Triphenylamine/tetrazine based π-conjugated systems as molecular donors for organic solar cells

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Alain-Rizzo, C. Quinton, G. Clavier, C. Dumas-Verdes and L. Vignau, New J. Chem., 2015, DOI:

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Triphenylamine/Tetrazine based π-Conjugated Systems as

Molecular Donors for Organic Solar Cells

Received 00th January 20xx,

Accepted 00th January 20xx

Cassandre Quinton,^aValérie Alain-Rizzo,^aCécile Dumas-Verdes,^aGilles Clavier,^aLaurence

Vignau^band Pierre Audebert^a

DOI: 10.1039/x0xx00000x

www.rsc.org/

Conjugated systems built by connecting one electron-donor triphenylamine to an electron-withdrawing tetrazine have

been prepared using various linkers. We describe here the synthesis, the electrochemical properties and some

photophysical properties of these molecules, emphasizing the dependence upon the type of linker between the groups

and an organic photovoltaic solar cell was prepared with one derivative.

this context, the question of the choice of the link between the

donor part and the acceptor part and its influence on the

establishment of an ICT emerges as a quite interesting

Introduction

s-Tetrazine (Tz) is a strong electron-withdrawing molecule^1,2

which finds many fields of applications such as retro Diels-

Alder cyclisation,^3-9energetic compounds,^10-16coordination

chemistry,^17-24electrofluorochromism.^25-34Very recently,

polymers containing s-tetrazine have been used in organic

photovoltaic (OPV) cells^35-39and there is one example of

transistor based on a tetrazine-naphthalene diimide system.⁴⁰

Triphenylamine (TPA) is a well-known electron-donor unit,

extensively investigated in diverse fields including

electrochromism,^41-47organic electronics^48-67or two-photon

absorption.^68-74

problem.

We report herein the synthesis, electrochemical and

photophysical studies of new TPA-Tz systems, supported by

theoretical calculations, together with the preliminary OPV

results. Ten compounds including four different linkers have

been thus investigated: compounds 1-4 with phenyl link,

compounds 5-6 with thienyl link, compound 7 with alkynyl link

and directly linked compounds 8-10 (Figure 1).

N

R

Recently we showed interest in the study of covalently linked

tetrazine-triphenylamine derivatives where the fluorescence

of the tetrazine unit could be switched on upon oxidation of

the triphenylamine unit.^31,33However it is interesting to notice,

that although these compounds can be regarded in principle as

donor–acceptor (D–A) systems, no intramolecular charge

transfer (ICT) bands were detected in the UV-vis spectra.

In fact, TPA and Tz units have never been covalently combined

in a conjugated linked D–A system, in which an ICT band from

the donor TPA moiety towards the accepting Tz ring is

expected to occur, with the aim of using such an assembly as

donor in an OPV cell. Indeed, the structure of efficient

molecular donors generally involves a combination of donor

and acceptor blocks. The goal is to create an ICT which

produces at the same time an extension of the absorption

spectrum towards longer wavelengths and a lowering of the

HOMO level leading to an increase in the open-circuit voltage

(Voc) of the OPV cell.⁷⁵In recent years, this approach has led

to the synthesis of different classes of active molecules.⁶⁰In

1

3

: R = TPA

2 : R = Br

: R = TPA

4 : R = Br

N

H₂₁C₁₀

R

N

S

N

O

S

C₁₀H₂₁

N

7

5

: R = Br

6 : R = TPA

N

R

MeO

N

OMe

9

: R = OMe

N

O

10 : R =

OMe

MeO

8

TPA

Fig. 1 Molecular structures of TPA-Tz systems 1-10

Results and discussions

Synthesis

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Design of tetrazine molecules 1-6 was rationalized in order to

get mono or di-substitutions of the tetrazine core.

First we were interested in introducing a phenyl group as a

bridge between the tetrazine unit and the triphenylamine

moiety and in studying the influence of the position of the

substituents on the phenyl bridge. Thus we targeted

corresponding nitrile 20 in 75% yield. The desired 3,6-bis(5-

bromo-4-decylthiophen-2-yl)-s-tetrazine 16 was obtained from

5-bromo-4-decylthiophene-2-carbonitrile 20 with 20% yield

using the Pinner reaction type described previously^76-79

followed by an oxidation.

NBS,

AcOH, CHCl₃

1. Mg, Et₂O

reflux, 2h

Br

S

bichromophores 1-4 (Figure 1). In order to synthesize the four

C₁₀H₂₁Br

chromophores, organometallic coupling reactions between

bis-(dibromophenyl)-s-tetrazine and functionalized TPA were

realized. First of all the dihydrotetrazines 11 and 12 were

successfully obtained using the Pinner type reaction^76-79which

involves sulphur addition on monohydrate hydrazine and then

reaction with an aromatic nitrile (Scheme 1). Compounds 11

and 12 were then directly oxidized with nitrogen dioxide⁸⁰

produced in situ to give the tetrazines 13 and 14. Purification

of 14 appeared to be difficult as it is an insoluble product, so

this explains its lower yield.

RT, 6h30

H₂₁C₁₀

2. 3-bromothiophene,

Ni(dppp)Cl_2,Et₂O

0°C - reflux, 3h

18 (67%)

17 (96%)

1. Et₂NLi, THF,

-78°C, 30 min

I₂, NH₄OH,

THF

Br

S

CHO

CN

2. DMF, -78°C - RT, 18h

H₂₁C₁₀

20 (75%)

RT, 6h

19 (70%)

Br

1. NH₂NH₂.H₂O, S

EtOH, reflux, 1h45

N

S

N

H₂₁C₁₀

C₁₀H₂₁

2. NaNO₂, AcOH

CH₂Cl₂, H₂O

0°C - RT, 2h

16 (20%)

Scheme 1. Synthesis of bis(bromophenyl)-s-tetrazines 13 and 14

Scheme 3. Synthesis of 3,6-bis(5-bromo-4-decylthiophen-2-yl)-s-tetrazine 16

Then triphenylamine stannane derivative 15 was obtained by

using described methods⁸¹and was used without further

purification (Scheme 2). Modest yield is due to the formation

of triphenylamine and tetrabutylstannane during the reaction.

Then triphenylamine stannane derivative 15 and tetrazine

compounds were bounded by a Stille cross coupling reaction,⁸²

using conditions which are efficient and compatible with the

tetrazine moiety.^{35,36,38,39,83}Because of the weak solubility of

14 in toluene (usual solvent for Stille reaction), we used

tetrahydrofuran (THF) as solvent.

Optimized Suzuki-Miyaura coupling⁹⁰conditions (compatible

with tetrazine moiety) were used with 3,6-bis(5-bromo-4-

decylthiophen-2-yl)-s-tetrazine 16. Indeed solution of 3,6-

bis(5-bromo-4-decylthiophen-2-yl)-s-tetrazine

16

and

tetrakistriphenylphosphine Pd(PPh₃)₄in toluene was mixed

with triphenylamineboronic acid solution in methanol and

aqueous sodium carbonate solution. The expected

bichromophores

5 and 6 were then isolated in 40% and 55%

yields respectively (Sheme 4).

Br

TPA

R

N

S

R

TPAB(OH)₂(2.3 equiv),

Pd(PPh₃)_4,Na₂CO₃

toluene, MeOH, H₂O

Br

R

5 (40%)

N

S

R

TPA

R

TPA

R

N

S

80°C, 6 days

R = C₁₀H₂₁

16

6 (55%)

Scheme 4. Synthesis of bichromophores 5 and 6

Scheme 2. Synthesis of bichromophores 1a, 1b, 2a, 2b

To get the new compounds 7-10, we used different strategies

for the synthesis of the tetrazine systems: Pinner-type

condensation of aromatic nitriles, nucleophilic substitution of

particularly electrodeficient tetrazine synthons or Suzuki-

Miyaura cross-coupling with specific tetrazine precursors.

The electrodeficient 3-chloro-6-morpholino-s-tetrazine 21

(Figure 2) was then chosen as starting material for the

We were also interested in the synthesis of bichromophores

linked with thiophene between triphenylamine and tetrazine

moieties. In order to increase the solubility, we chose to add

an alkyl chain on the thiophene moiety. The synthetic pathway

leading to 3,6-bis(5-bromo-4-decylthiophen-2-yl)-s-tetrazine

16

is

outlined

in

Scheme

3

synthesis of

7 as it can undergo nucleophilic substitution in

Scheme 3. 3-decylthiophene 17 was obtained in good yield by

very mild conditions. On the other hand, 3,6-bis(3-

bromophenyl)-s-tetrazine 13 and methylthiotetrazines 22 and

23 were selected to be functionalized according to cross-

Kumada-Corriu coupling between 3-bromothiophene and

decylmagnesium bromide synthesized in situ,⁸⁴using

a

literature procedure.^85,86Then 3-decylthiophene 17 was

brominated to give 2-bromo-3-decylthiophene 18

⁸⁷Treatment

coupling reactions, in order to lead respectively to

N

8,

9

N

and 10.

N

X

N

.

N

Cl

N

O

MeS

of 2-bromo-3-decylthiophene 18 with Et₂NLi in THF at -78°C for

30 minutes, followed by the addition of dimethylformamide,⁸⁸

gave the expected aldehyde 19 with 70% yield. 5-bromo-4-

decylthiophene-2-carboxaldehyde 19 was then oxidized in the

presence of diiode and ammoniacal solution⁸⁹to give the

N

Br

21

13

22: -X = -OMe

23

: -X=

N

O

Fig. 2 Tetrazine derivatives used as starting materials

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tetrazine 23 gave the best yields,⁹⁶we decided to undergo the

cross-coupling on these two synthons.

