Photophysical properties of phenanthro[9,10-d]imidazole-type fluorescent hosts upon inclusion of organic solvent molecules

Article abstract of DOI:10.1016/j.tet.2009.08.027

The crystal of phenanthro[9,10-d]imidazole-type fluorescent clathrate host (1) exhibits fluorescence enhancement behavior with a blue-shift of the emission maximum upon enclathration of organic solvent molecules such as 1-butanol and morpholine, whereas t

Full text of DOI:10.1016/j.tet.2009.08.027

Tetrahedron 65 (2009) 8336–8343
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Tetrahedron
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Photophysical properties of phenanthro[9,10-d]imidazole-type fluorescent hosts
upon inclusion of organic solvent molecules
*
*
Yousuke Ooyama , Hironori Kumaoka, Kazuki Uwada, 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 23 July 2009
Received in revised form 10 August 2009
Accepted 11 August 2009
Available online 14 August 2009
The crystal of phenanthro[9,10-d]imidazole-type fluorescent clathrate host (1) exhibits fluorescence
enhancement behavior with a blue-shift of the emission maximum upon enclathration of organic solvent
molecules such as 1-butanol and morpholine, whereas the crystal of 1 exhibits fluorescence enhance-
ment behavior with a red-shift of the emission maximum upon enclathration of carboxylic acid such as
acetic acid and propionic acid. The crystal structures of the guest-free and the guest-inclusion com-
pounds of 1 have been determined by X-ray analysis. On the bases of the spectral data and the crystal
structures, the effects of the enclathrated guest molecule on the solid-state photophysical properties of
the guest-inclusion compounds are discussed.
Keywords:
Solid-state fluorescence
Fluorescent clathrate
Crystal structures
Dyes
Ó 2009 Elsevier Ltd. All rights reserved.
Optical property
1. Introduction
a phenanthro[9,10-d]imidazole-type fluorescent clathrate host,
2-[4-(diphenylamino)phenyl]-1H-phenanthro[9,10-d]imidazole (1)
Organic fluorescent hosts, which exhibit sensitive color and
fluorescence intensity changes upon formation of host/guest-in-
clusion complexes in the crystalline state, can be one of the most
promising materials for the construction of desirable solid-state
fluorescent system.1–4 Some groups have reported that the crystal
of fluorescent host exhibits fluorescence enhancement behavior
upon enclathration of organic solvent molecules. The fluorescence
enhancement is greatly dependent on the identity of the enclath-
rated guest molecules. From the comparison of the X-ray crystal
structures of the guest-free and several clathrate compounds, it
with imidazole ring and diphenylamino group (Scheme 1). We
found that the crystal of 1 exhibits fluorescence enhancement be-
havior with a blue-shift of the emission maximum upon enclath-
ration of organic solvent molecules such as 1-butanol and
morpholine, whereas the crystal of 1 exhibits fluorescence en-
hancement behavior with a red shift of the emission maximum
upon enclathration of carboxylic acid such as acetic acid and pro-
pionic acid. Our results indicated that the modulation of the solid-
state fluorescence properties should be achieved by a combination
of the fluorescent clathrate host and guest molecule. In this paper,
on the bases of the spectral data and the X-ray crystal structures of
guest-inclusion compounds, the effects of the enclathrated guest
molecules on the solid-state photophysical properties of the
clathrate compounds are discussed.
was concluded that the destructions of the
p–p interactions or
continuous intermolecular hydrogen bonding between fluorescent
hosts by the enclathrated guest molecules are the main reason for
the guest-dependent fluorescence enhancement of the crystals.2–4
As the results, the improvement of solid-state fluorescence in-
tensity has been achieved. However, the modulation of solid-state
fluorescence wavelength controlled by enclathrated guest is not yet
successfully established.
For the purpose of controlling solid-state fluorescence wave-
length by clathrate formation, we have designed and synthesized
* 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).
