Room-temperature phosphorescence of crystalline 1,4-bis(aroyl)-2,5-dibromobenzenes

Article abstract of DOI:10.1002/ejoc.201501382

There is a growing interest in metal-free organic luminophores that exhibit phosphorescence at room temperature. We report herein that 1,4-bis(aroyl)-2,5-dibromobenzenes serve as a new class of such luminophores. The bis(aroyl)benzene derivatives were not emissive either in solution or in a doped polymer thin film. In contrast, crystals of bis(aroyl)benzenes showed photoluminescence under ambient conditions, which was subsequently confirmed as phosphorescence with a luminescence lifetime measurement. The emission color ranged from blue to green, depending on the nature of the aroyl groups, and the luminescent quantum yields were 0.05-0.18 at room temperature and 0.38-0.67 at 77 K. In each crystal, several intermolecular interactions such as C=O···H, Br···Br, C=O···Br, F···F, S···H, and MeO···H were observed, which contributed to the restriction of intramolecular motions, thereby diminishing the nonradiative decay process from the triplet excited states. Crystals of 1,4-bis(aroyl)-2,5-dibromobenzene exhibit phosphorescence at room temperature. The emission color of the crystals can be altered from blue to green by changing the aroyl groups. Intermolecular interactions that lead to suppression of intramolecular rotation resulting in the deactivation of the excited states were observed in the crystal lattice.

Full text of DOI:10.1002/ejoc.201501382

DOI: 10.1002/ejoc.201501382
Full Paper
Phosphorescence
Room-Temperature Phosphorescence of Crystalline
1,4-Bis(aroyl)-2,5-dibromobenzenes
Masaki Shimizu,*[a] Akinori Kimura,[a] and Hiroshi Sakaguchi[b]
Dedicated to Professor Stephen L. Buchwald on the occasion of his 60th birthday
Abstract: There is a growing interest in metal-free organic ranged from blue to green, depending on the nature of the
luminophores that exhibit phosphorescence at room tempera-
ture. We report herein that 1,4-bis(aroyl)-2,5-dibromobenzenes
serve as a new class of such luminophores. The bis(aroyl)-
benzene derivatives were not emissive either in solution or in
a doped polymer thin film. In contrast, crystals of bis(aroyl)-
benzenes showed photoluminescence under ambient condi-
tions, which was subsequently confirmed as phosphorescence
with a luminescence lifetime measurement. The emission color
aroyl groups, and the luminescent quantum yields were 0.05–
0.18 at room temperature and 0.38–0.67 at 77 K. In each crystal,
several intermolecular interactions such as C=O···H, Br···Br, C=
O···Br, F···F, S···H, and MeO···H were observed, which contrib-
uted to the restriction of intramolecular motions, thereby di-
minishing the nonradiative decay process from the triplet ex-
cited states.
Introduction
deriving RTP from metal-free organic chromophores.[9] For ex-
ample, Tang and co-workers reported that benzophenone and
its halogenated derivatives in crystals exhibited RTP.[8a] Mean-
while, Kim and co-workers demonstrated that co-crystals of 2,5-
bis(hexyloxy)-4-bromobenzaldehyde and 2,5-bis(hexyloxy)-1,4-
dibromobenzene were phosphorescent at room temperature
with high luminescence efficiency.[9b] The presence of an aryl-
carbonyl group and a halogen atom is a common structural
characteristic of the two examples given. An arylcarbonyl group
is essential for the generation of a triplet excited state through
intersystem crossing (ISC), whereas the presence of a bromine
atom promotes ISC and the radiation of phosphorescence.[3a]
To accelerate the fundamental research on RTP and its applica-
tions, the development of new phosphors is necessary.[4]
We previously developed 2,5-diamino-1,4-bis(benzoyl)benz-
enes as organic fluorophores that exhibited yellow to red emis-
sion in the solid state with high efficiency.[10] The diamino-
bis(benzoyl)benzenes were prepared from the corresponding
2,5-dibromo-1,4-bis(benzoyl)benzene (1b) through palladium-
catalyzed amination, using secondary amines under the condi-
tions developed by Buchwald and co-workers (Figure 1).[11]
Given that 1b possesses arylcarbonyl groups and bromine at-
oms, which are similar to compounds reported by Tang and
Kim,[8a,9b] we envisioned that 2,5-dibromo-1,4-bis(aroyl)benz-
ene derivatives of type 1 would behave as novel chromophores
Room-temperature phosphorescence (RTP) of metal-free or-
ganic compounds has attracted a great deal of attention as a
versatile tool in analytical chemistry for the past several dec-
ades.[1] In general, it is very difficult to observe phosphores-
cence at room temperature with organic chromophores that do
not contain precious metals such as iridium and platinum.[2]
This is because the rate of phosphorescence is slow owing to
the occurrence of spin flip, during which the molecule easily
loses the triplet excited energy through intramolecular motions
occurring at room temperature and through collisions with sol-
vent molecules.[3] Hence, it is a challenge to design and synthe-
size organic chromophores that exhibit RTP without the aid of
precious metals.[4] To suppress the deactivation of the long-
lived excited states by intramolecular motions and intermolec-
ular collisions, several approaches have been developed; these
include the use of special solvents,[5] adsorption of organic
phosphors onto solid media such as filter paper and silica,[6]
and the inclusion of phosphors into cyclodextrin or surfac-
tants.[7] Recently, the independent crystallization of phos-
phors[8] and co-crystallization of phosphors with halogen-bond-
ing donors or acceptors have emerged as new strategies for
[a] Faculty of Molecular Chemistry and Engineering,
Kyoto Institute of Technology,
1 Hashikami-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
E-mail: mshimizu@kit.ac.jp
http://www.cis.kit.ac.jp/~orgsynth/en/index.html
[b] Institute of Advanced Energy, Kyoto University,
Gokasho, Uji 611-0011, Kyoto, Japan
E-mail: sakaguchi.hiroshi.7z@kyoto-u.ac.jp
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejoc.201501382.
Figure 1. Molecular structures of 1,4-bis(aroyl)-2,5-dibromobenzenes 1.
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exhibiting crystallization-induced RTP. Herein, we report the The luminescent data of 1 are summarized in Table 1. As shown
synthesis, phosphorescent properties, and molecular as well as in Figure 3, the emission spectra of 1 were broad and distinct
packing structures of 1 in the crystalline form.
from each other, depending on the aroyl groups. The lumines-
cent quantum yields ranged from 0.05 to 0.18, which were gen-
erally at the same level of those of benzophenone derivatives
reported by Tang.[8a] The lifetimes of the observed lumines-
cence at room temperature were in the order of micro- to milli-
seconds, except for the emission of 1e at 412 nm. The photo-
luminescence of 1 was measured at 77 K in a glassy solvent
mixture of Et2O/isopentane/EtOH (5:5:2). The emission spectra
are shown in Figure 4 and the data are summarized in Table 1.
At 77 K, the spectrum belonging to each version of 1 blue-
shifted either slightly or significantly when compared with the
corresponding spectrum of the crystal obtained at room tem-
perature. With the exception of the thienyl derivative 1d, the
spectra of 1a–c and 1e at 77 K showed vibrational structures
that were similar to the phosphorescence spectrum of benzo-
phenone, and these signals almost overlapped with each other,
in contrast to those of the crystals shown in Figure 3. These
results suggest that the emission colors of the crystals are de-
pendent on the aroyl groups mainly because of the difference
in intermolecular interactions that occur in the crystal packing,
and they are not related to the electronic nature of the aroyl
groups. The quantum yields of the emission at 77 K (Φ = 0.38–
0.67) were much higher than those at room temperature, and
the emission lifetimes were again in the order of micro- to milli-
Results and Discussion
Synthesis
The different synthetic routes to 1 are shown in Scheme 1.
Treating dibromobenzenedicarbonyl dichloride[12]
2 with
Me(MeO)NH·HCl in the presence of pyridine gave the corre-
sponding Weinreb amide 3 in 98 % yield. The carbonyl addition
reaction of 4-CF3C6H4MgBr, C6H5MgBr, and 4-MeOC6H4MgBr to
3 proceeded smoothly in tetrahydrofuran (THF) at room tem-
perature, giving 1a, 1b, and 1e, respectively, in moderate to
excellent yields. On the other hand, the addition reaction of
3,5-(CF3)2C6H3MgBr[13] and 3-thienylmagnesium bromide[14] to
3 under the same or heated conditions did not produce the
desired compound. These results were probably ascribed to the
lower stability of the Grignard reagents under the conditions
employed. Next, 1c and 1d were synthesized from 2 in moder-
ate yields by a copper-mediated addition reaction using the
corresponding arylmagnesium reagents at either –10 or –20 to
–10 °C.[13]
Figure 2. Optical (a) and photoluminescent (b) images of 1 at room tempera-
ture (λex = 365 nm).
Table 1. Photoluminescent properties of 1.
