1
Caso 1: studio voltammetrico
di oligotiofeni “spider like”
“Spider-like” oligothiophenes
TNNααααseries: bithiophenyl pendants, (n
αααα−−−− 5) nodes
T.Benincori, M.Capaccio,F.De Angelis, L.Falciola, M.Muccini, P.Mussini,A.Ponti, S.Toffanin, P.Traldi, F.Sannicolò, Chem.Eur.J., 2008, 14, 459-471.
SS
S SS
T53T’53
SS
S S
S S
S
S
T84T’84
SS SS
S
S
S
S
SSS
T115T’115
SS
S
S S
S
S
SS
S
S
S S
S
T146T’146
SS
S
SS
S
S S
S
S
SS
S
S
S S
S
T177T’177
S
SS
S
S
S
S
S S
T95T95
S
S S
S
S
S
S
S S
S
S
SS
ST146T146
S
S
S
S
S
S
S
S
S
S S
S
S
SS
S
S
S
S
T197T197
TNNααααseries: thiophene pendants,(n
αααα−−−− 3) nodes
T.Benincori, V.Bonometti, F.De Angelis, L.Falciola, M.Muccini, P.Mussini, T. Pilati, S.Toffanin, F.Sannicolò, in preparation (2009)
2
Effective conjugation in branched oligothiophenes
Electrochemical propertiesFrom maxima From onsets
Spectroscopic properties
From maxima From onsets
The term from the “BT” series, having the lower node density, has
•Less positive Ep,a
•Less negative Ep,c
•Significantly lower Eg, both electrochemical and spectroscopic
vs
S
S S
S
S
S
S
S S
S
S
SS
S T146T146
SS
S
S S
S
S
SS
S
S
S S
S
T'146T’146
“Spider-like” oligothiophenes
TNNααααseries: bithiophenyl pendants, (n
αααα−−−− 5) nodes
T.Benincori, M.Capaccio,F.De Angelis, L.Falciola, M.Muccini, P.Mussini,A.Ponti, S.Toffanin, P.Traldi, F.Sannicolò, Chem.Eur.J., 2008, 14, 459-471.
SS
S SS
T53T’53
SS
S S
S S
S
S
T84T’84
SS SS
S
S
S
S
SSS
T115T’115
SS
S
S S
S
S
SS
S
S
S S
S
T146T’146
SS
S
SS
S
S S
S
S
SS
S
S
S S
S
T177T’177
S
SS
S
S
S
S
S S
T95T95
S
S S
S
S
S
S
S S
S
S
SS
ST146T146
S
S
S
S
S
S
S
S
S
S S
S
S
SS
S
S
S
S
T197T197
TNNααααseries: thiophene pendants,(n
αααα−−−− 3) nodes
T.Benincori, V.Bonometti, F.De Angelis, L.Falciola, M.Muccini, P.Mussini, T. Pilati, S.Toffanin, F.Sannicolò, in preparation (2009)
3
Polymerization ability in branched oligothiophenes
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40
E / V(SCE)
i /cv
0.5
200 mV/s
50 mV/s
100 mV/s
500 mV/s
1000 mV/s
2000 mV/s
-1
-0.5
0
0.5
1
1.5
2
2.5
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40
E / V(SCE)
i/ (cv
0.5)
20 mV/s
50 mV/s
100 mV/s
200 mV/s
500 mV/s
1 V/s
2 V/s
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40
E / V(SCE)
i /cv
0.5
200 mV/s
50 mV/s
100 mV/s
500 mV/s
1000 mV/s
2000 mV/s
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40
E /V(SCE)
i /(cv0.5)
200 mV/s
100 mV/s
500 mV/s
1000 mV/s
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40
E / V(SCE)
i/cv0.5
200 mV/s
20 mV/s
50 mV/s
100 mV/s
500 mV/s
1000 mV/s
2000 mV/s
T53 T84
T115
Fast polymer deposition Slower polymerdeposition
Two merging
reversible peaks
0.0005 M oligomerin CH2Cl2
+0.1 M TBAP
T146SS
S
S S
S
S
SS
S
S
S S
S
T177SS
S
SS
S
S S
S
S
SS
S
S
S S
S
A single reversible monoelectronic
peak accounting for 2 electrons per
oligomer
Caso 2: studio voltammetrico
di complessi “kiss lock”
4
“Kiss lock”
complexes
Solvent effect
polar DMF
apolar DCM
Caso 3: studio voltammetrico, EIS e
spettroelettrochimico di un
“charm-bracelet conducting polymer”
5
“Charm bracelet”
electroactive polymer
with
diRhenium complex
pendants
-3 -2.8 -2.6 -2.4 -2.2 -2 -1.8 -1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
E /V(SCE)
(i /(
cv0.5))/(A
cm-2 m
ol -1 d
m3
V-0
.5 s0
.5)ACN + TBATFB 0.1 M background
0.0005 M monomer cathodic scan
0.0005 M monomer anodic scan
scan restricted to HOMO LUMO gap
Free cpdt ligand
Complex with same pyridazine but two Cl ligands instead of H and OOCcpdt
N N
Re Re
S
S
A
A: Quasi reversible monoelectronic reduction of the pyridazine group;
B
