Impact of heterocirculene molecular symmetry upon two-dimensional crystallization

Abstract

Despite the development of crystal engineering, it remains a great challenge to predict the crystal structure even for the simplest molecules, and a clear link between molecular and crystal symmetry is missing in general. Here we demonstrate that the two-dimensional (2D) crystallization of heterocirculenes on a Au(111) surface is greatly affected by the molecular symmetry. By means of ultrahigh vacuum scanning tunneling microscopy, we observe a variety of 2D crystalline structures in the coverage range from submonolayer to monolayer for D8h-symmetric sulflower (C16S8), whereas D4h-symmetric selenosulflower (C16S4Se4) forms square and rectangular lattices at submonolayer and monolayer coverages, respectively. No long-range ordered structure is observed for C1h-symmetric selenosulflower (C16S5Se3) self-assembling at submonolayer coverage. Such different self-assembly behaviors for the heterocirculenes with reduced molecular symmetries derive from the tendency toward close packing and the molecular symmetry retention in 2D crystallization due to van der Waals interactions.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

“…STM investigations performed at the solvent–highly oriented pyrolytic graphite (HOPG) interface revealed the ability of these heteracirculenes to stabilize the “chickenwire” 2D polymorph of trimesic acid, and their propensity for self-aggregation . 2D crystallization of 158.3 , 158.4 , and C 16 S 5 Se 3 on a Au(111) surface revealed a considerable dependence of the self-assembly behavior on molecular symmetry …”

“…935 2D crystallization of 158.3, 158.4, and C 16 S 5 Se 3 on a Au (111) surface revealed a considerable dependence of the self-assembly behavior on molecular symmetry. 936 1,4-Naphthoquinone treated with strong acids undergoes self-condensation into a number of products including tetrabenzotetraoxa [8]circulene 159.1 (Scheme 159). Such condensations were already investigated in 1881, 937 but 159.1 was first isolated in 1933 by Erdtman, 938 who proposed a structure of the corresponding [6]circulene analogue (tribenzotrioxasumanene).…”

Supramolecular Chemistry: Host–Guest Molecular Complexes

“…However, it is slightly difficult to predict the composite crystal structure and associated interactions between interlinked molecules and their crystal symmetry in crystal engineering. Recently Xiao, W.D., and his research fellows verified the impact of molecular symmetry and crystallization of 2D heterocirculenes on the Au (111) substrate via STM observing D 8 h symmetric sulflower and D 4 h symmetric selenosulflower coverage from submonolayer to monolayer [ 32 ].…”

Aromaticity and photophysics of tetrasila- and tetragerma-annelated tetrathienylenes as new representatives of the hetero[8]circulene family

“…15 Due to the planar structure and very high molecular symmetry, the 8S and 4S4Se species also demonstrate supramolecular assembly into 2D and 3D arrays, which is extremely important for modulation of the chargetransport properties in such systems. 20,21 Very recently, Miyake et al synthesized novel representatives of heteroannelated tetrathienylenes called tetrasilatetrathia [8]circulene 22 (4S4SiEt 2 ) and tetragermatetrathia [8]circulene 23 (4S4GeEt 2 ) by a palladium-catalyzed silylation/germylation process with subsequent rhodium-catalyzed intramolecular dehydrogenative cyclization. A similar technique has been also applied for the synthesis of tetrabenzotetrathia [8]circulenes 24 (4S), which at the same time can be considered as tetrathiaannelated derivatives of tetraphenylene and tetrabenzoannelated derivatives of tetrathienylene ( Fig.…”