Date : 2014. 5. 15, 4:30 PM Place : Int"l conf. room, Bldg.25-1 -Abstract- Ultrathin insulating films grown on metal substrate has been a subject of great interest for investigation of individual adsorbate atoms and molecules using a scanning tunneling microscope (STM), because of electronic decoupling between the adsorbate and supporting metal surface under an STM junction. Here, I will talk about two representative works that we have done on the single molecule chemistry on the ultrathin insulating films on metal substrates. The chemical reactivity of a water molecule on an ultrathin MgO film supported by the Ag(100) substrate depends greatly on film thickness and be enhanced compared to that achieved with their bulk counterpart. The change of chemical reactivity of ultrathin MgO film depending on the film thickness can be explained by the strengthening of the interaction between the oxide and metal interface layers. Our results clearly show that such structural imperfections at the interface can improve the chemical reactivity of the MgO film supported by an Ag substrate. Optical properties of a single metal-free phthalocyanine (H2Pc) molecule on the 2-ML thick NaCl film supported by Ag(111) have been also studied by scanning tunneling luminescence spectroscopy. I will discuss about the single molecule reaction of a H2Pc molecule with tunneling electrons and accompanied optical property changes in a single-molecule luminescence spectra.