The consequence of unpaired electrons in organic molecules has fascinated and confounded chemists for over a century. The study of open-shell molecules has been rekindled in recent years as new ...synthetic methods, improved spectroscopic techniques and powerful computational tools have been brought to bear on this field. Nonetheless, it is the intrinsic instability of the biradical species that limits the practicality of this research. Here we report the synthesis and characterization of a molecule based on the diindenob,ianthracene framework that exhibits pronounced open-shell character yet possesses remarkable stability. The synthetic route is rapid, efficient and possible on the gram scale. The molecular structure was confirmed through single-crystal X-ray diffraction. From variable-temperature Raman spectroscopy and magnetic susceptibility measurements a thermally accessible triplet excited state was found. Organic field-effect transistor device data show an ambipolar performance with balanced electron and hole mobilities. Our results demonstrate the rational design and synthesis of an air- and temperature-stable biradical compound.
Rhodium-Catalyzed Boron Arylation of 1,2-Azaborines Rudebusch, Gabriel E.; Zakharov, Lev N.; Liu, Shih-Yuan
Angewandte Chemie (International ed.),
August 26, 2013, Letnik:
52, Številka:
35
Journal Article
Recenzirano
Odprti dostop
A Sn‐phony in B! BN isosteres of biphenyl compounds are prepared through Rh‐catalyzed cross‐coupling between 2‐chloro‐1,2‐azaborines and arylstannanes (see scheme). The synthetic method should enable ...investigations of structure–activity relationships (SARs) by expanding the chemical space of the pharmaceutically relevant biphenyl structure through BN/CC isosterism.
The reduced and oxidized states of an open-shell diindenob,ianthracene (DIAn) derivative have been investigated by experimental and theoretical techniques. As a result of moderate biradical ...character and the ability of cyclopenta-fused scaffolds to stabilize both positive and negative charges, DIAn exhibits rich redox chemistry with four observable and isolable charged states. Structural and electronic properties of the DIAn system are brought to light by UV–vis–NIR and Raman spectroelectrochemical measurements. Aromatization of the diindeno-fused anthracene core upon successive single-electron injections is revealed through single-crystal X-ray diffraction of radical anion and dianion salts. We present a rare case where the pseudoaromatic/quinoidal ground state of a neutral biradical polycyclic hydrocarbon leads to a stable cascade of five redox states. Our detailed investigation of the transformation of molecular structure along all four redox events provides a clearer understanding of the nature of charge carriers in ambipolar organic field-effect transistors.
We report the preparation and characterization of a new class of quinoidal thienoacenes. The synthetic route is efficient, high-yielding and scalable with the potential for further functionalization. ...Single crystal X-ray diffraction reveals that, as size increases, the molecules pack in progressively closer 1D arrangements. The title compounds are shown to have amphoteric redox behaviour by cyclic voltammetry. The anion radicals are studied by EPR spectrometry and by computations. The electron-accepting nature, NIR absorption and the low-lying LUMO energies (ca.-4.0 eV) allude to potential use in materials applications.
Frontal ring-opening metathesis polymerization (FROMP) has potential for use in rapid fabrication of structural polymers. However, the high activity of the ruthenium catalyst used for FROMP has ...limited the working time to <1 h. We report the use of alkyl phosphites as inhibitors for Grubbs’ type catalysts to substantially extend working time. Subtle changes in alkyl phosphite structure are shown to impact both pot life and frontal velocity. Specifically, by varying phosphite structure and concentration, we are able to control pot life between 0.25 and 30 h while still allowing FROMP to proceed at velocities between 1 and 8 cm/min to yield fully cured thermoset polymers. These results are of interest for conventional ROMP synthesis and may open the way to new FROMP-based manufacturing possibilities.
Redox‐controlled dimerization of tetrathiafulvalene (TTF) derivatives is an important tool for achieving reversible assemblies. Herein, the synthesis and characterization of indacene–TTF hybrids, in ...which the central core is fused to naphtho or benzothieno units, are reported. The orientation of these units has a strong influence on the redox properties, with regard to the number of electrons involved in the first oxidation event and the ability of the oxidized forms to associate. The formation of mixed‐valence and π‐dimer complexes is turned off for those systems in which geometrical constraints provide nonplanar π‐systems. Introduction of bulky substituents presents another way of preventing association, as revealed by studies of indenofluorene and diindenoanthracene scaffolds with (triisopropylsilyl)ethynyl groups. Horner–Wadsworth–Emmons reactions present a general synthetic protocol to access superextended TTFs, by using diones of polycyclic conjugated hydrocarbons as substrates.
Tuning redox properties: The formation of mixed‐valence (MV) complexes (cation⋅neutral) and π‐dimers (cation⋅ cation) upon oxidation of indacene‐extended tetrathiafulvalenes can be finely tuned by elongating the acene core in various ways (see figure). Cyclic voltammetry experiments show that the associations are prevented either by distorting the π‐system from planarity or by introducing bulky substituent groups.
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The synthesis and characterization of indacenediselenophene (IDS) and diindenoselenophene (DIS), the selenophene-containing analogues of indacenedithiophene (IDT) and ...diindenothiophene (DIT), respectively, are described. Cyclic voltammetry reveals that IDS and DIS both undergo two one-electron reductions and a one-electron oxidation and have narrower HOMO/LUMO energy gaps when compared to their thiophene-containing counterparts. The UV–Vis spectrum of IDS exhibits a red-shifted absorbance maximum with respect to the sulfur-containing IDT, and single crystal XRD shows close C–Se contacts of 3.407Å (IDS) and close C–C contacts of 3.358Å (DIS).
Extended tetrathiafulvalenes with central diindenothienoacene cores were prepared and studied for their redox and spectroelectrochemical properties, which depended strongly on the orientation of the ...thiophene rings. The cations undergo remarkably strong associations, rendering them attractive as redox-controllable tectons in supramolecular chemistry, and in one case crystals were grown by electrocrystallization.
A fundamental understanding of the inherent electronic and magnetic properties of open-shell diradicaloids is essential so that these properties can be modified to create molecules that meet the ...potential needs of industry. However, there have been very few attempts to date to systematically accomplish this in diradicaloid compounds. Here, we present the synthetic, spectroscopic, and computational investigation of a series of molecules based on the diindeno1,2-b:1′,2′-ganthracene framework. Calculations suggest that by altering the transfer integral term, tab, we are able to manipulate the diradical character and, thus, ΔEST within this series of molecules. Experimentally determined values by superconducting quantum interference device (SQUID) magnetometry show that we can effectively “tune” ΔEST of the five derivatives within a narrow 1.6 kcal mol−1 range.
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•A family of diradicaloid structures composed of nine fused rings was prepared•Systematic structural variation leads to rational changes in diradical character•Fine-tuning of the singlet-triplet energy gap to within a narrow 1.6 kcal mol−1 range
The study of diradicaloid (open-shell) molecules offers new insights into the fundamental nature of the π-electron bond as well as new avenues of research regarding chemical reactivity and unusual electronic and/or magnetic properties in π-expanded systems. Although literature has recently seen an increase in the number of new diradicaloids, there are a few cases in which structural modification is made to the original scaffold to modify these properties. If the posited materials applications for organic diradicaloids are to come to fruition, the ability to incrementally and rationally change molecule properties while maintaining stability will be essential. Here, we show how to design new diradicaloids by tuning the transfer integral term, tab. This series of compounds maintain the same 2,6-anthraceno π-conjugation of the quinoidal-diradical core, with only minor alteration to the molecular geometry, thus following an approach based on structure refinement.
Haley and co-workers report the synthesis and physical characterization of a family of diradicaloids on the basis of the diindenoanthracene framework. Computations suggested that altering the external fused rings on both sides of the pentacyclic core would yield systematic changes in their open-shell properties, results that have been corroborated experimentally. This structure refinement approach provides a deeper understanding on how to tune the intrinsic properties of diradicaloid compounds in a rational and predictable manner.
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