N-Type Doping of Organic Semiconductors: Immobilization via Covalent Anchoring

Article abstract of DOI:10.1021/acs.chemmater.9b01150

Electrical doping is an important tool in the design of organic devices to modify charge carrier concentration in and Fermi level position of organic layers. The undesired diffusion of dopant molecules within common transport materials adversely affects b

Full text of DOI:10.1021/acs.chemmater.9b01150

Subscriber access provided by University of Rochester | River Campus & Miner Libraries
Article
N-Type Doping of Organic Semiconductors:
Immobilization via Covalent Anchoring
Patrick Reiser, Frank S. Benneckendorf, Marc-Michael Barf, Lars Müller, Rainer Bäuerle, Sabina
Hillebrandt, Sebastian Beck, Robert Lovrincic, Eric Mankel, Jan Freudenberg, Daniel Jänsch,
Wolfgang Kowalsky, Annemarie Pucci, Wolfram Jaegermann, Uwe H.F. Bunz, and Klaus Müllen
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.9b01150 • Publication Date (Web): 15 May 2019
Downloaded from http://pubs.acs.org on May 16, 2019
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 10
Chemistry of Materials
1
2
3
4
5
6
7
8
9
N-Type Doping of Organic Semiconductors: Immobilization
via Covalent Anchoring
Patrick Reiser1,2,‡, Frank S. Benneckendorf2,3,‡, Marc-Michael Barf2,4, Lars Müller2,4, Rainer Bäuerle2,5, Sabina
Hillebrandt2,5,†, Sebastian Beck2,5, Robert Lovrincic2,4, Eric Mankel1,2, Jan Freudenberg2,3, Daniel Jänsch2,3,
Wolfgang Kowalsky2,4,5, Annemarie Pucci2,5, Wolfram Jaegermann1,2, Uwe H. F. Bunz2,3, Klaus Müllen2,6,*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1 Materials Science Department, Surface Science Division, TU Darmstadt, Otto-Berndt-Straße 3, 64287 Darmstadt, Germany
2 InnovationLab, Speyerer Straße 4, 69115 Heidelberg, Germany
3 Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
4 Institute for High-Frequency Technology, TU Braunschweig, Schleinitzstraße 22, 38106 Braunschweig, Germany
5 Kirchhoff Institute for Physics, Heidelberg University, Im Neuenheimer Feld 227, 69120 Heidelberg, Germany
6 Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
ABSTRACT: Electrical doping is an important tool in the design of organic devices to modify charge carrier concentration in and Fermi-level
positon of organic layers. The undesired diffusion of dopant molecules within common transport materials adversely affects both, lifetime and
device performance. To overcome this drawback, we developed a strategy to achieve immobilization of dopants through their covalent
attachment to the semiconductor host molecules. Derivatization of the commonly employed n-type dopant 2-(2-methoxyphenyl)-1,3-
dimethyl-2,3-dihydro-1H-benzoimidazole (o-MeO-DMBI) with a phenylazide enables the resulting o-AzBnO-DMBI to photochemically
generate a reactive nitrene, which subsequently binds covalently to the host material, 6,6-phenyl-C61-butyric acid methyl ester (PCBM). Both
the activation and addition reaction are monitored by mass spectrometry as well as optical and photoelectron spectroscopy. A suppression of
desorption and a decrease in volatility of the DMBI derivative in UHV was observed after activation of a bilayer structure of PCBM and
o-AzBnO-DMBI. Electrical measurements demonstrate that the immobilized o-AzBnO-DMBI can i) dope the PCBM at conductivities
comparable to values reported for o-MeO-DMBI in literature and ii) yield improved electrical stability measured in a lateral two terminal device
geometry. Our immobilization strategy is not limited to the specific system presented herein, but should also be applicable to other organic
semiconductor-dopant combinations.
conjugated polymers compared to molecular host materials.19–21
Even though the dopant lacks diffusion in the host matrix, this might
INTRODUCTION
The applications and benefits of electrical or electrochemical
doping in organic semiconductors are manifold.1,2 Suitable dopants
increase the conductivity of organic layers by several orders of
magnitude, for example in charge transport layers of organic light
emitting diodes (OLEDs).3 Promising thermoelectric devices can be
realized with doped conjugated polymers due to their low thermal
conductivity.4–6 Most importantly, doped layers enable quasi-Ohmic
contacts to metal electrodes which greatly improves charge carrier
injection and mitigates contact resistances due to offsets in energy
level alignment.7–9 A prerequisite for applying doped layers in
dedicated device stacks is stability, since diffusion of dopants into
adjacent active layers has been identified as a degradation
mechanism (e.g. exciton quenching), detrimental to photo-active
devices.10–14 Moreover diffusion of dopants can be problematic in
organic hole transport layers for planar perovskite solar cells.15
Consequently, stable and efficient doping of organic materials is of
high interest in present-day device fabrication. Replacing atomic
dopants such as halides or alkali metals by small molecular p- and n-
type dopants reduces volatility significantly.16 However, some host-
dopant systems still exhibit diffusivity of organic electron
donors/acceptors.17,18 This effect is more pronounced within
change when an electric field is applied. Recently, the migration of
molecular dopants in an electric field has been reported in poly(3-
hexylthiophene) (P3HT), and considered as drift effect.22 To
suppress dopant diffusion and drift, certain strategies have been
proposed and demonstrated, e.g. introduction of a dense dopant
blocking interlayer or filling of dopant pathways using a second
redox-inactive transport material.23–25 However, processing
becomes more difficult and possible complications concerning
charge transport or energy level alignment arise from the additional
dopant blocking materials.26 Furthermore, polar side chains were
introduced to a polymer to increase its dopant affinity, yielding an
improved thermal stability of molecular dopants and a higher
melting temperature.25 Larger molecular dopants offer a better
morphological stability as demonstrated by thermally activated
diffusion of dopants in molecular host systems.27 Beside physical
modifications like size or morphology, increased intermolecular
interaction also reduces the mobility of dopants. These include
dispersion force, dipole-dipole interactions, π-π interactions or even
hybridization.28 Charged dopants are much less diffusive than
neutral dopants due to electrostatic interactions.21,29 A covalent
bond between the dopant and the host molecule would allow much
ACS Paragon Plus Environment

Chemistry of Materials
Page 2 of 10
stronger “fixation” and ideally to an immobilization of both neutral and a benzyloxy functional group, respectively, and investigate their
1
2
3
4
5
6
7
8
and charged dopants. A pre-modification of the host with a
functional group that introduces self-doping was already used to
localize dopants in assembled thin films.30,31 For covalent bond
formation after blending, host and dopant have to have
complementary functional groups.32–34 This concept requires
modification of each transport material to fit the corresponding
dopant, which is not practical given the plethora of materials in use.
In order to be generally compatible with a wide scope of host
material, an anchor group for dopants needs an unspecific binding
method, e.g. by attachment to aliphatic C-H or olefinic C=C bonds
present in almost any organic semiconductor without introduction
of severe degradation or traps. A practical solution for this issue can
be derived from photochemical cross-linking as desolubilization
protocol:35 The utilization of various bis-azides for cross-linking,
thus preventing polymer strands from re-dissolution in solution-
processed heterostructures, is not limited to one specific
polymer.36,37 The azide is activated by deep-ultraviolet light (UV,
254 nm), inducing photolysis and generating reactive singlet
nitrenes. When properly substituted, these predominantly insert
into aliphatic CH-bonds and side-reactions38 involving triplet
pathways, aromatic insertion, attack upon other functional groups
or ketenimine ring expansion are suppressed.36,39,40 The latter is
found to be dominating only in solution for non-fluorinated aryl
azides,39,41 whereas in thin films or matrices, C-H insertion
prevails.42–45
doping and anchoring properties in blends with PCBM. Infrared and
photoelectron spectroscopy are employed to analyze the CH-
insertion or cycloaddition reaction and conductivity measurement
to verify doping with and without UV trigger. High-resolution mass
spectrometry verifies a covalent linkage of the dopant to PCBM. Our
immobilization strategy via nitrene generation is generally
applicable and not limited to a specific host-dopant system.
Furthermore, it is destined to improve stability, lifetime and
performance of doped organic devices by ideally suppressing both
detrimental diffusion and drift effects.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
RESULTS AND DISCUSSION
Synthesis and Immobilization Reactions
DMBI dopants are easily accessible via simple condensation
reactions according to Scheme 1. Introduction of a phenylazide is
achieved after etherification of salicylaldehyde employing 1-azido-4-
(bromomethyl)benzene (1) in DMF at room temperature
furnishing compound 2 in 85% yield, followed by condensation with
N1,N2-dimethylbenzene-1,2-diamine to afford o-AzBnO-DMBI in
40% yield. The characteristic IR absorption band of the azde
stretching vibration at 2109 cm-1 (see Figure 4 b and Figure S11)
confirms the azide functionalization.57
1,3-Dimethyl-2-phenyl-2,3-dihydro-1H-benzoimidazole
(DMBI) derivatives are effective, air-stable and thus easy-to-handle,
solution-processable n-type dopants. DMBIs are often used to dope
n-channel semiconductors, preferably PCBM46–51 or n-type
polymers.47,52 However, they seem to be more effective, in terms of
achieved maximum conductivity, in combination with PCBM than
with polymers like P(NDI2OD-T2) due to the poor miscibility of
dopant and polymer.6,47,53 Although the doping mechanism of
DMBI derivatives in, for example, PCBM has been investigated, it is
still under debate.48,51,54 The initial step either involves a hydride
transfer to the host or a hydrogen radical transfer with a subsequent
electron transfer – both mechanisms lead to the generation of
cationic DMBIs and PCBM radical anions responsible for the
doping effect.
H
N3
N3
OH
N
O
N3
N
H
HOAc
K2CO3
O
DMF, rt,
16 h
85%
DCM, rt,
45 min
40%
O
N
Br
O
N
2
1
o-AzBnO-DMBI
H
N
OH
O
N
H
HOAc
K2CO3
O
N
O
DMF, rt,
16 h
88%
DCM, rt,
30 min
52%
Br
O
N
In this work, we report the successful anchoring of an azide-
functionalized DMBI-based dopant in PCBM, employing a non-
specific immobilization strategy through covalent attachment to the
host while retaining its dopant strength compared to a non-
functionalized counterpart. We detail the synthesis of
o-AzBnO-DMBI and o-BnO-DMBI, in which the ortho-methoxy
group of o-MeO-DMBI55,56 is substituted by a (4-azidobenzyl)oxy)
3
4
o-BnO-DMBI
Scheme 1. Synthesis of o-AzBnO-DMBI and o-BnO-DMBI.
ACS Paragon Plus Environment

Page 3 of 10
Chemistry of Materials
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. XPS measurements of the N 1s core-level spectra of thermally annealed PCBM films doped with o-BnO-DMBI and o-AzBnO-DMBI in (d)-
(f). A schematic cartoon of N 1s peak components and their transformation in (a)-(c). Recorded spectra of PCBM doped with o-BnO-DMBI in (d)
for different annealing temperatures. The N 1s signal of PCBM doped with o-AzBnO-DMBI is shown in (e) together with the spectrum measured after
UV-activation and after annealing of the UV-activated film to 320 °C. A direct annealing of the o-AzBnO-DMBI:PCBM film without UV-treatment is
given in (f). The assignment of peak composition in (d)-(f) is inferred from contributions of DMBI in green and from the azide in blue. The expected
peak components of DMBI upon charge transfer and decomposition of pure azide are sketched in (a) and (b), respectively. For o-AzBnO-DMBI both
reactions of (a) and (b) can occur as illustrated in (c). The peak shapes of (a) and (b) are fitted to the data in (e)-(f) using a constrained model (see SI
for details). In the component fit, there is already a considerable fraction of charged dopants in (d)-(f) and possibly dissociated azide in (e) and (f) at
room temperature. The initial film thickness at room temperature is 15 nm, and changes in (d)-(f) for higher temperatures.
To elucidate the influence of the azide group on immobilization,
we synthesized the non-azido functionalized analogue and thus non-
immobilizable o-BnO-DMBI employing benzyl bromide (3) for the
Williamson ether synthesis. Both new dopants were isolated after
crystallization from petroleum ether/methanol or DCM/hexane,
respectively. The obtained colorless single crystals were suitable for
X-ray crystal analyses, unambiguously proving their structure (see
Supporting Information). In order to optimize the processing
parameters, we studied the stability of the newly synthesized
dopants as well as the literature known o-MeO-DMBI in solution
(see Supporting Information, Figure S13). NMR spectroscopy
revealed that the dopants are only fairly stable in solution: after one
day at ambient conditions (sunlight and air) in chloroform, oxidized
species can be seen. However, the dopant appears to be stable for
processing within several hours. In the solid state at -10°C however,
no degradation was observed over months.
S14).42,58 Irradiation at 254 nm excites the azide and induces nitrene
generation.42,45 Throughout this work, this wavelength is used to
initiate the immobilization process. Thermogravimetric analysis
(see Figure S15) of o-AzBnO-DMBI shows irreversible mass loss at
117 °C corresponding to the extrusion of nitrogen. During
additional heating/cooling cycles below the decomposition
temperature of 240 °C no further mass loss is observed. Similar to
the azide-functionalized dopant, o-BnO-DMBI exhibits a rather low
melting point at 108 °C (86 °C for o-AzBnO-DMBI) and
decomposes at 200 °C. To achieve maximum doping effects for the
host:DMBI blend annealing at 75°C is required.48 Thus,
o-AzBnO-DMBI is stable enough to test doping of the PCBM host
upon thermal treatment.
In the following, we provide spectroscopic data to corroborate
successful anchoring of the o-AzBnO-DMBI dopant. From X-ray
photoelectron spectroscopy (XPS) core-level spectra we gain
insight into the activation mechanism of both the dopant and the
anchor group as well as possible decomposition reactions. In order
to additionally test the thermal stability of the DMBI derivative in
the blend we annealed thin films of high doping concentration (50
In acetonitrile, the UV-vis spectrum of o-BnO-DMBI exhibits
absorption features at λ = 221 nm, 274 nm and 313 nm, whereas for
o-AzBnO-DMBI an additional absorption band at 253 nm is
detected and attributed to the azide functional group (Figure
ACS Paragon Plus Environment

Chemistry of Materials
Page 4 of 10
mol%) in ultra-high vacuum (UHV, 10-9 mbar) and measured XPS
completely resistant to desorption after UV-activation (see SI for
1
2
3
4
at each temperature step (for details see Figure S20). The N 1s
emission of o-AzBnO-DMBI contains a contribution of the
functional azide group and the DMBI core, illustrated in Figure 1c in
blue (azide) and in green (DMBI).
details). A similar trend is observed for thicker bilayer structures,
which means that in pure dopant films o-AzBnO-DMBI may also
react with neighboring dopants (see Figure S19).