To provide the alkynyl spacer between the TPA and Tz

substructures of compound 7, we used aromatic nucleophilic

3,6-di-(thiomethyl)-s-tetrazine 28 was then obtained according

to the method developed by Sandström.⁹⁷Then this precursor

underwent an aromatic nucleophilic substitution with sodium

methanolate on the one hand and with morpholine on the

other hand leading respectively to the expected

thiomethyltetrazines 22 (23%) and 23 (74%) (Scheme 7).

substitution of an alkynide on a chlorotetrazine (Scheme 5), a

method which has only once been briefly reported.¹First, 4-

(diphenylamino)-benzaldehyde 24 was obtained from

triphenylamine through a Vilsmeier-Haack reaction with a

reasonable yield (77%).⁵⁶The action of the Bestmann-Ohira

reagent 25⁹¹(previously synthesized using

a literature

procedure)^92,93led to 4-ethynyl-N,N-diphenylaniline 26 in 73%

yield. Finally, treatment of ethynyl compound 26 with BuLi in

THF at -78°C for 3h30, followed by addition of chlorotetrazine

21 (obtained by an aromatic nucleophilic substitution of 3,6-

Scheme 7. Synthesis of the tetrazine precursors 22 and 23

dichloro-s-tetrazine with morpholine), led to compound

7 in

A Suzuki-Miyaura cross-coupling between triphenylamine

boronic acid and each precursor 22 and 23 gave the expected

12% yield. It must be noted that the low yield for this last step,

was however mainly due to a low conversion of the starting

material since 48% of 26 was recovered at the end of the

reaction.

products 9 and 10 with respectively 15% and 29% yields

(Scheme 8).

Scheme 5. Synthesis of 7

Scheme 8. Synthesis of compounds

9 and 10

Finally we obtained ten new compounds 1-10

,

Synthesis of compound

8 where TPA and Tz are directly linked

was achieved using Hartwig-Buchwald coupling^94,95on synthon

13 (previously prepared with Pinner reaction^76,77on 3-

bromophenylnitrile) (Scheme 6). A first coupling between 3,6-

bis(3-bromophenyl)-s-tetrazine 13 and excess of anisidine gave

3,3'-(s-tetrazine-3,6-diyl)bis(N-(4-methoxyphenyl)aniline) 27

(40% yield). A second Hartwig-Buchwald coupling between 27

and bromoanisole gave the expected 3,3'-(s-tetrazine-3,6-

centrosymmetrical or not, according to original synthetic ways

in tetrazine chemistry. Thus, we can study the influence of the

nature of the linker between the active subunits on the

properties of our tetrazine-based compounds.

Electrochemical properties

The redox properties of all bichromophores were investigated

by cyclic voltammetry (CV). Electrochemical data of all dyads

are exemplified in Figure 3 for compound 8 and summarized in

Table 1. Two well defined redox systems can be identified

corresponding to the oxidation of the triphenylamine moiety

into its cation radical and to the reduction of tetrazine moiety

diyl)bis(N,N-bis(4-methoxyphenyl)aniline)

8 in 47% yield. To

the best of our knowledge, this is the first time that Hartwig-

Buchwald conditions on dibromoaryltetrazine are reported.

The same synthesis from 3,6-bis(4-bromophenyl)-s-tetrazine

isomer did not give the expected product because of

insolubility of the starting tetrazine.

into its anion radical. The triphenylamine oxidation peaks of

8

and all the other compounds are reversible whereas the

tetrazine electrochemistry is not entirely reversible. In the case

of the compounds 1, 3 and 4, the reduction is totally

irreversible and no standard potential could be determined.

No clear explanation can be given but a similar behavior has

been observed by J. Ding et al. in analogous compounds.³⁶

Scheme 6. Synthesis of

8

In order to link directly the tetrazine unit with the para

position of triphenylamine, we decided to use to the Suzuki-

Miyaura cross-coupling. Again, we were aware of only one

report where Suzuki-Miyaura conditions were used for the

direct functionalization of a tetrazine ring.⁹⁶As 3-methylthio-6-

morpholino-s-tetrazine 22 and 3-methoxy-6-methylthio-s-

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500 L.mol^-1.cm^-1) due to a forbidden n-

π* transition centered

on the tetrazine unit. This band is not always well-defined

because of its lower intensity. A last band appears around 400

nm for all the compounds where tetrazine moiety and

triphenylamine unit are conjugated but not in the case of

2

1

and because of the meta position of TPA on the phenyl link.

This band is most probably an intramolecular charge transfer

(ICT) band. Its molar absorption coefficient depends on the

strength of the electronic delocalization. Indeed the molar

absorption coefficient of 8, where tetrazine is linked to the

triphenylamine via the meta position, is only 3300 L.mol^-1.cm^-1

whereas the one of 6, where the tetrazine and triphenylamine

Fig. 3 Cyclic voltammetry of compounds

8

(C≈5 10^-3mol.dm^-3) in dichloromethane

moieties are linked through a thiophene, reaches 49000 L.mol^-

¹.cm^-1.

+ 0.1 mol.dm^-3Bu₄NPF₆. Potentials are referenced to Ag⁺/Ag. Scan rate: 50 mV.s^-

1

.

The reduction potential E^0/-1has a very low variation and is

around -1.45 V, except for the tetrazines 8, 9 and 10, where it

is ca. 150 mV higher, but these ones have a quite different

structure with much less donating substituents. The oxidation

potential E^1/0is around 0.45 V. It is slightly lower in the case of

8

because the triphenylamine is substituted with methoxy

donor groups which stabilize the cation radical and facilitate its

formation. Conversely, the oxidation potential is higher in the

cases of 9 and 10 because the electron-withdrawing tetrazine

is directly linked to the para position of the triphenylamine and

thus makes the oxidation more difficult. To summarize, it

seems, as previously observed with ferrocene-tetrazine

compounds^[5j]that the reduction potential of the tetrazine is

weakly affected by the substituents, while on the other hand,

the electron-withdrawing tetrazine induces a noticeable rise

on the oxidation potential of the triphenylamine, when it is

Fig.

4 Molar absorption coefficient of compounds 6, 8 and 10 in

dichloromethane. Conc of 10^-6M.

directly linked to it (compounds

9 and 10). Since the oxidation

process affects the HOMO and the reduction the LUMO, this

tends to show that there is an efficient mixing of the HOMOs

while the LUMO of the tetrazine is quite unaffected by the

substituents besides purely inductive effects.

Table 2. Photophysical properties for compounds 1-10 in dichloromethane:

, L.mol^-1.cm^-1)

absorption wavelength (

λ

, nm), molar absorption coefficient (

ε

λ₁

ε ₁

λ₂

-

ε ₂

-

λ₃

ε₃

1

2

304

300

64000

59000

68000

47000

35000

546 539

547 572

Table 1. Electrochemical data for compounds 1-10. Potentials are referenced to

Ferrocene. (The internal Ag wire reference electrode was checked versus

ferrocene). All measurements in dichloromethane + TBAPF₆on glassy carbon.

Compound E^0/-1(V) E^1/0(V) Compound E^0/-1(V) E^1/0(V)

-

3

303

412

401

441

373

424

360

59000

23000

25000

49000

33000

3300

sh

4

307

545 460

n.d. n.d.

1

2

3

4

5

-1.67^[a]

-1.43

0.44

0.45

0.47

6

7

8

9

10

-1.43

-1.46

-1.32

-1.31

-1.34

0.46

0.42

0.30

0.65

0.57

5

305

-1.50^[a]

-1.53^[a]

-1.44

6

306; 354

295

49000; 34000

24000

7

8

307

76000

sh

[a] peak value, non-reversible reduction

9

n.d.

30000

24000

n.d. n.d.

Photophysical properties

10

289

13000

The absorption spectra of 6, 8 and 10 in dichloromethane

sh: shoulder, n.d.: non-determined

solutions are displayed in Figure 4 and the absorption data are

collected in Table 2. These bichromophores display several

bands, the number depending on the delocalization between

the tetrazine moiety and the triphenylamine unit. For all

compounds, there are one or two intense bands in the UV

The absorption solvatochromism of this third band (between

360 and 440 nm) for compounds and 10 has been

3, 4, 6, 7, 9

studied in seven different solvents: cyclohexane (cy),

dichloromethane (DCM), tetrahydrofurane (THF), ethyl acetate

(AcOEt), acetonitrile (ACN), dimethylsulfoxyde (DMSO) and

ethanol (EtOH) and the results are gathered in Table 3. The

variation of the localization of the band is weak (around 7 nm)

region in agreement with

π-π* transitions located both on

tetrazine and triphenylamine units. The corresponding molar

absorption coefficient varies between 13000 and 76000 L.mol^-

¹.cm^-1depending on the nature of the substituents on the

tetrazine, which is reasonably high enough to be used in

organic solar cells. Another band is located at around 545 nm

and displays a weak molar absorption coefficient (around

in the case of the compounds 9 and 10 where the tetrazine

and triphenylamine units are directly linked and in the case of

7

which has an alkyne link. This is probably due to the fact that

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the different solvents have similar effects on the two orbitals other cases, the planar surface is constituted by the tetrazine

implied in this transition. However, the variation is, as moiety and the adjacent aromatic part(s). In the case of the

expected, more important (around 14 nm) in the case of the phenyl or thiophene links, the linker forms an angle with the

compounds

3

,

4

and

6

pathway. A general trend for all the compounds can be 41° for

which have an extended conjugated first adjacent phenyl of the triphenylamine: 40° for

6

3 and 4,

and and 50° for and . The angle is more

1

2

5

observed from the values given in Table 3. When increasing important for the thiophene linker because of the sterically

the polarity of the solvent from cyclohexane (apolar solvent) hindered alkyl chain. In all cases, the two phenyl groups at the

to dichloromethane (a little more polar one), one can see a end of triphenylamine are out of the plane.

bathochromic shift. Then, when the polarity further increases

(from DCM to ACN), a hypsochromic shift occurs. It shows that

the polarity influences the localization of the intramolecular

charge transfer band. A similar change has been reported on

the donor-acceptor compound 3-chloro-6-tetrathiafulvalene-s-

tetrazine.¹⁸Behaviors in DMSO or ethanol (high polar solvents)

are difficult to understand because there is no general trend

for all compounds.

Table 3. Absorption wavelength (λ, nm) of the intramolecular charge transfer band in

different solvents

Solvent

cy

DCM

412

401

441

373

360

THF

407

396

437

369

355

356

AcOEt

403

389

432

n.d.

353

356

ACN DMSO

EtOH

400

391

437

368

356

354

405

394

427

368

358

400

385

430

366

352

354

410

396

432

369

355

λ(3)

λ(4)

λ(6)

λ(7)

λ(9)

λ(10)

A more detailed study has been realized in the case of

compound

3 using a general and multiparameter scale

developed by Catalán⁹⁸based on four empirical scales: the

solvent polarizability (SP), dipolarity (SdP), acidity (SA) and

basicity (SB). The absorption wavenumber (v) is fitted with

these solvent parameters according to the equation:

ν =ν° + aSP + bSdP + cSA+ dSB

^Whereν° ^{is the gas phase wavenumber, and a, b, c and d are}

the regression coefficients describing the sensitivity of

ν

to

the different parameters. From this treatment, it appears that

this chromophore presents a solvatochromism dominated by

non-specific interactions as seen by the predominance of de

solvent polarizabilty parameter (a=-3715, b=118, c=91, d=157,

r²=0.87), as already observed for charge transfer

molecules.^99,100

Fig. 5 Calculated geometries of compounds 1-10

The lowest unoccupied molecular orbital (LUMO) is a π*-

orbital centered on the tetrazine ring, which reflects its

Finally, these compounds have a high absorbance and

solvatochromic intramolecular charge transfer band, which is

an important property for various applications such as organic

solar cell or two-photon absorption.

electron-withdrawing ability. Contrariwise, the highest

occupied molecular orbital (HOMO) is always a

π-orbital

localized on the triphenylamine and the adjacent linker. The

non-bounding orbital of the tetrazine is found at a lower

energy.

Molecular modelling

All compounds show one absorption band around 300 nm.

This absorption band is due to a transition from the π-orbital

to *-orbital both centered on the tetrazine unit and the

adjacent link (Figure 6a). The important overlap between the

orbitals of the latter transition explains the intense absorption.

Molecular modelling shows that the energetic gap between

these two orbitals varies slightly, depending on the molecules

(between 3.75 and 3.92 eV, Figure 6b), which is in agreement

with the experimental observation (maximal wavelength

Quantum chemical calculations were carried out on the ten

compounds. Geometry optimizations were first performed at

the B3LYP level of theory and with the 3-21g basis set. Time-

dependent density functional theory (TD-DFT) calculations at

the PBE0 level of theory with the 6-31+g(d) basis set were

subsequently performed. Note that a C₄chain was used

π

instead of a C₁₀chain in the case of

the calculations.

5 and 6 in order to shorten

All these compounds have a central planar part (Figure 5). In

the case of , this plane surface is constituted by the tetrazine

moiety and the phenyl ring which is linked to the alkyne. In the

between 295 and 307 nm). The energies of the

π

and

π*

6 are slightly

7

orbitals of the symmetrical compounds 3 and

1

,

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higher than the ones of the corresponding molecules with only

one triphenylamine moiety and Indeed, the

orbital centered on the triphenylamine unit to a

centered on the tetrazine ring and the link (Figure 8a). This is

π*-orbital

2,

4

5.

replacement of an inductive attractor bromine atom with a

donating triphenylamine core induces a destabilization of the

orbitals. In the case of 7, the orbitals are higher because the

electron-donating morpholine moiety is directly linked to the

tetrazine ring.

an intramolecular charge transfer band. The energetic gap

between these latter orbitals is higher in the case of 7, 9 and

10, compared to the other compounds (Figure 8b). It fits well

with the experimental observations since these three

molecules show the weakest absorption wavelength. The

energy of the

π

-orbital remains mainly constant whereas the

and 10. It is

π^∗-orbital is destabilized in the case of

7, 9

probably due to the donating effect of the methoxy or

morpholine groups which are directly linked to the tetrazine

ring. The experimental and calculated wavelengths do not fit

very well because intramolecular charge transfer bands can be

difficult to calculate precisely with standard programs.¹⁰¹

Fig. 6 a) Representation of the molecular orbitals involved in the absorption

band at 306 nm of 6; b) Energy levels of π (pink) and π*(green) orbitals involved

in the transition at around 300 nm of 1-7

A weak transition is found at around 550 nm. This is the

classical band localized on the tetrazine ring (n- *, Figure 7a),

π

usually responsible for the colors of the tetrazine molecules,

and the difference of symmetry of these orbitals explains the

weak molar absorption coefficient found experimentally and

also confirmed by calculations. For some compounds, this

band is hidden by a very intense band located close to it. As

with other tetrazine compounds, the localization of this band

does not vary since the energy difference between the pair of

orbital stays constant (from 3.52 to 4.09 eV, Figure 7b).

Fig. 8 a) Representation of the molecular orbitals involved in the absorption

band at 412 nm of 3; b) Energy levels of π (blue) and π* (green) orbitals involved

in the intramolecular charge transfer transition of 3-10

Organic solar cells

Knowing that the creation of an intramolecular charge transfer

in the donor considerably improves the power conversion

efficiency of the solar cell,¹⁰²we selected the compound

3 –

which displays the highest intramolecular charge transfer

band- to be tested as donor in an organic solar cell. Since

donor

donor/acceptor bilayer heterojunction solar cell structure was

chosen. Donor was first thermally evaporated (20 to 30 nm)

on ITO substrates precoated with a 30 nm-PEDOT-PSS layer.

Then fullerene C60 was evaporated on top on donor (25 to

3 is weakly soluble in most common organic solvents, a

3

40 nm) to achieve a donor/acceptor planar heterojunction.

The photovoltaic parameters have been measured under

simulated solar illumination in AM 1.5 conditions at 100

mW/cm². The influence of thermal annealing and of the donor

and the C60 layers thicknesses on the photovoltaic

performance has been investigated. The best results were

Fig. 7 a) Representation of the molecular orbitals involved in the absorption

band at 550 nm of

involved in the transition at around 550 nm of 1-10

8; b) Energy levels of n (yellow) and π* (sky blue) orbitals

obtained with a 20 nm-thick layer of

3 annealed at 150 °C and

a 40 nm-thick layer of C60 (Fig. S18 and Table S12, Supporting

Information). This device exhibits a short-circuit current

density J_SCof 2.0 mA.cm^-2and an open-circuit voltage V_OCof

0.26 V. This low voltage is quite far from the expected

The compounds

exist in the case of the compounds

and the intensity of this absorption band are strongly

dependent on the compounds (360 nm<

L.mol^-1.cm^-1< <59000 L.mol^-1.cm^-1, Table 2). Molecular

3-

10 also exhibit a third band which does not

1

and . The localization

2

λ

<441 nm and 3300 theoretical value of 1.2 V obtained by the formula:¹⁰³

V_OCE_{LUMO(acceptor)}-E_HOMO(Donor)-0.3

ε

≈

modelling shows that this band is due to a transition from a π-

6 | J. Name., 2012, 00, 1-3

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ARTICLE

acceptor group by a phenyl, a thiophene or an alkyne linker

represents an efficient synthetic approach for engineering the

ICT and the LUMO energy level of donor triphenylamine

materials based on dipolar small donor-acceptor molecules.

Taking into account the simplicity of the devices used for

photovoltaic evaluation, these preliminary results suggest that

the use of a more advanced technology for the devices

fabrication can be expected to lead to higher performance.

Also, bulk heterojunction solar cells could be fabricated using

where 0.3 V is an empirical factor corresponding to the voltage

loss due to the presence of ohmic contacts at both

interfaces.¹⁰⁴E_LUMOand E_HOMOwere estimated from the

cyclovoltammograms according to the formula.¹⁰⁵

E_LUMO=-(E^1/0_onset(vs Fc/Fc⁺)+4.8)

E_HOMO=-(E^0/-1_onset(vs Fc/Fc⁺)+4.8)

Some voltage loss at interfaces can explain this value of 0.26 V.

Moreover, the high dark saturation current observed in the

devices also reduces V_OC.¹⁰⁶

A short-circuit current density of 2 mA.cm^-2shows that

excitons are actually generated and separated even if the

the soluble compound 6 as donor.

Experimental part

energy difference

donor and the LUMO of the acceptor C60 is not sufficient for

efficient charge separation. Furthermore, donor absorbs at

ꢀE of 0.1 eV between the LUMO of the

3

Spectroscopic measurements

3

UV-visible absorption spectra were recorded on a Cary 5000

spectrophotometer in 1 cm optical length quartz cuvettes.

