The synthesis, X-ray structure analysis, and photophysical characterization of 3,3′-diacetylstilbene

Article abstract of DOI:10.1016/j.molstruc.2011.08.045

3,3′-Diacetylstilbene was produced in modest yield (26%) from a palladium(II) acetate-catalyzed coupling reaction between triethoxyvinylsilane and the triazene 1-{3-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone. X-ray analysis of crystals of 3,3′-diacetylst

Full text of DOI:10.1016/j.molstruc.2011.08.045

Journal of Molecular Structure 1005 (2011) 167–171
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
The synthesis, X-ray structure analysis, and photophysical characterization
of 3,30-diacetylstilbene
Zachary Sharrett a, Andrés Villalpando b, Frank R. Fronczek b, Ralph Isovitsch a,
⇑
a Department of Chemistry, Whittier College, Whittier, CA 90608, United States
b Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, United States
a r t i c l e i n f o
a b s t r a c t
3,30-Diacetylstilbene was produced in modest yield (26%) from a palladium(II) acetate-catalyzed coupling
reaction between triethoxyvinylsilane and the triazene 1-{3-[(E)-morpholin-4-yldiazenyl]phenyl}etha-
none. X-ray analysis of crystals of 3,30-diacetylstilbene revealed a nearly planar molecule (average devi-
ation 0.037 Å) on a crystallographic inversion center. Its crystal packing was found to be composed of
sheets of individual molecules of the stilbene interacting through CAHꢀꢀꢀO hydrogen bonds with the
Article history:
Received 5 July 2011
Received in revised form 25 August 2011
Accepted 25 August 2011
Available online 6 September 2011
sheets in turn participating in two types of weak CAHꢀꢀꢀ
p
aromatic interactions. The room-temperature
pꢁ transi-
Keywords:
absorption spectra of 3,30-diacetylstilbene in propanenitrile and chloroform featured two
p
?
3,30-Diacetylstilbene
Palladium-catalyzed synthesis
Absorption spectra
Emission spectra
tions with maxima at approximately 250 and 300 nm. 3,30-Diacetylstilbene was observed to be lumines-
cent in room-temperature solution, in propanenitrile glass at 77 K, and in the solid state with maxima in
the range 385–470 nm. The broadness of the emission spectra qualitatively indicated the degree that 3,30-
diacetylstilbene aggregated in solution. Quantum yields of 2 in propanenitrile and chloroform solution
indicated that it had a higher fluorescence efficiency than 4,40-diacetylstilbene.
Quantum yield
X-ray crystal structure
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Studies of the photophysical properties of (E)-stilbene have con-
tinued for more than 40 years [1–3]. This work has served to cata-
lyze explorations into the predictable alteration of the emissive
properties of (E)-stilbene through changes in its functionality.
The selective tuning of the photophysical properties of (E)-stilbene
is of interest toward the end of preparing materials that contain an
(E)-stilbene moiety [4,5]. These materials exhibit novel photophys-
ical properties with potential applicability to many areas, such as
optoelectronic devices and materials [6,7].
Our research involves the synthesis of luminescent stilbenoid
metal–organic materials. The precursors for our target materials
are metal-binding ligands based on (E)-stilbene. With its easily
transformed acetyl groups and inherent luminescent properties
the novel stilbene 3,30-diacetylstilbene (2; Scheme 1) is an obvious
precursor for our ligands. In this work we present the first synthe-
sis of 2 as well as its X-ray crystal structure. We also present a de-
tailed photophysical characterization of 2, which was found to
absorb and emit light at shorter wavelengths than the 4,40-isomer,
as well as have a higher quantum yield.
2.1. General synthetic methods
Synthetic procedures were carried out using standard tech-
niques. Solvents and reagents were purchased from Sigma–Aldrich
or Acros Organics and used as received. Melting points were deter-
mined in open capillaries and are uncorrected. 1H- and 13C NMR
spectra were recorded on a JEOL ECX 300 MHz spectrometer using
TMS as the internal standard. IR spectra were recorded neat or as
KBr disks on a JASCO 460 FT-IR. Elemental analyses were done by
M-H-W Laboratories of Tucson, Arizona. Mass spectrometry was
provided by the Washington University Mass Spectrometry
Resource with support from the NIH National Center for Research
Resources (Grant No. P41RR0954).
