Crystallization-induced light-emission enhancement of diphenylmethane derivatives

Article abstract of DOI:10.1016/j.tet.2013.07.107

A family of diphenylmethane derivatives has been synthesized and their luminescence properties characterized. While in solution the compounds are weakly emissive, showing no aggregation-induced emission enhancement, the crystals of three dialkyl 5,5′-methylenebis(2-hydroxybenzoate) samples exhibit intense emission. This emission enhancement upon crystallization is ascribed to particular molecular packing, which stiffens the structure of the compounds via hydrogen bonds, preventing consecutive π-π interactions.

Full text of DOI:10.1016/j.tet.2013.07.107

Tetrahedron 69 (2013) 9329e9334
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Crystallization-induced light-emission enhancement
of diphenylmethane derivatives
,
b
,
a
b,
Samuel Guieu a , Joao Rocha , Artur M.S. Silva
*
*
~
a CICECO, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
b QOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 May 2013
Received in revised form 6 July 2013
Accepted 29 July 2013
Available online 29 August 2013
A family of diphenylmethane derivatives has been synthesized and their luminescence properties
characterized. While in solution the compounds are weakly emissive, showing no aggregation-induced
emission enhancement, the crystals of three dialkyl 5,50-methylenebis(2-hydroxybenzoate) samples
exhibit intense emission. This emission enhancement upon crystallization is ascribed to particular mo-
lecular packing, which stiffens the structure of the compounds via hydrogen bonds, preventing con-
secutive
pep interactions.
Keywords:
Ó 2013 Elsevier Ltd. All rights reserved.
Diphenylmethanes
Luminescence
Crystalline state
Molecular packing
1. Introduction
2. Results and discussion
2.1. Synthesis
Emissive solids are important materials for the development of
new devices,1 such as organic light emitting diodes, photoelectric
converters or lasers. Most fluorophores are luminescent in dilute
solutions, or as dopants in a glassy matrix, but become non-
emissive in the solid state, due to exciplex formation and non-
radiative decay through thermal relaxation.2
Diphenylmethane is a highly flexible core, which is present in
some natural molecules.3 Due to the ability to absorb UV light,4 the
diphenylmethane derivatives have been widely used as additives in
polymers, preventing their photo-degradation, with bisphenol
A being a well-known example. Not much attention has been giv-
en to their emissive properties,5 however, and to the best of
our knowledge no study is available on their room temperature
luminescence.
Diphenylmethane derivatives are usually synthesized using
double condensation of formaldehyde with the corresponding
phenyl derivative, catalyzed by a strong acid or base.6 This allows an
easy access to diphenylmethane derivatives bearing similar sub-
stituents on both phenyl rings. Compounds 1e3 were obtained in
reasonable yields using salicylic acid,7 salicylaldehyde8 or aceto-
phenone9 (Scheme 1, i).
Methylene disalicylic acid 1 was subsequently esterified using
the corresponding alcohol as solvent with a catalytic amount of
sulfuric acid. Dimethyl ester 4,10 diethyl ester 5,11 and dipropyl ester
Herein is reported the synthesis and luminescence properties
of six diphenylmethane derivatives. Some of them exhibit sur-
prisingly high quantum yields in the solid state at room temper-
ature, which has been rationalized by the study of their crystal
structure.
Scheme 1. Synthesis of compounds 1e6. Reagents and conditions: i)
0.5 equiv (CH2O)n, catalytic concd H2SO4, glacial AcOH, 90 ꢀC, 2e4 h; ii) MeOH, EtOH or
PrOH, catalytic concd H2SO4, 100 ꢀC, 12 h.
* Corresponding authors. Tel.: þ351 234 370714; fax: þ351 234 370084; e-mail
addresses: sguieu@ua.pt (S. Guieu), artur.silva@ua.pt (A.M.S. Silva).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.07.107

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S. Guieu et al. / Tetrahedron 69 (2013) 9329e9334
612 were obtained in reasonable yields after purification
(Scheme 1, ii).
The normalized solid state emission spectra of compounds 1e6
are shown in Fig. 2. All compounds are luminescent under UV ir-
radiation, except for compound 2 whose emission is very weak. The
emission of compounds 1 and 3 are blue shifted from solution to
solid state. Diacid 1 has a similar quantum yield in solution and in
the solid state, around 0.10. The emission efficiency of 3 is greatly
enhanced in the solid state, with a quantum yield of ca. 0.18,
compared to <0.01 in solution. Diesters 4e6 present a similar
emission maximum in solution and in the solid state, but their
quantum yield is much larger in the solid state.
