Organic Crystals with Near-Infrared Amplified Spontaneous Emissions Based on 2′-Hydroxychalcone Derivatives: Subtle Structure Modification but Great Property Change

Article abstract of DOI:10.1002/anie.201503914

A series of highly efficient deep red to near-infrared (NIR) emissive organic crystals 1-3 based on the structurally simple 2′-hydroxychalcone derivatives were synthesized through a simple one-step condensation reaction. Crystal 1 displays the highest qua

Full text of DOI:10.1002/anie.201503914

Angewandte
Chemie
International Edition: DOI: 10.1002/anie.201503914
German Edition: DOI: 10.1002/ange.201503914
Near-Infrared Spectroscopy
Organic Crystals with Near-Infrared Amplified Spontaneous Emissions
Based on 2’-Hydroxychalcone Derivatives: Subtle Structure Modifica-
tion but Great Property Change**
Xiao Cheng, Kai Wang, Shuo Huang, Houyu Zhang, Hongyu Zhang,* and Yue Wang
Abstract: A series of highly efficient deep red to near-infrared
(NIR) emissive organic crystals 1–3 based on the structurally
simple 2’-hydroxychalcone derivatives were synthesized
through a simple one-step condensation reaction. Crystal
1 displays the highest quantum yield (Ff) of 0.32 among the
reported organic single crystals with an emission maximum
(lem) over 710 nm. Comparison between the bright emissive
crystals 1–3 and the nearly nonluminous compounds 4–7
clearly gives evidence that a subtle structure modification can
arouse great property changes, which is instructive in designing
new high-efficiency organic luminescent materials. Notably,
crystals 1–3 exhibit amplified spontaneous emissions (ASE)
with extremely low thresholds. Thus, organic deep red to NIR
emissive crystals with very high Ff have been obtained and are
found to display the first example of NIR fluorescent crystal
ASE.
materials. The lasing properties of organic crystals can be
studied by means of amplified spontaneous emission (ASE).
Blue to orange fluorescent organic crystals displaying the
ASE property have been achieved in the past decade;[7]
however, deep red and NIR-luminescent ASE-active organic
crystals have not yet been reported, because it is really hard to
design organic NIR-fluorescent dyes simultaneously possess-
ing efficient solid-state emission as well as high crystallinity
with suitable size and shape.
Excited-state intramolecular proton transfer (ESIPT)-
active fluorophores and D-A skeletons are important com-
ponents in the research area for constructing long-wavelength
organic fluorescent molecules owing to their large Stokes-
shifted emission.[8] And the strategies such as modulating
molecular packing modes or tuning molecular conformations
usually contribute to the fluorescent quantum efficiency of
organic solids.[9] Following these considerations, we employ
ESIPT-active and D-A structured 2’-hydroxychalcone deriv-
atives 1–3 to construct NIR-emitting crystals (Figure 1). The
O
rganic materials that exhibit efficient luminescence in the
near-infrared (NIR) region have attracted much attention
recently because of their potential applications in bioimaging,
night vision devices, optical communication, and organic
light-emitting diodes (OLEDs).[1–4] A large p-conjugated
framework or strong donor–acceptor (D-A) skeleton is
commonly adopted as the basic structural unit to construct
NIR emitters. Thus, fluorescence quenching, the general
problem for luminescent organic solids, is particularly serious
for NIR fluorophores due to either attractive dipole–dipole
interactions or effective intermolecular p-stacking.[5] Due to
these negative influences, most of the reported efficient NIR
fluorophores in dilute solutions exhibit no or weak fluores-
cence in solid forms.[6] These depressing results greatly
obstruct the applications of NIR materials in optoelectronics
including OLEDs and organic solid-state lasers (OSLs).
Organic single crystals constructed from p-conjugated mol-
ecules have intrinsic properties of ordered molecular orien-
tation and high carrier mobility, and thereby are the most
likely candidates for electrically pumped organic laser
[*] X. Cheng, K. Wang, S. Huang, Dr. H. Zhang, Prof. Dr. H. Zhang,
Prof. Dr. Y. Wang
State Key Laboratory of Supramolecular Structure and Materials
College of Chemistry, Jilin University
Qianjin Street, Changchun (P. R. China)
E-mail: hongyuzhang@jlu.edu.cn
Figure 1. Molecular structures of 1–7 (the emission maxima l and
fluorescence efficiencies F of the solids are summarized herein) and
their photographs under daylight and UV irradiation.
