Flexible Alkyl Chains Research Articles

Effect of Molecular Structures of Donor Monomers of Polymers on Photovoltaic Properties.

This work investigates the photovoltaic properties of polymers that include different carbazole blocks as electron donors (D) but the same benzothiadiazole derivative as the electron acceptor (A). Five D–A copolymers are studied with ultrafast intramolecular exciton splitting and recombination dynamics to acquire the single-molecule structure and their photovoltaic performance relationship. The photovoltaic parameters such as energy level, optical band gap, and light-harvesting ability are highly dependent on the molecular structure of the donor monomer (including their appended flexible alkyl chain). Branched or linear alkyl groups on the same D block obviously vary the polymer steady-state absorption spectra and film morphology. For organic solar cells, this work allows tuning and control of the ultrafast dynamics, implying photovoltaic material design in the future.

Nonfullerene Small-Molecule Acceptors with Extended Optical Absorption Based on the “Spliced” Strategy for Organic Solar Cells

How to broaden the optical absorption of photovoltaic materials is one of the key issues in the design of high-performance organic solar cells. Nowadays, the sunlight of 400–550 nm wavelength range is not effectively utilized for most small-molecule nonfullerene acceptors. In this work, we proposed the “spliced” strategy of combining the acceptor–donor–acceptor type narrow band-gap small molecules and wide-band-gap perylene diimide (PDI) moieties via a flexible alkyl chain linkage, which could give the superposition effect of the absorption spectra, and three small-molecule acceptors (S1, S2, and S3) were designed based on various end-capping groups with different electron withdrawing abilities. Encouragingly, the as-constructed molecules can well make use of 400–550 nm sunlight with two independent absorption regions. Meanwhile, the aggregation of S1 with a highly planar end-capping group was dominated by both the PDI unit and main skeleton, while S2 and S3 exhibited PDI-controlled aggregation. When fabricated into organic solar cells, S1-based devices achieved a superior efficiency of 3.41% in comparison with those of the other two. The poor photovoltaic performance could be attributed to severe PDI aggregation, which can hinder the charge transfer through the main skeletons. This work could provide a new perspective to modulate optical absorption through the spliced strategy.

Anion conductive piperidinium based poly (ether sulfone): Synthesis, properties and cell performance

To fulfill most challenging demand for the anion exchange membranes (AEMs) combining long-term stability and high ion conductivity, a series of anion conducive poly (ether sulfone) (PES) functionalized with piperidinium-based quaternary ammonium directly in the backbone, incorporating different lengths of flexible alkyl chains was prepared via nucleophilic polycondensation and Menshutkin reaction. In this present work, a systematic study was conducted to investigate the effect of the extending side chains on various membrane properties. QAPIPPES-6 with an ion exchange capacity of 1.61 meq g−1 possess the laudable dimensional stability (only 10.4%, in-plane direction) and adequate hydroxide conductivity (84.4 mS cm−1) in the fully hydrated state at 80 °C. Atomic force microscopy (AFM) in tapping mode was performed to confirm the well-defined microphase separation occurred when the length of pendant spacers is ≥ 6. However, the extending side chains are founded to increase the risk of undergoing the Hofmann elimination but fail to enhance the steric hindrance effect to preserve the cation groups. Furthermore, a single H2/O2 fuel cell test for QAPIPPES-1 fabricated into a membrane electrode assembly was operated at 60 °C and exhibited a maximum power density of 216 mW cm−2 at a current density of 400 mA cm−2. These findings demonstrate that the piperidinium-functionalized AEMs with flexible pendant chains appear as the promising material in electrochemical energy devices.

