We are developing/applying second harmonic and sum frequency generation (SHG and SFG) for the study of adsorbates on single crystal surfaces. These surface selective spectroscopic techniques allow measurements of adsorbate orientation and ET dynamics on well-characterized crystalline surfaces. Despite intense interest of interfacial ET in nanomaterials, very little is known about the adsorption geometry of most sensitizer molecules on nanoparticle surfaces, hindering a detailed understanding of their ET dynamics. By comparing SHG and SFG signal under different polarization combinations of the input and output beams, the orientation of adsorbate molecules relative to the surface normal of single crystals can be determined. Furthermore, the ET rates on single crystal surfaces (for molecules with known adsorption geometry) can also be measured with high temporal resolution by an optical pulse pump and SHG or SFG probe scheme.  These detailed studies on well-characterized model systems provide important information for comparison with high level computational studies. This will help to understand the ET dynamics in more complex and less characterized nanomaterials.