[**] This work was supported by the National Natural Science
Foundation of China (51173067 and 21221063) and the Program for
Chang Jiang Scholars and Innovative Research Team in University
(No. IRT101713018).
D-A structure, intramolecular H-bond with ESIPT nature,
slip-packing structure and molecular planarization effectively
make the crystals 1–3 highly emissive in the deep red/NIR
region. To explore the emission mechanism of crystals 1–3,
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201503914.
Angew. Chem. Int. Ed. 2015, 54, 8369 –8373
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8369

.
Angewandte
Communications
the other four compounds 4–7 are synthesized. The optical
properties as well as crystal structures have been carefully
investigated. Notably, the slab-like crystals 1–3 display a light
propagation feature and thus their potential as candidates in
OSLs has been systematically investigated.
and 475 nm, respectively, coinciding with the experimental
results. In aprotic solvents, the emission spectra contain both
LE and ESIPT state emission, featured as combined broad
bands or dual-peak emission bands. In the protic solvent such
as methanol, a narrowed emission band is observed which is
assigned to the LE. Because of the D-A structure of this type
of molecules, the absorption and emission bands red shift to
a certain extent upon increasing the solvent polarity.
The fluorescence of crystals 1–3 are assigned to the
tautomer produced by ESIPT which results in an abnormally
large Stokes shift.[12] Considering the weak fluorescent nature
of the present molecules in solution, the bright NIR
fluorescence in crystals is very interesting. Thus, molecular
conformations and packing structures of these crystals are
crucial for understanding the bright NIR fluorescence.
Crystals 1–3 belong to the same space group and crystal
system, consistent with the similar crystal shape and fluores-
cence feature. As shown in Figures 3a and S5–S7, all the
Compounds 1–3 are known molecules, but their optical
properties are not fully investigated.[10] All the compounds are
synthesized according to the literature.[11] We obtained red
crystals with centimeter-scale size and slab-like shape based
on 1–3. As shown in Figure 1, the crystals display bright deep
red to NIR fluorescence (lem = 680–716 nm; Ff = 0.25–0.32),
although their solutions are almost non-emissive (Ff < 0.01).
Additionally, these compounds display size-dependent emis-
sion in the crystalline state. For instance, the emission
spectrum of 1 continually red shifts upon increasing the
crystal size (Figures S2–S3). In hexane, 1 displays a local
emission (LE) band peaking at 483 nm and a large Stokes-
shifted emission band peaking at 542 nm which is attributed
Figure 2. a) Potential energy surfaces in the gas phase and representa-
tion of the LE and ESIPT states of 1. The relative energies calculated
with the CAMB3LYP functional are given in kcalmolÀ1 relative to the
optimized geometry in S0. The TD-DFT vertical excitation energies and
oscillator strengths (f) was calculated with the PBE0 functional.
b) Absorption and emission in n-hexane (1”10À5 m) and crystal
emission of compound 1.
Figure 3. Molecular conformations and packing structures of crystals
for 1–3 (a and b), 4 (c and d), and 5 (e and f).
to the ESIPT-state emission (Figure 2b). Calculations on the
ground state (S0) and the lowest-energy excited singlet state
(S1) in the gas phase of 1 are conducted using the CAM-
B3LYP functional. Geometry optimizations in S1 starting
from the Franck–Condon state and the proton-transferred
structure give rise to two local minima corresponding to the
LE and ESIPT states, respectively (Figures 2a and S4). The
plausible potential energy surfaces are shown in Figure 2a.
The energies of two states relative to the optimized geometry
in S0 are + 3.18 and + 3.11 eV with calculated emission of 414
individual molecules take a rather planar conformation with
the dihedral angle between terminal benzene rings in the
range of 1.35–10.828 and show strong innate intramolecular
H-bonds between the carbonyl unit and hydroxy group
(1.753–1.790 Š). The strong intramolecular H-bonds greatly
increase the molecular rigidity and assist in activating the
molecular planarization. Each molecule in the crystal con-
nects its neighboring molecule in an edge-to-face mode
(Figure 3b), which avoids p–p interactions. Notably, the
linear and flat molecules pack into infinite molecular chains
8370
www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 8369 –8373

Angewandte
Chemie
with a typical slip-packing structure in which molecules avoid
excimer formation thereby enhancing the fluorescence of
solid samples. Introducing substituents such as methyl and
methoxyl at the para-position relative to the carbonyl group
does not greatly change the molecular conformation and
packing mode. However, these functional groups form non-
classical H-bonds which slightly alter the molecular micro-
environments. Thus, the shape and fluorescence of the bulk
crystals are affected in a certain degree.
isopropyl group is used in place of dimethylamino group in
compound 7 to disclose the effect of strong D-A structure on
the emission. The emission bands of both 6 and 7 in the solid
state display a large blueshift of more than 80 nm (Figure S9)
compared with 1. This finding strongly demonstrates that the
intramolecular H-bond and the D-A structure are crucially
important for the deep red/NIR emission of crystals 1–3.
Because all those compounds have the same chalcone
skeleton except for some partial changes, the distinctively
different emission behaviors between 1–3 and 4–7 demon-
strate that the structure modification is of great importance
for organic fluorophores. This also provides an easy but
effective strategy when designing new organic fluorescent
materials with high efficiency in the solid state.
Crystals 1–3 exhibit brighter emission on edge than on
their body, indicating that their emissions are highly confined
inside the crystals. These observations reflect that self-wave-
guided emission occurs in the crystals and thus these crystals
are possible candidates as organic deep red/NIR laser media.
To test this possibility, one isolated single crystal of 1 is excited
with a pulsed laser and the photoluminescence (PL) spectra
are subsequently collected from the edge area. At low
excitation power, the PL spectrum is featured as a broad
emission band peaking at about 714 nm, and an amplified
spontaneous emission is observed above a certain power
threshold. Figure 4a shows the power-dependent PL spectra
as well as the energy dependence of the luminescence
intensity and FWHM of the emissions. It shows a nonlinear
gain and a threshold characteristic of ASE. The threshold of
9.2 kWcmÀ2 pulseÀ1 calculated from the slope of peak inten-
sity versus pump energy curve is among the lowest values for
typical organic crystals. Thus, ASE of organic NIR-fluores-
cent organic crystals has been successfully realized, most
importantly, having the extremely low threshold value which
is a crucial parameter to evaluate the ASE property.
The ASE characteristics of the other two crystals 2 and 3
have also been checked. The thresholds of crystals 2 and 3 are
8.2 and 100 kWcmÀ2 pulseÀ1, respectively. Crystal 3 displays
unfavorable ASE characteristics and its PL spectra start to
narrow at high excitation laser powers. This probably
originates from its larger thickness compared with crystals
1 and 2 which should inevitably result in more defects in the
crystal, adverse to the self-waveguided emission. To verify
this, microcrystals with smaller thickness of compound 3
growing on a silicon substrate are prepared (Figure S10). The
laser beam radiates on a pile of microcrystals and ASE is
measured. The threshold of the microcrystals is
22 kWcmÀ2 pulseÀ1, smaller than that of the normal-sized
crystal 3. In addition, the gain coefficients of crystal 1 have
also been carried out by a successively variable pump stripe
method in which the lengths of pump stripe are adjusted by
a slit (Figure S11). The PL spectra become narrower upon
increasing the pump stripe length, and this narrowing occurs