Cyclohexane, dichloromethane, tetrahydrofurane, ethyl

acetate, acetonitrile, dimethylsulfoxyde and ethanol (SDS,

spectrometric grade) were used as solvents for absorption

measurements.

too low wavelengths to enable the collection of a large ratio of

the solar spectrum, which results in a rather low J_SC. However,

this value is close to the 2.4 mA.cm^-2obtained for a

triphenylamine/tetracyanobutadiene-based D-A-D system.⁶⁰

Combined with a fill-factor FF=0.42, these results led to a PCE

of 0.21%.

Electrochemistry

Dichloromethane (SDS, HPLC grade) and electrolyte salts

(tetrabutylammonium hexafluorophosphate from Fluka,

puriss.) were used without further purification. Cyclic

voltammetry was performed in a three-electrode cell with a

potentiostat (VersaSTAT4, Princeton Applied Research) driven

by a PC. Carbon electrode disk (1 mm diameter) was used as

the working electrode, whereas platinum wire and Ag⁺(0.01 M

in acetonitrile)/Ag were used, respectively, as the counter and

reference electrodes. All the investigated solutions were

deaerated by argon-bubbling for at least 2 min before

performing the electrochemical measurements. The reference

electrode was checked versus ferrocene as recommended by

IUPAC.

Quantum Chemical Calculations

Calculations were performed at the MESO calculation centre of

the ENS Cachan (Nec TX7 with 32 processors of type Itanium

2). Molecules were drawn with the Gaussview 03 software

using included templates and their geometry optimized at the

B3LYP/3-21g level of theory. Infrared spectra were calculated

on the final geometry to ascertain that a minimum was

obtained (no negative frequencies). Time-dependant density

functional theory (TD-DFT) calculations at the PBE0 level of

theory with the 6-31+g(d) basis set were subsequently

performed.

Fig. 9 Current vs voltage curves of a bilayer heterojunction 3:C60. Black circles: in the

dark. Red squares: under AM 1.5 white light illumination at 100 mW/cm².

While these first results are not as good as we could expect,

some further improvement may be achieved through an

optimization of the solar cell structure. For example the use of

a bulk heterojunction may improve charge separation and the

insertion of charge transport interlayers could improve V_OC

through the lowering of the dark saturation current.

Synthesis

Reagents were commercially available from Aldrich and used

without further purification. Column chromatography was

performed with SDS 0.040-0.063 mm silica gel. All compounds

Conclusions

1

were characterized by the usual analytical methods: H, ¹³C

NMR spectra were recorded with a JEOL ECS (400 MHz)

spectrometer. All chemical shifts are referenced to solvent

peak (J values are given in Hz). Melting points were measured

with a Kofler melting-point apparatus. IR spectra were

recorded with a Nicolet Avatar 330 FT-IR spectrometer.

In summary, symmetrical and unsymmetrical D-A-D π-

conjugated systems based on a tetrazine unit as acceptor and

triphenylamine moiety as donor have been synthesized. Some

of these compounds exhibit strong absorption in the visible

range due to an intramolecular charge transfer (ICT) band. We

have shown that the covalent bridging of the tetrazine

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Journal Name

The compounds 22¹⁰⁷

already described.

,

25^92,93and 28⁹⁷were synthesized as 3-(4’-bromophenyl),6-(N,N-diphenyl-4’-biphenylamine)-s-

tetrazine 4 General procedure for Stille cross-coupling with

General

procedure

for

Stille

cross-coupling

.

3,6-bis(4’-bromophenyl)-s-tetrazine (0.60 g, 1.5 mmol).

Dibromophenyltetrazine compound (1.0 eq, 0.1 M) and N,N- Chromatography conditions: CH₂Cl₂/PE (5/5)-CH₂Cl₂; Yield: 19%

(159 mg); mp: 258 °C; IR (

ν

_max/cm^-1): 3031-2917, 1604, 1584,

diphenyl-4-tributyltinaniline (1.1 eq for monosubstitution and

1

3.0 eq for disubstitution) were dissolved in toluene (for

) or THF (for and ). [Pd(PPh₃)₄] (5 mol% for each

substitution) was added and the reaction mixture was refluxed

for 10 hours (for and ) or 100 hours (for and ) under

1 and

1496, 1433, 1355, 1317, 1274, 1174, 1155, 1060, 916, 819; H

NMR (400 MHz, CDCl₃) δ (ppm): 8.69 (d, J=8.7 Hz, 2H), 8.53 (d,

J=8.2 Hz, 2H), 7.82 (d, J=8.2 Hz, 2H), 7.76 (d, J=8.2 Hz, 2H), 7.59

(d, J=8.2 Hz, 2H), 7.30 (d, J=7.8 and 7.3 Hz, 4H), 7.17 (d, J=8.7

Hz, 2H), 7.16 (d, J=8.7 Hz, 4H), 7.07 (dt, J=7.3 and 0.9 Hz, 2H);

¹³C NMR (100 MHz, CDCl₃) δ (ppm): 164.1; 163.4; 148.4; 147.5;

145.1; 133.2; 132.9; 132.8; 131.0; 129.5; 129.4; 128.7; 128.0;

127.9; 127.4; 125.0; 123.5; 123.4; HRMS-ESI (m/z): (M+H)⁺

calcd for C₃₂H₂₂N₅⁷⁹Br, 556.1131, found: 556.1140; UV-vis

2

3

4

1

2

3

4

argon. 30 mL of a solution of potassium fluoride was added

and the precipitate was removed by filtration on celite. The

filtrate was extracted with diethylether (2*50mL), the organic

layer was washed with water (100 mL) and dried over

anhydrous sodium sulfate Na₂SO₄. The crude product was

purified by a silicagel column chromatography to give an

orange solid.

(CH₂Cl₂): λ_max(ε)

=307 nm (61000 L.mol^-1.cm^-1) and 401 nm

(30100 L.mol^-1.cm^-1)

3,6-bis(N,N-diphenyl-3’-biphenylamine)-s-tetrazine 1 General

procedure for Stille cross-coupling with 3,6-bis(3’-

bromophenyl)-s-tetrazine (0.61 g, 1.6 mmol) Chromatography

conditions: cyclohexane/toluene: 5/5; Yield: 19% (217 mg);

4-(5-(6-(5-bromo-4-decylthiophen-2-yl)-s-tetrazin-3-yl)-3-

decylthiophen-2-yl)-N,N-diphenylaniline 5 and 4,4'-(5,5'-(s-

tetrazine-3,6-diyl)bis(3-decylthiophene-5,2-diyl))bis(N,N-

diphenylaniline)

6 To a solution of 3,6-bis(5-bromo-4-

mp: 92 °C; IR (ν

_max/cm^-1): 2920, 1587, 1515, 1483, 1382, 1271,

decylthiophen-2-yl)-s-tetrazine (0.25 g, 0.37 mmol, 1.0 eq) and

tetrakis(triphenylphosphine) palladium(0) Pd(PPh₃)₄(21 mg,

0.019 mmol, 5 mol%) in toluene (5 mL) were added first a

solution of triphenylamine boronic acid (0.24 g, 0.84 mmol, 2.3

eq) in methanol (1.5 mL) and then a aqueous solution of

sodium carbonate (2 M, 0.8 mL). The reaction mixture was

stirred at 80 °C under argon for 48 hours. A solution of

ammonium chloride (100 mL) was added and organic

compounds were extracted with dichloromethane (2*100 mL).

1

918, 835; H NMR (400 MHz, CDCl₃) δ (ppm): 8.91 (dd, J=1.8

and 1.8 Hz, 2H), 8.60 (ddd, J=7.8, 1.8 and 1.8 Hz, 2H), 7.85

(ddd, J=7.8, 1.8 and 0.9 Hz, 2H), 7.66 (dd, J=7.8 and 7.8 Hz, 2H),

7.61 (d, J=8.7 Hz, 4H), 7.31 (dd, J=8.7 and 7.3 Hz, 8H), 7.21-7.17

(m, 12H), 7.08 (dt, J=7.3 and 1.4 Hz, 4H); ¹³C NMR (100 MHz,

CDCl₃) δ (ppm): 164.1, 147.9, 147.7, 141.8, 133.8, 132.3, 130.8,

129.9, 129.5, 128.0, 126.3, 126.1, 124.7, 123.8, 123.3; HRMS-

ESI (m/z): (M+H)⁺calcd for C₅₀H₃₆N₆, 721.3080, found:

721.3098; UV-vis (CH₂Cl₂)

:

λ_max

(ε)

=304 nm (64000 L.mol^-1.cm^-The combined organic phases were washed with a saturated

solution of sodium chloride (250 mL), dried over anhydrous

sodium sulfate, filtrated and concentrated under reduced

¹) and 546 nm (540 L.mol^-1.cm^-1)

3-(3’-bromophenyl),6-(N,-diphenyl-3’-biphenylamine)-s-

tetrazine 2 General procedure for Stille cross-coupling with pressure. The crude product was purified by a silicagel column

3,6-bis(3’-bromophenyl)-s-tetrazine (0.20 g, 0.51 mmol). chromatography (CH₂Cl₂/PE: 6.5/3.5) to give two orange solids

Chromatography conditions: cyclohexane/toluene: 5/5; Yield:

ν

5

(Yield :42% (0.13 g)) and

5

6

: mp: <50 °C; IR (

(Yield: 57% (0.20 g)).