5
6
7
8
To assign the N 1s peak components of o-AzBnO-DMBI
correctly, it is instructive to analyze spectral changes expected from
DMBI and the azide group, sketched in Figure 1a and 3b,
respectively. The spectra of o-BnO-DMBI in Figure 1d only exhibit
peak components of DMBI core located at 402.5 eV and 400 eV. We
identify the nitrogen emission at 402.5 eV as charged dopants having
formed a radical and transferred an electron to PCBM. This
assignment agrees with the N 1s emission of the ionic DMBI salt at
ca. 402.5 eV reported in literature.59 With rising temperature the
peak component at 400 eV transforms into charged DMBI species at
402.5 eV, which correlates with an increase in conductivity observed
for annealed PCBM films doped with DMBI. The N 1s signal
reported for pure azides sketched in Figure 1b has three components
whereas two components coincide between 400 eV and 402 eV
leaving a single peak component isolated at high binding
energies.60,61 From density functional theory (DFT) calculations it is
known that the central nitrogen in R-N=Nδ+=Nδ- is electron-
deficient and has an N 1s level at high binding energies.62 Azide
decomposition triggered by UV light or thermal energy leads to
nitrogen release and ideally to the generation of singlet nitrene,
which can then form new carbon nitrogen bonds. Regarding the
azide in o-AzBnO-DMBI, the peak component at 405 eV in Figure
1e was therefore assigned to the central nitrogen and the
contribution of the lateral nitrogen atoms to be between 400 eV and
402 eV. Upon UV activation at room temperature in Figure 1e, the
former peak at 405 eV vanishes completely, reducing the peak area
around 402 eV and increasing at 400 eV. During annealing of the
doped PCBM film in Figure 1f the N 1s emission at 405 eV
disappears above 100 °C suggesting that the azide group becomes
thermally activated and produces a nitrene. As a result, carbon
nitrogen bonds are formed causing an additional N 1s emission at
400 eV which persists at temperatures higher than 300 °C. At the
same time, the DMBI part of o-AzBnO-DMBI donates an electron,
similar to o-BnO-DMBI, thus transferring the peak component at
400 eV into the charged DMBI species at 402.5 eV. When reaching
higher temperature in UHV, pure and o-BnO-DMBI-doped PCBM
completely evaporates from the substrate at 300 °C and 200 °C,
respectively. Interestingly, the film doped with o-AzBnO-DMBI is
stable even beyond 300 °C and only a partial decrease in coverage is
observed. However, from the N 1s emission we infer that the N 1s
peak component at 402.5 eV, attributed to charged dopants,
disappears almost completely above 210 °C leaving only carbon-
nitrogen-bonds at 400 eV when approaching 320 °C in Figure 1 (for
details see Figure S20).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. MALDI high-resolution mass spectrometry data are plotted for
a blend of PCBM and o-AzBnO-DMBI in (a) and after UV-treatment in
(b) on a log-scale. In principle, the MALDI laser used for desorption can
cause azide decomposition but we find a pronounced main peak at 370.2
m/z assigned to intact o-AzBnO-DMBI in (a). Comparable ESI spectra
can be found in Figure S24-S26. Only trace amounts of unfavorable
amine products are detected at 344.2 m/z in both (a) and (b) relative to
o-AzBnO-DMBI at 370.2 m/z.
At room temperature, pure and untreated o-AzBnO-DMBI is
volatile under UHV conditions as observed by XPS. However, when
o-AzBnO-DMBI is sequentially processed on top of PCBM in
monolayer-range thickness, a desorption experiment in UVH at
room temperature reveals that the anchoring of o-AzBnO-DMBI
also appears to be quantitative, rendering o-AzBnO-DMBI
ACS Paragon Plus Environment

Page 5 of 10
Chemistry of Materials
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Figure 3. a) Conductivities of pure and doped PCBM layers with a molar doping ratio of 10:1 as cast, after UV treatment and after subsequent annealing.
b) UPS spectra of pure and doped PCBM layers with a molar doping ratio of 10:1 as cast, after UV treatment and after subsequent annealing. The
secondary electron cutoff with respect to the vacuum level as well as the homo onset with respect to the Fermi level are given. c) Calculated energy
levels of pure and doped PCBM layers with a band gap of 2.4 eV.
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Concerning the anchoring mechanism, it is known that azides
Doping and Functional Characterization
react with fullerenes in a 1,3-dipolar [3+2] cycloadditions affording
The conductivity measurements were performed under nitrogen
triazolines,63,64 which, upon thermal treatment, undergo loss of
on pure and doped PCBM layers (host-to-dopant ratio: 10:1),
nitrogen,65,66 or [2+1] cycloaddition with nitrenes yield
spuncast from chlorobenzene onto pre-structured silver contacts on
aziridinofullerenes or azafulleroids.67,68 Additionally, CH-insertion
glass substrates (Figure 3a and Figure S17). Whereas neat PCBM
into the alkyl chains of PCBM, though much less probable, may
thin films exhibit conductivities in the range of 10-6 S/m, this
occur. To demonstrate covalent attachment of the dopant to the
characteristic value rises up to 0.1 S/m and 0.01 S/m for as-cast films
host, blends of o-AzBnO-DMBI and PCBM were analyzed by
doped with o-AzBnO-DMBI and o-BnO-DMBI, respectively. A
electrospray-ionization (ESI) and matrix-assisted laser
final annealing step for doped films at 75 °C increases the
desorption/ionization
(MALDI)
high-resolution
mass
conductivity further to 1 S/m. After UV-treatment (254 nm) of as-
cast films, the conductivities of the doped PCBM layers decrease by
roughly half an order of magnitude in comparison to as-cast blends.
The subsequent thermal treatment (1 h at 75°C) increases the
conductivities for both dopants by more than two orders of
magnitude to 1 S/m. In total this is a gain of six orders of magnitude
compared to neat PCBM layers (see Figure 3a).
spectrometry. We prepared blends of PCBM and o-AzBnO-DMBI
at 25 mol% in a solution of chlorobenzene which were subsequently
dried in vacuo. Azide activation was achieved by either annealing at
135 ° C or UV-activation of spin-cast thin films, which were
redissolved and the material dried afterwards. Whereas no [3+2]
cycloaddition products are found after simple blending, additional
peaks of covalent PCBM-nitrene adducts at 1253.2 m/z (attributed
to [PCBM+(o-AzBnO-DMBI)-H-N2]+) are detected after heating
to 135 °C (thermal azide generation) or photochemical activation
(Figure 2 and Figure S24, S26). Photochemical activation is the
more benign method as in the ESI spectra (Figure S25)
fragmentation of the ether bond within the thermal activated blends
is detected. We find comparably small mass peaks for amines (these
may also be a fragment of mass spectroscopy created during
ionization)69,70 and unreacted azide from the UV-activated blends
(Figure 2). We attribute the latter to the slightly modified sample
preparation for mass spectroscopy because IR- and XPS experiments
(Figure 4 and 3) demonstrate quantitative azide photolysis.
