Molecular Dipole Research Articles

Ultralow Ion Migration and X-Ray Response from Strong Dipole Moments in (Br-EA)2PbBr4 Perovskite Single Crystals.

2D hybrid perovskites composed of quantum-well structures demonstrate immense potential in optoelectronics because of their unique combination of environmental stability and optoelectrical properties. However, improving electrical properties via quantum-well engineering results in severe ion migration and inferior chemical stability. In this study, a novel strategy to avoid the above trade-off between electrical properties and stability for modifying the electric field profile in perovskites through molecular design is proposed. To this end, ethylammonium (EA) cations are substituted with 2-bromoethylamine (Br-EA) cations and fabricate pure 2D perovskite (Br-EA)2PbBr4 single crystals. The molecular dipole moments of the Br-EA cations and induced electric field impart several novel features to the X-ray response, including a ferro-response current, reverse current, and super-high Voc of 95V. The resulting X-ray detectors achieve a sensitivity of 540.7 µC Gyair -1 cm-2 with an extra 38.1% gained from local dipoles, an impressive limit of detection of 9.8 nGyair s-1, and an ultralow dark current drift of 3.69 × 10-8 nA cm-1 s-1 V-1 at -100V. This study presents valuable insights into the novel effects of dipole moments of A-site cations on the properties of perovskite materials and inspires further exploration of their potential applications.

Theoretical Investigations of Bioactive Substituted 2‐Amino‐3,5‐dicarbonitrile‐6‐thiopyridine Derivatives

AbstractThis study utilizes the density functional theory (DFT) (B3LYP method and 6–31 + G* basis set)‐based method to theoretically investigate substituted 2‐amino‐3,5‐dicarbonitrile‐6‐thiopyridine derivatives within a prevalent multicomponent reaction involving aldehyde, malononitrile, and thiophenol. Various reactivity descriptors, including frontier molecular orbitals, dipole moment, polarizability, and molecular electrostatic potential, are computed to understand the variations in reactivity and stability of these compounds. The results demonstrate the reliability of DFT‐derived descriptors in predicting chemical reactivity and provide valuable insights for further research and practical applications in the field of chemical reactivity and reaction mechanisms. Geometric parameters, along with thermodynamic variables, such as standard enthalpies (ΔH), entropies (ΔS), Gibbs free energy (ΔG), and global reactivity descriptors (ionization potential (I), electron affinity (A), chemical hardness (η), softness (σ), global softness (S), chemical potential (μ), global electrophilicity (ω), and nucleophilicity index (N), are calculated to gain insight into the dynamics of these interactions and variations in reactivity and stability.

Unsymmetric Protonation Driven Highly Efficient H2O2 Photosynthesis in Supramolecular Photocatalysts via One-Step Two-Electron Oxygen Reduction.

Photocatalytic hydrogen peroxide (H2O2) production has emerged as an attractive alternative to the traditional anthraquinone process. However, its performance is often hindered by low selectivity and sluggish kinetics of oxygen reduction reaction (ORR). Herein, we report an anthrazoline-based supramolecular photocatalyst, SA-SADF-H+, featuring an unsymmetric protonation structure for H2O2 photosynthesis from water and air.The introduction of unsymmetric protonation disrupts the initial mirror symmetry of SADF, significantly enhancing the molecular dipole and facilitating efficient charge separation and electron transfer. Additionally, this modification increases the hydrophilicity of SA-SADF-H+, enabling the interaction of water and dissolved oxygen with the catalytic sites. The altered electron density distribution creates numerous dual active sites for Yeager-type O2 adsorption, facilitating an efficient ORR towards H2O2 via a direct one-step two-electron pathway. Notably, SA-SADF-H+ achieves an outstanding photocatalytic H2O2 production at a rate of 4667 μmol L-1 h-1, with a remarkable solar-to-chemical conversion (SCC) of 1.35%, surpassing most organic photocatalytic systems. Furthermore, SA-SADF-H+ demonstrates remarkable photocatalytic antibacterial activity, achieving 100% antibacterial efficiency against Staphylococcus aureus within 60 min.

Electric Fields in Polymeric Systems.

