Poly -CPDT films decorated with dinuclear Re(I) complex ...users.unimi.it/ECEA/VBonometti Lochow.pdf · CPDT-COOH is an excellent building block for this purpose: it doesn’t lose

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


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


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

T.L. Stott, M.O. Wolf, Coord. Chem. Rev, 2003, 246, 89–101

Our approach…


++

enhanced polymerization attitudeenhanced polymerization attitude

high high optical optical density density changechange

highhigh coloration efficiencycoloration efficiency

ease ease of of modulation by chemical structure modificationsmodulation by chemical structure modifications

SS

OSS

CPDTCPDT

SS

H

O

OH


H

H

CH3

[Re[Re22(CO)(CO)66((µµµµµµµµ--1,21,2--diazine)(diazine)(µµµµµµµµ--X)X)22], ], X = H or Cl

intense yellow/green emission due to intense yellow/green emission due to 33MLCT statesMLCT states

modulation effect of the diazine substituents onmodulation effect of the diazine substituents on

wavelengths, lifetimes, QY. wavelengths, lifetimes, QY.

applications as phosphorescent dopants in OLEDs. applications as phosphorescent dopants in OLEDs.

Cl derivatives: PLQY up to 53%Cl derivatives: PLQY up to 53%

H derivatives: PLQY < 1% but easierH derivatives: PLQY < 1% but easier functionalization functionalization

Our approach…


SS

H

O

OH

SS

O

H

HNN

CH3

O

H

OC

NN

CH3

SS

H

H

NN

CH3

O

SS

H+

+

toluene, ∆∆∆∆

toluene, ∆∆∆∆

14

2[Re2(CO)6(µ-1,2-diazine)(µ-X)2]


Excellent electropolymerizationExcellent electropolymerization

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


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


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

Electrochemical characterization: electropolymerization ability


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


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


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.

O

H

OC

NN

CH3

SS

H

Electrochemical characterization: charge trapping effect


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


(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


(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

Electrochemical characterization: Spectroelectrochemistry


-0.39 V: the film is neutral

496 nm: π−π* transition of the thiophene backbone410 nm: 1MLCT transition

10-cycle polymer films deposited onto ITO-coated glass electrodes, MeCN + 0.1 M TBABF4

at negative values:no changes in the UV spectrum because of the

lack of electronic lack of electronic

communicationcommunicationbetween the thiophene

backbone and the piridazine moieties.

redshift with increasing thickness (increased conjugation)almost unchanged (diazine is not involved in conjugation)

increasing potential:

abs of PT fragment disappears

no change in 1MLCT band

new band at 830 nm:

formation of radical cation

at 1.20 V: increase of the two abs bands

at 687 and 1050 nm:formation of dication

O

H

OC

NN

CH3

SS

H

n

Conclusions


Our molecules provide an interesting example of a both redox and conducting polymer

CPDT-COOH is an excellent building block for this purpose: it doesn’t lose its polymerization ability even after being linked to the complex

At a molecular level, the spectroelectrochemical properties of both the building blocks are additives

Work is in progress with a more complete solid state characterization, to reveal/clarify

possible local or delocalized phenomena (i.e., charge trapping)

and to find applications for optical electrochromic devices

Documents

Poly -CPDT films decorated with dinuclear Re(I) complex ...users.unimi.it/ECEA/VBonometti Lochow.pdf · CPDT-COOH is an excellent building block for this purpose: it doesn’t lose