Influence Of Side Chains Research Articles

Triptycene-trisaroyleneimidazoles as non-fullerene acceptors – Influence of side-chains on solubility, device morphology and performance

The use of non-fullerene acceptors in bulk heterojunction organic solar cells offers the possibility of complementary absorption, adjustment of the electronic energy levels and improved stability and performance. Triptycene-trisaroyleneimidazoles (TTAI) represent a new class of three dimensional acceptor molecules with great promise for application in organic photovoltaic devices. We synthesized six TTAI derivatives in which the molecular symmetry and solubility are varied. We show that these changes do not affect the optoelectronic properties of the acceptor molecules, but have a profound effect on their performance in photovoltaic devices. Enhancing the solubility of the TTAI acceptors to match that of the donor polymer PTB7 resulted in an improved blend phase separation, evident from an enhanced open circuit voltage of 0.9 V and a doubling of the short circuit current as compared to derivatives with lower solubility. A maximum power conversion efficiency of 3.2% was obtained for TTAI with ethylhexyl side chains, demonstrating the potential of TTAI derivatives as electron acceptors.

Effects of alkyl or alkyloxy side chains in poly[4,6-bis(3′-dodecylthien-2′-yl)thieno-[3,4-c][1,2,5]thiadiazole-5′,5′-diyl-alt-2,5-di(alkyl or alkyloxy)-1,4-phenylene]: Synthesis, photophysics, and spectroelectrochemical and photovoltaic properties

New low-bandgap donor-acceptor functional copolymers, CDTDP and CDTDOP, composed of 4,6-bis-(3′-dodecylthien-2′-yl)thieno[3,4-c][1,2,5]thiadiazole (DT) and 2,5-didodecyl-1,4-phenylene (DP) or 2,5-didodecyloxy-1,4-phenylene (DOP) structural units, respectively, were synthesized by a rapid Suzuki coupling reaction of the corresponding comonomers in high-boiling-point solvents. The influence of alkyl and alkyloxy side-chains attached to the benzene ring on photophysical, thermochromic and electrochemical properties are reported. CDTDP exhibits absorption in the visible spectral region with long-wavelength maxima at 401–410 nm and 673–703 nm in solutions and at 461–467 nm and 827–841 nm in thin films. The absorption of CDTDOP in solution is significantly red-shifted, extending up to the near infrared region. CDTDOP shows more pronounced thermochromic changes. Both copolymers possess similar high values of electron affinity. CDTDOP with an alkyloxy side chain exhibits a lower ionization potential than that of CDTDP due to the stronger donor character of the substituted benzene unit, which narrows the bandgap value to 1.15 eV compared to that of 1.3 eV for CDTDP. Both copolymers exhibited interesting electrochromism. Spectroelectrochemical properties are shown for both oxidation and reduction. Optical switching is demonstrated and it is shown that response times depended on the side chain nature. Fast response times were detected for CDTDOP with alkyloxy side chains. Photovoltaic (PV) devices made of blends using the copolymers and a fullerene derivative, [6,6]-phenyl-C61-butyric acid methyl ester ([60]PCBM), exhibited different performances. PV devices with an active layer containing CDTDP exhibited higher power efficiency.

Effects of Side-Chain Length and Shape on Polytellurophene Molecular Order and Blend Morphology

We investigate the molecular order and thin film morphology of the conjugated polymer polytellurophene, in order to understand how the tellurium atom and the choice of side-chain influence the conjugated polymer’s backbone planarity and performance in organic transistors. We find that poly(3hexyltellurophene) (P3HTe) continues the trend from polythiophene (P3HT) to polyselenophene (P3HS): substitution with Tellurium leads to a more planar backbone, evident from the shifts of the C═C vibrational peak to lower wavenumbers (∼1389 cm–1) and a smaller optical band gap (∼1.4 eV). Resonant Raman spectroscopy revealed that molecular order was highly dependent on the structure of the P3ATe alkyl side-chain: a longer chains introduces kinetic hindrance, reducing the fraction of ordered phase obtained at room temperature, while a branched side-chain introduces steric hindrance, with intrinsic disorder present even when deposited at higher temperatures. When blended with the insulator HDPE, all three polymers exhibit...

