Emission and transient absorption measurements of substitution effects of C-C triple bonds on relaxation processes of the fluorescent state of naphthalenes

Article abstract of DOI:10.1007/s11164-012-0652-4

Photophysical and photochemical properties of naphthalenes substituted with trimethylsilylethynyl, tert-butylethynyl, and trimethylsilylbutadiynyl groups were investigated by measurement of fluorescence yields, lifetimes, and triplet absorption. Introducing trimethylsilylethynyl and tert-butylethynyl groups to the 1-position of the naphthalene skeleton substantially enhanced fluorescence and intersystem crossing (ISC). The rates of fluorescence of 2-substituted naphthalenes were low. The effect of ethynyl groups on the 1-substituted naphthalenes was rationalized in terms of an increase of the transition moment along the short axis of the naphthalene skeleton. Substitution of the trimethylsilylbutadiynyl group at the 1 or 2-position of the naphthalene skeleton caused a considerable decrease in the fluorescence yield (approximately 0.01) and an increase in the ISC yield (0.99).

Full text of DOI:10.1007/s11164-012-0652-4

Res Chem Intermed (2013) 39:321–345
DOI 10.1007/s11164-012-0652-4
Emission and transient absorption measurements
of substitution effects of C–C triple bonds on relaxation
processes of the fluorescent state of naphthalenes
Minoru Yamaji
Tomohiro Maeda
Kazuhiko Mizuno
•
Hajime Maeda
Kengo Asai
•
Keita Minamida
Gen-Ichi Konishi
•
•
•
•
Received: 16 October 2011 / Accepted: 16 February 2012 / Published online: 6 July 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Photophysical and photochemical properties of naphthalenes substituted
with trimethylsilylethynyl, tert-butylethynyl, and trimethylsilylbutadiynyl groups
were investigated by measurement of fluorescence yields, lifetimes, and triplet
absorption. Introducing trimethylsilylethynyl and tert-butylethynyl groups to the
1
-position of the naphthalene skeleton substantially enhanced fluorescence and
intersystem crossing (ISC). The rates of fluorescence of 2-substituted naphthalenes
were low. The effect of ethynyl groups on the 1-substituted naphthalenes was
rationalized in terms of an increase of the transition moment along the short axis of
the naphthalene skeleton. Substitution of the trimethylsilylbutadiynyl group at the 1
This article is dedicated to Professor Kazuhiko Mizuno on his retirement.
M. Yamaji (&)
Department of Chemistry and Chemical Biology, Graduate School of Engineering,
Gunma University, Kiryu, Gunma 376-8515, Japan
e-mail: yamaji@gunma-u.ac.jp
H. Maeda (&) ꢀ K. Minamida ꢀ T. Maeda ꢀ K. Mizuno (&)
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University,
Sakai, Osaka 599-8531, Japan
e-mail: maeda-h@t.kanazawa-u.ac.jp
K. Mizuno
e-mail: mizuno@chem.osakafu-u.ac.jp
Present Address:
H. Maeda
Division of Material Sciences, Graduate School of Natural Science and Technology, Kanazawa
University, Kanazawa 920-1192, Japan
K. Asai ꢀ G.-I. Konishi
Graduate School of Science and Engineering, Tokyo Institute of Technology Ookayama,
Meguro-ku, Tokyo 152-8552, Japan
123

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M. Yamaji et al.
or 2-position of the naphthalene skeleton caused a considerable decrease in the
fluorescence yield (approximately 0.01) and an increase in the ISC yield (0.99).
Keywords Fluorescence ꢀ Intersystem crossing ꢀ Naphthalene ꢀ Triplet–triplet
absorption ꢀ Triple bond
Introduction
Three competitive photophysical pathways, fluorescence, internal conversion (IC) to
the ground state (S ), and intersystem crossing (ISC) to the lowest triplet state (T ),
can lead to deactivation from the lowest excited singlet states (S ) of aromatic
0
1
1
compounds in solution [1, 2]. Recently, with the objective of developing high-yield
fluorescent materials, a number of synthetic studies of silyl-substituted aromatic
compounds have been reported [3–25]. The increased fluorescence yield can be
explained in two ways [19]. One is that introduction of silyl groups into fused
aromatic systems causes a bathochromic shift, which increases the molar absorption
coefficients (e). Because the fluorescence rate constants (k ) are linearly related to e,
f
substitution with silyl groups, for example trialkylsilyl and triphenylsilyl groups,
substantially increases fluorescence rate or quantum yield. The other is that silyl
substitution stabilizes the S state energy so that it is lower than the corresponding
1
second triplet (T ) state energy. Therefore, ISC is negligible. For some aromatic
2
compounds rates of IC from the S state to the S state are negligible. In these cases,
1
0
a substantial increase in the fluorescence yield is expected. In recent studies,
silylethynyl groups have been introduced to fundamental fused aromatic skeletons,
for example anthracene [16–19], triphenylene [13], pentacene [9], and pyrene [21].
These compounds have intense fluorescence compared with the original aromatic
compounds. The mechanism of enhancement of the fluorescence yield in these
silylethynylated compounds has not been revealed. Understanding of the function of
ethynyl groups on excited aromatic compounds requires detailed investigations
based on photophysical data for the deactivation processes of the excited states.
Ermolaev’s rule is known to apply to the S states of naphthalene derivatives, so
1
the rate of IC is negligible, and deactivation of the S1 state is governed by
fluorescence and ISC processes [2]. When the fluorescence yields and lifetimes of
these naphthalenes have been determined, the rates of the fluorescence and ISC
processes could be readily estimated. Therefore, naphthalenes with a variety of
ethynyl moieties are ideal for studies on the effects of the substituent groups on
photophysical deactivation processes.
In this work, we prepared a series of naphthalene derivatives with trimethylsil-
ylethynyl (TMSE), tert-butylethynyl (BuE), trimethylsilylbutadiynyl (TMSB),
methoxy (MeO), and cyano (CN) groups (Scheme 1). The fluorescence spectra,
yields, lifetimes, and triplet absorption spectra were measured for these compounds
in solution. On the basis of photophysical data for the rates of fluorescence and ISC,
the effects of introducing these substituent groups on the fluorescence states were
studied. In the text, the transition moments in the excited singlet states of the
1
1
naphthalene derivatives used in this work are expressed as L and L , which have
a
b
1
23

Emission and transient absorption measurements
323
directions along the short and long axes, respectively, of the naphthalene skeleton
Scheme 1).
(
Results and discussion
Effects of substituent groups and positions on the fluorescent state
Figure 1 shows absorption, fluorescence, and phosphorescence spectra of naphtha-
lenes substituted in the 1 and 2 positions with TMSE and BuE groups.
All the absorption and emission spectra revealed well-resolved vibrational
structures. The excitation spectra for the fluorescence and phosphorescence were the
same as the corresponding absorption spectra. The 0–0 origins of the absorption and
fluorescence spectra were clearly visible. The absorption spectra features of
1
1
-substituted naphthalenes are characterized by overlap of the L band with the
a
1
1
corresponding L band [26–28]. The S / S character was because of the L
b
1
0
a
1
transition. For the 2, 2,6, and 2,7-substituted naphthalenes, the L band, which was
a
located in the higher wavenumber region with relatively large absorptivity (e), was
1
clearly separated from the L band in the absorption spectra. The e values of the
b
compounds used in this study are listed in Table 1. It is worth noting that their e
4
3
-1
-1
values (*10 dm mol cm ) are one order of magnitude greater than that of
3
3
-1
-1
naphthalene (*10 dm mol cm ). In the absorption spectrum of
1
256TMSENp, the L and L bands were clearly separated, and the transition
1
1
character of the compound was, thus, similar to that of 2-substituted naphthalene.
a b
The S state energies (E ) of the compounds were determined from the average
1
S
energies of the 0–0 origins of the corresponding absorption and fluorescence
spectra. The triplet energies (E ) were determined from the 0–0 origins of the
T
phosphorescence spectra. The E and E values are listed in Table 1. These values
T
S
seemed to decrease as the number of substituent groups increased, and were
independent of substituent position and type of terminating group (tert-butyl and
TMS).
1La
R1
R7
R6
R2
R3
1Lb
R5
R4
R1 - R7 = H,
SiMe3 (TMSE),
tBu (BuE) or
C
C SiMe (TMSB)
C
C
C
C
C
C
3
Scheme 1 Substituent positions of the naphthalene derivatives used in this work (left) and directions of
the transition moments in the excited singlet states of naphthalene (right). The abbreviations are
explained and the corresponding substituent groups are identified in Table 2
123

324
M. Yamaji et al.
Fig. 1 Absorption (black) and
fluorescence (blue) spectra in
cyclohexane at 295 K and
phosphorescence spectra (red) in
a mixture of methylcyclohexane
and isopentane (3:1 v/v) at 77 K
for 1TMSENp (a), 1BuENp (b),
14TMSENp (c), 14BuENp (d),
15TMSENp (e), 2TMSENp (f),
2BuENp (g), 26TMSENp (h),
26BuENp (i), 27TMSENp (j),
and 1256TMSENp (k). The
intensity of each spectrum is
normalized. The duplicated
absorption spectra are magnified
for a clear view of the
vibrational structures
Assuming that Ermolaev’s rule is applicable to the naphthalene derivatives used
in this work, their ISC yields (UISC) were obtained by use of Eq. 1 using the
fluorescence yields (UF).
UISC ¼ 1 ꢁ UF
The fluorescence and ISC rates (k and k ) listed in Table 1 were estimated by use
ð1Þ
f
isc
of Eqs. 2 and 3 using the fluorescence lifetimes (s ) and the corresponding quantum
F
yields (U and UISC), respectively.
F
kf ¼ UFsꢁF
The k values of the 1-substituted naphthalenes increased by one or two orders of
1
ð2Þ
f
magnitude as the number of the substituent groups increased, and was independent
of the terminating group (tert-butyl or TMS). By contrast, compared with the k
f
6
value (2.1 9 10 s ) of naphthalene, the k values of the 2-substituted naphtha-
-1
f
lenes were all of the same order of magnitude and were not affected by the number
of TMSE and BuE groups. Because the k value is closely related to the direction
f
1
23

Emission and transient absorption measurements
325
123

326
M. Yamaji et al.
1
23

Emission and transient absorption measurements
327
Fig. 2 Transient absorption
spectra at 100 ns obtained upon
266-nm or 308-nm laser pulsing
in cyclohexane solutions of
1TMSENp (a), 1BuENp (b),
14TMSENp (c), 14BuENp (d),
15TMSENp (e), 2TMSENp (f),
2BuENp (g), 26TMSENp (h),
26BuENp (i), 27TMSENp
(
j) and 1256TMSENp (k). The
absorbance changes (DA) are
normalized
and the magnitude of the transition moment, the increase in k with introduction of
f
TMSE and BuE groups in the 1-position of the naphthalene skeleton can be inter-
preted as an increase in the transition moment [1].
kisc ¼ UISCsꢁF
From the kisc values of the 1-substituted naphthalenes, it can be inferred that the ISC
1
ð3Þ
from the S to T state and fluorescence can be enhanced by substitution with TMSE
1
1
and BuE. Generally, the ISC mechanism is interpreted in terms of the spin–orbit
interaction, and the kisc is expressed by Fermi’s golden rule [2].
X
2
kisc
¼
q ꢀ \T jH jS [ ꢀ F
ð4Þ
f
f
SO
i
In Eq. 4, |S[and |T[are the wavefunctions for the initial excited singlet state (S )
i
f
1
and the final triplet state (T ), respectively; q is the density of the final state; and
1
f
HSO and F are the Hamiltonians for the spin–orbit interaction and the Franck–
Condon factor between the initial and final states, respectively. The perturbation
123

