Relationship between molecular stacking and optical properties of 9,10-bis((4-N,N-dialkylamino)styryl) anthracene crystals: The cooperation of excitonic and dipolar coupling

Article abstract of DOI:10.1002/chem.201402369

Five 9,10-bis((4-N,N-dialkylamino)styryl) anthracene derivatives (DSA-C1-DSA-C7) with different length alkyl chains were synthesized. They showed the same color in dilute solutions but different colors in crystals. The absorption, photoluminescence, and fluorescence decay indicate that there exist both excitonic and dipolar coupling in crystals of DSA-C1-DSA-C7. X-ray crystallographic analysis revealed that all the crystals belong to the triclinic space group P1 with one molecule per unit cell and that the molecules in every crystal have the identical orientation. This offers ideal samples to investigate the impact of the molecular stacking on the optical properties of the crystals. For the first time, the cooperation of excitonic and dipolar coupling has been comprehensively studied, and the contribution to the spectral shift from the excitonic and dipolar couplings quantitatively obtained. The experiments of amplified spontaneous emission (ASE) together with measurements of the quantum efficiency further confirmed this interpretation. The results suggest that the excitonic and dipolar couplings between the adjacent molecules are both important and jointly induce the spectral shifts of the crystals.

Full text of DOI:10.1002/chem.201402369

DOI: 10.1002/chem.201402369
Full Paper
&
Structure–Property Relationships
Relationship between Molecular Stacking and Optical Properties
of 9,10-Bis((4-N,N-dialkylamino)styryl) Anthracene Crystals: The
Cooperation of Excitonic and Dipolar Coupling
Feng Li,[a] Na Gao,[a] Hai Xu,[a] Wei Liu,[b] Hui Shang,[a] Wenjun Yang,[b] and Ming Zhang*[a]
Abstract: Five 9,10-bis((4-N,N-dialkylamino)styryl) anthracene
derivatives (DSA-C1–DSA-C7) with different length alkyl
chains were synthesized. They showed the same color in
dilute solutions but different colors in crystals. The absorp-
tion, photoluminescence, and fluorescence decay indicate
that there exist both excitonic and dipolar coupling in crys-
tals of DSA-C1–DSA-C7. X-ray crystallographic analysis re-
vealed that all the crystals belong to the triclinic space
lar stacking on the optical properties of the crystals. For the
first time, the cooperation of excitonic and dipolar coupling
has been comprehensively studied, and the contribution to
the spectral shift from the excitonic and dipolar couplings
quantitatively obtained. The experiments of amplified spon-
taneous emission (ASE) together with measurements of the
quantum efficiency further confirmed this interpretation. The
results suggest that the excitonic and dipolar couplings be-
tween the adjacent molecules are both important and jointly
induce the spectral shifts of the crystals.
¯
group P1 with one molecule per unit cell and that the mole-
cules in every crystal have the identical orientation. This
offers ideal samples to investigate the impact of the molecu-
Introduction
ported hydrogen-bonded stacking-induced emission of amino-
benzoic acid compounds.[14,29,39] Kitamura et al. could tune the
solid-state optical properties of tetracenes by the length of the
alkyl side chain.[19] Mizuguchi et al. investigated the correlation
between the spectral shifts of crystals and the structure of
crystals of diketopyrrolopyrrole pigments and quinacridone de-
rivatives.[20,21] Ma et al. found a stable cross-stacking mode in
the crystalline state of 2,5-diphenyl-1,4-distyrylbenzene, which
has a high fluorescence quantum yield.[27] Saito et al. controlled
the solid-state properties of p-conjugated systems by macrocy-
clic restriction with flexible alkylene linkers.[25] Das et al. studied
the correlation between molecular packing and the solid-state
photophysical properties of a series of diphenyl butadiene de-
rivatives.[24,40,41] Gierschner et al. and Park et al. investigated the
consequences of different packing motifs in single crystals of
a series of distyrylbenzene derivatives on the photophysical
and laser properties.[42–44]
Organic single crystals constructed by p-conjugated molecules
have attracted a great deal of interest in the field of optoelec-
tronic devices such as optically pumped lasers,[1–3] field-effect
transistors (FETs),[4–7] electroluminescence (EL) devices,[8,9] and
photovoltaic cells[10–12] due to their high thermal stability, their
highly ordered structure, and their high carrier mobility. Gener-
ally, optical and electrical properties of organic crystals like ab-
sorption, luminescence, and carriers mobility are governed not
only by the structure of the monomolecules, but also by their
stacking patterns, which can be influenced strongly through
noncovalent intermolecular interactions such as hydrogen
bonding, p–p, CꢀH···pi interactions, etc.[3,13–29] Thus, under-
standing and controlling molecular stacking patterns are fun-
damental issues for obtaining the desired optical and electrical
properties of organic crystals.[18–21,23,30–37] There are many publi-
cations dealing with the relationship between molecular stack-
ing and optical properties. For instance, Bao et al. reviewed
strategies to tune molecular packing of organic semiconduc-
tors and their impact on charge transport.[38] Wang et al. re-
In general, there are two types of coupling that can affect
the optical properties of organic crystals. One is the excitonic
coupling, that is, an excimer, which is referred to the dimers
that exist only in the excited state and the ground state of the
pair is dissociative. The other is the dipolar coupling, that is, H-
aggregate or J-aggregate formation that describes the situa-
tion in which two or more identical molecules are close to
each other in a special spatial arrangement.[30,32] Up to date,
most of the works about the structure–property relationship of
organic crystals focused either on the excitonic coupling or on
the dipolar coupling, and the works studying the cooperation
of both couplings are rare. Actually, some molecules can form
H-aggregats in crystals with a blue-shifted absorption but
a red-shifted fluorescence.[42,45] In this work, we report our re-
[a] Prof. F. Li, N. Gao, Prof. H. Xu, Dr. H. Shang, Prof. M. Zhang
State Key Laboratory of Supramolecular Structure and Materials
Jilin University, 2699 Qianjin Avenue, Changchun (P.R. China)
E-mail: zhming@jlu.edu.cn
[b] Dr. W. Liu, Prof. W. Yang
Key Laboratory of Rubber-plastics of Ministry of Education
Qingdao University of Science & Technology
53-Zhengzhou Road, Qingdao, 266042 (P.R. China)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201402369.
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Figure 2. PL spectra of 9,10-bis((4-N,N-dialkylamino)styryl)anthracene crystals
(DSA-C1–DSA-C7) and images of a) dilute dichloromethane solution
Figure 1. Absorption and PL spectra of the 9,10-bis((4-N,N-dialkylamino)styr-
yl) anthracene derivatives (DSA-C1–DSA-C7) in dilute dichloromethane solu-
tion. The inset shows the molecular structural formulas of DSA-C1–DSA-C7.
~
!
&
(
*
=DSA-C1, =DSA-C3, =DSA-C4, =DSA-C6, and 3 =DSA-C7) and
b) crystals (under UV light of l=365 nm).
sults on 9,10-bis((4-N,N-dialkylamino)styryl) anthracenes with
different length of the alkyl chain (DSA-C1–DSA-C7), where the
number in the dubbed names represents the amount of
carbon atoms in each tail chain (inset of Figure 1). They have
the same optical properties in solution but different optical
properties in the crystal state. Our study about the molecular
stacking and optical properties of crystals of compounds DSA-
C1–DSA-C7 now shows that the cooperation of excitonic cou-
pling and dipolar coupling induces the observed spectral
shifts.
Results and Discussion
Figure 3. Absorption spectra of the 9,10-bis((4-N,N-dialkylamino)styryl) an-
&
*
thracenes in films. =DSA-C1 (l=300, 339, 452 nm), =DSA-C3 (l=259,
Synthesis and optical properties in solution and crystal form
~
!
282, 338, 450 nm), =DSA-C4 (l=260, 283, 335, 438 nm), =DSA-C6
(l=259, 283, 339, 451 nm), and 3 =DSA-C7 (l=259, 283, 339, 451 nm).
The five compounds were synthesized according to the report-
ed procedures and the details can be found in the Supporting
Information.[26]
DSA-C1–DSA-C7 possess a pale yellow color in diluted di-
chloromethane solution as shown in Figure 2a, and their ab-
sorption and photoluminescence (PL) spectra are provided in
Figure 1. As can be seen, the absorption and PL spectra of
these compounds in dilute solution are almost the same,
which indicates the single-molecule properties of the com-
pounds come from the 9,10-bis((4-N,N-dialkylamino)styryl) an-
thracene, and the alkyl chains at the end do not participate in
the absorption and emission processes.
measured the absorption spectra of solid films of the five com-
pounds, alternatively, as can be seen in Figure 3. The peak po-
sitions of films and solutions of DSA-C1–DSA-C7 are summar-
ized in Table S2 in the Supporting Information. We can see
that peaks larger than l=400 nm in crystals are slightly red
shifted compared to those in solution except for compound
DSA-C4. We also measured the absorption spectra of the crys-
tals by diffuse reflectance spectroscopy (see Figure S13 in the
Supporting Information). The absorption edges of the different
crystals are shifted pronouncedly opposite to those of the
dilute solutions (see Table S3 in the Supporting Information).
