Mild conditions for deuteration of primary and secondary arylamines for the synthesis of deuterated optoelectronic organic molecules

Article abstract of DOI:10.3390/molecules191118604

Deuterated arylamines demonstrate great potential for use in optoelectronic devices, but their widespread utility requires a method for large-scale synthesis. The incorporation of these deuterated materials into optoelectronic devices also provides the op

Full text of DOI:10.3390/molecules191118604

Molecules 2014, 19, 18604-18617; doi:10.3390/molecules191118604
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Mild Conditions for Deuteration of Primary and Secondary
Arylamines for the Synthesis of Deuterated Optoelectronic
Organic Molecules
Anwen M. Krause-Heuer, Nageshwar R. Yepuri, Tamim A. Darwish * and Peter J. Holden
National Deuteration Facility, Bragg Institute, Australian Nuclear Science and Technology
Organisation (ANSTO), Locked Bag 2001, Kirrawee DC, NSW 2232, Australia;
E-Mails: anwen.krause-heuer@ansto.gov.au (A.M.K.-H.); nageshwar.yepuri@ansto.gov.au (N.R.Y.);
peter.holden@ansto.gov.au (P.J.H.)
* Author to whom correspondence should be addressed; E-Mail: tamim.darwish@ansto.gov.au;
Tel.: +61-2-9717-9080.
External Editors: Peter V. Bonnesen and Kunlun Hong
Received: 5 September 2014; in revised form: 29 October 2014 / Accepted: 4 November 2014 /
Published: 13 November 2014
Abstract: Deuterated arylamines demonstrate great potential for use in optoelectronic
devices, but their widespread utility requires a method for large-scale synthesis. The
incorporation of these deuterated materials into optoelectronic devices also provides the
opportunity for studies of the functioning device using neutron reflectometry based on the
difference in the scattering length density between protonated and deuterated compounds.
Here we report mild deuteration conditions utilising standard laboratory glassware for the
deuteration of: diphenylamine, N-phenylnaphthylamine, N-phenyl-o-phenylenediamine and
1-naphthylamine (via H/D exchange in D2O at 80 °C, catalysed by Pt/C and Pd/C). These
conditions were not successful in the deuteration of triphenylamine or N,N-dimethylaniline,
suggesting that these mild conditions are not suitable for the deuteration of tertiary
arylamines, but are likely to be applicable for the deuteration of other primary and
secondary arylamines. The deuterated arylamines can then be used for synthesis of larger
organic molecules or polymers with optoelectronic applications.
Keywords: arylamine; deuteration; H/D exchange; neutron reflectrometry;
OLED; optoelectronics

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1. Introduction
The discovery of the conductive properties of organic materials has led to the development of the
large and expanding field of organic optoelectronics and conductive polymers, which encompasses
technologies such as organic light-emitting diodes (OLED), organic photovoltaics (OPV) and dye
sensitised solar cells (DSSC). In addition to their excellent electronic properties, the family of arylamines
has favourable properties such as ion transfer processes, redox properties, and photoelectrochemical
behaviour [1–6]. It has also been reported that arylamine compounds have strong electrochromic
properties when they are oxidized [1–3,7]. Electron rich arylamine-based compounds (such as N,N'-di(1-
naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-
benzidine (TPD) and N,N'-di(1-naphthyl)-N,N'-diphenyl-4,4'-biphenyldiamine (NAD), Figure 1) are
widely used as components in hole transport materials [8,9]. Electron deficient molecules found in
OLED, such as 1,3,5-tris(N-phenylbenzimidizol-2-yl)benzene [10,11] (TPBI, Figure 1), are also
prepared from arylamine derivatives.
Among conducting polymers, polyaniline (PANI, Figure 1), a polymer of the simplest form of
arylamine, stands out due to its favourable properties (such as air and moisture stability) and multiple
applications. Polyaniline exists in three different oxidation states that have different properties (e.g.
conductivity, colour), with these properties able to be exploited in sensors or electrochromic devices.
Other applications for polyaniline include use in antistatic coatings [12] and hole injection layers [13].
Polymeric arylamines are also attractive due to ease of thin film fabrication via solution processing [14].
Figure 1. Chemical structures of compounds used for hole transport (NPD, NAD, TPD)
and electron transport (TPBI) in OLED devices, and the conducting polymer
polyaniline (PANI).
N
N
N
N
NPD
N
N
N
N
N
N
TPBI
TPD
H
N
N
N
N
N
N
H
m
n
n + m = 1
NAD
PANI

