Bright white-light emission from a single organic compound in the solid state

Article abstract of DOI:10.1002/anie.201400155

White-light-emitting materials and devices have attracted enormous interest because of their great potential for various lighting applications. We herein describe the light-emitting properties of a series of new difunctional organic molecules of remarkably simple structure consisting of two terminal 4-pyridone push-pull subunits separated by a polymethylene chain. They were found to emit almost pure white light as a single organic compound in the solid state, as well as when incorporated in a polymer film. To the best of our knowledge, they are the simplest white-light-emitting organic molecules reported to date. A bright idea: Remarkably simple organic molecules, based on two 4-pyridone head groups located at the termini of a polymethylene chain, emit bright white light in the solid state. The emission band, which results from excited monomer molecules and stacked excimers, is almost flat over the visible range. Incorporation into a polymeric material gives white-light-emitting films, a feature of potential applied interest.

Full text of DOI:10.1002/anie.201400155

Angewandte
Chemie
DOI: 10.1002/anie.201400155
White-Light Emission
Bright White-Light Emission from a Single Organic Compound in the
Solid Sate**
Qing-Yuan Yang and Jean-Marie Lehn*
Dedicated to Helmut Schwarz on the occasion of his 70th birthday
Abstract: White-light-emitting materials and devices have
attracted enormous interest because of their great potential
for various lighting applications. We herein describe the light-
emitting properties of a series of new difunctional organic
molecules of remarkably simple structure consisting of two
terminal 4-pyridone push–pull subunits separated by a poly-
methylene chain. They were found to emit almost “pure” white
light as a single organic compound in the solid state, as well as
when incorporated in a polymer film. To the best of our
knowledge, they are the simplest white-light-emitting organic
molecules reported to date.
Such is the case for a system composed of benzo[a]xanthene
and benzo[b]xanthene derivatives,[4a] for organic molecules
containing complementary emitting units between which
energy transfer is blocked because of excited-state intra-
molecular proton transfer,[4b,c] for an organic molecule based
on p-conjugated carbazole-substituted phenylenynes,[4d] for
an organic dye that displays panchromatic emission,[4e] and for
electroluminescent white-light-emitting organic molecules.[4f]
However, these molecules have complicated structures and
require intricate synthetic strategies, features that may hinder
their practical use. Thus, achieving white-light emission from
small molecules with simple structures is an exciting challenge
in synthetic chemistry as well as in photochemistry and
photophysics.
Herein, we report the light-emission properties of new
difunctional organic molecules of simple structure and easy
access that are based on two terminal push–pull moieties
separated by a polymethylene chain: the molecules D1a–D1e
containing two 4-pyridone units and the compounds D2–D4
bearing different but related head groups, which were studied
for comparison purposes. The corresponding monofunctional
molecules M1–M4 were also examined as reference com-
pounds (Scheme 1).
D
espite an active search for white-light-emitting materials
and devices,[1] most of the materials reported so far rely on the
combination of different emitters (red/blue/green or blue/
orange) to cover the visible range from 400 to 700 nm, which
may cause problems such as color aging or different require-
ments for device fabrication.[2] Compared to the multicom-
ponent white-light sources, direct emission of white light from
a single-component entity may be expected to avoid the
drawbacks of combined emitters, thus giving rise to white
light of higher quality.[3,4] Therefore, the search for new
molecules that can directly emit white light is clearly of
interest and importance. In molecular species, single-compo-
nent white-light emission has been generated from two
families of compounds: a) metal complexes[3] and b) purely
organic molecules.[4] White-light-emitting single-organic mol-
ecules are scarce and, to date, only a few have been reported.
