Solid-state fluorescence changes of 2-(4-cyanophenyl)-5-[4-(diethylamino)- phenyl]-3H-imidazo[4,5-a]naphthalene upon inclusion of organic solvent molecules

Article abstract of DOI:10.1002/ejoc.200800832

Novel imidazo[4,5-a]naphthalene-type fluorescent clathrate host 2-(4-cyanophenyl)-5-[4-(diethylamino)phenyl]-3H-imidazo[ 4,5-a]naphthalene (2), with two possible tautomeric forms (A and B) of the imidazole ring, was developed. The crystal of fluorophore 2

Full text of DOI:10.1002/ejoc.200800832

FULL PAPER
DOI: 10.1002/ejoc.200800832
Solid-State Fluorescence Changes of 2-(4-Cyanophenyl)-5-[4-(diethylamino)-
phenyl]-3H-imidazo[4,5-a]naphthalene upon Inclusion of Organic Solvent
Molecules
Yousuke Ooyama,*[a] Shinobu Nagano,[a] Miyako Okamura,[a] and Katsuhira Yoshida*[a]
Keywords: Dyes / Clathrates / Nitrogen heterocycles / Fluorescence / Inclusion compounds
Novel imidazo[4,5-a]naphthalene-type fluorescent clathrate
host 2-(4-cyanophenyl)-5-[4-(diethylamino)phenyl]-3H-imid-
azo[4,5-a]naphthalene (2), with two possible tautomeric
forms (A and B) of the imidazole ring, was developed. The
crystal of fluorophore 2 exhibits sensitive colour change and
fluorescence enhancement behaviour with a blueshift in the
emission maximum upon enclathration of various kinds of or-
ganic solvent molecules. The crystal structures of the guest-
free and clathrate compounds of 2 were determined by X-
ray analysis. On the basis of spectroscopic data and crystal
structures, the effects of the enclathrated guest on the solid-
state photophysical properties of the clathrate compounds
are discussed.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
host–guest inclusion complexes are useful materials for elu-
cidation of solid-state optical properties.[5,6] Recently, Imai
et al. showed that a solid-state fluorescent host system was
created by self-assembly of a 21-helical columnar organic
fluorophore composed of (1R,2S)-2-amino-1,2-diphenyle-
thanol and fluorescent 1-pyrenecarboxylic acid. The solid-
state fluorescence of this host system changes depending
on the guest molecules owing to their slight variations in
molecular size and shape.[7] Therefore, an organic fluores-
cent host can be the most promising material for the con-
struction of desirable solid-state fluorescent system.
Introduction
Solid-state fluorescence of organic fluorescent dyes has
recently attracted increasing interest, because of their many
uses both in the fundamental research fields of solid-state
photochemistry and polymorphism and in the applied field
of optoelectronic devices.[1] For the design of desirable so-
lid-state fluorescent materials, it is very important to obtain
information about the relationship between the photophysi-
cal properties and the chemical and crystal structures of
fluorophores. During the last decade some studies demon-
strated that the key point in designing new organic solid-
state fluorescent dyes is to remove the intermolecular inter-
actions between fluorophores causing fluorescence quench-
ing in molecular aggregation states. For example, the intro-
duction of bulky substituents to the original fluorophores[2]
and the construction of nonplanar structures with sterically
hindered substituents[3] are known to be very useful meth-
ods for solving the problem of fluorescence quenching by
molecular aggregation. As another approach, Tohnai and
Miyata et al. proposed the possibility of a tunable solid-
state fluorescence system consisting of an organic salt with
a primary amine. In the system, the fluorescence intensity
can be controlled by changing the chain length of the alkyl
group on the amine.[4]
In our previous works, we reported novel benzo-
furano[3,2-b]naphthoquinol-type,[5] imidazo[5,4-a]anthra-
quinol-type,[8] 5-hydroxy-5-substituent-benzo[b]naphtho[1,2-d]-
furan-6-one-type[9]
and
phenanthro[9,10-d]imidazole-
type[10] fluorescent hosts, whose crystals exhibit a dramatic
fluorescence enhancement upon inclusion of various
amines, organic solvents and carboxylic acids. In particular,
imidazo[5,4-a]anthraquinol-type fluorophores, in which
two tautomeric forms (A and B) are possible for the imid-
azole ring, can include various kinds of organic solvent
molecules in the crystalline state by changing the tauto-
meric form of the imidazole ring. A dramatic fluorescence
enhancement and a blueshift in the absorption and fluores-
cence wavelength maxima are observed depending on the
enclathrated guest molecules. From comparison of the X-
ray crystal structures of the guest-free and clathrate com-
pounds, it was concluded that the destruction of the π–π
interactions and the intermolecular hydrogen bonds bind-
ing fluorophores by the enclathrated guest molecules are
the main reason for the guest-dependent fluorescence en-
hancement and the blueshift in the absorption and fluores-
In contrast, organic fluorescent hosts that exhibit sensi-
tive colour and fluorescence changes upon formation of
[a] Department of Material Science, Faculty of Science Kochi
University,
Akebono-cho, Kochi 780-8520, Japan
Fax: +81-88-844-8359
E-mail: yooyama@hiroshima-u.ac.jp
kyoshida@cc.kochi-u.ac.jp
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Y. Ooyama, S. Nagano, M. Okamura, K. Yoshida
FULL PAPER
cence maxima of the crystals. Consequently, it is expected presence of an excess amount of ammonium acetate in ace-
that the fluorescent hosts condensed with imidazole ring tic acid.