Eco‐Compatible Solvent‐Processed Organic Photovoltaic Cells with Over 16% Efficiency

Recent advances in nonfullerene acceptors (NFAs) have enabled the rapid increase in power conversion efficiencies (PCEs) of organic photovoltaic (OPV) cells. However, this progress is achieved using highly toxic solvents, which are not suitable for the scalable large-area processing method, becoming one of the biggest factors hindering the mass production and commercial applications of OPVs. Therefore, it is of great importance to get good eco-compatible processability when designing efficient OPV materials. Here, to achieve high efficiency and good processability of the NFAs in eco-compatible solvents, the flexible alkyl chains of the highly efficient NFA BTP-4F-8 (also known as Y6) are modified and BTP-4F-12 is synthesized. Combining with the polymer donor PBDB-TF, BTP-4F-12 shows the best PCE of 16.4%. Importantly, when the polymer donor PBDB-TF is replaced by T1 with better solubility, various eco-compatible solvents can be applied to fabricate OPV cells. Finally, over 14% efficiency is obtained with tetrahydrofuran (THF) as the processing solvent for 1.07 cm2 OPV cells by the blade-coating method. These results indicate that the simple modification of the side chain can be used to tune the processability of active layer materials and thus make it more applicable for the mass production with environmentally benign solvents.

Effect of alkyl chain length on the wetting behavior of imidazolium based ionic liquids: A molecular dynamics study

Molecular dynamics (MD) simulations are performed to investigate the wetting behavior of imidazolium-based ionic liquids (ILs), which mainly consist of an imidazolium ring with a flexible alkyl chain attachment. The length of the alkyl chain can be easily manipulated to modulate the wetting properties of the ILs. To understand the role of the alkyl chain, we investigate the wetting behavior of two room-temperature ionic liquids (RTILs), 1,3-dimethylimidazolium tetra-fluoroborate [DMIM][BF4] and 1-propyl-3-methylimidazolium tetra-fluoroborate [PrMIM][BF4], on a graphite surface. Furthermore, the effects of the droplet size and temperature on the contact angle of the IL droplets are investigated. The wetting behaviors of both IL droplets are characterized using a density profile and orientation order parameter profile along the axis normal to the surface. The length of the alkyl chain is found to be crucial for modulating the wetting properties of the ILs. With an increase in the length of the alkyl chain, the contact angle of the droplet decreases, which is also in line with experimental results [1,2]. The wetting of the IL droplets strongly depends on the temperature and the relative fluid-fluid and fluid-substrate interactions. With the increase in temperature, the contact angle of the IL droplet decreases, resulting in the formation of a single layer film at a high temperature. In addition, the behavior of the contact angle of the IL droplet is analyzed through the surface tension as well as the graphite-IL interfacial tension. Furthermore, considering the anisotropic properties of the imidazolium-based ILs, we calculate the contact angles for cylindrical filaments (2D) on the graphite surface and compare the obtained values with the contact angle obtained from the spherical droplet (3D). The contact angle of the cylindrical droplet is found to have a negligible system size effect as compared to the case with the spherical droplet.

Synthesis and characterization of cardanol containing tetra-functional fluorene-based benzoxazine resin having two different oxazine ring structures

A new cardanol containing tetra-functional fluorene-based (t-BF-a-c) benzoxazine resins has been successfully synthesized via two-stage Mannich condensation reaction. The monomer contains simultaneous diamine- and bisphenol-type oxazine rings. The FTIR, 1H and 13C NMR tests were performed to confirm the structure of intermediates and t-BF-a-c benzoxazine. The rheological properties and curing behavior of the resin and thermal and thermomechanical properties of the corresponding polymer (poly (t-BF-a-c)) were evaluated by rheometer, differential scanning calorimeter, thermogravimetric analysis, and dynamic mechanical analyzer. The synthesized benzoxazine resin displays good processability and wide process window due to the incorporation of cardanol. Poly (t-BF-a-c) exhibits much higher glass transition temperature (373 °C) than corresponding bi-functional polybenzoxazines and better thermal stability than mono- and bi-functional cardanol-based polybenzoxazines. With the introduction of the flexible long alkyl chain of cardanol, the brittleness of fluorene-based polybenzoxazine is greatly modified without sacrificing thermal properties of the polymer.

