Substituent effect of 2,3-dicyanopyrazine dyes on solid-state fluorescence

Article abstract of DOI:10.1246/bcsj.79.799

Some pyrazine dyes based on the same chromophoric system with different steric nature were synthesized to evaluate the correlation between solid-state fluorescence and molecular arrangement. It was confirmed that the solid-state fluorescence is significan

Full text of DOI:10.1246/bcsj.79.799

Ó 2006 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 79, No. 5, 799–805 (2006)
799
Substituent Effect of 2,3-Dicyanopyrazine Dyes
on Solid-State Fluorescence
1
ꢀ2
1
ꢀ1
Emi Horiguchi, Shinya Matsumoto, Kazumasa Funabiki, and Masaki Matsui
1
Department of Materials Science and Technology, Faculty of Engineering, Gifu University,
1-1 Yanagido, Gifu 501-1193
2
Department of Environmental Sciences, Faculty of Education and Human Sciences,
Yokohama National University, 79-2 Tokiwadai, Hodogaya-ku, Yokohama 240-8501
Received August 19, 2005; E-mail: smatsu@edhs.ynu.ac.jp
Some pyrazine dyes based on the same chromophoric system with different steric nature were synthesized to eval-
uate the correlation between solid-state fluorescence and molecular arrangement. It was confirmed that the solid-state
fluorescence is significantly correlated with the prevention of complete stacking between chromophoric systems in
the crystalline state. This result suggests that the introduction of bulky substituents to fluorescent dyes should be made
on substantial positions for preventing the complete stacking between the chromophoric systems on the basis of the crys-
tal structure.
Organic fluorescent dyes are one of the most exciting sub-
jects in functional dye chemistry in recent decades. Many stud-
ies on fluorescent dyes have been particularly dedicated to
develop the characteristics of an organic electroluminescence
the solid state in many fluorescent dyes for red emitters. In
the course of our studies on dicyanodiazepine dyes, the solid-
state fluorescence was found to be significantly correlated with
the prevention of complete stacking between the chromophoric
6
(
EL) device, which is the basic technology towards the forth-
systems in the crystalline state. The theoretical treatment of
1
coming EL displays. The most serious problem in the applica-
tion of organic dyes to the emitter materials is fluorescence
quenching in both condensed and crystalline states. The incor-
poration of bulky substituents to a fluorophore is a well-known
strategy to gain intensive fluorescence in both states to prevent
molecular stacking between ꢀ-conjugated systems. The mo-
lecular stacking between ꢀ-conjugated systems has been con-
sidered as a major cause for fluorescence quenching due to
intermolecular interactions. However, the actual influence of
molecular stacking on the fluorescent properties is not under-
stood well. Furthermore, especially in the solid state, a well-
defined explanation of the role of intermolecular interactions
the electronic states of a parallel dimer, corresponding to a
complete stacking pair of molecules, reveals that the dimer
formation causes fluorescence quenching due to symmetrical
limitation.8 For example, non-fluorescent H-aggregates and
concentration-dependent fluorescence quenching are interpret-
ed on this basis. However, practical correlation between mo-
lecular aggregates in a given system and their fluorescence
quenching have not been reported so far. Our result suggested
that the effective introduction of bulky substituents should be
made on fluorescent dyes for preventing the complete stacking.
We then made an attempt to verify this result with the expan-
sion of the fluorophore into the relative 2,3-dicyanopyrazine
skeleton. Pyrazine dyes were intensively developed in the
1990’s as a novel dye chromophore by Matsuoka’s group.9
These dyes have attracted attention as a new functional dye
because of their strong fluorescence. The dyes with large sub-
stituents show strong fluorescence even in single crystals and
vacuum deposited films. However, in the cases of the dyes
with small substituents, fluorescence quenching generally oc-
(so-called ꢀ–ꢀ interaction) by experiment has not been given
so far. In fact, in order to obtain the intense fluorescence in
organic solids, modification of molecular structure has been
performed by trial and error. The substantial direction of the
design of dye molecules for fluorescent solid materials has
been required. Hence, many attempts have been made for
2
organic fluorescent compounds in single crystals, inclusion
3
4
2b
crystals, and condensed states to clarify the solid correlation
among molecular structure, crystal structure, and fluorescent
properties in the solid state.
curs in the solid state. In this paper, the substituent effect
on the solid-state fluorescence was examined in some new
red-fluorescent 2,3-dicyanopyrazine dyes. Fluorescent proper-
ties in the crystalline state are discussed on the basis of the
crystal structure and intermolecular interactions.
