Modification of Supramolecular Binding Motifs Induced By Substrate Registry: Formation of Self‐Assembled Macrocycles and Chain‐Like Patterns

Abstract

The self‐assembly properties of two ZnII porphyrin isomers on Cu(111) are studied at different coverage by means of scanning tunneling microscopy (STM). Both isomers are substituted in their meso‐positions by two voluminous 3,5‐di(tert‐butyl)phenyl and two rod‐like 4′‐cyanobiphenyl groups, respectively. In the trans‐isomer, the two 4′‐cyanobiphenyl groups are opposite to each other, whereas they are located at right angle in the cis‐isomer. For coverage up to one monolayer, the cis‐substituted porphyrins self‐assemble to form oligomeric macrocycles held together by antiparallel CN⋅⋅⋅CN dipolar interactions and CN⋅⋅⋅H‐C(sp2) hydrogen bonding. Cyclic trimers and tetramers occur most frequently but everything from cyclic dimers to hexamers can be observed. Upon annealing of the samples at temperatures >150 °C, dimeric macrocyclic structures are observed, in which the two porphyrins are bridged by Cu atoms, originating from the surface, under formation of two CN⋅⋅⋅Cu⋅⋅⋅NC coordination bonds. The trans‐isomer builds up linear chains on Cu(111) at low coverage, whereas for higher coverage the molecules assemble in a periodic, densely packed structure. Both cis‐ and trans‐bis(4′‐cyanobiphenyl)‐substituted ZnII porphyrins behave very differently on Cu(111) compared to similar porphyrins in literature on less reactive surfaces such as Au(111) and Ag(111). On the latter surfaces, there is no signal visible between molecular orientation and the crystal directions of the substrate, whereas on Cu(111), very strong adsorbate–substrate interactions have a dominating influence on all observed structures. This strong porphyrin–substrate interaction enables a much broader variety of structures, including also less favorable intermolecular bonding motifs and geometries.

Cyano‐Functionalized Triarylamines on Coinage Metal Surfaces: Interplay of Intermolecular and Molecule–Substrate Interactions

“…Such coordination bonds between cyano groups and native copper atoms were reported, for example, for cyano-functionalized porphyrin or helicene molecules on Cu(111). [14,15] Although the coordinated metal atom is generally not visible by STM, enhanced contrasti sv isible at the positiono ft he coordinated metal atom under specific tunnelling conditions, which is generally assumed to be as ignature for metal coordination ( Figure S8a in the Supporting Information). [21,28,29] X-ray photoelectron spectroscopy (XPS) measurements…”

“…[13] The study of molecular self-assembly of organic molecules functionalized with cyano groupsi sp articularly interesting, because the asymmetric charge distribution of the cyano group with the negatively polarized Na tom leads to the formation of al ocal internal dipole.T he cyano group can not only participate in H-bonding and dipolar coupling, but it can also efficiently coordinate to av ariety of metals. [14][15][16][17] Different molecular patternss uch as 0D clusters, 1D chains and 2D islands can be createdb yc hanging the number of cyano groups and/or their relative position, as was demonstrated for cyanofunctionalized porphyrin and polyphenylene derivatives. [4,14,18] Herein, we report on the self-assembly of the cyanofunctionalized planarized triarylamined erivative 4,4,8,8,12,12-hexamethyl-4H,8H,12H-benzo[1,9]quinolizino[3,4,5,6,7-defg]acridine-2,6,10-tricarbonitrile (1,S cheme1)o nc oinage metal (111) surfaces.…”

“…[14][15][16][17] Different molecular patternss uch as 0D clusters, 1D chains and 2D islands can be createdb yc hanging the number of cyano groups and/or their relative position, as was demonstrated for cyanofunctionalized porphyrin and polyphenylene derivatives. [4,14,18] Herein, we report on the self-assembly of the cyanofunctionalized planarized triarylamined erivative 4,4,8,8,12,12-hexamethyl-4H,8H,12H-benzo[1,9]quinolizino[3,4,5,6,7-defg]acridine-2,6,10-tricarbonitrile (1,S cheme1)o nc oinage metal (111) surfaces. Such planarized triarylamines, so-called heterotriangulenes, are at presento fg rowing interest owing to their potential as stable electron-rich building blocksf or optoelectronic organic materials.…”

Studying the dynamic behaviour of porphyrins as prototype functional molecules by scanning tunnelling microscopy close to room temperature

“…[10][11][12][13][14][15] The enormous potential of porphyrins for the fabrication of tailor-made functional molecular architectures on well-defined substrates has stimulated significant activities in fundamental research. 4,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] In this contribution, we review recent advances in the understanding of the dynamic behaviour of porphyrins, as representatives of organic molecules, adsorbed on a Cu(111) single crystal surface in ultra-high vacuum (UHV). Based on temperaturedependent measurements of individual molecules, the kinetics and energetics of diffusion 33,34 and rotation, 34 of the so-called self-metalation reaction 35,36 and finally of conformational switching of particular free base porphyrins 37 can be determined.…”

Interplay of hydrogen bonding and molecule–substrate interaction in self-assembled adlayer structures of a hydroxyphenyl-substituted porphyrin

“…[1][2][3] The construction of desired molecular network architectures on suitable substrates is achieved by the self-assembly of molecular building blocks, which is mainly controlled by a complex interplay between non-covalent bonds such as hydrogen bonds, van der Waals and electrostatic interactions, and the epitaxy on the substrate. [4][5][6][7][8][9][10][11][12][13][14] From the knowledge gained about the delicate balance between intermolecular and molecule-substrate interactions, the functional nano-networks can then be tuned by adjusting functional groups of the molecule to gain the desired architectures [15][16][17] and the interface electronic structure for the specific application. Therefore, it is important that the molecular orientation, configuration and conformation, and the interactions between the adsorbed molecules and the substrate as well as between molecules can be identified and understood, e.g.…”