This report describes the synthetic strategies toward and optoelectronic properties of substructures of the non-natural, planar carbon networks graphyne and graphdiyne, which are based on the ...dehydrobenzo12annulene and dehydrobenzo18annulene framework, respectively.
The literature has seen a large increase in the number of new carbon‐based organic diradicals/diradicaloids in recent years. While a plethora of new and exciting structures have been created, there ...seemingly is a gap in knowledge of what fundamental electronic parameters are in play and thus how to rationally manipulate said parameters to “fine tune” the resultant diradical properties. Since 2014, the Haley group has been exploring methods to systematically alter the diradical character and the singlet‐triplet energy gap in said class of molecules. Our entrance into organic diradicals began with the π‐expansion of the benzene core of indeno1,2‐bfluorene up to the anthracene core of diindenoanthracene (DIAn). DIAn possessed moderate diradical character (y = 0.62) with a surprising level of stability (more than 2 months in solution). From this molecular blueprint for producing stable diradicals, the Haley lab has investigated how to fine tune diradical properties via structural changes in two key positions: (a) the length of the acene core and (b) thoughtful exchange of the outer arenes. With this strategy at our disposal, we can make large scale changes to the diradical character index and singlet‐triplet energy gap through changing the core length, and these properties can be further fine‐tuned in a series of closely related diradicals by careful exchange of the outer arenes utilizing the straightforward methods described in this mini‐review.
The blueprint for stable organic diradicals based on a diindenoacene scaffold. There are two areas of potential modification (a) altering the core length (shown in blue) and/or (b) outer arene exchange (shown in orange).
Highly conjugated hydrocarbons have attracted interest for use as active materials in electronic devices such as organic field effect transistors (OFET) and organic photovoltaics (OPV). In this ...Account, we review our progress in synthesizing and studying a new class of small molecules for potential use as organic semiconductors. The idea originated from prior research on octadehydrodibenz12annulene, as the system can undergo double transannular cyclization to yield the indeno1,2-bfluorene skeleton. Subsequent functionalization afforded the first stable, well-characterized indeno1,2-bfluorene derivatives, albeit in minute quantities (tens of milligrams). The preparation of these formally antiaromatic compounds has since been optimized: the new synthetic routes utilize inexpensive starting materials, involve robust and high-yielding transformations, and are amenable to considerably larger scale reaction. We have since researched the chemical space of indeno1,2-bfluorenes and related quinoidal structures by substitution with a number of functional groups and by permutation of the indenofluorene scaffold. These modifications have allowed us to explore fundamental concepts such as biradical character and antiaromaticity, important considerations when tuning electronic properties to yield functional organic materials. Altering the outer rings by exchange of carbocycles for heterocycles or by inclusion of additional rings as part of the fully conjugated skeleton is one strategy we have examined. Fusing these different aryl groups to s-indacene revealed a dependence of the antiaromaticity of the indacene core upon the outer group. Computational analysis of a series of indeno1,2-bfluorene derivatives uncovered an array of different levels of antiaromaticity in the core of the indeno1,2-bfluorene derivatives, with one of the benzothiophene derivatives calculated to be as antiaromatic as the parent s-indacene itself. Conversely, we have prepared compounds with expanded cores, starting with the naphthalene-based fluoreno4,3-cfluorene, which was produced through a similar route as the indeno1,2-bfluorene, using a dione as the key intermediate. Similar to indeno1,2-bfluorene, fluoreno4,3-cfluorene showed a closed shell ground state, with no evidence of open shell character even upon heating to 170 °C. Increasing the size of the quinoidal core to three rings afforded a diindenob,ianthracene (DIAn) derivative, a compound with a much more complex electronic picture. To produce DIAn, a new synthetic route was devised involving a Friedel–Crafts alkylation to form the five-membered ring and a DDQ oxidation to produce the final compound. DIAn displayed NMR signals that were broadened at room temperature and disappeared when heated, indicative of a molecule with significant biradical character. Extensive computational and experimental investigation verified the controllable expression of its biradical character, with DIAn best described with a ground state that lies between a closed shell compound and a open-shell singlet biradical, with ready access to a thermally populated triplet state.
