Extended fluorochromism of anthracene trimers with a meta-substituted triphenylamine or triphenylphosphine core

Article abstract of DOI:10.1002/asia.201200310

Combining meta-triphenylamine or triphenylphosphine with three anthracene fluorophores gives rise to fluorescent non-planar triskelions 1 and 2. The emissive properties of 1 are highly solvatochromic, yielding blue to pale green and even pale yellow fluor

Full text of DOI:10.1002/asia.201200310

DOI: 10.1002/asia.201200310
Extended Fluorochromism of Anthracene Trimers with a meta-Substituted
Triphenylamine or Triphenylphosphine Core
Zhiou Li, Hiromi Ishizuka, Yoshihisa Sei, Munetaka Akita, and Michito Yoshizawa*[a]
Abstract: Combining meta-triphenylamine or triphenylphosphine with three an-
thracene fluorophores gives rise to fluorescent non-planar triskelions 1 and 2. The
emissive properties of 1 are highly solvatochromic, yielding blue to pale green and
even pale yellow fluorescence, whereas the blue emission of 2 is solvent-insensi-
tive. Anthracene trimers 1 and 2 are both emissive in the solid state, displaying
yellow and pale green fluorescence, respectively, with moderate quantum yields.
Keywords: anthracene
cence · solvatochromism · triphenyl-
amine · triphenylphosphine
·
fluores-
Introduction
Synthetically simple, stable organic fluorophores with high
quantum yield and tunable emission are of utmost impor-
tance in the development of photoresponsive sensors, supra-
molecules, and materials, yet the preparation remains a sig-
nificant challenge.[1–5] Anthracene is a well-studied electron
acceptor but still an intriguing blue-emitting module for the
synthesis of new functional fluorophores.[6] Triphenylamine
Scheme 1. Fluorophores 1 and 2 with three anthracene rings assembled
(TPA) and triphenylphosphine (TPP) are well-known elec-
tron donors that can be used to establish a central scaffold
around which multiple fluorophores, such as anthracene, can
be quickly assembled. These trimeric assemblies, which re-
semble “triskelion” when connected at the meta-position,[7]
provide an unusual geometrical array of pendant fluoro-
phores with potential applications as functional emissive
compounds; however, the chemistry remains largely unex-
plored.[8,9] Furthermore, the three-fold symmetry of a tris(m-
anthrylphenyl)amine or -phosphine should disrupt the typi-
cal solid-state packing of anthracene derivatives[6] and en-
hance the solid-state emission.[10,11]
around a single triphenylamine (TPA) or triphenylphosphine (TPP) core.
both solution and the solid states. Triskelion 1 is highly sol-
vatofluorochromic, yielding blue to pale yellow emission,
whereas emission from 2 is insensitive to solvent polarity.
Furthermore, as expected, solids of 1 and 2 emit yellow and
pale green fluorescence, respectively, with moderate quan-
tum yields. The photophysical properties of the para deriva-
tives were also studied to reveal the relationship between
structure and emission.
Thus, we designed new fluorophores 1 and 2, each with
three anthracene moieties assembled around a single TPA
or TPP core (Scheme 1). The anthracenes are placed at
meta position on the phenyl groups relative to the central
heteroatom to enforce conformational restriction and to
ensure that all aromatic rings are held orthogonal.[12] It was
anticipated that the non-planar divergent structures would
give rise to unusual intra- and intermolecular interactions
and unique photophysical features. Herein, we report the
unique emission properties of anthracene trimers 1 and 2 in
Results and Discussion
Triply-branched anthracene trimers 1 and 2 were prepared
by the following simple procedures. First, chloro- and nitro-
phenylanthracenes 3a,b were synthesized from 9-bromoan-
thracene using the Suzuki–Miyaura cross-coupling protocol
(Figure 1a). After the conversion of the nitro group of 3b
into the amine 3c, a palladium-catalyzed Buchwald–Hartwig
reaction of the chloro- and aminophenylanthracenes was
carried out to afford 1 in 70% yield.[13] Treatment of anthra-
quinone with 3-bromophenyllithium and consecutive dehy-
dration gave 9-(3-bromophenyl)anthracene (3d). A three-
fold addition of the lithiated species of this compound to tri-
methyl phosphite afforded 2 in 47% yield (Figure 1b).[14]
The structures of 1 and 2 were confirmed by NMR spec-
troscopy and MALDI-TOF mass spectrometry.[15] In the
[a] Z. Li, H. Ishizuka, Y. Sei, Prof. Dr. M. Akita, Dr. M. Yoshizawa
Chemical Resources Laboratory
Tokyo Institute of Technology
4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)
Fax : (+81)45-924-5230
E-mail: yoshizawa.m.ac@m.titech.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201200310.