2.2. UVevis absorption and fluorescence spectra
The absorption and emission spectra of compounds 1e6 in THF
are presented in Fig. 1, and the key features summarized in Table 1.
The absorption maxima are observed at ca. 320 nm for 1 and 4e6,
and ca. 340 nm for 2 and 3. The molar extinction coefficients are in
the range 20,000e30,000 dm3 molꢁ1 cmꢁ1 for all compounds. The
fluorescence maximum (Fmax) is observed at ca. 460 nm for diacid 1,
with a large Stroke shift of ca. 140 nm. Fmax are red shifted for
dialdehyde 2 and diketone 3, ca. 485 and 520 nm, with larger Stroke
shifts of ca.150 and 180 nm, respectively. The emissions of the three
diesters 4e6 are very similar, with Fmax ca. 470 nm. The large Stroke
shifts are indicative of intramolecular charge transfer in the excited
state, which for compounds 1e6, could be explained by the
tautomerisation-transfer of the labile proton from the hydroxyl to
the carbonyl group.13,14
Fig. 2. Normalized solid-state emission spectra (excitation at 280 nm for 1 and 2, at
320 nm for 3e6).
2.3. Aggregation-induced emission enhancement test
Aggregation-induced emission enhancement (AIEE) tests were
performed in THF/water mixed solvents. For all compounds, the
solution turned cloudy at 80% water.
For diacid 1, the emission maximum shifts from 458 to 417 nm
when the water content increases but no enhancement in the
emission is observed. This is an expected result because the
quantum yield is roughly the same in the solution and solid state.
For dialdehyde 2, the emission maximum remains the same at ca.
500 nm, with a constant very weak emission. As the quantum
yields are very small both in solution and solid state, this result is
not surprising. For the diketone 3, the emission remains very weak
with increasing water content, as a broad band at ca. 500 nm (no
emission enhancement even when the solution turns cloudy). The
results for the three diesters 4e6 are similar, and Fig. 3 depicts the
AIEE test for diester 6 as an example. As the water content in-
creases, the emission maximum remains unchanged at ca. 470 nm.
The emission intensity decreases from 0% to 60% water, increasing
from 80% to 95% water by a factor 2, too small to allow concluding
that the diesters 4e6 exhibit a clear AIEE effect.
Fig. 1. Absorption spectra (solid lines) measured at 3ꢂ10ꢁ5 mol Lꢁ1 and emission
spectra (dotted lines, lex¼310 nm) measured at 3ꢂ10ꢁ3 mol Lꢁ1 in THF at 20 ꢀC.
Table 1
Absorption and emission data for compounds 1e6
Compounds In THF
Solid state
lmax (εmax) nm Fmaxb nm
f
fc
0.10 141
SSd nm Fmax
f
fe
a
b
1
2
3
4
5
6
317 (32,600)
337 (19,800)
337 (25,700)
317 (17,000)
317 (25,700)
318 (19,200)
458
486
519
472
476
471
428
542
498
474
465
469
0.07
<0.01 149
<0.01 182
0.02 155
0.02 159
0.03 153
<0.01
0.18
0.28
0.68
0.54
a
b
c
Measured at the concentration of 3ꢂ10ꢁ5 mol Lꢁ1 at 25 ꢀC.
Excitation wavelength was 310 nm.
Other mixed solvents systems were used to test the AIEE
properties of compounds 3e6, such as ethanol/water and metha-
nol/water, which gave results similar to THF/water, and dichloro-
methane/hexane and THF/hexane, for which no aggregate formed
and the emission intensity decreased slightly.
Determined by comparison with fluorescein in 0.01 mol Lꢁ1 NaOH in water
(
f
f¼0.90).
d
Stroke shift.
e
Determined by absolute PL quantum yield measurement in the powder form
(compound 1) or in the crystalline form (compounds 2e6).
None of the compounds show a clear AIEE, which is at odds with
the quantum yield increase observed from the solution to solid
state for compounds 3e6. In order to rationalize this feature, we
looked at the organization of the molecules in the solid state.