Polymer-based electronic devices are limited by slow transport and recombination of newly separated charges. Built-in electric fields, which arise from compositional gradients, are known to improve charge separation, directional charge transport, and to reduce recombination. Yet, the optimization of these fields through the rational design of polymeric materials is not prevalent. Indeed, polymers are disordered and generate nonuniform electric fields that are hard to measure, and therefore, hard to optimize. Here, we review work focusing on the intentional optimization of electric fields in polymeric systems with applications to catalysis, energy conversion, and storage. This includes chemical tuning of constituent monomers, linkers, morphology, etc. that result in stronger molecular dipoles, polarizability or crystallinity. We also review techniques to characterize electric fields in polymers and emerging processing strategies based on electric fields. These studies demonstrate the benefits of optimizing electric fields in polymers. However, rational design is often restricted to the molecular scale, deriving new pendants on, or linkers between, monomers. This does not always translate in strong electric fields at the polymer level, because they strongly depend on the monomer orientation. A better control of the morphology and monomer-to-polymer scaling relationship is therefore crucial to enhance electric fields in polymeric materials.

Screening Fluorination Additives for Efficient Perovskite Light-Emitting Diodes.

Fluorinated additives are proposed to address the issue of domain polydispersity in quasi-2D perovskites. However, the lack of established screening criteria for these additives necessitates a laborious and costly trial-and-error process. Herein, this work explores the behind nature for the first time how various fluorination in fluorinated additives affect domain distribution in quasi-2D perovskites. The studies reveal that fully fluorinated additives could suppress undesirable low-dimensional domains, facilitating efficient energy transfer, while partially fluorinated additives adversely cause deteriorated optical properties. The observed trend is ascribed to the molecular dipole moment of the fluorinated additives, offering a reasonable explanation for experimental phenomena that has never been reported before. By employing fully fluorinated additives, the fabricated sky-blue perovskite light-emitting diodes (PeLEDs) deliver a peak external quantum efficiency (EQE) of 20.38% (@488nm), marking as one of the highest efficiencies reported to date. The finding provides a screening criterion for fluorinated additives to realize efficient PeLEDs.

Fluorine/bromine/selenium multi-heteroatoms substituted dual-asymmetric electron acceptors for o-xylene processed organic solar cells with 19.12% efficiency

AbstractThe development of high-performance near-infrared (NIR) absorbing electron acceptors is a major challenge in achieving high short-circuit current density (JSC) to increase power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, three new multi-heteroatomized Y-series acceptors (bi-asy-Y-Br, bi-asy-Y-FBr, and bi-asy-Y-FBrF) were developed by combining dual-asymmetric selenium-fused core and brominated end-groups with different numbers of fluorine substitutions. With gradually increasing fluorination, three acceptors exhibit red-shift absorption. Among them, bi-asy-Y-FBrF presents planar molecular geometry, the maximum average electrostatic potential, and the minimum molecular dipole moment, which are conducive to intramolecular packing and charge transport. Moreover, D18:bi-asy-Y-FBrF active layer presents higher crystallinity, more suitable phase separation, and reduced charge recombination compared to D18:bi-asy-Y-Br and D18:bi-asy-Y-FBr blends. Consequently, among theses binary OSCs, D18:bi-asy-Y-FBrF device achieves a higher PCE of 15.74% with an enhanced JSC of 26.28 mA cm−2, while D18:bi-asy-Y-Br device obtains a moderate PCE of 15.04% with the highest open-circuit voltage (VOC) of 0.926 V. Inspired by its high VOC and complementary absorption with NIR-absorbing BTP-eC9 as acceptor, bi-asy-Y-Br is introduced into binary D18:BTP-eC9 to construct ternary OSCs, achieving a further boosted PCE of 19.12%, which is among the top values for the reported green solvent processed OSCs.

