Adsorption of diisocyanides on gold

Four known diisocyanides, 1,6-diisocyanohexane (1), 1,12-diisocyanododecane (2), 1,4-phenylenediisocyanide (3), 4,4'-biphenyldiisocyanide (4), and two new diisocyanides, 4,4"-p-terphenyldiisocyanide (5) and 1,4-di(4-isocyanop henylacetelynyl)-2-ethylbenzene (6), were used to prepare self-assembled mo nolayers (SAMs) on gold. The SAMs were characterized by ellipsometry, by me asurement of the advancing water droplet contact angle, and by reflection a bsorption infrared (RAIR) spectroscopy. SAMs prepared from the diisocyanide s 1 and 2, which have a flexible alkyl chain between the two isocyanide end groups, were found to form monolayer films in which both isocyanide groups are bound to the surface. SAMs prepared from the diisocyanides 3-6, which have rigid aryl or phenylethynyl structures between the two isocyanide end groups, were found to bind to gold through one CN group. Analyses of the RA IR spectra of these SAMs are consistent with surface selection rules for ad sorbates that are oriented with their long molecular axis normal to the sur face. Measurements of advancing water droplet contact angles and ellipsomet ric film thicknesses of SAMs prepared from 3-6 further support a surface st ructure in which the diisocyanide molecules are oriented vertically with on e CN group bound to the surface and the other remote from the surface.