The luminescence of the different compounds in THF ranges
from almost non-emissive (2 and 3) and weakly luminescent (di-
esters 4e6,
f
f¼0.02e0.03) to a maximum quantum yield of ca. 0.10
(diacid 1). This order for the increasing luminescence of com-
pounds 1e6 may be explained by the increasing strength of the
intramolecular hydrogen bond between the hydroxyl proton and
the carbonyl oxygen atom, which rigidifies the structures inhibiting
non-emissive thermal relaxation.14
2.4. Solid state structure and single-crystal X-ray diffraction
Single crystals suitable for X-ray diffraction (XRD) were ob-
tained for compounds 2e5 by slow evaporation of a solution in

S. Guieu et al. / Tetrahedron 69 (2013) 9329e9334
9331
Fig. 3. AIEE test for the dipropyl ester 6 in THF/H2O mixtures, at 0.5ꢂ10ꢁ4 M, excitation at 310 nm.
dichloromethane. Despite all our efforts, crystals suitable for X-ray
diffraction could not be obtained for compound 1 and 6. Compound
1 seems amorphous, and compound 6 seems crystalline, but a sin-
gle crystal could not be isolated. The crystal structure of com-
pounds 2,9 3,9 and 410b was already reported. Based on the unit cell
dimensions obtained from the single crystals we grew, the struc-
tures we obtained are the same as the published ones, so the
published data have been used in the discussion below.
The XRD structure of dialdehyde 29 is shown in Fig. 4. The two
salicylaldehyde moieties are not related by symmetry. Intra-
molecular phenolic OeH/O hydrogen bonds with carboxyl O-atom
acceptors are present in both salicylaldehyde moieties. The mole-
cules are arranged in a chain fashion through two types of in-
teractions: on one side, a centrosymmetric cyclic intermolecular
OeH/O hydrogen bonding association; on the other side,
a CeH/H contact through Van der Waals interactions is combined
with
stacking interactions (see front view). Thus, compound 2 has con-
secutive stacking interactions.
p stacking. These chains are aligned and connected through p
pep
Fig. 5. Single-crystal XRD structure of diketone 3.
The XRD structure of diester 410b is shown in Fig. 6. The two
methyl salicylate parts are related by crystallographic twofold ro-
tational symmetry. Intramolecular OeH/O hydrogen bonds are
present and centrosymmetric cyclic intermolecular OeH/O hy-
drogen bonds link the molecules into infinite chains. These chains
are parallel and cross-linked by CeH/O hydrogen bonds between
the methyl group and the methoxy oxygen. Along the b axis, the
molecules seat on top of each other, with the shortest contact be-
tween the carbon of the COOMe and the CeCH2 carbon being ca.
ꢀ
3.38(0) A (see front view). The top view reveals that the phenyl
rings, even if close to each other and parallel, do not seat on top of
Fig. 4. Single-crystal XRD structure of dialdehyde 2.
each other, and therefore there is no
p stacking.
The single-crystal X-ray crystallography of diester 515 is shown
in Fig. 7. The ethyl salicylate moieties are related by crystallographic
twofold rotational symmetry. Intramolecular OeH/O hydrogen
bonds are present and the molecules are arranged in a chain
fashion through intermolecular CeH/O hydrogen bonds. These
chains have approximately a square section and are aligned down
the c axis. They are in contact through Van der Waals interactions.
The side view and top view reveal that the phenyl rings do not seat
The XRD structure of diketone 39 is shown in Fig. 5. The two 20-
hydroxyacetophenone moieties are related by crystallographic
symmetry. Intramolecular phenolic OeH/O hydrogen bonds with
carboxyl O-atom acceptors are present in both moieties. The mol-
ecules are organized in sheets, with one dimensional OeH/O
hydrogen bonded chains on each extremity. The sheets in-
terconnect via CeH/O contacts between the methyl and alcohol
groups forming another chain structure orthogonal to the sheets
on top of each other, and therefore there is no
crystal.
p stacking in the
(see side view). No
p stacking is present.

9332
S. Guieu et al. / Tetrahedron 69 (2013) 9329e9334
hydrogen bonds also force the molecules to organize without
pep
interactions, which also enhances their fluorescence intensity.