Influence of glutamic acid residues and pH on the properties of transmembrane helices

Negatively charged side chains are important for the function of particular ion channels and certain other membrane proteins. To investigate the influence of single glutamic acid side chains on helices that span lipid-bilayer membranes, we have employed GWALP23 (acetyl-GGALW5LALALALALALALW19LAGA-amide) as a favorable host peptide framework. We substituted individual Leu residues with Glu residues (L12E or L14E or L16E) and incorporated specific 2H-labeled alanine residues within the core helical region or near the ends of the sequence. Solid-state 2H NMR spectra reveal little change for the core labels in GWALP23-E12, –E14 and –E16 over a pH range of 4 to 12.5, with the spectra being broader for samples in DOPC compared to DLPC bilayers. The spectra for samples with deuterium labels near the helix ends on alanines 3 and 21 show modest pH-dependent changes in the extent of unwinding of the helix terminals in DLPC and DOPC bilayers. The combined results indicate minor overall responses of these transmembrane helices to changes in pH, with the most buried residue E12 showing no pH dependence. While the Glu residues E14 and E16 may have high pKa values in the lipid bilayer environment, it is also possible that a paucity of helix response is masking the pKa values. Interestingly, when E16 is present, spectral changes at high pH report significant local unwinding of the core helix. Our results are consistent with the expectation that buried carboxyl groups aggressively hold their protons and/or waters of hydration.

Influence of polymer side chains on the photovoltaic performance of non-fullerene organic solar cells

The side chains of polymers had a great influence on their molecular packing, energy level, blend morphology and photovoltaic performance. The PCEs of 7.28% and 1.55% were obtained for alkoxy and alkylthio-substituted polymer based non-fullerene solar cells, respectively.

Influence of amino acid side chains on the formation of two component self-assembling nanofibrous hydrogels

Supramolecular co-assembly of amino acid derivatives capped with NDI and Py moieties undergoing supramolecular hydrogelation was developed.

Side Chain Influence on the Mechanical Properties and Water Uptake of Confined Comb-Shaped Cationic Polymer Thin Films

Water uptake is measured for ≈100 nm and ≈60 μm thick quaternized comb-shaped poly(2,6-dimethyl-1,4-phenylene oxide) (QA-PPO) polymers with 0, 6, 10, and 16 carbon alkyl side chains to probe the influence of thin film confinement. The thin film modulus is measured to probe the effect of side chain length on the thin film modulus and the ensuing water uptake. Increasing the alkyl side chain length results in increased modulus, decreased swelling strain, and decreased water uptake due to the lengthening of the n-alkyl side chains. Confinement effects on the comb-shaped QA-PPO water uptake are expressed through increased water uptake in the thin film compared to the bulk membrane. The thin films also exhibit a different water sorption mechanism consistent with two types of water compared to the bulk membranes that exhibit a single type of water sorption.

Turning electron transfer ‘on-off’ in peptides through side-bridge gating

Electrochemical studies are reported on a series of peptides to determine the influence of different side-chains and backbone rigidity on electron transfer, to progress the field of molecular electronics. Specifically, these peptides share either a common helical or β-strand conformation to cover a range of secondary structures, to fully investigate the influence of backbone rigidity. Two types of side-chain tethers, either triazole-containing or alkene-containing, are also compared to investigate these effects on electron transfer. Our results showed that the observed formal potentials (Eo) and electron transfer rate constants (ket) fall into two distinct groups. The peptides constrained via a side-chain tether exhibited high formal potentials and low electron transfer rate constants, whereas the linear peptides displayed low formal potentials and high electron transfer rate constants. This was found to occur irrespective of the backbone conformation, or the nature of the side-chain constraint. The vast formal potential shifts (as much as 482mV) and the large disparity in the electron transfer rate constants (as much as 97%) between the constrained and linear peptides, provides two distinct states (i.e. on/off) with a sizeable differential, which is ideal for the design of molecular switches.

Fine Control of Side Chains in Random π‐Conjugated Terpolymers for Organic Photovoltaics

Rational molecular design of π‐conjugated donor polymers is critical for developing high‐performance organic solar cells. Random copolymerization strategy is a facile method of synergistic fine‐tuning the light absorption, HOMO/LUMO energy levels, charge mobility, and solubility of donor (D)–acceptor (A) copolymers. Terpolymers PF8TBT which composed of three components, i.e., electron‐rich 9,9‐dioctylfluorene (F8), electron‐deficient benzothiadiazole (BT), and π‐bridge thiophene (T) moieties, are designed in such a way that only F8 unit possesses soluble side‐chains. This strategy enables a facile and precise control of the influences of side chains on solubility, energy levels, molecular packing, and fullerene (PCBM) intercalation of PF8TBT. The optimal terpolymer PF8TBT21 (F8:T:BT = 0.67:1:0.33 mol%) maximally balances the solubility and the PL quenching efficiency with PCBM while exhibiting notable π–π stacking. The resulting additive‐free inverted photovoltaic cell based on the PF8TBT21:PCBM blend shows a power conversion efficiency of 3.88% with an impressive open‐circuit voltage close to 1 V. image

Self-assembly of aromatic biscarbamate gelators: effect of spacer length on the gelation and rheology

