Doublet Open‐Shell Graphene Fragments

Abstract

Recent advances in neutral delocalized radical species based on polycyclic aromatic hydrocarbons with fused hexagonal rings, herein defined as doublet open-shell graphene fragments, are summarized in this review. A few simple yet useful theoretical approaches for structural analysis and molecular design were introduced at first. Then, based on the number of fused hexagonal rings, molecular systems with different size, symmetry and edge structure were discussed with emphasis on those isolated in the crystalline form. Their unique self-association behavior, chemical reactivity and physical properties were summarized and discussed, and insights on their functions and potential applications were provided.

Stability and Reactivity of the Phenalene and Olympicene Isomers

“…However, the selection of PAHs applicable in electronic devices is limited by the requirements for a high product yield and long lifetime. For example, linear acenes comprising more than five benzene rings exhibit instability due to their low ionization potentials and narrow band gaps. , Therefore, considerable attention has been directed toward neutral radicals derived from planar polycyclic aromatic hydrocarbons wherein unpaired electrons delocalized through the carbon skeleton . Examples include phenalenyl (Scheme ), which has been synthesized previously by both a mass growth process and a chemical route, as well as the more recently synthesized olympicenyl (Scheme ).…”

“…8,9 Therefore, considerable attention has been directed toward neutral radicals derived from planar polycyclic aromatic hydrocarbons wherein unpaired electrons delocalized through the carbon skeleton. 10 Examples include phenalenyl (Scheme 1), which has been synthesized previously by both a mass growth process 11 and a chemical route, 12 as well as the more recently synthesized olympicenyl (Scheme 1). 13 Investigations have also been performed on spin delocalization in open-shell PAHs derived from the helicene structure.…”

N-2,6-Di(isopropyl)phenyl-2-azaphenalenyl radical cations

“…The diisopropyl groups are well protected at the reactive C–N–C moiety of 4a , and occupy the space between the 2-azaphenalenyl planes. Because the distance of both azaphenalenyl planes is far from the sum of the van der Waals (vdW) radius of two carbon atoms (3.42 Å), 1 minimal π-dimer character 10 was observed in this compound. The two C–N bond lengths in the crystal structure of 4a are nearly identical (1.354 and 1.355 Å), and the average (1.355 Å) is longer than the C–N bonds (1.348 Å) in 3a (Fig.…”

“…Phenalenyl ( 1 ) is a well-known open-shell compound with high symmetry and the smallest odd-alternant π-conjugated hydrocarbon neutral radical. 1 Therefore, the electronic, structural and chemical properties of 1 and its derivatives have been extensively explored. 2–4 The phenalenyl system should provide a desirable platform for constructing stable radicals.…”