1
300 K[a]
77 K[b]
λem (nm)[c] Φ[d]
τ (%)[e]
λem (nm)[c] Φ[d]
τ
1a
448
462
474
498
0.18
0.14
0.08
89 μs (85)
0.4 ms (15)
418
448
478
412
434
463
424
452
478
458
0.42
0.51
0.38
3.8 μs
0.3 ms
1.1 ms
0.5 μs
1b
1c
26 μs (95)
81 μs (5)
0.2 ms
1.9 ms
32.2 μs
0.4 ms
1.3 ms
0.2 ms
2.5 ms
4.2 μs
Scheme 1. Synthesis of 1.
5.9 μs (16)
39 μs (84)
1d
1e
0.14
0.05
0.9 ms (48)
1.6 ms (52)
1.4 ns
6.2 ms (38)
41.2 ms (62)
0.49
0.67
Photoluminescent Properties
412
530
419
444
475
18.3 ms
None of the versions of 1 were emissive at room temperature,
either in solution or in a doped poly(methyl methacrylate) film.
On the other hand, crystals of 1 emitted blue to green light
under ambient conditions (i.e., at room temperature and in air)
upon UV irradiation at 365 nm, as shown in Figure 2. Thus, 1
exhibited crystallization-induced phosphorescence emission.
[a] Excitation of 1 in crystal was performed at 365 nm in air. [b] Excitation of
1 in a mixture of Et2O/isopentane/EtOH (5:5:2) was performed at 260 nm.
[c] Wavelengths at emission maxima. [d] Absolute quantum yield (Φ) was
determined using a calibrated integrating sphere system. [e] Lifetimes with
distribution (%) in parentheses.
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seconds. Therefore, the emission of 1 observed at room and lattice (see below) that would result in a loss of excited energy
low temperatures was concluded to be phosphorescence.
through intermolecular aromatic π–π interactions.
Figure 3. Emission spectra of 1 from the crystal at room temperature (λex
=
365 nm).
Figure 4. Emission spectra of 1 in a mixture of Et2O/isopentane/EtOH (5:5:2)
at 77 K (λex = 260 nm).
Molecular and Crystal Structures
To gain insight into the intermolecular interactions in the crys-
tals of 1, we carried out X-ray diffraction analysis of the single
crystals.[15] Compounds 1a–e crystallized in the triclinic space
group P1 from EtOAc (1a), the rhombohedral space group R3¯
¯
from CH2Cl2/hexane (1b), the monoclinic space group P21/c
from CH2Cl2/hexane (1c), the monoclinic space group P21/n
from CH2Cl2/hexane (1d), and the triclinic space group P1¯ from
THF/MeOH (1e). As shown in Figure 5, the respective molecular
structures of 1a–e are centrosymmetric with an inversion center
at the centroid of the central benzene ring. The dihedral angels
of the central benzene ring and carbonyl group (∠C1–C2–C3–
O), and the outer benzene ring and carbonyl group (∠C5–C4–
C3–O) are summarized in Table 2. In all cases, aroyl groups (Ar–
C=O) consisting of outer benzene ring and carbonyl group were
almost flat. The aroyl moieties deviated from the plane of the
central benzene ring, probably owing to the steric repulsion
between the aroyl moieties and bromine atoms attached at the
ortho-positions. Thus, all versions of 1 adopted twisted confor-
Figure 5. Molecular structures of 1.
Crystal packing diagrams of 1a–e are shown in Figures 6, 7,
mations to avoid a dense packing conformation in the crystal 8, 9, and 10. In the case of 1a, the distance between two adja-
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Table 2. Dihedral angles between the aromatic ring and the carbonyl group.
Dihedral angle
1a
1b
1c
1d
1e
∠C1–C2–C3–O
∠C5–C4–C3–O
60.4
18.5
58.6
23.9
124.9
–13.1
104.9
–5.3
104.1
–5.5
cent Br atoms (3.315 Å) is shorter than the sum of van der Waals
radius of Br (1.95 Å),[16] indicating that Br···Br interactions are
present in the crystal lattice (Figure 6, a).[17] The interaction
means that the central benzene rings align in a head-to-tail
fashion. The aroyl groups are oriented upside down with regard
to the plane formed by the central benzene rings. Another in-
termolecular interaction is seen between the carbonyl oxygen
and aromatic hydrogen at the ortho position of the CF3 group
(Figure 6, b). The atomic distance is 2.422 Å, which is shorter
than the sum of van der Waals radii of O (1.40 Å) and H
(1.20 Å).[16] The hydrogen bonds force each molecule to arrange
in a way that forms a ladder.
Figure 7. Crystal packing diagram of 1b (units in Å).
