Noncovalent Conformational Locks Research Articles

As Aggregation‐Induced Emission Meets with Noncovalent Conformational Locks: Subtly Regulating NIR‐II Molecules for Multimodal Imaging‐Navigated Synergistic Therapies

Phototheranostics is growing into a sparking frontier in disease treatment. Developing single molecular species synchronously featured by powerful absorption capacity, superior second near‐infrared (NIR‐II) fluorescence and prominent photothermal conversion ability is highly desirable for phototheranostics, yet remains formidably challenging. In this work, we propose a molecular design philosophy that the integration of noncovalent conformational locks (NoCLs) with aggregation‐induced emission (AIE) in a single formulation is able to boost multiple photophysical properties for efficient phototheranostics. The introduction of NoCLs skeleton with conformation‐locking feature in the center of molecular architecture indeed elevates the structural planarity and rigidity, which simultaneously promotes the absorption capacity and bathochromic‐shifts the emission wavelength centered in NIR‐II region. Meanwhile, the AIE tendency mainly originated from flexibly propeller‐like geometry at the ends of molecular architecture eventually endows the molecule with satisfactory emission intensity and photothermal conversion in aggregates. Consequently, by utilizing the optimized molecule, unprecedented performance on NIR‐II fluorescence‐photoacoustic‐photothermal trimodal imaging‐guided photothermal‐chemo synergistic therapy is demonstrated by the precise tumor diagnosis and complete tumor ablation.

As Aggregation-Induced Emission Meets with Noncovalent Conformational Locks: Subtly Regulating NIR-II Molecules for Multimodal Imaging-Navigated Synergistic Therapies.

Phototheranostics is growing into a sparking frontier in disease treatment. Developing single molecular species synchronously featured by powerful absorption capacity, superior second near-infrared (NIR-II) fluorescence and prominent photothermal conversion ability is highly desirable for phototheranostics, yet remains formidably challenging. In this work, we propose a molecular design philosophy that the integration of noncovalent conformational locks (NoCLs) with aggregation-induced emission (AIE) in a single formulation is able to boost multiple photophysical properties for efficient phototheranostics. The introduction of NoCLs skeleton with conformation-locking feature in the center of molecular architecture indeed elevates the structural planarity and rigidity, which simultaneously promotes the absorption capacity and bathochromic-shifts the emission wavelength centered in NIR-II region. Meanwhile, the AIE tendency mainly originated from flexibly propeller-like geometry at the ends of molecular architecture eventually endows the molecule with satisfactory emission intensity and photothermal conversion in aggregates. Consequently, by utilizing the optimized molecule, unprecedented performance on NIR-II fluorescence-photoacoustic-photothermal trimodal imaging-guided photothermal-chemo synergistic therapy is demonstrated by the precise tumor diagnosis and complete tumor ablation.

Boosted hydrogen evolution in conjugated polymer photocatalyst by noncovalent conformation-locked architecture

A synergetic effect of noncovalent conformational locks (NCLs) and molecular framework engineering on the performance of polymeric photocatalysts is comprehensively investigated by tuning fluorination as well as framework structure with linear or planar backbone of conjugated polymers on the basis of the 2,2′-bithiophene and pyrene building blocks. Both fluorine-induced NCLs and molecular framework structure have beneficial influence on the electronic structure, photon absorption, nanomorphology and porosity, and charge migration/separation of conjugated polymers. As a result, the noncovalent conformation-locked conjugated polymer Py-2F2T achieves a significant high hydrogen evolution rate of 404.8 mmol h−1 under the conditions of being visible-light-driven and cocatalyst-free, which is 2.5- and 202.4-fold as those of the planar counterpart without NCLs and the linear counterpart with NCLs, respectively. Remarkably, Py-2F2T could show excellent apparent quantum yields of over 25.0 % at 450–600 nm irradiation with the highest value of 39.0 % at 575 nm. Overall, this work demonstrates the significance of the synergy of NCLs and molecular framework engineering for enhancing the photocatalytic activity, and the strategy of “noncovalent conformation-locked architecture” as a novel approach to the rational structure design of high-efficiency polymeric photocatalysts for visible-light-driven hydrogen evolution through water splitting.

