Photophysical properties of 1,3,6,8-tetrakis(arylethynyl)pyrenes with donor or acceptor substituents: their fluorescence solvatochromism and lightfastness

Article abstract of DOI:10.1016/j.tet.2009.08.079

We prepared a series of 1,3,6,8-tetrakis(arylethynyl)pyrenes with donor or acceptor substituents and investigated their photophysical properties. Solvent polarity hardly affected on the UV/vis spectra of all of the tetrakis(arylethynyl)pyrenes used in thi

Full text of DOI:10.1016/j.tet.2009.08.079

Tetrahedron 65 (2009) 9357–9361
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Photophysical properties of 1,3,6,8-tetrakis(arylethynyl)pyrenes with donor
or acceptor substituents: their fluorescence solvatochromism and lightfastness
,
a
b
c
c
Kazuhisa Fujimoto a , Hisao Shimizu , Masaru Furusyo , Seiji Akiyama , Mio Ishida ,
*
Utako Furukawa c, Toshiaki Yokoo c, Masahiko Inouye a
,
*
a Graduate School of Pharmaceutical Sciences, University of Toyama, Sugitani 2630, Toyama 930-0194, Japan
b Analysis Technology Research Center, Sumitomo Electric Industries Ltd., 1-1-1 Koyakita, Itami, Hyogo 664-0016, Japan
c Research and Development Division, Mitsubishi Chemical Group, Science and Technology Research Center, Inc., 1000 Kamoshida, Aoba, Yokohama 227-8502, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 August 2009
Received in revised form 30 August 2009
Accepted 31 August 2009
Available online 3 September 2009
We prepared a series of 1,3,6,8-tetrakis(arylethynyl)pyrenes with donor or acceptor substituents and
investigated their photophysical properties. Solvent polarity hardly affected on the UV/vis spectra of all of
the tetrakis(arylethynyl)pyrenes used in this study. On the other hand, electron-donating groups, NMe2
and NPh2 groups imparted fluorescence solvatochromicity to the skeleton by intramolecular charge
transfer in the excited state. Furthermore, a tetrakis(arylethynyl)pyrene showed better lightfastness upon
exposure to laboratory weathering using a xenon long arc lamp than coumarin.
Keywords:
Photochemistry
Ó 2009 Elsevier Ltd. All rights reserved.
Fluorescence solvatochromism
Tetrakis(arylethynyl)pyrene
1. Introduction
shows two-photon absorption and electroluminescence proper-
ties.8,9 However, systematic studies on the variously substituted
Acetylene has been widely employed for linking
units and for effectively extending the -conjugation. The progress
of such -conjugated materials by means of acetylene chemistry has
p
-conjugated
(arylethynyl)pyrenes remain elusive especially for their
photophysical characteristics. We also have been investigating the
photophysical properties of various (arylethynyl)pyrene de-
rivatives.6,10 Here we report the comprehensive studies on photo-
physical properties of tetrakis(arylethynyl)pyrenes with donor or
acceptor substituents.