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Figure 2. X-ray crystal structure of 2’: ball-and-stick representation of
a,b) open and c,d) closed conformations (P: orange ball).
Figure 1. Synthesis of anthracene trimers 1 (a) and 2 (b). Conditions and
reagents: i) 3-chlorophenylboronic acid, [Pd
ii) 3-nitrophenylboronic acid, [PdCl2A(PhCN)2],
908C; iii) SnCl2, THF, EtOH, H2O, 95 8C; iv) [Pd
ACHTUNGTRENNUNG
tive orientations of the anthracene panels are different be-
tween the two isomers, both structures showed twisted, non-
planar three-fold symmetry.
G
PACHTUNGTRENNUNG
E
PACHTUNGTRENNUNG
tBuOK, toluene, 1108C; v) 1. nBuLi, TMEDA, THF, À808C; 2. anthrone,
toluene, À808C; 3. HCl, H2O, RT; vi) 1. nBuLi, THF, À808C; 2. P-
The UV/Vis spectrum of 1 in CH2Cl2 showed two charac-
teristic absorption bands around 310 and 370 nm, which can
be attributed to the n-p* transitions of the TPA unit and the
p-p* transitions of the anthracene moieties (Figure 3a). The
absorption bands are similar to those of the individual com-
ponents, triphenylamine and anthracene, indicating that
each aromatic unit is electronically isolated due to the pre-
ferred orthogonal conformations of the anthryl and phenyl
rings. Other than the strong absorption at 310 nm present in
TPA and 1, the absorption spectrum of 2 is quite similar to
that of 1 (Figure 3a). The emission spectrum of 1 in CH2Cl2
displayed a broad emission band ranging from 400 to
580 nm (lmax =480 nm, FF =18%; Figure 3b) upon irradia-
tion at 365 nm. The emission spectrum of 2, however, closely
resembled that of anthracene and 3d (lmax =421 nm, FF =
70%; Figure 3b).
The differences between 1 and 2 became further pro-
nounced upon changing the solvent polarity.[17] The emission
of 1 is highly sensitive to the solvent polarity, with the
maxima varying over 100 nm (Figure 3c).The CIE chroma-
ticity diagram (CIE=International Commission on Illumi-
nation) of 1 shows the change in emission color from blue
to yellow (Figure 3e).[18,19] In non-polar solvents, such as
benzene, the emission spectra of 1 resemble those of 2 with
a lmax of about 415 nm. As the solvent polarity increased,
the Stokes shift progressively increased and the emission of
1 changed from blue to yellow. The maximum Stokes shift
for 1 was observed in DMSO (Dlmax ꢀ140 nm). In stark con-
trast, the emission of 2 remained effectively unchanged with
increasing solvent polarity. The absolute quantum yield (FF)
A
drofuran. 1H NMR spectra (400 MHz, CDCl3, RT, aromatic region) of
1 (c) and 2 (d).
