Conformational Lock Research Articles

Interplay Between the N→C Dative Bond, Intramolecular Chalcogen Bond and π Conjugation in the Complexes Formed by Cyclo[18]carbon and C14 Polyyne with 1,2,5-Chalcogenadiazoles.

The N→C dative bond (DB), intramolecular chalcogen bond and π conjugation play important roles in determining the structures and properties of some molecular carbon materials and organic/polymeric photovoltaic materials. In this work, the interplay between the N→C DB, intramolecular chalcogen bond and π conjugation in the complexes formed by cyclo[18]carbon and C14 polyyne with 1,2,5-chalcogenadiazoles has been investigated in detail by using reliable quantum chemical calculations. This study has made four main findings. First, only the Te-containing complexes bound by N→C DBs are much more stable than their corresponding van der Waals (vdW) complexes. Second, in addition to through-bond π conjugations, through-space π conjugations also exist in some Se/Te-containing complexes bound by N→C DBs. Third, the cooperativity between intramolecular chalcogen bond, π conjugation between two monomers and N→C DB is not very strong and can be ignored. Fourth, compared to π conjugations, intramolecular Ch⋅⋅⋅C (Ch=O, S, Se, Te) chalcogen bonds play a secondary role in stabilizing the complexes bound by N→C DBs. These findings clearly indicate that the role of "conformational lock", popular in the field of organic optoelectronic materials, may have been greatly overestimated.

Correlation of Dimer-Linker-Induced Conformational Lock with Nonradiative Energy Loss in Organic Solar Cells

Correlation of Dimer-Linker-Induced Conformational Lock with Nonradiative Energy Loss in Organic Solar Cells

Enhanced Fill Factor and Efficiency of Ternary Organic Solar Cells by a New Asymmetric Non-Fullerene Small Molecule Acceptor.

Asymmetric non-fullerene small molecules acceptor (as-NF-SMAs) exhibit greater vitality in photovoltaic materials compared to their symmetric counterparts due to their larger dipole moments and stronger intermolecular interactions, which facilitate exciton dissociation and charge transmission in organic solar cells (OSCs). Here, we introduced a new as-NF-SMAs, named IDT-TNIC, as the third component in ternary organic solar cells (TOSCs). The asymmetric IDT-TNIC used indacenodithiophene (IDT) as the central core, alkylthio-thiophene as a unilateral π-bridge and extended end groups as electron-withdrawing. Due to the non-covalent conformational lock (NCL) established between O⋅⋅⋅S and S⋅⋅⋅S, the IDT-TNIC molecule preserves its coplanar structure effectively. Furthermore, IDT-TNIC exhibits complementary absorption and excellent compatibility with donor and acceptor materials, as well as optimized ladder energy level arrangement, resulting in a higher and more balanced μh/μe value, more homogeneous and suitable phase separation morphology in TOSCs. Thus, the PCE of the TOSCs reached 17 % when the weight ratio of PM6 : Y6 : IDT-TNIC was 1 : 1.1 : 0.1, and it is noteworthy that when the device area was increased to 1 cm2, the PCE could still be maintained at over 14 %. Detailed studies and analysis indicate that IDT-TNIC has great potential as a third component in OSCs and for large-scale printing in the future.

Manipulating noncovalent conformational lock via side‐chain engineering for luminescence at aggregate level

AbstractThe unfavorable photochemical processes at the molecular level have become a barrier limiting the use of aromatic amides as high‐performance luminescent materials. Herein, we propose a reliable strategy for manipulating noncovalent conformational lock (NCL) via side‐chain engineering to burst out eye‐catching luminescence at the aggregate level. Contrary to the invisible emission in dilute solutions, dyad OO with a three‐centered H‐bond gave the wondrous crystallization‐induced emission with a quantum yield of 66.8% and clusterization‐triggered emission, which were much brighter than those of isomers. Theoretical calculations demonstrate that crystallization‐induced planarized intramolecular charge transfer (PICT), conformation rigidification, and through‐space conjugation (TSC) are responsible for aggregate‐state luminescence. Robust NCL composed of intramolecular N‐H···O interactions could boost molecular rigidity and planarity, thus greatly facilitating PICT and TSC. This study would inspire researchers to design efficient luminescent materials at the aggregate level via rational conformational control.

Incorporation of Diketopyrrolopyrrole into Polythiophene for the Preparation of Organic Polymer Transistors.

