Analytical and structural evaluation of poly(3-hexylthiophene)s formed by chemical oxidative

coupling methods: the role of experimental conditions in their design

Warren SolfiellMcCarley Research GroupDepartment of ChemistryLouisiana State University

Baton RougeNovember 16 2009

1

Pyrrole Monomer capped dendrimer

Oxidative coupling

Reducing agent

Oligomerized monomer units

DAB-(Py)32

2

Capture and release dendrimers

N

N

N

N

N

N

N

N

N

N

N

N

link to dendrimer

N

N

N

N

R

R

R

R

N

N

N

N

R

R

R

X-

R

n

n

Reduction

N

N

N

R

R

R

OxidativeOligomerizaton

N

R

polaron

N

N

N

N

R

R

R

X-

R

n

bipolaron

X-

FurtherOxidation

neutral polymer

oxidized

reduced

3

Oxidation of poly(pyrrole)s for capture and release

S

oligo(3-alkylthiophene)

nS S

S

H

H

R

R

R

R

N

R

N

R

N

R

N

R

N

R

N

R

N

R

N

R

N

R

N

R

H

H

oligo(N-alkylpyrrole)

n

Heterocyclic Conducting Polymers

4

•Field Effect Transistors•Oganic/biological sensors•OLEDs•Flexible Displays•Solar Cells•Antistatic•Printable conductive ink•Anti-corrosion•RFID tags

5

1.00 mmol of FeCl3 in 12.5 mL solvent used (80 mM)

stir 1 hour (@RT) under argon

1.00 mmol of monomerin 12.5 mL solvent used (80 mM)

quench with MeOH

24 hours

then washed and extractedwith 300 mL 2.0N HCl

and 200 mL chloroform

solid polymer is filtered off

chloroform is rotary-evaporatedand polymer film

is dried under highvacuum to constant mass

6

Polymerization procedure for chemical oxidative coupling

S S H

SH

SSH H Soxidation

dimer

S

S H

H

+ + ++

+

-2H+ oxidationR FeCl3 RR

R

R R

S

R

R

R

S

S

+

R

RH

S

S

SE1 E2

R R

R

n

C. head-to-tail-head-to-head

S

S

SE1 E2

R R

R

n

D. tail-to-tail-head-to-head

S E2

R

n

S

S

R

R

E1

A. head-to-tail-head-to-tail

S

S

S E2E1

R R

Rn

B. tail-to-tail-head-to-tail

oligomerization

7

Oxidation pathway for heterocyclic conducting polymers

OVERVIEWS E2

R

n

SS

R

R

E1

A. head-to-tail-head-to-tail

SS

S E2E1

R R

Rn

B. tail-to-tail-head-to-tail

SS

SE1 E2

R R

Rn

C. head-to-tail-head-to-head

S

S

SE1 E2

R R

Rn

D. tail-to-tail-head-to-head8

Figured adapted from; www.psrc.usm.edu/ mauritz/images/maldi2b.jpg

Matrix-assisted laser desorption and ionization (MALDI)

9

Figure adapted from; Dass, C. Principles and Practice of Biological Mass Spectrometry; Wiley-Interscience: New York, 2001.

2

1

2

zV

mL

v

Lt

MALDI- Time of flight (Tof) Mass spectrometry

10

Mend = Mpeak - Mcat - nMrep

Mend = Mpeak - Mprot - nMrep

Mend = Mpeak - Melec - nMrep

[M].+

MALDI- Time of flight (Tof) Mass spectrometry

11

and http://www.sci.sdsu.edu/TFrey/Bio750/Chroma4.gif

figures adapted from; http://content.answers.com/main/content/img/McGrawHill/Encyclopedia/images/CE283900FG0010.gif

Size exclusion chromatography (SEC)

12

Part One: Modifications to polymerization procedures for chemical oxidative coupling of poly(3-hexylthiophene)s

