Open-shell singlet diradicaloids display unique electronic, nonlinear optical, and magnetic activity and could become novel molecular materials for organic electronics, photonics, and spintronics. However, design and synthesis of diradicaloids with a significant polyradical character is a challenging task for chemists. In this Article, we report our efforts toward a tetraradicaloid system. A series of potential tetraradicaloids by fusion of two p-quinodimethane (p-QDM) units with naphthalene or benzene rings in different modes were synthesized. Their model compounds containing one p-QDM moiety were also prepared and compared. Their ground-state structures, physical properties, and chemical reactivity were systematically investigated by various experimental methods such as steady-state and transient absorption, two-photon absorption, X-ray crystallographic analysis, electron spin resonance, superconducting quantum interference device, and electrochemistry, assisted by density functional theory calculations. It was found that their diradical and tetraradical characters show a clear dependence on the fusion mode. Upon the introduction of more five-membered rings, the diradical characters greatly decrease. This difference can be explained by the pro-aromaticity/antiaromaticity of the molecules as well as the intramolecular charge transfer. Our comprehensive studies provide a guideline for the design and synthesis of stable open-shell singlet polycyclic hydrocarbons with significant polyradical characters.
Bibliographical noteFunding Information:
J.W. acknowledges financial support from the MOE Tier 3 programme (MOE2014-T3-1-004), MOE Tier 2 grant (MOE2014-T2-1-080), and A*STAR JCO grant (1431AFG100). This work at Yonsei University was supported by the Global Frontier R&D Program on Center for MultiscaleEnergy System funded by the National Research Foundation under the Ministry of Science, ICT & Future, Korea (NRF-2014M3A6A7060583). H.Y. and N.A. acknowledge the financial support by Grants-in-Aid for Scientific Research (KAKENHI) nos. 25288092, 26620167, 26105004, and 26288038 from the Japan Society for the Promotion of Science (JSPS). K.-W.H. is thankful for financial support from KAUST. We thank Dr. Bruno Donnadieu for crystallographic analysis on some samples. We thank Professor Michael Haley (University of Oregon) and Professor Yoshito Tobe (Osaka University) for helpful discussions.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry