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New Journal of Chemistry

Supporting Information

Facile polymerization method for poly(3,4-ethylenedioxythiophene)

and related polymers using iodine vapour

Sonal Guptaab and Asit Patra*ab

aPhotovoltaic Metrology Section, Advanced Materials & Device Metrology Division, CSIR-National Physical

Laboratory, Dr. K. S. Krishnan Marg, New Delhi-110012, India bAcademy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, India

Note added after first publication

This supporting information replaces the version published on 18th September 2019, which contained errors in Fig. S1(a).

Table of content

1. Synthesis of monomers………………………………………..S2

2. General procedure for dedoping of polymers………………..S5

3. Preparation of polymer films for UV-vis measurement……..S5

4. Sample preparation procedure for GPC……………………..S6

5. Proposed mechanism of the polymerization………………….S6

6. NMR, GPC, UV-vis, FT-IR and CV data……………… …...S7

7. References………………………………………………… …S16

Electronic Supplementary Material (ESI) for New Journal of Chemistry.This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2020

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1. Synthesis of monomers

Monomers 2,5-dichloro-3,4-ethylenedioxythiophene (DCEDOT)1, 2,5-dibromo-3,4-

ethylenedioxythiophene (DBEDOT)1, 2,5-diiodo-3,4-ethylenedioxythiophene (DIEDOT)1, 2,5-

dibromo-3,4-propylenedioxythiophene (DBProDOT)2, DBEDOT-C63, and DBEDOT-C8

3 were

prepared by previously reported method.

Synthesis of 2,5-dibromo-3,4-propylenedioxythiophene (DBProDOT; M3)

OO

S

ProDOT

S

MeO OMe OH OH

PTSA

Toluene

NBS

CHCl3

OO

S

DBProDOT

BrBr

56% 91%

Synthesis of ProDOT. To a well stirred solution of 3,4-dimethoxythiophene (1.0 g, 6.9 mmol) in dry

toluene (50 mL) was added 4 equivalents of propane-1,3-diol and followed by p-toluenesulphonic

acid (PTSA) (80 mg). The resulting reaction mixture was allowed to stir for 48 hours at 100 °C with

under N2 atmosphere. The resulting mixture was diluted with 100 mL H2O and extracted with ether

(3× 50 mL). The combined organic extracts were washed with brine, dried over Na2SO4. After that,

solvent was evaporated and purified by the column chromatography to produce ProDOT in 56%

yield (600 mg). UV-vis (hexane) 𝜆max at 250 nm, 1H NMR (600 MHz, CDCl3) δ 6.51 (s, 2H), 4.06 (t,

J=5.4 Hz, 4H), 2.18 (t, J=5.4 Hz, 2H), 13C NMR (150 MHz, CDCl3) δ 150.8, 106.5, 71.3 and 33.9.

Synthesis of DBProDOT (M3). To a well stirred solution of ProDOT (300 mg, 1.92 mmol) in 20

mL dry CHCl3 at 0 °C, was added 2 equivalents of n-bromosuccinimide (NBS) in small portions. The

resulting reaction mixture was allowed to stir for 1.0 hour at room temperature. The reaction mixture

was diluted with 30 mL H2O and extracted with chloroform (3× 25 mL) and dried over Na2SO4. The

solvent was evaporated under reduce pressure and purification was carried out by column

chromatography. The compound DBProDOT was obtained in 91% yield (550 mg) as a white solid.

UV-vis (hexane) 𝜆max at 253 nm; 1H NMR (500 MHz, CDCl3) δ 4.16 (t, J=5.0 Hz, 4H), 2.28-2.22 (m,

2H).

S3

Synthesis of 2,5-diiodo-3,4-propylenedioxythiophene (DIProDOT; M4)

OO

S

CH3COOH, Hg(OAc)2

20°C

I2

CH3CNAcOHg HgOAc

ProDOT 1 DIProDOT

OO

SII

OO

S

75% 48%

Synthesis of 2,5-diacetoxymercuri-ProDOT (1). To a well stirred solution of ProDOT (1.0 g, 6.4

mmol) in acetic acid (60 mL) at 20 °C, was added drop-wise a solution of mercury (II) acetate

[Hg(OAc)2] (4.085 g, 12.8 mmol) in acetic acid (100 mL) over 2 hours. The resulting reaction

mixture was allowed to stir for 12 hours. A white precipitate was appeared and resulting precipitate

was filtered and washed with methanol followed by diethyl ether. The filtered product was dried

under vacuum to give 1 as a white solid (3.25 g, 75%). Without further characterization, the

compound was used for next step.

