Branched Alkyl Side Chains Research Articles

Polymer coating by oxidative polymerization of a new dopamine analogue with two amino groups

In our quest to expand the comprehensive chemistry of polydopamine and its catechol-containing analogous adhesive polymers we developed a new monomer, specifically 4-[3-amino-2-(aminomethyl)propyl]benzene-1,2-diol ADA. This compound is an analogue of dopamine characterized by an elongated and branched alkyl side chain that incorporates two amino groups. ADA was synthesized in two steps from 3,4-dihydroxybenzaldehyde in high yields. Exposure to air in aqueous Tris solution initiated polymerization leading to a dark colored product PADA that can adhere to surfaces forming continuous layers. The product was analyzed by FTIR, NMR, UV–vis-spectroscopy, AFM, HR-ESI-MS spectrometry, XPS, DPV, DLS and contact angle measurement. Based on these analyses, a general structure of the product is proposed as along with a mechanism of its formation. Notably, the properties of PADA are distinct from those of polydopamine offering different potential application. In particular, the additional amino groups could be used for interesting linkage of other functional moieties.

The Multi-Functional Third Acceptor Realizes the Synergistic Improvement in Photovoltaic Parameters and the High-Ratio Tolerance of Ternary Organic Photovoltaics.

The ternary strategy proves effective for breakthroughs in organic photovoltaics (OPVs). Elevating three photovoltaic parameters synergistically, especially the proportion-insensitive third component, is crucial for efficient ternary devices. This work introduces a molecular design strategy by comprehensively analyzing asymmetric end groups, side-chain engineering, and halogenation to explore the outstanding optoelectronic properties of the proportion-insensitive third component in efficient ternary systems. Three asymmetric non-fullerene acceptors (BTP-SA1, BTP-SA2, and BTP-SA3) are synthesized based on the Y6 framework and incorporated as the third component into the D18:Y6 binary system. BTP-SA3, featuring asymmetric terminal (difluoro-indone and dichloride-cyanoindone terminal), with branched alkyl side chains, exhibited high open-circuit voltage (VOC), balanced crystallinity and compatibility, achieving synergistic enhancements in VOC (0.862V), short circuit-current density (JSC, 27.52mA cm-2), fill fact (FF, 81.01%), and power convert efficiency (PCE, 19.19%). Device based on D18/Y6:BTP-SA3 (layer-by-layer processed) reached a high efficiency of 19.36%, demonstrating a high tolerance for BTP-SA3 (10-50%). This work provides novel insights into optimizing OPVs performances in multi-component systems and designing components with enhanced tolerance.

Simple-Structured Acceptor with Highly Interconnected Electron-Transport Pathway Enables High-Efficiency Organic Solar Cells.

Achieving desirable charge-transport highway is of vital importance for high-performance organic solar cells (OSCs). Here, it is shown how molecular packing arrangements can be regulated via tuning the alkyl-chain topology, thus resulting in a 3D network stacking and highly interconnected pathway for electron transport in a simple-structured nonfused-ring electron acceptor (NFREA) with branched alkyl side-chains. As a result, a record-breaking power conversion efficiency of 17.38% (certificated 16.59%) is achieved for NFREA-based devices, thus providing an opportunity for constructing low-cost and high-efficiency OSCs.

Physically crosslinked polyacrylates by quadruple hydrogen bonding side chains.

Dynamic polymer materials can be obtained by introducing supramolecular interactions between the polymer chains. Here we report on the preparation and mechanical properties of poly(methyl acrylate) (PMA) and poly(n-butyl acrylate) (PBA) funcionalized with ureidopyrimidinone (UPy) in the side chains. In contrast to the traditional UPy with a methyl group, the selected UPy motif contained a branched alkyl side chain, which enhances solubility, compatibility with the polymer matrix and potentially prevents stacking of UPy dimers. Low molar mass PMA and PBA were synthesized via Cu(0)-mediated radical polymerization and allyl bonds were introduced with different degrees of functionalization by stoichiometrically controlled transesterification with allyl alcohol. The allyl esters served as functional handles for UPy attachment via UV-initiated radical thiol-ene coupling. The PMA-UPy materials displayed a more glassy appearance, in contrast to the rubbery PBA-UPy polymer networks, associated to its higher glass transition temperature. The mechanical properties of the resulting hydrogen bonded polymer networks were assessed by thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical thermal analysis and tensile testing, followed by rheological analysis of the network dynamics. Furthermore, the effect of associative groups on the linear viscoelastic response is discussed based on a modified sticky Rouse model indicating the absence of significant aggregation or phase separation of the UPY units.