can include various kinds of organic solvent molecules and
exhibit desirable solid-state fluorescent properties according benzene are shown in Figure 1. Fluorophore 2 exhibits in-
to the change in the crystal structures by changing the tau- tense absorption bands at around 386 nm (εmax
tomeric form of the imidazole ring.
27200 dm3 mol–1 cm–1) and a single intense fluorescence
The absorption and fluorescence spectra of 2 in
=
In connection with this research, we further developed band at around 479 nm. The fluorescence quantum yield
the novel imidazo[4,5-a]naphthalene-type fluorescent clath- (Φ) is 0.91.
rate host 2-(4-cyanophenyl)-5-[4-(diethylamino)phenyl]-3H-
imidazo[4,5-a]naphthalene (2), which exhibits tautomerism
(A and B) of the imidazole ring. Here, we report sensitive
colour and fluorescence changes of 2 upon enclathration of
organic solvent molecules in the solid state. The X-ray crys-
tal structures of 2 and its guest-inclusion compounds were
determined, on the basis of which the enclathrated guest
effects on the solid-state fluorescence properties are dis-
cussed.
Results and Discussion
In the molecular design of fluorescent clathrate hosts, it
Figure 1. Normalized absorption (– – –) (2.5ϫ10–5 ) and fluores-
cence (–––) (2.5ϫ10–6 , λex = 386 nm) spectra of 2 in benzene.
is required that specific structural units such as a rigid
backbone (fluorophore skeleton), bulky substituents and
anchor groups are combined.[11–13] In order to create new
fluorescent clathrate hosts, we employed the imidazo[4,5-a]-
naphthalene-type fluorophore with an imidazole ring as the
anchor group. Because two tautomeric forms (A and B) are
possible for the imidazole ring, it is expected that the fluo-
rescent hosts condensed with the imidazole ring can include
various kinds of organic solvent molecules and exhibit de-
sirable solid-state fluorescent properties according to the
changes in the crystal structures induced by the changing
tautomeric forms. Thus, we designed and synthesized the
imidazo[4,5-a]naphthalene-type fluorescent clathrate host
2-(4-cyanophenyl)-5-[4-(diethyllamino)phenyl]-3H-imidazo-
[4,5-a]naphthalene (2; Scheme 1).
Measured under oxygen-free conditions.
Inclusion Ability in the Crystalline State
In order to investigate the inclusion ability of 2, we
recrystallized fluorophore 2 from various organic solvents.
We found that fluorophore 2 yields various host–guest in-
clusion compounds in stoichiometric ratios with organic
solvent molecules such as ethanol, ethyl acetate, morpholine
and 1,4-dioxane in the crystalline state. These results sug-
gest that the imidazole ring is effective to fix guest mole-
cules in the crystalline state. The guest-free crystal was ob-
tained by recrystallization of 2 from acetonitrile. The char-
acteristics of the guest-free and various inclusion crystals
obtained by recrystallization of 2 are summarized in
Table 1. In comparison to the guest-free crystal, the colour
of the guest-inclusion crystals varied from yellowish orange
to yellow and a dramatic fluorescence enhancement was ob-
served.
Thermal analyses (TG and DTA) were performed to in-
vestigate the thermal stability of the clathrate crystals, and
the thermal analysis data are shown in Table 1. The guest-
release patterns were considerably different depending on
the identity of the enclathrated solvent molecules, and the
guest-release temperatures for the all guest-inclusion crys-
tals were higher than their original boiling points of the
Scheme 1. (i) N,N-diethylaniline, NiCl2·4H2O, CH3COOH/H2O
(4:1), 7 d, room temp., 58%; (ii) p-cyanobenzaldehyde,
CH3COONH4, CH3COOH, 1 h, 80 °C, 75 %.