Synthesis of DIProDOT (M4). To the stirred solution of 1 (3.25 g, 4.7 mmol) in acetonitrile (250

mL), was added drop-wise a solution of iodine (2.43 g, 9.6 mmol) in acetonitrile (200 mL). A

yellow-orange colored solution was obtained. After concentration of the resulting solution, saturated

solution of potassium iodide was added. The combined resulting mixture was diluted with 100 mL

H2O, extracted with chloroform (3×50 mL) and finally dried over Na2SO4. The organic solvent was

evaporated and purification was carried out by column chromatography. The compound DIProDOT

was obtained in 48% yield (90 mg) as a light brown colored solid. UV-vis (hexane) 𝜆max at 328 nm;

1H NMR (500 MHz, CDCl3) δ 4.09 (t, J=5.0 Hz, 4H), 2.20-2.16 (m, 2H).

Synthesis of hexyl-2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT-C6; M5)

OO

S

C6H13

S

MeO OMe

PTSA

Toluene

NBS

CHCl3

HO OH

C6H13

OO

S

C6H13

BrBr

EDOT-C6 DBEDOT-C668% 89%

Synthesis of EDOT-C6. To a well stirred solution of 3,4-dimethoxythiophene (420 mg, 2.92 mmol)

in dry toluene (20 mL) was added 4 equivalents of 1,2-octanediol and followed by p-

toluenesulphonic acid (PTSA) (50 mg). The resulting reaction mixture was allowed to stir for 30

hours at 100 °C with under N2 atmosphere. The resulting mixture was diluted with 100 mL H2O and

extracted with ether (3× 50 mL). The combined organic extracts were washed with brine, dried over

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Na2SO4. After that, solvent was evaporated under reduce pressure and purified by the column

chromatography. The pale yellow oily liquid EDOT-C6 was obtained in 68% yield (448 mg). UV-vis

(hexane) 𝜆max at 257 nm; 1H NMR (500 MHz, CDCl3) δ 6.32 (s, 2H), 4.19-4.10 (m, 2H), 3.89 (dd,

J=11.5 and 8.0 Hz, 1H), 1.72-1.50 (m, 4H), 1.40-1.21 (m, 6H), 0.91 (t, J = 7.0 Hz, 3H).

Synthesis of DBEDOT-C6 (M5). To a well stirred solution of EDOT-C6 (300 mg, 1.32 mmol) in 20

mL dry CHCl3 at 0 °C, was added 2 equivalents (470 mg, 2.64 mmol) of n-bromosuccinimide (NBS)

in small portions. The resulting reaction mixture was allowed to stir for 1.0 hour at room

temperature. The resulting mixture was then diluted with 30 mL H2O and extracted with chloroform

(3× 25 mL) and dried over Na2SO4. After that, solvent was evaporated and purification was carried

out by column chromatography. The compound DBEDOT-C6 was obtained in 89% yield (454 mg)

as a pale yellow oily liquid. 1H NMR (500 MHz, CDCl3) δ 4.17 (dd, J=3.0 and 11.5 Hz, 1H), 4.14-

4.04 (m, 1H), 3.85 (dd, J=11.5 and 3.0 Hz, 1H), 1.72-1.62 (m, 2H), 1.56-1.17 (m, 8H), 0.83 (t, J =

7.0 Hz, 3H).

Synthesis of octyl-2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT-C8; M6)

OO

S

C8H17

S

MeO OMe

PTSA

Toluene

NBS

CHCl3

HO OH

C8H17

OO

S

C8H17

BrBr

EDOT-C8 DBEDOT-C864% 92%

Synthesis of EDOT-C8. To a well stirred solution of 3,4-dimethoxythiophene (400 mg, 2.77 mmol)

in dry toluene (20 mL) was added 4 equivalents of 1,2-decanediol and followed by p-

toluenesulphonic acid (PTSA) (50 mg). The resulting reaction mixture was allowed to stir for 30

hours at 100 °C with under N2 atmosphere. The resulting mixture was diluted with 100 mL H2O and

extracted with ether (3× 50 mL). The combined organic extracts were washed with brine, dried over

Na2SO4. After that, solvent was evaporated and purified by the column chromatography. The pale

yellow oily liquid EDOT-C8 was obtained in 64% yield (450 mg) and was characterized by UV-vis-

NIR absorption and NMR spectroscopy. UV-vis (hexane) 𝜆max at 256 nm; 1H NMR (500 MHz,

CDCl3) δ 6.30 (s, 2H), 4.16-4.08 (m, 2H), 3.86 (dd, J=11.5 and 8.0 Hz, 1H), 1.71-1.50 (m, 4H), 1.40-

1.20 (m, 10H), 0.88 (t, J = 7.0 Hz, 3H).