Impact of length of branched alkyl side chains on thiazolothiazole-based small molecular acceptors in non-fullerene polymer solar cells.

It has been reported that the length of branched alkyl side chains on fused-ring electron acceptors confers different impacts on properties versus solubility of BJH blends. However, because this impact on a non-fused acceptor backbone has rarely been studied, we examined the impact of molecular optimization from alkyl chain tuning based on non-fused thiazolothiazole small-molecule acceptors. The length of the side chain on the thiophene bridge was modified from 2-butyloctyl to 2-ethylhexyl, which corresponds to small molecules TTz3(C4C6) and TTz3(C2C4), respectively. Compared with the reported TTz3(C6C8) with long alkyl side chains, TTz3(C4C6) and TTz3(C2C4) exhibited stronger molecular aggregation, higher absorption coefficients, and greater redshifted UV absorption. Unexpectedly, after the alkyl chain was slightly shortened in this type of acceptor system, devices were successfully fabricated, but it was necessary to reduce the blending concentration at low rotation speeds due to the sharp decrease in the solubility of corresponding acceptor materials. Thus, the obtained unfavorable thickness and morphology of the active layer caused a decrease in Jsc and FF. As a consequence, TTz3(C4C6)- and TTz3(C2C4)-based devices showed an unsatisfactory power conversion efficiency of 6.02% and 2.71%, respectively, when donors were paired with the wide bandgap donor J71, which is inferior to that of TTz3(C6C8)-based devices (8.76%). These results indicate that it is challenging to determine the limit of the adjustable range of side chains to modify non-fused thiazolothiazole small-molecule acceptors for high-performance non-fullerene solar cells.

Miscibility‐Driven Morphology Tuning as the Critical Role for Designing Efficient Nonfused Ring Electron Acceptors

A clear understanding of the structure–performance relationship is important for promoting the evolution of designing efficient nonfused ring electron acceptors (NFREAs). Inspired by the above intention, herein, a side‐by‐side study is carried out based on three newly developed NFREAs by regulating rigid conjugation and flexible side chains, yielding PhNT‐4Cl, PhNC‐4Cl, and PhNP‐4Cl. It is unveiled that reduced miscibility by extending rigid conjugation can help to form nanofiber features, thus allowing high crystallinity, and a hindered overaggregation tendency by increasing steric hindrance of flexible side chain can help to form suitable domain sizes, thus avoiding severe charge recombination. As a result, PhNC‐4Cl with cyclopentadithiophene building block and branched alkyl side chains achieves a good balance in the earlier two aspects, thus enabling a higher efficiency of 14.01% with both higher photocurrent and fill factor, relative to PhNT‐4Cl (6.95%) and PhNP‐4Cl (6.31%). This work points out the critical role of miscibility‐driven morphology tuning on the device performance, thus guiding the molecular design toward efficient NFREAs.

Impact of the spatial structure of alkyl chains on properties of thiophene-substituted diketopyrrolopyrroles: Part I – Langmuir layer study

Slight changes in the dye structures may cause significant differences in molecular organization and aggregation ability of the dyes that determine their properties and usefulness for particular applications. The objects of our study were the dyes from the oligothiophene-substituted diketopyrrolopyrrole (DPP) group with alkyl chains in the terminal and side positions. The subject of our interest was to check the effect of the spatial structure (straight or branched) of DPP’s side alkyl chains on the dyes’ behavior in two-dimensional systems, the process of creating Langmuir layers at the air-water interface and the properties of Langmuir-Schaefer layers on a solid substrate. The course of isotherms of the dyes recorded during the compression process of Langmuir layers showed notable differences, and for the dye with a branched side alkyl chain, an isotherm inflection below 10 mN/m was observed. The process of layer formation was also thoroughly investigated using a Brewster angle microscope and measurements of changes in surface potential. Analysis of isotherms supported by density functional theory calculations suggests that the layers formed at the air-water interface are not monomolecular, consisting of monomers, but are built of aggregated (dimeric or tetrameric) dye forms. More stable layers were formed for the straight than branched alkyl side chains attached to the dyes. Morphologies of Langmuir-Schaefer layers transferred onto quartz were studied using confocal microscopy. The results confirmed that even a slight change in the spatial structure of the side alkyl chains of the investigated dyes determines their thermodynamic properties and organization of the thin film. Finally, a model of the arrangement of DPP dye molecules in thin layers was proposed.

