Design and Functions of Semiconducting Fused Polycyclic Furans for Optoelectronic Applications

Expanded benzofuran-decorated twistacene derivatives: synthesis, characterization and single-component white electroluminescence

Two novel phenanthro[9,10-b]benzofuran and pyreno[4,5-b]benzofuran modified twistacene derivatives, 9 and 10, have been successfully synthesized via Suzuki coupling and then characterized. The photophysical properties were examined and DFT calculations were carried out in a comparative manner, and both molecules emitted strong blue light in organic solvents and in the solid state. Impressively, fabricated electroluminescent devices based on these single emitters radiate pure white light.

Fluoride-Ion-Catalyzed Synthesis of Ladder-type Conjugated Benzobisbenzofurans via Intramolecular Nucleophilic Aromatic Substitution Reaction under Metal-free and Mild Conditions

The fluoride-ion-catalyzed synthesis of benzobisbenzofuran derivatives is described. Fluorine-containing aryl silyl ethers were reacted with 5 mol % of Bu₄NF to give desired compounds in high yield under mild conditions. Syn-selective cyclization reaction was discovered for a particular compound as a kinetic product. Computational analysis revealed that the fluorine substituents in the anti-type benzobisbenzofurans affect the order of the molecular orbitals.

ZnCl2 -Catalyzed [4+1] Annulation of Alkylthio-Substituted Enaminones and Enaminothiones with Sulfur Ylides

Concise construction of furan and thiophene units has played an important role in the synthesis of potentially bioactive compounds and functional materials. Herein, an efficient Lewis acid ZnCl₂ catalyzed [4+1] annulation of alkylthio-substituted enaminones is reported, that is, α-oxo ketene N,S-acetals with sulfur ylides to afford 2-acyl-3-aminofuran derivatives. In a similar fashion, [4+1] annulation of the corresponding enaminothiones, that is, α-thioxo ketene N,S-acetals, with sulfur ylides efficiently proceeded to give multisubstituted 3-aminothiophenes. This method features wide substrate scopes as well as broad functional group tolerance, offering a concise route to highly functionalized furans and thiophenes.

Access to tetracyclic aromatics with bridgehead metals via metalla-click reactions

The never-ending pursuits for exploring aromatic molecular architectures result in the large libraries of aromatics with fascinating structures, which have greatly broadened the scope of aromaticity. Despite extensive efforts that have been paid to develop aromatic frameworks, the construction of polycyclic aromatics that share a bridgehead atom with more than three rings has never been accomplished. Here, an unprecedented family of aromatics, in which a metal center shared by 4 five-membered aromatic rings, has been achieved by using the metalla-click reactions with excellent yields and remarkable regioselectivity. The distinctive tetracyclic aromatics exhibit a broad absorption in the ultraviolet-visible near-infrared region and excellent thermal stability in air, enabling their potential applications in photoelectric materials and biomedicine. This study now makes it possible to incorporate four aromatic rings with one common sharing metal center by a straightforward strategy that would promote further development of previously unknown polycyclic complex motifs in aromatic chemistry.

Efficient access to fluorescent benzofuro[3,2-b]carbazoles via TFA-promoted cascade annulations of sulfur ylides, 2-hydroxy-β-nitrostyrenes and indoles

An efficient, TFA-promoted cascade annulation of sulfur ylides, 2-hydroxy-β-nitrostyrenes and indoles was established.

New fused conjugated molecules with fused thiophene and pyran units for organic electronic materials

Rigid and planar conjugated molecules have substantial significance due to their potential applications in organic electronics. Herein we report two highly fused ladder type conjugated molecules, TTCTTC and TTTCTTTC, with up to 10 fused rings in which the fused-thiophene rings are fused to the chromeno[6,5,4-def]chromene unit. Both molecules show high HOMO levels and accordingly they can be oxidized into their radical cations with absorptions extending to 1300 nm in the presence of trifluoroacetic acid. Thin films of TTCTTC and TTTCTTTC exhibit p-type semiconductor properties with hole mobilities up to 0.39 cm² V⁻¹ s⁻¹. Moreover, TTCTTC shows a high fluorescence quantum yield of up to 16.5% in the solid state.

