Synthesis and Properties of a New Class of Fully Conjugated Azahexacene Analogues

Acenes are a traditional class of polycyclic aromatic hydrocarbons (PAHs) which attracted considerable interest during the last decade because of their outstanding p‐channel semiconductor properties. More recently, N‐heteroacenes have been prepared. These molecules have been shown to be more stable and can exhibit n‐channel semiconductor properties. Inspired by these archetype PAHs, we synthesized a novel class of highly persistent azahexacene analogues 3 a – d . These molecules are composed of a core of four fused five‐membered rings derived from their respective diketopyrrolopyrroles. These new π‐conjugated scaffolds show broad and intense absorption in the visible region and possess low‐lying HOMO and LUMO levels, leading to much better stability compared to that of acenes and most heteroacenes.     

Synthesis, structures, and properties of unsymmetrical heteroacenes containing both pyrrole and furan rings

Unsymmetrical heteroacenes, 11-phenylbenzofuro[3,2-b]carbazole (Ph-BFC) and its alkoxylated derivatives, were readily synthesized by palladium-catalyzed double N-arylation of arylamines. They characteristically form antiparallel cofacial pi-stacking arrangements, which may result from their unsymmetrical structures. Their physical properties show their potential for application as active layers in organic field-effect transistors.     

(2,1-a)-Indenofluorene derivatives: syntheses, X-ray structures, optical and electrochemical properties

Two novel fluorophores based on the (2,1-a)-indenofluorenyl backbone, dispiro[fluorene-9,11'-indeno[2,1-a]fluorene-12',9'-fluorene], (2,1-a)-DSF-IF and 11,12-dihydroindeno[2,1-a]fluorene (2,1-a)-IF have been prepared through original and efficient synthetic approaches. After consideration of synthetic features, the structural, optical and electrochemical properties of these new blue/violet emitters have been studied in detail by a combined experimental and theoretical approach. The properties of the (2,1-a)-DSF-IF and (2,1-a)-IF are also compared to those of their corresponding positional isomers based on the (1,2-b)-indenofluorenyl backbone and those of related dispirofluorene heteroacenes.     

Synthesis of Alternating Donor–Acceptor Ladder‐Type Molecules and Investigation of Their Multiple Charge‐Transfer Pathways

We describe the synthesis as well as the optical and charge‐transport properties of a series of donor–acceptor (D‐A) ladder‐type heteroacenes. These molecules are stable, soluble, and contain up to 24 fused rings. Structural analyses indicated that the backbones of S 10r and Se 10r are bent in single crystals. The three 10‐ring heteroacenes were functionalized with thiol anchoring groups and used for single‐molecular conductance measurements. The highest conductance was observed for molecular wires containing a benzoselenadiazole (BSD) moiety, which exhibits the narrowest band gap. Multiple charge‐transport pathways were observed in molecular wires containing either benzothiadiazole (BTD) or BSD. The conductance is a complex function of both energy gap and orbital alignment.     

Putting the 'N' in ACENE: pyrazinacenes and their structural relatives

Acenes have emerged as an important class of organic electronic material. Related heteroatom-substituted compounds, or heteroacenes, introduce an important means for modulating properties and improving materials' stability. In this perspective, we will review the historical origins of the heteroacenes and discuss recent progress in the field of acene and related compounds containing fused 1,4-diazabenzene units, i.e. pyrazine, also known as the 'pyrazinacenes'. We focus not only on the types of materials that have been prepared but also on their chemical and physical properties, including synthetic procedures, electronic properties, self-assembly characteristics, and we also introduce some of the computational studies aimed at understanding the more unusual behaviours of this group of compounds, such as protic tautomerism and aromaticity/antiaromaticity.     

Conjugated ladder-type heteroacenes bearing pyrrole and thiophene ring units: facile synthesis and characterization

Ladder-type heteroacenes containing pyrrole and thiophene rings, dibenzo[b,b']thieno[2,3-f:5,4-f']-carbazoles (DBTCZ, 1), and diindolo[3,2-b:2',3'-h]benzo[1,2-b:4,5-b']bis[1]benzothiophene (DIBBBT, 2), were facilely synthesized through proper precursors (7, 11, and 18) respectively. The key step is a triflic acid induced intramolecular electrophilic coupling reaction of corresponding aromatic methyl sulfoxides with activated aromatic building blocks, which enables regioselective ring closure. Both precursors (7 and 11) toward DBTCZ gave the symmetrical product but with solubilizing alkyl chains in two different fashions. DIBBBT was also synthesized as the extended ladder-type heteroacene with defined structure. These obtained heteroacenes are fully characterized (mass spectrometry, NMR, elemental analysis), and their X-ray analysis and optical and electrochemical properties are reported.     

Non-classical heteroacenes: synthesis and properties of anthra[2,3-c:6,7-c']dithiophene derivatives

A new class of linear heteroacenes, anthra[2,3-c:6,7-c']dithiophenes, containing non-classical (non-Kekulé) thiophene in a 22-electron π-conjugated system have been prepared by electrochemical reduction. The electronic properties have been studied by DFT calculations and spectroelectrochemistry, supporting the formation of a triplet electronic structure.     

Layered Electron Acceptors by Dimerization of Acenes End‐ Capped with 1,2,5‐Thiadiazoles

Layered electron acceptors D1 – 4 equipped with terminal 1,2,5‐thiadiazole groups have been constructed using a one‐pot protocol of acene dimerization. Their molecular structures are determined using single‐crystal X‐ray diffraction analysis. Photophysical and electrochemical properties of these molecules present a marked dependence on conjugation length and molecular geometry. An aggregation‐induced emission peak and an intramolecular excimer emission (IEE) band were observed for D2 and D4 , respectively. This work paves the way for the efficient synthesis of layered heteroacenes.     

General synthesis of thiophene and selenophene-based heteroacenes

[reaction: see text] A new intramolecular triple cyclization of bis(o-haloaryl)diacetylenes, via dilithiation followed by reaction with chalcogen elements, produces pi-conjugated compounds containing heterole-1,2-dichalcogenin-heterole fused tricyclic skeletons. The subsequent dechalcogenation with copper metal affords a series of thiophene- and selenophene-based heteroacenes.     

Layered Thiadiazoloquinoxaline‐Containing Long Pyrene‐Fused N‐Heteroacenes

Three thiadiazoloquinoxaline‐containing long pyrene‐fused N‐heteroacenes with 8, 13, and 18 rings were designed and synthesized. They show high electron affinities (EAs) of approximately 4.1 eV, which were derived from the onset of the reduction peaks in cyclic voltammetry. Crystal structure analysis revealed in‐plane extension through close contacts between thiadiazole units as well as layered packing, enabling in‐plane and interlayer electron transport. Organic field‐effect transistor devices provided electron mobilities, which suggest a potential way to enhance the charge transport in long N‐heteroacenes.     

Construction of new heteroacenes based on benzo[b]thieno[2,3-d]thiophene / quinoline or 1,8-naphthyridine systems using the Friedländer reaction

Two new classes of heteroacenes, namely benzo[4′,5′]thieno[2′,3′:4,5]thieno[3,2-b]quinolines and benzo[4′,5′]thieno[2′,3′:4,5]thieno[3,2-b][1,8]naphthyridines, have been formed using the Friedländer reaction to annulate the benzo[b]thieno[2,3-d]thiophene scaffold to quinoline or 1,8-naphthyridine fragments. In accordance with this synthetic strategy, benzo[b]thieno[2,3-d]thiophen-3(2H)-ones were treated with 2-aminobenzaldehydes or 2-aminonicotinaldehyde in the presence of pyrrolidine in glacial acetic acid at reflux to give the desired quinoline- or 1,8-naphthyridine-fused compounds, respectively. The optical and electrochemical properties of selected heteroacenes were determined.     

Effect of alicyclic ring size on the photophysical and photochemical properties of bis(arylidene)cycloalkanone compounds

A series of bis(arylidene)cycloalkanone compounds based on cyclobutanone, cyclopentanone, cyclohexanone and cycloheptanone, C4-C7, respectively, with a D-π-A-π-D structure containing the same donor and acceptor but different alicyclic rings was prepared. The effects of alicyclic ring size on the photophysical, photochemical and electrochemical properties of these compounds were investigated systematically. We found that an increase of the number of carbons in the central alicyclic ring leads to changes in geometry, which has significant effects on the conjugation, and photophysical and photochemical properties. These effects include decreases in the fluorescence quantum yield, transient lifetimes, peak extinction coefficients, and the singlet oxygen quantum yield with the increase of the ring size. The one-photon absorption spectra, the two-photon absorption (2PA) spectra, and the fluorescence spectra all show a hypsochromic shift with increasing ring size. The results of this study provide guidance for the design of new cycloketone-based D-π-A-π-D 2PA compounds for photopolymerization and photodynamic therapy applications.     

磷杂Fries重排反应用于合成2-芘基膦化合物

芘具有良好的刚性平面和高的荧光量子产率,是有机光电材料研究中重要的结构单元,由于其电子结构特点,芘的2位官能团化非常困难.利用易得的1-芘醇和H-亚磷酸酯或有机磷氯化合物合成了一系列1-芘基磷酸酯化合物,经磷杂Fries重排反应在温和条件下实现了芘2位的磷酰化,并得到相应的2-磷酰基芘衍生物.该类化合物还为新型含磷共轭化合物芘并1,3-氧杂磷杂环戊二烯的研究奠定了基础.本研究不但为芘类化合物的官能团化提供了一个新方法,而且为新型含磷共轭化合物的设计与合成开辟了新路线,并对合成的新型芘类化合物的紫外吸收和荧光发射等性质进行了初步测定.     

Dimesitylboryl‐Decorated Azaarene: Synthesis,Enhanced Stability and Optoelectronic Property

The instability of large acenes and analogues usually limits their wide potentials in organic devices. Thus, effectively constructing large acenes or heteroacenes and examining their optoelectronic properties are of great interest. We herein describe the synthesis, optoelectronic behaviors and electroluminescent property of dimesitylboryl‐decorated azaarene 5 and its homologue 7 . The former emits strong green fluorescence in non‐polar solvents but yellow light in polar solvents. The latter emits a blue light in various organic solvents. Moreover, their electrochemical behavior, photostability and electroluminescent property were further studied in a comparative manner, and the experimental findings suggest that the desired heteroarenes are appealing materials for fabricating electroluminescent devices.     

Preparation and characterization of Ni(dpedt)(pddt) and Ni(dpedt)(pddt)·CS2, where dpedt is diphenylethylenedithiolate and pddt is 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate

The unsymmetrical nickel 1,2-dithiolene complex based on diphenylethylenedithiolate (dpedt) and 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate (pddt) was prepared and characterized. Depending on the conditions of crystallization, it is possible to obtain the complex in two different crystalline forms. X-ray structure studies recognize these forms as Ni(dpedt)(pddt) and Ni(dpedt)(pddt)·CS₂. The experimental optical and electrochemical parameters are in a good agreement with the calculated ones, using the corresponding parameters of the symmetrical complexes, Ni(dpedt)₂ and Ni(pddt)₂. The HOMO and LUMO energy levels, obtained from optical and electrochemical measurements, are very close to the Fermi energy of (metallic) Au. The chemical and electrochemical properties of both forms showed that they are stable in air and could be candidate materials for optics and electronics.     

Unsymmetrical Pyrene‐Fused Phthalocyanine Derivatives: Synthesis,Structure, and Properties

Novel pyrene‐fused unsymmetrical phthalocyanine derivatives 2,3,9,10,16,17‐hexakis(2,6‐dimethylphenoxy)‐22,25‐diaza(2,7‐di‐tert‐butylpyrene)[4,5]phthalocyaninato zinc complex Zn[Pc(Pz‐pyrene)(OC₈H₉)₆] ( 1 ) and 2,3,9,10‐tra(2,6‐dimethylphenoxy)‐15,18,22,25‐traza(2,7‐di‐tert‐butylpyrene)[4,5]phthalocyaninato zinc compound Zn[Pc(Pz‐pyrene)₂(OC₈H₉)₄] ( 2 ) were isolated for the first time. These unsymmetrical pyrene‐fused phthalocyanine derivatives have been characterized by a wide range of spectroscopic and electrochemical methods. In particular, the pyrene‐fused phthalocyanine structure was unambiguously revealed on the basis of single crystal X‐ray diffraction analysis of 1 , representing the first structurally characterized phthalocyanine derivative fused with an aromatic moiety larger than benzene.     

