Amphiphilic inclusion spaces for various guests and regulation of fluorescence intensity of 1,8-bis(4-aminophenyl)anthracene crystals

Article abstract of DOI:10.1002/chem.201304541

A host framework for inclusion of various guest molecules was investigated by preparation of inclusion crystals of 1,8-bis(4-aminophenyl)anthracene (1,8-BAPA) with organic solvents. X-ray crystallographic analysis revealed construction of the same inclusion space incorporating 1,8-BAPA and eight guest molecules including both non-polar (benzene) and polar guests (N,N-dimethylformamide, DMF). Fluorescence efficiencies varied depending on guest molecule polarity; DMF inclusion crystals exhibited the highest fluorescence intensity (Φ_F=0.40), four times as high as that of a benzene inclusion crystal (Φ_F=0.10). According to systematic investigations of inclusion phenomena, strong host-guest interactions and filling of the inclusion space led to a high fluorescence intensity. Temperature-dependent fluorescence spectral measurements revealed these factors effectively immobilised the host framework. Although hydrogen bonding commonly decreases fluorescence intensity, the present study demonstrated that such strong interactions provide excellent conditions for fluorescence enhancement. Thus, this remarkable behaviour has potential application toward sensing of highly polar molecules, such as biogenic compounds. Immobilisation by guests from within: Inclusion crystals of 1,8-bis(4-aminophenyl)anthracene (1,8-BAPA) constructed the same inclusion space for eight guest molecules including not only non-polar guests (benzene) but also polar guests (DMF; see scheme). Fluorescence efficiencies varied depending on guest molecule polarity. Strong host-guest interactions and filling of the inclusion space led to a high fluorescence intensity.

Full text of DOI:10.1002/chem.201304541

DOI: 10.1002/chem.201304541
Full Paper
&
Inclusion Crystals
Amphiphilic Inclusion Spaces for Various Guests and Regulation
of Fluorescence Intensity of 1,8-Bis(4-aminophenyl)anthracene
Crystals
Misa Sugino,[a] Keisuke Hatanaka,[a] Yusuke Araki,[a] Ichiro Hisaki,[a] Mikiji Miyata,[a] and
Norimitsu Tohnai*[a, b]
Abstract: A host framework for inclusion of various guest
molecules was investigated by preparation of inclusion crys-
tals of 1,8-bis(4-aminophenyl)anthracene (1,8-BAPA) with or-
ganic solvents. X-ray crystallographic analysis revealed con-
struction of the same inclusion space incorporating 1,8-BAPA
and eight guest molecules including both non-polar (ben-
zene) and polar guests (N,N-dimethylformamide, DMF). Fluo-
rescence efficiencies varied depending on guest molecule
polarity; DMF inclusion crystals exhibited the highest fluores-
cence intensity (FF =0.40), four times as high as that of
a benzene inclusion crystal (FF =0.10). According to system-
atic investigations of inclusion phenomena, strong host–
guest interactions and filling of the inclusion space led to
a high fluorescence intensity. Temperature-dependent fluo-
rescence spectral measurements revealed these factors ef-
fectively immobilised the host framework. Although hydro-
gen bonding commonly decreases fluorescence intensity,
the present study demonstrated that such strong interac-
tions provide excellent conditions for fluorescence enhance-
ment. Thus, this remarkable behaviour has potential applica-
tion toward sensing of highly polar molecules, such as bio-
genic compounds.
Introduction
hancement is one of the key properties to consider in the
design of solid-state fluorescence materials. It is known that
strong p–p interactions and/or hydrogen bonds lead to de-
creases in fluorescence in the solid state.[6e,8,9] This means that
highly polar guests in hydrogen-bonding sites are regarded as
fluorescence quenchers. On the other hand, hydrogen bonds
play a role in the construction of stable supramolecular struc-
tures;[10] namely, hydrogen bonds in inclusion crystals stabilise
the host framework.