Fused conjugated molecules TTCTTC and TTTCTTTC with up to ten heterocycles were constructed by fusing fused-thiophene to the chromeno[6,5,4-def]chromene unit.

Heteroatom-bridged heterofluorenes: a theoretical study on molecular structures and optoelectronic properties

A double heteroatom introduction strategy was proposed and theoretically investigated to construct highly rigid π-conjugated small molecules and polymers for optoelectronic applications.

Ruthenium(ii)-catalyzed chemoselective deacylative annulation of 1,3-diones with sulfoxonium ylides via C-C bond activation

The first successful example of deacylative annulation of 1,3-diones with sulfoxonium ylides was achieved through Ru(ii)-catalyzed C-C bond activation. The excellent chemoselectivity and broad substrate scope render this method a practical and versatile approach for the preparation of (hetero)aryl and alkenyl substituted furans, which are valuable units in many biologically active compounds and functional materials. A preliminary mechanistic study reveals that this process involves a deacylative α-ruthenation to generate key alkyl Ru(ii) intermediates with the release of a benzoic acid fragment.

Tandem Ullmann-Goldberg Cross-Coupling/Cyclopalladation-Reductive Elimination Reactions and Related Sequences Leading to Polyfunctionalized Benzofurans, Indoles, and Phthalanes

On exposure to a combination of Cu[I]- and Pd[0]-based catalysts, compounds such as 1 and 7 engage in tandem Ullmann-Goldberg cross-coupling and cyclopalladation-reductive elimination reactions to give benzofurans such as 8. Related reactions involving hetero-Michael additions of o-halogenated phenols or anilines to propiolates and the Pd[0]-catalyzed cyclization of the resulting conjugates provide, in a one-pot process, alternately functionalized benzofurans, indoles, or phthalanes.

Direct synthesis of highly functionalized furans from donor-acceptor cyclopropanes via DBU-mediated ring expansion reactions

A DBU-mediated, unprecedented formal ring expansion reaction of 2-acyl-3-arylcyclopropane-1,1-dicarbonitriles for the synthesis of multisubstituted furan derivatives is reported. This transformation represents the regioselective ring-opening reaction of cyclopropane-1,1-dicarbonitriles and annulation using an intramolecular addition cascade reaction protocol for the synthesis of fully substituted furans includes use of readily available starting materials, mild reaction conditions, and it is transition-metal catalyst free, has good functional tolerance, and broad substrate scope.

Phosphindole fused pyrrolo[3,2-b]pyrroles: a new single-molecule junction for charge transport

A new family of phosphindole fused ladder-type heteroacenes with a pyrrolo[3,2-b]pyrrole core were synthesized and characterized, which show good luminescence efficiency, high thermostability and tunable conductance.

Intramolecular Electrophilic Cyclization Approach to 6-Substituted Naphtho[2,1- b]benzofurans: Novel Dual-State Emissive Fluorophores with Blue Emission

A regiospecific synthesis of naphtho[2,1- b]benzofurans with a substituent at the C6 position was achieved via intramolecular 6-endo-dig electrophilic cyclization under acidic conditions to construct the central aromatic C ring. Screening of the synthesized compounds using a high-content imaging system enabled us to discover novel dual state emissive compounds 2{ 1,6}, 2{ 1,8}, and 2{ 4,3}, which are highly emissive with blue emission in their solid states as well as in solution states in most solvents. In addition, the compounds 2{ 4,3}, 2{ 4,12}, and 2{ 5,13} were found to be the most cell permeable in HeLa cells for live cell imaging with negligible phototoxicity.

Synthesis of Benzofuran Derivatives through Cascade Radical Cyclization/Intermolecular Coupling of 2-Azaallyls

Benzofurans are among the most popular structural units in bioactive natural products, however, the synthesis of such structures by radical cyclization cascade reactions is rare. Herein, we report a mild and broadly applicable method for the construction of complex benzofurylethylamine derivatives through a unique radical cyclization cascade mechanism. Single-electron transfer (SET) from 2-azaallyl anions to 2-iodo aryl allenyl ethers initiates a radical cyclization that is followed by intermolecular radical-radical coupling. This expedient approach enables the synthesis of a range of polycyclic benzofurans that would otherwise be difficult to prepare.

Triindolo-Truxene Derivatives: Design, Synthesis, and Fine-Tuning of Electronic Properties and Molecular Assembly through Molecular Engineering

Triindolo-truxene, a C₃ -symmetric molecule with a large π-conjugated plane, has six methylene carbon atoms and three aromatic carbon atoms that can be facilely functionalized. Herein, butyl, carbonyl, cyano, and/or malononitrile groups were introduced at six methylene carbon atoms (6-, 14-, 22- or 8-, 16-, 24-positions) and/or three aromatic carbon atoms (2-, 10-, and 18-positions) of triindolo-truxene to produce eight derivatives. Their photophysical properties, electrochemical properties, and molecular assembly can be effectively modulated by substituents and substitution patterns. Incorporation of electron-deficient groups led to redshifts in both the absorption and emission of these derivatives and also lowered their HOMO and LUMO levels. Different substitution patterns resulted in the different intramolecular donor-acceptor interactions. Electron-deficient substituents at the methylene carbon atoms in the 6-, 14-, and 22-positions led to intramolecular charge transfer from the fluorene arms to the truxene core, whereas the corresponding substitutions at the methylene carbon atoms in the 8-, 16-, and 24-positions resulted in intramolecular charge transfer from the truxene core to the fluorene arms. The molecular packing in single crystals and molecular aggregation in solution are also influenced by the substituents and substitution patterns. This work provides a straightforward strategy to alter the properties of triindolo-truxene.

One-pot synthesis and property study on thieno[3,2-b]furan compounds

Based on the regioselective intermolecular Suzuki coupling and subsequent intramolecular Ullmann coupling reactions, one-pot synthesis of benzo[4,5]thieno[3,2-b]benzofurans (BTBFs) has been developed.

Synthesis of 2,3-bis-organochalcogenyl-benzo[b]chalcogenophenes promoted by Oxone®

We report here an alternative and tunable metal-free synthesis of benzo[b]chalcogenophenes via the electrophilic cyclization of 2-functionalized chalcogenoalkynes promoted by Oxone®.

Probing non-covalent interactions driving molecular assembly in organo-electronic building blocks

One co-crystal structure characterized to identify and quantify various non-covalent interactions with spectroscopy, X-ray crystallography and density functional theory computations.

Direct construction of 2,3-unsubstituted benzofurans and benzothiophenes via a metal-free catalyzed intramolecular Friedel–Crafts reaction

A highly effective and straightforward method for the construction of 2,3-unsubstituted benzofurans and benzothiophenes has been developed.

Ruthenium-catalyzed tandem annulation/arylation for the synthesis of unsymmetrical bis(heteroaryl)methanes

A new Ru-catalyzed tandem furan annulation/arylation strategy has been developed to afford unsymmetrical bis(heteroaryl)methanes by a reaction between propargyl amines and indoles. A series of bis(heteroaryl)methanes containing furan and indole as well as indole and imidazopyridine moieties have been synthesized in high yields. The reaction possibly proceeds through furan annulation followed by nucleophilic addition of indole.

A quantitative topological descriptor for linear co-oligomer fusion

A purely topological descriptor for the quantitative classification of fully or partially fused linear quasi-one dimensional centre-symmetric molecules is proposed. The index also makes it possible to quantitatively correlate optoelectronic properties with the molecular topology without involving an explicit calculation of the molecular electronic structure.

1,2-Gold Carbene Transfer Empowers Regioselective Synthesis of Polysubstituted Furans

A gold-catalyzed cascade cycloisomerization/ring-opening reaction of allenyl ketones bearing a cyclopropyl moiety with a wide variety of alcohols or ketones is developed. This reaction involves an unprecedented 1,2-gold carbene transfer to provide regioselective and modular access to tri- or tetrasubstituted furans in moderate to high yields and with broad substrate tolerability.