Fluorescence characteristics of naphthalene dendrimers at low concentration in aqueous solution

Article abstract of DOI:10.1246/bcsj.82.242

Water-soluble naphthalene dendrimers WN1, WN2, and WN3, together with the lipophilic compounds NI, N2, and N3 were prepared and their photochemical properties were examined. Whereas lipophilic dendrimers NI, N2, and N3 gave monomer emission peaking at 330

Full text of DOI:10.1246/bcsj.82.242

242
Bull. Chem. Soc. Jpn. Vol. 82, No. 2, 242–248 (2009)
© 2009 The Chemical Society of Japan
Fluorescence Characteristics of Naphthalene Dendrimers
at Low Concentration in Aqueous Solution
Ryosuke Akatsuka,1 Yoshihiro Shinohara,2 Tomoo Sato,1 Yoshinobu Nishimura,1 and Tatsuo Arai*1
1Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571
2Research Facility Center for Science and Technology, University of Tsukuba, Tsukuba 305-8571
Received August 25, 2008; E-mail: arai@chem.tsukuba.ac.jp
Water-soluble naphthalene dendrimers WN1, WN2, and WN3, together with the lipophilic compounds N1, N2, and
N3 were prepared and their photochemical properties were examined. Whereas lipophilic dendrimers N1, N2, and N3
gave monomer emission peaking at 330Í340 nm, water-soluble dendrimers WN1, WN2, and WN3 gave not only the
monomer emission at 330Í340 nm but also excimer emission peaking at 400 nm in aqueous solution under considerably
diluted conditions. The relative intensity of the excimer fluorescence at longer wavelengths compared to the monomer
emission depended on the dendrimer generation and the concentration of dendrimer and added salt (KCl). In particular the
excimer emission of the second generation dendrimer is considerably higher than those of the first and the third generation
dendrimers. Based on these experimental results, the aggregation and the excimer formation of water-soluble naphthalene
dendrimers in aqueous solution depending on the generation and the conditions were discussed.
Dendrimers are expected to have unusual chemical and/or
periphery.15 However, naphthalene excimer formed by inter-
molecular interaction in very dilute solution has not yet been
reported. Accordingly, we are interested in preparing and
studying the photochemical properties of water-soluble naph-
thalene dendrimers WN1, WN2, and WN3, together with the
lipophilic compounds N1, N2, and N3. In this case, the effect
of aromatic ring size on fluorescence properties arising from
intermolecular interaction can be expected. In this report,
typical fluorescence spectra at longer wavelength due to the
excimer was explored with water-soluble naphthalene dendri-
mers in connection to both concentration and salt effects on the
fluorescence properties, especially for the second generation of
dendrimer.
physical properties and many studies concerning dendrimer
effects have been reported.1Í5 We have prepared several kinds
of dendrimers exhibiting photochemical and photophysical
properties, which could be explained by usual analytical
processes. Among these, stilbene dendrimers having large
substituents of benzyl ether dendrons or polyphenylene
dendrons exhibited either fluorescence or photochemical
isomerization and almost no effect of the large dendron
substituents was observed.6Í8 However, the introduction of
hydrophilic groups such as carboxylate anion at the periphery
of the benzene ring of the benzyl ether stilbene dendrimers
enabled these compounds to be soluble in water and to exhibit
unusual ultrafast photoisomerization of the C=C double bond
(in the range of tens of nanoseconds) and rather slow molecular
structural change (ca. ms) due to the reorientation of surround-
ing dendron groups after the geometric isomerization of the
C=C double bond of the stilbene core.9,10 Thus, photochemical
properties of water-soluble photoresponsive dendrimers seem
to be interesting.
Results and Discussion
Absorption Spectra.
Figure 1 shows the absorption
spectra of N1, N2, and N3 in THF. The absorption edge for
these compounds was observed at slightly shorter than 320 nm.
The absorption spectrum of N1 showed vibrational structures
We have already prepared water-soluble dendrimers of
polyaromatic hydrocarbon such as pyrene and observed
fluorescence emission due to the excimer or aggregated form
of the core pyrene group even at relatively low concentration of
ca. 10Õ4 M.11 Thus, the water-soluble fluorescent molecules
may give aggregates showing characteristic fluorescence at
longer wavelength in contrast to the monomer emission.
