Image of the Month

November 2017

On the critical role of the substrate: the adsorption behaviour of tetrabenzoporphyrins on different metal surfaces

Fig. 4 Overview of the supramolecular phases and the derived structural models for 2HTPTBP on Cu(111) at different coverages (a–c: relatively low coverage; d–f: medium coverage; g–i: monolayer coverage; all the STM images were measured at RT). The red and yellow ovals indicate the individual molecules with different orientations. The intermolecular T-type-like interactions and p–p stacking interactions in the structural models are highlighted by green lines and black parallel lines, respectively. The van der Waals interactions between the phenyl groups of two neighbouring molecules are marked by green dashed lines. Tunnelling parameters: (a) U = 1.0 V, I = 30 pA; (b) U = 1.6 V, I = 30 pA; (d, e, g and h) U = 1.1 V, I = 30 pA.

Abstract
The adsorption behaviour of 2H-5,10,15,20-tetraphenyltetrabenzoporphyrin (2HTPTBP) on different metal surfaces, i.e., Ag(111), Cu(111), Cu(110), and Cu(110)–(2 􏰀 1)O was investigated by scanning tunnelling microscopy at room temperature. The adsorption of 2HTPTBP on Ag(111) leads to the formation of a well- ordered two-dimensional (2D) island structure due to the mutual stabilization through the intermolecular p–p stacking and T-type-like interactions of phenyl and benzene substituents of neighboring molecules. For 2HTPTBP on Cu(111), the formed 2D supramolecular structures exhibit a coverage-dependent behaviour, which can be understood from the interplay of molecule–substrate and molecule–molecule interactions. In contrast, on Cu(110) the 2HTPTBP molecules form dispersed one-dimensional (1D) molecular chains along the [11%0] direction of the substrate due to relatively strong attractive molecule– substrate interactions. Furthermore, we demonstrate that the reconstruction of the Cu(110) surface by oxygen atoms yields a change in dimensionality of the resulting nanostructures from 1D on Cu(110) to 2D on (2 􏰀 1) oxygen-reconstructed Cu(110), induced by a decreased molecule–substrate interaction combined with attractive molecule–molecule interactions. This comprehensive study on these prototypical systems enables us to deepen the understanding of the particular role of the substrate concerning the adsorption behavior of organic molecules on metal surfaces and thus to tweak the ordering in functional molecular architectures.

Reference:
Physical Chemistry Chemical Physics 19.30 (2017): 20281-20289

Credits:
Liang Zhang, ab Michael Lepper, ab Michael Stark,ab Teresa Menzel,ab
Dominik Lungerich,bc Norbert Jux,bc Wolfgang Hieringer,bd Hans-Peter Steinru ̈ckab and Hubertus Marbach*ab

a Lehrstuhl fu ̈r Physikalische Chemie II, Universita ̈t Erlangen-Nu ̈rnberg, Egerlandstr. 3, 91058 Erlangen, Germany. E-mail: [email protected]

b Interdisciplinary Center for Molecular Materials (ICMM), Universita ̈t Erlangen-Nu ̈rnberg, Germany

c Lehrstuhl fu ̈r Organische Chemie II, Universita ̈t Erlangen-Nu ̈rnberg, Henkestr. 42, 91054 Erlangen, Germany

d Lehrstuhl fu ̈r Theoretische Chemie, Universita ̈t Erlangen-Nu ̈rnberg, Egerlandstr. 3, 91058 Erlangen, Germany

† Electronic supplementary information (ESI) available: The structure models of 2HTPTBP on Cu(111), the STM images of 2HTPTBP on Cu(110) after annealing and the atomic Cartesian coordinates for the calculated gas phase model. See DOI: 10.1039/c7cp03731g

Microscope:
UHV VT Beetle 300