-TPE in a functioning LED device.

Effect of Geometrical Structure, Drying, and Synthetic Method on Aminated Chitosan-Coated Magnetic Nanoparticles Utility for HSA Effective Immobilization.

Human serum albumin (HSA) is one of the most frequently immobilized proteins on the surface of carriers, including magnetic nanoparticles. This is because the drug-HSA interaction study is one of the basic pharmacokinetic parameters determined for drugs. In spite of many works describing the immobilization of HSA and the binding of active substances, research describing the influence of the used support on the effectiveness of immobilization is missing. There are also no reports about the effect of the support drying method on the effectiveness of protein immobilization. This paper examines the effect of both the method of functionalizing the polymer coating covering magnetic nanoparticles (MNPs), and the drying methods for the immobilization of HSA. Albumin was immobilized on three types of aminated chitosan-coated nanoparticles with a different content of amino groups long distanced from the surface Fe3O4-CS-Et(NH2)1-3. The obtained results showed that both the synthesis method and the method of drying nanoparticles have a large impact on the effectiveness of immobilization. Due to the fact that the results obtained for Fe3O4-CS-Et(NH2)2 significantly differ from those obtained for the others, the influence of the geometry of the shell structure on the ability to bind HSA was also explained by molecular dynamics.

Conductance Photoswitching of Metal-Organic Frameworks with Embedded Spiropyran.

Conductive metal-organic frameworks (MOFs) as well as smart, stimuli-responsive MOF materials have attracted considerable attention with respect to advanced applications in energy harvesting and storage as well as in signal processing. Here, the conductance of MOF films of type UiO-67 with embedded photoswitchable nitro-substituted spiropyrans was investigated. Under UV irradiation, the spiropyran (SP) reversibly isomerizes to the open merocyanine (MC) form, a zwitterionic molecule with an extended conjugated π-system. The light-induced SP-MC isomerization allows for remote control over the conductance of the SP@UiO-67 MOF film, and the conductance can be increased by one order of magnitude. This research has the potential to contribute to the development of a new generation of photoelectronic devices based on smart hybrid materials.

Photoconductivity in Metal-Organic Framework (MOF) Thin Films.

Photoconductivity is a characteristic property of semi-conductors. Herein, we present a photo-conducting crystalline metal-organic framework (MOF) thin film with an on-off photocurrent ratio of two orders of magnitude. These oriented, surface-mounted MOF thin films (SURMOFs), contain porphyrin in the framework backbone and C60 guests, loaded in the pores using a layer-by-layer process. By comparison with results obtained for reference MOF structures and based on DFT calculations, we conclude that donor-acceptor interactions between the porphyrin of the host MOF and the C60 guests give rise to a rapid charge separation. Subsequently, holes and electrons are transported through separate channels formed by porphyrin and by C60 , respectively. The ability to tune the properties and energy levels of the porphyrin and fullerene, along with the controlled organization of donor-acceptor pairs in this regular framework offers potential to increase the photoconduction on-off ratio.

Solvation of diclofenac in water from atomistic molecular dynamics simulations - interplay between solute-solute and solute-solvent interactions.

The solubility-permeability relationship of active pharmaceutical ingredients determines the efficacy of their usage. Diclofenac (DCL), which is a widely used nonsteroidal anti-inflammatory drug, is characterized by extremely good membrane permeability, but low water solubility limiting drug effectiveness. The present research focuses on the fundamental explanation of this limitation using the combination of ab initio and classical molecular dynamics simulations of different ionic forms of DCL in water, namely, ionized, un-ionized and the mixture of them both. The analysis of diclofenac solvation in an aqueous environment is used to understand the origin of drug precipitation, especially in gastric pH. The used computational approach reveals the formation of micelle-like self-associated aggregates of diclofenac in water as the result of intermolecular π-π interactions and C-Hπ hydrogen bonds. The DCL aggregation in water is shown to depend mostly on drug concentration, protonation and temperature of the aqueous environment. The detected self-association properties of the drug in water are likely to be of great importance during the development of new drug formulations and fabrication of drug adsorbents for wastewater.