Molecular modeling analyses of functionalized cellulose

Functionalization of cellulose with nanomaterials and functional groups is essential for enhancing its properties for specific applications, such as flexible sensors and printed electronics. This study employs Hartree Fock (HF) and Density Functional Theory (DFT) calculations to investigate the vibrational spectra of cellulose, identifying DFT: B3LYP/3–21 g** as the optimal model aligning with experimental spectra. Using this model, we examined the impact of functionalizing cellulose with various groups (OH, NH2, COOH, CH3, CHO, CN, SH) and graphene oxide (GO) on its electronic properties. The results indicate that cellulose functionalized with GO (Cellulose-GO) has the lowest bandgap energy (0.1687 eV), and improvements in reactivity, stability, and electronic properties were confirmed through Molecular Electrostatic Potential (MESP) and Total Dipole Moment (TDM) analyses. The spectrum of Density of States (DOS) for the cellulose functionalized with different groups shows several peaks, indicating various energy levels where electronic states are concentrated. The Projected Density of States (PDOS) analysis reveals how different functional groups affect the electronic structure of cellulose. Moreover, the (Cellulose-GO) composite was characterized using an Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectrometer, revealing interaction through the OH group of CH2OH, as indicated by a new band at 1710 cm−1, consistent with theoretical predictions. Overall, this study demonstrates that functionalization with GO enhances cellulose’s responsiveness, degradation, and electrical properties, making it suitable for applications in flexible electronic devices and protective barriers against corrosion.

Coarse-grained polarizable soft solvent models, with applications in dissipative particle dynamics.

We critically examine a broad class of explicitly polarizable soft solvent models aimed at applications in dissipative particle dynamics. We obtain the dielectric permittivity using the fluctuating box dipole method in linear response theory and verify the models in relation to several test cases, including demonstrating ion desorption from an oil-water interface due to image charge effects. We additionally compute the Kirkwood factor and find that it uniformly lies in the range gK≃0.7-0.8, indicating that dipole-dipole correlations are not negligible in these models. This is supported by the measurements of dipole-dipole correlation functions. As a consequence, Onsager theory over-predicts the dielectric permittivity by 20%-30%. The mean square molecular dipole moment can be accurately estimated with a first-order Wertheim perturbation theory.

Theoretical Investigations of 2H‐Iminopyran Derivatives: A Computational Chemistry Approach

AbstractThis study is a theoretical approach to elucidate the structural, energetic, and spectroscopic properties of already synthesized derivatives of 2H‐iminopyran (4a–4j) by us. Our findings reveal that molecular symmetry, dipole moment, polarizability, and global reactivity descriptors significantly influence the behavior of these compounds within the context of multicomponent reactions. Molecular electrostatic potential surfaces (MEPS) provide valuable insights into potential reactive sites and intermolecular interactions, crucial for understanding the efficiency and selectivity of multicomponent processes that are found to be in accordance with the experimental results. Thermodynamic analysis offers further clarification on the driving forces behind the formation of these compounds. These insights can be leveraged to optimize reaction conditions, design novel multicomponent strategies, and predict the outcome of future synthetic endeavors in this area.

Boosting spontaneous orientation polarization of polar molecules based on fluoroalkyl and phthalimide units

Polar organic molecules form spontaneous polarization in vacuum-deposited films by permanent dipole orientations in the films, originating from the molecule’s potential ability to align itself on the film surface during deposition. This study focuses on developing polar molecules that exhibit spontaneous orientation polarization (SOP) and possess a high surface potential. In the proposed molecular design, a hexafluoropropane (6F) unit facilitates spontaneous molecular orientation to align the permanent dipoles, and a phthalimide unit induces strong molecular polarization. Furthermore, the introduction of phthalimides into the molecular backbone raises the glass transition temperature of the molecules, leading to the suppression of molecular mobility on the film surface during film deposition and an improvement in the dipole orientation. The resulting surface potential slope is approximately 280 mV nm−1 without substrate temperature control. Furthermore, this work proposes a method using position isomers as a design strategy to tune the SOP polarity. The substitution position of the strong polar units influences the direction of the total molecular dipoles and affects the SOP polarity of the 6F-based molecules. The proposed molecular designs in this study provide wide tunability of the SOP intensity and polarity, which contributes to highly efficient organic optoelectronic and energy-harvesting devices.

