Efficient NIR-light emission from solid-state complexes of boron difluoride with 2′-hydroxychalcone derivatives

Article abstract of DOI:10.1002/chem.201201812

This article describes a series of nine complexes of boron difluoride with 2'-hydroxychacone derivatives. These dyes were synthesized very simply and exhibited intense NIR emission in the solid state. Complexation with boron was shown to impart very stron

Full text of DOI:10.1002/chem.201201812

FULL PAPER
DOI: 10.1002/chem.201201812
Efficient NIR-Light Emission from Solid-State Complexes of Boron
Difluoride with 2’-Hydroxychalcone Derivatives
Anthony D’Alꢀo,*[a] David Gachet,[a] Vasile Heresanu,[a] Michel Giorgi,[b] and
Frꢀdꢀric Fages*[a]
Dedicated to Dr. Hubert Le Bozec on the occasion of his 60th birthday
Abstract: This article describes a series
of nine complexes of boron difluoride
with 2’-hydroxychacone derivatives.
These dyes were synthesized very
simply and exhibited intense NIR emis-
sion in the solid state. Complexation
with boron was shown to impart very
strong donor–acceptor character into
the excited state of these dyes, which
further shifted their emission towards
the NIR region (up to 855 nm for dye
5b, which contained the strongly do-
nating triphenylamine group). Striking-
ly, these optical features were obtained
for crystalline solids, which are charac-
terized by high molecular order and
tight packing, two features that are
conventionally believed to be detri-
mental to luminescence in organic crys-
tals. Remarkably, the emission of light
from the p-stacked molecules did not
occur at the expense of the emission
quantum yield. Indeed, in the case of
pyrene-containing dye 4, for example, a
fluorescence quantum yield of about
15% with a fluorescence emission max-
imum at 755 nm were obtained in the
solid state. Moreover, dye 3a and ace-
tonaphthone-based compounds 1b, 2b,
and 3b showed no evidence of degra-
dation as solutions in CH2Cl2 that con-
tained EtOH. In particular, solutions
of brightly fluorescent compound 3a
(brightness:
eꢀFf =45000mꢀ1 cmꢀ1)
could be stored for long periods with-
out any detectable changes in its opti-
cal properties. All together, these new
dyes possess a set of very interesting
properties that make them promising
solid-state NIR fluorophores for appli-
cations in materials science.
Keywords: boron
chromophores
near-infrared emission
·
chalcones
·
·
·
dyes/pigments
Introduction
as solid emitters and values of their photoluminescence
quantum yields in the condensed phase are very scarce and
usually low.
Light-emissive solids are key materials in a range of technol-
ogies, including chemical sensing, bioimaging, information
displays and processing, and telecommunications.[1] Al-
though a large number of fully organic fluorophores have
been found to be efficient in the visible spectrum, those that
emit deep-red- or near-infrared (NIR) light with significant
efficiency in the condensed phase still remain much less
common.[2] The most-popular NIR-emissive organic dyes
belong to the class of polymethines[3] but also include oxa-
zine and thiazine derivatives,[3] rylenes,[4] squaraines,[5] bor-
ondipyrromethanes (BODIPYs),[6] and low-band-gap p-con-
jugated oligomers.[7] Despite numerous studies, only very
few of these compounds have been reported to be effective
Chalcones are a well-known class of dyes[8] that have
found numerous applications in linear- and nonlinear-optical
materials.[9–12] Naturally-occurring chalcone-based pigments
have been proposed as an attractive source of “green” mate-
rials for bio-organic electronics and -photonics.[13] Although
the solution-state photophysics of chalcones is well-docu-
mented,[11] that of boron complexes of 2’-hydroxy-substitut-
ed analogues has received little attention[12] and nothing is
known about their solid-state fluorescence. This class of
molecules was investigated for potential applications as
laser dyes[14] or dopants in photorefractive polymeric materi-
als.[15] The main limitation in the use of chalcones as fluoro-
phores is their weak fluorescence efficiency in solution be-
cause excited-state dynamics in liquids is governed by intra-
molecular torsional motions and by photoisomerization
processes, which offer privileged funnels for the radiation-
less deactivation of the first singlet excited state. 4-Substitut-
ed chalcones with electron-donating groups belong to the
class of donor-acceptor (D–A) push-pull molecules and,
thus, exhibit strongly Stokes-shifted fluorescence emission
that can reach the NIR region in solution.[11] Recent reports
have described the ability of dipolar dyes[16] and p-stacked
charge-transfer (CT) complexes[17] to display efficient emis-
[a] Dr. A. D’Alꢁo, Dr. D. Gachet, Dr. V. Heresanu, Prof. F. Fages
Aix-Marseille Universitꢁ, CNRS, CINaM UMR 7325
Campus de Luminy, Case 913, 13288 Marseille (France)
Fax : (+33)491-829-301
E-mail: daleo@cinam.univ-mrs.fr
frederic.fages@univ-amu.fr
[b] Dr. M. Giorgi
Aix-Marseille Universitꢁ, CNRS, Spectropole FR 1739
Campus Scientifique de Saint Jꢁrꢂme, 13397 Marseille (France)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201812.
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
1
&
ÞÞ
These are not the final page numbers!

sion in the solid state; however, in these examples, emission
occurred in the visible-light region. Thus, we decided to use
boron-complexation with 2’-hydroxychacones to further en-
hance the push-pull character of the arylpropenone skele-
ton, with the idea that the resulting decrease in the
HOMO–LUMO gap could impart solid-state difluorodioxa-
borine chalcone dyes with NIR emission. During the course
of our investigation on a broad series of boron-difluoride
complexes of 2’-hydroxychalcones, we indeed observed that
these compounds had a general propensity to deliver solid-
state emission that ranged from visible- to NIR light de-
pending on the molecular structure, which, to the best of
our knowledge, has not been reported before.
Scheme 2. Synthetic route to the 2’-hydroxychalcone skeleton and its
boron-difluoride complex.
Herein, we report on a selection of difluorodioxaborine
chalcone derivatives (Scheme 1) that were chosen to illus-
and pyrenyl aromatic groups, with their large dimensions
and flat shape, represented attractive p-stacking units that
have already been shown to be useful for the generation of
optoelectronic materials.[18] We show that replacing the ace-
tophenone unit by acetonaphthone in part B (Scheme 2) not
only affected the optical properties of the dyes but also pro-
vided a remarkable gain in stability in solution. Moreover,
halogen atoms were also introduced onto the B ring because
halogen–halogen interactions are known to have a signifi-
cant influence on molecular arrangement in the crystal.[19]
Much to our surprise, compound 5b, which contained two
iodine atoms, was observed to be fluorescent in the solid
state. Herein, we describe the spectroscopic properties of
the difluorodioxaborine chalcones in solution and in the
solid state. These results show that NIR fluorescence emis-
sion originates from electronically interacting fluorophores
in tightly packed solid-state assemblies.
Results and Discussion
2’-Hydroxychalcone ligands 1a/b-H, 2a/b-H, 3a/b-H, 4-H,
and 5a/b-H were obtained very simply by using a Claisen–
Schmidt reaction between various aldehydes and acetophe-
nones/acetonaphthones in EtOH as the solvent and sodium
hydroxide as a base (Scheme 2). Complexation to boron was
performed quantitatively by reacting the ligands with a
slight excess of boron trifluoride etherate in CH2Cl2. Dyes
1a/b, 2a/b, 3a/b, 4, and 5a/b were obtained as darkly col-
ored solids and characterized by using 1H-, 13C- and
19F NMR spectroscopy, MS, and elemental analysis.
Scheme 1. Structures of the boron-difluoride complexes of 2’-hydroxy-
chalcones 1a/b–3a/b, 4, and 5a/b.