Benzodipyrrolidone-based donor-acceptor semiconducting polymers with high hole mobility and noncovalent conformational locks

Constructing highly coplanar polymer backbone plays an important role in boosting the carrier mobility of organic field effect transistors (OFETs) devices. In this study, based on noncovalent conformational locks strategy, we synthesized the electron-acceptor (A) monomer via introducing 3-dodecylthiophene on strong electron-deficient planar benzodipyrrolidone and the electron-donor (D) monomers containing different numbers (0–2) of fluorine atoms at different positon. A series of novel D-A copolymers, namely PBDP-F0, PBDP-F1 and PBDP-F2 with different backbone conformational locks through F⋯S and F⋯H–C noncovalent interactions, were obtained via Stille polycondensation. For the application in an organic field-effect transistor, all the polymers exhibited p-type charge transport characteristics and good performance with the highest hole mobilities as 0.24 cm2 V−1 s−1 for PBDP-F0, 0.87 cm2 V−1 s−1 for PBDP-F1 and 1.93 cm2 V−1 s−1 for PBDP-F2, respectively. AFM and GIXRD investigations indicated that all polymers take predominantly edge-on orientation packing mode because of the rigid and coplanar backbone conformation and the annealing films exhibited small π-π stacking distances of 3.73, 3.71 and 3.69 Å for PBDP-F0, PBDP-F1 and PBDP-F2 respectively. This work demonstrates that modified BDP-based D-A copolymers with conformational locks has a potential application in the high-performance semiconductor materials.

Structural Isomeric Effect on Spin Transport in Molecular Semiconductors.

Molecular semiconductor (MSC) is a promising candidate for spintronic applications benefiting from its long spin lifetime caused by light elemental-composition essence and thus weak spin-orbit coupling (SOC). According to current knowledge, the SOC effect, normally dominated by the elemental composition, is the main spin-relaxation causation in MSCs, and thus the molecular structure-induced SOC change is one of the most concerned issues. In theoretical study, molecular isomerism, a most prototype phenomenon, has long been considered to possess little difference on spin transport previously, since elemental compositions of isomers are totally the same. However, here in this study, quite different spin-transport performances are demonstrated in ITIC and its structural isomers BDTIC experimentally, for the first time, though the charge transport and molecular stacking of the two films are very similar. By further experiments of electron-paramagnetic resonance and density-functional-theory calculations, it is revealed that noncovalent-conformational locks (NCLs) formed in BDTIC can lead to enhancement of SOC and thus decrease the spin lifetime. Hence, this study suggests the influences from the structural-isomeric effect must be considered for developing highly efficient spin-transport MSCs, which also provides a reliable theoretical basis for solving the great challenge of quantificational measurement of NCLs in films in the future.

Low-Cost Nonfused-Ring Electron Acceptors Enabled by Noncovalent Conformational Locks.

ConspectusSince the first bilayer-structured organic solar cells (OSCs) in 1986, fullerenes and their derivatives have dominated the landscape for two decades due to their unique properties. In recent years, the breakthrough in nonfullerene acceptors (NFAs) was mainly attributed to the development of fused-ring electron acceptors (FREAs), whose photovoltaic performance surpassed that of fullerene derivatives. Through the unremitting efforts of the whole community, the power conversion efficiencies (PCEs) have surpassed 19% in FREA-based OSCs. However, FREAs generally suffered from complex synthetic approaches and high product costs, which hindered large-scale production. Therefore, many researchers are seeking a new type of NFA to achieve cost-effective, highly efficient OSCs.In collaboration with Marks and Facchetti in 2012, Huang et al. (Huang, H. J. Am. Chem. Soc. 2012, 134, 10966-10973, 10.1021/ja303401s) proposed the concept of "noncovalent conformational locks" (NoCLs). In the following years, our group has been focusing on the theoretical and experimental exploration of NoCLs, revealing their fundamental nature, formulating a simple descriptor for quantifying their strength, and employing this approach to achieve high-performance organic/polymeric semiconductors for optoelectronics, such as OSCs, thin-film transistors, room-temperature phosphorescence, and photodetectors. The NoCLs strategy has been proven to be a simple and effective approach for enhancing molecular rigidity and planarity, thus improving the charge transport mobilities of organic/polymeric semiconductors, attributed to reduced reorganization energy and suppressed nonradiative decay.In 2018, Chen et al. (Li, S. Adv. Mater. 2018, 30, 1705208, 10.1002/adma.201705208) reported the first example of nonfused-ring electron acceptors (NFREAs) with intramolecular noncovalent F···H interactions. The NoCLs strategy is essential in NFREAs, as it simplifies the conjugated structures while maintaining high coplanarity comparable to that of FREAs. Due to their simple structures and concise synthesis routes, NFREAs show great potential for achieving cost-effective and highly efficient OSCs. In this Account, we provide an overview of our efforts in developing NFREAs with the NoCLs strategy. We begin with a discussion on the distinct features of NFREAs compared with FREAs, and the structural simplification from FREAs to NFREAs to completely NFREAs. Next, we examine several selected typical examples of NFREAs with remarkable photovoltaic performance, aiming to provide an in-depth exploration of the molecular design principle and structure-property-performance relationships. Then, we discuss how to achieve a balance among efficiency, stability, and cost through a two-in-one strategy of polymerized NFREAs (PNFREAs). Finally, we offer our views on the current challenges and future prospects of NFREAs. We hope this Account will trigger intensive research interest in this field, thus propelling OSCs into a new stage.

