A Modular and Catalytic Methodology To Access 2,5-Furan-Based Phenylene/Thiophene Oligomers through a One-Pot Decarboxylative Cross-Coupling from 5-Bromofurfural

A library of 2,5-furan-based phenylene/thiophene oligomers were synthesized starting from 5-bromofurfural, a derivative of biomass-derived furfural. Varied electronic groups are coupled onto the furan motif, followed by the installation of a phenylene or thiophene central linker through a one-pot Pd-catalyzed decarboxylative cross-coupling reaction. Resulting oligomers containing the furan-phenylene-furan core possess high photoluminescent quantum yields in solution (83-98%), which are crucial for optoelectronic devices. Absorbance and photoluminescence maxima are tuned by changing peripheral functional groups and the center linker coupled onto the furan backbone.

C3-Symmetric Indole-Based Truxenes: Design, Synthesis, and Photophysical Studies

In recent years, truxenes and related polyaromatic hydrocarbons (PAHs) have engrossed ample interest of the scientific community because of their ease of synthesis, functionalizations, and use as building blocks for the synthesis of fullerene fragments, liquid crystals, larger polyarenes, and C3-tripod materials. In the present work, we have disclosed an ingenious method for the construction of various indolo-truxene hybrid molecules in good yields (52-90%), by means of the acid-catalyzed cotrimerization, Friedel-Crafts acylation, and Fischer indole synthesis, and fully characterized them through the standard spectroscopic techniques. The photophysical properties of the thus-prepared compounds have also been investigated using steady-state absorption and fluorescence and time-resolved fluorescence spectroscopy techniques. Moreover, the density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been studied to correlate them with the measured photophysical properties of the synthesized indolo-truxene derivatives.

Recent advances in the synthesis of dibenzofurans

This review reports recent accesses to the dibenzofuran nucleus described in the literature since 2008. This article starts with synthesizing dibenzofurans by creating the C-O bond of the furan ring. In the following section, we evoke the formation of dibenzofurans by cyclizing diarylether derivatives. The last part of this update concerns the construction of dibenzofurans from benzofuran or phenol derivatives. Representative examples showing the scope of these processes illustrate new approaches and biological activities of dibenzofurans. Reaction mechanisms explaining certain dibenzofuran formation are described, as suggested by their authors.

Synthesis and Properties of Achiral and Chiral Dipyrenoheteroles and Related Compounds

Achiral and chiral isomers of dipyrenoheteroles were synthesized via alkyne benzannulation. The electronic properties of these compounds were examined using cyclic voltammetry and differential pulse voltammetry. The enantiomers of the chiral isomers were separated, and their optical properties were examined in circular dichroism and circularly polarized luminescence studies. The chiral isomers exhibited a large bathochromic shift, relative to the achiral isomer, in both absorbance and fluorescence, resulting from decreased symmetry, rather than a change in the size of the backbone.

High-performance five-ring-fused organic semiconductors for field-effect transistors

Organic molecular semiconductors have been paid great attention due to their advantages of low-temperature processability, low fabrication cost, good flexibility, and excellent electronic properties. As a typical example of five-ring-fused organic semiconductors, a single crystal of pentacene shows a high mobility of up to 40 cm² V^-1 s^-1, indicating its potential application in organic electronics. However, the photo- and optical instabilities of pentacene make it unsuitable for commercial applications. But, molecular engineering, for both the five-ring-fused building block and side chains, has been performed to improve the stability of materials as well as maintain high mobility. Here, several groups (thiophenes, pyrroles, furans, etc.) are introduced to design and replace one or more benzene rings of pentacene and construct novel five-ring-fused organic semiconductors. In this review article, ∼500 five-ring-fused organic prototype molecules and their derivatives are summarized to provide a general understanding of this catalogue material for application in organic field-effect transistors. The results indicate that many five-ring-fused organic semiconductors can achieve high mobilities of more than 1 cm² V^-1 s^-1, and a hole mobility of up to 18.9 cm² V^-1 s^-1 can be obtained, while an electron mobility of 27.8 cm² V^-1 s^-1 can be achieved in five-ring-fused organic semiconductors. The HOMO-LUMO levels, the synthesis process, the molecular packing, and the side-chain engineering of five-ring-fused organic semiconductors are analyzed. The current problems, conclusions, and perspectives are also provided.