UV-photoelectron spectroscopic (UPS) measurements of
corresponding PCBM layers on silicon are presented in Figure 3b.
The secondary electron cutoffs of o-AzBnO-DMBI-doped PCBM
reveal strong shifts which translate to a reduction of the work
function of ca. 300 meV compared to the neat PCBM layer.
Additionally, in doped layers the highest occupied molecular orbital
(HOMO) broadens and the HOMO maximum shifts by 250 meV
to higher binding energies compared to undoped PCBM, and is
accompanied by a shift of the core-level emission lines (see Figure
S19). For a comparison, Naab et al. observed a Fermi-level shift of
500 meV in a PCBM blend with 1 wt% o-MeO-DMBI on ITO.51
ACS Paragon Plus Environment

Chemistry of Materials
Page 6 of 10
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. a) I-V curves of annealed layers as cast and after UV treatment. b) Relative IR transmission spectra of 30 nm thick pure and doped PCBM
layers with a molar doping ratio of 10:1. The spectra were measured on as cast layers and after UV treatment as given in the legend. Dividing of the
spectra after the UV treatment by the as cast spectra reveal the relative spectral change caused by the UV treatment. The vibrational mode of the azide
group at 2109 cm-1 is marked in (b) and strongly reduced by the UV treatment.
The Fermi-level shift goes along with an increase of free charge
carrier concentration and thus leads to an increased conductivity
revealing a strong n-type doping effect of both DMBI derivatives in
PCBM. Annealing of the thin film results in an additional shift of the
Fermi-level towards the LUMO of ca. 50-100 meV for oAzBnO-
DMBI arriving at a total 350-400 meV shift. Furthermore, we find a
broadening of the emission of the HOMO level, yielding an increase
of tail states for doped PCBM films. The results of the UPS
measurements were used to calculate the energy level diagrams of
pure and doped PCBM layer that are depicted in Figure 3c),
assuming a constant band-gap of ca. 2 - 2.5 eV.71–73
before and after UV exposure, given in Figure 4b, do not show an
oxidation of the PCBM bulk material meaning that the observed
oxidation takes place only at the surface. Unfortunately, this hinders
the further evaluation of the UV treated doped PCBM layers by UPS
since the observed surface degradation strongly influences the
measured Fermi-level position. IR transmission measurements of
PCBM layers doped with o-AzBnO-DMBI before and after UV
treatment are presented in Figure 4b. (See SI for additional spectra).
Due to the doping concentration of 10 mol%, most of the observed
vibrational modes stem from PCBM and fail to reveal a change
caused by the UV treatment. Only the characteristic vibrational
mode of the dopant’s azide group at 2109 cm-1 vanishes completely,
revealing a quantitative activation and dissociation of the azide by
UV light.
Figure 4a shows I-V curves of doped o-AzBno-DMBI and
o-Bno-DMBI PCBM layers as-cast and after UV treatment. At high
electric field strength, the untreated films including o-AzBnO-
DMBI features pronounced rise and subsequent fall-off in current.
As a result, the I-V curve displays a distinct hysteresis, which can be
also observed when repeating the cycle (slightly shifted to higher
voltages). This can be explained either by contact modification
and/or by ionic migration. A drift of charged dopant molecules away
from a contact causes a similar hysteresis in IV curves which was
found for films of poly(3-hexylthiophen-2,5-diyl) (P3HT) doped
CONCLUSION
In this work, we detail the synthesis of o-AzBnO-DMBI, a
derivative of the literature known o-MeO-DMBI. An azidophenyl
group is introduced to DMBI by etherification of salicylaldehyde
employing 1-azido-4-(bromomethyl)benzene and a subsequent
condensation with N1,N2-dimethylbenzene-1,2-diamine. The
modification of DMBI with a reactive azide aims at providing a
universally applicable anchor-like functional group which should be
able to covalently bind to a wide scope of common organic
semiconductors. By creating a covalent bond with the host material
the dopant is expected to be immobilized or at least rendered
significantly less mobile, which ideally reduces problems in devices
arising from diffusion or drift of dopants. In an exemplary study, o-
AzBnO-DMBI was blended with PCBM and activated by UV light
in order to generate highly reactive nitrenes to ultimately form
covalent carbon-nitrogen bonds between PCBM and the dopant.
The azide activation was monitored by infrared- and photoelectron
spectroscopy. High resolution mass spectrometry reveals addition
products, firmly demonstrating the covalent attachment of the
dopant to PCBM molecules. The thermal stability of o-AzBnO-
DMBI in the blend was tested by annealing thin films of high doping
with
the
p-dopants
2,3,5,6-tetrafluoro-7,7,8,8-
tetracyanoquinodimethane (F4TCNQ) and molybdenum tris[1-
(methoxycarbonyl)-2-(trifluoromethyl)-ethane-1,2-dithiolene]
(Mo(tfd-CO2Me)3)).22 On the other hand, the I-V curve of a o-
AzBnO-DMBI doped layer that was UV treated (followed by a final
annealing step) display no or reduced hysteresis on average. This
observation is a first indication for a successful dopant
immobilization after nitrene generation. Moreover, hysteresis
persists in o-BnO-DMBI-doped and UV-treated PCBM, suggesting
that the observed characteristic is not due to changes in morphology
during UV irradiation but reactions of o-AzBnO-DMBI.
The HOMO level of PCBM broadens after UV exposure which is
attributed to an oxidation of the thin film surface most likely from
residual oxygen in the glovebox triggered by UV light (measured by
XPS in Figure S18). IR transmission measurements of PCBM layers
ACS Paragon Plus Environment

Page 7 of 10
Chemistry of Materials
using the Semiconductor Parameter Analyzer 4155C by Agilent
concentration in UHV and by measuring temperature dependent
1
2
3
4
5
6
7
8
XPS. We find that the activated dopant renders the doped film more
resistant to desorption when approaching the desorption
temperature of PCBM in UHV. At room temperature activation of
o-AzBnO-DMBI in a bilayer structure was shown to prevent
desorption from PCBM under UHV. IV-measurements further
prove that UV-activated o-AzBnO-DMBI maintains its doping
properties giving rise to conductivities typical for blends of DMBI
and PCBM. At high electric field strength, the UV-activated doped
PCBM films show no or neglectable hysteresis, but a pronounced
hysteresis is observed if o-AzBnO-DMBI is not exposed to UV light.
The increased electrical stability can be explained by a suppression
of dopant drift due to anchoring of the dopant to PCBM after
activation.
Technologies which reads out corresponding currents for
conductivity determination. Conductivities were then calculated
from a set of at least three different samples.
Photoelectron spectroscopy. Photoelectron spectroscopy (PES)
measurements were carried out using a PHI5000 Versa Probe
scanning photoelectron spectrometer which was equipped with a
monochromated Al Kα X-ray source at 1486.7 eV photon energy for
X-ray photoelectron spectroscopy (XPS) and a differentially
pumped helium discharge lamp operated to achieve He-I emission
at 21.2 eV photon energy for ultraviolet photoelectron spectroscopy
(UPS). The focused X-ray spot is approximately 200 μm in diameter
and be moved to a different position on the sample for longer
acquisition in order to avoid radiation damage.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The great advantage of our approach is the use of unspecific
binding of the intermediately generated reactive dopand towards the
host material, offering instant application to a plethora of organic
semiconductors. Although chemical derivatization of dopants,
either n- or p-type, may be challenging due to the instabilities
resulting from their extreme frontier molecular orbital energies,
azide incorporation is possible and has the potential to reduce
undesired drift and diffusion in multilayer stacks of OLEDs or OPV
and can be applied for p-n homo-junctions based on polymers. The
appropriate chemical derivatization of p-type dopants such as
F4TCNQ and F6TCNNQ is on-going in our laboratories.
Mass spectrometry. The mass spectra were recorded using the
following instruments: JEOL JMS-700 magnetic sector (EI); Bruker
ApexQehybrid 9.4
T
FT-ICR (ESI, DART); Finnigan
LCQquadrupole ion trap (DART); Bruker Autoflex Speed
(MALDI).
ASSOCIATED CONTENT
Supporting Information: Synthesis, NMR spectroscopy, Crystal
structure, IR-spectroscopy, NMR stability test, UV-Vis absorption,
TGA/DSC, ESI Mass spectra, XPS analysis.
EXPERIMENTALS
AUTHOR INFORMATION
Synthesis. All reactions requiring exclusion of oxygen and
moisture were carried out in heat-gun dried glassware under a dry
and oxygen free nitrogen or argon atmosphere using Schlenk and
glovebox techniques. All reagents were obtained from commercial
suppliers and were used without further purification if not otherwise
stated. Deuterated solvents were purchased from Sigma-Aldrich
Laborchemikalien GmbH (Seelze, Germany).
Corresponding Author
* E-mail: muellen@mpip-mainz.mpg.de (K.M.)
Present Addresses
† S.H.: University of St Andrews, North Haugh, St Andrews
KY16 9SS, United Kingdom.
Author Contributions
Sample Preparation for Analysis. If not noted otherwise, the
dopants and PCBM were dissolved separately in chlorobenzene at a
concentration of 5 g L-1 for XPS, 10 g L-1 for IRs/IV-measurements
and were mixed right before spin-coating. The dopants were kept in
solution for 5-10 min but the PCBM solution was stirred over night
at 50 °C. The films were spin-coated at 1000 rpm for 60 s in a
nitrogen glovebox on cut n-doped Silicon wafer for XPS, intrinsic
silicon for IR and on glass for IV-measurements. Activation by UV
light was performed with a mercury-vapor lamp GPH135T5L/4
from Peschl UV-products with a nominal UV-C power of 1.2 W at
254 nm in the glovebox. The penlight was mounted on a stand at a
distance of 10 cm above the sample. We measured a UV-intensity at
the sample position using a Newport power-meter 1936-C equipped
with a photodiode 818-UV plus attenuator and obtain a power
density of 0.8 mW cm-2 for a 20 min exposure time.
‡ These authors contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
We gratefully acknowledge the German Federal Ministry of Education
and Research (BMBF) for financial support within the InterPhase
project (FKZ 13N13659, 13N13656, 13N13657 and 13N13658). We
thankfully acknowledge the mass spectroscopy data acquired by the
mass spectroscopy facility at OCI Heidelberg under the supervision of
Dr. J. Gross. We thank Dr. Frank Rominger for single-crystal X-ray
diffraction of our title compounds
ABBREVIATIONS
IR-spectroscopy. For IR transmission measurements a Fourier-
Transform IR spectrometer (Vertex80v, Bruker) was used. To
prevent absorptions from ambient air (H20 and CO2) the
spectrometer was evacuated to 3 mbar. All samples were recorded
near normal transmittance (7°) with a MCT detector and a
resolution of 4 cm-1. For each spectrum 200 scans were averaged.
1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzoimidazole (DMBI),
2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzoimidazole
(o-MeO-DMBI),
2-(2-(benzyloxy)phenyl)-1,3-dimethyl-2,3-dihydro-1H-
benzoimidazole (o-BnO-DMBI), ; 2-(2-((4-azidobenzyl)oxy)phenyl)-
1,3-dimethyl-2,3-dihydro-1H-benzoimidazole (o-AzBnO-DMBI).
Electrical Measurements. IV measurements were performed
under nitrogen atmosphere at room temperature. For this purpose
finger-like structured silver contacts with channel lengths between
25 µm and 30 µm were used. Voltages were applied on these contacts
REFERENCES
(1)
Lüssem, B.; Riede, M.; Leo, K. Doping of Organic Semiconductors.
Physica Status Solidi (A) Applications and Materials Science. Wiley-
Blackwell January 1, 2013, pp 9–43.
ACS Paragon Plus Environment

Chemistry of Materials
Page 8 of 10
(2)
(3)
(4)
Pfeiffer, M.; Leo, K.; Zhou, X.; Huang, J. S.; Hofmann, M.; Werner, A.;
(21)
Reiser, P.; Müller, L.; Sivanesan, V.; Lovrincic, R.; Barlow, S.; Marder,
Blochwitz-Nimoth, J. Doped Organic Semiconductors: Physics and
Application in Light Emitting Diodes. Org. Electron. 2003, 4 (2–3),
89–103.
S. R.; Pucci, A.; Jaegermann, W.; Mankel, E.; Beck, S. Dopant
Diffusion in Sequentially Doped Poly(3-Hexylthiophene) Studied by
Infrared and Photoelectron Spectroscopy. J. Phys. Chem. C 2018, 122
(26), 14518–14527.
Müller, L.; Rhim, S.-Y.; Sivanesan, V.; Wang, D.; Hietzschold, S.;
Reiser, P.; Mankel, E.; Beck, S.; Barlow, S.; Marder, S. R.; et al. Electric-
Field-Controlled Dopant Distribution in Organic Semiconductors.
Adv. Mater. 2017, 1701466--n/a.
Mor, G. K.; Jones, D.; Le, T. P.; Shang, Z.; Weathers, P. J.;
Woltermann, M. K. B.; Vakhshouri, K.; Williams, B. P.; Tohran, S. A.;
Saito, T.; et al. Contact Doping with Sub-Monolayers of Strong
Polyelectrolytes for Organic Photovoltaics. Adv. Energy Mater. 2014,
4 (13), 1400439--n/a.
Dai, A.; Wan, A.; Magee, C.; Zhang, Y.; Barlow, S.; Marder, S. R.;
Kahn, A. Investigation of P-Dopant Diffusion in Polymer Films and
Bulk Heterojunctions: Stable Spatially-Confined Doping for All-
Solution Processed Solar Cells. Org. Electron. 2015, 23, 151–157.
Li, J.; Rochester, C. W.; Jacobs, I. E.; Aasen, E. W.; Friedrich, S.;
Stroeve, P.; Moulé, A. J. The Effect of Thermal Annealing on Dopant
Site Choice in Conjugated Polymers. Org. Electron. 2016, 33, 23–31.
Ishii, H.; Sugiyama, K.; Ito, E.; Seki, K. Energy Level Alignment and
Interfacial Electronic Structures at Organic/Metal and
Organic/Organic Interfaces. Adv. Mater. 1999, 11 (8), 605–625.
Li, J.; Rochester, C. W.; Jacobs, I. E.; Friedrich, S.; Stroeve, P.; Riede,
M.; Moulé, A. J. Measurement of Small Molecular Dopant F4TCNQ
and C60F36 Diffusion in Organic Bilayer Architectures. ACS Appl.
Mater. Interfaces 2015, 7 (51), 28420–28428.
1
2
3
4
5
6
7
8
Pfeiffer, M.; Fritz, T.; Blochwitz, J.; Nollau, A.; Plönnigs, B.; Beyer, A.;
Leo, K. Controlled Doping of Molecular Organic Layers: Physics and
Device Prospects. In Advances in Solid State Physics 39; Kramer, B.,
Ed.; Springer Berlin Heidelberg: Berlin, Heidelberg, 1999; pp 77–90.
Bubnova, O.; Khan, Z. U.; Malti, A.; Braun, S.; Fahlman, M.; Berggren,
M.; Crispin, X. Optimization of the Thermoelectric Figure of Merit in
the Conducting Polymer Poly(3,4-Ethylenedioxythiophene). Nat.
Mater. 2011, 10, 429.
Hynynen, J.; Kiefer, D.; Muller, C. Influence of Crystallinity on the
Thermoelectric Power Factor of P3HT Vapour-Doped with
F4TCNQ. RSC Adv. 2018, 8 (3), 1593–1599.
Liu, J.; Qiu, L.; Portale, G.; Koopmans, M.; ten Brink, G.; Hummelen,
J. C.; Koster, L. J. A. N-Type Organic Thermoelectrics: Improved
Power Factor by Tailoring Host–Dopant Miscibility. Adv. Mater.
2017, 29 (36), 1701641--n/a.
Shen, Y.; Hosseini, A. R.; Wong, M. H.; Malliaras, G. G. How To Make
Ohmic Contacts to Organic Semiconductors. ChemPhysChem 2004,
5 (1), 16–25.
Gross, M.; Müller, D. C.; Nothofer, H.-G.; Scherf, U.; Neher, D.;
Bräuchle, C.; Meerholz, K. Improving the Performance of Doped π-
Conjugated Polymers for Use in Organic Light-Emitting Diodes.
Nature 2000, 405 (6787), 661–665.
Ganzorig, C.; Fujihira, M. Improved Drive Voltages of Organic
Electroluminescent Devices with an Efficient P-Type Aromatic
Diamine Hole-Injection Layer. Appl. Phys. Lett. 2000, 77 (25), 4211–
4213.
(22)
(23)
9
(5)
(6)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(24)
(25)
(26)
(27)
(7)
(8)
(9)
(28)
(29)
Sutton, C.; Risko, C.; Brédas, J.-L. Noncovalent Intermolecular
Interactions in Organic Electronic Materials: Implications for the
Molecular Packing vs Electronic Properties of Acenes. Chem. Mater.
2016, 28 (1), 3–16.
(10)
(11)
(12)
(13)
D’Andrade, B. W.; Forrest, S. R.; Chwang, A. B. Operational Stability
of Electrophosphorescent Devices Containing
p and n Doped
Transport Layers. Appl. Phys. Lett. 2003, 83 (19), 3858–3860.
Li, J.; Koshnick, C.; Diallo, S. O.; Ackling, S.; Huang, D. M.; Jacobs, I.
E.; Harrelson, T. F.; Hong, K.; Zhang, G.; Beckett, J.; et al.
Quantitative Measurements of the Temperature-Dependent
Microscopic and Macroscopic Dynamics of a Molecular Dopant in a
Conjugated Polymer. Macromolecules 2017, 50 (14), 5476–5489.
Russ, B.; Robb, M. J.; Brunetti, F. G.; Miller, P. L.; Perry, E. E.; Patel,
S. N.; Ho, V.; Chang, W. B.; Urban, J. J.; Chabinyc, M. L.; et al. Power
Factor Enhancement in Solution-Processed Organic n-Type
Thermoelectrics through Molecular Design. Adv. Mater. 2014, 26
(21), 3473–3477.
Arkhipov, V. I.; Emelianova, E. V; Bässler, H. Quenching of Excitons
in Doped Disordered Organic Semiconductors. Phys. Rev. B 2004, 70
(20), 205205.
Arkhipov, V. I.; Emelianova, E. V; Bassler, H. On the Role of Spectral
Diffusion of Excitons in Sensitized Photoconduction in Conjugated
Polymers. Chem. Phys. Lett. 2004, 383 (1–2), 166–170.
Tyagi, P.; Tuli, S.; Srivastava, R. Study of Fluorescence Quenching
Due to 2, 3, 5, 6-Tetrafluoro-7, 7′, 8, 8′-Tetracyano Quinodimethane
and Its Solid State Diffusion Analysis Using Photoluminescence
Spectroscopy. J. Chem. Phys. 2015, 142 (5), 54707.
Ferguson, A. J.; Kopidakis, N.; Shaheen, S. E.; Rumbles, G. Quenching
of Excitons by Holes in Poly(3-Hexylthiophene) Films. J. Phys. Chem.
C 2008, 112 (26), 9865–9871.
Correa-Baena, J. P.; Tress, W.; Domanski, K.; Anaraki, E. H.; Turren-
Cruz, S. H.; Roose, B.; Boix, P. P.; Grätzel, M.; Saliba, M.; Abate, A.; et
al. Identifying and Suppressing Interfacial Recombination to Achieve
High Open-Circuit Voltage in Perovskite Solar Cells. Energy Environ.
Sci. 2017, 10 (5), 1207–1212.
Parthasarathy, G.; Shen, C.; Kahn, A.; Forrest, S. R. Lithium Doping
of Semiconducting Organic Charge Transport Materials. J. Appl. Phys.
2001, 89 (9), 4986–4992.
Duhm, S.; Salzmann, I.; Bröker, B.; Glowatzki, H.; Johnson, R. L.;
Koch, N. Interdiffusion of Molecular Acceptors through Organic
Layers to Metal Substrates Mimics Doping-Related Energy Level
Shifts. Appl. Phys. Lett. 2009, 95 (9).
Gao, W.; Kahn, A. Controlled P-Doping of Zinc Phthalocyanine by
Coevaporation with Tetrafluorotetracyanoquinodimethane: A Direct
and Inverse Photoemission Study. Appl. Phys. Lett. 2001, 79 (24),
4040–4042.
Jacobs, I. E.; Aasen, E. W.; Oliveira, J. L.; Fonseca, T. N.; Roehling, J.
D.; Li, J.; Zhang, G.; Augustine, M. P.; Mascal, M.; Moule, A. J.
Comparison of Solution-Mixed and Sequentially Processed
P3HT:F4TCNQ Films: Effect of Doping-Induced Aggregation on
Film Morphology. J. Mater. Chem. C 2016, 4 (16), 3454–3466.
Hynynen, J.; Kiefer, D.; Yu, L.; Kroon, R.; Munir, R.; Amassian, A.;
Kemerink, M.; Müller, C. Enhanced Electrical Conductivity of
(30)
(31)
Chen, W.; Jiao, W.; Li, D.; Sun, X.; Guo, X.; Lei, M.; Wang, Q.; Li, Y.