We wondered why the AIEE test failed with these compounds,
and investigated the solid-state structure of the aggregate. None of
the compounds gave crystals by slow evaporation of a solution in
THF/water mixture, and only amorphous solids were obtained. The
FTIR spectra of the crystal obtained by slow evaporation of a solu-
tion in dichloromethane and of the solid obtained by slow evapo-
ration of a solution in THF/water mixture were compared. They all
show similar features and the spectra of diester 4 are depicted in
Fig. 8, as an example. The amorphous solid displays two sharp
bands at ca. 3650 and 860 cmꢁ1, which are absent from the spec-
trum of the crystal, and are attributed to free OeH vibrational and
stretching vibration, respectively. The hydrogen bonded OeH
stretching is still present at ca. 3200 cmꢁ1, while the carbonyl band
shifts. The aromatic CeH vibration bands also appear stronger. All
this indicates that water molecules are present in the solid not as
free molecules but interacting with the oxygen atoms of compound
4. As a consequence, the solid-state packing should be different
from the crystal. The hydrogen-bonded chains are probably dis-
Fig. 6. Single crystal XRD structure of diester 4.
rupted and the polar environment may favor the pep interactions
between the molecules, which would explain why the emission is
quenched in the aggregate form.
Fig. 7. Single-crystal XRD structure of diester 5.
Fig. 8. FTIR spectra of diester 4 crystallized from dichloromethane and precipitated
from a THF/water mixture.
The intensity of the emission in the solid state depends on the
packing motif and on the stiffening of the molecular structure,
enhancing or hindering the thermal relaxation. Consecutive
pep
interactions dramatically reduce the solid-state fluorescence in-
tensity.16 In contrast, strong hydrogen bonding, rigidifying the
structure, and preventing the torsional vibration of phenyl rings17
or carbonyl groups,14 may promote the solid-state emission. Al-
though none of the compounds presented here show AIEE, com-
pounds 3e6 have higher quantum yields in the solid state than in
solution. Compound 1 is an amorphous solid, probably lacking the
organization needed to stiffen its structure. Compound 2 has con-
3. Conclusion
While diphenylmethane derivatives have been used mainly for
their UV absorption properties in dilute conditions, this study
shows that some of them are highly emissive in the crystalline state
(ff up to 0.63). When water is present, the compounds do not ex-
hibit AIEE due to the disruption of the crystal packing, but
they show crystallization-induced emission enhancement. This is
attributed to particular forms of crystal packing efficiently ham-
pering the molecular motion and preventing consecutive
interactions.
secutive
state emission intensity is low. Compounds 3e5 have chain or
sheets structures with strong hydrogen bonds and no in-
pep interactions and, thus, it is fair to expect that its solid-
pep
pep
teractions, and it is likely that the compound 6 has a similar or-
ganization. Each carbonyl accepts two hydrogen bonds. The excited
state is likely the result of the tautomerisation-transfer of the labile
proton from the hydroxyl to the carbonyl group. Two strong intra
and inter-molecular hydrogen bonds are still present, restricting
the torsional vibrations of the protonated carbonyl and of the ar-
omatic rings, thus preventing the thermal relaxation of the excited
state through non-emissive processes. These particularly strong
4. Experimental
4.1. General
The UVevis absorption spectra were recorded using a UV-2501
PC Shimadzu spectrophotometer. The photoluminescence spectra

S. Guieu et al. / Tetrahedron 69 (2013) 9329e9334
9333
4
3
were recorded at room temperature with a modular double gra-
ting excitation spectrofluorimeter with a TRIAX 320 emission
monochromator (Fluorolog-3, Horiba Scientific) coupled to a R928
Hamamatsu photomultiplier, using a front face acquisition mode.
The excitation source was a 450 W Xe arc lamp. The emission
spectra were corrected for detection and optical spectral response
of the spectrofluorimeter and the excitation spectra were corrected
for the spectral distribution of the lamp intensity using a photodi-
ode reference detector.
aromatic CH), 7.28 (dd, JHeH 2.1, JHeH 8.7 Hz, 2H, aromatic CH),
3
6.93 (d, JHeH 8.7 Hz, 2H, aromatic CH), 3.91 (s, 2H, CH2), 2.60 (s,
6H, CH3).