Polythiophene, as a class of potential electron donor units, is widely used in organic electronics such as transistors. In this work, a novel polymeric material, PDPPTT-FT, was prepared by incorporating the electron acceptor unit into the polythiophene system. The incorporation of the DPP molecule assists in improving the solubility of the material and provides a convenient method for the preparation of field effect transistors via subsequent solution processing. The introduction of fluorine atoms forms a good intramolecular conformational lock, and theoretical calculations show that the structure displays excellent co-planarity and regularity. Grazing incidence wide-angle X-ray (GIWAXS) results indicate that the PDPPTT-FT is highly crystalline, which facilitates carrier migration within and between polymer chains. The hole mobility of this π-conjugated material is as high as 0.30 cm2 V-1 s-1 in organic transistor measurements, demonstrating the great potential of this polymer material in the field of optoelectronics.

Designing thickness-insensitive cathode interlayers via constructing noncovalently conformational locks for highly efficient non-fullerene organic solar cells

A notable PCE of 15.31% was achieved for a thick cathode interlayer (53 nm) based on PF-BDT with “Noncovalent conformational lock”, which stands out as one of the highest reported PCEs for organic cathode interlayer with a thickness exceeding 50 nm.

Dual Chalcogen-Bonding Interactions for the Conformational Control of Urea.

Dual chalcogen-bonding interactions is proposed as a novel means for the conformational control of urea derivatives. The formation of a chalcogen-bonding interaction at both sides of the urea carbonyl group was unambiguously confirmed by X-ray diffraction as well as computational studies including non-covalent interaction (NCI) plot index analysis, quantum theory of atoms in molecules (QTAIM) analysis, and natural bond orbital (NBO) analysis via DFT calculations. By virtue of this dual interaction, urea derivatives that bear chalcogen atoms (X=S and Se) adopt a planar structure via the carbonyl oxygen (O) with an X⋅⋅⋅O⋅⋅⋅X arrangement on the same side of the molecule. The rigidity of the conformational lock was evaluated using the molecular arrangement in the crystal and the rotational barrier of benzochalcogenophene ring, which indicated a stronger conformational lock in benzoselenophene than in benzothiophene urea derivatives. Furthermore, the acidity of the urea derivatives increases according to the Lewis-acidic properties of the chalcogen-bonding interactions, whereby benzoselenophene urea is more acidic than benzothiophene urea. Tweezer-shaped urea derivatives were prepared, and their stereostructure proved the viability of the conformational control for defining the location of the substituents on the urea framework.

On the Conformation of Dimeric Acceptors and Their Polymer Solar Cells with Efficiency over 18 .

The determination of molecular conformations of oligomeric acceptors (OAs) and their impact on molecular packing are crucial for understanding the photovoltaic performance of their resulting polymer solar cells (PSCs) but have not been well studied yet. Herein, we synthesized two dimeric acceptor materials, DIBP3F-Se and DIBP3F-S, which bridged two segments of Y6-derivatives by selenophene and thiophene, respectively. Theoretical simulation and experimental 1D and 2D NMR spectroscopic studies prove that both dimers exhibit O-shaped conformations other than S- or U-shaped counter-ones. Notably, this O-shaped conformation is likely governed by a distinctive "conformational lock" mechanism, arising from the intensified intramolecular π-π interactions among their two terminal groups within the dimers. PSCs based on DIBP3F-Se deliver a maximum efficiency of 18.09 %, outperforming DIBP3F-S-based cells (16.11 %) and ranking among the highest efficiencies for OA-based PSCs. This work demonstrates a facile method to obtain OA conformations and highlights the potential of dimeric acceptors for high-performance PSCs.

On the Conformation of Dimeric Acceptors and Their Polymer Solar Cells with Efficiency over 18 %

AbstractThe determination of molecular conformations of oligomeric acceptors (OAs) and their impact on molecular packing are crucial for understanding the photovoltaic performance of their resulting polymer solar cells (PSCs) but have not been well studied yet. Herein, we synthesized two dimeric acceptor materials, DIBP3F‐Se and DIBP3F‐S, which bridged two segments of Y6‐derivatives by selenophene and thiophene, respectively. Theoretical simulation and experimental 1D and 2D NMR spectroscopic studies prove that both dimers exhibit O‐shaped conformations other than S‐ or U‐shaped counter‐ones. Notably, this O‐shaped conformation is likely governed by a distinctive “conformational lock” mechanism, arising from the intensified intramolecular π–π interactions among their two terminal groups within the dimers. PSCs based on DIBP3F‐Se deliver a maximum efficiency of 18.09 %, outperforming DIBP3F‐S‐based cells (16.11 %) and ranking among the highest efficiencies for OA‐based PSCs. This work demonstrates a facile method to obtain OA conformations and highlights the potential of dimeric acceptors for high‐performance PSCs.

Exploring Electronic Characteristics of Acceptor-Donor-Acceptor-Type Molecules by Single-Molecule Charge Transport.

The electronic characteristics of organic optoelectronic materials determine the performance of corresponding devices. Clarifying the relationship between molecular structure and electronic characteristics at the single-molecule level can help to achieve high performance for organic optoelectronic materials and devices, especially for organic photovoltaics. In this work, a typical acceptor-donor-acceptor (A-D-A)-type molecule is explored by combining theoretical and experimental studies to reveal the intrinsic electronic characteristics at the single-molecule level. Specifically, the A-D-A-type molecule with 1,1-dicyano methylene-3-indanone (INCN) acceptor units exhibits an enhanced conductance in single-molecule junctions when compared with the control donor molecule, because the acceptor units of the A-D-A-type molecule contribute additional transport channels. In addition, through opening the S∙∙∙O noncovalent conformational lock by protonation to expose the -S anchoring sites, the charge transport of the D central part is detected, proving that the conductive orbitals contributed by the INCN acceptor groups can penetrate the whole A-D-A molecule. These results provide important insights into the development of high-performance organic optoelectronic materials and devices toward practical applications.

Insights into structure-property relationships in ionic liquids using cyclic perfluoroalkylsulfonylimides.

Room temperature ionic liquids of cyclic sulfonimide anions ncPFSI (ring size: n = 4-6) with the cations [EMIm]+ (1-ethyl-3-methylimidazolium), [BMIm]+ (1-butyl-3-methylimidazolium) and [BMPL]+ (BMPL = 1-butyl-1-methylpyrrolidinium) have been synthesized. Their solid-state structures have been elucidated by single-crystal X-ray diffraction and their physicochemical properties (thermal behaviour and stability, dynamic viscosity and specific conductivity) have been assessed. In addition, the ion diffusion was studied by pulsed field gradient stimulated echo (PFGSTE) NMR spectroscopy. The decisive influence of the ring size of the cyclic sulfonimide anions on the physicochemical properties of the ILs has been revealed. All ILs show different properties compared to those of the non-cyclic TFSI anion. While these differences are especially distinct for ILs with the very rigid 6cPFSI anion, the 5-membered ring anion 5cPFSI was found to result in ILs with relatively similar properties. The difference between the properties of the TFSI anion and the cyclic sulfonimide anions has been rationalized by the rigidity (conformational lock) of the cyclic sulfonimide anions. The comparison of selected IL properties was augmented by MD simulations. These highlight the importance of π+-π+ interactions between pairs of [EMIm]+ cations in the liquid phase. The π+-π+ interactions are evident for the solid state from the molecular structures of the [EMIm]+-ILs with the three cyclic imide anions determined by single-crystal X-ray diffraction.

Backbone coplanarity manipulation via hydrogen bonding to boost the n-type performance of polymeric mixed conductors operating in aqueous electrolyte.

The development of high-performance n-type semiconducting polymers remains a significant challenge. Reported here is the construction of a coplanar backbone via intramolecular hydrogen bonds to dramatically enhance the performance of n-type polymeric mixed conductors operating in aqueous electrolyte. Specifically, glycolated naphthalene tetracarboxylicdiimide (gNDI) couples with vinylene and thiophene to give gNDI-V and gNDI-T, respectively. The hydrogen bonding functionalities are fused to the backbone to ensure a more coplanar backbone and much tighter π-π stacking of gNDI-V than gNDI-T, which is evidenced by density functional theory simulations and grazing-incidence wide-angle X-ray scattering. Importantly, these copolymers are fabricated as the active layer of the aqueous-based electrochromic devices and organic electrochemical transistors (OECTs). gNDI-V exhibits a larger electrochromic contrast (ΔT = 30%) and a higher coloration efficiency (1988 cm2 C-1) than gNDI-T owing to its more efficient ionic-electronic coupling. Moreover, gNDI-V gives the highest electron mobility (0.014 cm2 V-1 s-1) and μC* (2.31 FV-1 cm-1 s-1) reported to date for NDI-based copolymers in OECTs, attributed to the improved thin-film crystallinity and molecular packing promoted by hydrogen bonds. Overall, this work marks a remarkable advance in the n-type polymeric mixed conductors and the hydrogen bond functionalization strategy opens up an avenue to access desirable performance metrics for aqueous-based electrochemical devices.

Allosteric inhibition of HTRA1 activity by a conformational lock mechanism to treat age-related macular degeneration

The trimeric serine protease HTRA1 is a genetic risk factor associated with geographic atrophy (GA), a currently untreatable form of age-related macular degeneration. Here, we describe the allosteric inhibition mechanism of HTRA1 by a clinical Fab fragment, currently being evaluated for GA treatment. Using cryo-EM, X-ray crystallography and biochemical assays we identify the exposed LoopA of HTRA1 as the sole Fab epitope, which is approximately 30 Å away from the active site. The cryo-EM structure of the HTRA1:Fab complex in combination with molecular dynamics simulations revealed that Fab binding to LoopA locks HTRA1 in a non-competent conformational state, incapable of supporting catalysis. Moreover, grafting the HTRA1-LoopA epitope onto HTRA2 and HTRA3 transferred the allosteric inhibition mechanism. This suggests a conserved conformational lock mechanism across the HTRA family and a critical role of LoopA for catalysis, which was supported by the reduced activity of HTRA1-3 upon LoopA deletion or perturbation. This study reveals the long-range inhibition mechanism of the clinical Fab and identifies an essential function of the exposed LoopA for activity of HTRA family proteases.

A Theoretical Design of Chiral Molecules through Conformational Lock towards Circularly Polarized Luminescence

Circularly polarized (CP) light has shown great potential in quantum computing, optical communications, and three-dimensional displays. It is still a challenge to produce high-efficiency and high-purity CP light. Herein, we proposed a strategy to design chiral organic small molecules for CP light generation. These kinds of chiral molecules are formed by achiral light-emitting groups and achiral alkyl chains through conformational lock, which indicates that chirality can also be introduced into achiral light-emitting groups through rational molecular design. The chirality of these molecules can be further tuned by changing the length of the alkyl chains connecting the diketopyrrolopyrrole unit. The chiroptical properties of these molecules are confirmed by calculated electronic circular dichroism and chiral emission spectra, and further confirmed in experiments. The strategy developed in this work will greatly enlarge the candidate library of chiral luminescent materials.

Isomerization of Noncovalently Conformational Lock in Nonfused Electron Acceptor toward Efficient Organic Solar Cells

Isomerization of Noncovalently Conformational Lock in Nonfused Electron Acceptor toward Efficient Organic Solar Cells

Conformationally locked cis-1,2-diaminocyclohexane-based chiral ligands for asymmetric catalysis

An efficient synthesis for a new conformationally locked chiral cis-1,2-diaminocyclohexane scaffold has been developed. The conformational lock allows for convenient symmetrical derivatization of the amino groups through the reductive amination strategy. A series of optically pure chiral ligands based on the cis-DACH scaffold has been generated to demonstrate a proof-of-concept for these ligands as chiral catalysts in the asymmetric Henry reaction. Excellent yields with moderate enantioselectivity were demonstrated at room temperature, with an increase in enantioselectivity at lower temperatures, showing the potential of this new type of cis-DACH ligand.

Design of Non-fused Ring Acceptors toward High-Performance, Stable, and Low-Cost Organic Photovoltaics

ConspectusToward future commercial applications of organic solar cells (OSCs), organic photovoltaic materials that enable high efficiency, excellent stability, and low cost should be developed. Fused-ring electron acceptors (FREAs) have declared that OSCs are capable of showing efficiencies over 19%, whereas stability and cost are not solved yet. As the counterparts of FREAs, non-fused ring electron acceptors (NFREAs) are more flexible in molecular design. They have better stability because of the reduction of intramolecular tension via breaking fused backbone and have more advantages in cost with the reduction of synthetic complexity. However, the challenge for NFREAs is the relatively lower efficiencies (around 15% at current stage), which require better molecular designs for addressing the issues of conformational unicity and effective molecular packing.In this Account, we comprehensively summarize works about NFREAs carried out in our group from three main frameworks, including molecular design and efficiency optimization, material cost, and stability. First, in the part of molecular design and efficiency optimization, the existing rotatable single bond in NFREAs will bring the problem of conformational uncertainty, but it can be solved through proper molecular design, which also regulates the energy levels, light absorption range, and the packing mode of the molecule for obtaining higher performance. Thus, in this part, we discuss the evolution of NFREAs in three aspects, including molecular skeleton optimization, terminal modification, and side chain engineering. Many strategies are used in the design of a molecular skeleton, such as utilizing the quinoid effect, introducing functional groups with the electron push–pulling effect, and using multiple conformational lock. Furthermore, simplifying the skeleton is also the preferred development tendency. As for the terminal, the main modification strategy is adjusting the conjugation length and halogen atoms. What is more, by adjusting the side chain to induce appropriate steric hindrance, we can fix the orientation of molecules, thus regulating molecular packing modes. Second, regarding material cost, we compare the synthesis complexities between state-of-the-art FREAs and NFREAs. Because the synthesis processes of NFREAs reduce the complex cyclization reactions, the synthesis routes are greatly simplified, and the molecule can be obtained through three minimal steps. Third, regarding stability, we analyze the workable strategies used in NFREAs from the views of intrinsic material stability, photostability, and thermal stability. Finally, we conclude the challenges that should be conquered for NFREAs and propose perspectives that could be performed for NFREAs, with the hope of pushing the development of OSCs toward high performance, stability, and low cost.

