The synthesis of the full family of bromothiazoles has been revisited in order to update and optimize their production. The species reported include 2-bromothiazole, 4-bromothiazole, 5-bromothiazole, 2,4-dibromothiazole, 2,5-dibromothiazole, 4,5-dibromothiazole, and 2,4,5-tribromothiazole, the majority of which are produced via sequential bromination and debromination steps. This complete family can now be produced without the use of elemental bromine, and the presented methods have allowed the physical and NMR spectroscopic characterization of the full family to be reported for the first time.

The preparation of tetrabutylammonium bis[2-(2-thienyl)-4,5-thiazoledithiolato]nickelate(1–) is presented as the first example of a new family of π-extended fused-ring metal dithiolenes. The optical, electronic, and structural properties of this complex have been characterized by UV/Vis-NIR spectroscopy, cyclic voltammetry, and X-ray crystallography. Comparison of these properties to the analogous nickel thiophenedithiolene shows that incorporation of nitrogen into the fused ring stabilizes the frontier orbitals of the thiazole-based complex, while preserving the planar geometry, electronic delocalization, and low-energy NIR absorption of the previous thiophene-based species.

A series of thiophene-fused nickel dithiolene complexes have been prepared via synthetic methods which allow the addition of peripheral aryl groups to the fused thiophene of the dithiolene ligand, thus providing access to a range of structural and electronic modifications to the dithiolene core. X-ray structural studies of the anionic complexes show that the peripheral aryl rings lie in near-perfect coplanarity to the dithiolene core and can form π-stacked columns with N-methylpyridinium cations. Density functional theory calculations show significant delocalization of the frontier orbital electron density into the peripheral aryl rings. The complexes exhibit tunable, intense near-IR (NIR) absorption in the range of 1076–1160 nm with molar absorptivity as high as 25100 M–1 cm–1 in solution. The electronic tunability as well as the desirable solid-state packing arrangements of these systems suggests significant potential as NIR-absorbing materials for optoelectronic applications.

The application of sterically hindered palladium catalysts to the regioselective hydrodebromination of 2,3,5-tribromothiophene has been studied in detail, including the effects of catalyst choice, solvent, reaction time, and temperature, as well as the method of NaBH4 addition and the role of chelating additives to effect NaBH4 solubility. Ultimately it was determined that the background reaction between NaBH4 and bromothiophenes is too facile to allow both total conversion and high selectivity. Optimized conditions finally allowed a selectivity of ca. 16:1 with overall conversion of 100%. However, complications of overdebromination under these conditions still limit the yield of the desired 2,3-dibromothiophene to 65%.

As a single system of chemical nomenclature is used worldwide, it is the universal language of chemistry and thus a critical component to effectively communicate with others in the field. Of course, in the same way that chemistry as a discipline covers a wide range of topics and classes of chemical compounds, the associated nomenclature of the field can also be subdivided into separate ‘dialects’, each of which addresses different classes of chemical species and contains its own set of specialized rules for the systemic naming of the included compounds. Polycyclic fused-ring arenes and heterocycles are classes of organic compounds that are finding growing importance in polymer chemistry, materials science, and pharmaceutical chemistry, yet the nomenclature of these compounds is rarely covered even in graduate texts and students are thus not taught how to apply this nomenclature as needed. As such, the current report aims to present the basic rules and application of fused-ring nomenclature such that one can apply it to most common cases.

Although thiophene-based materials are among the most widely studied conjugated materials for a number of technological applications, most discussions of emissive conjugated materials have focused on other systems, primarily due to the lower emission quantum yields of thiophene-based systems. Over the last decade, however, this has begun to change with the development of new highly emissive thiophene-based materials. In this review, we provide an overview of fluorescent thiophene-based materials and their applications, highlighting in particular the various methods employed to achieve highly emissive materials, as well as a variety of reported applications including fluorescent biomarkers and organic light emitting diodes.

The 18-electron rule and the corresponding methods for counting the total valence electrons of transition metal complexes are among the most useful basic tools in modern inorganic chemistry, particularly in its application to organometallic species. While in its simplest representation, the 18-electron rule is explained in that a closed, stable noble gas configuration of ns2(n-1)d10np6 is achieved with 18 valence electrons, this does not adequately explain the trends and exceptions seen in practice. As such, this report presents a deeper discussion of the 18-electron rule via molecular orbital models, stressing the roles of both σ- and π-bonding effects. This discussion thus aims to provide a better understanding of the relationship between electron count and stability, while also illustrating which factors can determine adherence (or not) to this commonly utilized rule. Lastly, the two common methods for electron counting (ionic and covalent models) are also presented with practical examples to provide the complete ability to apply the 18-electron rule.

A series of thieno[3,4-b]pyrazine-based oligomers were synthesized via Stille cross-coupling as models of electronic structure–function relationships in thieno[3,4-b]pyrazine-based conjugated materials. The prepared oligomers include two oligothieno[3,4-b]pyrazine series from monomer to trimer, as well as a series of mixed terthienyls in which the ratio of thieno[3,4-b]pyrazine to either thiophene or 3,4-ethylene-dioxythiophene has been varied. The full oligomeric series was then thoroughly investigated via photo-physical and electrochemical studies, along with theoretical calculations, in order to correlate the effect of conjugation length and oligomer composition with the resulting electronic and optical properties. The corresponding relationships revealed should then provide more advanced models for the elucidation of donor–acceptor interactions in both homopolymeric and copolymeric materials of thieno[3,4-b]pyrazines.

•Electropolymerization of thieno[3,4-b]pyrazine-based terthienyls gave polymeric thin films.•Materials produced exhibited band gaps ranging from 1.01 to 1.77 eV.•Band gaps and frontier orbitals can be tuned by choice of thieno[3,4-b]pyrazine side chains.The tunability of the electronic and optical properties of thieno[3,4-b]pyrazine-based terthienyls utilizing electron-donating and electron-withdrawing side chains and their corresponding polymers have been investigated. As previously shown for the thieno[3,4-b]pyrazine monomers, the addition of electron-donating groups results in higher HOMO–LUMO energies in the oligomers and higher Eg values in the resulting polymers. Correspondingly, the use of electron-withdrawing groups provides reduced HOMO–LUMO energies and lower Eg values. The electronic effect of the side chains is diminished in comparison to the thieno[3,4-b]pyrazine analogs. However, the application of electron-withdrawing functionalized thieno[3,4-b]pyrazine-based terthienyls appears to be a promising approach for the production of low Eg materials.

The application of dithieno[3,2-b:2′,3′-d]pyrroles (DTPs) in conjugated organic polymers has resulted in a variety of materials with reduced and low band gaps that exhibit high carrier mobilities, as well as enhanced solution and solid-state fluorescence. While DTP-based materials date back to the early 1990s, significant advances in the preparation and scope of these materials have been reported over the past decade. In this current report, we provide the first full review of DTP-based materials, highlighting in particular the recent advances made in the synthesis of both monomeric DTPs and their resulting materials, as well as the current progress of their application to various devices, including FETs, OPVs, OLEDs, and electrochromics.

Synthetic methods have been developed for the preparation of new 2,3-dihalo- and 2,3-ditriflato-5,7-bis(2-thienyl)thieno[3,4-b]pyrazines. From these reactive intermediates, a variety of new 2,3-difunctionalized 5,7-bis(2-thienyl)thieno[3,4-b]pyrazines have been produced as precursors to conjugated materials. Structural, electronic, and optical characterization of these new analogues illustrate the extent to which the electronic nature of the functional groups can be used to tune the electronic properties of these thieno[3,4-b]pyrazine-based terthienyl units.

A series of eight conjugated oligomers consisting of central dithieno[3,2-b:2′,3′-d]pyrroles (DTPs) end-capped with either thienyl or phenyl groups have been prepared from N-alkyl-, N-aryl-, and N-acyl-dithieno[3,2-b:2′,3′-d]pyrroles via Stille and Suzuki cross-coupling. The DTP-based quaterthiophene, N-phenyl-2,6-bis(2-thienyl)dithieno-[3,2-b:2′,3′-d]pyrrole was characterized via X-ray crystallography and was found to crystallize in the orthorhombic space group Pna21 with a = 10.8666(3) Å, b = 22.8858(6) Å, c = 7.4246(2) Å, and Z = 4. The full oligomeric series was thoroughly investigated via photophysical, electrochemical, and DFT calculations in order to correlate the cumulative effects of both aryl end-groups and N-functionalization on the resulting optical and electronic properties. Through such molecular tuning, it was found to be possible to modulate the HOMO energy by as much as 0.32 V and to generate highly fluorescent oligomers with solution fluorescence efficiencies as high as 92%.

A series of 2,3-difunctionalized 5,7-bis(2-thienyl)thieno[3,4-b]pyrazines containing electron-donating and electron-withdrawing side chains are reported to evaluate the potential tuning effect of the side chains on the electronic properties of these common terthienyl building blocks. In order to further study the resulting effects of such side chains in polymeric materials, the dihexyloxy-functionalized terthienyl was copolymerized with fluorene and its electronic properties compared with a number of analogous materials.

The application of fused-ring thieno[3,4-b]pyrazines in conjugated organic polymers has been found to be a powerful approach to the production of low band gap materials. While thieno[3,4-b]pyrazine-based materials date back to the early 1990s, significant advances in the preparation and scope of thieno[3,4-b]pyrazine-based materials have been reported in recent years, primarily in response to the increasing demand for reduced band gap materials in photovoltaic devices. In this review, we provide an overview of thieno[3,4-b]pyrazines and their application to conjugated materials, highlighting in particular the recent advances in the breadth of thieno[3,4-b]pyrazine building blocks and the promise of tuning materials to achieve optimal properties for specific applications.

The synthesis and characterization of the extended thieno[3,4-b]pyrazine analogues acenaphtho[1,2-b]thieno[3,4-e]pyrazine (3a), 3,4-dibromoacenaphtho[1,2-b]thieno[3,4-e]pyrazine (3b), 3-octylacenaphtho[1,2-b]thieno[3,4-e]pyrazine (3c), dibenzo[f,h]thieno[3,4-b]quinoxaline (4), and thieno[3′,4′:5,6]pyrazino[2,3-f][1,10]phenanthroline (5) are reported. Comparison of structural, electrochemical, and photophysical properties to those of simple thieno[3,4-b]pyrazines are provided in order to provide structure–function relationships within this series of compounds.

Dithieno[3,2-b:2′,3′-d]pyrrole-arylene copolymers have been prepared via Stille coupling to produce soluble, processable materials with good molecular weights. Solution and solid-state characterization of the copolymers is described, including photophysical and electrochemical studies, and these properties are compared to those of the parent poly(dithieno[3,2-b:2′,3′-d]pyrrole)s as well as analogous bithiophene-arylene copolymers. Poly(N-decyldithieno[3,2-b:2′,3′-d]pyrrole) and the newly generated copolymers were then used as emissive layers to fabricate initial LEDs, and the initial evaluation of their device performance is presented.

A new class of dithieno[3,2-b:2′,3′-d]pyrroles (DTPs) incorporating N-acyl groups have been prepared from 3-bromothiophene via copper-catalyzed amidation. The utilization of various electron-withdrawing acyl groups has allowed stabilization of the HOMO and LUMO energy levels of these popular building blocks for conjugated materials. The synthesis and characterization of this new class of compounds is described, including electrochemical and photophysical data for all compounds and X-ray structural data for the octanoyl, benzoyl, and cyclohexanoyl functionalized compounds. Initial polymers generated via electropolymerization are also reported.

Dithieno[3,2-b:2′,3′-d]pyrrole-based terthiophene and quaterthiophene analogues have been prepared from N-functionalized dithieno[3,2-b:2′,3′-d]pyrroles (DTPs) via Stille coupling. In order to thoroughly study the structure–function property relationships within these DTP-based oligothiophenes, an oligomer series was prepared that allows for the investigation of a number of structural effects including chain length, thiophene functionalization, and pyrrole N-functionalization. As pyrrole N-functionalization allows the incorporation of solubilizing side chains without the unwanted steric interactions that typically reduce backbone planarity, the effect of the bulk of these side chains on the optical properties in both solution and the solid state has been carefully investigated. The DTP-based quaterthiophene, N-tert-butyl-2,6-bis(2′-thienyl)dithieno[3,2-b:2′,3′-d]pyrrole was characterized via X-ray crystallography and was found to crystallize in the monoclinic space group P21/c with a = 17.489(4) Å, b = 7.8855(16) Å, c = 14.540(3) Å, β = 108.37(3)°, and Z = 4. The effect of side chains on the solid-state packing of the DTP-based quaterthiophenes was further investigated through X-ray diffraction of solution processed thin films. In comparison to the parent oligothiophenes, the resulting DTP-based systems exhibit enhanced fluorescence efficiencies in solution (up to 66%) and measurable solid-state emission from thin films.

A number of conjugated polymer systems can be generated via electropolymerization, including polythiophenes and polyanilines. While both have been reported to polymerize anodically via radical coupling, the presence of the aniline nitrogen plays a significant role in the mechanism of electropolymerization. In this study, the electropolymerization mechanism of 3-(N-alkylamino)thiophenes, structural hybrids of thiophene and aniline, is studied utilizing experimental and theoretical methods. Synthesis of new short chain 3-(N-alkylamino)thiophenes is discussed, and a mechanism of electropolymerization is proposed whereby oxidation occurs through removal of a nitrogen lone pair electron, followed by a chemical step resulting in radical contribution at the 2-position of the thiophene ring. Coupling of these final radical cations thus results in a typical poly(α−α′-thiophene) backbone.

The effect of electron-donating and electron-withdrawing side chains on the electronic properties of thieno[3,4-b]pyrazines and their corresponding homopolymers have been investigated. Contrary to common trends in polythiophene materials, the addition of electron-donating groups results in higher HOMO–LUMO energies in the monomers and higher Eg values in the resulting polymers. The use of electron-withdrawing groups, however, provides reduced HOMO–LUMO energies and lower Eg values. The application of electron-withdrawing functionalized thieno[3,4-b]pyrazines appears to be a promising new approach for the production of low Eg materials.

A new nickel complex consisting of extended thiophenedithiolene ligands has been synthesized. The complex has been characterized by UV–vis–NIR spectroscopy, mass spectrometry, cyclic voltammetry, and X-ray crystallography. The complex exhibits significant electron delocalization into the peripheral thiophene rings. The −1 complex displays diamagnetic behavior in the solid state, but is paramagnetic (S = 1/2) in solution. X-ray analysis shows a number of close contacts which could explain the diamagnetism.

The preparation of a new conjugated polymer with a low band gap of ∼0.5 eV has been accomplished via the electropolymerization of acenaphto[1,2-b]thieno[3,4-e]pyrazine.

Using new nitration protocols, we have been able to efficiently dinitrate 2,5-dihalothiophenes with yields of ∼80–95%. The resulting products 2,5-dibromo-3,4-dinitrothiophene (1), 2,5-dichloro-3,4-dinitrothiophene (2), 2-bromo-5-chloro-3,4-dinitrothiophene (3), as well as the analogous 2-bromo-3,4-dinitrothiophene (4), all crystallize easily allowing their characterization via X-ray crystallography. Crystallization of 1 occurs in the monoclinic space group C2/c with a = 14.547(3) Å, b = 7.3534(15) Å, c = 10.775(2) Å, β = 128.89(3)°, and Z = 4. Crystallization of 2 occurs in the tetragonal space group I-42d with a = 9.9398(14) Å, b = 9.9398(14) Å, c = 16.866(3) Å, and Z = 8. Crystallization of 3 occurs as a pseudo-merohedral twin in the triclinic space group P-1 with a = 7.340(5) Å, b = 8.094(5) Å, c = 9.112(5) Å, α = 82.059(5)°, β = 66.232(5)°, γ = 63.021(5)°, and Z = 2. Crystallization of 4 occurs in the triclinic space group P-1 with a = 7.1787(14) Å, b = 7.4092(15) Å, c = 8.3151(17) Å, α = 101.67(3)°, β = 96.00(3)°, γ = 116.13(3)°, and Z = 2. The structures of all compounds exhibit the formation of interesting solid-state assemblies due to halogen-bonding interactions between the halogen and nitro groups.

A series of eight conjugated oligomers consisting of central dithieno[3,2-b:2′,3′-d]pyrroles (DTPs) end-capped with either thienyl or phenyl groups have been prepared from N-alkyl-, N-aryl-, and N-acyl-dithieno[3,2-b:2′,3′-d]pyrroles via Stille and Suzuki cross-coupling. The DTP-based quaterthiophene, N-phenyl-2,6-bis(2-thienyl)dithieno-[3,2-b:2′,3′-d]pyrrole was characterized via X-ray crystallography and was found to crystallize in the orthorhombic space group Pna21 with a = 10.8666(3) Å, b = 22.8858(6) Å, c = 7.4246(2) Å, and Z = 4. The full oligomeric series was thoroughly investigated via photophysical, electrochemical, and DFT calculations in order to correlate the cumulative effects of both aryl end-groups and N-functionalization on the resulting optical and electronic properties. Through such molecular tuning, it was found to be possible to modulate the HOMO energy by as much as 0.32 V and to generate highly fluorescent oligomers with solution fluorescence efficiencies as high as 92%.

Although thiophene-based materials are among the most widely studied conjugated materials for a number of technological applications, most discussions of emissive conjugated materials have focused on other systems, primarily due to the lower emission quantum yields of thiophene-based systems. Over the last decade, however, this has begun to change with the development of new highly emissive thiophene-based materials. In this review, we provide an overview of fluorescent thiophene-based materials and their applications, highlighting in particular the various methods employed to achieve highly emissive materials, as well as a variety of reported applications including fluorescent biomarkers and organic light emitting diodes.

The application of fused-ring thieno[3,4-b]pyrazines in conjugated organic polymers has been found to be a powerful approach to the production of low band gap materials. While thieno[3,4-b]pyrazine-based materials date back to the early 1990s, significant advances in the preparation and scope of thieno[3,4-b]pyrazine-based materials have been reported in recent years, primarily in response to the increasing demand for reduced band gap materials in photovoltaic devices. In this review, we provide an overview of thieno[3,4-b]pyrazines and their application to conjugated materials, highlighting in particular the recent advances in the breadth of thieno[3,4-b]pyrazine building blocks and the promise of tuning materials to achieve optimal properties for specific applications.

A series of thieno[3,4-b]pyrazine-based oligomers were synthesized via Stille cross-coupling as models of electronic structure–function relationships in thieno[3,4-b]pyrazine-based conjugated materials. The prepared oligomers include two oligothieno[3,4-b]pyrazine series from monomer to trimer, as well as a series of mixed terthienyls in which the ratio of thieno[3,4-b]pyrazine to either thiophene or 3,4-ethylene-dioxythiophene has been varied. The full oligomeric series was then thoroughly investigated via photo-physical and electrochemical studies, along with theoretical calculations, in order to correlate the effect of conjugation length and oligomer composition with the resulting electronic and optical properties. The corresponding relationships revealed should then provide more advanced models for the elucidation of donor–acceptor interactions in both homopolymeric and copolymeric materials of thieno[3,4-b]pyrazines.

Dithieno[3,2-b:2′,3′-d]pyrrole-based terthiophene and quaterthiophene analogues have been prepared from N-functionalized dithieno[3,2-b:2′,3′-d]pyrroles (DTPs) via Stille coupling. In order to thoroughly study the structure–function property relationships within these DTP-based oligothiophenes, an oligomer series was prepared that allows for the investigation of a number of structural effects including chain length, thiophene functionalization, and pyrrole N-functionalization. As pyrrole N-functionalization allows the incorporation of solubilizing side chains without the unwanted steric interactions that typically reduce backbone planarity, the effect of the bulk of these side chains on the optical properties in both solution and the solid state has been carefully investigated. The DTP-based quaterthiophene, N-tert-butyl-2,6-bis(2′-thienyl)dithieno[3,2-b:2′,3′-d]pyrrole was characterized via X-ray crystallography and was found to crystallize in the monoclinic space group P21/c with a = 17.489(4) Å, b = 7.8855(16) Å, c = 14.540(3) Å, β = 108.37(3)°, and Z = 4. The effect of side chains on the solid-state packing of the DTP-based quaterthiophenes was further investigated through X-ray diffraction of solution processed thin films. In comparison to the parent oligothiophenes, the resulting DTP-based systems exhibit enhanced fluorescence efficiencies in solution (up to 66%) and measurable solid-state emission from thin films.