Spectrally Switchable Photodetection with Near-Infrared-Absorbing Covalent Organic Frameworks

Article abstract of DOI:10.1021/jacs.7b06599

Most covalent organic frameworks (COFs) to date are made from relatively small aromatic subunits, which can only absorb the high-energy part of the visible spectrum. We have developed near-infrared-absorbing low bandgap COFs by incorporating donor-accepto

Full text of DOI:10.1021/jacs.7b06599

Article
pubs.acs.org/JACS
Spectrally Switchable Photodetection with Near-Infrared-Absorbing
Covalent Organic Frameworks
Derya Bessinger,† Laura Ascherl,† Florian Auras,*,†,‡ and Thomas Bein*,†
†Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU), Butenandtstraße 5-13, 81377
Munich, Germany
‡Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
S
* Supporting Information
ABSTRACT: Most covalent organic frameworks (COFs) to date
are made from relatively small aromatic subunits, which can only
absorb the high-energy part of the visible spectrum. We have
developed near-infrared-absorbing low bandgap COFs by incorpo-
rating donor−acceptor-type isoindigo- and thienoisoindigo-based
building blocks. The new materials are intensely colored solids with a
high degree of long-range order and a pseudo-quadratic pore
geometry. Growing the COF as a vertically oriented thin film allows
for the construction of an ordered interdigitated heterojunction
through infiltration with a complementary semiconductor. Applying
a thienoisoindigo-COF:fullerene heterojunction as the photoactive
component, we realized the first COF-based UV- to NIR-responsive
photodetector. We found that the spectral response of the device is reversibly switchable between blue- and red-sensitive, and
green- and NIR-responsive. To the best of our knowledge, this is the first time that such nearly complete inversion of spectral
sensitivity of a photodetector has been achieved. This effect could lead to potential applications in information technology or
spectral imaging.
extended molecules, shifting the building block absorption into
the NIR cannot be achieved by simply extending the length of
the π-conjugated backbone. However, combining electron-rich
and -deficient moieties within the same building block can lead
to additional charge-transfer transitions at energies well below
the fundamental π−π* transition.25
INTRODUCTION
■
Constructing covalent organic frameworks (COFs) from rigid
organic building blocks has opened a synthetic route to a broad
range of tailor-made porous materials,1−3 whereby key
properties such as the pore structure, optical properties and
electronic coupling between the individual subunits can be
tuned via the selection of suitable building blocks.4−6 The
materials realized this way offer a unique combination of high
thermal and mechanical stability,7 very high surface areas,8,9 and
high density and accessibility of the functional organic building
blocks,10 thus rendering them suitable for potential applications
in gas storage and separation,11 catalysis and photocatalysis,12,13
and optoelectronics.14−16
The geometry of stacked two-dimensional (2D) COFs can
be designed to tune the π-overlap between the individual
layers,17,18 thus creating conductive columns and/or facilitating
long-range exciton transport.19−21 Initial studies have shown
that COFs can act as the active component in interdigitated
heterojunction photovoltaic devices.22−24 Due to the limited
absorption capabilities of the building blocks used in these
studies, however, the devices could only harvest light in the
blue and green spectral regions with appreciable quantum
efficiency. Extension of the absorption capabilities into the red
and near-infrared (NIR) spectral regions that encompass most
of the solar photons would therefore be highly desirable.
Since the maximum length of COF building blocks to date is
limited to only 1−2 nm due to the increasing flexibility of more
One of the most effective components in this context is the
highly electron-deficient isoindigo (II), an isomer of the
naturally occurring indigo dye. Pairing isoindigo with an
appropriate electron-rich counterpart leads to a strong
intramolecular donor−acceptor charge delocalization in con-
jugated polymeric semiconductors, hence shifting the absorp-
tion onset well into the NIR regime.26 Bulk heterojunction
solar cells with isoindigo-based low-band gap copolymers
recently exceeded a power conversion efficiency of 9% with
very high short-circuit currents of above 17 mA cm−2.27 The
planarity and the highly polar nature of the isoindigo unit
facilitate aggregation and give rise to exceptionally crystalline
polymers, leading to high charge carrier mobilities and thus
rendering isoindigo-containing polymers interesting candidates
for organic field-effect transistor applications.28,29 Given these
excellent electronic and optoelectronic properties, it would be
highly desirable to be able to incorporate and study isoindigo-
Received: June 25, 2017
© XXXX American Chemical Society
A
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Figure 1. (a) Co-condensation of 1,3,6,8-tetrakis(4-aminophenyl)pyrene (Py) with 2 equiv of the (thieno-)isoindigo-bridged dialdehydes pII, pTII,
and tTII leads to the formation of the respective imine-linked 2D COFs. (b) The cut-out of the simulated Py-pII COF structure reveals that the pII
building block is not entirely flat. Steric repulsion causes a rotation of the terminal phenyls vs the isoindigo core. Additionally, the repulsion between
the ketones and adjacent hydrogen atoms leads to a slight distortion of the core itself. (c) These steric constraints are considerably relaxed when the
benzene rings are replaced by thiophenes, resulting in a planar thienoisoindigo core. While the terminal phenyl rings remain slightly rotated vs the
core in the case of pTII, exchanging them for thiophenes (d) yields the virtually planar tTII building block.
based building blocks in the precisely defined environment of a
COF.30
In solution, the optical absorption spectrum of the pII
building block exhibits two main absorption bands that are
typical for donor−acceptor molecules (Supporting Information
(SI), Figure S5a). The band at 370−470 nm has been
attributed to the isoindigo π−π* transitions, whereas the lower-
energy band between 470 and 620 nm is due to an
intramolecular charge transfer (ICT) between the electron-
deficient isoindigo moiety and the more electron-rich phenyl-
enes.31 The optical band gap, estimated from the corresponding
Tauc plot for a direct allowed transition, is 2.06 eV (SI, Figure
S5b).
Given the geometry of the building block (Figure 1b) and
the strong tendency of isoindigo-based molecules to form
closely packed, slightly offset cofacial aggregates,32 the
construction of a geometrically compatible framework is crucial
for obtaining a highly crystalline COF. Force-field- and density
functional theory (DFT)-based simulations indicate that a
synchronized slip-stacked arrangement in a pseudo-quadratic
network, as induced by 1,3,6,8-tetrakis(4-aminophenyl)pyrene
(Py), could match the geometric requirements of the pII unit
very well.17 Among the known multidentate amine building
blocks, Py has proven to produce some of the closest-packed
In this work, we have developed a series of isoindigo- and
thienoisoindigo-based building blocks and have applied them in
the synthesis of highly crystalline imine-linked 2D COFs. The
resulting materials are porous and intensely colored solids that
absorb light throughout the visible and NIR spectral region.
Growing vertically oriented thin films of these materials allows
for the subsequent infiltration of the pores with a
complementary semiconductor. The resulting ordered inter-
digitated heterojunction was employed as the active layer in the
first COF-based NIR-sensitive and voltage-switchable photo-
detector.
RESULTS AND DISCUSSION
■
To create an isoindigo-bridged COF, we designed a new 6,6′-
bis(4-formylphenyl)-N,N′-dibutyl-isoindigo (pII) building
block. The terminal aldehyde hereby provides the chemical
functionality for reversible imine formation, while the butyl
chains ensure sufficient solubility during COF synthesis (Figure
1a).
