Selective functionalization by switching the adsorption linkage of a bi-functional organic molecule, 1-dimethylamino-2-propyne (DMAP), on Si(100) has been studied using high-resolution electron energy loss spectroscopy (HREELS) and scanning tunneling microscopy (STM). The HREELS and STM results clearly indicate that DMAP adsorbs at the down dimer atom of Si(100)c(4 x 2) through an N --> Si dative bond leaving the -CdropCH unit of DMAP free at low temperature (65-90 K). The adsorption linkage is switching from the N --> Si dative bond to the Si-C di-sigma bonds by annealing the adsorbed surface to 300 K, and thus the tertiary amino group becomes free. (C) 2004 Elsevier B.V. All rights reserved.