Modification of Molecular Conductance by in Situ Deprotection of Thiol-Based Porphyrin

ACS Appl Mater Interfaces. 2017 May 17;9(19):15901-15906. doi: 10.1021/acsami.6b14841. Epub 2017 May 8.

Abstract

Acetylthio-protected free base porphyrins are used to form scanning tunneling microscope-molecular break junctions. The porphyrin molecules are deprotected in situ, before the self-assembly. Two types of molecular junctions are formed in the junctions: Au-S-Por-SAc-Au and Au-S-Por-S-Au. Lower conductance values and higher conductance values are observed. Computational modeling attributes the lower conductance to the Au-S-Por-SAc-Au junctions and the higher conductance to the Au-S-Por-S-Au junctions. First-principles calculation suggests that the reduced conductance in the protected porphyrin originates from the presence of the acetyl end groups (-COCH3), rather than from the elongation of the sulfur-gold (S-Au) bonds at the tip-molecule interface.

Keywords: Green’s function density functional theory; in situ deprotection; molecular break junctions; molecular conductance; porphyrin; scanning tunneling microscope.