Solubilizing Side Chains Research Articles

Controlling conjugated polymer morphology by precise oxygen position in single-ether side chains.

Recently, polar side chains have emerged as a functional tool to enhance conjugated polymer doping properties by improving the polymer miscibility with polar chemical dopants and facilitate solvated ion uptake. In this work, we design and investigate a novel family of side chains containing a single ether function, enabling the modulation of the oxygen atom position along the side chain. A meticulous investigation of this new polymer series by differential scanning calorimetry, fast scanning chip calorimetry and X-ray scattering shows that polymers bearing single-ether side chains can show high degree of crystallinity under proper conditions. Importantly, due to a gauche effect allowing the side chain to bend at the oxygen atom, the degree of crystallinity of polymers can be controlled by the position of the oxygen atom along the side chain. The further the oxygen atom is from the conjugated backbone, the more crystalline the polymer becomes. In addition, for all new polymers, high thermomechanical properties are demonstrated, leading to remarkable electrical conductivities and thermoelectric power factors in rub-aligned and sequentially doped thin films. This work confirms the potential of single-ether side chains to be used as polar solubilizing side chains for the design of a next generation of p- and n-type semiconducting polymers with increased affinity to polar dopants while maintaining high molecular order.

Supramolecular Polymerization of all-cis-Fluorinated Cyclohexanes: Influence of Side Chains

Custom-designed materials based on supramolecular polymers are of interest for applications in organic electronics and biomedicine. Recently, we have shown that derivatives of the highly polar compound all-cis hexafluorocyclohexane undergo seeded polymerization and can therefore be used to prepare soluble nanofibers with controlled length. In this work, we aimed to explore the scope of this process. We studied the supramolecular polymerization of six all-cis-fluorinated cyclohexane monomers, with five differing in the solubilizing side chains and one in the secondary supramolecular binding site. In studies on controlled supramolecular polymerization, we found that three of the monomers could be induced to polymerize by ultrasound irradiation and four by addition of seeds. For these latter examples, we were able to identify a solvent mixture that led to spontaneous polymerization and hysteresis in heating and cooling curves. These results show that the living supramolecular polymerization of fluorinated cyclohexanes is not limited to one particular monomer, but that side chains exhibiting a strong solvophobic effect that cannot be compensated within the binary solvent “window” represent a limitation to the approach. We also demonstrate that nanofibers based on stacks of fluorinated cyclohexanes can be dissociated by addition of chloride ions.

Improved Characterization of Polyoxazolidinones by Incorporating Solubilizing Side Chains

Improved Characterization of Polyoxazolidinones by Incorporating Solubilizing Side Chains

The anti-oxidative potential of ginger extract and its constituent on meat protein isolate under induced Fenton oxidation

Ginger extract has been reported to possess antioxidant properties. However, components isolated from ginger have been rarely reported to inhibit oxidation. Herein, the antioxidant properties of ginger and purified components derived from it (6-gingerol, zingerone, rutin, quercetin, and kaempferol) were confirmed by using HPLC and were further used to investigate its effect on lamb meat. Myofibrillar proteins isolated (MPI) from lamb meat were incubated with ginger and its constituents under induced Fenton oxidation (1.0 mmol/L FeCl3, 0.1 mmol/L Asc, and 20 mmol/L H2O2) for 1, 3,5, and 7 h. Incubating meat protein isolate in the absence of ginger extract or its components resulted in a substantial drop in sulfhydryl groups, an increase in protein carbonyl content, and a corresponding increase in TBARS content. However, ginger extract and its constituents demonstrated antioxidant properties, which might be attributed to their hydroxyl groups and suitable solubilizing side chains. Overall, ginger extract exhibited the highest antioxidant capabilities of all treated samples, suggesting that ginger extracts may be used as a natural antioxidant in meat and lipid/protein-containing processed products. Significance of the studyGinger extract is also frequently used as a herbal medicine due to its anti-inflammatory, anti-cancer, and antibacterial qualities. Nonvolatile pungent chemicals found in ginger, such as gingerol, shogaols, paradols, and zingerone, as well as kaempferol, rutin, and other phenolic compounds, have been confirmed in ginger extract and have been shown to have antioxidant action driven by free radical elimination. Despite these findings, ginger extract and its pure constituent components have seldom been shown to have the ability to slow protein and lipid oxidation in meat and meat-related products. The effect of ginger extracts on the oxidative stability of myofibriller protein isolate has never been investigated. Exploiting the phenolic content of ginger extract may result in a discovery that would have a huge influence on both the ginger and meat industries as well as other food processing sectors. The first aim of our study was to confirm the presence of six selected phenolic compounds (rutin, kaempferol, 6-gingerol, zingerone, naringenin, and quercetin) in ginger as reported by literature, and the second objective was to determine the efficacy of ginger extracts and its purified constituents on myofibrillar protein isolate treated under induced Fenton oxidation.