Intramolecular Hydrogen Bonds in Low-Molecular-Weight Polyethylene Glycol.

We used static DFT calculations to analyze, in detail, the intramolecular hydrogen bonds formed in low-molecular-weight polyethylene glycol (PEG) with two to five repeat subunits. Both red-shifted O-H⋅⋅⋅O and blue-shifting C-H⋅⋅⋅O hydrogen bonds, which control the structural flexibility of PEG, were detected. To estimate the strength of these hydrogen bonds, the quantum theory of atoms in molecules was used. Car-Parrinello molecular dynamics simulations were used to mimic the structural rearrangements and hydrogen-bond breaking/formation in the PEG molecule at 300 K. The time evolution of the H⋅⋅⋅O bond length and valence angles of the formed hydrogen bonds were fully analyzed. The characteristic hydrogen-bonding patterns of low-molecular-weight PEG were described with an estimation of their lifetime. The theoretical results obtained, in particular the presence of weak C-H⋅⋅⋅O hydrogen bonds, could serve as an explanation of the PEG structural stability in the experimental investigation.

Structural, Vibrational and Electronic Properties of Defective Single-Walled Carbon Nanotubes Functionalised with Carboxyl Groups: Theoretical Studies.

Covalent sidewall functionalisation of defective zigzag single-walled carbon nanotubes [SWCNTs(10,0)] with COOH groups is investigated by using DFT. Four types of point defects are considered: vacancy (V), divacancy [V2 (5-8-5), V2 (555-777)], adatom (AA) and Stone-Wales (SW). The energetic, structural, electronic and vibrational properties of these systems are analysed. Decreasing reactivity is observed in the following order: AA>V>V2 (555-777)>V2 (5-8-5)>SW. These studies also demonstrate that the position in which a carboxyl group is attached to a defective SWCNT is of primary importance. Saturation of two-coordinate carbon atoms in systems with the vacancy V-7 and with the adatom AA-1(2) is 3.5-4 times more energetically favourable than saturation of three-coordinate carbon atoms for all studied systems. Vibrational analysis for these two systems shows significant redshifts of the ν(CO) stretching vibration of 96 and 123 cm-1 compared to that for carboxylated pristine systems. Detailed electronic-structure analysis of the most stable carboxylated systems is also presented.

Enantiomer Differentiation by Interaction-Specific Prediction of Residual Dipolar Couplings in Spherical-like Molecules.

Residual Dipolar Couplings (RDCs) are averaged dipolar couplings between nuclear spins of atoms in a molecule that can be measured by nuclear magnetic resonance (NMR) spectroscopy upon partial alignment by a chiral alignment medium. The estimation of differences in alignment of enantiomers may, in principle, enable the determination of absolute configuration. Here, we use molecular dynamics (MD) simulations to mimic the alignment of chiral molecules (i.e., isopinocampheol, quinuclidin-3-ol, borneol, and camphor) to the chiral poly-γ-benzyl-L-glutamate (PBLG) polymer to predict RDCs in silico and compare calculated and experimentally measured residual dipolar couplings for the four enantiomeric pairs. The aim is to validate the computational scheme for the prediction of RDCs in chiral molecules and understand the interaction leading to the alignment in more detail. We determine the indispensable importance of hydrogen bonds between a chiral molecule and the alignment medium on the overall quality of the simulated alignment and interaction poses toward high agreement with experiments. A good correlation with experimental data is found for camphor and isopinocampheol, while the correlation for quinuclidin-3-ol and borneol is lower. We attribute this observation to the high difficulty of the RDC prediction for rather almost spherical molecules. The study reveals that the prediction of alignment with small enantiomeric differences is possible with an MD-based approach; however, extended simulation times (e.g., 50-100 µs) are required to sufficiently reduce the statistical uncertainty. This may be further used for the determination of the relative, as well as absolute, configuration of chiral molecules.