Identification and optimisation of a pyrimidopyridone series of IRAK4 inhibitors

In this article, we report the discovery of a series of pyrimidopyridones as inhibitors of IRAK4 kinase. From a previously disclosed 5-azaquinazoline series, we found that switching the pyridine ring for an N-substituted pyridone gave a novel hinge binding scaffold which retained potency against IRAK4. Importantly, introduction of the carbonyl established an internal hydrogen bond with the 4-NH, establishing a conformational lock and allowing truncation of the large basic substituent to a 1-methylcyclopyl group. Subsequent optimisation, facilitated by X-ray crystal structures, allowed identification of preferred substituents at both the pyridone core and pyrazole. Subsequent combinations of optimal groups allowed control of lipophilicity and identification of potent and selective inhibitors of IRAK4 with better in vitro permeability and lower clearance.

Nonfused Ring Electron Acceptors for Efficient Organic Solar Cells Enabled by Multiple Intramolecular Conformational Locks

Nonfused ring electron acceptors (NFREAs) have become a research hotspot of organic solar cells (OSCs) due to their facile synthesis. However, efficient NFREAs not only need to maintain the advantages of FREAs but also need to optimize the molecular structure of the conjugate backbone to achieve good planarity. Therefore, choosing the appropriate building blocks is a prerequisite for achieving efficient OSCs. Here, two simple NFREAs 2T2CSi-4F and 4T2CSi-4F, based on diester-thieno[3,2-b]thiophene (2T2C) as the central core unit and 4,4-di-2-ethylhexyl-dithieno[3,2-b:2′,3′-d]silole (DTSi) or thieno[3,2-b]thiophene (TT) as the conjugated linking unit, were designed and synthesized. The density function theory results manifest that the oxygen atom of the thiophene ester group can form O···S interaction with the sulfur atom. Introducing noncovalent interactions can form multiple intramolecular conformational locks, which greatly enhance the molecular planarity. In addition, 2T2CSi-4F with a symmetrical structure exhibits red-shifted absorption, shallower lowest unoccupied molecular orbital energy levels, and stronger crystallinity than 4T2CSi-4F. Therefore, the PBDB-T:2T2CSi-4F device with favorable molecular packing and morphology achieves a higher power conversion efficiency of 10.04%. Our work demonstrates that the 2T2C unit and multimolecular conformational lock strategy are conducive to the development of efficient NFREAs.

Highly Efficient Non-Fused-Ring Electron Acceptors Enabled by the Conformational Lock and Structural Isomerization Effects.

Two novel nonfused-ring electron acceptors (N-FREAs) namely DTP-out-F and DTP-in-F, containing 2,5-difluorophenylene central core flanked with DTP blocks and end-capped with IC-2F terminals were designed and synthesized. The C-H···F noncovalent interactions between F atom of 2,5-difluorophenylene and H-3 and H-6 from DTP moiety (for DTP-in-F and DTP-out-F, respectively) locked the molecular conformation within a planar geometry. Benefiting from asymmetric nature of DTP block, the two different connection positions (2- or 7-position) of DTP to 2,5-difluorophenylene afforded the structural isomers of DTP-in-F and DTP-out-F, which affected the overall properties of these N-FREAs, especially the molecular packing behaviors. The more preferred J-aggregation and face-on packing of DTP-in-F shifted the absorption to slightly longer wavelength and provided a polymer-like extended crystal transport channels for improving the charge transport. Therefore, the power conversion efficiency (PCE) was significantly improved from 3.97% of DTP-out-F-based devices to 10.66% of DTP-in-F-based devices. These results reveal the great potential of isomerization strategy to develop high-performance N-FREAs.