High-Yielding Alkyne-Tetracyanoethylene Addition Reactions: A Powerful Tool for Analyzing Alkyne-Linked Conjugated Polymer Structures

Full Paper

1758

High-Yielding Alkyne-TetracyanoethyleneAddition Reactions: A Powerful Tool forAnalyzing Alkyne-Linked ConjugatedPolymer Structuresa

Hiroyuki Fujita, Kazuma Tsuboi, Tsuyoshi Michinobu*

Poly(o-phenyleneethynylene) and poly(o-phenylenebutadiynylene) derivatives are synthesizedby the Sonogashira polycondensation or oxidative polymerization of an asymmetric monomer,3,4-diethynyl-N,N-dihexylaniline. Postfunctionalization of the poly(o-phenyleneethylene)derivatives is unsuccessful due to the occurrence of undesired side reactions. In contrast, thepoly(o-phenylenebutadiynylene) derivative is converted into the donor–acceptor type polymerwithout side reactions. The resulting polymer features a well-defined charge-transfer (CT) bandin the Vis–NIR region and redox activity in both theanodic and cathodic directions. The results suggestthat the oxidative polymerization mainly proceedsthrough the pseudo two-step pathway.

Introduction

Alkyne-linked conjugated polymers, such as poly(aryl-

eneethynylene)s and poly(arylenebutadiynylene)s, are an

important class of organic materials due to their excellent

luminescent, conducting, and magnetic properties.[1]

Structure–property relationship studies revealed that the

regioregularity of the polymers is an important factor for

optimizing these properties.[2] Poly(aryleneethynylene)s

H. Fujita, K. TsuboiDepartment of Organic and Polymeric Materials, Tokyo Instituteof Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552,JapanT. MichinobuGlobal Edge Institute, Tokyo Institute of Technology, 2-12-1Ookayama, Meguro-ku, Tokyo 152-8550, JapanE-mail: [email protected]. MichinobuPRESTO, Japan Science and Technology Agency (JST), Japan

a Supporting Information for this article is available from the WileyOnline Library or from the author.

Macromol. Chem. Phys. 2011, 212, 1758–1766

� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonline

are usually synthesized by a reductive polymerization

method, namely Sonogashira polycondensation between

the diethynylated monomers and dihalogeno counter

comonomers. In contrast, most poly(arylenebutadiynyl-

ene)s are obtained by self-polycondensation using an

acetylenic oxidative coupling reaction of the diethynylar-

ene derivatives. In both cases, regioirregular polymers are

obtained from asymmetric monomers. The 1H NMR spectra

sometimes provide useful information about the polymer

structures. However, there are no other techniques capable

of quantifying the extent of the polymer regioregularity.

We have recently focused on the highly efficient addition

reactions between electron-rich alkynes and strong accep-

tor molecules, such as tetracyanoethylene (TCNE) and

7,7,8,8-tetracyanoquinodimethane (TCNQ), forming non-

planar donor–acceptor chromophores via thermal [2þ 2]

cycloaddition followed by ring opening (Scheme 1).[3] The

reactivity mainly depends on the electron-donating groups

substituted by the alkyne moiety as well as the acceptor

molecules. It was found that the p- and o-dialkylanilino-

donors produced the desired donor–acceptor chromophores

in quantitative yields under mild conditions, whereas the

library.com DOI: 10.1002/macp.201100198

R

EDG CNNCEDG R

NC CN

+R CN

CN

EDG

NC CN

CNCN

NC CN

EDG:N(alkyl)2 N(alkyl)2

Scheme 1. Thermal addition reaction between alkynes activated by electron-donating groups (EDGs) and a strong acceptor molecule, TCNE.

High-Yielding Alkyne-Tetracyanoethylene Addition Reactions: . . .

www.mcp-journal.de

m-dialkylanilino-donors did not activate the alkyne moi-

eties.[4] It was also shown that TCNE usually displayed a

higher reactivity compared to TCNQ and its derivatives.[5]

The main advantages of using this class of reactions are that

no special purification process is required because of the

absence of byproducts. In addition, the reaction progress

can be traced by monitoring the low energy CT bands of the

donor–acceptor type products. Application of these reac-

tions to the postfunctionalization of polymers enabled the

introduction of the donor–acceptor moieties in polymer

main chains or side chains.[6] When alkynes of the polymer

main chains were functionalized, donor–acceptor alternat-

ing polymers resulted.[7] Postfunctionalization of the side

chain alkynes of the semiconducting polymers lowered the

polymer energy levels in a controlled manner.[8] Very

recently, we also succeeded in quantifying the alkyne

amounts of the polymer terminals, which allowed for the

estimation of the molecular weights.[9] It should be noted

that the quantification of the alkyne amounts in polymers

has been elusive because common spectroscopic tech-

niques, such as 13C NMR and IR spectroscopies, are non-

quantitative methods. In addition, elemental analyses do

not provide reliable data for polymers due to the presence of

terminal groups.

In this paper, we report the postfunctionalization of the

regioirregular poly(o-phenyleneethynylene) and poly(o-

phenylenebutadiynylene) derivatives, in which the main

chain alkynes are activated by dialkylaniline groups. The

postfunctional TCNE addition reaction progress is based on

the TCNE reactivity of the model compounds. The TCNE

addition amounts are estimated from the UV–Vis–NIR

spectroscopy, and the regioregularity of the precursor

polymers is also considered.