Impact of DNA on interactions between core proteins of Hepatitis B virus-like particles comprising different C-terminals.

Hepatitis B virus (HBV) virus-like particles (VLPs) are promising therapeutic agents derived from HBV core proteins (Cp). This study investigates the assembly dynamics of HBV VLPs, which is crucial for their potential as drug carriers or gene delivery systems. Coarse-grained molecular dynamics simulations explore the impact of C-terminal domain length (in the Cp ranging from Cp149 to wild-type Cp183) on Cp assembly and stability, particularly in the presence of DNA. Our findings reveal that the C-terminal nucleic acid binding region significantly influences Cp assembly and stability of trimers comprising Cp dimers. Shorter C-terminal domains (Cp164, Cp167) enhance stability and protein-protein interactions, while interactions between naturally occurring Cp183 are destabilized in the absence of DNA. Interestingly, DNA addition further stabilizes Cp assemblies, and this effect is influenced by the length of the nucleic acid binding region. Shorter C-terminal domains show less dependency on DNA content. This stabilization is attributed to electrostatic forces between positively charged C-terminal chains and negatively charged nucleic acids. Our study sheds light on the molecular mechanisms governing protein-protein and protein-DNA interactions in HBV VLP assembly, providing insights into Cp processability and informing the development of efficient gene therapy carriers using VLP technology.

Two- and three-photon processes during photopolymerization in 3D laser printing.

The performance of a photoinitiator is key to control efficiency and resolution in 3D laser nanoprinting. Upon light absorption, a cascade of competing photophysical processes leads to photochemical reactions toward radical formation that initiates free radical polymerization (FRP). Here, we investigate 7-diethylamino-3-thenoylcoumarin (DETC), belonging to an efficient and frequently used class of photoinitiators in 3D laser printing, and explain the molecular bases of FRP initiation upon DETC photoactivation. Depending on the presence of a co-initiator, DETC causes radical generation either upon two-photon- or three-photon excitation, but the mechanism for these processes is not well understood so far. Here, we show that the unique three-photon based radical formation by DETC, in the absence of a co-initiator, results from its excitation to highly excited triplet states. They allow a hydrogen-atom transfer reaction from the pentaerythritol triacrylate (PETA) monomer to DETC, enabling the formation of the reactive PETA alkyl radical, which initiates FRP. The formation of active DETC radicals is demonstrated to be less spontaneous. In contrast, photoinitiation in the presence of an onium salt co-initiator proceeds via intermolecular electron transfer after the photosensitization of the photoinitiator to the lowest triplet excited state. Our quantum mechanical calculations demonstrate photophysical processes upon the multiphoton activation of DETC and explain different reactions for the radical formation upon DETC photoactivation. This investigation for the first time describes possible pathways of FRP initiation in 3D laser nanoprinting and permits further rational design of efficient photoinitiators to increase the speed and sensitivity of 3D laser nanoprinting.

On-off conduction photoswitching in modelled spiropyran-based metal-organic frameworks.

Materials with photoswitchable electronic properties and conductance values that can be reversibly changed over many orders of magnitude are highly desirable. Metal-organic framework (MOF) films functionalized with photoresponsive spiropyran molecules demonstrated the general possibility to switch the conduction by light with potentially large on-off-ratios. However, the fabrication of MOF materials in a trial-and-error approach is cumbersome and would benefit significantly from in silico molecular design. Based on the previous proof-of-principle investigation, here, we design photoswitchable MOFs which incorporate spiropyran photoswitches at controlled positions with defined intermolecular distances and orientations. Using multiscale modelling and automated workflow protocols, four MOF candidates are characterized and their potential for photoswitching the conductivity is explored. Using ab initio calculations of the electronic coupling between the molecules in the MOF, we show that lattice distances and vibrational flexibility tremendously modulate the possible conduction photoswitching between spiropyran- and merocyanine-based MOFs upon light absorption, resulting in average on-off ratios higher than 530 and 4200 for p- and n-conduction switching, respectively. Further functionalization of the photoswitches with electron-donating/-withdrawing groups is demonstrated to shift the energy levels of the frontier orbitals, permitting a guided design of new spiropyran-based photoswitches towards controlled modification between electron and hole conduction in a MOF.