1H NMR spectrum of 1, nine signals deriving from meta-
phenylene (Ha,b,c,d) and anthracence rings (He,f,g,h,i) were
found in the range of 7.0–8.5 ppm (Figure 1c). The Hf signal
of the anthracene moieties of 1 was shifted upfield to
7.01 ppm (Dd=À0.36 ppm) relative to the corresponding
signal of 9-(3-chlorophenyl)anthracene, which is indicative
of shielding effects due to the adjacent anthracenes (Fig-
ure 1c). Signals Hf and He of 2 were shifted further upfield
compared to those of 1 (Figure 1d). A single 31P NMR
signal of 2 was found at À4.12 ppm with a slight shift (Dd=
À0.56 ppm) relative to triphenylphosphine. MALDI-TOF
MS analysis unambiguously confirmed the composition of
1 and 2 with molecular weights of 773.17 and 790.93, respec-
tively. Finally, the purity of 1 and 2 was verified by elemen-
tal analysis.
We were unable to prepare single crystals of 1 and 2 even
after extensive crystallization attempts. To facilitate crystalli-
zation, 2-methoxyethoxy groups were attached to the meta-
phenylene moieties of 2, which gave rise to the analogue
2’.[15] Single crystals suitable for X-ray crystallographic anal-
ysis were obtained by the slow concentration of a CHCl3 so-
lution of 2’ at room temperature. The crystal structure
showed the presence of two crystallographically independ-
ent structures with open and closed conformations (Fig-
ure 2a,b and 2c,d), respectively, for 2’.[16] Though the rela-
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Anthracene Trimers with a meta-Substituted Triphenylamine or Triphenylphosphine Core
shift on solvent polarity (Fig-
ure 3 f). Thus, similar to para-
substituted dialkylaminopheny-
lanthracenes, the emissive prop-
erties of 1 are consistent with
a highly polarized intramolecu-
lar charge-transfer excited state
which, by steric constraints, is
twisted (TICT).[20,21] Unlike ni-
trogen, the lone pair of phos-
phorus ineffectively overlaps
with the phenyl-anthryl p-
system and, therefore, a sol-
vent-sensitive TICT state was
not observed for 2.
Density functional theory
(DFT) calculations of anthra-
cene trimers 1 and 2 at the
B3LYP/6-31G* level confirmed
the orthogonal geometries and
lent further insight into the
origin of the observed emissive
properties. The average dihe-
dral angles between the anthryl
and phenyl rings of 1 and 2 are
89.9 and 82.8 degrees, respec-
tively (Figure 4a and 4b). The
molecules adopt twisted, non-
planar configurations, which
prohibit intramolecular p-de-
localization configurations and
prevent effective intermolecular
p-stacking motifs. The HOMO
of 1 is delocalized on the TPA
moiety whereas the LUMO of
1 is delocalized on only two of
the three anthracene rings (Fig-
ure 4c). The HOMO of 2, on
the other hand, is localized on
a
single anthracene and the
LUMO of 2 is delocalized over
all three anthracenes (Fig-
ure 4d). Thus, the phosphine
center is not involved in the
photophysical processes of
2
and the observed emission
arises only from the anthracene
moieties.
The unusual non-planar geo-
metries of triskelions 1 and 2
resulted in enhanced solid-state
emission. In the solid state, 1 is
an orange powder and, upon ir-
Figure 3. a) UV/Vis (CH2Cl2, RT) and b) fluorescence (CH2Cl2, RT, lex =365 nm) spectra of 1, 2, and 3d.
Insets: Photographs of solutions of 1 and 2 in CH2Cl2 a) without and b) with irradiation at 365 nm. c,d) Sol-
vent-dependent emission spectra (RT, 0.03 mm, lex =365 nm) of 1 (c) and 4 (d). e) CIE coordinate diagram of
1 in various solvents; RT, lex =365 nm. f) Plot of emission energy of 1 and 4 against solvent ET values.
of 1 roughly correlated with solvent polarity and decreased
with increasing polarity: benzene (41%), THF (21%), and
DMSO (6%). The plot of the emission energy of 1 against
Reichardtꢁs ET value reveals the dependence of the Stokes
radiation at 365 nm, strong yellow emission was observed
with a lmax of 570 nm and an absolute quantum yield of
21% (Figure 5a and 5b). Compound 2 is a pale yellow
powder and, upon irradiation, pale green emission was ob-
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Figure 6. Chemical structures of 2a–c.
porting Information). In sharp contrast to trimers 1 and 2,
solid mixtures of anthracene and TPA or TPP at ratios of
3:1 gave only the standard blue emission from the anthra-
cene fluorophore (lmax =425 nm) upon irradiation (Fig-
ure S30 in the Supporting Information).
