Poly Poly - - CPDT films CPDT films decorated with decorated with d d inuclear Re(I) complex inuclear Re(I) complex chromophore pendants: chromophore pendants: electrochemical and spectroscopic properties electrochemical and spectroscopic properties SMCBS’2011 Surface modification for chemical and biochemical sensing 5 th International Workshop, Lochów, 4-8 November 2011 G. D’Alfonso, M. Panigati, E. Quartapelle Procopio, F. Sannicolò, G. Rampinini, P.R. Mussini, V. Bonometti
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PolyPoly--CPDT films CPDT films
decorated withdecorated with ddinuclear Re(I) complex inuclear Re(I) complex
chromophore pendants:chromophore pendants:
electrochemical and spectroscopic propertieselectrochemical and spectroscopic properties
SMCBS’2011
Surface modification for chemical and biochemical sensing
5th International Workshop, Łochów, 4-8 November 2011
G. D’Alfonso, M. Panigati, E. Quartapelle Procopio, F. Sannicolò, G. Rampinini, P.R. Mussini, V. Bonometti
Introduction
Poly-CPDT films decorated with dinuclear Re(I) complex chromophore pendants: electrochemical and spectroscopic properties
ElectrochromismElectrochromism::change in colour upon polarization
ApplicationsApplications::smart windows
information displayslight shutters
variable-reflectance mirrors
Introduction
Poly-CPDT films decorated with dinuclear Re(I) complex chromophore pendants: electrochemical and spectroscopic properties
ElectrochromicElectrochromic materialsmaterials
P. Beaujuge, J.R. Reynolds, Chem. Rev., 2010, 110, 268–320R.J. Mortimer, Annu. Rev. Mater. Res., 2011, 41, 241–68M. Higuchi et al., J. Inorg. Organomet. Polym., 2009, 19, 74–78
transition metal oxides transitiontransition metalmetal complexescomplexesprussian blue systemsviologensmetal phtalocyaninesconducting polymersconducting polymers
PProDOT
Advantages Advantages of of conducting polymersconducting polymers::
low power consumption cheap fast switching easier processing techniques wide range of colours
low cycle life
Introduction
Poly-CPDT films decorated with dinuclear Re(I) complex chromophore pendants: electrochemical and spectroscopic properties
Polymers Polymers + + Transition Transition Metal Metal Ions Ions
coupling of the chemicalchemical, opticaloptical and electronicelectronic properties of the metal moiety to those of the polymer
novel electrochromic novel electrochromic and and photochromic propertiesphotochromic properties
Anchoring methodsAnchoring methods
of the M or M of the M or M complexcomplex: :
as an electronic isolated as an electronic isolated pendant pendant groupgroup
as an electronically coupledas an electronically coupled pendantpendant groupgroup
inserted intoinserted into thethe conjugation pathconjugation path
the the presence presence of metal of metal complexes helps complexes helps the the formation formation of of
an ordered structure during polymerizationan ordered structure during polymerization
Rh complex is hanging Rh complex is hanging on the on the backbone without perturbing backbone without perturbing the the polymer propertiespolymer properties
we obtain both we obtain both a a redox polymer redox polymer and a and a conducting polymerconducting polymer..
cpdt=O
0,0
0,2
0,4
0,6
0,8
1,0
200 300 400 500 600 700
[nm]
abs
13
L13
SS
O
H
NN
CH3
O
SS
H
UV-Vis spectroscopy
Poly-CPDT films decorated with dinuclear Re(I) complex chromophore pendants: electrochemical and spectroscopic properties
413 nm: new absorption band, strongly affected by solvent effect: 1MLCT in agreement with the lack of conjugation between the metal scaffold and thiophene moiety
cpdt-COOH
0
0,2
0,4
0,6
0,8
1
200 300 400 500 600
≅≅≅≅ [nm]
abs
14
L14
SS
H
O
OH
O
H
OC
NN
CH3
SS
H
SS
O
269 nm, 300 nm: π−π∗ transitions of the thiophene system475 nm: HOMO-LUMO transition. HOMO is on the C atoms of the two thiophenes LUMO is on the bridge constituted by the C=O.(DFT calculations)
H
NN
CH3
O
SS
H
Significant variation of the spectrumketone becomes alcohol disappearance of the 475 nm bandπ−π∗ transitions almost unchanged359 nm: band strongly affected by solvent effect: 1MLCT transition from M to the diazine
SS
H
O
OH
O
H
OC
NN
CH3
SS
H
242 nm, 317 nm: π−π∗ transitions of the thiophene system
Electrochemical characterization: monomers
Poly-CPDT films decorated with dinuclear Re(I) complex chromophore pendants: electrochemical and spectroscopic properties
MeCN + 0.1 M TBABF4 forcomplex /monomer 2, free ligand COOH-CPDT And the corresponding complex 2' having Cl bridging ligands.SS
H
O
OH
O
H
OC
NN
CH3
SS
H
H
H
NN
CH3
2
Cl
Cl
Radical cation on thiophene α-position
oxidation of the binuclear Rh core of the complex
electron poorer because of two Cl bridging ligands.