Synthesis,Structural Characterization,and Optical Properties of Benzene-Fused Tetracyclic and Pentacyclic Stiboles

The expectation that antimony (Sb) compounds should display phosphorescence emissions based on the “heavy element effect” prompted our interest in the introduction of antimony to a biaryl as the bridging atom in a fused heterole system. Herein, the synthesis, molecular structures, and optical properties of novel benzene-fused heteroacenes containing antimony or arsenic atoms are described. The stiboles and arsole were prepared by the condensation of dibromo(phenyl)stibane or dichloro(phenyl)arsine with dilithium intermediates derived from the corresponding dibromo compounds. Nuclear magnetic resonance (NMR) spectroscopy and X-ray crystal analysis revealed that the linear pentacyclic stibole was highly symmetric in both the solution and crystal states. In contrast, the curved pentacyclic stibole adopted a helical structure in solution, and surprisingly, only M helical molecules were crystallized from the racemate. All synthesized compounds produced very weak or no emissions at room temperature or in the solid state. In contrast, the linear penta- and tetracyclic stiboles exhibited clear phosphorescence emissions in the CHCl₃ frozen matrix at 77 K under aerobic conditions.     

Synthesis of ladder-type pi-conjugated heteroacenes via palladium-catalyzed double N-arylation and intramolecular O-arylation

Ladder-type heteroacenes containing pyrrole or furan rings, indolo[3,2-b]carbazoles and dibenzo[d,d']benzo[1,2-b:4,5-b']difurans, were effectively synthesized from the common intermediates, 2,5-bis(o-chloroaryl)hydroquinones. The key reactions are palladium-catalyzed double N-arylation of aniline and intramolecular O-arylation, which enable regioselective ring closure. In addition to the parent indolo[3,2-b]carbazole and dibenzo[d,d']benzo[1,2-b:4,5-b']difuran, their derivatives with an alkyl or cyano group were first synthesized. Photophysical and electrochemical studies showed that the obtained heteroacenes have lower HOMO energy levels and larger band gaps than the corresponding hydrocarbon acene, pentacene. An X-ray analysis of dibenzo[d,d']benzo[1,2-b:4,5-b']difuran revealed that it was packed in herringbone fashion.     

具有双极性端枝的3D结构化合物的合成及光学性能

通过Friedel-Crafts和Suzuki等反应合成了4种由核心和D-π-A双极性端基组成的3D结构类树枝状化合物, 并采用热重分析(TGA), 差热扫描量热分析和循环伏安等手段对其进行了表征. 结果表明, 该类化合物具有良好的热稳定性和电化学稳定性; 核的引入大大降低了端基D-π-A固态时分子间的聚集效应. 分子内电荷转移(ICT)导致化合物溶剂化效应的产生, 且其发光强度随着溶剂极性的变化而改变, 呈现正、 负溶致动力学现象.     

Thiophene- and selenophene-based heteroacenes: combined quantum chemical DFT and spectroscopic Raman and UV-Vis-NIR study

In this article, we report the characterization of a series of thiophene- and selenophene-based heteroacenes, materials with potential applications in organic electronics. In contrast to the usual alpha-oligothiophenes, these annelated oligomers have a larger band gap than most semiconductors currently used in the fabrication of organic field-effect transistors (OFETs) and therefore they are expected to be more stable in air. The synthesis of these fused-ring molecular materials was motivated by the notion that a more rigid and planar structure should reduce defects (such as torsion about single bonds between alpha-linked units or S-syn defects) and thus improve pi-conjugation for better charge-carrier mobility. The conjugational properties of these heteroacenes have been investigated by means of FT-Raman spectroscopy, revealing that pi-conjugation increases with the increasing number of annelated rings. DFT and TDDFT quantum chemical calculations have been performed, at the B3LYP/6-31G** level, to assess information regarding the minimum-energy molecular structure, topologies, and absolute energies of the frontier molecular orbitals around the gap, vibrational normal modes related to the main Raman features, and vertical one-electron excitations giving rise to the main optical absorptions.