Thus, the variation of the onset of the absorption spectra
suggests that there should exist dipolar coupling in the five
crystals.
Five single crystals of DSA-C1–DSA-C7 have been successful-
ly obtained by the vapor diffusion method in which dichloro-
methane was used as the favorable solvent and methanol as
the unfavorable solvent. Under the irradiation of UV light at
l=365 nm, the single crystals of DSA-C1–DSA-C7 show differ-
ent colors ranging from yellow to red, as displayed in Fig-
ure 2b. The PL spectra of the crystals are also depicted in
Figure 2. The peak positions are in the following order: DSA-C3
(l=565 nm)<DSA-C4 (l=567 nm)<DSA-C6 (l=580 nm)<
DSA-C1 (l=593 nm)<DSA-C7 (l=609 nm). It is difficult to
obtain the absorption spectra of crystals directly, therefore, we
Figure 4 depicts the fluorescence decay curves of the five
crystals (excited by a picosecond semiconductor laser at l=
375 nm). The curve of DSA-C1 displays a mono-exponential
decay and the curves of DSA-C3–DSA-C7 display a bi-exponen-
tial decay. The fitting details can be found in the Supporting
Information. Table 1 summarizes the fitting parameters. We
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long axis of the molecules according to the density functional
theory (DFT) calculations by using the B3LYP hybrid functional
with the 6-31G(d, p) basis set through Gaussian 09.[46] That is,
every molecular transition dipole is parallel to the others in
each crystal.
To present the stacking patterns of the crystals clearly, we
used a set of rules of color in the schematic diagram. For ex-
ample, a partial illustration of the X-ray structure of DSA-C1
containing eight monomolecules is shown in Figure 5, the
red!pink is used to display the molecules along the a axis,
red!yellow to show the molecules along the b axis, red!
blue to show the molecules along the c axis. This set of rules
of color presenting the molecules along different axes was
extended to all crystals of DSA-C1–DSA-C7 in the following
figures.
Figure 4. Fluorescence decay curves (detected at the peak wavelength of
the PL spectra) of the 9,10-bis((4-N,N-dialkylamino)styryl) anthracene crystals
~
!
&
*
^
=DSA-C1, =DSA-C3, =DSA-C4, =DSA-C6, and =DSA-C7), the in-
(
strumental response (3 =IRF) is given for comparison. The inset shows the
enlarged curves at the beginning of the decay.
Table 1. Parameters of the fluorescence decay curves of the five crystals.
Compound
l [nm]
t1 [ns]
t2 [ns]
A1
A2
t
[a] [ns]
DSA-C1
DSA-C3
DSA-C4
DSA-C6
DSA-C7
593
565
567
580
609
2.99
1.16
1.67
1.18
1.16
1
2.99
1.50
2.18
1.68
1.72
2.67
3.62
2.79
2.67
0.5988
0.5644
0.4877
0.4268
0.4012
0.4356
0.5123
0.5732
[a] The weighted-average lifetime was calculated by: 1/t=A1/t1+A2/t2.
Figure 5. A diagram presenting the molecules along different axis by using
different colors (red and pink, blue and pale blue, yellow and pale yellow).
also measured the fluorescent lifetime of the five compounds
in dilute solution. All dilute solutions show a rapid decay,
which is beyond the response limit of our instrument, but one
thing we are sure is that all the lifetimes of the dilute solutions
are less than 0.2 ns. Thus, the weighted-average lifetimes of
DSA-C1–DSA-C7 in crystals are much longer than those in
dilute solution. This is one characteristic for excimer formation.
In the inset of Figure 4, there exists delay time between the
maximum of the decay curves of DSA-C1–DSA-C7 crystals and
that of the instrumental response (IRF), and the shortest delay
time is about 0.8 ns. The delay time corresponds to the dy-
namic formation of excited dimers, which is another character-
istic of excimer formation. The above-mentioned two charac-
teristics added by the structureless and red-shifted broadened
spectra of the crystals indicate that the emission of the five
crystals at least have the component of excimer emission, that
is, emission from excitonic coupling.
In the single crystal of DSA-C1, the molecules are self-assem-
bled together by three-dimensional, net-like supramolecular in-
teractions. There exists aromatic CꢀH···p bonds between ben-
zene and anthracene. DSA-C1-I, -II, and -III present the aromat-
ic CꢀH···p bonds along the a, b, and c axis, respectively, as
shown in Figure 6. The details of the intermolecular bonds are
collected in Table 2.
In the single crystal of DSA-C3, the molecules are firstly self-
assembled together by one aliphatic CꢀH···p (DSA-C3-I) bond
along the a axis, forming columns. Then the columns are self-
assembled together in parallel along the b and c axes by the
combination of van der Waals forces and steric hindrance
effect, thereby forming the crystal. The procedure is shown in
Figure 7. In the single crystal of DSA-C4, the molecules are self-
assembled together in the same way as described for DSA-C3,
only the reacting distance and angle of the CꢀH···p bond are
a little different, as can be seen from Table 2.
Crystal structures
X-ray crystallographic analyses were performed to clarify the
stacking patterns of the crystals. The results indicate that all
the crystals of DSA-C1–DSA-C7 belong to the triclinic space
In the single crystal of DSA-C6, the molecules are firstly self-
assembled into one plane (plane ab) by two-dimensional, net-
like supramolecular interactions including three CꢀH···p bonds.
One is an aromatic CꢀH···p (DSA-C6-I) bond, where the anthra-
cene moiety donates an hydrogen atom and the benzene unit
acts as the acceptor. The other two are aliphatic CꢀH···p (DSA-
C6-II and DSA-C6-III) bonds. Then the planes are pack together
¯
group P1 with one molecule per unit cell (Z=1, see Table S1 in
the Supporting Information for the crystallographic data), and
that the molecules in every crystal have the identical orienta-
tion. The polarization axes of all compounds are along the
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Figure 6. Formation procedure of a DSA-C1 crystal. From the single mole-
cule (a) to the three-dimensional, net-like stacking (e) by CꢀH···p bonds
along the a axis (b), CꢀH···p bonds along the b axis (c), and CꢀH···p bonds
along the c axis (d).
Figure 7. Formation procedure of a DSA-C3 crystal. From the single mole-
cule (a) to columns by CꢀH···p bonds along the a axis (b), and then the
columns stack together (c), thereby forming the crystal.
Table 2. Parameters of the CꢀH···p bonds in the crystals.
CꢀH···p
H···ring
distance [ꢁ]
C···ring
distance [ꢁ]
CꢀH···ring
angle [8]
bond
DSA-C1-I
DSA-C1-II
DSA-C1-III
DSA-C3-I
DSA-C4-I
DSA-C6-I
DSA-C6-II
DSA-C6-III
DSA-C7-I
DSA-C7-II
DSA-C7-III
3.10
3.07
2.90
2.76
2.74
2.93
3.18
3.05
2.99
2.90
2.88
3.80
3.69
3.69
3.51
3.55
3.72
3.93
3.83
3.76
3.83
3.73
134
125
143
138
147
144
136
138
140
161
146
in parallel along the c axis by the combination of van der
Waals forces and steric hindrance effects, thereby forming the
crystal. Figure 8 shows the procedure. In the single crystal of
DSA-C7, the molecules are self-assembled together in the simi-
lar way of described for DSA-C6, see Figure S5 in the Support-
ing Information for the details of the three CꢀH···p bonds. The
distances and angles of the three CꢀH···p bonds are slightly
different from those in the DSA-C6 single crystal, see Table 2.
The crystal packing diagram with a unit cell and molecular
conformation in the single crystals of DSA-C1–DSA-C7 can be
found in the Supporting Information.
Discussion
The molecules of DSA-C1–DSA-C7 have the same arrangement
(slipped-parallel arrangement) in the crystal structure, and only
the slip angles and distances are different, which offers ideal
experimental samples correlating the slip angle and distance
with color.
Figure 8. Formation procedure of a DSA-C6 crystal. From the single mole-
cule (a) to the layer overspread plane ab (b) by CꢀH···p bonds (c), (c) is ob-
tained by partially enlarging (b), and then the planes stack together along
the c axis (d), thereby forming the crystal.
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Curtis et al. defined the pitch and roll displacements to mea-
sure the p overlap between adjacent parallel molecules in crys-
tals.[47] The pitch and roll displacements are referred to the dis-
placement between adjacent molecules relative to one another
in the direction of the long molecular axis and the short mo-
lecular axis, respectively. The pitch and roll displacements and
the distances between the adjacent molecules along different
axes and in different planes for crystals of DSA-C1–DSA-C7 are
shown in Table 3.
the chromophores in the dimer. The values of q and r can be
found in Table 3.
