Azulene Methacrylate Polymers: Synthesis, Electronic Properties, and Solar Cell Fabrication

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.

Synthesis, Structural, and Optical Properties of Azuleno[1,2-c]pyran-1-ones: Bro̷nsted Acid-Mediated Cyclization of 2-Azulenylalkynes

Pyrones and their aromatic ring-fused derivatives have gained significant attention due to their diverse biological activities and potential as foundational frameworks for advanced materials. In this paper, we describe a proficient approach for the preparation of azuleno[1,2-c]pyran-1-ones, which are difficult to produce by using conventional methods. The synthesis was achieved through Bro̷nsted acid-mediated cyclization of 2-azulenylalkynes. The structural and optical properties of azuleno[1,2-c]pyran-1-ones were characterized by single-crystal X-ray analysis, NMR, UV/vis, and fluorescence spectroscopies. Under acidic conditions, these compounds displayed notable spectral alterations and emission, distinct from their spectra in neutral medium. These results suggest that azuleno[1,2-c]pyran-1-ones hold great potential for applications in organic electronic materials and fluorescent pH sensors.

Prospects for useful fission from singlet states higher than S1 in aggregated organic chromophores

The few known reports and the likely prospects of finding new efficient routes to exciton fission from higher excited singlet states, Sn (n > 1), are reviewed. Aggregates of molecules that have large S2-S1 electronic energy spacings and/or emit measurable "contra-Kasha" emission may offer further opportunities. Among these, electronically excited molecular systems that exhibit known efficient (T1 + T1) triplet-triplet annihilation producing S2 could exhibit efficient singlet fission in aggregates when appropriately substituted to meet the necessary energy requirements. The potential problem of loss of triplet excitons via 2T1 → Tn>1 + S0 triplet-triplet annihilation following (S2 + S0) singlet fission is addressed. Aggregates of substituted azulenes and aliphatic thiones and dithiones are particularly attractive and are discussed in detail.

Unravelling the Superiority of Nonbenzenoid Acepleiadylene as a Building Block for Organic Semiconducting Materials

Acepleiadylene (APD), a nonbenzenoid isomer of pyrene, exhibits a unique charge-separated character with a large molecular dipole and a small optical gap. However, APD has never been explored in optoelectronic materials to take advantage of these appealing properties. Here, we employ APD as a building block in organic semiconducting materials for the first time, and unravel the superiority of nonbenzenoid APD in electronic applications. We have synthesized an APD derivative (APD-IID) with APD as the terminal donor moieties and isoindigo (IID) as the acceptor core. Theoretical and experimental investigations reveal that APD-IID has an obvious charge-separated structure and enhanced intermolecular interactions as compared with its pyrene-based isomers. As a result, APD-IID displays significantly higher hole mobilities than those of the pyrene-based counterparts. These results imply the advantages of employing APD in semiconducting materials and great potential of nonbenzenoid polycyclic arenes for optoelectronic applications.

Tuning Dipole Orientation of 2,6-Azulene Units in Conjugated Copolymers by C–H Activation Strategy toward High-Performance Organic Semiconductor

Azulene has aroused widespread interest for constructing optoelectronic materials. However, controlling the dipole orientation of 2,6-azulene units in the conjugated polymer backbone is a significant challenge so far. Herein, by C-H activation strategy, three 2,6-azulene-TPD-based conjugated copolymers with different dipole arrangements were synthesized, where TPD = thieno[3,4-c]pyrrole-4,6-dione. The dipole arrangements of 2,6-azulene units were random for P(AzTPD-1), head-to-head/tail-to-tail for P(AzTPD-2), and head-to-tail for P(AzTPD-3). These polymers exhibited unipolar n-type semiconductor characteristics in organic field effect transistors. Moreover, regioregular polymer P(AzTPD-3) displayed the best device performance with an electron mobility of up to 0.33 cm² V^-1 s^-1, which makes P(AzTPD-3) a high-performance n-type polymeric semiconductor. These results demonstrate that incorporation of 2,6-azulene units into the polymeric backbone together with the regulation of the dipole orientation of 2,6-azulene units is an effective strategy for obtaining high-performance organic optoelectronic materials.