Scheme 1. Chemical structure of the phenanthro[9,10-d]imidazole-type fluorescent
clathrate host (1).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.08.027

Y. Ooyama et al. / Tetrahedron 65 (2009) 8336–8343
8337
Table 1
2. Results and discussion
Spectroscopic properties of 1 in solution
/nma
[
3max/dm3 molꢀ1 cmꢀ1
]
lflmax/nmb
401, 417sh 0.73
Fc
SSd Dlmax
abs
2.1. Spectroscopic properties of 1 in solution
Solvent
l
max
1,4-Dioxane 365 (40,500), 381 (38,700)sh
36
52
50
52
Ethanol
1-Butanol
365 (38,300), 373 (36,300)sh
366 (38,700), 373 (36,400)sh
417
416
419
502
0.82
0.80
0.52
The absorption and fluorescence spectra of 1 in 1,4-dioxane,
ethanol, 1-butanol, morpholine, and acetic acid are shown in
Figure 1, and the absorption and fluorescence spectral data sum-
marized in Table 1. The fluorophore 1 exhibits an absorption band
at around 365 nm with a shoulder at around 380 nm in both 1,4-
dioxane and morpholine. The corresponding fluorescence band
was observed at 401 nm with a shoulder at 417 nm in 1,4-dioxane
and at 419 nm in morpholine. On the other hand, in both ethanol
and 1-butanol the fluorophore 1 exhibits an absorption band at
around 365 nm with a shoulder at 373 nm and a fluorescence
band at around 417 nm. Interestingly, in acetic acid, the absorption
band of 1 appeared at around 384 nm, which was red-shifted by
19 nm compared with that observed in 1,4-dioxane. The corre-
sponding fluorescence maximum was observed at around 502 nm,
which was red-shifted by 101 nm compared with that in 1,4-di-
oxane. The absorption and fluorescence maxima of 2-(40-(N,N-
dimethylamino)phenyl)benzimidazole in acidic solution were
red-shifted compared with that in neutral solution, which has
been reported by Dogra et al.5 It was elucidated that the red-shifts
Morpholine 367 (44,100), 383 (40,700)sh
Acetic acid
384 (42,300)
0.32 118
a
1.0ꢁ10ꢀ5 M.
b
1.0ꢁ10ꢀ6 M.
c
The
F values were determined by using a calibrated integrating sphere system
(
lex¼363 nm).
d
Stokes shift value.
are induced by the protonation to an imino nitrogen atom of
imidazole ring. In our case, it was considered that the observed
red-shifts of 1 in acetic acid are caused by the protonation to an
imino nitrogen atom of imidazole ring, as shown in Scheme 2. The
fluorescence quantum yield (F) of 1 in 1,4-dioxane, ethanol, 1-
butanol, morpholine, and acetic acid are 0.73, 0.82, 0.80, 0.52, and
0.32, respectively.
2.2. Semi-empirical MO calculations (AM1, CNDO/S)
In order to understand the photophysical properties of 2-[4-
(diphenylamino)phenyl]-1H-phenanthro[9,10-d]imidazole (1), we
have carried out semi-empirical molecular orbital (MO) cal-
culations of 1 by the CNDO/S method6 after geometrical opti-
mizations MOPAC/AM1 method.7 Furthermore, we estimated the
photophysical properties for 1Hþ with the protonated imidazole
ring, because it was assumed that the imino nitrogen atom of
imidazole ring is protonated in acidic solution. The optimized
geometry of 1 shows that the bond lengths between two nitro-
gens (N-1 and N-2) and C-2 in imidazole ring are 1.36 Å and
1.41 Å, respectively (Fig. 2). This result shows that the differences
between the two lengths for 1 are attributed to the C–N single
bond and the C]N double bond of imidazole ring. On the other
hand, the two bond lengths for 1Hþ are both 1.39 Å, which re-
veals the contribution of the resonance structure 1Hþ(I) as
shown in Scheme 2. The bond lengths between C-3 of phenyl
group and C-2 in imidazole ring are 1.46 Å for 1 and 1.44 Å for
1Hþ, and the bond lengths between C-1 of phenyl group and the
nitrogen atom (N-3) of diphenylamino group are 1.41 Å for 1 and
1.38 Å for 1Hþ. The two bond lengths of 1Hþ are shorter than
those of 1, which indicates the contribution of the resonance
structure 1Hþ(II) (Scheme 1). The calculated absorption wave-
lengths and the nature of the transition of the absorption bands
are summarized in Table 2. The calculated absorption wave-
lengths and the oscillator strength values of 1 and 1Hþ are
comparable with the observed spectra in 1,4-dioxane and acetic
acid, respectively; the calculated absorption wavelength of 1Hþ is
shifted to longer wavelength compared to that of 1, which is in
good agreement with the experimental data in 1,4-dioxane and
acetic acid. Therefore, the red-shift of 1 in acetic acid was
explained by strong resonance interaction of the diphenylamino
group with the protonated imidazole ring, leading to the reso-
nance hybrid of 1Hþ(I) and 1Hþ(II).