Synthesis of DBEDOT-C8 (M6). To a well stirred solution of EDOT-C8 (300 mg, 1.18 mmol) in 20

mL dry CHCl3 at 0 °C, was added 2 equivalents of n-bromosuccinimide (NBS) (420 mg, 2.36 mmol)

in small portions. The resulting reaction mixture was allowed to stir for around 1.0 hour at room

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temperature. The resulting solution was then diluted with 30 mL H2O and extracted with chloroform

(3× 25 mL) and dried over Na2SO4. After that, solvent was evaporated and purification was carried

out by column chromatography. The compound DBEDOT-C8 was obtained in 92% yield (448 mg)

as a yellow oily liquid. The compound was characterized by NMR spectroscopy. 1H NMR (500

MHz, CDCl3) δ, 4.23 (dd, J=2.0 and 11.5 Hz, 1H), 4.17-4.12 (m, 1H), 3.92 (dd, J=11.5 and 7.0 Hz,

1H), 1.72-1.50 (m, 4H), 1.46-1.23 (m, 10H), 0.91 (t, J = 7.0 Hz, 3H).

2. General procedure for dedoping of polymers.

To a stirred mixture of as prepared polymer (100 mg) in deoxygenated CHCl3 (10 mL) at

room temperature was added hydrazine hydrate (50 mg in 2 mL acetonitrile). (Solvents CHCl3,

MeOH and hexane were purged with dry N2 for 30 minutes for deoxygenation). The resulting

mixture was stirred overnight at room temperature. CHCl3 was removed under reduced pressure and

the resulting residue was collected in to a Whatman extraction thimble under N2 atmosphere. The

resulting dedoped black residue was purified by repeated Soxhlet extraction with deoxygenated

MeOH (6 cycles) and hexane (6 cycles). For insoluble polymers (br-PEDOT, i-PEDOT, br-

PProDOT and i-PProDOT), after Soxhlet extraction, the resulting polymer was dried under reduced

pressure and the polymers were kept under N2 atmosphere. For soluble polymers (PEDOT-C6 and

PEDOT-C8), after Soxhlet extraction, the resulting polymer in Whatman extraction thimble was

further Soxhlet extraction with deoxygenated CHCl3. After few cycles the soluble portion of the

polymer in CHCl3 was collected in to round bottom flask and finally CHCl3 was removed under

reduced pressure yielded deep black blue polymers.

Further doping of the dedoped polymers

About 50 mg of elemental iodine was placed in the bottom of a vial (10 mL). Then a well-ground

powder of dedoped polymer (100 mg) in a Whatman paper was hung in the vial (10 mL). The iodine

vapour was slowly diffused to polymer at room temperature and continued for 6 hours for further

doping.

3. Preparation of polymer films for UV-vis measurement.

For insoluble polymers (br-PEDOT, i-PEDOT, br-PProDOT and i-PProDOT). Neutral polymer

(dedoped) was crushed into very fine powder. The fine powder (10 mg) was put into deoxygenated

CHCl3 (2 mL) and make a suspension mixture under N2 atmosphere. The resulting suspension

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mixture was drop-cast on the glass slide and spread over the slide and dried under N2 atmosphere.

This slide was used for UV-vis measurements.

For soluble polymers (PEDOT-C6 and PEDOT-C8). Neutral polymer (dedoped) (10 mg) was

dissolved into deoxygenated CHCl3 (2 mL) and make a solution under N2 atmosphere. The resulting

solution was drop-casted on the glass slide and spread over the slide and dried under N2 atmosphere.

This slide was used for UV-vis measurements.

4. Sample preparation procedure for GPC

The polymer was dissolved initially in CHCl3 (2 mg/mL), and allowed to solubilize for 3 hours

period at 50 °C. Then at room temperature the solution was filtered through a Millipore 0.5 µm filter.

Injections of ~200 µL were performed and retention times were calibrated against narrow molecular

weight polystyrene standards.

5. Proposed mechanism of the polymerization

The polymerization occurs by an oxidation of DBEDOT promoted by I2 to produce radical cation.

