Revisiting Acepleiadylene: Two-Step Synthesis and π-Extension toward Nonbenzenoid Nanographene

Abstract

Acepleiadylene (APD), a nonbenzenoid nonalternant isomer of pyrene, exhibits different electronic properties from pyrene, but has been rarely studied since its first synthesis in 1956, probably due to the difficulties in synthesis and further derivatization. In this work, we revisited this long-known compound and developed a new two-step synthetic route to efficiently access APD on the gram scale. Theoretical and experimental characterizations elucidated the unique properties of APD as compared with its benzenoid isomer pyrene, particularly revealing its dipolar structure with a narrow optical gap. The functionalization of APD was demonstrated for the first time, providing doubly brominated APD as a key precursor for further π-extension. As a proof of concept, a π-extended APD and a cyclotrimer nanographene (C 48 H 24 ) were constructed, opening up new avenues to nonbenzenoid nanographenes with low HOMO−LUMO gaps.

The road to bis‐periazulene (cyclohepta[def]fluorene): Realizing one of the long‐standing dreams in nonalternant hydrocarbons

“…[63] (D) Wang et al's facile synthetic route for 36 and further π extensions. [64] Cyclohepta[bc]acenaphthylene 37 was reported in 1955 by Reid et al [70] They synthesized 37 from the butyric acid derivative in three steps and isolated it as a dark red crystalline solid (Figure 9B). The electronic absorption spectrum of 37 in hexane conforms to that of azulene itself, and the onset of the longest absorption reaches at 650 nm.…”

Bis-periazulene (Cyclohepta[def]fluorene) as a Nonalternant Isomer of Pyrene: Synthesis and Characterization of Its Triaryl Derivatives

“…Nonalternant hydrocarbons have recently experienced a remarkable resurgence. − Their unique electron configurations and molecular orbital characteristics are derived from topological differences of the π-electron network, which is produced by replacing hexagons of alternant hydrocarbons with a pentagon and heptagon pair . One seminal example of a nonalternant hydrocarbon is azulene.…”

“…The hexagons within 1 adopt o -quinoidal forms in the closed-shell Kekulé structure ( 1a - A ), which should peripherally delocalize the 14π-system via an equivalent resonance/interconversion. , When the quinoidal forms are transformed into the benzenoid forms, two possible structures are considered. One is the charge-separated polarized structure ( 1a - B ), which is reminiscent of the contribution of the embedded azulene core. ,− The other is the open-shell diradical structure ( 1a - C ), where an m -quinodi­methane subunit, a typical non-disjoint non-Kekulé diradical, − engages in the stabilization of the triplet state. These considerations prompted us to synthesize 1 and unveil its electronic structures, including the actual ground state.…”

A Dislocated Twin‐Locking Acceptor‐Donor‐Acceptor Configuration for Efficient Delayed Fluorescence with Multiple Through‐Space Charge Transfer

“…Organic polycyclic aromatic hydrocarbons (PAHs) materials with graphene structural characteristics have attracted enormous attention in recent years for the development of thermally activated delayed fluorescent (TADF) emitters, since their optoelectronic properties can be precisely tuned by molecular engineering. [1][2][3][4][5][6][7][8][9] As well-demonstrated in the multiple resonance (MR) TADF materials based on boron and nitrogen (B,N) doped PAHs, the large molecular rigidity of these emitters can significantly reduce nonradiative decay and increase photoluminescence quantum yields (Φ PL ). [10][11][12][13][14][15][16] However, these planarized molecules usually suffer from severe aggregation-caused emission quenching (ACQ) in the solid state.…”