Wide Bandgap Conjugated Polymers Based on Difluorobenzoxadiazole for Efficient Non-Fullerene Organic Solar Cells.

Wide bandgap polymers with a donor-acceptor alternating structure play a key role in constructing high-efficiency organic solar cells (OSCs). However, only a handful of high-performance polymers are available owing to the limited choices of acceptor units. 5,6-Difluorobenzo[c][1,2,5]oxadiazole (ffBX) is a promising acceptor unit with high ionization potential, and can afford high charge carrier mobility and strong aggregation for the resulting polymers. Historically, ffBX is successfully used in constructing high-performance polymer donors for fullerene-based OSCs. However, this unit is far less been explored in non-fullerene OSCs. In this work, three ffBX-based wide bandgap polymers (Oc00, Oc25, and Oc50) with varied solubilizing side chain content for application in non-fullerene OSCs are reported. The polymers show matched energy levels and complementary optical absorption with the state-of-the-art non-fullerene acceptor Y6. Moreover, the polymer solubility, solid state packing, and bulk-heterojunction morphology are finely tuned via side chain engineering. Encouragingly, a decent efficiency of 14.25% is realized by the polymer Oc25 when blended with Y6 due to the efficient charge transport and favorable active layer morphology. These results suggest the promising prospect of ffBX in constructing high-performance polymer donors for non-fullerene OSCs.

(Invited) On-Surface Synthesis of Acene Polymers

The design and study of π-conjugated polymers has received great attention along the last decades. The relevant optical and electronic properties stemming from their delocalised π-electrons allow for a number of applications in the emerging field of organic electronics. However, the inherent limited solubility of planar π-conjugated systems hinders their development, forcing chemists to introduce ancillary solubilising side-chains. On the other hand, ultrahigh-vacuum on-surface synthesis has become a powerful discipline that enables designing with atomistic precision a new plethora of molecular compounds, polymers, and nanomaterials that otherwise are unachievable by conventional organic chemistry.Herein we present a novel on-surface chemical transformation that allows obtaining π-conjugated acene polymers from simple aromatic molecules carrying =CBr2 functionalities. The deposition of such precursors on an Au(111) surface gives rise to close-packed assemblies. Thermal annealing promotes the debromination of the species that thereafter homocouple and give rise to long anthracene wires linked by acetylene bridges, featuring a bandgap of 1.5 eV (see figure below).When larger acenes or periacenes are used (i.e. pentacene, bisanthene, peripentacene) the resulting polymers undergo dramatic structural and electronic changes. Non-contact-AFM evince that the benzoid subunits evolve from aromatic (anthracene) to quinoid (pentacene, bisanthene...), while the alkyne linkers turn into cumulenic. The STM images allow witnessing the HOMO-LUMO levels crossing from anthracene to pentacene. This swap destabilises the aromatic structure and enables a biradical-quinoid one, that permit almost vanishing bandgaps below 0.35 eV. These findings can also be rationalised by topological band gap theory: DFT, tight binding and GW calculations predict that polymers these quasi-metallic polymers exhibit a topologically non-trivial electronic structure. Our results herald novel pathways to engineer π-conjugated polymers on solid surfaces, addressing the relevant family of acenes and, thus, contributing to develop the field of on-surface chemistry and to steer the design of modern low bandgap polymers. Figure 1