p
p
strongly depended on the development of Sonogashira coupling
reaction.1 Thereby, many attractive acetylene-linked molecules have
emerged such as for semiconducting polymers,2 macrocyclic mole-
cules,3 helical polymers,4 and energy transfer cassettes.5 Previously,
we have synthesized a variety of alkynylpyrene derivatives from
mono- to tetrabromopyrenes and arylacetylenes by Sonogashira
coupling reaction, and comprehensively examined their photo-
physical properties.6 The alkynylpyrenes thus prepared showed not
only long absorption and emission wavelengths but also high fluo-
rescence quantum yields as compared with pyrene itself. Addition-
ally, the alkynylpyrene skeleton could be applied to practically useful
fluorescence probes for proteins and DNAs. Other research groups
have reported that mono-substituted (arylethynyl)pyrenes such as
[4-(N,N-dimethylamino)phenylethynyl]pyrene display fluorescence
solvatochromism by intramolecular charge transfer (ICT) mecha-
nism.7 Recently, interesting papers have beenpublished by Kim et al.,
in which tetrakis [4-(N,N-dimethylamino)phenylethynyl]pyrene
2. Results and discussion
2.1. Synthesis of tetrakis(arylethynyl)pyrenes
Figure
1 shows the chemical structures of tetrakis(aryl-
ethynyl)pyrenes 1–5 used in this study. These compounds consist of
pyrene, acetylene, and aryl moieties: the aryl moieties include R
substituents at the para position against the acetylene one, and the R
is electron-donating, H, or electron-withdrawing group.10 Pyrene
itself is electrically neutral, so that its electric characteristic will de-
pendonthoseof theRsubstituentsthroughp-conjugation.Therefore,
when the R is an electron-donating group, the pyrene moiety is en-
visaged to behave as an acceptor, and vice versa. The tetrakis(aryl-
ethynyl)pyrenes 1–5 were prepared by Sonogashira coupling reaction
of tetrabromopyrene with the corresponding arylacetylenes (Fig. 1).
Although we synthesized two more acceptor-modified tetrakis(aryl-
ethynyl)pyrenes (R¼NO2, CN) in addition to 4 and 5, they were hardly
purified because of their poor solubilities in common solvents.
* Corresponding authors. Tel.: þ81 76 434 7526; fax: þ81 76 434 5049 (K.F.); tel.:
þ81 76 434 7525; fax: þ81 76 434 5049 (M.I.).
E-mail addresses: fujimoto@pha.u-toyama.ac.jp (K. Fujimoto), inouye@pha.u-
toyama.ac.jp (M. Inouye).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.08.079

9358
K. Fujimoto et al. / Tetrahedron 65 (2009) 9357–9361
Table 1
Absorbance and fluorescence data of 1–5 in various solvents and a PMMA film
R
Solvents
Absorptiona
Fluorescencea
Stokes’
shift
(nm)
b
labs
log
3
lem
Ffc
(nm)
(Mꢁ1 cmꢁ1
)
(nm)
1 (NMe2)
1,4-Dioxane
CHCl3
THF
508
510
515
515
513
525
514
4.89
4.84
4.81
4.86
4.85
4.86
535
543
548
556
619
633
54
0.63
0.75
0.46
0.59
0.055
0.031
0.66e
27
33
33
CH2Cl2
CH3CN
DMF
41
106
108
30
Filmd
2 (NPh2)
3 (H)
THF
509
512
465
464
467
476
4.76
4.84
546
535
4.81
4.81
482
494
0.64
0.32e
0.99
0.53e
0.98
0.90
37
23
16
17
15
18
Filmd
THF
Figure 1. Tetrakis(arylethynyl)pyrenes 1–5 and their synthetic scheme.
Filmd
THF
Furthermore, the poor solubilities hampered us from obtaining clear
UV/vis and fluorescence spectra with standard spectrometers.
4 (CF3)
5 (CO2Et)
4.74
4.78
THF
a
[1–5]¼1.0ꢀ10ꢁ6 M.
b
c
labs is the absorption band appearing at the longest wavelength.
2.2. Solvatochromism of tetrakis(arylethynyl)pyrenes
Fluorescence quantum yields, determined by fluorescein (Ff¼0.85 in 0.1 M
NaOH) as a reference compound.
d
The film was prepared from PMMA in THF (19 wt %), and 1–3 were dispersed in
To explore the influence of the R substituents upon the ab-
sorption and emission of 1–5, their UV/vis and fluorescence spectra
were measured at the concentration of 1.0ꢀ10ꢁ6 M in THF. THF was
selected because all of 1–5 revealed relatively good solubilities in
this solvent. The absorption maximum (labs) of the neutral 3 was
the film.
e
Absolute fluorescence quantum yields.