Experimental Section

Materials

All reagents were purchased form Kanto, Tokyo Kasei, Wako, and

Aldrich and used as received.

www.MaterialsViews.com

Macromol. Chem. Phys. 20

� 2011 WILEY-VCH Verlag Gmb

General Measurements

1H NMR and 13C NMR spectra were recorded on a JEOL model AL300

spectrometer at 20 8C. Deuterated chloroform and deuterated

benzene were used as solvents. Chemical shifts are reported in ppm

(parts per million) using either tetramethylsilane (TMS) or residual

solvent signals as an internal reference. Coupling constants (J) are

given in Hz. The resonance multiplicity is described as s (singlet), d

(doublet), t (triplet), and m (multiplet). Infrared (IR) spectra were

recorded on a JASCO FT/IR-4100 spectrometer in the range from

4 000 to 400 cm�1. MALDI-TOF MS spectra were measured on a

Shimadzu/Karatos AXIMA-CFR mass spectrometer using dithranol

as a matrix. Gel permeation chromatography (GPC) was measured

on a JASCO system (PU-2080, CO-2065, RI-2031 and AS-2055)

equipped with polystyrene gel column (Shodex KF-804L) using THF

as an eluent at a flow rate of 1.0 mL �min�1 after calibration with

standard polystyrenes. UV–Vis spectra were recorded on a JASCO V-

630 or V-670 spectrophotometer. For time-dependent UV–Vis–

NIMR measurements of a pre-heated P2 solution in o-dichlor-

obenzene (2.5 mL) with a TCNE solution, a 1 cm quartz cuvette

charged with a stir bar and the V-670 spectrophotometer equipped

with an EHC-716 temperature controller were employed. The

spectra were measured at 0.1 min interevals. Thermogravimetric

analysis (TGA) was carried out on a Rigaku TG 8120 under nitrogen

flow at a scanning rate of 10 8C �min�1.

Synthesis

2-[4-(Dihexylamino)phenyl]-3-{[4-(dihexylamino)phenyl]ethynyl}buta-1,3-diene-1,1,4,4-tetracarbonitrile (5)

TCNE (9.38 mg, 0.073 mmol) was added to a solution of 4 (41.6 mg,

0.073 mmol) in CH2Cl2 (4.5 mL). After stirring at 20 8C for 1 h under

argon, the solvent was evaporated, yielding the desired product as

red-black solid (51 mg, 100%).

M.p. 145–147 8C; 1H NMR (300 MHz, CDCl3): d(ppm)¼0.91

(t, J¼6.2 Hz, 12 H), 1.33 (m, 24 H), 1.62 (m, 8 H), 3.36 (m, 8 H),

6.59 (d, J¼ 9.0 Hz, 2 H), 6.66 (d, J¼9.3 Hz, 2 H), 7.45 (d, J¼8.7 Hz, 2 H),

7.81 (d, J¼ 9.3 Hz, 2 H); 13C NMR (75 MHz, CDCl3 d): d(ppm)¼13.89,

22.50, 26.55, 27.07, 27.16, 31.43, 31.47, 51.07, 51.29, 72.62, 86.69,

90.57, 104.38, 111.57, 111.62, 111.75, 112.69, 113.53, 114.80, 116.96,

125.91, 132.66, 136.20, 149.86, 151.35, 152.81, 160.81; IR (KBr):

n¼2 956, 2 929, 2 857, 2 215, 2 138, 1 603, 1 559, 1 534, 1 507, 1 490,

11, 212, 1758–1766

H & Co. KGaA, Weinheim1759

1760

www.mcp-journal.de

H. Fujita, K. Tsuboi, T. Michinobu

1 457, 1 416, 1 368, 1 295, 1 219, 1 188, 1 118, 1 016, 993, 817, 591,

543 cm�1; MALDI-TOF MS (dithranol) m/z: [M–H]� calcd

for C46H59N6: 695.48; found, 695.39.

2-[4-(Dihexylamino)phenyl]-3-{[3-(dihexylamino)phenyl]ethynyl}buta-1,3-diene-1,1,4,4-tetracabonitrile (7)

TCNE (9.37 mg, 0.073 mmol) was added to a solution of 6 (41.6 mg,

0.073 mmol) in CH2Cl2 (4.5 mL). After stirring at 20 8C for 1 h under

argon, the solvent was evaporated, yielding the desired product as

brown–black solid (51 mg, 97% from 1H NMR spectrum).

M.p. 54–59 8C; 1H NMR (300 MHz, CDCl3): d(ppm)¼ 0.90 (m, 12 H),

1.33 (m, 24 H), 1.59 (m, 8 H), 3.25 (t, J¼7.5 Hz, 4 H), 3.39 (t, J¼7.8 Hz, 4

H), 6.68 (d, J¼4.8 Hz, 2 H), 6.77 (m, 2 H), 6.86 (d, J¼7.5 Hz, 1 H), 7.21 (t,

J¼ 8.0 Hz, 1 H), 7.80 (d, J¼4.6 Hz, 2 H); 13C NMR (75 MHz, CDCl3):

d(ppm)¼ 13.94, 13.98, 22.55, 22.60, 26.59, 26.66, 26.90, 27.20, 31.47,

31.60, 50.84, 51.39, 85.28, 93.57, 110.49, 111.52, 111.95, 113.44,

114.58, 115.41, 116.07, 116.64, 119.88, 120.09, 120.29, 129.62,

132.64, 148.04, 151.21, 152.996, 159.52; IR (ATR): n¼ 2 956, 2 929,

2 858, 2 215, 2 170, 2 068, 1 604, 1 567, 1 532, 1 495, 1 466, 1 456,

1 417, 1 355, 1 323, 1 295, 1 258, 1 215, 1 185, 1 149, 1 119, 988, 900,

819, 797, 773, 726, 679 cm�1.