Facile Fabrication of Flexible, Robust, and Superhydrophobic Hybrid Aerogel

Silica aerogels, which are constructed with silica nanoparticles and numerous nanoscale pores, have many outstanding attributes, but they are usually brittle and hydrophilic. For the construction of a robust aerogel, the novel polyhedral oligomeric silsesquioxane (POSS) was introduced to prepare a series of aerogels possessing particles covered with elastic cushion to improve the mechanical property. The multialkoxy POSS, which possessed stiff Si-O-Si nanocages and flexible alkyl chains, was synthesized via thiol-ene click chemistry. After a facile and efficient approach, a partially ordered structure of SiO2 nanoparticles and organic elastic cushion would form spontaneously within the aerogels. With the POSS as the only precursor, several outstanding attributes were achieved in a single aerogel such as high specific surface area (SSA), high compression strength, high compression modulus, and noticeable compression flexibility. Meanwhile, the aerogel was superhydrophobic of which the contact angle (CA) was higher than 153°. Moreover, the potential application of oil-water separation is also presented.

Bisthiophene/triazole based 4,6-diamino-1,3,5-triazine triblock polyphiles: Synthesis, self-assembly and metal binding properties

Two series of 4,6-diamino-1,3,5-triazine triblock polyphiles consisting of an extremely long bisthiophene/triazole based rigid cores, with flexible alkyl chains at one end and a polar 4,6-diamino-1,3,5-triazine at the other end were synthesized. Colhex/p6mm mesophases were displayed by all bisthiophene based 4,6-diamino-1,3,5-triazine derivatives, whereas both Colhex/p6mm and CubI/Pm3¯n mesophases could be formed by corresponding triazole based 4,6-diamino-1,3,5-triazine derivatives. Evidence for the formation of the extra H-bonding between central triazole units and terminal 4,6-diaminotriazine groups which was responsible for the formation of cubic phases in triazole based compounds was obtained based on FT-IR measurements. Additionally, these triblock polyphiles can form organogels with interesting morphologies in different solvents. The influence of the alkyl chain length and the polarities of the heterocycles (bisthiophene/triazole) on the self-assembly of these compounds was systematically studied. Finally, these triblock polyphiles showed dual selectivities towards Pb2+ and Fe3+ ions.

Tuning Emission Wavelength of Polymorphous Crystal via Controllable Alkyl Chain Stacking and Its Vapor‐ and Thermo‐Responsive Fluorescence

Tuning fluorescence colour of solid-state materials has become a topic of increasing interest for both fundamental mechanism study and practical applications such as sensors, optical recording and security printing. In this work, a fluorescent colour tuneable molecule BA-C16 is rationally designed and facilely synthesized by attaching flexible long alkyl chains to 2-hydroxybenzophenone azine (BA), which shows both aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics. Compared to BA, the simple introduction of long alkyl chains in BA-C16 leads to an emission wavelength redshift from 542 to 558 nm. This strategy of extending emission wavelength is rarely reported, and is ascribed to the enlarged through-space π-conjugation between interplanar molecules in the aggregate of BA-C16. Three crystals of BA-C16 are obtained with green, yellowish green and yellow emission. According to characterization by X-ray crystallography, X-ray powder diffraction and differential scanning calorimetry, alkyl chains play an important role in inducing different stacking modes of the three crystals, which further leads to polymorph-dependent fluorescence colour. BA-C16 exhibits tuneable solid-state fluorescence upon vapor fumigation, or annealing based on a transition between a "near-monomer" crystalline state and a "dimer" crystalline state. BA-C16 is further applied for rewritable fluorescence printing tuned by vapor- and thermal-treatment.

Self-recovering mechanochromic luminescent material with aggregation-induced emission: Implication for pressure sensor

In this work, we report the synthesis and emission behavior of a new compound, (E)-butyl 4-(((2-hydroxynaphthalen-1-yl)methylene)amino)benzoate (BOMAB). The molecular design includes twisted conformation and the incorporation of electron donor (D), acceptor (A) and a flexible alkyl chain. The compound shows both intramolecular charge transfer (ICT) character and aggregation-induced emission (AIE) nature. Furthermore, it exhibits mechanochromic luminescence: The solid powder gives strong emission but shows remarkable quenching with a bathochromic-shift after grinding, demonstrating high contrast. More importantly, the force-induced emission state can change back to the initial state without any treatment, showing self-recovery ability. Raising the temperature will accelerate the self-recovering process but partly quench the emission due to thermal motion of molecules. It takes 180 min for the ground sample to fully recover at 20 °C but only 18 min for that at 80 °C. As verified by crystallographic data, the phase transition is not a necessary condition for the mechanochromic nature of BOMAB. Such self-recovering mechanochromic luminescence can be attributed to the combined effect of conformational change and partly disordered packing. This makes BOMAB superior to other counterparts on account of its sensitivity and reusability. We developed a new type of pressure sensor using this material. In the quantitative mechanical test, the sensor shows a remarkable emission loss with the external pressure, and gives a linear relation with the pressure in lower range (0–73.2 N). The detection limit of the pressure sensor is 12.16 Mpa, showing high sensitivity.