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Figure 2. (a) Experimental PXRD pattern (black dots) of the Py-pII COF. Rietveld refinement (red line) using the C2/m-symmetric DFT-
optimized structure model shown in (b) provides a very good fit to the experimental data with only minimal differences (the green line shows the
difference plot between the experimental and the Rietveld-refined PXRD patterns; Rwp = 7.86%, Rp = 13.9%). Bragg positions are indicated by blue
ticks. Inset, magnified view of the 2θ > 8° region. (b) The Py-pII COF unit cell with the viewing direction normal to the a−b plane (left) and along
b (right), and the Connolly surface calculated for a nitrogen-sized probe molecule. Crystallographic data are available as Supporting Information. (c)
High-resolution TEM image of a polycrystalline Py-pII COF sample showing the pseudo-quadratic arrangement of the mesopores (top right), and
the parallel alignment of the pore channels (top and bottom left). Inset, magnified view onto a COF domain showing the pseudo-quadratic geometry
with a periodicity of 4.0 0.2 nm. (d) Nitrogen sorption isotherm recorded at 77 K. Insets, QSDFT calculation using an equilibrium model yields a
very narrow pore size distribution centered at 3.3 nm with an additional porosity at around 2.5 nm due to the pII alkyl chains. These values agree
very well with the wall-to-wall distance and the reduced pore diameter due to the alkyl chains derived from the Rietveld-refined structure model
(purple and blue arrows).
COFs with significant π-overlap within the self-assembled
columns of both subunits and excellent crystallinity.16,33,34
The imine-linked Py-pII COF was obtained via acid-
catalyzed solvothermal synthesis as a dark purple powder (see
the SI for experimental details).
(Figure 2c). Domains that are oriented along the crystallo-
graphic c axis show the pseudo-quadratic arrangement with a
periodicity of 4.0 0.2 nm, in excellent agreement with the in-
plane pyrene-to-pyrene distance of 3.93 nm in the Rietveld-
refined COF structure.
Successful formation of a crystalline framework was
confirmed by powder X-ray diffraction (PXRD; Figure 2a).
The diffraction pattern exhibits a number of well-defined
reflections and only weak background, highlighting the high
degree of long-range order in this material. Rietveld refinement
in the monoclinic space group C2/m using a DFT optimized
structure model reproduced the experimental pattern very well
and yielded the lattice parameters a = 5.52 0.02 nm, b = 5.62
0.02 nm, c = 0.38 0.01 nm, and β = 75 4° (Figure 2b).
Owing to the large number of light atoms in the unit cell and
the peak broadening due to the inherent flexibility of the COF
network it is not possible to refine the coordinates of individual
atoms. We therefore observe some deviations in the intensities
of higher-index reflections that are primarily attributed to slight
differences between the DFT-optimized structure model and
the actual COF structure.
The nitrogen sorption isotherm of the Py-pII COF exhibits a
type IV isotherm shape with a sharp step around p/p0 = 0.24
(Figure 2d). Pore size analysis by quenched solid density
functional theory (QSDFT) using an equilibrium model for
cylindrical pores reveals a distribution ranging from 2.1 to 3.4
nm with a main pore diameter of 3.3 nm and a second
maximum at 2.5 nm. Unlike most COFs reported to date, the
Py-pII COF features butyl chains that extend into the pore,
giving rise to a shamrock-shaped cross-section and resulting in
more than one pore size. We notice that the maximum of the
pore size distribution is in excellent agreement with the
simulated wall-to-wall distance of 3.4 nm, while the porosity at
smaller pore diameter coincides with the reduced pore width of
2.5 nm due to the alkyl chains.35 The Brunauer−Emmett−
Teller (BET) surface area is 1613 m2 g−1 with a total pore
volume of 1.06 cm3 g−1, in reasonable agreement with the
Connolly surface of 2255 m2 g−1 and a theoretical pore volume
of 1.35 cm3 g−1, confirming that the pores are open and
High-resolution transmission electron microscopy (TEM)
further confirms the formation of a periodic, porous framework
C
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Figure 3. (a,d) Experimental PXRD patterns (black dots) of the thienoisoindigo-bridged Py-pTII and Py-tTII COFs, respectively. For both COFs,
Pawley refinements (red lines) in the space group C2/m provide an excellent fit to the experimental data. Insets, magnified view of the 2θ > 8°
region. The simulated PXRD patterns (gray lines) based on the structure models shown in (b) and (e), respectively, agree very well with the
experimental and refined patterns of the frameworks. Differences in the peak intensities might stem from slight differences between the simulations
and the actual COF structures. (b,e) The Py-pTII and Py-tTII COF unit cells with the viewing direction normal to the a−b plane (left) and along b
(right), and the Connolly surfaces calculated for a nitrogen-sized probe molecule. (c,f) Nitrogen sorption isotherms recorded at 77 K. Insets,
QSDFT calculations using an equilibrium model yield very narrow pore size distributions with maxima at 3.0 and 3.1 nm, respectively, and an
additional porosity at around 2.2 nm due to the alkyl chains of the thienoisoindigo moieties. These values agree very well with the wall-to-wall
distances and the reduced pore diameters due to the alkyl chains derived from the refined structure models (blue and green arrows).