2.2. Photophysical measurements
Emission and absorption spectra were recorded from solutions
prepared from propanenitrile (99% purity) and spectrophotometric
grade chloroform utilizing a HoribaJobinYvon FluoroMax-4 fluo-
rometer and a Hewlett Packard 8453 diode array spectrometer.
All solutions were approximately 5–6 ꢂ 10ꢃ6 M and were deoxy-
genated with argon. Emission spectra were corrected for detector
response utilizing a correction curve supplied by the fluorometer
manufacturer.
⇑
Corresponding author. Tel.: +1 562 907 4200x4499.
E-mail address: risovits@whittier.edu (R. Isovitsch).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.08.045

168
Z. Sharrett et al. / Journal of Molecular Structure 1005 (2011) 167–171
N N
O
1. NaNO2, 6 M HCl
2. morpholine
3. sat. aq. NaHCO3
NH2
N
2
H3C
H3C
O
O
1
1. MeOH/HBF4, Pd(OAc)2
2. triethoxyvinylsilane
3. Pd(OAc)2
H3C
O
H3C
O
2
Scheme 1. The synthesis of 3,30-diacetylstilbene (2).
Fluorescence quantum yields were determined at room temper-
0.43 mmol) was added followed by the dropwise addition of tri-
ethoxyvinylsilane (4.53 mL, 21.4 mmol in 10.0 mL methanol) over
5 min; the solution became light brown. A second portion of
Pd(OAc)2 (0.096 g, 0.43 mmol) was added and the mixture was
stirred at room temperature for 30 min. It was then heated be-
tween 40 and 45 °C for 20 min, and then refluxed for 20 min. The
volume of the reaction was then reduced to 40 mL and 75 mL
H2O added. A gray solid formed and was collected by suction
filtration, washed with H2O, and air-dried. The gray solid was
recrystallized twice from benzene to give 1.55 g (26%) of 2 as tan
crystals.
ature using propanenitrile and chloroform solutions of 2 (kex = 292
and 295 nm respectively) by comparison with scintillation grade
(E)-stilbene (kmax,em = 350 nm; Ufl = 0.023 in deoxygenated aceto-
nitrile at room temperature) [5,8]. The absorbances of the (E)-stil-
bene standard solution and propanenitrile and chloroform
solutions of 2 were kept below 0.1 to avoid inner filter effects
and optically matched to within 6–10%. The fluorescence quantum
yield values reported in Table 2 are averages of three trials.
2.3. Preparation of 1-{3-[(E)-morpholin-4-yldiazenyl]phenyl}
ethanone (1)
M.P. 193–194 °C. IR (KBr): 3046, 2963, 1676, 1596 cmꢃ1 1H
.
NMR (300 MHz, CD2Cl2): 2.60 (s, 6 H); 7.25 (s, 2H); 7.47 (t,
3J = 7.57 Hz, 2H); 7.73 (dt, 3J = 7.91 Hz, 2H); 7.83 (dt, 3J = 7.57 Hz,
2H); 8.10 (t, 2H). 13C NMR (75 MHz, CD2Cl2): 26.7, 126.2, 127.7,
128.9, 129.1, 130.9, 137.5, 137.7, 197.7. Anal. Calc. for C18H16O2
(264.32): C, 81.79; H, 6.10; Found: C, 82.00; H, 6.11. HR–ESI–MS:
265.1222 ([M+H]+; calc. 265.1223).
1-(3-Aminophenyl)ethanone (3.00 g, 22.2 mmol) was added to
7 mL of 6 M HCl and heated to yield a clear yellow–orange solution,
which was cooled to 0 °C to induce the formation of a yellow–or-
ange solid. The solid was maintained at 0 °C and a solution of
1.66 g (24.1 mmol) of NaNO2 in 4 mL of H2O was added dropwise
over 10 min, with good stirring of the reaction mixture. A dark am-
ber solution resulted. To this stirred solution, 2.2 mL (2.18 g,
25.0 mmol) of morpholine was added dropwise over 10 min,
resulting in the formation of a dark orange precipitate. The mixture
was allowed to warm to room temperature and brought to pH 8
with saturated aqueous NaHCO3, which resulted in the formation
of a red–orange oil. The aqueous mixture was extracted three
times with 40 mL of CH2Cl2. The CH2Cl2 portions were combined,
dried with MgSO4 and evaporated to yield 5.03 g (96%) of 1 as a
red–orange oil.