Generally, solvatochromism depends on the extent of charge
separation in the ground state of a chromophore. Therefore, density
functional theoretical (DFT) calculationwas performed for assessing
the charge separation in the ground states of 1 and 4. Figure S2 in
Supplementary data displays optimized structures and HOMO and
LUMO states for 1 and 4 in a dielectric constant corresponding to
CHCl3. The benzene moieties in them adopted coplanar structures
against the pyrene core, and all of HOMO and LUMO delocalized. In
other solvents, similar results were obtained. Therefore, solvent
polarity hardly affects on the ground states of 1 and 4, supporting no
solvatochromicity of the tetrakis(arylethynyl)pyrenes.
observed at 465 nm (log
by ca. 80 and 60 nm as compared with those of phenyl-
3
¼4.84), which bathochromically shifted
ethynylpyrene (382 nm, log
3
¼4.65) and bis(phenylethynyl)pyrene
(407 nm, log
3
¼4.74) in EtOH, respectively (Fig. 2, Table 1).6 The
bathochromic shift is most likely due to the extension of
p-con-
jugation with increase of the number of phenylethynyl groups on
the pyrene core. The molar extinction coefficient also increased
with the extension of
p-conjugation. The donor-modified 1
(R¼NMe2, 515 nm) and 2 (R¼NPh2, 509 nm) showed much longer
absorption maxima than that of the neutral 3, while the acceptor-
modified 4 (R¼CF3) and 5 (R¼CO2C2H5) were sluggish. The longer
absorption maxima for 1 and 2 would be attributed to the electron
delocalization between the para-substituted donors and the pyrene
core through the phenylethynyl moieties.11 For evaluating the sol-
vatochromism of the tetrakis(arylethynyl)pyrenes, their UV/vis
spectra were measured in various solvents, polarities of which
increase in the following order: 1,4-dioxane<chloroform<dichloro-
methane<THF<acetonitrilexDMF. As shown in Figure S1 in
Supplementary data, the donor-modified 1 and 2 showed almost
the same UV/vis spectra regardless of solvent polarity, and other
tetrakis(arylethynyl)pyrenes also behaved as 1 and 2 did (data not
shown).
2.3. Fluorescence solvatochromism of
tetrakis(arylethynyl)pyrenes
Figure 3 shows the normalized-fluorescence spectra of 1–5 at
the concentration of 1.0ꢀ10ꢁ6 M in THF. The electron-donating 1
and 2 revealed bathochromically shifted emissions than 3–5. The
magnitude of the Stokes’ shifts for 1 and 2 approximately doubled
relative to those for 3–5 (Table 1), and the vibronic bands for 1 and
2 tend to deform and broaden. Since THF possesses a moderate
1
1 (R = NMe2)
2 (R = NPh2)
3 (R = H)
1 (R = NMe2)
2 (R = NPh2)
4 (R = CF3)
5 (R = CO2Et)
3 (R = H)
0.1
4 (R = CF3)
5 (R = CO2Et)
0.5
0.05
0
500
600
700
0
300
400
500
Wavelength (nm)
Wavelength (nm)
Figure 3. Normalized-fluorescence spectra of 1–5 in THF: [1–5]¼1.0ꢀ10ꢁ6 M. All of 1–
5 were excited at the each labs wavelength.
Figure 2. UV/vis spectra of 1–5 in THF: [1–5]¼1.0ꢀ10ꢁ6 M.

K. Fujimoto et al. / Tetrahedron 65 (2009) 9357–9361
9359
solvent polarity, it might interact with the excited states of the
donor-modified alkynylpyrenes. Next, fluorescence spectra for 1–5
were measured in various solvents for certifying the influence of
solvent polarity on their emission.
