Heptagon‐Embedded Pentacene: Synthesis, Structures, and Thin‐Film Transistors of Dibenzo[d,d′]benzo[1,2‐a:4,5‐a′]dicycloheptenes

Abstract

This study presents a new class of conjugated polycyclic molecules that contain seven-membered rings, detailing their synthesis, crystal structures and semiconductor properties. These molecules have a nearly flat C6-C7-C6-C7-C6 polycyclic framework with a p-quinodimethane core. With field-effect mobilities of up to 0.76 cm(2) V(-1) s(-1) as measured from solution-processed thin-film transistors, these molecules are alternatives to the well-studied pentacene analogues for applications in organic electronic devices.

Heptagons in Aromatics: From Monocyclic to Polycyclic

“…With the five hexa [7]circulene moieties having either P or M chirality around the seven-membered ring, 6a exists as a pair of enantiomers with PMPMP and MPMPM configuration in the crystals. However, 6a and 6b are conformationally flexible and racemize rapidly in solution as indicated by 1 H NMR.…”

“…Starting from 2,5-dibromo-1,4-distyrylbenzene, the author's group synthesized silylethynylated derivatives of 4a, namely 4b-d. [7] In particular, 4b is an interesting analogue of 6,13-bis((triisopropylsilyl)ethynyl)pentacene (5), a well-known solution-processed organic semiconductor for applications in organic thin-film transistors (OTFTs). The HOMO and LUMO levels of 4b were estimated as −4.92 eV and −3.14 eV respectively, from the reversible reduction and oxidation peaks in the cyclic voltammogram.…”

“…Heptagon-embedded polycyclic arenes can serve as fragments, model compounds, and, in principle, synthetic precursors for negatively curved carbon nanomaterials. The first member of the negatively curved heptagon-containing polycyclic arenes is [7]circulene, which was first synthesized by the Yamamoto group in 1983. [11] A few new examples of such negatively curved polycyclic arenes were reported recently.…”

Antiaromatic character of cycloheptatriene-bis-annelated indenofluorene framework mainly originated from heptafulvene segment

“…An alternative approach to access antiaromatic frameworks relies on the use of methylenecycloheptatriene (heptafulvene) segments to form tricyclic 16π-electron benzo[1, 2:4, 5]di[7]annulene (BDA), whereas pristine heptalene exhibits nonaromatic character due to its twisted non-planar geometry 40 . Although several polycyclic hydrocarbons containing a BDA framework have been synthesized 41–47 , the development of BDA-based antiaromatic compounds is still limited due to the difficulty of (1) the molecular design to incorporate heptafulvene units into the π-conjugated systems and (2) the synthetic method for the construction of seven-membered rings 41,42,44–46 . In contrast to the fulvene unit, the formation of cycloheptatrienyl cation by one-electron oxidation of heptafulvene leads to aromatic stabilization.…”

“…In contrast to the fulvene unit, the formation of cycloheptatrienyl cation by one-electron oxidation of heptafulvene leads to aromatic stabilization. Thus, the thin-film of 1 showed hole-transporting characteristics in organic field-effect transistor (OFET) devices 44–46 . However, irrespective of these electronically complemental properties, fundamental studies to directly investigate the antiaromatic character between the ID and BDA frameworks have not been carried out so far.…”