Diazene sulphonate as a cross-linking agent for polymers with pendant triarylamine hole-conducting units

Article abstract of DOI:10.1515/chempap-2016-0063

Diazene sulphonates are readily available compounds which are soluble in water and polar solvents. They strongly absorb the UV-VIS light and they decompose under UV irradiation via radical or ionic intermediates. These properties render them valuable, e.g. for analytical purposes and for photo-printing. In this presentation, it will be demonstrated that polymers with a pendant diazene sulphonate function as cross-linking agents and with pendant aromatic amines as hole-transporters can be considered as useful materials for organic light-emitting device (OLED) technology.

Full text of DOI:10.1515/chempap-2016-0063

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Chemical Papers 70 (9) 1238–1252 (2016)
DOI: 10.1515/chempap-2016-0063
ORIGINAL PAPER
Diazene sulphonate as a cross-linking agent for polymers
with pendant triarylamine hole-conducting units
b
c
aEva Baranovicova, Andrej Stasko, Oskar Nuyken*
aBiomedical Centre BioMed, Division of Neuroscience, Comenius University, Jessenius Faculty of Medicine,
Malá Hora 4, 036 01 Martin, Slovakia
bDepartment of Physical Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology,
Radlinského 9, 812 37 Bratislava, Slovakia
cWacker-Lehrstuhl fu¨r Makromolekulare Chemie, TU Mu¨nchen, Lichtenbergstrasse 4, 85747 Garching, Germany
Received 12 November 2015; Revised 8 February 2016; Accepted 9 February 2016
Dedicated to Prof. Dr. Robert Kerber on the occasion of his 90th birthday
Diazene sulphonates are readily available compounds which are soluble in water and polar sol-
vents. They strongly absorb the UV-VIS light and they decompose under UV irradiation via radical
or ionic intermediates. These properties render them valuable, e.g. for analytical purposes and for
photo-printing. In this presentation, it will be demonstrated that polymers with a pendant diazene
sulphonate function as cross-linking agents and with pendant aromatic amines as hole-transporters
can be considered as useful materials for organic light-emitting device (OLED) technology.
c
ꢀ 2016 Institute of Chemistry, Slovak Academy of Sciences
Keywords: diazene sulphonate, polymer, OLED, cross-linking
Introduction
Diazene sulphonates are compounds in which an
SO−3 M+ functional group is connected with an aro-
—
matic unit via an —N N— bridge (Fig. 1).
—
These compounds can exist in their quite stable
trans form (Fig. 2) and also in their less stable cis
form. The first examples of this class of compound
were described as early as 1869 (Schmitt & Glutz,
1869). However, the structure remained a matter for
discussion for many years (Hantzsch, 1894; Hanztsch
& Borghaus, 1897; Bamberger, 1894; Freeman & Le
F`evre, 1951; Hodgson & Marsden, 1943; van der Veen
et al., 1966). Finally, it was determined that an equi-
librium exists between the trans and cis forms which
can be influenced photochemically (Lewis & Suhr,
1959; de Jonge & Dijkstra, 1956; van Beek et al.,
1967a, 1967b; Jonker et al., 1968).
Fig. 1. Structural formula of aryl diazene sulphonate.
position mechanism of diazene sulphonates in differ-
ent solvents (Fig. 2), it could be concluded that the
decomposition followed an ionic route in an aqueous
solution, whereas radicals were detected as interme-
diates when the photo-chemical decomposition was
carried out in ethanol (EtOH) or less polar solvents
(Knepper, 1987; Franzke et al., 1992a, 1992b; Staško
et al., 1993; Rapta et al., 1992).
Substituted diazene sulphonates have been used
in photo-sensitive materials (Spiertz & van Beek,
From detailed photochemical studies of the decom-
*Corresponding author, e-mail: oskar.nuyken@mytum.de
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E. Baranovicova et al./Chemical Papers 70 (9) 1238–1252 (2016)
1239
Fig. 3. Photo-decomposition of polymeric diazene sulphonates.
Reaction conditions: i) hν, water (pathway a); ii) hν,
polymer film (pathway b).
Fig. 2. Radical (pathway a) and ionic (pathway b) decompo-
sition routes of aryldiazene sulphonate.
1974; Yang & Cao, 2004; Girad, 1972). In the lat-
ter, diazonium intermediates play a key role due to
their capacity to couple with suitable compounds
to form dyes. Another application is as surface-
active agents which become photo-sensitive due to
their diazene sulphonate functionality (Nuyken et
al., 1994, 1995; Mezger et al., 1996; Dunkin et al.,
1996; Eastoe, 2006). Polymers containing pendant
diazene sulphonate functions (Dauth, 1991; Eastoe,
2006; Dauth et al., 1992; Nuyken & Voit, 1989, 1997;
Nuyken et al., 1991, 1993) change their solubility af-
ter photo-decomposition from water-soluble to water-
insoluble (Fig. 2) or alternatively become cross-linked
(Fig. 3). Both effects open a number of avenues for var-
ious applications. In the radical pathway, each avail-
complexes can be formed between hydrocarbon or flu-
orocarbon surfactants and diazene sulphonate poly-
mers. These complexes exhibit a high structural or-
der which can be maintained and even stabilised by
photo-cross-linking of the diazene sulphonate func-
tion groups (Schn¨oller, 1996; Thu¨nemann et al., 1999;
Geckeler et al., 2000).