N,N-Dihexyl-3-iodoaniline (11)

1-Iodohexane (16.1 g, 75.9 mmol) and Na2CO3 (4.25 g, 40.1 mmol)

were added to a solution of 3-iodoaniline (5.00 g, 22.8 mmol) in

dehydrated DMF (60 mL) under nitrogen. The mixture was stirred at

95 8C for 20 h. After cooling to 20 8C, the mixture was washed with

water (200 mL) and extracted with EtOAc. The organic phase was

washed with water and brine, and dried over Na2SO4. After

filtration, the solvents were evaporated. Column chromatography

(SiO2, hexane) afforded the desired product as transparent oil

(8.34 g, 94%).1H NMR (300 MHz, CDCl3): d(ppm)¼0.96 (t, J¼ 4.1 Hz, 6 H), 1.36

(m, 12 H), 1.59 (m, 4 H), 3.24 (t, J¼ 7.5 Hz, 4 H), 6.60 (dd, J¼6.9 and

1.5 Hz, 1 H), 6.88–6.99 (m, 3 H); 13C NMR (75 MHz, CDCl3):

d(ppm)¼ 14.03, 22.63, 26.73, 26.93, 31.62, 50.82, 95.77, 110.69,

120.16, 123.77, 130.41, 149.16; IR (KBr): n¼ 2 955, 2 928, 2 856, 1 586,

1 549, 1 490, 1 466, 1 370, 1 316, 1 292, 1 253, 1 199, 1 178, 1 108,

1 095, 1 073, 977, 888, 830, 755, 724, 682, 653 cm�1; MALDI-TOF MS

(dithranol) m/z: [M–H]– calcd for C18H29IN: 386.13; found, 385.90.

N,N-Dihexyl-3,4-diiodoaniline (12)

Benzyltrimethylammonium dichloroiodate (180 mg, 0.517 mmol)

and CaCO3 (67 mg, 0.669 mmol) were added to a solution of 11

(200 mg, 0.516 mmol) in CH2Cl2 (8 mL) and MeOH (3 mL). The

mixture was stirred at 20 8C for 1 h. After the filtration of

precipitates, the filtrate was evaporated. Column chromatography

(SiO2, hexane) afforded the desired product as yellow oil (236 mg,

89%).1H NMR (300 MHz, CDCl3): d(ppm)¼0.89 (t, J¼ 6.6 Hz, 6 H), 1.29

(m, 12 H), 1.51 (m, 4 H), 3.16 (t, J¼ 7.5 Hz, 4 H), 6.30 (dd, J¼6.0 and

3.0 Hz, 1 H), 7.11 (d, J¼ 3.0 Hz, 1 H), 7.48 (d, J¼ 9.0 Hz, 1 H); 13C NMR

(75 MHz, CDCl3): d(ppm)¼14.02, 22.58, 26.63, 26.78, 31.55, 50.78,

87.79, 108.55, 113.35, 122.25, 138.68, 148.31; IR (KBr): n¼2 953,

2 926, 2 855, 1 577, 1 525, 1 468, 1 368, 1 252, 1 198, 1 175, 1 106, 982,

829, 794 cm�1; MALDI-TOF MS (dithranol) m/z: [M–H]� calcd

for C18H28 I2N: 512.0; found, 511.9.



N,N-Dihexyl-3,4-bis[(trimethylsilyl)ethynyl]aniline (13)

Trimethylsilylacetylene (4.17 mL, 29.5 mmol), [PdCl2(PPh3)2]

(276 mg, 0.393 mmol), and CuI (138 mg, 0.725 mmol) were added

under nitrogen to a degassed solution of 12 (5.05 g, 9.84 mmol) in

iPr2NH (60 mL). The mixture was stirred at 20 8C for 18 h. Hexane

was added and filtered. Removal of the solvents in vacuo, followed

by column chromatography (SiO2, hexane/CH2Cl2 4:1) afforded the

desired product as pale red oil (1.81 g, 41%).1H NMR (300 MHz, CDCl3): d(ppm)¼ 0.17 (s, 9 H), 0.26 (s, 9 H), 0.89

(t, J¼6.2 Hz, 9 H), 1.29 (m, 12 H), 1.52 (m, 4 H), 3.21 (t, J¼ 7.5 Hz, 4 H),

6.46 (dd, J¼6.9 and 2.0 Hz, 1 H), 6.64 (d, J¼2.1 Hz, 1 H), 7.24 (d,

J¼ 8.7 Hz, 1 H); 13C NMR (75 MHz, CDCl3): d(ppm)¼�0.18, 0.00,

13.73, 13.83, 22.34, 26.38, 26.73, 31.29, 31.33, 50.42, 87.75, 94.15,

96.06, 104.18, 104.47, 111.39, 114.24, 126.24, 133.18, 147.18; IR

(KBr): n¼ 2 958, 2 929, 2 858, 2 150, 1 597, 1 538, 1 502, 1 467, 1 371,

1 248, 1 111, 866, 842, 759 cm�1; MALDI-TOF MS (dithranol) m/z:

[M–H]� calcd for C28H46NSi2: 452.3; found, 452.5.