13

S

SS

TerthiopheneMW 248.4

CH3

CN

CNH3C

H3CCH3

trans-2-[3-(4-tert-Butylphenyl)-2-methyl-2-propenylidene]malononitrile

MW 250.34

"DCTB"

Matrix assisted laser desorption and ionization (MALDI) matrices

14

750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 35000

2000

4000

6000

8000

10000

Abundance

m/z

0 1300 2600 3900 52000.00

7.50x102

1.50x103

2.25x103

3.00x103

n =

30

n =

29

n =

28

n =

27

n =

26

n =

25

n =

24

n =

23

n =

22

n =

21

n =

20

n =

19

n =

18

n =

17

n =

16

n =

15

n =

14

n =

10

n =

9

n =

8

n =

13

n =

12

n =

11

¾n

= 7

n =

6

n =

5

Rela

tive A

bundance

m/z

MALDI spectra P3HT made in chloroform -Top spectra terthiophene matrix -Bottom spectra DCTB matrix

15

MALDI spectrum P3HT made in nitromethanewith 1:2.5 monomer:oxidant ratio

terthiophene matrix

16

0 1600 3200 4800 64000.0

5.0x102

1.0x103

1.5x103

2.0x103

n =

10

n =

9

n =

36

n =

35

n =

34

n =

33

n =

32

n =

31

n =

30

n =

29

n =

28

n =

27

n =

26

n =

25

n =

24

n =

23

n =

22

n =

21

n =

20

n =

19

n =

18

n =

17

n =

16

n =

15

n =

14

n =

13

n =

11

n =

8

n =

12

n =

7

n =

6

IS

IS

Rela

tive A

bundance

m/z

IS

1000 1025 1050 10750.00

6.30x102

1.26x103

1.89x103

Rel

ativ

e A

bund

ance

m/z

n = 6 [M]·

E1= H, E

2= H

E1= H, E

2= O

E1= H, E

2= Cl

E1= Cl, E

2= Cl

1150 1175 1200 1225 12500.00

3.30x102

6.60x102

9.90x102R

elat

ive

Ab

un

dan

ce

m/z

n = 7 [M]·

E1= H, E

2= H

E1= H, E

2= O

E1= H, E

2= Cl

E1= Cl, E

2= Cl

MALDI spectra solid P3HT made in nitromethane DCTB matrix

spectrum

17

0 1500 3000 4500 60000

2500

5000

7500

10000R

ela

tive A

bundance

m/z

825 850 875 9000

100

200

300

400

Observed H, H calculated H, O calculated H, Cl calculated

Rel

ativ

e A

bund

ance

m/z

End-group analysisn = 5

[M]·+

1150 1175 1200 1225 12500

250

500

750

1000

Observed H, H calculated H, O calculated H, Cl calculated

Rel

ativ

e A

bund

ance

m/z

End-group analysisn = 7

[M]·+

MALDI spectra soluble P3HT made in nitromethane DCTB matrix

spectrum

18

1H-NMR P3HT made in nitromethane

-soluble fraction above-Solid precipitate below

67%

26%

19

Conclusions-Part One

• DCTB, a previously unreported matrix for use with poly(alkylthiophene)s, is preferable and beneficial for MALDI analysis of these materials

• Soluble material from the chemical oxidative coupling polymerization of these materials is not useful product

• Decreasing the monomer to oxidant ratio for these polymerizations does reduce the chlorine addition to these materials but does not produce only hydrogen

terminated product

• Ion discrimination does occur during MALDI ionization between chlorinated and non-chlorinated oligomers which is dependent on the extent of halogenation

• Sample preparation and choice of matrices is crucial

20

Part Two: Characterization of effects to the physicalproperties of poly(3-hexylthiophene)s

made by chemical oxidation at low-temperatures

21

0 1600 3200 4800 64000.0

5.0x102

1.0x103

1.5x103

2.0x103

n =

10

n =

9

n =

36

n =

35

n =

34

n =

33

n =

32

n =

31

n =

30

n =

29

n =

28

n =

27

n =

26

n =

25

n =

24

n =

23

n =

22

n =

21

n =

20

n =

19

n =

18

n =

17

n =

16

n =

15

n =

14

n =

13

n =

11

n =

8

n =

12

n =

7

n =

6

IS

IS

Rela

tive A

bundance

m/z

IS

1000 1025 1050 10750.00

6.30x102

1.26x103

1.89x103

Rel

ativ

e A

bund

ance

m/z

n = 6 [M]·

E1= H, E

2= H

E1= H, E

2= O

E1= H, E

2= Cl

E1= Cl, E

2= Cl

1150 1175 1200 1225 12500.00

3.30x102

6.60x102

9.90x102R

elat

ive

Ab

un

dan

ce

m/z

n = 7 [M]·

E1= H, E

2= H

E1= H, E

2= O

E1= H, E

2= Cl

E1= Cl, E

2= Cl

MALDI spectra solid P3HT made in nitromethane @ room temperature DCTB matrix

spectrum

22

0 1600 3200 4800 6400

7.50x102

1.50x103

2.25x103

3.00x103

n =

3

n =

36

n =

35

n =

34

n =

33

n =

32

n =

31

n =

30

n =

29

n =

28

¾ n

= 2

7

n =

26

n =

25

n =

24

n =

23

n =

22

n =

21

n =

20

n =

19

n =

18

n =

17

n =

16 n =

15

n =

14

n =

13

n =

12

n =

11

n =

10

n =

9

n =

8 n =

7

n =

6

IS

IS

n =

5

IS

Rela

tive A

bundance

m/z

1000 1025 1050 10750.00

6.30x102

1.26x103

1.89x103

Rel

ativ

e A

bund

ance

m/z

[M]·n = 6

E1= H, E

2= H

E1= H, E

2= O

E1= H, E

2= Cl

E1= Cl, E

2= Cl

1150 1175 1200 1225 12500.00

4.40x102

8.80x102

1.32x103

E1= H, E

2= H

E1= H, E

2= O

E1= H, E

2= Cl

E1= Cl, E

2= Cl

Rel

ativ

e A

bund

ance

m/z

[M]·n = 7

MALDI spectra solid P3HT made in nitromethane @ - 30 ºC DCTB matrix

spectrum

23

0 1300 2600 3900 52000.00

7.50x102

1.50x103

2.25x103

3.00x103

n =

30

n =

29

n =

28

n =

27

n =

26

n =

25

n =

24

n =

23

n =

22

n =

21

n =

20

n =

19

n =

18

n =

17

n =

16

n =

15

n =

14

n =

10

n =

9

n =

8

n =

13

n =

12

n =

11

¾n

= 7

n =

6

n =

5

Rela

tive A

bundance

m/z

1000 1025 1050 10750.00

2.50x102

5.00x102

7.50x102

1.00x103

E1= H, E

2= H

E1= H, E

2= Cl

E1= Cl, E

2= Cl

Rel

ativ

e A

bund

ance

m/z

[M]·n = 6

825 850 875 9000.00

4.40x102

8.80x102

1.32x103

[M]·n = 5

E1= H, E

2= H

E1= H, E

2= Cl

E1= Cl, E

2= Cl

Rel

ativ

e A

bund

ance

m/z

MALDI spectra solid P3HT made in chloroform @ room temperature DCTB matrix

spectrum

24

1000 1025 1050 10750.00

3.80x102

7.60x102

1.14x103

Rel

ativ

e A

bund

ance

m/z

E1= H, E

2= H

E1= H, E

2= Cl

E1= Cl, E

2= Cl

[M]·n = 6

1150 1175 1200 1225 12500.00

3.80x102

7.60x102

1.14x103

Rel

ativ

e A

bund

ance

m/z

[M]·n = 7

E1= H, E

2= H

E1= H, E

2= Cl

E1= Cl, E

2= Cl

0 1300 2600 3900 52000.00

7.50x102

1.50x103

2.25x103

3.00x103

n =

30

n =

29

n =

28

n =

27

n =

26

n =

25

n =

24

n =