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There is much interest in the development of new organic molecules with specific/tuneable and
desirable electrochemical properties. Effort has been focused on improving the low electricity-to-light
conversion efficiency, as well as the poor high-voltage stability that plagues OLED devices. One
mechanism investigated has been the replacement of hydrogen with deuterium in the organic
molecules in these devices. While it is often assumed that this substitution does not significantly
change the chemical and optoelectronic properties of the parent compound, this does not take into
account the relatively large difference in mass between hydrogen and deuterium, which can result in
different physical properties (such as polarity and molecular volume). In a heavier isotope, its
zero-point energy is lowered due to its lower potential and vibrational energy levels. These physical
differences may result in deuterated molecules behaving differently in non-covalent interactions (such
as π-π stacking or hydrogen bonding) compared to their protonated analogues and so it is of relevance
to also study the properties of optoelectronic devices containing deuterated molecules.
It has been recently reported that selective deuteration of conducting polymers alters the
optoelectronic properties of the molecules [15,16], with D-polymers showing a substantially larger
magnetoresistance compared to the protonated form [16]. The deuteration of the emitting molecule
tris-(8-hydroxyquinoline)aluminium (Alq3) resulted in an OLED device with enhanced light-emitting
efficiency and high-voltage stability, compared to the respective protonated device [17]. The
deuteration of tris-(2-phenylpyridine)iridium resulted in increased high-voltage stability, as well as
extended device lifetime [18]. As such, there is particular interest in deuterated molecules for use in
optoelectronic devices.
This isotopic substitution is also performed in order to exploit the difference in neutron scattering
length between hydrogen (−0.3742 fm) and deuterium (0.6671 fm) for neutron studies. The
morphological stability of the organic layers in OLED devices can affect both the efficiency and the
device total life-time [19–23], with heat generation during the operation of the device resulting in
instability at the interfaces. Investigations of buried interfaces within functioning OLED devices
presents a number of difficulties, and so neutron reflectometry has become a key method for
investigations at the interfaces of thin films [8,17,24–30]. Selected combinations of protonated and
deuterated components enhance the scattering contrast, providing the ability to probe the structures of
individual components within a functional device [31–33].
The preparation of optoelectronic devices requires large quantities of the desired organic molecules,
and so efficient synthesis of these materials is necessary, especially if deuterated molecules are
required. An advantage of polymeric materials is that the polymerisation can be conducted and
processed on a large scale at relatively low cost, with many of the applications (sensors, functional
coatings, catalysts, etc.) of conducting polymers requiring large quantities of material. Therefore,
developing bulk syntheses of the deuteration form of the monomers for conducting polymers would be
especially important for practical reasons.
There are a variety of methods for performing hydrogen/deuterium-exchange reactions at carbon
centres; these methods include pH-dependent exchange and exchange catalysed by either a
homogeneous or heterogeneous catalyst. The source of deuterium for exchange is often D2O, but these
reactions can also be performed using D2 [34] or deuterated protic solvents to provide labile deuterium
atoms. Hydrothermal reaction conditions are also often necessary to achieve high levels of deuterium
incorporation, however, these reactions require specialised vessels, which come at significant cost,