Understanding and controlling the electronic structure of molecules is crucial when designing and optimizing new organic semiconductor materials. We report the regioselective synthesis of eight ...π-expanded diarenoindacene analogues based on the indeno1,2-bfluorene framework along with the computational investigation of an array of diareno-fused antiaromatic compounds possessing s-indacene, pentalene, or cyclobutadiene cores. Analysis of the experimental and computationally derived optoelectronic properties uncovered a linear correlation between the bond order of the fused arene bond and the paratropicity strength of the antiaromatic unit. The E red 1 for the pentalene and indacene core molecules correlates well with their calculated NICSπZZ values. The findings of this study can be used to predict the properties of, and thus rationally design, new diareno-fused antiaromatic molecules for use as organic semiconductors.
The conceptual connections between 4n Hückel antiaromaticity, disjoint orbitals, correlation energy, pro‐aromaticity and diradical character for a variety of extended π‐conjugated systems, including ...some salient recent examples of nanographenes and polycyclic aromatic radicals, are provided based on their 4nannulene peripheries. The realization of such structure–property relationships has led to a beneficial pedagogic exercise establishing design guidelines for diradicaloids. The antiaromatic fingerprint of the 4nannulene peripheries upon orbital interactions due to internal covalent connectors gives insights into the diradicaloid property of a diversity of π‐conjugated molecules that have fascinated chemists recently.
A conceptual electronic structure trip from 4n Hückel antiaromatics to diradicaloids and to more hierarchical complex molecular shapes made by internal covalent hybridization of the peripheral 4n π‐electron circuit is described. Focus is on the underlying physical organic chemistry implications.
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.
Of the five possible indenofluorene regioisomers, examples of a fully conjugated indeno1,2‐afluorene scaffold have so far remained elusive. This work reports the preparation and characterization of ...7,12‐dimesitylindeno1,2‐afluorene as a highly reactive species. Experimental and computational data support the notion of a molecule with pronounced diradical character that exists in a triplet ground state. As such, both NICS and ACID calculations suggest that the indeno1,2‐afluorene scaffold is weakly Baird aromatic. Reduction of the unstable red solid with Cs metal produces the dianion of the title compound, from which single crystals could be obtained and X‐ray data acquired, thus fully corroborating the proposed indeno1,2‐afluorene hydrocarbon core.
Not a matter of IF but when: Described is the preparation of the last elusive indenofluorene (IF) regioisomer. While the body of circumstantial spectroscopic data support formation of the highly reactive triplet diradicaloid, definitive structural proof is provided by X‐ray diffraction analysis of crystals of the dianion, obtained by reduction of the indeno1,2‐afluorene with Cs metal.
Recent Advances in Metallabenzene Chemistry Landorf, Christopher W.; Haley, Michael M.
Angewandte Chemie (International ed.),
June 12, 2006, Letnik:
45, Številka:
24
Journal Article
Recenzirano
Research into aromatic metallacycles, though discussed in the literature over the last quarter century, has undergone a major expansion since 2000. A wide variety of new metallabenzenes, encompassing ...new synthetic methods and new metal centers, is now available. New aromatic metallacycle topologies (iridanaphthalene, osmabenzynes) have been isolated and characterized. The first metallabenzene valence isomers (iridabenzvalenes, rhodabenzvalenes) and constitutional isomers (isoosmabenzenes) are now known. This review discusses the synthesis, chemistry, and physical properties of these intriguing aromatic compounds.
Chemical chameleons—with regard to properties normally associated with aromaticity—aptly describe metallabenzenes (see scheme for examples), as they exhibit delocalized bonding, possess downfield 1H NMR chemical shifts, and form arene‐coordination complexes, but are often distinctly nonplanar, undergo 4+2 cycloaddition reactions, and rearrange to form cyclopentadiene complexes. This Review describes their synthesis, chemistry, and unusual physical properties.
Whether tetra‐tert‐butyl‐s‐indacene is a symmetric D2h structure or a bond‐alternating C2h structure remains a standing puzzle. Close agreement between experimental and computed proton chemical ...shifts based on minima structures optimized at the M06‐2X, ωB97X‐D, and M11 levels confirm a bond‐localized C2h symmetry, which is consistent with the expected strong antiaromaticity of TtB‐s‐indacene.
The structure of tetra‐tert‐butyl‐s‐indacene is a computational challenge. Highly correlated methods and popular DFT functionals predict a bond‐delocalized D2h symmetry, but excellent agreement between experimental and computed proton chemical shifts suggests a true C2h geometry.
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