Furan Substitution Research Articles

Reducing Interfacial Recombination in Inverted Perovskite Solar Cells With Selenophene-Substituted PCBM: Comparison With Thiophene and Furan Substitution.

Reducing the interfacial recombination and improving the charge transfer capability of charge transport layers are effective strategies to enhance the efficiency and stability of perovskite solar cells (PSCs). This study evaluates, for the first time, the effects of selenophene substitution in the chemical structure of phenyl-butyric acid methyl ester (PCBM) on the performance and stability of inverted PSCs. Selenophene substitution was compared to thiophene and furan substitutions, and the reference PCBM without chalcogenophene moiety. Additionally, this study investigates the differences between using the fullerene cages C70 and C60 in the PCBM chemical structure. The photovoltaic results demonstrate that, with an adequate control of the thickness of the electron transport layer (ETL), incorporating the selenophene moiety in the structures of fullerenes enhances the photovoltaic parameters of PSCs. This improvement results from the reduction in trap-assisted recombination, an increase in electron mobility, and the improved charge extraction processes. The use of C70, as opposed to C60, allows for the preparation of a series of ETLs with comparable thicknesses, although slightly lower efficiencies. This feature facilitates a systematic comparative analysis focused on variations in the electron properties of ETLs, thereby avoiding the inclusion of issues related to thickness and charge recombination processes.

Mechanism of the Aza-Piancatelli Reaction: Scope and Limitations of Furan Substitution in Donor-Acceptor Stenhouse Adduct Synthesis.

The aza-Piancatelli reaction has been widely used to synthesize donor–acceptor Stenhouse adducts (DASAs), a new class of molecular photoswitches with unique properties. However, the substitution pattern of furan cores has been limited to position 3, as 3,4-disubstituted furans remain unreactive. Herein, we explore the aza-Piancatelli reaction mechanism using density functional theory (DFT) calculations to understand the influence of the different substituents on the reactivity. We found that all the reaction pathways are kinetically accessible, but the driving force of the reaction is lost in disubstituted furans due to the loss of conjugation in the DASA products. Finally, a simple model is proposed to guide the design of synthetic routes using this reaction.

Impact of Furan Substitution on the Optoelectronic Properties of Biphenylyl/Thiophene Derivatives for Light-Emitting Transistors.

Biphenylyl/thiophene systems are known for their ambipolar behavior and good optical emissivity. However, often these systems alone are not enough to fabricate the commercial-grade light-emitting devices. In particular, our recent experimental and theoretical analyses on the three-ring-constituting thiophenes end capped with biphenylyl have shown good electrical properties but lack of good optical properties. From a materials science perspective, one way to improve the properties is to modify their structure and integrate it with additional moieties. In recent years, furan moieties have proven to be a potential substitution for thiophene to improve the organic semiconductive materials properties. In the present work, we systematically substituted different proportions of furan rings in the biphenylyl/thiophene core and studied their optoelectronic properties, aiming toward organic light-emitting transistor applications. We have found that the molecular planarity plays a vital role on the optoelectronic properties of the system. The lower electronegativity of the O atom offers better optical properties in the furan-substituted systems. Further, the furan substitution significantly affects the molecular planarity, which in turn affects the system mobility. As a result, we observed drastic changes in the optoelectronic properties of two furan-substituted systems. Interestingly, addition of furan has reduced the electron mobility by one fold compared to the pristine thiophene-based derivative. Such a variation is interpreted to be due to the low average electronic coupling in furan systems. Overall, systems with all furan and one ring of furan in the center end capped with thiophene have shown better optoelectronic properties. This molecular architecture favors more planarity in the system with good electrical properties and transition dipole moments, which would both play a vital role in the construction of an organic light-emitting transistor.

Sulfoxide‐Controlled Stereoselective Aza‐Piancatelli Reaction

AbstractThe development of a stereoselective aza‐Piancatelli reaction to access 4‐aminocyclopentenones is reported. This transformation relies on the use of chiral o‐sulfinyl anilines as chiral inductors to afford the targeted products in good to excellent yields. Remarkably, the high value‐added cyclopentenones could be obtained in drs up to >95:5, depending upon the furan substitution pattern.magnified image

A bioactive hyaluronic acid–based hydrogel cross-linked by Diels–Alder reaction for promoting neurite outgrowth of PC12 cells

In order to improve neurite outgrowth on the in situ formed hyaluronic acid–based hydrogel, furan and methacrylate groups were grafted on hyaluronic acid successively. Furthermore, a laminin-derived peptide CQAASIKVAV was covalently immobilized via the Michael addition. The furan- and peptide-modified hyaluronic acid was then cross-linked in situ by mixing with bismaleimide poly(ethylene glycol) at 37 °C to obtain a bioactive hyaluronic acid–based hydrogel. The hyaluronic acid derivatives were characterized by 1H NMR and Fourier transform infrared spectroscopy. The gelation, swelling, and mechanical property of the hydrogels were analyzed. The modulus of the hydrogel could be tuned by changing furan substitution degree, while the peptide concentration could be changed by the ratio of furan- and peptide-modified hyaluronic acid with hyaluronic acid–furan. In vitro culture of PC12 cells showed that the longest neurite outgrowth appeared on the hyaluronic acid–poly(ethylene glycol) hydrogel with the highest peptide content (the substitution degree of peptide in furan- and peptide-modified hyaluronic acid was 23 %) and a lower threshold modulus of 4.5 kPa. The furan and methacrylate-functionalized hyaluronic acid provides a versatile platform for diverse functionalization and can be used for modulation of other cell behaviors as well.

Protease degradable, hyaluronic acid based hydrogels provide a platform for breast cancer cell invasion

Event Abstract Back to Event Protease degradable, hyaluronic acid based hydrogels provide a platform for breast cancer cell invasion Stephanie A. Fisher1, 2, Priya N. Anandakumaran2, Shawn C. Owen1, 2* and Molly S. Shoichet1, 2, 3* 1 University of Toronto, Department of Chemical Engineering and Applied Chemistry, Canada 2 University of Toronto, Institute of Biomaterials and Biomedical Engineering, Canada 3 University of Toronto, Department of Chemistry, Canada Introduction: The role of the microenvironment in cancer invasion is not well understood. The microenvironment is a complex composition of extracellular matrix (ECM), signaling molecules, and stromal cells. Current in vitro models of the tumor microenvironment consist of cells suspended in ill- defined or synthetic matrices, which limit experimental reproducibility and fail to recapitulate the native microenvironment. To improve these in vitro matrices, hydrogels must be well defined and easily modified to incorporate features of the microenvironment[1]. In the current study, a defined hyaluronic acid (HA) hydrogel crossliked with ECM mimetic peptides was developed to elucidate the role of the tumor microenvironment on breast cancer progression Materials: HA was purchased from Lifecore Biomedical. Fmoc protected amino acids were purchased from AnaSpec. Collagenase IV was purchased from Sigma-Aldrich. GM6001 MMP inhibitor was purchased from EMD Millipore. Methods: HA hydrogels were formed via Diels Alder click chemistry by reacting furan functionalized HA with bis-maleimide peptide crosslinkers[2] containing either an matrix metalloproteinase (MMP) cleavable (MMPx) or non-cleavable (GAGx) sequence. Peptides were synthesized using Fmoc chemistry. Crosslink density was tuned by altering HA furan substitution. Invasive MDA-MB-231 breast cancer cells were seeded on HA/MMPx with 32, 40, and 55% furan substation (low, medium, and high crosslink density) and invasion was measured. To confirm MMP sensitivity, HA/MMPx and HA/GAGx were treated with collagenase and the change in mass was measured. MDA-MB-231 cells were seeded on HA/GAGx or HA/MMPx with or without GM6001 and invasion was measured. Results: Increased HA/MMPx crosslink density significantly decreased invasion (Figure 1). Figure 1: MDA-MB-231 invasion in low, medium and high crosslink density HA/MMPx. A) Normalized to medium crosslink density (n=3, day 4). B) Reconstruction of MDA-MB-231 invasion. HA/MMPx degraded in collagenase while HA/GAGx had little change in mass (not shown). MDA-MB-231 cells invaded further into HA/MMPx compared to HA/GAGx (Figure 2). GM6001 decreased MDA-MB-231 invasion into HA/MMPx (not shown). Figure 2: MDA-MB-231 invasion in HA/MMPx and HA/GAGx. A) Normalized to HA/MMPx (n=3, day 4). B) Reconstruction of MDA-MB-231 invasion. Discussion: To invade into ECM, cells must either squeeze through matrix pores or use proteases to locally degrade the ECM. Invasion into high crosslink density HA/MMPx was reduced relative to low crosslink density due to more crosslinks needing to be locally degraded. The degradation of HA/MMPx in collagenase confirmed that MMPx is sensitive to MMPs. MDA-MB-231 cells secrete MMPs and invaded twice as far into HA/MMPx compared to HA/GAGx. Invasion into HA/MMPx in the presence of GM6001 was reduced, but not eliminated due to the ability of MDA-MB-231 cells to switch between proteolytic-dependent and –independent invasion. Conclusion: An HA based hydrogel was developed for use as an in vitro breast cancer microenvironment. MDA-MB-231 invasion was enhanced by MMP cleavable crosslinks and low crosslink density. Future work will incorporate additional signaling molecules into HA/MMPx to elucidate the role of components of the microenvironment on breast cancer invasion. Natural Sciences and Engineering Research Council of Canada (NSERC)

Electrochemical synthesis of polymer based on 4-(2-furyl) benzenamine: Electrochemical properties, characterization and applications

Abstract 4-(2-Furyl) benzenamine (FBA), was successfully synthesized by a simple method including substitution of furan on p-nitroaniline followed by reduction of nitro group. Structure of the synthesized monomer was verified using IR, 1H NMR and GC–MS techniques. Corresponding poly(4-(2-furyl) benzenamine) (PFBA) was electrochemically synthesized in acidic aqueous and organic solutions by cyclic potential sweep method. Characterization of the resulting polymer was performed by cyclic voltammetry (CV), IR, UV–vis spectroscopy, and scanning electron microscopy (SEM). Effect of solvent on the electroactivity of the polymer modified electrode was investigated. The HOMO, LUMO levels and band gap energies of the doped and undoped form of the PFBA were calculated using UV–vis and CV data. The electrochromic properties and corrosion behavior of PFBA were studied. The electrochromic properties of the copolymer film, electrochemically coated on transparent conductive oxide, corroborate multi-color electrochromic behavior of the polymer whenever the applied potential was switched from reducing (yellow) to oxidizing status (green). The FBA polymer was found to exhibit enhanced corrosion protection effect on steel electrode in comparison with corresponding polyaniline (PANI) and polyfuran (PFu) homopolymers based on series of electrochemical measurements in 3.5 wt% NaCl electrolyte solutions.

Controlling Crystallite Orientation of Diketopyrrolopyrrole‐Based Small Molecules in Thin Films for Highly Reproducible Multilevel Memory Device: Role of Furan Substitution

For the organic memory device with vertically arranged electrodes, controlling the film‐packing to achieve highly oriented crystallite arrangement is critical but challenging for obtaining the satisfied performance. Here, the effect of backbone planarity on the crystallite orientation is studied. Two diketopyrrolopyrrole‐based small molecules (NI2PDPP and NI2FDPP) are synthesized with increasing planarity by furan substitution for phenyl rings. Upon thin‐film analysis by atomic force microscopy, X‐ray diffraction, and grazing‐incidence small‐angle X‐ray scattering, the orientations of these crystallites are demonstrated to be well controlled through tailoring molecular planarity. The highly planar NI2FDPP in film prefers out‐of‐plane crystallite orientation with respect to the substrate normal while the nonplanar NI2PDPP displays less ordered packing with a broad orientation distribution relative to the substrate. As a result, NI2FDPP‐based memory device exhibits superior multilevel performance. More importantly, the oriented crystallite arrangement favors uniformity in NI2FDPP thin film, thus, the device displays higher reproducibility of memory effects. This study provides an effective synthetic strategy for designing multilevel memory materials with favorable crystallite orientation.

Heteroaromatic variation in amorphous 1,6-methano[10]annulene-based charge-transporting organic semiconductors

π-Conjugated 1,6-methano[10]annulene-diketopyrrolopyrrole copolymers containing thiophene and/or furan rings were synthesized to determine the tolerance of heteroaromatic composition for amorphous semiconductors. Thiophene and furan were incorporated within the conjugated main chain adjacent to the annulene and diketopyrrolopyrrole comonomers to influence the optoelectronic properties of the highly disordered bulk materials. All polymers synthesized were shown to be amorphous by differential scanning calorimetry despite the relatively low alkyl chain substitution. The furan-containing copolymers showed higher energy bandgaps (HOMO–LUMO gaps) than the thiophene-based polymers, but increasing furan substitution resulted in higher hole mobilities: values ranged from 1.6 × 10−4 cm2 V−1 s−1 for all-thiophene polymers to 7.0 × 10−4 cm2 V−1 s−1 for all-furan polymers. AFM images reveal that the furan containing polymers form higher-quality films upon solution processing, a consequence of the higher solubility of the furan-based polymers. These results add to the growing literature precedent illustrating the value of furan as a component of both semicrystalline and now amorphous conjugated polymers.

Hyaluronic Acid Click Hydrogels Emulate the Extracellular Matrix

Hydrogels are used to create 3D microenvironments with properties that direct cell function. The current study demonstrates the versatility of hyaluronic acid (HA)-based hydrogels with independent control over hydrogel properties such as mechanics, architecture, and the spatial distribution of biological factors. Hydrogels were prepared by reacting furan-modified HA with bis-maleimide-poly(ethylene glycol) in a Diels-Alder click reaction. Biomolecules were photopatterned into the hydrogel by two-photon laser processing, resulting in spatially defined growth factor gradients. The Young's modulus was controlled by either changing the hydrogel concentration or the furan substitution on the HA backbone, thereby decoupling the hydrogel concentration from mechanical properties. Porosity was controlled by cryogelation, and the pore size distribution, by the thaw temperature. The addition of galactose further influenced the porosity, pore size, and Young's modulus of the cryogels. These HA-based hydrogels offer a tunable platform with a diversity of properties for directing cell function, with applications in tissue engineering and regenerative medicine.

Regiochemical Effects of Furan Substitution on the Electronic Properties and Solid-State Structure of Partial Fused-Ring Oligothiophenes

Oligomers containing the new fused-ring heterocyclic conjugated building block thieno[3,2-b]furan were synthesized, and the effects associated with furan ring substitution into fused-ring oligothiophenes on the electronic properties and solid-state structure were assessed. A series of four-ring oligomers which vary in the degree of furan ring substitution and the regiochemistry of placement were synthesized via Stille cross-coupling and oxidative homocoupling strategies. The electronic properties of these oligomers were studied by UV-vis absorption and fluorescence spectroscopies. Substitution of furan rings at the terminal positions yields oligomers with a narrower HOMO-LUMO gap relative to the all-thiophene analogue 2,2'-bithieno[3,2-b]thiophene, and incorporation of furan rings at the interior positions results in oligomers with an increase in rigidity and a higher fluorescence quantum yield. Packing motifs of the oligomers were determined using single crystal X-ray diffraction. In contrast to the herringbone crystal packing observed for nonfused oligothiophenes, oligofurans, thiophene-furan hybrid oligomers, and the all-thiophene analogue 2,2'-bithieno[3,2-b]thiophene, all three regioisomers derived from the dimerization of thieno[3,2-b]furan arrange in a π-stacked packing motif in the solid state.

Side-Chain Tunability of Furan-Containing Low-Band-Gap Polymers Provides Control of Structural Order in Efficient Solar Cells

The solution-processability of conjugated polymers in organic solvents has classically been achieved by modulating the size and branching of alkyl substituents appended to the backbone. However, these substituents impact structural order and charge transport properties in thin-film devices. As a result, a trade-off must be found between material solubility and insulating alkyl content. It was recently shown that the substitution of furan for thiophene in the backbone of the polymer PDPP2FT significantly improves polymer solubility, allowing for the use of shorter branched side chains while maintaining high device efficiency. In this report, we use PDPP2FT to demonstrate that linear alkyl side chains can be used to promote thin-film nanostructural order. In particular, linear side chains are shown to shorten π-π stacking distances between backbones and increase the correlation lengths of both π-π stacking and lamellar spacing, leading to a substantial increase in the efficiency of bulk heterojunction solar cells.

Substituent Effects on the Reversibility of Furan–Maleimide Cycloadditions

The effects of furan and maleimide substitution on the dynamic reversibility of their Diels-Alder reactivity have been investigated computationally and by (1)H NMR spectroscopy. Furan and furan derivatives bearing methoxy, methyl, or formyl groups at their 2- or 3-positions were investigated with maleimide and maleimide derivatives bearing N-methyl, N-allyl, and N-phenyl substituents. Computational predictions indicate that electronic and regiochemical effects of furan substitution significantly influence their Diels-Alder reactivity with maleimide, with reaction free energies of exo adduct formation ranging from ΔG = -9.4 to 0.9 kcal/mol and transition state barriers to exo adduct formation ranging from ΔG(‡) = 18.9 to 25.6 kcal/mol. Much less variation was observed for the reactivity of N-substituted maleimide derivatives and furan, with reaction and transition state free energies each falling within a range of 1.1 kcal/mol. Dynamic exchange experiments monitored by (1)H NMR spectroscopy support computational predictions. The results indicate the reactivity and reversibility of furan-maleimide cycloadditions can be tuned significantly through the addition of appropriate substituents and have implications in the use of furan and maleimide derivatives in the construction of thermally responsive organic materials.

Photophysical studies of mixed furan, pyrrole, and thiophene-containing oligomers with three and five rings

The photophysics of several oligomers containing mixed furan, pyrrole, and thiophene heterocyclic systems is reported. The mixed systems contain three rings and five rings of the heterocycles. Comprehensive spectroscopic and photophysical data were obtained and all of the rate constants kF, kIC, and kISC were evaluated. The lowest singlet excited state is of (1)B-like origin in any solvent. It is possible to have a reasonable understanding of the photophysics of the mixed ring systems compared to all the thiophene analogs if it is considered that some π–electron decoupling occurs at the site of the pyrrole or furan substitution, although this cannot be the total answer, as is discussed.

ChemInform Abstract: Synthetic Approaches Towards Phorbols via the Ultra‐High‐Pressure Mediated Intramolecular Diels—Alder Reaction of Furans (IMDAF): Effect of Furan Substitution.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthetic approaches towards phorbols via the ultra-high-pressure mediated intramolecular Diels–Alder reaction of furans (IMDAF): effect of furan substitution

Tricyclic structures having the functionality and stereochemistry inherent in phorbol and its analogues may be rapidly constructed by an ultra-high pressure IMDAF reaction. The nature of the 2-thioether substituent on the furan diene is critical for the success of the key cycloaddition reaction.

Electronic absorption and emission spectral data and fluorescence quantum yields of bridgedp-oligophenylenes, bi- to deciphenyls, and related furans and carbazoles

Absorption and fluorescence emission spectral data, as well as fluorescence quantum yields (Φf), were determined for 41p-oligophenylene compounds containing 2-6, 8, and 10 benzene rings. Of 29 compounds containing carbon-bridged rings (fluorenes), 28 were dialkylated on each bridge for improved solubility and photostability. Absorption maxima for oligophenylenes were observed at wavelengths as long as 366 nm, emission maxima to 437 nm, and molar extinction coefficients (ɛ) as large as 153,000 L/mol-cm; all three exceeded predicted maximum values for the corresponding unbridged oligophenylenes. The substitution of furan for benzene or carbazole for a fluorene (two examples each) bathochromically shifted absorption and emission maxima. Dialkylated carbon bridges bathochromically shifted absorption and emission maxima, and lowered Φf in biphenyl and in one terphenyl analogue, but appeared to cause no diminution of Φf in higher oligophenylenes. Bis(2-methoxyethyl) substitution on the bridges, incorporated to provide solubility in polar solvents, lowered Φf in all examples. Tertiary alkyl substituents on terminal rings bathochromically shifted the absorption and emission maxima and generally increased Φf. The "loose bolt" effect, which lowers Φf in mononuclear substituted benzenes, may operate in 9,9-dialkylfluorenes, but not in 2,7-di-t-butylfluorene or in higher oligophenylenes. Cyclic ether and methoxy substituents as auxofluors on terminal rings generally bathochromically shifted absorption and emission maxima and increased ɛ and Φf. Cyano substituents bathochromically shifted absorption and emission maxima, and increased ɛ, but lowered Φf slightly.