From Colorless to Near-Infrared S-Heteroarene Isomers: Unexpected Cycloaromatization of Cyclopenta[b]thiopyran Catalyzed by PtCl2

Linear Non-benzenoid Isomer of Acene Fusing Chrysene with Azulene Units

Non-benzenoid polycyclic aromatic hydrocarbons (PAHs) have received considerable attention owing to their distinctive optical and electrical properties. Nevertheless, the synthesis and optoelectronic application of non-benzenoid PAHs remain challenging. Herein, we present a facile synthesis of linear non-benzenoid PAH with an armchair edge, diACh, by fusing chrysene with two azulene units. We systematically investigated the optical and electrical properties, which were also compared to its isomers, including benzenoid and non-benzenoid zigzag edge isomers. diACh exhibits global aromaticity, good planarity, and suitable highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels. The protonation of diACh in solution successively forms a stable tropylium cation and dication. Moreover, the neutral, cationic, and dicationic states of diACh can be transformed with remarkable reversibility during the protonation-deprotonation process, as confirmed by ultraviolet-visible absorptions, fluorescence spectra, 1H nuclear magnetic resonance, and theoretical calculations. Additionally, we fabricate p-type organic field-effect transistor (OFET) devices based on diACh with hole mobility up to 0.026 cm2 V-1 s-1, and we further develop OFET-based acid vapor sensors with good sensitivity, recyclability, and selectivity. These findings underscore the unique properties of linear non-benzenoid PAHs with an armchair edge engendered by the fusion of azulene with the acene backbone, showcasing prospective applications in organic optoelectronics.

Thiopyran-Fused Polycyclic Aromatic Compounds Synthesized via Pt(II)-Catalyzed One-Pot Ring-Expansion and 6-endo Cyclization Reactions

A series of thiopyran-fused polycyclic aromatic hydrocarbons (PAHs) have been straightforwardly synthesized from 2,5-di(1-en-3-ynyl)thiophene-containing precursors via one-pot ring-expansion and 6-endo cyclization reactions. The reaction monitoring and the density function theoretical calculation suggest that the ring-expansion reaction occurs prior to 6-endo cyclization. Moreover, the absorption profiles of the thiopyran-fused PAHs suggest that the π-conjugation extension on the side of the cyclopentadiene ring in the cyclopenta[b]thiochromene core is predominant in prolonging the effective conjugation length, while the effect from extension on the other side is negligible. Furthermore, all of the thiopyran-fused PAHs exhibit halochromic properties. Upon the addition of trifluoromethanesulfonic acid, fluorescence "off-on" switches can be found for these thiopyran-fused PAHs. Therefore, this work not only provides a new synthetic approach for one-pot ring-expansion and 6-endo cyclization reactions but also expands the diversity of thiopyran-fused PAHs.

C-H arylation of thiopyran derivatives with aryl halides

A C-H arylation of thiopyran derivatives with aryl halides has been developed. Under the catalysis of Pd(OAc)2/Ag2CO3, the C-H arylation takes place at the α-position of the thiopyran ring. When dibromo-substituted compounds are used as reactants, double C-H arylations may occur on the same thiopyran ring at its α- and β-positions.

Thiopyran-Fused Mono and Double Helicenes with Low Band Gaps via Simultaneous Ring Expansion and 6-endo Cyclizations

Mono and double helicenes (M5, M6, D5, and D6) containing six-membered thiopyran rings have been successfully prepared via simultaneous ring expansion and 6-endo cycloisomerizations from the corresponding precursors with five-membered thiophene rings. Although D5 and D6 exhibit similar chemical structures, they demonstrate completely different helical structures because of their distinct steric clashes caused by the incorporated methyl groups. Moreover, all of the thiopyran-fused helicenes exhibit broad absorption bands covering the visible and near-infrared regions.

Reducing Contact Resistance in Organic Field-Effect Transistors: A Comprehensive Comparison between 2D and Microrod Single Crystals

A comprehensive comparison of organic single crystals based on a single material but with different dimensions provides a unique approach to probe their carrier injection mechanism. In this report, both two-dimensional (2D) and microrod single crystals with the same crystalline structure of an identical thiopyran derivative, 7,14-dioctylnaphtho[2,1-f:6,5-f']bis(cyclopentane[b]thiopyran) (C₈-SS), are grown on a glycerol surface with the space-confined method. Organic field-effect transistors (OFETs) based on the 2D C₈-SS single crystal exhibit superior performance compared with those based on the microrod single crystal, particularly in their contact resistance (R_C). It is demonstrated that the resistance of the crystal bulk in the contact region plays a key role in R_C of the OFETs. Thus, among the 30 devices tested, the microrod OFETs typically appear contact-limited, whereas the 2D OFETs possess significantly reduced R_C arising from the tiny thickness of the 2D single crystal. The 2D OFETs show high operational stability and high channel mobility up to 5.7 cm²/V·s. The elucidation of the contact behavior highlights the merits and great potential of 2D molecular single crystals in organic electronics.

Conjugation Extension and Halochromic Behaviors of S-Fused Polycyclic Aromatic Hydrocarbons Bearing Cyclopenta[b]thiopyran Moieties

Three S-fused polycyclic aromatic hydrocarbons (PAHs) bearing cyclopenta[b]thiopyran moieties have been designed and successfully synthesized. With the conjugation extension, the absorption onset of the longest PAH reaches 1110 nm. All the three S-fused PAHs exhibit significant halochromic properties in both solution and solid states. Upon protonation, the proton is incorporated on the cyclopentadiene ring while the positive charge is localized on the thiopyrylium ring. Moreover, no significant difference can be found for the two shorter PAHs upon the protonation by different organic acids, such as trifluoroacetic acid (TFA) and trifluoromethanesulfonic acid (TfOH), while the longest PAH can be only mono-protonated by TFA but di-protonated by stronger TfOH. Furthermore, after protonation, the non-emissive S-fused PAHs exhibit strong fluorescence and can be regenerated by simply neutralization with triethylamine. The enhanced emission of mono-protonated products stem from S₂ →S₀ transitions, which disobey the Kasha's rule.

Crystal Engineering of Angular-Shaped Heteroarenes Based on Cyclopenta[b]thiopyran for Controlling the Charge Carrier Mobility

Cyclopenta[b]thiopyran, isomeric to benzo[b]thiophene while isoelectronic to azulene, is involved as a building block to construct soluble organic semiconductors for field-effect transistors. Two series of angular-shaped heteroarenes based on cyclopenta[b]thiopyran, that is, C_n-SS (n = 4, 6, 8, 10) with different linear alkyl groups and C₈-SS-Cl^m (m = 2, 3, 4) with chlorides substituted at different positions, have been straightforward synthesized. The obtained seven S-heteroarenes exhibit intriguing and similar photophysical and electrochemical properties, such as near-infrared absorption and high-energy levels of the highest occupied molecular orbitals. Nevertheless, the S-heteroarenes with identical π-conjugated skeletons demonstrate completely different molecular packing structures, which is proofed to be the key determinate factor for the charge carrier mobilities. Upon the engineering of the pendant alkyl lengths, the highest hole mobility in the C_n-SS series is achieved for C₈-SS (1.1 cm² V^-1 s^-1) with moderate alkyl length. The further incorporation of chlorides on C₈-SS results in the shortened intermolecular H···S contacts and the interplane distances. Most interestingly, when chlorine-containing chloroform and chlorobenzene are used as crystallization solvents, single crystals of C₈-SS-Cl^m with different packing structures are produced owing to the intermolecular interactions among the solute and solvent molecules. Upon further engineering of the chlorination position and the crystallization solvent, the maximum hole mobility in the ambient air improves to 2.7 cm² V^-1 s^-1 for C₈-SS-Cl² crystallized from chlorobenzene, suggesting that the introduction of the accessible chlorides is a feasible pathway to engineering the crystal structures and controlling the charge transport characteristics.

N-Acenoacenes

The syntheses of new, fourfold alkynylated tetraazaacenoacenes (tetraazaanthracenoanthracene, tetraazatetracenotetracene and tetraazapentacenopentacene) are reported. This novel heteroacenoacene motif exhibits surprisingly strong electronic coupling between its constituting diazaacene units.

Cyclopenta[b]thiopyran and cyclopenta[b]selenopyran based heteroarenes: electronic communication between S- and/or Se-fused aromatics

Electronic communications between S- and/or Se-heteroarenes containing cyclopenta[b]thiopyran and cyclopenta[b]selenopyran moieties have been investigated.