π‐Extendedperi‐Acenes: Recent Progress in Synthesis and Characterization

Abstract

Nanographenes (NGs) with open-shell character have gained intense attention due to their potential applications in future organic nanoelectronics and spintronics. Among them, NGs bearing a pair of parallel zigzag edges, such as acenes and periacenes (PAs) bestow unique (opto)electronic and magnetic properties owing to their localized non-bonding π-state. However, their reactive zigzag edges impart intrinsic instability, leading to the challenging synthesis. The recent development of synthetic strategies provided access to several π-extended PAs, which were considered unrealistic for decades. Notably, their laterally π-extended structures of zigzag-edged graphene nanoribbons was realised via on-surface synthesis. However, synthesis of π-extended PAs in solution is still in its infancy, more intensive scientific efforts are needed to surpass the existing challenges regarding stability and solubility. This Review provides an overview of recent progress in the synthesis and characterization of PAs through a bottom-up synthetic strategy, including on-surface and solution-phase chemistry. In addition, views on existing challenges and the future prospects are also provided.

Synthesis of Bioctacene‐Incorporated Nanographene with Near‐Infrared Chiroptical Properties

“…Nanographenes (NGs) have attracted widespread attention because of their fascinating physicochemical properties, which can be drastically modulated by changing their size, shape, and especially edge structures [1] . In particular, the presence of zigzag edges, corresponding to acene substructures, imparts NGs with unique optoelectronic and magnetic properties, [2] such as relatively small energy gaps, [3] a high photoluminescence quantum yield (PLQY), [4] stimulated emission, [5] and open‐shell di‐ to multiradical characteristics [2, 6] . Periacenes, comprising two rows of peri ‐fused acenes, is one of the most intriguing classes of NGs with zigzag edges and have been targets of recent synthetic efforts [6] .…”

“…[2,6] Periacenes, comprising two rows of perifused acenes, is one of the most intriguing classes of NGs with zigzag edges and have been targets of recent synthetic efforts. [6] In 2018, two groups independently described the synthesis of peritetracene, achieving its isolation and crystallization as well as revealing its open-shell biradical character and reactivity toward the Diels-Alder reaction at the bay regions, leading to circumanthracene. [7] Nevertheless, the preparation of peripentacene has been realized only on a metal surface under ultrahigh vacuum (UHV), [8] and periheptacene needs to be characterized in situ due to its low stability, [9] impeding its in-depth investigations and applications.…”

“…[1] In particular, the presence of zigzag edges, corresponding to acene substructures, imparts NGs with unique optoelectronic and magnetic properties, [2] such as relatively small energy gaps, [3] a high photoluminescence quantum yield (PLQY), [4] stimulated emission, [5] and open-shell di-to multiradical characteristics. [2,6] Periacenes, comprising two rows of perifused acenes, is one of the most intriguing classes of NGs with zigzag edges and have been targets of recent synthetic efforts. [6] In 2018, two groups independently described the synthesis of peritetracene, achieving its isolation and crystallization as well as revealing its open-shell biradical character and reactivity toward the Diels-Alder reaction at the bay regions, leading to circumanthracene.…”

Peri-Tetracene from 1,1′-Bitetracene: Zipping up Structurally Defined Graphene Nanoribbons

“…5−7 Peri-acenes exhibit a two-dimensionally enlarged π-conjugated electron system that results from the lateral fusion of two acene molecules. 8 While the smallest peri-acenes, namely, perylene (2-PA) and bisanthene (3-PA), were synthesized by Scholl et al 9 in 1910 and Clar in 1948, 10 respectively, the synthesis of higher periacenes evokes some challenges. The first higher PA (n ≥ 4, with n denoting the number of benzene rings along the zigzag axis), 5-PA, was detected as a side product by mass spectrometry only in 2005.…”

peri-Acenoacene Ribbons with Zigzag BN-Doped Peripheries

“…( m , n )- peri -Acenes exhibit orthogonal zigzag and armchair edges and derive from the fusion of an m number of [ n ]­acenes at their peri -position. − Instead, ( m , n )- peri -acenoacenes are nanographenes with two zigzag peripheries with a 60° angle (Figure a) and are the rarest examples. − When the annulated [ n ]­acenes display different n , one could refer to either n - peri -acenoacenes (i.e., triangulenes) or ( m , n , n -1, n -2, . .…”