Fluorophore 2 is conveniently synthesized as shown in guest. Interestingly, after releasing solvent molecules, only
Scheme 1. We first prepared 4-[4-(diethylamino)phenyl]-1,2- morpholine inclusion crystal showed the original melting
naphthoquinone (1) in 58% yield by the reaction of sodium point at around 245 °C; the morpholine inclusion crystal
1,2-naphthoquinone-4-sulfonate with N,N-diethylaniline in shows two endothermic peaks associated with the guest re-
acetic acid in the presence of nickel(II) chloride. Next, flu- lease and melting points. The TG and DTA profiles of the
orophore 2 was synthesized in 58% yield by the reaction morpholine and ethanol inclusion crystals are shown in
of p-cyanobenzaldehyde with 1,2-naphthoquinone 1 in the Figure 2. From the visual observation of the thermal sta-
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Solid-State Fluorescence Changes upon Inclusion of Organic Solvent Molecules
Table 1. Host–guest molar ratio, crystal form, crystal colour and thermal analysis of the guest-free and guest-inclusion crystals of 2.
Guest
Host/Guest
Crystal
Crystal colour
TG weight loss [%]
Guest loss endo-
therm
Host 2 melt
(molar ratio)
form
Calculation Observation
peak point [°C]
endotherm peak point
[°C]
None
Morpholine
Ethanol
Ethyl acetate
1,4-Dioxane
1:0
1:1
1:1
2:1
2:1
Prism
Prism
Leaflet
Needle
Needle
Yellowish orange
Yellowish orange
Yellowish orange
Yellow
0
0
–
245
245
–
–
–
17.29
9.96
9.56
9.56
17.23
9.63
9.85
9.63
146
138
159
176
Yellow
bility of the clathrate crystals, the morpholine inclusion decreased, so that the photophysical properties of the guest-
crystal melted around 245 °C. In contrast, the other guest released guest-inclusion crystals are close to that of the as-
inclusion crystals melted at the temperature of guest release. prepared guest-free crystal.
It is known that some host–guest inclusion crystals melt
with concomitant release of the guest; thus, it was consid-
Solid-State Fluorescence Enhancement Behaviour upon
Formation of Guest-Inclusion Crystals
ered that the degree of orientational disorder with the con-
comitant release of the guest is already close to that of the
liquid.[14] Actually, comparison of the X-ray crystal struc-
tures of the guest-free and guest-inclusion compounds dem-
onstrated that the packing structures of the guest-free and
morpholine-inclusion compounds are quite similar to each
other (See Figures 4 and 5). Thus, in the case of the morph-
oline-inclusion crystal, it was revealed that the crystal struc-
ture was not destroying after release of the guest was com-
plete, which explained the appearance of the two endother-
mic peaks associated with the release of the guest and the
melting points. In all the guest-released guest-inclusion
crystals, the fluorescence excitation and fluorescence max-
ima were redshifted and their fluorescence intensities were
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 guest-
inclusion crystals were measured (Figure 3). In comparison
to the guest-free crystal, the excitation and emission max-
ima of the guest-inclusion crystals exhibit a blueshift and
the fluorescence intensity is enhanced to various degrees
depending on the identity of the enclathrated guest mole-
cules. However, the fluorescence intensity of the morpholine
inclusion crystal is almost the same as the guest-free host
crystal. The guest-free host crystal exhibits relatively weak
fluorescence with an emission maximum at 536 nm,
whereas the guest-inclusion crystals exhibit much stronger
fluorescence intensity with the emission maximum blue-
shifted to around 491–517 nm. In comparison with the
guest-free crystal, the fluorescence intensities of the guest-
inclusion crystals were ca. 1.6-fold in ethanol-, ca. 2.1-fold
in ethyl acetate- and ca. 4.8-fold in 1,4-dioxane-inclusion
Figure 3. Solid-state excitation (– – –) and fluorescence (–––) spec-
tra of the guest-free and guest inclusion crystals of 2: (a) 2 (guest-
free): λex = 451 nm, λem = 536 nm, Φ = 0.06; (b) 2·morpholine: λex
= 452 nm, λem = 517 nm, Φ = 0.05; (c) 2·ethanol: λex = 451 nm,
λem = 515 nm, Φ = 0.08; (d) 2·ethyl acetate: λex = 446 nm, λem
491 nm, Φ = 0.10; (e) 2·1,4-dioxane: λex = 440 nm, λem = 495 nm,
Φ = 0.26.
=
Figure 2. TG and DTA traces for the guest inclusion compounds:
(a) 2·morpholine and (b) 2·ethanol.
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Y. Ooyama, S. Nagano, M. Okamura, K. Yoshida
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crystals. The solid-state fluorescence quantum yield (Φ) in- cyanophenyl moieties in the two hosts. There are 16
creases in the order of 2·1,4-dioxane (Φ = 0.26) Ͼ 2·ethyl (= 8ϫ2) and 14 (= 7ϫ2) short interatomic π–π contacts of
acetate (Φ = 0.10) Ͼ 2·ethanol (Φ = 0.08) Ͼ 2 (guest-free) less than 3.6 Å in the pair of hosts for the guest-free host
(Φ = 0.06) ≈ 2·morpholine (Φ = 0.05).
and 2·morpholine (H/G, 1:1) crystals, respectively. The
average distance of the interatomic π–π contacts is ca.
3.51 Å for the guest-free compound and ca. 3.48 Å for
2·morpholine, which suggest strong π–π interactions. In the
crystal of 2·morpholine, the intramolecular hydrogen bonds
are observed between the host and the guest: the protons
of the imidazole ring of 2 point towards the oxygen atom
of morpholine [N(2)–H(1)···O(1) 172(2)°, N(2)···O(1)
2.881(6) Å].
Relation between Solid-State Fluorescence Properties and
X-ray Crystal Structures of Various Clathrate Compounds
of 2
To understand the enclathrated guest effects on the fluo-
rescence properties of the crystal, the crystal structures of
the guest-free and guest-inclusion compounds were deter-
mined by X-ray diffraction analysis.
Figures 4–8 show the X-ray crystal structures of the
guest-free and guest-inclusion compounds. The tautomeric
forms (A and B) of the imidazole ring of host 2 in the crys-
talline state changed depending on the enclathrated guest
molecules. Host 2 adopts tautomeric form A in the crystals
of 2·morpholine and 2·ethanol and form B in the crystals
of the guest-free host and 2·1,4-dioxane. Interestingly, in the
crystal of 2·ethyl acetate, there are two crystallographically
independent host molecules; one is form A, and the other
is form B. These results indicate that host 2 can include
various guest molecules by changing the tautomeric form
of the imidazole ring. The torsion angles between the naph-
thoimidazole plane and the p-cyanophenyl group are 0.5–
10° for all the compounds, which shows that the two rings
are coplanar. In contrast, the p-diethylaminophenyl groups
are twisted from the naphthoimidazole plane by about 50–
70° for all the compounds.
Figures 4 and 5 show the molecular packing structure for
the guest-free host and 2·morpholine (H/G, 1:1) crystals,
respectively. Both crystals are built up by the π-stacking ar-
rangements between the naphthoimidazole rings and the p-
Figure 5. Crystal structure of 2·morpholine: (a) a stereoview of the
molecular packing structure; (b) schematic structure; (c) top view
of the pairs of fluorophores.
In contrast, the crystal of 2·ethanol (H/G, 1:1) is made
up by the stacking arrangements that avoid short contacts
between the chromophores (Figure 6). There are 4 (= 2ϫ2)
short interatomic contacts of less than 3.6 Å between the
host molecules (Figure 6c). The average distance of the in-
teratomic π–π contacts is ca. 3.52 Å, which is a long dis-
tance in comparison to those of the guest-free host and
2·morpholine. A 1D chain ranging alternately host and
guest (···H···G···H···) is formed through intermolecular hy-
drogen bonding between the hydroxy group of the ethanol
molecule and the imidazole ring of the host molecule; the
proton of an imidazole ring of the host is directed towards
the oxygen atom of the guest [N(2)–H(1)···O(1) 159(4)°,
Figure 4. Crystal structure of 2: (a) a stereoview of the molecular
packing structure; (b) schematic structure; (c) top view of the pairs
of fluorophores.