The mono- and difunctional compounds M1 and D1 were
synthesized by direct alkylation at the nitrogen site of 4-
hydroxypyridine with the corresponding halo- or a,w-diha-
loalkanes through a slight modification of a known reaction.[5]
Compounds M2 and D2 were prepared from 4-(4-hydroxy-
phenyl)pyridine[6] through a slight modification of a known
reaction.[7] Compounds M3, M4, D3, and D4 were obtained
according to a modified literature procedure.[8] Alkylation of
4-hydroxyquinoline, 9(10H)-acridone, and 4-(4-hydroxyphe-
nyl)pyridine gave the N-substituted products directly. How-
ever, alkylation of 4-hydroxypyridine can produce either N-
substituted pyridones or O-substituted pyridines depending
on the specific alkylating agent and conditions.[9–11] In the
present study, the alkylation of 4-hydroxypyridine with a,w-
dibromoalkanes produced a mixture of N- and O-alkylation
products. The symmetrical di-N-substituted pyridone is the
dominant product. The unsymmetrical by-product, where the
central chain is connected to the nitrogen site of one terminal
heterocyclic group and to the oxygen atom of the other one,
can be easily separated. After purification, the purity of the
symmetrical di-N-substituted pyridone can be increased to
[*] Dr. Q. Y. Yang, Prof. Dr. J. M. Lehn
Lehn Institute of Functional Materials, School of Chemistry and
Chemical Engineering, Sun Yat-Sen University
Guangzhou 510275 (China)
and
Laboratoire de Chimie Supramolꢀculaire, Institut de Science et
d’Ingꢀnierie Supramolꢀculaires (ISIS)
Universitꢀ de Strasbourg
8 allꢀe Gaspard Monge, Strasbourg 67000 (France)
E-mail: lehn@unistra.fr
[**] We thank Chien-Wei Hsu for time-resolved fluorescence measure-
ments, Corinne Bailly for the crystal-structure determination, and
Dr. Laura Maggini for the SEM imaging. We also thank Prof. Bernard
Valeur for helpful comments. Q.-Y.Y. thanks the China Postdoctoral
Science Foundation (2012M510203, 2013T60819), the Leading
Talent Project in Guangdong Province (31000-3210003), and the 973
Program of China (2012CB821701) for financial support. This
research was supported in part by the ANR-10-BLAN-717.
1
99.8% (as judged by integration of the H NMR spectrum).
Detailed synthetic, isolation, and purification procedures for
all the compounds are described in the Supporting Informa-
tion.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201400155.
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Supporting
Information).
Similar luminescence prop-
erties are shown by the other
D1 compounds, D1a, D1b,
D1d, and D1e (see Fig-
ure S5 in the Supporting
Information). The shoulder
at short wavelength is remi-
niscent of the emission band
from the monofunctional
M1 and may thus be
assigned to emission from
the terminal groups of the
difunctional D1c. One may
hypothesize that the high-
Scheme 1. Structures of the monofunctional M and difunctional D compounds investigated.
The absorption and emission spectra of the monosubsti-
tuted M1–M4 (see Figure S1 in the Supporting Information)
and those of the disubstituted D1–D4 compounds (see
Figure 1 for D1c and D2; see Figure S2 in the Supporting
Information for D3 and D4) in dilute solution are similar.
D1a–D1e have the same head group and differ only by the
Figure 2. Emission spectra of molecules M1, D1c, M2, and D2 in the
solid state with CIE coordinates under excitation at 365 nm.
energy emissions are due to intrachromophore p-p* transi-
tions and that the low-energy ones result from excited stacked
groups covering a range from intermolecular excimers to
excited oligomers (see also the crystal structure, Figure 6; for
simplicity, when the term excimer is used for our data, it is
meant to describe the actual white-light-emitting entity).[12–15]
Further information to this end, was provided by the
emission spectra of M1 and D1c at different concentrations
(see Figures S6 and S7 in the Supporting Information). In
both cases, a new emission band appeared at 480 nm as the
concentration was increased. This band may be assigned to an
excimer emission in solution and not involving the excited
oligomers formed in the solid state.
To probe the origin of the long-wavelength emissions, the
photoluminescence excitation spectra of D1c were measured
in the solid state for emissions at 445 and 560 nm (see
Figure S8 in the Supporting Information). The emissions at
the two wavelengths are similar, thus suggesting that they
should have a common excitation pathway, and excluding the
possibility of the formation of a new fluorophore. Accord-
ingly, the long-wavelength emissions of D1c should result
from excimers. The monosubstituted molecule M1 also shows
an excimer emission at 523 nm, but its intensity is much
weaker and narrower, thereby resulting in the emission of
blue light instead of white light. This may be due to a different
packing of the pyridone moieties in M1 compared to D1c (see
below).