Inclusion phenomena are utilised in numerous versatile appli-
cations not only for storage,[1] separation,[2] and catalysis,[3] but
also for advanced functions, such as memory[4] and sensing.[5,6]
In particular, organic inclusion crystals composed of polycyclic
aromatic hydrocarbons have attracted much attention owing
to their ability to enhance the functionality of organic lumines-
cent materials.[4d,6] For example, Stalke et al. reported that tolu-
ene inclusion crystals are suitable for luminescent chemosens-
ing, as their displayed fluorescent intensity is easily changed
by the desorption-adsorption of guest molecules.[6b] Hence
such inclusion systems appear to be appropriate for the poten-
tial tuning of fluorescent properties.
We have previously reported that fluorophore rigidity pre-
vents non-radiation processes and enhances solid-state fluores-
cence efficiencies of crystals composed of organic salts.[11] In
this work, we focused on identifying the correlation between
inclusion phenomena of guest molecules and fluorophore ri-
gidity. P. Sozzani et al. demonstrated that weak host–guest in-
teractions effectively modify robustness of nanochannel archi-
tecture.[12] In view of this study, stronger host–guest interac-
tions in inclusion crystals are thought to stabilise the host
framework. Fluorescence intensity is assumed to be enhanced
by guest molecules in the case of a host framework composed
of fluorophores. Moreover, a host framework design with high
inclusion ability leads to modulation of the fluorescent intensi-
ties. However, it is difficult to demonstrate these phenomena
because molecular conformations and/or molecular arrange-
ments of host molecules are usually altered through self-as-
sembly with guests. These factors have a cooperative effect on
the fluorescence properties in inclusion crystals. Therefore, the
exploration of critical influences for modulation of solid-state
Because host–guest interactions are important for modifica-
tion of inclusion system optical functionality, their correlations
with fluorescence properties have been investigated by using
various inclusion crystals.[6–9] In particular, fluorescence en-
[a] M. Sugino, K. Hatanaka, Y. Araki, Dr. I. Hisaki, Prof. Dr. M. Miyata,
Dr. N. Tohnai
Department of Material and Life Science
Graduate School of Engineering, Osaka University
2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)
Fax: (+81)6-6879-7404
E-mail: tohnai@mls.eng.osaka-u.ac.jp
[b] Dr. N. Tohnai
Japan Science and Technology Agency (JST) PRESTO
4-1-8 Honcho Kawaguchi, Saitama 332-0012 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201304541.
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Scheme 1. Chemical structures of 1,8-BAPA and guest molecules.
fluorescence properties is often complicated by multiple fac-
tors.
We employed here inclusion crystals composed of 1,8-bis(4-
aminophenyl)anthracene (1,8-BAPA) and organic solvents
(Scheme 1). Bulky substituents on the anthracene moiety,
namely 1,8-phenyl substitution, contribute to the formation of
an inclusion space associated with steric hindrance.[13] Amino
group introduction further aids in capture of various organic
solvents through hydrogen bonding. In this system, the solid-
state fluorescence efficiencies varied depending on the guest
molecules employed. Detailed analyses of correlations between
fluorescence properties and inclusion behaviours of guest mol-
ecules in the 1,8-BAPA crystals were also performed. To the
best of our knowledge, this is the first attempt at utilising hy-
drogen bonds for the fluorescence enhancement of organic in-
clusion crystals.
Results and Discussion
Synthesis of 1,8-BAPA
1,8-BAPA (1) was synthesised by using the synthetic route out-
lined in Scheme 2. According to an established procedure,[14]
1,8-BAPA (1) was prepared by deprotection of Boc-protected
Figure 1. Crystal structures of inclusion crystals of 1,8-BAPA with a) 1,4-diox-
ane, b) benzene, c) chloroform, d) THF, e) dichloromethane, f) 2-propanol,
g) 1-propanol, and h) DMF. The details are given in Figures S2–S9 in the Sup-
porting Information.
