Asymmetric Molecules Research Articles

Employing symmetry-breaking strategy to reduce self-aggregation of donor in blend films to control morphology for all-small-molecule organic solar cells

In this work, we employed symmetry-breaking strategy to construct A-π-D-π-A typed small molecule donors SMD1, SMD2 and SMD3 to reduce the self-aggregation in blends and form ideal phase separation morphology. The effect of different side chains and terminal groups on the photovoltaic properties of these asymmetric small molecule donors were investigated in detail. SMD3 shows more red-shifted absorption and weaker self-aggregation than SMD1 and SMD2. Consequently, SMD3:PC71BM blend films show homogenous morphology, which is beneficial for exciton dissociation and charge transport. As a result, SMD3:PC71BM based devices exhibit the highest power conversion efficiency (PCE) of 4.67%. Our investigation proved that the benzene-alkoxyl and thiophene-alkylthiol are ideal candidates for side chains on BDT and 3-isooctyl rhodanine is an ideal terminal group for asymmetric small molecular donors.

Thermally Stable Organic Field-Effect Transistors Based on Asymmetric BTBT Derivatives for High Performance Solar-Blind Photodetectors.

High‐performance solar‐blind photodetectors are widely studied due to their unique significance in military and industrial applications. Yet the rational molecular design for materials to possess strong absorption in solar‐blind region is rarely addressed. Here, an organic solar‐blind photodetector is reported by designing a novel asymmetric molecule integrated strong solar‐blind absorption with high charge transport property. Such alkyl substituted [1]benzothieno[3,2‐b][1]‐benzothiophene (BTBT) derivatives Cn‐BTBTN (n = 6, 8, and 10) can be easily assembled into 2D molecular crystals and perform high mobility up to 3.28 cm2 V−1s−1, which is two orders of magnitude higher than the non‐substituted core BTBTN. Cn‐BTBTNs also exhibit dramatically higher thermal stability than the symmetric alkyl substituted C8‐BTBT. Moreover, C10‐BTBTN films with the highest mobility and strongest solar‐blind absorption among the Cn‐BTBTNs are applied for solar‐blind photodetectors, which reveal record‐high photosensitivity and detectivity up to 1.60 × 107 and 7.70 × 1014 Jones. Photodetector arrays and flexible devices are also successfully fabricated. The design strategy can provide guidelines for developing materials featuring high thermal stability and stimulating such materials in solar‐blind photodetector application.

Classical and Quantum Controllability of a Rotating Asymmetric Molecule

We study both the classical and quantum rotational dynamics of an asymmetric top molecule, controlled through three orthogonal electric fields that interact with its dipole moment. The main difficulties in studying the controllability of these infinite-dimensional quantum systems are the presence of severe spectral degeneracies in the drift Hamiltonian and the nonsolvability of the stationary free Schrödinger equation, which lead us to apply a perturbative Lie algebraic approach. In this paper we show that, while the classical equations given by the Hamiltonian system on $$\mathrm{SO}(3)\times {\mathbb {R}}^3$$ are controllable for all values of the rotational constants and all dipole configurations, the Schödinger equation for the quantum evolution on $$L^2(\mathrm{SO}(3){,{\mathbb {C}}})$$ is approximately controllable for almost all values of the rotational constants if and only if the dipole is not parallel to any of the principal axes of inertia of the asymmetric rigid body.

Asymmetric donor-acceptor molecule-regulated core-shell-solvation electrolyte for high-voltage aqueous batteries

<h2>Summary</h2> Salt-concentrated aqueous electrolytes show a wider electrochemical window than conventional aqueous electrolytes, yet still suffer from significant hydrogen evolution reaction (HER) at <1.9 V versus Li⁺/Li. Introducing organic compounds was reported to alleviate HER, but all reported organic additives are flammable, inevitably compromising the safety property. Here, we report a new all-nonflammable-ingredient aqueous electrolyte via hybridizing with nonflammable methylurea. The structurally asymmetric methylurea molecules possessing both donor and acceptor functional groups regulate the hydrogen bonding network, resulting in peculiar nanoscale core-shell-like clusters. Such unique solution structure allows localized super-high salt concentration in the electrolyte and suppresses HER at 0.5 V versus Li⁺/Li, achieving a 4.5 V electrochemical window. Under a harsh testing condition with low electrolyte loading, no excess Li resource, no electrode precoating, and conventional aluminum current collectors, this electrolyte realizes a stable cycling of a rocking-chair NbO₂|LiMn₂O₄ full cell (∼175 Wh kg^–1) without compromising the safety property.