Tailoring liquid crystalline self-assembly and de Vries behavior of azulenes via lateral and core substitution

The azulene moiety is a highly attractive building block in optoelectronic applications due to its unique properties. For high-performing devices, the molecular orientation is crucial and can be controlled through liquid-crystalline self-assembly. Recent work showed that liquid crystalline derivatives bearing the 2-phenyl-azulene-1-nitrile core formed broad de Vries-type SmA and SmC phases. For exact understanding of the structure-property relationship, a series of 2-(hetero)aryl-azulenes has been synthesized varying the chain linkage, the lateral substituent, and the aromatic ring. Small changes of the molecular structure determined whether the orthogonal SmA phase or the tilted SmC phase is predominant. Implementation of alkyne chains instead of alkoxy chains resulted in the reduction of phase transition temperatures and formation of mesophases at room temperature. Furthermore, de Vries-like behavior was investigated and reduction values between R = 0.35 and 0.74 were measured which supported the hypothesis that in this system de Vries-like behavior is caused by steric repulsion of the lateral substituent. The control of the phase geometry by the molecular structure might be used for improved molecular orientation in optoelectronic materials.

Synthesis of donor-acceptor compounds based on azulene

At present, non-benzenoid aromatic hydrocarbons are widely used as precursors for the synthesis of new materials with useful electronic properties. In particular, the non-alternative aromatic hydrocarbon azulen with a unique dipole structure and a tendency to form stabilized radical ions should be predetermined as a building block for obtaining new π-conjugated systems with interesting optoelectronic properties. This article discusses the directed synthesis and study of optical properties of new donor-acceptor compounds based on azulene. It was shown that for the synthesis of donor-acceptor phenylketone azulenes, the reaction of directed (to positions С1 and С3) acylation with benzoyl chloride in the presence of Li2MnCl4 in tetrahydrofuran was used for the first time as a key step. It was found that push-pull phenyldicyanovinyl azulenes obtained by Knoevenagel condensation of azulenylketones with malononitrile flow easily (with an increase in the yield of end products) in the presence of pyridine in dimethyl sulfoxide. Electron UV-visible spectra of phenyldicyanovinyl azulene compounds showed strong absorption bands in the visible region (λmax = 452 and 434 nm) caused by intense intramolecular charge transfer between the donor azulene ring and the acceptor phenyldicyanovinyl group.

Liquid crystalline self-assembly of azulene-thiophene hybrids and their applications as OFET materials

Orientational control within thin films is crucial for the preparation of organic field effect transistors (OFETs). The highly ordered liquid crystalline smectic E phase (SmE) is known as a powerful template for solution processed thin films. Here, we describe the synthesis and characterization of three novel azulene-thiophene hybrid materials. Liquid crystalline characterization showed the presence of wide SmE phases. Thin films were prepared by spin-coating at mesophase temperature. Due to the self-aligning properties of the SmE phase uniformly flat films with good molecular alignment were manufactured. Top contact bottom gate OFETs showed mobilities up to (3.3 ± 0.5) × 10^-3 cm² V^-1 s^-1.

Azulene-Containing Squaraines for Photoacoustic Imaging and Photothermal Therapy

Photoacoustic imaging (PAI) guided photothermal therapy (PTT) can realize real-time diagnosis and in situ treatment of cancer at the same time. Absorption in the near-infrared (NIR) region with large molar extinction coefficient (ε) and high value of photothermal conversion efficiency (PCE) are key prerequisites for photothermal agents (PTAs) to realize dual PAI and PTT treatments. Squaraines have stable quinoid structures with strong planarity and rigidity, in favor of the NIR absorption and high ε values. On the other hand, azulene derivatives mostly have very faint fluorescence emission, which is beneficial for photothermal transformation. Herein, two azulene-containing squaraines Az-SQ-1 and Az-SQ-2 are synthesized as high-performance PTAs. In comparison with Az-SQ-1, Az-SQ-2 possesses larger ε_max of 3 × 10⁵ M^-1 cm^-1 at 780 nm in organic solution and higher PCE of 53.2% in the form of nanoparticles under 808 nm laser irradiation. Accordingly, Az-SQ-2 NPs present stronger photoacoustic signals (about 15.1-times the background signal) and more efficient suppression of tumor growth. Our research indicates that the introduction of azulene unit to traditional NIR dyes is a simple but effective approach to obtain outstanding PTAs in the aspect of phototheranostics.