Figure 1. Absorption (left) and emission (right) spectra of solutions
(5ꢁ10ꢀ5 m in methanol) of the disubstituted compounds D1c (excited
at 280 nm) and D2 (excited at 339 nm).
length of the alkane chain. After an initial exploration of the
photophysical properties, D1c was chosen as the representa-
tive molecule, and the same dodecyl alkane chain was used in
D2–D4. The absorption spectra of all compounds M1–M4 and
D1–D4 display intense bands at wavelengths below 500 nm.
1
These absorptions are assigned to intraligand p-p* transi-
tions of the molecules, as confirmed by DFT computational
studies (see below). Compounds M1–M4 and D1–D4 all emit
blue light in dilute methanol.
In the solid state, in contrast to the solutions, the
monosubstituted M1 and disubstituted D1 compounds display
remarkably different room-temperature photoluminescence
(PL) spectra, as shown in Figure 2 for M1 and D1c (see
Figure S3 in the Supporting Information for the PL spectra of
M3, D3, M4, and D4). Whereas M1 emits blue light and shows
emission bands centered around 450 nm, D1 emits bluish-
white to white light. Most remarkably, D1c displays a strong
white-light emission, which corresponds to a very broad band
that covers the whole visible range extending from 400 to
750 nm as well as a band at 560 nm and a shoulder at 445 nm
(a deconvolution of the two bands is shown in Figure S4 in the
Time-dependent profiles of the monomer and excimer
emission of D1c and D2 were measured in the solid state. The
lifetime of the monomer emission (445 nm) of D1c reveals
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a biexponential decay feature with t = 7.8 and 20.9 ns. Such
lifetimes are characteristic of ligand-centered (LC) emissions
and may originate from p-p* transitions as well as intraligand
charge transfer (ILCT). The time evolution of the excimer
emission (560 nm) shows a different biexponential decay, with
longer lifetimes of t = 46.1 and 103.4 ns. Similar results have
been obtained for the decay of the monomer and excimer
emission of D2, with the biexponential decays having life-
times of t = 2.4 and 14.6 ns and of t = 19.6 and 63.8 ns,
respectively.
Figure 3. Emission spectra of D1c (left) and D2 (right) at increasing
concentrations in PMMA films under excitation at 365 nm. The
percentages of D1c (from 5% to 58%) and D2 (from 1% to 54%) (by
weight) in PMMA increase from the bottom to the top emission
curves (as indicated). The CIE values for the emission of D1c are, for
example, (0.28, 0.33) at 50% and (0.30, 0.34) at 58% dopant (see
Figure S10 in the Supporting Information) and for D2 emission (0.51,
0.39) at 54% dopant. For photographs of the white-light-emitting films
see Figure S14 in the Supporting Information.
Compounds M2 and D2 both show in the solid state
a broad band centered around 590 nm, in the region of the
long-wavelength region of the emission of D1c. In addition,
D2 also gives a weak emission at short wavelength (410 nm).
As in the case of D1c, the latter high-energy emission of D2
may be assigned to intrachromophore p-p* transitions,
whereas the low-energy band (590 nm) would again result
from excimer emission in both compounds. The fact that
compound M2 already displays strong excimer emission may
be attributed to the larger size of the chromophoric terminal
group, as the more extended push–pull head group allows for
more efficient stacking, thus resulting in excimer emission
even as a monofunctional entity. In contrast, M3, M4, D3, and
D4 do not show excimer emission in the solid state (see
Figure S3 in the Supporting Information). So one may
speculate that the difference in the relative disposition of
the molecules in the solid state resulting from the different
shapes of the head groups (and to a lesser extent from their
different polarity) have a large impact on the photophysical
properties. Thus, D1 and D2, which contain the elongated,
prolate push–pull moieties (pyridone and pyridinylidenecy-
clohexa-2,5-dienone, respectively), might pack in the solid
state so as to give excimer emission, whereas D3 and D4,
which contain larger and laterally extended oblate terminal
groups (quinolinone and acridinone), are less prone to give an
arrangement suitable for excimer emission (see Figure S9 in
the Supporting Information). The more commensurate size
between the head groups and the hydrocarbon spacer chain
may allow for better stacking in the cases of D1 and D2 than
in the cases of D3 and D4.
