Open-Shell Nonbenzenoid Nanographenes Containing Two Pairs of Pentagonal and Heptagonal Rings

• Published in: Journal of the American Chemical Society Vol. 141; no. 30; pp. 12011 - 12020
• Main Authors: Liu, Junzhi, Mishra, Shantanu, Pignedoli, Carlo A, Passerone, Daniele, Urgel, José I, Fabrizio, Alberto, Lohr, Thorsten G, Ma, Ji, Komber, Hartmut, Baumgarten, Martin, Corminboeuf, Clémence, Berger, Reinhard, Ruffieux, Pascal, Müllen, Klaus, Fasel, Roman, Feng, Xinliang
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 31.07.2019; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; energy; gold; Physical Sciences; polycyclic aromatic hydrocarbons; quantum mechanics; scanning tunneling microscopy; Science & Technology; spectroscopy; topology; AROMATIC-COMPOUNDS; GRAPHENE NANORIBBONS
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.9b04718

Nonbenzenoid carbocyclic rings are postulated to serve as important structural elements toward tuning the chemical and electronic properties of extended polycyclic aromatic hydrocarbons (PAHs, or namely nanographenes), necessitating a rational and atomically precise synthetic approach toward their fabrication. Here, using a combined bottom-up in-solution and on-surface synthetic approach, we report the synthesis of nonbenzenoid open-shell nanographenes containing two pairs of embedded pentagonal and heptagonal rings. Extensive characterization of the resultant nanographene in solution shows a low optical gap, and an open-shell singlet ground state with a low singlet–triplet gap. Employing ultra-high-resolution scanning tunneling microscopy and spectroscopy, we conduct atomic-scale structural and electronic studies on a cyclopenta-fused derivative on a Au(111) surface. The resultant five to seven rings embedded nanographene displays an extremely narrow energy gap of 0.27 eV and exhibits a pronounced open-shell biradical character close to 1 (y 0 = 0.92). Our experimental results are supported by mean-field and multiconfigurational quantum chemical calculations. Access to large nanographenes with a combination of nonbenzenoid topologies and open-shell character should have wide implications in harnessing new functionalities toward the realization of future organic electronic and spintronic devices.