Copolymers containing pendant diazene sulphon-
ate groups are of interest, not only because these poly-
mers can be water-soluble but also because of their
photochemical behaviour. Both properties can be suc-
cessfully exploited for the preparation of cross-linked
layers in an organic light-emitting device (OLED) dis-
play (Lichnerova, 2005).
OLEDs have attracted attention due to their use
in panel displays. A typical OLED consists of two or-
ganic layers (electron and hole-transport layers), em-
bedded between two electrodes. When a voltage is ap-
plied to the electrodes the charges start moving in the
device under the influence of the electric field. Elec-
trons leave the cathode and holes move from the an-
ode in the opposite direction. When an electron meets
a hole, they combine and an exciton is formed. The
exciton generates a photon whose energy corresponds
to the energy gap after completion of its exciton life-
time. A multilayer OLED can be manufactured by
different processes. The production of small-molecule
devices and displays usually involves a thermal evap-
oration in a vacuum. It is used in the production of
more expensive devices and its use is limited for larger
areas. An alternative entails the processing of poly-
mers in solution; spin-coating and inkjet-printing are
two methods commonly used for depositing thin poly-
mer films from solution. For example, Nuyken et al.
.
able molecule containing H can serve as an H radical
donor; furthermore, the phenyl radicals can combine,
thereby affording diphenyl (see pathway b in Fig. 3).
The photo-decomposition of films prepared from
such polymers has been successfully used for offset-
printing and surface-patterning (Nuyken et al., 1992,
1989; Matusche, 1995; Matusche et al., 1995; van Aert
et al., 2001; Dauth, 1991; Voit et al., 2006, 2010; Tr-
ogisch, 2003; Reichenbach, 2011; Georgi, 2014). One
application results from the heterolytic splitting of the
diazene sulphonate function in water after UV irradi-
ation and the coupling reaction of the diazonium in-
termediate with model phenols and natural phenolic
compounds. Preliminary tests have shown such poly-
mers to be suitable as analytical reagents in rapid as-
says (Matusche, 1995; Matusche et al., 1997a, 1997b;
Nuyken & Voit, 1997). Due to their thermal stabil-
ity, diazene sulphonates can be considered as rela-
tively safe sources of diazonium ions. Furthermore,
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E. Baranovicova et al./Chemical Papers 70 (9) 1238–1252 (2016)
spin-coated oxetane group polymers then cross-linked
the films (Nuyken et al., 2006; Schelter et al., 2010;
Nuyken, 2014). Such films can be cross-linked using
UV light via a cationic ring-opening polymerisation
to yield insoluble films. As an alternative to oxetane,
benzocyclobutene (Nuyken, 2014; Ma et al., 2007) or
trifluorovinyl ether (Liu et al., 2000) units in the poly-
mer side-chains can be exploited as the photo- or ther-
mally cross-linkable group. To the best of our knowl-
edge, no attempt has been reported in which diazene
sulphonate units have been used as cross-linking func-
tional groups for OLED technology. However, they
can be considered as of particular interest, not only
because of their simple synthesis but also because of
their effect on the solubility of the starting polymer.
They even become water-soluble at higher diazene
sulphonate concentrations.
Hole-transport materials for OLED are often based
on triarylamine or its derivatives. The synthesis and
characterisation of side-chain polymers functionalised
with hole-transporting units and photo-cross-linkable
diazene sulphonate groups, which can be used in
the solution-based preparation of multilayer OLEDs,
are the subject of this paper. As hole-transporting
units, three types of triarylamine monomers were co-
polymerised with three types of diazene sulphonate-
based monomers as cross-linking agents. The model
polymers were characterised by cyclic voltammetry
(CV) as well as by NMR, UV-VIS and EPR spec-
troscopies.
25.6 mmol) and Pd2(dba)2 (5.3 mg, 5.8 mmol) in
toluene (20 mL) (catalyst B) were stirred at ambient
temperature under an argon atmosphere for 20 min.
All polymerisations were carried out in an N,N-
dimethylformamide (DMF) solution at 70◦C, after re-
peated degassing, with azobisisobutyronitrile (AIBN)
(5 mole %) as a radical initiator under nitrogen atmo-
sphere (for more details of the initial reaction mixture,
see Table 1). After 20 h, the reaction was stopped by
opening the reaction to the air. Polymers A, B, I, J,
K, L, M, N, O, P and R were precipitated in methanol
(MeOH), polymers C, E, G, H in EtOH, and polymers
D and F in diethyl ether (Table 1).
4-Bromo-N,N-diphenylbenzenamine (I)
Triphenylamine (25 g, 102 mmol) and N-bromo-
succinimide (19 g, 106 mmol) were refluxed in cy-
clohexane (400 mL) at 80◦C for 10 h. The solid by-
products were filtered and the cyclohexane was evap-
orated. The residual brown oil was dissolved in EtOH
(350 mL) and the solvent was slowly evaporated until
the product precipitated.
N 1-(Diphenylmethylene)-N 4,N 4-diphenyl-1,4-
benzenediamine (II)
Compound I (7 g, 23.2 mmol), benzophenone
imine (5.06 g, 28 mmol) and sodium tert-butoxide
(3.12 g, 32 mmol) were suspended in toluene (60 mL).
Catalyst A was added and the reaction mixture was
stirred at 95◦C for 20 h under a nitrogen atmosphere.
The reaction was stopped by opening the reaction to
the air and the insoluble material was removed by fil-
tration. The evaporation of toluene afforded an orange
product which was re-crystallised from MeOH.
Experimental
A Bluepoint 2 (Hoenle UV technology) apparatus
was used for UV irradiation. UV-VIS spectra were
obtained with a Varian Cary 3 spectrometer using
tetrahydrofuran (THF) as a solvent and polymer lay-
ers coated onto indium tin oxide (ITO). EPR spec-
tra were measured on a Bruker EPR, X/Band, TM-
110 (ER 4103 TM) instrument; light source: HPA
400/30S (400 W, Philipps, λmax = 365 nm); solvent:
dimethyl sulphoxide (DMSO) and polymer films on
glass tube. Cyclic voltammetry was performed using a
PS4/300PC built-in potentiostat-galvanostat (Gamry
Instruments) using acetonitrile/tetrabutylammonium
hexafluorophosphate (TBAHF6) as an electrolyte and
N 1,N 1-Diphenyl-1,4-benzenediamine (III)
Aq. HCl (15 mass %, 9 mL) was slowly added drop-
wise into the solution of II (7.2 g, 17 mmol) in THF
(100 mL) followed by the addition of water (25 mL)
and stirring at ambient temperature for 30 min. The
by-products were extracted with a mixture of ethyl
acetate (EtOAc)/hexane (ϕr = 2 : 1). The water phase
was neutralised with aq. NaOH (10 mass %) and the
product precipitated at pH 8.
1
calomel electrode as a reference. H (300 MHz) and
13C (75 MHz) NMR spectra were measured on a
Bruker ARX 300 instrument.
N-[4-(Diphenylamino)phenyl]-2-methylacryl-
The reagents for monomer syntheses and the sol-
vents for the Hartwig–Buchwald aminations were pur-
chased from Fluka. The solvents were dried and kept
under an argon atmosphere. Unless stated other-
wise, the conditions for catalyst preparation were as
follows: 1,1ꢀ-bis(diphenylphosphino)ferrocene (DPPF)
(7.1 mg, 12.8 mmol) and bis(dibenzylideneacetone)
palladium(0) (Pd2(dba)2) (5.3 mg, 5.8 mmol) in
toluene (15 mL) (catalyst A) or DPPF (14.2 mg,
amide (IV, Amine 1)
Triethylamine (TEA) (1 mL, 7.2 mmol) was
added to the solution of III (0.94 g, 3.6 mmol) in
dichloromethane (DCM) (10 mL) and the mixture was
cooled to 0◦C. Methacryloyl chloride (0.52 g, 5 mmol)
was then added slowly and the mixture was stirred at
0◦C for 2 h. The solvent was evaporated, followed by
the addition of EtOAc (10 mL) and filtration of insolu-
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E. Baranovicova et al./Chemical Papers 70 (9) 1238–1252 (2016)
Table 1. Preparative dataa and characteristics of co- and terpolymers
1241
Amine
Type Mole %
Azo
Styrene
Amount
Polymer
DMF/
Mnb/
PDIb Yield/
Amount
1000 mg
Type Mole %
Amount
Mole %
mL (g mol−1
) %
A
B
C
D
E
F
G
H
I
1 (IV )
1 (IV )
2 (IX )
2 (IX )
2 (IX )
1 (IV )
1 (IV )
35
60
35
35
30
50
75
1 (XVII)
1 (XVII)
2 (XVIII)
3 (XIX )
5
128 mg
0.43 mmol
300 mg
1.01 mmol
372 mg
