Drastic solid-state fluorescence enhancement behaviour of imidazo[4,5-a]naphthalene-type fluorescent hosts upon inclusion of polyethers and tert-butyl alcohol

Article abstract of DOI:10.1016/j.tet.2008.12.003

As one of the most promising materials for the construction of desirable solid-state fluorescent system, new solid-state fluorescent host-guest system, which consists of the imidazo[4,5-a]naphthalene-type fluorescent hosts 2 and sterically hindered guest

Full text of DOI:10.1016/j.tet.2008.12.003

Tetrahedron 65 (2009) 1467–1474
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Drastic solid-state fluorescence enhancement behaviour of imidazo[4,5-a]-
naphthalene-type fluorescent hosts upon inclusion of polyethers
and tert-butyl alcohol
*
*
Yousuke Ooyama , Shinobu Nagano, Katsuhira Yoshida
Department of Material Science, Faculty of Science, Kochi University, Akebono-cho, Kochi 780-8520, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 October 2008
Received in revised form 30 November 2008
Accepted 1 December 2008
Available online 7 December 2008
As one of the most promising materials for the construction of desirable solid-state fluorescent system,
new solid-state fluorescent host–guest system, which consists of the imidazo[4,5-a]naphthalene-type
fluorescent hosts 2 and sterically hindered guest molecules were designed and prepared. The crystals of
2 exhibit sensitive colour change and drastic fluorescence enhancement behaviour upon polyethers
(diethylene glycol dimethyl ether (DGDM), diethylene glycol diethyl ether (DGDE) and diethylene glycol
dibutyl ether (DGDB)) or tert-butyl alcohol. A comparison of the X-ray crystal structures of the guest-free
and polyether- and tert-butyl alcohol-inclusion compounds indicates that the enclathrated polyether or
Keywords:
Dyes
Clathrate
tert-butyl alcohol molecule decrease the p-stacking between hosts and enlarge the distance between the
host–host aromatic planes. On the bases of the spectral data and the crystal structures, the effects of the
enclathrated sterically hindered guest on the drastic solid-state fluorescence enhancement behaviour of
the host–guest crystals are discussed.
Polyethers
Crystal structures
Solid-state fluorescence
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
most promising materials for the construction of desirable solid-
state fluorescent system.4,7 In the previous paper,8 we have reported
Solid-state organic fluorescent dyes have created considerable
interest in recent years for their potential application to optoelec-
tronics such as organic light emitting diode1 and photoelectric
conversion systems.2 From the standpoint of developing an effec-
tive optoelectronics device, many researches have been conducted
on the correlation between the solid-state fluorescence properties
and the molecular packing structures on the basis of the X-ray
crystal structures. It has been revealed that strong intermolecular
novel imidazo[4,5-a]naphthalene-type fluorescent clathrate host,
2-(4-cyanophenyl)-5-[4-(dibutylamino)phenyl]-3H-imidazo[4,5-a]-
naphthalene (2a) exhibiting tautomerism (A and B) on the imid-
azole ring. It was found that the fluorophore 2a can include various
guest molecules such as morpholine, ethanol, 1,4-dioxane and ethyl
acetate in the crystalline state by changing the tautomeric forms A
and B. A fluorescence enhancement and a blue shift of the ab-
sorption and fluorescence wavelength maxima are observed
depending on the enclathrated guest molecules. From the com-
parison of the X-ray crystal structures of the guest-free and several
clathrate compounds, we have concluded the destructions of the
p–p
interaction3,4 or continuous intermolecular hydrogen bond-
ing5 between neighbouring fluorophores is a principal factor of
fluorescence quenching in the solid state. Thus, the key point in
design of strong solid-state fluorescent dyes is to remove the
intermolecular interactions between fluorophores causing fluo-
rescence quenching in molecular aggregation states. In particular,
the introduction of bulky substituents to the original fluorophores
is known to be very useful methods for solving the problem of
fluorescence quenching by aggregation.6
p–p interactions between fluorophores by the enclathrated guest
molecules are the main reason for the guest-dependent fluores-
cence enhancement and the blue shift of the absorption and fluo-
rescence maxima of the crystals.
In connection with this research, we have designed and pre-
pared new solid-state fluorescent host–guest system, which con-
sists of the imidazo[4,5-a]naphthalene-type fluorescent host 2 and
sterically hindered guest molecules such as polyethers (diethylene
glycol dimethyl ether (DGDM), diethylene glycol diethyl ether
(DGDE) and diethylene glycol dibutyl ether (DGDB)) and tert-butyl
alcohol. It is expected that this host–guest system with sterically
On the other hand, organic fluorescent host, which can exhibit
sensitive colour and fluorescence changes upon formation of host–
guest inclusion complexes in the crystalline state can be one of the
hindered guest molecules causes the destructions of the
teractions between fluorophores comparable to the introduction of
bulky substituents to the original fluorophore skeleton. Here, we
p–p in-
* Corresponding authors. Tel.: þ81 88 844 8296; fax: þ81 88 844 8359.
E-mail addresses: yooyama@hiroshima-u.ac.jp (Y. Ooyama), kyoshida@cc.
kochi-u.ac.jp (K. Yoshida).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.12.003

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Y. Ooyama et al. / Tetrahedron 65 (2009) 1467–1474
CN
CN
O
HN
O
N
N
X
NH
X
O
O
X
(i)
(ii)
SO3Na
NR2
B-form
NR2
NR2
2
1
A-form
a: R = Et, X = H
b: R = Bu, X = H
c: R = Et, X = Me
a: R = Et, X = H
b: R = Bu, X = H
c: R = Et, X = Me
Scheme 1. Reagents and conditions: (i) 1a: N,N-dialkylaniline, NiCl2$4H2O, CH3COOH/H2O [4:1 (v/v)], 7 days, rt, 58% for 1b, 50% for 1b and 46% for 1c; (ii) p-cyanobenzaldehyde,
CH3COONH4, CH3COOH, 1 h, 80 ꢁC, 75% for 2a, 74% for 2b and 75% for 2c.
report a drastic fluorescence enhancement behaviour of imi-
dazo[4,5-a]naphthalene-type fluorescent hosts 2a–2c upon
enclathration of polyethers or tert-butyl alcohol in the solid state.
