Series Of Oligomers Research Articles

Helical Ladder Oligomers Exhibit Amplified Circularly Polarized Emission

AbstractEstablishing design principles to engineer molecules that exhibit strong circularly polarized luminescence (CPL)‐brightness across the UV, visible and NIR spectral range remains an unsolved challenge. To achieve a large CPL‐brightness, the main difficulty is to optimize the luminescence dissymmetry factor glum. Herein is described the discovery that a multi‐helicene system based on a series of annulated [6]helicenes and perylenediimides, exhibits larger‐than‐linear amplification of glum with helicene length. Large enhanced fluorescent quantum yields and large extinction coefficients are also observed for this length series. Consequently, this series of oligomers exhibit exceptional CPL brightness (BCPL) above 1 × 103 mol−1 cm−1. Using computational methods based on density functional theory (DFT), the experimental trend shows that the increase of glum is due to the progressive alignment of magnetic (|m|) and electric transition (|µ|) dipole moment vectors, as the helical backbone grows longer.

Radical Anions of Porphyrin Molecular Wires: Delocalization and Dynamics.

The delocalization length of charge carriers in organic semiconductors influences their mobility and is an important factor in the design of functional materials. Here, we have studied the radical anions of a series of linear and cyclic butadiyne-linked porphyrin oligomers using CW-EPR, 1H Mims ENDOR and NIR/MIR spectroelectrochemistry together with DFT calculations and multiscale molecular modeling. Low-temperature hyperfine EPR spectroscopy and optical data show that polarons are delocalized nonuniformly over about four porphyrins with most of the spin density on just two units even in the cyclic structures, in which all porphyrin sites are identical. Room temperature CW-EPR spectra indicate a larger spatial distribution of spin density on the EPR time scale. We introduce a combined molecular dynamics simulations and DFT approach to demonstrate that dynamic migration of delocalized polarons can occur in porphyrin oligomers and that this fully accounts for the apparent spin density distribution at room temperature. This method is a powerful tool in both the study and development of molecular wires and molecular electronics.

Conjugation Length Dependence of Intramolecular Singlet Fission in a Series of Regioregular Oligo 3-Alkyl(thienylene-vinylene)s.

Activated intramolecular singlet fission is known to occur in the conjugated polymer polythienylene-vinylene (P3TV). Instead, efficient intersystem crossing has been observed in a short 3-alkyl(thienylene-vinylene) dimer. Here, we investigate a series of oligomers covering the conjugation length gap between the dimer and polymer. We confirm that the polymer and longer oligomers undergo activated intramolecular singlet fission, while the shorter oligomers with less than 3 units predominantly undergo efficient intersystem crossing. For the longer oligomers, the intermediate state of singlet fission is assigned to the 3Ag- covalent state of triplet pair character, as predicted by several computational studies. Our results point to potential pitfalls when assigning triplet production pathways solely with transient absorption spectroscopy.

Individually Tunable Energy Levels of Oligomers Based on N-B←N Units.

Opto-electronic properties and device performance of organic semiconductors are mainly determined by energy levels of their frontier molecular orbitals, e.g. lowest unoccupied molecular orbital (ELUMO) and highest occupied molecular orbital (EHOMO) in the ground state, first singlet state (ES1) and first triplet state (ET1) in the excited state. These energy levels are always intricately intertwined. Herein, we report a series of monodisperse oligomers based on double B←N bridged bipyridine (BNBP) units. With the increasing number of repeating units, the oligomers exhibit gradually downshifted ELUMO and nearly unchanged EHOMO due to the different distribution of the frontier molecular orbitals of the oligomers. Moreover, the oligomers exhibit gradually decreasing ES1 and nearly unchanged ET1 because of the different contributions of the charge transfer component in the excited state. This work provides new insight into energy level tuning of organic semiconductors, which is important for high-performance organic opto-electronic devices.

Individually Tunable Energy Levels of Oligomers Based on N−B←N Units

AbstractOpto‐electronic properties and device performance of organic semiconductors are mainly determined by energy levels of their frontier molecular orbitals, e.g. lowest unoccupied molecular orbital (ELUMO) and highest occupied molecular orbital (EHOMO) in the ground state, first singlet state (ES1) and first triplet state (ET1) in the excited state. These energy levels are always intricately intertwined. Herein, we report a series of monodisperse oligomers based on double B←N bridged bipyridine (BNBP) units. With the increasing number of repeating units, the oligomers exhibit gradually downshifted ELUMO and nearly unchanged EHOMO due to the different distribution of the frontier molecular orbitals of the oligomers. Moreover, the oligomers exhibit gradually decreasing ES1 and nearly unchanged ET1 because of the different contributions of the charge transfer component in the excited state. This work provides new insight into energy level tuning of organic semiconductors, which is important for high‐performance organic opto‐electronic devices.

