Tuning topochemical polymerization of diacetylenes: A joint synthetic, structural, photophysical, and theoretical study of a series ofanalogues of aknown reactive monomer, 1,6-bis(diphenylamino)-2,4-hexadiyne (THD)

Chem. Mater. 2010, 22, 3961–3982 3961

DOI:10.1021/cm1008703

Tuning Topochemical Polymerization of Diacetylenes: A Joint Synthetic,

Structural, Photophysical, and Theoretical Study of a Series of Analogues of

a Known Reactive Monomer, 1,6-Bis(diphenylamino)-2,4-hexadiyne (THD)

†

‡

ꢀ ^

Jerome Deschamps, Mirela Balog, Bruno Boury, Mouna Ben Yahia,

ꢀ

‡

Jean-Sebastien Filhol, Arie van der Lee, Antoine Al Choueiry, Thierry Barisien,

§

#

Laurent Legrand,^#Michel Schott,^#and Sylvain G. Dutremez*^,†

^†Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM2-ENSCM-UM1, Equipe CMOS,

ꢀ ^ ꢁ

Universite Montpellier II, Bat. 17, CC 1701, Place Eugene Bataillon, 34095 Montpellier Cedex 5, France,

^‡Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM2-ENSCM-UM1, Equipe CTMM,

Universiteꢀ Montpellier II, Ba^t. 15, CC 1501, Place Eugeꢁne Bataillon, 34095 Montpellier Cedex 5, France,

§

ꢀ

Institut Europeen des Membranes, CNRS-UMR 5635, Universite Montpellier II, Case Courrier 047, Place

Eugene Bataillon, 34095 Montpellier Cedex 5, France, and Institut des NanoSciences de Paris, UMR 75 88

ꢀ

#

ꢁ

ꢀ

CNRS, Universite Pierre et Marie Curie-Paris 6, Campus Boucicaut, 140, rue de Lourmel, 75015 Paris, France

Received March 26, 2010. Revised Manuscript Received May 17, 2010

Several analogues of 1,6-bis(diphenylamino)-2,4-hexadiyne (THD) have been prepared and their

thermal and photochemical solid-state polymerization reactivity assessed. The compounds involved

in this investigation are 1,6-bis(dibenzylamino)-2,4-hexadiyne (1), 1,6-bis(di-p-tolylamino)-2,4-hexa-

diyne (2), 1,6-bis(dipentafluorophenylamino)-2,4-hexadiyne (3), 1,6-bis((N-pentafluorophenyl)phenyl-

amino)-2,4-hexadiyne (4), 1,12-bis(diphenylamino)-5,7-dodecadiyne (5), and 1,10-bis(diphenylamino)-

4,6-decadiyne (6). Compound 6is the only diacetylene that showed measurable polymerization reactivity,

and this behavior was rationalized on the basis of X-ray crystallographic results. Yet, diyne 6 is much less

reactive than THD, so the preparation of weakly polymerized single crystals of 6 proved to be possible

and the study of the spectroscopic properties of “diluted” poly-6 chains feasible. Unlike poly-THD, poly-

6 is quite soluble in organic solvents such as chloroform and THF, so determination by SEC of the

molecular weight of this polydiacetylene (PDA) could be achieved, M_n= 150000-300 000 Da. The

polymeric chains generated by γ-ray irradiation of single crystals of 6 are highly luminescent, which lends

strong support to poly-6 being a red phase PDA similarly to poly-THD. The transition energy of the

exciton for poly-6, about 2.4 eV, is much higher than that of poly-THD, 2.171 eV at 16 K. This difference

was rationalized on the basis of dissimilarities in the C₁dC₄C₁dC₄dihedral angle between the two

3 3 3

polymers. The structure of poly-6in its monomer matrix was obtained by DFT calculations and, based on

this structure, the C₁dC₄C₁dC₄dihedral angle of the PDA chain found to be 140ꢀ. The

3 3 3

C₁dC₄C₁dC₄dihedral angle in poly-THD, based on the known X-ray crystal structure of this

3 3 3

polymer, is 167ꢀ. Thus, poly-6 appears to be a new structural type of PDAs; it is also a good model for the

study of the relationship that exists between chain conformation and electronic structure.

Introduction

only CPs that can be obtained in a highly ordered state,

either as macroscopic polymer crystals,^1-5or as perfectly

regular isolated chains in their monomer crystal matrix.⁶

In this respect, PDAs are the best known approximation

to a theoretician’s view of a CP, and therefore, they are

useful models for studying electronic properties of CPs in

the absence (or near absence) of disorder. This situation

contrasts with what is observed for all of the other CPs,

which are usually amorphous or semicrystalline.

Polydiacetylenes (PDAs) are conjugated polymers

(CPs) with the general formula (dCR-CtC-CR⁰d)_n

where R and R⁰are two of many possible molecular

groups that may or may not be different. PDAs are the

*Corresponding author. E-mail: dutremez@univ-montp2.fr.

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r

2010 American Chemical Society

Published on Web 06/11/2010

pubs.acs.org/cm

3962 Chem. Mater., Vol. 22, No. 13, 2010

Deschamps et al.

Scheme 1. Schematic Representation of the Topochemical

Principle for Diacetylene Polymerization

their very strong absorption appears in different regions

of the visible spectrum. The most frequent colors are

traditionally named ,blue. and ,red., with absorption

maxima at room temperature around 620 and 540 nm,

respectively. The same PDA (that is, with the same side

groups) can be found in both colors with a first order

transition between them.^10-16However, the geometrical

changes that must necessarily correspond to the large

absorption shifts are small, in fact, small enough in some

cases to have passed unnoticed in structural studies.¹⁷

Moreover, the different colors have very different emis-

sion properties, blue PDAs being virtually nonlumine-

scent and red ones showing a strong emission, at least at

low temperature.¹⁸

Synthesizing and studying PDAs with different colors

is a worthy undertaking for two main reasons: (i) funda-

mentally, it is important to understand how geometrical

changes affect the electronic properties of CPs, in parti-

cular the consequences of electronic correlations; (ii) in

The high order in PDA samples is due to their peculiar

(in fact, almost unique) polymerization process. Poly-

merization proceeds in the solid crystalline state and is a

topochemical reaction,^7,8meaning that all of the reaction

steps (initiation by formation of a dimer radical or radical

ion, and propagation) are under control of the reactive

site geometry and, more generally, of the overall mono-

mer crystal packing. In fact, the limiting step is usually

initiation, which is sketched in Scheme 1.⁹

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˚

Scheme 1) must be in the range of 4.7 to 5.2 A; (ii) R_vmust

˚

be smaller than 4 A, with a lower limit of 3.4 A corre-

sponding to van der Waals contact between reacting

carbon atoms; (iii) the angle γ between the diacetylene

(DA) rod and the translational vector must be close to

45ꢀ. All three geometrical requirements should be met in

order to secure a close contact between the C₁atom of one

DA rod and the C₄atom of the neighboring rod, in the

reactive monomer crystal.^2,3These conditions can be

fulfilled by a judicious choice of the DA side groups,

noting that these groups contain most of the atoms in the

molecule and play a leading role in the monomer crystal

packing. Therefore, crystal engineering starting from a

known reactive DA can lead to new PDAs with new

properties.

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Article

Chem. Mater., Vol. 22, No. 13, 2010 3963

terms of applications, the color transition of PDAs is

being used to develop various types of sensors, so under-

standing these color changes should help improving on

existing sensing devices. In this connection, for well-

chosen side groups, dramatic color changes are observed

when PDAs are subjected to an external stimulus such as

stress,¹⁹heat,^10,16,20pH change,²¹chemical change (dehy-

dration),²²interaction with chemicals and biochemi-

cals.^20a-c,f-h,23The color changes that are observed are

typically from blue to red and vice versa, but other colors

are known, especially purple.^17,24The difference in fluore-

scence properties has also been utilized advantageously in

PDA-based sensing materials.^23g,l,25Finally, other detec-

tion schemes are possible, for instance, that different

colors correspond to different Raman signatures.

Over the past few years, we have been engaged in a

research program aimed at studying the spectroscopic

properties of PDA chains isolated in their monomer

single crystal matrix.⁶Red poly-3BCMU chains (poly-

3BCMU = poly[4,6-decadiyne-1,10-diol bis([(n-butoxycar-

bonyl)methyl]urethane)]) have been shown to be perfect

organic quantum wires on which electronic excitations are

spatially coherent over the chain length, meaning that the

excitations are states of the whole chain and are not

localized on any specific part of it.^26-28One can conjecture

that this phenomenon should be observable for other CPs

provided they can be obtained in the same very high degree

of order as poly-3BCMU chains.

Scheme 2. Chemical Structure of 1,6-Bis(diphenylamino)-2,4-

hexadiyne (THD)

for red PDAs; (ii) to be able to study groups of red chains

without interference from other types of chains; (iii) to

prepare chains of different geometries in order to study

the relationship between geometry and electronic proper-

ties, in the light of the assumption that blue chains are

planar while all of the others are nonplanar, i.e., twisted.

If so, different twist angles will lead to different electronic

properties.

In this context, our goal was not to prepare another

example of a PDA crystal containing 100% polymer, but

to obtain a material where high-molecular-weight PDA

chains would be diluted in their crystalline monomer

matrix.

We first investigated a PDA named poly-THD (THD =

1,6-bis(diphenylamino)-2,4-hexadiyne, Scheme 2), one of

the rare materials where nonplanar chains were found cry-

stallographically. In this polymer, successive repeat units

are alternatively rotated clockwise and anticlockwise with

respect to the mean plane of the chain, resulting in a R-

C₄C₁-R dihedral angle (see Scheme 1) of 166ꢀ (for

Red poly-3BCMU chains have an advantage which, at

the same time, is a drawback: their very high dilution in

the monomer crystal allows the study of a single chain;

yet, red chains represent only a minority of all chains

present in the crystal, the vast majority being blue chains.

Consequently, many studies such as pump-probe experi-

ments are precluded.^29-31

We turned to other diacetylenes susceptible of produ-

cing exclusively red fluorescent PDA chains for three

reasons: (i) to prove that the property of perfect quantum

wire observed for poly-3BCMU chains is indeed general

3 3 3

planar chains this angle is 180ꢀ).³²This PDA has been

studied previously.^33-35Its spectrocopic properties can be

compared with those of poly-TCDU (poly-TCDU = poly-

(5,7-decadiyne-1,12-diol-bis phenylurethane)), regarded in

the past as a prototype for red PDAs,³⁶and with those of

isolated poly-3BCMU red chains.⁶The absorption max-

imum of the enyne backbone of poly-THD is observed at

568 nm (room temperature value);^33,37it is red-shifted by

comparison with that of poly-TCDU³⁸(λ_max≈ 530 nm) and

that of red poly-3BCMU⁶(λ_max≈ 535 nm). Still, its position

is at a much higher energy than that of blue PDAs (λ_max

≈

620 nm). Poly-THD is strongly fluorescent at low tempera-

ture but only weakly at room temperature because of the

opening of a very efficient nonradiative decay channel.³⁷In

this respect, its behavior is quite similar to that of poly-

3BCMU chains.

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3964 Chem. Mater., Vol. 22, No. 13, 2010

Scheme 3. Chemical Structures of Diacetylenes 1-6

Deschamps et al.

identical to the experimental one and, also, two other

minima, one corresponding to a planar chain and the other

to a much more twisted structure.³⁹These two polymorphs

have not been observed experimentally (although there are

reports⁴⁰of a surface phase in poly-THD crystals), and

these findings suggest that other chain geometries might

become accessible by a slight modification of the structure

of the THD monomer.

Six THD analogues with slightly different side groups

have been prepared (compounds 1-6 in Scheme 3), but

only one of them, 6, has a crystalline arrangement suitable

for topochemical polymerization and is indeed reactive,

and its polymer is soluble in common organic solvents. In

effect, the crystal structures of these molecules result from

a delicate balance between several types of weak interac-

tions, some of them being intrastack and others inter-

stack. When the leading interactions are intrastack,

columnar assemblies are observed in which every other

molecule is crystallographically equivalent (A-B-A-B

arrangement). When the leading interactions are inter-

stack, columnar assemblies are observed in which all of

the molecules are crystallographically equivalent (A-A-

A-A arrangement). The former arrangement is condu-

cive to topochemical polymerization and the latter is not.

Polymerization of 6 is best performed by γ irradiation.

The amount of polymer formed x_pincreases linearly with

the dose up to 25 MRad, at which stage x_p≈ 0.18. It

would be possible to increase further the polymer con-

tents (unless a phase transition to an inactive phase occurs

at higher doses), but one would then reach a region where

radiation damage becomes significant; typical G values

for cross-linking or degradation are 0.5-2.⁴¹So, a struc-

tural study of a fully polymerized crystal is probably out

of reach. Structural information about the polymer has

been obtained in favorable cases by studying the structure

of a polymer-monomer mixed crystal.^42-44Such a study

is planned.

Yet, in a first step, the computational method that was

successful for poly-THD³⁹was applied. Because it requires

a 3D periodic system, a model ordered (6)_0.5-(poly-6)_0.5

mixed crystal was studied, each chain being surrounded

by four monomer stacks and each monomer stack by four

chains (see Figure 6). The method and results are pre-

sented in the penultimate paragraph.

Results and Discussion

Preparation of Alkynes 7-12. Propargyl amines 7 and 8

(Scheme 4) were synthesized by allowing the parent amine

to react with propargyl bromide in tetrahydrofuran

(THF), with use of potassium hydroxide as a base and 18-

crown-6 as a phase-transfer agent. Propargyl amines 9and 10

were prepared similarly using potassium carbonate as a base

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Article

Chem. Mater., Vol. 22, No. 13, 2010 3965

Scheme 4. Chemical Structures of Alkynes 7-14

center of gravity of the phenyl ring.⁴⁹The H Cg distances

3 3 3

found here are slightly longer than the average one reported

˚

in the literature (2.76 A), suggesting weaker C_arom-H

π

3 3 3

interactions.⁵⁰There is also one short contact between a CH₂

hydrogen and an aromatic carbon atom (d(H C_arom) =

3 3 3

˚

2.881 A, —C-H

Two consecutive molecules in a given stack are sepa-

C_arom= 159.9ꢀ).