Scheme 2. Synthesis of 1,8-BAPA (1).
yellow needle-like crystals. These crystal structures were deter-
mined from powder X-ray diffraction (PXRD) analyses and
single-crystal X-ray studies.[17] These results revealed that the
eight organic solvents were enclathrated within the same in-
clusion space in the 1,8-BAPA framework (Figure 1 and Fig-
ure S1 in the Supporting Information).
target product 3 resulting from Suzuki coupling of 1,8-dibro-
moanthracene (2)[15] and tert-butyl 4-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl) phenylcarbamate in the presence of a palla-
dium(0) catalyst.[16]
Figure 2 shows the host framework and inclusion space
within 1,8-BAPA crystals, illustrating the porous structure con-
taining a 1D channel in the crystalline state. The inclusion
space consists of a hydrophilic wall composed of amino
groups and a hydrophobic wall formed by the edges of an-
thracene moieties; the structure suggests that this space is
able to form not only hydrogen bonds, but also van der Waals
Crystal structures and inclusion ability
Crystallisation of 1,8-BAPA was accomplished from eight organ-
ic solvents: 1,4-dioxane, benzene, chloroform, tetrahydrofuran
(THF), dichloromethane, 2-propanol, 1-propanol, and N,N-dime-
thylformamide (DMF). Crystallisation from all solvents yielded
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tion steps, the T-shaped stacking arrangement in par-
ticular not only has an awkward shape, but also con-
tains both hydrophilic and hydrophobic moieties in
the pitted area (Figure 3c). These characteristic fea-
tures have significant advantages for guest molecule
inclusion. Hence, it is suggested that the T-shaped
stacking arrangement is an important component of
the host framework with high inclusion ability.
Photophysical properties in various organic sol-
vents
Figure 2. Inclusion space of 1,8-BAPA in the crystalline state. Hydrogen atoms are omit-
ted for clarity. In the inclusion space, nitrogen and carbon are indicated by dark grey and
light grey, respectively.
The solvatochromic behaviours of amino-substituted
aromatic compounds in organic solvents are
known.[18] In the present study, 1,8-BAPA emissions
showed a dependence on solvent polarity, emitting
interactions with guest molecules. Accordingly, crystallisation
of 1,8-BAPA yielded a versatile host framework with an amphi-
philic channel.
from blue in benzene (emission lmax =455 nm) to yellow in
DMF (emission lmax =550 nm) (Figure 4); in contrast, such
a bathochromic shift was not observed in solutions of 1,8-di-
phenylanthracene (Figure S10 IN THE Supporting Information).
Additionally, only a small shift in the excitation spectra of 1,8-
BAPA solutions was observed. These results suggested that the
strong solvatochromic behaviour is derived from stabilisation
of the excited species with charge separation in a twisted in-
ternal charge-transfer (TICT) state; following hydrogen-bond
formation between 1,8-BAPA and solvent.[19] Fluorescence effi-
ciencies increased in the lower polarity solvents, for example,
0.52 and 0.45 for benzene and 1,4-dioxane, respectively. Even
though the polarity also affects the efficiencies, this solvent de-
pendence is small, as shown in Table 1.
Hierarchical construction of the host framework is represent-
ed schematically in Figure 3; 1,8-BAPA molecules do not adopt
a coplanar structure, but rather a twisted structure between
the two aniline groups of the anthracene moiety (Figure 3a).
Such a twisted structure forces 1,8-BAPA to adopt an awkward
shape that is favourable for construction of inclusion spaces.
First, two 1,8-BAPA molecules form a basic unit through HÀN
hydrogen bonding (Figure 3b). This hydrogen-bond network
was not disrupted, even by inclusion of highly polar solvents;
such as 1-propanol and DMF, indicating the stability of the
basic unit. Next, the basic units form a T-shaped stacking ar-
rangement owing to a strong edge-to-face CH–p interaction
among the anthracene moieties of 1,8-BAPAs (Figure 3c). Final-
ly, weak CH–p interactions promote aggregation of the stack-
ing arrangement into a host framework with an amphiphilic
channel (Figure 3d). Consequently, the host frameworks are
constructed by the self-assembly process as described in the
above-mentioned steps. Additionally, the amphiphilic channel
is stabilised by inclusion of guest molecules. In the construc-
Solid-state fluorescence properties of inclusion crystals
Solutions of 1,8-BAPA emitted fluorescence from blue to
yellow depending on the organic solvent used (Dlem =95 nm).