Cu-Catalyzed Dehydrogenative C-O Cyclization for the Synthesis of Furan-Fused Thienoacenes

The first Cu-catalyzed dehydrogenative C-O cyclization for the synthesis of furan-fused thienoacenes is described. A variety of heteroacenes including a thieno[3,2-b]furan or a thieno[2,3-b]furan skeleton were synthesized by intramolecular C-H/O-H coupling. The use of a mixed solvent of N-methyl-2-pyrrolidone, ethylene glycol monomethyl ether, and toluene was essential for suppressing side reactions and efficiently promoting the reaction. Double C-O cyclization was also conducted to afford highly π-expanded furan-fused thienoacenes.

Catalyst-Free Synthesis of O-Heteroacenes by Ladderization of Fluorinated Oligophenylenes

A novel catalyst-free approach to benzoannulated oxygen-containing heterocycles from fluorinated oligophenylenes is reported. Unlike existing methods, the presented reaction does not require an oxygen-containing precursor and relies on an external oxygen source, potassium tert-butoxide, which serves as an O2- synthon. The radical nature of the reaction facilitates nucleophilic substitution even in the presence of strong electron-donating groups and enables de-tert-butylation required for the complete annulation. Also demonstrated is the applicability of the method to introduce five-, six-, and seven-membered rings containing oxygen, whereas multiple annulations also open up a short synthetic path to ladder-type O-heteroacenes and oligodibenzofurans.

Alkyl-Substituted Selenium-Bridged V-Shaped Organic Semiconductors Exhibiting High Hole Mobility and Unusual Aggregation Behavior

Toward the development of high-performance organic semiconductors (OSCs), carrier mobility is the most important requirement for next-generation OSC-based electronics. The strategy is that OSCs consisting of a highly extended π-electron core exhibit two-dimensional (2D) aggregated structures to offer effective charge transport. However, such OSCs, in general, show poor solubility in common organic solvents, resulting in limited solution processability. This is a critical trade-off between the development of OSCs with simultaneous high carrier mobility and suitable solubility. To address this issue, herein, five-membered ring-fused selenium-bridged V-shaped binaphthalene with decyl substituents (C₁₀-DNS-VW) is developed and synthesized by an efficient method. C₁₀-DNS-VW exhibits significantly high solubility for solution processes. Notably, C₁₀-DNS-VW forms a one-dimensional π-stacked packing motif (1D motif) and a 2D herringbone (HB) packing motif (2D motif), depending on the crystal growth condition. On the other hand, the fabrication of thin films by means of both solution process and vacuum deposition techniques forms only the 2D HB motif. External stress tests such as heating and exposure to solvent vapor indicated that 1D and 2D motifs could be synergistically induced by the total balance of intermolecular interactions. Finally, the single-crystalline films of C₁₀-DNS-VW by solution process exhibit carrier mobility up to 11 cm² V^-1 s^-1 with suitable transistor stability under ambient conditions for more than two months, indicating that C₁₀-DNS-VW is one of the most promising candidates for breaking the trade-off in the field of solution-processed technologies.

Facile Construction of Furanoacenes by a Three-Step Sequence Going through Disilyl-exo-cyclic Dienes

Facile synthesis of various benzonaphthofurans was achieved by intramolecular hydroarylation of 1,4-disilyl-2-aryloxy-1,3-enynes followed by cycloaddition with arynes or alkenes and finally desilylaromatization. The three-step transformation can be operated sequentially in one-pot, providing with a range of furanoacenes easily and highly effectively.

Robust, high-performance n-type organic semiconductors

Organic semiconductors (OSCs) are important active materials for the fabrication of next-generation organic-based electronics. However, the development of n-type OSCs lags behind that of p-type OSCs in terms of charge-carrier mobility and environmental stability. This is due to the absence of molecular designs that satisfy the requirements. The present study describes the design and synthesis of n-type OSCs based on challenging molecular features involving a π-electron core containing electronegative N atoms and substituents. The unique π-electron system simultaneously reinforces both electronic and structural interactions. The current n-type OSCs exhibit high electron mobilities with high reliability, atmospheric stability, and robustness against environmental and heat stresses and are superior to other existing n-type OSCs. This molecular design represents a rational strategy for the development of high-end organic-based electronics.

Interface Engineering in Organic Field-Effect Transistors: Principles, Applications, and Perspectives

Heterogeneous interfaces that are ubiquitous in optoelectronic devices play a key role in the device performance and have led to the prosperity of today's microelectronics. Interface engineering provides an effective and promising approach to enhancing the device performance of organic field-effect transistors (OFETs) and even developing new functions. In fact, researchers from different disciplines have devoted considerable attention to this concept, which has started to evolve from simple improvement of the device performance to sophisticated construction of novel functionalities, indicating great potential for further applications in broad areas ranging from integrated circuits and energy conversion to catalysis and chemical/biological sensors. In this review article, we provide a timely and comprehensive overview of current efficient approaches developed for building various delicate functional interfaces in OFETs, including interfaces within the semiconductor layers, semiconductor/electrode interfaces, semiconductor/dielectric interfaces, and semiconductor/environment interfaces. We also highlight the major contributions and new concepts of integrating molecular functionalities into electrical circuits, which have been neglected in most previous reviews. This review will provide a fundamental understanding of the interplay between the molecular structure, assembly, and emergent functions at the molecular level and consequently offer novel insights into designing a new generation of multifunctional integrated circuits and sensors toward practical applications.

New efficient synthesis of benzofuro[2,3-b]pyrroles utilizing a reactive nitrilium trapping approach by an acid-promoted cascade addition/cyclization sequence

The first p-TSA·H₂O-catalyzed highly efficient one-pot cascade reaction for the synthesis of novel fused tricyclic benzofuro[2,3-b]pyrroles has been discovered.

Homochiral Asymmetric-Shaped Electron-Transporting Materials for Efficient Non-Fullerene Perovskite Solar Cells

A design strategy is proposed for electron-transporting materials (ETMs) with homochiral asymmetric-shaped groups for highly efficient non-fullerene perovskite solar cells (PSCs). The electron transporting N,N'-bis[(R)-1-phenylethyl]naphthalene-1,4,5,8-tetracarboxylic diimide (NDI-PhE) consists of two asymmetric-shaped chiral (R)-1-phenylethyl (PhE) groups that act as solubilizing groups by reducing molecular symmetry and increasing the free volume. NDI-PhE exhibits excellent film-forming ability with high solubility in various organic solvents [about two times higher solubility than the widely used fullerene-based phenyl-C₆₁ -butyric acid methyl ester (PCBM) in o-dichlorobenzene]. NDI-PhE ETM-based inverted PSCs exhibit very high power conversion efficiencies (PCE) of up to 20.5 % with an average PCE of 18.74±0.95 %, which are higher than those of PCBM ETM-based PSCs. The high PCE of NDI-PhE ETM-based PSCs may be attributed to good film-forming abilities and to three-dimensional isotropic electron transporting capabilities. Therefore, introducing homochiral asymmetric-shaped groups onto charge-transporting materials is a good strategy for achieving high device performance.

Hydroarylation of 2-Aryloxybut-1-en-3-ynes via Pd/Acid-Catalyzed C-H Bond Activation: A Concise Synthesis of 2,3-Bismethylene-2,3-dihydrobenzofurans

An intramolecular exo-hydroarylation of 2-aryloxy-1,4-disilylbut-1-en-3-ynes via ortho-C-H bond activation under palladium(0) and acid catalysis was found to give 2,3-bis(silylmethylidene)-2,3-dihydrobenzofurans. The two silyl groups present probably promoted the reaction and played a key role in stabilizing the diene moiety in the product. The products readily led to functionalized condensed cycles by a Diels-Alder reaction.

Design and Functions of Semiconducting Fused Polycyclic Furans for Optoelectronic Applications

The fused polycyclic furan structure is a ubiquitous motif in naturally occurring organic compounds. However, they had been rarely seen in the literature of organic electronic research until very recently, probably because of the lack of stability of simple furans under conditions that the compounds experience in the active layer of the device. Nonetheless, from the viewpoint of molecular structure, furans look to have potential merits as organic semiconductors such as thiophenes, which are more popular in the organic electronic area. For example, the small atomic radius and large electronegativity of oxygen will increase intermolecular molecular orbital (MO) overlap and hence facilitate charge transporting ability in the solid state. In this Account, we describe the molecular design and optoelectronic applications of fused polycyclic furans, such as benzodifurans (BDFs), naphthodifurans (NDFs), and anthradifurans (ADFs). The molecular design that was exploited in this study crucially depends on the synthetic flexibility of a "modular" synthetic strategy that we purposely developed and reviewed in a separate report. Our synthetic strategy comprises two steps carried out in situ: cyclization of an o-alkynylphenol into a zincio benzofuran and its electrophilic Negishi-type trapping to obtain a range of multisubstituted fused furan compounds. These compounds are found to possess electronic structures resembling those of fused polyaromatic hydrocarbons, such as acenes or phenacenes, rather than oxygen-bridged phenylenevinylene, along with unique characteristics: a wide HOMO-LUMO gap originating from the weak aromaticity of the furan rings, an intense photoluminescent character, and mechanofluorochromism. Semiconducting properties of fused furans are also excellent among organic materials: some BDF derivatives show high hole mobility on the order of 10^-3 cm²/(V s) in the amorphous state using time-of-flight (TOF) technique. The p-type BDFs exhibit high performance as hole-transporting material in heterojunction organic light-emitting diodes (OLEDs), while carbazole-substituted BDFs (CZBDFs) are ambipolar with well-balanced high carrier mobility for both hole and electron and serve as host materials for full-color electroluminescence in both hetero- and homojunction architectures. More π-expanded NDFs showed good crystallinity and are effective active materials for organic field-effect transistors (OFETs) with a high hole mobility of up to 3.6 cm²/(V s) using a solution process. These studies have illustrated the high potential of fused polycyclic furans in organic electronics research, which thus far have attracted much less attention than their thiophene congeners.

Synthesis and characterization of semiaromatic polyamides comprising benzofurobenzofuran repeating units

Extended π-conjugated segments such as benzofurobenzofuran can be included into polyamides with high glass transition temperatures.

Syntheses of dibenzo[d,d']benzo[2,1-b:3,4-b']difuran derivatives and their application to organic field-effect transistors

Ladder-type π-conjugated compounds containing a benzo[2,1-b:3,4-b']difuran skeleton, such as dibenzo[d,d']benzo[2,1-b:3,4-b']difuran (syn-DBBDF) and dinaphtho[2,3-d:2',3'-d']benzo[2,1-b:3,4-b']difuran (syn-DNBDF) were synthesized. Their photophysical and electrochemical properties were revealed by UV-vis absorption and photoluminescence spectroscopy and cyclic voltammetry. Organic field-effect transistors (OFETs) were fabricated with these compounds as organic semiconductors, and their semiconducting properties were evaluated. OFETs with syn-DBBDF and syn-DNBDF showed typical p-type characteristics with hole mobilities of <1.5 × 10(-3) cm(2)·V(-1)·s(-1) and <1.0 × 10(-1) cm(2)·V(-1)·s(-1), respectively.

High performance oxygen-bridged N-shaped semiconductors with a stabilized crystal phase and blue luminescence

Here, we describe an oxygen-bridged N-shaped π-electron core, dinaphtho[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]difuran (DNBDF), as a new entity of organic semiconducting materials.

Effect of donor strength of extended alkyl auxiliary groups on optoelectronic and charge transport properties of novel naphtha[2,1-b:6,5-b']difuran derivatives: simple yet effective strategy

The present study spotlights the designing of new derivatives of 2,7-bis (4-octylphenyl) naphtho [2,1-b:6,5-b'] difuran (C8-DPNDF) by substituting the alkyl groups (methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups) at para position. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods are employed to optimize the molecular structures in ground and first excited states, respectively. Several electro-optical properties including hole/electron reorganization energies (λh/λe), electron affinities (EAs), ionization potentials (IPs), molecular electrostatic potentials (MEP), and frontier molecular orbitals (FMOs) have been evaluated. Furthermore their transfer integrals and intrinsic mobilities values have also been calculated. From this study, it is found that hole mobility of octyl containing derivative is raised to 4.69 cm(2) V(-1) s(-1). Moreover with attaching octyl group, hole transfer integral values have also been enhanced in newly designed derivatives. The balanced hole and electron reorganization energies, and improved transfer integrals lead to enhanced mobility in derivatives with octyl group, highlighting them as an efficient hole transfer material. Unlike the other electro-optical properties, the intrinsic hole mobility has increased because of transfer integral values of octyl containing derivative C8-DPNDF due to the dense and close crystal packing of C8-DPNDF. However, photostability of furan-based materials has not changed by increasing length of extended alkyl chain. Thus our present investigation highlights the importance of alkyl auxiliary groups that are often neglected/replaced with simple methyl group to save computation costs. Graphical Abstract The hole and electron reorganization energies of naphtho[2,1-b:6,5-b']difuran derivatives.

First synthesis of naphthalene annulated oxepins

Highly condensed oxepins have been prepared in good yields from their corresponding diols by etherification using p-toluenesulfonic acid.