Linker Engineering Research Articles

Impact of Linker Engineering in Core‐Linked Dimeric Acceptors for High‐Performance Organic Solar Cells

Impact of Linker Engineering in Core‐Linked Dimeric Acceptors for High‐Performance Organic Solar Cells

Efficient and Photostable Organic Solar Cells Achieved by Alloyed Dimer Acceptors with Tailored Linker Structures

AbstractHigh power conversion efficiency (PCE) and long‐term stability are prerequisites for commercialization of organic solar cells (OSCs). Herein, two dimer acceptors (DYTVT and DYTCVT) are developed with different properties through linker engineering, and study their effects as alloy‐like acceptors on the photovoltaic performance and photostability of OSCs. These ternary OSCs effectively combine the advantages of both dimer acceptors. DYTVT, characterized by its high backbone planarity, ensures elevated electron mobility and high glass‐transition temperature (Tg), leading to efficient charge transport and enhanced photostability of OSCs. Conversely, DYTCVT, with its significant dipole moment and electrostatic potential, enhances compatibility of the alloy acceptors with donors and refines the blend morphology, facilitating efficient charge generation in OSCs. Consequently, D18:DYTVT:DYTCVT OSCs exhibit higher PCE (18.4%) compared to D18:MYT (monomer acceptor, PCE = 16.5%), D18:DYTVT (PCE = 17.4%), and D18:DYTCVT (PCE = 17.0%) OSCs. Furthermore, owing to higher Tg of alloy acceptors (133 °C) than MYT (Tg = 80 °C) and DYTCVT (Tg = 120 °C), D18:DYTVT:DYTCVT OSCs have significantly higher photostability (t80% lifetime = 4250 h under 1‐sun illumination) compared to D18:MYT (t80% lifetime = 40 h) and D18:DYTCVT OSCs (t80% lifetime = 2910 h).

Linker Engineering toward Tunable Emission Behavior of Porous Interpenetrated Zr-Organic Frameworks.

Conjugated molecules with donor-acceptor-donor (D-A-D) moieties have garnered significant attention for their ability to form luminescent metal-organic frameworks (LMOFs). D-A-D molecules feature tunable bandgaps, which can be varied systematically to control the fluorescence wavelength of LMOFs. In this study, we prepared and characterized the fluorescence properties of two porous interpenetrated Zr-organic frameworks (PIZOFs) constructed using 4,4'-(benzo[c][1,2,5]selenadiazole-4,7-diylbis(ethyne-2,1-diyl))dibenzoic acid (L-Se) or 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(ethyne-2,1-diyl))dibenzoic acid (L-S) as linkers. The corresponding MOFs are denoted as PIZOF-Se and PIZOF-S, respectively. Through our investigation, we explored the correlation between the structure of the frameworks and their respective optical properties. Our findings revealed that there are distinct differences in the fluorescence properties of the two PIZOFs. Specifically, the fluorescence of PIZOF-S is red-shifted from that characteristic of the corresponding linker, L-S. By contrast, the fluorescence of PIZOF-Se is substantially blue-shifted from that of linker L-Se. The emission of mixed-linker MOFs is explored by combining L-S or L-Se with structurally analogous, but nonfluorescent linker, 4,4'-((perfluoro-1,4-phenylene)bis(ethyne-2,1-diyl))dibenzoic acid (L-F). Based on steady-state and time-resolved photoluminescence experiments, as well as confocal fluorescence microscopy combined with fluorescence lifetime imaging (FILM), we demonstrated that linker engineering is an effective method to tune the emission behavior of LMOFs.

Linker Mediated Electronic-State Manipulation of Conjugated Organic Polymers Enabling Highly Efficient Oxygen Reduction.