Low molecular weight biscarbamate organogelators (LMWBGs) with simple molecular structures that could gel different types of organic solvents were synthesized. The LMWBGs were composed of a long hydrophobic tail of linear fatty alcohol (C8–C18) and an aromatic core and could gel organic solvents such as xylene, toluene, NMP, cyclohexanol and chlorobenzene at a concentration of 10–15 mg/mL. Gelation studies indicated that the alkyl chain length residues did not affect the gelation time which was generally around 10–15 min leading to opaque gels in all the solvents. The gels in p-xylene were studied by FTIR spectroscopy and differential scanning calorimetry (DSC) for the nature of the interactions between the gelators and the solvent. FTIR spectroscopic studies revealed that hydrogen bonding and van der Waals interactions were the driving forces for the formation of the gels, while solid-state UV–visible studies revealed the existence of π–π interaction in the xerogel. The gel melting temperatures were found to decrease and then increase with increasing alkyl chain length as observed in DSC. The microscopic observations (FE-SEM) suggested that the gelator molecules self-assembled leading to nano- and microfibres in the turbid gel, and as the alkyl chain length increased, the width of the fibres increased. Rheological studies evinced the viscoelastic nature of the soft gels viscoelasticity increased with increasing gelator concentration, while fluidity increased with increasing chain length. The X-ray diffraction analysis revealed that in the xerogels from p-xylene the molecules aggregated into a layered structure. This study on the influence of alkyl side chains shows that hydrogen bonding and van der Waals interactions play a significant role in the morphology of such self-assembled structures.

Self-assembly of crystalline nanotubes from monodisperse amphiphilic diblock copolypeptoid tiles

The folding and assembly of sequence-defined polymers into precisely ordered nanostructures promises a class of well-defined biomimetic architectures with specific function. Amphiphilic diblock copolymers are known to self-assemble in water to form a variety of nanostructured morphologies including spheres, disks, cylinders, and vesicles. In all of these cases, the predominant driving force for assembly is the formation of a hydrophobic core that excludes water, whereas the hydrophilic blocks are solvated and extend into the aqueous phase. However, such polymer systems typically have broad molar mass distributions and lack the purity and sequence-defined structure often associated with biologically derived polymers. Here, we demonstrate that purified, monodisperse amphiphilic diblock copolypeptoids, with chemically distinct domains that are congruent in size and shape, can behave like molecular tile units that spontaneously assemble into hollow, crystalline nanotubes in water. The nanotubes consist of stacked, porous crystalline rings, and are held together primarily by side-chain van der Waals interactions. The peptoid nanotubes form without a central hydrophobic core, chirality, a hydrogen bond network, and electrostatic or π-π interactions. These results demonstrate the remarkable structure-directing influence of n-alkane and ethyleneoxy side chains in polymer self-assembly. More broadly, this work suggests that flexible, low-molecular-weight sequence-defined polymers can serve as molecular tile units that can assemble into precision supramolecular architectures.

Influence of side chains on the self-alignment capability of electroluminescent polyfluorenes.

We report a significant role of side chains in the propagation of molecular orientation upon annealing the liquid crystal phase of polyfluorenes. Direct rubbing of poly(9,9-di(octyl)fluorene) led to the orientation of polymer segments in the top-most region of the film and enhanced propagation of this orientation along the rubbing direction was observed upon annealing. In contrast, the rubbing-induced molecular orientation of poly(9,9-di(ethylhexyl)fluorene) segments completely disappeared upon annealing in the nematic melt state. The higher order of the side chain structures in poly(9,9-di(octyl)fluorene) were found to allow the propagation of the three-dimensional molecular alignment. From integrated experimental and density functional theory studies, we propose that side chain interdigitation generates a unique alignment behavior of poly(9,9-di(octyl)fluorene).

D–A conjugated polymers based on thieno[3,2-b]indole (TI) and 2,1,3-benzodiathiazole (BT) derivatives: synthesis, characterization and side-chain influence on photovoltaic properties

Thieno[3,2-b]indole (TI) derivatives were developed via Cadogan annulation for constructing D–A copolymers. Their performance in photovoltaic cells were finely tuned by side-chain engineering.

Influence of the amino acid side chain on peptide bond hydrolysis catalyzed by a dimeric Zr(iv)-substituted Keggin type polyoxometalate

Structurally different dipeptides were hydrolyzed by [{α-PW11O39Zr-(μ-OH)(H2O)}2]8−. The rate constants were dependent on bulkiness and chemical nature of the dipeptide.

Low band gap diketopyrrolopyrrole-based small molecule bulk heterojunction solar cells: influence of terminal side chain on morphology and photovoltaic performance

Two low band gap small molecules based on DPP with different terminal side chains were synthesized. They show similar physical properties but different photovoltaic property.

The influence of alkyl side chains on molecular packing and solar cell performance of dithienopyrrole-based oligothiophenes

Dithienopyrrole-based small molecular materials were developed achieving PCEs up to 5.3% in bulk-heterojunction organic solar cells by the tuning of the alkyl substitution pattern and use of a solvent additive.

Solution-processable small molecule semiconductors based on pyrene-fused bisimidazole and influence of alkyl side-chain on the charge transport

Soluble small molecule semiconductors based on pyrene-fused biimidazole and side-chain effects on the semiconducting properties.

Gas-phase microsolvation of ubiquitin: investigation of crown ether complexation sites using ion mobility-mass spectrometry.

In this study the gas-phase structure of ubiquitin and its lysine-to-arginine mutants was investigated using ion mobility-mass spectrometry (IM-MS) and electron transfer dissociation-mass spectrometry (ETD-MS). Crown ether molecules were attached to positive charge sites of the proteins and the resulting non-covalent complexes were analysed. Collision induced dissociation (CID) experiments revealed relative energy differences between the wild type and the mutant crown-ether complexes. ETD-MS experiments were performed to identify the crown ether binding sites. Although not all of the binding sites could be revealed, the data confirm that the first crown ether is able to bind to the N-terminus. IM-MS experiments show a more compact structure for specific charge states of wild type ubiquitin when crown ethers are attached. However, data on ubiquitin mutants reveal that only specific lysine residues contribute to the effect of charge microsolvation. A compaction is only observed for one of the investigated mutants, in which the lysine has no proximate interaction partner. On the other hand when the lysine residues are involved in salt bridges, attachment of crown ethers has little effect on the structure.

Side Chain Influence on the Morphology and Photovoltaic Performance of 5-Fluoro-6-alkyloxybenzothiadiazole and Benzodithiophene Based Conjugated Polymers.

Three conjugated polymers (P1-P3) with benzodithiophene derivatives as the donor unit, 5-fluoro-6-(2-hexyldecyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5] thiadiazole as the acceptor unit and thiophene as the spacer were designed, synthesized, and used as donor materials for polymer solar cells (PSCs). The influence of side chains at the benzodithiophene unit on the performance of PSCs was investigated. PSCs with the blend of P2:PC71BM (1:2, by weight) as the active layer show the highest power conversion efficiency (PCE) of 6.88%, with an open circuit voltage (Voc) of 0.76 V, a short circuit current (Jsc) of 14.67 mA/cm(2), and a fill factor (FF) of 0.62. Our research revealed that the variation of side chains had a great influence on the morphology of blend films, which is crucial to the performance of PSCs. As indicated by transmission electron microscopy, the blends of P1:PC71BM (1:2) and P2:PC71BM (1:2) formed nanofibers, whereas the blends of P3:PC71BM (1:2) formed spherical domains. Therefore, we concluded that formation of a more interpenetrating phase-separated donor-acceptor network with a larger interfacial area and proper percolation in the blends from P1 to P2 is mainly responsible for better performance in the corresponding devices.

One short cysteine-rich sequence pattern - two different disulfide-bonded structures - a molecular dynamics simulation study.

The nematocyst walls of Hydra are formed by proteins containing small cysteine-rich domains (CRDs) of ~25 amino acids. The first CRD of nematocyst outer all antigen (NW1) and the C-terminal CRD of minicollagen-1 (Mcol1C) contain six cysteines at identical sequence positions, however adopt different disulfide bonded structures. NW1 shows the disulfide connectivities C2-C14/C6-C19/C10-C18 and Mcol1C C2-C18/C6-C14/C10-C19. To analyze if both show structural preferences in the open, non-disulfide bonded form, which explain the formation of either disulfide connectivity pattern, molecular dynamics (MD) simulations at different temperatures were performed. NW1 maintained in the 100-ns MD simulations at 283 K a rather compact fold that is stabilized by specific hydrogen bonds. The Mcol1C structure fluctuated overall more, however stayed most of the time also rather compact. The analysis of the backbone Φ/ψ angles indicated different turn propensities for NW1 and Mcol1C, which mostly can be explained based on published data about the influence of different amino acid side chains on the local backbone conformation. Whereas a folded precursor mechanism may be considered for NW1, Mcol1C may fold according to the quasi-stochastic folding model involving disulfide bond reshuffling and conformational changes, locking the native disulfide conformations. The study further demonstrates the power of MD simulations to detect local structural preferences in rather dynamic systems such as the open, non-disulfide bonded forms of NW1 and Mcol1C, which complement published information from NMR backbone residual dipolar couplings. Because the backbone structural preferences encoded by the amino acid sequence embedding the cysteines influence which disulfide connectivities are formed, the data are generally interesting for a better understanding of oxidative folding and the design of disulfide stabilized therapeutics.