Supplementary Material (ESI) for Chemical Communications
This journal is © The Royal Society of Chemistry 2002
Supplementary data
A New Redox Site as an Alternative to Ferrocene to Study Electron Transfer in
Self-Assembled Monolayers
Cédric Hortholary, Freddy Minc, Christophe Coudret,* Jacques Bonvoisin* and Jean-Pierre
Launay
CEMES-CNRS, 29 rue Jeanne Marvig, BP4347, 31055 Toulouse cedex 4, France. Fax: +33 5
62 25 79 99; Tel: +33 5 62 25 78 59;
AC voltammograms
2,10E-07
71900 Hz
44300 Hz
1,90E-07
|Y/w| (-1.rad-1.s)
1,70E-07
27280 Hz
16800 Hz
10350 Hz
1,50E-07
6370 Hz
564 Hz
1,30E-07
1,10E-07
9,00E-08
7,00E-08
5,00E-08
-0,1
0
0,1
0,2
0,3
0,4
0,5
0,6
E (V vs. ref)
Representative ac Voltammograms at seven different frequencies for a
gold ball electrode coated with A and 11-mercaptoundecanol (ratio 1:15).
Voltammograms were acquired in a 1 M NaClO4 electrolyte, with bias
potential applied vs a Ag/AgCl reference electrode.
Determination of the amount of the redox active molecules
In the model of a Nernstian distribution of states perturbed by a superimposed
potential oscillation, the average number of redox sites is proportional, for the low frequency
region to the amplitude of the faradaic response of the SAM. The latter is obtained from our
experimental ac voltammograms by subtracting the background (capacitive) admittance
(recorded at 0.05 V) from the peak one. Our SAM preparation protocol gives a reproducible
coverage of 2.2 10-11 mol/cm2 .
F² 
Y
 2 
No
 peak   4RT 
with  the pulsation of the superimposed potential oscillation and No the number of moles
adsorbate.
Supplementary Material (ESI) for Chemical Communications
This journal is © The Royal Society of Chemistry 2002
Randles equivalent circuit and data processing
For an adsorbed redox active species in a concentrated supporting electrolyte, the
electrode behavior is modelled as the following equivalent circuit
CDL
Rsol
CAds
RCT
Randles equivalent circuit. Rsol : uncompensated solution resistance ; CDL :
double layer capacitance ; Cads : adsorption capacitance ; RCT : charge
transfer resistance.
The experimental data are fitted according the following law:
 ²   ² 

4ko² 


 1  ² 
4ko ² 

1/ 2
i peak Y peak

i back Y back
with ko=1/ (2 RCT CAds) and =1+ CAds / CDL
SAM preparation
A mixed monolayer of the redox active molecule (0.1 mM) and 11-mercaptoundecanol
is prepared by immersing a gold ball electrode in a coating solution in ethanol (ratio 1:15)
during 15 minutes at room temperature, and then in a 1 mM 11-mercaptoundecanol solution
in ethanol during 4 hours. This optimizes the crystalization of the alkane thiol monolayer and
removes defective species placed at the SAM grain boundaries. It is probed by the evaluation
of dispersion of the ET.