Synthesis and properties of shape memory poly(aryl ether ketone)s

Thermally responsive shape memory polymers have received great attention in the fields of biomedicine and aerospace. A new type of thermoplastic shape memory polymer with excellent mechanical and thermal properties was synthesized. A new reactable monomer with flexible alkyl chain was first designed and synthesized, then introducing it into the main chain structure of poly(aryl ether ketone)s. The alternating chain structure of the soft and hard segments and the H-Bonding between the carboxyl groups on the side chains both serve as physical cross-linking points in the polymer network, thereby imparting shape memory properties to the polymers. Polymers with more flexible segments exhibit better shape memory performance in terms of high shape fixing ratio and high shape recovery ratio.

Optically Tunable Field Effect Transistors with Conjugated Polymer Entailing Azobenzene Groups in the Side Chains

AbstractSemiconducting conjugated polymers with photoswitching behavior are highly demanded for field‐effect transistors (FETs) with tunable electronic properties. Herein a new design strategy is established for photoresponsive conjugated polymers by incorporating photochromic units (azobenzene) into the flexible side alkyl chains. It is shown that azobenzene groups in the side chains of the DPP (diketopyrrolopyrrole)‐quaterthiophene polymer (PDAZO) can undergo trans/cis photoisomerization in fully reversible and fast manner. Optically tunable FETs with bistable states are successfully fabricated with thin films of PDAZO. The drain‐source currents are reduced by 80.1% after UV light irradiation for ≈28 s, which are easily restored after further visible light irradiation for ≈33 s. Such fast optically tunable FETs are not reported before. Moreover, such current photomodulation can be implemented for multiple light irradiation cycles with good photofatigue resistance. Additionally, thin film charge mobility of PDAZO can be reversibly modulated by alternating UV and visible light irradiations. On the basis of theoretical calculations and GIWAXS data, it is hypothesized that the dipole moment and configuration changes associated with the trans‐/cis‐photoisomerization of azobenzene groups in PDAZO can affect the respective intra‐chain and inter‐chain charge transporting, which is responsible for the optically tunable behavior for FETs with thin films of PDAZO.

Arylic versus Alkylic-Hydrophobic Linkers Determine the Supramolecular Structure and Optoelectronic Properties of Tripodal Amphiphilic Push-Pull Thiazoles.

The supramolecular structures and their constituents essentially determine the optoelectronic properties of thin films. The introduction of amphiphilicity to the constituents and interface assembly is one established technique to control supramolecular structures and resulting material properties. To yield amphiphilicity, rather hydrophobic chromophores are linked to hydrophilic head groups via flexible alkyl chains. In the present work, we investigate whether replacement of the alkyl linkers by a phenylene linker, that is, replacing an electrically isolating moiety with a potentially semiconducting one, increases the conductivity through the resulting layers. After investigating the influence of the linker on molecular properties of the 2-(4- N, N-dimethylaminophenyl)-4-hydroxy-5-nitrophenyl-1,3 thiazoles exemplarily used in this work, we produce supramolecular structures by means of the Langmuir-Blodgett (LB) technique. Atomic force microscopy (AFM) and UV-vis absorption spectroscopy reveal that thin films made from the more rigid thiazole bearing the arylic linker feature a more homogeneous and stable supramolecular structure as compared to those made from the thiazole dye containing the flexible alkylic linker. Finally, conductive AFM (cAFM) results disclose that the LB films made from the thiazole bearing the π-conjugated arylic linker are less conductive than their counterparts based on the alkylic linkers. In the latter layers, the alkylic linkers provide sufficient motional degrees of freedom to allow for supramolecular rearrangement upon electrical operation during cAFM measurements, hence yielding supramolecular structures featuring increased conductivity with successive cAFM measurements. This work highlights the importance of supramolecular structures for optoelectronic properties by presenting a case where supramolecular effects excel the property changes introduced by molecular modifications.

Bio-based reactive diluent derived from cardanol and its application in polyurethane acrylate (PUA) coatings with high performance

A UV-curable cardanol-based monomer (ECGE) was prepared using cardanol and epichlorohydrin, followed by epoxidation of the unsaturation in alkyl side chains of cardanol segments. After its chemical structure was confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance (1H NMR), ECGE was used as a reactive diluent to copolymerize with castor oil-based polyurethane acrylate (PUA) and a series of UV-curable coatings were prepared. Results showed that the viscosity and volume shrinkage of the UV-curable PUA system decreased significantly after the introduction of cardanol-based monomer while maintaining reasonably high bio-renewable contents; when containing 50% of ECGE, the biomass content reaches 66.2%, which is 1.41 times that of pure resin. In addition, the coating properties were evaluated to determine hardness, adhesion, flexibility, and water resistance. The properties of UV-curable thermoset were also studied using tensile testing, dynamic mechanical thermal analysis, and thermogravimetric analysis. The cardanol-based coatings showed excellent adhesion, flexibility, medium hardness, and enhanced char yield although tensile strength, tensile modulus and glass transition temperatures were somewhat diminished. All these performances can be attributed to the unique architectures of ECGE that combined the structural features of rigid benzene ring and long flexible alkyl chains. The UV-curing behavior was determined using real-time IR, and the results indicated that the conversion of unsaturated bond was increased with more concentration of ECGE.

Hierarchical Self-Assembly of Supramolecular Coordination Polymers Using Giant Metal-Organic Nanocapsules as Building Blocks.

Controlling the self-assembly of giant molecular building blocks into complex architectures with similar hierarchy to biological species remains a major challenge in supramolecular chemistry. Akin to protein structure, here we present the self-assembly of giant molecular nanocapsules into supramolecular coordination polymers with controlled hierarchy from primary to secondary and tertiary structures. First, we successfully prepared discrete nanocapsules (secondary structures) consisting of multicomponents, such as organic macrocycles and metal-based secondary building units (primary structures). Second, these nanocapsules can self-organize into various 2D and 3D supramolecular coordination polymers (tertiary structures) through coordination-driven assembly. The periphery 24 flexible alkyl chains and 24 metal ions available for potential coordination make these nanocapsules comparable to functionalized solid nanoparticles with non-specific binding sites at the surface and allow the nanocapsules to self-adjust their orientations and coordination modes to facilitate the self-assembly process. This study sheds light on the self-assembly of giant building units with complex molecular structures and opens up possibilities for the design of new hierarchical architectures with innovative properties and functions in many applications such as biomimics, biomedicine, and molecular devices.

Photophysics of "Floppy" Dyads as Potential Biomembrane Probes.

In the study a dyad (C6 probe), constructed of two dyes with highly different hydrophobicities, was investigated by steady-state and time-resolved spectroscopic techniques in chloroform, methanol, and in phospholipid vesicles, respectively. The dyad was built on two dyes: the lipophilic benzo[a]pyrene (BaP) and the hydrophilic sulforhodamine B (SRB). The dyes were linked via a short, but flexible alkyl chain (six C-atoms). Based on their spectroscopic properties, BaP and SRB showed a very efficient non-radiative resonance energy transfer in solution. Incorporation into a lipid bilayer limited the relative flexibility (degree of freedom) between donor and acceptor and was used for the investigation of fundamental photophysical aspects (especially of FRET) as well as to elucidate the potential of the dyad to probe the interface of vesicles (or cells). The location of the two dyes in vesicles and their respective accessibility for interactions with dye-specific antibodies was investigated. Based on the alteration of the anisotropy, on the rotational correlation time as well as on the diffusion coefficient the incorporation of the C6 probe into the vesicles was evaluated. Especially the limitation in the relative movements of the two dyes was considered and used to differentiate between potential parameters, that influence the energy transfer in the dyad. Transient absorption spectroscopy (TAS) and pulsed-interleave single molecule fluorescence experiments were performed to better understand the intramolecular interactions in the dyad. Finally, in a showcase for a biosensing application of the dyads, the binding of an SRB-specific antibody was investigated when the dyad was incorporated in vesicles. Graphical Abstract.

Enhancing Optical Gain Stability for a Deep-Blue Emitter Enabled by a Low-Loss Transparent Matrix

Efficient organic gain media with high optical gain and good photostability are highly desirable for organic semiconductor lasers. To shed light on the rational molecular design, in this work, a novel deep-blue organic emitter consisting of a carbazole core substituted by a diphenylamine-functionalized triazine unit and two arms of bifluorene with flexible alkyl chains (denoted as C2) was designed and synthesized. Various basic photophysics and amplified spontaneous emission (ASE) characterizations were conducted with a particular focus to unravel the impact of the molecular structure on the photostability. Relatively low ASE threshold of 7.0 μJ/cm2, high net gain coefficient of 79.9 cm–1 (under 40-fold threshold pump fluence), and low optical loss coefficient of 7.0 cm–1 were recorded for C2 in neat films. For comparison, C2 was also dispersed into polystyrene (PS), a low-loss transparent matrix, with various ratios to form PS-C2 blend films. Among them, a 50 wt % PS-C2 blend film exhibited a high gain c...

Dilational rheological properites of oxyethylated fatty acid methyl esters at kerosene-water interface

Dilational rheological properties of oxyethylated fatty acid methyl esters (FMEEs) with different structure (C12E5、C14E5、C16E5 and C18=E5) at kerosene-water interface have been investigated as a function of time, frequency and bulk concentration by the oscillating drop method. The experimental results show that the dilational modulus increases with an increase in the alkyl chain length for FMEEs with saturated alkyl chains (C12E5、C14E5 and C16E5) due to the enhanced hydrophobic interaction among the molecules at interface and the slowed diffusion-exchange process. At the same time, the phase angles are relative low, which embodies characteristics of nonionic surfactants containing EO chain. As for C18=E5, the introduction of a double bone causes a decrease in the dilational modulus and a slight increase in the phase angle, as evidenced by an increase in the value of the slope of curve, because the flexible unsaturated alkyl chain enhances the diffusion-exchange process. Moreover, the modulus vs interfacial pressure curve passes through a maximum during higher interfacial pressure range for C18=E5, which indicates that the interfacial rearrangement process affects the nature of adsorption layer.

Synthesis and mesomorphic properties of a series of dimers derived from thioether-terminated and cholesteryl

ABSTRACTThe synthesis and material properties of a series of new liquid crystalline compounds containing thioether and cholesteryl, these homologues with different alkyl chain lengths of 2–8, are reported. Thermal analysis shows that all oligomers have wide mesophase temperature ranges with high thermal stability. The oligomers were determined by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). The molecule not only successfully exhibits strong optical properties and rainbow colours, but also the cholesteric helical pitch decreased with increasing temperature. The mesogenic incidence and tendency were found to be strongly dependent on the numbers of carbon in the flexible alkyl chain. Even members formed widely mesophase compared to odd members that showed narrower ones. The reflection wavelengths of 6S8Ch are almost across the entire visible region when they are heated, which offer tremendous potential for various optical applications. Also, it not only shows a lower transition temperature but also has a narrower cholesteric phase compared to analogues with alkoxy groups. These results not only provide practical design principles for the synthesis of new sulphur-containing LC materials with optical applications, also make a significant contribution to use as thermally sensitive liquid crystal devices requiring fast response.

A Strategy of "Self-Isolated Enhanced Emission" to Achieve Highly Emissive Dual-State Emission for Organic Luminescent Materials.

Currently, the commonly developed organic luminescent materials (OLMs) usually exhibit poor luminescent performance in aggregated solid states compared with their well-dissolved solution states, making it a tough goal to achieve the highly emissive dual-state emission. To overcome this limitation, a "self-isolated enhanced emission" (SIEE) strategy through flexible alkyl chains to suppress the emission-quenched π-π stacking in solids is proposed here and, based on this guideline, remarkable emission efficiency with photoluminescence quantum yields up to 99.72 % in solution and 77.46 % in the solid state are achieved for the SIEE constructed DBBT-C8, which is then successfully used in solid-state displays and data encryption.