Self-assembled monolayers with charge-transfer functional groups: Immobilization of the electron donor TMPD and the electron acceptor TCNQ

Spontaneously adsorbed molecular films containing derivatives of the electron donor tetramethylphenylenediamine (TMPD) or the electron acceptor tetracyanoquinodimethane (TCNQ) are formed by exposure of polycrystalline Au to 1 mM solutions of an alkanethiol TMPD reagent or an alkyl disulfide TCNQ species, respectively. Characterization of these redox-active films by cyclic voltammetry establishes the presence of (3.3 ± 0.3) x 10^-10 mol/cm² of redox-active TMPD groups in the case of TMPD films and (2.4 ± 0.5) x 10^-0 mol/cm² of redox-active TCNQ groups in the case of the TCNQ films. These films readily undergo charge-transfer reactions with complementary electron acceptors and donors as verified by reflection-absorption infrared spectroscopy and laser desorption mass spectrometry. These film provide convenient approaches for exploiting well-known charge-transfer chemistry in interfacial adhesion measurements and for tailoring the electronic structure of metal-organic interfaces.