core.7b,13 Relationship between Stokes’ shift and the difference in the
dipole moments can be related by the Lippert–Mataga equation:
D
v ¼ 2
D
m2eg
D
f =hca3 þ const;
Figure 4a and Figure S3 in Supplementary data demonstrate the
normalized-fluorescence spectra of 1 and 2, respectively, in the
same series of solvents used for the UV/vis analysis. The emission
color for 1 changed from light green in 1,4-dioxane via yellow to red
in DMF (Fig. 4b). The Stokes’ shifts for 1 and 2 consecutively in-
creased, accompanying the disappearance of their vibronic bands,
with increase of the solvent polarity (Table 1 and Table S1 in Sup-
plementary data). In the case of 1, the difference in the shift spans
ca. 80 nm from 1,4-dioxane to DMF. The donor-modified 1 and 2
retained relatively high quantum yields in these solvents except for
CH3CN and DMF. In general, fluorophores, of which emission
wavelengths are beyond 600 nm, tend to show low quantum yields
caused by the vibrational energy of polar solvents.12 On the other
hand, 3–5 did not show such fluorescence solvatochromism (Fig. S4
in Supplementary data). Thus, only donor groups, NMe2 and NPh2
were found to afford fluorescence solvatochromicity to the tetra-
kis(phenylethynyl)pyrene skeleton. The emission wavelength of 1
in DMF is 631 nm, which is ca. 90 nm longer than that of mono-
substituted [4-(N,N-dimethylamino)phenylethynyl]pyrene pre-
viously reported by Ho et al.7b This longer emission wavelength
must be attributed to the tetra-substitution in 1.
hꢀ
ꢁ.ꢀ
ꢁi
D
f ¼ ½ð
3
ꢁ 1Þ ð2
3
þ 1Þꢂ ꢁ n2 ꢁ 1
2n2 þ 1
=
where
D
v and Dmeg, are Stokes’ shift and the difference in the dipole
moment between the excited and ground states, respectively;
the orientation polarizability; h is Planck’s constant; c is the ve-
locity of light; a is the Onsager radius around a fluorophore; is the
dielectric constant; n is refractive index.14–16 To calculate Dmeg, the
Stokes’ shifts for 1 were plotted against the f values in the mixed
solvents of 1,4-dioxane and acetonitrile varying their proportion
(Fig. 5).13g From the slope according to the Lippert–Mataga equa-
tion, the Dmeg value for 1 was estimated to be ca. 30 D, meaning that
the dipole moment of 1 drastically changed from the ground to the
excited states.17 On the basis of the large Dmeg value and the DFT
analysis for the ground states, one might suppose that charge
separation can exist only in the excited states of the donor-modi-
fied tetrakis(phenylethynyl)pyrenes. The Lippert–Mataga plot for
the various solvents used in this study also gave a relatively good
Df is
3
D
proportion between the Stokes’ shifts of 1 and their
Df values
(Fig. S5 in Supplementary data).13g The pyrene core in 1 can behave
as an acceptor moiety against the dimethylamino groups to give
rise to fluorescence solvatochromicity probably based on ICT
mechanism. To reinforce the ICT mechanism, time-dependent DFT
calculations for 1 and 4 were tried to shed light on their HOMO and
LUMO in the excited states.13b,f Unfortunately, the calculation
hardly converged owing to the molecular size of 1 and 4. Never-
theless, the findings obtained from UV/vis and fluorescence spectra
and Lippert–Mataga analysis imply that the charge separation ari-
ses in the excited states of the donor-modified 1 and 2.
(a)
1
1,4-dioxane
CHCl3
THF
CH2Cl2
CH3CN
DMF
0.5
3
0
500
600
700
800
Wavelength (nm)
(b)
2
0.20
0.25
0.30
Δ
Figure 5. Plots of the Stokes’ shift
Dv versus the solvent polarity
Df, derived from fluo-
rescence spectra of1 ina series of 1,4-dioxane/acetonitrile mixtures;
mixture using and values calculated using the molar fractions as follows:
cacetonitrileꢀ38.8þcdioxaneꢀ2.218; n¼cacetonitrileꢀ1.3442þcdioxaneꢀ1.4224; cacetonitrile
cdioxane¼1.
Df is obtained foreach
Figure 4. (a) Normalized-fluorescence spectra of 1 at the concentration of 1.0ꢀ10ꢁ6 M
in 1,4-dioxane, chloroform, dichloromethane, THF, acetonitrile, and DMF. The excita-
tion wavelength in each solvent was the corresponding labs in the solvent. (b) Fluo-
rescence photograph of 1; solvent polarity increases in the following order from left to
right: 1,4-dioxane, chloroform, dichloromethane, THF, acetonitrile, and DMF.
3
n
3¼
þ
2.5. Photophysical properties of tetrakis(arylethynyl)pyrenes
in PMMA films
2.4. Origin of fluorescence solvatochromism
Such large Stokes’ shift observed for 1 and 2 in polar solvents may
result from the difference in the dipole moments between the delo-
calized ground state and the highly localized excited one. The highly
localized excited state must come from the intramolecular charge
transfer (ICT) between the NMe2 (NPh2) groups and the pyrene
To assess the possibilities of tetrakis(arylethynyl)pyrenes as
a photomaterial, polymethylmethacrylate (PMMA) films of 1–3 and
coumarin were prepared. Photophysical data (labs, lem, and Ff) for
1–3 in the film were shown in Table 1. The absorption and emission
wavelengths for 1–3 in the film almost correspond to those in THF.

9360
K. Fujimoto et al. / Tetrahedron 65 (2009) 9357–9361
The films including 1–3 and coumarin were exposed to laboratory
weathering using a xenon long arc lamp in order to explore their
lightfastness (Fig. 6). After the exposure for 80 h, ca. 30% of 2 sur-
vived, whereas most of coumarin underwent degradation. Diary-
lamino groups were reported to be a good auxofluorophore for
imparting photostability to 1,4-distyrylbenzene cores as compared
with dialkylamino ones by Kauffman and Monya.18 The similar
substituent effect is considered to work on the 1,3,6,8-tetra-
kis(phenylethynyl)pyrene core.
tetrabromopyrene19
,
4-(dimethylamino)phenylacetylene20
(6),
(4-ethynylphenyl)diphenylamine21 (7), [4-(ethoxycarbonyl)phenyl]-
acetylene22 (10) were prepared according to published procedures.
The 1,3,6,8-tetrakis(arylethynyl)pyrenes 1,8 3,19 and 419 published
previously were synthesized in the same synthetic procedure as that
for 2 and 5 vide infra.
4.3. Spectroscopic measurements in solution
Steady state absorption and emission spectra were recorded at
298 K using a 1 cm pass length cell. Fluorescence quantum yields
were determined by using fluorescein (Ff¼0.85 in 0.1 M NaOH)23 as
a reference compound. The fluorescence quantum yields were
calculated according to the following equation.
1
0.5
0
h
i
FfðsampleÞ
¼
FfðstandardÞ ꢀ Astandard=Asample
h
i
h
i
2
ꢀ Isample=Istandard ꢀ nsample=nstandard
In this equation, Ff(sample) and Ff(standard) are the quantum yields
of a sample and a standard, respectively. Asample, Isample, and nsample
are the optical density, the integrated emission intensity at the
excitation wavelength, and the value of refractive index for
the sample, respectively. Astandard, Istandard, and nstandard are those for
the standard.
0
40
Exposure Time (h)
80
4.4. Preparation of PMMA films
Figure 6. Normalized intensities derived from the excitation spectra of 1–3 and cou-
marin in the PMMA film after exposure to artificial sunlight through a UV-cut filter at
40 ꢃC, plotted against the exposure time: 6 for 1, B for 2, , for 3, and ꢀ for coumarin.
A 6.5 kW xenon long arc lamp was used as a light source. The relative humidity was
controlled to be ca. 50%. The samples were fixed away from ca. 310 mm of the light
source.
Each chromophore was dissolved in a PMMA/THF solution
(19 wt %). A PET film (A6 size) was coated with the solution (1.5 mL)
including a chromophore by spin coating. After dried up at room
temperature for 1 h, the coated film was subjected to various
spectroscopic measurements. When a chromophore is hard to be
fully dissolved in the medium, its PMMA film was prepared in the
dispersed state.