The results of the absorption and emission spectra as well as
of the fluorescent lifetime in solution and crystal of DSA-C1–
DSA-C7 have shown that there exists both excitonic and dipo-
lar couplings in crystals. So the total energy difference be-
tween the excited states in crystal and in dilute solution can
be expressed as Equation (2):
DEtotal ¼ DEdiþDEex ¼ k ð1ꢀ3 cos 2qÞ=r3þDEex
In order to choose the biggest p-overlap between adjacent
molecules, the three parameters (pitch displacement, roll dis-
placement, and distance) should be as small as possible. Ac-
cording to the above-described principle, the adjacent mole-
cules along the c axis in the crystal of DSA-C1, along the a axis
in the crystals of DSA-C3 and DSA-C4, in plane ab in the crystal
of DSA-C6, and along the b axis in the crystal of DSA-C7 are
chosen to investigate the dipolar coupling between them, as
shown in Figure 9.
ð2Þ
DEdi and DEex represent the energy difference between the
excited state in the crystal and in dilute solution caused by the
dipolar and excitonic couplings, respectively, k is the propor-
tional coefficiency.
We calculated the values of (1ꢀ3cos2q)/r3, as well as the
values of the energy difference from the PL spectra of the crys-
tals and the dilute solutions. Then we plotted the curve of the
energy difference as a function of (1ꢀ3cos2q)/r3 and fitted it
by using Equation (2), as shown in Figure 10. The fitted Equa-
tion (3) is given below.
According to the dipolar coupling theory,[30,32] there is Equa-
tion (1):
DEdi / ð1ꢀ3 cos 2qÞ=r3
ð1Þ
DEtotal ¼ 38:53 ð1ꢀ3 cos 2qÞ=r3ꢀ0:074
ð3Þ
DEdi represents the energy difference between the excited
state in the dimer and in the monomer, q stands for the pitch
angle, r is defined as the distance between the centroids of
The correlation coefficient R2 of the fitting is not very high
(0.69). The difference of the torsion angles (the vinylene–an-
thryl torsion angle and vinylene–phenyl torsion
angle) between the monomolecules and the crystals
is small (see Table S4 in the Supporting Information),
Table 3. Pitch (x) displacement, roll (y) displacement, z displacement, and r for all
so we consider them as the minor factor affecting
the optical properties of the crystals in this work, but
it still has some effect. In additions, only when the
roll displacements are zero, Equation (1) can be strict-
ly obeyed, actually they are not zero (see Table 3).
The above-mentioned two reasons induce the low R2
value. However, from Equation (3), we still quantita-
tively obtained the contribution to the spectral shift
from the dipolar and excitonic couplings, respective-
ly. Here, the intercept is ꢀ0.074 eV, meaning that the
spectra will be red shifted by 19 nm from l=559 nm
(emission from the dilute solution) to l=578 nm
(emission from the crystal) for DSA-C1 and by 20 nm
from l=564 nm (emission from the dilute solution)
to l=584 nm for DSA-C3–DSA-C7 (emission from the
crystal) due to the excitonic coupling (Dlexcitonic). The
total spectral shift (Dltotal) subtracted by 19 nm (DSA-
C1) or 20 nm (DSA-C3–DSA-C7) is the contribution
from the dipolar coupling (Dldipolar, Table 4).
neighboring molecules in crystals of DSA-C1–DSA-C7.