Azulene-Embedded [n]Helicenes (n=5, 6 and 7)

Azulene is a non-benzenoid aromatic building block with unique chemical structure and physicochemical properties. By using the "bottom-up" synthetic strategy, we synthesized three azulene-embedded [n]helicenes ([n]AzHs, n=5, 6 and 7), in which one terminal azulene subunit was fused with n-2 benzene rings. P- and M-enantiomers were observed in the packing diagrams of [5]-, and [6]AzHs. However, P- and M-[7]AzHs could be isolated by recrystallization of the racemic mixture. These [n]AzHs were endowed with new properties through the azulene moiety such as low-lying first electric state (S₁ ), small optical energy gap and anti-Kasha emission. [6]-, and [7]AzHs exhibit strong chiroptical responses with high absorption dissymmetry factor (g_abs ) maxima of about 0.02, which is among the highest |g_abs | values of helicenes in the visible range. These azulene-embedded [n]helicenes contribute to the non-benzenoid helicene library and allow the structure-property relationships to be better understood.

Synthesis, Reactivity, and Properties of Benz[a]azulenes via the [8 + 2] Cycloaddition of 2H-Cyclohepta[b]furan-2-ones with an Enamine

Starting with the reaction of 2H-cyclohepta[b]furan-2-ones with an enamine, which was prepared from 4-tert-butylcyclohexanone and pyrrolidine, benz[a]azulenes having both formyl and tert-butyl groups were obtained in the three-step sequence. Subsequently, both the formyl and tert-butyl groups were eliminated by heating the benz[a]azulene derivatives in 100% H₃PO₄ to give benz[a]azulenes without these substituents in high yields. In terms of product yield, this method is the best one ever reported for the synthesis of the parent benz[a]azulene so far. The conversion of the benz[a]azulene derivatives with a formyl group into cyclohept[a]acenaphthylen-3-one derivatives was also investigated via Knoevenagel condensation with dimethyl malonate, followed by Brønsted acid-mediated intramolecular cyclization. The structural features including the bond alternation in the benz[a]azulene derivatives were revealed by NMR studies, NICS calculations, and a single-crystal X-ray structural analysis. The optical and electrochemical properties of a series of benz[a]azulene derivatives were evaluated by UV/Vis, fluorescence spectroscopy, and voltammetry experiments. As a result, we found that some benz[a]azulene derivatives showed remarkable luminescence in acidic media. In addition, the benz[a]azulene derivatives with the electron-withdrawing group and cyclohept[a]acenaphthylen-3-one derivative displayed good reversibility in the spectral changes under the electrochemical redox conditions.

Proton-responsive azulene-based conjugated polymer with nonvolatile memory effects

We report an azulene-based conjugated polymer, PAV, which exhibits proton-gated and electrical-gated changes in its conductivity.

Azulene Bridged π-Distorted Chromophores: The Influence of Structural Symmetry on Optoelectrochemical and Photovoltaic Parameters

Conjugated chromophores possessing π-twisted functionality such as tetracyanobutadiene (TCBD) have emerged as promising active layer materials for organic photovoltaics (OPVs). In this study, we disclose the synthesis of two azulenyl chromophores containing one and two TCBD groups. The symmetrical and unsymmetrical structural characteristics of these molecules inflict dissimilar optoelectronic and electrochemical properties. Based on molar absorptivity, aggregation behavior, HOMO-LUMO energies and other quantum chemical parameters, the symmetrical molecule (TATC2) appears to be a better non-fullerene acceptor (NFA) compared to its unsymmetrical counterpart (TATC1). For instance, higher absorptivity and deeper HOMO-LUMO levels for TATC2 (23950 M-1  cm-1 ; -6.01 eV/-3.86 eV) over TATC1 (12200 M1  cm-1 ; -5.46 eV/-3.64 eV) was observed. Validating this structure-property relationship on solar cell prototypes exhibited higher photovoltaic parameters (VOC =0.54 V, FF=0.48, JSC =6.42 mA/cm2 ) for TATC2 than TATC1 (VOC =0.47 V, FF=0.38, JSC =5.77 mA/cm2 ). Though the device parameters are not high, this work uncovers the intrinsic properties of azulene-tethered twisted chromophores as potential π-semiconductor choice for NFA solar cells. In particular, this report explores the utility of azulene-based π-twisted semiconductors as acceptor material for OPVs with cell efficiencies of 1.70 and 1.04 % for TATC2 and TATC1 respectively.