3. Conclusion
In summary, we have developed a variety of 1,3,6,8-tetra-
kis(arylethynyl)pyrenes bearing electron-donating or electron-
withdrawing groups and examined their photophysical properties.
The donor-modified tetrakis(arylethynyl)pyrenes showed fluores-
cence solvatochromism on the basis of ICT mechanism, while the
acceptor-modified ones never did. Additionally, a donor-modified
tetrakis(arylethynyl)pyrene was found to be stable under labora-
4.5. Computational work
Geometry optimize calculation was carried out for 1 and 4 by
using Gaussian 03W program. Hybrid density functional (B3LYP)
level of theory in conjunction with 6-31G(d) basis sets has been
used.24
tory
weathering
as
compared
with
coumarin.
The
tetrakis(arylethynyl)pyrenes are expected to be applicable to bio-
probes for hydrophobic pockets in various biomolecules and
photomaterials.
4.6. Preparation of tetrakis(arylethynyl)pyrenes 2 and 5
4.6.1. 1,3,6,8-Tetrakis{[4-(N,N0-diphenylamino)phenyl]ethynyl}pyr-
ene (2). A degassed THF/Et3N (150þ40 mL) mixed solution of
1,3,6,8-tetrabromopyrene19 (0.12 g, 0.232 mmol), Pd(t-Bu3P)2
(24 mg, 0.0470 mmol), CuI (4.4 mg, 0.0231 mmol), and (4-ethynyl-
phenyl)diphenylamine20 (7) (0.281 g, 1.04 mmol) was refluxed for
48 h. The reaction mixture was then cooled to room temperature
and filtered. The filtrate was evaporated, and the residue was
purified by chromatography (silica gel; eluent, CHCl3) to give 2 (red
powder): yield 42% (0.124 g); mp >320 ꢃC (dec); IR (KBr):
~
4. Experimental
4.1. General methods
1H NMR spectra were recorded at 300 MHz. The 13C NMR spectra
for 1,3,6,8-tetrakis(arylethynyl)pyrenes could not be measured
because their highly concentrated solutions in various common
organic solvents were not available due to their poor solubility.
Absolute fluorescence quantum yields were measured with a com-
mercial spectrometer equipped with an integrating sphere, radius
of which is 3.3 inch. FABMS and MALDI-MS experiments were
performed with 3-nitrobenzyl alcohol and retinoic acid as a matrix,
respectively. Melting points are uncorrected.
n
¼ 2196 cmꢁ1; 1H NMR (THF-d8)
¼7.06–7.16 (m, 16H), 7.28–7.33
d
(m,16H), 7.60 (d, J¼8.7 Hz, 8H), 8.39 (s, 2H), 8.78 (s, 4H); MS (MALDI)
m/z calcd for C96H62N4: 1270.5; found: 1270.7 [M]þ; HRMS (FAB)
m/z calcd for C96H63N4: 1271.5053; found: 1271.5026 [MþH]þ.
4.6.2. 1,3,6,8-Tetrakis[(4-ethoxycarbonylphenyl)ethynyl]pyrene (5). A
degassed THF/Et3N (30þ30 mL) mixed solution of 1,3,6,8-tetra-
bromopyrene19 (0.46 g, 0.888 mmol), PdCl2(PPh3)2 (31 mg,
0.0442 mmol), CuI (8.5 mg, 0.0446 mmol), and [4-(ethoxy-
carbonyl)phenyl]acetylene21 (10) (0.697 g, 4.0 mmol) was refluxed
for 24 h. The reaction mixture was then cooled to room temperature
4.2. Materials
Reagents were purchased from commercial sources and
used without further purification. The following compounds 1,3,6,8-

K. Fujimoto et al. / Tetrahedron 65 (2009) 9357–9361
9361
9. Oh, J.-W.; Lee, Y. O.; Kim, T. H.; Ko, K. C.; Lee, J. Y.; Kim, H.; Kim, J. S. Angew.
Chem., Int. Ed. 2009, 48, 2522–2524.