To the authors’ knowledge, there is no solid-state fluorescent host–
guest system with such polyethers as guest molecules. The
enclathrated guest effects on the solid-state photophysical prop-
erties and the crystal packing structures of the fluorophores 2 are
discussed on the basis of the results of the X-ray crystal structures
of guest-inclusion compounds.
respectively. The absorption and fluorescence maxima of 2c are
slightly blue-shifted compared to those of 2a and 2b, and the value
F
of 2c is lower than those of 2a and 2b. This result is attributed to
decrease of the -conjugation arising from steric hindrance
p
between 4-(diethylamino)-2-methyl-phenyl group and the imi-
dazo[4,5-a]naphthalene plane of 2c.
2.2. Preparation of guest-inclusion crystals
The preparation of polyether and tert-butyl alcohol-inclusion
crystals was attempted by recrystallization from the three poly-
ethers (DGDM, DGDE and DGDB) and tert-butyl alcohol solutions,
respectively. Hosts 2a–2c formed 1:2 inclusion crystals with tert-
butyl alcohol. In the cases of 2a and 2c, the 2:1 inclusion crystals
with DGDM, DGDE and DGDB were obtained. On the other hand,
host 2b formed 1:1 inclusion crystal with DGDM, DGDE and DGDB.
The guest-free crystal of 2a was obtained by recrystallization of it
from acetonitrile. However, in the cases of 2b and 2c, the guest-free
crystals were not obtained, because the hosts formed inclusion
crystals with either water or guest solvent molecule, or both. We
have found that host 2a yields inclusion compounds in stoichio-
metric ratios with various alcohols such as ethanol, 1-butanol and
sec-butyl alcohol. The characteristics of polyethers and alcohols
inclusion crystals of 2a–2c are summarized in Table 1. Compared to
the guest-free crystal of 2a, the colour of the guest-inclusion
crystals of 2a–2c varied from orange to light yellow and a drastic
fluorescence enhancement was observed.
2. Results and discussion
2.1. Synthesis and spectroscopic properties of imidazo[4,5-
a]naphthalene-type fluorescent hosts (2a–2c)
The synthetic pathways of imidazo[4,5-a]naphthalene-type
fluorescent clathrate hosts (2a–2c) are outlined in Scheme 1. So-
dium 1,2-naphthoquinone-4-sulfonate reacted with N,N-dia-
lkylaniline in the presence of nickel(II) chloride to produce the
corresponding 4-aryl-1,2-naphthoquinones 1a–1c in 46–58% yield.
Next, the fluorophores 2a–2c were synthesized in 74–75% yield
by the reaction of p-cyanobenzaldehyde with the corresponding
1a–1c.
The absorption and fluorescence spectra of 2a–2c in benzene are
shown in Figure 1. The fluorophores 2a–2c exhibit intense ab-
sorption bands at 386, 386 and 383 nm (3max¼27,200, 27,700 and
25,900 dm3 molꢀ1 cmꢀ1, respectively) and a single intense fluo-
rescence band at around 479, 478 and 474 nm, respectively. The
fluorescence quantum yields (F) of 2a–2c are 0.91, 0.92 and 0.89,
Table 1
Host/guest molar ratio, crystal form and crystal colour of the guest-free and the
guest-inclusion crystals of 2a–2c
Host Guest
None
Host/guest (molar ratio) Crystal form Crystal colour
1/0
1/1
1/2
Prism
Leaflet
Prism
Yellowish orange
Yellowish orange
Yellow
Ethanol
1-Butanol
2a
sec-Butyl alcohol 1/1
tert-Butyl alcohol 1/2
Needle
Leaflet
Prism
Needle
Needle
Leaflet
Prism
Prism
Prism
Leaflet
Leaflet
Leaflet
Leaflet
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Light yellow
Yellow
DGDM
DGDE
DGDB
2/1
2/1
2/1
2b
2c
tert-Butyl alcohol 1/2
DGDM
DGDE
DGDB
1/1
1/1
1/1
tert-Butyl alcohol 1/2
Yellow
DGDM
DGDE
DGDB
2/1
2/1
2/1
Light yellow
Light yellow
Light yellow
Figure 1. Normalized absorption (/) and fluorescence (d) spectra of 2a–2c in
benzene.

Y. Ooyama et al. / Tetrahedron 65 (2009) 1467–1474
1469
Figure 3. Solid-state excitation (/) and fluorescence (d) spectra of the guest-free and
the polyether-inclusion crystals of 2a–2c: (a) 2a (guest-free): lex¼451 nm,
lem¼536 nm; (b) 2a$DGDM: lex¼444 nm, lem¼493 nm; (c) 2a$DGDE: lex¼444 nm,
lem¼495 nm; (d) 2a$DGDB: lex¼444 nm, lem¼497 nm; (e) 2b$DGDM: lex¼446 nm,
lem¼500 nm; (f) 2b$DGDE: lex¼430 nm, lem¼479 nm; (g) 2b$DGDB: lex¼447 nm,
lem¼497 nm; (h) 2c$DGDM: lex¼447 nm, lem¼494 nm; (i) 2c$DGDE: lex¼440 nm,
lem¼480 nm; (j) 2c$DGDB: lex¼435 nm, lem¼474 nm.
Figure 2. Solid-state excitation (/) and fluorescence (d) spectra of the guest-free and
the alcohol-inclusion crystals of 2a–2c: (a) 2a (guest-free): lex¼451 nm, lem¼536 nm;
(b) 2a$ethanol: lex¼451 nm, lem¼515 nm; (c) 2a$1-butanol: lex¼446 nm,
lem¼499 nm; (d) 2a$sec-butyl alcohol: lex¼442 nm, lem¼494 nm; (e) 2a$tert-buty
alcohol: lex¼440 nm, lem¼481 nm; (f) 2b$tert-buty alcohol: lex¼443 nm,
lem¼492 nm; (g) 2c$tert-buty alcohol: lex¼439 nm, lem¼475 nm.
2.3. Solid-state fluorescence enhancement behaviour upon
formation of guest-inclusion crystals
alcohol-inclusion crystals. It is noteworthy that the emission
maxima of tert-butyl alcohol-inclusion crystals both of 2a and 2c,
DGDE-inclusion crystals both 2b and 2c, and DGDB-inclusion
crystal of 2c are similar to those in benzene. Consequently, these
results demonstrated that the solid-state photophysical properties
In order to investigate the effect of clathrate formation on the
solid-state photophysical properties, the fluorescence excitation
and emission spectra of the guest-free and the guest-inclusion
crystals were measured. Compared to the guest-free crystal of 2a,
the excitation and emission maxima of the alcohol-inclusion crys-
tals except the sec-butyl alcohol-inclusion crystal exhibit a blue
shift and the fluorescence intensity is enhanced to various degrees
depending on the identity of the enclathrated alcohol molecules
(Fig. 2). The guest-free crystal of 2a exhibits relatively weak fluo-
rescence with emission maximum at 536 nm, while the alcohol-
inclusion crystals exhibit much stronger fluorescence intensity
with the emission maximum blue shifted to around 475–515 nm.
Relative fluorescence intensity (RFI), which was determined by
considering the fluorescence intensity of crystal 2a as 1.0, increases
in the following order: ethanol-inclusion crystal (RFI¼1.6)<1-bu-
tanol-inclusion crystal (RFI¼2.6)<tert-butyl alcohol-inclusion
crystal (RFI¼4.7). The tert-butyl alcohol-inclusion crystals exhibit
the strongest fluorescence intensity of the alcohol-inclusion crys-
tals. The fluorescence intensities of tert-butyl alcohol-inclusion
crystals of 2b (RFI¼3.0) and 2c (RFI¼5.8) are also stronger than
those of the guest-free and alcohol-inclusion crystals of 2a.
Of particular interest are the solid-state photophysical proper-
ties of polyether-inclusion crystals (Fig. 3). In the cases of 2a and 2c,
the RFI is in the following order: DGDM-inclusion crystal (RFI¼2.2
for 2a and 3.1 for 2c)<DGDB-inclusion crystal (RFI¼3.2 for 2a and
3.7 for 2c)<DGDE-inclusion crystal (RFI¼6.3 for 2a and 7.3 for 2c).
On the other hand, in the case of 2b, the DGDM-inclusion crystal
(RFI¼6.0) exhibits the strongest fluorescence intensity among the
polyether-inclusion crystals (RFI¼4.1 for DGDE-inclusion crystal
and 5.0 for DGDB-inclusion crystal). The fluorescence maximum of
polyether-inclusion crystals shifts to shorter wavelength with an
increase in the fluorescence intensity, as with the case of tert-butyl
Figure 4. Crystal structure of 2a: (a) a stereoview of the molecular packing structure
and (b) top view of the pairs of fluorophores.

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Y. Ooyama et al. / Tetrahedron 65 (2009) 1467–1474
of the five guest-inclusion crystals are close to their photophysical
properties in solution.
fluorescence enhancement and the blue shift of the absorption and
fluorescence maxima of the crystals.
Thus, in order to investigate the enclathrated guest effects on
a drastic fluorescence enhancement behaviour of the polyether-
and tert-butyl-inclusion crystals, the crystal structures of the
DGDM- and tert-butyl alcohol-inclusion compounds for 2a and 2b
have been determined by X-ray diffraction analysis. Figures 5–8
show the X-ray crystal structures of the guest-inclusion com-
pounds. The tautomeric forms (A and B) of imidazole ring of 2 in the
crystalline state were changed depending on the enclathrated guest
molecules. The tautomeric form of 2 is A-form in the crystals of
2a$DGDM and 2b$DGDM and B-form in the crystals of the guest-
free, 2a$tert-butyl alcohol, 2b$tert-butyl alcohol. In the crystal of
2a$DGDM, there are two crystallographically independent host
molecules. These results indicate that host 2 can include various
guest molecules by changing the tautomeric form on the imidazole
ring.
2.4. Relation between the solid-state fluorescence properties
and X-ray crystal structures of guest-inclusion compounds
As shown in the previous sections, the guest-free crystals of 2a
exhibit relatively weak fluorescence, whereas the polyether- and
tert-butyl alcohol-inclusion crystals of 2a–2c exhibit stronger
fluorescence with a blue-shifted emission maximum. The crystal
structures of the guest-free crystal of 2a and the ethanol, mor-
pholine, 1,4-dioxane and ethyl acetate-inclusion compounds have
already been determined by X-ray diffraction and are reported in
the preceding paper.8 The packing structure of 2a demonstrates
that the crystal is built up by the
the naphthoimidazole and the p-cyanophenyl moieties in the two
hosts (Fig. 4). We have proposed that the close overlap of the
host molecules causes interactions, leading to the strong
p-stacking arrangements between
p–p
The crystal of 2a$tert-butyl alcohol is made up by the
arrangements that avoid short contacts between the chromo-
phores. There are no short contacts of less than 3.60 Å between
the neighbouring fluorophores, which indicates a considerable
destruction of the interactions (Fig. 5c). An one-dimensional
p-stacking
p–p
fluorescence quenching of the guest-free crystal. From the com-
parison of the X-ray crystal structures of the guest-free and the
guest-inclusion compounds, we have concluded the destructions of
p–p
p–p
the
p–p interactions between fluorophores by the enclathrated
chain of (/H/G/G/) is formed through three-type in-
termolecular hydrogen bonding between host and guest and
guest molecules are the main reason for the guest-dependent
Figure 5. Crystal structure of 2a$tert-butyl alcohol: (a) a stereoview of the molecular
Figure 6. Crystal structure of 2b$tert-butyl alcohol: (a) a stereoview of the molecular
packing structure, (b) schematic structure and (c) top view of the pairs of fluorophores.
packing structure, (b) schematic structure and (c) top view of the pairs of fluorophores.

Y. Ooyama et al. / Tetrahedron 65 (2009) 1467–1474
1471
Figure 8. Crystal structure of 2b$DGDM: (a) a stereoview of the molecular packing
structure, (b) schematic structure and (c) top view of the pairs of fluorophores.
Figure 7. Crystal structure of 2a$DGDM: (a) a stereoview of the molecular packing
structure, (b) schematic structure and (c) top view of the pairs of fluorophores.
the hydroxyl proton of the guest is directing towards the oxygen of
another guest (O(2)H(43)/O(1) angle¼168(5)ꢁ, O(2)/O(1) dis-
tance¼2.815(4) Å). There are 20 (¼10ꢂ2) short interatomic con-
tacts of less than 3.6 Å between the host molecules (Fig. 6c). The
between two guests; a proton of an imidazole ring in the host is
directing towards the oxygen of the guest (N(1)H(2)/O(2)
angle¼173(3)ꢁ, N(1)/O(2) distance¼2.800(4) Å), the hydroxyl
proton of another guest is directing towards the imino nitrogen of
the host (O(1)H(25)/N(2) angle¼175(3)ꢁ, O(1)/N(2) dis-
tance¼2.799(3) Å), and the hydroxyl proton of the guest is directing
towards the oxygen of another guest (O(2)H(35)/O(1)
angle¼169(2)ꢁ, O(2)/O(1) distance¼2.694(3) Å) (Fig. 5b).
average distance of the interatomic
p–p contacts is ca. 3.52 Å, re-
spectively, which is a large distance in comparison with the guest-
free crystal of 2a.
The crystal of 2a$DGDM is also built up by the
p-stacking ar-
rangements between the naphthoimidazole and the p-cyanophenyl
moieties in the two hosts (Fig. 7). There are 15 short interatomic
p–
p
contacts between the two hosts. The average distance of the
On the other hand, the crystal of 2b$tert-butyl alcohol is built up
by the hydrogen bonded cluster unit composed of two hosts and
four tert-butyl alcohol molecules. As shown in Figure 6a and b, the
hydroxyl proton of the guest is directing towards the imino nitro-
gen of host (O(1)H(33)/N(2) angle¼175(4)ꢁ, O(1)/N(2) dis-
tance¼2.817(5) Å) and the proton of the host is directing towards
the oxygen of another guest (N(1)H(1)/O(2) angle¼176(4)ꢁ,
N(1)/O(2) distance¼2.853(4) Å). In addition, the two tert-butyl
alcohol molecules are bound by intermolecular hydrogen bonds:
interatomic contacts is ca. 3.47 Å, which suggests in-
p–
p
p–p
teractions. The two-type intramolecular hydrogen bonds are ob-
served between the host and the guest; the proton of imidazole
ring in host is directing towards the central oxygen of DGDM
molecule (N(2)H(1)/O(2) angle¼171(2)ꢁ, N(2)/O(2) distance¼
2.904(3) Å) and the proton of imidazole ring in another crystallo-
graphically independent host is directing towards the side oxygen
of the DGDM molecule (N(6)H(25)/O(3) angle¼175(3)/, N(6)/
O(3) distance¼2.873(3) Å). Figure 8a shows the molecular packing

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Y. Ooyama et al. / Tetrahedron 65 (2009) 1467–1474
structure for the crystal of 2b$DGDM. There are no intermolecular
hydrogen bonding interactions and no short contacts of less
than 3.60 Å between the neighbouring fluorophores, which in-
dicates a considerable destruction of the interactions. The
spectrophotometer and fluorescence spectra were measured with
a JASCO FP-777 spectrophotometer. The fluorescence quantum
p–p
yields (
thracene (
F) in benzene were determined using 9,10-diphenylan-
F
p
–
p
¼0.67, lex¼357 nm)9 in benzene as the standard. For
intramolecular hydrogen bonds are observed between the host and
the guest. As shown in Figure 8b, the proton of the imidazole of host
have two proton acceptors and become bifurcated-donor hydrogen
to form the three-centred hydrogen bonding arrangements with
the central and side oxygen atoms of guest (N(2)H(1)/O(2)
angle¼131(2)ꢁ, N(2)/O(2) distance¼3.004(3) Å and N(2)H(1)/
O(3) angle¼156(2)ꢁ, N(2)/O(3) distance¼3.047(3) Å).
the measurement of the solid-state fluorescence excitation and
emission spectra of the crystals, Jasco FP-1060 attachment was
used. 1H NMR spectra were recorded on a JNM-LA-400 (400 MHz)
FT NMR spectrometer with tetramethylsilane (TMS) as an internal
standard.
4.2. Synthesis
A comparison of the above five crystal structures confirms that
the strength of the
p–
p
interactions decreases in the following
4.2.1. General synthetic procedure for 4-aryl-1,2-naphthoquinones
order: 2a (guest-free)>2a$DGDM>2b$tert-butyl alcohol>2a$tert-
butyl alcohol>2b$DGDM. As seen in Figures 2 and 3, the solid-state
fluorescence intensity is the reverse order. These results confirm
1a–1c
A
solution of sodium 1,2-naphthoquinone-4-sulfonate
(38.4 mmol), N,N-dialkylaniline (57.6 mmol) and NiCl2$4H2O
(38.4 mmol) in CH3COOH/H2O [4:1 (v/v)] (200 ml) was stirred at
room temperature for 7 days. The reaction mixture was poured into
water. The solution was neutralized with aq Na2CO3 and extracted
with CH2Cl2. The organic extract was washed with water and
evaporated. The residue was chromatographed on silica gel (CH2Cl2
as eluent) to give 1a–1c.
that the differences in the destruction of the host–host
p–p in-
teractions by enclathration of the guest molecules are reflected on
the solid-state fluorescence intensity of the crystals. On the other
hand, in our previous works,5,8 we have demonstrated that con-
tinuous intermolecular hydrogen bonding between hosts (/H/
H/) or an one-dimensional chain ranging alternately host and
guest (/H/G/H/) is a principal factor of fluorescence quenching
in the solid state. In the crystal of 2a$tert-butyl alcohol, an
one-dimensional chain of (/H/G/G/) is formed through the
intermolecular hydrogen bonding between host and guest and
between two guests. It was considered that the continuous
intermolecular hydrogen bonding of (/H/G/G/) hardly con-
tribute to quenching of the solid-state fluorescence. Therefore, the
X-ray crystal structures of the polyether- and tert-butyl alcohol-
4.2.2. 4-[4-(Diethylamino)phenyl]-[1,2]naphthoquinone (1a)
Yield 58%; mp 116–118 ꢁC; 1H NMR (400 MHz, DMSO-d6, TMS)
d
¼1.13 (t, 6H), 3.42 (m, 4H), 6.29 (s, 1H), 6.79 (d, J¼8.7 Hz, 2H), 6.39
(d, J¼8.7 Hz, 2H), 7.61 (m, 1H), 7.72 (m, 1H), 7.72 (m, 2H), 8.03 (m,
1H); IR (KBr):
n
¼1650, 1603 cmꢀ1; MS [m/z] %: 305 (100) [Mþ].
4.2.3. 4-[4-(Dibutylamino)phenyl]-[1,2]naphthoquinone (1b)
Yield 50%; mp 94–97 ꢁC; 1H NMR (400 MHz, DMSO-d6, TMS)
inclusion crystals demonstrated that the destructions of the
p–p
interactions between host molecules by the enclathrated sterically
hindered guest molecules are the main reason for a drastic fluo-
rescence enhancement of the crystals.
d
¼0.92 (t, 6H), 1.34 (m, 4H), 1.54 (m, 4H), 3.42 (m, 4H), 6.29 (s, 1H),
6.76 (d, J¼8.9 Hz, 2H), 7.37 (d, J¼8.9 Hz, 2H), 7.53 (m, 1H), 7.61 (m,
1H), 7.72 (m, 1H), 8.02 (m, 1H); IR (KBr):
n
¼1645, 1601 cmꢀ1
.
3. Conclusions
4.2.4. 4-[4-(Diethylamino)-2-methyl-phenyl]-[1,2]naphtho-
quinone (1c)
As one of the most promising materials for the construction of
desirable solid-state fluorescent system, we have designed and
prepared the solid-state fluorescent host–guest system, which
consists of novel imidazo[4,5-a]naphthalene-type fluorescent hosts
2 and sterically hindered guest molecules such as polyethers and
tert-butyl alcohol. The host–guest crystals composed of 2 and
polyethers or tert-butyl alcohol exhibit strong solid-state fluores-
cence intensity compared to the guest-free crystal of 2. The X-ray
crystal structures of the polyether- and tert-butyl alcohol-inclusion
Yield 46%; mp 143–147 ꢁC; 1H NMR (400 MHz, CDCl3, TMS)
d
¼1.12 (t, 6H), 2.18 (s, 3H), 3.42 (m, 4H), 6.37 (s, 1H), 6.60 (m, 2H),
7.05 (d, J¼9.3 Hz, 1H), 7.14 (d, J¼7.8 Hz, 1H), 7.47–7.56 (m, 2H), 8.17
(m, 1H); IR (KBr):
n
¼1654, 1608 cmꢀ1
.
4.2.5. General synthetic procedure for compounds (2a–2c) by the
reaction of 4-aryl-1,2-naphthoquinones (1a–1c) with p-cyano-
benzaldehyde
A solution of 1 (18.45 mmol), p-cyanobenzaldehyde (18.5 mmol)
and ammonium acetate (0.3 mol) in acetic acid (170 ml) was stirred
at 80 ꢁC for 1 h. The reaction mixture was neutralized with aq
Na2CO3 and extracted with CH2Cl2. The organic extract was washed
with water and evaporated. The residue was chromatographed on
silica gel (CH2Cl2/ethyl acetate¼10:1 as eluent) to give 2.
crystals demonstrated that the destructions of the p–p interactions
between host molecules by the enclathrated sterically hindered
guest molecules are the main reason for a drastic fluorescence
enhancement of the crystals. Thus, new-type solid-state fluores-
cence system has been constructed by the fluorescent host and
sterically hindered guest molecules. Furthermore, new useful in-
formation concerning the solid-state fluorescence has been
obtained: the continuous intermolecular hydrogen bonding of
(/H/G/G/) hardly contribute to quenching of the solid-state
fluorescence.
4.2.6. 2-(4-Cyanophenyl)-5-[4-(diethylamino)phenyl]-3H-imidazo-
[4,5-a]naphthalene (2a)
Yield 75%; mp 244–247 ꢁC; 1H NMR (400 MHz, DMSO-d6, TMS)
d
¼1.15 (t, 6H), 3.34 (m, 4H), 6.80 (d, J¼8.5 Hz, 2H), 7.31 (d, J¼8.3 Hz,
2H), 7.46 (m, 1H), 7.54 (s, 1H), 7.65 (m, 1H), 7.96 (d, J¼8.3 Hz, 1H),
8.04 (d, J¼8.1 Hz, 2H), 8.41 (d, J¼7.8 Hz, 2H), 8.58 (d, J¼6.6 Hz, 1H);
4. Experimental section
4.1. General procedure
IR (KBr):
n
¼2220 cmꢀ1. Anal. Calcd (%) for C28H24N4: C 80.74, H 5.81,
N 13.45; found: C 80.88, H 5.61, N 13.68.
Elemental analyses were measured with a Perkin Elmer 2400 II
CHN analyzer. IR spectra were recorded on a JASCO FT/IR-5300
spectrophotometer for samples in KBr pellet form. Single-crystal
X-ray diffraction was performed on Rigaku AFC7S diffractometer.
4.2.7. 2-(4-Cyanophenyl)-5-[4-(dibutylamino)phenyl]-3H-imidazo-
[4,5-a]naphthalene (2b)
Yield 74%; mp 198–200 ꢁC; 1H NMR (400 MHz, DMSO-d6, TMS)
d¼0.95 (t, 6H), 1.36 (m, 4H), 1.57 (m, 4H), 3.34 (m, 4H), 6.75 (d,
Absorption spectra were observed with
a JASCO U-best30
J¼7.6 Hz, 2H), 7.30 (d, J¼7.3 Hz, 2H), 7.46 (m, 1H), 7.54 (s, 1H), 7.65

Y. Ooyama et al. / Tetrahedron 65 (2009) 1467–1474
1473
(m, 1H), 7.96 (d, J¼8.3 Hz, 1H), 8.04 (d, J¼6.7 Hz, 2H), 8.41 (d,
4.3.7. Compound 2a$diethylene glycol dibutyl ether (H/G¼2/1)
J¼6.7 Hz, 2H), 8.58 (d, J¼8.3 Hz, 1H); IR (KBr):
n
¼2217 cmꢀ1. Anal.
Host 2a (300 mg) was dissolved by warming in diethylene glycol
dibutyl ether (6 ml), and the resulting solution was allowed to stand
at room temperature. The crystals (yellow, needle, 256 mg) were
collected and dried on the filter paper. Anal. Calcd (%) for
C68H74N8O3: C 77.68, H 7.09, N 10.66; found: C 77.48, H 7.45, N 10.49.
Calcd (%) for C32H32N4: C 81.32, H 6.82, N 11.85; found: C 80.93, H
6.89, N 11.84.
4.2.8. 2-(4-Cyanophenyl)-5-[4-(diethylamino)-2-methyl-phenyl]-
3H-imidazo[4,5-a]naphthalene (2c)
Yield 75%; mp 245–248 ꢁC; 1H NMR (400 MHz, DMSO-d6, TMS)
4.3.8. Compound 2b$ethanol (H/G¼1/1)
d
¼1.15 (t, 6H), 3.34 (m, 4H), 1.94 (s, 1H), 6.61 (m, 1H), 6.65 (s, 1H),
Host 2b (200 mg) was dissolved by warming in ethanol (5 ml),
and the resulting solution was allowed to stand at room tempera-
ture. The crystals (yellow, prism, 200 mg) were collected and dried
on the filter paper. Anal. Calcd (%) for C34H38N4O: C, 78.73; H, 7.38;
N, 10.08. found: C, 78.46; H, 7.19; N, 10.82.