3,4-Diethynyl-N,N-dihexylaniline (14)

K2CO3 (3.92 g, 28.4 mmol) was added to a solution of 13 (1.00 g,

2.20 mmol) in MeOH (40 mL) and THF (24 mL). After stirring for 2 h,

CH2Cl2 was added. The organic phase was washed with water

and evaporated. Column chromatography (hexane/CH2Cl2 1:1)

afforded the desired product as red oil (651 mg, 96%).1H NMR (300 MHz, C6D6): d(ppm)¼ 0.87 (t, J¼7.1 Hz, 6 H), 0.96–

1.38 (m, 16 H), 2.86 (t, J¼ 7.7 Hz, 4 H), 2.99 (s, 1 H), 3.07 (s, 1 H), 6.35

(dd, J¼ 6.0 and 2.9 Hz, 1 H), 6.90 (d, J¼2.7 Hz, 1 H), 7.44 (d, J¼ 8.7 Hz,

1 H); 13C NMR (75 MHz, C6D6): d(ppm)¼ 14.27, 23.03, 26.94, 27.31,

31.95, 50.90, 79.07, 80.40, 83.51, 112.35, 115.65, 126.9, 134.30,

148.00; IR (KBr): n¼3 308, 2 928, 2 857, 2 101, 1 598, 1 541, 1 504,

1 466, 1 371, 1 254, 1 208, 1 097, 848, 808, 642 cm�1; MALDI-TOF MS

(dithranol) m/z: [M–H]– calcd for C22H30N: 308.2; found, 308.5.

P1

[PdCl2(PPh3)2] (2.8 mg, 0.004 mmol) and CuI (1.3 mg, 0.007 mmol)

were added to a degassed solution of 12 (51.2 mg, 0.100 mmol) and

14 (31.0 mg, 0.100 mmol) in toluene (1.9 mL) and iPr2NH (0.6 mL)

under nitrogen. The mixture was stirred at 80 8C for 24 h. After that,

iodobenzene (0.012 mL, 0.108 mmol) was added and further stirred

for 8 h. After cooling to 20 8C, the reaction mixture was poured into

MeOH and the precipitate was collected (25.2 mg, 32.7%).1H NMR (300 MHz, C6D6): d(ppm)¼0.50–2.00 (br m, 22n H), 3.04

(br m, 4n H), 6.20–8.00 (m, 3n H); IR (KBr): n¼ 2 954, 2 928, 2 856,

1 593, 1 536, 1 498, 1 466, 1 394, 1 369, 1 292, 1 252, 1 175, 1 109, 991,

805, 726, 686, 642, 564 cm�1.

P2

CuCl (15.1 mg, 0.153 mmol) andN,N,N0,N0-tetramethylethylenedia-

mine (0.133 mL, 0.893 mmol) were added to a solution of 14

(109 mg, 0.300 mmol) in toluene (2.0 mL). The mixture was stirred at

60 8C for 24 h under air. After that, phenylacetylene (0.036 mL,

0.328 mmol) was added and further stirred for 12 h. After cooling to

20 8C, the reaction mixture was poured into MeOH and the

precipitate was collected (79.4 mg, 72.2%).1H NMR (300 MHz, C6D6): d(ppm)¼0.60–1.75 (br m, 22n H), 2.95

(br m, 4n H), 6.38 (br s, n H), 6.87 (br s, n H), 7.40 (br s, n H); IR (KBr):

n¼2 950, 2 928, 2 856, 2 206, 2 137, 1 591, 1 534, 1 499, 1 466, 1 397,

11, 212, 1758–1766

H & Co. KGaA, Weinheim www.MaterialsViews.com


www.mcp-journal.de

1 368, 1 294, 1 252, 1 228, 1 175, 1 108, 984, 885, 843, 805, 726,

566 cm�1.

P3

TCNE (3.73 mg, 0.0291 mmol) was added under nitrogen to a

solution of P2 (15.0 mg, 0.0488 mmol repeat unit�1) in o-

dichlorobenzene (6.82 mL). The mixture was stirred at 110 8C for

1.5 h. The solvent was evaporated and excess TCNE was sublimed to

afford 0.56 equiv. of TCNE-adducted polymer P3 (18.1 mg, 98%).1H NMR (300 MHz, C6D6): d(ppm)¼0.50–2.00 (br m, 22n H), 3.00

(br m, 4n H), 6.20–8.00 (m, 3n H); IR (KBr): n¼ 2 955, 2 925, 2 856,

2 215, 2 149, 1 591, 1 538, 1 506, 1 468, 1 404, 1 366, 1 293, 1 254,

1 227, 1 200, 1 173, 1 134, 1 114, 1 105, 1 016, 848, 805, 766, 725 cm�1;

Anal. calcd for [(C22H29N)0.44n þ (C28H29N5)0.56n]: C 81.03, H 7.96, N

11.01; found: C 80.92, H 8.25, N 10.83.

Results and Discussion

Model Compounds

It was previously demonstrated that the alkyne-TCNE

addition reaction could be applied to dialkyne molecules

with phenylene spacers.[4] When the p- and m-phenylene

spacers were employed, the desired TCNE bisadducts were

C6H13)2N N(C6H13)2

CNNC

NCCN

(C6H13)2N

TCNE

(a)

(C6H13)2N N(C6H13)2

(b)

TCNE (C

(C6H13)2NTCNE (C

N(C6H13)2

TCNE

N(C6H13)2

(C6H13)2N

21

4

6

8

Scheme 2. TCNE addition to (a) o-diethynylbenzene derivative 1 and




obtained in very high yields. In contrast, an unknown side

reaction occurred in the case of the o-phenylene spacer.

