Molecular Tuning in Diaryl-Capped Pyrrolo[2,3-d:5,4-d']bisthiazoles: Effects of Terminal Aryl Unit and Comparison to Dithieno[3,2-b:2',3'-d]pyrrole Analogues.

A series of six conjugated oligomers consisting of a central pyrrolo[2,3-d:5,4-d']bisthiazole (PBTz) end-capped with either thienyl, furyl, or phenyl groups have been prepared from N-alkyl-and N-aryl-pyrrolo[2,3-d:5,4-d']bisthiazoles via Stille and Negishi cross-coupling. The full oligomeric series was thoroughly investigated via photophysical and electrochemical studies, in parallel with density functional theory (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 comparison with the analogous dithieno[3,2-b:2',3'-d]pyrrole (DTP) materials, the effect of replacing DTP with PBTz on the material HOMO energy and visible light absorption is quantified.

Probing the nature of donor-acceptor effects in conjugated materials: a joint experimental and computational study of model conjugated oligomers.

A series of model oligomers consisting of combinations of a traditional strong donor unit (3,4-ethylenedioxythiophene), a traditional strong acceptor unit (benzo[c][1,2,5]thiadiazole), and the ambipolar unit thieno[3,4-b]pyrazine were synthesized via cross-coupling methods. The prepared oligomers include all six possible dimeric combinations in order to characterize the extent and nature of donor-acceptor effects commonly used in the design of conjugated materials, with particular focus on understanding how the inclusion of ambipolar units influences donor-acceptor frameworks. The full oligomeric series was thoroughly investigated via photophysical and electrochemical studies, in parallel with density functional theory (DFT) calculations, in order to correlate the nature and extent of donor-acceptor effects on both frontier orbital energies and the desired narrowing of the HOMO-LUMO energy gap. The corresponding relationships revealed should then provide a deeper understanding of donor-acceptor interactions and their application to conjugated materials.

From Parkesine to Celluloid: The Birth of Organic Plastics.

The birth of modern organic plastics can be traced back to the mid-1800s with various semi-synthetic plastics derived from cellulose nitrate. Examples of such materials include Parkesine introduced by Alexander Parkes in 1860 and celluloid introduced by John Wesley Hyatt in 1870. The history and development of these early materials is presented, while also attempting to clarify the differences between the related materials collodion, Parkesine, and celluloid.

Pyrrolo[2,3-d:5,4-d']bisthiazoles: Alternate Synthetic Routes and a Comparative Study to Analogous Fused-Ring Bithiophenes.

New synthetic methods have been developed for the preparation of 4-alkyl- and 4-aryl-pyrrolo[2,3-d:5,4-d']bisthiazole (PBTz) building blocks from 2,4-thiazolidinedione. The resulting PBTz products have been fully characterized via structural, electronic, and optical methods, thus allowing full comparison to the previously reported dithieno[3,2-b:2',3'-d]pyrrole (DTP) analogues. Such comparisons then allow a detailed discussion of the relative electronic effects of the various methods utilized to tune the properties of the parent DTP building block.

Synthesis and Characterization of Bis[1]benzothieno[3,2-b:2',3'-d]pyrroles: Quantitative Effects of Benzannulation on Dithieno[3,2-b:2',3'-d]pyrroles.

The synthesis of four N-functionalized bis[1]benzothieno[3,2-b:2',3'-d]pyrroles (BBTPs) is reported in order to provide a more detailed characterization of these fused-ring units, as well as increase the scope of known BBTP units available for application to conjugated materials. The optical, electronic, and structural properties of the resulting BBTP units have been compared to the parent N-alkyl- and N-aryl-dithieno[3,2-b:2',3'-d]pyrroles (DTPs), as well as their corresponding 2,6-diphenyl derivatives, in order to fully quantify the relative electronic effects resulting from benzannulation of the parent DTP building block. Such comparative analysis reveals that benzannulation results in a red-shifted absorbance, but to a lesser extent than simple phenyl-capping of the DTP. More surprising is that benzannulation results in stabilization of the BBTP HOMO, compared to the destabilization normally observed with extending the conjugation length of the backbone.

Synthesis of Brominated Thiazoles via Sequential Bromination-Debromination Methods.

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.

Thiophene-Fused Nickel Dithiolenes: A Synthetic Scaffold for Highly Delocalized π-Electron Systems.

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.

Thieno[3,4-b]pyrazine-based oligothiophenes: simple models of donor-acceptor polymeric materials.

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.

2,3-Bis(2-pyridyl)thieno[3,4-b]pyrazine and its ruthenium(II) complexes: a new bidentate bridging ligand for enhanced metal-metal communication.

A new bidentate bridging ligand, bis(2-pyridyl)thieno[3,4-b]pyrazine is reported, along with its mono- and bi-metallic Ru(II) complexes as representative examples. Spectroscopic, electrochemical and X-ray crystallographic characterization of these species is reported, with the separation of the two Ru(III)/Ru(II) couples of the bimetallic complex suggesting better metal-metal communication than classical polypyridyl analogues.

Synthesis and characterization of thieno[3,4-b]pyrazine-based terthienyls: tunable precursors for low band gap conjugated materials.

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.

Molecular tuning in highly fluorescent dithieno[3,2-b:2',3'-d]pyrrole-based oligomers: effects of N-functionalization and terminal aryl unit.

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 Pna2(1) 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%.

Structural effects on the electronic properties of extended fused-ring thieno[3,4-b]pyrazine analogues.

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.

Solution and solid-state properties of highly fluorescent dithieno[3,2-b:2',3'-d]pyrrole-based oligothiophenes.

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 P2(1)/c with a = 17.489(4) Å, b = 7.8855(16) Å, c = 14.540(3) Å, ß = 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.

Conjugated and Conducting Organic Polymers: The First 150 Years.

Conductive organic polymers are most commonly generated from the oxidation or reduction of conjugated polymers. Although such conjugated polymers are typically viewed as modern materials, the earliest examples of these polymers date back to the early 19th century. The modern era of conjugated polymers began with the first reports of their conductive nature in the early 1960s. However, it was advances in the 1970s that brought particular focus to these materials with the first example of conductivity values in the metallic regime, for which the 2000 Nobel Prize in Chemistry was awarded to Hideki Shirakawa, Alan MacDiarmid, and Alan Heeger. Unfortunately, the historical narrative of these polymers is currently quite muddled in the primary literature, with various inaccuracies commonly propagated. In an effort to present a more accurate account as a resource for the field, the present report will review the first 150 years of the four primary parent polymers-polyaniline, polypyrrole, polyacetylene, and polythiophene, from their early origins in 1834 to their rapid development in the mid-1980s.

Reduced band gap dithieno[3,2-b:2',3'-d]pyrroles: new n-type organic materials via unexpected reactivity.

Direct addition of tetracyanoethylene to N-(p-hexylphenyl)dithieno[3,2-b:2',3'-d]pyrrole yields not only the aromatic mono- and bis-tricyanovinyl-substituted products but also a quinoidal product with dicyanomethylene groups. The analogous reaction with dithieno[3,2-b:2',3'-d]thiophene yields exclusively the aromatic mono-tricyanovinyl product. The aromatic and quinoidal products possess red-shifted absorptions, increased electron affinities, and favorable pi-stacking motifs in comparison to the unsubstituted oligomers.

Poly(acenaphtho[1,2-b]thieno[3,4-e]pyrazine): a new low band gap conjugated polymer.

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

Synthesis and characterization of new 2,3-disubstituted thieno[3,4-b]pyrazines: tunable building blocks for low band gap conjugated materials.

Synthetic methods have been developed for the preparation of new 2,3-dihalothieno[3,4-b]pyrazines, from which a variety of new 2,3-difunctionalized 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 the thieno[3,4-b]pyrazine unit.

Revisiting the Early History of Synthetic Polymers: Critiques and New Insights.

This essay seeks to clarify existing confusion in terminology regarding the history of polymers, plastics, and macromolecules, and explores various factors that complicate the early history of macromolecules. It also suggests reasons why materials such as polyaniline, an early fully synthetic polymer that found widespread commercial application in dyes, have not previously been treated in accounts of polymer history.

Poly(thieno[3,4-b]pyrazine-alt-2,1,3-benzothiadiazole)s: A New Design Paradigm in Low Band Gap Polymers.

A new design paradigm for the production of low band gap polymers is reported, in which an ambipolar unit exhibiting both donor and acceptor properties is combined with a conventional acceptor. As initial examples of this approach, the synthesis of two alternating copolymers of thieno[3,4-b]pyrazine and 2,1,3-benzothiadiazole via direct arylation polymerization is reported to give soluble, processable materials with band gaps of 0.97 and 1.05 eV. Although direct arylation polymerization has been previously used to synthesize donor-acceptor materials with band gaps below 1.5 eV, this represents only the second material generated by this polymerization method with a band gap below 1.0 eV.

Synthesis, Characterization, and Electropolymerization of Extended Fused-Ring Thieno[3,4-b]pyrazine-Based Terthienyls.

The synthesis, characterization, and electropolymerization of a series of extended fused-ring thieno[3,4-b]pyrazine-based terthienyls are reported. The target terthienyls contain a central extended thieno[3,4-b]pyrazine analogue containing 2-thienyl units at the reactive α-positions of the central thiophene. The extended fused-ring thieno[3,4-b]pyrazine analogues studied include acenaphtho[1,2-b]thieno[3,4-e]pyrazine, dibenzo[f,h]thieno[3,4-b]quinoxaline, and thieno[3',4':5,6]-pyrazino[2,3-f][1,10]phenanthroline. Comparison of the electrochemical and photophysical properties to simple thieno[3,4-b]pyrazine-based terthienyls and their polymeric analogues are reported in order to provide structure-function relationships within this series of compounds and materials.