1c. The hydrogen bond between the aromatic hydrogen atom
(sandwiched between two CF3 groups) and the fluorine atom
of a CF3 group of the neighboring molecule has a distance of
2.663 Å.[19] Hence, the rotational freedom of the aroyl groups is
firmly restricted by the double fixation. The F···F contact be-
tween the closest CF3 groups in adjacent molecules is 2.908 Å,
which is smaller than the sum of van der Waals radii of two
fluorine atoms (2.94 Å).[20] The F···F contact means that mol-
ecules 1c align along the long axis of the molecular skeleton.
Figure 6. Crystal packing diagram of 1a (units in Å).
Figure 8. Crystal packing diagram of 1c (units in Å).
The distance of bromine and carbonyl oxygen atoms in 1b
is 3.307 Å, which is shorter than the sum of van der Waals radii
of Br (1.95 Å) and O (1.40 Å), as shown in Figure 7 (a). Thus, the
intramolecular rotation of carbonyl groups of 1b in the crystal
is locked by the intermolecular Br···O=C interactions.[18] In addi-
tion, aromatic hydrogen atoms of the central benzene ring also
interact with carbonyl oxygen atoms (i.e., through a distance of
2.552 Å) to form a tape-like supramolecular assembly (Figure 7,
b).
The single crystal of 1d includes a close contact (2.519 Å)
between the carbonyl oxygen and the aromatic hydrogen of
the central benzene ring, so that the central benzene rings of
adjacent molecules are positioned in a staircase pattern (Fig-
ure 9). The distance between the sulfur atom of the thiophene
ring and the hydrogen atom at the 5-position of the thiophene
ring (i.e., belonging to the neighboring molecule) is 2.907 Å,
As shown in Figure 8, an intermolecular interaction between which is shorter than the sum of van der Waals radii of sulfur
the aromatic hydrogen atoms of the central benzene ring with (1.85 Å) and hydrogen (1.20 Å),[16] indicating the presence of
the carbonyl oxygen atoms (2.433 Å) is present in the crystal of S···H–C interaction in the crystal of 1d.[21]
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molecules in the crystals; these interactions consisted of halo-
gen bonding, hydrogen bonding, and F–F interactions. Investi-
gations into metal- and halogen-free organic chromophores
that exhibit efficient RTP are in progress.
Experimental Section
General: Melting points (Mp) were determined with a Seiko Instru-
ment Inc. TG/DTA6200. 1H NMR spectra were measured with a
Bruker Avance II 300 (300 MHz) spectrometer. The chemical shifts
of 1H NMR signals are expressed in parts per million downfield
relative to the internal tetramethylsilane standard (δ = 0 ppm) or
chloroform (δ = 7.26 ppm). Splitting patterns are indicated as s,
singlet; d, doublet; q, quartet; or sept, septet. 13C NMR spectra were
measured with a Bruker Avance II 300 (75 MHz) spectrometer with
tetramethylsilane as an internal standard (δ = 0 ppm) or [D]chloro-
form (δ = 77.0 ppm). 19F NMR spectra were measured with a Bruker
Avance II 300 (282 MHz) spectrometer with C6F6 as an internal
standard (δ = –163.7 ppm). Chemical shift values are given in parts
per million downfield relative to the internal standards. Infrared
spectra (IR) were recorded with a Shimadzu FTIR-8400 spectrometer.
Fast atom bombardment, high-resolution mass spectrometry (FAB-
HRMS) analyses were performed with a JEOL JMS-700 spectrometer.
TLC analyses were performed using Merck Kieselgel 60 F254 silica
plates. Silica gel column chromatography was carried out using
Merck's Kieselgel 60 (230–400 mesh). Reagent-grade dichlorometh-
ane and THF were passed through two packed columns of neutral
alumina and copper oxide under a nitrogen atmosphere before use.
All reactions were carried out under an argon atmosphere. Prepara-
tion and characterization data of 1a and 1b have been reported
previously.[10]
Figure 9. Crystal packing diagram of 1d (units in Å).
In the crystal of 1e, intermolecular interactions involving C=
O···H–C(central benzene ring) is found with a contact distance
of 2.488 Å (Figure 10). The central benzene rings line up in a
staircase pattern through hydrogen bonding, as observed in the
crystal of 1d. Each oxygen atom of both methoxy groups in
one molecule interacts with the aromatic hydrogen atoms ortho
to the methoxy groups of the adjacent molecules. Thus, each
1e crystal exhibits double short contact (2.369 Å) at the molec-
ular termini, forming the shape of twisted tapes through hydro-
gen bonding interactions in the crystal.
