Thienothiophenes, Dithienothiophenes, and Thienoacenes: Syntheses, Oligomers, Polymers, and Properties

A divergent one-pot thiol-Michael strategy to create β-thiophene-fused porphyrins

A divergent one-pot domino strategy for the synthesis of nickel(II) and copper(II) β-thiophene-fused 5,10,15,20-tetraarylporphyrins was developed through a thiol-Michael addition of thioglycolic/thiolactic acid to the corresponding 2-iminoporphyrins, formed in situ after the reaction of nickel(II) and copper(II) 2-formyl-5,10,15,20-tetraarylporphyrins with sterically hindered tert-butylamine in 1,2-dichloroethane at 80 °C. Interestingly, the reaction of 2-formylporphyrins with comparatively less sterically hindered primary amines and thioglycolic acid afforded a mixture of β-substituted porphyrinic thiazolidinones and β-thiophene-fused porphyrins. A similar one-pot thiol-Michael protocol was applied to construct a novel free-base thieno[2,3-b]-meso-tetrakis(4-methoxyphenyl)porphyrin, which underwent zinc insertion by using zinc acetate in a CHCl3-MeOH mixture and afforded zinc(II) β-thiophene-fused meso-tetrakis(4-methoxyphenyl)porphyrin in an appreciable isolated yield. On photophysical evaluation, these new porphyrins displayed a modest bathochromically shifted electronic absorption in contrast to meso-tetraarylporphyrin building blocks.

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.

Optimized Incorporation of Furan into Diketopyrrolopyrrole-Based Conjugated Polymers for Organic Field-Effect Transistors

Flexible electronics have received considerable attention in the past decades due to their promising application in rollable display screens, wearable devices, implantable devices, and other electronic applications. In particular, conjugated polymers are favored for flexible electronics due to their mechanical flexibility and potential for solution-processed fabrication techniques, such as blade-coating, roll-to-roll printing, and high-throughput printing allowing for high-performance transistor devices. Thiophene is the prevailing conjugated unit to construct these conjugated polymers due to its favorable electronic properties. On the other hand, furans are among the few conjugated moieties that are easily derived from bio renewable resources. To promote sustainability, we selectively introduced furan into the conjugated backbone of a high-mobility polymer scaffold and systematically studied the effect on the microstructure and charge transport. We show that partially and selectively replacing thiophene units with furan can yield nearly comparable performance compared to the all-thiophene polymer. This strategy offers an improvement in the sustainability of the polymer by incorporating bio-sourced furan without sacrificing the high-performance characteristics. Meanwhile, polymers with incorrect or complete furan incorporation show reduced mobilities. This work serves to develop coherent structure-morphology-performance relationships; such knowledge will establish guidelines for the future development of sustainable, furan-based conjugated materials.

Catalyst/Metal/Solvent-Free Markovnikov Hydrothiolation of Unactivated Alkenes with Dithiocarbamic Acids

Catalyst-free Markovnikov-selective hydrothiolation of unactivated alkenes still remains a great challenge. Herein, we develop a catalyst/metal/solvent-free methodology for the Markovnikov hydrothiolation of unactivated alkenes with in situ prepared dithiocarbamic acids, providing a wide array of alkyl dithiocarbamates. A variety of terminal, internal, cyclic, and acyclic unactivated alkenes were applied successfully in this protocol. This three-component thiol-ene reaction can be considered as a new family of click reactions.

A Domino Protocol toward High-performance Unsymmetrical Dibenzo[d,d']thieno[2,3-b;4,5-b']dithiophenes Semiconductors

Unsymmetric organic semiconductors have many advantages such as good solubility, rich intermolecular interactions for potential various optoelectronic applications. However, their synthesis is more challenging due to intricate structures thus normally suffering tedious synthesis. Herein, we report a trisulfur radical anion (S3⋅-) triggered domino thienannulation strategy for the synthesis of dibenzo[d,d']thieno[2,3-b;4,5-b']dithiophenes (DBTDTs) using readily available 1-halo-2-ethynylbenzenes as starting materials. This domino protocol features no metal catalyst and the formation of six C-S and one C-C bonds in a one-pot reaction. Mechanistic study revealed a unique domino radical anion pathway. Single crystal structure analysis of unsymmetric DBTDT shows that its unique unsymmetric structure endows rich and multiple weak S⋅⋅⋅S interactions between molecules, which enables the large intermolecular transfer integrals of 86 meV and efficient charge transport performance with a carrier mobility of 1.52 cm2 V-1 s-1. This study provides a facile and highly efficient synthetic strategy for more high-performance unsymmetric organic semiconductors.