The para-substituted anthracene trimers 4 and 5, the re-
spective analogues of 1 and 2, were prepared to better ex-
amine the relationship between structure and emission.[15] In
a manner similar to 1, emission of 4 in solution was solvato-
chromic, with lmax ranging from 435 to 546 nm (Dlmax
ꢀ110 nm) and moderate to high quantum yields (FF =23–
79%; Figure 3d and Table S1 in the Supporting Informa-
tion). However, as a powder, 4 gave pale green emission,
similar to 2, with a lower quantum yield (FF =9%) than
that of 1 (lmax =570, FF =21%; Figure 5). Only blue emis-
sion from anthracene was observed from phosphorus ana-
logue 5 in solution (FF =70%) and in the solid state (FF =
16%; Figure 5).
The differences in the solid-state emissive properties
should be related to the random aggregation of anthracene
moieties. Anthracene trimers 1 and 2 adopt non-planar, or-
thogonal conformations with steric crowding (Figure 4a,b).
Powder X-ray diffraction revealed that powders of 1 and 2
have no ordered structure (Figure S30 in the Supporting In-
formation) and we presume that the non-planar three-fold
symmetry prevents the usual packing of the anthracene fluo-
rophores and gives rise to the unusual solid-state emis-
sion.[10,11] By contrast, anthracene trimers 4 and 5 adopt rela-
tively planar, divergent conformations without steric crowd-
ing (Figure 7b), which allow the usual intermolecular inter-
actions or packing between the fluorophores.
Figure 4. Space-filling representation of the optimized structure of a) 1
and b) 2. Representation of the frontier molecular orbitals of c) 1 showing
HOMO (À5.06 eV) and LUMO (À1.61 eV) and d) 2 showing HOMO
(À5.15 eV) and LUMO (À1.62 eV), obtained from the DFT calculation
(B3LYP/6-31G* level).
Conclusions
In summary, we prepared non-planar, anthracene trimers
1 and 2 with a meta-substituted triphenylamine or triphenyl-
Figure 5. a) Solid-state emission spectra of 1, 2, 4, and 5. b) CIE coordi-
nate diagram of 1 (x=0.46, y=0.49), 2 (0.24, 0.37), 4 (0.23, 0.43), and 5
(0.21, 0.26) in the solid state, and 1 and 2 in CH2Cl2 solution. Inset:
a) Photographs of 1 and 2 in the solid state without (top) and with
(bottom) irradiation at 365 nm.
served with a lmax of 500 nm and FF of 35%. Oxidation,
methylation, and boranation of the phosphorus center of 2
gave rise to 2a–c, respectively, in high yields (Figure 6 and
Scheme S1 in the Supporting Information), and pale green
emission (lmax ꢀ510 nm) with FF =15, 4, and 30% was ob-
served from their respective solids (Figure S28 in the Sup-
Figure 7. a) Molecular structure of para-substituted anthracene trimers 4
and 5. b) Space-filling representation of the optimized structure of 4
(DFT calculation at the B3LYP/6-31G* level).
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Anthracene Trimers with a meta-Substituted Triphenylamine or Triphenylphosphine Core
0.35 mmol) in dry THF (5 mL)was added dropwise to the solution at
phosphine core. The nitrogen-containing 1 exhibits a polar-
ized TICT emission that can be modulated over approxi-
mately 140 nm, from blue to pale yellow, in solution. The
phosphorus analogue 2 exhibits blue, anthracene-based
emission in solution. Due to their unusual three-fold geome-
try, both 1 and 2 exhibit enhanced emission in the solid
state, that is, yellow and pale green fluorescence, respective-
ly, with moderate quantum yields. Whereas fluorophore p-
systems are typically modified and expanded through linear
para-substitutions, we emphasize that divergent molecular
assemblies of meta-substituted fluorophores can provide
a new direction for achieving novel materials with enhanced
emissive properties.