We have developed a new fluorophore for red emitters
5
based on a nonplanar dicyanodiazepine skeleton and investi-
gated the correlation among molecular structure, crystal struc-
6
Results and Discussion
ture, and solid-state fluorescence. Among the three kinds of
emitters for primary colors, red, green, and blue, for full-col-
ored EL devices, red emitters have usually been prepared with
dopants. Only lesser kinds of red emitters without dopants are
Synthesis of 5,6-Disubstituted 2,3-Dicyanopyrazine Dyes.
The chromophore in the present study is closely related to the
dicyanodiazepine chromophoric system. The cyano groups in a
pyrazine ring work as an acceptor and the amino group conju-
7
known, since fluorescence quenching is usually observed in
Published on the web May 12, 2006; DOI: 10.1246/bcsj.79.799

8
00 Bull. Chem. Soc. Jpn. Vol. 79, No. 5 (2006)
Solid-State Fluorescence of Dicyanopyrazines
gated to the pyrazine ring through a styryl moiety acts as a do-
nor. From the previous study on dicyanodiazepine dyes, the in-
troduction of substituents around both the donor and the accep-
tor moieties can prevent the complete stacking of molecules.6
Substituent effects were thus examined by two positions in the
present chromophoric system, on the amino group and on the
pyrazine ring at the 6-position. The 5,6-disubstituted 2,3-di-
cyanopyrazines 7a–7d, 8, and 9 were prepared as shown in
Scheme 1. Diaminomaleonitrile (DAMN, 1) reacted with the
O
Me
O
R
diones 2a–2d in the presence of aqueous hydrochloric acid
ꢁ3
NC
NC
NH2
NH2
NC
NC
N
Me
R
2
a-d
(
3 mol dm ) to give the 6-substituted 2,3-dicyano-5-methyl-
6
pyrazines 3a–3d in 74–89% yields. Then, the condensation
of 3a–3d with the aromatic aldehydes 4–6 gave the 5,6-disub-
stituted 2,3-dicyanopyrazines 7a–7d, 8, and 9 in low to mod-
erate yields.
Optical Properties of 5,6-Disubstituted 2,3-Dicyanopyra-
zine Dyes in Solution and in the Solid State. The UV–vis
absorption and fluorescence spectra of 7a–7d in toluene are
shown in Fig. 1 and their characteristics are summarized in
Table 1. No significant difference was observed in the absorp-
tion (ꢁmax) and fluorescence maxima (Fmax) among 7a–7d,
since the electronic structure is influenced little by the substitu-
aq. HCl, EtOH
N
1
3a-d
H
O
Ar
Ar
-6
NC
NC
N
N
4
6
Piperidine, Benzene
R
7
a-d, 8 and 9
R: 2a, 3a = H, 2b, 3b = Me, 2c, 3c = Ph, 2d, 3d = t-Bu
Ar: 4 =
NEt2 5 =
N(n-Bu)2 6 =
N
0
.5
800
600
400
R
Ar
7a
7
a
7
b
7
7
7
7
a
b
c
d
H
NEt2
0.4
7
c
7
c
7
d
Me
Ph
NEt2
0
0
.3
.2
UV-vis
7b
FL
NEt2
t-Bu
t-Bu
NEt2
7d
200
8
0.1
N(n-Bu)2
0
0
3
00
400
500
600
700
800
9
t-Bu
N
Wavelength / nm
Fig. 1. UV–vis absorption and fluorescence spectra of 7a–
5
7d (1 ꢂ 10ꢁ mol dm ) in toluene.
ꢁ3
Scheme 1.
Table 1. UV–Vis Absorption and Fluorescence Properties of 7–9
a)
b)
Toluene
c)
Powder
c)
Compd
R
Ar
ꢀfd)
SS
e)
ꢁ
max /nm
f)
Fmax /nm
RFI
g)
SS
e)
ꢁ
max ("max)/nm
Fmax /nm
h)
h)
h)
7
a
H
NEt2
495 (43300)
582
0.94
87
71
88
71
69
527
526
543
519
522
—
—
—
7
b
Me
Ph
NEt2
497 (37300)
497 (34600)
493 (27000)
496 (33300)
568
585
563
565
0.43
0.82
0.22
0.25
660
—h)
634
625
5
134
—h)
115
103
7
c
NEt2
—h)
100
31
7
d
t-Bu
t-Bu
NEt2
8
N(n-Bu)2
9
t-Bu
N
521 (26400)
591
0.33
70
561
—h)
—h)
—h)
ꢁ
5
ꢁ3
ꢃ
a) Measured at the concentration of 1:0 ꢂ 10 mol dm at 25 C. b) Ground crystals. c) Excited with the absorption maximum.
ꢁ
3
d) The fluorescence quantum yields were determined using quinine sulfate in 0.1 mol dm
ex ¼ 366 nm) as the standard. e) Stokes shift. f) Diffuse reflectance spectra (given in Kubelka–Monk units). g) The relative fluores-
cence intensity was determined by considering the fluorescence intensity of 7d to be 100. h) Too weak to be measured.
sulfuric acid (ꢀf ¼ 0:55,
ꢁ

E. Horiguchi et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 5 (2006)
801
0
0
0
0
0
0
.5
.4
.3
.2
.1
400
9
7
d
8
3
2
1
00
00
00
0
7d
9
8
7d
UV-vis
FL
8
7b
7
a, 7c, 9
300
400
500
600
700
800
550
600
650
700
750
800
Wavelength / nm
Wavelength / nm
Fig. 2. UV–vis absorption and fluorescence spectra of 7d,
8
Fig. 3. Fluorescence spectra of 7–9 in powdered form.
a)
, and 9 (1 ꢂ 10ꢁ mol dm ) in toluene.
5
ꢁ3
(
ent R. The dyes 7a–7d showed their ꢁmax around 493–497 nm
and the Fmax were observed around 563–585 nm. The molar
absorption coefficients ("max) were found to depend slightly
on the substituent R. The "max value decreased in the order
of dyes: 7a (43300) > 7b (37300) > 7c (34600) > 7d (27000)
as the size increased of the substituent R. The present effect of
the substituent on "max is in good accordance with the calcu-
lated result by semi-empirical molecular orbital calculations
(b)
7a
7b
7c
7d
8
9
Fig. 4. Photographs of ground crystals of dyes 7–9 under
(
(Table S1). The dyes 7a–7d exhibit relatively high fluores-
a) room light and (b) 254 nm light.
cence quantum yields (ꢀf) of 0.22–0.94. The dyes with flexi-
ble substituents 7b and 7d were found to show smaller ꢀf val-
ues than 7a and 7c. This result reflects the influence of sub-
stituents on fluorescent quantum yields. Flexible substituents
are considered to promote the non-radiative relaxation to re-
duce the fluorescent quantum yield.10 The UV–vis absorption
and fluorescence spectra of 7d, 8, and 9 in toluene are shown
in Fig. 2 and their characteristics are summarized in Table 1.
The ꢁmax of 9 was observed at 521 nm, being much more
bathochromic than the diethylamino 7d and dibutylamino 8
derivatives. This is caused by the strong electro-donating prop-
erty of the 9-julolidinyl group because the donor character of
the amino nitrogen is improved by ring closure as compared
with flexible dialkylamino derivatives. The Fmax also showed
a bathochromic shift from 563 to 591 nm. The relatively low
imum wavelength or relative intensity. The Fmax of 7b, 7d, and
8 were also found to shift bathochromically as compared with
those in toluene.11 This remarkable change in the relative fluo-
rescence intensity must be affected by intermolecular interac-
tions in the solid state. Therefore, an attempt to analyze their
crystal structures was made to investigate the difference in fluo-
rescence intensity between in solution and in the solid state.
Crystal Structure Analysis. Crystal structure analysis was
successfully carried out on 7a, 7c, 7d, and 8. Unfortunately,
good single crystals for structure analysis were not obtained
for 7b or 9.
The molecules of 7a, 7c, 7d, and 8 were found to have a pla-
nar ꢀ-conjugated system. Dihedral angles between the pyra-
zine and the phenyl rings are 0.68, 5.58, 12.2, and 4.67 for
ꢃ
ꢀ
f of these derivatives is probably attributed to the effect of
7a, 7c, 7d, and 8, respectively. The planarity of the chromo-
phoric system composed of a dicyanopyrazine ring with an
amino styryl moiety was also estimated by mean deviation
from the least-squares plane. The calculated mean deviations
the flexible t-butyl group at the 6-position. The similar Stokes
shifts of 7–9 imply that there is no considerable difference in
their excited electronic states. These results also indicate that
˚
7
–9 can be used as a red-emitting dopant.
The optical properties of 7–9 in the solid state are of great
were 0.001, 0.056, 0.094, and 0.056 A for 7a, 7c, 7d, and 8,
respectively. In addition, all of them showed small bond alter-
ation and there is no significant difference in bond lengths. The
electronic structure of a molecule in single crystals for these
dyes is therefore considered to be almost the same. This is con-
firmed by means of molecular orbital calculations using the
fractional coordinates as given in the Supporting Information
(Table S2).