Supporting Information). The observation of such a concen-
tration-dependent emission may be attributed to excimer
emission caused by denser packing of molecules at increased
concentrations, as in the crystal lattice of D1c (see below). To
gain more information about the origin of the emission, a film
containing 50% D1c dopant was investigated by scanning
electron microscopy (SEM). The images obtained showed the
presence of microcrystalline inclusions (see Figure S12 in the
Supporting Information), thus indicating that the emission
was due to solid-state material dispersed in the film.
Similarly, in the case of D2, as the concentration increases
from 1% to 54 wt%, in addition to the weak emission
observed at 410 nm, a much more intense low-energy
structureless emission develops at about 600 nm (Figure 3).
Again such a concentration-dependent emission likely arises
from intermolecular excimer emission.[12–14] The fact that
compound M2 itself displays excimer emission may be due to
the fact that the more-extended push–pull head group allows
for more efficient stacking, thereby resulting in excimer
emission even as a monofunctional entity.
In a further experiment, a sample of D1c was melted
(1078C) and its emission spectra were recorded as it cooled
down to room temperature (258C; Figure 4). In the molten
state, D1c showed strong high-energy emission at 445 nm,
assigned to intramolecular p-p* transitions, with very weak
low-energy excimer emission. In the melt, the polar pyridone
units are in a disordered state and cannot form excimers
effectively, thus emitting blue light. The intensity of the
excimer emission developed progressively on cooling from
1078C to 258C over 0–45 min, until the solidified sample
again produced bright white light. One may expect that on the
way to the solid state, the arrangement of the chromophores
changes from nondirectional to directional alignment, becom-
ing more and more organized, so that the pyridone units can
form excimers effectively. The excitation spectra of D1c in
the molten state for emissions at 445 and 560 nm are similar
(see Figure S13 in the Supporting Information).
The striking difference between D1c and D2 is that the
emission spectrum of the former extends over the whole
range of wavelengths, whereas that of the latter presents very
weak emission between 400 and 500 nm (Figure 2).
To further investigate the formation of excimers in the
elongated push–pull molecules, the emission spectra of D1c
and D2 were also measured in polymer films containing
increasing amounts of the two compounds. These films were
prepared by spin-coating a mixture of solutions of D1c (or
D2) and polymethylmethacrylate (PMMA) in dichlorome-
thane. In the case of D1c, the film formed at a low dopant
concentration of 5 wt% at 298 K exhibited the blue light
emission of isolated D1c molecules (Figure 3), similar to the
emission in solution (Figure 1). Increasing the concentration
in the range 5–58 wt% resulted in a low-energy structureless
emission developing at about 550 nm, thereby finally yielding
a spectrum similar to that of D1c in the solid state at high
concentration (Figure 3; see also the chromaticity coordinates
in Figure S10 and the excitation spectra in Figure S11 in the
The other four D1 molecules with the same head group as
D1c present similar white-light emission in the solid state.
D1a, D1b, and D1e emit bluish white light with CIE
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(CIE) diagrams. Importantly, excitation at different wave-
lengths (350–420 nm) gives the same white-light emission.
Thus, emission of bright-white light from a single organic
molecule can be achieved under irradiation in the near-UV
region and into the visible range. Notably and of potential
practical interest, the emission from the PMMA film at 58%
D1c doping (Figure 3) is even flatter over the wide 425–
600 nm range than that of the solid D1c itself, with a CIE
coefficient of (0.30, 0.34).