Synthesis of [1]Benzothieno[3,2-b][1]benzothiophenes through Iodine-Mediated Sulfur Insertion Reaction

[1]Benzothieno[3,2-b][1]benzothiophenes (BTBTs) are important molecules that have been extensively studied as high-performance organic field-effect transistors (OFETs). Therefore, it is important to develop a simple synthetic method for these molecules. In this paper, a synthetic method to obtain the BTBTs from 2-arylbenzo[b]thiophenes and elemental sulfur, in which two C-S bonds are formed at once, is described. In this method, molecular iodine plays a very important role as an additive. The role of iodine is discussed in the presumed reaction pathways.

Aromaticity in the Electronic Ground and Lowest Triplet States of Molecules with Fused Thiophene Rings

Analysis of the variations of the off-nucleus isotropic magnetic shielding, σiso(r), around thiophene, thienothiophenes, dithienothiophenes and sulflowers in their electronic ground (S0) and lowest triplet (T1) states reveals that some of the features of aromaticity and bonding in these molecules do not fit in with predictions based on the popular Hückel's and Baird's rules. Despite having 4n π electrons, the S0 states of the sulflowers are shown to be aromatic, due to the local aromaticities of the individual thiophene rings. To reduce its T1 antiaromaticity, the geometry of thiophene changes considerably between S0 and T1: In addition to losing planarity, the carbon-carbon two 'double' and one 'single' bonds in S0 turn into two 'single' and one 'double' bonds in T1. Well-defined Baird-style aromaticity reversals are observed between the S0 and T1 states of only three of the twelve thiophene-based compounds investigated in this work, in contrast, the sulflower with six thiophene rings which is weakly aromatic in S0 becomes more aromatic in T1. The results suggest that the change in aromaticity between the S0 and T1 states in longer chains of fused rings is likely to affect mostly the central ring (or the pair of central rings); rings sufficiently far away from the central ring(s) can retain aromatic character.

A novel thienothiophene-based "dual-responsive" probe for rapid, selective and sensitive detection of hypochlorite

BACKGROUND

Hypochlorite/hypochlorous acid (ClO-/HOCl) is a biologically crucial reactive oxygen species (ROS), produced in living organisms and has a critical role as an antimicrobial agent in the natural defense system. However, when ClO- is produced excessively, it can lead to the oxidative damage of biomolecules, resulting in organ damage and various diseases. Therefore, it is imperative to have a straightforward, quick and reliable method for over watching the minimum amount of ClO- in different environments.

RESULTS

Herein, a new probe TTM, containing thienothiophene and malononitrile units, was developed for exceptionally selective and sensitive hypochlorite (ClO-) detection. TTM demonstrated a rapid "turn-on" fluorescence response (<30 s), naked-eye detection (colorimetric), voltammetric read-out with anodic scan, low detection limit (LOD = 0.58 μM and 1.43 μM for optical and electrochemical methods, respectively) and applicability in detecting ClO- in real water samples and living cells.

SIGNIFICANCE AND NOVELTY

This study represents one of the rare examples of a small thienothiophene-based molecule for both optical and electrochemical detections of ClO- in an aqueous medium.

Exploring Tunable Properties, Solvent-Modulated Dynamics, and Novel C(sp3)-H Activation Mechanisms in Electron Donor-Acceptor Complexes

Electron donor-acceptor (EDA) complex photochemistry has emerged as a vibrant area in visible-light-mediated synthetic radical chemistry. However, theoretical insights into the reaction mechanisms remain limited. Our study investigates the influence of solvent polarity and halogen atom types on radical reaction pathways in EDA complexes. We demonstrate that solvent polarity modulates the charge transfer and spatial arrangement within EDA complexes, thereby influencing their stability and reaction kinetics. Iodide ions play a crucial role in facilitating free radical generation and stabilizing reaction intermediates. Different halogen atom types exhibit distinct effects on radical reactions. Variations in radical concentration and solvent environment further affect the pathway selectivity. Additionally, light conditions influence the free radical generation and pathway selectivity. Our findings enhance the understanding of EDA complex photochemistry and radical reactions, offering insights for organic synthesis and photochemistry applications.

Understanding the effects of sulfur di-oxidation and side chain engineering on absorption and fluorescence of oligothiophene: A theoretical study

Oligothiophene and its derivatives have broad applications in organic electronics because of its stability, easy functionalization, and broad color adjustability, and excellent charge carrier mobility. However, the effects of sulfur di-oxidation and side alkyl chains on the absorption and fluorescence of oligothiophene are still not well understood. In this article, we have applied density functional theory (DFT) and time-dependent DFT (TDDFT) to study a series of quinquethiophene compounds functionalized with S,S-dioxide and side alkyl chains, which were experimentally synthesized. Through benchmark calculations, we have found a reliable computational method, and successfully reproduced experimental UV-Vis absorption and fluorescence emission spectra well. Furthermore, the calculated reorganization energy of these molecules could explain the energy differences between absorption and emission spectra. Last but not lease, we also have calculated the fluorescence quantum yield efficiency (Фfl) of two compounds with good planarity in this series, and the trend of calculated values is consistent with experiment. Our work gives an insight to the effects of sulfur di-oxidation and side chain engineering on absorption and fluorescence of oligothiophene.

I2/DMSO-mediated oxidative C-C and C-heteroatom bond formation: a sustainable approach to chemical synthesis

The I2/DMSO pair has emerged as a versatile, efficient, practical, and eco-friendly catalyst system, playing a significant role as a mild oxidative system, and thus employed as a good alternative to metal catalysts in synthetic chemistry. Presently, I2/DMSO is a thriving catalytic system that is used in preparing C-C and C-X (X = O/S/N/Se/Cl/Br) bonds, resulting in the formation of various bioactive molecules. Many processes utilize this system, including in situ glyoxal synthesis by diverse sp, sp2, and sp3 functionalities via iodination and subsequent Kornblum oxidation. Focusing on oxidation processes, this study examines the synergistic effect of dimethyl sulfoxide (DMSO) and molecular iodine in improving synthetic techniques. We provide a comprehensive overview of the research progress on the I2/DMSO catalytic system for the formation of C-C and C-heteroatom bonds from 2018 to the present. Additionally, the future prospects of this research field are discussed.

Transition-metal-free four-component reaction of nitriles and disulfides/diselenides

One-pot synthesis of structurally diverse sulfurized/selenated 4-aminopyrimidines has been reported via t-BuOK/K2S2O8-promoted four-component reaction of mixed nitriles and disulfides/diselenides. Mechanistic studies indicate that the reaction proceeds through radical and ionic pathways, and an alkenyl sulfide serves as a key intermediate.

Update on novel synthetic approaches towards the construction of carbazole nuclei: a review

The carbazole scaffold is a significant entity in organic compounds due to its variety of biological and synthetic applications. Traditionally, carbazole skeletons have been synthesized either via the Grabe-Ullman method, Clemo-Perkin method or Tauber method. With the passage of time, these methods have been modified and explored to accomplish the synthesis of target compounds. These methods include hydroarylations, C-H activations, annulations and cyclization reactions mediated by a variety of catalysts to construct carbazole-based compounds. This brief review article intends to provide recent updates on important methodological developments reported for the synthesis of carbazole nuclei covering 2019-2023.

Thia[n]helicenes with long persistent phosphorescence

Helicenes with persistent luminescence have received relatively little attention, despite their demonstrated highly efficient intersystem crossing (ISC) from the excited singlet to the triplet state. Herein, we designed a series of ortho-fused aromatics by combining dithieno[2,3-b:3',2'-d]thiophene (DTT) with annulated benzene fragments, denoted as TB[n]H (n = 3-8), to achieve persistent luminescence. Wherein, thia[n]helicenes (n = 5-8) exhibited intense phosphorescence with millisecond-range lifetimes (τp) at 77 K. Particularly interesting was the observation that the odd-numbered ring helicenes displayed longer τp values than their neighboring even-numbered counterparts. Notably, TB[7]H showcased the longest τp of 628 ms. This phenomenon can be attributed to the more favorable ISC channels and stronger spin-orbital coupling (SOC) of old-numbered helicenes than even-numbered ones. Furthermore, both conformers of TB[7]H exhibited significant circularly polarized phosphorescent (CPP) responses, with luminescence dissymmetry factors (glum) of 0.015 and -0.014. These discoveries suggest that thiahelicenes may be a specific class of organic phosphorescent and CPP materials.