Molecules 2014, 19
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especially for vessels capable of performing multigram synthesis [35–37]. Here we report a general
procedure and four example compounds (1–4, Figure 2) utilising mild reaction conditions and standard
laboratory glassware for the multi-gram scale deuteration of primary and secondary arylamines that are
used in optoelectronic applications.
Figure 2. The structures of the four deuterated arylamines 1–4 synthesised in this study.
D
H
D
D
D
D
D
D
H
N
H
N
D
D
D
D
D
D
D
D D
1
D D
2
D
D
D
D
D
NH2
NH2
H
N
D
D
D
D
D
D
D
D
D D
3
D
D
D
D
4
2. Results and Discussion
The synthesis of deuterated polyaromatic molecules for optoelectronic devices can be performed in
a variety of ways, starting from either deuterated precursors that are assembled via standard organic
chemistry techniques, or by performing hydrogen-deuterium exchange on the protonated molecule.
The synthesis of three of the deuterated molecules we describe in this study (1, 2 and 3, Figure 2) has
been previously reported, using Buchwald-Hartwig cross coupling of the respective deuterated amines
and deuterated aryl halides. For example, synthesis of 1 can be achieved by the reaction of
d5-bromobenzene and d5-aniline (Scheme 1) [38], with the synthesis of 2 [38–40] and 3 [41] performed
in a similar manner. In all cases, the deuterated starting materials are very expensive and so this method
is not feasible for the large scale synthesis required for optoelectronic applications or conductive
polymers. 3 has previously been synthesised via the ruthenium catalysed reaction of d10-azobenzene with
isopropanol, however the desired product was only produced in 35% yield, with some undesired
H-exchange also observed at positions ortho- to the NH2 [42]. Alternatively, deuteration of arylamines
has been conducted using H/D exchange in D2O at high (>250 °C) temperature.
Scheme 1. The synthesis of 1 via the Buchwald-Hartwig cross coupling of
d5-bromobenzene and d5-aniline.
D
D
D
D
H
N
D
D
Br
D
H2N
D
D
D
D
D
D
D
Pd2(dba)3/PPh3
+
NaOt-Bu/toluene
D D
D
D
D
D
1

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18608
The H/D exchange of aniline has been performed in D2O (without catalyst) at 260 °C for 24 h,
however, this method only reported significant deuterium exchange at the ortho- (47%) and
para- (64%) positions, with only 3% exchange observed at the meta-position [43]. The use of near
critical D2O (325 °C) and a polymer-supported sulfonic acid catalyst synthesised d7-aniline with 81%
overall deuterium incorporation [44]. The use of a lower temperature (250 °C) and shorter reaction
time (2 h) in the absence of catalyst also supported the previous finding that deuteration only occurs at
the o- and p-positions, although in this case higher exchange was observed at these positions
(>90% exchange) [44]. To our knowledge, H/D exchange has not been previously attempted for
N-phenylnaphthylamine and N-phenyl-o-phenylenediamine, with H/D exchange reactions for
diphenylamine and 1-naphthylamine only reported at high temperature.
1 has been synthesised via acid-catalysed H/D exchange of diphenylamine in D2O (250 °C) [45],
however, this requires the specialised high-pressure equipment capable of withstanding these harsh
conditions. The metal-catalysed H/D exchange of 1-naphthylamine in D2O utilising microwave and
150 °C has been previously used to synthesise 4 [46], however deuteration via this technique is limited
by its small capacity (<100 mg). Alternatively, the nitration and subsequent reduction of
d8-naphthylene has successfully yielded 4 on ~1 g scale [47], however d8-naphthylene is quite
expensive, making large scale synthesis of 4 undesirable via this method. Protonated 1-naphthylamine
is significantly cheaper, and so the development of mild reaction conditions for the deuteration of
1-naphthylamine would reduce costs and eliminate the need for additional synthetic steps.
It has been shown more recently that the use of a Pt/C catalyst can facilitate the H/D exchange in
D2O of the aromatic hydrogens of aniline (and a variety of other single-ring aniline-type compounds,
such as 1,2-diaminobenzene and 2-propylaniline) at room temperature, with increased deuterium
incorporation achieved at 80 °C (up to 98% overall deuterium incorporation) in moderate (50%–60%)
chemical yield [48,49]. The comparatively mild conditions facilitated by these catalysts are clearly
more favourable than high temperatures (>250 °C) required for performing H/D exchange reactions in
the absence of the catalysts, but these conditions have not been applied to multi-ring systems or
secondary arylamines.
In this study successful deuteration of the primary and secondary arylamines 1–4 has been achieved
on multi-gram scale using mild reaction conditions similar to those that have been used previously for
aniline. The mild-deuteration of the compounds reported herein has applications in the preparation of
optoelectronic devices as the molecules can be produced on larger scale, comparatively cheaply and
using standard laboratory equipment. The advantages are two-fold; functioning devices containing
deuterated components can be studied using neutron scattering, and the optoelectronic devices
produced may also have enhanced efficiency and stability.
Here we have performed the synthesis of 1–4 via H/D exchange in D2O, facilitated by a
combination of Pd/C (~1 mol %) and Pt/C (~1.5 mol %), with the reaction mixture purged with N2(g)
and then H2(g) prior to heating at 80 °C for 4–24 h (Scheme 2). For compound 4 it was found that at
longer reaction times, some saturation of the aromatic system was observed; the majority of the
saturation occurred on the ring bearing the aniline moiety. Heating at 80 °C for 4 h resulted in overall
deuteration of 90%, with the compound purified by recrystallisation in 84% yield, with no significant
saturation observed. A 4 h reaction time was then also employed in the synthesis of compounds 1 and
2, where no significant saturation was observed.

Molecules 2014, 19
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Scheme 2. The synthesis of deuterated arylamines 1–4 via H/D exchange in D2O,
catalyzed by Pt/C and Pd/C.
D
D
D
D
H
N
H
N
D
D
D
D
Pt/C, Pd/C, D2O
4 h, 80 °C
D D
1
diphenylamine
96% overall deuteration, 72% yield
D
H
D
D
*
D
H
N
H
N
Pt/C, Pd/C, D2O
4 h, 80 °C
D
D
D
D D
2
N-phenylnaphthylamine
D
D
88% overall deuteration, 90% yield
NH2
D
NH2
H
H
N
D
D
D
D
N
Pt/C, Pd/C, D2O
24 h, 80 °C
D D
3
N-phenyl-o-phenylenediamine
D
D
90% overall deuteration, 65% yield
D
NH2
NH2
*
D
D
D
D
Pt/C, Pd/C, D2O
4 h, 80 °C
D
D
1-naphthylamine
4
88% overall deuteration, 84% yield
D
D
D D
N
D
D
D
D
Pt/C, Pd/C, D2O/THF
4 h & 24 h, 80 °C
N
D
D
D
D
triphenylamine
D
D
D
0% overall deuteration
D3C
D
CD3
D
N
N
Pt/C, Pd/C, D2O
4 h & 24 h, 80 °C
D
D
N,N-dimethylaniline
D
0% overall deuteration
Compound 1 was produced in 72% yield following purification by recrystallisation, with 96%
overall deuteration achieved. Compound 2 was produced in 90% yield, with 88% overall deuteration
achieved. One position on 2 (marked by * on 2 in Scheme 2) appeared to undergo no H/D exchange as
observed in the 1H- and 2H-NMR spectra, which contributed to the lower overall deuteration level. It is
likely that the lack of H/D exchange at this position is due to a combination of steric crowding from
the phenyl ring and hydrogen bonding with the amine group. Incomplete deuteration (to a lesser
extent) of the analogous position was observed in compound 4 (marked with * in Scheme 2), where
H-bonding with the amine group is the contributing factor. Compound 3 required a longer reaction
time of 24 h to achieve 90% overall deuteration with 65% yield after column chromatography; only