Dimer
Pitch (x)
Roll (y)
z[a]
r[b]
[ꢁ]
systems
displacement [ꢁ]
displacement [ꢁ]
displacement [ꢁ]
DSA-C1
along the a axis
along the b axis
along the c axis
in plane ac[c]
DSA-C3
7.33
6.08
8.02
2.36
7.02
1.29
3.65
5.40
7.02
5.09
4.21
9.11
9.29
9.51
15.36
15.93
along the a axis
along the b axis
along the c axis
DSA-C4
2.55
5.38
9.89
2.01
7.13
11.87
4.42
7.44
15.69
5.11
9.19
18.55
along the a axis
along the b axis
along the c axis
DSA-C6
2.66
5.45
15.16
2.40
7.37
5.81
4.62
7.72
11.81
5.34
9.45
19.21
along the a axis
along the b axis
in plane ab
7.87
1.49
9.36
7.38
10.22
2.85
7.33
10.87
5.82
9.56
5.81
10.77
10.97
11.02
11.79
17.27
along the c axis
in space abc
DSA-C7
6.90
16.26
0.36
3.20
From Table 4 we can see that the dipolar coupling
causes the blue-shifted spectra for the crystals of
DSA-C3, DSA-C4, and DSA-C6 and the red-shifted
spectra for the crystals of DSA-C1 and DSA-C7. This
means that the crystals of DSA-C3 and DSA-C4 are H-
aggregates, and the crystals of DSA-C1 and DSA-C7
are J-aggregates. For the crystal of DSA-C6, the spec-
tral shift caused by dipolar coupling is only ꢀ3 nm,
and the distance between the selected adjacent mol-
along the a axis
along the b axis
in plane ab
6.46
9.20
15.66
0.67
4.33
0.77
5.10
6.30
4.81
4.02
9.02
10.38
16.17
14.96
along the c axis
14.14
14.95
[a] The z displacement is determined by r and the pitch angle. [b] The value of r
stands for the distance between the centroids of the chromophores in a dimer.
[c] The plane ac represents the plane determined by the a axis and the c axis, as well
as plane ab represents the plane determined by the a axis and the b axis. Space abc
means the three-dimensional space determined by the a, b, and c axes.
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Figure 10. Energy difference DE (calculated from the peak position of the PL
spectra of the crystals and the dilute solutions) as a function of (1ꢀ3cos2q)/
3
&
r ( ). They can be linear fitted by using Equation (2), (solid line). The slope
is 38.53, the intercept is ꢀ0.074, and R2 is 0.69.
Table 4. Optical properties of the DSA series in solution and in the solid
state (single crystals) at room temperature: emission (lem) wavelengths,
spectral shift, and quantum yields (fF).
DSA-C1
559
DSA-C3
564
DSA-C4
564
DSA-C6
564
DSA-C7
564
solution
lem [nm]
solid state
lem [nm]
Dltotal [nm]
Dlexcitonic [nm]
Dldipolar [nm]
fF[a] [%]
594
35
19
16
59.4
565
1
20
ꢀ19
29.2
567
3
20
ꢀ17
21.2
581
17
20
ꢀ3
43.8
609
45
20
25
52
[a] fF is the PL efficiency of the crystals.
According to the dipolar coupling theory,[30,32] the interaction
of the parallel transition dipoles will induce the excited state
to split into two levels. For the J-aggregation, the lower-split
level transition is allowed and the higher-split level transition is
forbidden; for the H-aggregation, it is reversed, as shown in
Figure S14 in the Supporting Information. So the crystals with
J-aggregation have the high quantum efficiency, whereas the
crystals with H-aggregation have the low quantum efficiency.
This has been confirmed by the measurements of the quantum
efficiency of the crystals (see Table 4). When the molecules are
excited, electrons firstly jump into the higher-split level and
then quickly relax into the lower-split level. Because the lower-
split level is relatively stable, electrons are gathered in it. Be-
cause the lower-split level transition is allowed for J-aggrega-
tion, the gathered electrons in the lower-split level induce the
inversion, which is a necessary condition for ASE. That is why
ASE is observed in crystals of DSA-C1 and DSA-C7.
Figure 9. Dominant interactions, pitch angle between the adjacent mole-
cules with the biggest p-overlap, and distance between the centroids of the
neighbor chromophores in each crystal.
ecules is 5.82 ꢁ, which is the biggest one in the five crystals.
So the spectral shift induced by dipolar coupling can be ne-
glected in the crystal of DSA-C6. The experiments of amplified
spontaneous emission (ASE) have been performed for the five
crystals. The results indicate that there is no ASE in crystals of
DSA-C3, DSA-C4, and DSA-C6, whereas there exists ASE in the
crystal of DSA-C1 (see Ref. [26]) and DSA-C7 (Figures S11 and
S12 in the Supporting Information, respectively).
Conclusion
Five 9,10-bis((4-N,N-dialkylamino)styryl) anthracene derivatives
(DSA-C1–DSA-C7) with different length alkyl chains were syn-
thesized. They showed the same color in dilute solutions but
different colors in the crystal state. X-ray crystallographic analy-
ses reveal that all the crystals of DSA-C1–DSA-C7 belong to the
¯
triclinic space group P1 with one molecule per unit cell and
Chem. Eur. J. 2014, 20, 9991 – 9997
www.chemeurj.org
9996 ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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Published online on July 10, 2014
Chem. Eur. J. 2014, 20, 9991 – 9997
www.chemeurj.org
9997
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim