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. 2016 Nov 30:7:13620.
doi: 10.1038/ncomms13620.

Stacked antiaromatic porphyrins

Ryo Nozawa  1 , Hiroko Tanaka  1 , Won-Young Cha  2 , Yongseok Hong  2 , Ichiro Hisaki  3 , Soji Shimizu  4 , Ji-Young Shin  1 , Tim Kowalczyk  5 , Stephan Irle  6 , Dongho Kim  2 , Hiroshi Shinokubo  1
Affiliations

Stacked antiaromatic porphyrins

Ryo Nozawa et al. Nat Commun. .

Abstract

Aromaticity is a key concept in organic chemistry. Even though this concept has already been theoretically extrapolated to three dimensions, it usually still remains restricted to planar molecules in organic chemistry textbooks. Stacking of antiaromatic π-systems has been proposed to induce three-dimensional aromaticity as a result of strong frontier orbital interactions. However, experimental evidence to support this prediction still remains elusive so far. Here we report that close stacking of antiaromatic porphyrins diminishes their inherent antiaromaticity in the solid state as well as in solution. The antiaromatic stacking furthermore allows a delocalization of the π-electrons, which enhances the two-photon absorption cross-section values of the antiaromatic porphyrins. This feature enables the dynamic switching of the non-linear optical properties by controlling the arrangement of antiaromatic π-systems on the basis of intermolecular orbital interactions.

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Figures

Figure 1
Figure 1. Structures of antiaromatic superphane 1 and norcorroles.
The bold lines in 3a and 3b indicate one of their 16 π-electronic circuits.
Figure 2
Figure 2. Synthesis and solid-state structure of 3b.
(a) Synthetic route to 3b, (b) oblique view of 3b and (c) top view of 3b (atomic displacement parameters set at 50% probability).
Figure 3
Figure 3. Synthesis and aromaticity of stacked norcorrole dimer 5b.
(a) Synthetic route to 5b (DMI=1,3-dimethyl-2-imidazolidinone), (b) molecular structure of 5b (atomic displacement parameters set at 50% probability; phenyl groups and hydrogen atoms omitted for clarity) and (c) NICS values of 3a and 5b at several points (mean values of two norcorrole units).
Figure 4
Figure 4. Stability of 5b and 4b.
Thermal decomposition experiments of 4b and 5b at 80 °C under air.
Figure 5
Figure 5. Optical properties of 4b and 5b.
(a) Absorption (bottom) and MCD (top) spectra of norcorrole monomer 4b in CH2Cl2 and (b) absorption (bottom) and MCD (top) spectra of norcorrole dimer 5b in CH2Cl2.
See this image and copyright information in PMC

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