ν

28% (80 mg); mp: 205 °C; IR (

_max/cm^-1): 3034-2917, 1586, Characterisations of

_max/cm^-1): 2962, 2924,

1495, 1485, 1438, 1383, 1356, 1317, 1273, 915, 820; H NMR 2853, 1592, 1550, 1492, 1465, 1330, 1261, 1095, 1071, 1018,

1

(400 MHz, CDCl₃) δ (ppm): 8.87 (s, 1H), 8.81 (s, 1H), 8.59-8.56 800; H NMR (400 MHz, CDCl₃) δ (ppm): 8.12 (s, 1H), 8.08 (s,

(m, 2H), 7.84 (d, J=7.8 Hz, 1H), 7.76 (d, J=7.8 Hz, 1H), 7.65 (dd, 1H), 7.37 (d, J=8.7 Hz, 2H), 7.30 (dd, J=8.2 and 7.3 Hz, 4H), 7.17

J=7.8 and 7.8 Hz, 1H), 7,59 (d, J=8.7 Hz, 2H), 7,48 (dd, J=7.8 and (dd, J=8.7 and 0.9 Hz, 4H), 7.12 (d, J=8.7 Hz, 2H), 7.08 (t, J=7.3

7.8 Hz, 1H), 7,31 (dd, J=8.2 and 7.3 Hz, 4H), 7.20-7.16 (m, 6H), Hz, 2H), 2.74 (t, J=7.3 Hz, 2H), 2.69 (t, J=7.3 Hz, 2H), 1.75-1.65

7.07 (t, J=7.3 Hz, 2H); ¹³C NMR (100 MHz, CDCl₃) δ (ppm): (m, 4H), 1.39-1.19 (m, 28H), 0.88 (t, J=6.8 Hz, 3H), 0.87 (t, J=6.8

164.3, 163.1, 147.9, 147.6, 141.9, 135.6, 133.9, 133.7, 132.1, Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ (ppm): 161.5, 161.2,

131.1, 130.9 (2C), 129.9, 129.5, 127.9, 126.5, 126.4, 126.2, 148.2, 147.4, 146.1, 145.6, 140.6, 135.8, 133.5, 132.6, 132.8,

124.7, 123.7, 123.6, 123.3; HRMS-ESI (m/z): (M+H)⁺calcd for 130.0, 129.6, 127.5, 127.1, 125.2, 123.7, 122.6, 32.1(2C),

C₃₂H₂₂N₅⁷⁹Br,

(CH₂Cl₂) λ_max

L.mol^-1.cm^-1)

556.1131,

found:

556.1134;

UV-vis 30.9(2C), 30.5(2C), 29.8(2C), 29.7(2C), 29.5(2C), 29.4(2C),

29.0(2C), 22.8(2C), 14.3(2C); HRMS-MALDI (m/z): (M)^•+calcd

for C₄₈H₅₈BrN₅S₂, 847.3317, found 847.3298 (100%); UV-vis

:

(ε)

=300 nm (59000 L.mol^-1.cm^-1) and 547 nm (570

3,6-bis(N,N-diphenyl-4’-biphenylamine)-s-tetrazine 3 General (CH₂Cl₂)

procedure for Stille cross-coupling with 3,6-bis(4’- L.mol^-1.cm^-1)

bromophenyl)-s-tetrazine (0.21 g, 0.53 mmol).

Chromatography conditions: CH₂Cl₂/PE (9/1)-CH₂Cl₂; Yield: 24%

: λ_max(ε)

=305 nm (34800 L.mol^-1.cm^-1), 354 nm (34000

and

Characterisations of

1591, 1548, 1492, 1461, 1329, 1282, 1180, 1070, 837; H NMR

ν

_max/cm^-1): 1483, 1271; H NMR (400 (400 MHz, CDCl₃) δ (ppm): 8.12 (s, 2H), 7.38 (d, J=8.7 Hz, 4H),

441

nm

(25100

L.mol^-1.cm^-1);

6

: mp: 90 °C; IR (

ν

_max/cm^-1): 2923, 2853,

1

(71 mg); mp: 102 °C; IR (

MHz, CDCl₃) δ (ppm): 8.70 (d, J=8.2 Hz, 4H), 7.82 (d, J=8.2 Hz, 7.31 (dd, J=8.2 and 7.8 Hz, 8H), 7.18 (d, J=7.8 Hz, 8H), 7.12 (d,

4H), 7,59 (d, J=8.7 Hz, 4H), 7,30 (dd, J=8.2 and 7.3 Hz, 8H), J=8.7 Hz, 4H), 7.08 (t, J=7.3Hz, 4H), 2.75 (t, J=7.8 Hz, 4H), 1.65

7.19-7.15 (m, 12H), 7.07 (t, J=6.9 Hz, 4H); ¹³C NMR (100 MHz, (tt, J=7.3 and 6.9 Hz, 4H), 1.40-1.27 (m, 28H), 0.89 (t, J=6.8 Hz,

CDCl₃) δ (ppm): 163.8; 148.3; 147.6; 144.9; 133.3; 131.7; 129.5; 6H); ¹³C NMR (100 MHz, CDCl₃) δ (ppm): 161.1, 148.1, 147.4,

128.5; 128.0; 127.4; 124.9; 123.5 (2C); HRMS-ESI (m/z): (M+H)⁺145.9, 140.5, 133.3, 132.8, 129.9, 129.5, 127.2, 125.1, 123.6,

calcd for C₅₀H₃₆N₆, 721.3080, found: 721.3079; UV-vis 122.6, 32.0, 30.1, 29.7 (2C), 29.6 (2C), 29.5, 29.0, 22.8, 14.3;

HRMS-MALDI (m/z): (M)^•+calcd for C₆₆H₇₂N₆S₂, 1012.5254,

found 1012.5240; UV-vis (CH₂Cl₂) λ_max=306 nm (49100

L.mol^-1.cm^-1) and 441 nm (49300 L.mol^-1.cm^-1)

(CH₂Cl₂): λ_max(ε)

=304 nm (70700 L.mol^-1.cm^-1) and 412 nm

(58600 L.mol^-1.cm^-1)

:

(ε)

8 | J. Name., 2012, 00, 1-3

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4-((6-morpholino-s-tetrazin-3-yl)ethynyl)-N,N-diphenylaniline

To a solution of 4-ethynyl-N,N-diphenylaniline 26 (205 mg,

124.4, 124.0, 121.4, 56.5; IR (

ν

_max/cm^-1): 2918, 1587, 1493,

1383, 1273, 1173, 1041, 942, 849; mp: 96 °C; HRMS-ESI (m/z):

7

(M)⁺calcd for C₂₁H₁₇N₅O, 355.1433, found: 355.1427; UV-vis

0.61 mmol, 1.0 eq) in distilled THF (2 mL) at – 78 °C under

argon was added butyllithium (2.5 M in hexane, 0.330 mL,

0.825 mmol, 1.08 eq). Mixture was stirred for 3h30 from -80°C

to room temperature. Then it was added to a solution of 4-(6-

chloro-s-tetrazin-3-yl)morpholine 21 (153 mg, 0.761 mmol,

1.25 eq) in distilled THF (2 mL). Mixture was then stirred at

room temperature for 30 minutes. All volatile compounds

were removed by concentration under reduced pressure. The

crude product was solubilized in 2 mL of THF. 18 mL of

petroleum ether were added and product precipitated. A red

(CH₂Cl₂)

1.31, 0.65 V

3-(4’-triphenylamine)-6-morpholino-s-tetrazine 10 To

: λ_max(ε)=360 (29900) ; E° (C, CH₂Cl₂) vs ferrocene: -

a

solution of 3-methylthio-6-morpholino-s-tetrazine 23 (62 mg,

0.29 mmol, 1.0 eq) and 4-(N,N-diphenylamino)phenylboronic

acid (166 mg, 0.57 mmol, 2.0 eq) in 1,2-dimethoxyethane

(5 mL) were added copper thiophene-2-carboxylate (110 mg,

0,58 mmol, 2,0 eq) and tetrakis(triphenylphosphine)

palladium(0) Pd(PPh₃)₄(19 mg, 0.015 mmol, 5 mol%). Mixture

was heated at 180 °C under argon for 30 min with microwaves.

Dichloromethane (10 mL) and saturated ammonium chloride

solution (15 mL) were added. Aqueous phase was extracted

with dichloromethane (3*15 mL). The combined organic

phases were dried over anhydrous sodium sulfate, filtrated

and concentrated under reduced pressure. The crude product

was purified by a silicagel column chromatography (DCM) to

give a red solid (34 mg, 29%). ¹H NMR (400 MHz, CDCl₃) δ: 8.23

(d, J=9.2 Hz, 2H), 7.29 (dd, J=8.2 and 7.3 Hz, 4H), 7.17-7.13 (m,

1

solid was obtained by filtration (39 mg, 12%). H NMR (400

MHz, CDCl₃) δ: 7.49 (d, J=8.7 Hz, 2H), 7.30 (dd, J=8.3 and 7.3

Hz, 4H), 7.14 (d, J=7.8 Hz, 4H), 7.10 (t, J=7.3 Hz, 2H), 7.00 (d,

J=8.7 Hz, 2H), 4.05 (t, J=4.9 Hz, 4H), 3.86 (t, J=4.9 Hz, 4H); ¹³C

NMR (100 MHz, CDCl₃) δ: 157.9, 151.6, 149.4, 146.9, 133.4,

129.7, 125.6, 124.3, 121.4, 113.2, 95.2, 82.6, 66.6, 43.8; IR (

σ

in cm^-1): 2215, 1586, 1547, 1537, 1509, 1493, 1333, 1316,

1287, 1266, 1165, 1113, 1043, 946, 837; m.p.: 196°C; HRMS-

ESI, m/z : [M+H]⁺calcd. for C₂₆H₂₂N₆O [M+H]⁺435.1928, found

435.1925; UV-vis (CH₂Cl₂): λ_max(ε)=295 (23900), 373 (32900); 6H), 7.08 (t, J=7.3 Hz, 2H), 4.02 (t, J=4.8 Hz, 4H), 3.86 (t, J=4.8