A noncovalent backbone planarization strategy increases the NIR-II extinction coefficients for gas/phototheranostic applications.

We propose a noncovalent backbone planarization strategy to fabricate a gas/phototheranostic nanocomposite (B-E-NO NPs) in the near-infrared-II (NIR-II, 1000-1700 nm) window by incorporating noncovalent conformational locks. B-E-NO NPs display a giant NIR-II extinction coefficient, realizing multimodal imaging-guided high-efficiency NIR-II photothermal therapy (η = 45.4%) and thermal-initiated nitric oxide combination therapy.

Non-fullerene acceptors with thiazole π-bridge for organic solar cells

Intramolecular noncovalent conformational locks (NoCLs) have been found to be effective in increasing the rigidity and planarity of the molecular backbone. This, in turn, leads to reduced recombination energy and improved intramolecular charge transport mobility, resulting in significant enhancements in the photovoltaic performance of organic solar cell (OSC) devices. To take advantage of this effect, we designed and synthesized two small molecule non-fullerene acceptors (NFAs) with A-π-D-π-A structures using thiazole (Tz): IDTz-IC4F and IDTz-IC4Cl. With the synergistic assistance of NoCLs and halogenated end groups, the NFAs IDTz-IC4F and IDTz-IC4Cl exhibited power conversion efficiencies (PCEs) of 6.20 % and 6.06 %, respectively. This study presents a strategy for enhancing the PCE of OSCs by incorporating cooperative NoCLs and halogen end groups, providing an exciting avenue for designing high-performance non-fullerene materials in the future.

Utilizing Noncovalent Conformational Locks to Create Through-Space Charge Transport

Creating through-space electron transport (ET) channels in the molecular backbone has been rarely explored in molecular electronics. Here, we demonstrated that through-space channels could be readily created by substituting the H atom of the central benzene in a starting molecule 1,4-dithiophene-benzen (DT-B) with F, which forms an interaction with the thiophene S and gives rise to the F–S type noncovalent conformational locks (NCLs). Single-molecule conductance investigation showed the molecular conductance was increasingly larger with more F substituents. A theoretical study revealed that NCLs play a major role in enhancing the ET rates, which not only led to better π-conjugation but also created additional through-space transport channels.

A 2.20 eV Bandgap Polymer Donor for Efficient Colorful Semitransparent Organic Solar Cells

AbstractSemitransparent organic solar cells (ST‐OSCs) have attracted increasing attention due to their promising prospect in building‐integrated photovoltaics. Generally, efficient ST‐OSCs with good average visible transmittance (AVT) can be realized by developing active layer materials with light absorption far from the visible light range. Herein, the development of ultrawide bandgap polymer donors with near‐ultraviolet absorption, paired with near‐infrared acceptors, is proposed to achieve high‐performance ST‐OSCs. The key points for the design of ultrawide bandgap polymers include constructing donor–donor type conjugated skeleton, suppressing the quinoidal resonance effect, and minimizing the twist of conjugated skeleton via noncovalent conformational locks. As a proof of concept, a polymer named PBOF with an optical bandgap of 2.20 eV is synthesized, which exhibited largely reduced overlap with the human eye photopic response spectrum and afforded a power conversion efficiency (PCE) of 16.40% in opaque device. As a result, ST‐OSCs with a PCE over 10% and an AVT over 30% are achieved without optical modulation. Moreover, colorful ST‐OSCs with visual aesthetics can be achieved by tuning the donor/acceptor weight ratio in active layer benefiting from the ultrawide bandgap nature of PBOF. This study demonstrates the great potential of ultrawide bandgap polymers for efficient colorful ST‐OSCs.

Asymmetric Non-Fullerene Small Molecule Acceptor with Unidirectional Non-Fused π-Bridge and Extended Terminal Group for High-Efficiency Organic Solar Cells.

We designed and synthesized an asymmetric non-fullerene small molecule acceptor (NF-SMA) IDT-TNIC with an A–D–π–A structure, based on an indacenodithiophene (IDT) central core, with a unidirectional non-fused alkylthio-thiophene (T) π-bridge, and 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b]naphthalen-1-ylidene)malononitrile (NIC) extended terminal groups. IDT-TNIC molecules still maintain a good coplanar structure, which benefits from the non-covalent conformational locks (NCL) between O···S and S···S. The asymmetric structure increases the molecular dipole moment, and the extended terminal group broadens the absorption of the material, resulting in an excellent photovoltaic performance of IDT-TNIC. The photovoltaic device, based on PBDB-T:IDT-TNIC, exhibits an energetic PCE of 11.32% with a high Voc of 0.87 V, high Jsc of 19.85 mA cm−2, and a low energy loss of 0.57 eV. More importantly, IDT-TNICs with asymmetric structures show a superior property compared to symmetric IDT-Ns. The results demonstrate that it is an effectual strategy to enhance the properties of asymmetric A–D–π–A-based NF-SMAs with non-fused NCL π-bridges and extended terminal groups.

Highly Sensitive Broad Light Response Organic Photodetectors from Pyrrolo[3,4-c]pyrrole-1,4-dione-Based Conjugated Polymer with Noncovalent Conformational Locks

Highly Sensitive Broad Light Response Organic Photodetectors from Pyrrolo[3,4-<i>c</i>]pyrrole-1,4-dione-Based Conjugated Polymer with Noncovalent Conformational Locks

High-Performance Non-fullerene organic solar cells enabled by noncovalent Conformational locks and Side-Chain engineering

Three novel small molecular acceptors (SMAs) BO-2F, BO-C8-2F and BO-C2C6-C8-2F were designed and synthesized. These acceptors all possess planar molecular backbone because of the introduction of intramolecular noncovalent interaction. Among them, BO-C2C6-C8-2F with four side chains, which has the highest solubility, can form more appropriate nanomorphology when blending with PBDB-T. Hence, organic solar cells (OSCs) based on PBDB-T:BO-C2C6-C8-2F displayed an outstanding power convesion efficiency (PCE) of 14.25%, which is higher than BO-2F and BO-C8-2F based ones. To the best of our knowledge, the PCE of 14.25% is one of the highest for the OSCs based on A-π-D-π-A type SMAs. Our results have demonstrated that the combination of side-chain engineering and intramolecular conformation lock has a great prospect in the design of high performance SMAs for OSCs.

The effect of non-covalent conformational locks on intra-molecular charge transport of OPV units.

Although organic photovoltaic (OPV) molecules containing non-covalent conformational locks (NCLs) are demonstrated with superior device scale charge transport, the NCLs' working mechanism at the molecular level has not been directly addressed or revealed. Herein, three widely used OPV building blocks DT-BT, DT-FBT, and DT-OBT were prepared and comparatively researched for their intra-molecule charge transport (ICT) based on single molecular conductance measurements and theoretical calculation. The measured conductance (G) of the three molecules displays an order of GDT-BT < GDT-FBT < GDT-OBT, contradicting the conductivity order predicted by tunnelling theory. Further research demonstrated that this change was mainly caused by NCLs embedded in DT-FBT and DT-OBT, resulting in more efficient charge transporting pathways, evidenced by their HOMOs showing hyper-conjugation characteristics.

Noncovalent interaction enables planar and efficient propeller-like perylene diimide acceptors for polymer solar cells

The development of non-fullerene small molecule acceptors enabled fast increasing top power conversion efficiency of polymer solar cells (PSCs). Perylene diimide (PDI) derivatives are among the most promising non-fullerene small molecule acceptors for their relatively straightforward accessible PDI chromophores readily deliver high electron mobility and intensive photon absorption in visible range. In this work, we demonstrated noncovalent interaction as a third strategy of connecting the PDI arms to the center core of propeller-like PDI derivatives other than flexible and all fused linkages through designing and synthesizing two novel PDI derivatives. Thiophene-annulated PDI arms were connected to a small electron withdrawing 1,3,5-triazine center core where N⋯S noncovalent conformational locks restricted the distortion of molecules. Fine tuning of the aggregation tendency of the PDI derivative by introducing N-annulation at the outer bay position of each PDI arms which achieved an outstanding power conversion efficiency reaching 10.52%, which is one of the top PCEs of PDI-based PSCs.

High‐Performance Noncovalently Fused‐Ring Electron Acceptors for Organic Solar Cells Enabled by Noncovalent Intramolecular Interactions and End‐Group Engineering

AbstractNoncovalently fused‐ring electron acceptors (NFREAs) have attracted much attention in recent years owing to their advantages of simple synthetic routes, high yields and low costs. However, the efficiencies of NFREAs based organic solar cells (OSCs) are still far behind those of fused‐ring electron acceptors (FREAs). Herein, a series of NFREAs with S⋅⋅⋅O noncovalent intramolecular interactions were designed and synthesized with a two‐step synthetic route. Upon introducing π‐extended end‐groups into the backbones, the electronic properties, charge transport, film morphology, and energy loss were precisely tuned by fine‐tuning the degree of multi‐fluorination. As a result, a record PCE of 14.53 % in labs and a certified PCE of 13.8 % for NFREAs based devices were obtained. This contribution demonstrated that combining the strategies of noncovalent conformational locks and π‐extended end‐group engineering is a simple and effective way to explore high‐performance NFREAs.

High-Performance Noncovalently Fused-Ring Electron Acceptors for Organic Solar Cells Enabled by Noncovalent Intramolecular Interactions and End-Group Engineering.

Noncovalently fused-ring electron acceptors (NFREAs) have attracted much attention in recent years owing to their advantages of simple synthetic routes, high yields and low costs. However, the efficiencies of NFREAs based organic solar cells (OSCs) are still far behind those of fused-ring electron acceptors (FREAs). Herein, a series of NFREAs with S⋅⋅⋅O noncovalent intramolecular interactions were designed and synthesized with a two-step synthetic route. Upon introducing π-extended end-groups into the backbones, the electronic properties, charge transport, film morphology, and energy loss were precisely tuned by fine-tuning the degree of multi-fluorination. As a result, a record PCE of 14.53 % in labs and a certified PCE of 13.8 % for NFREAs based devices were obtained. This contribution demonstrated that combining the strategies of noncovalent conformational locks and π-extended end-group engineering is a simple and effective way to explore high-performance NFREAs.

P⋯O noncovalent conformational locks for constructing highly planar Bis(diphenylphosphanyl) Bi(benzofurano)

Bis(diphenylphosphanyl) bi(benzofurano) (BBFP) and Bis(diphenylphosphanyl) bi(benzothiophene) (BBTP) were synthesized by the reaction of dilithio(benzothienylbenzofuran) or dilithio(benzothienylbenzothiophene) with Diphenylphosphinic chloride, then reduced with trichlorosilane to afford the target. Optical and electrochemical measurements of the products and their DFT calculations revealed that P⋯O noncovalent conformational locks played an important role in constructing highly planar BBFP, while BBTP showed a distorted structure. As a result, the photoluminescence (PL) quantum yields of BBFP measured as solids were 0.25. In contrast, the PL quantum yields of BBTP was too low to be detected.

S⋯Cl intramolecular interaction: An efficient strategy to improve power conversion efficiency of organic solar cells

Noncovalent conformational locks (NCLs) including S⋯N, Se⋯O, and S⋯O etc. Have been an effective strategy to improve the planarity and rigidity, and charge transport mobility of organic/polymeric semiconductors. Herein, by replacing methyl group (ITMIC) with chlorine (ITCIC) in the π-bridge, the planarity and rigidity of the π-conjugated skeleton was enhanced by introduction of S⋯Cl NCLs, thus the charge transport mobility was improved accordingly. As a result, PM6:ITCIC based organic solar cells showed impressive PCE of 11.34%, much higher than that based on PM6:ITMIC. This contribution demonstrated a novel kind NCLs (S⋯Cl) for improving the performance of organic solar cells.

A2-D-A1-D-A2-type small molecule acceptors incorporated with electron-deficient core for non-fullerene organic solar cells

Two A2-D-A1-D-A2-type small molecule acceptors (SMAs), DFB-dIDT and BT-dIDT with 2,5-difluorobenzene (DFB) or benzothiadiazole (BT) as electron-withdrawing core (A1) and a derivative of indanone as A2 units, were prepared for applications in organic solar cells (OSCs). The results indicate that BT unit is more beneficial to forming multiple noncovalent conformational locks of N⋯S and N⋯H between BT and IDT unit than DFB in the core, so BT-dIDT showed better molecular coplanarity, higher-lying HOMO energy level, more red-shifted spectrum, superior molar absorption coefficient (1.60 × 105 M−1 cm−1 at 696 nm), more complementary absorption spectrum with PBDB-T and better photovoltaic performance than DFB-dIDT. As a result, the BT-dIDT-based OSCs blending with PBDB-T exhibited higher power conversion efficiency (PCE) value of 10.52% with higher Jsc of 18.59 mA cm−2 than that of the DFB-dIDT-based devices (PCE of 6.71% with Jsc of 15.58 mA cm−2). These results demonstrate that the A2-D-A1-D-A2-type SMAs incorporated with a suitable electron-deficient core are promising candidates for high performance OSCs.