more rapidly at higher pump energy, consistent with the
prediction of ASE theory.[14] The polarized emission of crystal
1 is detected by using a polarizer in front of the optical fiber at
the pump energy of 127 kWcmÀ2 pulseÀ1. A scatterplot is
shown in Figure S12, depicting the PL intensity in change of
the relative angles between the crystal and the polarizer. Its
The solutions under frozen condition and films of these
compounds doped in polymethylmethacrylate (1–10 wt%)
emit very weak fluorescence (Figure S8), demonstrating that
the restriction of intramolecular rotation is likely not the key
role to activate the bright light of the crystals. To further gain
insights into the reason why compounds 1–3 are not
fluorescent in dispersed states but brightly emissive in
crystals, we synthesized compound 4[13a] and obtained red
slab-like crystals whose color and shape are quite similar to
those of crystals 1–3 (Figure 1). Crystals of 4 have similar
edge-to-face packing structures with 1–3 (Figure 3c,d). How-
ever, the individual molecule of 4 takes a rather bent and
twisted molecular conformation. This crystal is weakly
fluorescent (lem = 720 nm; Ff < 0.01) although there are no
negative factors for fluorescence such as intermolecular p-
stacking and dipole–dipole interactions in the crystal packing
structure. This finding strongly indicates the crucial effect of
molecular planarization on the fluorescence quantum yield
for crystals 1–3. Compound 5[13b] is next synthesized to
demonstrate the vital effect of slip-packing mode and edge-
to-face arrangement structure on the high efficiency of
crystals 1–3 (Figure 1). A similar red slab-like crystal of 5 is
achieved. Nevertheless, the crystal is nearly non-emissive
(lem = 699 nm; Ff < 0.01). The molecules in crystal 5 have
a relatively planar conformation (Figure 3e), similar with
those in crystals 1–3. The difference of crystal structures
between 5 and 1–3 is the molecular packing structure. As
shown in Figure 3 f, unlike the edge-to-face packing mode of
molecules in crystals 1–3, every two molecules in crystal 5
take a face-to-face packing structure with strong p–p
interactions; on the other hand, each molecule has strong
dipole–dipole interactions with its neighboring molecule,
which undoubtedly has an adverse effect on the quantum
yield. The different packing structures make crystal 5 nearly
non-emissive, whereas crystals 1–3 are highly fluorescent.
Meanwhile, from the comparison of crystal structures among
crystals 4, 5, and 1–3, we can draw the conclusion that the
molecular conformation and molecular packing structure of
these molecules can be tuned by the position of the
substituent. Considering the much similar molecular struc-
tures and the greatly different emission behaviors of these
compounds, it is easy to find that the substituent modification
has great importance on tuning the solid-state emissions of
organic materials.
For a further understanding of the deep red/NIR emission
of crystals 1–3, 2’-methoxychalcone derivative 6[13c] and
isopropyl-substituted 7[13d] are synthesized (Figure 1). In 6,
the hydroxy group is replaced by a methoxy group. Con-
sequently, there is no intramolecular H-bond in compound 6.
In other words, the ESIPT process cannot occur. The
Angew. Chem. Int. Ed. 2015, 54, 8369 –8373
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
8371

.
Angewandte
Communications
thresholds, which suggests their possible application as
organic deep red/NIR laser crystals.
Keywords: amplified spontaneous emission ·
near-infrared spectroscopy · organic crystals · proton transfer ·
p-conjugation
How to cite: Angew. Chem. Int. Ed. 2015, 54, 8369–8373
Angew. Chem. 2015, 127, 8489–8493
[1] a) B. N. G. Giepmans, S. R. Adams, M. H. Ellisman, R. Y. Tsien,
Science 2006, 312, 217; b) T. Weil, T. Vosch, J. Hofkens, K.
Peneva, K. Müllen, Angew. Chem. Int. Ed. 2010, 49, 9068;
Angew. Chem. 2010, 122, 9252; c) D. Oushiki, H. Kojima, T.
Terai, M. Arita, K. Hanaoka, Y. Urano, T. Nagano, J. Am. Chem.
Soc. 2010, 132, 2795; d) N. Karton-Lifshin, E. Segal, L. Omer, M.
Portnoy, R. Satchi-Fainaro, D. Shabat, J. Am. Chem. Soc. 2011,
133, 10960; e) X. Zhang, J. Yu, Y. Rong, F. Ye, D. T. Chiu, K.
Uvdal, Chem. Sci. 2013, 4, 2143.
[2] D. Y. Kim, D. W. Song, N. Chopra, P. D. Somer, F. So, Adv. Mater.
2010, 22, 2260.
[3] a) N. Tessler, V. Medvedev, M. Kazes, S. Kan, U. Banin, Science
2002, 295, 1506; b) G. Qian, Z. Y. Wang, Chem. Asian J. 2010, 5,
1006.