4.3. Synthesis of the esters 4e6
4.3.1. Dimethyl 5,50-methylenebis(2-hydroxy-benzoate) 4.10 Concen
trated sulfuric acid (0.1 mL, catalytic) was slowly added to a solution
of 5,50-methylenebis(2-hydroxybenzoic acid) (2.0 g, 6.9 mmol) in
methanol (100 mL) at room temperature, and the solution was
stirred at 100 ꢀC for 12 h. The solvent was then evaporated under
reduced pressure, and silica gel flash column chromatography (el-
uent: dichloromethane) of the residue gave the product as a white
solid (0.84 g, 38%) and some starting material (1.02 g). Slow evap-
oration of a concentrated solution in dichloromethane gave color-
less crystals suitable for X-ray diffraction. Mp 108e110 ꢀC; 1H NMR
For compounds 2e5, a colorless single crystal was selected for
indexing and, for compound 5, data collection at 150 K on a Nonius-
based Kappa Bruker diffractometer equipped with a charge-
ꢀ
coupled device (CCD) area detector and MoK
a
(l
¼0.7107 A) radia-
tion. Absorption corrections were applied using the multi-scan
semi-empirical method implemented in SADABS.18 The structure
was solved by direct methods using the program SHELXS-9719 and
refined by full-matrix least-square refinement on F2 using the
program SHELXL-97. All non-hydrogen atoms were refined aniso-
tropically. The hydrogen atoms were visible on the difference
Fourier map, placed in geometrically calculated positions and in-
cluded in the final refinement using the ‘riding’ model with iso-
tropic temperature factors fixed at 1.2 times that of the parent
atom.
(300.13 MHz, CDCl3, 25 ꢀC):
d
¼10.64 (s, 2H, OH), 7.62 (d, 4JHeH 2.4 Hz,
2H, aromatic CH), 7.25 (dd, 4JHeH 2.4, 3JHeH 8.7 Hz, 2H, aromatic CH),
3
6.92 (d, JHeH 8.7 Hz, 2H, aromatic CH), 3.93 (s, 6H, CH3), 3.84 (s,
2H, CH2).
4.3.2. Diethyl 5,50-methylenebis(2-hydroxy-benzoate) 5.11 Concen
trated sulfuric acid (0.01 mL, catalytic) was slowly added to
a solution of 5,50-methylenebis(2-hydroxybenzoic acid) (288 mg,
1.0 mmol) in ethanol (20 mL) at room temperature, and the so-
lution was stirred at 100 ꢀC for 12 h. The solvent was then
evaporated under reduced pressure, and silica gel flash column
chromatography (eluent: dichloromethane) of the residue gave
the product as a white solid (43 mg, 13%) and some starting
material (210 mg). Slow evaporation of a concentrated solution in
dichloromethane gave colorless crystals suitable for X-ray dif-
4.2. Synthesis of diphenylmethane derivatives 1e3
4.2.1. 5,50-Methylenebis(2-hydroxybenzoic acid) 1.7 Concentrated
sulfuric acid (1.0 mL, catalytic) was slowly added to a suspension of
salicylic acid (10.0 g, 72.5 mmol) and formaldehyde (1.09 g,
36.2 mmol) in glacial acetic acid (30 mL) at room temperature. The
solution was stirred at 90 ꢀC for 2 h. It was then poured on iced
water (50 mL), the solid that formed was collected by filtration and
washed with water (50 mL) and methanol (50 mL). The product
was obtained as an off-white solid (8.07 g, 77%). Mp 248e250 ꢀC
fraction. Mp 105e107 ꢀC (lit.11 220e222 ꢀC); 1H NMR
4
(300.13 MHz, CDCl3, 25 ꢀC):
d
¼10.73 (s, 2H, OH), 7.65 (d, JHeH
4
3
2.4 Hz, 2H, aromatic CH), 7.23 (dd, JHeH 2.4, JHeH 8.7 Hz, 2H,
(lit.7b 238e240 ꢀC); 1H NMR (300.13 MHz, DMSO-d6, 25 ꢀC):
d
¼7.61
3
aromatic CH), 6.90 (d, JHeH 8.7 Hz, 2H, aromatic CH), 4.39 (q,
(d, 4JHeH 2.4 Hz, 2H, aromatic CH), 7.36 (dd, 4JHeH 2.4, 3JHeH 8.7 Hz,
3JHeH 7.2 Hz, 4H, CH2eCH3), 3.85 (s, 2H, CH2), 1.41 (t, 3JHeH 7.2 Hz,
6H, CH2eCH3).
3
2H, aromatic CH), 6.88 (d, JHeH 8.7 Hz, 2H, aromatic CH), 3.85 (s,
2H, CH2).