Cross Self-n-Doping and Electron Transfer Model in a Stable and
(14)
(15)
Highly Conductive Fullerene Ammonium Iodide:
A Promising
Cathode Interlayer in Organic Solar Cells. Chem. Mater. 2016, 28 (4),
1227–1235.
Shlyakhtenko, L. S.; Gall, A. A.; Weimer, J. J.; Hawn, D. D.;
Lyubchenko, Y. L. Atomic Force Microscopy Imaging of DNA
Covalently Immobilized on a Functionalized Mica Substrate. Biophys.
J. 1999, 77 (1), 568–576.
Dhal, P. K.; Babu, G. N.; Sudhakaran, S.; Borkar, P. S. Immobilization
of Penicillin Acylase by Covalent Linkage on Vinyl Copolymers
Containing Epoxy Groups. Die Makromol. Chemie, Rapid Commun.
1985, 6 (2), 91–95.
Lobnik, A.; Oehme, I.; Murkovic, I.; Wolfbeis, O. S. PH Optical
Sensors Based on Sol-Gels: Chemical Doping versus Covalent
Immobilization. Anal. Chim. Acta 1998, 367 (1–3), 159–165.
Freudenberg, J.; Jänsch, D.; Hinkel, F.; Bunz, U. H. F. Immobilization
Strategies for Organic Semiconducting Conjugated Polymers.
Chemical Reviews. American Chemical Society June 13, 2018, pp
5598–5689.
Png, R.-Q.; Chia, P.-J.; Tang, J.-C.; Liu, B.; Sivaramakrishnan, S.;
Zhou, M.; Khong, S.-H.; Chan, H. S. O.; Burroughes, J. H.; Chua, L.-
L.; et al. High-Performance Polymer Semiconducting Heterostructure
Devices by Nitrene-Mediated Photocrosslinking of Alkyl Side Chains.
Nat. Mater. 2009, 9, 152.
Cho, N.; Yip, H. L.; Davies, J. A.; Kazarinoff, P. D.; Zeigler, D. F.;
Durban, M. M.; Segawa, Y.; Malley, K. M.; Luscombe, C. K.; Jen, A. K.
Y. In-Situ Crosslinking and n-Doping of Semiconducting Polymers
and Their Application as Efficient Electron-Transporting Materials in
Inverted Polymer Solar Cells. Adv. Energy Mater. 2011, 1 (6), 1148–
(32)
(33)
(16)
(17)
(34)
(35)
(18)
(19)
(36)
(37)
(20)
Molecularly
P-Doped
Poly(3-Hexylthiophene)
through
Understanding the Correlation with Solid-State Order.
Macromolecules 2017, 50 (20), 8140–8148.
ACS Paragon Plus Environment

Page 9 of 10
Chemistry of Materials
1153.
Based
on
Solution-Sheared
Doped
6,13-
(38)
Bräse, S.; Gil, C.; Knepper, K.; Zimmermann, V. Organic Azides: An
Exploding Diversity of a Unique Class of Compounds. Angewandte
Chemie - International Edition. Wiley-Blackwell August 19, 2005, pp
5188–5240.
Poe, R.; Schnapp, K.; Young, M. J. T.; Grayzar, J.; Platz, M. S.
Chemistry and Kinetics of Singlet Pentafluorophenylnitrene. J. Am.
Chem. Soc. 1992, 114 (13), 5054–5067.
Marcinek, A.; Platz, M. S.; Chan, S. Y.; Floresca, R.; Rajagopalan, K.;
Golinski, M.; Watt, D. Unusually Long Lifetimes of the Singlet
Nitrenes Derived from 4-Azido-2,3,5,6-Tetrafluorobenzamides. J.
Phys. Chem. 1994, 98 (2), 412–419.
Leyva, E.; Jennifer, M.; Young, T.; Platz, M. S. High Yields of Formal
CH Insertion Products in the Reactions of Polyfluorinated Aromatic
Nitrenes. J. Am. Chem. Soc. 1986, 108 (26), 8307–8309.
Murase, S.; Shibata, K.; Furukawa, H.; Miyashita, Y.; Horie, K. Large
Photoinduced Refractive Index Increase in Polymer Films Containing
Phenylazide Maintaining Their Transparency and Thermal Stability.
Polym. J. 2003, 35 (2), 203–207.
Bis(Triisopropylsilylethynyl)Pentacene Thin Films. Adv. Mater.
2013, 25 (33), 4663–4667.
Wu, H.-C.; Lee, W.-Y.; Naab, B. D.; Lu, C.; Bao, Z.; Chen, W.-C. N-
Type Doped Conjugated Polymer for Nonvolatile Memory. Adv.
Mater. 2017, 29 (16), 1605166.
1
2
3
4
5
6
7
8
(56)
(39)
(40)
(57)
(58)
Lieber, E.; Rao, C. N. R.; Hoffman, C. W. W.; Chao, T. S. Infrared
Spectra of Organic Azides. Anal. Chem. 1957, 29 (6), 916–918.
Yuan, R. D.; Xue, J. D.; Zheng, X. M. Structural Dynamics of Phenyl
Azide in Light-Absorbing Excited States: Resonance Raman and
Quantum Mechanical Calculation Study. In Chinese Journal of
Chemical Physics; Chinese Physical Society, 2016; Vol. 29, pp 21–30.
Schwarze, M.; Naab, B. D.; Tietze, M. L.; Scholz, R.; Pahner, P.;
Bussolotti, F.; Kera, S.; Kasemann, D.; Bao, Z.; Leo, K. Analyzing the
N-Doping Mechanism of an Air-Stable Small-Molecule Precursor.
ACS Appl. Mater. Interfaces 2018, 10 (1), 1340–1346.
Gouget-Laemmel, A. C.; Yang, J.; Lodhi, M. A.; Siriwardena, A.;
Aureau, D.; Boukherroub, R.; Chazalviel, J. N.; Ozanam, F.; Szunerits,
S. Functionalization of Azide-Terminated Silicon Surfaces with
Glycans Using Click Chemistry: XPS and FTIR Study. J. Phys. Chem.
C 2013, 117 (1), 368–375.
9
(41)
(42)
(59)
(60)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(43)
(44)
Reiser, A.; Leyshon, L. J.; Johnston, L. Effect of Matrix Rigidity on the
Reactions of Aromatic Nitrenes in Polymers. Trans. Faraday Soc.
1971, 67 (0), 2389–2396.
(61)
(62)
Stenehjem, E. D.; Ziatdinov, V. R.; Stack, T. D. P.; Chidsey, C. E. D.
Gas-Phase Azide Functionalization of Carbon. J. Am. Chem. Soc.
2013, 135 (3), 1110–1116.
Reddington, S. C.; Rizkallah, P. J.; Watson, P. D.; Pearson, R.;
Tippmann, E. M.; Jones, D. D. Different Photochemical Events of a
Genetically Encoded Phenyl Azide Define and Modulate GFP
Fluorescence. Angew. Chemie - Int. Ed. 2013, 52 (23), 5974–5977.
Cai, S. X.; Glenn, D. J.; Kanska, M.; Wybourne, M. N.; Keana, J. F. W.
Development of Highly Efficient Deep-UV and Electron Beam
Mediated Cross-Linkers: Synthesis and Photolysis of
Bis(Perfluorophenyl) Azides. Chem. Mater. 1994, 6 (10), 1822–1829.
Kim, S. S.; Bae, S.; Jo, W. H. Performance Enhancement of Planar
Heterojunction Perovskite Solar Cells by N-Doping of the Electron
Transporting Layer. Chem. Commun. 2015, 51 (98), 17413–17416.
Naab, B. D.; Zhang, S.; Vandewal, K.; Salleo, A.; Barlow, S.; Marder, S.
R.; Bao, Z. Effective Solution- and Vacuum-Processed n-Doping by
Dimers of Benzimidazoline Radicals. Adv. Mater. 2014, 26 (25),
4268–4272.
Wei, P.; Oh, J. H.; Dong, G.; Bao, Z. Use of a 1 H -Benzoimidazole
Derivative as an n -Type Dopant and to Enable Air-Stable Solution-
Processed n -Channel Organic Thin-Film Transistors. J. Am. Chem.
Soc. 2010, 132 (26), 8852–8853.
Kwon, G.; Kim, K.; Choi, B. D.; Roh, J.; Lee, C.; Noh, Y. Y.; Seo, S. Y.;
Kim, M. G.; Kim, C. Multifunctional Organic-Semiconductor
Interfacial Layers for Solution-Processed Oxide-Semiconductor Thin-
Film Transistor. Adv. Mater. 2017, 29 (21), 1607055.
Rossbauer, S.; Müller, C.; Anthopoulos, T. D. Comparative Study of
the N-Type Doping Efficiency in Solution-Processed Fullerenes and
Fullerene Derivatives. Adv. Funct. Mater. 2014, 24 (45), 7116–7124.
Naab, B. D.; Guo, S.; Olthof, S.; Evans, E. G. B.; Wei, P.; Millhauser,
G. L.; Kahn, A.; Barlow, S.; Marder, S. R.; Bao, Z. Mechanistic Study
on the Solution-Phase n-Doping of 1,3-Dimethyl-2-Aryl-2, 3-
Dihydro-1H-Benzoimidazole Derivatives. J. Am. Chem. Soc. 2013,
135 (40), 15018–15025.
Lu, M.; Nicolai, H. T.; Wetzelaer, G.-J. J. A. H.; Blom, P. W. M. N-
Type Doping of Poly(p-Phenylene Vinylene) with Air-Stable
Dopants. Appl. Phys. Lett. 2011, 99 (17), 173302.
Kiefer, D.; Giovannitti, A.; Sun, H.; Biskup, T.; Hofmann, A.;
Koopmans, M.; Cendra, C.; Weber, S.; Anton Koster, L. J.; Olsson, E.;
et al. Enhanced N-Doping Efficiency of a Naphthalenediimide-Based
Copolymer through Polar Side Chains for Organic Thermoelectrics.
ACS Energy Lett. 2018, 3 (2), 278–285.
Chen, F. F.; Wang, F. Electronic Structure of the Azide Group in 3-
Azido-3- Deoxythymidine (AZT) Compared to Small Azide
Compounds. Molecules 2009, 14 (7), 2656–2668.
Grösser, T.; Prato, M.; Lucchini, V.; Hirsch, A.; Wudl, F.
Ringexpansion Des Fullerengerüstes Durch Hochregioselektive
Bildung von Diazafulleroiden. Angew. Chemie 1995, 107 (12), 1462–
1464.
Cases, M.; Duran, M.; Mestres, J.; Martín, N.; Solà, M. Mechanism of
the Addition Reaction of Alkyl Azides to [60]Fullerene and the
Subsequent N2extrusion to Form Monoimino-[60]Fullerenes. J. Org.
Chem. 2001, 66 (2), 433–442.
Grösser, T.; Prato, M.; Lucchini, V.; Hirsch, A.; Wudl, F. Ring
Expansion of the Fullerene Core by Highly Regioselective Formation
of Diazafulleroids. Angew. Chemie Int. Ed. English 1995, 34 (12),
1343–1345.
(45)
(63)
(64)
(65)
(46)
(47)
(48)
(49)
(66)
(67)
Hirsch, A. Addition Reactions of Buckminsterfullerene (C60).
Synthesis (Stuttg). 1995, 1995 (08), 895–913.
Nakahodo, T.; Okada, M.; Morita, H.; Yoshimura, T.; Ishitsuka, M.
O.; Tsuchiya, T.; Maeda, Y.; Fujihara, H.; Akasaka, T.; Gao, X.; et al.
[2+1] Cycloaddition of Nitrene onto C60 Revisited: Interconversion
between an Aziridinofullerene and an Azafulleroid. Angew. Chemie -
Int. Ed. 2008, 47 (7), 1298–1300.
Smith, A. B.; Tokuyama, H. Nitrene Additions to [60]Fullerene Do
Not Generate [6,5] Aziridines. Tetrahedron 1996, 52 (14), 5257–
5262.
Knochenmuss, R.; Zenobi, R. MALDI Ionization: The Role of In-
Plume Processes. Chem. Rev. 2003, 103 (2), 441–452.
El-Aneed, A.; Cohen, A.; Banoub, J. Mass Spectrometry, Review of the
Basics: Electrospray, MALDI, and Commonly Used Mass Analyzers.
Applied Spectroscopy Reviews. Taylor & Francis Group April 2009,
pp 210–230.
Yoo, S. H.; Kum, J. M.; Cho, S. O. Tuning the Electronic Band
Structure of Pcbm by Electron Irradiation. Nanoscale Res. Lett. 2011,
6 (1), 1–7.
Chang, R. P. H.; Hains, A. W.; Irwin, M. D.; Marks, T. J.; Buchholz, D.
B. P-Type Semiconducting Nickel Oxide as an Efficiency-Enhancing
Anode Interfacial Layer in Polymer Bulk-Heterojunction Solar Cells.
Proc. Natl. Acad. Sci. 2008, 105 (8), 2783–2787.
Maibach, J.; Mankel, E.; Mayer, T.; Jaegermann, W. The Band Energy
Diagram of PCBM-DH6T Bulk Heterojunction Solar Cells:
Synchrotron-Induced Photoelectron Spectroscopy on Solution
Processed DH6T:PCBM Blends and in Situ Prepared PCBM/DH6T
Interfaces. J. Mater. Chem. C 2013, 1 (45), 7635–7642.
(50)
(51)
(68)
(69)
(70)
(52)
(53)
(71)
(72)
(54)
(55)
Zhu, X. Q.; Zhang, M. T.; Yu, A.; Wang, C. H.; Cheng, J. P. Hydride,
Hydrogen Atom, Proton, and Electron Transfer Driving Forces of
Various Five-Membered Heterocyclic Organic Hydrides and Their
Reaction Intermediates in Acetonitrile. J. Am. Chem. Soc. 2008, 130
(8), 2501–2516.
(73)
Bao, Z.; Himmelberger, S.; Lussem, B.; Naab, B. D.; Salleo, A.;
Vandewal, K.; Wei, P.; Diao, Y. High Mobility N-Type Transistors
ACS Paragon Plus Environment

Chemistry of Materials
Page 10 of 10
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Insert Table of Contents artwork here
10
ACS Paragon Plus Environment