1.44 mmol
597 mg
2.02 mmol
389 mg
1.36 mmol
181 mg
0.61 mmol
261 mg
1.01 mmol
173 mg
0.58 mmol
225 mg
0.76 mmol
245 mg
0.83 mmol
141 mg
0.48 mmol
92 mg
0.31 mmol
207 mg
0.70 mmol
100 mg
0.39 mmol
407 mg
1.52 mmol
271 mg
60
20
40
30
50
40
–
814 mg
7.83 mmol
105 mg
1.01 mmol
240 mg
2.31 mmol
180 mg
1.73 mmol
350 mg
3.36 mmol
254 mg
2.44 mmol
–
3
3
4
4
4
3
3
3
3
3
3
3
4
4
3
3
106000 1.71 76
3.04 mmol
1000 mg
3.04 mmol
1000 mg
2.02 mmol
1000 mg
2.02 mmol
1000 mg
2.02 mmol
1000 mg
3.04 mmol
1000 mg
20
25
35
20
10
25
15
20
15
15
35
10
10
30
20
87000
32000
17900
44500
97200
41000
78000
1.93 68
1.58 44
1.33 48
1.50 82
2.01 86
1.64 66
1.77 65
1 (XVII)
1 (XVII)
2 (XVIII)
3 (XIX )
3.04 mmol
1000 mg
3 (XV ) 45
40
–
162 mg
1.55 mmol
–
1.75 mmol
1000 mg
3.04 mmol
1000 mg
1 (IV )
1 (IV )
80
55
1 (XVII)
1 (XVII)
1 (XVII)
1 (XVII)
1 (XVII)
2 (XVIII)
1 (XVII)
3 (XIX )
262000 7.22 93
J
30
30
–
173 mg
1.66 mmol
100 mg
0.95 mmol
–
39000
67000
3.04 84
1.13 77
3.04 mmol
1000 mg
1.75 mmol
1000 mg
L
3 (XV ) 55
2 (IX ) 65
M
N
O
P
R
102000 2.88 91
2.02 mmol
1000 mg
1.75 mmol
1000 mg
3 (XV ) 25
3 (XV ) 45
65
45
40
40
473 mg
4.55 mmol
182 mg
1.75 mmol
211 mg
8700
7400
1.37 57
1.42 61
1.86 85
1.69 66
1.75 mmol
500 mg
1.52 mmol
1000 mg
1 (IV )
2 (IX )
30
40
96000
72000
2.03 mmol
210 mg
2.02 mmol
1.01 mmol
2.02 mmol
a) E.g. polymer A was obtained from 1000 mg of Amine 1, 128 mg of Azo 1 and 814 mg of styrene in 3 mL of DMF, using AIBN as
radical initiator at 70◦C for 24 h; b) molar mass (Mn) and polydispersity index (PDI) were determined by GPC using poly(methyl
methacrylate) standards and dimethylacetamide as eluent.
ble triethylammonium chloride. The solvent was then
evaporated to 1/5 of its volume and the residual mix-
ture was added drop-wise into n-hexane to precipitate
the desired product.
(10.61 g, 45 mmol) and sodium tert-butoxide (2.1 g, 22
mmol) in toluene (50 mL) and the mixture was stirred
at 95◦C for 12 h under an argon atmosphere. The re-
action was stopped by opening the reaction to the air
and the insoluble material was removed by filtration.
The product was isolated by column chromatography.
First, 1,4,-dibromobenzene was eluted with cyclohex-
ane followed by elution of the product with toluene.
N 1,N 1,N 4-Triphenyl-1,4-benzenediamine (V)
Catalyst B was added to the solution of I (8.5 g,
26.2 mmol), aniline (7.34 g, 78.7 mmol) and sodium
tert-butoxide (3.12 g, 32 mmol) in toluene (65 mL)
and the mixture was stirred overnight at 90◦C under
an argon atmosphere. The reaction was stopped by
opening the reaction to the air and the insoluble ma-
terial was removed by filtration. The product was pu-
rified by flash-column chromatography using toluene
as the eluent.
N 1-{4-[(Diphenylmethylene)amino]phenyl}
-N 1,N 4,N 4-triphenyl-1,4-benzenediamine
(VII)
Catalyst A (in 10 mL of toluene) was added to the
solution of VI (6 g, 12.4 mmol), benzophenone imine
(3.4 g, 18.5 mmol) and sodium tert-butoxide (2.0 g,
20.8 mmol) in toluene (80 mL) and the mixture was
stirred at 90◦C for 2 h under an argon atmosphere.
The reaction was stopped by opening the reaction to
the air and the insoluble material was removed by fil-
tration. After removal of the solvent by evaporation,
the orange product was re-crystallised from MeOH.
N 1-(4-Bromophenyl)-N 1,N 4,N 4-triphenyl-
1,4-benzenediamine (VI)
Catalyst B (in 10 mL of toluene) was added to the
solution of V (5.5 g, 15 mmol), 1,4-dibromobenzene
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