title: Pushing extended p-quinodimethanes to the limit: stable tetracyano-oligo(N-annulated perylene)quinodimethanes with tunable ground states.
abstract: p-Quinodimethane (p-QDM) is a fundamental building block for the design of π-conjugated systems with low band gap and open-shell biradical character. However, synthesis of extended p-QDMs has usually suffered from their intrinsic high reactivity and poor solubility. In this work, benzannulation together with terminal cyano-substitution was demonstrated to be an efficient approach for the synthesis of a series of soluble and stable tetracyano-oligo(N-annulated perylene)quinodimethanes nPer-CN (n = 1-6), with the longest molecule having 12 para-linked benzenoid rings! The geometry and electronic structures of these oligomers were investigated by steady-state and transient absorption spectroscopy, nuclear magnetic resonance, electron spin resonance, superconducting quantum interference device, and FT Raman spectroscopy assisted by density functional theory calculations. They showed tunable ground states, varying from a closed-shell quinoidal structure for monomer, to a singlet biradical for dimer, trimer, and tetramer, and to a triplet biradical for pentamer and hexamer. Large two-photon absorption cross-section values were observed in the near-infrared range, which also exhibited a clear chain-length dependence.
authors.affiliation: Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore.
authors.forename: Zebing
authors.initials: Z
authors.lastname: Zeng
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Ishida
authors.forename: José L
authors.initials: JL
authors.lastname: Zafra
authors.forename: Xiaojian
authors.initials: X
authors.lastname: Zhu
authors.forename: Young Mo
authors.initials: YM
authors.lastname: Sung
authors.forename: Nina
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authors.lastname: Bao
authors.forename: Richard D
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authors.lastname: Webster
authors.forename: Byung Sun
authors.initials: BS
authors.lastname: Lee
authors.forename: Run-Wei
authors.initials: RW
authors.lastname: Li
authors.forename: Wangdong
authors.initials: W
authors.lastname: Zeng
authors.forename: Yuan
authors.initials: Y
authors.lastname: Li
authors.forename: Chunyan
authors.initials: C
authors.lastname: Chi
authors.forename: Juan T
authors.initials: JT
authors.lastname: López Navarrete
authors.forename: Jun
authors.initials: J
authors.lastname: Ding
authors.forename: Juan
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authors.lastname: Casado
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.forename: Jishan
authors.initials: J
authors.lastname: Wu