Preparation of 3: A flame-dried Schlenk tube was charged with 2
(9.38 g, 26.0 mmol) and MeO(Me)NH·HCl (6.03 g, 61.8 mmol). The
tube was evacuated and filled with argon gas. After this evacua-
tion–argon-filling operation was repeated twice, dichloromethane
(100 mL) was introduced into the tube. To the solution was added
pyridine (10.0 mL, 124 mmol) at 0 °C and the resulting solution was
stirred at room temperature for 13 h. The reaction was then
quenched with 2
M HCl aq. (50 mL), the aqueous layer was extracted
with dichloromethane (3 × 80 mL) and the combined organic layer
was washed with brine (30 mL) and dried with anhydrous magne-
sium sulfate. The organic solvent was removed in vacuo to give
crude 3 (10.44 g, 25.5 mmol, 98 %) as a colorless solid, which was
used in the next step without further purification.
Figure 10. Crystal packing diagram of 1e (units in Å).
Synthesis of 1c: To a solution of 3,5-(CF3)2C6H3MgCl·LiCl (0.73
M in
THF, 3.38 mL, 2.47 mmol) in a Schlenk tube (prepared according to
the reported procedure),[13] was added a solution of CuCN·2LiCl
(1.0
M
in THF, 0.49 mL, 0.49 mmol) at –20 °C. The mixture was stirred
Conclusions
at –20 °C for 45 min, and a solution of 2 (0.20
M
in THF, 3.10 mL,
We have demonstrated that 1,4-bis(aroyl)-2,5-dibromobenzenes 0.62 mmol) was added to the tube at –20 °C. The resulting mixture
was stirred at –10 °C for 14 h, then the reaction was quenched with
saturated aq. NH4Cl solution (3 mL). To the mixture was added wa-
in crystals serve as organic chromophores exhibiting RTP. The
colors of the phosphorescence can be altered from blue to
green by changing the aroyl groups. No photoluminescence
was observed with bis(aroyl)benzenes in solution at room tem-
perature, but the benzene compounds showed brilliant blue
phosphorescence with good quantum yields in a glassy solvent
at 77 K. These results suggest that the rigidification of intra-
molecular motion is essential for the emergence of the crystalli-
zation-induced RTP. X-ray analysis of the single crystals showed
ter (3 mL) and aq. NH3 solution (15
M, 10 mL). The aqueous layer
was extracted with dichloromethane (3 × 20 mL), and the combined
organic layer was washed with brine (20 mL) and dried with anhy-
drous magnesium sulfate. Removal of organic solvent in vacuo gave
the crude product, which was purified by column chromatography
on silica gel (hexane/ethyl acetate, 9:1) to afford 1c (0.24 g,
0.34 mmol, 55 %) as a colorless solid. Recrystallization of isolated
1c was performed twice (CH2Cl2/hexane then CH2Cl2/MeOH) for the
that several close contacts were present among adjacent measurement of the crystal's photophysical properties, m.p. 204 °C
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1
(dec). Rf = 0.40 (hexane/EtOAc, 9:1). H NMR (CDCl3, 300 MHz): δ =
Acknowledgments
7.72 (s, 2 H), 8.18 (s, 2 H), 8.27 (s, 4 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 119.1, 122.6 (q, J = 271.5 Hz), 127.6 (sept, J = 3.8 Hz),
129.8 (d, J = 3.0 Hz), 132.5 (q, J = 33.8 Hz), 133.7, 136.7, 142.3 ppm.
This work was supported by Japan Society for the Promotion
of Science (JSPS) KAKENHI (grant numbers 24655122,
15H03795), and by the Institute of Advanced Energy, Kyoto Uni-
versity (Joint Usage/Research Program on Zero-Emission Energy
Research, ZE27A-4). The authors acknowledge Prof. Wei Jun Jin
(Beijing Normal University) for providing a reprint of their article
on phosphorescent co-crystals.
19F NMR (CDCl , 282 MHz): δ = –64.9 ppm. IR (KBr): ν = 3086, 3026,
˜
3
1682, 1616, 1383, 1319, 1284, 1234, 1180, 1157, 1138, 1126, 1111,
1074, 916, 848, 790, 711, 700, 680 cm–1. FAB–HRMS: m/z calcd. for
C
24H9O2Br2F12 [M]+ 714.8778; found 714.8776.