On the other hand, all of the inclusion crystals showed a green
fluorescence (Table 1 and Figure 5), with only a small difference
in their emission spectra (Dlem =26 nm). This result means that
Figure 3. Construction of host framework. First, a) 1,8-BAPA forms b) the basic unit. Next, CH–p interactions between the basic units lead to c) formation of
a T-shaped stacking arrangement. Finally, the host framework is constructed through weak CH–p interactions between d) the T-shaped stacking arrange-
ments.
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Table 1. Dielectric constants and photophysical properties of 1,8-BAPA in
various solvents and the solid state.
Guest
Dielectric
Solution
lex
Crystals
lex
[d]
[f]
constant lem
FF
lem
FF
[a]
[FmÀ1
]
[nm][b] [nm][c]
[nm][e] [nm][c]
1,4-dioxane
benzene
chloroform
THF
2.24
2.28
4.90
7.58
463
455
461
477
462
533
535
550
391
388
387
394
387
387
388
409
0.45
0.52
0.40
0.39
0.34
0.42
0.39
0.41
506
493
497
502
497
506
506
519
444
438
442
450
440
438
439
450
0.24
0.10
0.11
0.34
0.11
0.10
0.30
0.40
dichloromethane 9.45
2-propanol
1-propanol
DMF
18.3
22.2
36.7
[a] Dielectric constants of the solvents at 20 or 258C. [b] Maximum wave-
length of fluorescence emission spectra excited at 385 nm. [c] Wave-
lengths of fluorescence excitation spectra monitored at their respective
emission peaks. [d] Relative fluorescence quantum yield. Standards used
were Rhodamine 6G: FF =0.94 in EtOH.[20] [e] Maximum wavelengths of
fluorescence emission spectra excited at 340 nm. [f] Absolute fluores-
cence quantum yield.
Figure 4. a) Photographs of 1,8-BAPA in solvents (from left: 1,4-dioxane, ben-
zene, chloroform, THF, dichloromethane, 2-propanol, 1-propanol and DMF)
under UV irradiation (l=365 nm). b) Fluorescence excitation and c) emission
spectra of 1,8-BAPA (1ꢁ10À5 m) in various solvents. Excitation wavelength
for the emission spectra is 385 nm. Excitation spectra were recorded at their
respective emission peaks.
the solid-state fluorescence colours are more deeply respon-
sive to the host framework rather than the polarity of guests.
Molecular orbital calculations described the extension of p-
conjugation length of 1,8-BAPA molecules in all inclusion crys-
tals, in which p-conjugation of the twisted structures was delo-
calised to amino groups in the highest occupied molecular or-
bital (HOMO) level in all crystals (Figures S11–S13 in the Sup-
porting Information). As shown in Figure 1, 1,8-BAPA assem-
bled into a similar crystal structure in all of the inclusion crys-
tals prepared. In the crystals, 1,8-BAPA exhibit
a CH–p
interaction among neighbouring phenyl groups and anthra-
cene moieties, including formation of an edge-to-face T-
shaped geometry.[21] Therefore, the basic colour of the inclu-
sion crystals, that is, green fluorescence, is derived from the ex-
tension of p-conjugation length and the packing manner.
Figure 5. a) Photographs of inclusion crystals composed of 1,8-BAPA under
UV irradiation (l=365 nm). b) Fluorescence excitation and c) emission spec-
tra of the inclusion crystals. Excitation wavelength for the emission spectra
is 340 nm. Excitation spectra were recorded at their respective emission
peaks.
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Solid-state fluorescence efficiencies of inclusion crystals
Interestingly, fluorescence efficiencies of the crystals changed
drastically depending on the nature of inclusion guests, in con-
trast to the fluorescence colours. Table 1 presents the absolute
fluorescence efficiencies of the inclusion crystals. The DMF in-
clusion crystal exhibited a fourfold higher fluorescence efficien-
cy (FF =0.40) than that of the benzene inclusion crystal. Such
behaviour indicates that, in contrast to solution behaviour, the
efficiency is modulated by other factors in the crystalline state.