3 3 3

˚

rated by a distance of 5.539 A. This distance rules out

significant intrastack π π interactions.^51-53Stronger,

3 3 3

yet still weak, π π interactions are observed between

3 3 3

phenyl rings from separate stacks. In this case, the

˚

centroid centroid distance is 4.211 A and the angle

between the centroid-centroid vector and the ring normal

28.44ꢀ. This primary OFF interaction combined with the

2.99 A C_arom-H π contact discussed previously gen-

erates a pattern that is reminiscent of the P4AE (parallel

4-fold aryl embrace) secondary motif found in metal

phenanthroline complexes.⁵⁴

3 3 3

˚

3 3 3

and, in the case of 10, N,N-dimethylformamide (DMF) as a

solvent; no 18-crown-6 was used. Propargyl amines 11 and 12

were obtained by allowing tosylated alkynes 13 and 14 to

react with lithium diphenylamide in THF. Diphenylamine,

dibenzylamine, and di-p-tolylamine were obtained from

commercial sources. Bis(pentafluorophenyl)amine and

(N-pentafluorophenyl)phenylamine were synthesized follow-

ing reported methods.^45,46

Syntheses of Diacetylenes 1-6. Symmetrical diynes 1-6

(Scheme 3) were synthesized by oxidative dimerization of

alkynes 7-12 following the Hay coupling protocole.⁴⁷For

the syntheses of 1-4, typically used acetone was replaced

with methanol, and for the syntheses of 5 and 6, acetone

was replaced with 1,2-dimethoxyethane (DME).

Structure of 1,6-Bis(di-p-tolylamino)-2,4-hexadiyne (2).

Diacetylene 2 crystallizes in the triclinic space group P1

with Z = 1 (Table 1). There is one-half of a molecule in the

asymmetric unit.⁴⁸In the solid state (Figure 2), molecules of

2 pile up in stacks in the a direction. There are no short

C_arom-H aryl contacts. The only short contacts that

3 3 3

are observed are CH₂aryl, CH₃aryl, and C_arom

H

-

3 3 3

C_spinteractions. For the first interaction, the H Cg

3 3 3

˚

distance is 2.64 A, the C-H Cg angle 147.3ꢀ, and the

3 3 3

angle between the H-Cg axis and the ring normal 4.65ꢀ (Cg

is the centroid position of the aryl group). For the second

˚

contact, the H Cg distance is 2.95 A, the C-H Cg

3 3 3

angle 151.5ꢀ, and the angle between the H-Cg axis and the

ring normal 5.26ꢀ. For the third interaction, the H C_sp

Structure of 1,6-Bis(dibenzylamino)-2,4-hexadiyne (1).

Diacetylene 1 crystallizes in the triclinic space group P1

with Z = 1 (Table 1). There is one-half of a molecule in the

asymmetric unit.⁴⁸Inthe solid state (Figure 1), moleculesof

1 pile up in stacks in the a direction. There are two short

3 3 3

˚

distance is 2.895 A and the C_arom-H C_spangle 145.7ꢀ.

Two consecutive molecules in a given stack are separated

3 3 3

˚

by a distance of 6.127 A. This distance rules out significant

intrastack π π interactions.^51-53There is one offset face-

3 3 3

to-face π π interaction between aryl groups from separate

stacks, yet this interaction is quite weak: the centroid

phenyl phenyl contacts between molecules belonging to

separate stacks. Edge-on interactions as those observed in

3 3 3

strands of poly-THD are not present.³²For the first con-

˚

centroid distance is 4.897 A and the angle between the

centroid-centroid vector and the ring normal 31.81ꢀ. This

tact, the H Cg distance is 2.84 A, the C-H Cg angle

3 3 3

primary OFF interaction combined with the CH₃aryl

147.2ꢀ, and the angle between the H-Cg axis and the ring

3 3 3

contact discussed previously generates here again a pattern

that is reminiscent of the P4AE secondary motif found in

metal phenanthroline complexes.⁵⁴Unlike the situation

found in 1, however, the assembly is looser.

normal 2.97ꢀ (Cg is the centroid position of the phenyl ring).

˚

For the second contact, the H Cg distance is 2.99 A, the

3 3 3

C-H Cg angle 131.7ꢀ, and the angle between the H-Cg

3 3 3

axis and the ring normal 12.89ꢀ. These interactions are of

type III according to Malone’s classification, that is, the

C-H vector faces in an oblique fashion the phenyl ring it

interacts with and the hydrogen atom sits nearly above the

Structure of 1,6-Bis(dipentafluorophenylamino)-2,4-hexa-

diyne (3). Compound 3 crystallizes in the monoclinic space

group P2₁/n with Z=2 (Table 1). In the unit cell, the

molecule sits on a center of inversion.⁴⁸Molecules of 3 pile

(45) Koppang, R. Acta Chem. Scand. 1971, 25, 3067–3071.

(46) Koppang, R. J. Fluorine Chem. 1995, 74, 177–179.

(47) (a) Hay, A. S. J. Org. Chem. 1962, 27, 3320–3321. (b) Walton,

D. R. M.; Waugh, F. J. Organomet. Chem. 1972, 37, 45–56. (c)

Eastmond, R.; Johnson, T. R.; Walton, D. R. M. Tetrahedron 1972,

28, 4601–4616. (d) Ghose, B. N. Synth. React. Inorg. Met.-Org.

Chem. 1994, 24, 29–52. (e) Brandsma, L. Studies in Organic Chem-

istry 34: Preparative Acetylenic Chemistry, 2nd ed.; Elsevier:

Amsterdam, 1988; p 219.

(48) CCDC-746114 (1), CCDC-746116 (2), CCDC-746111 (3), CCDC-

746112 (4), CCDC-746115 (5), and CCDC-746113 (6) contain the

supplementary crystallographic data for this paper. These data can

be obtained free of charge from the Cambridge Crystallographic

Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

(49) Malone, J. F.; Murray, C. M.; Charlton, M. H.; Docherty, R.;

Lavery, A. J. J. Chem. Soc., Faraday Trans. 1997, 93, 3429–3436.

(50) Umezawa, Y.; Tsuboyama, S.; Honda, K.; Uzawa, J.; Nishio, M.

Bull. Chem. Soc. Jpn. 1998, 71, 1207–1213.

(51) Moon, H.; Zeis, R.; Borkent, E.-J.; Besnard, C.; Lovinger, A. J.;

Siegrist, T.; Kloc, C.; Bao, Z. J. Am. Chem. Soc. 2004, 126, 15322–

15323.

ꢂꢂ ꢀ

(52) Sokolov, A. N.; Friscic, T.; MacGillivray, L. R. J. Am. Chem. Soc.

2006, 128, 2806–2807.

(53) Janiak, C. J. Chem. Soc., Dalton Trans. 2000, 3885–3896.

(54) (a) Russell, V.; Scudder, M.; Dance, I. J. Chem. Soc., Dalton Trans.

2001, 789–799. (b) Dance, I. CrystEngComm 2003, 5, 208–221.

3966 Chem. Mater., Vol. 22, No. 13, 2010

Table 1. Crystal Data and Experimental Details of Data Collection and Refinement for Compounds 1-6

Deschamps et al.

1

2

3

4

5

6

empirical formula

fw

C₃₄H₃₂N₂

468.64

colorless rod

C₃₄H₃₂N₂

468.64

colorless block

C₃₀H₄F₂₀N₂

772.35

colorless stick

C₃₀H₁₄F₁₀N₂

592.43

colorless plate

C₃₆H₃₆N₂

496.70

colorless prism

C₃₄H₃₂N₂

468.62

colorless platelet

cryst color and habit

cryst size (mm³)

cryst syst

0.12 ꢀ 0.15 ꢀ 0.35 0.15 ꢀ 0.16 ꢀ 0.45 0.05 ꢀ 0.12 ꢀ 0.50

0.02 ꢀ 0.06 ꢀ 0.30 0.28 ꢀ 0.30 ꢀ 0.50 0.05 ꢀ 0.15 ꢀ 0.20

triclinic

P1 (No. 2)

5.5393(8)

9.8301(10)

13.3335(13)

68.610(9)

79.331(8)

87.370(10)

664.15(14)

1

triclinic

P1 (No. 2)

6.1269(11)

9.5278(11)

12.720(2)

103.70(1)

102.77(1)

102.73(1)

673.78(19)

1

monoclinic

P2₁/n (No. 14)

5.6906(10)

8.920(3)

27.215(7)

90

monoclinic

P2₁/n (No. 14)

20.947(6)

6.109(2)

22.286(6)

90

triclinic

P1 (No. 2)

8.3279(8)

10.1420(10)

17.6024(17)

90.294(8)

101.661(8)

100.022(8)

1432.6(2)

2

monoclinic

P2₁/n (No. 14)

9.9484(7)

16.0893(12)

16.7643(13)

90

space group

˚

a (A)

˚

b (A)

˚

c (A)

R (deg)

β (deg)

γ (deg)

96.690(18)

90

95.38(3)

90

98.697(4)

90

3

˚

V (A )

Z

T (K)

1372.0(6)

2

173

2839.3(15)

4

173

2652.5(3)

4

180

173

1.172

173

1.155

173

1.151

F

_calcd(g cm^-3

F(000)

)

1.869

756

1.386

1192

1.173

1000

250

0.68

250

0.67

532

0.66

μ (mm^-1

)

_min, T_max

2.07

0.97, 0.99

0.71073

1.28

0.99, 1.00

0.71073

0.68

0.902, 0.988

0.71073

T 0.93, 0.97

graphite-monochromated 0.71073

0.82721, 1.00000

0.71073

0.88622, 1.00000

0.71073

˚

Mo_KRradiation (A)

θ range (deg)

index ranges

3.2241-32.1630

3.259-32.437

-8 e h e 9,

-14 e k e 14,

-19 e l e 18

11512

2.736-32.451

-8 e h e 7,

-13 e k e 12,

-40 e l e 38

23485

2.803-32.381

-30 e h e 30,

-9 e k e 8,

-32 e l e 33

48109

2.959-32.422

-11 e h e 11,

-13 e k e 14,

-25 e l e 25

24260

1.76-26.37

-12 e h e 12,

-20 e k e 20,

-18 e l e 20

29768

-8 e h e 8,

-14 e k e 13,

-19 e l e 19

11220

data collected

unique data, R_int

4247, 0.021

1399 (n = 3)

163, 0

4270, 0.027

1813 (n = 2)

163, 0

4520, 0.025

980 (n = 2)

235, 0

9058, 0.139

551 (n = 2)

169, 0

9020, 0.026

3682 (n = 2)

343, 0

5425, 0.0333

4037 (n = 2)

325, 0

obsd data (I_o> nσ(I_o))

L.S. params, restraints

R,^aR_w^b(obsd reflns)

R,^aR_w^b(all reflns)

weighting scheme^c,d

0.0365, 0.0381

0.1281, 0.0475

28.7, -44.6, 25.3,

-9.62

0.000121

1.0363

0.0368, 0.0404

0.0949, 0.0540

3.26, -1.88, 3.71,

-0.758, 0.999

0.000145

0.0217, 0.0220

0.1658, 0.0406

12.8, -18.4,

15.0, -6.02, 2.95

0.002431

0.1001, 0.0966

0.4767, 0.2014

14.0, -10.2, 11.1

0.0346, 0.0379

0.0997, 0.0799

3.91, -0.963, 2.32

0.0389, 0.0842

0.0617, 0.0948

0.0379, 0.6852

max shift/esd

GOF

0.006548

1.1211

0.009629

1.1048

0.001

1.021

1.1305

-0.16, 0.17

1.2424

-0.14, 0.14

-3

˚

ΔF_min, ΔF_max(e A

)

-0.17, 0.16

-0.56, 1.02

-0.16, 0.19

-0.2, 0.189

^aR = Σ ||F_o| - |F_c||/Σ |F_o|. ^bR_w= [Σ (w (F_o- F_c²)²)/Σ (w (F_o²)²)]^1/2

.

^cFor compounds 1-5, w = [weight][1 - (ΔF/6σ(F))²]²; [weight] = 1.0/

2

[A₀T₀(x) þ A₁T₁(x) þ ... þ A_n-1T_n-1(x)] where A_iare the Chebychev coefficients listed in the Table and x = F_calcd/F_max

.

^dFor diacetylene 6, w =

1/[σ²(F_o²) þ (aP)²þ bP]; P = (F_oþ 2F_c²)/3, and the values of a and b are given in the Table.

2

Figure 1. View along the a axis showing the organization of 1 in the crystalline state.

Article

Chem. Mater., Vol. 22, No. 13, 2010 3967

Figure 2. View along the a axis showing the organization of 2 in the crystalline state.

up in stacks in the a direction (Figure 3). Two consecutive

molecules in a given stack are separated by a distance of

˚

interaction.^51-53The shortest π π interaction is ob-

served between a phenyl ring and a pentafluorophenyl

group from a different stack. In this case, the centroid

3 3 3

5.691 A. Such a long distance precludes significant π

interaction.^51-53There is one offset face-to-face π

π

3 3 3

˚

centroid distance is 4.783 A and the angle between the

interaction between pentafluorophenyl rings from separate

centroid-centroid vector and the ring normal 19.78ꢀ. This

stacks, yet this interaction is quite weak: the centroid

˚

centroid distance is 4.912 A and the angle between the

interaction is different from the phenyl perfluorophenyl

3 3 3

face-to-face stacking interaction typically observed in single-

component organic molecules or cocrystals in which both

groups are present.⁵⁶Interestingly, segregation prevails in

centroid-centroid vector and the ring normal 50.39ꢀ.

The structure exhibits numerous C-F

C_aryl, C-F

3 3 3 3 3 3

C_sp, C-F F, and C-H F interactions between mole-

3 3 3

cules from separate stacks.⁵⁵There are eight different

˚

(56) (a) Naae, D. G. Acta Crystallogr., Sect. B 1979, 35, 2765–2768. (b)

Williams, J. H. Acc. Chem. Res. 1993, 26, 593–598. (c) Coates, G. W.;

Dunn, A. R.; Henling, L. M.; Dougherty, D. A.; Grubbs, R. H. Angew.

Chem., Int. Ed. 1997, 36, 248–251. (d) Coates, G. W.; Dunn, A. R.;

Henling, L. M.; Ziller, J. W.; Lobkovsky, E. B.; Grubbs, R. H. J. Am.

Chem. Soc. 1998, 120, 3641–3649. (e) Ponzini, F.; Zagha, R.;

Hardcastle, K.; Siegel, J. S. Angew. Chem., Int. Ed. 2000, 39, 2323–

2325. (f) Liu, J.; Murray, E. M.; Young, V. G., Jr. Chem. Commun.

2003, 1904–1905. (g) Meyer, E. A.; Castellano, R. K.; Diederich, F.

Angew. Chem., Int. Ed. 2003, 42, 1210–1250. (h) Smith, C. E.; Smith,

P. S.; Thomas, R. Ll.; Robins, E. G.; Collings, J. C.; Dai, C.; Scott, A. J.;

Borwick, S.; Batsanov, A. S.; Watt, S. W.; Clark, S. J.; Viney, C.;

Howard, J. A. K.; Clegg, W.; Marder, T. B. J. Mater. Chem. 2004, 14,

413–420. (i) Watt, S. W.; Dai, C.; Scott, A. J.; Burke, J. M.; Thomas, R.

Ll.; Collings, J. C.; Viney, C.; Clegg, W.; Marder, T. B. Angew. Chem.,

Int. Ed. 2004, 43, 3061–3063. (j) Xu, R.; Gramlich, V.; Frauenrath, H.

J. Am. Chem. Soc. 2006, 128, 5541–5547.

(57) (a) Cox, E. G.; Cruickshank, D. W. J.; Smith, J. A. S. Proc. R. Soc.

London, Ser. A 1958, 247, 1–21. (b) Burley, S. K.; Petsko, G. A.

Science 1985, 229, 23–28. (c) Perutz, M. F.; Fermi, G.; Abraham, D. J.;

Poyart, C.; Bursaux, E. J. Am. Chem. Soc. 1986, 108, 1064–1078. (d)

Burley, S. K.; Petsko, G. A. J. Am. Chem. Soc. 1986, 108, 7995–8001.

(e) Askew, B.; Ballester, P.; Buhr, C.; Jeong, K. S.; Jones, S.; Parris, K.;

Williams, K.; Rebek, J., Jr. J. Am. Chem. Soc. 1989, 111, 1082–1090.

(f) Jorgensen, W. L.; Severance, D. L. J. Am. Chem. Soc. 1990, 112,

4768–4774. (g) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc.

1990, 112, 5525–5534. (h) Hunter, C. A. Chem. Soc. Rev. 1994, 23,

101–109. (i) Dougherty, D. A. In Molecular Recognition: Receptors

C-F

C_arylcontacts spanning the range 3.095-3.162 A.

There is one C-F C_spcontact for which the F C_sp

3 3 3

3 3 3 3 3 3

˚

distance is 2.979 A. There are three different C-F

F

3 3 3

˚

contacts for which d(F F) = 2.722, 2.904, and 2.907 A.

3 3 3

There are two distinct C-H F interactions for which

3 3 3

˚

d(H F) = 2.616 and 2.638 A.

3 3 3

Structure of 1,6-Bis((N-pentafluorophenyl)phenylamino)-

2,4-hexadiyne (4). Compound 4 crystallizes in the mono-

clinic space group P2₁/n with Z = 4 (Table 1). There is one

molecule per asymmetric unit.⁴⁸Molecules of 4 pile up in

stacks in the b direction (Figure 4). Two consecutive mole-

˚

cules in a given stack are separated by a distance of 6.109 A.

Such a long distance precludes significant intrastack π

π

3 3 3

€

(55) (a) Thalladi, V. R.; Weiss, H.-C.; Blaser, D.; Boese, R.; Nangia, A.;

Desiraju, G. R. J. Am. Chem. Soc. 1998, 120, 8702–8710. (b) Renak,

M. L.; Bartholomew, G. P.; Wang, S.; Ricatto, P. J.; Lachicotte, R. J.;

Bazan, G. C. J. Am. Chem. Soc. 1999, 121, 7787–7799. (c) Dai, C.;

Nguyen, P.; Marder, T. B.; Scott, A. J.; Clegg, W.; Viney, C. Chem.

Commun. 1999, 2493–2494. (d) Lorenzo, S.; Lewis, G. R.; Dance, I.

New J. Chem. 2000, 24, 295–304. (e) Adams, N.; Cowley, A. R.;

Dubberley, S. R.; Sealey, A. J.; Skinner, M. E. G.; Mountford, P. Chem.

Commun. 2001, 2738–2739. (f) Hair, G. S.; Cowley, A. H.; Gorden,

J. D.; Jones, J. N.; Jones, R. A.; Macdonald, C. L. B. Chem. Commun.

2003, 424–425.

€

for Molecular Guests; Vogtle, F., Ed.; Comprehensive Supramolecular

Chemistry; Pergamon: London, 1996; Vol. 2, Chapter 6, pp 195-209.

€

(j) Weiss, H.-C.; Blaser, D.; Boese, R.; Doughan, B. M.; Haley, M. M.

Chem. Commun. 1997, 1703–1704.

3968 Chem. Mater., Vol. 22, No. 13, 2010

Deschamps et al.

Figure 3. View along the a axis showing the organization of 3 in the crystalline state.

Figure 4. View along the b axis showing the organization of 4 in the crystalline state.

˚

for which d(H F) = 2.456, 2.659, and 2.662 A. The

the structure of 4: phenyl groups stack on top of one another,

and the same is true for pentafluorophenyl groups.

3 3 3

lengths of the two separate CH₂F contacts are 2.271

˚

3 3 3

The structure exhibits numerous C-F

C

_aryl, C-F F,

and 2.464 A. There is one edge-to-face C-H πinteraction

3 3 3

C_arom-H F, CH₂F, and C_arom-H phenyl interac-

between nearby phenyl rings: the H(54)-C(29)-C(30)-

H(55) fragment of the first ring interacts with the C(31⁰)

and C(29⁰) carbon atoms of the second ring. In this case, the

3 3 3 3 3 3 3 3 3

tions between molecules from separate stacks.^55,57The

two distinct C-F _arylcontacts have distances of 3.111

C

3 3 3

0

˚

and 3.116 A and the two C-F F contacts of 2.623 and

C(29)-H(54) C(31 ) distance is 2.772 A and the C(30)-

3 3 3

2.736 A. There are three different C_arom-H Finteractions

3₀3 3

˚

H(55) C(29 ) distance 2.952 A.

3 3 3

Article

Chem. Mater., Vol. 22, No. 13, 2010 3969

Figure 5. View along the b axis showing the organization of 5 in the crystalline state.

Structure of 1,12-Bis(diphenylamino)-5,7-dodecadiyne

(5). Compound 5 crystallizes in the triclinic space group

P1 with Z = 2 (Table 1). There is one entire molecule in

the asymmetric unit.⁴⁸The structure exhibits numerous

numerous phenyl phenyl interactions (Figure 6). There

3 3 3

are two phenyl phenyl interactions with geometries re-

3 3 3

sembling tilted T structures. For these interactions, the H

Cg distances and C-H Cg angles (Cg is the centroid

3 3 3

˚

phenyl phenyl interactions (Figure 5). There are two

phenyl phenyl interactions with geometries resembling

position of the phenyl ring) are as follows: 2.799 A (160.41ꢀ),

3 3 3

˚

2.866 A (149.82ꢀ). There are two edge-to-face C-H

interactions between phenyl rings. In the first edge-to-face

π

3 3 3

tilted T structures. For these interactions, the H Cg

distances and C-H Cg angles (Cg is the centroid position

3 3 3

interaction, the H(34)-C(34)-C(35)-H(35) fragment in-

teracts with the C(11)-C(12)-C(13)-C(14)-C(15)-C(16)

3 3 3

˚

of the phenyl ring) are as follows: 3.131 A (161.74ꢀ), 3.169 A

(140.18ꢀ). There are three other phenyl phenyl interac-

tions with geometries resembling tilted T structures but, in

these cases, the C-H vector points to a specific aromatic

carbon atom rather than to the phenyl centroid. The

˚

phenyl ring (d(H(34) C(14)) = 3.117 A and d(H(35)

3 3 3

˚

C(11)) = 2.993 A). In the second edge-to-face interaction,

the H(18)-C(18)-C(20)-H(20) fragment interacts with the

C(24)-C(25)-C(26)-C(27)-C(28)-C(29) phenyl ring

˚

H

C

_aromdistances, along with the corresponding C_arom

˚

-

(d(H(18) C(24)) = 3.024 A and d(H(20) C(27)) =

3 3 3

˚

C_aromangles, are as follows: 2.803 A (161.60ꢀ), 2.866 A

3.102 A). Here again, these edge-to-face interactions resemble

those found in poly-THD.³²There are two short C_arom-H

˚

(148.85ꢀ), 2.884 A (122.82ꢀ). There are two edge-to-face

C-H π interactions between phenyl rings. In the first

edge-to-face interaction, the H(45)-C(10)-C(9)-H(44)

fragment interacts with the C(2)-C(3) edge of the C(1)-

C(2)-C(3)-C(4)-C(5)-C(6) phenyl ring. In this case, the

3 3 3

C_arominteractions with no specific geometries for which

˚

3 3 3

d(H C_arom)=2.873 A and —C_arom-H C_arom=140.68ꢀ,

3 3 3

and d(H

C

˚

C

_arom) = 2.876 A and —C_arom-H

3 3 3

_arom=137.84ꢀ. Three short CH₂

served with the following geometrical parameters: d(H

3 3 3

C

_spcontacts are ob-

3 3 3

˚

H(45) C(3) distance is 2.885 A and the H(44) C(2)

˚

distance 3.266 A. In the second edge-to-face interaction, the

3 3 3

˚

C_sp)=2.721 A and —C-H C_sp=147.99ꢀ, d(H C_sp)=

3 3 3

˚

H(40)-C(4)-C(5)-H(39) fragment interacts with the C(33)-

2.816 A and —C-H C_sp=132.28ꢀ, and d(H C_sp)=

3 3 3 3 3 3

˚

C(34)-C(35)-C(36)-C(37)-C(38) phenyl ring (d(H(40)

2.895 A and —C-H C_sp=125.08ꢀ. Also, there is one

3 3 3

˚

C(35)) = 2.956 A and d(H(39) C(38)) = 3.348 A). These

˚

short C_arom-H C_spcontact for which d(H C_sp) =

3 3 3 3 3 3

3 3 3

˚

edge-on interactions are quite similar to those observed in

poly-THD.³²There is also one short CH₂C_spcontact

2.894 A and —C_arom-H C_sp= 153.22ꢀ.

3 3 3

1,10-Bis(diphenylamino)-4,6-decadiyne (6): A New Polymeri-

zable Diacetylene. Close examination of the packings of 1, 2, 3,

and 4 indicates that the molecules are not suitably oriented for

topochemical polymerization. The geometrical parameters d,

R_v, and γ (see Table 2) differ significantly from Baughman’s

criteria for topochemical polymerization (vide supra).

3 3 3

˚

(d(H C_sp) = 2.798 A, —C-H C_sp= 163.21ꢀ) and

3 3 3

˚

one short CH₂phenyl contact (d(H Cg) = 2.792 A,

3 3 3 3 3 3

—C-H Cg = 159.27ꢀ).

3 3 3

Structure of 1,10-Bis(diphenylamino)-4,6-decadiyne (6).

Compound 6 crystallizes in the monoclinic space group

P2₁/n with Z = 4 (Table 1). There is one entire molecule in

the asymmetric unit.⁴⁸The structure is sustained by

Molecules of 5pile up in columns in the bdirection. In each

column, the distance between two consecutive molecules is

3970 Chem. Mater., Vol. 22, No. 13, 2010

Deschamps et al.

Figure 6. View along the a axis showing the organization of 6 in the crystalline state.

Table 2. Geometrical Parameters for Diacetylenes 1-6^a

˚

10.142 A. Such a long distance makes polymerization along

an axis passing through the centers of the molecules unlikely.

Interestingly, polymerization appears to be possible along an

axis that runs parallel to the b direction and is located in the

middle of two stacks, i.e. passing through a center of inversion

of the unit cell (Figure 5). In this way, two stacks combine

into a bigger one; in this bigger stack, reacting molecules are

closer and alternate sides along the polymerization axis. This

situation resembles a “wrinkled carpet”.

˚

d (A)

˚

R_v(A)

compd

γ (deg)

1

2

3

4

5

5.539

6.127

5.691

6.109

5.192

5.818

4.937

5.281

3.60

4.155

4.506

5.554

4.1834

3.7670

3.4946

3.573

39.9

42.6

52.36

66.56

53.61

40.21

45.36

41.39

6

^ad, R_v, and γ are defined in Scheme 1.