Long-range enhancement for fluorescence and Raman spectroscopy using Ag nanoislands protected with column-structured silica overlayer

We demonstrate long-range enhancement of fluorescence and Raman scattering using a dense random array of Ag nanoislands (AgNIs) coated with column-structured silica (CSS) overlayer of over 100 nm thickness, namely, remote plasmonic-like enhancement (RPE). The CSS layer provides physical and chemical protection, reducing the impact between analyte molecules and metal nanostructures. RPE plates are fabricated with high productivity using sputtering and chemical immersion in gold(I)/halide solution. The RPE plate significantly enhances Raman scattering and fluorescence, even without proximity between analyte molecules and metal nanostructures. The maximum enhancement factors are 107-fold for Raman scattering and 102-fold for fluorescence. RPE is successfully applied to enhance fluorescence biosensing of intracellular signalling dynamics in HeLa cells and Raman histological imaging of oesophagus tissues. Our findings present an interesting deviation from the conventional near-field enhancement theory, as they cannot be readily explained within its framework. However, based on the phenomenological aspects we have demonstrated, the observed enhancement is likely associated with the remote resonant coupling between the localised surface plasmon of AgNIs and the molecular transition dipole of the analyte, facilitated through the CSS structure. Although further investigation is warranted to fully understand the underlying mechanisms, the RPE plate offers practical advantages, such as high productivity and biocompatibility, making it a valuable tool for biosensing and biomolecular analysis in chemistry, biology, and medicine. We anticipate that RPE will advance as a versatile analytical tool for enhanced biosensing using Raman and fluorescence analysis in various biological contexts.

Effect of weak intermolecular interactions on the ionization of benzene derivatives dimers.

The interactions between π-systems in dimers of aromatic molecules lead to particularly stable conformations within the relative orientations of the monomers. Extensive research has been conducted on the properties of these complexes in the neutral state. However, in recent decades, there has been a significant surge in applications harnessing these structures for electrical purposes. Therefore, this study places particular emphasis on a deeper understanding of the redox properties of these compounds and how to modify them. To achieve this, we have focused on modeling the effect of a wide range of functional groups on the redox properties of benzene derivatives, observing a correlation between these properties and the change in the molecular dipole moment. Then, we investigated the effect of π-stacking interactions on these properties in dimers formed by either identical or different monomers. In both cases, there is an enhancement of the reducing character of the systems due to these interactions. Upon oxidation, the charge is distributed proportionally to the redox potential of each monomer. Therefore, if there is heterogeneity in these potentials, the properties of the complete cationic system will be influenced by the monomer with a greater tendency to undergo oxidation. The considered models serve as an excellent example for studying the behavior of nucleobases in DNA or aromatic amino acids, among others.

Influence of terminal moiety on PCE of DSSCs: An In Silico study based on triazatruxene-benzothiadiazole dye

Our study utilized an experimentally synthesized dye as a reference molecule, employing a donor-π linker-acceptor (D-π-A) framework for organic solar cells. The molecule featured a triazatruxene group linked with alkyl branches as the donor and ethynyl benzoic acid as the acceptor, connected through a derivative of benzothiadiazole as the π linker. To improve optoelectronic and photovoltaic properties, ten theoretically designed dyes (ZA1–ZA10) are proposed, differing from the reference (R) by modifying the terminal acceptor moiety. Various quantum analyses, including frontier molecular orbitals, optical properties, reorganization energies, binding energies, transition density matrices (TDM), molecular electrostatic potential (MEP), dipole moment, and density of states were carried out at DFT/B3LYP/6-31G(d,p). Ground state geometries revealed a co-planar morphology in ZA1–ZA10, facilitating efficient charge transportation. TDM and MEP illustrated improved electronic transitions in the excited states. Computational analyses revealed superior photovoltaic properties of ZA1–ZA10. Notably, ZA5 exhibited the most significant redshift (1021 nm) in absorption, lowest bandgap (1.44 eV), smallest transition energy (1.21 eV), least binding energy (0.23 eV), and improved charge mobilities. Results from the adsorption of ZA1-ZA10 on the TiO2 layer confirmed their anchoring potential and effective injection of electrons to anatase (TiO2)9. These significant outcomes promise the potential and novelty of our designed dyes for higher power conversion efficiencies (PCE) in dye-sensitized solar cells (DSSCs).

Asymmetric Charge Distribution in One-dimensional Metal-Organic Assemblies to Promote Photocatalytic Hydrogen Evolution.

The local charge distribution of photocatalyst is crucial to the catalytic activity due to its influence on the charge separation process. Herein, we report two one-dimensional Ni-based metal-organic assemblies for efficient photocatalytic hydrogen evolution without using noble-metal cocatalysts. By adjusting the aromatic ring in the center of the tricarboxylic ligand, the photocatalytic hydrogen evolution activity was increased from 1715 to 2652 μmol h-1 g-1. The detailed mechanism study shows that the introduced nitrogen atoms in the ligands of the metal-organic coordination assembly could modulate the local charge distribution, and yielding a significant enhancement of the molecular dipole moment which engenders a propulsive force for the effective separation and transport of photoinduced charge carriers. This work provides insights into the local charge distribution via ligand modulation for enhancing the activity of photocatalysts.

A Diphosphonic Acid-Based Interlayer for Highly Efficient and Stable Inverted Perovskite Solar Cells.

We investigate an interlayer of 6,6'-bis(4-(bis(4-methoxyphenyl)amino)phenyl)-[1,1'-binaphthalene]-(2,2'-diyl)bis(oxy)bis(propane-3,1-diyl)bis(phosphonic acid) (BINOL-PA) with undoped poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) coverage. The incorporation of the 1,10-bi-2-naphthol central core enhances π-π stacking and reduces charge recombination at the interface. Compared to PTAA alone (0.95 eV), BINOL-PA/PTAA exhibits a shorter distance from the Fermi energy (EF) to the valence-band maximum (VBM) (0.36 eV). Two phosphoric acid units in BINOL-PA fine-tune the molecular dipoles. Theoretical calculations reveal electrostatic surface potential differences between BINOL-PA and PTAA in their backbone structure. Open-circuit voltage decay (OCVD) and electrochemical impedance spectroscopy (EIS) results suggest suppressed interface recombination. The photovoltaic conversion efficiency (PCE), short-circuit current density (JSC), open-circuit voltage (VOC), and fill factor (FF) for the BINOL-PA/PTAA device are measured as 21.02%, 22.67 mA cm-2, 1.12 V, and 82.8%, respectively, all higher than those achieved by the PTAA device with a PCE of 18%. BINOL-PA/PTAA significantly elevates VOC and FF values compared with dopant-free PTAA alone. The champion device retains over 89% of its initial PCE after being exposed to an ambient environment without encapsulation for more than 30 days. The thermal aging test conducted under a nitrogen atmosphere demonstrates that the efficiency retention rate for BINOL-PA/PTAA displays 60% of its initial efficiency after 1500 h.

Charge Carrier Dynamics at the Perovskite Interface with Self-Assembled Monolayers.

Self-assembled monolayers (SAMs) deposited on the hole-collecting electrodes of p-i-n perovskite solar cells effectively replace bulky hole transporting layers. However, the mechanism by which monolayers control the electronic processes and how they depend on the properties of the monolayer molecules remain poorly understood. In this study, we developed a simplified perovskite solar cell imitator with blocked electron extraction to investigate the photocurrent dynamics between the perovskite and the hole-collecting ITO electrode. We investigated the photoluminescence and photovoltage dynamics under short laser pulse excitation and addressed the influence of bulky and monomolecular hole transport layers. Our findings reveal that the photovoltage dynamics is significantly affected by the properties of the transport and perovskite layers, which in turn depend on the methods of sample preparation and exploration. Photocurrent dynamics is determined by several processes, including charge carrier displacement in the local electric field, hole transport to ITO, trapping of holes in interface trap states, and electron-hole recombination at the interface. We propose a model that takes into account molecular dipole moments and their ionization potentials to partially explain the different influences of different monolayers on the hole extraction and interfacial recombination rates. Additionally, the photovoltage dynamics also strongly depends on the illumination of the sample and shows memory effects that persist over minutes and hours and are attributed to the redistribution of ions.

Controlling Polarization‐Induced Polaron Accumulation in OLEDs via Device Design

AbstractSpontaneous alignment of molecular electric dipole moments, known as spontaneous orientation polarization (SOP), is present in many organic electronic materials. The SOP‐induced field changes the internal voltage distribution within the device, altering polaron injection and accumulation. The important role of SOP in organic light‐emitting devices (OLEDs) has recently been emphasized with clear links between dipole alignment and device efficiency and operational lifetime. Prior work has thus sought to engineer SOP via changes in thin film composition or processing conditions. These efforts have generally been directed at the OLED electron transport layer, which can show strong SOP. This work takes a different approach, focusing instead on how changes in device architecture can be applied to tune the magnitude and dynamics of polaron accumulation in response to SOP. In this work, it is demonstrated that the introduction of SOP into the device emissive layer offers control over the spatial location of accumulation. In parallel, insertion of a spacer layer between the hole transport and emissive layers can be used to tune the polaron accumulation rate and density during device operation. Both of these architectural changes permit an increase in OLED efficiency and a pathway around the deleterious impact of SOP‐induced polaron accumulation.