4.3.3. Dipropyl 5,50-methylenebis(2-hydroxy-benzoate) 6.12 Concen
trated sulfuric acid (0.01 mL, catalytic) was slowly added to
a solution of 5,50-methylenebis(2-hydroxybenzoic acid) (288 mg,
1.0 mmol) in propanol (20 mL) at room temperature, and the
solution was stirred at 100 ꢀC for 12 h. The solvent was then
evaporated under reduced pressure, and silica gel flash column
chromatography (eluent: dichloromethane) of the residue gave
the product as a white oily solid (45 mg, 12%) and some starting
material (195 mg). Mp 78e80 ꢀC (lit. not reported); 1H
4.2.2. 5,50-Methylenebis(2-hydroxybenzaldehyde) 2.8 Concentrated
sulfuric acid (1.0 mL, catalytic) was slowly added to a suspension
of salicylaldehyde (12.2 g, 100 mmol) and formaldehyde (1.5 g,
50 mmol) in glacial acetic acid (30 mL) at room temperature, and
the solution was stirred at 90 ꢀC for 4 h. It was then poured on
iced water (50 mL), the solid that formed was collected by fil-
tration and washed with water (50 mL) and light petroleum
(50 mL). The product was obtained as an off-white solid (6.9 g,
54%). Mp 128e130 ꢀC (lit.20 141e142 ꢀC); 1H NMR (300.13 MHz,
NMR (300.13 MHz, CDCl3, 25 ꢀC):
d
¼10.72 (s, 2H, OH), 7.65
CDCl3, 25 ꢀC):
d
¼10.92 (s, 2H, OH), 9.85 (s, 2H, CHO), 7.35 (dd,
4
4 3
(d, JHeH 2.4 Hz, 2H, aromatic CH), 7.24 (dd, JHeH 2.4, JHeH
8.4 Hz, 2H, aromatic CH), 6.91 (d, JHeH 8.4 Hz, 2H, aromatic CH),
4.29 (t, JHeH 6.6 Hz, 4H, CH2eCH2eCH3), 3.86 (s, 2H, CH2),
3
4
4JHeH 2.1, JHeH 8.4 Hz, 2H, aromatic CH), 7.32 (d, JHeH 2.1 Hz,
3
3
2H, aromatic CH), 6.96 (d, JHeH 8.4 Hz, 2H, aromatic CH), 3.96 (s,
3
2H, CH2).
3
1.80 (m, 4H, CH2eCH2eCH3), 1.02 (t, JHeH 7.2 Hz, 6H,
CH2eCH2eCH3).
4.2.3. 5,50-Methylenebis(2-hydroxyacetophenone) 3.9 Concentrated
sulfuric acid (0.5 mL, catalytic) was slowly added to a suspension
of 20-hydroxyacetophenone (5.0 g, 36.7 mmol) and formaldehyde
(550 mg, 18.35 mmol) in glacial acetic acid (15 mL) at room
temperature, and the solution was stirred at 90 ꢀC for 2 h. It was
then poured on ice (50 mL), the solid that formed was collected by
filtration and washed with water (50 mL) and methanol (50 mL).
Silica gel flash column chromatography (eluent: dichloro-
methane) of the residue gave the product as a white solid
(1.0 g, 19%). Slow evaporation of a concentrated solution in
dichloromethane gave yellowish crystals suitable for X-ray dif-
Acknowledgements
Thanks are due to the University of Aveiro and the Portu-
~
^
guese Fundac¸ ao para a Ciencia e a Tecnologia (FCT) for funding
the Organic Chemistry Research Unit (project PEst-C/QUI/
UI0062/2013), the CICECO Associate Laboratory (PEst-C/CTM/
LA0011/2013), and the Portuguese National NMR Network
~
(RNRMN). The authors thank R.A.S. Ferreira and P. Brandao for
their help in the PL measurements and XRD, respectively. S.G.
also thanks the FCT for a postdoctoral grant (SFRH/BPD/70702/
2010).
fraction. Mp 147e149 ꢀC (lit.9 143 ꢀC); 1H NMR (300.13 MHz,
4
CDCl3, 25 ꢀC):
d
¼12.17 (s, 2H, OH), 7.50 (d, JHeH 2.1 Hz, 2H,

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S. Guieu et al. / Tetrahedron 69 (2013) 9329e9334
8. Marvel, C. S.; Tarkoy, N. J. Am. Chem. Soc. 1957, 79, 6000e6002.
Supplementary data
9. Barba, V.; Betanzos, I. J. Organomet. Chem. 2007, 692, 4903e4908.
ꢁ
10. (a) Meric, R.; Vigneron, J.-P.; Lehn, J.-M. J. Chem. Soc., Chem. Commun. 1993,
These data contain the single crystal X-ray crystallographic data
for compound 5. Supplementary data related to this article can be
found at http://dx.doi.org/10.1016/j.tet.2013.07.107.