E° (C, CH₂Cl₂) vs ferrocene: -1.46, 0.42 V

Hz, 4H); ¹³C NMR (100 MHz, CDCl₃) δ: 160.5, 159.5, 150.4,

147.2, 129.6, 127.4, 125.5 (2C), 124.0, 122.1, 66.6, 43.9; IR

3,3'-(s-tetrazine-3,6-diyl)bis(N,N-bis(4-

methoxyphenyl)aniline) 8 To a solution of 3,3'-(s-tetrazine-

(ν

_max/cm^-1): 2917, 2850, 1589, 1511, 1491, 1450, 1393, 1316,

1177, 1118, 942, 847; mp: 170 °C; HRMS-ESI (m/z): (M)⁺calcd

for C₂₄H₂₂N₆O, 410.1855, found: 410.1846; UV-vis

(CH₂Cl₂): λ_max(ε)=289 (13400) ; 360 (23900); E° (C, CH₂Cl₂) vs

ferrocene: -1.34, 0.57 V

3,6-diyl)bis(N-(4-methoxyphenyl)aniline)

27

(85

mg,

0.18 mmol, 1.0 eq) and cesium carbonate Cs₂CO₃(190 mg,

0.58 mmol, 3.3 eq) in distilled toluene (10 mL) under argon

were added 1-bromo-4-methoxybenzene (0.20 mL, 1.6 mmol,

9.0 eq) and bis(tri-tert-butylphosphine)palladium(0) Pd(PtBu₃)₂

(15 mg, 0.029 mmol, 0.15 eq). Mixture was refluxed under

argon for 6 days. All volatile compounds were removed by

concentration under reduced pressure. The crude product was

purified by a silicagel column chromatography (PE/DCM (2/8))

to give a purple solid (29 mg, 47%). ¹H NMR (400 MHz, CDCl₃)

δ: 8.17 (dd, J=2.3 and 1.8 Hz, 2H), 8.06 (ddd, J=7.3, 1.8 and 0.9

Hz, 2H), 7.35 (dd, J=7.8 and 7.8 Hz, 2H), 7.15 (ddd, J=8.2, 2.3

and 0.9 Hz, 2H), 7.09 (d, J=8.7 Hz, 8H), 6.83 (d, J=9.2 Hz, 8H),

3.80 (s, 12H); ¹³C NMR (100 MHz, CDCl₃) δ: 163.9, 156.2, 150.0,

140.5, 132.7, 130.0, 126.9, 124.2, 119.8, 119.0, 115.0, 55.6; IR

General procedure for Pinner reaction and oxidation

To a solution of nitrile (1.0 eq) in ethanol (0.3 M) were added

monohydrate hydrazine (4.0 eq) and sulfur (0.6 eq). The

mixture was refluxed until complete reaction as judged by TLC.

All volatile substances were removed by concentration under

reduced pressure to give a yellow solid used without further

purification. The yellow solid (1 eq) was dissolved in

dichloromethane (0.3 M). A solution of sodium nitrite (6 eq) in

water (0.3 M) was added. Acetic acid (5 eq) was added

dropwise at 0 °C. The mixture was stirred at room temperature

until complete reaction as judged by TLC. Organic compounds

were extracted with dichloromethane. The combined organic

phases were dried over anhydrous sodium sulfate, filtrated

(

ν

_max/cm^-1): 1582, 1504, 1451, 1383, 1240, 1034, 917, 828; mp:

256 °C; HRMS-ESI (m/z): (M+H)⁺calcd for C₄₂H₃₆N₆O₄,

689.2876, found: 689.2885; UV-vis (CH₂Cl₂) λ_max

(71000) ; 422 (3100); E° (C, CH₂Cl₂) vs ferrocene: -1.32, 0.30 V.

:

(

ε)

=306 and concentrated under reduced pressure. The crude product

was purified by silica gel flash chromatography to give a pink

3-methoxy-6-(4’-triphenylamine)-s-tetrazine 9 To a solution of or red powder.

3-methoxy-6-methylthio-s-tetrazine 22 (100 mg, 0.63 mmol, 3,6-bis(3’-bromophenyl)-s-tetrazine 13 General procedure for

1.0 eq) and 4-(N,N-diphenylamino)phenylboronic acid (279 Pinner reaction and oxidation with 3-bromobenzonitrile (1.8 g,

mg, 0.97 mmol, 1.5 eq) in 1,2-dimethoxyethane (5 mL) were 9.9 mmol). Chromatography conditions: CH₂Cl₂/Petroleum

added copper thiophene-2-carboxylate (239 mg, 1,26 mmol,

Ether(PE): 5/5; Yield: 74% (1.43 g); mp: 244 °C; IR (ν

_max/cm^-1):

2,0 eq) and tetrakis(triphenylphosphine) palladium(0)

Pd(PPh₃)₄(40 mg, 0.03 mmol, 5 mol%). Mixture was heated at

1433, 1381, 1299, 1091, 1056, 922, 888, 795, 767, 738, 686,

679; ¹H NMR (400 MHz, CDCl₃) δ (ppm): 8.83 (dd, J=1.8 and 1.8

Hz, 2H), 8.60 (ddd, J=7.8, 1.8 and 0.9 Hz, 2H), 7.79 (ddd, J=7.8,

1.8 and 0.9 Hz, 2H), 7.51 (dd, J=7.8 and 7.8 Hz, 2H); ¹³C NMR

(100 MHz, CDCl₃) δ (ppm): 163.4, 136.0, 133.7, 131.1, 131.0,

126.7, 123.7; HRMS-MALDI (m/z): (M+H)⁺calcd for C₁₄H₈Br₂N₄,

392.9173 (100%), 390.9194 (51%), 394.9153 (49%), found:

392.9184 (100%), 390.9187 (52%), 394.9172 (48%); UV-vis

180 °C under argon for

2 hours with microwaves.

Dichloromethane (10 mL) and saturated ammonium chloride

solution (15 mL) were added. Organic compounds were

extracted with dichloromethane (3*15 mL). The combined

organic phases were dried over anhydrous sodium sulfate,

filtrated and concentrated under reduced pressure. The crude

product was purified by a silicagel column chromatography

(PE/DCM (7/3 to 5/5)) to give a red solid (39 mg, 15%). ¹H NMR

(400 MHz, CDCl₃) δ: 8.32 (d, J=8.7 Hz, 2H) ; 7.33 (dd, J=7.8 and

7.3 Hz, 4H) ; 7.20-7.11 (m, 8H), 4.33 (s, 3H); ¹³C NMR (100

MHz, CDCl₃) δ: 166.6, 163.0, 151.4, 146.8, 129.7, 128.5, 125.8,

(CH₂Cl₂): λ_max=294 and 547 nm

3,6–bis(4’-bromophenyl)-s-tetrazine 14 General procedure for

Pinner reaction and oxidation with 4-bromobenzonitrile (1.8 g,

10.0 mmol). Chromatography conditions: CH₂Cl₂; Yield: 35%

(686 mg); mp: > 260 °C (lit.,^108,109290-292 and 337 °C); IR

J. Name., 2013, 00, 1-3 | 9

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ARTICLE

Journal Name

_max/cm^-1): 1587, 1406, 1392, 1105, 1068, 1006, 915, 836,

concentrated under reduced pressure. The crude product was

purified by a silicagel column chromatography (hexane) to give

a colorless liquid. Yield: 69% (1.9 g). H NMR (400 MHz, CDCl₃)

(

ν

1

825; H NMR (400 MHz, CDCl₃) δ (ppm): 7.87 (d, J=8.7 Hz, 4H);

7.64 (d, J=8.7 Hz, 4H); ¹³C NMR (100 MHz, CDCl₃) δ (ppm):

1

δ: 7.16 (d, J=5.6 Hz, 1H), 6.77 (d, J=5.6 Hz, 1H), 2.54 (t, J=7.6

Hz, 2H), 1.55 (tt, J=7.6 and 7.6 Hz, 2H), 1.30-1.25 (m, 14H), 0.86

(t, J=7.2 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 142.1, 128.4,

125.3, 108.4, 32.1, 29.9, 29.8, 29.7, 29.6, 29.54, 29.48, 29.4,

22.8, 14.3.

167.4; 132.7; 129.4; 129.0; 125.9; UV-vis (CH₂Cl₂)

and 547 nm

: λ_max=314

Synthesis of N,N-diphenyl-4-tributyltinaniline 15 1.6 M

solution of nBuLi in hexane (3.4 mL, 5.4 mmol, 1.0 eq) was

added dropwise to a solution of 4-bromo-N,N-triphenylamine

(1.8 g, 5.4 mmol, 1.0 eq) in THF (48 mL) at -78°C and stirred for

45min at this temperature. Bu₃SnCl (1.6 mL, 5.7 mmol, 1.1 eq)

was added and the reaction mixture was stirred for 4h30 at

room temperature under argon. After removing all volatile

5-bromo-4-decylthiophene-2-carboxaldehyde 19 At -78 °C

under argon, to THF (12 mL) was added first Et₂NLi (1.0 g, 13

mmol, 2.1 eq) and then 2-bromo-3-decylthiophene (1.9 g,

6.1 mmol, 1.0 eq). The reaction mixture was stirred at -78 °C

for 30 minutes before dimethylformamide (2.4 mL, 31 mmol,

5.1 eq) was added. The reaction mixture was stirred for 18

hours from -78 °C to room temperature. 1 M hydrochloric acid

(120 mL) was added and organic compounds were extracted

with ethyl acetate (3*100 mL). The combined organic phases

were washed with saturated sodium chloride solution (250

mL), dried over anhydrous magnesium sulfate, filtrated and

concentrated under reduced pressure. The crude product was

purified by a silicagel column chromatography (CH₂Cl₂/PE) to

materials

under

reduced

pressure

N,N-diphenyl-4-

tributyltinaniline was obtained as colorless oil (1.4 g, 2.7 mmol,

50%). ¹H NMR (400 MHz, CDCl₃) δ (ppm): 7.32 (d, J=8.2 Hz, 2H)

; 7.25 (dd, J=8.7 and 7.3 Hz, 4H), 7.11 (dd, J=7.3 and 1.5 Hz,

4H), 7.04 (d, J=8.7 Hz, 2H), 7.01 (t, J=7.3 Hz, 2H), 1.60-1.50 (m,

6H), 1.38-1.29 (m, 6H), 1.05-1.00 (m, 6H), 0.89 (t, J=7.3 Hz, 9H)

3,6-bis(5-bromo-4-decylthiophen-2-yl)-s-tetrazine 16 General

procedure for Pinner reaction and oxidation with 5-bromo-4-

decylthiophene-2-carbonitrile

Chromatography conditions: CH₂Cl₂/PE:8/2; Yield: 65% (0.51

(0.75

g,

2.3

mmol).

give a colorless liquid. Yield: 70% (1.4 g). IR (ν

_max/cm^-1): 2971,

2921, 1669, 1427, 1407, 1394, 1377, 1233, 1150, 1066, 1057,

g); mp: 83 °C; IR (

ν

_max/cm^-1): 2950, 2911, 2849, 1551, 1471,

1

1028, 892, 879, 868; H NMR (400 MHz, CDCl₃) δ: 9.75 (s, 1H),

1

1454, 1437, 1394, 1372, 1264, 1182, 1069, 910, 852, 837; H

NMR (400 MHz, CDCl₃) δ (ppm): 7.93 (s, 2H), 2.63 (t, J=7.6 Hz,

4H), 1.65 (tt, J=7.5 and 7.5 Hz, 4H), 1.34-1.27 (m, 28H), 0.88 (t,

J=6.9 Hz, 6H); ¹³C NMR (100 MHz, CDCl₃) δ (ppm): 160.8, 144.8,

135.1, 131.6, 118.1, 32.0, 29.8, 29.74, 29.70, 29.6, 29.52,

29.47, 29.3, 22.8, 14.3; HRMS-EI (m/z): (M)^•+calcd for

C₃₀H₄₄⁷⁹BrN₄S₂, 682.1374, found: 682.1379

7.48 (s, 1H), 2.59 (t, J=7.4 Hz, 2H), 1.61 (tt, J=7.4 and 7.4 Hz,

2H), 1.5-1.2 (m, 14H), 0.88 (t, J=6.6 Hz, 3H); ¹³C NMR (100

MHz, CDCl₃) δ: 181.7, 143.9, 142.9, 136.7, 121.9, 31.9, 29.6,

29.6, 29.5, 29.4, 29.34, 29.32, 29.1, 22.7, 14.1

5-bromo-4-decylthiophene-2-carbonitrile 20 33% Ammoniacal

solution (42 mL) was added to a solution of 5-bromo-4-

decylthiophene-2-carboxaldehyde (0.83 g, 2.5 mmol, 1.0 eq) in

THF (8 mL). Iodine (1.3 g, 5.0 mmol, 2.0 eq) was then added.

Mixture was stirred at room temperature for 3 hours. 5%

Sodium thiosulfate solution (20 mL) was then added. Organic

compounds were extracted with ethyl acetate (3*30 mL). The

combined organic phases were dried over anhydrous sodium

sulfate, filtrated and concentrated under reduced pressure.

The crude product was purified by a silicagel column

chromatography (CH₂Cl₂/PE: 3/7) to give a colorless oil. Yield:

3-decylthiophene 17 1-bromodecane (5.8 mL, 37 mmol, 1.7

eq) was added dropwise to a solution of iodine (60 mg, 0.24

mmol, 0.01 eq) and magnesium (0.92 g, 38 mmol, 1.7 eq) in

diethylether (30 mL). The reaction mixture was refluxed for 2

hours under argon and then cooled down to room

temperature. This solution was added at 0°C to a solution of 3-

bromothiophene (2.0 mL, 21 mmol, 1.0 eq) and dichloro(1,3-

bis(diphenylphosphino)propane)nickel (135 mg, 0.25 mmol,

0.01 eq) in diethylether (20 mL). The reaction mixture was

refluxed for 16 hours under argon and then cooled down to

room temperature. Water (50 mL) was added and organic

compounds were extracted with diethylether (5*100 mL). The

combined organic phases were washed with saturated sodium

chloride solution (300 mL), dried over anhydrous sodium

sulfate, filtrated and concentrated under reduced pressure.

The crude product was purified by a silicagel column

chromatography (hexane) to give a colorless liquid. Yield: 96%

(4.61g). ¹H NMR (400 MHz, CDCl₃) δ (ppm): 7.21 (m, 1H), 6.92-

6.90 (m, 2H), 2.60 (t, J=7.8 Hz, 2H), 1.59 (tt, J=7.8 and 6.9 Hz,

2H), 1.30-1.15 (m, 14H), 0.86 (t, J=6.9 Hz, 3H); ¹³C NMR (100

MHz, CDCl₃) δ (ppm): 143.4, 128.4, 125.2, 119.9, 32.1, 30.7,

30.4, 29.9, 29.78, 29.77, 29.6, 29.5, 22.9, 14.3

87% (0.72 g). IR (

ν

_max/cm^-1): 2950, 2912, 2850, 2217, 1552,

1

1454, 1437, 1394, 1182, 1069, 910, 852, 837; H NMR (400

MHz, CDCl₃) δ: 7.30 (s, 1H), 2.55 (t, J=7.6 Hz, 2H), 1.56 (tt, J=7.3

and 7.3 Hz, 2H), 1.32-1.22 (m, 14H), 0.81 (t, J=6.8 Hz, 3H); ¹³C

NMR (100 MHz, CDCl₃) δ: 143.2, 138.0, 116.7, 113.4, 109.4,

31.8, 29.5, 29.4, 29.3, 29.2 (2C), 29.1, 29.0, 22.6, 14.1

4-(6-chloro-s-tetrazin-3-yl)morpholine 21 To a solution of

morpholine (0.58 mL, 6.62 mmol, 1.0 eq) in anhydrous CH₂Cl₂

(125 mL) were added 3,6-dichlorotetrazine (1.00 g, 6.62 mmol,

1.0 eq), and 2,4,6-collidine (0.88 mL, 6.62 mmol, 1.0 eq). The

mixture was stirred at room temperature for 1 hour then

concentrated under reduced pressure. The crude product was

purified by a silica gel column chromatography (DCM) to give a

1

red solid (1.30 g, 97%). H NMR (400 MHz, CDCl₃) δ: 3.99 (t,

J=4.8 Hz, 4H), 3.85 (t, J=4.8, 4H). ¹³C NMR (100 MHz, CDCl₃) δ:

2-bromo-3-decylthiophene 18 To

decylthiophene (2.0 g, 8.9 mmol, 1.0 eq) in a mixture of

a

solution of 3-

solvents acetic acid/chloroform (1/1, 30 mL) was portionwise 160.5, 159.7, 66.4, 44.0; IR (σ

in cm^-1): 2980, 2915, 2988, 2861,

added N-bromosuccinimide (1.6 g, 8.9 mmol, 1.0 eq) at 0 °C 1535, 1445, 1361, 1269, 1251, 1189, 1119, 962, 945, 852; m.p.:

and without light. The reaction mixture was stirred at room 120°C (lit.¹¹⁰115-117).

temperature for 17 hours before being poured into iced water 3-methylthio-6-morpholino-s-tetrazine 23 To a solution of

(100 mL). Organic compounds were extracted with chloroform 3,6-di(methylthio)-s-tetrazine 28 (343 mg, 1.93 mmol, 1.0 eq)

(5*100 mL). The combined organic phases were washed with in acetonitrile (7 mL) was added morpholine (0.21 mL,

water (2*200 mL) and saturated sodium chloride solution (200 2.4 mmol, 1.3 eq). Mixture was refluxed for 96 hours. All

mL), dried over anhydrous sodium sulfate, filtrated and volatile compounds were removed by concentration under

10 | J. Name., 2012, 00, 1-3

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ARTICLE

reduced pressure. The crude product was purified by a silicagel DMSO) δ: 163.6, 154.7, 146.7, 135.4, 132.8, 130.4, 121.9,

column chromatography (PE/ethyl acetate (1/5)) to give a red

117.3, 115.1, 114.9, 112.5, 55.4; IR (ν

_max/cm^-1): 3384, 1598,

1504, 1452, 1381, 1292, 1236, 1226, 1033, 934, 841; mp: 185

°C; HRMS-ESI (m/z) : (M+H)⁺calcd for C₂₈H₂₅N₆O₂, 477.2039,

solid (300 mg, 74%). ¹H NMR (400 MHz, CDCl₃) δ: 3,92 (t, J=4.6

Hz, 4H), 3.83 (t, J=4.6 Hz, 4H), 2.66 (s, 3H); ¹³C NMR (100 MHz,

CDCl₃) δ: 166.7, 160.5, 66.5, 43.8, 13.7; IR (ν

_max/cm^-1): 2930, found 477.203

2861, 1364, 1189, 1038, 942; mp: 138 °C (lit.⁹⁶131-132).

4-(N,N-diphenylamino)benzaldehyde 24 To a solution of

phosphorus oxychloride (1.85 mL, 20 mmol, 1.0 eq) in

dimethylformamide (5.6 mL, 73 mmol, 3.7 eq) at 0°C under

argon was added triphenylamine (5.00 g, 20 mmol, 1.0 eq).

The mixture was stirred at 70°C for 24 hours. Then it was

poured onto the ice and neutralized with saturated sodium

carbonate solution (20 mL). The aqueous layer was extracted

with CH₂Cl₂(3*20 mL). The combined organic layers were

dried over anhydrous sodium sulfate, filtered and

concentrated under reduced pressure. The crude product was

purified by a silica gel flash chromatography [DCM] to give 24

(4.22 g, 77%) as yellow solid. ¹H NMR (400 MHz, CDCl₃) δ: 9.80

(s, 1H), 7.67 (d, J=8.7 Hz, 2H), 7.34 (dd, J=7.8 and 7.8 Hz, 4H),

7.16 (m, 6H), 7.01 (d, J=8.7 Hz, 2H); ¹³C NMR (100 MHz, CDCl₃)

δ: 190.6, 153.5, 146.3, 131.4, 129.9, 129.2, 126.4, 125.2, 119.5;

Acknowledgements

C. Q, V. A.-R, C. D.-V, G. C, L. V. and P. A thank the CNRS and

the Ministry of French Research for funding the project.

Notes and references

1

2

3

4

G. Clavier and P. Audebert, Chem. Rev., 2010, 110, 3299.

N. Saracoglu, Tetrahedron, 2007, 63, 4199.

R. A. Carboni and R. V. Lindsey, J. Am. Chem. Soc., 1959, 81, 4342.

G. L. Rusinov, R. I. Ishmetova, N. I. Latosh, I. N. Ganebnych, O. N.

Chupakhin and V. A. Potemkin, Russ. Chem. Bull,. 2000, 49, 355.

5

6

7

8

9

D. L. Boger, Tetrahedron, 1983, 39, 2869.

D. L. Boger, Chem. Rev., 1986, 86, 781.

J. F. Vivat, H. Adams and J. P. A. Harrity, Org. Lett., 2009, 12, 160.

T. J. Sparey and T. Harrison, Tetrahedron Lett., 1998, 39, 5873.

N. K. Devaraj and R. Weissleder, Acc. Chem. Res., 2011, 44, 816.

IR (σ

in cm^-1): 1687, 1583, 1504, 1488, 1330, 1304, 1289, 1220,

1155, 824; m.p.: 132°C (lit.¹¹¹132).

4-ethynyl-N,N-diphenylaniline 26 To a solution of Ohira

Bestmann reagent (377 mg, 1.96 mmol, 1.52 eq) in methanol

10 D. E. Chavez, M. A. Hiskey and N. D. Naud, Propellants, Explos.

Pyrotech., 2004, 29, 209.

(10 mL) were added

a

solution of de 4-(N,N-

11 H. Gao and J. M. Shreeve, Chem. Rev., 2011, 111, 7377.

12 J. Neutz, O. Grosshardt, S. Schäufele, H. Schuppler and W.

Schweikert, Propellants Explos. Pyrotech., 2003, 28, 181.

13 K. R. Jorgensen, G. A. Oyedepo and A. K. Wilson, J. Hazard.

Mater., 2011, 186, 583.

diphenylamino)benzaldehyde 24 (353 mg, 1.29 mmol, 1.0 eq)

in dichloromethane (10 mL) and potassium carbonate K₂CO₃

(677 mg, 4.90 mmol, 3.80 eq). The mixture was refluxed under

argon at room temperature for 24 hours. The crude product

was filtrated on clarcel and neutralized with a solution of

sodium hydrogenocarbonate NaHCO₃(10%, 20 mL). Aqueous

phase was extracted with dichloromethane (3*20 mL). The

organic phase was washed with brine (60 mL), dried on

anhydrous sodium sulfate Na₂SO₄, filtrated and concentrated

under reduced pressure. The crude product was purified by a

silicagel column chromatography (PE to PE/DCM (9/1)) to give

a white solid (253 mg, 73%). ¹H NMR (400 MHz, CDCl₃) δ: 7.35

(d, J=8.7 Hz, 2H), 7.28 (dd, J=7.8 and 7.3 Hz, 4H), 7.13 (dd,

J=7.8 and 0.9 Hz, 4H), 7.07 (tt, J=7.3 and 0.9 Hz, 2H), 7.00 (d,

J=8.7 Hz, 2H), 3.02 (s, 1H). ¹³C NMR (100 MHz, CDCl₃) δ: 148.4,

147.2, 133.1, 129.5, 125.1, 123.7, 122.4, 114.9, 84.0, 76.4; IR

14 Y. Zhou, X. Long and Y. Shu, Journal of molecular modeling, 2010,

16, 1021.

15 T. Wei, J. Wu, W. Zhu, C. Zhang and H. Xiao, Journal of molecular

modeling, 2012, 18, 3467.

16 J. Kerth and S. Löbbecke, Propellants Explos. Pyrotech., 2002, 27

,

111.

17 J. Yuasa, A. Mitsui and T. Kawai, Chem. Commun., 2011, 47, 5807.

18 F. Pop, J. Ding, L. M. L. Daku, A. Hauser and N. Avarvari, RSC

Adv., 2013, , 3218.

3

19 W. Kaim, Coord. Chem. Rev., 2002, 230, 127.

(σ

in cm^-1): 3289, 3265, 2988, 2901, 2102, 1585, 1503, 1484,

1406, 1394, 1382, 1283, 1261, 1066, 1057, 1028, 893, 880,

20 U. Keppeler, S. Deger, A. Lange and M. Hanack, Angew. Chem. Int.

Ed., 1987, 26, 344.

847, 829; m.p.: 110°C (lit.¹¹²108-109).

21 M. Glöckle, W. Kaim, N. E. Katz, M. García Posse, E. H. Cutin and

J. Fiedler, Inorg. Chem., 1999, 38, 3270.

3,3'-(s-tetrazine-3,6-diyl)bis(N-(4-methoxyphenyl)aniline) 27

To a solution of anisidine (178 mg, 1.45 mmol, 1.9 eq) and

cesium carbonate Cs₂CO₃(761 mg, 2.34 mmol, 3.1 eq) in

distilled toluene (8 mL) under argon were added 3,6-bis(3’-

bromophenyl)-s-tetrazine 13 (300 mg, 0.765 mmol, 1.0 eq) and

bis(tri-tert-butylphosphine)palladium(0) Pd(PtBu₃)₂(42 mg,

0.081 mmol, 0.1 eq). Mixture was refluxed under argon for 19

hours. Anisidine (88 mg, 0.72 mmol, 0.9 eq), Pd(PtBu₃)₂(18

mg, 0.035 mmol, 0.04 eq) and Cs₂CO₃(350 mg, 1.07 mmol,

1.43 eq) were then added. Mixture was refluxed under argon

for 17 hours. All volatile compounds are removed by

concentration under reduced pressure. The crude product was

purified by a silicagel column chromatography (DCM) to give a

22 M. Glöckle and W. Kaim, Angew. Chem. Int. Ed., 1999, 38, 3072.

23 M. Glöckle, W. Kaim, A. Klein, E. Roduner, G. Hübner, S. Zalis, J.

van Slageren, F. Renz, and P. Gütlich, Inorg. Chem., 2001, 40, 2256.

24 O. Schneider and M. Hanack, Angew. Chem., 1983, 95, 804.

25 Y. Kim, E. Kim, G. Clavier and P. Audebert, Chem. Commun., 2006,

3612.

26 F. Miomandre, R. Méallet-Renault, J. J. Vachon, R. B. Pansu and P.

Audebert, Chem. Commun., 2008, 16, 1913.

27 Y. Kim, J. Do, E. Kim, G. Clavier, L. Galmiche and P. Audebert, J.

Electroanal. Chem., 2009, 632, 201.

28 C. Dumas-Verdes, F. Miomandre, E. Lépicier, O. Galangau, T. T.

Vu, G. Clavier, R. Méallet-Renault and P. Audebert, Eur. J. Org. Chem.,

2010, 13, 2525.

1

red solid (146 mg, 40%). H NMR (400 MHz, DMSO) δ: 8.28 (s,

2H, NH), 8.13 (s, 2H), 7.89 (d, J=7.8 Hz, 2H), 7.48 (dd, J=7.8 and

7.8 Hz, 2H), 7.21 (dd, J=7.8 and 2.3 Hz, 2H), 7.18 (d, J=8.7 Hz,

4H), 6.97 (d, J=8.7 Hz, 4H), 3.78 (s, 6H); ¹³C NMR (100 MHz,

J. Name., 2013, 00, 1-3 | 11

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ARTICLE

Journal Name

29 F. Miomandre, E. Lépicier, S. Munteanu, O. Galangau, J. F. 59 D. Thirion, J. Rault-Berthelot, L. Vignau and C. Poriel, Org. Lett.,

Audibert, R. Méallet-Renault, P. Audebert and R. B. Pansu, ACS Appl. 2011, 13, 4418.

Mater. Interfaces, 2011,

3, 690.

60 A. Leliège, P. Blanchard, T. Rousseau and J. Roncali, Org. Lett.,

30 F. Miomandre, C. Allain, G. Clavier, J. F. Audibert, R. B. Pansu, P. 2011, 13, 3098.

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