Macrocycles composed of biphenylene and butadiyne units with antiaromatic character
Shoko Nagayama1, Hiroki Kawakatsu1, Daisuke Asai1
1Department of Applied Chemistry, School of Science and Technology, Meiji University 1-1-1 Higashimita, Tama-ku Kawasaki Kanagawa 214-8571 Japan tahara@meiji.ac.jp.
Abstract:
Herein, we report the synthesis and characterization of π-conjugated macrocycles, with diameters over 2.4 nanometers, composed of biphenylene and butadiyne units. Specifically, biphenylene-2,7-diyl-butadiyne-1,4-diyl (BB) macrocycles were synthesized via the intermolecular Hay coupling reaction of a 2,7-diethynylbiphenylene derivative. The BB macrocycles exhibited absorption bands extending up to ∼600 nm and emitted red luminescence. Moreover, scanning tunneling microscopy observations revealed that the BB macrocycles formed self-assembled molecular networks at the liquid-graphite interface, showing higher tunneling efficiency. The BB macrocycles exhibited high energy levels of the highest occupied molecular orbitals and narrow energy gaps due to the elongated π-electron conjugation through the biphenylene units. Theoretically predicted responses to an external magnetic field using quantum chemical calculations of BB macrocycle models revealed reinforced antiaromatic character at four-membered rings. The present information will advance the structural design and property tuning of macrocyclic compounds with antiaromatic character.
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