However, the molecular arrangement is quite different.
Figures 5a–5d illustrate the observed stacking motifs for each
dye. All dyes have two types of stacking structures between
the chromophoric systems. In 7a, molecules are stacked along
the c-axis. The two molecules surrounded by a circle in Fig. 5a
are completely stacked on each other in a head-to-tail fashion.
importance and interest. Table 1 also lists the diffuse reflec-
tance and the fluorescence properties of 7–9 in powdered form.
The solid-state fluorescence spectra of 7–9 in ground crystals
and their photographs are shown in Figs. 3 and 4, respectively.
The ꢁmax were observed around 519–561 nm. Though no re-
markable difference was observed in the Fmax among 7b, 7d,
and 8, the relative fluorescent intensities were found to be sig-
nificantly different. The dye that exhibits the strongest fluores-
cence in powdered form, 7d, also showed the smallest fluores-
cent quantum yield in a toluene solution. The next brightest
dye was 8, followed by 7b. Surprisingly, the fluorescence in-
tensities of 7a, 7c, and 9 were too weak to determine the max-

8
02 Bull. Chem. Soc. Jpn. Vol. 79, No. 5 (2006)
Solid-State Fluorescence of Dicyanopyrazines
3
3
.623 Å
3.523 Å
.468 Å
3.379 Å
(
a)
(b)
3.512 Å
3.575 Å
3.595 Å
3.444 Å
(c)
(d)
Fig. 5. Stacking motifs for (a) 7a, (b) 7c, (c) 7d, and (d) 8.
The upper molecule is also stacked in parallel and in a head-to-
tail fashion, but it is twisted along the long molecular axis by
a similar pattern of molecular stacking, as shown in Figs. 5c
and 5d, respectively. In both dyes, molecules are stacked along
the a-axis (Figs. S3 and S4). The molecules are inserted to the
molecular arrangement of the inverted fragment along the a-
axis. Each molecule is found to be well overlapped, but the
overlaps are slightly shifted. Interplanar distances between
the chromophoric systems are calculated to be about 3.575
ꢃ
about 34 . Hence, one-dimensional molecular columns form
along the c-axis in which the complete stack pairs are stacked
ꢃ
alternatively twisted along their long axis by about 34
(Fig. S1). Interplanar distances between the chromophoric sys-
˚
tems are calculated to be about 3.468 and 3.623 A for the com-
plete and twisted stack pairs, respectively.
The molecules are arranged in a herring-bone fashion in 7c
˚
˚
and 3.595 A for 7d, and 3.512 and 3.444 A for 8, respectively.
In these dyes, significant structural differences were ob-
served in the degree of overlap of the chromophoric systems
and their interplanar distances. These structural features should
be related to the fluorescent properties in the solid state.2
(Fig. S2), but two types of molecular stacking are also recog-
nized. The molecules are stacked along the direction normal to
the (213) plane. Two molecules surrounded by a circle in
Fig. 5b form a completely stacked pair in a head-to-tail fash-
ion. The lower molecule is also stacked in parallel but less
overlapped than the upper one. Interplanar distances between
the chromophoric systems are calculated to be about 3.523
a,2g,2j,2l
A large overlap as well as a short interplanar distance can be
correlated with the decrease in fluorescence intensity in the
solid state. The complete overlap of a chromophoric system
is considered to be a parallel dimer. The most typical example
of a parallel dimer is H-aggregates, which are generally known
to be non-fluorescent. This characteristic is successfully inter-
˚
and 3.379 A for the complete stack and less-overlapped pairs,
respectively. The very short distance of the lower pair may be
due to the small repulsion between the planes because of the
small overlap of molecules.
8
preted by theoretical description: the optical transition for the
lower energy state of a parallel dimer, in which the transition
dipoles are packed in a head-to-tail fashion, is forbidden due to
Dyes with a t-butyl group on a pyrazine ring, 7d and 8, have

E. Horiguchi et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 5 (2006)
803
the out-of-phase symmetry and gives no fluorescence. In the
case of single crystals, there are many molecules around a
given molecule, thus, we have to consider the whole interac-
tion between many molecule pairs in order to examine the
electronic energy levels of molecular crystals. However, our
previous study clearly showed that only the complete overlap
of chromophoric systems should dominate the fluorescence
Sigma-Aldrich. 1-Phenyl-1,2-propanedione (2c) and 4-(diethyl-
amino)benzaldehyde (4) were purchased from Tokyo Kasei Co.,
Ltd. Diacetyl (2b) was purchased from Nakalai Tesque. 4,4-Di-
methyl-2,3-pentanedione (2d),12 2,3-dicyano-5-methylpyrazine
(
3a),13 2,3-dicyano-5,6-dimethylpyrazine (3b),13 and 1,1,7,7-tetra-
methyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizine-9-carbalde-
hyde (6)14 were prepared as described in the literature.
