An official website of the United States government
Abstract Herein we report the synthesis and characterization of four donor/acceptor‐fuseds‐indacenes via the late‐stage oxidation of a family of unsymmetrical benzofuran/benzothiophene‐s‐indacene regioisomers. A thorough study of their properties through experimental and computational analysis has revealed the effect of asymmetry on the molecular properties associated with antiaromaticity, as well as a strong correlation between antiaromaticity and intramolecular charge transfer (ICT). The strength of the charge transfer depends on the fusion orientation of the donor and acceptor motifs relative to thes‐indacene core. The two most antiaromatic oxidized isomers exhibit strong evidence of ICT with 30 and 40 nm solvatochromic shifts.
more »
« less
Synthesis and Properties of Benzo‐Fused Indeno[2,1‐ c ]fluorenes
Abstract A set of fully‐conjugated indenofluorenes has been synthesized and confirmed by solid‐state structure analysis. The indeno[2,1‐c]fluorenes and their benzo‐fused analogues all contain the antiaromaticas‐indacene core. The molecules possess high electron affinities and show a broad absorption that reaches into the near‐IR region of the electromagnetic spectrum. All of the featured compounds reversibly accept up to two electrons as revealed by cyclic voltammetry. Analysis of molecule tropicity using NICS‐XY scan calculations shows that, while theas‐indacene core is less paratropic thans‐indacene, benz[a]‐annulation further reduces the antiaromaticity of the core. Antiaromatic strength of theas‐indacene core can also be tuned by the position of fusion of additional arenes on the outer rings.
more »
« less
- Award ID(s):
- 1625529
- PAR ID:
- 10102063
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – An Asian Journal
- Volume:
- 14
- Issue:
- 10
- ISSN:
- 1861-4728
- Format(s):
- Medium: X Size: p. 1737-1744
- Size(s):
- p. 1737-1744
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract We examine the effects of fusing two benzofurans tos‐indacene (indacenodibenzofurans, IDBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units. Synthesis via 3‐functionalized benzofuran yieldssyn‐IDBF andsyn‐IIDBF.syn‐IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character forsyn‐IIDBF. In the case of theanti‐isomers, synthesized via 2‐substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring‐opening reaction during the final dearomatization step. All the results are compared to the benzothiophene‐fused analogues and show that the increased electronegativity of oxygen in thesyn‐fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity. Forsyn‐IIDBF increased diradical character results from rearomati‐zation of the core naphthalene unit in order to relieve this paratropicity.more » « less
-
Abstract Fusion of aromatic subunits to stabilize an antiaromatic core allows the isolation and study of otherwise unstable paratropic systems. A complete study of a series of six naphthothiophene‐fuseds‐indacene isomers is herein described. Additionally, the structural modifications resulted in increased π–π overlap in the solid state, which was further explored through changing the sterically blocking mesityl group to (triisopropylsilyl)ethynyl in three derivatives. The computed antiaromaticity of the six isomers is compared to the observed physical properties, such as NMR chemical shift, UV‐vis, and CV data. We find that the calculations predict the most antiaromatic isomer and give a general estimation of the relative degree of paratropicity for the remaining isomers, when compared to the experimental results.more » « less
-
Abstract A recent publication by Wu and co‐workers demonstrated that the workhorse functional B3LYP tends to overemphasize the delocalization in antiaromatic molecules, leading to poor agreement between the calculated proton NMR values and the experimentally obtained numbers. Rather, they showed that the M11 functional affords the best agreement between theory and experiment. We have computationally re‐examined our previously published NICS‐XY scan data using M11‐determined geometries and find that, aside from the placement ofs‐indacene, the antiaromaticity trends for both sets of data are essentially identical.more » « less
-
Abstract Whether tetra‐tert‐butyl‐s‐indacene is a symmetricD2hstructure or a bond‐alternatingC2hstructure 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‐localizedC2hsymmetry, which is consistent with the expected strong antiaromaticity of TtB‐s‐indacene.more » « less