À808C. The resultant mixture was warmed to RT over a period of 1 d,
and the crude product was extracted with CH2Cl2. Subsequently, the com-
bined organic layer was dried over MgSO4, filtrated, and concentrated
under reduce pressure. The crude product was purified by gel permeation
chromatography (CHCl3) to afford anthracene trimer 2 as a yellow solid
(0.155 g, 0.196 mmol, 47% yield). 1H NMR (400 MHz, CDCl3, RT): d=
6.91 (dd, J=8.8, 8.8 Hz, 6H), 7.34 (m, 9H), 7.42 (d, J=8.8 Hz, 6H), 7.55
(dd, J=7.4, 7.6 Hz, 6H), 7.60 (d, J=7.2 Hz, 3H), 7.66 (dd, J=7.6, 9.2 Hz,
6H), 7.99 (d, J=8.4 Hz, 6H), 8.46 ppm (s, 3H); 13C NMR (100 MHz,
CDCl3, RT): d=125.2, 125.5, 126.6, 126.7, 128.3, 128.8 (d, JCP =7.4 Hz),
130.2, 131.4, 132.1, 133.1 (d, JCP =21.4 Hz), 136.4 (d, JCP =17.8 Hz), 136.5,
137.6 (d, JCP =12.5 Hz), 139.3 ppm (d, JCP =6.3 Hz); 31P NMR (121 MHz,
CDCl3, RT): d=À4.12 ppm; FT-IR (KBr): n˜ =3048, 1441, 1392, 1355,
1220, 1167, 1098, 1014, 953, 884, 842, 772, 734, 706, 459 cmÀ1; MALDI-
TOF MS (dithranol): m/z calcd. for C60H39P: 790.99, found 791.29
[M+H]+; HR MS (ESI): m/z calcd. for C60H39PNa: 813.2687, found
813.2680 [M+Na]+; elemental anal. (%) calcd. for C60H39P·2.35H2O: C
86.48, H 5.29; found: C 86.17, H 4.96.
Experimental Section
Synthesis and X-ray Crystal Data of 2’
General
9-(3-Bromo-5-(2-methoxyethoxy)phenyl)anthracene (0.570 g, 1.40 mmol)
and dry THF (40 mL) were added to a 2-neck 100 mL glass flask under
a N2 atmosphere. A solution of nBuLi (0.52 mL, 1.4 mmol) in n-hexane
(2.69m) was added dropwise to this flask at À808C under a N2 atmos-
phere. After stirring at À808C for 1 h, a solution of trimethylphosphite
(4.0 mL, 0.40 mmol) in dry n-hexane (15 mL) was added dropwise at
À808C. The resultant mixture was warmed to RT over a period of 1 d.