6
Synthesis of 2,3-Dicyanopyrazines (3c and 3d). To an etha-
nol solution (20 mL) of DAMN (1) (1.08 g, 10 mmol) were added
quenching. The fluorescence quenching of 7a and 7c is thus
considered to be caused by forming a complete overlapped
pair in the crystalline state. The fluorescence of 9 was found
to be quenched in the solid state. We have no crystal structure
of 9, but the complete overlapped pair might also be formed in
the crystalline state to deactivate excitation energies. Actually,
ꢁ3
3
(
mol dm of aqueous hydrochloric acid (6 mL) and the diones 2
10 mmol). The mixture was refluxed for 30 min. After the reac-
tion was completed, the mixture was cooled to room temperature.
The solvent was partially removed in vacuo. The residue was
poured into water, filtered, washed with water, and then dried.
The product was recrystallized (3c: ethanol; 3d: hexane). The
physical and spectral data are shown below.
˚
two diffraction peaks were observed around 3.4 A by powder
X-ray diffraction of 9. This result suggests the existence of
two stacking pairs of molecules. On the other hand, in com-
pounds 7d and 8, there is no complete overlap of chromopho-
ric systems, so that they emit even in the crystalline state. The
difference in their relative fluorescence intensity could be cor-
related with the interplanar distance of the stacking pairs. The
larger the interplanar distances, the more intense the solid-state
fluorescence. We also have no crystal structure of 7b, which
exhibits very weak fluorescence in the solid state. Compound
2
,3-Dicyano-5-methyl-6-phenylpyrazine (3c): Yield 82%;
mp 135–137 C; IR (KBr)/cm 2244 (CN); 1H NMR (CDCl3)
ꢃ
ꢁ1
ꢂ 2.84 (s, 3H), 7.55–7.61 (m, 3H), 7.66–7.68 (m, 2H); EIMS (70
eV) m=z (rel intensity) 220 (M ; 69), 219 (100), 117 (13), 103
þ
(48), 76 (16). Anal. Found: C, 70.81; H, 3.87; N, 25.52%. Calcd
for C H N : C, 70.90; H, 3.66; N, 25.44%.
13
8
4
5-t-Butyl-2,3-dicyano-6-methylpyrazine (3d): Yield 74%;
mp 90–93 C; IR (KBr)/cm 2232 (CN); 1H NMR (CDCl3) ꢂ
1.49 (s, 9H), 2.90 (s, 3H); 13C NMR (CDCl3) ꢂ 25.5, 28.7, 39.4,
113.1, 113.3, 128.8, 129.3, 157.2, 166.3; EIMS (70 eV) m=z (rel
ꢃ
ꢁ1
7
b has a relatively small substituent on the pyrazine ring com-
pared with 7d and 8. The interplanar distance between the
chromophoric systems can be considered to be shortened to
give weak fluorescence.
þ
intensity) 200 (M ; 19), 185 (100), 158 (19), 57 (17). Anal.
Found: C, 66.02; H, 6.04; N, 28.24%. Calcd for C11H12N4: C,
6
5.98; H, 6.04; N, 27.98%.
Synthesis of 5,6-Disubstituted 2,3-Dicyanopyrazine Dyes
Conclusion
(
(
7a–7d, 8, and 9). To a benzene solution (15 mL) of 3a–3d
1 mmol) were added piperidine (5 drops) and the aromatic alde-
The substituent effect of some new 2,3-dicyanopyrazine
dyes on solid-state fluorescence was investigated on the basis
of the crystal structures. The complete overlap between the
chromophoric systems was found to dominate fluorescence
quenching in the solid state. The fluorescence intensity in the
solid state was also found to be influenced by an interplanar
distance between chormophoric systems. Our results indicate
that organic molecules for solid-state fluorescent materials
should be designed to prevent complete stacking by the effec-
tive incorporation of bulky substituents to the chromophoric
systems.
hydes 4–6 (1 mmol). The mixture was refluxed (7a: 50 h, 7b: 51 h,
c: 71 h, 7d: 47 h, 8: 88 h, and 9: 69 h). After the reaction was
7
completed, the mixture was cooled to room temperature. After
removing the solvent, the product was isolated by silica-gel col-
umn chromatography (dichloromethane) and recrystallized (7a–
7
d: benzene, 8: hexane, and 9: ethyl acetate). The physical and
spectral data are shown below.
