End-group Modification Research Articles

Open-vessel polymerization of N-carboxyanhydride (NCA) for polypeptide synthesis.

Synthetic polypeptides, also known as poly(α-amino acids), have the same polyamide backbone structures as natural proteins and peptides. As an important class of biomaterials, polypeptides have been widely used because of their biocompatibility, bioactivity and biodegradability. Ring-opening polymerization of N-carboxyanhydride (NCA) is a classical and widely used method for the synthesis of polypeptides. The dominantly used primary amine-initiated NCA polymerization can yield well-defined polymers and complex macromolecular architectures, but the reaction is slow and sensitive to moisture, making it necessary to use anhydrous solvents and a glovebox. One solution is to use lithium hexamethyldisilazide (LiHMDS) as the initiator, as described in this protocol. LiHMDS-initiated NCA polymerization is less sensitive to moisture and can be carried out in an open vessel outside the glovebox. It is also very fast; the reaction can be complete within 5 min to produce 30-mer polypeptides. In this protocol, poly(γ-benzyl-L-glutamate) is prepared as an example, but the protocol can easily be adapted to the synthesis of other polypeptides by generating NCAs from different amino acids, making it particularly suitable for the efficient parallel synthesis of polypeptide libraries. We provide detailed procedures for NCA synthesis and purification, the method of polymer end-group modification and measurement of polymerization kinetics and reactivity ratio. The procedure for synthesis of monomers and polymerization to form polypeptides requires <1 d. The superfast and open-vessel NCA polymerization method described here will probably enable a wide range of applications in the synthesis and functional study of polypeptide biomaterials.

End-group modification in a fluorene-terminated efficient hole transport materials for organic and perovskite solar cells

End-group modification in a fluorene-terminated efficient hole transport materials for organic and perovskite solar cells

Theoretical study on the effect of end groups and core ring numbers in non-fullerene acceptors for organic solar cells

Modifying the skeleton, side chains and end groups of non-fullerene acceptors (NFAs) is important approach to improve the photovoltaic performance of organic solar cells. We selected PBDB-T as the donor and INIC, INIC1, INIC2, ITCC, ITCPTC and ITIC as the acceptors in order to study the difference in NFAs. The geometries, electronic structures, excited state properties, excited-state lifetimes and rate constants of charge transfer (CT), charge recombination (CR) and exciton dissociation (ED) processes of the monomers and PBDB-T:NFA complexes have been investigated by means of density functional theory and time-dependent density functional theory. The research reveals that fluorination of end groups, thienyl substitution and increase in the number of central rings result in the decrease in the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Fluorine substitution and increase in central ring numbers cause redshift of the absorption spectrum for NFAs. NFAs with fluorine substitution have a larger maximum electrostatic potential, which facilitates CT at the donor:NFA heterojunction interfaces. Fluorine substitution and thienyl substitution decrease the NFA's CT distances, indicating that both fluorine and thienyl substitutions affect the CT rate. Fluorine substitution, thienyl modification of end groups and increase in central ring numbers also reduce the exciton binding energy, which is beneficial for decreasing CR and improving ED efficiency.

Theoretical designing of 9,9'-dicarbazole-based dye via end-group modification for indoor DSSC applications

Molecular modeling has garnered significant attention in the realm of organic solar cells (OSCs) because it holds the promise of producing more efficient OSCs with notably enhanced power conversion efficiency (PCE). In this quest, we have undertaken a strategic modification of the acceptor moieties within the recently synthesized metal-free dicarbazole-based organic dye Cz-2, resulting in five novel theoretical dyes, designated as PT1-PT5. Numerous simulations encompassed both the newly designed compounds and the reference (Cz-2) by using DFT and TD-DFT, a comprehensive characterization aimed at enhancing photovoltaic and optoelectronic properties. We probed into the analysis of ground state geometry, frontier molecular orbitals, transition density matrix, optical properties, density of state, binding energy, molecular electrostatic potential, reorganizational energy, open-circuit voltage, and fill factor. Our findings unveiled a common trend among all the theoretical dyes, a reduction in band gap (Eg), a notable red-shift in absorbance ranging from 434 nm to 554 nm, and lowered binding and excitation energy. The decreased reorganization energy i.e., λ e and λ h, spanning a range from 0.0040 to 0.0052 eV and 0.0043 to 0.0075 eV respectively, promised significantly enhanced charge mobility. Intriguingly, the binding energies of all the designed compounds consistently registered values lower than that of reference (R), with figures ranging from 0.55 to 0.64 eV, compared to the binding energy of R (0.67 eV). These dyes show significant potential for indoor photovoltaics as they can absorb light in the visible range for indoor renewable energy applications. Our comprehensive analyses suggest that PT1-PT5 are promising candidates with great potential for advancing the field of renewable energy.