7.02 (d, J¼8.3 Hz, 1H), 7.41 (m, 1H), 7.47 (m, 2H), 8.04 (d, J¼8.3 Hz,
2H), 8.41 (d, J¼8.3 Hz, 2H), 8.57 (d, J¼8.1 Hz, 1H); IR (KBr):
n
¼2225 cmꢀ1. Anal. Calcd (%) for C29H26N4: C 80.09, H 6.09, N 13.01;
found: C 80.83, H 6.02, N 13.06.
4.3.9. Compound 2b$tert-butyl alcohol (H/G¼1/2)
4.3. Preparation of guest-inclusion crystals
Host 2b (450 mg) was dissolved by warming in tert-butyl alco-
hol (19 ml), and the resulting solution was allowed to stand at room
temperature. The crystals (yellow, leaflet, 344 mg) were collected
and dried on the filter paper. Anal. Calcd (%) for C40H52N4O2: C
77.38, H 8.44, N 9.02; found: C 77.73, H 8.74, N 9.28.
The host compound 2 was dissolved with heating in respective
guest–solvent. The solution was filtered and kept for a few days at
room temperature. The crystals that formed were collected by fil-
tration. The host (H)/guest (G) stoichiometric ratio of the inclusion
compounds was determined by means of 1H NMR integration and
CHN analysis.
4.3.10. Compound 2b$diethylene glycol dimethyl ether (H/G¼1/1)
Host 2b (220 mg) was dissolved by warming in diethylene glycol
dimethyl ether (1 ml), and the resulting solution was allowed to
stand at room temperature. The crystals (yellow, prism, 123 mg)
were collected and dried on the filter paper. Anal. Calcd (%) for
C38H46N4O3: C 75.22, H 7.64, N 9.23; found: C 75.19, H 7.69, N 9.23.
4.3.1. Compound 2a$ethanol (H/G¼1/1)
Host 2a (420 mg) was dissolved by warming in ethanol (18 ml),
and the resulting solution was allowed to stand at room tempera-
ture. The crystals (yellow, leaflet, 322 mg) were collected and dried
on the filter paper. Anal. Calcd (%) for C30H30N4O: C 77.89, H 6.54, N
12.11; found: C 77.60, H 6.24, N 11.92.
4.3.11. Compound 2b$diethylene glycol diethyl ether (H/G¼1/1)
Host 2b (300 mg) was dissolved by warming in diethylene glycol
diethyl ether (1 ml), and the resulting solution was allowed to stand
at room temperature. The crystals (yellow, prism, 250 mg) were
collected and dried on the filter paper. Anal. Calcd (%) for
C40H50N4O3: C 75.68, H 7.94, N 8.83; found: C 75.98, H 8.23, N 8.77.
4.3.2. Compound 2a$1-butanol (H/G¼1/2)
Host 2a (300 mg) was dissolved by warming in 1-butanol (5 ml),
and the resulting solution was allowed to stand at room tempera-
ture. The crystals (yellow, prism, 252 mg) were collected and dried
on the filter paper. Anal. Calcd (%) for C36H44N4O2: C 76.56, H 7.85, N
9.92; found: C 76.36, H 7.70, N 10.18.
4.3.12. Compound 2b$diethylene glycol dibutyl ether (H/G¼1/1)
Host 2b (300 mg) was dissolved by warming in diethylene glycol
diethyl ether (1 ml), and the resulting solution was allowed to stand
at room temperature. The crystals (yellow, prism, 210 mg) were
collected and dried on the filter paper. Elemental analysis could not
beperformed, becausethecrystalwasunstableatroomtemperature.
4.3.3. Compound 2a$sec-butyl alcohol (H/G¼1/1)
Host 2a (100 mg) was dissolved by warming in sec-butyl alcohol
(28 ml), and the resulting solution was allowed to stand at room
temperature. The crystals (yellow, needle, 68 mg) were collected
and dried on the filter paper. Anal. Calcd (%) for C32H34N4O: C 78.43,
H 6.98, N 11.40; found: C 78.18, H 7.12, N 11.40.
4.3.13. Compound 2c$tert-butyl alcohol (H/G¼1/2)
Host 2c (520 mg) was dissolved by warming in tert-butyl alcohol
(60 ml), and the resulting solution was allowed to stand at room
temperature. The crystals (yellow, leaflet, 175 mg) were collected
and dried on the filter paper. Anal. Calcd (%) for C37H46N4O2: C
76.78, H 8.01, N 9.68; found: C 76.62, H 8.20, N 9.70.
4.3.4. Compound 2a$tert-butyl alcohol (H/G¼1/2)
Host 2a (100 mg) was dissolved by warming in tert-butyl alco-
hol (14 ml), and the resulting solution was allowed to stand at room
temperature. The crystals (yellow, prism, 99 mg) were collected
and dried on the filter paper. Anal. Calcd (%) for C36H44N4O2: C
76.56, H 7.85, N 9.92; found: C 76.52, H 8.13, N 9.64.
4.3.14. Compound 2c$diethylene glycol dimethyl ether (H/G¼2/1)
Host 2c (300 mg) was dissolved by warming in diethylene glycol
dimethyl ether (3 ml), and the resulting solution was allowed to
stand at room temperature. The crystals (yellow, leaflet, 250 mg)
were collected and dried on the filter paper. Anal. Calcd (%) for
C64H66N8O3: C 77.23, H 6.68, N 11.26; found: C 77.18, H 6.77, N 11.26.
4.3.5. Compound 2a$diethylene glycol dimethyl ether (H/G¼2/1)
Host 2a (300 mg) was dissolved by warming in diethylene glycol
dimethyl ether (2.5 ml), and the resulting solution was allowed to
stand at room temperature. The crystals (yellow, prism, 178 mg)
were collected and dried on the filter paper. Anal. Calcd (%) for
C69H62N8O3: C 76.99, H 6.46, N 11.59; found: C 76.88, H 6.51, N 11.66.
4.3.15. Compound 2c$diethylene glycol diethyl ether (H/G¼2/1)
Host 2c (300 mg) was dissolved by warming in diethylene glycol
diethyl ether (4 ml), and the resulting solution was allowed to stand
at room temperature. The crystals (yellow, leaflet, 180 mg) were
collected and dried on the filter paper. Anal. Calcd (%) for
C66H70N8O3: C 77.46, H 6.89, N 10.95; found: C 77.99, H 7.04, N 11.03.