Absorption Coefficient and Optical Contrast Modulation through Side Chain Engineering of Electrochromic Polymers

Conjugated polymers can be electrochemically bleached to achieve colored-to-transmissive electrochromic switching. This work presents a side chain engineering approach to enhance colored state absorptivity of an electrochromic polymer, while maintaining high transmissivity in the bleached state. A series of dioxythiophene copolymers with systematic variations in their branched alkyl side chains have been used to understand side chain influence on solubility, aggregation, film morphology and optical constants. By increasing the chromophore density through an appropriate choice of side chains, the absorption coefficient of the colored polymer can be improved by almost 50%, with minimal influence on bleached-state absorption coefficients over the visible region. As such, solution-processed films of high absorbance can be prepared using thin polymer layers to achieve fast electrochromic switching and highly transmissive bleached states. Under optimized conditions, optical contrasts nearing 80% can be reached at the wavelength of maximum absorbance, among the highest reported for solution-processed, cathodically coloring electrochromic polymers. The improved absorption coefficients are especially useful in enhancing the electrochromic performance in the low transmittance regime (colored state transmittance <20%), providing useful insights for designing high contrast electrochromic materials.

Antibacterial Synnepyrroles from Human-Associated Nocardiopsis sp. Show Protonophore Activity and Disrupt the Bacterial Cytoplasmic Membrane.

Actinobacteria have traditionally been an important source of bioactive natural products, although many genera remain poorly explored. Here, we report a group of distinctive pyrrole-containing natural products, named synnepyrroles, from Nocardiopsis synnemataformans. Detailed structural characterization by mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy combined with isotope-labeling experiments revealed their molecular structures and biosynthetic precursors acetate, propionate, aspartate, and (for branched analogues) valine. The biosynthetic data points toward an unusual pathway for pyrrole formation via condensation of aspartate with diverse fatty acids that give rise to a unique pyrrole-3,4-dicarboxylate core and variable linear or terminally branched alkyl side chains. In addition, the bioactivity and mode of action of synnepyrrole A were characterized in Bacillus subtilis. Orienting assessment of the phenotype of synnepyrrole A-treated bacteria by high-resolution microscopy suggested the cytoplasmic membrane as the target structure. Further characterization of the membrane effects demonstrated dissipation of the membrane potential and intracellular acidification indicative of protonophore activity. At slightly higher concentrations, synnepyrrole A compromised the barrier function of the cytoplasmic membrane, allowing the passage of otherwise membrane-impermeable dye molecules.

Intermolecular CH-π Electrons Interaction in Poly (9,9-dioctylfluorenyl-2,7-diyl) (PFO): An Experimental and Theoretical Study.

This study demonstrates the presence of CH-π interaction in poly [9,9-dioctylfluorenyl-2,7-diyl] (PFO-1) due to an aggregate formation of PFO-1 in the liquid state. The absorption spectra of PFO-1 in certain solvents at low concentrations showed a single band at 390 nm. However, when using high concentrations, a new band at 437 nm appeared. This band is due to the aggregate formation of PFO-1. The aggregate formation occurs as a result of the CH interaction of the n-alkyl side chains with π-electrons in the benzene ring. The optical characteristics of another conjugated polymer of poly [9,9-di-(2-ethylhexyl)-fluorenyl-2,7-diyl] (PFO-2) were investigated to confirm the CH-π interaction. The absorption showed only one wavelength at 390 nm without any new band at the end of the spectrum, even at higher concentrations and lower temperatures. The main reason for the absence of aggregate formation in PFO-2 is the sterical hindrance caused by the branched alkyl side chains. In addition, Density Functional Theory (DFT) was used to compute the HOMO–LUMO transitions, electron charge distribution, and frontier molecular orbitals for each polymer. The Mulliken charge distribution and demonstrated a notable difference in the reactivity of the alkyl side chain, confirming the higher ability of PFO-1 to form CH-π bonds. docking model emphasized that the band at 437 nm could be attributed to the interaction between CH in the n-alkyl side chain and π bonds in the aromatic rings of PFO-1.

Nitrogen-bridged star-shaped fused-ring electron acceptors for organic solar cells

Two kinds of nitrogen-bridged star-shaped fused-ring electron acceptors based on benzo[1,2-b:3,4-b’-5,6-b’’]tri(4-H-dithieno[3,2-b:2’,3’-d]pyrrole) (BTDTP) core with linear and branched alkyl side chains on bridging nitrogen atoms are developed. Both electron acceptors exhibit strong intramolecular charge transfer absorption bands at 500–800 nm (molar extinction coefficient of 3.0 × 105 M −1 cm−1) with narrow optical bandgaps around 1.58 eV, but reveal different molecular packing and morphology. Compared to acceptor with linear side chains, the acceptor bearing branched side chains exhibits ordered face-on orientation with tight π-π stacking, as well as more favorable phase separation morphology and balanced charge transport when blended with polymer donor PM6. Organic solar cell device based on acceptors bearing branched side chains achieves a power conversion efficiency (PCE) of 9.95% with a fill factor of 74.98% and a short-circuit current density of 14.90 mA cm−2, which is much superior to the device using acceptors bearing linear side chains (a PCE of 6.74%).

