Persistent peri-Heptacene: Synthesis and In Situ Characterization

M R Ajayakumar; Ji Ma; Andrea Lucotti; Karl Sebastian Schellhammer; Gianluca Serra; Evgenia Dmitrieva; Marco Rosenkranz; Hartmut Komber; Junzhi Liu; Frank Ortmann; Matteo Tommasini; Xinliang Feng

doi:10.1002/anie.202102757

Persistent peri-Heptacene: Synthesis and In Situ Characterization

Angew Chem Int Ed Engl. 2021 Jun 14;60(25):13853-13858. doi: 10.1002/anie.202102757. Epub 2021 May 12.

Authors

Affiliations

¹ Center for Advancing Electronics Dresden (cfaed) & Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Mommsenstrasse 4, 01062, Dresden, Germany.
² Dipartimento di Chimica, Materiali ed Ingegneria Chimica "G. Natta", Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milano, Italy.
³ Center for Advancing Electronics Dresden, Technische Universität Dresden, Helmholtzstraße 18, 01069, Dresden, Germany.
⁴ Center of Spectroelectrochemistry, Leibniz Institute for Solid State and Materials Research (IFW), Helmholtzstraße 20, 01069, Dresden, Germany.
⁵ Leibniz-Institut for Polymerforschung Dresden e. V., Hohe Straße 6, 01069, Dresden, Germany.
⁶ Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, 999077, Hong Kong, P. R. China.
⁷ Department of Chemistry, Technische Universität München, Lichtenbergstr. 4, 85748, Garching b. München, Germany.

Abstract

n-peri-Acenes (n-PAs) have gained interest as model systems of zigzag-edged graphene nanoribbons for potential applications in nanoelectronics and spintronics. However, the synthesis of n-PAs larger than peri-tetracene remains challenging because of their intrinsic open-shell character and high reactivity. Presented here is the synthesis of a hitherto unknown n-PA, that is, peri-heptacene (7-PA), in which the reactive zigzag edges are kinetically protected with eight 4-tBu-C₆ H₄ groups. The formation of 7-PA is validated by high-resolution mass spectrometry and in situ FT-Raman spectroscopy. 7-PA displays a narrow optical energy gap of 1.01 eV and exhibits persistent stability (t_1/2 ≈25 min) under inert conditions. Moreover, electron-spin resonance measurements and theoretical studies reveal that 7-PA exhibits an open-shell feature and a significant tetraradical character. This strategy could be considered a modular approach for the construction of next-generation (3 N+1)-PAs (where N≥3).

Keywords: Scholl reaction; acenes; graphene; nanostructures; radicals.