Peer-Reviewed Journal Details
Mandatory Fields
Forster, RJ;Pellegrin, Y;Keyes, TE
2007
August
Electrochemistry Communications
PH effects on the rate of heterogeneous electron transfer across a fluorine doped tin oxide/monolayer interface
Published
9 ()
Optional Fields
SELF-ASSEMBLED MONOLAYERS SPONTANEOUSLY ADSORBED MONOLAYERS REDOX CENTERS TRANSFER DYNAMICS METAL-ELECTRODES GOLD ELECTRODES ELECTROCHEMISTRY TEMPERATURE KINETICS SEMICONDUCTOR
9
1899
1906
Spontaneously adsorbed monolayers of [Ru(bpy)(2)PIC](PF(6))(2) have been formed on fluorine doped tin oxide macro- and microelectrodes, bpy is 2,2'-bipyridyl and PIC is 2-(4-carboxyphenyl)imidazo[4,5-f][1,10]phenanthroline. These monolayers exhibit well-defined, almost ideal electrochemical responses over a wide range of voltammetric scan rates. The formal potential of the R u(2+/3+) process shifts by less than 30 mV upon immobilization suggesting that the monolayers are well solvated. Significantly, chronoamperometry, conducted on a microsecond timescale, reveals that protonation of the PIC bridging ligand modulates the rate of interfacial electron transfer. The heterogeneous electron transfer rate constant, measured at an overpotential of +50 mV, decreases from 7.0 +/- 1.1 x 10(5) to 0.7 +/- 0.1 x 10(5) s(-1) as the pH of the supporting electrolyte is increased from 1.7 to 9.3. These observations are consistent with the redox mechanism occurring via a heterogeneous electron transfer process, the rate of PIC which depends on the energy difference between the metal d pi-orbitals and the lowest unoccupied molecular orbital (LUMO) of the bridge. Protonation of the bridging ligand decreases this energy gap, resulting in an overall increase in the rate of the redox reaction. Significantly, despite the close proximity of the luminophores to a conducting surface, the monolayers remain luminescent suggesting that the electronically excited state is only weakly coupled to the electrode surface. This is consistent with bipyridyl as the site of the excited state in the metal complex. (c) 2007 Elsevier B.V. All rights reserved.
NEW YORK
1388-2481
10.1016/j.elecom.2007.04.022
Grant Details