To relate the optical properties to the molecular arrange-
ment in the solid state, more complete structural data are
desirable. Fortunately, single crystals of the white-light-
emitting molecule D1c could be grown on cooling a hot
aqueous solution (see the Supporting Information). Single-
crystal X-ray structural analysis confirmed the alkylation of 4-
hydroxypyridine to give a symmetrical di-N-substituted
pyridone molecule. The asymmetric unit contains half a cen-
trosymmetric D1c molecule and one molecule of water. In the
crystal lattice, the ligands are packed through intermolecular
stacking between two planar pyridones as well as hydrogen
bonding between the carbonyl oxygen atom and the water
molecules. Pairs of planar pyridones are in contact, separated
by about 3.6 ꢁ, and in a shifted head-to-tail geometry
(Figure 6). Most importantly, the nitrogen sites, which repre-
Figure 4. Emission spectra of D1c on cooling from the molten state
(1078C) to the solid state (258C) under excitation at 365 nm. Emission
curves from the bottom to the top were measured at the various times
(indicated in minutes) on progressive cooling from the melt.
coordinates of (0.28, 0.33), (0.28, 0.35), and (0.28, 0.37),
respectively. D1c and D1d emit white light with CIE
coordinates of (0.34, 0.36) and (0.33, 0.34), respectively, very
close to pure white light (CIE: 0.33, 0.33). The five molecules
D1a–D1e differ by the length of the alkyl chain connecting
the two N-substituted pyridones, which may lead to different
packing arrangements[16] and result in slightly different
arrangements of the polar pyridone chromophores, thus
producing slightly different white-light emissions. They give
high emission quantum yields ranging from 30% to 33% (see
Table S2 in the Supporting Information). The emission
properties of the molecules D1c and D2 under excitation at
365 nm are illustrated in Figure 5, together with the corre-
sponding 1931 Commission Internationale de LꢀEclairage
Figure 6. X-ray solid-state molecular structure of the white-light-emit-
ting molecule D1c: a) illustration of the relative disposition and
intermolecular interactions of two molecules. b) side view showing the
packing and the interaction between adjacent units in each stack of
molecules. The solvent molecules are omitted for clarity.
sent the positive end of the electric dipole (about 7.9 D) of the
polar 4-pyridone groups, are located on top of each other and,
therefore, interact in a repulsive manner. We recall that an
excimer is formed by the stabilization of a dimer structure in
the excited state at a geometry for which the intermolecular
interactions are repulsive in the ground state.[13,17] Emission
thus occurs from the minimum of the excited state to
Figure 5. Top: Solid-state photoluminescent spectra of D1c and D2
under excitation at 365 nm; bottom: chromaticity coordinates (CIE)
and photographs of the name of our Institute ISIS written with the
white-light-emitting D1c (left; CIE: 0.34, 0.36) and the orange-light
emitting D2 (right; CIE: 0.46, 0.48) molecules. The optical photo-
graphs were taken under irradiation at 365 nm. The emission curves
have been superimposed on the spectrum of white light.
4
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a repulsive region of the ground state. Therefore, the energy
change is smaller than in the isolated chromophore, and the
emission from the excimer is red-shifted (see Figure S15 in the
Supporting Information). The special intermolecular posi-
tioning of the pyridone groups in the solid state of D1c,
together with the excited oligomer character enhance these
features and may be considered as the major factors for the
broad white-light emission. The slight differences in the
emission properties along the D1a–D1e series may result
from small changes in the arrangement through a contribution
from the packing of the hydrocarbon chains to generate the
final disposition. The shortest distance between two hydro-
carbon chains is 3.96 ꢁ (see also Figure S16 in the Supporting
Information).
DFT/TDDFT calculations were performed on the white-
light-emitting molecule D1c as well as on D2 to gain insight
into the optical features of the excimer formation. To avoid
the complexity of periodic structures, D1c was truncated into
the 4-pyridone fragment from the crystal structure for the
computation. The ground-state geometries were optimized
for both molecules and their Frontier Molecular Orbitals
(FMOs) are displayed in Figure 7. In addition, similar
are collected in Table S3 in the Supporting Information. The
theoretical values for the S0!S1 (1p!p*) transitions compare
well with the experimental absorption bands.