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Solid-State Fluorescence Changes upon Inclusion of Organic Solvent Molecules
N(2)···O(1) 2.844(7) Å] and the hydroxy proton of the guest form B is directed towards the carbonyl oxygen atom of the
is directed towards an imino nitrogen atom of another guest molecule [N(1)–H(1)···O(1) 177(4)°, N(1)···O(1)
host molecule [O(1)–H(25)···N(1) 172(6)°, O(1)···N(1) 2.908(5) Å]. Furthermore, the neighbouring hosts with
2.952(6) Å], as shown in Figure 6b.
form A and form B are connected by an intermolecular
hydrogen bond between the proton of the imidazole ring
and the cyano nitrogen atom [N(6)–H(25)···N(3) 161(4)°,
N(6)···N(3) 3.027(7) Å].
Figure 6. Crystal structure of 2·ethanol: (a) a stereoview of the mo-
lecular packing structure; (b) schematic structure; (c) top view of
the pairs of fluorophores.
Figure 7 shows the molecular packing structure for the
crystal of 2·ethyl acetate (H/G, 2:1). The crystal is made up
of two types of stacking arrangements. One arrangement
involves π stacking between the hosts with form B (Fig-
ure 7b,c: I) or form A (Figure 7b,d: II), and the other ar-
rangement involves π stacking between the host with form
A and the host with form B (Figure 7b,e: III): the former
involves π stacking between the naphthoimidazole π planes
containing the p-cyanophenyl moiety, and the latter in-
Figure 7. Crystal structure of 2·ethyl acetate: (a) a stereoview of
the molecular packing structure; (b) schematic structure; (c) top
view of the pairs of fluorophores with form B (stacking I); (d) with
form A (stacking II); (e) π stacking between the host with form A
and the host with form B (stacking III).
Figure 8 shows the molecular packing structure for the
volves π stacking between the imidazole rings containing crystal of 2·1,4-dioxane (H/G, 2:1). The crystal is made up
the p-cyanophenyl moiety. There are 18, 10 and 15 short of two types of stacking arrangements that avoid short con-
interatomic contacts of less than 3.6 Å, respectively. The tacts between the chromophores. There are eight (Figure 8c:
average distance of the interatomic π–π contacts is ca. 3.53, I) and four (Figure 8d: II) short interatomic contacts of less
3.52 and 3.52 Å, respectively, which is a long distance in than 3.6 Å, and the average distance of the interatomic π–
comparison with those of the guest-free host and π contacts is ca. 3.54 and 3.57 Å, respectively, which is a
2·morpholine and almost the same as that of 2·ethanol. The large distance in comparison with those of 2·morpholine,
enclathrated ethyl acetate molecule is bound to one host 2·ethanol and 2·ethyl acetate. The enclathrated 1,4-dioxane
molecule through an intermolecular hydrogen bond, in molecule is tightly bound to two host molecules by two
which the proton of the imidazole ring of the host with intermolecular hydrogen bonds, in which the proton of the
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Y. Ooyama, S. Nagano, M. Okamura, K. Yoshida
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imidazole ring of the host is directed towards the oxygen guest (···H···G···H···) was only observed in 2·ethanol, which
atom of the guest [N(1)–H(1)···O(1) 172(8)°, N(1)···O(1) is a principal factor leading to fluorescence quenching in
2.91(1) Å], which may stabilize the crystal of 2·1,4-dioxane: the solid state. Therefore, it is confirmed from these data
the guest release temperature of 2·1,4-dioxane is consider- that the crystal of 2·1,4-dioxane exhibits comparatively
ably higher than those of the others guest-inclusion crystals strong fluorescent intensity because of the destruction of
(Table 1).
the π–π interactions and no continuous intermolecular hy-
drogen bonding between hosts in comparison with the cases
of 2·morpholine, 2·ethanol and 2·ethyl acetate.
Conclusions
It was found that fluorophore 2 can include various guest
molecules in the crystalline state by changing the tauto-
meric form of the imidazole ring. Solid-state fluorescence
enhancement and a blueshift in the absorption and fluores-
cence wavelength maxima are observed depending on the
enclathrated guest molecules. From comparison of the X-
ray crystal structures of the guest-free and several clathrate
compounds, we concluded that the differences in the de-
struction of the host–host π–π interactions by enclathration
of the guest molecules are reflected in the solid-state fluo-
rescence intensity and the fluorescence wavelength maxima
of the crystals. Furthermore, it was found that the existence
of continuous intermolecular hydrogen bonds ranging alter-
nately fluorescent host and guest (···H···G···H···) lead to a
strong solid-state fluorescence quenching behaviour. Thus,
new useful information concerning the solid-state fluores-
cence of fluorescent organic hosts has been obtained.
Experimental Section
General: Elemental analyses were measured with a Perkin–Elmer
2400 II CHN analyzer. IR spectra were recorded with a JASCO
FT/IR-5300 spectrophotometer for samples in KBr pellet form.