monoelectronic, EC and C reversible ET
centered on the pyridazine ring,
hardly affected by the Rh auxiliary bridging ligands
Poly-CPDT films decorated with dinuclear Re(I) complex chromophore pendants: electrochemical and spectroscopic properties
SS
H
O
OH
GC electrode, MeCN+0.1 M TBABF4, [COOH-CPDT]= 0.5 mM
GC electrode, MeCN+0.1 M TBABF4, [Rh-CPDT-COOH]=0.25 mM
Fast and regular polymerization
on different electrode materials (Pt,Au,GC,ITO)
with different supporting electrolytes
Monomer peak
is always present
No threshold
current even after 60 cycles!
Excellent conductivity of the film!
earlier onset (sterical reasons?)
CV pattern is more reversiblemore reversible and wellwell--structuredstructured, the presence of the decorating complex pendants results
in a more regular 3more regular 3--D architectureD architecture, with better defined redox site energies, and higher ion and electron conductivity,
a necessary condition for a facile doping/undoping processfacile doping/undoping process.
O
H
OC
NN
CH3
SS
H
n
Electrochemical characterization: film stability
Poly-CPDT films decorated with dinuclear Re(I) complex chromophore pendants: electrochemical and spectroscopic properties
GC electrode+60 cycles, MeCN + 0.1 M THexABF4
remarkable stability remarkable stability
even upon even upon
prolonged cyclingprolonged cycling
GC electrode+60 cycles, MeCN + 0.1 M THexABF4
two thiophene oxidation peaks, merging at higher
scan rates
1st peak: CT mechanism thermodynamically favoured but kinetically hinderedlinked to difficulties in counterion/coion ingress/egress, and therefore occurring at ease only at very low v
2nd peak: gradually prevailing with increasing vthermodynamically more demanding, but kinetically more favouredIt corresponds to an higher number of available reaction sites
NSF
Qn =
number of elementary charges
exchanged per electrode surface unit
O
H
OC
NN
CH3
SS
H
n
SLOWscan rates
FASTscan rates
Electrochemical characterization: EQCM
Poly-CPDT films decorated with dinuclear Re(I) complex chromophore pendants: electrochemical and spectroscopic properties
Regular growth of the film on a Au-coated quartz crystalin MeCN + 0.1 M TBAPF6
periodic fine structure corresponding to the ingress/egress of ions and solvent.
negative variation in the first half-cycle (the oxidative one) positive variation in the second half-cycle (the reductive one)
cation egress upon polymer oxidation.
complexity of the fine structure more than one electron tranfer.
Poly-CPDT films decorated with dinuclear Re(I) complex chromophore pendants: electrochemical and spectroscopic properties
Charge trapping Charge trapping
phenomenon involves a phenomenon involves a
supramolecular supramolecular
reorganization within the reorganization within the
polymer chain assemblypolymer chain assembly
Charge trapping effect observed on many electrode materials
and with many supporting electrolytes
electron rich and an electron poor moiety
unconjugatedbut located on the same molecule,
strict regioselectivity of the polymerization process, leads
to a linear poly-CPDT regularly decorated with
complex pendants
GC + 60-cycle electropolymerization, MeCN+ 0.1 M TBABF4
O
H
OC
NN
CH3
SS
H
n
Electrochemical characterization: EIS
Poly-CPDT films decorated with dinuclear Re(I) complex chromophore pendants: electrochemical and spectroscopic properties
(a) (b)
(c) (d)
neutral state: purely capacitive
behaviour
p-doped state:
1.1. High frequenciesHigh frequencies: the rds is the ET RC parallel circuit
C=capacity of the interphase electrode/polymer
R=activation barrier for the CT
2.2. Medium frequenciesMedium frequencies: the rds is the diffusion of charges within the polymer Warburg element
3.3. Low frequenciesLow frequencies: CT can no more proceed;in this charge-saturation state the system behaves as a capacitor
Electrochemical characterization: EIS
Poly-CPDT films decorated with dinuclear Re(I) complex chromophore pendants: electrochemical and spectroscopic properties
(a) (b)
(c) (d)
At increasingly positive potentials
the electron transfer begins!(smaller diameter of semicircles)
-0.29 V: R » 8000 Ω
-0.02 V: R » 2300 Ωthe electron transfer becomes easier
+0.27 V: R » 100 ΩCT resistance is dramatically lower "diffusive" Warburg section unperceivable, pointing to high conductivity (electronic and ionic) within the polymer
+0.51 V:the CT resistance is nearly unperceivablethe diffusion quite unperceivable the system soon reaches the capacitive behaviour