Simultaneous strengthening and toughening of PLA with full recyclability enabled by resin-microsphere-modified L-lactide oligomers

Various strategies have been developed to improve the brittleness of poly (lactic acid) (PLA), most of which still suffer from the toughness-strength trade-off dilemma. Herein, we prepared phenol–formaldehyde-resin microspheres (PFM) with aliphatic hydroxyl groups to initiate L-lactide polymerization and synthesized a series of PFM-modified L-lactide oligomers (PFM-OLLA) bearing different arm lengths. PFM-OLLA were then physically blended with commercial PLA in different weight ratios to prepare synchronously strengthened and toughened PFM-OLLA/PLA composites. After blending with 4 % PFM2.5-OLLA (PFM content: 2.5 %), the mechanical properties of the PFM2.5-OLLA/PLA composites were best. PFM2.5-OLLA efficiently improved the crystallization behaviors of the PFM2.5-OLLA/PLA composites, thereby significantly enhancing their strength and toughness. The maximum tensile yield strength (40.2 MPa), elongation at break (85.7 %), and impact strength (20.8 kJ/m2) of PFM2.5-OLLA/PLA composites could respectively increase by 44.2 %, 465.7 %, and 100 %, compared to the values of neat PLA. The microscopic strengthening and toughening mechanisms were attributed to the rigidity of PFM, and the heterogeneous nucleating ability as well as larger free volume of PFM2.5-OLLA, whereas the visual toughening effects were attributed to multiple crazing and shear yielding phenomena. After simple alcoholysis and filtration, the polymer components were completely converted into methyl lactate. The recycled PFM, exhibiting excellent chemical stability, were reused to synthesize a new PFM-OLLA for strengthening and toughening PLA. This study provides a sustainable strategy for the development of high-performance PLA engineering materials showing great application potentials in the automotive, electronics and housing fields.

Non-linear disulphide-centred S-shaped oligomers containing inner and outer spacers with lateral Schiff base: synthesis and mesomorphic properties

ABSTRACT A new series of non-linear S-shaped oligomers [bis-6-(2-((4-methoxyphenyl-imino)methyl)-5-(4’-hexyloxy-4-biphenyloxycarbonyl)-phenoxy)alkyl]disulphide have been synthesised and characterised. The present oligomers consist of a central disulphide (S-S) linkage, Schiff base, outer alkyl spacer (n 1 = six carbons) and inner alkyl spacer (n 2 = six to eleven carbons). Upon cooling, all the oligomers show monotropic nematic phase. The odd–even effect was found at the transition temperature of Cr-I (TCr-I) and temperature range from isotropization to crystallisation (∆TI-Cr). However, the odd–even effect was not observed at the transition temperatures of I-N and N-Cr as the values decrease when n 2 increases. The representative oligomer with n 2 = 7 undergone photoisomerisation behaviour and completed the conversion from trans to cis within a duration of 13 mins and vice versa (up to 1200 min). Optimized molecular structures of oligomers with n 2 = 6 and 7 were obtained from TMoleX, and their length-to-breadth ratio can be reasonably employed to explain the odd–even effect in TCr-I, ∆TI-Cr and the reduction of its values in entropy change (∆SI-N/R).

Biodegradation of polybutylene succinate by an extracellular esterase from Pseudomonas mendocina

An extracellular esterase (HP) with polybutylene succinate (PBS)-degrading ability was identified from Pseudomonas mendocina SA-1503. The HP also had the ability to degrade poly(3-hydroxybutyrate-co-4-hydroxybutyrate) and polycaprolactone. This HP had optimal activity at pH 9.0 and 40 °C and remained stable at pH 8.0–9.0 and temperatures of 30–40 °C. Mn2+ promoted the enzyme activity. HP could hydrolyze all p-NP fatty acid ester substrates containing even numbers of carbon atoms from C2 to C18 and had the highest catalytic activity for the p-NP C6 substrate. After 60 h of HP-catalyzed degradation, PBS films experienced a weight loss of more than 60%. Butanedioic acid, 1,4-butanediol, and a series of oligomers were detected in the degradation products of PBS by HP. Further structural analysis of HP revealed that it could be classified as a microbial esterase of α/β hydrolase superfamily and contained a conserved catalytic triad structure (Ser-148, Asp-198, and His-228) with a relatively exposed active site.

Thiophene Oligomers with Low Cost and Easy Synthesis for Efficient Organic Solar Cells

Hole‐transporting layer (HTL) materials with sufficient hole collection ability, noncorrosive nature, and easy preparation are strongly desired for the field of organic solar cells (OSCs). The development of new materials and synthetic methods has been proved to be the essential approach to improve the HTL performances. Herein, a series of thiophene oligomers TO‐P1, TO‐P2, and TO‐P3 are designed and synthesized through coupling reaction by using the polyoxometalates as the oxidizing reagents. The thiophene oligomers can be readily synthesized under ambient condition with high yield. Among the as‐prepared thiophene oligomers, TO‐P2 exhibits neutral pH, sufficient work function, and high conductivity, endowing the HTL with excellent hole collection ability. Also, TO‐P2 possesses good chemical stability and satisfied solution processability, which is important for practical use. By using TO‐P2 as HTL, OSC shows a photovoltaic efficiency of 17.25%. Furthermore, TO‐P2 is a universal HTL that can be used to fabricate efficient OSCs with various active layers. More importantly, TO‐P2 shows good compatibility with large‐area processing technique. A 1 cm2 OSC is fabricated by using a blade‐coated TO‐P2 HTL, exhibiting a power conversion efficiency of 15.0%. The easy preparation and noncorrosive nature endow TO‐P2 with great potential application in OSCs.

Deciphering the complexity of the chemicals in food packaging materials using molecular networks

Chemicals from packaging materials might be transferred into food resulting in consumer exposure. Identifying these migrated chemicals is highly challenging and crucial to perform their safety assessment, usually starting by the understanding of the chemical composition of the packaging material itself. This study explores the use of the Molecular Networking (MN) approach to support identification of the extracted chemicals. Two formulations of bioplastics were analyzed using Liquid Chromatography hyphenated to High-Resolution Mass Spectrometry. Data processing and interpretation using a conventional manual method was performed as a point of comparison to understand the power of MN. Interestingly, only the MN approach facilitated the identification of unknown chemicals belonging to a novel oligomer series containing the azelaic acid monomer. The MN approach provided a faster visualization of chemical families in addition to the highlight of unrelated chemicals enabling to prioritize chemicals for further investigation improving the safety assessment of packaging materials.

Polyacrylate epoxide oligomers with robust photo‐crosslinked and thermomechanical properties enabled by controlling copolymerizing molecular weight distribution

AbstractPhoto‐triggering curing coatings have advantages of improving production efficiency, reducing pollution emissions, and contributing to green environmental protection. However, making the trade‐off between appropriate viscosity and UV‐curing properties in a high‐performing polymer system remains a formidable challenge. In this paper, firstly, a series of acrylate copolymer oligomers (named as PAAR) were synthesized using methyl methacrylate (MMA), butyl acrylate (BA), and glycidyl methacrylate (GMA), then methacrylic acid (MAA) was grafted utilizing the reaction between carboxyl group in MAA with epoxy group in oligomer to introduce double bonds. By adjusting the oligomer molecular weight to control the viscosity and changing the GMA ratio to obtain suitable double bonds content. As a result, the number molecular weight (Mn) of the thus‐obtained PAAR oligomers were less than 3000 Da, and the polymer dispersity indexes (PDI) were lower than 1.8. Photo‐polymerization kinetics revealed that the coating prepared using the oligomers could be fully cross‐linked by UV light triggering within 60 s, achieving a high transparency of 90% along with favorable thermal and mechanical properties. Furthermore, it was confirmed that the water resistance on the surface of the cured films and hydrophobicity were more influenced by the presence of hydroxyl groups.

Sequential Synthesis and Secondary Structure Analysis of Two Classes of Perylene Bisimide Oligomers.

An iterative step-by-step synthetic approach is employed to form perylene bisimide (PBI) oligomers of defined sizes by connecting the PBI units through their imide positions via a benzyl linker. The versatility of this approach was showcased by its successful implementation on two different PBI building blocks to achieve two separate series of oligomers (up to the pentamer) with modulated conformations: one with an open random coil oligomer and one with an H-type foldamer architecture.

Characterization of Excited-State Electronic Structure in Diblock π-Conjugated Oligomers with Adjustable Linker Electronic Coupling.

Diblock conjugated oligomers are π-conjugated molecules that contain two segments having distinct frontier orbital energies and HOMO-LUMO gap offsets. These oligomers are of fundamental interest to understand how the distinct π-conjugated segments interact and modify their excited state properties. The current paper reports a study of two series of diblock oligomers that contain oligothiophene (Tn) and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT) segments that are coupled by either ethynyl (-C≡C-) or trans-(-C≡C-)2Pt(II)(PBu3)2 acetylide linkers. In these structures, the Tn segment is electron rich (donor), and the TBT is electron poor (acceptor). The diblock oligomers are characterized by steady-state and time-resolved spectroscopy, including UV-visible absorption, fluorescence, fluorescence lifetimes, and ultrafast transient absorption spectroscopy. Studies are compared in several solvents of different polarity and with different excitation wavelengths. The results reveal that the (-C≡C-) linked oligomers feature a delocalized excited state that takes on a charge transfer (CT) character in more polar media. In the (-C≡C-)2Pt(II)(PBu3)2-linked oligomers, there is weak coupling between the Tn and TBT segments. Consequently, short wavelength excitation selectively excites the Tn segment, which then undergoes ultrafast energy transfer (~1 ps) to afford a TBT-localized excited state.

Transformation of metoprolol in UV/PDS process: Role and mechanisms of degradation and polymerization

Advanced oxidation processes for the treatment of organic pollutants in wastewater suffer from difficulties in mineralization, potential risks of dissolved residues, and high oxidant consumption. In this study, radical-initiated polymerization is dominated in an UV/peroxydisulfate (PDS) process to eliminate organic pollutant of pharmaceutical metoprolol (MTP). Compared with an ideal degradation-based UV/PDS process, the present process can save four fifths of PDS consumption at the same dissolved organic carbon removal of 47.3%. Simultaneously, organic carbon can be recovered from aqueous solution by separating solid polymers at a ratio of 50% of the initial chemical oxygen demand. The chemical structure of products was analyzed to infer the transformation pathways of MTP. Unlike previous studies on simple organic pollutants that the polymerization can occur independently, the polymerization of MTP is dependent on the partial degradation of MTP, and the main monomer in polymerization is a dominant degradation product (4-(2-methoxyethyl)-phenol, denoted as DP151). The separated solid polymers are formed by repeated oxidation and coupling of DP151 or its derivatives through a series of intermediate oligomers. This proof-of-concept study demonstrates the advantage of polymerization-dominated mechanism on dealing with large organic molecules with complex structures, as well as the potential of UV/PDS process for simultaneous organic pollution reduction and organic carbon recovery from aqueous solution.

Nucleophilic Aromatic Substitution (SNAr) as an Approach to Challenging Nitrogen-Bridged BODIPY Oligomers.

A series of nitrogen-bridged BODIPY oligomers were synthesized via nucleophilic aromatic substitution (SNAr) as a convenient approach. Further transformations achieved novel α,α-aryl BODIPY dimers as well as a BODIPY hexamer efficiently. These BODIPY oligomers showed good photophysical properties, such as apparent absorption and emission both in visible and near-infrared regions. Interestingly, the high air and photothermal stability, strong NIR absorption, and high photothermal conversion rates of hexamer B6 suggest potential applications in photothermal therapy.

Enhanced circularly polarized luminescence emission promoted by achiral dichroic oligomers of F8BT in cholesteric liquid crystal

In the exploration of circularly polarized luminescence (CPL) materials, doping cholesteric liquid crystals (CLCs) with achiral dyes is a common strategy. Conjugated polymers are favored as achiral dyes for their superior luminescent properties. In this study, a series of oligomers (M1-M3) and the conjugated polymer F8BT were synthesized to systematically assess the impact of the length of the conjugated backbone on CPL signals of CLCs doped with conjugated polymers. As the length rose from M1 to M3, CPL intensity concurrently increased (|glum| increased from 0.35 to 0.84), attributable to enhanced dichroism (order parameter, SF increased from 0.20 to 0.56). In contrast, F8BT polymer resulted in diminished CPL intensity (|glum| = 0.64) due to the reduced compatibility. Achieving a balance between dichroism and compatibility is crucial for optimizing CPL in conjugated polymer-doped CLCs. The guiding principle established here may have broad applicability in other CPL assemblies, offering a strategic avenue to engineer high-performance CPL materials with conjugated polymer.

Preparation of Peptoid Antifreeze Agents and Their Structure-Property Relationship.

The development of nontoxic and efficient antifreeze agents for organ cryopreservation is crucial. However, the research remains highly challenging. In this study, we designed and synthesized a series of peptoid oligomers using the solid-phase submonomer synthesis method by mimicking the amphiphilic structures of antifreeze proteins (AFPs). The obtained peptoid oligomers showed excellent antifreeze properties, reducing the ice crystal growth rate and inhibiting ice recrystallization. The effects of the hydrophobicity and sequence of the peptoid side chains were also studied to reveal the structure-property relationship. The prepared peptoid oligomers were detected as non-cytotoxic and considered to be useful in the biological field. We hope that the peptoid oligomers presented in this study can provide effective strategies for the design of biological cryoprotectants for organ preservation in the future.

Stereochemical Heterogeneity Analysis of Polylactides by Multidimensional Liquid Chromatography.

A new and robust high-performance liquid chromatography (HPLC) method that separates poly(lactic acid) (PLA) according to its stereochemical composition is presented. Using this method, poly(l-lactide) incorporating trace amounts of meso-lactide resulting from the racemization is separated from the pristine polymer. To prove this aspect in more detail, a representative poly(l-lactic acid) standard, assumed to be highly homogeneous, was separated using this method. The result showed that this was not the case as a fraction incorporating meso-lactide due to racemization occurring during the synthesis is separated. Employing two-dimensional liquid chromatography (2D-LC), the molar mass differences of the separated species were investigated, and fractions with similar molecular sizes were detected, confirming that the LC separation is solely based on stereochemical heterogeneity. The sample was further fractionated by preparative HPLC, followed by an in-depth analysis of the fractions using homonuclear decoupling in proton nuclear magnetic resonance (1H NMR). Convincing results that unveiled significant differences in the stereochemistry of the isolated PLA fractions were obtained. Subsequent analysis by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) also confirmed oligomer series with different end group structures, indicating that the applied HPLC method is very sensitive to minor variations in stereochemistry and end groups. This integrated approach offers detailed insight into the structural characteristics of PLA polymers, contributing to a better understanding of their composition and potential applications.

Poly(iminoborane)s with Aromatic Side Groups: Insights into the Microstructure from Monodisperse Model Oligomers

AbstractWhile certain inorganic main‐group polymers such as silicones (polysiloxanes) are ubiquitous in our everyday life, poly(iminoborane)s have been elusive for a long time. Incorporation of heterocyclic building blocks into their backbone has recently enabled access to the first derivatives of this inorganic‐polymer class, as this approach effectively prevents undesired side‐reactions to borazines. Information about the microstructure of these cyclolinear macromolecules, however, has been scarce. Herein, we present the synthesis of a series of monodisperse oligomers with up to 7 boron and 8 nitrogen atoms, representing the longest well‐defined molecular [>B=N<]x chain to date. We accomplished to characterize six of them structurally in the solid state by single‐crystal X‐ray diffraction, thus providing valuable insight into the microstructure of poly(iminoborane)s. In addition, we report on the synthesis of new poly(iminoborane) derivatives featuring aryl side groups, with an increased content of unsubstituted phenyl groups. The p‐(n‐butyl)phenyl‐substituted species 13 represents the highest‐molecular‐weight sample of this class of inorganic polymers to date.

Multi-targeting oligopyridiniums: Rational design for biofilm dispersion and bacterial persister eradication

The development of effective antibacterial drugs to combat bacterial infections, particularly the biofilm-related infections, remains a challenge. There are two important features of bacterial biofilms, which are well-known critical factors causing biofilms hard-to-treat in clinical, including the dense and impermeable extracellular polymeric substances (EPS) and the metabolically repressed dormant and persistent bacterial population embedded. These characteristics largely increase the difficulty for regular antibiotic treatment due to insufficient penetration into EPS. In addition, the dormant bacteria are insensitive to the growth-inhibiting mechanism of traditional antibiotics. Herein, we explore the potential of a series of new oligopyridinium-based oligomers bearing a multi-biomacromolecule targeting function as the potent bacterial biofilm eradication agent. These oligomers were rationally designed to be “charge-on-backbone” that can offer a special alternating amphiphilicity. This novel and unique feature endows high affinity to bacterial membrane lipids, DNAs as well as proteins. Such a broad multi-targeting nature of molecules not only enables its penetration into EPS, but also plays vital roles in the bactericidal mechanism of action that is highly effective against dormant and persistent bacteria. Our in vitro, ex vivo, and in vivo studies demonstrated that OPc3, one of the most effective derivatives, was able to offer excellent antibacterial potency against a variety of bacteria and effectively eliminate biofilms in zebrafish models and mouse wound biofilm infection models.