2.5. X-ray crystal-structure analysis of 3,30-diacetylstilbene (2)
An X-ray quality crystal of 3,30-diacetylstilbene (2) was used
for data collection at T = 90 K on a Nonius KappaCCD diffractom-
eter equipped with an Oxford Cryosystems Cryostream chiller
and graphite-monochromated Mo K
a radiation (k = 0.71073 Å).
The structure was solved by direct methods, and structure refine-
ment was carried out using SHELXL-97 [9]. All H-atoms were vis-
ible in difference maps, but were placed in idealized positions
during refinement, with a torsional parameter refined for the
Me group.
IR (neat): 3066, 2968, 1684, 1585, 1442 cmꢃ1
.
1H NMR
(300 MHz, CDCl3): 2.65 (s, 3H); 3.85 (m, 8H); 7.44 (t, 1 H,
3J = 7.57, 7.91 Hz); 7.65 (dt, 1 H, 3J = 7.91 Hz); 7.80 (dt, 1 H,
3J = 7.91 Hz); 8.01 (t, 1 H). 13C NMR (75 MHz, CDCl3): 26.8; 48.1;
66.3; 120.7; 125.4; 126.0; 129.0; 138.1; 150.5; 198.2. Anal. Calc.
for C12H15N3O2 (233.26): C, 61.79; H, 6.48, N, 18.01. Found: C,
61.63; H, 6.22; N, 18.14. HR–ESI–MS: 234.1236 ([M+H]+; calc.
234.1237).
3. Results and discussion
3.1. Synthesis of 2
There are numerous synthetic protocols for the preparation of
substituted (E)-stilbene derivatives [10]. Many of these methods
employ reaction conditions that would be detrimental to reactive
moieties, such as acetyl substituents, and thus require the use of
protecting groups, which would add additional steps and purifica-
tion procedures. An example of these difficulties is the synthesis of
4,40-diacetylstilbene by Zimmerman and Stille [11].
2.4. Preparation of 3,30-diacetylstilbene (2)
To
a stirred suspension of 1-{3-[(E)-morpholin-4-yldiaze-
nyl]phenyl}ethanone (10.0 g, 42.9 mmol) in 85 mL of methanol at
0 °C, 10.7 mL (87.8 mmol) of 50% HBF4 were added dropwise over
10 min. The mixture was brought to room temperature; an orange
suspension resulted. To this suspension, Pd(OAc)2 (0.096 g,
Newer syntheses that utilize palladium catalysis and mild reac-
tion conditions overcome the difficulties inherent in the classic

Z. Sharrett et al. / Journal of Molecular Structure 1005 (2011) 167–171
169
methods of (E)-stilbene preparation [12,13]. Our preparation of 2
extends the work of Sengupta and co-workers and is depicted in
Scheme 1 [14,15]. This route to disubstituted (E)-stilbene deriva-
tives is attractive because of its operational simplicity and its ste-
reoselectivity for the (E)-stereoisomer. It also employs mild
reaction conditions using common and economical starting
materials.
The featured synthesis of 2 began with the preparation of the
novel triazene 1-{3-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone,
compound 1, which is an easily prepared and handled equivalent
for the in situ generation of a diazonium ion. Careful extraction of
the reaction mixture gave analytically pure 1 in 96% yield.
Compound 1 exhibited the expected spectroscopic characteris-
tics, except for the 13C NMR spectrum. The resonances for the aro-
matic ring and the Ac group were observed along with a singlet and
a broad singlet at 66.3 and 48.1 ppm respectively for the C-atoms
of the morpholine ring. The assignment of these signals to the mor-
pholine C-atoms was supported by the HMQC NMR spectrum of 1,
which showed connection between these signals and the morpho-
line protons at 3.85 ppm. The broad singlet was observed because
All bond lengths and angles of 2 correlated well with the values
for other stilbene derivatives, such as 4,40-diacetylstilbene, 4,40-
dicyanostilbene, 3-methylstilbene as well as a more complex nitro-
stilbene derivative [16,18–20].
