Self‐Assembled Monolayers of Alkoxy‐Substituted Octadehydrodibenzo[12]annulenes on a Graphite Surface: Attempts at peri‐Benzopolyacene Formation by On‐Surface Polymerization

Abstract

Self-assembled monolayers of a series of tetraalkoxy-substituted octadehydrodibenzo[12]annulene (DBA) derivatives 1c-g possessing butadiyne linkages were studied at the 1,2,4-trichlorobenzene (TCB) or 1-phenyloctane/graphite interface by scanning tunneling microscopy (STM). The purpose of this research is not only to investigate the structural variation of two-dimensional (2D) monolayers, but also to assess a possibility for peri-benzopolyacene formation by two-dimensionally controlled polymerization on a surface. As a result, the formation of three structures, porous, linear, and lamella structures, were observed by changing the alkyl chain length and the solute concentration. The formation of multilayers of the lamella structure was often observed for all compounds. The selection of molecular networks is basically ascribed to intermolecular and molecule-substrate interactions per unit area and network density. The selective appearance of the linear structure of 1d is attributed to favorable epitaxial registry matching between the substrate lattice and the overlayer lattice. Even though the closest interatomic distance between the diacetylenic units of the DBAs in the lamella structure (approximately 0.6 nm) is slightly larger compared to the typical distances necessary for topochemical polymerization, the reactivity toward external stimuli (electronic-pulse irradiation from an STM tip and UV irradiation) was investigated. Unfortunately, no evidence for polymerization of the DBAs on the surface was observed. The present results indicate the necessity for further designing a suitable system for the on-surface construction of structurally novel conjugated polymers, which are otherwise difficult to prepare.

Conjugated Macrocycles: Concepts and Applications

“…[54] The structure of the 2D networks of 63 depended on the length of the alkyl chain, and incorporation of a C 18 alkyl chain length led to the chains aligning in a parallel fashion to form a lamellar structure. Although the closest interatomic distance between the diacetylenic units of 63 (R = OC 18 H 37 ) is only slightly greater than the typical distances necessary for topochemical polymerization to produce 64, no evidence for polymerization on the surface was observed.…”

Konjugierte Makrocyclen: Konzepte und Anwendungen

“…[54] Tahara und Tobe beschrieben vor kurzem, dass Verbindung 63 selbstorganisierte Monoschichten bildet (Schema 11 b). [54] Die Struktur des 2D-Netzwerks von 63 hing von der Länge der Alkylkette ab, und unter Verwendung einer C 18 -Alkylkette richteten sich die Ketten auf parallele Weise zur Bildung einer lamellenartigen Struktur aus.…”

“…[54] Tahara und Tobe beschrieben vor kurzem, dass Verbindung 63 selbstorganisierte Monoschichten bildet (Schema 11 b). [54] Die Struktur des 2D-Netzwerks von 63 hing von der Länge der Alkylkette ab, und unter Verwendung einer C 18 -Alkylkette richteten sich die Ketten auf parallele Weise zur Bildung einer lamellenartigen Struktur aus. Obwohl die kleinsten interatomaren Abstände zwischen den Diacetyleneinheiten von 63 (R = OC 18 H 37 ) nur geringfügig grçßer sind als die typischen Abstände, die für eine topochemische Polymerisation zur Erzeugung von 64 nçtig sind, waren keine Anhaltspunkte für eine Polymerisation auf der Oberfläche zu beobachten.…”

π‐Conjugated Macrocycles Bearing Angle‐Strained Alkynes

“…Dehydrobenzo[12]annulene 77 a was synthesized by Eglinton, Raphael, and co‐workers by using copper‐mediated coupling, and the strained structure was confirmed later by X‐ray crystallographic analysis of 77 b (∠ sp =165–167°) . Its symmetrical and planar π‐conjugated structure induced the formation of self‐assemblies, such as nanofibers and gels . As expected from the highly strained structure, the strain‐promoted double azide–alkyne cycloaddition of 77 c takes place regioselectively to give adduct 79 (Figure c) .…”