Synthesis of 1d: To a solution of 3-thienylMgCl·LiCl (0.95
8.40 mL, 7.98 mmol) in a Schlenk tube (prepared according to the
reported procedure),[14] was added a solution of CuCN·2LiCl (1.0
in THF, 1.60 mL, 1.60 mmol) at –20 °C. The mixture was stirred at
–20 °C for 45 min, and a solution of 2 (0.25 in THF, 8.20 mL,
M in THF,
M
Keywords: Luminescence · Crystal engineering · Arenes ·
Bromine · Ketones
M
2.05 mmol) was added to the tube at –20 °C. The resulting mixture
was stirred at –10 °C for 15 h, then the reaction was quenched with
saturated aq. NH4Cl solution (10 mL). To the mixture was added
[1] a) M. E. Díaz-García, A. Fernández-González, R. Badía-Laíño, Appl. Spec-
trosc. Rev. 2007, 42, 605–624; b) J. Kuijt, F. Ariese, U. A. T. Brinkman, C.
Gooijer, Anal. Chim. Acta 2003, 488, 135–171.
[2] a) H. Yersin, A. F. Rausch, R. Czerwieniec, T. Hofbeck, T. Fischer, Coord.
Chem. Rev. 2011, 255, 2622–2652; b) Y. Chi, P.-T. Chou, Chem. Soc. Rev.
2010, 39, 638–655; c) R. C. Evans, P. Douglas, C. J. Winscom, Coord. Chem.
Rev. 2006, 250, 2093–2126.
[3] a) N. J. Turro, Modern Molecular Photochemistry, University Science Books,
Sausalito, 1978; b) S. K. Lower, M. A. El-Sayed, Chem. Rev. 1966, 66, 199–
241. RTP of bromo- and formyl-substituted fluorene derivative in chloro-
form was reported, see: c) J. Xu, A. Takai, Y. Kobayashi, M. Takeuchi,
Chem. Commun. 2013, 49, 8447–8449.
[4] S. Mukherjee, P. Thilagar, Chem. Commun. 2015, 51, 10988–11003.
[5] a) C. A. Parker, C. G. Hatchard, J. Phys. Chem. 1962, 66, 2506–2511; b)
W. D. K. Clark, A. D. Litt, C. Steel, J. Am. Chem. Soc. 1969, 91, 5413–5415;
c) R. B. Bonner, M. K. DeArmond, G. H. Wahl, J. Am. Chem. Soc. 1972, 94,
988–989.
[6] a) E. M. Schulman, C. Walling, Science 1972, 178, 53–54; b) E. M. Schul-
man, C. Walling, J. Phys. Chem. 1973, 77, 902–905; c) R. A. Paynter, S. L.
Wellons, J. D. Winefordner, Anal. Chem. 1974, 46, 736–738; d) S. L. Wel-
lons, R. A. Paynter, J. D. Winefordner, Spectrochim. Acta Part A 1974, 30,
2133–2140; e) C. D. Ford, R. J. Hurtubise, Anal. Chem. 1980, 52, 656–662;
f) S. M. Ramasamy, R. J. Hurtubise, Anal. Chem. 1982, 54, 2477–2481.
[7] a) L. J. C. Love, M. Skrilec, J. G. Habarta, Anal. Chem. 1980, 52, 754–759;
b) S. Scypinski, L. J. Cline Love, Anal. Chem. 1984, 56, 322–327; c) S.
Scypinski, L. J. Cline Love, Anal. Chem. 1984, 56, 331–336; d) A. Mu-
ñoz de la Peña, M. C. Mahedero, A. Bautista Sánchez, Analusis 2000, 28,
670–678.
[8] a) W. Z. Yuan, X. Y. Shen, H. Zhao, J. W. Y. Lam, L. Tang, P. Lu, C. Wang, Y.
Liu, Z. Wang, Q. Zheng, J. Z. Sun, Y. Ma, B. Z. Tang, J. Phys. Chem. C 2010,
114, 6090–6099; b) G.-P. Yong, Y.-M. Zhang, W.-L. She, Y.-Z. Li, J. Mater.
Chem. 2011, 21, 18520–18522; c) Y. Gong, Y. Tan, H. Li, Y. Zhang, W. Yuan,
Y. Zhang, J. Sun, B. Z. Tang, Sci. China Chem. 2013, 56, 1183–1186; d)
S. K. Maity, S. Bera, A. Paikar, A. Pramanik, D. Haldar, Chem. Commun.
2013, 49, 9051–9053; e) Y. Gong, L. Zhao, Q. Peng, D. Fan, W. Z. Yuan, Y.
Zhang, B. Z. Tang, Chem. Sci. 2015, 6, 4438–4444; f) J. Li, Y. Jiang, J.
