Influence of chemical structure on the stability and the conductance of   porphyrin single-molecule junctions
  Porphyrin molecules can form stable single molecule junctions without anchoring groups. Adding thiol end groups and pyridine axial groups yields more stable junctions with an increased spread in low-bias conductance. This is a result of different bridging geometries during breaking, the stability of which is demonstrated in time-dependent conductance measurements. This is in strong contrast with rod like molecules which show one preferential binding geometry. 
Mickael L. Perrin, Ferry Prins, Christian A. Martin, Ahson J. Shaikh,   Rienk Eelkema, Jan H. van Esch, Tomas Briza, Robert ...
cond-mat.mes-hall