The radical cation reacts with another monomer unit to form radical cation dimer followed by the

release of bromine (Scheme 1) or iodine (Scheme 2). During the polymerization process, bromine

and iodine generated in bromo and iodo derivative respectively act as dopant for the resulting

polymers. It is significant to mention that Br2 is a strong oxidizing agent so oxidizes I- to I2 and itself

reduces to Br-. Following the same procedure leads to the formation of polymers.4

S

OO

BrBrS

OO

BrBr

S

OO

BrBr

S

OO

BrS

OO

Br

Br

Br

I2I

Br

S

O

BrS

OO

Br

-Br2

S

OO

BrS

OO

BrS

OOn

Br2 + 2I - I2 + Br -

S

OO

BrBr

Scheme S1. Proposed mechanism for the iodine vapour polymerization of br-PEDOT

S7

S

OO

IIS

OO

II

S

OO

II

S

OO

IS

OO

I

I

I

I2I

I

S

O

IS

OO

I

-I2

S

OO

IS

OO

IS

OOn

S

OO

II

Scheme S2. Proposed mechanism for the iodine vapour polymerization of i-PEDOT.

6. NMR, GPC, UV-vis, FT-IR and CV data

OO

S

C6H13

n

(a)

S8

0 10 20 30 40

0

5

10

Inte

nsity

Retention time (minute)

(c)

0 10 20 30 40

0

5

10

15

20

Inte

nsity

Retention time (minute)

(d)

Fig. S1. 1H NMR of neutral (a) PEDOT-C6 in CDCl3, (b) PEDOT-C8 in CDCl3 and GPC curve of (c)

PEDOT-C6 and (d) PEDOT-C8 in CHCl3. GPC measurements were performed in CHCl3 at 40 °C and

molecular weight of polymer is calculated from the retention time using polystyrene standard

reference kit.

OO

S

C8H17

n

(b)

S9

400 600 800 10000.0

0.1

0.2

0.3

0.4

Ab

so

rptio

n

Wavelength (nm)

PEDOT

Fig. S2. UV-vis spectrum of electrochemically polymerized PEDOT on ITO coated glass in

monomer free 0.1 M TBAPF6 in acetonitrile at applied potential of -0.8 V (neutral state or undoped).

Polymer film on ITO was prepared by electropolymerization of EDOT monomer at 0.1 M TBAPF6

in acetonitrile at scan rate 50 mV/s between -1.0 V to 1.6 V.

400 600 800 10000.00

0.02

0.04

0.06

0.08

0.10

Ab

so

rptio

n

Wavelength (nm)

P3 (br-PProDOT)

P4 (i-PProDOT)

473 nm

512 nm

442 nm

Fig. S3. UV-vis spectra of PProDOT polymers films on glass slide prepared by iodine vapour

polymerization.

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400 500 600 700 800

0.0

0.1

0.2

0.3

Abso

rptio

n

Wavelength (nm)

PEDOT-C6

643 nm

590 nm555 nm

Fig. S4. UV-vis spectrum of PEDOT-C6 polymer in CHCl3 prepared by iodine vapour

polymerization.

400 600 800 1000

0.0

0.2

0.4

0.6

0.8

Absorp

tion

Wavelength (nm)

PEDOT-C8

639 nm

589 nm550 nm

Fig. S5. UV-vis-NIR spectrum of PEDOT-C8 polymer film prepared by iodine vapour

polymerization.

3000 2500 2000 1500 1000 500

Tra

nsm

itta

nce

(%

)

Wavenumber (cm-1)

PEDOT by SSP

P1 (br-PEDOT)

P2 (i-PEDOT)

(A)

(B)

(C)

Fig. S6. FT-IR spectra of the (A) PEDOT by SSP, (B) br-PEDOT and (C) i-PEDOT in KBr pellet.

S11

3000 2500 2000 1500 1000 500

Tra

nsm

itta

nce

(%)

Wavenumber (cm-1)

P3 (br-PProDOT)

P4 (i-PProDOT)

(A)

(B)

Fig. S7. FT-IR spectra of the (A) br-PProDOT and (B) i-PProDOT in KBr pellet.

-0.8 -0.4 0.0 0.4-2

-1

0

1

2

Curr

ent

den

sity

(m

A/c

m2)

Potential (V)

50 mV/s

75 mV/s

100 mV/s

125 mV/s

150 mV/s

200 mV/s

Fig. S8. CV of PEDOT synthesized by SSP on glassy carbon electrode with Ag/Ag+ as the reference

electrode in 0.1 M TBAPF6 in acetonitrile at different scan rates.

