The selective assembly of carboxyphenyl substituted porphyrins on the Au (111) surface has been studied using scanning tunneling microscopy. We find that conformational isomers of the porphyrins are induced upon adsorption and are selectively assembled into hydrogen-bonded supramolecular clusters or wires on the surface. The conformation selective assembly is attributed to the coplanar intermolecular interactions between hydrogen-bonded carboxyphenyl groups. (C) 2004 American Institute of Physics.