Cheng, Y. Zhang, H. Su, J. W. Y. Lam, H. H. Y. Sung, K. S. Wong, H. S. Kwok,
B. Z. Tang, Phys. Chem. Chem. Phys. 2015, 17, 1134–1141; g) S. Kuno, H.
Akeno, H. Ohtani, H. Yuasa, Phys. Chem. Chem. Phys. 2015, 17, 15989–
15995; h) P. Xue, J. Sun, P. Chen, P. Wang, B. Yao, P. Gong, Z. Zhang, R.
Lu, Chem. Commun. 2015, 51, 10381–10384; i) G.-P. Yong, C. Shen, C.
Zhang, Y.-M. Zhao, J. Mater. Chem. C 2015, 3, 9048–9052; j) Y. Gong, G.
Chen, Q. Peng, W. Z. Yuan, Y. Xie, S. Li, Y. Zhang, B. Z. Tang, Adv. Mater.
2015, 27, 6195–6201.
water (10 mL) and aq. NH3 solution (15 M, 15 mL). The aqueous layer
was extracted with dichloromethane (3 × 20 mL), and the combined
organic layer was washed with brine (20 mL) and dried with anhy-
drous magnesium sulfate. Removal of organic solvent in vacuo gave
the crude product, which was purified by column chromatography
on silica gel (hexane/ethyl acetate, 5:1) to afford 1d (0.62 g,
1.34 mmol, 65 %) as a colorless solid. Isolated 1d was recrystallized
twice from CH2Cl2/hexane for the measurement of crystal's photo-
physical properties, m.p. 208 °C. Rf = 0.27 (hexane/EtOAc, 5:1). 1H
NMR (CDCl3, 300 MHz): δ = 7.42 (dd, J = 5.1, 2.4 Hz, 2 H), 7.59 (dd,
J = 5.1, 1.2 Hz, 2 H), 7.65 (s, 2 H), 7.89 (dd, J = 2.4, 1.2 Hz, 2 H) ppm.
13C NMR (CDCl3, 75 MHz): δ = 118.2, 127.3, 127.5, 132.9, 136.7, 140.5,
143.6, 186.9 ppm. IR (KBr): ν = 3093, 1660, 1508, 1408, 1392, 1329,
˜
1269, 1247, 1145, 1060, 896, 856, 813, 736 cm–1. FAB–HRMS: m/z
calcd. for C16H9O2Br2S2 [M]+ 454.8411; found 454.8394.
Synthesis of 1e: A flame-dried Schlenk tube was charged with 3
(1.21 g, 2.95 mmol), evacuated, and filled with argon gas. The evac-
uation–argon-filling operation was repeated twice. To the tube was
added THF and then a solution of 4-MeOC6H4MgBr (0.83
M in THF,
12 mL, 9.96 mmol) at room temperature. The reaction mixture was
stirred at room temperature for 24 h, then the reaction was
quenched with saturated aq. NH4Cl solution (30 mL). Water (20 mL)
was added to the resulting solution and the aqueous layer was
extracted with dichloromethane (3 × 40 mL), and the combined
organic layer was washed with brine (30 mL) and dried with anhy-
drous magnesium sulfate. Removal of organic solvent in vacuo gave
the crude product, which was purified by column chromatography
on silica gel (hexane/ethyl acetate, 5:1) to give 1e (1.32 g,
2.62 mmol, 89 %) as a colorless solid. Recrystallization of isolated
1e was performed three times (dichloromethane/hexane × 2 and
THF × 1) for the measurement of crystal's photophysical properties,
m.p. 192 °C. Rf = 0.14 (hexane/EtOAc, 5:1). 1H NMR (CDCl3, 300 MHz):
δ = 3.91 (s, 6 H), 6.99 (d, J = 9.0 Hz, 4 H), 7.58 (s, 2 H), 7.82 (d, J =
9.0 Hz, 4 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 55.7, 114.2, 118.4,
128.2, 132.8 (2 C), 143.4, 164.7, 192.3 ppm. IR (KBr): ν = 3090, 2937,
˜
2843, 1667, 1601, 1575, 1510, 1419, 1337, 1317, 1305, 1259, 1250,
1175, 1152, 1063, 1030, 927, 891, 856 cm–1. FAB–HRMS: m/z calcd.
for C22H17O4Br2 [M]+ 502.9495; found 502.9502.
[9] a) X. Pang, W. Jin, in: Halogen Bonding II, vol. 359 (Eds.: P. Metrangolo, G.
Resnati), Springer International Publishing, 2015, p. 115–146; b) O. Bol-
ton, K. Lee, H. J. Kim, K. Y. Lin, J. Kim, Nature Chem. 2011, 3, 205–210; c)
H. Y. Gao, X. R. Zhao, H. Wang, X. Pang, W. J. Jin, Cryst. Growth Des. 2012,
12, 4377–4387; d) X. Pang, H. Wang, X. R. Zhao, W. J. Jin, CrystEngComm
2013, 15, 2722–2730; e) D. Lee, O. Bolton, B. C. Kim, J. H. Youk, S. Takay-
ama, J. Kim, J. Am. Chem. Soc. 2013, 135, 6325–6329; f) A. Mukherjee, S.
Tothadi, G. R. Desiraju, Acc. Chem. Res. 2014, 47, 2514–2524; g) H. Wang,
R. X. Hu, X. Pang, H. Y. Gao, W. J. Jin, CrystEngComm 2014, 16, 7942–
7948; h) O. Bolton, D. Lee, J. Jung, J. Kim, Chem. Mater. 2014, 26, 6644–
Measurement of Photoluminescence: Spectroscopic-grade sol-
vents for photoluminescence measurements were purchased from
Kanto Chemical Co., Inc. and degassed with argon before use. Lumi-
nescence spectra and absolute quantum yields were recorded with
a Hamamatsu Photonics C9920–02 Absolute PL Quantum Yield
Measurement System, and the luminescence lifetimes were meas-
ured with a Hamamatsu Photonics Quantaurus-Tau instrument.
Eur. J. Org. Chem. 2016, 467–473
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Full Paper
6649; i) S. d'Agostino, F. Grepioni, D. Braga, B. Ventura, Cryst. Growth Des.
2015, 15, 2039–2045. RTP of a phosphor dispersed in an amorphous
host material was also reported, see: j) S. Hirata, K. Totani, J. Zhang, T.
Yamashita, H. Kaji, S. R. Marder, T. Watanabe, C. Adachi, Adv. Funct. Mater.
2013, 23, 3386–3397.
[17] For examples of Br···Br interaction in crystals, see: a) J. N. Moorthy, P.
Venkatakrishnan, P. Mal, S. Dixit, P. Venugopalan, Cryst. Growth Des. 2003,
3, 581–585; b) M. B. Zaman, K. A. Udachin, J. A. Ripmeester, Cryst. Growth
Des. 2004, 4, 585–589.
[18] For examples of C=O···Br interaction in crystals, see: a) ref. 9b; b) ref.
17b.
[19] For examples of H···F interaction in crystals, see: a) K. Merz, M. V. Evers,
F. Uhl, R. I. Zubatyuk, O. V. Shishkin, Cryst. Growth Des. 2014, 14, 3124–
3130; b) V. R. Hathwar, D. Chopra, P. Panini, T. N. Guru Row, Cryst. Growth
Des. 2014, 14, 5366–5369.
[20] For examples of F···F interactions in crystals, see: a) M. Pérez-Torralba,
M. Á. García, C. López, M. C. Torralba, M. R. Torres, R. M. Claramunt, J.
Elguero, Cryst. Growth Des. 2014, 14, 3499–3509; b) D. Chopra, K. Nagara-
jan, T. N. Guru Row, Cryst. Growth Des. 2005, 5, 1035–1039.
[21] The S···H–C interaction was reportedly observed in the crystal of di-
thienopyrrole derivative, see: H. Mo, K. R. Radke, K. Ogawa, C. L. Heth,
B. T. Erpelding, S. C. Rasmussen, Phys. Chem. Chem. Phys. 2010, 12,
14585–14595.
[10]
[11]
[12]
M. Shimizu, Y. Asai, Y. Takeda, A. Yamatani, T. Hiyama, Tetrahedron Lett.
2011, 52, 4084–4089.
a) M. D. Charles, P. Schultz, S. L. Buchwald, Org. Lett. 2005, 7, 3965–3968;
b) D. S. Surry, S. L. Buchwald, Chem. Sci. 2011, 2, 27–50.
Y. Yao, J. M. Tour, Macromolecules 1999, 32, 2455–2461.
[13] F. M. Piller, A. Metzger, M. A. Schade, B. A. Haag, A. Gavryushin, P. Kno-
chel, Chem. Eur. J. 2009, 15, 7192–7202.
[14] A. Krasovskiy, P. Knochel, Angew. Chem. Int. Ed. 2004, 43, 3333–3336;
Angew. Chem. 2004, 116, 3396.
[15] CCDC 1425366 (for 1a), 1426974 (for 1b), 1425733 (for 1c), 1425678 (for
1d), and 1425679 (for 1e) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre.
[16] J. Emsley, The Elements, 3rd edition, Oxford University Press, Oxford, UK,
2000.
Received: January 1, 2015
Published Online: January 5, 2016
Eur. J. Org. Chem. 2016, 467–473
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© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim