Twisted Conformation Research Articles

Bis(naphthobipyrrolyl)methene-derived hexapyrrolic BODIPY as a single-molecule helicate with near-infrared emission.

Helically twisted bis(naphthobipyrrolyl)methene-derived open-chain hexapyrroles have been synthesized as HCl salts and the corresponding BODIPY. Their solid-state structures elucidated by single-crystal X-ray diffraction analysis clearly showed the presence of intramolecular hydrogen bonds, which were concluded to play a pivotal role in stabilizing the twisted conformation. Both molecules were observed to be NIR active, with the BODIPY moiety emission extending beyond 800 nm.

Multifunctional Fluorescent Materials with Reversible Mechanochromism and Distinct Photochromism

AbstractIt is extremely significant and desirable to integrate the fascinating mechanochromism and photochromism in one simple molecule. Herein, two intriguing cyanostilbene‐containing triphenylamine (TPA)/tetraphenylethylene (TPE) derivatives (Z‐TPA‐MB and Z‐TPE‐MB) are elaborately designed, which not only display excellent aggregation‐induced emission (AIE) properties with high solid‐state fluorescence quantum yields (60.9% and 63.8%) but also exhibit reversible and high contrast mechanochromism and distinct photochromism. The powders of Z‐TPA‐MB and Z‐TPE‐MB both exhibit large red‐shift under mechanical stimulation based on the highly twisted conformation and the resulting loose packing mode, accompanied by significant changes in apparent and fluorescent colors. Meanwhile, their solid‐state fluorescence can be reversibly switched between crystalline and amorphous structures through alternating grinding and solvent fuming, exhibiting good fatigue resistance. In addition, the molecules also exhibit distinct dual‐mode photochromic behaviors owing to the presence of cyanostilbene moieties: under 420/365 nm light irradiation, the fluorescence of which decreases in solution owing to the photo‐isomerization, while decreases and blue‐shifts in the aggregated state owing to the photodimerization reactions. The reversible, tractable, and high‐contrast mechanochromism and distinct photochromism of the cyanostilbene‐containing molecules endow them with excellent application prospects in the field of rewritable papers and photo‐patterning.

Molecular Twisting Affects the Solid-State Photochemical Reactions of Unsaturated Ketones and the Photomechanical Effects of Molecular Crystals.

Three groups of chalcone derivatives and their analogues involving halogen atoms (X=F, Cl, Br) have been synthesized. Firstly, the nearly planar acyclic chalcone derivatives were inclined to undergo photo-induced stereospecific [2+2] cycloaddition, which triggered the crystals to exhibit macroscopic motions of bending or cracking. In particular, the single-crystal-to-single-crystal transformation happened upon UV irradiation of the crystals, which was helpful for the understanding photomechanical effects. Cyclic 3,4-dihydronaphthalene-based chalcone analogues possess a more twisted conformation, and they tend to undergo trans-cis isomerization. No photomechanical effect was observed for the crystals of the cyclic chalcone analogues due to the lower isomerization rate. The twist degree of chroman-based molecules was in between of the first two, [2+2] cycloaddition and trans-cis isomerization simultaneously took place in crystals. Photo-induced bending and twisting were observed for the crystals of chroman-based chalcone analogues. Therefore, the differences in molecular dihedral angles in α,β-unsaturated ketones were responsible for their photochemical characters and in turn to tune the photomechanical effects. In this work, a bridge between the molecular structures and solid-state photochemical reactions triggered photomechanical crystals is built.

Light-Responsive Oligothiophenes Incorporating Photochromic Torsional Switches.

We present a quaterthiophene and sexithiophene that can reversibly change their effective π-conjugation length through photoexcitation. The reported compounds make use of light-responsive molecular actuators consisting of an azobenzene attached to a bithiophene unit by both direct and linker-assisted bonding. Upon exposure to 350 nm light, the azobenzene undergoes trans-to-cis isomerization, thus mechanically inducing the oligothiophene to assume a planar conformation (extended π-conjugation). Exposure to 254 nm wavelength promotes azobenzene cis-to-trans isomerization, forcing the thiophenic backbones to twist out of planarity (confined π-conjugation). Twisted conformations are also reached by cis-to-trans thermal relaxation at a rate that increases proportionally with the conjugation length of the oligothiophene moiety. The molecular conformations of quaterthiophene and sexithiophene were characterized by using steady-state UV-vis spectroscopy, X-ray crystallography and quantum-chemical modeling. Finally, we tested the proposed light-responsive oligothiophenes in field-effect transistors to probe the photo-induced tuning of their electronic properties.

Bis(4-hy-droxy-phen-yl) 1,4-phenyl-enebiscarbamate.

The title compound, C20H16N2O6 (systematic name: 4-hy-droxy-phenyl N-{4-[(4-hy-droxy-phen-oxy-carbon-yl)amino]-phen-yl}carbamate), contains two urethane groups substituting the central benzene ring in para positions. The mol-ecule is centrosymmetric, and displays a twisted conformation for the three aromatic rings [the dihedral angle between central benzene ring and the urethane group is 33.4 (6)°, and that between the latter and the terminal ring is 65.1 (1)°]. In the crystal, a three-dimensional framework is formed through O-H⋯O and N-H⋯O hydrogen bonds involving the hy-droxy and urethane functional groups, respectively.

Highly twisted luminogen based on asymmetric D-A-D’ type dicyanovinyl derivative decorated dibenzofuran and carbazole with aggregation-induced emission enhancement and obvious mechanochromic behavior

A novel asymmetric D-A-D’ type dicyanovinyl derivative DBF-DCN-Cz, which was constructed with a dibenzofuran unit and a carbazole moiety bridged by a dicyanovinyl spacer, was designed and synthesized. It was found that the luminogen DBF-DCN-Cz showed unique intramolecular charge transfer (ICT) process from electron-donating carbazole unit to electron-accepting dicyanovinyl moiety. Optical studies and theoretical calculations indicated that DBF-DCN-Cz possessed highly twisted conformation and aggregation-induced emission enhancement (AIEE) property because of the presence of the large steric hindrance. Interestingly, the emitting color of solid powder of DBF-DCN-Cz changed from initial bright yellow to orange after grinding, showing obvious mechanochromic luminescence (MCL). XRD and DSC experiments confirmed that the MCL phenomenon originated from the phase transition from crystalline to amorphous states. This work might broaden the knowledge for AIE-active MCL materials and laid the foundation for their extensive applications.

A new modification of oxonium trimetaphosphimate monohydrate

AbstractMetaphosphimates are possible precursors for oxonitridophosphates. A new polymorph of trimetaphosphimic acid, in fact an oxonium trimetaphosphimate monohydrate, crystallizes in the monoclinic space group P21/c. It exhibits coin‐roll‐like stacks of H2(PO2NH)3− anions in a rectangular pattern, whereas these form a hexagonal arrangement in the known polymorph. Ring conformation analysis reveals a state between boat and twist conformations, closer to the boat conformation. Temperature‐dependent powder diffraction shows decomposition upon heating to ca. 100 °C.

A Versatile Tetraphenylethene Derivative Bearing Excitation Wavelength Dependent Emission, Multistate Mechanochromism, Reversible Photochromism, and Circularly Polarized Luminescence and Its Applications in Multimodal Anticounterfeiting

A Versatile Tetraphenylethene Derivative Bearing Excitation Wavelength Dependent Emission, Multistate Mechanochromism, Reversible Photochromism, and Circularly Polarized Luminescence and Its Applications in Multimodal Anticounterfeiting

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Regulation of multiple dimeric states of E-cadherin by adhesion activating antibodies revealed through Cryo-EM and X-ray crystallography.

E-cadherin adhesion is regulated at the cell surface, a process that can be replicated by activating antibodies. We use cryo-electron microscopy (EM) and X-ray crystallography to examine functional states of the cadherin adhesive dimer. This dimer is mediated by N-terminal beta strand-swapping involving Trp2, and forms via a different transient X-dimer intermediate. X-dimers are observed in cryo-EM along with monomers and strand-swap dimers, indicating that X-dimers form stable interactions. A novel EC4-mediated dimer was also observed. Activating Fab binding caused no gross structural changes in E-cadherin monomers, but can facilitate strand swapping. Moreover, activating Fab binding is incompatible with the formation of the X-dimer. Both cryo-EM and X-ray crystallography reveal a distinctive twisted strand-swap dimer conformation caused by an outward shift in the N-terminal beta strand that may represent a strengthened state. Thus, regulation of adhesion involves changes in cadherin dimer configurations.

Novel Ortho‐Linkage Donor‐Acceptor Type Host Materials for Efficiently Red Phosphorescence Organic Light‐Emitting Diodes

AbstractHigh performance device is the key issue for organic light‐emitting diodes (OLEDs) industrialization. In this instance, efficient hosts, emitters, as well as other functional layer materials are essential for the realization of high‐performance OLEDs. Herein, we develop a series of D−A type host materials, TPATRZ, CzTRZ, and POXTRZ with ortho‐linking strategy. The ortho‐linkage makes TPATRZ, CzTRZ, and POXTRZ highly twisted conformations, which reducing the degree of intramolecular conjugation and maintain high triplet energies of these materials. The red phosphorescence organic light emitting diodes by using Ir(piq)2(acac) as dopant, TPATRZ, CzTRZ, and POXTRZ as host materials achieved relative high device performance with over 20 % external quantum efficiency and flat efficiency roll‐off. The EQEs of the champion devices remain above 22 % at the practical luminance (500 and 1000 cd m−2). The device hosted by POXTRZ achieved the highest external quantum efficiency of 24.0 %, as well as smallest efficiency roll‐off of 6.3 % at 1000 cd m−2. These results further extend the possibilities of ortho‐linkage D−A type host materials and make them have a promising application in OLEDs.

19F-NMR Unveils the Ligand-Induced Conformation of a Catalytically Inactive Twisted Homodimer of tRNA-Guanine Transglycosylase.

Understanding the structural arrangements of protein oligomers can support the design of ligands that interfere with their function in order to develop new therapeutic concepts for disease treatment. Recent crystallographic studies have elucidated a novel twisted and functionally inactive form of the homodimeric enzyme tRNA-guanine transglycosylase (TGT), a putative target in the fight against shigellosis. Active-site ligands have been identified that stimulate the rearrangement of one monomeric subunit by 130° against the other one to form an inactive twisted homodimer state. To assess whether the crystallographic observations also reflect the conformation in solution and rule out effects from crystal packing, we performed 19F-NMR spectroscopy with the introduction of 5-fluorotryptophans at four sites in TGT. The inhibitor-induced conformation of TGT in solution was assessed based on 19F-NMR chemical shift perturbations. We investigated the effect of C(4) substituted lin-benzoguanine ligands and identified a correlation between dynamic protein rearrangements and ligand-binding features in the corresponding crystal structures. These involve the destabilization of a helix next to the active site and the integrity of a flexible loop-helix motif. Ligands that either completely lack an attached C(4) substituent or use it to stabilize the geometry of the functionally competent dimer state do not indicate the presence of the twisted dimer form in the NMR spectra. The perturbation of crucial structural motifs in the inhibitors correlates with an increasing formation of the inactive twisted dimer state, suggesting these ligands are able to shift a conformational equilibrium from active C2-symmetric to inactive twisted dimer conformations. These findings suggest a novel concept for the design of drug candidates for further development.

Parallel versus Twisted Pentacenes: Conformational Impact on Singlet Fission.

We placed two pentacene chromophores at the termini of a diacetylene linker to investigate the impact of excitation wavelength, conformational flexibility, and vibronic coupling on singlet fission. Photoexcitation of the low-energy absorption results in a superposed mixture of states, which transform on an ultrafast time-scale into a spin-correlated and vibronically coupled/hot delocalized triplet pair 1(T1T1)deloc. Regardless of temperature, the lifetime for 1(T1T1)deloc is less than 2 ps. In contrast, photoexcitation of the high-energy absorption results in the formation of 1(T1T1)deloc lasting 1.0 ps, which then decays at room temperature within 4 ps via triplet-triplet annihilation. Lowering the temperature enables 1(T1T1)deloc to delocalize and vibronically decouple, in turn affording 1(T1T1)loc. In addition, our results suggest that the quasi-free rotation at the diacetylene spacer may lead to twisted conformations with very low SF quantum yields, highlighting the need of controlling this structural aspect in the design of new singlet fission active molecules.

Tuning memory behavior from volatile to nonvolatile by increasing the linear segment length of hyperbranched copolyimides

In this work, three donor-acceptor contained hyperbranched copolyimides (O30-coPI, O50-coPI and O70-coPI) with different linear segment length were synthesized by varying the feed ratio of monomers. The memory device based on O30-coPI showed an unstable volatile static random access memory (SRAM) behavior, while the devices based on O50-coPI and O70-coPI with longer linear segment exhibited stable non-volatile write once read many times memory (WORM) behavior. Theoretical simulations based on density functional theory (DFT) showed that the linear segment induce a twisted conformation, which helps to stabilize the charge-separation state. As the linear segment grows, the conformation becomes more distorted, resulting in a more stable charge-separated state. Compared to O30-coPI, O50-coPI and O70-coPI have longer linear segment and more twisted conformations, thus they exhibit non-volatile memory behavior. This work demonstrates that the memory behavior can be controlled by changing the linear segment length of HB-coPI, providing a practicable strategy for the design of polymer memory materials.

Facile synthesis of phenothiazine-pyrazine-based donor-acceptor-donor regioisomers: Influence of molecular geometry on aggregation-induced emission

Aggregation-induced emission (AIE) fluorescent molecules are in great demand due to the wide range of applications. In this article, three regioisomers namely, o-PyPTZ, m-PyPTZ and p-PyPTZ, with pyrazine (Py) as acceptor and phenothiazine (PTZ) as donor, were rationally designed and synthesized. Phenothiazine moieties are attached to pyrazine core as peripheral groups at 2,3- 2,5- and 2,6-positions. The attachment of bulky PTZ pendants at different position of pyrazine core could influence the molecular packing modes, resulting in discrete photophysical and electronic properties. The resulting regioisomers are weakly fluorescent in dilute solutions but highly emissive upon aggregate formation, verifying their AIE activities. They are thermally and morphologically stable with degradation temperature of 372–407 °C. Single-crystal structures of three isomers indicate their twisted conformation. A detailed comparison of the photophysical, electronic and structural properties of these isomers has been made with a view to studying the outcome of the positional change.

Tunable Solid-State Thermochromism: Alkyl Chain Length-Dependent Conformational Isomerization of Bianthrones.

The introduction of linear alkoxy chains into bianthrone promoted the aggregation of the minor twisted conformer and made it compete with the major folded conformer in the solid-state. Rapid evaporation approach to the methoxy- and n-butoxy-substituted derivatives provided powder mixtures of folded and twisted conformers as metastable solids. Upon heating the powders, different lengths of alkyl chains converged to different conformers via solid-state isomerization reaction with an apparent color change. Monitoring by FT-IR spectroscopy and powder XRD ensured that these isomerization reactions involve only conformational isomerization without pyrolysis. In addition, single crystal X-ray structure analysis revealed that twisted conformers with longer alkyl chains are stabilized in the solid-state by the synergistic effect of their inter-chain hydrophobic interactions and π-π stacking interactions.

From para to ortho: Incarnating conventional TADF molecules into AIE-TADF molecules for highly-efficient non-doped OLEDs

Conventional thermally activated delayed fluorescence (TADF) molecules are generally constructed by planar moieties with a linear donor–acceptor (D-A) configuration but suffer from aggregation-caused quenching (ACQ). Herein, we provide a strategy to develop aggregation-induced emission TADF (AIE-TADF) emitters that are consisted of ACQ moieties through the substitute change from para-, meta- to ortho-position, which means incarnating conventional TADF molecules into AIE-TADF molecules. The ortho-substituted molecule exhibits a highly twisted conformation to hinder π-π stacking and thus avoids ACQ, while a large D-A twisted angle contributes to fast reversible intersystem crossing and low non-radiative decay, thus facilitating the AIE-TADF feature in neat film. The ortho-substituted molecule renders the non-doped devices with a high external quantum efficiency of 22.14%. These results certify that adjusting substitute position is a simple and practical strategy for the development of high-efficiency TADF materials and devices.

Efficient deep-red hot exciton electroluminescent emitters with fine-tuning of excited states via locally large twisted conformation

The precise regulation of excited state is a challenge to emitters for achieving highly efficient non-doped deep-red electroluminescence (EL). Herein, we used triphenylamine and phenoxazine as donors and benzo[c][1,2,5]thiadiazole as an acceptor to construct a hot exciton skeleton. Then chemically modified the phenoxazine by locally large twisted conformation to obtain N,N-diphenyl-4-(7-(10-phenyl-10H-phenoxazin-3-yl)benzo[c][1,2,5]thiadiazol-4-yl)aniline (TPAPH), 4-(7-(10-(4-ethoxyphenyl)-10H-phenoxazin-3-yl)benzo[c][1,2,5]thiadiazol-4-yl)-N,N-diphenylaniline (TPAPHOC2), and 4-(3-(7-(4-(diphenylamino)phenyl)benzo[c][1,2,5]thiadiazol-4-yl)-10H-phenoxazin-10-yl)benzonitrile (TPAPHCN), thereby achieving excited state perturbation. As a result, three emitters exhibited aggregation-induced emission enhancement and hybridized local and charge transfers characteristics based on photophysical experimentals. In EL, the TPAPH-, TPAPHOC2-, and TPAPHCN-based non-doped devices achieved deep-red emission with Commission International de L’Eclairage coordinates of (0.68, 0.32), (0.69, 0.31), and (0.66, 0.34) and with emission peaks at 660, 669, and 647 nm, respectively. The maximum external quantum efficiencies were 5.3%, 3.7%, and 6.0%, respectively. The results of this study not only realize the non-doped deep-red OLEDs with high performance but also indicate that the presence of locally large twisted conformation presented an efficient manner for exploring precise excited state tuning for fluorescent emitter.

Highly Efficient Aggregation-Induced Enhanced Electrochemiluminescence of Cyanophenyl-Functionalized Tetraphenylethene and Its Application in Biothiols Analysis.

Exploring new electrochemiluminescence (ECL) luminophores with high ECL efficiency and good stability in aqueous solution is in great demand for biological sensing. In this work, highly efficient aggregation-induced enhanced ECL of cyanophenyl-functionalized tetraphenylethene (tetra[4-(4-cyanophenyl)phenyl]ethene, TCPPE) and its application in biothiols analysis were reported. TCPPE contains four 4-cyanophenyl groups covalently attached to the tetraphenylethene (TPE) core, generating a nonplanar three-dimensional twisted conformation structure. TCPPE nanoparticles (NPs) with an average size of 15.84 nm were prepared by a precipitation method. High ECL efficiency (593%, CdS as standard) and stable ECL emission (over one month) were obtained for TCPPE NPs in aqueous solution. The unique properties of TCPPE NPs could be ascribed to the efficient suppression of nonradiative transition, the decrease of the energy gap, and the increase of anionic radical stability, which were proved by theoretical calculation and electrochemical and fluorescence methods. Contrasting aggregation-induced ECL chromic emission was first observed for TCPPE NPs. As a proof-of-methodology, an ECL method was developed for three biothiol assays with detection limits of 6, 7, and 300 nM for cysteine, homocysteine, and glutathione, respectively. This work demonstrates that TCPPE NPs are promising ECL luminophores, and the incorporation of appropriate substituents into luminophores can improve ECL efficiency and radical stability.

Novel A-π-A-D type perylene diimide acceptor for high-performance fullerene-free organic solar cells

Two novel PDI-based acceptors PDI-SPAc and FPDI-SPAc, which contain perylene diimide (PDI) and a quasi-two-dimensional (quasi-2D) fused PDI (FPDI), respectively, with electron-rich unit 10 H-spiro[acridan-9,9′-fluorene] (SPAc), were designed and synthesized to investigate their application in non-fullerene organic solar cells (NF-OSCs). Expectedly, FPDI-SPAc obtained a fairly twisted conformation in consequence of the quasi-2D configuration of FPDI unit and significant dihedral angle between FPDI and SPAc units. Geometry of PDI-SPAc containing only dihedral angle between PDI and SPAc units was confirmed, too. The optical properties, electron energy levels, charge transport properties, photovoltaic performance, charge dissociation probabilities, and surface morphology were systematically investigated subsequently. By blending with a narrow band-gap polymer PTB7-Th as the polymer donor, NF-OSC based on PTB7-Th:FPDI-SPAc achieved a power conversion efficiency (PCE) of 3.92% with the dominant configuration characteristic, whereas the PDI-SPAc-based NF-OSC exhibited a PCE of only 0.32% with a significantly reduced short-circuit current density (Jsc) of 1.2 mA/cm2. The interesting results indicate that, the quasi-2D structure of FPDI unit produced impressive effect on the photovoltaic performances of the FPDI derivative acceptors, which can demonstrate that quasi-2D structure is a better electron-deficient segment in comparison with PDI for the design of n-type photovoltaic materials.