Crystals of 2 were composed of sheets of individual molecules
of 2 engaged in weak CAHꢀꢀꢀO hydrogen bonding (see Fig. S1 in
Supplementary material). This CAHꢀꢀꢀO (C1HAO1 interaction oc-
curred between neighboring alkene hydrogen atoms and carbonyl
oxygen atoms with a HꢀꢀꢀO1 distance of approximately 2.4 Å, a
C1ꢀꢀꢀO1 distance of 3.384(12) Å, and a C1HꢀꢀꢀO1 bond angle of
166.55(2)°. This type of hydrogen bonding has been observed in
the architecture of numerous supramolecular systems that possess
carbonyl moieties [21–24].
The
CAHꢀꢀꢀ
p
p
-systems of sheets of 2 participated in two different, weak
aromatic intersheet interactions (see Figs. S2 and S3 in
Supplementary material). The first CAHꢀꢀꢀ
p
interaction is between
a methyl hydrogen atom (C9H) and the
p-system of a phenyl ring
(C2AC7) with a Hꢀꢀꢀring centroid distance of approximately 3.4 Å, a
C9-ring centroid distance of 4.150(2) Å and a C9AHꢀꢀꢀring centroid
bond angle of 133.55(2)°. The second CAHꢀꢀꢀ
p
interaction is be-
the partial
p
-character of the NAN single bond inhibited its rota-
tween an alkene hydrogen atom (C1H) and the p-system of a phe-
tion, which resulted in the magnetic nonequivalence of the 3-
and 5-carbon atoms in the morpholine ring [16,17]. The identity
of the triazene was corroborated by a HR–ESI–MS that had an
[M+H]+ peak at m/z = 234.1236, which was within 1.0 ppm of the
calculate value.
nyl ring (C2AC7) with a Hꢀꢀꢀring centroid distance of approximately
3.6 Å, a C1-ring centroid distance of 4.245(2) Å and a C9AHꢀꢀꢀring
centroid bond angle of 123.39(2)°. These types of CAHꢀꢀꢀ
p aromatic
interactions have been documented in other stilbene derivatives as
well as other molecules that possess aromatic moieties [19,25–28].
Compound 1 was combined with triethoxyvinylsilane in a
Pd(OAc)2-catalyzed coupling reaction to produce compound 2 in
low but usable yield (26%). The spectra of 2 compared well with
a similar stilbene derivative [16]. The identity and purity of 2 were
supported by an acceptable elemental analysis. The HR–ESI–MS of
2 exhibited an [M+H]+ peak at m/z = 265.1222, that was approxi-
mately 1.0 ppm lower than the calculated value.
3.3. Photophysics of 2
When a molecule of (E)-stilbene absorbs light, the first excited
state singlet, S1, is produced. The main deactivation pathway for
S1 has been found to be torsion about the central C@C bond, which
results in a mixture of (E)- and (Z)-stilbene. The second most likely
deactivation pathway for S1 is fluorescence [2].
The experimental photophysical data for compound 2 are com-
pared to the literature photophysical data for (E)-stilbene in Table
2. The electronic-absorption and -emission spectra of 2 in propane-
nitrile and chloroform solution are presented in Figs. 3 and 4,
respectively.
Each of the room-temperature absorption spectra of 2 had two
bands that were relatively insensitive to solvent polarity (propane-
nitrile versus chloroform): one near 250 nm and the other at
approximately 300 nm that had a longer wavelength shoulder.
The absorption maxima of 2 were blue-shifted 40–50 nm when
compared those of 4,40-diacetylstilbene, which is not unexpected
due to the decreased conjugation of the acetyl groups in the 3,30-
position [29]. The splitting of the band at 300 nm into a maximum
and a shoulder is attributed to the reduced symmetry of 2 as com-
pared to 4,40-diacetylstilbene, which results in a splitting of energy
levels [30].
3.2. X-ray analysis of 2
Recrystallization of 2 from benzene yielded tan crystals that
were suitable for X-ray analysis. Selected bond lengths for 2 are
presented in Table 1, while its ORTEP representation and crystal
packing are shown in Figs. 1 and 2, respectively. Table 3 contains
the crystal data and structure refinement details of compound 2.
Molecules of 2 have crystallographic inversion symmetry and
adopt the (E)-geometry about the central C@C bond (C1AC1i), with
a C1iAC1AC2 bond angle of 125.43(12)° and a C1AC1i bond length
of 1.344(2) Å (symmetry code i is defined as 2 ꢃ x, 1 ꢃ y, 2 ꢃ z).