Because of the shorter singlet lifetime and smaller aromatic
skeleton of naphthalene compared to pyrene, it is not easy to
observe the fluorescence emission of naphthalene in excimer or
aggregated form in solution at low concentrations. In contrast
to this, naphthalene excimer was observed by fluorescence
emission in solid state,12 polymers,13 photodimers,14 and
dendrimers having several naphthalene chromophores at the
Figure 1. Absorption spectra of N1, N2, and N3 in THF.
Published on the web February 13, 2009; doi:10.1246/bcsj.82.242

R. Akatsuka et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 2 (2009)
243
Table 1. Spectroscopic
Dendrimers
Parameters
of
Naphthalene
(a)
-
¾
-
max FL.
max UV
Compound
Ìf
/nm
/MÕ1 cmÕ1 c)
/nm
N1a)
271, 281, 292
271, 281, 292
274, 281
270, 280, 290
273
10300
14200
28200
7800
12400
22100
329, 338 3.5 © 10Õ3
328, 338 3.0 © 10Õ3
328, 338 2.1 © 10Õ3
328, 338 1.1 © 10Õ3
329Í340 2.9 © 10Õ3
329Í340 4.0 © 10Õ3
N2a)
N3a)
WN1b)
WN2b)
WN3b)
275
a) In THF. b) In 0.1 M KOH aqueous solution. c) At 280 nm.
(b)
Figure 2. Absorption spectra of WN1, WN2, and WN3 in
0.1 M KOH aqueous solution.
peaking at 271, 281, and 292 nm (Table 1). With increasing
generation, the molar extinction coefficient of the absorption
maxima at 271 and 281 nm increased, resulting in a broadened
spectrum. This increase is explained by the increase of benzyl
ether dendron groups with increasing generation. The small
absorbance around 310 nm is almost the same among these
compounds.
Figure 2 shows absorption spectra of WN1, WN2, and WN3
in 0.1 M KOH aqueous solution. In this case, WN1 showed
vibrational structure peaking at 270, 280, and 290 nm. The
spectral profile of the absorption spectra of WN2 became broad
and the molar extinction coefficient increased in comparison
with those of WN1, indicating that the conformation or
molecular environment of WN2 is different from that of WN1.
The extinction coefficient of WN3 shorter than 295 nm was
greater than that of WN2 indicating that the molecular structure
seems to be similar between WN2 and WN3, because the
observed band shorter than 295 nm is due to the benzyl ether
dendron groups and the number of the benzyl ether groups is
almost double in WN3 compared to WN2.
(c)
Figure 3. Change in the absorption spectra upon the
addition of KCl for (a) WN1, (b) WN2, and (c) WN3 in
0.001 M KOH aqueous solution.
exhibited similar spectral profile and intensity in fluorescence
spectra peaking at 330 and 340 nm and are assigned to
naphthalene monomer emission. The edge of fluorescence
spectra was observed at 420 nm for all the compounds. The
singlet excitation energy is calculated from the fluorescence
maximum (330 nm) to be 87 kcal molÕ1 (1 kcal = 4.184 kJ).
While the fluorescence excitation spectra of 1-methylnaphtha-
lene has quite similar spectral profile to the absorption spectra,
those of N1ÍN3 are different from their absorption spectra, but
are similar to the spectral profile of 1-methylnaphthalene. The
dendron groups of N1ÍN3 absorb light at similar spectral
region to the naphthalene, but the dendron groups with
carbomethoxy substituents at the terminal of the benzene ring
could not transfer the excitation energy to the core naphthalene
as already observed for stilbene-cored dendrimers.16 Therefore,
the excitation spectra of the dendrimers should exhibit a
different spectral profile from their absorption spectra. Thus,
the observed differences could be explained by the overlap of
the absorption spectra between the dendrons and the core
As shown in Figure 3, addition of KCl to the solution
slightly changed the absorption spectra leading to decrease of
absorbance at the maximum wavelength and broadening the
spectral profile. In particular the absorbance at 280 nm in WN2
in 0.001 M KOH aqueous solution slightly decreased and the
absorbance at 300 nm increased with increasing concentration
of KCl, in contrast to WN1 and WN3.
