In searching for a redox switch, Matsuda, Ishikawa and co-workers¹ landed on 13,14-picenedione 1, which could, at least in principle, be reduced by reacting with H₂ to form the diol 2. The back reaction could then occur via the reaction with oxygen gas.

They first optimized the geometries of both compounds at B3PW91/6-311+G(2d), and these geometries are shown in Figure 1. TD-DFT computations then predicted that 1 would be yellow (maximum absorption at 412nm) and 2 would be colorless (maximum absorption at 378nm). Furthermore, 1 should have no fluorescence while 2 should fluoresce at 464nm and be blue.

1

2

Figure 1. B3PW91/6-311+G(2d) optimized geometries of 1 and 2.

Of particular note is that the geometry of 1 is twisted, with the O-C-C-O dihedral angle being 34.9°, while there is essentially no such twisting in 2 (its O-C-C-O dihedral angle is 0.7°). The twisting in 1 manifests in antiaromatic character of the central ring, with NICS(0)=+13.2ppm, while the central ring of 2 is aromatic, with NICS(0)=-10.0. The redox properties therefore reflect the change in the aromatic character.

They next synthesized 2 and reduced it with hydrogen gas to 1. The x-ray crystal structure of 1 shows a twisted structure (O-C-C-O dihedral of 28.87°). As predicted, 1 is yellow and 2 is colorless, and 1 has no fluorescence while 2 fluoresces blue.

References

(1) Urakawa, K.; Sumimoto, M.; Arisawa, M.; Matsuda, M.; Ishikawa, H. "Redox Switching of Orthoquinone-Containing Aromatic Compounds with Hydrogen and Oxygen Gas," Angew. Chem. Int. Ed. 2016, 55, 7432-7436, DOI: 10.1002/anie.201601906.

InChIs

1: InChI=1S/C22H12O2/c23-21-19-15-7-3-1-5-13(15)9-11-17(19)18-12-10-14-6-2-4-8-16(14)20(18)22(21)24/h1-12H
InChIKey=ASVNSCAISPNPGI-UHFFFAOYSA-N

2: InChI=InChI=1S/C22H14O2/c23-21-19-15-7-3-1-5-13(15)9-11-17(19)18-12-10-14-6-2-4-8-16(14)20(18)22(21)24/h1-12,23-24H
InChIKey=KZHNWJFXGDGIDE-UHFFFAOYSA-N