Excimer formation in D1c was investigated by exploring
several relative dispositions of two 4-pyridone groups, keep-
ing their geometry frozen. Several dimer structures were
obtained by rotating one of the molecules along the N-N axis
or by changing the interplanar distance. Among those,
Figure 7b displays the LUMO energies of the anti dimer
and syn dimer at an interplanar distance of 3.6 ꢁ. In the
dimer, these LUMO energies have been split, but the
HOMOs are little affected. Moreover, the anti dimer is
calculated to be more stable than the syn dimer by 11.5 kcal
molꢀ1, which corresponds to the head-to-tail orientation
found in the crystal structure of D1c (Figure S18 in the
Supporting Information depicts the effect of the intermolec-
ular interactions on the FMO energies of the anti dimer as
a function of the distance between the two units). At
a moderate spacing (4.0 ꢁ), the interaction between the
LUMOs of the pyridone groups is already substantial and the
energy gap between HOMO and LUMO (DE(LUMO-HOMO)) is
reduced. At shorter intermolecular separations, this interac-
tion increases and the DE(LUMO-HOMO) value becomes smaller,
so that the excimer formation observed in the anti dimer leads
to emission at longer wavelengths, as observed. These
theoretical results are thus in good agreement with the
experimental data. Excited states extending over more than
two stacked groups may contribute to emission at longer
wavelengths than that of the excimer.[12]
In conclusion, we synthesized and investigated a series of
difunctional molecules bearing polar moieties at the ends of
polymethylene chains. Their photophysical properties in the
solid state depend on the nature of the head groups, which
determine their emission properties. The introduction of 4-
pyridone moieties as head groups gave a novel class of
particularly simple difunctional organic molecules [pyridone]-
(CH2)n-[pyridone] (D1) displaying white-light emission with
high quantum yields in the solid state. The striking feature
results from the remarkable simultaneous occurrence of
emission of the isolated molecule type at short wavelengths
and very broad emission from excited oligomers at longer
wavelengths, with relative emission intensities such as to yield
a plateau-type band covering a wide domain in the visible
range and thus generating bright and almost pure white light.
Such emission from structurally simple organic molecules is
remarkable and promises potential implementation in future
applications. Of particular significance in this respect is the
possibility to prepare white-light-emitting polymeric films.
Finally, one may note that these properties are, in effect, of
collective supramolecular nature, as they result from the
special intermolecular positioning of the molecules and their
mutual interaction.
Figure 7. a) Frontier molecular orbitals of D1c and D2 in the electronic
ground state. b) LUMO orbitals for the anti (head-to-tail, as in the
crystal structure) and syn arrangements of dimers of two 4-pyridone
moieties in D1c at an interplanar distance of 3.6 ꢂ.
computational studies were performed on the representative
fragments of D3 and D4 (see Figure S17 in the Supporting
Information). The calculations also gave the dipole moments
of the chromophoric groups (see Scheme S1 in the Supporting
Information).
As shown in Figure 7a, the electron distribution in the
HOMOꢀ1 and the LUMO+1 in compounds D1c and D2
localizes at the side of the oxygen atom and of the nitrogen
atom, respectively. This electron transfer from nitrogen to
oxygen represents the electron-donor/electron-acceptor dis-
tribution in the conjugated N-C-C-O fragment. The photo-
physical properties and energies of the FMOs of D1c and D2
Received: January 7, 2014
Revised: February 4, 2014
Published online: && &&, &&&&
Keywords: fluorescence · pyridones · solid-state emission ·
.
thin films · white-light emission
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Commun. 2010, 46, 8002 – 8004; f) J. Y. Li, D. Liu, C. Ma, O.
Lengyel, C. S. Lee, C. H. Tung, S. T. Lee, Adv. Mater. 2004, 16,
1538 – 1541; g) for white-light emission from a two-component
micellar system, see X. Zhang, D. Gçrl, F. Wꢂrthner, Chem.
Commun. 2013, 49, 8178 – 8180.
[1] a) G. M. Farinola, R. Ragni, Chem. Soc. Rev. 2011, 40, 3467 –
3482; b) B. W. DꢀAndrade, S. R. Forrest, Adv. Mater. 2004, 16,
1585 – 1595; c) C. Ulbricht, B. Beyer, C. Friebe, A. Winter, U. S.
Schubert, Adv. Mater. 2009, 21, 4418 – 4441; d) S. C. F. Kui, P. K.
Chow, G. S. M. Tong, S. L. Lai, G. Cheng, C. C. Kwok, K. H.
Low, M. Y. Ko, C. M. Che, Chem. Eur. J. 2013, 19, 69 – 73;
e) H. C. Su, H. F. Chen, F. C. Fang, C. C. Liu, C. C. Wu, K. T.