2.3. Preparation of guest-inclusion crystals
The guest-free crystal of 1 was obtained by recrystallization of
it from acetonitrile. The preparation of guest-inclusion crystals
was attempted by recrystallization from the respective guest–
solvent or guest-containing solvents. We have found that the host
1 yields inclusion compounds in stoichiometric ratios with acetic
acid, propionic acid, 1-butanol, and morpholine. Interestingly, the
Figure 1. (a) Absorption and (b) fluorescence spectra of 1 in 1,4-dioxane, ethanol,
1-butanol, morpholine, and acetic acid.

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Y. Ooyama et al. / Tetrahedron 65 (2009) 8336–8343
Scheme 2.
Table 2
host 1 formed inclusion crystals with both morpholine and water
by recrystallization from a mixture of morpholine and water. The
characteristics of the guest-free and various guest-inclusion
crystals obtained by co-crystallization of 1 from various solutions
are summarized in Table 3. Compared to milk-white of the guest-
free crystal, the color of the guest-inclusion crystals varied from
white to yellow and a dramatic fluorescence enhancement was
observed.
Calculated absorption spectra for 1 and 1Hþ
Species
m
/Da
Absorption (calcd)
CI componentc
Dm/Dd
lmax/nm
fb
1
4.28
4.49
373
452
0.82
0.85
HOMO/LUMO (77%)
HOMO/LUMO (85%)
2.98
4.68
1Hþ
a
The values of the dipole moment in the ground state.
Oscillator strength.
The transition is shown by an arrow from one orbital to another, followed by its
b
c
percentage CI (configuration interaction) component.
d
The values of the difference in the dipole moment between the excited and the
ground states.
Table 3
Host–guest molar ratio, crystal form, and crystal color of the guest-free and the
guest-inclusion crystals of 1
Host Guest
Host/guest (molar ratio) Crystal form Crystal color
1
None
Acetic acid
Propionic acid 1:2
1-Butanol
1:0
1:1
Needle
Prism
Prism
Prism
Prism
Milk-white
Yellow
Yellow
Yellowish white
White
1:1
2:1:2H2O
Morpholine
2.4. Solid-state fluorescence change upon formation of guest-
inclusion crystals
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 (Fig. 3). The solid-state photophysical changes are
greatly dependent on the identity of the enclathrated guest mole-
cules. Compared to the guest-free crystal, the excitation and emission
maxima of the 1-butanol- and morpholine-inclusion crystals exhibit
a blue-shift, whereas those of acetic acid- and propionic acid-in-
clusion crystals exhibit a red shift. The fluorescence intensities of all
the guest-inclusion crystals are enhanced to various degrees
depending on the identity of the enclathrated guest molecules. The
416 nm band observed in the excitation spectrum of the guest-free
crystals is blue-shifted to 413 nm and 398 nm in those of the 1-bu-
tanol- and morpholine-inclusion crystals, respectively, or red-shifted
to 447 nm and 440 nm in those of the acetic acid- and propionic acid-
inclusion crystals, respectively. The guest-free host crystal exhibits
relatively weak fluorescence with emission maximum at 460 nm,
Figure 2. Calculated electron density changes accompanying the first electronic ex-
citation of 1 and 1Hþ. The black and white lobes signify decrease and increase in
electron density accompanying the electronic transition. Their areas indicate the
magnitude of the electron density change.

Y. Ooyama et al. / Tetrahedron 65 (2009) 8336–8343
8339
while the guest-inclusion crystals exhibit much stronger fluores-
cence intensity with the blue-shift of emission maximum to 459 nm
and 432 nm in those of the 1-butanol- and morpholine-inclusion
crystals, respectively, or the red-shift of emission maximum to
483 nm and 469 nm in those of the acetic acid- and propionic acid-
inclusion crystals, respectively. Relative fluorescence intensity (RFI),
which was determined by considering the fluorescence intensity of
crystal 1 as 1.0, increases in the following order: 1$acetic acid
(RFI¼1.1)<1$1-butanol (RFI¼2.7)<1$morpholine (RFI¼3.0)<1$pro-
pionic acid (RFI¼4.6). These results indicate that the solid-state
photophysical changes upon enclathration of guest molecules reflect
strictly the changes inmolecular packinginduced by the enclathrated
guest molecules in the crystals.