4.3.6. Compound 2a$diethylene glycol diethyl ether (H/G¼2/1)
Host 2a (330 mg) was dissolved by warming in diethylene glycol
diethyl ether (2 ml), and the resulting solution was allowed to stand
at room temperature. The crystals (yellow, needle, 225 mg) were
collected and dried on the filter paper. Elemental analysis could not
be performed, because the crystal was unstable at room
temperature.
4.3.16. Compound 2c$diethylene glycol dibutyl ether (H/G¼2/1)
Host 2c (300 mg) was dissolved by warming in diethylene glycol
diethyl ether (4 ml), and the resulting solution was allowed to stand

1474
Y. Ooyama et al. / Tetrahedron 65 (2009) 1467–1474
at room temperature. The crystals (yellow, leaflet, 195 mg) were
collected and dried on the filter paper. Elemental analysis could not
beperformed, becausethecrystalwasunstableatroomtemperature.
structures were expanded using Fourier techniques.12 The non-
hydrogen atoms were refined anisotropically. Some hydrogen
atoms were refined isotropically, the rest were fixed geometrically
and not refined. Crystallographic data: C38H46N4O3, M¼606.81,
4.4. X-ray crystallographic studies
triclinic, a¼11.146(2), b¼17.006(3), c¼9.830(2) Å,
a
¼95.83(2)ꢁ,
b
¼103.82(1)ꢁ,
g
¼80.45(1)ꢁ, U¼1780.5(5) Å3, rcalcd¼1.132 g cmꢀ3
,
The reflection data were collected at 23ꢃ1 ꢁC on a Rigaku AFC7S
T¼296.2 K, space group P1 (no.2), Z¼2,
m(Mo K
a
)¼0.72 cmꢀ1, 6622
four-circle diffractometer by 2
q–u
scan technique, and using graph-
reflections measured, 6269 unique (Rint¼0.017), which were used
ite-monochromated Mo K
a
(l¼0.71069 Å) radiation at 50 kV and
in all calculations. The final
R
indices [I>2
s
(I)], R1¼0.0671,
30 mA. In all case, the data were corrected for Lorentz and polariza-
tion effects. A correction for secondary extinction was applied. The
reflection intensities were monitored by three standard reflections
for every 150 reflections. An empirical absorption correction based
on azimuthal scans of several reflections was applied. All calculations
were performed using the teXsan10 crystallographic software pack-
age of Molecular Structure Corporation. Crystallographic data (ex-
cluding structure factors) have been deposited with Cambridge
Crystallographic Data Centre (CCDC) as supplementary publication
numbers CCDC-692724 (2a), CCDC-692729 (2a$tert-butyl alcohol),
CCDC-692730 (2a$diethylene glycol dimethyl ether), CCDC-692731
(2b$tert-butyl alcohol) and CCDC-692732 (2b$diethylene glycol di-
methyl ether). These data can be obtained free of charge from the
CCDC via www.ccdc.cam.au.uk/data_request/cif.
wR(F2)¼0.1599.
Acknowledgements
This work was partially supported by a Grant-in-Aid for Science
and Research from the Ministry of Education, Science, Sport and
Culture of Japan (Grant 18350100) and by a Special Research Grant
for Green Science from Kochi University.
References and notes
1. (a) Tang, C. W.; VansSlyke, S. A. Appl. Phys. Lett. 1987, 51, 913; (b) Tang, C. W.;
VansSlyke, S. A.; Chen, C. H. J. Appl. Phys. 1989, 65, 3610; (c) Wong, K.-C.; Chien,
Y.-Y.; Chen, R.-T.; Wang, C.-F.; Liu, Y.-T.; Chiang, H.-H.; Hsieh, P.-Y.; Wu, C.-C.;
Chou, C. H.; Su, Y. O.; Lee, G.-H.; Peng, S.-M. J. Am. Chem. Soc. 2002, 124, 11576;
(d) Tonzola, C. J.; Alam, M. M.; Kaminsky, W. K.; Jenekhe, S. A. J. Am. Chem. Soc.
2003, 125, 13548; (e) Yeh, H.-C.; Chan, L.-H.; Wu, W.-C.; Chen, C.-T. J. Mater.
Chem. 2004, 14, 1293; (f) Chen, C.-T. Chem. Mater. 2004, 16, 4389; (g) Chiang,
C.-L.; Wu, M.-F.; Dai, D.-C.; Wen, Y.-S.; Wang, J.-K.; Chen, C.-T. Adv. Funct. Mater.
2005, 15, 231; (h) Berner, D.; Klein, C.; Nazeeruddin, M. D.; de Angelis, F.;
Castellani, M.; Bugnon, P.; Scopelliti, R.; Zuppiroli, L.; Graetzel, M. J. Mater. Chem.
2006, 16, 4468.
2. (a) Wang, Z.-S.; Li, F.-Y.; Hang, C.-H.; Wang, L.; Wei, M.; Jin, L.-P.; Li, N.-Q. J. Phys.
Chem. B 2000, 104, 9676; (b) Ehret, A.; Stuhl, L.; Spitler, M. T. J. Phys. Chem. B
2001, 105, 9960; (c) Hara, K.; Sato, T.; Katoh, R.; Furube, A.; Ohga, Y.; Shinpo, A.;
Suga, S.; Sayama, K.; Sugihara, H.; Arakawa, H. J. Phys. Chem. B 2003, 107, 597;
(d) Thomas, K. R. J.; Kin, J. T.; Hsu, Y.-C.; Ho, K.-C. Chem. Commun. 2005, 4098;
(e) Hagberg, D. P.; Edvinsson, T.; Marinado, T.; Boschloo, G.; Hagfeld, A.; Sun, L.
Chem. Commun. 2006, 2245; (f) Li, S.-L.; Jiang, K.-J.; Shao, K.-F.; Yang, L.-M.
Chem. Commun. 2006, 2792.
3. (a) Yeh, H.-C.; Wu, W.-C.; Wen, Y.-S.; Dai, D.-C.; Wang, J.-K.; Chen, C.-T. J. Org.
Chem. 2004, 69, 6455; (b) Horiguchi, E.; Matsumoto, S.; Funabiki, K.; Matsui, M.
Bull. Chem. Soc. Jpn. 2005, 78, 1167; (c) Dreuw, A.; Plo¨tner, J.; Lorenz, L.;
Wachtveitl, J.; Djanhan, J. E.; Bru¨ ning, J.; Metz, T.; Bolte, M.; Schmidt, M. U.
Angew. Chem., Int. Ed. 2005, 44, 7783.
4. (a) Yoshida, K.; Miyazaki, H.; Miura, Y.; Ooyama, Y.; Watanabe, S. Chem. Lett.
1999, 837; (b) Yoshida, K.; Ooyama, Y.; Tanikawa, S.; Watanabe, S. Chem. Lett.
2000, 714; (c) Yoshida, K.; Ooyama, Y.; Tanikawa, S.; Watanabe, S. J. Chem. Soc.,
Perkin Trans. 2 2002, 708; (d) Ooyama, Y.; Yoshida, K. New J. Chem. 2005, 29,
1204; (e) Ooyama, Y.; Yoshida, K. Eur. J. Org. Chem. 2008, 15, 2564.
5. (a) Yoshida, K.; Uwada, K.; Kumaoka, H.; Bu, L.; Watanabe, S. Chem. Lett.
2001, 808; (b) Ooyama, Y.; Nakamura, T.; Yoshida, K. New J. Chem. 2005, 29,
447.
6. (a) Langhals, H.; Potrawa, T.; No¨th, H.; Linti, G. Angew. Chem., Int. Ed. Engl. 1989,
28, 478; (b) Langhals, H.; Ismael, R.; Yu¨ru¨k, O. Tetrahedron 2001, 56, 5435; (c)
Yoshida, K.; Ooyama, Y.; Miyazaki, H.; Watanabe, S. J. Chem. Soc., Perkin Trans. 2
2002, 700; (d) Ooyama, Y.; Okamoto, T.; Yamaguchi, T.; Suzuki, T.; Hayashi, A.;
Yoshida, K. Chem.dEur. J. 2006, 7827; (e) Ooyama, Y.; Harima, Y. Chem. Lett.
2006, 902; (f) Ooyama, Y.; Yoshikawa, S.; Watanabe, S.; Yoshida, K. Org. Biomol.
Chem. 2006, 4, 3406; (g) Ooyama, Y.; Kagawa, Y.; Harima, Y. Eur. J. Org. Chem.
2007, 22, 3613; (h) Ooyama, Y.; Mamura, T.; Yoshida, K. Eur. J. Org. Chem. 2007,
30, 5010; (i) Ooyama, Y.; Mamura, T.; Yoshida, K. Tetrahedron Lett. 2007, 48,
5791; (j) Ooyama, Y.; Yoshikawa, S.; Watanabe, S.; Yoshida, K. Org. Biomol. Chem.
2007, 5, 1260.
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Matsubara, Y. Chem. Asian J. 2008, 3, 625.
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4.4.1. Crystal of 2a$tert-butyl alcohol
The transmission factors ranged from 0.98 to 1.00. The crystal
structure was solved by direct methods using SIR 92.11 The struc-
tures were expanded using Fourier techniques.12 The non-hydro-
gen atoms were refined anisotropically. Some hydrogen atoms
were refined isotropically, the rest were fixed geometrically and not
refined. Crystallographic data: C36H44N4O2, M¼564.77, monoclinic,
a¼16.590(2),
b¼9.337(3),
c¼22.968(3) Å,
b
¼105.285(9)ꢁ,
U¼3432.0(10) Å3, rcalcd¼1.260 g cmꢀ3, T¼296.2 K, space group P21/
n (no. 14), Z¼4,
m
(Mo K
a
)¼0.68 cmꢀ1, 6279 reflections measured,
6043 unique (Rint¼0.033), which were used in all calculations. The
final R indices [I>2
s
(I)], R1¼0.0625, wR(F2)¼0.139.
4.4.2. Crystal of 2a$diethylene glycol dimethyl ether
The transmission factors ranged from 0.94 to 1.00. The crystal
structure was solved by direct methods using SIR 92.11 The struc-
tures were expanded using Fourier techniques.12 The non-hydro-
gen atoms were refined anisotropically. Some hydrogen atoms
were refined isotropically, the rest were fixed geometrically and not
refined. Crystallographic data: C62H62N8O3, M¼967.22, triclinic,
a¼11.526(2), b¼27.029(2), c¼9.134(2) Å,
a
¼91.08(1)ꢁ,
b
¼111.54(2)ꢁ,
T¼296.2 K,
g
¼84.632(9)ꢁ, U¼2634.7(8) Å3, rcalcd¼1.219 g cmꢀ3
,
space group P1 (no. 2), Z¼2,
m
(Mo K
a
)¼1.53 cmꢀ1, 9690 reflections
measured, 9187 unique (Rint¼0.025), which were used in all cal-
culations. The final R indices [I>2
s
(I)], R1¼0.0546, wR(F2)¼0.1262.
4.4.3. Crystal of 2b$tert-butyl alcohol
The transmission factors ranged from 0.96 to 1.00. The crystal
structure was solved by direct methods using SIR 92.11 The structures
were expanded using Fourier techniques.12 The non-hydrogen atoms
were refined anisotropically. Some hydrogen atoms were refined
isotropically, the rest were fixed geometrically and not refined.
Crystallographic data: C40H52N4O2, M¼620.88, triclinic, a¼12.260(2),
b¼15.046(1), c¼10.716(1) Å,
a
¼96.299(9)ꢁ,
b
¼90.19(1)ꢁ,
g
¼75.561
(9)ꢁ, U¼1902.0(4) Å3, rcalcd¼1.084 g cmꢀ3, T¼296.2 K, space group
9. Heller, C. A.; Henry, R. A.; Mclaughlin, B. A.; Bills, D. E. J. Chem. Eng. Data 1974,
19, 214.
10. teXsan; Crystal Structure Analysis Package, Molecular Structure Corporation:
The Woodlands, TX, 1985 and 1992.
11. Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.; Giacovazzo, C.; Guagliardi,
A.; Polidori, G. J. Appl. Crystallogr. 1994, 27, 435.
P1 (no. 2), Z¼2,
m
(Mo K
a
)¼0.67 cmꢀ1, 7075 reflections measured,
6688 unique (Rint¼0.027), which were used in all calculations. The
final R indices [I>2
s
(I)], R1¼0.0705, wR(F2)¼0.1486.
12. DIRDIF94: Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Gelder, R.; Israel, R.; Smits, J. M. M. The DIRIF94 Program System, Technical Report
of the Crystallography Laboratory; University of Nijmegen: The Netherlands,
1994.
4.4.4. Crystal of 2b$diethylene glycol dimethyl ether
The transmission factors ranged from 0.99 to 1.00. The crystal
structure was solved by direct methods using SIR 92.11 The