3-Chloro-1-propanol dissociatively adsorbs on the Si(111)-7 x 7 surface via the OH dissociation with the C-Cl bond unperturbed at 110 K. The C-Cl bond was then cleaved by a 193 nm photon to produce one radical site on the C atom, which subsequently reacted with one nearby physisorbed benzonitrile molecule via the cyano group to form a second covalently bonded organic layer. The newly generated radical site on the cyano group abstracts a nearby H atom. In this work, we successfully constructed the second chemically attached organic layer on the Si(111)-7 x 7 surface and demonstrated that photochemical methods are powerful tools in organic modification of silicon surfaces.