So far, hydrogen bonds have been reported to cause not only
the bathochromic shift, but also fluorescence quench-
ing.[9,18,19,22] Contrary to such a general belief, the hydrogen
bonds in 1,8-BAPA inclusion crystals assisted in the improve-
ment of fluorescence intensity.
In order to explain this anomalous phenomenon, we fo-
cused on the nature of molecular interactions in the inclusion
crystals. Solid-state fluorescence behaviours have been often
discussed in relation to p–p interactions between fluorophores
in the literature.[8,9] However, in this case, intermolecular inter-
actions among fluorophores are almost identical because the
fluorophore, 1,8-BAPA as a host molecule, forms a similar host
framework for every guest. It is suggested that the differences
in the solid-state fluorescence efficiencies is attributed to these
inclusion phenomena.
Figure 6. Inclusion behaviour of a) benzene and b) DMF in the crystalline
state. Four crystallographically independent host molecules and three guest
molecules exist in the crystal structure of benzene inclusion crystal. Other in-
clusion behaviours of benzene are shown in Figure S2 in the Supporting In-
formation.
In the crystals displaying low efficiencies, guests were en-
clathrated mainly by the hydrophobic wall of the inclusion
space with weak host–guest interactions. For example, ben-
zene formed CH–p and NH–p interactions with aniline groups
of the host molecule (Figure 6a). In particular, the phenyl moi-
eties of the aromatic wall showed interactions with every
guest as shown in Figures S2–S9 in the Supporting Informa-
tion. Owing to this host–guest interaction, the aromatic wall
effectively includes various low-polarity guests, such as ben-
zene, chloroform, and dichloromethane.
Table 2. Ratio of host and guest, length of host–guest hydrogen bond,
unit volumes, free volumes, and their ratio of inclusion crystals for 1,8-
BAPA.
Guest
Host–
guest
ratio
NÀH···O
Vunit
[ꢂ3][a]
Vfreevolume
[ꢂ3][b]
Vfreevolume/
Vunit [%][c]
[ꢂ]
benzene
4:3
1:1
1:1
1:1
1:1
1:1
1:1
1:1
–
3.75
–
8893.9
4485.8
4453.5
4388.8
4420.9
4447.0
4456.2
4462.7
705.6
378.6
364.7
397.1
159.2
329.1
263.0
264.0
7.93
8.44
8.19
9.05
3.60
7.40
5.90
5.91
On the other hand, the inclusion crystals showing higher ef-
ficiencies exhibited host–guest hydrogen bonding and CH–p
interactions. Figure 6b shows the inclusion phenomenon ex-
hibited by the highly polar guest DMF. A methyl group of DMF
formed a CH–p interaction with a phenyl moiety of the hydro-
phobic wall. Furthermore, the oxygen atom of DMF showed
a strong interaction with amino groups of the hydrophilic wall
in the inclusion space. These results indicate that high-polarity
guests with strong host–guest interactions have an advantage
in that fluorescence intensity is increased. We have previously
reported that fluorophore immobilisation in the organic salt
prevents their vibrational fluorescence deactivation. It is there-
fore concluded that the host–guest interaction, especially hy-
drogen bonding, allows for host framework immobilisation;
namely, the host framework is stabilised by guests from within.
There are no strict requirements for guest molecules in the
1,8-BAPA inclusion system that modulate the solid state fluo-
rescent intensity. Because of the high inclusion ability, it is pos-
sible to choose the fluorescent modulator freely.
2-propanol
chloroform
dichloromethane
1,4-dioxane
1-propanol
THF
–
3.33
3.48
3.51
3.04
DMF
[a] Vunit is the total unit cell volume determined from X-ray crystallograph-
ic studies. [b] Vfreevolume is the free unit cell volume calculated with a 1.2 ꢂ
radius probe. [c] Ratio of the free volume in unit cell to unit volume=
Vfreevolume/Vunit ꢁ100.
ratio of the free volume in the unit cell to unit volume, indicat-
ing that the filling of the inclusion space also improved the
fluorescence intensity, along with strong host–guest interac-
tions including hydrogen bonds. From these cooperative ef-
fects, 1,8-BAPA may have applicability toward structural isomer
recognition. For example, the inclusion crystal of 1-propanol
actually exhibited threefold fluorescence intensity as compared
with that of 2-propanol (Table 1); in the former crystal inclusion
system there are stronger host–guest interactions and higher
guest occupancies.