23

n =

22

n =

21

n =

20

n =

19

n =

18

n =

17

n =

16

n =

15

n =

14

n =

13

n =

12

n =

11

n =

10

n =

9 n =

8 n =

7

n =

6

n =

5

Relative A

bundance

m/z

MALDI spectra solid P3HT made in chloroform @ - 30 ºC DCTB matrix

spectrum

25

A B

C D78%

77%

51%

65%

Chloroform Nitromethane

26

1H-NMR comparisons of room temperature and low-temperature polymerizations

Conclusions-Part Two

• Shift in equilibrium between active species (Fe2Cl5+ /FeCl2

+ ) could

be attributed to reduced chlorination as the result of several factors• FeCl3 becomes more soluble during these low-temperature polymerizations

• Dielectric constant slightly increases

• Reaction time increases (from 1 to 24 hours)

• Low temperature slows kinetics of reaction

• Regio-regularity only slightly improves for certain solvents•Still a random event

•Radical lifetimes are dependent on solvent and prolonged with reduced temperature

•Oxidation potentials are reduced as oligomer chain grows and oligomer-oligomer coupling may be preferable for certain solvents regardless of temperature

Equation 1 2FeCl3 FeCl2+ + FeCl4¯

Equation 2 2FeCl3 Fe2Cl5+ + Cl¯

27

Part Three: Characterization of solvent effects on polymerization and physical properties of

poly(3-hexylthiophene)s made by chemical oxidation

28

Solventpermittivity

(ϵ)@20 ◦C

donor number (DN)

kcal/mol

acceptor number (AN)

chloroform 4.8 negligible 23nitromethane 37 2.7 20.5

carbon tetrachloride 2.2 9 8.61,2-dichloroethane 10.4 negligible 100* SbCl5 in DCE

acetonitrile 36.6 14.1 19.3toluene 2.4 0.1 8.2* benzene

nitrobenzene 35.7 4.4 14.8hexane 1.9   0*benzene 2.3 0.01 8.2

dichloromethane 9.1    Benzonitrile 26 11.9 15.5nitropropane 17    diethyl ether 4.3 19.2 3.9

triethyl amine 2.4 61* neglibleacetone 21 17 12.5

Bromoform 4.4    

Solvents employed for solvent effect studies

29

0 1300 2600 39000.00

1.50x103

3.00x103

4.50x103

6.00x103R

elative A

bundance

m/z

Solid poly(3-hexylthiophene) formed in 1, 2-dichloroethane with iron III chlorideat RT for 1 hr using 1:1 mon:oxidant ratio; DCTB matrix

81% regio-regular

MALDI spectra solid P3HT made in 1, 2-dichloroethane @ room temperature; DCTB matrix

1,2 -dichloroethane

ɛ r = 10.4An = 100 *Dn = negligibleYield = 25% (45 mg)

spectrum

30

1H-NMR of P3HT made in 1,2-dichloroethane at room temperature

0 1300 2600 39000.0

5.0x102

1.0x103

1.5x103

2.0x103R

elative A

bundance

m/z

Solid poly(3-hexylthiophene) formed in acetonitrile with iron III chlorideat RT for 1 hr using 1:1 mon:oxidant ratio; DCTB matrix

75% regio-regular

MALDI spectra solid P3HT made in acetonitrile @ room temperature; DCTB matrix

acetonitrile

ɛ r = 36.6An =19.3Dn =14.1Yield = 27% (46 mg)

spectrum

31

1H-NMR of P3HT made in acetonitrile at room temperature

0 1400 2800 42000

750

1500

2250

3000R

elative A

bundance

m/z

poly(3-hexylthiophene) formed with ferric chloride in nitrobenzeneat room temp for 1 hour using 1:1 mon:ox ratio

67% regio-regular

MALDI spectra solid P3HT made in nitrobenzene @ room temperature; DCTB matrix

nitrobenzene

ɛ r = 35.7An = 14.8Dn = 4.4Yield = 13% (21 mg)

spectrum

32

1H-NMR of P3HT made in nitrobenzeneat room temperature

Comparison of number average (Mn) molecular weights from SEC

33

Comparison of polydispersities from SEC

34

Conclusions-Part Three

• Solvents with strong Lewis basicity (large Donor number) complex the active species of oxidant disabling active species interaction with monomer

• Degree of polymerization may depend more on active species interaction with solvent than monomer

• Large dielectric constants (i.e. solubility) is not the only reason for presence of tetrachloroferrate ion (as is the case with acetonitrile)

• Appears as though solvents with large dielectric constants and with strong Lewis acidity (large Acceptor number) shift equilibrium to tetrachloroferrate population

• Solvent plays a large role in lifetimes of ionic species i.e monomer, dimer , trimer etc. influencing polymer growth and therefore regioregularity

• Solvent also influences coupling rates reflected in regioregularity

Equation 1 2FeCl3 FeCl2+ + FeCl4¯

Equation 2 2FeCl3 Fe2Cl5+ + Cl¯

35

Part Four: Semi-preparative size exclusion chromatography for the fractionation of

poly(3-hexylthiophene)s made by chemical oxidation

36

10.4 11.7 13.0 14.3 15.6 16.9 18.2 19.5 20.8 22.1 23.40.1

0.2

0.3

0.4

0.5

0.6

0.7

12111098765432

SEC on semi-prep column of 7.6 mg/mL solid p3ht formed in tolueneat RT with iron(I I I) chloride for 1 hour using 1:1 mon:ox ratio1 mL injection 10 mL/min flow rate; 12 collection @ 1 min/ea

Inte

nsit

y

Ve (mL)

1

37

Fraction 3 - 77%

Fraction 1 - 77% 1H-NMR spectra of toluene fractions collected from semi-prep GPC

38

Fraction 6 - 68%

Fraction 4 - 77%

1H-NMR spectra of toluene fractions collected from semi-prep GPC

39

Fraction 8 - 55%

Fraction 7 - 62% 1H-NMR spectra of toluene fractions collected from semi-prep GPC

40

300 450 600 7500.00

0.63

1.26

1.89

D042_1 D042_2 D042_3 D042_4 D042_5 D042_6 D042_7 D042_8A

U

Wavelength (nm)

D042_all Toluene RT 1 to 1 1 hour solidUV-Vis spectrum of toluene fractions from semi-prep GPC

41

Conclusions-Part Four• Appears to be different structures or states of polymer as represented

by interactions of analyte with gel permeation column

• Semi-preparative fractionation seems to be able to effectively separate analyte for molecular weight and structural studies with some modification to procedure

• Evidence of change in regularity for different molecular weights which makes sense as larger polymer should be more regular material

• Procedure may enable obtaining more desirable product made through chemical oxidative coupling polymerization

42

Future Work

• Experiments to further confirm shifts of active species dependent on solvent and temperature

• Examine fractions obtained from semi-preparative GPC with MALDI for clarification of species or reasons for different interactions with GPC column

• Use fractions from semi-preparative GPC in order to further separate individual oligomers, greater than n = 14, in large enough quantities to investigate thoroughly using HPLC

43

Acknowledgements• Prof. Robin L. McCarley• McCarley Research Group• Dr. Rebecca Brauch• Dr. Rafael Cueto• Dr. Evgueni Nesterov• Dr. Azeem Hasan• Dr. Dan Pu• Dr. Kermit Murray • Louisiana State Economic Development Asst.

44