Bis(2,2':6',2''-terpyridine)-ruthenium(II) bis-(perchlorate) hemihydrate.

The asymmetric unit of the title compound, [Ru(C(15)H(11)N(3))(2)](ClO(4))(2)·0.5H(2)O, contains one ruthenium-terpiridine complex cation, two perchlorate anions and one half-mol-ecule of water. Face-to-face and face-to-edge π-stacking inter-actions between terpyridine units [centroid-centroid distances = 3.793 (2) and 3.801 (2)  Å] stabilize the crystal lattice The partially occupied water mol-ecule inter-acts with two perchlorate ions via O-H⋯O hydrogen bonds. In the crystal lattice, the complex cations, perchlorate ion-water pairs and the second perchlorate anions are arranged into columns along b direction.

Tris(1,10-phenanthroline-κ(2) N,N')ruthenium(II) bis-(perchlorate).

The asymmetric unit of the title compound, [Ru(C12H8N2)3](ClO4)2, contains one octahedrally coordinated Ru(II) cation of the ruthenium-phenanthroline complex and three differently occupied perchlorate anions: two, denoted A and B, are located on the twofold axis while another, denoted C, is positioned in the proximity of the twofold screw axis. Perchlorate anions B and C are severely disordered. The occupancies of the two major conformers of anion B refined to 0.302 (6) and 0.198 (6). Perchlorate ion C was modeled in two alternate conformations which refined to occupancies of 0.552 (10) and 0.448 (10).

Analytical Model of CVD Growth of Graphene on Cu(111) Surface.

Although the CVD synthesis of graphene on Cu(111) is an industrial process of outstanding importance, its theoretical description and modeling are hampered by its multiscale nature and the large number of elementary reactions involved. In this work, we propose an analytical model of graphene nucleation and growth on Cu(111) surfaces based on the combination of kinetic nucleation theory and the DFT simulations of elementary steps. In the framework of the proposed model, the mechanism of graphene nucleation is analyzed with particular emphasis on the roles played by the two main feeding species, C and C2. Our analysis reveals unexpected patterns of graphene growth, not typical for classical nucleation theories. In addition, we show that the proposed theory allows for the reproduction of the experimentally observed characteristics of polycrystalline graphene samples in the most computationally efficient way.

Adsorption of sulfur mustard on clean and water-saturated ZnO(101¯0): Structural diversity from first-principles calculations.

We investigate the adsorption of a chemical warfare agent, namely sulfur mustard (SM), on clean and water-saturated ZnO(101¯0) surfaces using density functional theory calculations to understand the first step of its efficient neutralization to less toxic chemical compounds. We determine the relative stability of various SM conformers adsorbed at different sites on both ZnO surfaces. The unique hydrogen bonding patterns obtained for the idealized clean and the more realistic water-saturated ZnO surface are analyzed and their influence on the stability of the SM@ZnO structures is demonstrated. We find that absolute values of the calculated binding and interaction energies are significantly higher for the clean than for the water-saturated ZnO surface due to the formation of Cl⋯Zn and S⋯Zn contacts. The high adsorptive reactivity of the clean ZnO surface is also evident from the strong structural changes of the initial local energy minimum gas-phase conformations of the SM molecules upon adsorption. This phenomenon is not observed for the water-saturated ZnO surface, which has almost no impact on the SM conformation after adsorption, leaving it as it exists in the gas phase. The insights from the results obtained provide a missing piece toward the understanding of the complex mechanism of SM neutralization on ZnO surfaces.