Furthermore, guest occupancies appeared to have an effec-
tive role in solid-state fluorescence intensities (Table 2). Appa-
rently, the fluorescence intensity increased with a decreasing
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tional fluorescence materials such as molecular sensing appli-
cations specific to highly polar biomolecules.
Experimental Section
General methods
All chemicals and solvents (except those for photophysical mea-
surements) were commercially available and used without any pu-
rification.
Synthesis of tert-butyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxabor-
olan-2-yl) phenylcarbamate
4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)amine (5.1 g, 23.2 mmol)
and (Boc)2O (8.0 g, 31.4 mmol) were mixed in toluene (200 mL) at
1008C for 1 day. The brown mixture was evaporated and extracted
with EtOAc. The extracts were washed with 0.1n HCl (200 mL) and
saturated NaCl (200 mL), dried over Na2SO4 and concentrated.
Washing with n-hexane (50 mL) gave the product as a white
1
powder (6.3 g, 86%). H NMR (270 MHz, [D6]DMSO): d=9.54 (s, 1H,
NH), 7.54 (d, J=8.4 Hz, 2H, ArH), 7.45 (d, J=8.4 Hz, 2H, ArH), 1.46
(s, 9H, CH3), 1.26 ppm (s, 12H, CH3): EI-MS: m/z: 319 [M+].
Synthesis of tert-butyl 4,4’-(anthracene-1,8-diyl)bis(4,1-phen-
ylene) dicarbamate (3)
Figure 7. Temperature-dependent fluorescence emission of a) benzene inclu-
sion crystal and b) DMF inclusion crystal.
1,8-Dibromoanthracene 2, the precursor of 3, was synthesised
from 1,8-dichloroanthraquinone in 46% according to reported liter-
ature.[15] Toluene (155 mL), ethanol (35 mL) and 2mK2CO3 solution
(10 mL) were added to a mixture of 5 (1.0 g, 3.07 mmol), tert-butyl
Measurements of temperature-dependent emission spectra
also established this enhancement in fluorescence intensity
(Figure 7). Benzene inclusion crystals showed a substantial
temperature-dependent enhancement in the fluorescence in-
tensity. It is proposed that this crystal is significantly affected
by the vibrational deactivation. In contrast, only a small en-
hancement was evident in the case of DMF inclusion crystals.
These results indicated that the DMF inclusion crystal effective-
ly prevents vibrational deactivation, even at room temperature,
by immobilisation of the host framework. Consequently, the
solid-state fluorescence efficiency is effectively improved by
guest-induced internal stabilisation of the host framework.
4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)
phenylcarbamate
(2.2 g, 6.75 mmol) and tetrakis(triphenylphosphine)palladium (0)
(0.18 g, 0.15 mmol) under N2 atmosphere. The reaction mixture
was heated at 1108C. After stirring for 3.5 days, the colour of reac-
tion mixture was turned from yellow to dark violet. The reaction
mixture was cooled to room temperature and filtered. The filtrate
were evaporated and extracted with CH2Cl2 (150 mL). The extracts
were washed with brine (150 mL) and water (150 mL), dried over
Na2SO4 and concentrated. Column chromatography on silica gel
(CH2Cl2) gave the product as a lemon yellow powder (1.2 g, 72%).
1H NMR (270 MHz, [D6]DMSO): d=1.52 (s, 18H, CH3), 7.38 (d, J=
6.8 Hz, 2H, ArH), 7.47 (d, J=8.1 Hz, 4H, ArH), 7.55–7.606 (m, 6H,
ArH), 8.09 (d, J=8.6 Hz, 2H, ArH), 8.70 (s, 1H, ArH), 8.72 (s, 1H,
ArH), 9.37 ppm (s, 1H, NH): EI-MS: m/z: 560 [M+].