Ground state of asymmetric tops with DMRG: Water in one dimension.

We propose an approach to compute the ground state properties of collections of interacting asymmetric top molecules based on the density matrix renormalization group method. Linear chains of rigid water molecules of varying sizes and density are used to illustrate the method. A primitive computational basis of asymmetric top eigenstates with nuclear spin symmetry is used, and the many-body wave function is represented as a matrix product state. We introduce a singular value decomposition approach in order to represent general interaction potentials as matrix product operators. The method can be used to describe linear chains containing up to 50 water molecules. Properties such as the ground state energy, the von-Neumann entanglement entropy, and orientational correlation functions are computed. The effect of basis set truncation on the convergence of ground state properties is assessed. It is shown that specific intermolecular distance regions can be grouped by their von-Neumann entanglement entropy, which in turn can be associated with electric dipole-dipole alignment and hydrogen bond formation. Additionally, by assuming conservation of local spin states, we present our approach to be capable of calculating chains with different arrangements of the para and ortho spin isomers of water and demonstrate that for the water dimer.

Compromising Charge Generation and Recombination with Asymmetric Molecule for High‐Performance Binary Organic Photovoltaics with Over 18% Certified Efficiency

AbstractBalancing the charge generation and recombination constitutes a major challenge to break the current limit of organic photovoltaics (OPVs). To address this issue, an asymmetric non‐fullerene acceptor, namely the AC9, is developed and high‐performance OPV with a champion efficiency of 18.43% (18.1% certified) is demonstrated. This represents the record value among binary OPVs. Comprehensive analysis on exciton dissociation, charge collection, carrier transport, and recombination has been carried out, unveiling that the improved device performance of asymmetric AC9‐based OPVs is originated from a better compromise between charge generation and non‐radiative charge recombination, compared with the corresponding symmetric ones. This work provides a high‐performing molecule and paves the way for high‐performance OPVs through asymmetric molecular design.

Metastable Dion-Jacobson 2D structure enables efficient and stable perovskite solar cells.

The performance of three-dimensional (3D) organic-inorganic halide perovskite solar cells (PSCs) can be enhanced through surface treatment with 2D layered perovskites that have efficient charge transport. We maximized hole transport across the layers of a metastable Dion-Jacobson (DJ) 2D perovskite that tuned the orientational arrangements of asymmetric bulky organic molecules. The reduced energy barrier for hole transport increased out-of-plane transport rates by a factor of 4 to 5, and the power conversion efficiency (PCE) for the 2D PSC was 4.9%. With the metastable DJ 2D surface layer, the PCE of three common 3D PSCs was enhanced by approximately 12 to 16% and could reach approximately 24.7%. For a triple-cation–mixed-halide PSC, 90% of the initial PCE was retained after 1000 hours of 1-sun operation at ~40°C in nitrogen.

Coherent effects in energy absorption in double quantum dot molecule – Metal nanoparticle hybrids

We theoretically study the optical properties of a hybrid structure consisting of a metal nanoparticle (MNP) and an asymmetric double semiconductor quantum dot (SQD) molecule, which are coupled together, via long-range Coulomb interaction. We derive and solve numerically the relevant density-matrix equations and use electromagnetic calculations to evaluate the energy absorption rate of the MNP and the asymmetric double SQD molecule, separately, as well as, the total absorption rate for the entire hybrid structure, as a function of the energy of an applied electromagnetic field , for two different applied field polarization directions. We also investigate the impact of the applied field intensity and the electron tunnelling coupling rate on the spectral profiles, for several values of the interparticle distance. The Autler-Townes splitting and double nonlinear Fano effects are obtained in the absorption spectra of the asymmetric double SQD molecule, the MNP and the total system.

Orientational control of molecular scale thermoelectricity.

Through a comprehensive theoretical study, we demonstrate that single-molecule junctions formed from asymmetric molecules with different terminal groups can exhibit Seebeck coefficients, whose sign depends on the orientation of the molecule within the junction. Three anthracene-based molecules are studied, one of which exhibits this bi-thermoelectric behaviour, due to the presence of a thioacetate terminal group at one end and a pyridyl terminal group at the other. A pre-requisite for obtaining this behaviour is the use of junction electrodes formed from different materials. In our case, we use gold as the bottom electrode and graphene-coated gold as the top electrode. This demonstration of bi-thermoelecricity means that if molecules with alternating orientations can be deposited on a substrate, then they form a basis for boosting the thermovoltage in molecular-scale thermoelectric energy generators (TEGs).