B: Oxidation of the thiophene group(s), resulting in radical cation formation in α-thiophene position and therefore affording polymerization
C
C: Oxidation of the two Rh centers, taking place at a more positive potential than in the reference complex since the bridging ligands are on the whole less electron attracting
By comparison with free HOOC−−−−Cpdt ligand and the 3-Me-pyridazine complex without cpdt, the CV peaks of the new conjugate can be assigned as follows:
Redox processes of monomer
6
Cycling around peak B, theconjugate affords efficientelectrochemicalpolymerization on GC, Pt, and ITO electrodes :
-4
-3
-2
-1
0
1
2
3
4
5
6
-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5
E /V(SCE)
(i /(
cv0.5))/(A
cm
-2 mol -1 d
m3 V
-0.5 s
0.5)
ACN TEATFB 0.1M (background)
0.0005 M monomer
-200.0
-150.0
-100.0
-50.0
0.0
50.0
100.0
150.0
200.0
0 0.2 0.4 0.6 0.8 1 1.2 1.4
E /V(SCE)
(i /(
cv
))/(A cm
mo
l d
mV
s)
IVIXIIXVIIIXXIVXXXXXXVIXLIIXLVIIILIVLX
The resulting polymer
•is stable in a monomer free solution;
•exhibits two subsequent reversible oxidation peaks, whose relative charge ratio is regularly depending on the potential scan rate (possibly, on account of different rates of the counter ion ingress/egress)
-15
-10
-5
0
5
10
15
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
E /V(SCE)
(i/(
cv))/(A
cm
-2 mol -1 d
m3 V
-0.5 s
0.5)
0.005 V/s
0.01 V/s
0.02 V/s
0.1 V/s
0.2 V/s
0.5 V/s
1 V/s
2 V/s
5 V/s
10 V/s
The polymer also exhibits
charge-trapping features
which strongly
depend on the potential
scan rate, strongly
affecting the negative
charging of the polymer
(possibly, again on
account of different rates of the counter
ion ingress /egress)
Stability and charge trapping in the resulting film
7
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
300 400 500 600 700 800 900 1000 1100
λ / nm
A
0 V0.10 V0.20 V0.30 V0.40 V0.50 V0.60 V0.65 V0.70 V0.75 V0.80 V0.85 V0.90 V0.95 V1.00 V1.05 V1.10 V1.15 V1.20 V
Spectroelectrochemistry on the resulting film
A three−electrode UV−vis
spectroelectrochemical cell Upon polymer charging the UV-vis
characteristics radically changes
(electrochromic effect)
Recording UV spectra
at increasingly positive potentials
8
Una nuova frontiera:
elettroanalisi chirale
Chiral molecular recognition, of outstanding importance in biological and pharmaceutical fields, is the highest form of the molecular recognition, implying to measure energetic differences often very small between diastereoisomeric complexes.
In particular, chiral sensing is much more critical than chiral separations, since in direct chiral sensing devices there is only one single unitary process of separationcorresponding to one theoretical plate in chromatographic separations.
[1] M. Trojanowicz, M. Kaniewska, Electrochemical Chiral Sensors and Biosensors, Electroanalysis, 2009, 21, 229.[2] A. Berthod, Chiral recognition mechanisms, Analytical Chemistry, 2006, 78, 2093.[3] J. Zhang, M.T.Albelda, Y.Liu, J.W.Canary, Chiral Nanotechnology, 2005, 17, 404.
Chiral molecular recognition
Right
Right Left
Right
lower
energy
higher
energy
3-point match: lower energy 2-point match: higher energy
adapted from www.nobelprize.org
from Ref. [2]
9
Chiral molecular recognition depends on
difference in stability constants of
diastereoisomeric complexes with applied
selectors
Chiral selectors, natural and synthetic
Natural selectors: proteins, polysaccharides, cyclodextrins, macrocyclic glycopeptides, alkaloids…
Synthetic selectors: ligand exchangers, ligands forming π,π complexes, molecularly imprinted polymers, chiral crown ethers, polymers…
A. Berthod,Chiral recognition mechanisms,
Analytical Chemistry, 2006, 78, 2093.
Already widely applied with separation and spectroscopic techniques
Chiral electroanalytical sensors
Many efforts have been devoted to achieve chiral electroanalytical sensors based on artificial selectors, following many strategies, such as
•electrodes modified with chiral SAMs, chiral sylane derivatives, adsorbed chiral reagents
•electrodes modified with polymers with “external” stereocentres
•electrodes molecularly imprinted with chiral templates
•electrodes modified with molecular layers asymmetrically grown by magnetopolarization
•chiral metal surfaces
•chiral organic thin-film transistors
However,
•in many cases poor or labile enantioselectivity is observed using of electrode materials with a chirality source localized or external respect to the bulk material
•even the most successful attempts almost invariably resulted in the detection of a difference in current intensity between the signals of the two antipodes;
•the chiral enantioselective layer is in many instances not of general use, but tailored for a given probe;
• many preparation procedures are very sophisticated/expensive…
• … and/or the active films fragile.
10
A recent breakthrough: “inherently chiral” electrodes,effective tools for chiral voltammetry
“Inherently chiral” electrode surfaces
The stereogenic element coincides with the whole main molecular backbone
70° angle, 45 kcal mol-1 racemization energy barrier (cannot be overcome at room T)
(Electro)oligomerization
Films of (mostly cyclic) inherently chiral oligomers
The electroactive oligomer films exhibit outstanding enantioselection propertiestowards many chiral analytes, opening the way to effective chiral voltammetry
Angew. Chemie 2014
Chemistry 2014
Chem. Science 2015
Anal. Bioanal. Chem. 2016
An alternative strategy to achieve chiral electroanalysis:working on achiral electrodes in chiral working media
As an alternative strategy, chiral electroanalysis might also be achieved working on an achiral electrode in a chiral medium.
Possibilities:
Chiral organic solvents
Chiral supporting electrolytes
Increasingly more ordered at the
electrode/solution interphase, resulting
in increasing enantioselective
effects Chiral ionic liquids (CILs)
11
21
With chiral ionic liquids (CILs), such a high degree of supramolecular organization can induce a significant chirality transfer from the solvent to the dissolved species. Analogously with the electrode case, this attitude could be maximized by the “inherent chirality” strategy, that is, working in “inherently chiral” ionic liquids ICILs.
Ionic liquids, Chiral ionic liquids, Inherently chiral ionic liquids
ILs have an intrinsically high supramolecular order; they are assumed to display a behavior similar to highly organized liquid polymers.
C.P. Frizzo, M.A.P. Martins et al.,CrystEngComm. 2015, 17, 2996
22
Implementing the inherent chirality concept in ionic liquids: the rationale
Most ionic liquids have N-heteroaromatic cations with long alkyl substituents (to lower their melting point)
Homotopic moieties → higher intermolecular organization and easier supramolecular interactions then common CILs.
Inherently chiral salts
(Di)alkylation
1,1’-bibenzimidazolium salts 3,3’-bicollidinium salts
1,1’-bibenzimidazole 3,3’-bicollidineAtropoisomeric scaffolds
bi-N-heteroaromatic cations with a rotational barrier arising from sterical hindrance between alkyl substituents could yield inherently chiral ionic liquids ICILs.
12
General character of the enantioselection capability of the new compound family (I)
The enantiomer discrimination capability also holds changing the achiral ionic liquid medium and is modulated by the nature of the available counteranions Moreover, it increases with additive concentration.
(S)- FcA
(R)- FcA
Enantiopure probes
Inherently chiral additive
in BMIMBF4, on achiral Au screen printed electrode
0.005 M additivein BMIMBF4
0.01 M additivein BMIMBF4
0.03 M additivein BMIMBF4
A linear trend is observed of ∆Ep vs log cadditive, reminding of the classical Kolthoff and Lingane equation of redox processes with complex formation
General character of the enantioselection capability of the new compound family (II)
(S)- FcA (R)- FcA
HO
O
OMe
NH2
HO
HO
O
OMe
NH2
HO
L- and D-
DOPA
methylester
(R) and (S)
enantiomers of
BT2T4 inherently
chiral monomer
Using the same diethyl additive in
BMIMPF6 achiral IL
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