Although the TCNE monoadduct 2 was obtained from the

reaction of 1 and TCNE, the second TCNE addition to the

remaining alkyne of 2 did not proceed (Scheme 2a). A

similar result was reported for the derivative with azulene

donors in place of the dialkylaniline donors.[10] In both

cases, the chemical structures of the final products could not

be identified.

In order to avoid this side reaction, the expansion of the

acetylenic spacer length is known to be effective.[11] There-

fore, the reactivity of the dialkylaniline-substituted buta-

diyne moieties was also studied. As expected, the p-anilino

donors strongly activated the alkynes. Thus, TCNE addition to

the model precursors 4 and 6 in CH2Cl2 afforded the TCNE

monoadducts 5 and 7, respectively, in nearly quantitative

yields at room temperature (Scheme 2b). In contrast, the

m-anilino donors did not activate the butadiyne moieties

due to the formal cross-conjugation. Accordingly, 8 did not

undergo any reactions with TCNE and fully recovered. Note

that the second TCNE addition to the butadiyne moieties was

recently reported by Diederich et al., but the application to

polymer reactions seems difficult due to the moderate yields

(ca. 80%) performed under harsher conditions.[12]

N(C6H13)2

CNNC

NCCN

(C6H13)2N

NCCN

CNNC

N(C6H13)2

TCNE

6H13)2NCN

NC

CNNC

N(C6H13)2

6H13)2NCN

NC

CNNC

N(C6H13)2

CNNC

CNNC

N(C6H13)2

(C6H13)2N

3

5

7

9

(b) 1,4-diphenylbuta-1,3-diyne derivatives 4, 6, and 8.

11, 212, 1758–1766


1762

www.mcp-journal.de


Polymer Synthesis

Based on the reactivity study of the model compounds,

the poly(o-phenyleneethynylene) and poly(o-phenylene-

butadiynylene) derivatives, P1 and P2, were designed as

novel alkyne-linked conjugated polymers. Starting from

the commercially available 3-iodoaniline 10, alkylation of

the amino group followed by iodination with benzyltri-

methylammonium dichloroiodate (BTMAICl2) yielded one

of the key monomers 12 in 84% yield (2 steps) (Scheme 3).

Subsequently, the Sonogashira coupling of 12 with

trimethylsilylacetylene followed by deprotection of the silyl

groups with K2CO3 provided the other key monomer 14 in a

moderate yield (39% in 2 steps). All compounds were

chemically stable under ambient conditions and their

chemical structures were fully substantiated by the conven-

tional methods, such as 1H- and 13C NMR, IR, and MALDI-TOF

MS (Figure 1SI and 2SI, Supporting Information).

The Sonogashira polycondensation between 12 and 14

was performed in toluene under standard conditions

[PdCl2(PPh3)2, CuI, iPr2NH, 80 8C, 24 h] yielding the regioir-

NH2

I

N(C6H13)2

I

N(C6H13

II

a) b)

10 11 12

Scheme 3. Synthesis of monomers: a) nC6H13I, Na2CO3, DMF, 95 8C, 2PdCl2(PPh3)2, CuI, iPr2NH, 20 8C, 18 h; d) K2CO3, MeOH/THF, 20 8C, 2 h.

N(C6H13)2

14

I

P1

n

N(C6H13)2

P2

N(C6H13)2

n

a)

b)

Scheme 4. Synthesis of alkyne-linked o-phenylene polymers: a) 1. 12,12 h; b) 1. O2, CuCl, TMEDA, toluene, 60 8C, 24 h, 2. phenylacetylene,



regular poly(o-phenyleneethynylene) derivative P1

(Scheme 4). After the polymerization, iodobenzene was

added and the mixture was further stirred at 80 8C for 12 h in

order to protect the terminal alkynes. Acetylenic oxidative

polymerization of 14 was also performed under the Hay

conditions [O2, CuCl, N,N,N0,N0-tetramethylethylenedia-

mine (TMEDA)] at 60 8C for 24 h. Additional stirring in

the presence of phenylacetylene for 12 h provided the

protection of the terminal alkynes. Both P1 and P2 showed

good solubilities in common organic solvents, such as

toluene, CHCl3, CH2Cl2, and THF. The number average

molecular weight (Mn) and polydispersity (Mw=Mn) of P1,

determined by GPC using THF as the eluent, was 2 300 and

1.26, respectively (Table 1). This molecular weight corre-

sponds to approximately eight repeat units. The Mn and

Mw=Mn ofP2were 2 600 and 1.43, respectively, correspond-

ing to�8–9 repeat units. The 1H NMR and IR spectra of both

polymers suggested the absence of the terminal alkynes. In

the 1H NMR spectra, peaks at 2.99 and 3.07 ppm ascribed to

the terminal alkynes of14 completely disappeared after the

polymerization (Figure 1SI, Supporting Information). Simi-

)2 N(C6H13)2

SiMe3Me3Si

N(C6H13)2

c) d)

1314

0h; b) BTMAICl2, CaCO3, CH2Cl2/MeOH, 20 8C, 1 h; c) HC CSi(CH3)3,

N(C6H13)2

nNCCN

CNNC

N(C6H13)2

x1-x

P3

c)

PdCl2(PPh3)2, CuI, iPr2NH/toluene, 80 8C, 24 h, 2. iodobenzene, 80 8C,60 8C, 12 h; c) TCNE, o-dichlorobenzene, 80 8C, 1.5 h.

11, 212, 1758–1766


Table 1. Molecular weights and thermal properties of polymers.

Mna) Mw

a) Mw=Mna) Td5%/-Cb)

P1 2 300 2 900 1.26 228

P2 2 600 3 700 1.43 346

P3 2 500 3 800 1.52 264

a)Molecular weights determined by GPC (eluent: THF, calibrated by

standard polystyrenes); b)The 5 and 10% weight loss temperatures

determined by TGA at the heating rate of 10 8C �min�1.


www.mcp-journal.de

lar to this change, a sharp peak at 3 308 cm�1 ascribed to the

C–H vibration of the terminal alkynes of 14 also disap-

peared (Figure 2 SI, Supporting Information).

The thermal stability of P1 and P2 was evaluated by a

TGA. Due to the effective protection of the terminal alkynes,

both polymers displayed a high thermal stability. No

decomposition occurred at least up to ca. 160 8C (Figure 3SI,

Supporting Information). The 5% decomposition tempera-

tures (Td5%) are summarized in Table 1. The poly(phenyl-

enebutadiynylene) P2 was more thermally stable when

compared to the poly(phenyleneethynylene) P1.

Postfunctionalization

First, the postfunctionalization of P1 and P2with TCNE was

examined by UV-Vis-NIR spectroscopy. Because the result-

ing donor-acceptor chromophores feature well-defined CT

bands in the low energy region, the reaction progress was

traced by monitoring these bands. As previously reported

for the postfunctionalization of the conjugated polymer

main chains, TCNE addition did not proceed at room

temperature and mild heating was required.[7] Based on the

TGA results, the reaction temperatures were selected so

that no thermal decomposition occurred. For example,

the heating of P2 and a stoichiometric amount of TCNE in

Figure 1. (a) Time-dependent (0–1 200min) UV–Vis–NIR spectra of the rthe reaction rate calculated from the CT band absorbance versus tim




o-dichlorobenzene gradually changed the solution color.

Figure 1a displays the spectral change at 70 8C. The original

peaks centered at 340 and 402 nm started to decrease,

whereas a new CT band emerged at 596 nm, suggesting the

formation of donor-acceptor chromophores. The CT band

position is close to that of the model compound 5 (550 nm)

(Figure 4SI, Supporting Information). The presence of an

isosbestic point at 439 nm indicates the absence of any

undesired side reactions. Higher temperatures resulted in

smoother reactions, as shown in the plots of the CT band

increase during the course of the reactions (Figure 1b). In the

temperature range of 40–70 8C, the reactions were almost

completed after 20 h.

Subsequently, the addition amounts were determined by

the titration experiments of TCNE. The UV–Vis–NIR spectral

changes of P1 and P2 upon the stepwise addition of 0.1

equiv. of TCNE in o-dichlorobenzene at 110 8C are shown in

Figure 2. Poly(o-phenyleneethynylene) P1 exhibited an

irregular increase in the low energy band with the

increasing amount of TCNE (Figure 2a). This result clearly

suggested the occurrence of a side reaction, as seen in the

model compound 2 (vide supra). It was postulated that the

side reaction followed the initial TCNE addition reaction. In

order to investigate the effect of the regioregularity, the

regioregular poly(o-phenyleneethynylene) derivative P4

was also synthesized by the self-polycondensation of 3-

bromo-4-ethynyl-N,N-dihexylaniline 19 using Sonogashira

coupling (Scheme 1SI, Supporting Information). TheMn and

Mw=Mn of P4 were 1 900 and 1.32, which were comparable

to those of P1. TCNE titration of this regioregular counter

polymer P4 displayed a spectral change without isosbestic

points (Figure 5SI, Supporting Information). This spectral

behavior is similar to that of P1, indicating that the side

reaction always occurs at theo-diethynylbenzene moieties,

regardless of the regioregularity. In contrast, the post-

functionalization of poly(o-phenylenebutadiynylene) P2

proceeded in the anticipated mechanism without side

eaction of P2with TCNE in o-dichlorobenzene at 70 8C and (b) plots ofe at various temperatures.

11, 212, 1758–1766


Figure 2. UV–Vis–NIR spectral change of (a) P1 and (b) P2 upon TCNE titration in o-dichlorobenzene at 110 8C.

1764

www.mcp-journal.de


reactions. A well-defined CT band ascribed to the intramo-

lecular donor-acceptor interactions appeared, and a linear

increase in the absorbance continued up to 0.6 equiv. of the

TCNE addition (Figure 2b). The further addition of TCNE did

not induce any spectral change.

The TCNE titration results enabled the synthesis of the

donor-acceptor type polymer P3. The heating of P2 and

TCNE (0.60 equiv.) in o-dichlorobenzene to 110 8C, followed

by removal of the solvent and excess TCNE (if any) in vacuo,

afforded the black-colored polymer P3. It is worth noting

that no special purification processes, such as chromato-

graphy and reprecipitation methods, are required.

Although the molecular weights of P3 were almost the

same as those of the precursor polymer P2 (Table 1), the

successful postfunctionalizaton was verified by 1H NMR

and IR spectroscopies as well as elemental analysis. After

the introduction of the bulky 1,1,4,4-tetracyanobuta-1,3-

diene moieties, the aromatic peak protons of the 1H NMR

spectrum became broader due to the steric hindrance

(Figure 1SI, Supporting Information). In the IR spectra, weak

vibrational peaks at 2 137 and 2 206 cm�1 ascribed to the

2100215022002250

Tran

smitt

ance

(a.u

.)

Wavenumber (cm-1)

(a)

(b)

Figure 3. ATR-FT-IR spectra of (a) P2 and (b) P3.



internal alkyne moieties of the precursor polymer P2 were

clearly replaced by strong cyano peaks at 2 149 and

2 214 cm�1 for P3 (Figure 3). The elemental analysis of P3

suggested the TCNE addition amount (x) of 0.56, showing

nearly good agreement with the titration experiments (vide

supra). The TGA ofP3 revealed a high thermal stability with

the Td5% value of 264 8C, ensuring no thermal decomposi-

tion during postfunctionalization (Table 1 and Figure 3SI,

Supporting Information).

The postfunctionalization based on the alkyne-TCNE

addition reaction causes a significant band gap narrowing,

as represented by the UV–Vis–NIR spectra and electro-

chemical redox potentials. Cyclic voltammograms (CVs) of

P1–P3 were measured in CH2Cl2 with 0.1 M (nC4H9)4NClO4

at 20 8C. The precursor polymers P1 and P2 showed only

reversible oxidation waves with the onset potential

(Eox,onset) of –0.13 and –0.07 V (vs. Fcþ/Fc), respectively,

while P3 (x¼ 0.56) displayed the anodically shifted Eox,onset

of 0.42 V and new reversible reduction waves with the onset

potential (Ered,onset) of –0.61 V (Table 2 and Figure 6SI,

Supporting Information). The reduction potentials were

ascribed to the newly formed 1,1,4,4-tetracyanobuta-1,3-

diene moieties, and the anodic shift in the Eox,onset value can

be explained by the efficient intramolecular donor–

acceptor interactions. Thus, the electrochemical band gap

ofP3, calculated from theEox,onset andEred,onset, amounted to

1.03 V, which was in agreement with the optical band gap

(1.00 eV).

Precursor Polymer Structure

It was shown that clean postfunctionalization using the

alkyne-TCNE addition reaction was achieved only for the

poly(o-phenylenebutadiynylene) derivative. The extent of

the regioregularity of P2 or the acetylenic oxidation

polymerization mechanism will be discussed in this section

under the assumption that all the alkyne moieties of P2

11, 212, 1758–1766


Table 2. Summary of electrochemical and optical data of polymers.

Polymer Eox,onset/Va) Ered, onset/Va) D(Eox,onset – Eox,onset)/Va) lend/nm [eV]b)

P1 �0.13 – – 958 (1.29)

P2 �0.07 – – 721 (1.72)

P3 0.42 �0.61 1.03 1 243 (1.00)

a)Measured in CH2Cl2 with 0.1 M (nC4H9)4NClO4 at 20 8C. Potentials versus Fcþ/Fc; b)Measured in CH2Cl2 at 20 8C.


www.mcp-journal.de

activated by the p-dihexylanilino donors undergo the

addition reaction with TCNE.

Acetylenic oxidative coupling has been recognized as a

powerful technique for constructing expanded p-systems

and macrocyclic compounds.[13] Taking into account the

reaction mechanism, facilitated deprotonation of the

terminal alkynes will promote the formation of Cu-

acetylide intermediates.[14] It is thought that the alkyne

at the 4-position of 14 has a lower acid dissociation ability

compared to the alkyne at the 3-position, because of the

linear conjugation with the electron-donating amino

group. Accordingly, the dimerization of 14 mainly occurs

at the 3-alkyne position, yielding the major dimeric

N(C6H13)2

(C6H13)2N

(C6H13)2N

N(C6H13)2

N(C

14

onimronimrojam

N(C6H13)2

(C6H13)2N

N(C6H13)2

(C6H13)2N

N(C6H13)2

(C6H13)2N

oxidative polymerization

++

P2

Figure 4. A schematic pathway of oxidative polymerization of 14. Reacfor TCNE addition are indicated by the arrows.




intermediate as shown in Figure 4. After most of the 3-

alkynes are consumed, the resulting dimers further

undergo oxidative polymerization at the 4-alkyne posi-

tions, yielding P2. Thus, the main component of P2 is most

likely a head-to-head (or tail-to-tail) coupled dimer unit.

This idea was supported by the saturation point of the TCNE

addition. With the molecular weight and the presence of the

terminal structures in mind, the 0.60 equiv. determined by

UV–Vis–NIR spectroscopy and the 0.56 equiv. by elemental

analysis are reasonable values. Note that the fully

regioregular polymer can be functionalized up to 1.0 equiv.

of TCNE. Furthermore, the CT band position of P3 (lmax

596 nm) was closer to that of 5 (lmax 550 nm) than that of 7

N(C6H13)2

6H13)2

r

tive alkynes of P2

11, 212, 1758–1766

H & Co. KGaA, Weinhe

(lmax 452 nm). A slight bathochromic

shift of P3 compared to 5 is due to the

extended effective conjugation length.

Conclusion

In summary, we applied the alkyne-TCNE

addition reaction to the postfunctionali-

zation of the poly(o-phenyleneethyn-

ylene) and poly(o-phenylenebutadiyn-

ylene) derivatives. Although undesired

side reactions occurred for the former

polymers, the latter polymer was suc-

cessfully converted to donor–acceptor

type polymers. Saturation by the TCNE

titration experiments and elemental

analysis of the donor–acceptor type

polymer suggested the addition yield of

�56–60%. This value allowed for further

consideration of the polymerization

mechanism and the precursor polymer

structure. Acetylenic oxidative coupling

of the asymmetric monomer initially

underwent homo-coupling to afford the

symmetric dimer. Subsequently, this

dimer was polymerized under Hay con-

ditions, preferentially yielding a head-to-

head (or tail-to-tail) type poly(o-phenyl-

enebutadiyne) derivative.

im1765

1766

www.mcp-journal.de


It was previously shown that the high-yielding alkyne-

TCNE addition reaction is a useful method for preparing

donor–acceptor type aromatic polymers. This study

demonstrated that this reaction can also be employed as

a new method for analyzing alkyne-containing polymer

structures.

Acknowledgements: This work was supported by a Grant-in-Aidfor Scientific Research and the Special Coordination Funds forPromoting Science and Technology from MEXT, Japan.

Received: April 2, 2011; Revised: May 14, 2011; Published online:June 21, 2011; DOI: 10.1002/macp.201100198

Keywords: conjugated polymers; electrochemistry; functionali-zation of polymers

[1] [1a] U. H. F. Bunz, Chem. Rev. 2000, 100, 1605; [1b] J. M. Tour,Acc. Chem. Res. 2000, 33, 791; [1c] C. Weder, Poly(aryleneethy-nylene)s: From Synthesis to Application, Vol. 177, Springer,Berlin 2005; [1d] J. Liu, J. W. Y. Lam, B. Z. Tang, Chem. Rev.2009, 109, 5799; [1e] U. H. F. Bunz, Macromol. Rapid Commun.2009, 30, 772; [1f] M. Leclerc, J.-F. Morin, Design and Synthesisof Conjugated Polymers, Wiley-VCH, Weinheim 2010;[1g] T. Yamamoto, Bull. Chem. Soc. Jpn. 2010, 83, 431.

[2] [2a] H. Nishide, T. Maeda, K. Oyaizu, E. Tsuchida, J. Org. Chem.1999, 64, 7129; [2b] H. Nishide, M. Takahashi, J. Takashima,Y.-J. Pu, E. Tsuchida, J. Org. Chem. 1999, 64, 7375.

[3] [3a] T. Michinobu, J. C. May, J. H. Lim, C. Boudon, J.-P. Gissel-brecht, P. Seiler, M. Gross, I. Biaggio, F. Diederich, Chem.



Commun. 2005, 737; [3b] M. Kivala, F. Diederich, Acc. Chem.Res. 2009, 42, 235; [3c] S-i. Kato, F. Diederich, Chem. Commun.2010, 46, 1994.

[4] T. Michinobu, C. Boudon, J.-P. Gisselbrecht, P. Seiler, B. Frank,N. N. P. Moonen, M. Gross, F. Diederich, Chem. Eur. J. 2006, 12,1889.

[5] [5a] M. Kivala, C. Boudon, J.-P. Gisselbrecht, P. Seiler, M. Gross,F. Diederich, Chem. Commun. 2007, 4731; [5b] M. Kivala,C. Boudon, J.-P. Gisselbrecht, B. Enko, P. Seiler, I. B. Muller,N. Langer, P. D. Jarowski, G. Gescheidt, F. Diederich, Chem. Eur.J. 2009, 15, 4111.

[6] [6a] T. Michinobu, Pure Appl. Chem. 2010, 82, 1001; [6b]T. Michinobu, Chem. Soc. Rev. 2011, 40, 2306.

[7] [7a] T. Michinobu, H. Kumazawa, K. Noguchi, K. Shigehara,Macromolecules 2009, 42, 5903; [7b] T. Michinobu, H. Fujita,Materials 2010, 3, 4773; [7c] Y. Yuan, T. Michinobu,M. Ashizawa, T. Mori, J. Polym. Sci., Part A: Polym. Chem.2011, 49, 1013.

[8] [8a] T. Michinobu, J. Am. Chem. Soc. 2008, 130, 14074; [8b]Y. Li, T. Michinobu, Polym. Chem. 2010, 1, 72; [8c] Y. Li,K. Tsuboi, T. Michinobu, Macromolecules 2010, 43, 5277;[8d] Y. Yuan, T. Michinobu, J. Polym. Sci., Part A: Polym. Chem.2011, 49, 225; [8e] Y. Li, T. Hyakutake, T. Michinobu, Chem.Lett. 2011, 40, 570.

[9] D. Wang, T. Michinobu, J. Polym. Sci., Part A: Polym. Chem.2011, 49, 72.

[10] [10a] T. Shoji, S. Ito, K. Toyota, M. Yasunami, N. Morita, Chem.Eur. J. 2008, 14, 8398; [10b] T. Shoji, S. Ito, T. Iwamoto,M. Yasunami, N. Morita, Eur. J. Org. Chem. 2009, 4316.

[11] M. Kivala, T. Stanoeva, T. Michinobu, B. Frank, G. Gescheidt,F. Diederich, Chem. Eur. J. 2008, 14, 7638.

[12] B. Breiten, Y.-L. Wu, P. D. Jarowski, J.-P. Gisselbrecht,C. Boudon, M. Griesser, C. Onitsch, G. Gescheidt, W. B. Schwei-zer, N. Langer, C. Lennartz, F. Diederich, Chem. Sci. 2011, 2, 88.

[13] P. Siemsen, R. C. Livingston, F. Diederich, Angew. Chem., Int.Ed. 2000, 39, 2632.

[14] L. Fomina, B. Vazquez, E. Tkatchouk, S. Fomine, Tetrahedron2002, 58, 6741.

11, 212, 1758–1766


Documents

High-Yielding Alkyne-Tetracyanoethylene Addition Reactions: A Powerful Tool for Analyzing Alkyne-Linked Conjugated Polymer Structures