The crude product was extracted with CH2Cl2 and then combined organic
layer was dried over MgSO4, filtrated, and concentrated under reduce
pressure. The crude product was then purified by gel permeation chroma-
NMR spectra were recorded on a Bruker Avance-400 spectrometer. In-
frared (IR) spectra were recorded on a JASCO FT/IR-4100 spectropho-
tometer. MALDI-TOF and ESI-TOF mass spectrometries were mea-
sured on Shimadzu AXIMA-CFR Plus and Bruker micrOTOF II instru-
ments, respectively. Absolute photoluminescence (PL) quantum yield
was measured on a Hamamatsu C9920–02G system with an integration
sphere. UV/Vis and fluorescence spectra were obtained by using JASCO
V-670DS and SHIMADZU RF-5300PC spectrometers, respectively. Ele-
mental analysis was carried out by using a LECO CHNS-932 VTF-900
analyzer. X-ray powder diffraction patterns were recorded on a Bruker
New D8 ADVANCE X-ray diffractometer. Time-resolved absorption
and emission spectra analyses were carried out using a Hamamatsu
C7700-ABS-N with C7700–01 high dynamic range streak camera and
Continuum Minilite system. Solvents and reagents were purchased from
Tokyo Chemical Industry Co., Ltd., WAKO Pure Chemical Industries
Ltd., Kanto Chemical Co., Inc., Sigma–Aldrich, and Cambridge Isotope
Laboratories, Inc, respectively
tography (CHCl3) to afford anthracene trimer 2’ as
a yellow solid
(0.250 g, 0.247 mmol, 62% yield). 1H NMR (400 MHz, CDCl3, RT): d=
3.40 (s, 9H), 3.70 (t, J=4.6 Hz, 6H), 4.07 (t, J=4.6 Hz, 6H), 6.91–6.95
(m, 9H), 7.12–7.22 (m, 6H), 7.35 (dd, J=6.4, 8.4 Hz, 6H), 7.47 (d, J=
8.8 Hz, 6H), 7.99 (d, J=8.4 Hz, 6H), 8.46 ppm (s, 3H); 13C NMR
(100 MHz, CDCl3, RT): d=59.3, 67,6, 71.2, 118.3, 119.2 (d, JCP =22.1 Hz),
125.2, 125.6, 126.7, 128.2, 129.1 (d, JCP =18.8 Hz), 130.1, 131.4, 136.3,
138.8 (d,
JCP =12.8 Hz), 140.6 (d, JCP =7.2 Hz), 159.1 ppm (d, JCP =
8.9 Hz); 31P NMR (121 MHz, CDCl3, RT): d=À1.91 ppm; FT-IR (KBr):
n˜ =3049, 2924, 2877, 2362, 1571, 1444, 1406, 1356, 1261, 1237, 1126, 1065,
Synthesis of Anthracene Trimer 1
9-(3-Aminophenyl)anthracene (0.301 g, 1.04 mmol), 9-(3-chlorophenyl)-
anthracene (0.697 g, 2.41 mmol), and tBuOK (0.746 g, 6.65 mmol) were
added to a 2-neck 100 mL glass flask under a N2 atmosphere. Next, a solu-
886, 737, 704 cmÀ1
; MALDI-TOF MS (dithranol): m/z calcd. for
C69H57O6P [M]+: 1012.39, found 1012.10.
C69H57N4O7P, Mr =1029.12, trigonal, R3, a=18.935(4) ꢃ, b=18.935 (4) ꢃ,
c=51.597(11) ꢃ, a=908, b=908, g=1208, V=16021(6) ꢃ3, Z=12,
tion of P
ACHTUNGTRENNUNG
1calcd =1.280 gcmÀ3, F
ACHTUNGTRENNUNG
a 50 mL glass flask containing Pd CTHNUGTRENNUNG
and dry toluene (25 mL). After stirring the mixture for 30 min at RT, it
was added to the 100 mL flask and then the resulting solution was stirred
for 72 h at 1108C, followed by concentration under reduce pressure. The
crude product was extracted with CH2Cl2 (50 mL ꢂ 3)and washed with
aqueous NaCl. Subsequently, it was purified by chromatography on
a short silica-gel column (CHCl3) and by gel permeation chromatography
to afford anthracene trimer 1 as an orange solid (0.567 g, 0.733 mmol,
a
AHCTUNGTRENNUNG(
contains the supplementary crystallographic data of 2’. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam. ac.uk/data_request/cif.
1
70% yield). H NMR (400 MHz, CDCl3, RT): d=7.01 (m, 9H), 7.36 (dd,
J=8.0, 8.8 Hz, 6H), 7.44 (m, 9H), 7.58 (d, J=8.8 Hz, 6H), 8.00 (d, J=
8.8 Hz, 6H), 8.47 ppm (s, 3H). 13C NMR (100 MHz, CDCl3, RT): d=
123.2, 125.1, 125.4, 125.9, 126.5, 126.6, 127.0, 128.1, 129.3, 130.0, 131.3,
136.5, 140.0, 147.7 ppm; FT-IR (KBr): n˜ =3050, 2360, 1592, 1570, 1478,
1440, 1357, 1315, 1261, 883, 842, 788, 734, 708 cmÀ1; MALDI-TOF MS
(dithranol): m/z calcd. for C60H39N 773.31, found 773.17 [M]+; elemental
anal. (%) calcd. for C60H39N·0.65CHCl3: C 85.54, H 4.69, N 1.64, found:
C 85.64, H 4.62, N 1.62.