Looking down the polymerization axis, all of the odd-

numbered molecules are crystallographically equivalent,

and the same is true for even-numbered molecules. As a

result, two sets of geometrical parameters must be con-

sidered to determine whether topochemical polymeriza-

tion is possible. For the first set of possibly reacting

Similarly to 5, the polymerization axis cannot encom-

pass the centers of all of the CtC-CtC fragments in each

stack and must be located in-between them. It is parallel

to the a axis and goes through a center of inversion of the

unit cell. It follows that two sets of geometrical parameters

must be considered to determine whether topochemical

polymerization is possible. For the first group of possibly

reacting molecules (odd-even couple), the stacking dis-

˚

molecules, the stacking distance d (Scheme 1) is 5.818 A,

˚

and the perpendicular distance R_vis 3.7670 A. The γ

angle between a diacetylene rod and an axis passing

through the centers of the molecules is 40.21ꢀ. For

the second set of molecules, the stacking distance d is

˚

tance d (Scheme 1) is 4.937 A, and the perpendicular

˚

5.192 A, and the perpendicular distance R_vis 4.1834 A.

The γ angle between a diacetylene rod and an axis passing

through the centers of the molecules is 53.61ꢀ. These

geometrical parameters do not match Baughman’s cri-

teria for topochemical polymerization although they are

close (vide supra).

distance R_vis 3.4946 A. The γ angle between a diacetylene

rod and an axis passing through the centers of the mole-

cules is 45.36ꢀ. For the second group of molecules

(even-odd couple), the stacking distance d is 5.281 A,

and the perpendicular distance R_vis 3.573 A. The γ angle

˚

between a diacetylene rod and an axis passing through the

centers of the molecules is 41.39ꢀ. The first set of geome-

trical parameters thus matches perfectly Baughman’s cri-

teria for topochemical polymerization and the second one

is quite close (vide supra).

It is noteworthy that the crystal structure of 6 is at 180 K,

whereas polymerization is carried out at or near room

temperature. Nevertheless, this situation does not introduce

Molecules of 6 pile up in columns in the a direction

(Figure 6). The axes of the columns are all parallel but the

stacks are not aligned identically: each column is sand-

wiched perpendicularly by two other columns. The

CtC-CtC fragmentsof the moleculesin the central stack

face the NPh₂parts of the molecules from the contiguous

stacks. A similar situation was not observed in 5.

Article

Chem. Mater., Vol. 22, No. 13, 2010 3971

any significant error. Indeed, spectroscopic studies (vide

infra) show smooth and modest variations between these

two temperatures, indicative of the absence of any phase

transition. Furthermore, thermal expansion is estimated to

be about 1% considering typical expansion coefficients for

van der Waals crystals, such changes being too small to

grossly affect the geometry of the reacting centers.

In conclusion, the presence of C_arom-H π interac-

3 3 3

tions between molecules susceptible of getting linked via

topochemical polymerization is essential to obtain a

reactive THD analogue. These interactions contribute

to generating columnar assemblies with an A-B-A-B

type arrangement in which each molecule is shifted side-

ways with respect to the two surrounding ones along the

polymerization axis. Such interactions are present in the

crystal structures of 5 and 6. Yet, the longer hydrocarbon

spacer between the CtC-CtC fragment and the NPh₂

group in 5 makes this latter diacetylene unreactive. Thus,

by a slight modification of the length of this spacer, it is

possible to fine-tune the reactivity of THD analogues.

Modifications of the THD skeleton resulting in the loss of

Figure 7. Room temperature absorption spectrum of a chloroform solu-

tion of pure poly-6 at a concentration of 0.05 mg mL^-1(solid line). The

dashed line corresponds to the absorption spectrum of N-methyldiphe-

nylamine at 20 ꢀC in methylcyclohexane (data from Forster et al.⁶¹).

€

value is typical of PDAs in a yellow solution.^58a,60Two

additional bands are observed around 250 and 300 nm in

Figure 7 that originate from the side groups of poly-6;

the positions of these bands compare well with those of

N-methyldiphenylamine in methylcyclohexane solution

(dashed line).⁶¹

these intracolumn C_arom-H π interactions lead to

3 3 3

unreactive monomers. This is observed for diacetylenes

1-4. In these diacetylenes, the leading interactions are

interstack, so these contacts do not contribute to making

possibly reacting molecules closer. In 1-4, columns with

an A-A-A-A arrangement are observed in which all of

the molecules are equivalent and lie far apart.

A number average molecular weight, M_n, of 300 000 Da was

found experimentally by size exclusion chromatography

(SEC) for poly-6 dissolved in THF, with use of commonly

employed polystyrene calibration. However, it has been ob-

served for some PDAs that this calibration overestimates the

masses by a factor of up to 2 (see Experimental Section), so the

real molecular weight could be as low as 150 000 Da. As we do

not know the actual correction factor for poly-6, we believe

it is more appropriate to give a range for M_n, between

150 000 and 300 000 Da. Likewise, the polymerization

index N_nspans the range 320-650. The measured polydis-

persity is close to 3. Similar polydispersities have been meas-

ured for other PDAs, e.g., 2.66 for poly-TS12 (TS12 =

dodeca-5,7-diyne-1,12-ylene-bis(p-toluenesulfonate)^58cand

2.5 for poly-4BCMU (4BCMU = 5,7-dodecadiyne-1,12-diol

bis([(n-butoxycarbony1)methyl]urethane)),⁵⁹yet much lar-

ger values may be found in some cases. There is no satisfac-

tory explanation for such large polydispersities. Because

PDAs are formed by a solid-state topochemical reaction,

the usual mass distributions may not apply.

Thus, we have succeeded in preparing an analogue

of poly-THD that is soluble in chloroform, a typical

solvent for neutral PDAs. Clearly, the presence of two

-CH₂CH₂CH₂- fragments in the starting monomer is an

asset and greatly improves the solubility of the final poly-

mer. This aspect is of outmost importance for applications

requiring the preparation of films.

The fact that poly-6 is soluble in organic solvents such

as chloroform is important for another reason: it allows

determination of the polymer contents in more or less

polymerized crystals. This is easily accomplished by

recording the UV-visible spectrum of the dissolved

Polymerization Studies. Among the six DAs studied in

this work, compound 6 is the only one for which crystallo-

graphy suggests that topochemical polymerization

should be possible. We show thereafter that this diacetyl-

ene indeed polymerizes in the solid state, thermally and

photochemically (UV and γ). The resulting PDA, poly-6,

has been characterized spectroscopically in the solid state,

and because this polymer is soluble in organic solvents,

solution studies have also been carried out.

Absorption Studies of Poly-6 and Molecular Weight

Determination. Figure 7 shows the UV-visible absorp-

tion spectrum of a chloroform solution of the polymer at

a concentration of 0.05 mg mL^-1. A structureless band is

observed at λ_max≈ 470 nm that is absent from the

spectrum of the nonirradiated monomer. Previous studies

on solutions of neutral PDAs have shown a similar

absorption band.⁵⁸This band is characteristic of the so-

called yellow state of PDAs in good solvents, that is

solvents in which the macromolecules are isolated, coiled,

worm-like chains.^58c,59From absorption spectra such as

the one shown in Figure 7, it is possible to calculate the

extinction coefficient of the polymer in a good solvent at

λ

_max, in this case R = 40200 ( 1500 L mol^-1cm^-1; this

(58) See among many references: (a) Patel, G. N.; Chance, R. R.; Witt,

J. D. J. Chem. Phys. 1979, 70, 4387–4392. (b) Plachetta, C.; Rau,

N. O.; Hauck, A.; Schulz, R. C. Makromol. Chem., Rapid Commun.

1982, 3, 249–254. (c) Wenz, G.; M€uller, M. A.; Schmidt, M.; Wegner,

ꢀ

G. Macromolecules 1984, 17, 837–850. (d) Aime, J. P.; Bargain, F.;

Fave, J. L.; Rawiso, M.; Schott, M. J. Chem. Phys. 1988, 89, 6477–

6483. (e) Li, Y.; Chu, B. Macromolecules 1991, 24, 4115–4122.

(59) Rawiso, M.; Aime, J. P.; Fave, J. L.; Schott, M.; Muller, M. A.;

Schmidt, M.; Baumgartl, H.; Wegner, G. J. Phys. (Paris) 1988, 49,

861–880.

ꢀ

(60) Spagnoli, S.; Berrehar, J.; Lapersonne-Meyer, C.; Schott, M.;

ꢀ

€

Rameau, A.; Rawiso, M. Macromolecules 1996, 29, 5615–5620.

(61) Forster, E. W.; Grellmann, K. H.; Linschitz, H. J. Am. Chem. Soc.

€

1973, 95, 3108–3115.

3972 Chem. Mater., Vol. 22, No. 13, 2010

Deschamps et al.

crystal and making use of the extinction coefficient

determined previously.

UV Polymerization. Two parts of the same crystal were

irradiated at 340 and 275 nm respectively, at 20 ꢀC. The

diphenylamino (DPA) side groups absorb at both wave-

lengths whereas the CtC-CtC reactive group absorbs

only at 275 nm, yet weakly.⁷⁰At 340 nm, the optical

density of the crystal was ∼2, so light was almost com-

pletely absorbed in the bulk. At 275 nm, the absorption is

much larger, so light is totally absorbed in a thin layer

near the surface. At that latter wavelength, R ≈ 100 cm^-1

for the CtC-CtC group, so only a small fraction of all

photons is absorbed by this group.

The UV reactivity is very low. At 340 nm, x_p≈ 2.7 ꢀ

10^-7after 1.45 ꢀ 10⁵s under a photon flux of 1.7 ꢀ 10¹¹

photons cm^-2s^-1, so the number of monomers included

in a polymer chain per absorbed photon is η_p≈ 1.65 ꢀ

10^-2. The same value is found at 275 nm within the

experimental uncertainty, (10%. With a number average

polymerization index N_nin the range 320-650, an initia-

tion yield per absorbed photon can be estimated, 2.5 ꢀ

10^-5e η_i= η_p/N_ne 5 ꢀ 10^-5. This value is nearly 2

orders of magnitude smaller than that found for thor-

oughly studied pTS.⁷¹η_pvaries somewhat among crys-

tals, so it may be that initiation occurs preferentially at

defects of unknown nature.

Photoreactivity at 340 nm shows that the reactive

CtC-CtC groups are excited by energy transfer from

the DPA groups. This is allowed by the relative positions

of the excited states. The lowest singlet state of DPA

groups is at ∼3.85 eV,⁷²well below the CtC-CtC one at

4.5 eV,⁷⁰so energy transfer cannot occur in the singlet

state. But the triplet energies are very close, ∼3.1 eV for

DPA groups⁷³and ∼3.1 eV for the only CtC-CtC

fragment where it is known,⁷⁴so there will be a finite

probability of populating the CtC-CtC triplet at room

temperature, by energy transfer in the triplet state follow-

ing intersystem crossing within the DPA groups. Indeed,

We have measured the absorption dichroism of single

crystals of 6 polymerized to very low extents with γ-rays;

it is 220 ( 20. From the knowledge of the thickness of the

crystals and their polymer contents (see Experimental

Section), it is indeed possible to determine the extinction

coefficients in perpendicular polarization (the electric

field of the incident light being perpendicular to the chain

in the crystal), in this case R_^= 3300 ( 200 cm^-1, and in

parallel polarization, R_//= (7.3 ( 1.1) ꢀ 10⁵cm^-1. This

latter value is similar to that found for other PDAs.⁶⁰

Furthermore, such a piece of information allows direct

determination of the polymer contents x_pof any studied

single crystal without having to dissolve it.

Thermal Reactivity. Diacetylene 6 is almost unreactive

thermally. Indeed, a polymer content x_p≈ 2.6 ꢀ 10^-7was

found after 2.6 ꢀ 10⁵s at 22 ꢀC in the dark, which

corresponds to a rate k_th≈1ꢀ 10^{-12 -1}

s . Similar experiments

performed at 45 ꢀC (k_th≈ 6.3 ꢀ 10^-12s^-1) and 70 ꢀC (k_th≈

3.5 ꢀ 10^-11s^-1) yield an activation energy E_act≈ 0.65 (

0.05 eV. These values of k_i^(therm)and E_actlead to a very small

preexponential term, suggesting that the reaction occurs only

at particular sites. Then the reaction stops when the sites have

all reacted, as is the case for several DAs with hydrogen-

bonded side groups, for instance 4BCMU.⁶²

This rate may be compared with that of the best studied

DA 2,4-hexadiyne-1,6-diol bis(p-toluenesulfonate), known in

the literature as pTS, for which thermal reactivity is

intrinsic.^63-68It is considered as “low” in the initial stages

of the reaction (a so-called induction period), then accelerates

after a few percents in polymer (poly-pTS) are reached. The

rate of poly-pTS formation in the induction period at 70 ꢀC is

1.7 ꢀ 10^-6s^{-1 67,68}

,

nearly 5 orders of magnitude larger than

the rate of poly-6 formation. Considering that, in the case of

pTS, chains formed in the induction period are short (ca. 30

units),⁶⁷while the chains obtained by irradiation of 6 have

lengths spanning the range 320-650 units (see above), the

˚

the CtC-CtC rods are 5-6 A away from not only the

DPA groups of the same molecule, but also from DPA

groups of molecules in nearest neighbor stacks (Figure 6).

It may be concluded that photopolymerization of 6 is

initiated in the diacetylene triplet state, populated by

energy transfer from the side group triplet. A detailed

study of the phopolymerization of another DA, pTS, has

led to the conclusion that initiation occurs in the diace-

tylene triplet state as well.⁹

A similar situation where the side groups absorb at a

lower energy than the diacetylene moiety occurs in several

other DAs, for instance in DCH (DCH = 1,6-bis(N-car-

bazolyl)-2,4-hexadiyne). Complete polymerization of

DCH can be achieved thermally or by γ-irradiation,⁷⁵

ratio of initiation rates between 6 and pTS is nearly 1 ꢀ 10^-6

.

Thermal reactivity of DA crystals and powders has

been studied by recording, in a DSC apparatus, the heat

evolved during a linear temperature increase.^66,68,69The

very low thermal reactivity of 6 suggests that no significant

heat evolution should be detected. Nevertheless, such an

experiment was performed and, indeed, no exotherm ascrib-

able to thermal polymerization was observed near 70 ꢀC,

below the melting endotherm at 85.5 ꢀC. As a result, thermal

polymerization of 6 was not studied further.

ꢀ

(62) Spagnoli, S. Ph.D. Thesis, Universite Paris 7, Paris, France, 1995.

(63) Wegner, G. Makromol. Chem. 1971, 145, 85–94.

(64) Bloor, D.; Koski, L.; Stevens, G. C.; Preston, F. H.; Ando, D. J.

J. Mater. Sci. 1975, 10, 1678–1688.

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(70) Berrehar, J.; Lapersonne-Meyer, C.; Schott, M.; Weiser, G. Chem.

(65) McGhie, A. R.; Kalyanaraman, P. S.; Garito, A. F. J. Polym. Sci.,

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Chem. Soc. 1978, 100, 6644–6649.

(67) Albouy, P. A.; Keller, P.; Pouget, J. P. J. Am. Chem. Soc. 1982, 104,

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Article

Chem. Mater., Vol. 22, No. 13, 2010 3973

Table 3. γ-Ray Irradiation Results for Diacetylenes 1-6

The large reactivity difference between UV and γ irradia-

tion is reminiscent of 3BCMU.⁷⁹In 3BCMU, this situation

was rationalized as being due to a large difference in initiation

probabilities between neutral and ionized states. UV irradia-

tion creates only neutral excited states while γ irradiation also

creates ionic states (cations and anions). Free charges gener-

ated by Compton scattering and subsequent relaxation of the

electrons will eventually localize according to the values (in

the crystal) of the ionization potentials I_cand electron

affinities A_cof the CtC-CtC and DPA groups. From

the study of charge transfer complexes formed by DPA

groups in solution (that is, a condensed phase though liquid),

I_c(DPA) ≈ 7.4 eV was deduced.⁸⁰The gas phase ionization

potential of dimethyldiacetylene is 8.9 eV,^81,82and I_chas been

measured on at least two DA crystals, pTS with I_c=7.1eV,⁸³

and tricosadiynoic acid⁸⁴with I_c= 7.0 eV. These values lead

to a polarization correction in the solid of about 1.8 eV, a

typical value for this kind of molecular crystal. Thus, positive

charges will rather localize on the diacetylene group. It was

concluded by Spagnoli et al.⁷⁹that the electron affinity of

CtC-CtC groups is close to zero. The corresponding value

for DPA groups is not available but is likely to be larger. As a

result, the electron will rather reside on the side groups, a

situation similar to that of 3BCMU and 4BCMU.⁷⁹

γ-ray dose

compd^a(MRad)

presence PDA content

of PDA^b

color change

(wt %)^b

1

2

3

4

5

6

0.390

0.590

0.550

0.645

0.38

0.565

2

no

from white

yes

0.35

0.55

2.5

5.4

12.5

18.5

to pale yellow,

deep orange, or red

depending on the

irradiation dose

7

19.5

25

^aThe irradiation experiments were carried out on microcrystalline

powders (compounds 1-5) or crystals (compound 6). ^bThe presence of

PDA was assessed and its amount determined by recording the absorp-

tion spectrum of the irradiated material in chloroform solution.

but the UV reactivity of this diacetylene is very low. It has

been shown that absorption by the carbazolyl groups can

indeed initiate the reaction,⁷⁶yet with very low yield. The

comparison between 6 and DCH cannot be pushed too far,

however, as the DCH monomer structure is far less favorable

to polymerization than that of 6, and complete γ-polymer-

ization implies a phase transition.⁷⁷Consequently, even the

initial γ-reactivity of DCH is low: about 10 MRad are

needed to reach a polymer content of about 1.5%.^75,77

γ-Ray Polymerization. Crystals were irradiated up to a

dose of 25 MRad (see Table 3). The polymer content x_p

increases linearly with the dose, although the reactivity

may be somewhat larger at x_p< 0.02. The rate is 7.5 ꢀ

10^-3per MRad. So, the number of monomers included in

a chain per 100 eV deposited in the crystal, G_p, is about

16, and the number of initiations per 100 eV, G_i= G_p/N_n,

spans the range 2.5-5 ꢀ 10^-2. This is a low reactivity. For

instance, for pTS at low doses, G_pis 20 times larger and

G_iis around 200 times larger.^66,78Yet, there are many

DAs with reactivities comparable to that of 6.

The γ-ray reactivity of 6 is much higher than its UV

reactivity: the number of initiations per 100 eV (about

20 photons) would be around 1 ꢀ 10^-3for UV photo-

polymerization.

The linear increase in polymer contents as a function of

irradiation dose leads to the following conclusions:

(i) Polymerization may be initiated on any monomer

and, at the very early stages of the process, an increased

contribution of more reactive sites is possible.

In the present case, the reactivity difference can be due

either to a difference in initiation rates as in 3BCMU or to

the fact that charge transfer to the reactive groups is more

efficient than neutral excitation transfer. Thus, γ-ray

induced initiation in 6 is likely to be predominantly

cationic, the cations being produced by transfer of a

charge initially produced elsewhere in the crystal. Note

that there has been a thorough study of UV-induced

polymerization of pTS and, to a lesser extent, of some

9

78

€

of its analogues (see the reviews by Sixl and Bassler ),

but there is no similar work on γ-induced reaction.

Spectroscopic Studies of Partially Polymerized Single

Crystals. The Raman, absorption and luminescence stud-

ies presented here were performed on two separate single

crystals of 6 irradiated with different doses of γ-rays,

0.38 MRad for crystal C1 (x_p= 3 ꢀ 10^-3) and 4500 Rad

for crystal C2 (x_p≈ 3 ꢀ 10^-5).

Raman studies were conducted at various temperatures

on the most irradiated crystal C1 as this crystal gives a

better signal-to-noise ratio. The Raman spectrum of crystal

C1 was measured at 15 K (Figure 8) to allow direct

comparison with the vibration mode frequencies calculated

at 0 K (see computational results, below). At 15 K, the

experimental stretching frequencies of the double bond

(ν_D) and the triple bond (ν_T) for the conjugated system in

(ii) The polymerization conditions do not change at

least up to x_p≈ 0.2. This observation suggests that N_nand

η_i(γ) remain constant, meaning that the geometrical

conditions of initiation and propagation do not change

significantly. This is consistent with the similarity that

exists between the experimental crystal structure of 6 and

the calculated structure (vide infra) of an ordered mixed

(79) Schott, M.; Spagnoli, S.; Weiser, G. Chem. Phys. 2007, 333, 246–

253.

(80) Briegleb, G.; Czekalla, J. Z. Elektrochem. Angew. Phys. Chem.

1959, 63, 6–12.

crystal (6)_0.5-(poly-6)_0.5

.

(81) Brogli, F.; Heilbronner, E.; Hornung, V.; Kloster-Jensen, E. Helv.

Chim. Acta 1973, 56, 2171–2178.

(76) Chance, R. R.; Baughman, R. H. 8th Molecular Crystal Sympo-

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(83) Murashov, A. A.; Silinsh, E. A.; Bassler, H. Chem. Phys. Lett. 1982,

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93, 148–150.

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3974 Chem. Mater., Vol. 22, No. 13, 2010

Deschamps et al.

In conclusion, the polymeric chains generated by γ-ray

irradiation of single crystals of 6 are highly luminescent.

The similarity between the spectroscopic features of these

chains and those of isolated red chains of poly-3BCMU,

known to be perfect quasi-1D quantum wires,^27,28suggests

that the former chains also have a high degree of order. The

spectroscopic properties of poly-6 chains compare well with

those of poly-THD chains which are strongly luminescent at

low temperature,^33,37the structural difference between their

monomers being two methylene groups per half-molecule.

Given that 6 is much less reactive than THD, the amount of

polymer produced by irradiation of single crystals of the

former diacetylene can be easily controlled. This is a quite

remarkable result, as it allows spectroscopic investigation of

polydiacetylenes in a large range of conditions and makes

possible the study of the relationship that exists between

chain conformation and electronic properties. As far as the

origin of the blue shift mentioned earlier is concerned, the

X-ray crystal structure of 6 suggests that it might be con-

nected with the unusual configuration of the polymer chains

(vide infra).

Figure 8. Raman spectrum of crystal C1 at 15 K. The excitation wave-

length was 647 nm. The polymer line intensities are enhanced by strong

preresonance. The double bond and triple bond stretching mode frequen-

cies are respectively 1491 ( 2 and 2073 ( 2 cm^-1at 15 K. The diacetylene

triple bond stretching mode frequency is 2259 ( 2 cm^-1. The spectrum is

not corrected for detection response.

Computational Studies of 6 and Poly-6. The high ther-

mal reactivity of THD allows the preparation of totally

polymerized poly-THD crystals of high enough quality to

allow structural determination of this polymer with high

accuracy.³²This is not the case for 6 because of its low

reactivity. To circumvent this difficulty, we have used

DFT methods to obtain the structure of poly-6. Prior to

doing that, however, we have assessed the accuracy of our

computational method by comparing the calculated

structure of monomer 6 with the experimental one.

Semilocal DFT-GGA methods like PBE are certainly

among the most efficient computational methods in con-

densed matter, but their drawback is that they do not

include the London dispersion part of the weak van der

Waals interactions.⁸⁸As a result, in molecular crystals,

covalent bonds are well-reproduced, whereas intermolecu-

lar distances and lattice parameters are overestimated. If

London forces are the dominant interactions, as is the case

in a noble gas crystal, this leads to unrealistic structures; but

in a molecular crystal, where other contributions dominate,

GGA-DFT can give fairly good structures. We have

checked this effect on our calculations by optimizing the

atomic positions and unit cell parameters of diacetylene 6,

starting from the experimental values. The computed fully

optimized (atomic positions and unit cell) structure is still

close to the experimental one with an expansion of the

lattice parameters by 5% (Table 4). This expansion is

reasonable for a DFT calculation, suggesting that the

contribution of dispersion forces to intermolecular forces

is moderate, and that dipole-dipole van der Waals inter-

actions dominate. Intramolecular distances are all within

the typical error of the method, that is around 2%. The

theoretically determined bond lengths agree well with the

values found for diacetylenes for which an X-ray crystal

structure has been reported.³

the ground state are 1491 ( 2 cm^-1and 2073 ( 2 cm^-1

,

respectively. The frequency of the Raman-active monomer

triple bond stretching mode is 2259 ( 2 cm^-1, which is

typical. Figure 8 also shows modes at lower frequencies that

will not be discussed here. In addition, plots of ν_Dand ν_T

versus temperature between 15 and 300 K (not shown) are

smooth, which indicates that no phase transition occurs as

temperature is changed.^85,86

Figure 9 shows the absorption and luminescence spec-

tra of crystal C2 at 13 K for a polarization of the

excitation parallel to the chains. The direction of the

chains is along the length of the crystal; this can be easily

verified by taking advantage of the high dichroism of the

crystal. Despite a blue shift of the bands as compared to

those of all other PDA crystals, the overall structures of

the absorption and luminescence spectra are typical of

polydiacetylenes, i.e., they show a main zero-phonon

excitonic line accompanied by weaker vibronic replicas.

The spectra shown in Figure 9 are well-resolved, and the

luminescence spectrum is nearly a mirror image of the

absorption spectrum. The lines are broadened at higher

temperatures.

The zero-phonon emission line width at 13 K might be

affected by reabsorption. The position (∼2.4 eV) of the

unperturbed emission line at this temperature can be

recovered by using the frequencies of the double bond

and triple bond stretching modes determined by Raman

spectroscopy (see Figure 8). In these conditions, a Stokes

shift less than ∼2 meV is estimated, the latter being

possibly zero. A detailed investigation of the spectro-

scopic properties of poly-6 will be presented elsewhere.⁸⁷

(85) Batchelder, D. N.; Bloor, D. Adv. Infrared Raman Spectrosc. 1984,

11, 133–209.

(86) Spagnoli, S.; Berrehar, J.; Fave, J.-L.; Schott, M. Chem. Phys. 2007,

333, 254–264.

(87) Al Choueiry, A.; Barisien, T.; Holcman, J.; Legrand, L.; Schott,

M.; Weiser, G.; Balog, M.; Deschamps, J.; Dutremez, S. G.; Filhol,

J.-S. Phys. Rev. B 2010, 81, 125208-1–125208-11.

(88) Kohn, W.; Meir, Y.; Makarov, D. E. Phys. Rev. Lett. 1998, 80,

4153–4156.

Article

Chem. Mater., Vol. 22, No. 13, 2010 3975

Figure 9. Absorption (solid line) and luminescence (dots) spectra of crystal C2 at T = 13 K for a polarization of the excitation parallel to the polymer

chains. For the luminescence measurements, the excitation was 2 mW at 488 nm.

Table 4. Comparison Between Calculated and Experimental Parameters for 6 and Poly-6^a,b

lattice params (distances torsion angle energy/unit cell

(kJ mol^-1

CꢁC

CdC

length (A) length (A)

C-C

length (A)

c

˚

in A and angles in deg)

˚

˚ ˚

R_v(A) d (A)

compd

θ (deg)

)

6 as calculated in

optimized unit cell

a = 10.48, R = 90.00,

b = 16.88, β = 97.01,

c = 17.41, γ = 90.00

0

1.224

1.360,

1.452,

1.453,

3.764,

3.804

5.164,

5.543

1.537-1.543

1.358,

1.449,

6 as calculated in

exp unit cell

a = 9.948, R = 90.0,

b = 16.089, β = 98.697,

c = 16.764, γ = 90.0

110.7

1.224

3.503,

3.541

4.906,

5.349

1.449,

1.533-1.540

1.379,

1.461,

1.464,

1.5217-1.5240

1.430

6 exp

a = 9.948, R = 90.0,

b = 16.089, β = 98.697,

c = 16.764, γ = 90.0

1.194,

1.196

3.4946, 4.937,

3.573 5.281

poly-6 as calculated in

optimized unit cell

a = 9.97, R = 83.86,

b = 17.59, β = 95.98,

c = 17.44, γ = 89.37

a = 9.948, R = 90.0,

b = 16.089, β = 98.697,

c = 16.764, γ = 90.0

119

136

-230.0

-104.5

1.236

1.239

1.387

1.393

poly-6 as calculated in

the unit cell of 6

1.427

^aThe torsion angle θ is depicted in Figure 10 and is equivalent to the R-C₄C₁-R dihedral angle in Scheme 1. ^bEnergies are relative to that of the

3 3 3

monomer in the optimized cell. ^cSee Scheme 1.

We have also obtained the optimized structure of 6 in the

experimental unit cell: intermolecular and intramolecular

distances are within 2% of the experimental ones. This

structure is only 0.5 kJ mol^-1per atom less stable than the

fully relaxed one, suggesting that the very weak forces missing

in the calculation are not important for our purpose. In both

cases, the unit cell size does not have much effect on vibration

frequency calculation results as the typical error is a systema-

tic overestimation by only 1-1.2% (Table 5). The computed

symmetric CtC stretching frequency of 6 is 2276 cm^-1in the

relaxed unit cell and 2286 cm^-1in the experimental unit cell,

in good agreement with the experimental value of 2259 cm^-1

at 15 K. Aromatic CdC vibrations for 6 are computed to be

in the following ranges: 1555-1558, 1570-1572, 1576-1583,

and 1591-1595 cm^-1(optimized unit cell), and 1563-1568,

1575-1576, 1581-1590, and 1600-1604 cm^-1(experimental

unit cell). The corresponding vibrations in the experimental

Our ground state calculations appear to reproduce well

the structure and properties of 6. On the basis of these

findings, we expect the computed structure of poly-6 to be

a faithful model of actual poly-6 with properties directly

comparable with the experimental results.

Poly-6 was generated computationally bearing in mind

the experimental situation, that is a monomer-polymer

mixed crystal in which polymer chains are surrounded by

monomer molecules. As the computational method requires a

3D periodic system and a not too large unit cell because of

computational cost, an ordered (monomer)_0.5-(polymer)_0.5

mixed crystal was considered: one out of the two monomer

stacks in the unit cell was replaced by a polymer chain. In this

situation, a polymer chain is surrounded by side groups from

nearest neighbor diacetylene stacks. The polymeric structure

was built by rotation of the monomer units until the distance

between the carbon atoms that get connected during the

spectrum are 1573, 1592, and 1604 cm^-1

.

polymerization process was 1.51 A, a distance reasonably

˚

3976 Chem. Mater., Vol. 22, No. 13, 2010

Deschamps et al.

Table 5. Comparison Between Calculated and Experimental Properties of 6 and Poly-6

CtC vibration

)

aromatic CdC

enyne CdC

compound

(cm^-1

vibration (cm^-1

)

vibration (cm^-1

)

DFT gap (eV)

color

6 as calculated in optimized unit cell

2276

1555-1558,

1570-1572,

1576-1583,

1591-1595

1563-1568,

1575-1576,

1581-1590,

1600-1604

1573,

2.91

6 as calculated in exp unit cell

6 exp at T = 300 K

2286

2.83

2256^a

1592,

1604

poly-6 as calculated in optimized unit cell

poly-6 as calculated in the unit cell of 6

poly-6 exp at T = 300 K

2075

2076

2045^b

1471,

1512

1458,

1494

1480^c

1.65

1.32

red

^aCtC vibration at 15 K = 2259 cm^{-1 b}CtC vibration at 15 K = 2073 cm^{-1 c}Enyne CdC vibration at 15 K = 1491 cm^-1

. . .

Figure 10. Structure of partially polymerized 6 as obtained from calculations using a fully relaxed cell. The torsion angle θ of the chain is shown in the

picture on the left-hand side.

close to the CdC bond length of a PDA chain. Then, the

atomic positions and unit-cell parameters were optimized.

By analogy with the situation found in pTS-poly-pTS

mixed crystals,^89,90the optimized unit cell at 50% poly-

mer contents should be close to that of the pure polymer,

whereas optimization in the monomer experimental cell

should mimic the situation of an isolated poly-6 chain in

its monomer crystal, giving some insight into the strain of

the chain in that situation. Hence, poly-6 was computed

in a fully relaxed unit cell and in the experimental cell of

monomer 6 as shown in Figure 10.

Formation of poly-6 is calculated to be exothermic by

108 (kJ mol^-1)/unit cell in the experimental cell as opposed

to 115 (kJ mol^-1)/unit cell in the optimized cell. This polymeri-

zation energy is smaller than that found for other polydiace-

tylenes such as poly-THD (135 kJ mol^-1per monomer),³⁹

poly-pTS (155 kJ mol^-1per monomer),^66,68,91and poly-[1,6-

bis(2,4-dinitrophenoxy)-2,4-hexadiyne] (135 kJ mol^-1per

monomer), known as poly-DNP.⁶⁹

ꢀ

(89) Aime, J.-P. Ph.D. Thesis, Universite Paris 7, Paris, France, 1984.

(90) Bloor, D.; Day, R. J.; Ando, D. J.; Motevalli, M. Brit. Polym. J.

1985, 17, 287–293.

(91) Chance, R. R.; Patel, G. N.; Turi, E. A.; Khanna, Y. P. J. Am.

Chem. Soc. 1978, 100, 1307–1309.

Article

For the fully optimized structure, the calculated unit

Chem. Mater., Vol. 22, No. 13, 2010 3977

3

cell volume decreases slightly from 3058 A to 3025 A

3

˚

upon polymerization; the decrease in the a cell parameter

due to formation of carbon-carbon bonds is compen-

sated by an increase in the b parameter. Packing of the

phenyl groups is not much affected by these changes and

is mostly conserved, even though some strain appears.

Most important is the fact that the polymeric chain is not

planar but is strongly twisted with a torsion angle θ, shown in

Figure 10 and equivalent to the R-C₄C₁-R dihedral angle

3 3 3

in Scheme 1, of 136ꢀ (it is 119ꢀ in the optimized cell). In a

recent study,³⁹we have shown that such a twisted structure

can be associated with a red phase PDA. The bond lengths of

the polymer backbone (Table 4) are consistent with those

computed previously for poly-THD³⁹and poly-[(1,6-bis-

(N-methylimidazolium)-2,4-hexadiyne)dibromide].⁹²

Figure 11. Band structure of partially polymerized6 in the monomer unit

cell. The relative coordinates of the given k-points are: Γ(0,0,0), F(0.5,0,0),

Q(0.5,0.5,0), and Z(0,0.5,0). Fermi level is at 0 eV.

Clearly, the correlation between optical absorption and

luminescence on the one hand, and ground state vibrational

frequencies (as obtained from resonant Raman scattering

for instance) on the other hand, may not be as unequivocal

as previously assumed. The question concerning the varia-

tion of vibrational frequencies of PDAs in relation to color

changes will be further discussed elsewhere.⁹⁵Let us only

point out here that elastic strain of a PDA chain may result

in large variations of both the absorption threshold and

vibrational frequencies; this has been well studied in poly-

pTS for instance. Frequency changes may be related to

anharmonicity, or indirectly to the effect of strain on the

electronic structure. Most experimental studies used long-

itudinal tensile strain, but compressive strain also leads to

large effects, of the opposite sign.⁸⁶Such effects may be at

play in poly-6 but hardly so in poly-THD.

The full vibration spectrum of poly-6 was next calcu-

lated, as comparison between computed and experimental

frequencies can provide some information about local

geometries.^93,94As opposed to typical planar PDAs, for

twisted PDA chains like poly-6 described herein and poly-

THD,³⁹two vibrational frequencies associated with the

CdC stretches are possibly Raman active. Calculations

using a relaxed unit cell yield a symmetric CtC stretching

frequency of 2075 cm^-1and CdC stretching frequencies of

1471 and 1512 cm^-1(Table 5). For poly-6 optimized in the

unit cell of 6, a symmetric CtC stretching frequency is

found at 2076 cm^-1, and CdC stretching frequencies are

found at 1458 and 1494 cm^-1. The relative intensities of the

corresponding Raman peaks cannot be easily computed at

this level of theory because of the size of the system.

However, taking into account the accuracy of the compu-

tational method, these stretching frequencies are equal to

We computed recently a model PDA with an unstrained

structure, poly-2,4-hexadiyne, that can be used as a

reference.³⁹The lack of any local structural stress in this

PDA is due to the absence of inter- and intrachain interac-

tions in the large chosen unit cell. We find that the C-C,

CdC, and CtC bonds of poly-6 (Table 4) are all longer by

the experimental ones at 15 K (2073 and 1491 cm^-1

,

respectively). Such a good agreement is a clear indication

that the calculated structure of poly-6 should be very close

to the experimental one and lends strong support to the

former being a good model of the latter.

˚

more than 0.01 A than those of the unstressed model chain

˚

with the same torsion angle of 119ꢀ, i.e., d(C-C) = 1.416 A,

˚

d(CdC) = 1.378 A, and d(CtC) = 1.228 A. Such an

observation suggests that the main chain of poly-6 is under

tensile stress. The strain is linked to the presence of bulky

substituents that govern crystal packing. In a Morse poten-

tial approach, all of the carbon-carbon bonds of poly-6 are

expected to be weakened due to anharmonicity, and asso-

ciated frequencies should be shifted toward lower values as

compared to those of the unstressed model (ν_T= 2142 cm^-1

and ν_D= 1519 cm^-1).³⁹Our calculations agree with this

reasoning. In addition, CtC bonds appear to be much more

sensitive to local stress than CdC bonds, certainly because of

a larger bond anharmonicity. This leads to a shift of the red

poly-6 frequencies toward values typically observed for blue

isomers, and to a large temperature dependence. Clearly, for

some PDAs, the interplay between the twisting of the

polymer chain and the strain in this chain can lead to

CtC and CdC Raman frequencies outside typical ranges.

The electronic band structure of half-polymerized 6

in the monomer unit cell was computed and is presented

Usually, blue phase PDAs have CtC stretching fre-

quencies around 2080 cm^-1and CdC stretching frequen-

cies around 1460 cm^-1. Red phase PDAs have CꢁC

stretching frequencies around 2120 cm^-1and CdC

stretching frequencies around 1520 cm^-1. The measured

CtC stretching frequency of poly-6 is suggestive of a blue

phase PDA, and the experimentally observed CdC

stretching frequency is at the boundary between a blue

phase and a red phase (Table 5). Yet, the fact that poly-6 is

strongly luminescent is a clear indication that it is a red

phase PDA;^34,37a similar dilemma between blue phase

and red phase PDAs has been encountered previously in

the case of poly-THD.³⁹

(92) Chougrani, K.; Deschamps, J.; Dutremez, S.; van der Lee, A.;

Barisien, T.; Legrand, L.; Schott, M.; Filhol, J.-S.; Boury, B.

Macromol. Rapid Commun. 2008, 29, 580–586.

(93) Filhol, J.-S.; Simon, D.; Sautet, P. J. Phys. Chem. B 2003, 107,

1604–1615.

(94) Ben Yahia, M.; Lemoigno, F.; Beuvier, T.; Filhol, J.-S.; Richard-

Plouet, M.; Brohan, L.; Doublet, M.-L. J. Chem. Phys. 2009, 130,

204501-1–204501-11.

(95) Filhol, J.-S., work in progress.

3978 Chem. Mater., Vol. 22, No. 13, 2010

Deschamps et al.

Figure 13. Comparison between the undulation found in poly-THD

chains and that found in poly-6 chains.

dihedral angle in Scheme 1 being different from 180ꢀ).³⁹It

was also put forth that the transition energy of the exciton is

an intrinsic property of the chain and that the electronic

nature of the substituents only have a modest influence on it.

Yet, distortion of the chains as a result of crystal packing

forces, to which the size of the substituents and the presence

of interactions with neighboring groups both contribute

largely, is of outmost importance. Hence, for red PDAs, a

multitude of conformational isomers is possible depending

on the nature of the substituents.

Figure 12. Calculated absorption spectrum of partially polymerized 6 in

the unit cell of the monomer.

in Figure 11. It corresponds to a direct band gap

semiconductor at Γ-point with a DFT gap of 1.32 eV.

The lowest strongly dispersed unoccupied band corre-

sponds to the π* system of the polymer; the eight highest

occupied bands, that do not exhibit much dispersion,

correspond to the nitrogen lone pairs of the amino

groups. The next highest band corresponding to the

polymer π system is located 0.27 eV below Fermi level.

Thus, the peculiarity of this polymer is to have inter-

mediate nitrogen bands inserted between the π-π* band

structure, similarly to what was found for poly-THD.³⁹

The absorption spectrum of poly-6 in the experimental

unit cell is presented in Figure 12; this spectrum was

computed using a scissor operator of 0.65 eV and a smearing

factor of 0.15 eV. It shows two large absorption bands

centered at about 312 and 505 nm. The first band is linked to

the NPh₂moiety and the second band to the enyne back-

bone of the polymer. Considering the 505 nm absorption,

poly-6 is expected to be a red phase PDA.¹⁷The calculated

absorption maximum is only 10 nm lower than the experi-

mental value in the crystal, i.e., 515 nm (see Figure 9).