Fluorescence Spectra.
Figure 4 shows absorption,
fluorescence, and fluorescence excitation spectra of 1-methyl-
naphthalene, N1, N2, and N3 in THF. Dendrimers N1ÍN3

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Fluorescence of Naphthalene Dendrimers
Abs
Em.340 nm
Ex.280 nm
Abs.
(a)
(a)
Em.340 nm
Ex.280 nm
250
250
250
250
300
300
300
350
400
450
450
450
450
250
250
250
300
350
400
450
550
550
Wavelength/nm
Wavelength/nm
Abs.
Abs.
(b)
Em.340 nm
Em.340 nm
Ex.280 nm
(b)
Ex.280 nm
350
400
300
350
400
450
500
Wavelength/nm
Wavelength/nm
Abs
Abs.
(c)
Em.340 nm
(c)
Em.340 nm
Ex.280 nm
Ex.280 nm
350
400
300
350
400
450
500
Wavelength/nm
Wavelength/nm
Figure 5. Absorption, fluorescence, and fluorescence
excitation spectra of (a) WN1 (7.7 © 10Õ6 M), (b) WN2
(3.2 © 10Õ6 M), and (c) WN3 (1.5 © 10Õ6 M) in 0.1 M
KOH aqueous solution.
Abs.
(d)
Em.340 nm
Ex.280 nm
However, in WN2 an apparent shoulder peak at around 400 nm
was observed. The fluorescence at around 330Í340 nm was
assigned to the monomer fluorescence of the naphthalene ring
and the broad fluorescence at longer wavelength (µ400 nm)
could be assigned to the fluorescence from the excimer or
aggregated form. In these compounds the fluorescence excita-
tion spectra and the absorption spectra are also different, which
also indicate the lack of energy transfer from the surrounding
dendron group to the core naphthalene.
300
350
Wavelength/nm
400
Figure 4. Absorption, fluorescence, and fluorescence ex-
citation spectra of (a) 1-methylnaphthalene, (b) N1 (7.7 ©
10Õ6 M), (c) N2 (3.2 © 10Õ6 M), and (d) N3 (1.5 © 10Õ6
M) in THF.
Table 1 summarizes the photochemical properties, absorp-
tion maxima (-max UV), molar extinction coefficient (¾) at
naphthalene and the lack of singlet energy transfer from the
dendron group to the core.
-max UV, fluorescence maxima (-max FL), and fluorescence
quantum yield (Ìf) of naphthalene dendrimers.
Figure 5 shows absorption, fluorescence, and fluorescence
excitation spectra of WN1, WN2, and WN3 in 0.1 M KOH
aqueous solution. WN1 and WN3 show fluorescence spectra
similar to N1 peaking at around 330 and 340 nm, while broad
fluorescence up to 500 nm was observed with low intensity.
Figure 6 shows the fluorescence spectra of WN1, WN2, and
WN3 at varying concentration in 0.1 M KOH aqueous solution.
These spectra were normalized respectively by fluorescence
intensity at 340 nm. The peaks at around 340 nm are fluo-
rescence from naphthalene monomer. The broad spectra

R. Akatsuka et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 2 (2009)
245
(a)
(a)
WN1
(b)
(b)
WN2
(c)
(c)
WN3
Figure 7. Change in the fluorescence spectra upon the
addition of KCl for (a) WN1, (b) WN2, and (c) WN3 in
0.001 M KOH aqueous solution. Excitation wavelength is
280 nm for all the experiments.
Figure 6. Effect of dendrimer concentration (1.0 © 10Õ5Í
1.0 © 10Õ4 M) on the fluorescence spectra of (a) WN1, (b)
WN2, and (c) WN3 in 0.1 M KOH aqueous solution.