Molecules 2014, 19
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~60% overall deuteration was observed at 4 h. No saturation was observed after 24 h. The need for
longer reaction time for the synthesis of 3 was likely attributed to the higher melting point (77–80 °C)
of this solid compared to 1 (50–53 °C), 2 (60–66 °C) and 4 (47–50 °C). High melting point compounds
are likely to have lower miscibility and solubility in D2O at 80 °C and therefore H/D exchange rate is
likely to be affected. It should be noted that higher overall deuteration levels for these compounds can
be achieved by returning the compound for a second cycle with fresh D2O and catalyst, however, for
the scope of this study single H/D exchange cycle was sufficient.
The deuteration of the tertiary arylamine triphenylamine was attempted using the same method
(Scheme 2). After 4 h at 80 °C, no deuteration was observed (as measured by mass spectroscopy), and
so THF was added to enhance the solubility of triphenylamine (m.p. 127 °C). The reaction continued
at 80 °C for a further 24 h, however, no deuteration was observed. This is not surprising, as the
literature reports H/D exchange of triphenylamine in D2O with platinum(IV) oxide catalyst at 250 °C
for 12 h [50]. Deuteration of the tertiary arylamine N,N-dimethylaniline, which has a much lower
melting point, 2 °C, was also attempted using this method (Scheme 2), with no deuteration observed at
either 4 or 24 h. This led us to generally conclude that the mild deuteration conditions presented here
are only applicable to primary and secondary arylamines.
It is apparent that the availability of the nitrogen lone pair influences the deuteration reaction. The
basicity of arylamine is reduced dramatically when moving from primary (pKa = ~4.6) and secondary
(pKa = ~0.8) to tertiary (pKa = ~−5). It is expected that the metal catalyst can be located in the vicinity
of the nitrogen atom of primary and secondary arylamines more so than that in the tertiary arylamine
since Pt and Pd have a quite high affinity for the nitrogen lone pair. This could be the reason why no
deuteration was observed in triphenylamine. Another possible explanation for this behaviour would be
the ability of the nitrogen lone pair in primary and secondary arylamines to form hydrogen bonding
with water (D2O), which enhances their miscibility and solubility at 80 °C. However the unsuccessful
deuteration of the liquid compound N,N-dimethylaniline suggests that miscibility is not the main
driving factor for the deuteration that is observed in the primary and secondary arylamines examples
used in this study.
The deuterated arylamines 1–4 can then be used for the synthesis of a variety of compounds with
photoelectronic applications, where direct deuteration of the final molecule is often not achievable due
to low solubility. For example, 2 can be used in the synthesis of d-NPD, 3 can be used in the synthesis
of d-TPBI, and 4 can be used in the synthesis of d-NAD (Scheme 3), using analogous methods to those
reported in the literature for the synthesis of the protonated compounds [10,51,52]. Loss of deuteration
via back-exchange is minimized due to the absence of protic solvents, indeed we did not observe any
back exchange in the synthesis of d-tris(4-carbazoyl-9-ylphenyl)amine (d-TCTA) from deuterated
carbazole [33]; this method is similar to those used for the synthesis of the compounds described
in Scheme 3.

Molecules 2014, 19
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Scheme 3. Utility of the deuterated compounds described in this study for the synthesis of
organic molecules (NPD [51], TPBi [10] and NAD [52]) with photoelectronic applications.
Pd(OAc)2/PPh3
NH
Br
Br
N
N
+
NaO-tBu/CH2Cl2
NPD
Cl
O
N
N
NH2
H
N
N
N
NMP, 180 °C, 6 h
+
Cl
Cl
O
O
N
N
NH2
TPBI
Cu, K2CO3
+
I
I
HN
NH
1,2-dichlorobenzene
+
Br
Pd2(dba)3/(tBu)3P
NaO-tBu/CH2Cl2
N
N
NAD
3. Experimental Section
3.1. Materials
Diphenylamine, N-phenyl-o-phenylenediamine, 1-naphthylamine, N-phenylnaphthylamine,
triphenylamine, N,N-dimethylaniline, platinum on carbon (10%), palladium on carbon (10%) and
Celite (545, reagent grade) were purchased from Sigma Aldrich (Sydney, Australia). D2O (99.8%) was
purchased from AECL, Ontario, Canada. NMR solvents were purchased from Cambridge Isotope
Laboratories, Inc. (Tewksbury, MA, USA) or Sigma Aldrich.
3.2. Instrumentation
1H-NMR (400 MHz), 13C-NMR (100.6 MHz) and 2H-NMR (61.4 MHz) spectra were recorded on a
Bruker 400 MHz spectrometer at 298 K. Chemical shifts, in parts per million, were referenced to the
residual signal of the corresponding NMR solvent. Deuterium NMR was performed using the probe’s
lock channel for direct observation. Electrospray ionization mass spectra (ESI-MS) were recorded on a
4000 QTrap AB Sciex spectrometer. The overall percentage deuteration of the molecules was
calculated by MS using the isotope distribution analysis of the different isotopologues. This was
calculated taking into consideration the 13C natural abundance (as determined from the mass spectrum
of the protonated material), whose contribution was subtracted from the peak area of each [M+1]
isotopologue to allow for accurate estimation of the percentage deuteration. The mean molecular

