title: TEMPO Monolayers on Si(100) Electrodes: Electrostatic Effects by the Electrolyte and Semiconductor Space-Charge on the Electroactivity of a Persistent Radical.
abstract: This work demonstrates the effect of electrostatic interactions on the electroactivity of a persistent organic free radical. This was achieved by chemisorption of molecules of 4-azido-2,2,6,6-tetramethyl-1-piperdinyloxy (4-azido-TEMPO) onto monolayer-modified Si(100) electrodes using a two-step chemical procedure to preserve the open-shell state and hence the electroactivity of the nitroxide radical. Kinetic and thermodynamic parameters for the surface electrochemical reaction are investigated experimentally and analyzed with the aid of electrochemical digital simulations and quantum-chemical calculations of a theoretical model of the tethered TEMPO system. Interactions between the electrolyte anions and the TEMPO grafted on highly doped, i.e., metallic, electrodes can be tuned to predictably manipulate the oxidizing power of surface nitroxide/oxoammonium redox couple, hence showing the practical importance of the electrostatics on the electrolyte side of the radical monolayer. Conversely, for monolayers prepared on the poorly doped electrodes, the electrostatic interactions between the tethered TEMPO units and the semiconductor-side, i.e., space-charge, become dominant and result in drastic kinetic changes to the electroactivity of the radical monolayer as well as electrochemical nonidealities that can be explained as an increase in the self-interaction "a" parameter that leads to the Frumkin isotherm.
authors.affiliation: ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, University of Wollongong , Wollongong, New South Wales 2500, Australia.
authors.forename: Long
authors.initials: L
authors.lastname: Zhang
authors.affiliation: ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, University of Wollongong , Wollongong, New South Wales 2500, Australia.
authors.forename: Yan Boris
authors.initials: YB
authors.lastname: Vogel
authors.affiliation: ARC Centre of Excellence for Electromaterials Science, Research School of Chemistry, Australian National University , Canberra, Australian Capital Territory 2601, Australia.
authors.forename: Benjamin B
authors.initials: BB
authors.lastname: Noble
authors.affiliation: School of Chemistry, Australian Centre for NanoMedicine and ARC Centre of Excellence for Convergent Bio-Nano Science and Technology, The University of New South Wales , Sydney, New South Wales 2052, Australia.
authors.forename: Vinicius R
authors.initials: VR
authors.lastname: Gonçales
authors.affiliation: Institut de Bioenginyeria de Catalunya (IBEC) , Baldiri Reixac 15-21, Barcelona 08028, Catalonia Spain.
authors.forename: Nadim
authors.initials: N
authors.lastname: Darwish
authors.affiliation: Bragg Institute, Australian Nuclear Science and Technology Organisation (ANSTO) , Locked Bag 2001, Kirrawee DC, New South Wales 2232, Australia.
authors.forename: Anton Le
authors.initials: AL
authors.lastname: Brun
authors.affiliation: School of Chemistry, Australian Centre for NanoMedicine and ARC Centre of Excellence for Convergent Bio-Nano Science and Technology, The University of New South Wales , Sydney, New South Wales 2052, Australia.
authors.forename: J Justin
authors.initials: JJ
authors.lastname: Gooding
authors.affiliation: ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, University of Wollongong , Wollongong, New South Wales 2500, Australia.
authors.forename: Gordon G
authors.initials: GG
authors.lastname: Wallace
authors.affiliation: ARC Centre of Excellence for Electromaterials Science, Research School of Chemistry, Australian National University , Canberra, Australian Capital Territory 2601, Australia.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Coote
authors.affiliation: ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, University of Wollongong , Wollongong, New South Wales 2500, Australia.
authors.forename: Simone
authors.initials: S
authors.lastname: Ciampi