In summary, the structure of poly-6 was computed and

some of its properties calculated. Agreement between

calculated and experimental values is quite good. Poly-6

is a red phase PDA with a 136ꢀ twisted enyne backbone

that absorbs in the blue part of the visible spectrum. Its

Raman CtC and CdC stretching frequencies are shifted

toward blue values because of tensile strain.

With this in mind, the fact that poly-6 absorbs higher

energy photons than poly-THD suggests that the former

polymer has a more twisted structure than the latter. We

have found that it is indeed the case: the C₁dC₄C₁dC₄

dihedral angle (see Scheme 1) is 167ꢀ in poly-THD and

140ꢀ in poly-6 (Figure 13). These angles match closely the

3 3 3

R-C₄C₁-R dihedral angles, 166ꢀ for poly-THD³²

3 3 3

and 136ꢀ for poly-6 optimized in the unit cell of the

monomer (Table 4).

The X-ray crystal structure of the monomer THD is not

known, so it is not possible to say to which extent the

wavy shape of the conjugated backbone resembles the

structure of the starting monomer. But the structure of 6

is known; in this case, the C₄C₁C₄C₁dihedral

3 3 3 3 3 3 3 3 3

angle formed by three reacting monomers (see Scheme 1)

is 140ꢀ, in excellent agreement with that found in the

polymer. This result was somewhat expected based on the

fact that diacetylene polymerization abides by the topo-

chemical concept (i.e., the reaction proceeds under minimal

atomic and molecular displacement). However, larger dif-

ferences are observed in the positions of the substituents

between the monomer and the polymer.

Conclusions

Several analogues of 1,6-bis(diphenylamino)-2,4-hexa-

diyne (THD) have been synthesized and their solid-state

structures determined by single-crystal X-ray diffraction.

It was found that a modification of the aromatic rings

(substitution of one or several phenyl hydrogens by

methyl or fluorine groups), or the introduction of methyl-

ene spacers between the nitrogen atoms and the phenyl

rings, led to an A-A-A-A arrangement of the diacetylenic

molecules in the unit cell. Such an arrangement is un-

favorable to polymerization of the CtC-CtC moieties

because these moieties lie too far apart from each other

along the polymerization axis. On the other hand, re-

placement of the methylene groups of THD by longer

spacers, (CH₂)₄in the case of 5 and (CH₂)₃in the case of 6,

yields an A-B-A-B structural arrangement of the

diacetylenic molecules. Such an arrangement is probably

Relationship between Spectroscopy and Structure of Poly-6.

The transition energy of the exciton for poly-THD, as

deduced from electroreflectance measurements, is 2.171 eV

at 16 K.³⁷Such a value is typical of red PDAs, that is around

2.2 eV. For poly-6, the transition energy of the exciton, as

determined from absorption and luminescence studies (vide

supra), is about 2.4 eV. Thus, poly-6 absorbs at a much

higher energy than poly-THD. It was suggested in a recent

computational study that the difference in exciton energies

between blue and red phase PDAs was due to conformational

differences in the polymer chains, blue chains being flat (the

R-C₁C₄-R dihedral angle in Scheme 1 being equal to

3 3 3

180ꢀ), and red chains being twisted (the R-C₁C₄-R

3 3 3

Article

Chem. Mater., Vol. 22, No. 13, 2010 3979

also present in THD but, since the X-ray crystal structure

of this compound is not known, this is not certain.

Diacetylene 5 does not polymerize in the solid state while

6 does, and this result agrees with the fact that 6 matches

Baughman’s criteria for topochemical polymerization

and 5 does not. The thermal solid-state polymerization

reactivity of 6 is low as well as its UV polymerization

reactivity, but its γ-ray polymerization reactivity is much

higher, suggesting that γ-ray induced initiation in 6 may

be predominantly cationic. Nonetheless, the solid-state

polymerization reactivity of 6 is much lower than that of

THD, thereby validating our working hypothesis that

modulation of the polymerization reactivity of THD

analogues via a molecular engineering approach should

be possible. Similar efforts have been made in the past

with pTS derivatives and BCMU analogues.

impurity of the NMR solvent and ¹³C chemical shifts to the

NMR solvent. ¹⁹F NMR spectra were recorded on a Bruker AC

250 or an AVANCE 300 spectrometer and were referenced to

CFCl₃. Infrared spectra were recorded on a Thermo Nicolet

Avatar 320 FT-IR spectrometer with a 4 cm^-1resolution. Absorp-

tion spectra of solutions and crystals were measured in the double

beam mode on a Cary 5000 double monochromator. Raman

spectra of powdered samples were obtained at room temperature

on a Bruker RFS100 FT spectrometer equipped with a continuous

YAG laser (λ = 1064 nm) as a light source and a germanium

detector. Single-crystal Raman and luminescence measurements

were performed with a Jobin Yvon Ramanor U1000 double

monochromator. Excitation used argon or krypton laser lines.

For variable-temperature (10-300 K) solid-state absorption,

Raman, and luminescence studies, a helium gas exchange cryostat

was utilized. FAB mass spectra were obtained on a Jeol JMS-

SX102A instrument and ESI mass spectra on a Micromass QTOF

€

spectrometer. Melting points were measured on a Buchi B-540

Poly-6 is soluble in organic solvents such as chloroform

and THF, so we were able to determine its molecular weight

by SEC, between 150 000 and 300 000 Da. The polymeric

chains generated by γ-ray irradiation of single crystals of 6

are highly luminescent, which signifies that poly-6 is a red

phase PDA just like poly-THD. In addition, the similarity

between the spectroscopic features of poly-6 chains and

those of isolated red chains of poly-3BCMU, known to be

perfect quasi-1D quantum wires,^27,28suggests that the for-

mer chains also have a high degree of order.

melting point apparatus and are uncorrected. C, H, N elemental

analyses were performed in-house using a Thermo Finnigan

FLASH EA 1112 Series analyzer.

Materials. The chemicals used in this study were obtained from

the following commercial sources: diphenylamine (Aldrich), di-

benzylamine (Avocado), di-p-tolylamine (Aldrich), 80 wt % solu-

tion of propargyl bromide in toluene (Acros Organics), 18-crown-6

(Acros Organics), 5-hexyn-1-ol (Alfa Aesar), 4-pentyn-1-ol (Alfa

Aesar), p-toluenesulfonyl chloride (Avocado), triethylamine

€

(Riedel-de Haen), 2.5 M solution of n-butyllithium in hexanes

(Aldrich), copper(I) chloride (Aldrich), TMEDA (Lancaster),

potassium hydroxide (Prolabo), potassium carbonate (Prolabo).

Solvents were purchased from the following suppliers: THF

(Prolabo), DMF (Acros Organics), methanol (Prolabo), DME

(Aldrich), ethyl acetate (Carlo Erba). Bis(pentafluorophenyl)amine

and (N-pentafluorophenyl)phenylamine were synthesized follow-

ing reported methods.^45,46

The structure of poly-6 in its monomer matrix was

obtained by DFT calculations. As anticipated from the

strong luminescence, it was found that poly-6 chains are

considerably twisted with a C₁dC₄C₁dC₄dihedral

3 3 3

angle of 140ꢀ. This angle is comparable to that found in

the starting monomer, 140ꢀ, suggesting that the arrange-

ment of the monomer molecules in the crystal lattice has a

decisive influence on the shape of the resulting polymeric

chain.

General Considerations. All of the syntheses involving air-

sensitive materials were carried out under an inert atmosphere of

argon using standard Schlenk-line techniques. Prior to use, THF

was distilled over sodium-benzophenone ketyl, and triethylamine

and TMEDA were distilled over calcium hydride. Diphenylamine

was purified by sublimation.

The transition energy of the exciton for poly-6, about

2.4 eV, is much higher than that of poly-THD, 2.171 eV at

16 K. On the basis of previous theoretical work on the

colors of PDAs,³⁹this difference was expected to be due

Syntheses of (N-Pentafluorophenyl)(N-phenyl)propargylamine

(7), N,N-Bis(p-tolyl)propargylamine (8), Dibenzylpropargylamine

(9), N,N-Bis(pentafluorophenyl)propargylamine (10), 5-Hexynyl-

diphenylamine (11), 4-Pentynyldiphenylamine (12), 5-Hexyn-1-p-

toluenesulfonate (13), and 4-Pentyn-1-p-toluenesulfonate (14). See

the Supporting Information.

to dissimilarities in the C₁dC₄C₁dC₄dihedral angle

between the two polymers. We have found that this is

3 3 3

true: the C₁dC₄C₁dC₄dihedral angle is 167ꢀ in poly-

3 3 3

THD and 140ꢀ in poly-6.

Hence, poly-6 is a new structural type of PDAs and

turns out to be a good model for the study of the relation-

ship that exists between chain conformation and electro-

nic structure. Work is currently ongoing to characterize

further poly-6 and, in particular, study the variation of its

photophysical properties as a function of polymer con-

tents. Also, the preparation of an analogue of 6 with

ethylene groups between the diacetylene fragment and the

NPh₂moieties instead of propylene groups will begin in

due course.

Synthesis of 1,6-Bis((N-pentafluorophenyl)phenylamino)-2,4-

hexadiyne (4). A mixture of CuCl (16.8 mg, 0.17 mmol),

TMEDA (0.31 mL), and methanol (20 mL) was prepared and

stirred for 30 min, after which time air was bubbled into it for

1 h. Alkyne 7 (0.5 g, 1.7 mmol) was added and the mixture was

stirred vigorously at room temperature for 24 h with continuous

air bubbling. A precipitate formed during the reaction. The

suspension was concentrated to dryness and the residue washed

with three 10 mL portions of methanol. The resulting solid was

dissolved in dichloromethane (30 mL). The dichloromethane

solution was washed with three 10 mL portions of deionized

water and dried over magnesium sulfate, and the solvent was

evaporated off. The residue was purified by column chromato-

graphy on silica gel with use of a 90:10 v/v mixture of

n-pentane and diethyl ether as eluent. A white solid was obtained

Experimental Section

Spectroscopic and Characterization Methods. Solution ¹H and

¹³C NMR spectra were obtained on a Bruker AVANCE DPX

200 instrument. ¹H chemical shifts were referenced to the protio

1

(0.35 g, 70%). Mp 85.3 ꢀC. H NMR (200.1 MHz, CDCl₃): δ

4.43 (s, 4H; H3), 6.79 (d, 4H; H9), 6.94-7.02 (m, 2H; H11),

3980 Chem. Mater., Vol. 22, No. 13, 2010

Deschamps et al.

7.26-7.36 (m, 4H; H10). ¹⁹F NMR (282.4 MHz, CDCl₃):

previously.^96,97Raman (neat powder): ν~ 3056, 2940, 2250,

3

δ -161.6 (m, 4F; F6), -156.2 (t, J_FF= 21.6 Hz, 2F; F7),

1605, 1004 cm^-1

.

-144.1 (m, 4F; F5). ¹³C NMR (50.3 MHz, CDCl₃): δ 42.3 (C3),

69.6 (C1), 74.2 (C2), 114.9 (C9), 120.4 (m; C4), 121.3 (C11),

Synthesis of 1,6-Bis(dipentafluorophenylamino)-2,4-hexadiyne (3).

Diyne 3 was prepared similarly to 2 by using 10 (0.70 g, 1.8 mmol)

instead of 8. A white solid was obtained (0.5 g, 72%). Mp 144.2 ꢀC.

¹H NMR (200.1 MHz, CDCl₃):δ4.45(s, 4H;H3). ¹⁹FNMR(235.4

MHz, CDCl₃):δ-162.2 (m, 8F; F6), -157.8 (t, ³J_FF= 21.7 Hz, 4F;

F7), -148.0 (m, 8F; F5). ¹³C NMR (50.3 MHz, CDCl₃): δ 45.4

(C3), 70.1 (C1), 73.6 (C2), 120.7 (m; C4), 138.4 (dm, ¹J_CF= 252 Hz;

C7), 140.0 (dm, ¹J_CF= 254 Hz; C6), 144.7 (dm, ¹J_CF= 249 Hz;

C5). Raman (neat powder): ν~ 2269, 1658 cm^-1. FABþ MS

(NOBA) m/z (%): 772 (19) [M]^þ, 424 (15) [M-N(C₆F₅)₂]^þ.

Elemental anal. Calcd (%) for C₃₀H₄F₂₀N₂(772.33): C, 46.65; H,

0.52; N, 3.63. Found: C, 45.85; H, 0.78; N, 3.69.

129.8 (C10), 138.8 (dm, ¹J_CF= 251 Hz; C7), 140.8 (dm, ¹J_CF

=

255 Hz; C6), 146.0 (C8), 146.0 (dm, ¹J_CF= 255 Hz; C5). Raman

(neat powder): ν~ 2256, 1654, 1602 cm^-1. FABþ MS (NOBA) m/z

(%): 592 (40) [M]^þ, 334 (58) [M-N(C₆H₅)(C₆F₅)]^þ. Elemental

anal. Calcd (%) for C₃₀H₁₄F₁₀N₂(592.43): C, 60.82; H, 2.38; N,

4.73. Found: C, 60.61; H, 3.35; N, 4.37.

Synthesis of 1,6-Bis(di-p-tolylamino)-2,4-hexadiyne (2). The

same protocol as that leading to 4 was followed except that 7 was

replaced with 8 (0.70 g, 3.0 mmol). In this case, a large amount of

precipitate formed after air bubbling for 30 h that was then

filtered on a glass frit and washed with methanol. The solid was

dissolved in dichloromethane. The dichloromethane solution

was washed three times with deionized water and dried over

magnesium sulfate, and the solvent was evaporated off. A white

solid was obtained (0.42 g, 60%). Mp 172.2 ꢀC. ¹H NMR (200.1

MHz, CDCl₃): δ 2.34 (s, 12H; H8), 4.42 (s, 4H; H3), 6.92-6.99

(m, 8H; H5), 7.10-7.14 (m, 8H; H6). ¹³C NMR (50.3 MHz,

CDCl₃): δ 21.1 (C8), 43.3 (C3), 69.0 (C1), 75.3 (C2), 121.6 (C5),

130.3 (C6), 132.0 (C7), 145.5 (C4). Raman (neat powder): ν~

3065, 2919, 2254, 1613, 807 cm^-1. FABþ MS (NOBA) m/z (%):

468 (23) [M]^þ, 210 (29) [(C₇H₇)₂NCH₂]^þ, 91 (20) [C₇H₇]^þ.

Elemental anal. Calcd (%) for C₃₄H₃₂N₂(468.63): C, 87.14;

H, 6.88; N, 5.98. Found: C, 85.68; H, 7.71; N, 5.80.

Synthesis of 1,12-Bis(diphenylamino)-5,7-dodecadiyne (5). Diyne

5 was prepared similarly to 4 by using 11 (2.0 g, 8.0 mmol) instead

of 7 and DME instead of methanol. The crude product was first

chromatographed on alumina with use of a 90:10 v/v mixture of

n-pentane and dichloromethane as eluent, then it was recrystallized

from acetone. A white solid was obtained (1.24 g, 62%). Mp

67.5 ꢀC. ¹H NMR (200.1 MHz, CDCl₃): δ 1.62 (m, 4H; H4), 1.81

(m, 4H; H5), 2.31 (t, ³J_HH= 6.7 Hz, 4H; H3), 3.75 (three peaks,

4H; H6), 6.94-7.04 (m, 12H; H8 and H10), 7.26-7.34 (m, 8H;

H9). ¹³C NMR (50.3 MHz, CDCl₃): δ 19.5 (C3), 26.3 (C4), 27.3

(C5), 52.1 (C6), 66.1 (C1), 77.6 (C2), 121.4 (C8), 121.6 (C10), 129.7

(C9), 148.4 (C7). Raman (neat powder): ν~ 3064, 2907, 2252, 1602,

1253, 994 cm^-1. FABþ MS (NOBA) m/z (%): 497 (52) [MþH]^þ,

328 (10) [M-N(C₆H₅)₂]^þ. Elemental anal. Calcd (%) for

C₃₆H₃₆N₂(496.68): C, 87.05; H, 7.31; N, 5.64. Found: C, 87.48;

H, 6.63; N, 5.46.

Synthesis of 1,6-Bis(dibenzylamino)-2,4-hexadiyne (1). Diyne

1 was prepared similarly to 2 by using 9 (4.65 g, 19.8 mmol)

instead of 8. A white solid was obtained (3.15 g, 68%).

Full characterization of this molecule has been reported

Synthesis of 1,10-Bis(diphenylamino)-4,6-decadiyne (6). Diyne

6 was prepared similarly to2 by using 12 (5.0 g, 21.2mmol) instead

of 8. The precipitate that formed during the reaction was collec-

ted, washed with n-pentane, and dissolved in dichloromethane.

The dichloromethane solution was washed several times with

(96) D’hooghe, M.; Van Brabandt, W.; De Kimpe, N. J. Org. Chem.

2004, 69, 2703–2710.

(97) Sharifi, A.; Mirzaei, M.; Naimi-Jamal, M. R. J. Chem. Res.

Synopsis 2002, 628–630.

Article

Chem. Mater., Vol. 22, No. 13, 2010 3981

deionized water, dried over magnesium sulfate, and the solvent

was evaporated off. A white solid was obtained (3.55 g, 71%). Mp

85.5 ꢀC. ¹H NMR (200.1 MHz, CDCl₃): δ 1.92 (five peaks, 4H;

H4), 2.38 (t, ³J_HH= 6.9 Hz, 4H; H3), 3.85 (three peaks, 4H; H5),

6.94-7.05 (m, 12H; H7 and H9), 7.25-7.35 (m, 8H; H8). ¹³C

NMR (50.3 MHz, CDCl₃): δ 16.4 (C3), 26.6 (C4), 51.4 (C5), 69.3

(C1), 84.1 (C2), 121.5 (C7), 121.8 (C9), 129.7 (C8), 148.4 (C6).

washed several times with acetone to remove any remaining

monomer. By doing so, tens of milligrams of pure polymer were

obtained.

Molecular Weight Measurements. The number (M_n) and mass

average (M_w) molecular weights of poly-6 chains contained in

single crystals of 6 exposed to γ-rays were measured by size

exclusion chromatography (SEC) at the Laboratoire de Chimie

Raman (neat powder): ν~ 2256, 1604, 1592, 1573 (shoulder) cm^-1

.

des Polymeres, UMR 7610 CNRS - Universite Pierre et Marie

Curie, Paris, France. The analytical setup was made of a Viscotek

VE 7510 GPC degasser, a Viscotek VE 5200 GPC autosampler, a

Waters 515 HPLC pump, three Polymer Laboratories PL-Mixed

columns placed in a thermostatted oven at 40 ꢀC, a Viscotek VE

3580 differential refractometer, and a Waters 484 UV-visible

detector. The eluent was distilled THF. A 3 mg mL^-1THF solution

of poly-6 was filtered through a 0.45 μm membrane prior to

injection. Calibration was performed using low polydispersity index

polystyrene standards. It is noteworthy that, for poly-4BCMU in

THF, use of polystyrene standards overestimates the masses by a

factor of about 2.⁹⁸A similar observation was made for another

conjugated polymer, poly(3-hexylthiophene).⁹⁹Assuming that this

correction is also valid for poly-6, the experimental results, M_n≈

300 000 Da and M_w≈ 870 000 Da, should be corrected to M_n≈

150 000 Da and M_w≈ 435 000 Da. But the influence of the side

group structure on the correction factor has not been studied, so we

believe it is more appropriate to give a range for M_n, 150 000-

300 000 Da.

ꢁ

ꢀ

FABþ MS (NOBA) m/z (%): 468 (52) [M]^þ. Elemental anal.

Calcd (%) for C₃₄H₃₂N₂(468.63): C, 87.14; H, 6.88; N, 5.98.

Found: C, 86.45; H, 7.22; N, 5.86.

Crystal Growth. Crystals of 6 were grown from acetone at 4 ꢀC

in the dark. Depending on the concentration of the mother liquor,

the dimensions and habits of the crystals can change significantly:

crystals with dimensions of approximately 5 ꢀ 1 ꢀ 0.3 mm³were

obtained when concentrated solutions were used (in this case the

nucleation rate is high), whereas crystals with a length of several

millimeters in each direction were obtained when dilute solutions

were employed.

X-ray Diffraction. Intensity measurements for compounds

1-5 were carried out at the joint X-ray scattering facility of the

ꢀ

Institut Charles Gerhardt and the Institut Europeen des Mem-

branes, Universite Montpellier II, France, with use of an Oxford

ꢀ

Diffraction Xcalibur-1 CCD diffractometer. The data collection

temperature was 173 K and the crystal-to-detector distance

50 mm; other data collection parameters were nearly identical in

all five experiments. A total of 678 exposures were taken using

ω-scans with oscillations of 1ꢀ. The counting time per frame varied

from 30 to 40 s. The data were corrected for possible intensity decay

and absorption using the empirical AbsPack procedure.¹⁰⁰All five

structures were solved by ab initio charge-flipping using the

SUPERFLIP¹⁰¹computer program and refined by least-squares

methods on F using CRYSTALS.¹⁰²One crystal (4) turned out to

be a poor scatterer. Consequently, for this crystal, atomic displace-

ment parameters were refined only isotropically in order to keep the

reflection-to-parameter ratio reasonable. Hydrogen atoms were in

general located in difference Fourier maps. Their geometries were

next regularized via refinement with soft restraints on bond lengths

and angles and soft restraints on U_iso(H) (in the range 1.2-1.5 times

Thermal Polymerization. A single crystal (thickness =310 μm)

of monomer 6 was kept at room temperature (22 ꢀC) for 160 h,

then heated isothermally in an oven at 45 ꢀC for the same amount

of time, then at 70 ꢀC. During polymerization, the absorption

spectrum of the crystal was recorded periodically on a Cary 5000

spectrometer. The polymer content was measured by making use

of the extinction coefficient parallel to the chains in the crystalline

state, R_//= (7.3 ( 1.1) ꢀ 10⁵cm^-1, determined in this work.

UV Polymerization. A crystal of diacetylene 6(thickness =450 μm)

was cut in two pieces. Both pieces were placed in a Cary 5000

spectrometer and subjected to UV irradiation. The first fragment

was irradiated at 275 nm with a power density of 375 nW/cm², the

second fragment at 340 nm with a power density of 100 nW/cm².

γ-Ray Polymerization. γ-Ray polymerization experiments

were carried out at the Research Section of the Curie Institute

in Paris (France) with use of a ¹³⁷Cs γ-ray source. The irradia-

tion equipment used was IBL 637 (CIS BIO International) nꢀ

95-22. The dose rate was 45 Gy/min.

Several batches of crystals of 6 were placed in glass tubes and

subjected to γ-ray irradiation. The transparent monomer crystals

turned yellow at low doses (see Table 3), and deep orange or red at

the highest doses. In the range of γ-ray doses under consideration,

from 0.4 to 25 MRad, the amount of poly-6 that was produced

scaled linearly with the irradiation dose. The γ-ray polymerization

rate, close to 0.75 wt % per MRad, was determined by dissolving

weighted amounts of crystals irradiated with known doses of

γ-rays and making use of the extinction coefficient measured in

solution.

U_eqof the parent atom). Lastly, their positions were refined with

riding constraints. Final R values and relevant crystallographic

data are given in Table 1.⁴⁸

Single-crystal X-ray diffraction analysis of 6 was performed

at the X-ray diffraction center of the Laboratoire de Chimie de

Coordination in Toulouse, France. Data were collected at 180 K

on a Bruker Kappa Apex II diffractometer equipped with an

Oxford Cryosystems cryostream cooler device. The final unit

cell parameters (Table 1) were refined from 8528 reflections. The

structure was solved by direct methods using SIR92,¹⁰³and the

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Pure poly-6 was obtained by washing irradiated crystals

with acetone (to dissolve the monomer) and collecting the

insoluble solid by filtration. The red material thus isolated was

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3982 Chem. Mater., Vol. 22, No. 13, 2010

Deschamps et al.

SHELXL97 program¹⁰⁴was used for full-matrix least-squares

refinement against F_o²using all reflections; both programs are part

of the 1.63 version of the WinGX suite.¹⁰⁵Atomic scattering factors

were taken from a standard source.¹⁰⁶All non-hydrogen atoms

were refined anisotropically. Hydrogen atoms were positioned

geometrically and refined using the riding model.⁴⁸

residual forces on the atoms were lower than 0.01 eV A^-1. The

˚

vibrational modes for the whole unit cells were obtained by discrete

calculation of the dynamical matrix followed by a diagonalization

procedure to determine the eigenvalues and eigenvectors. After

that, the eigenvector can be projected on the localized CdC and

CtC stretch of the polymer backbone for identification. The

optical absorption spectrum of poly-6 was computed from an

estimated dynamic dielectric constant using CASTEP.¹¹⁵A scissor

operator of 0.65 eV was used in the calculations to correct for

underestimation of the gap by DFT. Only band-to-band, not

excitonic, transitions are modeled.

Structural drawings (Figures 1-6) were prepared with use of

the three-dimensional visualization system for electronic and

structural analysis VESTA.¹⁰⁷

Computational Details. 0 K periodic electronic structure calcula-

tions were performed using density functional theory (DFT) within

the PBE¹⁰⁸generalized gradient approximation (GGA), and using

projector augmented-wave (PAW) pseudopotentials^109,110as im-

plemented in the VASP code.^111,112The choice of the PBE-GGA

functional allows to compute large systems with good accuracy and

has a limited computer cost.¹¹³AΓ-centered 4 ꢀ 1ꢀ 1k-point mesh

with a high k-point density in the direction of the conjugated

polymer chain was used. A coarser mesh in that direction induces

significant modifications of both monomer and polymer struc-

tures.¹¹⁴Larger k-point samplings are not needed in directions

perpendicular to the chain as no dispersion of the electronic band

structure is observed.

Acknowledgment. The Agence Nationale de la Recherche,

France, is gratefully acknowledged for financial support of

this work (Grant ANR-06-NANO-013). We are indebted to

Prof. Daniel Louvard, Head of the Research Department of

the Curie Institute (Paris, France), for allowing us to use the

IBL 637 for irradiation of the diacetylene compounds, and to

Ms. Charlotte Bourgeois from INSP for carrying out some of

the γ-ray irradiation experiments described herein. We

warmly thank Dr. J.-F. Morhange from INSP for his

participation in the Raman studies, Ms. Ibtissam Tahar-

ꢁ

Djebbar from the Laboratoire de Chimie des Polymeres,

6 and poly-6 were computed using a 550 eV cutoff with, in each

case, optimization of the atomic positions and, when needed,

optimization of the unit cell parameters. For all systems, the

ꢀ

UMR 7610 CNRS - Universite Pierre et Marie Curie (Paris,

France) for the SEC molecular weight determinations, and

Dr. Laure Vendier (Laboratoire de Chimie de Coordination,

UPR 8241, Toulouse, France) for solving the X-ray crystal

structure of compound 6. We are also grateful to the French

computational resource centers IDRIS and CINES for sup-

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Article Doi

Tuning topochemical polymerization of diacetylenes: A joint synthetic, structural, photophysical, and theoretical study of a series ofanalogues of aknown reactive monomer, 1,6-bis(diphenylamino)-2,4-hexadiyne (THD)

DOI: 10.1021/cm1008703

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