accessible. Due to the alkyl chains that split the pore into
smaller compartments with highly concave surfaces, the
Connolly surface tends to be systematically higher than the
surface that can be occupied by nitrogen molecules during the
sorption experiment.36
Recent studies on N,N′-dimethyl-isoindigo showed that due
to the steric repulsion between the protons of the benzene ring
and the oxygen atoms of the ketopyrrole, the molecule
crystallizes in a slightly twisted configuration with a rotation
of the two oxindole rings along the central double bond.32 In a
COF, such deviation from a truly planar conformation might
not only reduce the effective π-conjugation in the molecule, but
could also affect the crystallinity and stability of the framework.
Attempting to overcome these potential structural draw-
backs, thieno-modified versions of the isoindigo core have been
developed.37 In thienoisoindigo (TII), the unfavorable
repulsion between the ketones and the adjacent hydrogen
atoms is replaced by a favorable electrostatic attraction between
the sufficiently spaced ketones and sulfur atoms, thus rendering
the molecule entirely planar.38 In order to test the influence of
D
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Figure 4. (a) UV−vis-NIR diffuse reflectance spectra of the Py-pII, Py-pTII, and Py-tTII COF powders dispersed in BaSO4. (b) GISAXS pattern of
a Py-tTII COF film grown on ITO/MoOx indicating a predominant orientation of the COF domains with their a−b plane parallel to the substrate.
Inset, the simulated Py-tTII COF PXRD pattern. The reflections observed in the GISAXS pattern correspond to the 110, 020 and 200, 220, and 330
sets of lattice planes. (c) Spectral responsivity of the Py-tTII COF-based photodetector without external voltage bias (green) and the transmission
absorbance of the COF:PC71BM active layer (black). Gray lines indicate the optical band gaps of PC71BM and the COF. (d) Upon application of an
external voltage to the photodetector, the quantum efficiency in the green and NIR regions up to 750 nm is greatly enhanced. This is accompanied
by a reduced sensitivity to blue and red light, eventually leading to an inversion of the sensitivity profile across the visible spectrum at 1000 mV
reverse bias. (e) A qualitative description of these characteristics can be derived from modeling the spectral distributions of collected charge carriers.
While without voltage bias the device responds mostly to photons absorbed close to the front electrode (green line), the photoresponse at −1000
mV indicates a predominant sensitivity toward photons that penetrate deep into the active layer and are absorbed close to the back electrode (red
line). Inset, illustration of the photodetector device layout.
this added planarity on the structure and electronic properties
of our COFs, we constructed two TII-based building blocks
(Figure 1a). According to our structure simulations, the 5,5′-
bis(4-formylphenyl)-N,N′-dibutyl-thienoisoindigo (pTII) fea-
tures a planar core that is flanked by slightly tilted phenyl rings
(Figure 1c). Replacing the latter by thiophenes results in an
entirely planar conformation of the 5,5′-bis(2-formylthiophen-
5-yl)-N,N′-dibutyl-thienoisoindigo (tTII) building block (Fig-
ure 1d).
models displayed in Figures 3b and 3e, respectively, matched
the experimental patterns very well. The refined unit cell
parameters are a = 5.28 0.02 nm, b = 5.37 0.02 nm, c =
0.38 0.01 nm, and β = 75 5° for the Py-pTII COF, and a =
5.29 0.02 nm, b = 5.39 0.02 nm, c = 0.38 0.01 nm, and β
= 75 5° for the Py-tTII COF. In both COFs, the shorter
length and slightly different geometry of the TII building blocks
give rise to a more contracted framework compared to the Py-
pII COF.