None of the free ligands were fluorescent in solution or in
the solid state, which was consistent with the propensity of
2’-hydroxychalcone derivatives to undergo facile excited-
state intramolecular proton-transfer.[20] BF2-complexation
produced considerable red-shifts (>100 nm) of the maxi-
mum absorption wavelength in all of the compounds
(Table 1; also see the Supporting Information, Figure S1) as
a consequence of the enhanced dipolar character of the di-
fluorodioxaborine-containing species. Intramolecular CT
was evidenced by the positive solvatochromic shifts of both
the absorption- and emission bands (see the Supporting In-
formation, Figure S2). Concomitantly, BF2 complexation
trate some unprecedented NIR-emission properties. Com-
pounds 2a/b, 3a/b, 4, and 5a/b are new, whilst the synthesis
of compounds 1a and 1b has already been described in the
literature but their photophysical properties were not re-
ported.[12] This series served to outline the influence of the
nature of both the donor- and acceptor groups (A and B, re-
spectively, Scheme 2) on solid-state optical properties. Com-
pounds that contained carbazole (3a/b) and triphenylamine
units (TPA, 5a/b) were among the strongest push-pull struc-
tures that we have investigated so far. Methoxynaphthyl-
&
2
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Boron-Difluoride Complexes of 2’-Hydroxychalcone Derivatives
FULL PAPER
Table 1. Electronic absorption properties of the free 2’-hydroxychalcones
and their complexes with BF2 in CH2Cl2.
Free ligands
BF2 complexes
max
abs
max
l
e
l
e
Dl
ACHTUNGTRENNUNG
[cmꢀ1] (nm)
abs
[nm]
N
]
[nm]
N
]
1a
1b
2a
2b
3a
3b
4
367
363
402
388
405
425
432
464
465
26300
24680
30230
30895
35456
28690
28170
33420
32625
455
486
510
501
504
538
541
588
591
41190
37340
45930
49525
56300
47210
44190
68910
67320
5270 (88)
6970 (132)
5270 (108)
5815 (123)
4850 (99)
4940 (113)
4660 (109)
4545 (122)
4585 (126)
5a
5b
also led to a considerable increase in the oscillator strength
of the lowest-energy transition band.
Whilst weak intramolecular CT emission in the difluoro-
dioxaborine derivatives was recorded in general in CH2Cl2
solution, the carbazole-containing compounds (3a/b) exhib-
ited very intense fluorescence with high quantum yield (Ff)
Figure 1. Kinetic stability in CH2Cl2 that contained 0.5 vol% EtOH at
room temperature; the stability was monitored by measuring the absorb-
ance decay at the maximum absorption wavelength of the BF2 complexes
&
*
for compounds 1a ( ) and 1b ( ). Inset: corresponding changes in the
electronic absorption spectrum of compound 1b as a function of time.
thone unit relative to its acetophenone counterpart. In par-
ticular, solutions of brightly fluorescent compound 3a could
be stored for long periods of time without any detectable
changes in its optical properties. However, the remaining
compounds were subject to solvolysis under the same condi-
tions. The kinetics of decomplexation were followed by UV/
Vis spectroscopy of the boron complexes at regular time in-
tervals. Half-life values and kinetic rates were obtained by
plotting the decay of the absorbance value at the maximum
absorption wavelength versus time (Figure 1; also see the
Supporting Information, Figure S4). The pseudo-first-order
rate constant values (kobs) for dyes 1a, 2a, 4, and 5a/b were
in the range 5ꢀ10ꢀ5–5ꢀ10ꢀ4 sꢀ1 (see the Supporting Infor-
mation, Table S1) and strongly increased with larger
amounts of EtOH. Thus, manipulating solutions of this
series of compounds necessitated the use of carefully dried
solvents, whereas, in the case of inert dyes 1b, 2b, and 3a/b,
such drastic conditions were useless. We could even quickly
dilute their solutions in THF (0.15 mL, 0.1 mm) with water
(2.85 mL) at room temperature without observing any deg-
radation. Under these conditions, precipitation was much
faster than hydrolysis and stable suspensions of the aggre-
gated dyes could be obtained. The generation of nanosized
organic particles with NIR emission is a topical subject of
investigation[6f] and the BF2–chalcone dyes might represent
attractive candidates to this end. At this stage of the work,
we had not as yet attempted to optimize the synthesis of the
particles and control their size-distribution; hence, relatively
large particles were generated (about 900 nm for compound
1b; see the Supporting Information, Figure S5). In fact, they
were particularly useful for spectroscopic investigation (see
below). Moreover, it is important to note that all BF2–chal-
cones investigated herein displayed indefinite air- and mois-
ture-stability in the solid state and were stored under ambi-
ent conditions.
Table 2. Fluorescence-emission properties of BF2 complexes of 2’-hy-
droxychalcones in CH2Cl2 at room temperature.
max
em
l
[nm]
Dl [cmꢀ1
]
Ff
0.02
t [ns]
1a
1b
2a
2b
3a
3b
4
556
609
608
602
584
595
644
3992
4155
2855
3350
2720
1780
2956
0.41
0.40
1.1
0.42
2.8
0.02
0.14
0.025
0.795
0.49
0.29
2.25
1.6
[a]
[a]
[a]
[a]
5a
5b
–
–
–
–
–
–
–
–
[a]
[a]
[a]
[a]
[a] No emission (see text).
values (Table 2); in particular, compound 3a (Ff =79.5% in
CH2Cl2) possessed high optical brightness (eꢀFf =
45000mꢀ1 cmꢀ1). The fluorescence-decay lifetimes were in
the sub-nanosecond-to-nanosecond range (Table 2; also see
the Supporting Information, Figure S3), which is in keeping
with the known fast excited-state dynamics of chalcones in
solution.[11] The fluorescence emission in dyes 5a/b, which
contained the strong electron-donating TPA group, was to-
tally quenched, irrespective of the nature of the solvent. The
presence of the two heavy iodine atoms in compound 5b
was believed to favor intersystem crossing to the triplet ex-
cited state through an internal heavy-atom effect.
Because the hydrolytic cleavage of the BF2 chelate is a
possible pathway for the degradation of the compounds in
solution, we spectrophotometrically investigated the stability
of solutions of the dyes in CH2Cl2 that contained EtOH
(0.5 vol%) as a competing Lewis base. Importantly, dye 3a
and acetonaphthone-based compounds 1b, 2b, and 3b
showed no evidence of degradation under these conditions.
In the case of compounds 1a and 1b, Figure 1 shows the re-
markable chemical stabilization effect of the acetonaph-
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
3
&
ÞÞ
These are not the final page numbers!

A. D’Alꢁo, F. Fages et al.
Figure 2. Molecular packing of compound 1b, as determined by single-
crystal X-ray diffraction: a) view along the ac plane, which shows the
packing of the BF2 complexes of chalcones; b) view of the p-stacks along
the a axis. Hydrogen atoms are omitted for clarity.
We obtained crystals of dye 1b that were suitable for
single-crystal X-ray structure analysis (Figure 2; also see the
Supporting Information, Figure S6 and Table S2).[21] Com-
parison of the crystal structure of compound 1b with that
previously reported[12a] for compound 1a shows that both
dyes display an almost-coplanar p-conjugated system. As
has been seen in the crystals of dipolar chromophores,[22] an-
tiparallel molecular packing leads to discrete 1D p-stacks
along the crystallographic a axis for both compounds 1a and
1b. We note a face-to-face superimposition of the p-conju-
gated system of dye 1b with an almost equal interplanar dis-
tance (3.52 ꢄ) along the stacks, whilst molecules of com-
pound 1a feature a kind of pairwise association. Within the
tighter dimer unit (3.48 ꢄ), molecules of compound 1a are
longitudinally displaced with respect to each other, thereby
reducing the p contact area. In contrast, adjacent molecules
of neighboring dimers (3.54 ꢄ) experience full p-overlap, as
in the case of 1b. The molecular planes in the p-stacks are
canted relative to the stacking a axis by 26.88 and 178 in
compounds 1a and 1b, respectively. Unlike in compound
1a, molecules of compound 1b form parallel chains, in
which the head-to-tail dipoles are aligned along the c axis
with a distance of 4.56 ꢄ between the naphthalene-end of
one molecule and the anisole-end of the following molecule
(see the Supporting Information, Figure S7). These chains
Figure 3. Optical properties of the thin solid-films: a) normalized absorp-
tion spectra of compounds 1a (c), 1b (b), 2a (g), and 5a (d);
b) normalized emission spectra of compounds 1a (c), 1b (b), 2b
(g), 3b (d), and 5b (-··-).
solution, thereby featuring a H-like transition band,[23] which
correlated with solid-state chromophore-organization.
Second, compounds 1b, 2b, 3a/b, and 4 displayed complex
absorption spectra that were characteristic of excitons that
originated from chromophores with parallel- and antiparal-
lel transition dipoles. This situation is typically the one that
occurs in the crystal of compound 1b, in which p-stacks and
dipole chains provide the adequate molecular arrangements
for Davydov splitting into high- and low-energy compo-
nents, respectively.[24] Finally, the absorption profile of dye
2a contained a strongly bathochromically shifted band with
a smaller Stokes shift (2640 cmꢀ1) relative to the other com-
pounds. This value was even smaller than that recorded for
a solution in CH2Cl2 (2855 cmꢀ1). These peculiar features
suggest the formation of J-like assemblies[23,25] that are pre-
sumably directed by the participation of the chlorine atoms
in lattice-stabilization.
ꢀ
are connected together through F H contacts (2.66 ꢄ) and
form sheets parallel to the (100) planes. As a result, the
structure is lamellar; in turn, the sheets that are packed anti-
parallel along the a axis generate the aforementioned p-
stacks. The powder-diffraction patterns, as calculated from
the single-crystal structures of compounds 1a/b, were in per-
fect agreement with the experimental values (see the Sup-
porting Information, Figures S8 and S9). Except for com-
pound 5a, which was amorphous, the remaining compounds
gave high-quality crystalline samples (see the Supporting In-
formation, Figure S10).
The solid-state electronic absorption properties of thin
films that were drop-cast from solutions in CH2Cl2 were in-
vestigated in transmission mode (Figure 3a; also see the
Supporting Information, Figure S11). According to the
trends in their optical properties, BF2–chalcones 1–4 can be
classified into three types: First, the absorption spectrum of
compound 1a was hypsochromically shifted relative to the
All of these compounds were found to be emissive in the
solid state (Table 3, Figure S11). The highly crystalline pow-
ders exhibited emission profiles that were identical to those
of the thin films and colloidal particles. In the case of com-
&
4
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Boron-Difluoride Complexes of 2’-Hydroxychalcone Derivatives
FULL PAPER
Table 3. Spectroscopic properties of boron-difluoride complexes of 2’-hy-
droxychalcones 1a/b–3a/b, 4, and 5a/b in the solid state.
ing of the emitting energy level, thereby leading to emission
wavelengths in the deep-red- and NIR regions. Remarkably,
the emission of light from p-stacked molecules did not oper-
ate at the expense of the emission quantum yield in the case
of, for example, compounds 2a or 4. This observation is con-
sistent with several theoretical- and experimental studies
that have provided evidence for efficient fluorescence emis-
sion in tightly-packed p-conjugated systems[26] and especially
in solid-state dipolar dyes.[16] Interestingly, harnessing elec-
tronic interactions between aromatic units within multichro-
mophoric assemblies has served to produce unique photo-
physical properties.[17,27] To account for the remarkable emis-
sion properties of the BF2 complexes of the 2’-hydroxychal-
cones, other factors can also be invoked. Chromophore-pla-
narization, as seen in the crystal structures of compounds
1a/b and presumably also in the other compounds, can
largely contribute to enhance the exciton radiative relaxa-
tion and to ensure red-shifted absorption and emission in
the solid state with respect to the solution. Such a shift was
even larger than that in polar acetonitrile. As was rational-
ized for dyes that are subject to aggregation-induced emis-
sion phenomena,[1b] the favored solid-state fluorescence may
also stem from the restriction of photoisomerization and in-
tramolecular torsional motions, which are actually two very
efficient processes for chalcones in solution.[11] Moreover,
owing to the dipolar character of the BF2–chalcones, large
Stokes shifts were obtained, which may contribute to the de-
creased self-quenching in the condensed phase because of
reduced spectroscopic overlap.[28] The solid-state-emission
characteristics of these molecules are clearly connected with
their tight crystalline packing arrangement.[29] In particular,
the manner in which the fluorophores are assembled has
been shown to be critical in the generation of solid-state CT
complexes with enhanced emission intensity.[17] Understand-
ing the fate of excited states and, in particular, unraveling
the mutual contribution of intramolecular and interchromo-
phoric CT excitons in these materials will require in-depth
experimental investigation and theoretical analysis.[7a,30]
TPA-containing dyes 5a/b followed a different behavior.
Although only compound 5a was obtained as an amorphous
solid, both compounds were found to be filmogenic when
drop-cast from CH2Cl2, thereby forming glass-like, dark-col-
ored deposits with nice optical quality. Their absorption
spectra displayed a broad transition band that extended
from 400 to 800 nm (Figure 2a; also see the Supporting In-
formation, Figure S11). Outstandingly, compounds 5a and
5b exhibited solid-state emission at 850 and 855 nm, respec-
tively (Figure 2b; also see the Supporting Information, Fig-
ure S11). The Ff values were low, especially when compar-
ing compound 5a (0.35%) with compound 2a, but one has
to note that both compounds 5a and 5b were not emissive
in solution. In the case of compound 5b, the emission-decay
lifetime did not exceed 4 ns in the solid state, which was evi-
dence for fluorescence as a radiative deactivation process.
The emission spectrum of a frozen solution of compound 5b
at 77 K was located at higher energy relative to that of the
thin film (see the Supporting Information, Figure S13) and a
lmabasx [nm]
l
[nm]
Dl [cmꢀ1
]
Ff [%]
max
em
1a
1b
2a
2b
3a
3b
4
351, 418(s)[a]
438, 515, 562
534, 603
627
845
722
736
717
796
755
850
855
7975
5959
2733
3957
4710
4473
2729
4847
4433
21.0
0.5
19.5
2.5
8.0
1.5
15.5
0.5
0.1
464, 521, 570(s)[a]
424, 456, 536(s)[a]
487, 545, 587
565, 626(s)[a]
602
5a
5b
620
[a] Shoulder.
pound 1b, excitation at the red edge or at the maximum of
the absorption band of a single crystal, a powder sample,
and a thin film all resulted in the same fluorescence spec-
trum. These spectra displayed a broad emission band with a
maximum beyond 700 nm, except for compound 1a
(627 nm; Figure 3b). The red-shifts were about 100–155 nm
(1a: 71 nm) relative to the solution. Compared to organic
solids that emit in the deep-red/NIR region, the four dyes
1b, 2b, and 3a/b (with similar ground-state spectroscopic
features) displayed high Ff values that decreased with de-
creasing energy-gap. These compounds also displayed large
Stokes shifts (4000–6000 cmꢀ1), larger than their values in
solution, especially for dyes 3a/b, which contained the
strongly electron-donating carbazolyl group. Whilst the
solid-state Ff values for compounds 1b, 2b, 3a/b, and 4
were somewhat lower than their values in solution, com-
pounds 1a and 2a featured a marked opposite effect with
higher Ff (about 20%) in the solid state relative to their
values in solution (see the Supporting Information, Fig-
ure S12). Such a value for solids that emit in the visible
range is not uncommon but it is noteworthy that it was ob-
tained herein for compound 1a, which adopted the H-like
aggregation mode. Moreover, dyes 2a and 4 displayed the
highest Ff values (19.5% at 722 nm and 15.5% at 755 nm,
respectively) reported to date for a solid-state organic dye
with fluorescence emission at a wavelength beyond 700 nm.