Acknowledgements
This work was financially supported by the Japan Society for the Promo-
tion of Science (JSPS) via “Funding Program for Next Generation
World-Leading Researchers” and by the Japanese Ministry of Education,
Culture, Sports, Science and Technology (MEXT) via Grants-in-Aid for
Scientific Research on Innovative Areas “Coordination Programming”
(Area 2107, No. 21108011) and the global COE program (GCOE) “Edu-
cation and Research Center for Emergence of New Molecular Chemis-
try”. We thank Dr. Jeremy Klosterman for helpful discussions and Dr.
Tsutomu Yamauchi for assistance with powder X-ray diffraction analysis.
Synthesis of Anthracene Trimer 2
9-(3-Bromophenyl)anthracene (0.423 g, 1.27 mmol) and dry THF
(25 mL) were added to a 2-neck 50 mL glass flask under a N2 atmos-
phere. A solution of nBuLi (0.77 mL, 1.2 mmol) in n-hexane (1.63m) was
added dropwise to this flask at À808C under a N2 atmosphere. After stir-
ring at À808C for 1 h,
a solution of trimethylphosphite (0.51 mL,
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[15] See the Supporting Information.
[8] To the best of our knowledge, there have been no reports on meta-
substituted TPA and TPP with large aromatic rings and only a few
recent reports on the para-substituted TPAs. See: a) S.-L. Lai, Q.-X.
Tong, M.-Y. Chan, T.-W. Ng, M.-F. Lo, S.-T. Lee, C.-S. Lee, J. Mater.
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[16] The crystal of 2’ includes the phosphine oxide derivatives as disor-
1
dered molecules (~30%), as confirmed by H NMR analysis, due to
oxidation during the crystallization of 2’.
[17] V. Gutmann, Coord. Chem. Rev. 1976, 18, 225–255.
[18] Aminophenylanthracene 3c showed a solvent-dependent emission
(lmax =410 nm) but almost no solvatofluorochromic properties.
[19] The emission lifetimes (t) of 1 and 4 are 7.3 and 3.9 ns (in benzene),
14.2 and 6.1 ns (in CH2Cl2), and 12.5 and 10.3 ns (in DMSO), respec-
tively.
[20] a) A. Siemiarczuk, Z. R. Grabowski, A. KrꢆwczyÇski, M. Asher, M.
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[21] Compounds 1 and 2 did not show aggregation-induced emission en-
hancement (AIEE) properties but 1 showed weak aggregation-in-
duced emission (AIE) properties in a THF/H2O solution (Figure S29
in the Supporting Information).
Received: April 9, 2012
Published online: && &&, 0000
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www.chemasianj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!

FULL PAPERS
Fluorescent Triskelions: Combining
meta-triphenylamine or triphenylphos-
phine with three anthracene fluoro-
phores gives rise to fluorescent non-
planar triskelions 1 and 2. The emis-
sive properties of 1 are highly solvato-
chromic, yielding blue to pale green
and even pale yellow fluorescence,
whereas the blue emission of 2 is sol-
vent-insensitive. Anthracene trimers
1 and 2 are both emissive in the solid
state, displaying yellow and pale green
fluorescence, respectively, with moder-
ate quantum yields.
Fluorosphores
Zhiou Li, Hiromi Ishizuka,
Yoshihisa Sei, Munetaka Akita,
Michito Yoshizawa*
&&&& — &&&&
Extended Fluorochromism of Anthra-
cene Trimers with a meta-Substituted
Triphenylamine or Triphenylphosphine
Core
Chem. Asian J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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These are not the final page numbers! ÞÞ