Tuning the electronic and optical properties of small organic acenedithiophene molecular crystals for photovoltaic applications: First principles calculations

Periodic density functional theory was employed to investigate the impact of chemical modifications on the properties of π-conjugated acenedithiophene molecular crystals. Here, we highlight the importance of the β-methylthionation effect, the position of the sulfur atoms of the thiacycle group and their size, and the number of central benzene rings in the chemical modification strategy. Our results show that the introduction of the methylthio groups at the β-positions of the thiophene and the additional benzene ring at the center of the BDT crystal structure are a promising strategy to improve the performance of organic semiconductors, as observed experimentally. We found that β-MT-ADT exhibits large charge carrier mobility, which is in good agreement with the experimental results and comparable to that of rubrene. In addition, the electronic and optical properties of these ambipolar materials suggest promising performances with β-MT-ADT > ADT >β-MT-NDT > NDT > BEDT-BDT >β-MT-BDT > BDT. Moreover, functionalization with thiacycle-fused sulfur atoms of different sizes and numbers improve the properties of BDT but is still less efficient than the methylthionation effect. Overall, our findings suggest a promising molecular modification strategy for possibly high performance ambipolar organic semiconducting materials.

Dithiolation of Alkenyl Sulfonium Salts with Arylthiols to Access 1,2-Dithioalkanes

A dithiolation of alkenyl sulfonium salts with arylthiols is described, affording a series of 1,2-dithioalkanes in high yields. This protocol features mild and catalyst-free conditions and involves the formation of two C-S bonds sequentially via the regioselective addition of an arylthiol to the unsaturated C═C bonds, followed by the attack of another arylthiol to form 1,2-dithioalkanes exclusively.

The unexpected effect of ferrocenyl substituents on the photochemistry of dianthryl sulfoxides

Photoexcitation of ferrocenyl substituted dianthryl sulfoxide results in photochemical reaction products that differ from all known compounds of this class. This is enabled by energy transfer to a low-lying state, even in the case of the oxidized ferrocenium-containing compound.

Synthesis of [1]Benzothieno[2,3-b][1]benzothiophenes from 3-Arylbenzo[b]thiophenes through Iodine-Mediated Sulfur Insertion Reaction

The reaction of 3-arylbenzo[b]thiophenes and elemental sulfur to obtain [1]benzothieno[2,3-b][1]benzothiophenes (BTBTs) is reported. The addition of molecular iodine is essential for the reaction. In previous reactions that used 1,1-diarylethylenes as the starting material, side products that were difficult to separate were generated. The present reaction does not produce such side products and is therefore advantageous for obtaining BTBTs in high yield and purity.

Dimethyl Sulfoxide Provides Three Different Units in Synthesis of Chroman-4-ones Containing Sulfur and a Quaternary Carbon Center under HOAc Conditions

HOAc-promoted construction of chroman-4-ones with a sulfur atom and an α-carbonyl quaternary carbon center directly from ortho-hydroxyacetophenones and DMSO is described. In these unique reactions, DMSO is activated by HOAc and provides three different units (CH2, CH2OH, and CH2SMe) in the target molecules. This reaction displays good substrate scope and reaction yields with a series of substitutes. The mechanism showed that the three units were formed in sequential order.

Palladium-catalyzed asymmetric allenylic alkylation: construction of multiple chiral thiochromanone derivatives

The development of a new strategy for the construction of chiral cyclic sulfide-containing multiple stereogenic centers is highly desirable. Herein, by the combination of base-promoted retro-sulfa-Michael addition and palladium-catalyzed asymmetric allenylic alkylation, the streamlined synthesis of chiral thiochromanones containing two central chiralities (including a quaternary stereogenic center) and an axial chirality (allene unit) was successfully realized with up to 98% yield, 49.0 : 1 dr and >99% ee.

Recent synthetic approaches towards thienothiophenes: a potential template for biologically active compounds

Heterocyclic compounds are attractive candidates because of their vast applications in natural and physical sciences. Thienothiophene (TT) is an annulated ring of two thiophene rings with a stable and electron-rich structure. Thienothiophenes (TTs) fully represent the planar system, which can drastically alter or improve the fundamental properties of organic, π-conjugated materials when included into a molecular architecture. These molecules possessed many applications including, pharmaceutical as well as optoelectronic properties. Different isomeric forms of thienothiophene showed various applications such as antiviral, antitumor, antiglaucoma, antimicrobial, and as semiconductors, solar cells, organic field effect transistors, electroluminiscents etc. A number of methodologies were adopted to synthesize thienothiophene derivatives. In this review, we have addressed different synthetic strategies of various isomeric forms of thienothiophene that have been reported during last seven years, i.e., 2016-2022.

N-Iodosuccinimide-Mediated Synthesis of Benzo-Fused Bisimidazoles Enabled by a One-Pot Tandem Reaction of Fluorinated Propargyl Amidines

A N-iodosuccinimide (NIS)-mediated divergent and efficient tandem reaction between fluorinated propargyl amidines and aromatic o-diamines without any metal catalyst and additive under mild reaction conditions was developed for the synthesis of benzo-fused bisimidazoles in moderate to excellent yields. Preliminary mechanistic studies suggested that this reaction proceeded by an intermediate of secondary amine derived from 5-iodomethyl imidazole, and NIS played another role of oxidation reagent to promote the formation of a benzimidazole motif.

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.

Synthesis of Dithia[5]helicenes and Enantioselective Synthesis of Helically Chiral Thia[6]helicenes via Rh-Catalyzed Intramolecular [2 + 2 + 2] Cycloaddition of Triynes

Dithia[5]helicenes and helically chiral thia[6]helicenes were synthesized in high yields via a cationic Rh-catalyzed intramolecular [2 + 2 + 2] cycloaddition of triynes bearing sulfur-containing 1,6-diynes. Thia[6]helicene could be obtained with a high enantiomeric excess of P-isomers by using (S)-SEGPHOS as a chiral ligand. This protocol is the first example of the synthesis of thiahelicenes via [2 + 2 + 2] cycloaddition and can also be used for the asymmetric construction of an aza[6]helical skeleton.

Ion Transport in 2D Nanostructured π-Conjugated Thieno[3,2-b]thiophene-Based Liquid Crystal

Leveraging the self-assembling behavior of liquid crystals designed for controlling ion transport is of both fundamental and technological significance. Here, we have designed and prepared a liquid crystal that contains 2,5-bis(thien-2-yl)thieno[3,2-b]thiophene (BTTT) as mesogenic core and conjugated segment and symmetric tetra(ethylene oxide) (EO4) as polar side chains for ion-conducting regions. Driven by the crystallization of the BTTT cores, BTTT/dEO4 exhibits well-ordered smectic phases below 71.5 °C as confirmed by differential scanning calorimetry, polarized optical microscopy, temperature-dependent wide-angle X-ray scattering, and grazing incidence wide-angle X-ray scattering (GIWAXS). We adopted a combination of experimental GIWAXS and molecular dynamics (MD) simulations to better understand the molecular packing of BTTT/dEO4 films, particularly when loaded with the ion-conducting salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Ionic conduction of BTTT/dEO4 is realized by the addition of LiTFSI, with the material able to maintain smectic phases up to r = [Li⁺]/[EO] = 0.1. The highest ionic conductivity of 8 × 10^-3 S/cm was attained at an intermedium salt concentration of r = 0.05. It was also found that ion conduction in BTTT/dEO4 is enhanced by forming a smectic layered structure with irregular interfaces between the BTTT and EO4 layers and by the lateral film expansion upon salt addition. This can be explained by the enhancement of the misalignment and configurational entropy of the side chains, which increase their local mobility and that of the solvated ions. Our molecular design thus illustrates how, beyond the favorable energetic interactions that drive the assembly of ion solvating domains, modulation of entropic effects can also be favorably harnessed to improve ion conduction.

Dithieno[3,2-b:2',3'-d]thiophene (DTT): an emerging heterocyclic building block for future organic electronic materials & functional supramolecular chemistry

Heterocyclic compounds being potent biochemical materials are ubiquitous molecules in our life. Amongst, the five membered aromatic ring systems, thiophene has emerged as a remarkable entity in organic electronics owing to its (i) high resonance energy, (ii) more electrophilic reactivity than benzene, (iii) high π-electron density, (iv) planar structure and, (v) presence of vacant d-orbital in addition to the presence of loosely bind lone-pairs of electrons on sulfur atoms. In recent past, thiophene-fused molecule namely, dithienothiophene (DTT) has attracted a tremendous attention of the researchers worldwide due to their potential applicability in organic electronics such as in solar cells, electrochromic devices (ECDs), organic field effect transistors (OFETs), organic limiting diodes (OLEDs), fluorescent probes, redox switching and so forth because of their (i) higher charge mobility, (ii) extended π-conjugation, and (iii) better tuning of band gaps, etc. In this particular review article, we envisioned to report the recent advancements made on the DTT-based architectures not only because of the potential applicability of this valuable scaffold in organic electronic but also to motivate the young researchers worldwide to look for the challenging opportunities related to this privileged building block in both material sciences and functional supramolecular chemistry.

Phosphaacene as a structural analogue of thienoacenes for organic semiconductors

An air-stable λ³-phosphinine-containing polycyclic aromatic compound without steric protection was synthesized and its charge transport properties were evaluated, which revealed moderate hole mobility. This research is the first experimental demonstration of the organic electronic applications of low-coordinate phosphorus compounds.

Conjugated polymers based on selenophene building blocks

The intrinsic flexibility, solution processability, and optoelectronic properties of semiconducting conjugated polymers make them ideal candidates for use in a wide range of next-generation electronic devices. A virtually unlimited chemical design space has led to diverse polymeric architectures made from combinations of smaller molecular building blocks with desirable functionalities. Of these, thiophene is undoubtedly the most common due to its mixture of synthetic versatility, polymer backbone planarizing effects, and good optoelectronic characteristics. However, the success of thiophene has meant that other heterocycles, such as selenophene, remain relatively underexplored. This focus review discusses the challenges and material advantages of incorporating selenophene into conjugated polymer systems within the context of our contributions to the field. The early studies of poorly performing electrochemically synthesized polyselenophenes are outlined, progressing onto the model chemically synthesized alkylated homopolymers that revealed the key consequences of selenophene addition. We then review the various donor and donor-acceptor copolymer strategies that have exploited the properties of the selenium atom to enhance the performance of solar cells, transistors, and other organic electronic devices. Finally, we give our perspective on the state of the field and the fundamental material optimization studies required to realize the full potential of selenophene-containing conjugated polymers.

Non-covalent modification of single wall carbon nanotubes (SWCNTs) by thienothiophene derivatives

Non-covalent functionalization of single wall carbon nanotubes (SWCNTs) has been conducted using several binding agents with surface π-interaction forces in recent studies. Herein, we present the first example of non-covalent functionalization of sidewalls of SWCNTs using thienothiophene (TT) derivatives without requiring any binding agents. Synthesized TT derivatives, TT-CN-TPA, TT-CN-TPA2 and TT-COOH-TPA, were attached directly to SWCNTs through non-covalent interactions to obtain new TT-based SWCNT hybrids, HYBRID 1-3. Taking advantage of the presence of sulfur atoms in the structure of TT, HYBRID 1, as a representative, was treated with Au nanoparticles for the adsorption of Au by sulfur atoms, which generated clear TEM images of the particles. The images indicated the attachment of TTs to the surface of SWCNTs. Thus, the presence of sulfur atoms in TT units made the binding of TTs to SWCNTs observable via TEM analysis through adsorption of Au nanoparticles by the sulfur atoms. Surface interactions between TTs and SWCNTs of the new hybrids were also clarified by classical molecular dynamic simulations, a quantum mechanical study, and SEM, TEM, AFM and contact angle (CA) analyses. The minimum distance between a TT and a SWCNT reached up to 3.5 Å, identified with strong peaks on a radial distribution function (RDF), while maximum interaction energies were raised to -316.89 kcal mol^-1, which were determined using density functional theory (DFT).

Dimethyl Sulfoxide-Assisted, Iodine- and Ascorbic Acid-Catalyzed One-Pot Synthetic Approach for Constructing Highly Substituted Pyrazolo[1,5-a]quinoline Thioether Derivatives

A dimethyl sulfoxide-assisted and iodine/ascorbic acid-catalyzed simple approach to pyrazolo[1,5-a]quinoline thioether derivatives 22 is described. The compounds were identified using ¹H NMR, ¹³C NMR, high-resolution mass spectrometry, and single-crystal X-ray diffractometry. The pyrazolo[1,5-a]quinoline thioether was synthesized in a stepwise fashion through aryl sulfenylation and benzannulation strategies. The generated heteroaryl thioether compounds 23 were exposed to the benzannulation path to produce pyrazolo[1,5-a]quinoline thioether 22. The benzannulation reaction proceeds by way of diazotization of the pyrazole amine derivative 23, radical generation by the removal of nitrogen, and eventually trapping of the aryl radical with the support of phenylacetylene 19. A catalytic amount of ascorbic acid aided the benzannulation reaction. There were several other control studies conducted, including trapping reactions with isopropenyl acetate, tetramethylpiperidine N-oxyl reactions, and reactions without phenylacetylene. Since a change in the substitution has previously demonstrated substantial bioactivity, the core structure of pyrazole was evaluated for functional group tolerance. A reasonable mechanism is then proposed, accompanied by the support of control experiments and scope. A Suzuki reaction was used to create an aryl/heteroaryl compound 35 from one of the synthesized compounds 22b. In the controlled oxidation reaction paths, molecule 22a was selectively transformed into the corresponding sulfoxide 32 and sulfone 33.

Synthesis of I(III)/S(VI) reagents and their reactivity in photochemical cycloaddition reactions with unsaturated bonds

The development of novel methodologies for the introduction of the sulfoxonium group under mild conditions is appealing but remains underexplored. Herein we report the synthesis of a class of hypervalent iodine reagents with a transferrable sulfoxonium group. These compounds enable mixed iodonium-sulfoxonium ylide reactivity. These well-defined reagents are examined in visible-light-promoted cyclization reactions with a wide range of unsaturated bonds including alkenes, alkynes, nitriles, and allenes. Two distinct cyclization pathways are identified, which are controlled by the substituent of the unsaturated bond. The cycloaddition protocol features simple operation, mild reaction conditions, and excellent functional group tolerance, affording a broad range of sulfoxonium-containing cyclic structures in moderate to excellent yields. Furthermore, the sufoxonium group in the product can be transformed into diverse functional groups and structural motifs via single electron transfer and transition-metal catalysis.

Iron-Catalyzed Sulfonylthiocyanation of α,β-Unsaturated Amides/Esters via the Insertion of Sulfur Dioxide

An iron-catalyzed four-component sulfonylthiocyanation between α,β-unsaturated amides/esters, TMSNCS, aryldiazonium tetrafluoroborates, and sulfur dioxide (from SOgen) is demonstrated. This protocol is characterized by mild reaction conditions, good functional group compatibility, broad substrate scope, and good to excellent yields, providing a feasible method for the preparation of β-thiocyanated sulfone compounds. The preliminary mechanism investigation shows that a radical pathway may be involved in the process.

Selective C-S Bond Constructions Using Inorganic Sulfurs via Photoinduced Electron Donor-Acceptor Activation

By complementing traditional transition metal catalysis, photoinduced catalysis has emerged as a versatile and sustainable way to achieve carbon-heteroatom bond formation. This work discloses a visible-light-induced reaction for the formation of a C-S bond from aryl halides and inorganic sulfuration agents via electron donor-acceptor (EDA) complex photocatalysis. Divergent formations of organic sulfide and disulfide have been demonstrated under mild conditions. Preliminary mechanistic studies suggest that visible-light-induced intracomplex charge transfer within the monosulfide-anion-containing EDA complex permits the C-S bond construction reactivity.

Ni-catalyzed C-S bond construction and cleavage

Sulfur-containing compounds have attracted considerable interest due to their wide-ranging applications in pharmaceuticals, agriculture, natural products, and organic materials. The development of efficient and rapid methods for the construction and transformation of sulfur-containing compounds is of great importance. Since nickel is inexpensive and has a variety of valence states, strong nucleophilicity and low energy barriers for oxidative addition, the construction and transformation of sulfur-containing compounds by nickel-catalyzed cross-coupling have become important strategies. In addition, sulfur-containing compounds have also been playing increasingly important roles in the field of cross-coupling due to their thermodynamically stable but dynamic activity. This review will focus on nickel-catalyzed construction and transformation of various sulfide-containing compounds, such as sulfides, disulfides, and hypervalent sulfur-containing compounds.

Introducing a new 7-ring fused diindenone-dithieno[3,2-b:2',3'-d]thiophene unit as a promising component for organic semiconductor materials

A novel π-conjugated molecule, EtH-T-DI-DTT is reported, which is fused, rigid, and planar, featuring the electron-rich dithieno[3,2-b:2’,3’-d]thiophene (DTT) unit in the core of the structure. Adjacent to the electron-donating DTT core, there are indenone units with electron-withdrawing keto groups. To enable solubility in common organic solvents, the fused system is flanked by ethylhexylthiophene groups. The material is a dark, amorphous solid with an onset of absorption at 638 nm in CH₂Cl₂ solution, which corresponds to an optical gap of 1.94 eV. In films, the absorption onset wavelength is at 701 nm, which corresponds to 1.77 eV. An ionisation energy of 5.5 eV and an electron affinity of 3.3 eV were estimated by cyclic voltammetry measurements. We have applied this new molecule in organic field effect transistors. The material exhibited a p-type mobility up to 1.33 × 10⁻⁴ cm² V⁻¹ s⁻¹.

Two-Step Construction of Thiophene-Oxazole Dyads with Fluorescent Properties by the Ring Expansion of Aziridines

A general approach toward 2-thiophenylsubstituted oxazoles using aziridination of a double bond of (acyl)alkenyl thiophenes with the subsequent expansion of the aziridine ring is developed. The isolation of intermediate aziridine is not necessary. This expedient protocol covers a broad scope of readily available 2-, 3-, and benzothiophene derivatives, is practical and reliable, requires short reaction times, and is simple to set up and work up reaction mixtures. Thiophenyloxazoles, obtained by this method, exhibit fluorescence with high quantum yields.

Synthesis and crystal structures of unsymmetrical wave-shaped heptathienoacenes

Three unsymmetrical wave-shaped heptathienoacenes (UHT-1, UHT-2 and UHT-3) with sulfur atoms at different isomeric locations in the two terminal thiophene rings were designed and synthesized. The synthetic strategy contains two crucial steps, including the cross-coupling of two different dithienothiophene isomers (DTT) from dithieno[2,3-b:3',2'-d]thiophene (bb-DTT), dithieno[2,3-b:2',3'-d]thiophene (bt-DTT) and dithieno[2,3-b:3',4'-d]thiophene (bs-DTT) as building blocks through the Negishi coupling and intramolecular cyclization reactions with (SnBu₃)₂S. X-ray crystal structures of UHT-1, UHT-2 and UHT-3 show that the molecules adopt a wave-shaped geometry with multiple intermolecular interactions, such as S-S, S-C and S-H, which result in different crystal packing patterns. The isomeric location of the sulfur atoms of the two terminal thiophene rings of UHT-1, UHT-2 and UHT-3 plays an important role in tuning π-electronic conjugation and spectroscopic behaviors.

Multifunctional Heteropentalenes: From Synthesis to Optoelectronic Applications

In the broad family of heteropentalenes, the combination of two five-membered heterocyclic rings fused in the [3,2-b] mode has attracted the most significant attention. The relatively straightforward access to these structures, being a consequence of the advances in the last two decades, combined with their physicochemical properties which match the requirements associated with many applications has led to an explosion of applied research. In this Perspective, we will discuss the recent progress of heteropentalenes' usefulness as an active element of organic light-emitting diodes and organic field-effect transistors. Among the myriad of possible combinations for the different heteroatoms, thieno[3,2-b]thiophenes and 1,4-dihydropyrrolo[3,2-b]pyrroles are subject to the most intense studies. Together they comprise a potent optoelectronics tool resulting from the combination of appreciable photophysical properties, chemical reactivity, and straightforward synthesis.

5-Thiaporphyrinium cation: effect of sulphur incorporation on excited state dynamics

We synthesised thionium-ion embedded aromatic porphyrinoids: a free-base 5-thiaporphyrinium cation and its zinc complex. The sulphur atom effectively participates in the macrocyclic π-conjugation. Fluorescence quantum yields of thiaporphyrinium cations were lower than 1% unlike oxaporphyrinium cations. Detailed photophysical analysis and DFT calculations clarified the vibrational mode regarding the out-of-plane motion of the sulphur atom induced ultrafast quenching of the excited state in comparison to the corresponding oxaporphyrinium cations.

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.