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6 8 10 12 14 16-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Pe

ak C

urr

en

t D

en

sity

(mA

/cm

2)

(scan rate)1/2(mV/s)

Anodic current

Cathodic current

a)

6 8 10 12 14 16-9

-6

-3

0

3

6

9

(scan rate)1/2(mV/s)

Pe

ak C

urr

en

t D

en

sity

(mA

/cm

2)

Anodic Current

Cathodic Current

b)

6 8 10 12 14

-1

0

1

2

Pe

ak C

urr

en

t D

en

sity (

mA

/cm

2)

(scan rate)1/2 (mV/s)

Anodic Current

Cathodic Current

c)

Fig. S9. Plot of redox peak currents vs SQRT of scan rates derived from CV data of a) br-PEDOT at

50-225 mV/s scan rates; b) i-PEDOT at 50-225 mV/s scan rates and c) PEDOT synthesized by SSP

at 50-200 mV/s scan rates on a glassy carbon electrode in 0.1 M TBAPF6 in acetonitrile.

-0.8 -0.4 0.0 0.4 0.8 1.2

-8

-4

0

4

8

Curr

ent

Den

sity

(m

A/c

m2)

Potential (V)

25 mV/s

50 mV/s

75 mV/s

100 mV/s

125 mV/s

150 mV/s

175 mV/s

200 mV/s

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Fig. S10. CV of br-PPrODOT synthesized by iodine vapour polymerization on glassy carbon

electrode with Ag/Ag+ as the reference electrode in 0.1 M TBAPF6 in acetonitrile at different scan

rates.

-0.5 0.0 0.5 1.0-8.0

-4.0

0.0

4.0

8.0

Curr

ent

Den

sity

(mA

/cm

2)

Potential(V)

25 mV/s

50 mV/s

75 mV/s

100 mV/s

125 mV/s

150 mV/s

175 mV/s

200 mV/s

Fig. S11. CV of i-PPrODOT synthesized by iodine vapour polymerization on glassy carbon electrode

with Ag/Ag+ as the reference electrode in 0.1 M TBAPF6 in acetonitrile at different scan rates.

4 6 8 10 12 14-9

-6

-3

0

3

6

Pe

ak C

ure

nt D

en

sity

(mA

/cm

2)

(Scan rate)1/2(mV/s)

Anodic current

Cathodic Current

a)

4 6 8 10 12 14-8

-6

-4

-2

0

2

4

6

8

Peak C

urr

ent

Density

(mA

/cm

2)

(Scan Rate)1/2 (mV/s)

Anodic current

Cathodic current

b)

Fig. S12. Plot of redox peak currents vs SQRT of scan rates derived from CV data of (a) br-

PPrODOT at 25-200 mV/s scan rates and (b) i-PPrODOT at 25-200 mV/s scan rates on a glassy

carbon electrode in 0.1 M TBAPF6 in acetonitrile.

S14

250 300 350 400 4500.0

0.1

0.2

0.3

0.4

Abso

rba

nce

(a

.u)

Wavelength (nm)

(a)

250 300 350 400 450 5000.0

0.2

0.4

0.6

Abso

rba

nce

(a

.u)

Wavelength (nm)

(b)

Fig. S13.UV-vis absorption spectra of (a) EDOT-C6 and (b) EDOT-C8 in hexane.

300 350 400 450

0.1

0.2

0.3

0.4

0.5

Absorp

tion

Wavelength(nm)

(a)

225 250 275 300 325 3500.0

0.1

0.2

0.3

0.4

Ab

so

rptio

n

Wavelength(nm)

(b)

220 240 260 280 300 3200.0

0.1

0.2

0.3

Absorp

tion

Wavelength (nm)

(c)

Fig. S14. UV-vis absorption spectra of (a) DIProDOT, (b) DBrProDOT, and (c) ProDOT in hexane.

Fig. S15. 1H NMR spectrum of ProDOT at 600 MHz in CDCl3.

S15

Fig. S16. 13C NMR spectrum of ProDOT at 150 MHz in CDCl3.

Fig. S17. 1H NMR spectrum of DBProDOT at 500 MHz in CDCl3.

S16

Fig. S18. 1H NMR spectrum of DIProDOT at 500 MHz in CDCl3.

References

1. H. Meng, D. F. Perepichka, M. Bendikov, F. Wudl, G. Z. Pan, W. Yu, W. Dong, S. Brown, J. Am.

Chem. Soc., 2003, 125, 15151-15162.

2. B. Kim, J. K. Koh, J. Kim,W. S.Chi, J. H. Kim, E. Kim, ChemSusChem, 2012, 5, 2173-2180.

3. D. Bhardwaj, Shahjad, S. Gupta, P. Yadav, R. Bhargav, A. Patra, Chemistry Select, 2017, 2, 9570-

9562. DBEDOT-C8 was preapred according to the procedure adopted for the compound DBEDOT-

C6.

4. R. M. Walczak, J. K. Leonard, J. R. Reynolds, Macromolecules, 2008, 41, 691-700.