Theoretical insights into metal-free oligothiophene-centered dye with A–D–A framework via end group modification for DSSCs

Theoretical insights into metal-free oligothiophene-centered dye with A–D–A framework via end group modification for DSSCs

Effect of nitro-substituted ending group on the photovoltaic and photocatalytic performance of non-fullerene acceptors

The Y-series non-fullerene acceptors (NFAs) significantly enhance organic photovoltaic device efficiency, approaching 20%. Recent studies demonstrate their commendable photocatalytic performance in bulk heterojunction photocatalysis. Chemical modification of end groups emerges as a pivotal way to modulate molecular electrical and optical characteristics, thereby improving the organic solar cells (OSCs) performance. Among Y-series NFAs, 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene)propanedinitrile (INCN) and its derivatives stand out as the most successful end groups. However, a restricted range of modifying groups, such as the fluorine atom (–F) and the hydroxyl group (–OH), are currently employed to explore both the photovoltaic and photocatalytic properties of Y-series NFAs, research on other substituents for INCN remains largely unexplored to date. In this study, nitro-substituted end groups were incorporated into the Y6 skeleton, resulting in a new NFA, named Y6-NO. Simultaneously, INCN is incorporated into the Y6 skeleton to create Y6-IN as a reference molecule for simultaneously investigating the photovoltaic and photocatalytic properties of the two NFAs. In organic photovoltaics, Y6-NO, featuring nitro groups, exhibits a red-shifted absorption, lower molecular energy levels, and enhanced electron transport, leading to a superior power conversion efficiency (PCE) of 17.03 % for OSCs, as opposed to 10.45 % for Y6-IN. Conversely, in the photocatalytic hydrogen evolution reaction (HER) for water splitting, the nitro groups in Y6-NO lowers the energy level of the lowest unoccupied molecular orbital (LUMO), resulting in a reduced overpotential when combined with the co-catalyst Pt. Consequently, the HER rate of PM6:Y6-NO nanoparticles (72.2 mmol h−1 g−1) is lower than that of PM6:Y6-IN nanoparticles (108.5 mmol h−1 g−1). This study highlights that through judicious end-group chemical modification, the photovoltaic and photocatalytic properties of the acceptors can be effectively modulated.

Theoretical investigation of substituted end groups in thiophene‐phenyl‐thiophene (TPT) derivatives for high efficiency organic solar cells

AbstractThe field of organic solar cells has witnessed notable advancements in the past few years, mostly due to the development of novel materials for the active layer. The current investigations reveal the potential of nine previously unexplored molecules (TP1–TP9) designed by end group modification of TPT4F molecule. These molecules were investigated at MPW1PW91/6‐31G (d, p) with DFT and TD‐DFT approach to study the various photovoltaic and geometrical parameters. The results obtained through computations indicated improvement in the investigated parameters. The terminal group modification shifted the absorption maximum towards longer wavelength in the UV‐visible region. Highly conjugated modified acceptors reduced the band gap. The lower excitation energies increased the rate of charge transfer. The designed molecules showed improved excited state lifetime in comparison to the reference. The open circuit voltage was determined using the PTB7 polymer, which exhibited a noticeable improvement, especially in TP1 (1.70 eV), TP3 (1.75 eV), TP4 (1.68 eV), TP6 (1.85 eV), and TP7 (1.75 eV) when compared with reference (1.59 eV). Moreover, charge transfer investigations of designed molecules with PTB7 complex were performed by analyzing the concentration of charge transfer over molecular orbitals, that is, HOMO to LUMO. All of the preceding investigations targeted to achieve high‐efficiency organic cells reveal that the altered molecules can be considered effective candidates to tackle future energy problems.

Multiscale computational analysis of the effect of end group modification on PM6:BTP-x OSCs performance

Theoretical computational simulation are used to analyse the molecular stacking characteristics of PM6:BTP-x OSCs and the role of end group modifications.

Value addition of MXenes as photo-/electrocatalysts in water splitting for sustainable hydrogen production.

The energy transition from fossil fuel-based to renewable energy is a global agenda. At present, a major concern in the green hydrogen economy is the demand for clean fuels and non-noble materials to produce hydrogen through water splitting. Researchers are focusing on addressing this concern with the help of the development of appropriate non-noble-based photo-/electrocatalytic materials. A new class of two-dimensional materials, MXenes, have recently shown tremendous potential for water splitting to produce H2via a photoelectrochemical process. The unique properties of emerging 2D MXene materials, such as hydrophilic surface functionalities, higher surface-to-volume ratios, and inherent flexibility, present these materials as appropriate photo-/electrocatalytic materials. Unique value addition and innovative strategies such as the introduction of end-group modification, heterojunctions, and nanostructure engineering have shown the potential of MXene materials as emerging photo-/electrocatalysts for water splitting. When integrated with conventional noble metal catalysts, MXene-based catalysts demonstrated a lower overpotential for hydrogen and oxygen evolution reactions and a remarkable boost in performance for enhanced H2 production rates surpassing those of pristine noble metal-based catalysts. These promote future perspectives for the utilization of chemically synthesized MXenes as alternative photo-/electrocatalysts. Future research direction should focus on MXene synthesis and utilization for surface modification, composite formation, stabilization, and optimization in synthesis methods and post-synthesis treatments. This review highlights the progress in the understanding of fundamental mechanisms and issues associated with water splitting, influencing factors of MXenes, their value addition role, and application strategies for water splitting, including performance, challenges, and outlook of MXene-based photo-/electrocatalysts, in the last five years.

Biodegradable polyester copolymers: synthesis based on the Biginelli reaction, characterization, and evaluation of their application properties.

The Biginelli reaction, a three-component cyclocondensation reaction, is an important member of the multicomponent reaction (MCR) family. In this study, we conducted end-group modifications on a variety of biodegradable polyesters, including poly(1,4-butylene adipate) (PBA), poly(ε-caprolactone) (PCL), polylactic acid (PLA), and poly(p-dioxanone) (PPDO), based on the precursor polyethylene glycol (PEG). By combining two polymers through the Biginelli multi-component reaction, four new biodegradable polyester copolymers, namely DHPM-PBA, DHPM-PCL, DHPM-PLA, and DHPM-PPDO, were formed. These Biginelli reactions demonstrated exceptional completeness, validating the efficiency of the synthesis strategy. Although the introduction of various polyesters lead to different properties, such as crystallinity and cytotoxicity, the newly synthesized 3,4-dihydro-2(H)-pyrimidinone compounds (DHPMs) exhibit enhanced hydrophilicity and can self-assemble in water and N,N-dimethylformamide (DMF) solution to form micelles with a controllable size. Furthermore, DHPM-PPDO promotes cellular growth and has potential applications in wound healing and tissue engineering. In conclusion, this method demonstrates great universality and methodological significance and offers insights into the medical applications of polyethylene glycol.

Combining photocontrolled-cationic and anionic-group-transfer polymerizations using a universal mediator: enabling access to two- and three-mechanism block copolymers.

An ongoing challenge in polymer chemistry is accessing diverse block copolymers from multiple polymerization mechanisms and monomer classes. One strategy to accomplish this goal without intermediate compatibilization steps is the use of universal mediators. Thiocarbonyl thio (TCT) functional groups are well-known mediators to combine radical with either cationic or anionic polymerization, but a sequential cationic-anionic universal mediator system has never been reported. Herein, we report a TCT universal mediator that can sequentially perform photocontrolled cationic polymerization and thioacyl anionic group transfer polymerization to access poly(ethyl vinyl ether)-block-poly(thiirane) polymers for the first time. Thermal analyses of these block copolymers provide evidence of microphase separation. The success of this system, along with the established compatibility of radical polymerization, enabled us to further chain extend the cationic-anionic diblock using radical polymerization of N-isopropylacrylamide. The resulting terpolymer represents the first example of a triblock made from three different monomer classes incorporated via three different mechanisms without any end-group modification steps. The development of this simple, sequential synthesis using a universal mediator approach opens up new possibilities by providing facile access to diverse block copolymers of vinyl ethers, thiiranes, and acrylamides.

Hybrid Poly(β-amino ester) Triblock Copolymers Utilizing a RAFT Polymerization Grafting-From Methodology.

The biocompatibility, biodegradability, and responsiveness of poly(β-amino esters) (PBAEs) has led to their widespread use as biomaterials for drug and gene delivery. Nonetheless, the step-growth polymerization mechanism that yields PBAEs limits the scope for their structural optimization toward specific applications because of limited monomer choice and end-group modifications. Moreover, to date the post-synthetic functionalization of PBAEs has relied on grafting-to approaches, challenged by the need for efficient polymer-polymer coupling and potentially difficult post-conjugation purification. Here a novel grafting-from approach to grow reversible addition-fragmentation chain transfer (RAFT) polymers from a PBAE scaffold is described. This is achieved through PBAE conversion into a macromolecular chain transfer agent through a multistep capping procedure, followed by RAFT polymerization with a range of monomers to produce PBAE-RAFT hybrid triblock copolymers. Following successful synthesis, the potential biological applications of these ABA triblock copolymers are illustrated through assembly into polymeric micelles and encapsulation of a model hydrophobic drug, followed by successful nanoparticle (NP) uptake in breast cancer cells. The findings demonstrate this novel synthetic methodology can expand the scope of PBAEs as biomaterials.

High-Efficiency and Low-Energy-Loss Organic Solar Cells Enabled by Tuning the End Group Modification of the Terthiophene-Based Acceptor Molecules to Enhance Photovoltaic Properties.

In the current study, six nonfullerene small acceptor molecules were designed by end-group modification of terminal acceptors. Density functional theory calculations of all designed molecules were performed, and optoelectronic properties were computed by employing different functionals. Every constructed molecule has a significant bathochromic shift in the maximum absorption value (λmax) except AM6. AM1-AM4 molecules represented a narrow band gap (Eg) and low excitation energy values. The AM1-AM4 and AM6 molecules have higher electron mobility. Comparing AM2 to the reference molecule reveals that AM2 has higher hole mobilities. Compared to the reference molecule, all compounds have excellent light harvesting efficiency values compared to AM1 and AM2. The natural transition orbital investigation showed that AM5 and AM6 had significant electronic transitions. The open-circuit voltage (Voc) values of the computed molecules were calculated by combining the designed acceptor molecules with PTB7-Th. In light of the findings, it is concluded that the designed molecules can be further developed for organic solar cells (OSCs) with superior photovoltaic abilities.

Introducing thiazole units into small-molecule acceptors for efficient non-fullerene organic solar cells

The end-group modification engineering has been widely applied in non-fullerene acceptors (NFAs) to achieve high-performance organic solar cells (OSCs). Herein, we designed and synthesized a series of small-molecule acceptors (SMAs), namely ODTz-γ, ODTz-m, DTTz-γ and DTTz-m, which containing the electron-withdrawing thiazole units on the end groups at different position. These SMAs not only exhibited strong and broad absorption region from 500 nm to 900 nm, identical band gaps, but also the similar energy levels, indicating the position of thiazole units have trivial effect on their absorbance and energy levels. OSCs were fabricated by integrating an electron-donating polymer PBDB-T with these resultant electron-accepting materials. Devices based on ODTz-γexhibited an obviously higher power conversion efficiency over 12.0%, which outperformed those of obtained from devices based on other SMAs. Further characterization of the devices revealed that introducing the thiazole units into the γ position of end groups can enhance the charge transport mobility, suppress recombination, and improve the blend film morphology.