Alkyl side chain engineering enables high performance as-cast organic solar cells of over 17% efficiency

Achieving high-performance as-cast OSCs is crucial for industrialization in the future, owing to the advantages of better stability, environmental-friendly, and decreasing production cost. In this regard, we synthesized an A-DA′D-A type acceptor, Y6-eC6-BO, by shortening the straight alkyl side-chains on the thiophene position from C11 to C6 as well as lengthening the branched alkyl side-chains on the pyrrole position of Y6 to achieve a stronger crystallization and better miscibility than Y6. As a result, the corresponding chloroform-processed as-cast PM6: Y6-eC6-BO OSC showed a high PCE of 17.33%, which was one of the highest efficiencies of as-cast OSCs. And the as-cast PM6:Y6-eC6-BO OSCs processed from o-xylene displayed a PCE of 16.38%, as far as we know, this is among the highest efficiencies of non-halogenated-solvent processed as-cast OSCs. These results demonstrated tailoring the alkyl side-chain of NFAs is a feasible and simple approach to achieve high performance as-cast OSCs and provides guideline in molecular design in the future.

Physically Cross-Linked Polybutadiene by Quadruple Hydrogen Bonding through Side-Chain Incorporation of Ureidopyrimidinone with Branched Alkyl Side Chains

Physically Cross-Linked Polybutadiene by Quadruple Hydrogen Bonding through Side-Chain Incorporation of Ureidopyrimidinone with Branched Alkyl Side Chains

Rational Design of Highly Soluble and Crystalline Conjugated Polymers for High‐Performance Field‐Effect Transistors

AbstractConjugated polymers based on cyclopentadithiophene (CPDT) moieties are widely used in optoelectronics applications but rarely in field‐effect transistors (FETs). This is due to the steric hindrance at the tetrahedral center of the CPDT core, which is a critical problem requiring resolution without diminishing the polymer crystallinity and solubility. A bulky CPDT‐based high‐mobility copolymers are synthesized here, which shows excellent π–π stacking in the film states with good solubility. The addition of bulky ethylhexyl side chains to CPDT does not interfere with the molecular ordering and promotes the intercalation of linear alkyl chains on the co‐monomeric units. The resulting polymer forms bimodal packing structures with strong lamellar ordering and π–π interactions. Furthermore, the free volume generated by the bulky ethylhexyl side chains allows for a small amount of fullerene additive to be contained in the film state without interfering with the molecular ordering, leading to enhanced on/off ratios and hole mobilities of the resulting FETs. As a result, promising hole mobilities of up to 1.08–1.64 cm2 V−1 s−1 are achieved with the optimized FETs, which are the highest mobilities reported for CPDT‐based conjugated polymers containing branched alkyl side chains.

Reducing the side-chain influences of isoindigo-based polymer donors by backbone fluorination in photovoltaic applications

The effect of synergistic structural engineering (asymmetric side chains and backbone fluorination) for polymer donors in photovoltaic applications is investigated in this study. Six isoindigo (IID)-based polymer donors with slightly different side-chain and backbone designs are composed of a bithiophene (BT) or fluorinated bithiophene moiety to form two series of polymers [PII2T (P1–P3) and PII2TF (P4–P6)] while symmetric/asymmetric side-chain combinations are composed of decyltetradecane branched alkyl side chain (DT) and siloxane-terminated side chain (SiO–C8). The results indicate the different side chain design and backbone fluorination modulate the energy levels, crystalline properties, and molecular packing behaviors of the polymers. P2 and P5 with asymmetric side chains are showed to deliver the highest power conversion efficiency (PCE) in the respective series of PII2T and PII2TF. The morphological analyses reveals that the mismatched side-chain geometry results in a face-on dominated packing to yield superior device performance. Meanwhile, the fluorinated polymers (P4–P6) show superior performance than the corresponding non-fluorinated polymers (P1–P3). Moreover, backbone fluorination largely reduces the performance difference between the polymers with symmetric side chains and asymmetric sides chains. This work demonstrates that the synergistic effect of asymmetric side chains and backbone fluorination can be a rational design towards high-performance conjugated polymers.

