Seth C. Rasmussen

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.

Corrosion Control Coatings for Aluminum Alloys Based on Neutral and n-Doped Conjugated Polymers

Conjugated polymers (CPs) continue to be of interest for use as components of corrosion control coatings. For aluminum alloys, however, there is controversy and uncertainty regarding the protection mechanism(s), or indeed even whether corrosion protection by a CP is possible. Recent results from our laboratory indicate that, for an aluminum alloy coated with the oxidized form of polypyrrole (PPy), a passivation mechanism is not likely and that the dopant release mechanism may not be effective, especially in the presence of oxygen. An alternative approach is to utilize the neutral or reduced (n-doped) form of a conjugated polymer to cathodically protect the alloy and/or to serve as an oxygen scavenging coating. The CP coatings and alloy studied were neutral PPy and neutral or n-doped poly(2,3-dihexylthieno[3,4-b]pyrazine) on AA 2024-T3. Results from the scanning vibrating electrode technique and galvanic coupling measurements are presented to demonstrate the efficacy of this approach.

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.

How Glass Changed the World

Origins of glass: Myth and known history.- Development and growth of glass through the Roman period.- Reinventing an old material: Venice and the new glass.- Applications to chemical apparatus.- Impact on society and its effect on chemical progress.

The 18-electron rule and electron counting in transition metal compounds: theory and application

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.

Structure–function relationships in conjugated materials containing tunable thieno[3,4-b]pyrazine units

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 design and preparation of transition metal triad systems for excited-state charge separation

Abstract A series of multimetal complexes have been prepared with the intent of mimicking the charge separation process that occurs in photosynthesis. The systems have three component parts: antenna or absorbing fragment, electron donor, and electron acceptor. Synthetic modification of these components and the spacers which covalently couple these components will be discussed in terms of the thermodynamics and kinetics leading to the formation and lifetime of the charge-separated state. Systems with polyazine ruthenium(II) antenna, cyanoferrate(II) electron donors and a viologen electron acceptors will be described which have a lifetime of 37–86 ns.

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.

Tuning the Light Absorption of Donor–Acceptor Conjugated Polymers: Effects of Side Chains and ‘Spacer’ Units in Thieno[3,4-b]pyrazine-Fluorene Copolymers

Four donor–acceptor (D-A) copolymers of 2,3-difunctionalized thieno[3,4-b]pyrazine (TP) and 9,9-dioctylfluorene were prepared in order to illustrate the ability to tune the electronic and optical properties of TP-based D-A polymers by the choice of side chains on the TP unit. In addition, analogous polymers were prepared with and without thiophene spacer units in order to allow discussion of their effect on the material properties. This combination of effects allowed tuning of the band gap over the range of 1.6–2.1 eV. Full optical and electrochemical characterization is reported for all materials, as well as initial photovoltaic device data for representative materials.

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.