A DFT study for improving the photovoltaic performance of organic solar cells by designing symmetric non-fullerene acceptors by quantum chemical modification on pre-existed LC81 molecule

Minimizing the energy loss and improving the open circuit voltage of organic solar cells is still a primary concern for scientists working in this field. With the aim to enhance the photovoltaic performance of organic solar cells by minimizing energy loss and improving open circuit voltage, seven new acceptor molecules (LC1-LC7) are presented in this work. These molecules are designed by modifying the terminal acceptors of pre-existed “LC81” molecule based on an indacinodithiophene (IDT) fused core. The end-group modification approach is very fruitful in ameliorating the efficacy and optoelectric behavior of OSCs. The newly developed molecules presented remarkable improvements in performance-related parameters and optoelectronic properties. Among all designed molecules, LC7 exhibited the highest absorption maxima (λmax = 869 nm) with the lowest band-gap (1.79 eV), lowest excitation energy (Ex = 1.42 eV), lowest binding energy, and highest excited state lifetime (0.41 ns). The newly designed molecules LC2, LC3, and LC4 exhibited remarkably improved Voc that was 1.84 eV, 1.82 eV, and 1.79 eV accordingly, compared to the LC81 molecule with Voc of 1.74 eV LC2 molecule showed significant improvement in fill factor compared to the previously presented LC81 molecule. LC2, LC6, and LC7 showed a remarkable reduction in energy loss by showing Eloss values of 0.26 eV, 0.18 eV, and 0.25 eV than LC81 molecule (0.37 eV). These findings validate the supremacy of these developed molecules (especially LC2) as potential components of future OSCs.

Polymer nanoparticles deliver mRNA to the lung for mucosal vaccination.

An inhalable platform for messenger RNA (mRNA) therapeutics would enable minimally invasive and lung-targeted delivery for a host of pulmonary diseases. Development of lung-targeted mRNA therapeutics has been limited by poor transfection efficiency and risk of vehicle-induced pathology. Here, we report an inhalable polymer-based vehicle for delivery of therapeutic mRNAs to the lung. We optimized biodegradable poly(amine-co-ester) (PACE) polyplexes for mRNA delivery using end-group modifications and polyethylene glycol. These polyplexes achieved high transfection of mRNA throughout the lung, particularly in epithelial and antigen-presenting cells. We applied this technology to develop a mucosal vaccine for severe acute respiratory syndrome coronavirus 2 and found that intranasal vaccination with spike protein-encoding mRNA polyplexes induced potent cellular and humoral adaptive immunity and protected susceptible mice from lethal viral challenge. Together, these results demonstrate the translational potential of PACE polyplexes for therapeutic delivery of mRNA to the lungs.

Solvent-Free Chemical Recycling of Polymethacrylates made by ATRP and RAFT Polymerization: High-Yielding Depolymerization at Low Temperatures.

Although controlled radical polymerization is an excellent tool to make precision polymeric materials, reversal of the process to retrieve the starting monomer is far less explored despite the significance of chemical recycling. Here, we investigate the bulk depolymerization of RAFT and ATRP-synthesized polymers under identical conditions. RAFT-synthesized polymers undergo a relatively low-temperature solvent-free depolymerization back to monomer thanks to the partial in-situ transformation of the RAFT end-group to macromonomer. Instead, ATRP-synthesized polymers can only depolymerize at significantly higher temperatures (>350 ˚C) through random backbone scission. To aid a more complete depolymerization at even lower temperatures, we performed a facile and quantitative end-group modification strategy in which both ATRP and RAFT end-groups were successfully converted to macromonomers. The macromonomers triggered a lower temperature bulk depolymerization with an onset at 150 ˚C yielding up to 90% of monomer regeneration. The versatility of the methodology was demonstrated by a scalable depolymerization (~10 g of starting polymer) retrieving 84% of the starting monomer intact which could be subsequently used for further polymerization. This work presents a new low-energy approach for depolymerizing controlled radical polymers and creates many future opportunities as high-yielding, solvent-free and scalable depolymerization methods are sought.