Conclusion
Crystallisation of 1,8-BAPA allowed for the construction of am-
phiphilic inclusion spaces to accommodate eight various
guests. This host framework was attributed to advantageous
features of the host molecule: concave shape, twisted struc-
ture and two amino groups. Particularly, the amino groups not
only supported the host framework, but also aided in guest
capture. Although the host framework structure remained con-
sistent, the solid-state fluorescence intensities were modified
depending on the guest molecules employed. Comparison of
X-ray crystal structures and fluorescence properties revealed
that active host–guest interactions, including a hydrogen-bond
framework and high guest occupancy, effectively immobilised
the host framework, resulting in the enhancement in fluores-
cence intensity from within. This system allows for a broad
range of guest molecules as a fluorescent modulator. We hope
these findings provide a new strategy for investigation of func-
Synthesis of 1,8-bis(4-aminophenyl)anthracene (1)
Trifluoroacetic acid (6 mL) was added dropwise to a solution of 3
(0.76 g, 1.36 mmol) in CH2Cl2 (60 mL) at room temperature. After
stirring for 2.5 h, the mixture was evaporated and extracted with
CH2Cl2 (100 mL) and washed with saturated aqueous NaHCO3
(200 mL) and water (100 mL). The organic layer was dried over
Na2SO4 and concentrated in vacuo to yield 1 as light yellow solid
1
(0.48 g, 98%). H NMR (270 MHz, [D6]DMSO): d=5.19 (s, 4H, NH2),
6.67 (d, J=8.4 Hz, 4H, ArH), 7.25 (d, J=8.4 Hz, 4H, ArH), 7.29 (d,
J=6.5 Hz, 2H, ArH), 7.49 (dd, J=8.1 Hz, J=7.6 Hz, 2H, ArH), 8.00
(d, J=7.8 Hz, 2H, ArH), 8.63 (s, 1H, ArH), 8.84 ppm (s, 2H, ArH): EI-
MS: m/z: 360 [M+].
Preparation of single crystals
1,8-BAPA was dissolved in various organic solvents. Slow evapora-
tion of the solvent at room temperature gave the single crystals.
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Crystallographic analysis of single crystals
X-ray diffraction data of the inclusion crystals of 1,8-BAPA were col-
lected by using the synchrotron radiation (l=0.8000 ꢂ) the
BL18B1 in the SPring-8 with approval of JASRI (Proposal No.
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refinement, which was performed using SHELXL-97. All non-hydro-
gen atoms were refined with anisotropic displacement parameters
and hydrogen atoms were placed in idealised positions and refined
as rigid atoms with the relative isotropic displacement parameters.
Powder X-ray diffraction analysis
Powder X-ray diffraction (PXRD) patterns were measured by using
Rigaku Ultima IV using graphite-monochromatised CuKa radiation
(l=1.54178 ꢂ) at room temperature.
Fluorescence spectroscopy
Fluorescence spectra measurements and fluorescence quantum
yields were performed by using a FP-6500 spectrofluorometer
(JASCO) with ISF-513 fluorescence integrate sphere unit (JASCO).
The inclusion crystals of 1,8-BAPA were encapsulated in a cell for
solid-state fluorescence measurements from JASCO. The solutions
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This work was supported by the Research fellowships of the
Japan Society for the Promotion of Science (JSPS) for Young
Scientists and Grant-in-Aids for Scientific Research on Innova-
tive Areas (22685014, 24108723 and 24655124) from the Minis-
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(MEXT), Japan. M. Sugino thanks the GCOE Program of Osaka
University. The synchrotron radiation experiments were per-
formed at BL38B1 in the SPring-8 with the approval of the
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al no. 2012A1592 and 2013A1617).
Keywords: crystal engineering · fluorescence · host–guest
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Received: November 20, 2013
Published online on February 20, 2014
Chem. Eur. J. 2014, 20, 3069 – 3076
www.chemeurj.org
3076
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim