title: Toward Tetraradicaloid: The Effect of Fusion Mode on Radical Character and Chemical Reactivity.
abstract: 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.
authors.affiliation: Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Pan
authors.initials: P
authors.lastname: Hu
authors.affiliation: Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University , Seoul 120-749, Korea.
authors.forename: Sangsu
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Materials Science & Engineering, National University of Singapore , Singapore 119260, Singapore.
authors.forename: Tun Seng
authors.initials: TS
authors.lastname: Herng
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST) , 8916-5 Takayama-cho, Ikoma 630-0192, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Aratani
authors.affiliation: Division of Physical Science and Engineering and KAUST Catalysis Center, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Théo P
authors.initials: TP
authors.lastname: Gonçalves
authors.affiliation: Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Qingbiao
authors.initials: Q
authors.lastname: Qi
authors.affiliation: Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Xueliang
authors.initials: X
authors.lastname: Shi
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST) , 8916-5 Takayama-cho, Ikoma 630-0192, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Yamada
authors.affiliation: Division of Physical Science and Engineering and KAUST Catalysis Center, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Kuo-Wei
authors.initials: KW
authors.lastname: Huang
authors.affiliation: Department of Materials Science & Engineering, National University of Singapore , Singapore 119260, Singapore.
authors.forename: Jun
authors.initials: J
authors.lastname: Ding
authors.affiliation: Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University , Seoul 120-749, Korea.
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.affiliation: Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.|Institute of Materials Research and Engineering, A*STAR , 2 Fusionopolis Way, Innovis, #08-03, Singapore 117602, Singapore.
authors.forename: Jishan
authors.initials: J
authors.lastname: Wu