Conjugated polymers with tailorable composition and microarchitecture are propitious for modulating catalytic properties and deciphering inherent structure-performance relationships. Herein, we report a facile linker engineering strategy to manipulate the electronic states of metallophthalocyanine conjugated polymers and uncover the vital role of organic linkers in facilitating electrocatalytic oxygen reduction reaction (ORR). Specifically, a set of cobalt phthalocyanine conjugated polymers (CoPc-CPs) wrapped onto carbon nanotubes (denoted CNTs@CoPc-CPs) are judiciously crafted via in situ assembling square-planar cobalt tetraaminophthalocyanine (CoPc(NH2)4) with different linear aromatic dialdehyde-based organic linkers in the presence of CNTs. Intriguingly, upon varying the electronic characteristic of organic linkers from terephthalaldehyde (TA) to 2,5-thiophenedicarboxaldehyde (TDA) and then to thieno/thiophene-2,5-dicarboxaldehyde (bTDA), their corresponding CNTs@CoPc-CPs exhibit gradually improved electrocatalytic ORR performance. More importantly, theoretical calculations reveal that the charge transfer from CoPc units to electron-withdrawing linkers (i.e., TDA and bTDA) drives the delocalization of Co d-orbital electrons, thereby downshifting the Co d-band energy level. Accordingly, the active Co centers with more positive valence state exhibit optimized binding energy toward ORR-relevant intermediates and thus a balanced adsorption/desorption pathway that endows significant enhancement in electrocatalytic ORR. This work demonstrates a molecular-level engineering route for rationally designing efficient polymer catalysts and gaining insightful understanding of electrocatalytic mechanisms.

Linker Mediated Electronic‐State Manipulation of Conjugated Organic Polymers Enabling Highly Efficient Oxygen Reduction

AbstractConjugated polymers with tailorable composition and microarchitecture are propitious for modulating catalytic properties and deciphering inherent structure‐performance relationships. Herein, we report a facile linker engineering strategy to manipulate the electronic states of metallophthalocyanine conjugated polymers and uncover the vital role of organic linkers in facilitating electrocatalytic oxygen reduction reaction (ORR). Specifically, a set of cobalt phthalocyanine conjugated polymers (CoPc‐CPs) wrapped onto carbon nanotubes (denoted CNTs@CoPc‐CPs) are judiciously crafted via in situ assembling square‐planar cobalt tetraaminophthalocyanine (CoPc(NH2)4) with different linear aromatic dialdehyde‐based organic linkers in the presence of CNTs. Intriguingly, upon varying the electronic characteristic of organic linkers from terephthalaldehyde (TA) to 2,5‐thiophenedicarboxaldehyde (TDA) and then to thieno/thiophene‐2,5‐dicarboxaldehyde (bTDA), their corresponding CNTs@CoPc‐CPs exhibit gradually improved electrocatalytic ORR performance. More importantly, theoretical calculations reveal that the charge transfer from CoPc units to electron‐withdrawing linkers (i.e., TDA and bTDA) drives the delocalization of Co d‐orbital electrons, thereby downshifting the Co d‐band energy level. Accordingly, the active Co centers with more positive valence state exhibit optimized binding energy toward ORR‐relevant intermediates and thus a balanced adsorption/desorption pathway that endows significant enhancement in electrocatalytic ORR. This work demonstrates a molecular‐level engineering route for rationally designing efficient polymer catalysts and gaining insightful understanding of electrocatalytic mechanisms.

Triggered Release of Ampicillin from Metallic Implant Coatings for Combating Periprosthetic Infections.

Periprosthetic infections caused by Staphylococcus aureus (S. aureus) pose unique challenges in orthopedic surgeries, in part due to the bacterium's capacity to invade surrounding bone tissues besides forming recalcitrant biofilms on implant surfaces. We previously developed prophylactic implant coatings for the on-demand release of vancomycin, triggered by the cleavage of an oligonucleotide (Oligo) linker by micrococcal nuclease (MN) secreted by the Gram-positive bacterium, to eradicate S. aureus surrounding the implant in vitro and in vivo. Building upon this coating platform, here we explore the feasibility of extending the on-demand release to ampicillin, a broad-spectrum aminopenicillin β-lactam antibiotic that is more effective than vancomycin in killing Gram-negative bacteria that may accompany S. aureus infections. The amino group of ampicillin was successfully conjugated to the carboxyl end of an MN-sensitive Oligo covalently integrated in a polymethacrylate hydrogel coating applied to titanium alloy pins. The resultant Oligo-Ampicillin hydrogel coating released the β-lactam in the presence of S. aureus and successfully cleared nearby S. aureus in vitro. When the Oligo-Ampicillin-coated pin was delivered to a rat femoral canal inoculated with 1000 cfu S. aureus, it prevented periprosthetic infection with timely on-demand drug release. The clearance of the bacteria from the pin surface as well as surrounding tissue persisted over 3 months, with no local or systemic toxicity observed with the coating. The negatively charged Oligo fragment attached to ampicillin upon cleavage from the coating did diminish the antibiotic's potency against S. aureus and Escherichia coli (E. coli) to varying degrees, likely due to electrostatic repulsion by the anionic surfaces of the bacteria. Although the on-demand release of the β-lactam led to adequate killing of S. aureus but not E. coli in the presence of a mixture of the bacteria, strong inhibition of the colonization of the remaining E. coli on hydrogel coating was observed. These findings will inspire considerations of alternative broad-spectrum antibiotics, optimized drug conjugation, and Oligo linker engineering for more effective protection against polymicrobial periprosthetic infections.

Exploration of Molecular Nanoparticles as Soft Structural Materials and Their Structure-Property Relationship.

The search for alternative chemical systems other than polymers with chain topologies for soft structural materials raises general interests in fundamental materials and chemical sciences. It is also appealing from an engineering perspective for the urgent need to resolve the typical trade-offs of polymer systems. Herein, a subnanometer molecular cluster, polyhedral oligomeric silsesquioxanes, is assembled into molecular nanoparticles (MNPs) with star topology. Broadly tunable viscoelasticity can be realized by fine-tuning the MNPs' deformability. Being analogous to polymeric systems, the hierarchical structural relaxation dynamics can be observed, and their relaxation time and temperature dependence are dominated by the linker flexibilities. This not only provides microscopic understanding on MNP's unique viscoelasticity but also offers enormous opportunities for modulating their mechanical properties via linker engineering. Our work proves the possibility of applying structural units with particle topologies for the design of soft structural materials.

Directional design of the pyridine ligand functional block fine-tuned hydrophobicity to improve the electrocatalytic nitrogen fixation performance of the Co/Ni based MOFs-derived materials

A series of isostructural Co/Ni-MOFs with different linearly bridged bipyridines as organic linkers has been designed and synthesized. Experimental studies reveal that linker engineering by tuning the functional block of the pyridine-bridging units renders these MOFs derived materials with significantly improved electrocatalytic nitrogen reduction reactions (eNRR) to NH3. Among them, at −0.4 V vs reversible hydrogen electrode the one containing a 1,3,4-thiadiazole unit exhibits the best eNRR performance in 0.1 M Na2SO4 with the highest NH3 yield (39.7 μg h−1 mg−1) and Faraday efficiency (33.3 %). This excellent nitrogen fixation performance comes from the synergistic effect of the heterojunction formed by the Co2N component that is conducive to nitrogen fixation and the Co9S8 component that inhibits hydrogen evolution in the derived material. Significantly, the systematic tuning of the bridging ligands in MOFs provides a new pathway to develop eNRR electrocatalysts.

Linker engineering in UiO-68-type metal–organic frameworks for the photocatalytic thioamide cyclization

A mild, green, and sustainable visible-light-driven synthesis of 1,2,4-thiadiazole using a linker engineering method for systematically tuning the light absorption and charge-separation behavior is reported.

Linker Engineering in Mixed-Ligand Metal-Organic Frameworks for Simultaneously Enhanced Benzene Adsorption and Benzene/ Cyclohexane Separation

The development of metal-organic frameworks (MOFs) that simultaneously possess high adsorption capacity and selectivity for benzene (Bz)/cyclohexane (Cy) separation is a formidable challenge. In this study, we employ the mixed-ligand...

Linker engineering of benzothiadiazole and its derivative-based covalent organic frameworks for efficient photocatalytic oxidative amine coupling and hydrogen peroxide generation

Benzothiadiazole and its derivative-based COFs were prepared, in which benzothiadiazole-based COF exhibits superior photocatalytic aerobic oxidation of amine coupling, while the naphthothiadiazole-based COF shows the highest H2O2 production rate.

Micro-modulation of linkers of covalent organic frameworks as catalysts for 2e− oxygen reduction reaction

Covalent organic frameworks (COFs) are attractive as metal-free catalysts for the 2e− oxygen reduction reaction (ORR) towing to their tunable skeletons and porosities. However, the specific roles of their properties, such as crystallinity, porosity, dipole moment, and binding ability to reactants, in the catalytic performance are still unknown. In this work, we adopted a linker engineering strategy to reveal the crucial factors in determining the catalytic performance. The properties of the COFs were systematically engineered by altering the substituent groups in the linkers. The optimized Br-COF achieved a maximum selectivity of 86.2%, and a mass activity of 32.0 A g−1, which were 112% and 174% higher than those from unmodified COF, respectively. The experimental and theoretical results revealed that the reductive ability of the COFs exerted the most prominent effect on their catalytic activity and confirmed that the easy formation of an OOH* intermediate contributed to the high activity.

Linker Engineering for Reactive Oxygen Species Generation Efficiency in Ultra-Stable Nickel-Based Metal-Organic Frameworks.

Interfacial charge transfer on the surface of heterogeneous photocatalysts dictates the efficiency of reactive oxygen species (ROS) generation and therefore the efficiency of aerobic oxidation reactions. Reticular chemistry in metal-organic frameworks (MOFs) allows for the rational design of donor-acceptor pairs to optimize interfacial charge-transfer kinetics. Herein, we report a series of isostructural fcu-topology Ni8-MOFs (termed JNU-212, JNU-213, JNU-214, and JNU-215) with linearly bridged bipyrazoles as organic linkers. These crystalline Ni8-MOFs can maintain their structural integrity in 7 M NaOH at 100 °C for 24 h. Experimental studies reveal that linker engineering by tuning the electron-accepting capacity of the pyrazole-bridging units renders these Ni8-MOFs with significantly improved charge separation and transfer efficiency under visible-light irradiation. Among them, the one containing a benzoselenadiazole unit (JNU-214) exhibits the best photocatalytic performance in the aerobic oxidation of benzylamines with a conversion rate of 99% in 24 h. Recycling experiments were carried out to confirm the stability and reusability of JNU-214 as a robust heterogeneous catalyst. Significantly, the systematic modulation of the electron-accepting capacity of the bridging units in donor-acceptor-donor MOFs provides a new pathway to develop viable noble-metal-free heterogeneous photocatalysts for aerobic oxidation reactions.

Linker Engineering of Sandwich-Structured Metal-Organic Framework Composites for Optimized Photocatalytic H2 Production.

While the microenvironment around catalytic sites is recognized to be crucial in thermocatalysis, its roles in photocatalysis remain subtle. Herein, a series of sandwich-structured metal-organic framework (MOF) composites, UiO-66-NH2 @Pt@UiO-66-X (X means functional groups), have been rationally constructed for visible-light photocatalytic H2 production. By varying -X groups of UiO-66-X shell, the microenvironment of Pt sites and photosensitive UiO-66-NH2 core can be simultaneously modulated. Significantly, the MOF composites with identical light absorption and Pt loading present distinctly different photocatalytic H2 production rates, following -X group sequence of -H > -Br > -NA (naphthalene) > -OCH3 > -Cl > -NO2 . UiO-66-NH2 @Pt@UiO-66-H demonstrates H2 production rate up to 2708.2μmol g-1 h-1 , ∼222 times that of UiO-66-NH2 @Pt@UiO-66-NO2 . Mechanism investigations suggest that the variation of -X group can balance the charge separation of UiO-66-NH2 core and proton reduction ability of Pt, leading to the optimal activity of UiO-66-NH2 @Pt@UiO-66-H at the equilibrium point. This article is protected by copyright. All rights reserved.

Linker engineering to regulate fluorescence of 1,3,5-tris(phenylacetylene)benzene-based covalent organic frameworks for white light-emitting diodes and information encryption and decryption

Luminescent covalent organic frameworks (LCOFs) is a promising luminescent material with huge potential for various applications because it can integrate various chromophores into its porous ordered structure. A facile and effective approach to edit LCOFs emission is very necessary but remains a challenge. Herein, a rigidity-flexibility combination strategy to edit the luminescence properties of LCOFs was proposed by using a flexible fluorescent 1,3,5-tris(phenylacetylene) benzene with propeller-like conformation as center skeleton and linkers with different rigidity and conjugation degree. Since the conjugated degree of LCOFs’ frameworks depended on conformation of propeller-like 1,3,5-tris(phenylacetylene)benzene skeleton, the emission wavelengths of 1,3,5-tris (phenylacetylene)benzene-based LCOFs could be edited by linkers to tune conjugated degree of the frameworks. These 1,3,5-tris(phenylacetylene)benzene-based LCOFs emitted blue, green, yellow, orange and red light depending on the conjugation degree caused by the effect of the linkers of melem, terephthalic dihydrazide, hydrazine hydrate and p-phenylenediamine on the conformation of central skeleton. Binary or ternary mixed 1,3,5-tris(phenylacetylene)benzene-based LCOFs were used for white emission, white light-emitting diodes and information encryption/decryption. The work provides a simple yet efficient method to systematically edit the emission behaviors of LCOFs by linker engineering.

PASTE, Don't Cut: Genome Editing Tool Looks Beyond CRISPR and Prime

PASTE, Don't Cut: Genome Editing Tool Looks Beyond CRISPR and Prime

Linker engineering of larger POSS-based ultra-low-k dielectrics toward outstanding comprehensive properties

Low-dielectric-constant (low-k) materials are an indispensable part of microprocessors as they can alleviate electronic crosstalk, charge build-up, and signal propagation delay. However, existing low-k materials usually have k values higher than 2 and inferior thermo-mechanical properties, which restrict the development of microelectronic devices. Although we have recently discovered that larger polyhedral oligomeric silsesquioxanes (POSS) are useful building blocks for fabricating advanced ultra-low-k materials, it remains to be seen whether a POSS cage and linker could be leveraged to tune the structure-property of the materials and create ultra-low-k materials with improved comprehensive properties. Herein, we propose a series of POSS-based hybrid materials (i.e., c-TnPBn and c-TnFn, n = 8, 10, and 12) that consist of distinct POSS cages and linkers. When the linker is kept identical, the gradual enlargement of the POSS cage enhances the porosity/free volume fraction of materials, resulting in quasi-linearly reduced k values for the resulting materials (k = 1.93 for c-T12PB12, 2.14 for c-T12F12). Meanwhile, the materials’ comprehensive properties can be significantly improved by increasing the POSS cage size or varying the linker’s length and type. As a result, ultra-low-k materials with good processability, low surface roughness (< 0.40 nm), excellent thermostability (> 480 °C), mechanical properties (elastic modulus > 2.5 GPa), and hydrophobicity have been obtained, and the low-k values can be maintained under high temperature (e.g., 300 °C) and wet condition. This work reveals the critical contribution of POSS cage size and linker to the structure and properties of POSS-based low-k materials and offers promising materials for the future of the microelectronic industry.

New Type of Polymerized Small A-D-A Acceptors Constructed by Conjugation Extension in the Branched Direction

The current high-performance polymerized small molecular acceptors (PSMAs) are mainly polymerized through terminal groups of small molecular acceptors (SMAs), which will inevitably damage the preferred stackings of terminal groups and render an inferior photoelectric performance of all-polymer solar cells (all-PSCs). In order to liberate terminal groups for more efficient intermolecular stackings, a new pathway to construct PSMAs is explored by extending molecular conjugation in branched directions, thereby affording two PSMAs of SP-T and SP-TT with thiophene and bithiophene as linkers, respectively. Benefiting from more compact/ordered π–π stackings and superior morphology, the SP-T-based all-PSC exhibits facilitated charge generation/transport and suppressed recombination, thus yielding a greatly improved efficiency of 13.54% compared with 9.76% for the SP-TT-based one. Our work not only develops a new type of PSMA featuring much enhanced molecular packings but also demonstrates its great potential for achieving state-of-the-art all-PSCs through the delicate engineering of linkers.

Linker Engineering of Dimerized Small Molecule Acceptors for Highly Efficient and Stable Organic Solar Cells

High power conversion efficiency (PCE) and long-term stability are important requirements for commercialization of organic solar cells (OSCs). In this study, we demonstrate efficient (PCE = 18.60%) and stable (t80% lifetime > 4000 h) OSCs by developing a series of dimerized small-molecule acceptors (DSMAs). We prepared three different DSMAs (DYT, DYV, and DYTVT) by using different linkers (i.e., thiophene, vinylene, and thiophene– vinylene– thiophene), to connect their two Y-based building blocks. We find that the crystalline properties and glass transition temperature (Tg) of DSMAs can be systematically modulated by the linker selection. A DYV-based OSC achieves the highest PCE (18.60%) among the DSMA-based OSCs owing to the appropriate backbone rigidity of DYV, leading to an optimal blend morphology and high electron mobility. Importantly, the DYV-based OSC also demonstrates excellent operational stability under 1-sun illumination, i.e., a t80% lifetime of 4005 h.

Linker engineering toward near-infrared-I emissive metal-organic frameworks for amine detection.

Herein, organic linker-based near-infrared-I (NIR-I) emissive metal-organic frameworks (MOFs), with a maximum emission peak at 741 nm, were synthesized via linker engineering. By integration of stronger acceptor and donor groups into one linker, a significant bathochromic-shift is realized. This MOF exhibits great selectivity and sensitivity for aniline and p-phenylenediamine detection. This finding provides new insights into the rational design of NIR-MOFs for sensing and related applications.