Effect of multiple rescatterings on continuum harmonics from asymmetric molecules in multicycle lasers.

A wide range of harmonics especially continuum harmonics is a prerequisite for attosecond pulse generation. One can use longer-wavelength lasers to push the cutoff to a higher order. However, this does not translate to the same amount of continuum range extension because multiple rescattering phenomena are also enhanced in the process, potentially affecting the lower end of the continuum harmonics. It is then important to understand exactly how multiple rescatterings affect the harmonic structure and their response to various laser parameters, which is the main theme of this paper. Particularly, by applying the synchrosqueezed time-frequency transform and classical electron trajectory analysis to the asymmetric molecule carbon monoxide (CO), we justify that the multiple rescatterings indeed influence the periodicity of the harmonic spectra and the stable periodicity is, in fact, bounded by the first- and third-order returns. Moreover, for the first time, we find that the high-order rescatterings are asymmetric regarding the molecular rotation of 180°, but always correlate with the first-order returns. Our last result is that by breaking the laser symmetry in an appropriate way, the contribution of multiple rescatterings is removed so that the continuum region is entirely defined by the first-order return energies.

Imidazole cores for the construction of dopant-free asymmetric hole-transporting materials for efficient inverted perovskite solar cells

An asymmetric molecule endowed with an extended electron donor generates a PCE over 16% in n–i–p structured inverted PSCs.

Dynamic processes in transient phases during self-assembly of organic semiconductor thin films

Crystallization of organic semiconductor small molecules from solution proceeds in multiple steps. This study describes how asymmetric molecules lead to long-lived transient phases and their impact on carrier mobility for electronic devices.

Molecular origin of fast evaporation at the solid-water-vapor line in a sessile droplet.

By analyzing the behaviors of water molecules at the solid-water-vapor contact line, we explore the molecular origin of large evaporation rates at the contact line and find new ways to increase the evaporation of the droplet. In contrast to previous models considering macroscopic surroundings and the geometry of the droplet, here we study the behaviors of water molecules by introducing cohesive energy which includes interactions of water molecules with both other water molecules in the droplet and atoms in the substrate. Molecules at the contact line bear the smallest evaporating energy barrier and therefore, possess the largest possibility to evaporate. Further analyses show that the evaporation rate of the droplet is enhanced through the large length of the contact line. These analyses are corroborated by experiments, where the evaporation rate of the droplet is enhanced up to 30% by incorporating hollow glass spheres in the droplet. Our theoretical and experimental efforts illustrate the underlying molecular mechanisms of large evaporation rates of a droplet, providing new avenues to accelerate droplet evaporation.

Role of quantum-coherence dressed states on the Fresnel–Fizeau drag and optical properties of surface plasmon polaritons through asymmetric double quantum dot-metallic plasmonic interfaces

Owing to the exceptional structural-design flexibility and tunability of physical properties of quantum dots, the manipulation of light in view of surface plasmons via dots–based hybrid nanostructures and dots-metallic interfaces finds promising device applications. Hereby, we first demonstrate theoretically the role of intense laser-excited dressed states on the light propagation, optical properties, and lateral and rotary drag of surface plasmon polaritons (SPPs), via plasmon-assisted induced transparency (PIT). For this, we employed a scheme of plasmonic interface comprising an asymmetric double quantum dot molecule GaAs/AlGaAs in the Λ − type configuration embedded in gold metallic surface. In particular, using density-matrix formulation, we present a detailed analytical solution of the quantum dot system for the required eigenvalues in view of the dressed eigenstates. The dressed states played a vital role in the formation of PIT transparency and hence the manipulation of SPPs propagation, optical properties and SPPs drag, via quantum interference. The calculated theoretical results on the optical properties such as absorption and dispersion spectrum, group index, group velocity, group delay, phase delay, wave vector, propagation length and SPPs drag are further elaborated with aid of numerical simulation. The maximum calculated lateral and rotary SPPs drag was of order ± 6.0 × 10−8 m or rad, respectively. The value of SPPs propagation lengths calculated along and perpendicular to the dot-metallic interface are 3.3 × 10−7 m and 2.0 × 10−9 m, respectively.

