Covalent attachment of a transition metal coordination complex to functionalized oligo(phenylene-ethynylene) self-assembled monolayers

We have investigated the reaction of tetrakis(dimethylamido)titanium, Ti[N(CH3)(2)](4), with N-isopropyl-N-[4-(thien-3-ylethynyl) phenyl] amine and N-isopropyl-N-(4-{[4-(thien-3-ylethynyl) phenyl]ethynyl}-phenyl) amine self-assembled monolayers (SAMS), on polycrystalline Au substrates. The structure of the SAMS themselves has also been investigated. Both molecules form SAMS on polycrystalline Au bound by the thiophene group. The longer-molecular-backbone molecule forms a denser SAM, with molecules characterized by a smaller tilt angle. X-ray photoelectron spectroscopy (XPS) and angle-resolved XPS have been employed to examine the kinetics of adsorption, the spatial extent of reaction, and the stoichiometry of reaction. For both the SAMS, adsorption is described well by first-order Langmuirian kinetics, and adsorption is self-limiting from T-S = -50 to 30 degrees C. The use of angle-resolved XPS clearly demonstrates that the Ti[N(CH3)(2)](4) reacts exclusively with the isopropylamine end group via ligand exchange, and there is no penetration of the SAM, followed by reaction at the SAM-Au interface. Moreover, the SAM molecules remain bound to the Au surface via their thiopene functionalites. From XPS, we have found that, in both cases, approximately one Ti[N(CH3)(2)](4) is adsorbed per two SAM molecules.