Excitation wavelength is 280 nm for all the experiments.
excimer increased more than ten times with addition of
800 mM KCl.
peaking around 400 nm are attributed to the fluorescence from
the naphthalene excimer or aggregated form. The relative
intensity of the excimer fluorescence to monomer from WN2
increased with increasing concentration.
Effect of Dendrimer Generation on Fluorescence Spec-
tra. The absorption and fluorescence spectra in THF solution
for all the dendrimers examined (N1, N2, and N3) exhibited
normal spectra from the monomer, indicating that these
dendrimers exist as monomer in THF solution. Water-soluble
dendrimers WN1, WN2, and WN3 in aqueous solution show
similar absorption spectra to N1, N2, and N3 except for a
slightly different absorption profile at longer wavelength. The
remarkable difference between the fluorescence spectra of N2
in THF solution and of WN2 in aqueous solution was observed.
Especially, the increase of fluorescence intensity was observed
upon the addition of KCl in aqueous solution. Although the
effect of KCl on the spectral profile for WN2 and WN3 is
different, these results indicate that the added KCl accelerates
the formation of the excimer-like structure due to the
aggregation of dendrimers. The effect on the excimer fluo-
rescence is considerably larger for WN2 than for WN3
Figure 7 shows the change in the fluorescence spectra of
WN1, WN2, and WN3 in 0.001 M KOH aqueous solution upon
addition of KCl. The intensity of the fluorescence of WN1 is
almost independent of the concentration of KCl, but a small
decrease of the monomer fluorescence at 340 nm and small
increase of the excimer fluorescence intensity at 400 nm were
observed. On the other hand, the fluorescence spectra greatly
changed with increasing concentration of KCl in WN2 and
WN3. In the case of WN3, an increase of fluorescence intensity
over the whole spectral range was observed accompanying a
shoulder at 400 nm. In WN2, KCl affected the fluorescence
spectra remarkably. Whereas the intensity at 340 nm attributed
to the monomer fluorescence increased almost two times with
addition of KCl at 800 mM, the 400 nm fluorescence due to the

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Fluorescence of Naphthalene Dendrimers
gel column chromatography eluting with hexaneÍdichloromethane
(1:1) to give 137 mg of N1 (71.7%) as a white powder.
Mp: 190Í192 °C; H NMR (270 MHz, CDCl3): ¤ 3.90 (s, 6H,
indicating that the intramolecular interaction between the
naphthalene ring of dendrimer depends on the size of the
surrounding dendron group: the second generation dendrimer is
more appropriate for the formation of the excimer-like structure
due to the interaction of the naphthalene ring. The smaller
effect on the excimer fluorescence of WN3 can be explained by
the following discussion. Because of the relatively small
aromatic ring size of the naphthalene dendrimers, intramolec-
ular interaction of the naphthalene rings in WN3 is less
favorable than that in WN2. In the aggregated form, naph-
thalene rings can exist either with the surrounding dendron
groups of the different dendrimers or with naphthalene rings of
the different dendrimers. With increasing generation, the size of
the surrounding dendron group increases and the core naph-
thalene ring can find more room at the surrounding dendron
groups of the other dendrimers.
1
denÍCOOMe), 5.03 (s, 4H, denÍArÍCH2), 5.40 (s, 2H, ArÍCH2),
6.20 (d, J = 2.2 Hz, 2H, PhlÍH), 6.23 (t, J = 2.2 Hz, 1H, PhlÍH),
7.40Í7.55 (m, 8H, Nap + denÍArH), 7.84Í7.90 (m, 2H, NapÍ
ArH), 7.99Í8.02 (m, 5H, Nap + denÍArH); 13C NMR (125 MHz,
CDCl3): ¤ 52.09, 68.70, 69.35, 94.97, 95.08, 123.57, 125.26,
125.89, 126.46, 126.63, 126.93, 128.67, 129.07, 129.64, 129.82,
131.44, 131.91, 133.72, 141.89, 160.36, 160.76, 166.76; MALDI-
TOF-MS (m/z) calcd for C35H30O7Na [M + Na]+ = 585.19;
found, 585.66.
Synthesis of N2: G2ÍBr (131 mg, 0.262 mmol), core (31.8 mg,
0.119 mmol), 18-crown-6-ether (19.9 mg, 0.0752 mmol), and
K2CO3 (60.2 mg, 0.435 mmol) were suspended in 11 mL of THF
under nitrogen atmosphere. The mixture was heated under reflux
for 8 h. The solution was filtered and evaporated to dryness. The
crude product was purfied by silica gel column chromatography
eluting with hexaneÍdichloromethane (1:1) and GPC column
chromatography eluting with chloroform to give 46.2 mg of N2
(36.7%) as a white powder.
It should be mentioned here that the experiments in this
paper were performed at concentrations as low as 10Õ5Í10Õ6
M
and even at these very low concentrations naphthalene
emission of the excimer (or aggregated form) was effectively
observed with the aid of dendrimer structures with hydrophobic
interiors and hydrophilic exteriors to form molecular aggregate
with novel fluorescence properties.
In summary, the excimer fluorescence of naphthalene was
successfully observed for water-soluble dendrimers, which
depends on the generation of the dendrimers. Furthermore, the
effect of KCl salt to accelerate the formation of the dimer or the
aggregate to form excimer-like fluorescence was observed,
where the second generation dendrimer WN2 suffered the
highest effect on formation of excimer-like fluorescence.
1
Mp: 110Í112 °C; H NMR (270 MHz, CDCl3): ¤ 3.90 (s, 12H,
denÍCOOMe), 4.92 (s, 4H, denÍArÍCH2), 5.06 (s, 8H, denÍArÍ
CH2), 5.41 (s, 2H, ArÍCH2), 6.23 (t, J = 2.2 Hz, 1H, PhlÍH), 6.31
(d, J = 2.2 Hz, 2H, PhlÍH), 6.52 (t, J = 2.2 Hz, 2H, denÍArH),
6.67 (d, J = 2.2 Hz, 4H, denÍArH), 7.34Í7.57 (m, 12H, Nap +
denÍArH), 7.82Í8.04 (m, 11H, Nap + denÍArH); 13C NMR (125
MHz, CDCl3): ¤ 52.11, 68.69, 69.38, 69.81, 94.90, 94.94, 101.58,
106.48, 123.62, 125.28, 125.90, 126.47, 126.67, 126.89, 126.96,
128.67, 129.09, 129.64, 129.69, 129.78, 129.84, 132.00, 139.44,
141.86, 159.83, 160.48, 166.76; MALDI-TOF-MS (m/z) calcd for
C67H58O15Na [M + Na]+ = 1125.28; found, 1125.49.
Synthesis of N3: G3ÍBr (347 mg, 0.330 mmol), core (43 mg,
0.161 mmol), 18-crown-6-ether (16.0 mg, 0.06 mmol), and K2CO3
(83 mg, 6.00 mmol) were suspended in 14 mL of THF under
nitrogen atmosphere. The mixture was heated under reflux for 46 h.
The solution was filtered out and evaporated to dryness. The crude
product was purfied by silica gel column chromatography eluting
with hexaneÍdichloromethane (1:9) and GPC column chromatog-
raphy eluting with chloroform to give 164 mg of N3 (46.5%) as a
white powder.
Experimental
Dendrimers used in this study were synthesized as summarized
in Scheme 1. The structure of the dendrimers was determined by
several analytical data, as shown below, but the H NMR spectra
are summarized in Figure 8. Dendrons were synthesized according
to a reported procedure.17
1
Synthesis of the Core (Scheme 2).18 1-(Bromomethyl)naph-
thalene (0.957 g, 4.33 mmol) and K2CO3 (2.02 g, 14.6 mmol) were
suspended in 8 mL of DMF under nitrogen atmosphere at room
temperature. Phloroglucinol (1.22 g, 9.68 mmol) in 50 mL of DMF
was then added to the solution and the mixture was stirred for 10 h
at room temperature. The solution was filtered and evaporated to
dryness. Water (30 mL) and CH2Cl2 (30 mL) were then added to
the residue and the products were extracted three times with
CH2Cl2. The combined extracts were dried with MgSO4 and
evaporated to dryness. The crude product was purified by silica gel
column chromatography eluting with hexaneÍdichloromethane
(1:1) to give 0.260 g of the core (22.6%) as a white powder.