The crystal of 1$acetic acid (H/G¼1:1) is made up by a hydrogen
bonded clusterunit composed of two hosts andtwo acetic acidguests
(Fig. 4a). The two hosts and two guests are alternately linked by four
NH/O hydrogen bonds to form a centrosymmetric ring, inwhich the
imidazole ring is protonated by the acetic acid proton (N(1)H(1)/
O(1) angle¼174ꢂ, N(1)/O(1) distance¼2.609(3) Å and N(2)H(2)/
O(2) angle¼169ꢂ, N(2)/O(2) distance¼2.767(3)) (Fig. 4b). Actually,
the two bond lengths between two nitrogens (N(1) and N(2)) and
C(15) in imidazole ring are 1.34 Å and 1.35 Å, respectively, which are
nearly the same. There are two styles of stacking overlap be-
p–p
tween host molecules. One is the p–p overlapping between
the phenanthroimidazole and p-(diphenylamino)phenyl parts in
theclusterunit(Fig. 4b: stackingI). Theotherisobserved betweenthe
neighboring cluster units, where the phenanthrene ring parts are
overlapping (Fig. 4c: stacking II). There are 15 and 22 short in-
teratomic
the interatomic
which suggest strong
p
–
p
contacts of less than 3.6 Å, and the average distance of
contacts is ca. 3.48 Å and 3.54 Å, respectively,
interactions between the host molecules.
p–p
p–p
Figure 3. (a) Solid-state excitation and (b) fluorescence spectra of the guest-free and the
guest-inclusion crystals of 1; (A) 1 (guest-free): lex¼415 nm, lem¼460 nm; (B) 1$acetic acid:
lex¼447 nm, lem¼483 nm; (C) 1$1-butanol: lex¼413 nm, lem¼459 nm; (D) 1$morpholine:
lex¼398 nm, lem¼432 nm; (E) 1$propionic acid: lex¼440 nm, lem¼469 nm.
Figure 4. Crystal structure of 1$acetic acid; (a) a stereoview of the molecular packing
structure, (b) top view of a cluster unit (stacking I), and (c) a top view between two
cluster units (stacking II). The circles represented in (b) and (c) show short interatomic
2.5. Relation between the solid-state fluorescence properties
and X-ray crystal structures of guest-inclusion compounds
p–p contacts of less than 3.6 Å.
To understand the enclathrated guest effects on the fluores-
cence properties of the crystal, the crystal structures of the acetic
acid-, 1-butanol-, and morpholine-inclusion compounds of 1 have
been determined by X-ray diffraction analysis.
Like the crystal of 1$acetic acid, the crystal of 1$1-butanol
(H/G¼1:1) is built up by the hydrogen bonded cluster unit composed
of two hosts and two 1-butanol guests (Fig. 5a). However, although

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Y. Ooyama et al. / Tetrahedron 65 (2009) 8336–8343
the two hosts and two guests are alternately linked by four NH/O
hydrogenbondsto form a centrosymmetric ring, the imidazole ringof
the host is not protonated by the 1-butanol proton, in contrast to the
crystal of 1$acetic acid. As shown in Figure 5b, the proton of the im-
idazole ring of host is directing toward the oxygen of the guest
(N(1)H(1)/O(1) angle¼160(1)ꢂ, N(1)/O(1) distance¼2.871(3) Å)
and the hydroxyl proton of the guest is directing toward an imino
crystal of 1$morpholine is built up by the hydrogen bonded cluster
unit composed of two crystallographically independent host mol-
ecules and two water molecules, in which the imidazole ring of the
host is not protonated by the water molecule similar to the crystal
of 1$1-butanol. As shown in Figure 6b, in the cluster unit, the proton
of the imidazole ring of host is directing toward the oxygen of the
water molecule (N(1)H(1)/O(1) angle¼166ꢂ, N(1)/O(1) dis-
tance¼2.80(1) Å) and the hydroxyl proton of the water molecule is
directing toward an imino nitrogen of another host (O(1)H(48)/
N(5) angle¼172ꢂ, O(1)/N(5) distance¼3.04(1) Å). Thus, similar to
the crystal of 1$1-butanol, the bond lengths between two nitrogens
(N(1) and N(2)) and C(15) in imidazole ring are ca. 1.32 Å and ca.
1.37 Å, respectively. Interestingly, the morpholine molecule is
linked by a hydrogen bond to two water molecules in order to
connect the neighboring cluster units. Therefore, an continuous
intermolecular hydrogen bonding chain of (/H/H2O/G/H2O/)
is formed through two-type intermolecular hydrogen bonding
between morpholine molecule and two water molecules and the
above intermolecular hydrogen bonding between host and water
molecule in cluster unit; the proton of water molecule is directing
nitrogen of another host (O(1)H(2)/N(2)
*
angle¼166ꢂ, O(1)/N(2)
*
distance¼2.899(3) Å). The bond lengths between two nitrogens (N(1)
and N(2)) and C(15) in imidazole ring are 1.33 Å and 1.37 Å, re-
spectively, showing that the differences between the two lengths are
attributed to the C–N single bond and the C]N double bond of im-
idazole ring. Similar to the crystal of 1$acetic acid, there are two styles
of
lapping between the two hosts in the cluster unit (Fig. 5b: stacking I),
there are 17 short interatomic contacts of less than 3.6 Å, and the
average distance of the interatomic contacts is ca. 3.53 Å. On the
other hand, the overlapping of two hosts between the neigh-
boring cluster units in 1$1-butanol is smaller than that in1$acetic acid
(Fig. 5c: stacking II); there are 7 short interatomic contacts of less
than3.6 Å, andthe averagedistanceoftheinteratomic contactsis
ca. 3.47 Å, suggesting the reduction of the interactions between
p–p stacking overlap between host molecules. In the p–p over-
p–p
p–p
p–p
p–p
p–p
p–p
the host molecules in comparison with the crystal of 1$acetic acid.
Figure 5. Crystal structure of 1$1-butanol; (a) a stereoview of the molecular packing
structure, (b) top view of a cluster unit (stacking I), and (c) a top view between two
cluster units (stacking II). The circles represented in (b) and (c) show short interatomic
p–p contacts of less than 3.6 Å.
Figure 6. Crystal structure of 1$morpholine with 2H2O; (a) a stereoview of the mo-
lecular packing structure, (b) top view of a cluster unit (stacking I), and (c) a top view
between two cluster units (stacking II). The circles represented in (b) and (c) show
In the crystal of 1$morpholine (H/G/H2O¼2:1:2), there are two
crystallographically independent host molecules (Fig. 6a). The
short interatomic
p–p contacts of less than 3.6 Å.

Y. Ooyama et al. / Tetrahedron 65 (2009) 8336–8343
8341
toward the nitrogen of morpholine (O(2)H(49)/N(7) angle¼119ꢂ,
O(2)/N(7) distance¼2.76(1) Å) and the proton of water molecule
in another cluster unit is directing toward the oxygen of morpho-
line (O(1)H(47)/O(3) angle¼171ꢂ, O(1)/O(3) distance¼2.81(1) Å).
fluorescence enhancement behavior with a blue-shift of the emis-
sion maximum upon enclathration of organic solvent molecules
such as 1-butanol and morpholine, whereas the crystal of 1 exhibits
fluorescence enhancement behavior with a red-shift of the emis-
sion maximum upon enclathration of carboxylic acid such as acetic
acid and propionic acid. Our results indicated that the modulation
of the solid-state fluorescence properties should be achieved by
a combination of the fluorescent clathrate host and guest molecule;
the electronic structure of fluorescent host in the solid state and the
crystal structure are controlled by enclathration of the guests such
as neutral, acidic, and basic molecules.
There are two styles of
cules. In the
unit (Fig. 6b: stacking I), there are 10 short interatomic
tacts of less than 3.6 Å, and the average distance of the interatomic
contacts is ca. 3.53 Å. On the other hand, in the over-
lapping of two host between the neighboring cluster units (Fig. 6c:
stacking II), there are five short interatomic contacts of less
than 3.6 Å and the average distance of the interatomic contacts
is ca. 3.47 Å, suggesting the reduction of the interactions be-
p–p stacking overlap between host mole-
p
–p
overlapping between the two hosts in the cluster
con-
p–p
p–
p
p–p
p–p
p–p
p
–p
4. Experimental section
4.1. General procedure
tween the host molecules in comparison with the crystals of
1$acetic acid and 1$1-butanol.
On the bases of the solid-state photophysical data and the
crystal structures of the guest-inclusion compounds, we discuss
the effects of the enclathrated guest on the solid-state photo-
physical properties of the clathrate compounds. So far, it has been
Elemental analyses were measured with a Perkin Elmer 2400 II
CHN analyzer. IR spectra were recorded on a JASCO FT/IR-5300
spectrophotometer for samples in KBr pellet form. Single-crystal X-
ray diffraction was performed on Rigaku AFC7S diffractometer.
Absorption spectra were observed with a JASCO U-best30 spec-
trophotometer and fluorescence spectra were measured with
a JASCO FP-777 spectrophotometer. The fluorescence quantum
clarified that strong intermolecular
p–p interactions or continu-
ous intermolecular hydrogen bonding between neighboring fluo-
rophores induce the large red-shift of the absorption and
fluorescence maxima and an intense fluorescence quenching in
the solid state.2–4,8 The wavelengths of the fluorescence excitation
and emission maxima of guest-free crystal 1 are red-shifted by
50 nm and 59 nm compared with those of 1 in 1,4-dioxane, re-
spectively. Unfortunately, although it is difficult to obtain sufficient
sizes of single crystals for guest-free compound of 1 to carry out
the X-ray structural analysis, the weak solid-state fluorescence
intensity of guest-free crystal 1 is responsible for the above rea-
sons. A comparison of the above three crystal structures shows
yields (
F
) were determined by a Hamamatsu C9920-01 equipped
calibrated integrating sphere system
with CCD by using
a
(
lex¼363 nm). For the measurement of the solid-state fluorescence
excitation and emission spectra of the crystals, Jasco FP-1060 at-
tachment was used. 1H NMR spectra were recorded on a JNM-LA-
400 (400 MHz) FT NMR spectrometer with tetramethylsilane (TMS)
as an internal standard.
that the strength of the
rophores decrease in the following order: 1$acetic acid-
>1$butanol>1$morpholine. These results confirm that the
p
–
p
interactions between the fluo-
4.2. Synthesis of 2-[4-(diphenylamino)phenyl]-1H-
phenanthro[9,10-d]imidazole (1)
differences in the destruction of the host–host
p
–
p
interactions by
A solution of 9,10-phenanthrenequinone (1.54 g, 7.42 mmol),
p-diphenylaminobenzaldehyde (2.02 g, 7.40 mmol), and ammo-
nium acetate (9.14 g, 0.12 mol) in acetic acid (70 ml) was stirred at
110 ꢂC for 2 h. The reaction mixture was poured into ice-cold water.
The resulting precipitate was filtered, washed with water, and
dried. The residue was chromatographed on silica gel (CH2Cl2/ethyl
acetate¼10:1 as eluent) to give 1 (3.12 g, yield 91%) as an milk-
white powder; mp 310–313 ꢂC; 1H NMR (400 MHz, DMSO-d6, TMS)
enclathration of the guest molecules are reflected on the solid-
state fluorescence intensity of the crystals. On the other hand, in
our previous works,3 we have demonstrated that continuous in-
termolecular 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, whereas the continuous intermolecular hydrogen bonding of
(/H/G/G/) hardly contribute to quenching of the solid-state
fluorescence. The intermolecular hydrogen bonding chain of
(/H/H2O/G/H2O/) in the crystal of 1$morpholine is similar
to that of (/H/G/G/). Therefore, in the crystal of
d
¼7.10–7.14 (m, 8H), 7.35 (t, J¼7.07 Hz, 4H), 7.61 (t, J¼7.07 Hz, 2H),
7.71 (d, J¼7.07 Hz, 2H), 8.18 (d, J¼7.56 Hz, 2H), 8.53 (d, J¼7.81 Hz,
2H), 8.84 (d, J¼8.53 Hz, 2H), 7.54 (br, 1H, –NH); IR (KBr): ¼3083,
n
1591 cmꢀ1.Elemental analysis calcd (%) for C25H23N3: C, 85.87; H,
5.02; N, 9.10. Found: C, 86.06; H, 5.18; N. 9.37.
1$morpholine, the significant reductions of the
p–p interactions
between the host fluorophores by the enclathrated morpholine
molecule are the main reason for the dramatic fluorescence en-
hancement and the blue-shift of the absorption and fluorescence
maxima of the crystals. On the other hand, on the bases of the
absorption and fluorescence spectra of 1 in acetic acid, the semi-
empirical MO calculations and the X-ray crystal structure of
1$acetic acid, the protonation of the imidazole ring of host 1 in the
crystal of 1$acetic acid and 1$propionic acid would contribute to
a red-shift of the absorption and emission spectra of the crystals
because of an increase of intramolecular charge-transfer character
of the host fluorophore by strong resonance interaction of the
diphenylamino group with the protonated imidazole ring.
4.3. Preparation of guest-inclusion crystals
The host compound 1 was dissolved with heating in respective
guest–solvent. The solution was filtered and kept for a few days at
room temperature. The crystals that formed were collected by fil-
tration. The host (H)/guest (G) stoichiometric ratio of the inclusion
compounds was determined by means of 1H NMR integration and
CHN analysis.
4.3.1. Host 1 (guest-free). The host 1 (300 mg) was dissolved by
warming in acetonitrile (500 ml), and the resulting solution was
allowed to stand at room temperature. The crystals (milk-white,
needle, 120 mg) were collected and dried on the filter paper.
3. Conclusions
We have designed and synthesized a phenanthro[9,10-d]imid-
azole-type fluorescent clathrate host, 2-[4-(diphenylamino)-
phenyl]-1H-phenanthro[9,10-d]imidazole (1) with imidazole ring
and diphenylamino group. We found that the crystal of 1 exhibits
4.3.2. Crystal 1$acetic acid (H/G¼1:1). The host 1 (600 mg) was
dissolved by warming in a mixture of acetic acid and acetonitrile
(volume ratio of 1:10, 210 ml), and the resulting solution was
allowed to stand at room temperature. The crystals (yellow, prism,

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Y. Ooyama et al. / Tetrahedron 65 (2009) 8336–8343
313 mg) were collected and dried on the filter paper. Elemental
analysis calcd (%) for C35H27N3O2: C, 80.59; H, 5.34; N, 8.06. Found:
C, 80.41; H, 5.22; N 8.13.
(Rint¼0.037), which were used in all calculations. The final R indices
[I>2
s
(I)], R1¼0.063, wR(F2)¼0.163.
4.4.3. Crystal of 1$morpholine (H/G/H2O¼2:1:2) with 2H2O. The
transmission factors ranged from 0.96 to 1.00. The crystal structure
was solved by direct methods using SIR 92.10 The structures were
expanded using Fourier techniques.11 The non-hydrogen atoms were
refined anisotropically. Some hydrogen atoms were refined iso-
tropically, the rest were fixed geometrically and not refined. Crys-
tallographic data: C70H59N7O3, M¼1046.28, triclinic, a¼9.914(2),
4.3.3. Crystal 1$propionic acid (H/G¼1:2). The host 1 (300 mg) was
dissolved by warming in propionic acid (210 ml), and the resulting
solution was allowed to stand at room temperature. The crystals
(yellow, prism, 209 mg) were collected and dried on the filter pa-
per. Elemental analysis calcd (%) for C39H35N3O4: C, 76.83; H, 5.79;
N, 6.87. Found: C, 76.58; H, 5.74; N, 6.96.
b¼16.867(4), c¼8.617(2) Å,
a
¼103.48(2)ꢂ,
b
¼100.49(2)ꢂ,
g¼93.89
4.3.4. Crystal 1$1-butanol (H/G¼1:1). The host 1 (600 mg) was
dissolved by warming in 1-butanol (100 ml), and the resulting so-
lution was allowed to stand at room temperature. The crystals
(yellowish white, prism, 252 mg) were collected and dried on the
filter paper. Elemental analysis calcd (%) for C37H33N3O: C, 82.96; H,
6.21; N, 7.84. Found: C, 82.96; H, 6.30; N, 7.98.
(2)ꢂ, U¼1368.6(6) Å3, rcalcd¼1.269 g cmꢀ3, T¼296.2 K, space group P1
(no.1), Z¼2,
m
(Mo K
a
)¼0.79 cmꢀ1, 5162 reflections measured, 4813
unique (Rint¼0.041), which were used in all calculations. The final R
indices [I>2
s
(I)], R1¼0.042, wR(F2)¼0.137.
4.5. Computational methods
4.3.5. Crystal 1$morpholine (H/G/H2O¼2:1:2) with 2H2O. The host 1
(300 mg) was dissolved by warming in a mixture of morpholine
and water (volume ratio of 2:1, 300 ml), and the resulting solution
was allowed to stand at room temperature. The crystals (white,
prism, 141 mg) were collected and dried on the filter paper. Ele-
mental analysis calcd (%) for C70H59N7O3: C, 80.36; H, 5.68; N, 9.37.
Found: C, 80.34; H, 5.79; N, 9.47.
The semi-empirical calculations were carried out with the
WinMOPAC Ver. 3.9 package (Fujitsu, Chiba, Japan). Geometry cal-
culations in the ground state were made using the AM1 method.7
All geometries were completely optimized (keyword PRECISE) by
the eigenvector following routine (keyword EF). Experimental ab-
sorption spectra of the eight compounds were compared with their
absorption data by the semi-empirical method INDO/S (in-
termediate neglect of differential overlap/spectroscopic).6 All
CNDO/S calculations were performed using single excitation full
SCF/CI (self-consistent field/configuration interaction), which in-
cludes the configuration with one electron excited from any occu-
pied orbital to any unoccupied orbital, where 225 configurations
were considered [keyword CI (15 15)].
4.4. X-ray crystallographic studies
The reflection data were collected at 23ꢃ1 ꢂC on a Rigaku AFC7S
four-circle diffractometer by 2q–u scan technique, and using
graphite-monochromated Mo K
a
(l¼0.71069 Å) radiation at 50 kV
and 30 mA. In all cases, the data were corrected for Lorentz and
polarization effects. A correction for secondary extinction was ap-
plied. The reflection intensities were monitored by three standard
reflections for every 150 reflections. An empirical absorption cor-
rection based on azimuthal scans of several reflections was applied.
All calculations were performed using the teXsan9 crystallographic
software package of Molecular Structure Corporation. CCDC-
740523 (1$acetic acid), CCDC-740524 (1$1-butanol), and CCDC-
740525 (1$morpholine with 2H2O) contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.au.uk/data_request/cif.
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 21550181) and by a Special Research Grant
for Green Science from Kochi University.
References and notes
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K.; Kawaguchi, K.; Sato, T.; Tajima, N.; Kuroda, R.; Matsubara, Y. Chem. Asian J.
2008, 3, 625.
4.4.1. Crystal of 1$acetic acid (H/G¼1:1). The transmission factors
ranged from 0.99 to 1.00. The crystal structure was solved by direct
methods using SIR 92.10 The structures were expanded using Fourier
techniques.11 The non-hydrogen atoms were refined anisotropically.
Some hydrogen atoms were refined isotropically, the rest were fixed
geometrically and not refined. Crystallographic data: C35H27N3O2,
M¼521.62, monoclinic, a¼10.92(1), b¼10.050(3), c¼25.180(3) Å,
2. (a) Yoshida, K.; Miyazaki, H.; Miura, Y.; Ooyama, Y.; Watanabe, S. Chem. Lett.
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Int. Ed. 2003, 42, 783; (b) Scott, J. L.; Yamada, T.; Tanaka, K. New J. Chem.
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Zerner, M. C. Theor. Chim. Acta 1976, 42, 223; (c) Bacon, A. D.; Zerner, M. C. Theor.
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b
¼90.99(3)ꢂ, U¼2761(2) Å3, rcalcd¼1.254 g cmꢀ3, T¼296.2 K, space
group P21/n (no.14), Z¼4,
m(Mo
Ka
)¼0.79 cmꢀ1, 5123 reflections
measured, 4853 unique (Rint¼0.061), which were used in all cal-
culations. The final R indices [I>2
s
(I)], R1¼0.050, wR(F2)¼0.161.
4.4.2. Crystal of 1$1-butanol (H/G¼1:1). The transmission factors
ranged from 0.90 to 1.00. The crystal structure was solved by direct
methods using SIR 92.10 The structures were expanded using
Fourier techniques.11 The non-hydrogen atoms were refined an-
isotropically. Some hydrogen atoms were refined isotropically, the
rest were fixed geometrically and not refined. Crystallographic
data: C37H33N3O, M¼535.59, triclinic, a¼10.688(4), b¼13.987(7),
7. Dewar, M. J. S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J. J. P. J. Am. Chem. Soc. 1985,
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Yoshida, K.; Ooyama, Y.; Miyazaki, H.; Watanabe, S. J. Chem. Soc., Perkin Trans. 2
2002, 700; (d) Ooyama, Y.; Nakamura, T.; Yoshida, K. New J. Chem. 2005, 29,
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c¼10.027(2) Å,
a
¼91.43(3)ꢂ,
b
¼102.41(2)ꢂ,
g
¼91.89(3)ꢂ, U¼1462.2
(8) Å3, rcalcd¼1.217 g cmꢀ3, T¼296.2 K, space group P1 (no. 2), Z¼2,
m
(Mo K
a
)¼0.73 cmꢀ1, 5444 reflections measured, 5145 unique

Y. Ooyama et al. / Tetrahedron 65 (2009) 8336–8343
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