High Throughput Determination of Stern Volmer Quenching Constants for Common Photocatalysts and Quenchers

Mechanistic information on reactions proceeding via photoredox catalysis has enabled rational optimizations of existing reactions and revealed new synthetic pathways. One essential step in any photoredox reaction is catalyst quenching via photoinduced electron transfer or energy transfer with either a substrate, additive, or co-catalyst. Identification of the correct quencher using Stern-Volmer studies is a necessary step mechanistic understanding; however, such studies are often cumbersome, low throughput and require specialized luminescence instruments. This report describes a high throughput method to rapidly acquire series of Stern-Volmer constants, employing readily available fluorescence plate readers and 96 well-plates. By leveraging multi-channel pipettors or liquid dispensing robots in combination with fast plate readers, the sampling frequency for quenching studies can be improved by several orders of magnitude. This new high-throughput method enabled the rapid collection of 220 quenching constants for a library of 20 common photocatalysts with 11 common quenchers. The extensive Stern-Volmer constants table generated greatly facilitates the systematic comparison between quenchers and can provide guidance to the synthetic community interested in designing and understanding catalytic photoredox reaction

Synthesis, physical properties, and chemistry of donor/acceptor substituted pentacenes

Pentacenes bearing electron donating and/or withdrawing groups, namely methoxy, dialkylamino-, and nitroaryl moieties, are synthesized to afford polarized pentacenes. The optical, electrochemical, and chemical properties of these derivatives are explored. The cycloaddition reaction of selective derivatives with tetracyanoethylene (TCNE) is explored, and the experimental results are rationalized on the basis calculations using density functional theory (DFT). X-ray crystallographic data provides insight molecular structure and intermolecular interactions present in the solid-state.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Aryl substitution of pentacenes

A series of 11 new pentacene derivatives has been synthesized, with unsymmetrical substitution based on a trialkylsilylethynyl group at the 6-position and various aryl groups appended to the 13-position. The electronic and physical properties of the new pentacene chromophores have been analyzed by UV–vis spectroscopy (solution and thin films), thermoanalytical methods (DSC and TGA), cyclic voltammetry, as well as X-ray crystallography (for 8 derivatives). X-ray crystallography has been specifically used to study the influence of unsymmetrical substitution on the solid-state packing of the pentacene derivatives. The obtained results add to our ability to better predict substitution patterns that might be helpful for designing new semiconductors for use in solid-state devices

Alkyne Benzannulation Reactions For The Synthesis Of Novel Aromatic Architectures

Conspectus: Aromatic compounds and polymers are integrated into organic field effect transistors, light-emitting diodes, photovoltaic devices, and redox-flow batteries. These compounds and materials feature increasingly complex designs, and substituents influence energy levels, bandgaps, solution conformation, and crystal packing, all of which impact performance. However, many polycyclic aromatic hydrocarbons of interest are difficult to prepare because their substitution patterns lie outside the scope of current synthetic methods, as strategies for functionalizing benzene are often unselective when applied to naphthalene or larger systems. For example, cross-coupling and nucleophilic aromatic substitution reactions rely on prefunctionalized arenes, and even directed metalation methods most often modify positions near Lewis basic sites. Similarly, electrophilic aromatic substitutions access single regioisomers under substrate control. Cycloadditions provide a convergent route to densely functionalized aromatic compounds that compliment the above methods. After surveying cycloaddition reactions that might be used to modify the conjugated backbone of poly(phenylene ethynylene)s, we discovered that the Asao-Yamamoto benzannulation reaction is notably efficient. Although this reaction had been reported a decade earlier, its scope and usefulness for synthesizing complex aromatic systems had been under-recognized. This benzannulation reaction combines substituted 2-(phenylethynyl)benzaldehydes and substituted alkynes to form 2,3-substituted naphthalenes. The reaction tolerates a variety of sterically congested alkynes, making it well-suited for accessing poly- and oligo(ortho-arylene)s and contorted hexabenzocoronenes. In many cases in which asymmetric benzaldehyde and alkyne cycloaddition partners are used, the reaction is regiospecific based on the electronic character of the alkyne substrate. Recognizing these desirable features, we broadened the substrate scope to include silyl- and halogen-substituted alkynes. Through a combined experimental and computational approach, we have elucidated mechanistic insight and key principles that govern the regioselectivity outcome of the benzannulation of structurally diverse alkynes.We have applied these methods to prepare sterically hindered, shape-persistent aromatic systems, heterocyclic aromatic compounds, functionalized 2-aryne precursors, polyheterohalogenated naphthalenes, ortho-arylene foldamers, and graphene nanoribbons. As a result of these new synthetic avenues, aromatic structures with interesting properties were uncovered such as ambipolar charge transport in field effect transistors based on our graphene nanoribbons, conformational aspects of ortho-arylene architectures resulting from intramolecular ?-stacking, and modulation of frontier molecular orbitals via protonation of heteroatom containing aromatic systems. Given the availability of many substituted 2-(phenylethynyl)benzaldehydes and the regioselectivity of the benzannulation reaction, naphthalenes can be prepared with control of the substitution pattern at seven of the eight substitutable positions. Researchers in a range of fields are likely to benefit directly from newly accessible molecular and polymeric systems derived from polyfunctionalized naphthalenes

On- and Off-Cycle Catalyst Cooperativity in Anion-Binding Catalysis

Chiral, neutral H-bond donors have found widespread use as catalysts in enantio­selective reactions involving ion-pair intermediates. Herein, a systematic mechanistic study of a proto­typical anion-binding reaction, the thiourea-catalyzed enantio­selective alkylation of α-chloro­ethers, is detailed. This study reveals that the catalyst resting state is an inactive dimeric aggregate that must dissociate and then reassemble to form a 2:1 catalyst–substrate complex in the rate-determining transition structure. Insight into this mode of catalyst cooperativity sheds light on the practical limitations that have plagued many of the H-bond donor-catalyzed reactions developed to date and suggests design strategies for new, highly efficient catalyst structures

Synthesis and Properties of Isomerically Pure Anthrabisbenzothiophenes

The synthesis of three heptacyclic heteroacenes is described, namely anthra[2,3-<i>b</i>:7,6-<i>b</i>′]bis[1]benzothiophenes (ABBTs). A stepwise sequence of aldol reactions provides regiochemical control, affording only the <i>syn</i>-isomer. The ABBTs are characterized by X-ray crystallography, UV–vis absorption, and emission spectroscopy, as well as cyclic voltammetry. Field effect transistors based on solution-cast thin films of ABBT derivatives exhibit charge-carrier mobilities of as high as 0.013 cm²/(V s)