The interest in organic based molecular electronics has spurred new attempts to control electronic properties of single molecules. We are approaching this goal by looking at two systems: conductivity of thiol-based self-assembled monolayers (SAMs) and phenylene ethynylene oligomers deposited on Au surfaces, and viability of covalently tethering molecules to Si substrates. In both cases, the molecules have extended conjugated π-systems. In this report, we will present results of scanning tunneling microscope investigation of oligo (phenylene ethynylene)(OPE) inserted between molecules of monolayers of dodecanethiol self-assembled on Au(111)/mica substrates, and XPS results of phenylacetylene and 1-bromo-2-ethynylbenzene attached to Si (111) substrates. The investigated OPE are both unsubstituted and substituted with a single -NO2 group on the central ring [4,4’-(diethynylphenyl)-2’-nitro-1-benzenethiolate] inserted in the defects of dodecanethiol SAMs. The conductivity of those systems attached to Au varies as a function of time. Our results show no particular dependence of this variable conductivity on substitution and structure of the monolayer. In addition, preliminary experiments have been performed attaching phenylacetylene and 1-bromo-2-ethynylenebenzene to variously doped hydrogen terminated Si(111) surfaces in-situ using UV photon assisted propagation reactions. The object is to determine how the conductivity through the molecules depends upon the relative alignment of the substrate conduction and valence bands and the molecular bonding and antibonding levels.