The UV−vis spectra of pTII and tTII feature strong
absorption bands in the blue and the red-to-NIR regions (SI,
Figure S5a). While the π−π* transitions appear slightly blue-
shifted compared to the pII, the ICT bands of the TII building
blocks are much stronger and considerably red-shifted to 480−
730 nm and 500−750 nm for pTII and tTII, respectively. The
corresponding optical band gaps, estimated from Tauc plots for
direct allowed transitions, are 1.75 and 1.68 eV, respectively
(SI, Figure S5c,d).
Acid-catalyzed co-condensation of Py with two equivalents of
the TII building blocks yielded the Py-pTII and Py-tTII COFs
as dark blue- and green-colored powders, respectively. Pawley
refinement of the Py-pTII and Py-tTII COF PXRD patterns
(Figures 3a, d), using the force-field-optimized structure
The nitrogen sorption isotherms and corresponding
QSDFT-derived pore size distributions are qualitatively similar
to the Py-pII COF, but are, as anticipated from the refined
COF structures, slightly shifted toward smaller pore diameters
(Figures 3c, f). The pore size distribution exhibits again two
maxima that stem from the shamrock-shaped pore cross-
section. For both COFs, the main peak corresponds to the wall-
to-wall distance of 3.1 nm, and the smaller one relates to the
reduced pore diagonal due to the alkyl chains. The BET surface
areas are 1592 m2 g−1 and 1567 m2 g−1 with total pore volumes
of 0.96 cm3 g−1 and 0.85 cm3 g−1 for the Py-pTII and Py-tTII
COFs, respectively. As discussed above for the Py-pII COF,
differences between these values and the Connolly surface areas
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and theoretical pore volumes might arise from the pore
geometry.36
reverse bias to aid the extraction of the photogenerated charge
carriers, this can be increased to above 12 mA W−1 at −1000
mV (SI, Figure S8a).
The integration of the isoindigo- and thienoisoindigo-
containing building blocks produces strongly colored frame-
works that absorb light across the visible and parts of the NIR
spectrum (Figure 4a). The optical band gaps, estimated from
the corresponding Tauc plots for direct allowed transitions, are
1.78, 1.48, and 1.36 eV, for the Py-pII, Py-pTII, and Py-tTII
COFs, respectively (SI, Figure S6).
Besides increasing responsivity and external quantum
efficiency (EQE), applying a reverse bias has a profound effect
on the photoresponse spectrum (Figure 4d). At 0 mV bias, the
photodetector is sensitive toward blue and red light, and
relatively insensitive to green and NIR light shorter than 750
nm. With increasing reverse bias, the relative and absolute
sensitivities in the blue and red spectral region drop, while they
improve in the green and NIR regions, ultimately inverting the
sensitivity characteristics of the device throughout the 400−750
nm range. At longer wavelengths, where only the COF can be
photoexcited, the shape of the EQE spectrum is hardly affected
by applying a reverse bias.
In order to derive a qualitative description of these
observations, we modeled the spectral distribution of the
absorbed photons and hence the photogenerated charge
carriers throughout the active layer (see the SI, section J for
a detailed discussion). Considering the inevitable transport
losses in thick organic bulk heterojunctions, the probability of a
charge carrier pair to be collected at the respective electrodes,
ηcoll, depends on where in the active layer it has been generated.
ηcoll is hereby limited by the carrier species (electron or hole)
that has the shorter transport distance. Comparing the
measured EQE spectra to the simulated spectral distributions
of absorbed photons thus allows us to conclude from where
inside the active layer the collected charge carriers originate.
For the sake of simplicity, we focus our discussion on the two
extreme cases of a front-sensitive (ηcoll decreases with distance
from front electrode, i.e., the illuminated side) and a back-
sensitive (ηcoll increases toward back of the active layer) device
(SI, Figure S9).
We first consider the 300−750 nm region, where both
components of the heterojunction can be photoexcited.
Without an external bias voltage, the observed EQE resembles
the simulated photoresponse of a front-sensitive device,
suggesting that the device performance is limited by the
collection of holes at the front electrode (Figure 4e, green
lines). If a reverse bias is applied, however, the EQE spectrum
transforms into the photoresponse of a back-sensitive device,
indicating that under these conditions the collection of
electrons at the back electrode becomes the limiting factor
(Figure 4e, red lines). Here, the incident light has been
attenuated by the optically thick COF:PC71BM film and hence
the spectrum resembles the inverse of the absorption
spectrum.39,40 This voltage-switchable spectral response is
fully reversible (SI, Figure S8c).
In the longer-wavelength region, where only the COF can be
photoexcited, the EQE spectrum exhibits a relatively sharp peak
around 840 nm. Optical modeling of the absorbed photons in
this region (SI, Figure S9a) suggests that rather than
corresponding to an absorption feature of the COF, this peak
is caused by the balance between the penetration of light deep
into the active layer (limiting factor at 750−840 nm) and the
absorption capabilities of the COF (dominant factor at 840−
1100 nm). Here, the device is back-sensitive, i.e. limited by the
collection of electrons irrespective of the applied bias (Figure
4e, right part).
2D COFs possess very anisotropic electronic properties with
the highest conductivity typically being along the π-stacked
molecular columns. For application as an active component in a
photodiode structure, these columns should therefore be
aligned vertically to the substrate. The growth of oriented
films on non-epitaxial substrates, during which the inherent
anisotropy of the COF structure itself generates the preferred
vertical orientation, has previously been achieved for boronate
ester-linked COFs.19 We adapted this strategy for the growth of
the imine-linked Py-tTII COF on MoOx-modified indium−tin
oxide (ITO) transparent electrodes (see the SI for details).
Grazing-incidence small-angle X-ray scattering (GISAXS)
measurements confirm that the resulting COF films are highly
textured (Figure 4b). The intensity of the reflections
corresponding to the 110, 020 and 200, 220, and 330 sets of
lattice planes is highest directly above the sample horizon,
indicating that most COF domains are oriented with their a−b
plane parallel to the substrate (SI, Figure S7). Taking into
account the monoclinic unit cell, the π-stacked columns thus
extend away from the substrate at an angle of β = 75°. This
orientation also ensures that the pores are open toward the film
surface and can be used for the subsequent infiltration with a
complementary semiconductor.
For the construction of a COF-based NIR photodetector, we
infiltrated a 450 nm thick oriented Py-tTII COF film grown on
a hole-selective ITO/MoOx electrode with [6,6]-phenyl C71
butyric acid methyl ester (PC71BM), thus forming an ordered
interdigitated heterojunction. The device was completed by
deposition of an electron-selective back contact consisting of
poly[(9,9-bis(3-(N,N-dimethylamino)propyl)fluorene)-alt-
(9,9-dioctylfluorene)] (PFN) and Ag. While the degree of
infiltration cannot be assessed via photoluminescence (PL)
quenching19,22 for this particular COF due to its very low PL
quantum yield, comparing the COF:PC71BM photodetection
capabilities with a non-infiltrated COF-only device provides
evidence for a predominant filling of the COF pores (SI, Figure
S8d−f).
At short-circuit conditions the COF:PC71BM device exhibits
a panchromatic photoresponse ranging from 300 to 1100 nm
(Figure 4c, green line). For photon energies above the optical
band gap of PC71BM (i.e., λ < 750 nm), the spectral
responsivity follows the absorbance of the COF:PC71BM
heterojunction (Figure 4c, black line). The strong absorption
and responsivity bands centered at 450 and 650 nm,
respectively, are mainly attributed to the π−π* transitions
and the ICT band of tTII. At longer wavelengths, however, the
photodetector exhibits an additional sensitivity peak around
840 nm that does not reflect an absorption feature of the
COF:PC71BM heterojunction. This might be a first indication
that the photophysics of the device change at photon energies
at which only the COF can be photoexcited (see the discussion
below).
A more detailed analysis of the origin of these device
characteristics is beyond the scope of this work and will be the
subject of future studies.
In the absence of an external voltage bias, the peak
responsivity is 2.3 mA W−1 at 840 nm. When applying a
F
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CONCLUSION
■
In this work we have developed the first near-infrared-
absorbing 2D covalent organic frameworks. The incorporation
of donor−acceptor-type isoindigo- and thienoisoindigo-based
building blocks leads to the formation of strongly light
absorbing, stable and porous networks. Growing these materials
as an oriented thin film allowed us to construct an
interdigitated heterojunction upon infiltration of the COF
pores with a soluble fullerene derivative. This heterojunction
was successfully applied as the active layer in a UV- to NIR-
responsive photodetector. We found that the spectral response
of the device could be switched reversibly from blue- and red-
sensitive to green- and NIR-sensitive by changing the bias
voltage. To the best of our knowledge, this is the first time that
such nearly complete inversion of spectral sensitivity has been
observed. This effect could lead to potential applications in
information technology or spectral imaging. Future work will
be dedicated to developing a more quantitative understanding
of the COF photophysics.
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ASSOCIATED CONTENT
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■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/jacs.7b06599.
Schuster, J.; Linke, S.; Doblinger, M.; Feldmann, J.; Knochel, P.; Bein,
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X-ray crystallographic data for Py-pII COF (CIF)
AUTHOR INFORMATION
■
(22) Dogru, M.; Handloser, M.; Auras, F.; Kunz, T.; Medina, D.;
Hartschuh, A.; Knochel, P.; Bein, T. Angew. Chem., Int. Ed. 2013, 52,
2920.
Corresponding Authors
*fa355@cam.ac.uk
*bein@lmu.de
(23) Calik, M.; Auras, F.; Salonen, L. M.; Bader, K.; Grill, I.;
ORCID
Handloser, M.; Medina, D. D.; Dogru, M.; Lobermann, F.; Trauner,
̈
D.; Hartschuh, A.; Bein, T. J. Am. Chem. Soc. 2014, 136, 17802.
(24) Guo, J.; Xu, Y.; Jin, S.; Chen, L.; Kaji, T.; Honsho, Y.; Addicoat,
M. A.; Kim, J.; Saeki, A.; Ihee, H.; Seki, S.; Irle, S.; Hiramoto, M.; Jiang,
D. Nat. Commun. 2013, 4, 2736.
Florian Auras: 0000-0003-1709-4384
Notes
The authors declare no competing financial interest.
(25) Peet, J.; Kim, J. Y.; Coates, N. E.; Ma, W. L.; Moses, D.; Heeger,
A. J.; Bazan, G. C. Nat. Mater. 2007, 6, 497.
ACKNOWLEDGMENTS
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Niazi, M. R.; Yousaf, S. A.; Kirkus, M.; Chen, H.-Y.; Amassian, A.;
Durrant, J. R.; McCulloch, I. Adv. Mater. 2015, 27, 4702.
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The authors are grateful for funding from the German Science
Foundation (DFG; Research Cluster NIM) and the Free State
of Bavaria (Research Network SolTech). The research leading
to these results received funding from the European Research
Council under the European Union’s Seventh Framework
Programme (FP7/2007-2013)/ERC Grant Agreement No.
321339. The authors thank Dr. Markus Doblinger for the
transmission electron microscopy.
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