Highly Processable Covalent Organic Framework Gel Electrolyte Enabled by Side-Chain Engineering for Lithium-Ion Batteries.

Although covalent organic frameworks (COFs) with a graphene-like structure present unique chemical and physical properties, they are essentially insoluble and infusible crystalline powders with poor processability, hindering their further practical applications. How to improve the processability of COF materials is a major challenge in this field. In this contribution, we proposed a general side-chain engineering strategy to construct a gel-state COF with high processability. This method takes advantages of large and soft branched alkyl side chains as internal plasticizers to achieve the gelation of the COF. We systematically studied the influence of the length of the side chain on the COF gel formation. Benefitting from their machinability and flexibility, this novel COF gel can be easily processed into gel-type electrolytes with specific shape and thickness, which were further applied to assemble lithium-ion batteries that exhibited high cycling stability.

Highly Processable Covalent Organic Framework Gel Electrolyte Enabled by Side‐Chain Engineering for Lithium‐Ion Batteries

AbstractAlthough covalent organic frameworks (COFs) with a graphene‐like structure present unique chemical and physical properties, they are essentially insoluble and infusible crystalline powders with poor processability, hindering their further practical applications. How to improve the processability of COF materials is a major challenge in this field. In this contribution, we proposed a general side‐chain engineering strategy to construct a gel‐state COF with high processability. This method takes advantages of large and soft branched alkyl side chains as internal plasticizers to achieve the gelation of the COF. We systematically studied the influence of the length of the side chain on the COF gel formation. Benefitting from their machinability and flexibility, this novel COF gel can be easily processed into gel‐type electrolytes with specific shape and thickness, which were further applied to assemble lithium‐ion batteries that exhibited high cycling stability.

Synthesis of helical branched carbodiimide polymers with liquid crystalline properties

ABSTRACT Carbodiimide polymers are synthetic helical polymers that display unique properties depending on the functional groups attached to the polymer backbone. The amidine groups of the backbone present alternating amine- and imine-like groups. The properties of the polycarbodiimides have been studied by varying the sidechains of the polymer from linear to branched. In previous work, different arenes and straight aliphatic chains substituted polycarbodiimides have been used to evaluate the thermal and liquid crystalline properties of these polymers. In this study, we introduced bulky branched aliphatic and octadecyl side chains to the polymer backbone to generate a branched homopolymer and different branched/linear-chain copolymers. The effect of these side-chain combinations on the solid and solution properties of these polycarbodiimides was studied. It was observed that polycarbodiimides containing octadecyl and branched bulky alkyl groups showed different thermal events in the DSC plot at ~30°C. Also, we observed a decrease in thermal stability in the TGA thermogram as we increase the branched alkyl side chains of the polymers. The lyotropic liquid crystallinity was observed in all the branched copolymers that consist of both branched alkyl side chains and octadecyl functional groups in different ratios.

Synergistic Effects of Chlorination and Branched Alkyl Side Chain on the Photovoltaic Properties of Simple Non‐Fullerene Acceptors with Quinoxaline as the Core

To date, the fused-ring electron acceptors show the best photovoltaic performances, and the development of simple non-fullerene acceptors via intramolecular noncovalent interactions can reduce synthetic costs. In this work, four simple non-fullerene acceptors with an A-D-A'-D-A configuration (QCIC1, QCIC2, QCIC3, and QCIC4) were synthesized. They contained the same conjugated backbone (A': quinoxaline; D: cyclopentadithiophene; A: dicyano-indanone) but different halogen atoms and alkyl side chains. Due to the chlorination on the end-groups and the most and/or longest branched alkyl side chains on the backbone, the blended film composed of QCIC3 and donor poly{[2,6'-4,8-di(5-ethylhexylthienyl)benzo [1,2-b : 4,5-b']dithiophene]-alt-[5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c : 4',5'-c']dithiophene-4,8-dione)]} (PBDB-T) exhibited the strongest π-π stacking and the most suitable phase-separation domains among the four blended films. Therefore, the QCIC3-based organic solar cells yielded the highest power conversion efficiency of 10.55 %. This work provides a pathway to optimize the molecular arrangements and enhance the photovoltaic property of simple electron acceptors through subtle chemical modifications.

High-performance near-infrared organic phototransistors based on diketopyrrolopyrrole conjugated polymers with partial removal of long branched alkyl side chains

Near-infrared (NIR) phototransistors based on diketopyrrolopyrrole polymers with partial removal of side chains are reported with improved NIR photoresponses, which take advantage of both strengthened NIR absorption and improved charge transport.