1H NMR (270 MHz, CDCl3): ¤ 4.99 (s, 2H, ArÍOH), 5.43 (s,
2H, ArÍCH2), 6.00 (t, J = 2.0 Hz, 1H, ArH), 6.15 (d, J = 2.0 Hz,
2H, ArH), 7.43Í7.56 (m, 4H, NapÍH), 7.84Í7.91 (m, 2H, NapÍH),
7.99Í8.02 (m, 1H, NapÍArH).
Synthesis of Dendrimers, N1, N2, and N3 (Scheme 1).
Synthesis of N1: G1ÍBr (178 mg, 0.778 mmol), core (90.3 mg,
0.339 mmol), 18-crown-6-ether (42.5 mg, 0.160 mmol), and
K2CO3 (185 mg, 1.34 mmol) were added and suspended in
14 mL of THF under nitrogen atmosphere. The mixture was
heated under reflux for 5 h. The solution was filtered and
evaporated to dryness. The crude product was purified by silica
1
Mp: 120Í124 °C; H NMR (270 MHz, CDCl3): ¤ 3.87 (s, 24H,
denÍCOOMe), 4.88Í4.90 (m, 12H, denÍArÍCH2), 5.00 (s, 16H,
denÍArÍCH2), 5.35 (s, 2H, ArÍCH2), 6.25 (t, J = 2.2 Hz, 1H,
PhlÍH), 6.29 (d, J = 2.2 Hz, 2H, PhlÍH), 6.52 (t, J = 2.2 Hz, 6H,
denÍArH), 6.67 (d, J = 2.2 Hz, 12H, denÍArH), 7.34Í7.57 (m,
20H, Nap + denÍArH), 7.82Í8.04 (m, 19H, Nap + denÍArH);
13C NMR (125 MHz, CDCl3): ¤ 52.07, 68.63, 69.32, 69.77, 69.89,
94.90, 94.96, 101.46, 101.56, 106.35, 106.42, 123.59, 125.24,
125.87, 126.44, 126.62, 126.90, 128.63, 129.04, 129.64, 129.68,
129.74, 129.80, 133.69, 139.25, 139.39, 141.82, 159.80, 159.91,
160.51, 160.66, 166.70; MALDI-TOF-MS (m/z) calcd for
C
131H114O31Na [M + Na]+ = 2205.63; found, 2206.20.
Synthesis of WN1, WN2, and WN3. WN1: To the solution
of N1 (269 mg, 0.478 mmol) in tetrahydrofuran (11 mL) was added
1 M KOH aqueous solution (3 mL). Methanol (2 mL) was then
added to this two-phase system to give a homogeneous solution
and the solution was heated at reflux for 10 h during which time
precipitates formed. The reaction mixture was then evaporated to
dryness and the residue was dissolved in water. In order to
continue the hydrolysis the solution was heated at reflux for
another 12 h. After cooling to room temperature, the mixture was

R. Akatsuka et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 2 (2009)
247
(a)
(b)
WN1
N1
WN2
N2
WN3
N3
Figure 8. 1H NMR spectra of (a) N1, N2, and N3 in CDCl3 and (b) WN1, WN2, and WN3 in DMSO-d6.
stirred at room temperature for 30 min. Then, fully protonated
product at the peripheral carboxylate group was precipitated and
was collected by suction filtration and was dried to give the acid
form (226 mg, 88.6%).
(4 mL). Methanol (3 mL) was then added to this two-phase system
to give a homogeneous solution and the solution was heated at
reflux for 12 h during which time precipitates formed. The reaction
mixture was then evaporated to dryness and the residue was
dissolved in water. In order to continue the hydrolysis the solution
was heated at reflux for another 12 h. After cooling to room
temperature, the mixture was stirred at room temperature for
30 min. Then, fully protonated product at the peripheral carbox-
ylate group was precipitated and was collected by suction filtration
and was dried to give the acid form (152 mg, 89.4%).
1
Mp: 58Í60 °C; H NMR (270 MHz, DMSO-d6): ¤ 5.16 (s, 4H,
denÍArÍCH2), 5.50 (s, 2H, ArÍCH2), 6.31Í6.36 (m, 1H, PhlÍH),
6.41 (d, J = 1.9 Hz, 2H, PhlÍH), 7.52Í7.66 (m, 8H, Nap + denÍ
ArH), 7.93Í8.01 (m, 7H, Nap + denÍArH); 13C NMR (125 MHz,
CDCl3): ¤ 68.30, 69.13, 95.31, 95.34, 124.23, 125.71, 126.30,
126.79, 127.00, 127.72, 128.84, 129.04, 129.87, 130.56, 131.49,
132.74, 133.63, 142.38, 160.44, 160.73, 167.53; MALDI-TOF-MS
(m/z) calcd for C33H26O7Na [M + Na]+ = 557.06; found, 557.67.
1
Mp: 54Í56 °C; H NMR (270 MHz, DMSO-d6): ¤ 5.00 (s, 4H,
denÍArÍCH2), 5.17 (s, 8H, denÍArÍCH2), 5.49 (s, 2H, ArÍCH2),
6.27 (t, J = 2.2 Hz, 1H, PhlÍH), 6.37 (d, J = 2.2 Hz, 2H, PhlÍH),
6.51 (t, J = 2.2 Hz, 2H, denÍArH), 6.71 (d, J = 2.2 Hz, 4H, denÍ
WN2:
To the solution of N2 (180 mg, 0.163 mmol) in
tetrahydrofuran (10 mL) was added 1 M KOH aqueous solution

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Fluorescence of Naphthalene Dendrimers
Mp: 80Í83 °C; 1H NMR (270 MHz, DMSO-d6): ¤ 4.88Í4.90 (m,
12H, denÍArÍCH2), 5.00 (s, 16H, denÍArÍCH2), 5.35 (s, 2H, ArÍ
CH2), 6.25 (t, J = 2.2 Hz, 1H, PhlÍH), 6.29 (d, J = 2.2 Hz, 2H,
PhlÍH), 6.52 (t, J = 2.2 Hz, 6H, denÍArH), 6.67 (d, J = 2.2 Hz,
12H, denÍArH), 7.34Í7.57 (m, 20H, Nap + denÍArH), 7.82Í8.04
(m, 19H, Nap + denÍArH); 13C NMR (125 MHz, CDCl3): ¤ 68.77,
69.16, 94.90, 101.23, 106.56, 106.69, 125.39, 125.97, 126.10,
126.35, 127.45, 127.40, 128.48, 129.50, 130.85, 131.14, 132.42,
133.24, 133.28, 139.48, 139.54, 141.96, 155.96, 156.07, 159.23,
159.42, 159.50, 159.55, 160.17, 160.29, 167.14; MALDI-TOF-MS
(m/z) calcd for C123H98O31Na [M + Na]+ = 2093.59; found,
2095.23.
n = 1
N1; R = OMe
WN1; R = O-K+
This work was supported by a Grant-in-Aid for Science
Research in a Priority Area “New Frontiers in Photochromism
(No. 471)” from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), Japan.
n = 2
N2; R = OMe
WN2; R = O-K+
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n = 3
N3; R = OMe
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Scheme 1. Synthesis of dendrimer.
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MALDI-TOF-MS (m/z) calcd for C63H50O15Na [M + Na]+
1069.29; found, 1070.23.
=
WN3:
To a solution of N3 (120 mg, 0.0549 mmol) in
tetrahydrofuran (7 mL) was added 1 M KOH aqueous solution
(2 mL). Methanol (2 mL) was then added to this two-phase system
to give a homogeneous solution and the solution was heated at
reflux for 10 h during which time precipitates formed. The reaction
mixture was then evaporated to dryness and the residue was
dissolved in water. In order to continue the hydrolysis the solution
was heated at reflux for another 12 h. After cooling to room
temperature, the mixture was stirred at room temperature for
30 min. Then, fully protonated product at the peripheral carbox-
ylate group was precipitated and was collected by suction filtration
and was dried to give the acid form (91.0 mg, 80.0%).