Tetrahydrofuran Processable Organic Solar Cells with 19.45% Efficiency Realized by Introducing High Molecular Dipole Unit Into the Terpolymer.

Developing organic solar cells (OSCs) processable with halogen-free, non-aromatic solvents is crucial for practical applications, yet challenging due to the limited solubility of most photoactive materials. This study introduces high-performance terpolymers processable in tetrahydrofuran (THF) by incorporating dithienophthalimide (DPI) into the PM6 backbone. DPI extends the absorption band, lowers HOMO levels, and improves THF solubility and film crystallinity through its large dipole moment effect. Optimal PBD-10:L8-BO devices processed with THF achieved a competitive power conversion efficiency (PCE) of 18.79%, approaching chloroform-processed devices (19.04%). By introducing PBTz-F as a second donor, ternary OSCs reached an impressive 19.45% PCE when processed with THF. This improvement stems from enhanced photon generation, improved morphology, better charge transport, longer exciton lifetimes, efficient charge dissociation and collection, and suppressed recombination. These PCEs of 18.79% and 19.45% for binary and ternary blend OSCs, respectively, represent the highest reported efficiencies for OSCs processed with halogen-free, non-aromatic solvents. This work demonstrates significant progress in eco-friendly OSC fabrication, paving the way for more sustainable and commercially viable organic photovoltaic technologies.

Investigation of aluminum nitrate nanotube as the smart carriers for targeted delivery of gemcitabine anti-lung cancer drug

The potential of aluminum nitrate nanotube as a drug carrier for anti-lung cancer drug gemcitabine is examined based on the density functional theory (DFT) calculations. The adsorption geometries of gemcitabine drug onto the surface of nanotube are investigated for various orientation in order to attain the most stable configuration. Significant interaction is observed between the double bonded oxygen atom of the gemcitabine drug and aluminum atom of the nanocage. The charge transfer analysis indicates that there is significant interaction along with considerable charge transfer between gemcitabine and the aluminum nitrate nanotube. The electronic properties such as highest occupied molecular orbital, lowest unoccupied molecular orbitals energy levels, energy gap, chemical hardness, chemical potential, electrophilicity index, and dipole moment for the best three configurations of the complexation are examined. The recovery time calculations are also performed at 298.15 K temperature in order to study the drug desorption process on the targeted site. The stability of the complex is compared in both gas and aqueous medium. Eventually, this work interprets that aluminum nitrate nanotube can be considered to be suitable candidates for delivering gemcitabine anti-lung cancer drug in a biological system.

Asymmetric Modification of Carbazole Based Self-Assembled Monolayers by Hybrid Strategy for Inverted Perovskite Solar Cells.

Carbazole-based self-assembled molecules (SAMs) are widely applied in inverted perovskite solar cells (iPSCs) due to their unique molecular properties. However, the symmetrical structure of the carbazole-based SAMs makes it difficult to finely regulate their performance, which impedes the further enhancement of the efficiency and stability of iPSCs. This work demonstrates that by constructing an asymmetric carbazole core, 9H-thieno[2',3' : 4,5]thieno[3,2-b]indole) (TTID), the key properties of SAM molecules can be effectively regulated. It has been confirmed that the hybrid thieno[2,3-b]thiophene unit of this asymmetric core governs the energy level, the surface wettability, and the defect passivation capability of the SAMs, while the substituent of core has a greater impact on the molecular dipole and device stability. The synergistic effects from thieno[2,3-b]thiophene and fluorine lead to the KF-derived iPSC demonstrating a certified power conversion efficiency (PCE) of 25.17 % and excellent operational stability. This hybrid design concept offers a promising approach for the further structural modification of SAMs in iPSCs.