10. Shimizu, H.; Fujimoto, K.; Furusyo, M.; Maeda, H.; Nanai, Y.; Mizuno, K.; Inouye,
M. J. Org. Chem. 2007, 72, 1530–1533.
11. Toyota, K.; Kawasaki, S.; Yoshifuji, M. J. Org. Chem. 2004, 69, 5065–5070.
12. The HandbookdA Guide to Fluorescent Probes and Labeling Technologies, 10th ed.;
Molecular Probes Invitrogen Corp: Carlsbad, CA, 2005.
13. Recent papers for fluorescence solvatochromism: (a) Lee, Y. O.; Jung, H. S.; Lee,
J. H.; No, K.; Kim, J. S. Bull. Korean Chem. Soc. 2007, 28, 2107–2110; (b) Yuan,
M.-S.; Liu, Z.-Q.; Fang, Q. J. Org. Chem. 2007, 72, 7915–7922; (c) Adhikari, R. M.;
Mondal, R.; Shah, B. K.; Neckers, D. C. J. Org. Chem. 2007, 72, 4727–4732; (d)
Nikitina, E. A.; Odinokov, A. V.; Grigoriev, F. V.; Basilevsky, M. V.; Khlebunov,
A. A.; Sazhnikov, V. A.; Alfimov, M. V. J. Phys. Chem. B 2007, 111, 3953–3959;
(e) Vaidya, S.; Johnson, C.; Wang, X.-Y.; Schmehl, R. H. J. Photochem. Photobiol.,
A 2006, 187, 258–262; (f) Zhao, C.-H.; Wakamiya, A.; Inukai, Y.; Yamaguchi, S.
and poured into water. The resulting precipitate was filtered and
washed with MeOH (100 mL), CHCl3 (100 mL), and benzene (100 mL)
successiveꢃly and dried to give 5 (orange powder): yield 70% (0.554 g);
~
mp >300 C (dec); IR (KBr):
n
¼ 1272; 1717, 2201, 2226 cmꢁ1
;
1H
NMR(THF-d8)
d
¼1.41 (t, J¼7.2 Hz,12H), 4.39(m, 8H), 7.85 (d, J¼8.7 Hz,
8H), 8.11 (d, J¼8.7 Hz, 8H), 8.53 (s, 2H), 8.83 (s, 4H); HRMS (FAB) m/z
calcd for C60H43O8: 891.2958; found: 891.2933 [MþH]þ.
Supplementary data
UV/vis spectra of 1 and 2 in various solvents, absorbance and
fluorescence data of 2, graphical presentation for HOMO and LUMO
in 1 and 4, normalized-fluorescence spectra of 2–5, Lippert–Mataga
plot of 1, and 1H NMR spectra of 2 and 5. Supplementary data
associated with this article can be found in online version, at
doi:10.1016/j.tet.2009.08.079.
´
J. Am. Chem. Soc. 2006, 128, 15934–15935; (g) Vazquez, M. E.; Blanco, J. B.;
Imperiali, B. J. Am. Chem. Soc. 2005, 127, 1300–1306.
14. Mataga, N.; Kaifu, Y.; Koizumi, M. Bull. Chem. Soc. Jpn. 1956, 29, 465–470.
15. Lippert, V. E. Z. Elektrochem. 1957, 61, 962–975.
16. Valeur, B. Molecular Fluorescence; Willey-VCH: Weinheim, Germany, 2002.
17. The Onsager radius for 1 was determined to be 8.37 Å. This value had been cal-
culated as the Onsager radius for DMAEPy by Ho et al. with DFTcalculation.7b The
location relationship between the donor and the acceptor in 1 can be accounted
to be the same as that in the mono-substituted [4-(N,N-dimethylamino)-
phenylethynyl]pyrene.
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