Green Solvent‐Processed Hemi‐Isoindigo Polymers for Stable Temperature Sensors

AbstractA series of donor‐acceptor polymers, namely PTEB, PMEB, PEEB, and PPEB, are designed and synthesized for temperature sensing. The polymers are composed of hemi‐isoindigo as the acceptor unit, 3,3″‐bis(dodecyloxy)‐2,2″‐bithiophene as the donor unit, and thiophene as the spacer unit. Carbamate solubilizing side chains are used to increase the solubility of the polymers in a green solvent anisole. Furthermore, the carbamate side chains can be thermally removed to form solvent‐resistant polymers PTNB, PMNB, PENB, and PPNB, respectively. The removal of carbamate side chains also helps to elevate the highest occupied molecular orbital energy level of the polymer, thereby promoting p‐doping. PMNB, PENB, and PPNB films are doped with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) and used for fabricating temperature sensors on flexible polyethylene terephthalate substrates. The sensors exhibit high temperature coefficient of resistance (TCR) of up to −1.92 (±0.125)% °C−1 at 20–60 °C. This is the highest TCR achieved to date for resistor‐type temperature sensors using a non‐composite single conductive polymer. High sensitivity, green solvent processability, and mechanical flexibility make these temperature sensors promising for use in low‐cost, ubiquitous applications.

Solution-processable and functionalizable ultra-high molecular weight polymers via topochemical synthesis

Topochemical polymerization reactions hold the promise of producing ultra-high molecular weight crystalline polymers. However, the totality of topochemical polymerization reactions has failed to produce ultra-high molecular weight polymers that are both soluble and display variable functionality, which are restrained by the crystal-packing and reactivity requirements on their respective monomers in the solid state. Herein, we demonstrate the topochemical polymerization reaction of a family of para-azaquinodimethane compounds that undergo facile visible light and thermally initiated polymerization in the solid state, allowing for the first determination of a topochemical polymer crystal structure resolved via the cryoelectron microscopy technique of microcrystal electron diffraction. The topochemical polymerization reaction also displays excellent functional group tolerance, accommodating both solubilizing side chains and reactive groups that allow for post-polymerization functionalization. The thus-produced soluble ultra-high molecular weight polymers display superior capacitive energy storage properties. This study overcomes several synthetic and characterization challenges amongst topochemical polymerization reactions, representing a critical step toward their broader application.

Synthesis of Amorphous Conjugated Copolymers Based on Dithienosilole-Benzothiadiazole Dicarboxylic Imide with Tuned Optical Band Gaps and High Thermal Stability

Two alternating copolymers of dithienosilole (DTS) were designed and synthesized with small optical band gaps, flanked by thienyl units as electron-donor moieties and benzothiadiazole dicarboxylic imide (BTDI) as electron-acceptor moieties. The BTDI moieties were anchored to two different solubilizing side chains, namely 3,7-dimethyloctyl and n-octyl chains. An analysis of the effect of the electrochemical, optical, thermal, and structural characteristics of the resulting polymers along with their solubility and molecular weight is the subject of this paper. The Stille polymerization was used to synthesize PDTSDTBTDI-DMO and PDTSDTBTDI-8. The average molecular weight of PDTSDTBTDI-DMO and PDTSDTBTDI-8 is 14,600 and 5700 g mol−1, respectively. Both polymers have shown equivalent optical band gaps around 1.4 eV. The highest occupied molecular orbital (HOMO) levels of the polymers were comparable, around −5.2 eV. The lowest unoccupied molecular orbital (LUMO) values were −3.56 and −3.45 eV for PDTSDTBTDI-DMO and PDTSDTBTDI-8, respectively. At decomposition temperatures above 350 °C, both copolymers showed strong thermal stability. The studies of powder X-ray diffraction (XRD) have shown that they are amorphous in a solid-state.

Molecular Origin of Strain‐Induced Chain Alignment in PDPP‐Based Semiconducting Polymeric Thin Films

AbstractDonor–acceptor (D–A) type semiconducting polymers have shown great potential for the application of deformable and stretchable electronics in recent decades. However, due to their heterogeneous structure with rigid backbones and long solubilizing side chains, the fundamental understanding of their molecular picture upon mechanical deformation still lacks investigation. Here, the molecular orientation of diketopyrrolopyrrole (DPP)‐based D–A polymer thin films is probed under tensile deformation via both experimental measurements and molecular modeling. The detailed morphological analysis demonstrates highly aligned polymer crystallites upon deformation, while the degree of backbone alignment is limited within the crystalline domain. Besides, the aromatic ring on polymer backbones rotates parallel to the strain direction despite the relatively low overall chain anisotropy. The effect of side‐chain length on the DPP chain alignment is observed to be less noticeable. These observations are distinct from traditional linear‐chain semicrystalline polymers like polyethylene due to distinct characteristics of backbone/side‐chain combination and the crystallographic characteristics in DPP polymers. Furthermore, a stable and isotropic charge carrier mobility is obtained from fabricated organic field‐effect transistors. This study deconvolutes the alignment of different components within the thin‐film microstructure and highlights that crystallite rotation and chain slippage are the primary deformation mechanisms for semiconducting polymers.

Nonconjugated Terpolymer Acceptors with Two Different Fused-Ring Electron-Deficient Building Blocks for Efficient All-Polymer Solar Cells.

The ternary polymerization strategy of incorporating different donor and acceptor units forming terpolymers as photovoltaic materials has been proven advantageous in improving power conversion efficiencies (PCEs) of polymer solar cells (PSCs). Herein, a series of low band gap nonconjugated terpolymer acceptors based on two different fused-ring electron-deficient building blocks (IDIC16 and ITIC) with adjustable photoelectric properties were developed. As the third component, ITIC building blocks with a larger π-conjugation structure, shorter solubilizing side chains, and red-shifted absorption spectrum were incorporated into an IDIC16-based nonconjugated copolymer acceptor PF1-TS4, which built up the terpolymers with two conjugated building blocks linked by flexible thioalkyl chain-thiophene segments. With the increasing ITIC content, terpolymers show gradually broadened absorption spectra and slightly down-shifted lowest unoccupied molecular orbital levels. The active layer based on terpolymer PF1-TS4-60 with a 60% ITIC unit presents more balanced hole and electron mobilities, higher photoluminescence quenching efficiency, and improved morphology compared to those based on PF1-TS4. In all-polymer solar cells (all-PSCs), PF1-TS4-60, matched with a wide band gap polymer donor PM6, achieved a similar open-circuit voltage (Voc) of 0.99 V, a dramatically increased short-circuit current density (Jsc) of 15.30 mA cm–2, and fill factor (FF) of 61.4% compared to PF1-TS4 (Voc = 0.99 V, Jsc = 11.21 mA cm–2, and FF = 55.6%). As a result, the PF1-TS4-60-based all-PSCs achieved a PCE of 9.31%, which is ∼50% higher than the PF1-TS4-based ones (6.17%). The results demonstrate a promising approach to develop high-performance nonconjugated terpolymer acceptors for efficient all-PSCs by means of ternary polymerization using two different A–D–A-structured fused-ring electron-deficient building blocks.

Fabrication of Alternating Copolymers Based on Cyclopentadithiophene-Benzothiadiazole Dicarboxylic Imide with Reduced Optical Band Gap: Synthesis, Optical, Electrochemical, Thermal, and Structural Properties.

A series of alternating copolymers containing cyclopentadithiophene (CPDT) flanked by thienyl moieties as electron-donor units and benzothiadiazole dicarboxylic imide (BTDI) as electron-acceptor units were designed and synthesized for solar cell applications. Different solubilizing side chains, including 2-ethylhexyl chains and n-octyl chains were attached to CPDT units, whereas 3,7-dimethyloctyl chains and n-octyl chains were anchored to the BTDI moieties. The impact of these substituents on the solubilities, molecular weights, optical and electrochemical properties, and thermal and structural properties of the resulting polymers was investigated. PCPDTDTBTDI-EH, DMO was synthesized via Suzuki polymerization, whereas PCPDTDTBTDI-8, DMO, and PCPDTDTBTDI-EH, 8 were prepared through direct arylation polymerization. PCPDTDTBTDI-8, DMO has the highest number average molecular weight (Mn = 17,400 g mol−1) among all polymers prepared. The PCPDTDTBTDI-8, DMO and PCPDTDTBTDI-8, 8 which have n-octyl substituents on their CPDT units have comparable optical band gaps (Eg ~ 1.3 eV), which are around 0.1 eV lower than PCPDTDTBTDI-EH, DMO analogues that have 2-ethylhexyl substituents on their CPDT units. The polymers have their HOMO levels between −5.10 and −5.22 eV with PCPDTDTBTDI-EH, DMO having the deepest highest occupied molecular orbital (HOMO) energy level. The lowest unoccupied molecular orbital (LUMO) levels of the polymers are between −3.4 and −3.5 eV. All polymers exhibit good thermal stability with decomposition temperatures surpassing 350 °C. Powder X-ray diffraction (XRD) studies have shown that all polymers have the amorphous nature in solid state.

Solubilizing Side Chain Engineering: Efficient Strategy to Improve the Photovoltaic Performance of Novel Benzodithiophene‐Based (X‐DADAD)n Conjugated Polymers

Solubilizing Side Chain Engineering: Efficient Strategy to Improve the Photovoltaic Performance of Novel Benzodithiophene‐Based (X‐DADAD)<i>_n</i> Conjugated Polymers

Entropic Mixing Allows Monomeric-Like Absorption in Neat BODIPY Films.

Intermolecular interactions play a crucial role in materials chemistry because they govern thin film morphology. The photophysical properties of films of organic dyes are highly sensitive to the local environment, and a considerable effort has therefore been dedicated to engineering the morphology of organic thin films. Solubilizing side chains can successfully spatially separate chromophores, reducing detrimental intermolecular interactions. However, this strategy is also significantly decreasing achievable dye concentration. Here, five BODIPY derivatives containing small alkyl chains in the α‐position were synthesized and photophysically characterized. By blending two or more derivatives, the increase in entropy reduces aggregation and therefore produces films with extreme dye concentration and, at the same time almost solution like absorption properties. Such a film was placed inside an optical cavity and the achieved system was demonstrated to reach the strong exciton‐photon coupling regime by virtue of the achieved dye concentration and sharp absorption features of the film.

Functional 4H-Dithieno[3,2-b:2′,3′-d]pyrrole Derivatives in Base-Dopable Conjugated Polymers and Oligomers

A novel derivative of dithieno[3,2-b:2′,3′-d]pyrrole containing solubilizing side chains in the β-positions is reported and incorporated into a conjugated oligomer by a Pd-catalyzed direct arylatio...

Synthesis of a conjugated polymer for sensing ferric/ferrous cations based on dual responses

AbstractA conjugated polymer (PPETE‐RB) with poly[p‐(phenylene ethynylene)‐alt‐(thienylene‐ethynylene)] (PPETE) as the backbone with pendant rhodamine B (RB) groups in the close‐ring spirolactam form was synthesized. With long spacer between backbone and pedant groups as well as long solubilizing side chains, the polymer possesses good solubility in most organic solvents and relatively large molecular weight. The fluorescence of the conjugated polymer in THF exhibited selective dual responses upon adding Fe3+/Fe2+ but negligible response upon other cations. The emission around 481 nm (excited at 360 nm) decreased and that around 571 nm (excited at 520 nm) emerged and increased when increasing the concentration of iron ions. The responses to Fe3+ and Fe2+ are very similar. The limits of detection were found to fall in between 6 μM and 8 μM. The mechanism study showed that the quenching around 481 nm was due to the inner filter effect (IFE) between the Fe3+/Fe2+ and PPETE‐RB; while that enhancement around 571 nm could be attributed to the formation of fluorescent ring‐open structure from nonfluorescent spirolactam of pedant RB group upon Fe3+/Fe2+. Such dual and opposite responses provided more reliable information than single response for sensing applications.

Scaffold-Induced Diketopyrrolopyrrole Molecular Stacks in a Covalent Organic Framework.

In recent years, covalent organic frameworks (COFs) have attracted considerable attention due to their crystalline and porous nature, which positions them as intriguing candidates for diverse applications such as catalysis, sensing, or optoelectronics. The incorporation of dyes or semiconducting moieties into a rigid two-dimensional COF can offer emergent features such as enhanced light harvesting or charge transport. However, this approach can be challenging when dealing with dye molecules that exhibit a large aromatic backbone, since the steric demand of solubilizing side chains also needs to be integrated into the framework. Here, we report the successful synthesis of DPP2-HHTP-COF consisting of diketopyrrolopyrrole (DPP) diboronic acid and hexahydroxytriphenylene (HHTP) building blocks. The well-known boronate ester coupling motif guides the formation of a planar and rigid backbone and long-range molecular DPP stacks, resulting in a highly crystalline and porous material. DPP2-HHTP-COF exhibits excellent optical properties including strong absorption over the visible spectral range, broad emission into the NIR and a singlet lifetime of over 5 ns attributed to the formation of molecular stacks with J-type interactions between the DPP subcomponents in the COF. Electrical conductivity measurements of crystalline DPP2-HHTP-COF pellets revealed conductivity values of up to 10–6 S cm–1.

Influence of side-chain length and geometry on the thermal expansion behavior and polymorphism of naphthalene diimide-based thin films

In this work, we report on the thermally induced phase behavior and crystalline structures of a series of solution-processable naphthalene diimide (NDI)-based molecules with alkyl side chains of varying length and branching. Taking advantage of synchrotron-based in situ grazing-incidence wide-angle x-ray scattering, the most kinetically favorable thin film crystalline structures of each molecule at room temperature and at elevated temperatures were resolved. The extracted unit cell parameters of the kinetically favorable crystal structures as a function of temperature were used to quantify the anisotropic thermal expansion coefficients along the three principal crystallographic directions. In particular, it is found that long alkyl side chains can effectively suppress crystalline polymorphism and enhance thermal reversibility. The acquired knowledge regarding the thermally induced phase transitions of thin films based on NDI-based small molecules with varying solubilizing side chains serves as guidance for further molecular design and synthesis of high performance $n$-type small molecules.

Synthesis and Characterization of Cyclopentadithiophene and Thienothiophene-Based Polymers for Organic Thin-Film Transistors and Solar Cells

Novel donor-donor type alternating copolymers (8CDT-TT and 16CDT-TT) derived from cyclopentadithiophene (CDT) and thienothiophene (TT) moieties that differ from solubilizing side chains were successfully synthesized and characterized. After the synthesis of CDT-TT-based conjugated polymers with dioctyl and dihexadecyl side chains, their optical, thermal, structural and semiconducting properties were investigated. Organic thin-film transistors fabricated from 8CDT-TT and 16CDT-TT exhibit carrier mobilities as high as 3.92×10-4 and 1.05×10-3 cm2V-1s-1, respectively. Bulk heterojunction solar cells fabricated using a polymer:PCBM blend ratio of 1:3 exhibit power conversion efficiencies of 2.12 and 1.84% for 8CDT-TT and 16CDT-TT, respectively.

Perylene-Diimide Based Donor–Acceptor–Donor Type Small-Molecule Acceptors for Solution-Processable Organic Solar Cells

Development of nonfullerene acceptors plays an important role in the commercial availability of plastic solar cells. We report herein synthesis of bay-substituted donor–acceptor–donor (D–A–D)-type perylene diimide (PDI)-based small molecules (SM-1 to SM-4) by Suzuki coupling method and their use as acceptors in bulk heterojunction organic solar cells (BHJ-OSCs) with poly(3-hexylthiophene) (P3HT) polymer donor. We varied the number of electron-rich thiophene units and the solubilizing side chains and also evaluated the optical and electrochemical properties of the small molecules. The synthesized small molecules were confirmed by Fourier-transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and high-resolution mass spectroscopy (HR-MS). The small molecules showed extensive and strong absorption in the ultraviolet–visible (UV–Vis) region up to 750 nm, with bandgap ( $$E_{\rm{g}}^{\rm{opt}} $$ ) reduced below <2 eV. The energy levels of small molecules SM-1 to SM-4 were suitable for use as electron-accepting materials. The small molecules showed good thermal stability up to 300°C. BHJ-OSCs with SM-1 and P3HT polymer donor showed maximum power conversion efficiency (PCE) of 0.19% with V oc of 0.30 V, J sc of 1.72 mA cm−2, and fill factor (FF) of 37%. The PCE decreased with the number of thiophene units. The PCE of SM-2 was lower than that of SM-1. This difference in PCE can be explained by the higher aggregation tendency of the bithiophene compared with the thiophene unit. Introduction of the solubilizing group in the bay position increased the aggregation property, leading to much lower PCE than for the small molecules without solubilizing group.