reduced form of the complex is adsorbed in the Au surface and the reduction reaction
is connected with reorientation of the adsorbed metallosurfactant molecules.
The quantitative analysis of the orientation of the C–O phenolate groups in LB
films of the metallosurfactant molecules as a function of the electrode potential has
been done. The C–O bonds in the three phenolate groups have an average tilt of 60
in 1 LB and 75
in 5LB film, in the oxidized Fe
(III) L
N2O3 form of the complex.
During the reduction reaction the average tilt of the C–O phenolate bonds decreases
to 45
in the monolayer and 20
in multilayer assembly. After reduction these tilt
angles remain constant, until desorption potential is reached (E < À0.75 V vs
Ag/AgCl). Potential-driven re-adsorption of the reduced metallosurfactant on the
Au surface leads to further changes in the film orientation. In the 1LB the average tilt
of the C–O phenolate bonds increases to 70
. This result indicates that the redox
active centers undergo a 30
to 45
rotation during reduction, changing its average
orientation from a preferential parallel to a preferential normal to the metal surface.
The quantitative analysis of the ν as (C–O–C) and ν s (CH 2 ) modes in the aloxy chains
reflects the potential-dependent reorientation of the polar aloxy chains in the LB
films of the metallosurfactant. Figure 4.3 shows the calculated tilt angles.
As shown in Fig. 4.3a the transition dipole vector of the ν as (C–O–C) mode is
overlapped with the long axis of the aloxy chain whereas the transition dipole
vectors of the ν s (CH 2 ) is normal to this axis. In LB films of the oxidized form of
the metallosurfactant Fe
(III) L
N2O3 two aloxy chains make a small tilt (ca. 20
) with
respect to the surface normal. During reduction the chains adopt almost a parallel to
the surface orientation. Opposite changes in the tilt angle of the ν s (CH 2 ) mode are
observed (Fig. 4.3b). These two vectors are orthogonal to each other and indeed the
sum of these two tilt angles adds to 90
(Fig. 4.3b). This result illustrates clearly that
the aloxy chains follow the changes in the orientation of the redox-active center. This
example demonstrates that in situ PM IRRAS is applicable to study potential-driven
C
O
C
H H
H
O
C
C
a)
b)
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0
30
60
90
s (CH2) / degree
(COC) / degree
E / V vs Ag/AgCl
0
30
60
90
Fig. 4.3 (a) Structure of the aloxy chain in the metallosurfactant with indicated directions of the
transition dipole vectors of the ν as (C–O–C) (red arrow) and ν s (CH 2 ) (blue arrow) and ν as (CH 2 )
(black arrow) modes. (b) Plots of the calculated average tilt of the transition dipole vector of the
ν as (C–O–C) (red squares) and ν s (CH 2 ) (blue squares) as a function of the electrode potential. Black
squares show the sum of these two tilt angles. Copied with permission from [2]
4.1 In Situ PM IRRAS Studies of Redox-Active Molecular Films...
101
is connected with reorientation of the adsorbed metallosurfactant molecules.
The quantitative analysis of the orientation of the C–O phenolate groups in LB
films of the metallosurfactant molecules as a function of the electrode potential has
been done. The C–O bonds in the three phenolate groups have an average tilt of 60
in 1 LB and 75
in 5LB film, in the oxidized Fe
(III) L
N2O3 form of the complex.
During the reduction reaction the average tilt of the C–O phenolate bonds decreases
to 45
in the monolayer and 20
in multilayer assembly. After reduction these tilt
angles remain constant, until desorption potential is reached (E < À0.75 V vs
Ag/AgCl). Potential-driven re-adsorption of the reduced metallosurfactant on the
Au surface leads to further changes in the film orientation. In the 1LB the average tilt
of the C–O phenolate bonds increases to 70
. This result indicates that the redox
active centers undergo a 30
to 45
rotation during reduction, changing its average
orientation from a preferential parallel to a preferential normal to the metal surface.
The quantitative analysis of the ν as (C–O–C) and ν s (CH 2 ) modes in the aloxy chains
reflects the potential-dependent reorientation of the polar aloxy chains in the LB
films of the metallosurfactant. Figure 4.3 shows the calculated tilt angles.
As shown in Fig. 4.3a the transition dipole vector of the ν as (C–O–C) mode is
overlapped with the long axis of the aloxy chain whereas the transition dipole
vectors of the ν s (CH 2 ) is normal to this axis. In LB films of the oxidized form of
the metallosurfactant Fe
(III) L
N2O3 two aloxy chains make a small tilt (ca. 20
) with
respect to the surface normal. During reduction the chains adopt almost a parallel to
the surface orientation. Opposite changes in the tilt angle of the ν s (CH 2 ) mode are
observed (Fig. 4.3b). These two vectors are orthogonal to each other and indeed the
sum of these two tilt angles adds to 90
(Fig. 4.3b). This result illustrates clearly that
the aloxy chains follow the changes in the orientation of the redox-active center. This
example demonstrates that in situ PM IRRAS is applicable to study potential-driven
C
O
C
H H
H
O
C
C
a)
b)
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0
30
60
90
s (CH2) / degree
(COC) / degree
E / V vs Ag/AgCl
0
30
60
90
Fig. 4.3 (a) Structure of the aloxy chain in the metallosurfactant with indicated directions of the
transition dipole vectors of the ν as (C–O–C) (red arrow) and ν s (CH 2 ) (blue arrow) and ν as (CH 2 )
(black arrow) modes. (b) Plots of the calculated average tilt of the transition dipole vector of the
ν as (C–O–C) (red squares) and ν s (CH 2 ) (blue squares) as a function of the electrode potential. Black
squares show the sum of these two tilt angles. Copied with permission from [2]
4.1 In Situ PM IRRAS Studies of Redox-Active Molecular Films...
101