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.
Bibliographical noteFunding Information:
This work was supported by the Grant-in-Aid for Scientific Research on Innovative Areas (2601): p-System Figuration (JSPS KAKENHI grant numbers JP26102003 (to H.S.), JP15H00998 (to I.H.) and JP15H01001 (to S.S.) and by the Program for Leading Graduate Schools 'Integrative Graduate Education and Research in Green Natural Sciences' from MEXT, Japan. Crystallographic data were collected at the SPring-8 beam line BL38B1 with approval of the JASRI (proposal nos. 2015B1397 and 2016A1121). H.S. acknowledges the Asahi Glass Foundation for financial support. Research at Yonsei University was supported by the Samsung Science and Technology Foundation (SSTF-BA1402-10).
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)
- Physics and Astronomy(all)