~
129e131; (b) Guieu, S.; Brandao, P.; Rocha, J.; Silva, A. M. S. Acta Crystallogr.
2012, E68, o1404.
11. Nagaraj, A.; Reddy, C. S. J. Heterocycl. Chem. 2007, 44, 1357e1361.
12. Lapkin, I. I.; Orlova, L. D. Zh. Org. Khim. 1970, 6, 68e71.
13. Kozma, L.; Hornak, I.; Eroshtak, I.; Nemet, B. J. Appl. Spectrosc. 1990, 53,
851e855.
14. Hisaindee, S.; Zahid, O.; Meetani, M. A.; Graham, J. J. Fluoresc. 2012, 22,
677e683.
15. CCDC 938828 contains the supplementary crystallographic data for compound
5. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (0044) 1223-336-033; or e-mail:
References and notes
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3. See, for example: (a) Ye, Y. H.; Zhu, H. L.; Song, Y. C.; Liu, J. Y.; Tan, R. X. J. Nat.
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947e952.
4. Cui, G.-J.; Xu, X.-Y.; Lin, Y.-J.; Evans, D. G.; Li, D.-Q. Ind. Eng. Chem. Res. 2010, 49,
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5. (a) Wirz, D. R.; Wilson, D. L.; Schenk, G. H. Anal. Chem. 1974, 46, 896e900; (b)
Kasha, M.; Rawls, H. R.; El-Bayoumi, M. A. Pure Appl. Chem. 1965, 11, 371e392.
6. (a) Coffield, T. H.; Filbey, A. H.; Ecke, G. G.; Kolka, A. J. J. Am. Chem. Soc. 1957, 79,
5019e5023; (b) Bandgar, B. P.; Kasture, S. P. Monatsh. Chem. 2000, 131, 913e915;
(c) Sereda, G. A. Tetrahedron Lett. 2004, 45, 7265e7267; (d) Kumarraja, M.;
Pitchumani, K. Synth. Commun. 2003, 33, 105e111; (e) Kharasch, M. S.; Joshi, B.
S. J. Org. Chem. 1957, 22, 1435e1438.
deposit@ccdc.cam.ac.uk. Crystal data: C19H20O6, Mw¼344.35, monoclinic, C2/
ꢀ
c, Z¼4, a¼11.6206(4), b¼8.7856(3), c¼16.8516(5) A,
a
¼g
¼90ꢀ,
b
¼95.761(2)ꢀ,
Dcalcd¼1.336 g cmꢁ3, T¼150(2) K, F(000)¼728,
m
¼0.100 mmꢁ1, 7654 reflections
were corrected, 2297 unique (Rint¼0.0541), 1787 observed (I>2s (I)), R1¼0.
0396, wR2¼0.1016.
16. (a) Matsui, M.; Shibata, T.; Fukushima, M.; Kubota, Y.; Funabiki, K. Tetrahedron
2012, 68, 9936e9941; (b) Shirai, K.; Matsuoka, M.; Fukunishi, K. Dyes Pigm.
1999, 42, 95e101; (c) Shirai, K.; Matsuoka, M.; Matsumoto, S.; Shiro, M. Dyes
Pigm. 2003, 56, 83e87.
17. Guieu, S.; Rocha, J.; Silva, A. M. S. Tetrahedron Lett. 2013, 54, 2870e2873.
18. Sheldrick, G. M. SADABS V.2.01, Bruker/Siemens Area Detector Absorption Cor-
rection Program; Bruker AXS: Madison, WI, 1998.
€
19. Sheldrick, G. M. SHELXS-97; University of Gottingen: Germany, 2008.
20. Delogu, G.; Podda, G.; Corda, M.; Fadda, M. B.; Fais, A.; Era, B. Bioorg. Med. Chem.
Lett. 2010, 20, 6138e6140.
7. (a) Clemmensen, E.; Heitman, A. H. C. J. Am. Chem. Soc. 1911, 33, 733e745; (b)
Reddy, C. S.; Raghu, M. Chem. Pharm. Bull. 2008, 56, 1732e1734.