Wong, Y. H. Liu, S. M. Peng, J. Am. Chem. Soc. 2008, 130, 3413 –
3419; f) B. H. Zhang, G. P. Tan, C. S. Lam, B. Yao, C. L. Ho, L. H.
Liu, Z. Y. Xie, W. Y. Wong, J. Q. Ding, L. X. Wang, Adv. Mater.
2012, 24, 1873 – 1877; g) V. K. Praveen, C. Ranjith, N. Armaroli,
Angew. Chem. 2014, 126, 373 – 376; Angew. Chem. Int. Ed. 2014,
53, 365 – 368; h) B. DꢀAndrade, M. E. Thompson, S. R. Forrest,
Adv. Mater. 2002, 14, 147 – 151.
[2] a) G. L. Tu, C. Y. Mei, Q. G. Zhou, Y. X. Cheng, Y. H. Geng,
L. X. Wang, D. G. Ma, X. B. Jing, F. S. Wang, Adv. Funct. Mater.
2006, 16, 101 – 106; b) B. P. Yan, C. C. C. Cheung, S. C. F. Kui,
H. F. Xiang, V. A. L. Roy, S. J. Xu, C. M. Che, Adv. Mater. 2007,
19, 3599 – 3603; c) B. W. DꢀAndrade, R. J. Holmes, S. R. Forrest,
Adv. Mater. 2004, 16, 624 – 628.
[3] a) P. Coppo, M. Duati, V. N. Kozhevnikov, J. W. Hofstraat, L.
De Cola, Angew. Chem. 2005, 117, 1840 – 1844; Angew. Chem.
Int. Ed. 2005, 44, 1806 – 1810; b) A. H. Shelton, I. V. Sazanovich,
J. A. Weinstein, M. D. Ward, Chem. Commun. 2012, 48, 2749 –
2751; c) H. J. Bolink, F. De Angelis, E. Baranoff, C. Klein, S.
Fantacci, E. Coronado, M. Sessolo, K. Kalyanasundaram, M.
Gratzel, M. K. Nazeeruddin, Chem. Commun. 2009, 4672 – 4674;
d) D. Sykes, I. S. Tidmarsh, A. Barbieri, I. V. Sazanovich, J. A.
Weinstein, M. D. Ward, Inorg. Chem. 2011, 50, 11323 – 11339;
e) G. L. Law, K. L. Wong, H. L. Tam, K. W. Cheah, W. T. Wong,
Inorg. Chem. 2009, 48, 10492 – 10494; f) G. J. He, D. Guo, C. He,
X. L. Zhang, X. W. Zhao, C. Y. Duan, Angew. Chem. 2009, 121,
6248 – 6251; Angew. Chem. Int. Ed. 2009, 48, 6132 – 6135; g) V.
Adamovich, J. Brooks, A. Tamayo, A. M. Alexander, P. I.
Djurovich, B. W. DꢀAndrade, C. Adachi, S. R. Forrest, M. E.
Thompson, New J. Chem. 2002, 26, 1171 – 1178.
[5] S. K. Freeman, W. F. Ringk, P. E. Spoerri, J. Am. Chem. Soc.
1947, 69, 858 – 859.
[6] A. Das, J. C. Jeffery, J. P. Maher, J. A. McCleverty, E. Schatz,
M. D. Ward, G. Wollermann, Angew. Chem. 1992, 104, 1554 –
1556; Angew. Chem. Int. Ed. Engl. 1992, 31, 1515 – 1518.
[7] V. Diemer, H. Chaumeil, A. Defoin, P. Jacquesb, C. Carre,
Tetrahedron Lett. 2005, 46, 4737 – 4740.
[8] R. M. Acheson, E. C. Constable, J. Chem. Soc. Chem. Commun.
1980, 1065 – 1066.
[9] L. Johnson, Y. Kitahara, T. J. R. Weakley, J. F. W. Keana,
Tetrahedron Lett. 1993, 34, 5555 – 5558.
[10] H. Vorbrꢂggen, K. Krolikiewicz, Chem. Ber. 1984, 117, 1523 –
1541.
[11] A molecule containing three 4-hydroxypyridine/4-pyridone
groups was prepared in the course of an exploration of potential
multivalent ligands for luminescent rare-earth metal cations, see
Q. Y. Yang, K. Li, J. Luo, M. Pan, C. Y. Su, Chem. Commun.
2011, 47, 4234 – 4236.
[12] For a study of emission from an excited oligomer of stacked
anthracene molecules in the solid state, see T. Hinoue, Y.
Shigenoi, M. Sugino, Y. Mizobe, I. Hisaki, M. Miyata, N. Tohnai,
Chem. Eur. J. 2012, 18, 4634 – 4643.
[13] For a presentation of excimers, see B. Valeur, Molecular
Fluorescence: Principles and Applications, Wiley-VCH, Wein-
heim, 2002, pp. 94 – 98.
[14] For studies on excimers, see a) A. D. Q. Li, W. Wang, L. Q.
Wang, Chem. Eur. J. 2003, 9, 4594 – 4601; b) H. Yoo, J. Yang, A.
Yousef, M. R. Wasielewski, D. Kim, J. Am. Chem. Soc. 2010, 132,
3939 – 3944; c) J. M. Giaimo, J. V. Lockard, L. E. Sinks, A. M.
Scott, T. M. Wilson, M. R. Wasielewski, J. Phys. Chem. A 2008,
112, 2322 – 2330; d) F. Wꢂrthner, C. Thalacker, S. Diele, C.
Tschierske, Chem. Eur. J. 2001, 7, 2245 – 2253.
[4] a) Y. Yang, M. Lowry, C. M. Schowalter, S. O. Fakayode, J. O.
Escobedo, X. Xu, H. Zhang, T. J. Jensen, F. R. Fronczek, I. M.
Warner, R. M. Strongin, J. Am. Chem. Soc. 2006, 128, 14081 –
14092; b) S. Park, J. E. Kwon, S. H. Kim, J. Seo, K. Chung, S. Y.
Park, D. J. Jang, B. M. Medina, J. Gierschner, S. Y. Park, J. Am.
Chem. Soc. 2009, 131, 14043 – 14049; c) K. C. Tang, M. J. Chang,
T. Y. Lin, H. A. Pan, T. C. Fang, K. Y. Chen, W. Y. Hung, Y. H.
Hsu, P. T. Chou, J. Am. Chem. Soc. 2011, 133, 17738 – 17745;
d) Y. Liu, M. Nishiura, Y. Wang, Z. M. Hou, J. Am. Chem. Soc.
2006, 128, 5592 – 5593; e) P. Nandhikonda, D. Heagy, Chem.
[15] For intramolecular excimers, see also a) K. Zachariasse, W.
Kꢂhnle, Z. Phys. Chem. Neue Folge 1976, 101, 267; b) M. A.
Winnik, Chem. Rev. 1981, 81, 491 – 524; c) F. C. De Schryver, P.
Collart, J. Vandendriessche, R. Goedeweeck, A. Swinnen, M.
Van der Auweraer, Acc. Chem. Res. 1987, 20, 159 – 166; d) F. M.
Winnik, Chem. Rev. 1993, 93, 587 – 614.
[16] A. Neelakantan, R. Stine, J. K. Maranas, Macromolecules 2003,
36, 3721 – 3731.
[17] D. Kim, J. L. Bredas, J. Am. Chem. Soc. 2009, 131, 11371 – 11380.
6
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Angew. Chem. Int. Ed. 2014, 53, 1 – 7
These are not the final page numbers!

Angewandte
Chemie
Communications
White-Light Emission
A bright idea: Remarkably simple organic
molecules, based on two 4-pyridone head
groups located at the termini of a poly-
methylene chain, emit bright white light
in the solid state. The emission band,
which results from excited monomer
molecules and stacked excimers, is
almost flat over the visible range. Incor-
poration into a polymeric material gives
white-light-emitting films, a feature of
potential applied interest.
Q. Y. Yang, J. M. Lehn*
&&&& — &&&&
Bright White-Light Emission from
a Single Organic Compound in the Solid
Sate
Angew. Chem. Int. Ed. 2014, 53, 1 – 7
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
7
These are not the final page numbers!