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