Recently values of 6% at 743 nm[6f] and 30% at 702 nm[7b]
were reported and represented to date the highest values
found in literature.
D–A dyes are known to experience dipole-induced molec-
ular interactions in the condensed phase. To enhance the ra-
diative exciton relaxation in such systems, efforts have been
directed towards preventing the close packing in the solid
state by using, for example, bulky groups or spiro kinks.[1]
The impeding of dipole–dipole interactions was also found
to be effective in symmetrical molecular frameworks that
were built with the D–A–D (or A–D–A) electronic struc-
ture.[7] In that respect, BF2–chalcones behaved very differ-
ently in the sense that their optical properties were recorded
for crystalline solids that were characterized by molecular
order and tight packing, two features that are conventionally
thought to be detrimental to luminescence in organic crys-
tals. We surmise that this situation could explain the lower-
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
5
&
ÞÞ
These are not the final page numbers!

A. D’Alꢁo, F. Fages et al.
1b-H: Yield: 28%; 1H NMR (250 MHz, CDCl3): d=14.78 (s, 1H), 8.34
photoluminescence lifetime value in the range of several mi-
croseconds could be obtained, thus indicating the participa-
tion of the triplet manifold at low temperature.
(td, 3J
1H), 7.69 (d, 3J
(m, 3H), 7.42 (m, 1H), 7.40 (d, 3J
3J(H,H)=8.5 Hz, 1H), 7.80 (d, 3J
(H,H)=8.3 Hz, 4J(H,H)=0.8 Hz, 1H), 7.81 (d, 3J
ACHTUNGTRNEUNGN ACHTNUGTRENNUNG ACTUHNGTRENNUGN
ACHUTNGRENNUG CAHTUNGTRENNUNG
(H,H)=9.0 Hz, 1H), 7.61 (d, 3J
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
13C NMR (62.5 MHz, CDCl3): d=193.19, 164.26, 161.98, 144.94, 137.31,
130.52, 130.02, 127.55, 127.37, 125.83, 125.57, 124.47, 123.95, 118.07,
117.98, 114.52, 113.54, 55.42 ppm.
Conclusion
1b: 1H NMR (250 MHz, CDCl3): d=8.68 (td, 3J
4J(H,H)=1.0 Hz, 1H), 8.48 (d, 3J
(H,H)=15.0 Hz, 1H), 7.78 (m, 4H),
7.69 (d, 3J(H,H)=9.3 Hz, 1H), 7.62 (m, 1H), 7.54 (d, 3J
(H,H)=15.0 Hz,
1H), 7.35 (td, JCATHNUTGNEURNN(G H,H)=9.3 Hz, JACHTUNGTRNEG(NU H,H)=0.8 Hz, 1H), 7.05 (d, JACHTUNGTRENNUNG(H,H)=
ACHTUNGTREN(NUNG H,H)=8.3 Hz,
In conclusion, we have prepared a series of BF2 complexes
of 2’-hydroxychalcone derivatives that display high stability
in solution and in the solid-state, large Ff values in solution,
and intense NIR emission in closely packed solids. These
dyes were obtained in a straightforward manner according
to expeditious preparation- and facile purification proce-
dures. We are currently working towards the synthesis of an-
alogues with increased emission efficiency at wavelengths
well-beyond the 800 nm threshold. Moreover, materials that
are based on closely-packed dipolar dyes have recently been
shown to benefit from high charge-mobility.[31] Future work
will also involve evaluating the semiconducting properties of
BF2-containing chalcones and exploiting their NIR emission
and panchromatic absorption in displays and in solar-energy
technologies.
G
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
3
4
3
8.8 Hz, 2H), 3.95 ppm (s, 3H); 19F NMR (235 MHz, CDCl3): d=ꢀ140.88
10
11
ꢀ
ꢀ
( B F, 0.2), 140.94 ppm ( B F, 0.8).
2a-H: Yield: 58%; 1H NMR (250 MHz, CDCl3): d=13.49 (s, 1H), 8.13
(d, 3J(H,H)=15.3 Hz, 1H), 8.03 (s, 1H); 7.86 (d, 4J
ACTHNUGTRENNUGN ACHTUNGTRENNNUG
7.79 (m, 3H), 7.60 (d, 3J
A
ACHTUNGTRENNUNG
1H), 7.19 (m, 2H), 3.95 ppm (s, 3H); MS (ESI positive mode): m/z:
373.1 [M+H]+; MS (ESI negative mode): m/z: 371.0 [MꢀH]ꢀ; elemental
analysis calcd (%) for C20H14Cl2O3·1/6CH2Cl2: C 62.53, H 3.73; found:
C 62.65, H 3.72.
2a: Because of low solubility, NMR spectra could not be recorded. MS
(ESI positive mode): m/z: 443.0 [M+Na]+, 459.0 [M+K]+; elemental
analysis calcd (%) for C20H13BF2Cl2O3·1/4CH2Cl2: C 54.99, H 3.08;
found: C 54.78, H 3.08.
2b-H: Yield: 69%; 1H NMR (250 MHz, CDCl3): d=14.96 (s, 1H), 8.51
(d, 3J
7.88 (d, 3J
1H), 7.54 (t, 3J
(H,H)=8.5 Hz, 1H), 8.11 (d, 3J
ACHUTGTNRENNUG CAHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
C
ACHTUNGTRENNUNG
(m, 2H), 3.94 ppm (s, 3H); 13C NMR (62.5 MHz, CDCl3): d=193.16,
164.37, 159.14, 145.44, 137.35, 136.08, 130.88, 130.33, 130.17, 130.09,
128.76, 127.60, 127.38, 125.87, 125.56, 124.50, 124.48, 123.96, 119.58,
119.39, 118.13, 113.56, 106.10, 55.40 ppm; MS (ESI positive mode): m/z:
355.1 [M+H]+; MS (ESI negative mode): m/z: 353.1 [MꢀH]ꢀ; elemental
analysis calcd (%) for C24H18O3·1/4CH2Cl2: C 77.54, H 4.96; found:
C 77.72, H 5.03.
Experimental Section
General procedures: All solvents for the syntheses were of analytic
grade; spectroscopic measurements were carried out with spectroscopic-
grade solvents. NMR spectra (1H, 13C, and 19F) were recorded at RT on a
BRUKER AC 250 that operated at 250, 62.5, and 235 MHz for H-, 13C-,
1
2b: Because of low solubility, NMR spectra could not be recorded. MS
(ESI positive mode): m/z: 425.1 [M+Na]+, 441.1 [M+K]+; elemental
analysis calcd (%) for C24H17BF2O3·1/2CH2Cl2: C 66.18, H 4.08; found:
C 65.72, H 4.16.
and 19F nuclei, respectively. Data are listed in parts per million (ppm)
and are reported relative to tetramethylsilane (1H and 13C); residual sol-
vent peaks of the deuterated solvents were used as an internal standard.
MS and elemental analysis were performed at the Spectropole de Mar-
seille (http://www.spectropole.fr/).
