Full Papers
doi.org/10.1002/cplu.202100137
ChemPlusChem
mental importance because of their documented toxicity. The
synthesized compounds Fc-1 and Fc-2 were therefore applied
as receptors of aromatic compounds. For this purpose, the
compounds Fc-1 or Fc-2 were deposited on the electrode
surface. The CVs of the recognition layers (GC/Fc-Bu4NPF6-
Nafion®), obtained at the scan rates ranging from 0.005 to
1.0 V·sÀ 1, exhibited well-defined oxidation and reduction peaks
corresponding to the Fe2+/3+ redox couple in the ferrocene
unit. They are presented in Figure 5. The CV redox peak currents
scale linearly with the potential scan rate (insets in Figures 5A
and 5B), and this indicates the surface confined electrochemical
response, as it is expected for such films.
The sensitivity of Fc1 and Fc-2-receptors versus selected
aromatic compound, namely: pyrene (PY), chrysene (CHRS),
fluorene (FLU), phenanthrene (PHEN), 9,10-diphenylanthracene
(9,10-DPA) and 1,4-terphenyl (1,4-TER), was characterized ana-
lytically via the Fc oxidation current signal: functions of the
(RSD) were determined and are given in Table 1. In the
concentration range of aromatic compounds from 10 to 150 or
200 μM the dependencies between the current signal and the
concentration are linear. However, the calibration plots ob-
tained for GC/Fc-2-Bu4NPF6-Nafion® receptor have much better
sensitivity as compared to GC/Fc-1-Bu4NPF6-Nafion® receptor.
For all examined concentrations of aromatic compounds from
the analytical range the repeatability was good, and the relative
standard deviation was less than 5% (n=3). The electrode-to-
electrode reproducibility was also tested with nine different
electrodes, and the relative standard deviation was lower than
6%. The value of LOD was calculated as the mean background
value plus 3 standard deviations(x �3σ; n=3). The created
receptor layers enabled effective recognition of the studied
aromatic species, with the LOD values equaling to 0.5–2.9 μM.
differential pulse voltammograms (DPV) versus concentration of Conclusion
the selected aromatic compound (Figures 6 and 7). Regardless
of the type of aromatic compounds, along with the increase in
analyte concentration in the analyzed solution, significantly
more intense quenching of current signals was observed in the
case of Fc-1 receptor. Specific behavior was observed in the
case of Fc-2 receptor; the Fc current signal was significantly
enhanced in the presence of pyrene and fluorene. In the case of
other aromatic compounds, the signal gradually decreased as
the concentration of the analyte in the solution increased.
Taking into account the structure of the Fc receptors it can be
assumed that the studied aromatic compounds interact with
these Fc-receptors through a dynamic π-π stacking process.
This dynamic non-covalent process occurs when ligands
(analytes) of an appropriate size and chemical nature fit
themselves in with the phenyl rings. These ligands are mostly
polycyclic, aromatic, and planar. The pyrene and fluorene have
smaller planar fragment to form the non-covalent system with
Fc-receptor, thus, they rather play a role of a bridge between Fc
residues facilitating the exchange of an electron. The difference
in the intensities of the current signals of the Fc units in the
recognition layers before and after binding an analyte as a
function of its concentration were applied to construction of
the calibration curves, see insets in Figure 6 and 7. Based on
these plots, analytical parameters such as linear regression
equations, detection limits and relative standard deviations
In conclusion, we demonstrated that the ferrocenylated 2,4,6-
triphenyl-1,3,5-triazine-containing highly organized ferroceny-
lated molecule Fc-2, and a structural analog 1,3,5-triphenylben-
zene containing compound Fc-1, can be efficiently obtained
under mild conditions (isolated yield of 89% at room temper-
ature). Optimization experiments revealed that 1,4-dioxane was
the key solvent, enabling the efficient formation of the target
compound. The formation of the target C3-symemtric Fc-2 was
confirmed with various analytical techniques, including spectro-
scopic (NMR, FT-IR, FT-Raman) and microscopic (SEM) ones.
Electrochemical analyses revealed one pair of oxidation-reduc-
tion potentials for the studied Fc-doped compounds. Fc-1 and
Fc-2 were applied to the construction of the fully innovative
recognition layers (electrochemical sensors) toward the recog-
nition of selected polycyclic aromatic species, namely pyrene,
chrysene, fluorene, phenanthrene, 9,10-diphenylanthracene and
1,4-terphenyl. The calculated LOD values were low (0.5–2.9 μM),
which means that the Fc-1 or Fc-2 receptors provide good
parameters of the constructed sensors. Our work expands the
state-of-the-art of nitrogen-doped highly ordered molecules
bearing a ferrocene motif and their applications as functional
materials. Our future works in this topic will include the
preparation of Fc-2- and Fc-1-related structures, as well as the
examination of their new properties and functions.
Table 1. Analytical parameters of GC/Fc-Bu4NPF6-Nafion® receptors.
Linear regression equation
R2
Analytical range [μM]
LOD [μM]
RSD [%]
GC/Fc-1-Bu4NPF6-Nafion®
ΔI=(2.0�0.2)CPHEN +(0.03�0.02)
ΔI=(1.8�0.2)CCHRS +(0.02�0.01)
ΔI=(1.3�0.1)C9,10-DPA +(0.02�0.01)
ΔI=(2.9�0.2)C1,4-TER +(0.04�0.01)
0.985
0.986
0.991
0.994
10–150
10–150
10–200
2.9
2.6
2.4
1.5
3.7
3.4
4.9
4.5
10–200
GC/Fc-2-Bu4NPF6-Nafion®
ΔI=(7.6�0.2)CPYR +(0.02�0.02)
ΔI=(43.3�1.2)CFLU +(0.3�0.13)
ΔI=(12.7�0.4)CPHEN +(0.01�0.01)
ΔI=(8.5�0.6)CCHRS +(0.06�0.07)
ΔI=(10.7�0.6)C9,10-DPA +(0.06�0.06)
ΔI=(12.0�0.3)C1,4-TER +(0.01�0.03)
0.999
0.998
0.998
0.995
0.995
0.999
10–200
10–200
10–200
10–200
10–200
10–200
1.2
0.5
1.1
1.0
1.4
0.9
3.6
3.5
2.7
2.8
3.4
3.2
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