,3-Dicyano-5-[4-(diethylamino)styryl]pyrazine (7a): Yield
2
ꢃ
ꢁ1 2228 (CN); 1H NMR
3
6%; mp 207–210 C; IR (KBr)/cm
(
(
CDCl3) ꢂ 1.23 (t, J ¼ 7:1 Hz, 6H), 3.45 (q, J ¼ 7:1 Hz, 4H), 6.67
d, J ¼ 9:0 Hz, 2H), 6.83 (d, J ¼ 15:4 Hz, 1H), 7.49 (d, J ¼ 9:0
Experimental
13
Hz, 2H), 7.92 (d, J ¼ 15:4 Hz, 1H), 8.61 (s, 1H); C NMR
(CDCl3) ꢂ 12.7, 44.7, 111.6, 113.5, 114.1, 114.5, 121.9, 127.3,
131.0, 133.5, 143.7, 145.3, 150.2, 155.0; EIMS (70 eV) m=z (rel
Instruments.
Melting points were measured with a
Yanagimoto MP-S2 micro-melting-point apparatus. NMR spectra
were obtained with a Varian Inova 500 spectrometer. EIMS spec-
tra were recorded on a JEOL MS-700 spectrometer. IR spectra
were recorded on a Perkin-Elmer spectrum BX FT-IR system
for samples in KBr pellet form. Elemental analysis was performed
with a Yanaco MT-6 CHN corder. UV–vis absorption and fluores-
cence spectra were taken on Hitachi U-3500 and F-4500 spectro-
photometers, respectively. Diffuse reflectance spectra were taken
on a Perkin-Elmer Lambda-20 UV–vis spectrometer. Samples
were diluted with magnesium oxide. Solid-state fluorescence
spectra of ground crystals were determined with the front surface
accessory from a Perkin-Elmer LS-45 Luminescence spectrome-
ter. The fluorescence quantum yield was determined using quinine
þ
intensity) 303 (M ; 39), 289 (20), 288 (100). Anal. Found: C,
71.55; H, 5.72; N, 23.06%. Calcd for C18H17N5: C, 71.27; H,
5.65; N, 23.09%.
2,3-Dicyano-5-[4-(diethylamino)styryl]-6-methylpyrazine
ꢃ
ꢁ1
(7b): Yield 31%; mp 216–219 C; IR (KBr)/cm 2228 (CN);
1
H NMR (CDCl3) ꢂ 1.20 (t, J ¼ 7:1 Hz, 6H), 2.73 (s, 3H), 3.40
(q, J ¼ 7:1 Hz, 4H), 6.71 (d, J ¼ 9:0 Hz, 2H), 6.94 (d, J ¼ 15:1
Hz, 1H), 7.55 (d, J ¼ 9:0 Hz, 2H), 8.08 (d, J ¼ 15:1 Hz, 1H);
1
3
C NMR (CDCl3) ꢂ 12.7, 22.4, 44.7, 111.5, 112.3, 113.9,
114.3, 122.3, 126.5, 130.9, 131.0, 144.4, 150.1, 153.6, 154.4;
þ
EIMS (70 eV) m=z (rel intensity) 317 (M ; 41), 303 (22), 302
(100). Anal. Found: C, 71.63; H, 6.13; N, 21.76%. Calcd for
C19H19N5: C, 71.90; H, 6.03; N, 22.07%.
2,3-Dicyano-5-[4-(diethylamino)styryl]-6-phenylpyrazine
ꢁ
3
sulfate in 0.1 mol dm sulfuric acid as a reference (ꢀf ¼ 0:55,
ꢁ
em ¼ 366 nm).
ꢃ
ꢁ1
Materials. DAMN (1), methyl glyoxal 40% aqueous solution
2a), and 4-(dibutylamino)benzaldehyde (5) were purchased from
(7c): Yield 60%; mp 193–195 C; IR (KBr)/cm 2229 (CN);
1
(
H NMR (CDCl3) ꢂ 1.20 (t, J ¼ 7:1 Hz, 6H), 3.42 (q, J ¼ 7:1

8
04 Bull. Chem. Soc. Jpn. Vol. 79, No. 5 (2006)
Solid-State Fluorescence of Dicyanopyrazines
Hz, 4H), 6.63 (d, J ¼ 9:0 Hz, 2H), 7.00 (d, J ¼ 15:1 Hz, 1H), 7.38
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: +44 1223 336033;
e-mail: deposit@ccdc.cam.ac.uk), by quoting the publication cita-
tion and the deposition numbers for 7a (CCDC-263456), 7c
(CCDC-263457), 7d (CCDC-263458), and 8 (CCDC-263459), re-
spectively. Crystal data for 7a: C18H17N5, MW ¼ 303:37, mono-
clinic, C2=c, Z ¼ 8, a ¼ 21:462ð4Þ, b ¼ 13:629ð2Þ, c ¼ 14:463ð3Þ
(
(
d, J ¼ 9:0 Hz, 2H), 7.54–7.58 (m, 3H), 7.70–7.72 (m, 2H), 8.07
13
d, J ¼ 15:1 Hz, 1H); C NMR (CDCl3) ꢂ 12.6, 44.6, 111.4,
1
1
13.8, 114.1, 114.4, 122.3, 126.6, 128.9, 129.5, 130.7, 130.8,
35.4, 143.7, 149.9, 152.5, 154.1; EIMS (70 eV) m=z (rel intensi-
þ
ty) 379 (M ; 68), 365 (31), 364 (100). Anal. Found: C, 76.16; H,
5.71; N, 18.49%. Calcd for C24H21N5: C, 75.97; H, 5.58; N,
18.46%.
˚
ꢃ
ꢁ3
5
-t-Butyl-2,3-dicyano-6-[4-(diethylamino)styryl]pyrazine
A, ꢄ ¼ 127:71ð1Þ , Dcalcd ¼ 1:204 g cm , T ¼ 296 K, 12871 re-
flections were collected, 2858 unique (Rint ¼ 0:053), 1906 ob-
served (I > 2ꢅðIÞ), 227 parameters, R1 ¼ 0:071, wR2 ¼ 0:114,
GOF ¼ 1:05, refinement on F, 7c: C24H21N5, MW ¼ 379:46,
monoclinic, P21=n, Z ¼ 4, a ¼ 8:926ð3Þ, b ¼ 10:589ð3Þ, c ¼
ꢃ
ꢁ1
(
7d): Yield 55%; mp 226–229 C; IR (KBr)/cm 2232 (CN);
H NMR (CDCl3) ꢂ 1.22 (t, J ¼ 7:1 Hz, 6H), 1.51 (s, 9H), 3.44
q, J ¼ 7:1 Hz, 4H), 6.85 (d, J ¼ 9:0 Hz, 2H), 7.26 (d, J ¼ 14:9
1
(
Hz, 1H), 7.48 (d, J ¼ 9:0 Hz, 2H), 7.98 (d, J ¼ 14:9 Hz, 1H);
1
3
˚
ꢃ
ꢁ3
C NMR (CDCl3) ꢂ 12.7, 29.3, 39.2, 44.7, 111.6, 113.8, 114.4,
15.7, 122.6, 125.6, 130.0, 130.6, 143.0, 149.8, 153.0, 162.6;
22:116ð7Þ A, ꢄ ¼ 95:69ð3Þ , Dcalcd ¼ 1:212 g cm , T ¼ 296 K,
15256 reflections were collected, 3451 unique (Rint ¼ 0:063),
1391 observed (I > 2ꢅðIÞ), 283 parameters, R1 ¼ 0:046, wR2 ¼
1
EIMS (70 eV) m=z (rel intensity) 359 (M ; 59), 345 (32), 344
þ
2
(
100). Anal. Found: C, 73.68; H, 7.05; N, 19.44%. Calcd for
C22H25N5: C, 73.51; H, 7.01; N, 19.48%.
-t-Butyl-2,3-dicyano-6-[4-(dibutylamino)styryl]pyrazine
8): Yield 16%; mp 155–158 C; IR (KBr)/cm 2230 (CN);
H NMR (CDCl3) ꢂ 0.98 (t, J ¼ 7:6 Hz, 6H), 1.38 (sext, J ¼ 7:6
0:154, GOF ¼ 1:08, refinement on F , 7d: C22H25N5, MW ¼
ꢁ
359:47, triclinic, P1, Z ¼ 2, a ¼ 7:324ð2Þ, b ¼ 9:621ð2Þ, c ¼
˚
ꢃ
5
15:176ð3Þ A, ꢃ ¼ 107:84ð1Þ, ꢄ ¼ 95:69ð3Þ, ꢆ ¼ 99:64ð2Þ ,
ꢃ
ꢁ1
ꢁ3
(
1
Dcalcd ¼ 1:190 g cm , T ¼ 296 K, 8019 reflections were collect-
ed, 3159 unique (Rint ¼ 0:061), 2519 observed (I > 2ꢅðIÞ), 270
parameters, R1 ¼ 0:054, wR2 ¼ 0:166, GOF ¼ 0:97, refinement
Hz, 4H), 1.51 (s, 9H), 1.61 (quint, J ¼ 7:6 Hz, 4H), 3.35 (t, J ¼
2
ꢁ
7
:6 Hz, 4H), 6.66 (d, J ¼ 9:0 Hz, 2H), 7.23 (d, J ¼ 14:9 Hz, 1H),
on F , 8: C26H33N5, MW ¼ 415:58, triclinic, P1, Z ¼ 2, a ¼
1
3
˚
7
.49 (d, J ¼ 9:0 Hz, 2H), 8.00 (d, J ¼ 14:9 Hz, 1H); C NMR
7:022ð1Þ, b ¼ 9:586ð2Þ, c ¼ 19:272ð3Þ A, ꢃ ¼ 96:34ð2Þ, ꢄ ¼
ꢃ
ꢁ3
,
(
CDCl3) ꢂ 14.0, 20.3, 29.3, 29.5, 39.2, 50.9, 111.6, 113.8, 114.4,
101:85ð2Þ, ꢆ ¼ 93:64ð2Þ , Dcalcd ¼ 1:098 g cm
T ¼ 296 K,
115.6, 122.5, 125.5, 130.0, 130.5, 143.0, 150.2, 152.9, 162.6;
þ
EIMS (70 eV) m=z (rel intensity) 415 (M ; 40), 372 (100), 330
10044 reflections were collected, 3943 unique (Rint ¼ 0:047),
1853 observed (I > 2ꢅðIÞ), 310 parameters, R1 ¼ 0:066, wR2 ¼
2
(
29). Anal. Found: C, 75.19; H, 8.03; N, 16.77%. Calcd for
C26H33N5: C, 75.14; H, 8.00; N, 16.85%.
-t-Butyl-2,3-dicyano-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetra-
hydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]pyrazine (9):
0:181, GOF ¼ 1:05, refinement on F .
5
The authors wish to thank Mr. A. Koseki of Yokohama
National University for fluorescent measurements and Dr. T.
Kobayashi of Osaka Prefecture University for fruitful discus-
sions on solid-state fluorescence.
ꢃ
ꢁ1
1
Yield 33%; mp > 300 C; IR (KBr)/cm 2228 (CN); H NMR
(
3
8
3
1
CDCl3) ꢂ 1.33 (s, 12H), 1.52 (s, 9H), 1.77 (t, J ¼ 6:1 Hz, 4H),
.32 (t, J ¼ 6:1 Hz, 4H), 7.18 (d, J ¼ 14:9 Hz, 1H), 7.34 (s, 2H),
13
.00 (d, J ¼ 14:9 Hz, 1H); C NMR (CDCl3) ꢂ 29.3, 30.3, 32.1,
Supporting Information
5.8, 39.1, 46.7, 113.8, 114.5, 114.8, 122.1, 124.7, 125.1, 130.3,
43.1, 143.9, 153.0, 162.3; EIMS (70 eV) m=z (rel intensity) 439
The calculated UV–vis absorption band for the optimized struc-
ture of 7a–7d, 8, and 9 (Table S1), calculated UV–vis absorption
band for 7a, 7c, 7d, and 8 using the fractional coordinate sets of
X-ray analysis (Table S2), crystal structure of 7a (Fig. S1), crystal
structure of 7c (Fig. S2), crystal structure of 7d (Fig. S3), and
crystal structure of 8 (Fig. S4). This material is available free of
charge on the web at http://www.csj.jp/journals/bcsj/.
þ
(
M ; 100), 424 (42). Anal. Found: C, 76.09; H, 7.65; N, 15.76%.
Calcd for C28H33N5: C, 76.50; H, 7.57; N, 15.93%.
X-ray Crystallography. Single crystals of 7a, 7c, and 8 were
obtained by slow evaporation of benzene, toluene, and hexane
solutions, respectively. Those of 7d were grown by a solvent dif-
fusion method using hexane and dichloromethane. The diffraction
data were collected by a Rigaku Raxis RAPID-F imaging-plate
References
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˚
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