3a-H: Yield: 54%; 1H NMR (250 MHz, CDCl3): d=13.69 (s, 1H), 8.35
(d, 4J
G
G
R
General synthesis: In a 100 mL round-bottomed flask, derivatives of 2’-
hydroxyacetophenone or 1’-hydroxyacetonaphthone (1 molequiv) and
the appropriate aldehyde (1 molequiv) were dissolved in EtOH. Subse-
quently, a solution of sodium hydroxide (2.5 molequiv) in water (1 mL)
was added to the solution and the mixture was stirred for 16 h at 608C.
After cooling, the solution was acidified to pH 1 and the precipitate was
filtered through glass filter funnel. The solid was the recrystallized twice
from CH2Cl2/EtOH 1:1 to yield the pure 2’-hydroxychalcone ligands 1a/
b-H, 2a/b-H, 3a/b-H, 4, and 5a/b-H. In a 50 mL round-bottomed flask,
the 2’-hydroxychalcone derivatives (1 molequiv) was dissolved in CH2Cl2.
Boron trifluoride etherate (1.2 molequiv) was added and the solution
was heated at reflux for 2 h. The solution was concentrated, cooled to
RT, and the precipitate was filtered off, cleaned with Et2O, and dried in
air to yield the pure dyes 1a/b, 2a/b, 3a/b, 4, and 5a/b.
3J
3J
N
ACHTUNGTRENNUNG
7.52 (dd, J
3J(H,H)=7.8 Hz, 4J
R
3.85 ppm (s, 3H); 13C NMR (62.5 MHz, CDCl3): d=191.86, 166.59,
165.89, 146.02, 142.53, 141.53, 131.11, 126.54, 126.42, 125.88, 123.35,
122.66, 121.58, 120.50, 119.83, 116.97, 114.29, 108.90, 107.48, 101.06, 55.53,
29.24 ppm; MS (ESI positive mode): m/z: 358.1 [M+H]+; MS (ESI, nega-
tive mode): m/z: 356.1 [MꢀH]ꢀ; elemental analysis calcd (%) for
C23H19NO3·1/5CH3CH2OH: C 76.66, H 5.55, N 3.82; found: C 76.79,
H 5.47, N 3.80.
1
3
3a: H NMR (250 MHz, CDCl3): d=8.57 (d, J
(d, 4J(H,H)=1.3 Hz, 1H), 8.10 (d, 3J
(H,H)=8.3 Hz, 1H), 7.82 (m, 2H),
7.43 (m, 4H), 7.29 (d, 3J
ACHTUNGERTN(NUNG H,H)=14.8 Hz, 1H), 8.43
G
ACHTUNGTRENNUNG
1a-H: Yield: 21%; 1H NMR (250 MHz, CDCl3): d=12.98 (s, 1H), 7.96
AHCTUNGTRENNG(UN H,H)=7.5 Hz, 1H), 6.50 (m, 2H), 3.77 (s, 3H),
3.75 ppm (s, 3H); 19F NMR (235 MHz, CDCl3): d=ꢀ142.98 ( B F,
10
(m, 1H), 7.94 (d, 3J(H,H)=15.3 Hz, 1H), 7.66 (d, 3J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
ꢀ
11
7.57 (d, 3J
3J
ACHTUNGTRENNUNG
ꢀ
0.2F), ꢀ143.04 ppm ( B F, 0.8F); MS (ESI positive mode): m/z: 428.1
[M+Na]+, 444.1 [M+K]+; elemental analysis calcd (%) for
C23H18BF2NO3·1/8CH2Cl2: C 66.80, H 4.42, N 3.37; found: C 66.81,
H 4.50, N 3.58.
ACHTUNGTRENNUNG
d=193.69, 163.56, 162.04, 145.37, 136.16, 130.57, 129.54, 127.35, 120.13,
118.76, 118.60, 117.60, 114.53, 55.47 ppm.
3b-H: Yield: 63%; 1H NMR (250 MHz, CDCl3): d=15.14 (s, 1H), 8.51
1
3
1a: H NMR (250 MHz, CDCl3): d=8.53 (d, J
(dd, 3J(H,H)=8.0 Hz, 3J(H,H)=1.0 Hz, 1H), 7.80 (d, 3J
2H), 7.78 (m, 1H), 7.52 (d, 3J(H,H)=15.0 Hz, 1H), 7.19 (dd, 3J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
(d, 3J
8.17 (d, 3J
3H), 7.64 (t, 3J(H,H)=8.5 Hz, 1H), 7.54 (m, 2H), 7.44 (d, 3J
ACTHNUGERTNNUNG ACHTUNGTRENNUNG(H,H)=
(H,H)=8.0 Hz, 1H), 8.43 (s, 1H), 8.24 (d, 3J
ACHUTGTNRENNUG CAHTUNGTRENNUNG
G
G
ACHTUNGTRENNUNG
ACHUTNGRENNUG CAHTUNGTRENNUNG
(H,H)=8.0 Hz, 1H), 7.95 (d, 3J
G
8.8 Hz, 4J(H,H)=0.8 Hz, 1H), 7.07 (m, 1H), 7.05 ppm (d, 3J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
8.8 Hz, 2H); 19F NMR (235 MHz, CDCl3): d=ꢀ142.22 ( B F, 0.2),
8.3 Hz, 2H), 7.32 (m, 2H), 3.89 ppm (s, 3H); 13C NMR (62.5 MHz,
CDCl3): d=193.17, 164.23, 146.78, 142.69, 141.58, 137.27, 129.93, 127.39,
10
ꢀ
11
ꢀ
ꢀ142.28 ppm ( B F, 0.8).
&
6
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Boron-Difluoride Complexes of 2’-Hydroxychalcone Derivatives
FULL PAPER
126.74, 126.51, 125.92, 125.78, 125.63, 124.47, 124.09, 123.44, 122.71,
121.83, 120.57, 119.93, 177.99, 117.19, 113.66, 108.99, 108.94, 29.31 ppm;
MS (ESI positive mode): m/z: 378.0 [M+H]+; MS (ESI negative mode):
m/z: 376.1 [MꢀH]ꢀ; elemental analysis calcd (%) for C26H19NO2·1/
4CH2Cl2: C 79.08, H 4.93, N 3.51; found: C 79.39, H 4.87, N 3.55.
dilute-solution measurements (10 mm quartz cell) with a red-sensitive
Hamamatsu R928 photomultiplier tube for spectra up to 700 nm and a
Hamamatsu R406 photomultiplier tube for spectra above 700 nm. Special
care was taken to correct NIR-emission spectra that were obtained with
the latter device. According to the procedure described by Parker,[32] we
recorded the observed photomultiplier output Al at wavelength l, which
corresponded to the apparent emission spectrum. Al is given by [Eq. (1)],
where Fl and Sl are the corrected emission spectrum and the spectroscop-
ic sensitivity factor of the monochromator-photomultiplier setup, respec-
tively.
3b: Because of low solubility, NMR spectra could not be recorded. MS
(ESI positive mode): m/z: 447.9 [M+Na]+, 463.9 [M+K]+; elemental
analysis calcd (%) for C26H18BF2NO2·1/3(C2H5)2O: C 72.96, H 4.78,
N 3.11; C 72.73, H 4.45, N 3.26.
1
4-H: Yield: 64%; H NMR (250 MHz, CDCl3): d=13.02 (s, 1H), 9.11 (d,
3J
3J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H,H)=15.3 Hz, 1H), 8.59 (d, 3J
A
Al ¼ ðFlÞðSlÞ=l2
ð1Þ
ACHTUNGTRENNUNG
7.56 (m, 1H), 7.05 ppm (m, 2H); 13C NMR (62.5 MHz, CDCl3): d=
193.40, 163.75, 142.04, 136.40, 133.26, 131.29, 130.69, 130.58, 129.71,
129.01, 128.95, 128.32, 127.32, 126.41, 126.26, 126.10, 125.06, 124.99,
124.56, 124.27, 122.46, 121.86, 120.19, 118.91, 118.70 ppm; MS (ESI posi-
tive mode): m/z: 349.0 [M+H]+; MS (ESI negative mode): m/z: 347.1
[MꢀH]ꢀ; elemental analysis calcd (%) for C25H16O2: C 86.19, H 4.63;
found: C 86.17, H 4.54.
To calculate Sl, we used 4-N,N-dimethylamino-4’-nitrostilbene (DMANS)
as a standard NIR fluorophore for which its corrected emission spectrum
has been precisely determined (see the Supporting Information, Fig-
ure S14).[33] Luminescence quantum yields (Ff) were measured in dilute
solutions in CH2Cl2 with an absorbance of below 0.1 by using [Eq. (2],
where OD(l) is the absorbance at the excitation wavelength (l), n the re-
fractive index, and I the integrated luminescence intensity.
4: Because of low solubility, NMR spectra could not be recorded. MS
(ESI positive mode): m/z: 418.9 [M+Na]+, 434.9 [M+K]+; elemental
analysis calcd (%) for C25H15BF2O2: C 75.79, H 3.82; found: C 76.29,
H 3.93.
2
Ff x=Ff r ¼ ½ODrðlÞ=ODxðlÞꢁ½nx2=nr ꢁ½Ix=Irꢁ
ð2Þ
Subscripts “r” and “x” represent the reference compound and the
sample, respectively. The luminescence quantum yields were not correct-
ed with their refractive indices. Herein, the reference solution was ruthe-
nium trisbipyridine bischloride in water (Ffr =0.021) for compounds that
absorbed in the 450 nm region, whilst rhodamine B (Ffr =0.49) in EtOH
was used for excitation between 540 and 560 nm. Excitation of the refer-
ence- and sample compounds was performed at the same wavelength.
Solid-state luminescence quantum yields were measured on thin films for
all compounds and on suspensions of colloidal aggregates in water for
compounds 1b, 2b, and 3b. Emission spectra were obtained by using
front-face illumination. Identical values were found, within experimental
error, for compounds 1b, 2b, and 3b by using both techniques. The col-
loidal aggregate luminescence was compared to that of ruthenium trisbi-
pyridine bischloride in water (Ffr =0.021) and the luminescence quantum
yields were calculated by using Equation (2). Molecules for which the flu-
orescence quantum yields of thin films could be calibrated with those ob-
tained on aggregates were used as references for films of the other com-
pounds. All luminescence quantum yields were measured with an absorb-
ance below 0.1 on three different samples to minimize errors. We
checked that thin films gave constant absorbance values when recorded
at different places on the film surface.
5a-H: Yield: 29%; 1H NMR (250 MHz, CDCl3): d=13.64 (s, 1H), 7.95
(d, 3J
4J
(m, 6H), 7.02 ppm (d, 3J
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H,H)=15.3 Hz, 1H), 7.78 (d, 4J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H,H)=2.5 Hz, 1H), 7.52 (d, 3J
CDCl3): d=191.16, 159.98, 151.24, 147.52, 146.42, 135.26, 130.58, 129.65,
127.22, 126.61, 125.91, 124.72, 123.99, 123.04, 121.34, 120.74, 115.50 ppm;
MS (ESI positive mode): m/z: 460.0 [M+H]+; MS (ESI negative mode):
m/z: 458.1 [MꢀH]ꢀ; elemental analysis calcd (%) for C27H19Cl2NO2:
C 70.44, H 4.16, N 3.04; found: C 70.90, H 4.27, N 3.10.
1
3
5a: H NMR (250 MHz, CDCl3): d=8.75 (d, JACTHUNGTRENNNUG
(d, 4J
A
E
3J
3J
ACHTUNGTRENNUNG
19
10
ꢀ
(H,H)=9.0 Hz, 2H); F NMR (235 MHz, CDCl3): d=ꢀ143.56 ( B F,
11
A
ꢀ
0.2F), ꢀ143.62 ppm ( B F, 0.8F); MS (ESI, positive mode): m/z: 530.1
[M+Na]+, 546.1 [M+K]+; elemental analysis calcd (%) for
C27H18BF2Cl2NO2·1/5CH2Cl2: C 62.21, H 3.53, N 2.67; found: C 62.32,
H 3.71, N 2.71.
5b-H: Yield: 34%; 1H NMR (250 MHz, CDCl3): d=14.00 (s, 1H), 8.20
(d, 4J
(H,H)=1.8 Hz, 1H), 8.13 (d, 4J
E
3J
3J
3J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H,H)=15.0 Hz, 1H), 7.52 (d, 3J
Time-resolved fluorescence emission: For compounds that had very short
excited-state decays (<1 ns), luminescence-lifetime measurements were
performed by using time-correlated single-photon counting (TCSPC)
spectroscopy. In brief, femtosecond pulses (150 fs, 800 nm, 76 MHz) that
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
151.97, 151.21, 147.49, 146.43, 137.88, 130.56, 129.63, 126.67, 125.88,
124.68, 121.94, 120.77, 115.29, 88.46, 80.07 ppm; MS (ESI positive mode):
m/z: 643.8 [M+H]+; MS (ESI negative mode): m/z: 641.9 [MꢀH]ꢀ; ele-
mental analysis calcd (%) for C27H19I2NO2·1/2CH2Cl2: C 48.17, H 2.94,
N 2.04; found: C 48.16, H 2.87, N 2.05.
were generated by using
a tunable mode-locked Ti:Sapphire laser
(MaiTai HP, Spectra-Physics) were externally doubled by using a 1 mm-
thick BBO crystal. The pulse-repetition rate was slowed to 7.6 MHz by
using a pulse-picker (Model 3980, Spectra-Physics), thereby extending
the delay between consecutive pulses to 126 ns. The generated 400 nm
femtosecond pulses illuminated a 1 cm-thick cuvette that contained the
solution under study. The photoexcited fluorescence was collected at a
908 geometry and sent into a subtractive double-monochromator (DH10,
Jobin–Yvon) before being detected by a silicon avalanche photodiode
(PDM50CTC, Micro Photon Devices). The width of the entrance- and
exit slits ensured 1 nm spectroscopic resolution in the lifetime measure-
ments. A small part of the 800 nm laser beam was selected and sent to a
photodiode (TDA 200, Picoquant). The laser- and fluorescence signals
were subsequently sent to a correlator (PicoHarp 300, Picoquant). Thus,
the time of arrival of the fluorescence photons could be retrieved with
16 ps resolution and the fluorescence temporal decay could be recon-
structed. We estimated the temporal response of the setup to be 150 ps
FWHM. The instrumental response function (IRF) was systematically
measured for all experimental runs. In addition, we measured the tempo-
ral response of the solvent (CH2Cl2) at all wavelengths. This response
was then subtracted from the sample’s response. Longer-lifetime meas-
5b: 1H NMR (250 MHz, CDCl3): d=8.48 (d, 3J
ACHTUNGTRENNUNG
8.35 (d,4J
ACHTUNGTRENNUNG
G
R
3J
3J
10
ꢀ
(H,H)=8.8 Hz, 2H); F NMR (235 MHz, CDCl3): d=ꢀ143.58 ( B F,
11
G
0.2F), ꢀ143.64 ppm ( B F, 0.8F); MS (ESI positive mode): m/z: 713.8
[M+Na]+, 729.7 [M+K]+; elemental analysis calcd (%) for
C27H18BF2I2NO2·1/3(C2H5)2O: C 47.54, H 3.00, N 1.96; found: C 47.52,
H 2.83, N 2.08.
Steady-state optical spectroscopy: UV/Vis-absorption spectra were meas-
ured on a Varian Cary 50. Solid-state spectra were measured by drop-
casting a solution of the compound in dry CH2Cl2 onto a quartz plate
and correcting for a scattered-light background. Emission spectra were
measured on a Horiba-JobinYvon Fluorolog-3 spectrofluorimeter that
was equipped with three-slit double-grating excitation and a spectrograph
emission monochromator with dispersions of 2.1 nmmmꢀ1 (1200 groo-
vesmmꢀ1). Steady-state luminescence was excited by using unpolarized
light from a 450 W xenon CW lamp and detected at an angle of 908 for
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
7
&
ÞÞ
These are not the final page numbers!

A. D’Alꢁo, F. Fages et al.
urements were carried out on a HORIBA Jobin Yvon IBH FluoroLog-3
spectrofluorimeter that was adapted for time-correlated single-photon
counting. For these measurements, pulsed LEDs with an appropriate
wavelength were used. Emission was monitored perpendicular to the ex-
citation pulse and spectroscopic selection was achieved by passage
through the spectrograph. A thermoelectrically cooled single-photon-de-
tection module (HORIBA Jobin Yvon IBH, TBX-04-D) that incorporat-
ed a fast-rise-time photomultiplier tube, a wide-bandwidth preamplifier,
and a picosecond-constant fraction discriminator was used as the detec-
tor. Signals were acquired by using an IBH DataStation Hub photon-
counting module and data analysis was performed by using the commer-
cially available DAS 6 decay-analysis software package from HORIBA
Jobin Yvon IBH; the reported t values are given with an estimated un-
certainty of about 10%.
hedron Lett. 2010, 51, 6195–6198; f) J.-H. Olivier, J. Widmaier, R.
Ziessel, Chem. Eur. J. 2011, 17, 11709–11714.
[7] a) G. Qian, B. Dai, M. Luo, D. Yu, J. Zhan, Z. Zhang, D. Ma, Z. Y.
Wang, Chem. Mater. 2008, 20, 6208–6216; b) M. Shimizu, R. Kaki,
Y. Takeda, T. Hiyama, N. Nagai, H. Yamagishi, H. Furutani, Angew.
Chem. 2012, 124, 4171–4175; Angew. Chem. Int. Ed. 2012, 51, 4095–
4099; c) X. Du, Z. Y. Wang, Chem. Commun. 2011, 47, 4276–4278.
[8] St. v. Kostanecki, J. Tambor, Chem. Ber. 1899, 32, 1921–1926.
[9] a) R. A. Caldwell, M. Singh, J. Am. Chem. Soc. 1983, 105, 5139–
5140; b) Y. Wang, J. Phys. Chem. 1985, 89, 3799–3805; c) P. S.
Patila, S. M. Dharmaprakasha, K. Ramakrishnab, H.-K. Func, R. Sai
Santosh Kumard, D. Narayana Raod, J. Cryst. Growth 2007, 303,
520–524; d) C. Ruziꢁ, M. Krayer, J. S. Lindsey, Org. Lett. 2009, 11,
1761–1764; e) L. Mager, C. Melzer, M. Barzoukas, A. Fort, S. Mꢁry,
J.-F. Nicoud, Appl. Phys. Lett. 1997, 71, 2248–2250.
X-ray structure analysis: Crystals of dye 1b that were suitable for X-ray
analysis were obtained by the slow evaporation of a solution in CH2Cl2/
cyclohexane (10:1). Powder-diffraction measurements were realized in
transmission mode by using an INEL diffractometer that was equipped
with a linear detector INEL CPS 120 and a quartz curved monochroma-
[10] T. Teshima, M. Takeishi, T. Arai, New J. Chem. 2009, 33, 1393–1401.
[11] a) K. Rurack, M. L. Dekhtyar, J. L. Bricks, U. Resch-Genger, W.
Rettig, J. Phys. Chem. A 1999, 103, 9626–9635; b) K. Rurack, J. L.
Bricks, G. Reck, R. Radeglia, U. Resch-Genger, J. Phys. Chem. A
2000, 104, 3087–3109.
tor. The radiation length was 1.54056 ꢄ, which corresponded to CuKa1
.
The powder was deposited into glass capillaries with diameters of 0.5,
0.7, and 1 mm. For the samples in which the crystallites agglomerated
into quite large pieces, the powder was broken into small parts with a
sharp spatula; milling was not used so as to prevent any possible changes
in the crystalline structure. Iodine-containing samples were deposited
into capillaries with a diameter of 0.5 mm and those that contained chlor-
ine were deposited into capillaries with a diameter of 0.7 mm to diminish
the X-ray absorption into the samples and, thus, to obtain better X-ray
diffraction data. The intensity data for the single-crystal X-ray-diffraction
analysis of compound 1b were collected at RT on a Bruker-Nonius Kap-
paCCD diffractometer by using MoKa radiation (l=0.71073 ꢄ). Data col-
lection was performed with COLLECT,[34] cell-refinement and data-re-
duction were performed with DENZO/SCALEPACK.[35] The structure
was solved with SIR92[36] and SHELXL-97[37] was used for full-matrix
least-squares refinement. Then, the H atoms were introduced at idealized
positions and constrained to their parent atom during the last refine-
ments. Graphics were generated with MERCURY 2.4.
[12] a) H. Reyes, Ma. Conception Garcꢇa, B. M. Flores, H. Lꢈpez-Rebol-
ledo, R. Santillꢉn, N. Farfꢉn, J. Mex. Chem. Soc. 2006, 50, 106–113;
b) J. A. VanAllan, G. A. Reynolds, J. Heterocycl. Chem. 1969, 6, 29–
35; c) A. R. Alcantara, J. M. Marinas, J. V. Sinisterra, Tetrahedron
Lett. 1987, 28, 1515–1518; d) M. G. Marathey, J. Org. Chem. 1955,
20, 563–571; e) K. B. Raut, S. H. Wender, J. Org. Chem. 1960, 25,
50–52.
[13] S. A. Agarkar, R. R. Kulkarni, V. V. Dhas, A. A. Chinchansure, P.
Hazra, S. P. Joshi, S. B. Ogale, ACS Appl. Mater. Interfaces 2011, 3,
2440–2444.
[14] a) N. N. Vasil’ev, A. Ya. Gorelenko, I. I. Kalosha, V. A. Mezhentsev,
I. G. Tishchenko, V. A. Tolkachev, V. Ya. Tulach, A. P. Shkadarevich,
Zh. Prikl. Spektrosk. 1985, 42, 51–55; b) T. Kotowski, A. Orzeszko,
W. Skubiszak, T. Stacewicz, J. A. Soroka, Opt. Appl. 1984, 14, 267–
271.
[15] Y. Cui, Y. Zhang, P. N. Prasad, J. S. Schildkraut, D. J. Williams, Appl.
Phys. Lett. 1992, 61, 2132–2134.
[16] a) J. Massin, W. Dayoub, J.-C. Mulatier, C. Aronica, Y. Bretonniꢊre,
C. Andraud, Chem. Mater. 2011, 23, 862–873; b) U. Rçsch, S. Yao,
R. Wortmann, F. Wꢆrthner, Angew. Chem. 2006, 118, 7184–7188;
Angew. Chem. Int. Ed. 2006, 45, 7026–7030; c) W. Z. Yuan, Y.
Gong, S. Chen, X. Y. Shen, J. W. Y. Lam, P. Lu, Y. Lu, Z. Wang, R.
Hu, N. Xie, H. S. Kwok, Y. Zhang, J. Zhi Sun, B. Z. Tang, Chem.
Mater. 2012, 24, 1518–1528.
Acknowledgements
We thank Aix Marseille Universitꢁ and the CNRS for financial support.
A.D. and F.F. thank Dr. O. Maury and Dr. C. Andraud for kindly provid-
ing access to their spectroscopic facilities.
[17] M. D. Gujrati, N. S. Kumar, A. S. Brown, B. Captain, J. N. Wilson,
Langmuir 2011, 27, 6554–6558.
[18] a) T. M. Figueira-Duarte, K. Mꢆllen, Chem. Rev. 2011, 111, 7260–
7314; b) F. Moggia, C. Videlot-Ackermann, J. Ackermann, P.
Raynal, H. Brisset, F. Fages, J. Mater. Chem. 2006, 16, 2380–2386.
[19] a) M. Fourmiguꢁ, P. Batail, Chem. Rev. 2004, 104, 5379–5418;
b) G. R. Desiraju, R. Parthasarathy, J. Am. Chem. Soc. 1989, 111,
8725–8726.
[20] P.-T. Chou, M. L. Martinez, W. C. Cooper, J. Am. Chem. Soc. 1992,
114, 4943–4944.
[21] CCDC-873726 (1b) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
[1] a) M. Shimizu, T. Hiyama, Chem. Asian J. 2010, 5, 1516–1531; b) Y.
Hong, J. W. Y. Lama, B. Z. Tang, Chem. Commun. 2009, 4332–4353.
[2] a) G. Qian, Z. Y. Wang, Chem. Asian J. 2010, 5, 1006–1029; b) V. J.
Pansare, S. Hejazi, W. J. Faenza, R. K. Prudꢅhomme, Chem. Mater.
2012, 24, 812–827.
[3] R. Raghavachari, Near-Infrared Applications in Biotechnology,
Marcel Dekker, New York, 2001.
[4] a) Y. Geerts, H. Quante, H. Platz, R. Mahrt, M. Hopmeier, A.
Bohm, K. Mꢆllen, J. Mater. Chem. 1998, 8, 2357–2369; b) T. Weil, T.
Vosch, J. Hofkens, K. Peneva, K. Mꢆllen, Angew. Chem. 2010, 122,
9252–9278; Angew. Chem. Int. Ed. 2010, 49, 9068–9093.
[22] F. Wꢆrthner, S. Yao, T. Debaerdemaeker, R. Wortmann, J. Am.
Chem. Soc. 2002, 124, 9431–9447.
[5] U. Mayerhçffer, B. Fimmel, F. Wꢆrthner, Angew. Chem. 2012, 124,
168–171; Angew. Chem. Int. Ed. 2012, 51, 164–167.
[23] Despite the fact they do not display the typical spectroscopic charac-
teristics of perfect H- or J-aggregates (see ref. [25]), we classified ag-
gregates of compounds 1a and 2a as H- and J-like aggregates, re-
spectively, on the basis of the spectroscopic trend of their most-in-
tense absorption band.
[6] a) G. Ulrich, S. Goeb, A. De Nicola, P. Retailleau, R. Ziessel, J.
Org. Chem. 2011, 76, 4489–4505; b) G. Ulrich, R. Ziessel, A. Harri-
man, Angew. Chem. 2008, 120, 1202–1219; Angew. Chem. Int. Ed.
2008, 47, 1184–1201; c) K. Umezawa, A. Matsui, Y. Nakamura, D.
Citterio, K. Suzuki, Chem. Eur. J. 2009, 15, 1096–1106; d) M. Ben-
stead, G. H. Mehl, R. W. Boyle, Tetrahedron 2011, 67, 3573–3601;
e) Y. Kubota, J. Uehara, K. Funabiki, M. Ebihara, M. Matsui, Tetra-
[24] J. B. Birks, Photophysics of Aromatic Molecules, Wiley, New York,
1970.
&
8
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Boron-Difluoride Complexes of 2’-Hydroxychalcone Derivatives
FULL PAPER
[25] a) F. Wꢆrthner, T. E. Kaiser, C. R. Saha-Mçller, Angew. Chem. 2011,
123, 3436–3473; Angew. Chem. Int. Ed. 2011, 50, 3376–3410; b) J-
Aggregates (Ed.: T. Kobayashi), World Scientific, Singapore, 1996.
[26] a) J. Cornil, D. Beljonne, J.-P. Calbert, J.-L. Brꢁdas, Adv. Mater.
2001, 13, 1053–1067; b) F. C. Spano, Chem. Phys. Lett. 2000, 331, 7–
13; c) F. Meinardi, M. Cerminara, A. Sassella, A. Borghesi, P. Spear-
man, G. Bongiovanni, A. Mura, R. Tubino, Phys. Rev. Lett. 2002, 89,
157403.
[31] a) For a recent review, see: A. Mishra, P. Bꢋuerle, Angew. Chem.
2012, 124, 2060–2109; Angew. Chem. Int. Ed. 2012, 51, 2020–2067;
b) H. Bꢆrckstꢆmmer, E. V. Tulyakova, M. Deppisch, M. R. Lenze,
N. M. Kronenberg, M. Gsꢋnger, M. Stolte, K. Meerholz, F. Wꢆrth-
ner, Angew. Chem. 2011, 123, 11832–11836; Angew. Chem. Int. Ed.
2011, 50, 11628–11632.
[32] C. A. Parker, Photoluminescence of Solutions, Elsevier, Amsterdam,
1969.
[27] a) J. Gao, C. Strꢋssler, D. Tahmassebi, E. T. Kool, J. Am. Chem. Soc.
2002, 124, 11590–11591; b) H. Kashida, K. Sekiguchi, X. Liang, H.
Asanuma, J. Am. Chem. Soc. 2010, 132, 6223–6230.
[28] a) S. Jursenas, A. Gruodis, G. Kodis, M. Chachisvilis, V. Gulbinas,
E. A. Silinsh, L. Valkunas, J. Phys. Chem. B 1998, 102, 1086–1094;
[33] J. R. Lakowicz, Principles of Fluorescence Spectroscopy, 3rd ed.,
Kluwer, New York, 2006.
[34] COLLECT, Nonius BV, Delft, The Netherlands, 2001.
[35] Z. Otwinowski, W. Minor, Methods in Enzymology, in Macromolec-
ular Crystallography, Part A, Vol. 276 (Eds.: C. W. Carter, Jr., R. M.
Sweet), Academic Press, New York, 1997, pp. 307–326.
[36] A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M. C.
Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 1994, 27, 435.
[37] G. M. Sheldrick, Acta Crystallogr. A 2008, 64, 112–122.
´
b) V. Bulovic, P. E. Burrows, S. R. Forrest, J. A. Cronin, M. E.
Thompson, Chem. Phys. 1996, 210, 1–12.
[29] H. Langhals, T. Potrawa, H. Nçth, G. Linti, Angew. Chem. 1989,
101, 497–499; Angew. Chem. Int. Ed. Engl. 1989, 28, 478–480.
[30] a) F. C. Spano, J. Chem. Phys. 2003, 118, 981–994; b) F. Meinardi,
M. Cerminara, A. Sassella, R. Bonifacio, R. Tubino, Phys. Rev. Lett.
2003, 91, 247401.
Received: May 23, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
9
&
ÞÞ
These are not the final page numbers!

A. D’Alꢁo, F. Fages et al.
Near-Infrared Emission
A. D’Alꢀo,* D. Gachet, V. Heresanu,
M. Giorgi, F. Fages* ......... &&&& — &&&&
Efficient NIR-Light Emission from
Solid-State Complexes of Boron
Difluoride with 2’-Hydroxychalcone
Derivatives
Tint it black! Complexation with
boron difluoride converts 2’-hydroxy-
chalcone derivatives into strongly
absorbing/emitting dyes. These darkly
colored crystalline solids exhibit NIR
emission, owing to densely packed p-
stacks of dipolar chromophores.
&
10
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!