Copper-Catalyzed 3-Positional Amination of 2-Azulenols with O-Benzoylhydroxylamines

A copper-catalyzed ortho-selective amination of 2-azulenols with O-benzoylhydroxylamines (RR'N-OBz) to synthesize ortho-aminoazulenols is reported. A wide range of functional groups on amines are compatible, furnishing the corresponding amino-azulene derivatives in moderate to good yields. The further synthetic elaboration using 3-amino-2-azulenols as starting materials is demonstrated.

Chemical syntheses and salient features of azulene-containing homo- and copolymers

Azulene is a non-alternant, aromatic hydrocarbon with many exciting characteristics such as having a dipole moment, bright color, stimuli responsiveness, anti-Kasha photophysics, and a small HOMO-LUMO gap when compared to its isomer, naphthalene. These properties make azulene-containing polymers an intriguing entity in the field of functional polymers, especially for organic electronic applications like organic field-effect transistors (OFET) and photovoltaic (PV) cells. Since azulene has a fused five and seven-membered ring structure, it can be incorporated onto the polymer backbone through either of these rings or by involving both the rings. These azulene-connection patterns can influence the properties of the resulting polymers and the chemical synthesis in comparison to the electrochemical synthesis can be advantageous in obtaining desired patterns of substitution. Hence, this review article presents a comprehensive overview of the developments that have taken place in the last three decades in the field of chemical syntheses of azulene-containing homo- and copolymers, including brief descriptions of their key properties.

Synthesis and Halochromic Properties of 1,2,6-Tri- and 1,2,3,6-Tetra-aryl Azulenes

A series of novel 2,6-functionalized azulene molecules Azu1-3 with varied fluorene substituents at the 1- and 3-positions of azulene as well as at the 5'-position of 2-thiophene group were synthesized. Their electronic absorption and emission spectra at neutral and protonated states were examined. It was found that after functionalization with fluorenyl groups, Azu1-3 exhibited absorption maxima at 445, 451 to 468 nm, respectively. In contrast, their corresponding protonated species showed much redshifted absorption maxima at 560, 582 to 643 nm, respectively, mainly due to the extension of conjugation length and the large dipole moment along the C_2v axis of 2,6-substituted azulene molecules. Azu1-3 are non-fluorescent in their neutral forms, but became emissive in their protonated states. Analysis of absorption and emission spectra shows that substitution of the 1- or 3-position of azulene led to decrease in response to trifluoroacetic acid.

Azulene-Based π-Functional Materials: Design, Synthesis, and Applications

ConspectusAzulene, an isomer of naphthalene, is a molecule of historical interest for its unusual photophysical properties, including a beautiful blue color derived from the narrow HOMO-LUMO energy gap and anti-Kasha fluorescence from S₂ to S₀. More recently, it has attracted increasing attention for its novel electronic structure, including an electron-rich five-membered ring and an electron-deficient seven-membered ring with a dipole moment of 1.08 D resulting from resonance delocalization, its different reactivities at odd and even positions, and its stimuli-responsive behavior. As a key building block, azulene has been used in various fields because of its unique physicochemical properties. Recent studies have demonstrated the great potential of azulene for constructing advanced organic materials. However, exploring azulene-based materials has long been hindered by challenges in molecular design and synthesis. Most of the reported azulene-based materials have the azulene unit incorporated through the five-membered ring or seven-membered ring. Creating azulene-based novel building blocks for optoelectronics and using 2,6-connected azulene units to construct conjugated polymers that can adequately utilize the "donor-acceptor" structure of azulene remained underexplored before our contributions. Besides, for most azulene-fused polycyclic aromatic hydrocarbons (PAHs) and heteroaromatics, the azulene substructures were created during later synthesis stages, and the use of azulene derivatives as starting materials to design and synthesize PAHs and heteroaromatics intelligently is still limited.In this Account, we summarize our efforts on the design, synthesis, and applications of azulene-based π-functional materials. Our studies start with the creation of novel π-conjugated structures based on azulene. The design strategy, synthesis, and optoelectronic performance of the first class of azulene-based aromatic diimides, 2,2'-biazulene-1,1',3,3'-tetracarboxylic diimide (BAzDI) and its π-extended and π-bridged derivatives, are presented. Notably, antiparallel stacking between adjacent azulene units derived from azulene's dipole was observed in single crystals of BAzDI and its derivatives. Besides, we developed an azulene-fused isoindigo analogue, azulenoisoindigo, which combines the merits of both isoindigo and azulene, including reversible redox behavior and reversible proton responsiveness. Then we discuss our contributions to the design and synthesis of 2,6-azulene-based conjugated polymers. By incorporation of 2,6-connected azulene units into the polymeric backbone, two conjugated polymers with high organic field-effect transistor (OFET) performance were developed. Two 2,6-azulene-based polymers with proton responsiveness and high electrical conductivity upon protonation were also provided. We also discuss our recent studies on azulene-based heteroaromatics. Two azulene-fused BN-heteroaromatics were designed and synthesized, and they exhibited a selective response to fluoride ion and unexpected deboronization upon the addition of trifluoroacetic acid. An unexpected synthesis of azulene-pyridine-fused heteroaromatics (Az-Py) by reductive cyclization of 1-nitroazulenes and the OFET performance of Az-Py-1 are included. Afterward, we discuss several examples of azulene-capped organic conjugated molecules. The molecules capped with the five-membered ring of azulene favor hole transport, whereas the ones capped with the seven-membered ring favor electron transport.