Asymmetric, mixed-valence molecules for spectroscopic readout of quantum-dot cellular automata

Mixed-valence compounds may provide molecular devices for an energy-efficient, low-power, general-purpose computing paradigm known as quantum-dot cellular automata (QCA). Multiple redox centers on mixed-valence molecules provide a system of coupled quantum dots. The configuration of mobile charge on a double-quantum-dot (DQD) molecule encodes a bit of classical information robust at room temperature. When arranged in non-homogeneous patterns (circuits) on a substrate, local Coulomb coupling between molecules enables information processing. While single-electron transistors and single-electron boxes could provide low-temperature solutions for reading the state of a ∼1 nm scale molecule, we propose a room-temperature read-out scheme. Here, DQD molecules are designed with slightly dissimilar quantum dots. Ab initio calculations show that the binary device states of an asymmetric molecule have distinct Raman spectra. Additionally, the dots are similar enough that mobile charge is not trapped on either dot, allowing device switching driven by the charge configuration of a neighbor molecule. A technique such as tip-enhanced Raman spectroscopy could be used to detect the state of a circuit comprised of several QCA molecules.

Probing allosteric interactions in homo-oligomeric molecular machines using solution NMR spectroscopy

Developments in solution NMR spectroscopy have significantly impacted the biological questions that can now be addressed by this methodology. By means of illustration, we present here a perspective focusing on studies of a number of molecular machines that are critical for cellular homeostasis. The role of NMR in elucidating the structural dynamics of these important molecules is emphasized, focusing specifically on intersubunit allosteric communication in homo-oligomers. In many biophysical studies of oligomers, allostery is inferred by showing that models specifically including intersubunit communication best fit the data of interest. Ideally, however, experimental studies focusing on one subunit of a multisubunit system would be performed as an important complement to the more traditional bulk measurements in which signals from all components are measured simultaneously. Using an approach whereby asymmetric molecules are prepared in concert with NMR experiments focusing on the structural dynamics of individual protomers, we present examples of how intersubunit allostery can be directly observed in high-molecular-weight protein systems. These examples highlight some of the unique roles of solution NMR spectroscopy in studies of complex biomolecules and emphasize the important synergy between NMR and other atomic resolution biophysical methods.

Controlling the Pump-Probe Optical Response in Asymmetric Tunneling-Controlled Double Quantum Dot Molecule—Metal Nanoparticle Hybrids

In the present work, we investigate the modified nonlinear pump-probe optical properties due to the excitonic–plasmonic interaction of a double semiconductor quantum dot (SQD) molecule coupled to a metal nanoparticle (MNP). More specifically, we study the absorption and the dispersion spectra of a weak electromagnetic field in a hybrid structure with two counterparts, a molecule of two coupled SQDs, and a spherical MNP driven by a field of high intensity. We solve the relevant density matrix equations, calculate the first-order optical susceptibility of the probe field in the strong pumping regime, and investigate the way in which the distance between the two counterparts modifies the optical response, for a variety of values of the physical constants of the system, including the pump-field detuning, the tunnelling rate, and the energy separation gap associated with the excited states of the coupled SQDs.

Pyrene-based asymmetric hexaarylbenzene derivatives: Synthesis, crystal structures, and photophysical properties

Hexaarylbenzenes (HAB) and their derivatives have attracted considerable attention due to their fantastic molecular geometry and various applications in materials science. Herein, a set of novel, pyrene-based, asymmetric hexaarylbenzene molecules 3a–c and 10 were synthesized and fully characterized by using 1H/13C NMR, single crystal X-ray diffraction, high-resolution mass spectra (HRMS), UV–Vis and fluorescence spectroscopy, as well as density functional theory (DFT) calculations. The compounds show tunable-emission color from violet (366 nm) to deep blue emission (407 nm) following the order of 10 < 3a < 3b < 3c in solution, and the pyrene-based asymmetric hexaarylbenzenes show a red-shift to the (deep) blue region (in the range from 406 to 466 nm) with a narrow full width at half-maximum (FWHM) emission spectrum in films. On the other hand, as the expanding π-conjugated molecular frameworks decreased in the order of 3c > 3b > 3a > 10 > hexaphenylbenzene (HPB), the asymmetric hexaarylbenzenes exhibited clearer aggregation-induced emission characterestics. In addition, DFT calculations indicated that there is strong electronic communication between the pyrene unit and the neighboring phenyl rings by a through-space charge-transfer process, which would play a curial role in lowering the quantum yield in the molecular aggregation state. Thus, this article provides an efficient synthetic strategy on how to design and synthesise high-performance pyrene-based hexaarylbenzene derivatives with narrow FWHM bands for potential applications in organic electronics.