Thermogravimetric (TG) and differential thermal analysis (DTA)
spectra were performed with a Rigaku TG 8120. Single-crystal X-
ray diffraction was performed with
a Rigaku AFC7S dif-
fractometer. Absorption spectra were observed with a JASCO U-
best30 spectrophotometer and fluorescence spectra were measured
with a JASCO FP-777 spectrophotometer. The fluorescence quan-
tum yields (Φ) in benzene were determined by using 9,10-diphenyl-
anthracene (Φ = 0.67, λex = 357 nm)[15] in benzene as the standard.
The solid-state fluorescence quantum yields (Φ) were determined
by using a calibrated integrating sphere system (λex = 325 nm). For
the measurement of the solid-state fluorescence excitation and
emission spectra of the crystals, a Jasco FP-1060 attachment was
used. 1H NMR spectra were recorded with a JNM-LA-400
(400 MHz) FT NMR spectrometer with tetramethylsilane (TMS)
as an internal standard.
Figure 8. Crystal structure of 2·1,4-dioxane: (a) a stereoview of the
molecular packing structure; (b) schematic structure; (c) (stacking
I) and (d) (stacking II) top view of the π stacking between the
fluorophores.
On the basis of the solid-state photophysical data and
the crystal structures of the guest-free and guest-inclusion
compounds, we discuss the effects of the enclathrated guest
on the solid-state photophysical properties of the clathrate
compounds. A comparison of the above five crystal struc-
tures shows that the strength of the π–π interactions be-
tween the fluorophores decreases in the following order: 2
(guest-free) ≈ 2·morpholine Ͼ 2·ethyl acetate Ͼ 2·ethanol
Ͼ 2·1,4-dioxane. Strong intermolecular π–π interactions be-
tween the fluorophores induce a large redshift in the ab-
sorption and fluorescence maxima and an intense fluores-
cence quenching in the solid state.[2,3,5,9] However, the solid-
state fluorescence intensity of 2·ethanol is weaker than that
of 2·ethyl acetate. It is considered that the continuous inter-
4-[4-(Diethylamino)phenyl]-[1,2]naphthoquinone (1): A solution of
sodium 1,2-naphthoquinone-4-sulfonate (10.0 g, 38.4 mmol), N,N-
diethylaniline (8.6 g, 57.6 mmol) and NiCl2·4H2O (9.56 g,
38.4 mmol) in CH3COOH/H2O (4:1, 200 mL) was stirred at room
temperature for 7 d. The reaction mixture was poured into water.
The solution was neutralized with aqueous Na2CO3 and extracted
with CH2Cl2. The organic extract was washed with water, and the
solvent was evaporated. The residue was chromatographed on silica
1
gel (CH2Cl2) to give 1 (6.78 g, 58%). M.p. 116–118 °C. H NMR
molecular hydrogen bonding ranging alternately host and (400 MHz, [D6]DMSO, TMS): δ = 1.13 (t, 6 H), 3.42 (m, 4 H),
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Solid-State Fluorescence Changes upon Inclusion of Organic Solvent Molecules
6.29 (s, 1 H), 6.79 (d, J = 8.7 Hz, 2 H), 6.39 (d, J = 8.7 Hz, 2 H),
ular Structure Corporation. CCDC-692724 (for 2), -692725 (for
7.61 (m, 1 H), 7.72 (m, 1 H), 7.72 (m, 2 H), 8.03 (m, 1 H) ppm.
2·morpholine), -692726 (for 2·ethyl acetate), -692727 (for 2·ethanol)
and -692728 (for 2·1,4-dioxane) contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
IR (KBr): ν = 1650, 1603 cm–1. MS: m/z (%) = 305 (100) [M]+.
˜
2-(4-Cyanophenyl)-5-[4-(diethylamino)phenyl]-3H-imidazo[4,5-a]-
naphthalene (2): A solution of 1 (5.63 g, 18.45 mmol), p-cyanobenz-
aldehyde (2.42 g, 18.5 mmol) and ammonium acetate (22.75 g,
0.3 mol) in acetic acid (170 mL) was stirred at 80 °C for 1 h. The
reaction mixture was neutralized with aqueous Na2CO3 and ex-
tracted with CH2Cl2. The organic extract was washed with water,
and the solvent was evaporated. The residue was chromatographed
on silica gel (CH2Cl2/ethyl acetate, 10: 1) to give 2 (5.75 g, 75%).
M.p. 244–247 °C. 1H NMR (400 MHz, [D6]DMSO, TMS): δ = 1.15
(t, 6 H), 3.34 (m, 4 H), 6.80 (d, J = 8.5 Hz, 2 H), 7.31 (d, J =
8.3 Hz, 2 H), 7.46 (m, 1 H), 7.54 (s, 1 H), 7.65 (m, 1 H), 7.96 (d, J
= 8.3 Hz, 1 H), 8.04 (d, J = 8.1 Hz, 2 H), 8.41 (d, J = 7.8 Hz, 2 H),
Crystal of 2: The transmission factors ranged from 0.98 to 1.00.
The crystal structure was solved by direct methods by using SIR
92.[17] The structures were expanded by using Fourier techniques.[18]
Non-hydrogen atoms were refined anisotropically. Some hydrogen
atoms were refined isotropically, the rest were fixed geometrically
and not refined. Crystallographic data: C28H34N4, M = 416.52, mo-
noclinic, a = 11.665(2) Å, b = 12.531(2) Å, c = 15.743(2) Å, β =
107.38(1)°, U = 2196.2(6) Å3, ρcalcd. = 1.260 gcm–3, T = 296.2 K,
space group P21/a (no.14), Z = 4, µ(Mo-Kα) = 0.76 cm–1, 4078 re-
flections measured, 3868 unique (Rint = 0.023), which were used in
all calculations. The final R indices [IϾ2σ(I)], R1 = 0.053, wR(F2)
= 0.1185.
8.58 (d, J = 6.6 Hz, 1 H) ppm. IR (KBr): ν = 2220 cm–1. C H N
˜
28 34
4
(426.60): calcd. C 80.74, H 5.81, N 13.45; found C 80.88, H 5.61,
N 13.68.
Crystal of 2·Morpholine: The transmission factors ranged from 0.00
to 1.00. The crystal structure was solved by direct methods by using
SIR 92.[17] The structures were expanded by using Fourier tech-
niques.[18] Non-hydrogen atoms were refined anisotropically. Some
hydrogen atoms were refined isotropically, the rest were fixed geo-
metrically and not refined. Crystallographic data: C32H33N5O, M
= 503.65, triclinic, a = 10.786(3) Å, b = 16.031(7) Å, c = 8.461(2) Å,
Preparation of Guest-Inclusion Crystals: Host compound 2 was dis-
solved with heating in the respective guest solvent. The solution
was filtered and kept for a few days at room temperature. The crys-
tals that formed were collected by filtration. The host (H)/guest (G)
stoichiometric ratio of the inclusion compounds was determined
1
by H NMR integration and C, H, N analysis.
2 (Guest-Free): Host 2 (500 mg) was dissolved by warming in nitro-
methane (26 mL), and the resulting solution was allowed to stand
at room temperature. The crystals (orange-yellow, prism, 340 mg)
were collected and dried on the filter paper.
α = 98.18(3)°, β = 90.26(2)°, γ = 74.17(2)°, U = 1392.3(8) Å3, ρcalcd.
–3
¯
= 1.201 gcm , T = 296.2 K, space group P1 (no.2), Z = 2, µ(Mo-
Kα) = 0.75 cm–1, 5081 reflections measured, 5078 unique (Rint
=
0.026), which were used in all calculations. The final R indices
[IϾ2σ(I)], R1 = 0.0638, wR(F2) = 0.1406.
2·Morpholine (H/G, 1:1): Host 2 (200 mg) was dissolved by warm-
ing in morpholine (3 mL), and the resulting solution was allowed
to stand at room temperature. The crystals (yellow, prism, 184 mg)
were collected and dried on the filter paper. C32H33N5O (503.65):
calcd. C 76.31, H 6.60, N 13.91; found C 76.02, H 6.97, N 14.23.
Crystal of 2·Ethyl Acetate: The transmission factors ranged from
0.95 to 1.00. The crystal structure was solved by direct methods by
using SAPI 90.[19] The structures were expanded by using Fourier
techniques.[18] Non-hydrogen atoms were refined anisotropically.
Some hydrogen atoms were refined isotropically, the rest were fixed
geometrically and not refined. Crystallographic data: C60H56N8O2,
M = 921.15, triclinic, a = 13.153(2) Å, b = 18.937(2) Å, c =
2·Ethyl Acetate (H/G, 2:1): Host 2 (100 mg) was dissolved by
warming in ethyl acetate (2 mL), and the resulting solution was
allowed to stand at room temperature. The crystals (yellow, needle,
70 mg) were collected and dried on the filter paper. C60H56N8O2
(921.15): calcd. C 78.23, H 6.13, N 12.16; found C 78.43, H 6.17,
N 12.32.
11.983(2) Å, α = 100.55(1)°, β = 114.918(10)°, γ = 101.35(1)°, U =
–3
2532.5(7) Å3, ρcalcd. = 1.208 gcm , T = 296.2 K, space group P1
¯
(no.2), Z = 2, µ(Mo-Kα) = 0.75 cm–1, 9340 reflections measured,
9336 unique (Rint = 0.018), which were used in all calculations. The
final R indices [IϾ2σ(I)], R1 = 0.0727, wR(F2) = 0.1699.
2·Ethanol (H/G, 1:1): Host 2 (420 mg) was dissolved by warming
in ethanol (18 mL), and the resulting solution was allowed to stand
at room temperature. The crystals (yellow, leaflet, 322 mg) were
collected and dried on the filter paper. C30H30N4O (462.59): calcd.
C 77.89, H 6.54, N 12.11; found C 77.60, H 6.24, N 11.92.
Crystal of 2·Ethanol: The transmission factors ranged from 0.93 to
1.00. The crystal structure was solved by direct methods by using
SAPI 91.[20] The structures were expanded by using Fourier tech-
niques.[18] Non-hydrogen atoms were refined anisotropically. Some
hydrogen atoms were refined isotropically, the rest were fixed geo-
metrically and not refined. Crystallographic data: C30H30N4O, M
= 462.59, triclinic, a = 10.364(3) Å, b = 17.680(4) Å, c = 7.444(3) Å,
α = 98.23(3)°, β = 107.68(3)°, γ = 98.72(2)°, U = 1258.2(8) Å3, ρcalcd.
2·1,4-Dioxane (H/G, 2:1): Host 2 (300 mg) was dissolved by warm-
ing in 1,4-dioxane (4 mL), and the resulting solution was allowed
to stand at room temperature. The crystals (yellow, needle-like,
188 mg) were collected and dried on the filter paper. C60H56N8O2
(921.15): calcd. C 78.23, H 6.13, N 12.16; found C 78.39, H 6.05,
N 12.26.
–3
¯
= 1.221 gcm , T = 296.2 K, space group P1 (no.2), Z = 2, µ(Mo-
Kα) = 0.75 cm–1, 4801 reflections measured, 4431 unique (Rint
=
0.049), which were used in all calculations. The final R indices
X-ray Crystallographic Studies: The reflection data were collected
at 23Ϯ1 °C with a Rigaku AFC7S four-circle diffractometer by
2θ–ω scan technique and by using graphite-monochromated Mo-
Kα (λ = 0.71069 Å) radiation at 50 kV and 30 mA. In all cases, the
data were corrected for Lorentz and polarization effects. A correc-
tion for secondary extinction was applied. The reflection intensities
were monitored by three standard reflections for every 150 reflec-
tions. An empirical absorption correction based on azimuthal scans
of several reflections was applied. All calculations were performed
by using the teXsan[16] crystallographic software package of Molec-
[IϾ2σ(I)], R1 = 0.0716, wR(F2) = 0.1760.
Crystal of 2·1,4-Dioxane: The transmission factors ranged from
0.88 to 1.00. The crystal structure was solved by direct methods by
using SIR 92.[17] The structures were expanded by using Fourier
techniques.[18] Non-hydrogen atoms were refined anisotropically.
Some hydrogen atoms were refined isotropically, the rest were fixed
geometrically and not refined. Crystallographic data: C30H28N4O,
M = 460.58, triclinic, a = 9.36(1) Å, b = 19.14(1) Å, c = 7.355(3) Å,
α = 91.70(5)°, β = 107.67(6)°, γ = 86.17(8)°, U = 1253(1) Å3, ρcalcd.
Eur. J. Org. Chem. 2008, 5899–5906
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5905

Y. Ooyama, S. Nagano, M. Okamura, K. Yoshida
FULL PAPER
–3
¯
[4] Y. Mizobe, N. Tohnai, M. Miyata, Y. Hasegawa, Chem. Com-
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= 1.221 gcm , T = 296.2 K, space group P1 (no.2), Z = 2, µ(Mo-
Kα) = 0.75 cm–1, 4705 reflections measured, 4699 unique (Rint
=
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Acknowledgments
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.
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Published Online: November 5, 2008
5906
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 5899–5906