Molecules 2014, 19
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weight was calculated based on the overall percentage of deuteration, and this was used for the
calculation of mass yields. Automated medium pressure chromatography was conducted using a
Reveleris® flash chromatography system (Grace Davison, Rowville, VIC, Australia), with specific
chromatographic conditions given as details for the relevant compound.
3.3. General Method
The relevant protonated arylamine (1–12 g) was suspended in D2O (~25 mL per gram of arylamine)
in a two-neck round bottom flask, to which Pt/C (10% w/w, ~1 mol %) and Pd/C (10% w/w,
~1.5 mol %) were added. The flask was sealed, and the stirring reaction mixture was purged with one
balloon of N2(g), followed by one balloon of H2(g), ensuring that the flask was not pressurised. The
reaction mixture was heated at 80 °C for 4 h in the case of 1, 2 and 4, and 24 h in the case of 3. The
reaction mixture was allowed to cool, CH2Cl2 (~25 mL) was added to the reaction flask, and the
mixture filtered over Celite to remove the catalyst, which was then washed with CH2Cl2 (50–100 mL).
The filtrate was extracted with 3 × 50 mL CH2Cl2, the combined organics dried over Na2SO4, filtered
and evaporated to dryness to yield the deuterated product, characterized as follows:
d10-Diphenylamine (1). Compound 1 was synthesized according to the general procedure, utilizing 12
g of diphenylamine, 2 g of Pt/C and 2 g of Pd/C. The product was recrystallised from petroleum ether
1
to give cream coloured crystals (9.1g, 72%). H-NMR (400 MHz, d6-acetone): δ residual protons 7.36
2
(br s, 1H), 7.24 (s, 0.24H), 7.12 (s, 0.07H), 6.85 (s, 0.04H). H-NMR (61.4 MHz, d6-acetone): δ 7.28
(br), 7.17 (br), 6.89 (br). 13C-NMR (101 MHz, d6-acetone): δ 144.5 (m), 129.5 (m), 120.4 (m), 117.6 (m).
ESI-MS m/z: 180.1 [M+H]+. Overall 95.8% D levels with isotopic distribution d8 6.3%, d9 29.9%,
d10 63.9%.
d12-N-Phenylnaphthylamine (2). Compound 2 was synthesized according to the general procedure,
utilising 6 g of N-phenylnaphthylamine, 1 g of Pt/C and 1 g of Pd/C. No additional purification was
necessary, giving the product as a beige coloured solid (5.7 g, 90%). 1H-NMR (400 MHz, d6-acetone):
δ residual protons 8.18 (s, 1H), 7.89 (s, 0.05H), 7.56 (s, 0.06H), 7.48 (br s, 1H), 7.41 (s, 0.05H), 7.39
2
(s, 0.05H), 7.23 (s, 0.08H), 7.08 (s, 0.08H), 6.85 (s, 0.04H). H-NMR (61.4 MHz, d6-acetone): δ 7.94
(br), 7.67–7.36 (m), 7.28 (br), 7.13 (br), 6.90 (br). 13C NMR (101 MHz, d6-acetone): δ 146.1 (s), 140.4
(s), 135.7 (s), 129.4 (m), 128.6 (m), 128.5 (s), 126.4 (m), 126.3 (m), 125.6 (m), 123.2 (s, C-H*), 122.4
(m), 120.1 (m), 117.7 (m), 115.3 (m). ESI-MS m/z: 231.1 [M+H]+ overall 87.8% D levels with isotopic
distribution d7 1.3%, d8 2.6%, d9 7.8%, d10 27.2%, d11 51.5%, d12 9.4%.
d9-N-Phenyl-o-phenylenediamine (3). Compound 3 was synthesized according to the general
procedure, utilising 1 g of N-phenyl-o-phenylenediamine, 0.2 g of Pt/C and 0.2 g of Pd/C. The reaction
was heated for 24 h, with the standard work up employed. The product was purified using automated
medium pressure liquid chromatography (40 g silica column) with petroleum ether/ethyl acetate
1
(80:20) as mobile phase to yield a red/brown solid (0.65 g, 62%). H-NMR (400 MHz, d6-acetone): δ
residual protons 7.13 (s, 0.08 H), 7.06 (s, 0.04H), 6.91 (s, 0.04H), 6.82 (s, 0.04H), 6.75 (s, 0.07H), 6.70
(s, 0.04H), 6.61 (s, 0.04H), 6.43 (br s, 1H), 4.42 (br s, 2H). 2H-NMR (61.4 MHz, d6-acetone): δ 7.17 (br),
13
7.10 (br), 6.95 (br), 6.86 (br), 6.79 (br), 6.66 (br). C-NMR (101 MHz, d6-acetone): δ 146.5 (s), 143.2

Molecules 2014, 19
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(s), 128.5 (m), 128.2 (s), 124.7 (m), 124.3 (m), 117.7 (m), 117.0 (m), 115.2 (m), 114.5 (m). ESI-MS m/z:
194.1 [M+H]+. Overall 90.1% D levels with isotopic distribution d0 2.0%, d5 1.8%, d6 2.5%, d7 7.9%, d8
35.9%, d9 50.1%.
d7-1-Naphthylamine (4). Compound 4 was synthesised according to the general procedure, utilising 4 g
of 1-naphthylamine, 0.5 g of Pt/C and 0.5g of Pd/C. After heating for 4 h and cooling to room
temperature, the reaction mixture was basified by addition of 28% NH3(aq) (20 mL) before the standard
work up. The product was purified by recrystallization from petroleum ether to give needle type brown
coloured crystals (3.5 g, 83.5%). 1H-NMR (400 MHz, CD2Cl2): δ residual protons 7.86 (s, 0.27H), 7.50
(m, 0.08H), 7.34 (m, 0.09H), 6.81 (s, 0.04H), 4.21 (br s, 2H). 2H-NMR (61.4 MHz, CD2Cl2): δ 7.89 (br),
7.54 (br), 7.39 (br), 6.85 (br). 13C-NMR (101 MHz, CD2Cl2): δ 142.0 (s), 134.3 (s), 128.1 (m), 125.6 (m),
125.4 (m), 124.4 (m), 123.6 (s), 120.8 (s, C-H*), 120.4 (m), 118.5 (m), 109.3 (m). ESI-MS m/z: 151.2
[M+H]+ overall 88.0% D levels with isotopic distribution d3 0.7%, d4 2.4%, d5 10.7%, d6 29.9%, d7 44.2%.
4. Conclusions
This work describes the H/D exchange of primary and secondary arylamines, performed in D2O at
80 °C utilising Pt/C and Pd/C catalysts. These mild reaction conditions do not require any specialised
laboratory equipment and can produce deuterated arylamines in multi-gram quantities, with high
(>90%) levels of overall deuteration. The deuteration of organic molecules within optoelectronic
devices provides opportunities to study the functioning devices using neutron reflectometry, which is
able to exploit the scattering length differences between hydrogen and deuterium. These deuterated
arylamines can also be incorporated into optoelectronic devices, which may have better lifetime and
efficiency compared to the protonated version.
Supplementary Materials
1H-NMR, 2H-NMR and 13C-NMR spectra, as well as mass spectra are available for
compounds 1–4 in the supplementary material. Supplementary materials can be accessed at:
http://www.mdpi.com/1420-3049/19/11/18604/s1.
Acknowledgments
Synthesis of the molecules described here was conducted at the National Deuteration Facility and
was partly supported by the National Collaborative Research Infrastructure Strategy (NCRIS)—an
initiative of the Australian Government.
Author Contributions
TAD, NRY, AMKH and PJH designed research; AMKH, NRY and TAD performed research and
analysed the data, AMKH and TAD wrote the manuscript. All authors read and approved the
final manuscript.

Molecules 2014, 19
18614
Conflicts of Interest
The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds 1–4 are available from the authors upon request.
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