C4-aldehyde of guaiazulene: synthesis and derivatisation

Guaiazulene is an alkyl-substituted azulene available from natural sources and is a much lower cost starting material for the synthesis of azulene derivatives than azulene itself. Here we report an approach for the selective functionalisation of guaiazulene which takes advantage of the acidity of the protons on the guaiazulene C4 methyl group. The aldehyde produced by this approach constitutes a building block for the construction of azulenes substituted on the seven-membered ring. Derivatives of this aldehyde synthesised by alkenylation, reduction and condensation are reported, and the halochromic properties of a subset of these derivatives have been studied.

Azulene Functionalization by Iron-Mediated Addition to a Cyclohexadiene Scaffold

The functionalization of azulenes via reaction with cationic η5-iron carbonyl diene complexes under mild reaction conditions is demonstrated. A range of azulenes, including derivatives of naturally occurring guaiazulene, were investigated in reactions with three electrophilic iron complexes of varying electronic properties, affording the desired coupling products in 43-98% yield. The products were examined with UV-vis/fluorescence spectroscopy and showed interesting halochromic properties. Decomplexation and further derivatization of the products provide access to several different classes of 1-substituted azulenes, including a conjugated ketone and a fused tetracycle.

Water-dispersible conducting polyazulene and its application in thermoelectrics

We report on the facile synthesis of a water-dispersible conducting polymer, polyazulene-polystyrenesulfonate (PAZ:PSS), using PSS as a template. PAZ:PSS can achieve an overall conductivity up to 0.1 S cm^-1, and an ion Seebeck coefficient as high as 4500 μV K^-1, demonstrating that PAZ:PSS is another promising water-dispersible polymer for thermoelectrics.

Azulene in Polymers and Their Properties

Azulene, a unique isomer of naphthalene, has received much interest from researchers in different fields due to its unusual chemical structure with a negatively charged 5-membered ring fused with a positively charged 7-membered ring. In particular, incorporation of azulene into polymers has led to many interesting properties. This minireview covers functionalization methods of azulene at its various positions of 5- and 7-membered rings to form azulene derivatives including azulene monomers, and gives an overview of a wide range of azulene-containing polymers including poly(1,3-azulene), azulene-based copolymers with connectivity at 1,3-positions of the 5-membered ring, or 4,7-positions of the 7-membered ring, as well as copolymers with azulene units as side chains. Their chemical and physical properties together with applications of azulene-containing polymers have also been summarized.

Two Isomeric Azulene-Decorated Naphthodithiophene Diimide-based Triads: Molecular Orbital Distribution Controls Polarity Change of OFETs Through Connection Position

Altering the charge carrier transport polarities of organic semiconductors by molecular orbital distribution has gained great interest. Herein, we report two isomeric azulene-decorated naphthodithiophene diimide (NDTI)-based triads (e.g., NDTI-B2Az and NDTI-B6Az), in which two azulene units were connected with NDTI at the 2-position of the azulene ring in NDTI-B2Az, whereas two azulene units were incorporated with NDTI at the 6-position of the azulene ring in NDTI-B6Az. The two isomeric triads were excellently soluble in common organic solvents. Density functional theory calculations on the molecular orbital distributions of the triads reveal that the lowest unoccupied molecular orbitals are completely delocalized over the entire molecule for both NDTI-B2Az and NDTI-B6Az, indicating great potential for n-type transport behavior, whereas the highest occupied molecular orbitals are mainly delocalized over the entire molecule for NDTI-B2Az or only localized at the two terminal azulene units for NDTI-B6Az, implying great potential for p-type transport behavior for the former and a disadvantage of hole carrier transport for the latter. Under ambient conditions, solution-processed bottom-gate top-contact transistors based on NDTI-B2Az showed ambipolar field-effect transistor (FET) characteristics with high electron and hole mobilities of 0.32 (effective electron mobility ≈0.14 cm² V^-1 s^-1 according to a reliability factor of 43%) and 0.03 cm² V^-1 s^-1 (effective hole mobility ≈0.01 cm² V^-1 s^-1 according to a reliability factor of 33%), respectively, whereas a typically unipolar n-channel behavior is found for a film of NDTI-B6Az with a high electron mobility up to 0.13 cm² V^-1 s^-1 (effective electron mobility ≈0.06 cm² V^-1 s^-1 according to a reliability factor of 43%). The results indicate that the polarity change of organic FETs based on the two isomeric triads could be controlled by the molecular orbital distributions through the connection position between the azulene unit and NDTI.

A polycyclic aromatic hydrocarbon diradical with pH-responsive magnetic properties

By integrating azulene with a quinoid moiety, a novel non-alternant polycyclic aromatic hydrocarbon molecule BCHF1 exhibiting manifold zwitterionic, quinoidal and diradical behaviors is designed and synthesized. Its zwitterionic feature is evidenced by the changes shown by the ¹H-NMR and absorption spectra when the molecule undergoes reversible protonation and deprotonation reactions at varied pH. The diradical facet, manifesting a small singlet-triplet energy gap (ΔE _S-T), is characterized with a paramagnetic resonance signal detected by the EPR spectroscopy at room temperature. As the diradical properties are not observed in the protonated form, BCHF1+H⁺ , a pH-controlled reversible magnetic switching behavior is illustrated by monitoring the on and off cycles of EPR signals upon successively adding bases and acids to a solution or exposing a thin film of BCHF1+H⁺ to base vapor followed by acid vapor.

Direct synthesis of 2-arylazulenes by [8+2] cycloaddition of 2H-cyclohepta[b]furan-2-ones with silyl enol ethers

We developed a procedure for the direct synthesis of 2-arylazulenes, which were obtained in moderate to excellent yields, by [8+2] cycloaddition of 2H-cyclohepta[b]furan-2-ones with aryl-substituted silyl enol ethers. The structures of some 2-arylazulenes were clarified by single-crystal X-ray analysis. The 2-phenylazulene derivatives obtained by this study showed noticeable fluorescence in acidic media.

Three-component reaction of azulene, aryl glyoxal and 1,3-dicarbonyl compound for the synthesis of various azulene derivatives

A three-component reaction of an azulene, an aryl glyoxal and a 1,3-dicarbonyl compound has been elaborated to access a series of azulene derivatives. Some of these azulene-containing adducts were further subjected to post-MCR transformations to assemble azulene–heterocycle conjugates.

Three-component reaction of azulene, aryl glyoxal and 1,3-dicarbonyl compound and subsequent post-transformations provide access to three distinct types of azulene derivatives.

Incorporation of 1,3-Free-2,6-Connected Azulene Units into the Backbone of Conjugated Polymers: Improving Proton Responsiveness and Electrical Conductivity

Azulene as a potential building block for constructing organic/polymeric conjugated materials has attracted more and more attention due to its unique chemical structure and physicochemical properties. However, up to now, most reported azulene-based conjugated polymers have been dominated by the connection of the five-membered ring of azulene through 1,3-positions. Herein, by incorporating 1,3-free-2,6-connected azulene units into the polymeric backbone, two azulene-based all-carbon conjugated polymers P1 and P2 with different connection ways of 2,6-azulene and 2,7-fluorene units were presented. Protonation of these two polymers with trifluoroacetic acid leads to rapid and reversible color changes in both the solution and thin-film state. Moreover, these 1,3-free-2,6-connected azulene-based conjugated polymers exhibit high electrical conductivity (2.94 and 0.32 S/cm for P1 and P2, respectively) in thin film when doped by trifluoromethanesulfonic acid.

Azulene-Based BN-Heteroaromatics

Azulene, a nonalternant bicyclic aromatic hydrocarbon, has unique chemical and physical properties and is considered to be a promising building block for constructing novel polycyclic aromatic hydrocarbons (PAHs) and heteroaromatics. We present here the first two azulene-based BN-heteroaromatics Az-BN-1 and Az-BN-2. The chemical structures and optical and electrochemical properties of both compounds have been investigated, as well as their sensing behavior in response to fluoride ion. Az-BN-1 and Az-BN-2 show different photophysical properties from other reported BN-embedded PAHs, such as lower band gaps and unusual fluorescence. In addition, Az-BN-1 and Az-BN-2 exhibit unexpected deboronization upon addition of trifluoroacetic acid, which distinguishes them from other reported BN-heteroaromatics and can be ascribed to the unique property of the azulene unit.

Synthesis of Zwitterionic Copolymers via Copper-Mediated Aqueous Living Radical Grafting Polymerization on Starch

[2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) is a well-studied sulfobetaine-methacrylate as its zwitterionic structure allows the synthesis of polymers with attractive properties like antifouling and anti-polyelectrolyte behavior. In the present work, we report the Cu⁰-mediated living radical polymerization (Cu⁰-mediated LRP) of SBMA in sodium nitrate aqueous solution instead of previously reported solvents like trifluoroethanol and sodium chloride aqueous/alcoholic solution. Based on this, starch-g-polySBMA (St-g-PSBMA) was also synthesized homogeneously by using a water-soluble waxy potato starch-based macroinitiator and CuBr/hexamethylated tris(2-aminoethyl)amine (Me₆TREN) as the catalyst. The structure of the macroinitiator was characterized by ¹H-NMR, 13C-NMR, gHSQC, and FT-IR, while samples of PSBMA and St-g-PSBMA were characterized by ¹H-NMR and FT-IR. Monomer conversion was monitored by ¹H-NMR, on the basis of which the reaction kinetics were determined. Both kinetic study and GPC results indicate reasonable controlled polymerization. Furthermore, a preliminary study of the thermal response behavior was also carried through rheological tests performed on aqueous solutions of the prepared materials. Results show that branched zwitterionic polymers are more thermal-sensitive than linear ones.

Azulenes with aryl substituents bearing pentafluorosulfanyl groups: synthesis, spectroscopic and halochromic properties

Azulenes with SF₅-containing substituents gave significantly different spectroscopic responses to protonation depending on the regioisomer in question.

An axially chiral 1,1′-biazulene and its π-extended derivative: synthesis, structures and properties

Chiral organic π-conjugated molecules have been intensively investigated in the fields of chiral electronic materials and devices.

Sulfur-anchored azulene as a cathode material for Li–S batteries

A benzene-free and vinyl-free molecule, azulene, is used to polymerize with sulfur for new cathode material based Li–S batteries.

Synthesis of azulenophthalimides by phosphine-mediated annulation of 1,2-diformylazulenes with maleimides

The reaction of 1,2-diformylazulene with maleimides in the presence of PPh₃ gave the azulenophthalimides. The optical and electrochemical properties of the azulenophthalimides were investigated.

Synthesis of azuleno[2,1-b]thiophenes by cycloaddition of azulenylalkynes with elemental sulfur and their structural, optical and electrochemical properties

The reaction of several azulenylalkynes having an aryl substituent with elemental sulfur afforded the corresponding azuleno[2,1-b]thiophenes in good yields.

Catalytic Functionalization of C-H Bonds of Azulene by Carbene/Nitrene Incorporation

The selective catalytic functionalization of the C-H bond of azulene upon incorporation of carbene or nitrene units with metal-based catalysts is described. Ethyl diazoacetate or ArI═NTs are employed as carbene or nitrene precursors, respectively. The azulene derivatives are subsequently employed as building blocks toward more complex structures with potential use as biodegradable materials.