The polymorphism of porphyrin 2D assemblies at the liquid–graphite interface: the effect of a polar solvent additive and a flexible spacer on the face-on and edge-on type molecular arrangements

Self-assembly structures of 5,10,15,20-tetrakis(4-substituted phenyl)porphyrins at the liquid-graphite interface were investigated by scanning tunneling microscopy. We found that the presence of a small amount of a polar solvent, i.e., only 0.5 vol% of octanoic acid in phenyloctane, significantly affected the selective formation of the face-on polymorph over the edge-on one likely due to the solvent-molecule interactions at the 2D interface.