MXene-based Materials for Water Splitting: Synthesis and Modification.

With abundant metal site and tunable electronic structure, MXene is considered as a promising electrocatalyst for the conversion of energy molecules. In this review, the latest research progress on inexpensive MXene-based catalysts for water electrolysis is summarized. Typical preparation and modification methods and their advantages and disadvantages are briefly discussed, with a focus on the regulation and design of the surface interface electronic states, which improve the electrocatalytic performance of MXene-based materials. The main strategies for the electronic state modification include end-group modification, heteroatom doping, and heterostructure construction. Some limitations of MXene-based materials, which should be considered in the rational design of advanced MXene-based electrocatalyst, are also discussed. Finally, prospects for the rational design of Mxene-based electrocatalysts is proposed.

Synergistic modification of end groups in Quinoxaline fused core-based acceptor molecule to enhance its photovoltaic characteristics for superior organic solar cells

The competence of organic solar cells (OSCs) could be enhanced by improving the light absorption capabilities as well as the open-circuit voltage (Voc) of utilized molecules. To upgrade overall functionality of OSCs, seven new molecules were designed in this work using an end-cap alteration technique on Quinoxaline fused core-based non-fullerene acceptor (Qx-2) molecule. This technique is known to be quite advantageous in terms of improvement of the effectiveness and optoelectrical behavior of various OSCs. Critical parameters like the absorption maximum, frontier molecular orbitals, excitation energy, exciton binding energy, Voc, and fill factor of molecules were considered for the molecules thus designed. All newly designed molecules showed outstanding improvement in optoelectronic as well as performance-related properties. Out of all scrutinized molecules, Q1 exhibited highest wavelength of absorption peak (λmax = 779 nm) with the reduced band gap (1.90 eV), least excitation energy (Ex = 1.59 eV), along with the highest dipole moment (17.982950 D). Additionally, the newly designed compounds Q4, Q5, and Q6 exhibited significantly improved Vocs that were 1.55, 1.47, and 1.50 eV accordingly, as compared to the 1.37 eV of Qx-2 molecule. These molecules also showed remarkable improvement in fill factor attributed to direct correspondence of Voc with it. Inclusively, these results support the superiority of these newly developed molecules as prospective constituents of upgraded OSCs.

Improved Route to Linear Triblock Copolymers by Coupling with Glycidyl Ether-Activated Poly(ethylene oxide) Chains.

Poly(ethylene oxide) block copolymers (PEOz BCP) have been demonstrated to exhibit remarkably high lithium ion (Li+) conductivity for Li+ batteries applications. For linear poly(isoprene)-b-poly(styrene)-b-poly(ethylene oxide) triblock copolymers (PIxPSyPEOz), a pronounced maximum ion conductivity was reported for short PEOz molecular weights around 2 kg mol-1. To later enable a systematic exploration of the influence of the PIx and PSy block lengths and related morphologies on the ion conductivity, a synthetic method is needed where the short PEOz block length can be kept constant, while the PIx and PSy block lengths could be systematically and independently varied. Here, we introduce a glycidyl ether route that allows covalent attachment of pre-synthesized glycidyl-end functionalized PEOz chains to terminate PIxPSy BCPs. The attachment proceeds to full conversion in a simplified and reproducible one-pot polymerization such that PIxPSyPEOz with narrow chain length distribution and a fixed PEOz block length of z = 1.9 kg mol-1 and a Đ = 1.03 are obtained. The successful quantitative end group modification of the PEOz block was verified by nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). We demonstrate further that with a controlled casting process, ordered microphases with macroscopic long-range directional order can be fabricated, as demonstrated by small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has already been shown in a patent, published by us, that BCPs from the synthesis method presented here exhibit comparable or even higher ionic conductivities than those previously published. Therefore, this PEOz BCP system is ideally suitable to relate BCP morphology, order and orientation to macroscopic Li+ conductivity in Li+ batteries.