A unified evolutionary origin for the ubiquitous protein transporters SecY and YidC

BackgroundProtein transporters translocate hydrophilic segments of polypeptide across hydrophobic cell membranes. Two protein transporters are ubiquitous and date back to the last universal common ancestor: SecY and YidC. SecY consists of two pseudosymmetric halves, which together form a membrane-spanning protein-conducting channel. YidC is an asymmetric molecule with a protein-conducting hydrophilic groove that partially spans the membrane. Although both transporters mediate insertion of membrane proteins with short translocated domains, only SecY transports secretory proteins and membrane proteins with long translocated domains. The evolutionary origins of these ancient and essential transporters are not known.ResultsThe features conserved by the two halves of SecY indicate that their common ancestor was an antiparallel homodimeric channel. Structural searches with SecY’s halves detect exceptional similarity with YidC homologs. The SecY halves and YidC share a fold comprising a three-helix bundle interrupted by a helical hairpin. In YidC, this hairpin is cytoplasmic and facilitates substrate delivery, whereas in SecY, it is transmembrane and forms the substrate-binding lateral gate helices. In both transporters, the three-helix bundle forms a protein-conducting hydrophilic groove delimited by a conserved hydrophobic residue. Based on these similarities, we propose that SecY originated as a YidC homolog which formed a channel by juxtaposing two hydrophilic grooves in an antiparallel homodimer. We find that archaeal YidC and its eukaryotic descendants use this same dimerisation interface to heterodimerise with a conserved partner. YidC’s sufficiency for the function of simple cells is suggested by the results of reductive evolution in mitochondria and plastids, which tend to retain SecY only if they require translocation of large hydrophilic domains.ConclusionsSecY and YidC share previously unrecognised similarities in sequence, structure, mechanism, and function. Our delineation of a detailed correspondence between these two essential and ancient transporters enables a deeper mechanistic understanding of how each functions. Furthermore, key differences between them help explain how SecY performs its distinctive function in the recognition and translocation of secretory proteins. The unified theory presented here explains the evolution of these features, and thus reconstructs a key step in the origin of cells.

Theoretical Investigation of the Excited-State Dynamics Mechanism of the Asymmetric Two-Way Proton Transfer Molecule BTHMB.

An asymmetric two-way proton transfer molecule 3-(benzo[d]-thiazol-2-yl)-2-hydroxy-5-methoxybenzaldehyde (BTHMB) with the function of white-light emission was synthesized in a recent experiment (Bhattacharyya, A.; Mandal, S. K.; Guchhait, N. J. Phys. Chem. A 2019, 123, 10246). The particularity of this molecule is that there are two possible forms, one of which contained a six-membered H-bonded network toward a N atom (BTHMB-NH) present in the molecule as a proton acceptor and the other was toward an O atom (BTHMB-OH). Unfortunately, the experimental work lacked the theoretical explanation about the determination of the BTHMB-NH form and its excited-state intramolecular proton transfer (ESIPT) process under different solvents. Therefore, this study has explored these two points by means of the time-dependent density functional theory (TDDFT) method. The calculated relative energy and potential energy profile (PEP) of the transformation between BTHMB-NH and BTHMB-OH forms illustrated that BTHMB-NH was more stable, and the transfer from BTHMB-NH to BTHMB-OH was almost impossible at both S0 and S1 states under all solvents due to high potential energy barriers (PEBs) (11.67-21.59 kcal/mol). These calculated results provided the theoretical explanation and verification for the conclusion that the BTHMB molecule exists in the BTHMB-NH form in the experiment. Subsequently, the constructed PEPs of the ESIPT process for BTHMB-NH have proved that it was prone to the ESIPT process due to low PEBs (0.11-0.28 kcal/mol) at the S1 state. In particular, as the solvent polarity increased, the intensity of the intramolecular hydrogen bond (IHB) (O3-H4···N5) increased and the ESIPT process was more likely to occur. In addition, the twisted intramolecular charge-transfer (TICT) process was studied to explore the possible fluorescence quenching pathway of BTHMB-NH. Based on the PEPs of BTHMB-NH-T as a function of the N5-C6-C7-C8 dihedral angle at the S0 and S1 states, it is seen that the S0 state TICT process was inhibited due to the large PEBs (16.45-23.93 kcal/mol). Although the S1 state PEBs have been greatly reduced, they were still maintained at about 3.60 kcal/mol (3.60-3.84 kcal/mol), and hence, this process was still relatively difficult to occur. Due to the fact that BTHMB can be regarded as a standard in future designs involving red light and solvent-specific white-light emitters, a certain amount of investigative work on the ESIPT process was done in detail, and it paved the way for future research on the directionality of ESIPT in double ESIPT probes.