Planar Molecules Research Articles

Inorganic novel cubic halide perovskite Sr3AsI3: Strain-activated electronic and optical properties

In recent years, inorganic perovskite materials have attracted a lot of attention in the field of solar technology due to their exceptional structural, optical, and electronic properties. This study thoroughly investigated, using first-principles density-functional theory (FP-DFT), the impact of compressive and tensile strain on the structural, optical, and electrical properties of the inorganic cubic perovskite Sr3AsI3. The unstrained planar Sr3AsI3 molecule exhibits a direct bandgap of 1.265 eV value at Γ point. The bandgap of the Sr3AsI3 perovskite is lowered to 1.212 eV when the relativistic spin-orbital coupling (SOC) effect is subjected in the observations. In addition, the structure's bandgap exhibits a falling prevalence due to compressive strain and a slight rise due to tensile strain. The optical indicators such as dielectric functions, absorption coefficient, reflectivity, and electron loss function show that this component has a great ability to absorb in the visible range in accordance with band characteristics. When compressive strain is raised, it is discovered that the spikes of the dielectric constant of Sr3AsI3 move to lower photon energy (redshift), and conversely, while growing tensile strain, it exhibits increased photon energy changing behavior (blueshift). As a result, the Sr3AsI3 perovskite is regarded as being ideal for use in solar cells for the production of electricity and light management.

Four Slip-Stacked Arrangements, Three Types of Photophysics: Crystal Structure and Solid-State Fluorescence of 3,6-Diaryl Substituted Furo[3,4-c]furanone Polymorphs and Regioisomers.

Six symmetrical 3,6-diaryl (aryl=phenyl, 2-, 3- and 4-tolyl, 2,4- and 3,5-xylyl) substituted furo[3,4-c]furanones (DFF) were synthesized. The computational analysis, based on density functional theory, found eight possible centrosymmetrical slipped π-stack arrangements, formed according to electron repulsion minimization principle, as for previously reported for π-isoelectronic diketopyrrolopyrroles (DPP). One of these slipped stack arrangements was found to form infinite columns in the crystals of a new polymorph of parent phenyl derivative (with centre-to-centre distance CC=6.975 Å), other three types of stacks were found for 3-tolyl (CC=6.153 Å), 4-tolyl (CC=3.849 Å) and 2,4-xylyl (CC=4.856 Å) derivatives by single crystal X-ray diffractometry. All six derivatives show intense solution fluorescence in blue/green region, with a maximum driven entirely by a number and position of methyl substituents on phenyl rings. On the other hand, the solid-state fluorescence from yellow over orange to red is observed only for four derivatives and its presence/absence, spectral position and vibronic structure is driven exclusively by the slips in π-stacks (with interplanar distance always less than 3.5 Å) of almost planar DFF molecules, resulting in J-type emission, H-type excimer-like emission and H-type quenching.

Stable Deep‐Blue Electroluminescence from Hierarchical Crystalline Structure Based on Planar Conformational Terfluorenes: Benefits of Preventing Defect Structures Formation

AbstractLiner‐type organic conjugated molecules with 1D π‐electron delocalization present conformation‐dependent intramolecular optoelectronic behavior. Significantly different from non‐planar ones, the coplanar conformational backbone of π‐conjugated molecules can enhance intramolecular π‐electron delocalization and dominate intermolecular π‐electron coupling, which are the fundamental parameters for improving their optoelectronic properties. Herein, the effect of the formation of coplanar conformation on intermolecular packing and optoelectrical properties of liner‐type steric terfluorene (DSFX‐SFSO) toward solution‐processed deep‐blue organic light‐emitting diodes (OLEDs) is systematically demonstrated. Firstly, uniform and continuous crystalline films based on the planar conformational DSFX‐SFSO molecules are achieved via thermal annealing at 160 °C, which can avoid microscale crystallization processing. Contrary to amorphous ones, these hierarchical crystalline films present robust deep‐blue emission with an efficiency of > 60%, due to the suppression of defect structures. More interestingly, this hierarchical crystalline film has a stable and efficient deep‐blue electroluminescence (CIE: 0.15, 0.09) without the obvious defective green‐band emission, even at 500 mA cm−2, also further confirming the excellent and perfect molecular landscape to obtain single‐chromophore excitonic behavior from single planar‐terfluorene segments. Therefore, obtaining a uniform hierarchical structure based on planar conformational molecules is an effective strategy to optimize the optoelectrical properties for optoelectronic applications.

PH-Dependent Binding and Releasing Mechanism of Acetate in the Inner Water Cavity of Heliorhodopsin.

The high-resolution structure of heliorhodopsin crystallized at low pH reveals the presence of a planar triangle molecule, acetate, in the inner water cavity. Here, we investigate how the acetate molecule is stabilized at the counterion Glu107 moiety, using molecular dynamics (MD) simulations and a quantum mechanical/molecular mechanical (QM/MM) approach. QM/MM calculations indicate that the density is best described as acetate among triangle acids, including nitric acid and bicarbonate. The calculated protonation state indicates that protonated acetate donates an H-bond to deprotonated Glu107 in the low-pH crystal structure. The observed red-shift of ∼30 nm in the absorption wavelength with pKa ≈ 4 is likely due to the His23/His80 protonation, rather than the Glu107 protonation. MD simulations also show that acetate can exist at the Glu107 moiety only when it is protonated. When ionized, acetate is released from the Glu107 moiety via Asn101 at the channel bottleneck and Arg91 on the intracellular protein surface. These observations could explain how acetate binds at low pH and releases at high pH.

Pure Graphene Acts as an "Entropic Surfactant" at the Octanol-Water Interface.

Graphene oxide (GO) has proved itself as a nanomaterial capable of acting as a surfactant by lowering the interfacial tension of the oil-water interface due to its polar oxygen groups. However, the surfactant behavior of the pure graphene sheet─since prevention of edge oxidation in experimental setups is nontrivial─is still an unresolved issue in graphene research despite significant progress in the field in recent years. Here, we conduct both atomistic and coarse-grained simulations to demonstrate that─surprisingly─even pristine graphene, which only consists of hydrophobic carbon atoms, is attracted to the octanol-water interface and consequently reduces its surface tension by 2.3 kBT/nm2 or about 10 mN/m. Interestingly, the location of the free energy minimum is not precisely at the oil-water interface itself but is rather buried about two octanol layers into the octanol phase, being about 0.9 nm from the water phase. We demonstrate that the observed surfactant behavior is purely entropically driven and can be attributed to the unfavorable lipid-like structuring of octanol molecules at the free octanol-water interface. In essence, graphene enhances the inherent lipid-like behavior of octanol at the water interface rather than directly acting as a surfactant. Importantly, graphene does not display surfactant-like behavior in corresponding Martini coarse-grained simulations of the octanol-water system since the free liquid-liquid interface loses essential structure at the lower coarse-grained resolution. However, a similar surfactant behavior is recovered in coarse-grained simulations of longer alcohols such as dodecan-1-ol and hexadecan-1-ol. The observed discrepancies at different model resolutions enable us to construct a comprehensive model of the surfactant behavior of graphene at the octanol-water interface. The here-gained insights may facilitate the broader utilization of graphene in numerous domains of nanotechnology. Furthermore, since a drug's octanol-water partition coefficient is a crucial physicochemical parameter in rational drug discovery, we also believe that the universality of the here-illustrated entropic surfactant behavior of planar molecules deserves special attention in the drug design and development field.

Silver‐Catalyzed Tandem Reaction of β‐Alkynyl Ketones toward Spiro[isochromene‐1,4′‐quinoline] with Anticancer Activities

AbstractSpirocyclic frameworks could enhance the drug‐like properties of planar bioactive molecules by increasing their three‐dimensionality, making the development of synthetic methodology and bioactivity assays for spiro compounds highly attractive. This work reported the silver‐catalyzed tandem cycloisomerization/Povarov reaction between β‐alkynyl ketones and hexahydro‐1,3,5‐triazines, access to spiro[isochromene‐1,4’‐quinoline]. This synthetic protocol was characterized by remarkable efficiency, low catalyst‐loading and high diastereoselectivity. Moreover, the spirocyclic quinolines exhibited good cytotoxicity in U937 cells by activating the Notch‐signaling pathway exclusively.

Preparation of 2-Nitrocacalol Acetate From a Sesquiterpene Isolated From Roots of Psacalium decompositum. Evaluation of α-Glucosidase and Acetylcholinesterase Inhibition

Objective To introduce a nitrogen atom into the structure of the cacalol acetate and to evaluate the change in its ability to inhibit enzymes of therapeutic importance such as α-glucosidase and acetylcholinesterase (AChE), which are targeted in the development of drugs for the treatment of diabetes and Alzheimer’s disease (AD), respectively. Methods Cacalol acetate was obtained by subjecting the hexane and ethyl acetate extracts from the roots of Psacalium decompositum to acetylation conditions. Subsequently, the cacalol acetate was brought under nitration conditions using cerium (IV) ammonium nitrate and acetic anhydride to obtain 2-nitrocacalol acetate; this compound was characterized by nuclear magnetic resonance, mass spectrometry, and X-ray diffraction techniques. Additionally, the inhibitory activity of the ethyl acetate extract, the cacalol acetate, and the 2-nitrocacalol acetate was evaluated on the enzymes α-glucosidase and AChE. Finally, the possible mode of ligand–enzyme binding through molecular docking was established. Results The 2-nitrocacalol acetate was obtained with a 20% yield. Its crystallographic structure was obtained, to our knowledge, for the first time, corroborating the S configuration in C5, showing a mostly planar molecule, in which the C6, C7, and C14 atoms and the acetyl group leaving the plane. The ethyl acetate extract was that which significantly inhibited the α-glucosidase (95.8% at 100 μg/mL), while the 2-nitrocacalol acetate exhibited the highest inhibitory activity of the AChE (69.9% at 10 µg/mL). The 2-nitrocacalol acetate presented a favorable interaction energy with the AChE (−8.68 kcal/mol), highlighting the formation of two hydrogen bonds and hydrophobic interactions. Conclusions The 2-nitrocacalol acetate and its crystallographic structure were obtained, to our knowledge, for the first time providing a new modification to this sesquiterpene by introducing a nitro group, which was favored its ability to inhibit AChE. These structural modifications encourage future research in these sesquiterpenes as targets for the development of novel drugs that would be useful in clinical practice.

Biased Symmetry Breaking in the Formation of Intercalated Layered Double Hydroxides: toward Control of Homochiral Supramolecular Assembly.

Homochiral supramolecular assembly (HSA) based on achiral molecules has provided important clues to understand the origin of biological homochirality from the aspect of symmetry breaking. However, planar achiral molecules still face the challenge of forming HSA due to the lack of driving force for twisted stacking, which is a prerequisite for homochirality. Here, with the benefit of the formation of 2D intercalated layered double hydroxide (LDH, host-guest nanomaterials) in vortex motion, planar achiral guest molecules can form the chiral units with spatially asymmetrical structure in the confinement space of LDH. Once the LDH is removed, these chiral units are in a thermodynamic non-equilibrium state, which can be amplified to HSA by self-replicating. Especially, the homochiral bias can be predicted in advance by controlling the vortex direction. Therefore, this study breaks the bottleneck of complicated molecular design and provides a new technology to achieve HSA made of planar achiral molecules with definite handedness.

Sterically‐Hindered Molecular p‐Dopants Promote Integer Charge Transfer in Organic Semiconductors

AbstractMolecular p‐dopants designed to undergo electron transfer with organic semiconductors are typically planar molecules with high electron affinity. However, their planarity can promote the formation of ground‐state charge transfer complexes with the semiconductor host and results in fractional instead of integer charge transfer, which is highly detrimental to doping efficiency. Here, we show this process can be readily overcome by targeted dopant design exploiting steric hindrance. To this end, we synthesize and characterize the remarkably stable p‐dopant 2,2′,2′′‐(cyclopropane‐1,2,3‐triylidene)tris(2‐(perfluorophenyl)acetonitrile) comprising pendant functional groups that sterically shield its central core while retaining high electron affinity. Finally, we demonstrate it outperforms a planar dopant of identical electron affinity and increases the thin film conductivity by up to an order of magnitude. We believe exploiting steric hindrance represents a promising design strategy towards molecular dopants of enhanced doping efficiency.

Sterically-Hindered Molecular p-Dopants Promote Integer Charge Transfer in Organic Semiconductors.

Molecular p-dopants designed to undergo electron transfer with organic semiconductors are typically planar molecules with high electron affinity. However, their planarity can promote the formation of ground-state charge transfer complexes with the semiconductor host and results in fractional instead of integer charge transfer, which is highly detrimental to doping efficiency. Here, we show this process can be readily overcome by targeted dopant design exploiting steric hindrance. To this end, we synthesize and characterize the remarkably stable p-dopant 2,2',2''-(cyclopropane-1,2,3-triylidene)tris(2-(perfluorophenyl)acetonitrile) comprising pendant functional groups that sterically shield its central core while retaining high electron affinity. Finally, we demonstrate it outperforms a planar dopant of identical electron affinity and increases the thin film conductivity by up to an order of magnitude. We believe exploiting steric hindrance represents a promising design strategy towards molecular dopants of enhanced doping efficiency.

Translating Planar Heterocycles into Three-Dimensional Analogs by Photoinduced Hydrocarboxylation.

The rapid preparation of complex three-dimensional (3D) heterocyclic scaffolds is a key challenge in modern medicinal chemistry. Despite the increased probability of clinical success for small molecule therapeutic candidates with increased 3D complexity, new drug targets remain dominated by flat molecules due to the abundance of coupling reactions available for their construction. In principle, heteroarene hydrofunctionalization reactions offer an opportunity to transform readily accessible planar molecules into more three-dimensionally complex analogs through the introduction of a single molecular vector. Unfortunately, dearomative hydrofunctionalization reactions remain limited. Herein, we report a new strategy to enable the dearomative hydrocarboxylation of indoles and related heterocycles. This reaction represents a rare example of a heteroarene hydrofunctionalization that meets the numerous requirements for broad implementation in drug discovery. The transformation is highly chemoselective, broad in scope, operationally simple, and readily amenable to high-throughput experimentation (HTE). Accordingly, this process will allow existing libraries of heteroaromatic compounds to be translated into diverse 3D analogs and enable exploration of new classes of medicinally relevant molecules.

Translating Planar Heterocycles into Three‐Dimensional Analogs by Photoinduced Hydrocarboxylation**

AbstractThe rapid preparation of complex three‐dimensional (3D) heterocyclic scaffolds is a key challenge in modern medicinal chemistry. Despite the increased probability of clinical success for small molecule therapeutic candidates with increased 3D complexity, new drug targets remain dominated by flat molecules due to the abundance of coupling reactions available for their construction. In principle, heteroarene hydrofunctionalization reactions offer an opportunity to transform readily accessible planar molecules into more three‐dimensionally complex analogs through the introduction of a single molecular vector. Unfortunately, dearomative hydrofunctionalization reactions remain limited. Herein, we report a new strategy to enable the dearomative hydrocarboxylation of indoles and related heterocycles. This reaction represents a rare example of a heteroarene hydrofunctionalization that meets the numerous requirements for broad implementation in drug discovery. The transformation is highly chemoselective, broad in scope, operationally simple, and readily amenable to high‐throughput experimentation (HTE). Accordingly, this process will allow existing libraries of heteroaromatic compounds to be translated into diverse 3D analogs and enable exploration of new classes of medicinally relevant molecules.

Boron-π interactions in two 3-(dihydroxyboryl)anilinium salts analyzed by crystallographic studies and supported by the noncovalent interactions (NCI) index theoretical approach.

In the title compounds, 3-(dihydroxyboryl)anilinium bisulfate monohydrate, C6H9BNO2+·HSO4-·H2O (I), and 3-(dihydroxyboryl)anilinium methyl sulfate, C6H9BNO2+·CH3SO4- (II), the almost planar boronic acid molecules are linked by pairs of O-H...O hydrogen bonds, forming centrosymmetric motifs that can be described by the graph-set R22(8) motif. In both crystals, the B(OH)2 group acquires a syn-anti conformation (with respect to the H atoms). The presence of the hydrogen-bonding functional groups B(OH)2, NH3+, HSO4-, CH3SO4- and H2O generates three-dimensional hydrogen-bonded networks, in which the bisulfate (HSO4-) and methyl sulfate (CH3SO4-) counter-ions act as the central building blocks within the crystal structures. Furthermore, in both structures, the packing is stabilized by weak boron-π interactions, as shown by noncovalent interactions (NCI) index calculations.

Nanoarchitectonics of supramolecular porphyrins based on a bis(porphyrin) cleft molecule

This account describes the construction of supramolecular constructs based on our bis(porphyrin) cleft molecule. The bis(porphyrin) cleft molecule was originally synthesized as a tweezer-shaped host molecule for planar guest molecules. A detailed study on the bis(porphyrin) cleft molecule revealed that the bis(porphyrin) cleft molecule forms two kinds of supramolecular structures. One structure is a self-complementary dimer obtained through intermolecular hydrogen bonding, and the other structure is a host-guest complex, in which the electron-rich cleft cavity accommodates electron-deficient guests through donor-acceptor interactions. Through the two supramolecular structures, two distinct supramolecular polymers can be formed through self-complementary dimerization or donor-acceptor host-guest complexation. The supramolecular chain structures were modified by judiciously using two distinct supramolecular structures. In the main text, several results, including the binding capability of our bis(porphyrin) cleft molecule, the formation of supramolecular porphyrin complexes, and the supramolecular polymerization behaviors of the bis(porphyrin) cleft molecule, are reported. In conclusion, the future direction of the bis(porphyrin) cleft molecule is provided.

Boron Difluoride β-Diketonates: Structure and Phosphorescence

Phosphorescence data on boron difluoride β-diketonates of various structure have been systematized. Nonplanar boron difluoride molecules are characterized by the inversion of the S1 and T2 levels, which promotes efficient population of triplet levels and intense phosphorescence or delayed fluorescence of crystals. Planar molecules are characterized by a classical sequence of singlet and triplet levels and a coplanar arrangement of antiparallel molecules, which contributes to excimer delayed fluorescence.

Influence of the internal degrees of freedom of coronene molecules on the nonlinear dynamics of a columnar chain.

The nonlinear dynamics of a one-dimensional molecular crystal in the form of a chain of planar coronene molecules is analyzed. Using molecular dynamics, it is shown that a chain of coronene molecules supports acoustic solitons, rotobreathers, and discrete breathers. An increase in the size of planar molecules in a chain leads to an increase in the number of internal degrees of freedom. This results in an increase in the rate of emission of phonons from spatially localized nonlinear excitations and a decrease in their lifetime. Presented results contribute to the understanding of the effect of the rotational and internal vibrational modes of molecules on the nonlinear dynamics of molecular crystals.

Dual Chromophoric Meso‐Aryl BODIPYs with Aggregation Induced Red‐Emission Characteristics: Optical Properties and their Application in Fe3+ Detection

AbstractHerein, we report the design of meso‐aryl BODIPYs as a structural motif for aggregation‐caused quenching (ACQ) to aggregation‐induced emission (AIE) transformation. A series of meso‐aryl BODIPY derivatives were synthesized, by systematically increasing the size of the chromophore at the meso‐position from phenyl to pyrene. The effect of various factors, such as the aryl ring size, solvents, viscosity, and metal cations, on the photophysical properties was analyzed. The emission properties are well correlated with the flexibility of the aromatic ring for free rotation around the Caryl−CBODIPY bond. Accordingly, meso‐phenanthrene BODIPY (PhB) has the highest emission characteristics. The emission property of less bulky aryl‐substituted BODIPYs increases by increasing the solvent viscosity. The interaction of Fe3+ ions with aryl‐BODIPYs provides a prominent photophysical response based on Lewis‐acid supported decomplexation of BF2 in aryl‐BODIPYs. The bichromophoric meso‐aryl BODIPYs exhibit notable intramolecular excitation energy transfer from the aromatic ring to the BODIPY core, which is higher in meso‐anthracene BODIPY(AB). Hence, decorating BODIPYs with polycyclic aromatic systems generates a twisted structure, which inhibits the π‐π stacking between the planar aromatic molecules. This can be proposed as an effective approach at the molecular level to convert planar aryl luminophores having ACQ to AIEgens. Besides, the meso‐pyrene BODIPY derivative shows excellent mechanofluorochromic behaviour.

Influence of hemicellulose and lignin on intermolecular interaction between quinacridone and lignocellulosic fibers revealed by gel-state NMR and color measurements

Quinacridone, a π-conjugated planar molecule, and common red pigment in industrial and painting applications, easily aggregates to form large clusters of pigment particles, resulting in a reduction in color strength. Cotton-derived cellulose nanofiber (NF), which almost consists of cellulose without hemicellulose and lignin, has been found to adsorb quinacridone on the surface, which inhibits pigment aggregation. The aggregation inhibition property of cellulose NF was induced by the strong intermolecular interactions between cellulose and quinacridone. In this study, the properties of lignocellulosic fibers for suppressing the aggregation of quinacridone pigments were investigated to reveal the influence of hemicellulose and lignin on the intermolecular interactions between quinacridone and fibers. Two lignocellulosic fibers with different degrees of fibrillation were used as dispersants of the pigment. In the scanning electron microscopy (SEM) images of the quinacridone–lignocellulose mixture, quinacridone particles were observed along the lignocellulose fiber, indicating that the quinacridone particles were well-adsorbed on the fiber surface. Consequently, the color of the aqueous suspension of quinacridone–lignocellulose mixture became increasingly vivid as the weight ratio of the lignocellulose fibers increased and as the fiber was fibrillated. The nuclear Overhauser effect spectroscopy (NOESY)–nuclear magnetic resonance (NMR) spectrum for quinacridone–lignocellulose suspension in d-dimethyl sulfoxide showed several NOE cross-peaks between quinacridone and cellulose/hemicellulose, whereas no cross-peaks between quinacridone and lignin were observed. It can be concluded that cellulose and hemicellulose promote the adsorption of quinacridone on the fiber surface, whereas lignin does not interact with quinacridone, even though both are aromatic molecules. This suggests that the intermolecular interactions based on hydrogen bonding and CH–π attraction are more dominant than the π–π attraction between quinacridone and lignocellulosic fibers.

Selective adsorption of Crystal Violet via hydrogen bonded water bridges by InVO4

Selective adsorption is an effective method to achieve in the recovery of CV. We report that InVO4 is highly selective adsorbent for Crystal Violet (CV) from the water, which has much larger adsorption capacity (134.25 mg/g) than that of titanium dioxide, alumina, and silica gel (6.1–33.9 mg/g) although the specific surface areas of these solids are much larger than that of InVO4. The (200) facets of InVO4 exhibited the optimal sites for the selective-chemisorption of CV. The trigonal planar CV molecules are bonded to the (200) facets at all three vertices via a cationic quaternary amine and two tertiary amines. This adsorption mechanism mainly involved the formation of hydrogen-bonded water bridges (CV-N···H-O-H···O-VO3-In) on the basis of in-situ Fourier transform infrared (In-situ-FTIR). This study not only provides a new preparation method for vanadate adsorbent, but also provides a new idea for the recovery and utilization of CV in waste liquid.

A Simple Approach to Solution‐Processible Small‐Molecule Multi‐Resonance TADF Emitters for High‐Performance Narrowband OLEDs

AbstractMost multi‐resonance (MR) induced thermally activated delayed fluorescence (TADF) emitters generally exhibit strong aggregation and relatively worse solubility due to their rigid and planar molecule structures, which is highly undesirable for solution‐processible devices. Herein, a simple but feasible approach for solution‐processible small‐molecule MR‐TADF emitters is developed by incorporating two MR‐TADF units onto carbazole bridge bearing long alkyl chains. The obtained emitters demonstrate supreme film‐forming capability and narrowband emissions with full‐width at half‐maximums (FWHMs) of 22 nm. The resulting solution‐processed narrowband electroluminescent devices achieve maximum external quantum efficiency of 27.1 %, which represents the highest efficiency among the solution‐processed OLEDs based on MR‐TADF emitters. This simple approach reveals great potential of developing solution‐processible emitters for rigid and planar molecular structures.