[4] a) X. Du, J. Qi, Z. Zhang, D. Ma, Z. Y. Wang, Chem. Mater. 2012,
24, 2178; b) M. Casalboni, F. De Matteis, P. Prosposito, R.
Pizzoferrato, Appl. Phys. Lett. 1999, 75, 2172; c) G. Qian, Z.
Zhong, M. Luo, D. Yu, Z. Zhang, D. Ma, Z. Y. Wang, J. Phys.
Chem. C 2009, 113, 1589.
[5] a) J. Massin, W. Dayoub, J.-C. Mulatier, C. Aronica, Y. Breton-
ni›re, C. Andraud, Chem. Mater. 2011, 23, 862; b) O. Fenwick,
J. K. Sprafke, J. Binas, D. V. Kondratuk, F. D. Stasio, H. L.
Anderson, F. Cacialli, Nano Lett. 2011, 11, 2451; c) C.-K. Lim, S.
Kim, I. C. Kwon, C.-H. Ahn, S. Y. Park, Chem. Mater. 2009, 21,
5819.
Figure 4. PL spectra as a function of the pump laser energy and
dependence of the peak intensity and FWHM of emission spectra of
crystal 1 (a), 2 (b), and 3 (c).
[6] a) J. M. Baumes, J. J. Gassensmith, J. Giblin, J.-J. Lee, A. G.
White, W. J. Culligan, W. M. Leevy, M. Kuno, B. D. Smith, Nat.
Chem. 2010, 2, 1025; b) Y. Koide, Y. Urano, K. Hanaoka, T.
Terai, T. Nagano, J. Am. Chem. Soc. 2011, 133, 5680; c) Y.-S. Xie,
K. Yamaguchi, M. Toganoh, H. Uno, M. Suzuki, S. Mori, S. Saito,
A. Osuka, H. Furuta, Angew. Chem. Int. Ed. 2009, 48, 5496;
Angew. Chem. 2009, 121, 5604; d) Y. Yang, M. Lowry, X. Xu,
J. O. Escobedo, M. Sibrian-Vazquez, L. Wong, C. M. Schowalter,
T. J. Jensen, F. R. Fronczek, I. M. Warner, R. M. Strongin, Proc.
Natl. Acad. Sci. USA 2008, 105, 8829; e) S. T. Meek, E. E.
Nesterov, T. M. Swager, Org. Lett. 2008, 10, 2991; f) S. Sreejith,
K. P. Divya, A. Ajayaghosh, Angew. Chem. Int. Ed. 2008, 47,
7883; Angew. Chem. 2008, 120, 8001; g) U. Mayerhçffer, B.
Fimmel, F. Würthner, Angew. Chem. Int. Ed. 2012, 51, 164;
Angew. Chem. 2012, 124, 168.
[7] a) M. Ichikawa, R. Hibino, M. Inoue, T. Haritani, S. Hotta, T.
Koyama, Y. Taniguchi, Adv. Mater. 2003, 15, 213; b) S. Park, O.-
H. Kwon, S. Kim, S. Park, M.-G. Choi, M. Cha, S. Y. Park, D.-J.
Jang, J. Am. Chem. Soc. 2005, 127, 10070; c) Y. Li, F. Li, H.
Zhang, Z. Xie, W. Xie, H. Xu, B. Li, F. Shen, L. Ye, M. Hanif, D.
Ma, Y. Ma, Chem. Commun. 2007, 231; d) P. A. Losio, C.
Hunziker, P. Günter, Appl. Phys. Lett. 2007, 90, 241103; e) X.
Gu, J. Yao, G. Zhang, Y. Yan, C. Zhang, Q. Peng, Q. Liao, Y. Wu,
Z. Xu, Y. Zhao, H. Fu, D. Zhang, Adv. Funct. Mater. 2012, 22,
4862; f) H. Wang, F. Li, I. Ravia, B. Gao, Y. Li, V. Medvedev, H.
Sun, N. Tessler, Y. Ma, Adv. Funct. Mater. 2011, 21, 3770; g) Y.
Wang, T. Liu, L. Bu, J. Li, C. Yang, X. Li, Y. Tao, W. Yang, J.
Phys. Chem. C 2012, 116, 15576; h) M. Ichikawa, K. Nakamura,
M. Inoue, H. Mishima, T. Haritani, R. Hibino, T. Koyama, Y.
Taniguchi, Appl. Phys. Lett. 2005, 87, 221113.
fitting curve accord with the sine function and the difference
between the two angles corresponding to the maximum and
minimum is close to 908.
In conclusion, highly efficient slab-shaped deep red/NIR-
fluorescent organic crystals have been generated in large
amounts based on structurally simple molecules. The uniquely
high quantum yield in the long-wavelength emission region of
these crystals is demonstrated to originate from a combination
effect of the molecular D-A structure, ESIPT-active intra-
molecular H-bond, molecular planarization, and the molec-
ular packing structure without p–p interaction. Comparison
between the highly efficient 1–3 and nearly nonluminous 4–7
demonstrates the partial modification of the molecular
structure may play the key role in tuning the optical proper-
ties of organic fluorophores. The realization of solid-state
deep red/NIR fluorescence based on simple organic dyes
without large p-conjugated framework and bulky substitu-
tions will have particular impact on design strategies toward
deep red/NIR-emissive solids. These findings also exemplify
how the optical properties of organic crystals can be tuned in
a rational and efficient way by controlling the molecular
packing mode and molecular conformation. Another signifi-
cant point of the present study is that the slab-like deep red/
NIR crystals exhibit ASE characters with extremely low
8372
www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 8369 –8373

Angewandte
Chemie
[8] a) J. E. Kwon, S. Y. Park, Adv. Mater. 2011, 23, 3615; b) M.
Shimizu, R. Kaki, Y. Takeda, T. Hiyama, N. Nagai, H. Yamagishi,
H. Furutani, Angew. Chem. Int. Ed. 2012, 51, 4095; Angew.
Chem. 2012, 124, 4171; c) K. Wang, H. Zhang, S. Chen, G. Yang,
J. Zhang, W. Tian, Z. Su, Y. Wang, Adv. Mater. 2014, 26, 6168.
[9] a) S.-Y. Parka, M. Ebiharab, Y. Kubotaa, K. Funabikia, M.
Matsui, Dyes Pigm. 2009, 82, 258; b) L. Jiao, Y. Wu, Y. Ding, S.
Wang, P. Zhang, C. Yu, Y. Wei, X. Mu, E. Hao, Chem. Asian J.
2014, 9, 805.
[10] a) Z. Song, R. T. K. Kwok, E. Zhao, Z. He, Y. Hong, J. W. Y.
Lam, B. Liu, B. Z. Tang, ACS Appl. Mater. Interfaces 2014, 6,
17245; b) S. Dang, J. Liu, G. Wang, Hecheng Huaxue 2008, 16,
460; c) Y. P. Kim, H. Ban, S. S. Lim, N. Kimura, S. H. Jung, J. Ji, J.
Pharm. Pharmacol. 2001, 53, 1295.
[11] T. Teshima, M. Takeishi, T. Arai, New J. Chem. 2009, 33, 1393.
[12] T. Mutai, H. Tomoda, T. Ohkawa, Y. Yabe, Angew. Chem. Int.
Ed. 2008, 47, 9522; Angew. Chem. 2008, 120, 9664.
[13] a) B. S. Jayashree, B. K. Kuppast, K. N. Venugopala, Asian J.
Chem. 2007, 19, 1415; b) M. T. Nguyen, T. T. V. Bui, V. V.
Nguyen, V. T. Nguyen, Tap Chi Hoa Hoc 2008, 46, 577; c) M. L.
Edwards, D. M. Stemerick, P. S. Sunkara, J. Med. Chem. 1990, 33,
1948; d) S. V. Kostanecki, Ber. Dtsch. Chem. Ges. 1908, 40, 3669.
[14] M. D. McGehee, R. Gupta, S. Veenstra, E. K. Miller, M. A.
Díza-García, A. J. Heeger, Phys. Rev. B 1998, 58, 7035.
Received: April 29, 2015
Published online: June 3, 2015
Angew. Chem. Int. Ed. 2015, 54, 8369 –8373
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
8373