Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 85: Metal substrates: Adsorption of organic / bio molecules VII

O 85.6: Talk

Friday, March 26, 2010, 12:30–12:45, H36

modification of supramolecular binding motifs induced by substrate registry: formation of self-assembled macrocycles and chain-like patterns — •Saranyan Vijayaraghavan — Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel,Switzerland

The self-assembly properties of two ZnII porphyrin isomers on Cu(111) are studied at different coverage by means of an STM. Both isomers are substituted in their meso-positions by two voluminous 3,5-di(tert-butyl)phenyl and two 4*-cyanobiphenyl groups, respectively. In the trans-isomer, the two cyanobiphenyl groups are opposite to each other, whereas they are 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 frequently but everything from cyclic dimers to hexamers are observed. Upon annealing of the samples at >150 C, dimeric macrocyclic structures are observed, in which the two porphyrins are bridged by Cu atoms, as CN-Cu-NC coordination bonds. LInear chains are seen at low coverages on Cu111 and densely packed structure at high coverages. Both cis- and trans-bis(4*-cyanobiphenyl)-substituted ZnII porphyrins behave very differently on Cu(111) compared to similar porphyrins on less reactive surfaces such as Au(111) and Ag(111). A very strong molecule-substrate interaction is seen on Cu(111) which dominates all observed structures.