Compound
2 deviates only slightly from planarity with a
C1iAC1AC2AC3 torsion angle of ꢃ174.96(13)°. The acetyl groups
were found to be slightly twisted from the plane of the benzene
rings with a C3AC4AC8AC9 torsion angle of ꢃ176.74(9)°.
Both of the absorption bands of 2 were intense, with extinction
coefficients that ranged from 26,000 to 31,000 Mꢃ1 cmꢃ1. The mag-
nitude of the observed extinction coefficients is not unusual for
disubstituted (E)-stilbene derivatives and points to the bands aris-
Table 1
Selected bond lengths (Å) and angles (°) for compound
2.a
ing from
p ?
pꢁ transitions [31].
O(1)AC(8)
C(8)AC(9)
C(4)AC(8)
C(4)AC(5)
C(1)AC(2)
C(1)AC(1i)
1.2210(13)
1.5105(14)
1.4972(15)
1.3945(14)
1.4699(14)
1.344(2)
125.43(12)
118.50(9)
120.96(9)
119.41(9)
ꢃ174.96(13)
ꢃ176.74(9)
Maxima of the emission spectra obtained from solutions of 2
were observed to be slightly blue-shifted by 10–12 nm when com-
pared those of 4,40-diacetylstilbene [16]. The emission spectrum
from a propanenitrile solution of 2 was broad with a shoulder at
460 nm, while the spectrum obtained from chloroform solution
had a narrower band that had vibrational structure with two
clearly resolved maxima. The energy difference between the max-
ima was 1200 cmꢃ1, which corresponds to a vibrational mode of
the bond between an olefinic carbon and a phenyl ring of 2 [2].
There was a noticeable difference in the broadness of the emis-
sion spectra obtained from propanenitrile and chloroform solution,
C(1i)AC(1)AC(2)
C(4)AC(8)AC(9)
O(1)AC(8)AC(9)
C(5)AC(4)AC(3)
C(1i)AC(1)AC(2)AC(3)
C(3)AC(4)AC(8)AC(9)
a
Symmetry code i is defined as 2 ꢃ x, 1 ꢃ y, 2 ꢃ z.

170
Z. Sharrett et al. / Journal of Molecular Structure 1005 (2011) 167–171
Table 2
Table 3
Photophysical data for compound 2 and (E)-stilbene.a
Crystal data and structure refinement of compound 2.
kmax,abs nm
kmax,em nm (kex
nm)
Ufl
D
m1/2
Chemical formula C18H16O2
b
(e
)
(cmꢃ1
)
Formula weight
Crystal size (mm)
Crystal system
Space group
264.31
0.33 ꢂ 0.22 ꢂ 0.05
Compound 2
MeCH2CN solution
Triclinic
248(31,500)
292(29,400)
321(13,300)c
253(28,500)
295(26,800)
385(296)
460c
0.042
6680
ꢀ
P1
Unit cell dimensions
CHCl3 solution
399(296)
419
0.0027 3350
a (Å)
b (Å)
c (Å)
5.6819 (10)
7.604 (2)
8.515 (2)
112.524 (11)
100.058 (14)
96.822 (13)
327.56 (13)
1
327(11,000)c 443c
MeCH2CN glass at
77 K
Solid state
425(296)
5380
4550
a
(°)
b (°)
453(296)
469
c
(°)
V (Å3)
Z
(E)-stilbened
MeCN solution
Dx (Mg/m3)
1.340
0.09
295(28,500)
307(24,600)
350(295)
0.023
l
(mmꢃ1
)
h Range (°)
Index ranges
2.6–32.6
ꢃ8 6 h 6 8
ꢃ11 6 k 6 11
ꢃ12 6 l 6 12
9127
a
b
c
Spectra acquired at room temperature unless otherwise noted.
Extinction coefficients units Mꢃ1 cmꢃ1
.
Shoulder.
See Ref. [5].
d
Reflections collected
Independent reflections
2370
Reflections with I > 2
r
(I)
1752
R (int)
0.030
Refinement method
R1/wR2
Full-least squares matrix on F2
0.050/0.145
1.06
Goodness-of-fit on F2
Refined parameters
95
Residual density (eÅꢃ3
CCDC deposition no.
)
0.46, ꢃ0.25
825,691
explained in terms of aggregation of 2 being more extensive in
the more polar solvent. Aggregation of aromatic systems, such as
stilbene derivatives, has been observed to produce broadened
emission spectra that often exhibit longer wavelength shoulders
[30,32–34]. The broadness of the bands in the emission spectra
of 2 in the solid state and in a propanenitrile glass at 77 K
(Dm
1/2 = 4450 cmꢃ1 and 5380 cmꢃ1 respectively) provided further
evidence of its tendency to aggregate.
Fig. 1. ORTEP view of 3,30-diacetylstilbene (2). Ellipsoids are represented at the 50%
probability level.
In propanenitrile and chloroform room-temperature solution
the quantum yields of 2 were 0.042 and 0.0027. These values were
larger than the quantum yields of 4,40-diacetylstilbene, which are
0.0088 and 0.0015 in the same solvents [16]. The larger quantum
yields of 2 are likely due to the 3,30-substituents inhibiting the
relaxation of S1 through the torsion pathway via steric hindrance,
with the half-width of the emission band (Dm1/2) of the former
being 6680 cmꢃ1 and the latter 3350 cmꢃ1. The broadness of the
propanenitrile solution spectrum and the shoulder at 460 nm is
Fig. 2. Crystal packing in 3,30-diacetylstilbene (2) as viewed along the crystallographic c-axis.

Z. Sharrett et al. / Journal of Molecular Structure 1005 (2011) 167–171
171
perature solution-state absorption spectra of 2 in propanenitrile
and chloroform showed two bands whose extinction coefficient
magnitudes indicated that they arose from
p ?
pꢁ transitions.
Compound 2 was found to be luminescent in various media with
maxima that ranged from 385 to 470 nm. The broadness of the
bands observed in the emission spectra of 2 indicated the degree
of its aggregation in solution. The fluorescence quantum yield of
compound 2 is higher than 4,40-diacetylstilbene.
Acknowledgements
We thank the Fletcher Jones Foundation for funds to purchase
the fluorometer. Whittier College is acknowledged for support of
this research. The purchase of the diffractometer was made possi-
ble by Grant No. LEQSF (1999–2000)-ENH-TR-13, administered by
the Louisiana Board of Regents. Dr. Andrew Maverick is acknowl-
edged for helpful discussion.
Appendix A. Supplementary material
Fig. 3. Electronic absorption and emission spectra of compound 2. Absorption
spectrum in propanenitrile (—); room temperature emission spectrum in propane-
nitrile (kex = 296 nm) (---); emission spectrum in propanenitrile glass at 77 K
(kex = 296 nm) (ꢄꢄꢄ).
Fig. 2 and Figs. S1–S3 were created using Mercury 2.3, a pro-
gram for crystal structure visualization, that can be downloaded
for free from the Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk/products/mercury. CCDC 825691 con-
tains the supplementary crystallographic data for this paper. These
data can be obtained free of charge via http://www.ccdc.cam.ac.us/
conts/retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336003). Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.molstruc.
2011.08.045.
References
[1] J. Saltiel, J. Am. Chem. Soc. 89 (1967) 1036.
[2] D.H. Waldeck, Chem. Rev. 91 (1991) 415.
[3] A. Weigel, N.P. Ernsting, J. Phys. Chem. B 114 (2010) 7879.
[4] J.-S. Yang, S.-Y. Chiou, K.-L. Liau, J. Am. Chem. Soc. 124 (2002) 2518.
[5] J.C. Roberts, J.A. Pincock, J. Org. Chem. 71 (2006) 1480.
[6] F. Leyssner, S. Hagen, L. Óvári, J. Dokic, P. Saalfrank, M.V. Peters, S. Hecht, T.
Klamroth, P. Tegeder, J. Phys. Chem. C 114 (2010) 1231.
[7] B.-K. An, S.H. Gihm, J.W. Chung, C.R. Park, S.-K. Kwon, S.Y. Park, J. Am. Chem.
Soc. 131 (2009) 3950.
[8] J.R. Lakowicz, Principlesof FluorescenceSpectroscopy, Springer, New York, 2006.
[9] G.M. Sheldrick, Acta Cryst. A64 (2008) 112.
[10] H. Lebel, C. Ladjel, L. Bréthous, J. Am. Chem. Soc. 129 (2007) 13321.
[11] E.K. Zimmerman, J.K. Stille, Macromolecules 18 (1985) 321.
[12] E. Alacid, C. Nájera, J. Org. Chem. 74 (2009) 2321.
[13] Á. Gordillo, E. de Jesús, C. López-Mardomingo, Chem. Commun. (2007) 4056.
[14] S. Sengupta, S. Bhattacharyya, S.K. Sadhukhan, J. Chem. Soc. Perkins Tran. 1
(1998) 275.
Fig. 4. Electronic absorption and emission spectra of compound 2. Absorption
spectrum in chloroform (—); room temperature emission spectrum in chloroform
(kex = 296 nm) (---); room temperature solid state emission spectrum
(kex = 296 nm) (ꢄꢄꢄ).
[15] S. Sengupta, S.K. Sadhukhan, Org. Synth. 79 (2002) 52.
[16] C. Pye, F.R. Fronczek, R. Isovitsch, Helv. Chim. Acta 98 (2010) 1162.
[17] R. Tingley, M.B. Peori, R. Church, K. Vaughan, Can. J. Chem. 83 (2005) 1799.
[18] B. Nohra, S. Graule, C. Lescop, R. Réau, J. Am. Chem. Soc. 128 (2006) 3520.
[19] L. Gao, H. Peng, H.-W. He, Acta Cryst. E62 (2006) o5032.
[20] F. Gao, T. Xie, Z. Cheng, N. Hu, L. Yang, Y. Gong, A.S. Zhang, H. Li, J. Fluoresc. 18
(2008) 787.
[21] M. Khurram, N. Qureshi, M.D. Smith, Chem. Commun. (2006) 5006.
[22] R. Shukla, S.V. Lindeman, R. Rathore, Chem. Commun. (2007) 3717.
[23] X.-L. Gao, L.-P. Lu, M.-L. Zhu, Acta Cryst. C65 (2009) o123.
[24] T. Steiner, Chem. Commun. (1997) 727.
increasing the likelihood of deactivation through the fluorescence
pathway [30].
The quantum yield observed for 2 in propanenitrile was signif-
icantly larger than the quantum yield in chloroform. This result can
be rationalized in terms of the greater aggregation of 2 in propane-
nitrile (as evidenced by its emission spectra) and intermolecular
interactions of 2 with the propanenitrile, both of which would in-
hibit nonradiative deactivation of S1 through the torsion pathway
[5,30].
[25] G. Zhang, G. Yang, J.S. Ma, J. Chem. Crystallogr. 36 (2006) 631.
[26] T. Steiner, Angew. Chem. Int. Ed. 41 (2002) 49.
[27] J. Guo, B. Li, W. Wang, Y. Lai, Z. Kristallogr. – New Cryst. Struct. 223 (2008) 127.
[28] W.B. Jennings, B.M. Farrell, J.F. Malone, J. Org. Chem. 71 (2006) 2277.
[29] J.N. Murrell, The Theory of the Electronic Spectra of Organic Molecules,
Chapman and Hall Ltd., London, 1963.
[30] F.D. Lewis, W. Weigel, X. Zuo, J. Phys. Chem. A 105 (2001) 4691.
[31] D.L. Pavia, G.M. Lampman, G.S. Kriz, J.R. Vyvyan, Introduction to Spectroscopy,
fourth ed., Brooks Cole, Belmont, CA, 2009.
[32] J. Catalán, L. Zimányi, J. Saltiel, J. Am. Chem. Soc. 122 (2000) 2377.
[33] Y. Hong, J.W.Y. Lam, B.Z. Tang, Chem. Commun. (2009) 4332.
[34] K.A.N. Upamali, L.A. Estrada, P.K. De, X. Cai, J.A. Krause, D.C. Neckers, Langmuir
27 (2011) 1573.
4. Conclusions
A simple palladium-catalyzed synthesis of compound 2 was
presented. Recrystallization of 2 from benzene resulted in the for-
mation of tan crystals suitable for X-ray analysis. The solid state
structure of 2 consisted of sheets of nearly planar molecules of 2
that interacted through weak CAHꢀꢀꢀO hydrogen bonds while the
sheets interacted through two types of p-interactions. Room-tem-