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M. Yamaji et al.
Fig. 3 Absorption (black) and
fluorescence (blue) spectra in
cyclohexane at 295 K, and
phosphorescence spectra (red) in
a mixture of methylcyclohexane
and isopentane (3:1 v/v) at 77 K,
of 1TMSENp (a),
1TMSE4MeONp (b),
1TMSE4CNNp (c), 2TMSENp
(
2
d), 2TMSE6MeONp (e) and
TMSE6CNNp (f). The intensity
of each spectrum is normalized.
The duplicated absorption
spectra are magnified for a clear
view of the vibrational structures
Hamiltonian (HSO) can be expressed by use of the angular-momentum and spin-
momentum operators (l and s, respectively) and the spin–orbit coupling constant (f),
which gives a measure of the heavy atom effect.
HSO ¼ fðl ꢀ sÞ
Eq. 4 can then be rewritten as follows:
ð5Þ
X
2
2
kisc
¼
q ꢀ \T jl ꢀ sjS [ ꢀ F ꢀ f
ð6Þ
f
f
i
-
1
Here, the f values for C, H, and Si atoms are known to be 32, 0.24, and 130 cm
,
2
respectively [29]. The sums (R f ) of the squared f values for all the compounds
used in this work are listed in Table 1. The ratios of R f for TMSENp (R
f = 3.2 9 10 cm ) and BuENp (R f = 1.6 9 10 cm ) to that for naphthalene
(R f = 1.0 9 10 cm ) were estimated to be 3.2 and 1.6, respectively. The k
values of 1TMSENp, 1BuENp, and naphthalene were 4.7 9 10 , 3.3 9 10 , and
2
2
4
-2
2
4
-2
2
4
-2
isc
7 7
6
-1
2
7
.0 9 10 s , respectively, and the estimated ratios of R f might explain the
2
increase of kisc for 1TMSENp and 1BuENp. However, the R f ratios for
-2
2
4
1
-substituted naphthalenes with two TMSE or BuE groups (R f = 5.4 9 10 cm
4 -2
and 2.3 9 10 cm , respectively) to that for naphthalene could not be used to
rationalize the difference of two orders of magnitude in kisc for these 1-substituted
naphthalenes. Therefore, the mechanism of ISC enhancement by TMSE and BuE
groups cannot be simply interpreted by Fermi’s golden rule.
1
23

Emission and transient absorption measurements
329
Fig. 4 Transient absorption
spectra at 100 ns obtained upon
266-nm or 308-nm laser pulsing
in cyclohexane solutions of
1
1
1
TMSENp (a),
TMSE4MeONp (b),
TMSE4CNNp (c), 2TMSENp
(
2
d), 2TMSE6MeONp (e), and
TMSE6CNNp (f). The
absorbance changes (DA) are
normalized
Formation of triplet states was examined by observing triplet–triplet absorption.
Transient absorption spectra of the naphthalene derivatives were obtained by flash
photolysis techniques using a nanosecond laser pulse. Figure 2 shows the transient
absorption spectra obtained at 100 ns by laser photolysis of the TMSENp and
BuENp derivatives.
The intensity of all the transient absorption decreased within tens of microsec-
onds, and the decay was accelerated by the presence of dissolved oxygen. From
these observations, the transient signals obtained could be ascribed to the triplet–
triplet (T–T) absorption of the corresponding TMSENp and BuENp compounds.
T-T
The wavelengths of maximum absorption (kmax ) for the T–T absorption spectra are
listed in Table 1. It is interesting to classify the substituted positions in the
naphthalene skeleton by using the wavelengths of the triplet absorption bands. With
the 2-substituted naphthalenes, the triplet absorption bands were located at 420 nm,
whereas those of the 1-substituted compounds were located at 450 nm. The
absorption bands of triplet 15TMSENp and 1256TMSEN were located at 530 nm.
Effects of electron-donating and withdrawing groups on the fluorescent state
of TMSENp
To elucidate the electronic effects of substituent groups on photophysical processes
of the S states of the TMSENp compounds, we prepared TMSENp derivatives with
1
123

330
M. Yamaji et al.
Fig. 5 Absorption (black) and
fluorescence (blue) spectra in
cyclohexane at 295 K, and
phosphorescence spectra (red) in
a mixture of methylcyclohexane
and isopentane (3:1 v/v) at 77 K
for 1TMSENp (a), 1TMSBNp
(
2
b), 2TMSENp (c) and
TMSBNp (d). The intensity of
each spectrum is normalized.
The duplicated absorption
spectra are magnified for a clear
view of the vibrational structures
electron-donating (MeO) and electron-withdrawing groups (CN). The absorption,
fluorescence, and phosphorescence spectra of 1-TMSENp, 2-TMSENp, and their
derivatives are compared in Fig. 3.
The absorption and fluorescence spectra of 1TMSE4MeONp were similar to
those of 1TMSENp. Thus, the S / S character of these derivatives is because of
1
0
1
1
the L transition. In contrast, clear separation of the L band from the L band
1
a
a
b
was observed in the absorption spectra of 2TMSENp and its derivatives. From this
observation it can be inferred that the S / S character of the 2TMSENp
1
0
1
compounds is because of the Lb transition. The kf and k
1
values of
isc
-1
TMSE4MeONp and 1TMSE4CNNp were of the same order (10 s ) as those
8
of 14TMSENp, and the fluorescence and ISC processes were enhanced by
introduction of two TMSE groups into the 1 and 4-positions of the naphthalene
skeleton. These results indicate that enhancement of the k and k values of
f
isc
1TMSENp derivatives by substitution at the 4-position is efficient, irrespective of
the type of substituent (TMSE, MeO or CN). In a similar manner to the 2 and
6
1
-substituted TMSENp compounds, small variations in the k values (approximately
f
6
0 s ) were observed for 26TMSENp, 2TMSE6OMeNp, and 2TMSE6CNNp,
-1
although the kisc values of 2TMSE6OMeNp and 2TMSE6CNNp were substantially
7
larger than that (1.7 9 10 s ) of 26TMESNp.
-1
2
The sums (R f ) of the squared f values for TMSEMeONps and TMSECNNps
2
were examined to evaluate the heavy atom effect on k . Ratios of R f for
isc
2
4
-2
2
4
TMSEMeONp (R f = 5.7 9 10 cm ) and TMSECNNp (R f = 3.9 9 10
cm ) to that for TMSENp (R f = 3.2 9 10 cm ) were estimated to be 1.7 and
.2, respectively, although the estimated kisc values for the TMSEMeONp
-
2
2
4
-2
1
1
23

Emission and transient absorption measurements
331
Table 2 Abbreviations and substituent groups for the naphthalene derivatives used in this study
Compound
Substituent group
1
2
R
3
R
4
5
R
6
7
R
R
R
R
1
1
1
1
1
1
1
2
2
2
2
2
1
2
2
1
2
TMSENp
TMSE
BuE
TMSE
BuE
TMSE
TMSE
TMSE
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
BuENp
H
H
H
H
4TMSENp
4BuENp
H
TMSE
BuE
H
H
H
H
H
H
5TMSENp
TMSE4MeONp
TMSE4CNNp
TMSENp
H
TMSE
H
H
MeO
CN
H
H
H
H
H
H
TMSE
BuE
TMSE
BuE
TMSE
TMSE
TMSE
TMSE
H
H
H
BuENp
H
H
H
H
6TMSENp
6BuENp
H
H
H
TMSE
BuE
H
H
H
H
7TMSENp
256TMSENp
TMSE6MeONp
TMSE6CNNp
TMSBNp
H
H
H
TMSE
TMSE
H
H
TMSE
H
TMSE
MeO
CN
H
H
H
H
H
H
H
H
H
H
TMSB
H
H
H
TMSBNp
TMSB
H
H
H
The molecular structures, with the substituent positions, are given in Scheme 1
TMSE, trimethylsilylethynyl; BuE, tert-butylethynyl; TMSB, trimethylbutadiynyl; MeO, methoxy; CN,
cyano
compounds and TMSECNNp compounds were one order of magnitude larger than
those of the TMSENp compounds, irrespective of substituent positions. This
evaluation implies that the enhanced ISC of the TMSEMeONp compounds and
TMSECNNp compounds is not because of the heavy atom effect.
Figure 4 shows the transient absorption spectra obtained at 100 ns on laser flash
photolysis of TMSENp derivatives.
Decay of the transient signals was accelerated by the presence of dissolved
oxygen. Therefore, the transient absorption spectra can be attributed to the triplet
states of the corresponding TMSENp derivatives. The peak shapes and wavelength
region of the T–T absorption spectra were similar to those of the corresponding
TMSENp. The observation of the T–T absorption shows that the ISC process
proceeds by addition of a substituent at the 4 and 6-positions of 1TMSENp and
2
TMSENp, respectively.
Substitution effect of a butadiynyl moiety on the fluorescent state
Figure 5 compares the absorption, fluorescence and phosphorescence spectra of
TMSENp and TMSBNp.
123

332
M. Yamaji et al.
Fig. 6 Transient absorption
spectra at 100 ns obtained upon
266-nm or 308-nm laser pulsing
in cyclohexane solutions of
1
2
TMSENp (a), 1TMSBNp (b),
TMSENp (c) and 2TMSBNp
(
(
d). The absorbance changes
DA) are normalized
The absorption and fluorescence spectra of 1TMSBNp reveal vibrational
structures. Considering the similar absorption spectral features of 1TMSENp and
1
1
transition. With 2TMSBNp, because the L band was clearly separated from the
TMSBNp, the S / S character of 1TMSBNp was probably because of the L
1
0
a
1
a
1
L band in the absorption spectrum, the S / S character was plausibly because
b
1
0
1
of the L transition. Both the TMSBNp compounds had double-exponential decay
b
profiles for fluorescence, which had very short lifetime(s) of tens or hundreds of
picoseconds (Table 2). The origins of the double components are unknown.
Notably, the fluorescence yields (0.01) of the TMSBNp compounds were much
smaller than those of naphthalene (0.23) and the TMSENp compounds (0.30 for
1
TMSENp and 0.68 for 2TMSENp). Consequently, the ISC yields increased to 0.99.
The absolute values of kisc cannot be determined because the fluorescence had
double-exponential decay profiles.
Observation of the T–T absorption confirms that efficient ISC processes occur for
the TMSBNp compounds (Fig. 6).
The shapes of the T–T absorption spectra of the TMSENp and TMSBNp
compounds are very similar to each other although the peak wavelength of triplet
1
TMSBNp is red-shifted compared with that of triplet 1TMSENp. Replacing the
TMSE group with TMSB is more effective for changing the ISC yield of the
-substituted naphthalene (from 0.30 to 0.99) than it is for the 2-substituted
naphthalene (from 0.68 to 0.99).
To evaluate the heavy atom effect in TMBSNp, the ratio of R f for TMSENp (R
1
2
2
5
-2
2
5
-2
f = 3.2 9 10 cm ) to that for TMSBNp (R f = 3.4 9 10 cm ) was
estimated to be 1.05. Although the kisc values of the TMSBNp compounds cannot
1
23

Emission and transient absorption measurements
333
be determined accurately, the fluorescence lifetimes (B1 ns) suggest they are equal
8
to or larger than 10 s . The k values of 1-TMSENp and 2-TMSENp were
-1
isc
7
6
-1
2
4
contribute to increasing the k . Therefore, Fermi’s golden rule is invalid for
.7 9 10 and 3.0 9 10 s , respectively, which indicates the R f ratio does not
isc
explaining the mechanism of ISC enhancement by the TMSB group.
Conclusion
We prepared naphthalenes substituted with ethynyl and butadiynyl moieties
terminated with TMS or tert-butyl groups, and investigated the deactivation
properties of their fluorescent states by measurement of fluorescence yields (U ) and
F
lifetimes (s ) and triplet absorption. By use of Ermolaev’s rule for the decay
F
processes of the naphthalene S states, the ISC yields (U ) and rates (k ) were
1
ISC
isc
readily estimated, along with the fluorescence rates (k ). The kf values of
naphthalenes substituted at the 1-position with TMSE or BuE increased by one
order of magnitude as the number of substituents increased. Results for
f
1
the fluorescence process of 1-ethynylnaphthalenes. By contrast, the k values of the
TMSE4MeONp and 1TMSE4CNNp showed that MeO and CN groups enhanced
f
2
-ethynylnaphthalenes changed little in comparison with that of naphthalene. The
difference in between enhancement of the fluorescence process for 1 and
-ethynylnaphthalenes was understood in terms of the direction of the transition
2
moment in the naphthalene skeleton. The absorption spectra of the 1-ethynylnaph-
1
thalenes showed that the S / S character was because of the direction of the L
1
0
a
transition, which was parallel to the direction of the extended p-electron systems.
Therefore, the transition moment increased along the short axis of the naphthalene
skeleton, which increased the fluorescence rate (k ). The S / S character of the
f
1
1
0
2
long axis of the naphthalene skeleton), which was oblique to the direction of the
-ethynylnaphthalenes was because of the direction of the L transition (along the
b
extended p-electron system. Therefore, the transition moment changes less in the
2
-ethynylnaphthalenes. As the number of substituent groups increased, the ISC rates
k ) and k of the 1-ethynylnaphthalenes were enhanced, and those of the
(
isc
f
2
explain these trends in k . The observations of T–T absorption of the ethynyl-
-ethynylnaphthalenes did not change. The heavy-atom effect was not sufficient to
isc
naphthalenes used in this study are evidence of an efficient ISC process competing
with fluorescent deactivation from the S1 state. In other words, IC from the
fluorescent state to the S is negligible for fluorescence and ISC processes in these
0
systems. It was found that applying Ermolaev’s rule to the naphthalene derivatives
used in this study was appropriate.
Substitution of the naphthalene skeleton with TMSB has a large affect on the ISC
process. The UISC values of the TMSBNp compounds increased to 0.99 and the
fluorescence yields decreased to 0.01. Although the butadiynyl moiety looks like a
tandemdiethynyl, the effectonthe fluorescencepathwaywasquitedifferentfromthatof
diethynylnaphthalenes. Further studies of the effects of C–C triple bonds on the
photophysical processes of naphthalenes are in progress with hexatriynylnaphthalenes.
123

334
M. Yamaji et al.
Experimental
Reagents and apparatus for synthesis
Tetrahydrofuran (THF) was used as purchased (Kanto Kagaku, dehydrated). Et N was
3
distilled from KOH and was stored dry by addition of K CO . Dichloromethane was
3
2
distilled from CaCl2 and then CaH . Acetonitrile was distilled from CaH .
2
2
Tetramethylethylenediamine (TMEDA) was distilled from Ca(OH) . n-Bu NF (TBAF)
2
4
solution (1 M in THF) was prepared from commercially available n-Bu NFꢀ3H O and
4
2
dryTHF. Otherchemicalswereusedafterpurificationbydistillationorrecrystallization.
1
H NMR spectra were recorded on Varian Mercury-300 (300 MHz) or Jeol LMN-
EX400 (400 MHz) spectrometers, with Me Si as internal standard. IR spectra were
4
recorded on a Jasco FT/IR-230. Electron-impact (EI) mass spectra were recorded on a
Shimadzu GCMS-QP5050 (electron energy 70 eV) equipped with a GC-17A and DB-
5
MS column (J&W Scientific; serial no. 8696181). Chemical ionization (CI) mass
spectra were recorded on a Jeol JMS-DX303 with operating system. High-performance
liquid chromatography (HPLC) was performed with a recycling preparative HPLC
equipped with a Jasco PU-2086 Plus, RI-2031 Plus differential refractometer, and
Megapak GEL 201C columns (gel-permeation chromatography, GPC) using CHCl as
3
eluent. Column chromatography was conducted on Kanto-Chemical silica gel 60 N
spherical, neutral, 0.063–0.200 mm).
(
1
-(Trimethylsilylethynyl)naphthalene (1TMSENp)
1
-Naphthol (4.25 g, 29.5 mmol), toluene (60 mL), and 30 % (w/v) K PO aq.
3
4
(60 mL) were placed in a round-bottomed flask and the solution was stirred at 0 °C
for 30 min. Trifluoromethanesulfonic acid anhydride (10 g, 35.4 mmol) was slowly
added at 0 °C, carefully keeping the temperature below 10 °C. The solution was
then stirred at room temperature for 30 min. Toluene and H O were added, and the
organic extract was dried over MgSO . Filtration and evaporation gave a residue.
2
4
Column chromatography on silica gel (eluent hexane) gave 1-naphthyl trifluor-
omethanesulfonate (7.43 g, 91 % yield). Data for 1-naphthyl trifluoromethanesul-
1
fonate: colorless oil; H NMR (300 MHz, CDCl ) d 7.45 (d, J = 3.6 Hz, 1H), 7.46
3
(
d, J = 5.7 Hz, 1H), 7.55–7.66 (m, 2H), 7.85 (dd, J = 5.4, 3.9 Hz, 1H), 7.88–7.91
m, 1H), 8.07 (dd, J = 8.4, 1.2 Hz, 1H) ppm; GC–MS (EI) m/z (relative intensity,
(
?
?
?
%
) 276 (63, M ), 143 (96, M - SO CF ), 115 (100, C H ); IR (neat) m 3069,
-1
2
3
9 7
1
422 (OSO CF ), 1216 (OSO CF ), 1139 (OSO CF ) cm .
2 3 2 3 2 3
1
dry Et N (20 mL), CuI (143 mg, 0.75 mmol), Pd(PPh ) Cl (526 mg, 0.75 mmol),
-Naphthyl trifluoromethanesulfonate (6.91 g, 25.0 mmol), dry THF (20 mL),
3
3 2
2
and trimethylsilylacetylene (4.25 mL, 30.0 mmol) were placed in a round-bottomed
flask equipped with a Dimroth condenser, and the mixture was stirred for 20 h at
8
HCl aq., CHCl and H O were added. The organic extract was dried over Na SO ,
0 °C under an argon atmosphere. After neutralization of the solution with conc.
3
2
2
4
filtered, and then evaporated to give a residue. Purification by column chromatog-
raphy on silica gel (eluent hexane) and distillation under reduced pressure gave
1
-(trimethylsilylethynyl)naphthalene (1TMSENp, 4.42 g, 79 % yield). Data for
1
23

Emission and transient absorption measurements
335
1
1
TMSENp: pale yellow oil; bp 133–134 °C/0.5 mmHg; H NMR (300 MHz,
CDCl ) d 0.38 (s, 9H), 7.43 (dd, J = 8.1, 7.2 Hz, 1H), 7.51–7.64 (m, 2H), 7.74 (dd,
J = 7.2, 1.2 Hz, 1H), 7.82–7.87 (m, 2H), 8.38 (dd, J = 8.1, 0.9 Hz, 1H) ppm;
3
1
3
C
NMR (75 MHz, CDCl ) d 0.6 (3C), 99.5, 103.1, 120.7, 125.1, 126.1, 126.3, 126.8,
3
1
28.2, 128.9, 130.7, 133.0, 133.3 ppm; GC–MS (EI) m/z (relative intensity, %) 224
?
?
(
52, M ), 209 (100, M - CH ); IR (neat) m 3059, 2958, 2898, 2146 (C:C), 1392
3
-1
(
Si–CH ), 1250 (Si–CH ) cm
.
3
3
1
-(tert-Butylethynyl)naphthalene (1BuENp)
1
1
-Naphthyl trifluoromethanesulfonate (1.38 g, 5.0 mmol, see the synthesis of
TMSENp), dry THF (10 mL), dry Et N (10 mL), CuI (28.6 mg, 0.15 mmol),
3
Pd(PPh ) Cl (105 mg, 0.15 mmol), and tert-butylacetylene (0.74 mL, 6.0 mmol)
2
3
2
were placed in a round-bottomed flask equipped with a Dimroth condenser, and the
mixture was stirred for 20 h at 80 °C under an argon atmosphere. After
neutralization of the solution was conc. HCl aq., CHCl and H O were added.
3
2
The organic extract was dried over Na SO , filtered, and then evaporated to give a
2
4
residue. Purification by column chromatography on silica gel (eluent hexane) and
HPLC (GPC, eluent CHCl ) gave 1-tert-butylethynylnaphthalene (1BuENp,
3
1
81 mg, 56 % yield). Data for 1BuENp: colorless oil; H NMR (300 MHz, CDCl )
5
3
d 1.43 (s, 9H), 7.38 (dd, J = 8.1, 7.8 Hz, 1H), 7.46–7.57 (m, 2H), 7.60 (dd, J = 7.2,
1
.2 Hz, 1H), 7.76 (d, J = 8.4 Hz, 1H), 7.82 (d, J = 8.1 Hz, 1H), 8.30 (d, J =
?
.1 Hz, 1H) ppm; GC–MS (EI) m/z (relative intensity, %) 208 (72, M ), 193 (100,
8
?
-1
M - CH ); IR (neat) m 3058, 2968, 2927, 2898, 2866, 2225 (C:C) cm
.
3
1
,4-Bis(trimethylsilylethynyl)naphthalene (14TMSENp)
1,4-Dibromonaphthalene (2.86 g, 10 mmol), trimethylsilylacetylene (3.4 mL, 24 mmol),
Pd(PPh ) Cl (560 mg, 0.8 mmol), CuI (76 mg, 0.4 mmol), and dry piperidine (50 mL)
3
2
2
were placed in a round-bottomed flask equipped with a Dimroth condenser. The solution
was stirred at room temperature for 2 h, then heated to 80 °C and stirred for 14 h.
Purification by column chromatography on silica gel (eluent hexane to hexane–benzene
4:1), HPLC (GPC, eluent CHCl ), and recrystallization from methanol gave 1,4-
bis(trimethylsilylethynyl)naphthalene (14TMSENp, 3.05 g, 95 % yield). Data for
3
1
1
4TMSENp: colorless solid; mp 73.5–75 °C; H NMR (300 MHz, CDCl ) d 0.33 (s,
3
1
8H), 7.61 (dd, J = 3.3, 6.4 Hz, 2H), 7.62 (s, 2H), 8.33 (dd, J = 3.1, 6.4 Hz, 2H) ppm;
C NMR (75 MHz, CDCl ) d -14.72 (6C), 86.42 (2C), 87.79 (2C), 106.50 (2C), 111.53
1
3
3
(
2C), 112.24 (2C), 114.96 (2C), 118.02 (2C) ppm; MS (CI), m/z (relative intensity, %) 321
?
M ? 1, 100), 305 (4), 73 (1). Anal. Calcd for C H Si : C, 74.93; H, 7.55; Si, 17.52.
(
Found: C, 74.90; H, 7.40.
20 24 2
1
,4-Bis(tert-butylethynyl)naphthalene (14BuENp)
4BuENp was synthesized in a similar manner to 14TMSENp (see above) by using
1
tert-butylacetylene instead of trimethylsilylacetylene. Data for 14BuENp: H NMR
1
123

336
M. Yamaji et al.
(
300 MHz, CDCl ) d 1.42 (s, 18 H), 7.51 (s, 2 H), 7.52–7.59 (m, 2 H), 8.26–8.33
3
(
m, 2 H) ppm.
1
,5-Bis(trimethylsilylethynyl)naphthalene (15TMSENp)
To a stirred solution of naphthalene-1,5-diol (1.92 g, 12 mmol) in pyridine (24 mL)
was added (CF SO ) O (7.05 g, 4.20 mL, 25 mmol) at 0 °C. The solution was
3
2 2
stirred at room temperature for 1 day. The solution was poured into H O (50 mL),
2
and the product was extracted with toluene. The organic layer was washed with
1
dried over MgSO , and evaporated to give 1,5-bis(trifluoromethylsulfonyloxy)naph-
0 % HCl aq. (twice) and H O, and then saturated NaCl aq. The organic layer was
2
4
thalene (4.65 g, 91 % yield). Data for 1,5-bis(trifluoromethylsulfonyloxy)naphtha-
1
lene: H NMR (400 MHz, CDCl ) d 7.61 (d, J = 7.6 Hz, 2H), 7.69 (dd, J = 7.6,
3
8
.1 Hz, 2H), 8.13 (d, J = 8.1 Hz, 2H) ppm; IR (KBr) m 1609 (Ar–H), 1209 (C–F),
-1
1
141 (R-SO -OR), 756 (–CF ) cm
.
,5-Bis(trifluoromethylsulfonyloxy)naphthalene (1.27 g, 3.0 mmol), anhydrous
2
3
1
THF (30 mL), Et N (2.02 g, 2.80 mL, 20.0 mmol), Pd(PPh ) (0.17 g, 0.16 mmol),
3
3 4
CuI (0.033 g, 0. 17 mmol), and trimethylsilylacetylene (1.81 g, 2.60 mL,
8.4 mmol) were placed in a round-bottomed flask. The solution was stirred at
1
room temperature for 3 h, and then at 40 °C for 14 h. After cooling to room
temperature, the solvents were removed under reduced pressure. The product was
purified by column chromatography on silica gel (eluent CHCl –hexane 1:1). The
3
solid obtained by evaporation of the fraction was washed with methanol at 0 °C to
give 1,5-bis(trimethylsilylethynyl)naphthalene (15TMSENp, 365 mg, 38 % yield).
1
H NMR (CDCl , 400 MHz): d 0.33 (s, 18H), 7.50 (dd, J = 7.1, 8.5 Hz, 2H), 7.73
3
(
d, J = 7.1 Hz, 2H), 8.33 (d, J = 8.5 Hz, 2H) ppm; IR (KBr) m 2162, 2900, 2161,
-
140, 1406, 1427, 923, 845, 791 cm .
1
2
1
-Methoxy-4-(trimethylsilylethynyl)naphthalene (1TMSE4MeONp)
1
-Methoxynaphthalene (1.5 mL, 10 mmol) and CCl (50 mL) were placed in a
4
round-bottomed flask equipped with a Dimroth condenser and a dropping funnel. To
the stirred solution, Br (0.5 mL, 10 mmol) in CCl (20 mL) was slowly added via
2
4
the dropping funnel. The solution was stirred at room temperature for 24 h.
M HCl aq. was slowly added until the color of Br disappeared. Et O was added
and the organic extract was dried over Na SO and then evaporated. Purification by
1
2
2
2
4
column chromatography on silica gel (eluent hexane–EtOAc 10:1) gave 1-bromo-4-
methoxynaphthalene (1.94 g, 79 % yield). Data for 1-bromo-4-methoxynaphtha-
1
lene: yellow oil; H NMR (300 MHz, CDCl ) d 3.90 (s, 3H), 6.58 (d, J = 8.4 Hz,
3
1
H), 7.45–7.61 (m, 3H), 8.13 (d, J = 8.7 Hz, 1H), 8.23 (d, J = 8.1 Hz, 1H) ppm.
1
-Bromo-4-methoxynaphthalene (1.66 g, 7.0 mmol), dry Et N (10 mL), dry THF
3
(
10 mL), CuI (40 mg, 0.21 mmol), Pd(PPh ) Cl (148 mg, 0.21 mmol), and
3 2 2
trimethylsilylacetylene (3.0 mL, 21 mmol) were placed in a round-bottomed flask
equipped with a Dimroth condenser, and the mixture was stirred and heated under
reflux for 20 h under an argon atmosphere. After neutralization of the solution with
conc. HCl aq., CHCl and H O were added. The organic extract was dried over
3
2
1
23

Emission and transient absorption measurements
337
Na SO , filtered, and then evaporated to give a residue. Purification by column
2
4
chromatography on silica gel (eluent hexane–EtOAc 20:1) followed by recrystal-
lization from ethanol gave 1-methoxy-4-(trimethylsilylethynyl)naphthalene
(
1TMSE4MeONp, 920 mg, 52 % yield). Data for 1TMSE4MeONp: pink powder;
1
mp 68–71 °C; H NMR (300 MHz, CDCl ) d 0.33 (s, 9H), 4.02 (s, 3H), 6.75 (d,
3
J = 8.1 Hz, 1H), 7.48–7.62 (m, 2H), 7.64 (d, J = 8.1 Hz, 1H), 8.24–8.29 (m, 2H)
1
3
ppm; C NMR (75 MHz, CDCl ) d 0.7 (3C), 55.8, 97.4, 103.4, 103.5, 112.9, 122.2,
3
1
25.2, 125.7, 125.9, 127.3, 131.5, 134.3, 156.0 ppm; IR (KBr) m 3065, 3011, 2948,
146, 1277, 1250, 1092 cm ; GC–MS (EI) m/z (relative intensity, %) 254 (73,
-1
2
M ), 239 (100, M - CH ).
?
?
3
1
-Cyano-4-(trimethylsilylethynyl)naphthalene (1TMSE4CNNp)
1
-Naphthol (1.5 mL, 10 mmol) and CH CN (40 mL) were placed in a round-
3
bottomed flask. To the stirred solution, N-bromosuccinimide (1.78 g, 10 mmol) was
added, and the solution was stirred for 4 h at room temperature. After the solvent
was removed by evaporation, Et O and H O were added. The organic extract was
2
2
dried over Na SO , and then evaporated to give 4-bromo-1-naphthol (2.152 g, 96 %
2
4
1
yield). Data for 4-bromo-1-naphthol: colorless powder, mp 125–128 °C; H NMR
300 MHz, CDCl ) d 5.36 (s, 1H), 6.71 (d, J = 8.1 Hz, 1H), 7.52–7.64 (m, 3H),
(
3
8
.17 (d, J = 8.1 Hz, 1H), 8.20 (d, J = 7.5 Hz, 1H) ppm.
CuCN (903 mg, 10 mmol), 4-bromo-1-naphthol (2.008 g, 9.0 mmol), and N,N-
dimethylformamide (DMF) (10 mL) were placed in a round-bottomed flask
equipped with a Dimroth condenser. The flask was rapidly warmed to 135 °C in
oil bath previously heated to 135 °C, and then stirred for 18 h. After cooling to
room temperature, EtOAc (2 mL) was added, then 10 % NaOH aq. (5 mL). The
mixture was filtered through Celite. The filtrate was acidified to pH 2 by addition of
HCl aq. EtOAc was added, and the organic extract was evaporated. Et O and H O
2
2
were then added, and the ether extract was dried over Na SO , and evaporated to
2
4
give 4-cyano-1-naphthol (155 mg, 11 %). Data for 4-cyano-1-naphthol: brown
1
powder, mp 169–172 °C; H NMR (300 MHz, CDCl ) d 6.30 (s, 1H), 6.86
3
(
d, J = 8.1 Hz, 1H), 7.58–7.74 (m, 2H), 7.79 (d, J = 8.4 Hz, 1H), 8.17 (d, J =
.7 Hz, 1H), 8.28 (d, J = 9.3 Hz, 1H) ppm.
Et N (0.15 mL, 1.1 mmol), CH Cl (5 mL), and 4-cyano-1-naphthol (145 mg,
8
3
2
2
0
bath, (CF SO ) O (0.2 mL, 1.2 mmol) was slowly added with a syringe. The
.92 mmol) were placed in a round-bottomed flask. After cooling to 0 °C in an ice
3
2 2
solution was then warmed to room temperature and stirred for 48 h. Solvents were
removed by evaporation. The residue was dissolved in EtOH (4 mL), and H O
2
(6 mL) was added to give a suspension. Suction filtration gave solid 4-cyano-1-
naphthyl trifluoromethanesulfonate (222 mg, 80 % yield). Data for 4-cyano-
1
1
-naphthyl trifluoromethanesulfonate: brown needles, mp 90–91 °C; H NMR
(300 MHz, CDCl ) d 7.55 (d, J = 8.1 Hz, 1H), 7.79–7.88 (m, 2H), 7.97 (d,
J = 7.8 Hz, 1H), 8.18 (dd, J = 8.1, 1.8 Hz, 1H), 8.33 (dd, J = 7.2, 2.1 Hz, 1H)
3
-
1
ppm; IR (KBr) m 2918, 2850, 2226 (C:N), 1216, 1135 cm
.
-Cyano-1-naphthyl trifluoromethanesulfonate (180 mg, 0.60 mmol), dry Et N
4
3
(
2 mL), dry CH CN (1 mL), PPh3 (37 mg, 0.14 mmol), Pd(OAc)2 (14 mg,
3
123

338
M. Yamaji et al.
0.064 mmol), and trimethylsilylacetylene (0.11 mL, 0.78 mmol) were placed in a
round-bottomed flask equipped with a Dimroth condenser. The solution was heated
under reflux for 19 h under an argon atmosphere. EtOAc (20 mL) and H O were
2
added. The organic extract was dried over Na SO , filtered, and then evaporated.
2
4
Purification by column chromatography on silica gel (eluent hexane–EtOAc 10:1) and
then recrystallization from EtOH gave 1-cyano-4-(trimethylsilylethynyl)naphthalene
(
1TMSE4CNNp, 52 mg, 35 % yield). Data for 1TMSE4CNNp: yellow powder, mp
1
7
J = 7.5 Hz, 1H), 8.23–8.26 (m, 1H), 8.39–8.43 (m, 1H); C NMR (75 MHz, CDCl )
7–79 °C; H NMR (300 MHz, CDCl ) d 0.35 (s, 9H), 7.69–7.74 (m, 3H), 7.85 (d,
3
13
3
d 0.3 (3C), 77.3, 101.4, 104.5, 110.2, 117.6, 125.5, 127.0, 128.3, 128.9, 129.3, 131.6,
-
1
1
32.0, 132.9 ppm; IR (KBr) m 2954, 2225 (C:N), 2157 (C:C), 1247 cm ; GC–MS
? ?
(
EI) m/z (relative intensity, %) 249 (38, M ), 234 (100, M - CH ).
3
2
-(Trimethylsilylethynyl)naphthalene (2TMSENp)
2
-Naphthol (4.25 g, 29.5 mmol), toluene (50 mL), and 30 % (w/v) K PO aq.
4
3
(50 mL) were placed in a round-bottomed flask and the solution was stirred at 0 °C
for 30 min. Trifluoromethanesulfonic acid anhydride (10 g, 35.4 mmol) was slowly
added at 0 °C, carefully keeping the temperature below 10 °C. The solution was
then stirred at room temperature for 30 min. Toluene and H O were added, and the
organic extract was dried over MgSO . Filtration and evaporation gave a residue.
2
4
Column chromatography on silica gel (eluent hexane) gave 2-naphthyltrifluor-
omethanesulfonate (5.61 g, 69 % yield). Data for 2-naphthyl trifluoromethanesul-
1
fonate: colorless solid; H NMR (300 MHz, CDCl ) d 7.37 (dd, J = 9.3, 2.7 Hz,
3
1
J = 9.3 Hz, 1H) ppm; GC–MS (EI) m/z (relative intensity, %) 276 (40, M ), 143
H), 7.54–7.62 (m, 2H), 7.75 (d, J = 2.7 Hz, 1H), 7.85–7.91 (m, 2H), 7.93 (d,
?
?
?
(
65, M - SO CF ), 115 (100, C H ).
2 3 9 7
2
-Naphthyl trifluoromethanesulfonate (5.52 g, 20.0 mmol), dry THF (20 mL),
dry Et N (20 mL), CuI (115 mg, 0.60 mmol), Pd(PPh ) Cl (423 mg, 0.60 mmol),
3
3 2
2
and trimethylsilylacetylene (3.39 mL, 24.0 mmol) were placed in a round-bottomed
flask equipped with a Dimroth condenser, and the mixture was stirred for 20 h at
8
HCl aq., CHCl and H O were added. The organic extract was dried over Na SO ,
0 °C under an argon atmosphere. After neutralization of the solution with conc.
3
2
2
4
filtered, and then evaporated to give a residue. Purification by column chromatog-
raphy on silica gel (eluent hexane) followed by recrystallization from ethanol gave
2
2
-(trimethylsilylethynyl)naphthalene (2TMSENp, 3.92 g, 87 % yield). Data for
1
TMSENp: mp 38–40 °C; H NMR (300 MHz, CDCl ) d 0.29 (s, 9H), 7.46–7.52
3
(
m, 3H), 7.75–7.82 (m, 3H), 8.00 (s, 1H) ppm; GC–MS (EI) m/z (relative intensity,
?
?
%
) 224 (38, M ), 209 (100, M - CH ).
3
2
-(tert-Butylethynyl)naphthalene (2BuENp)
2
-Bromonaphthalene (1.04 g, 5.0 mmol), dry THF (10 mL), dry Et N (10 mL), CuI
3
(
(
28.1 mg, 0.15 mmol), Pd(PPh ) Cl (106 mg, 0.15 mmol), and tert-butylacetylene
3 2 2
0.74 mL, 6.0 mmol) were placed in a round-bottomed flask equipped with a
Dimroth condenser, and the mixture was stirred for 20 h at 80 °C under an argon
1
23

Emission and transient absorption measurements
339
atmosphere. After neutralization of the solution with conc. HCl aq., CHCl and H O
3
2
were added. The organic extract was dried over Na SO , filtered, and then
2
4
evaporated to give a residue. Purification by column chromatography on silica gel
eluent hexane) followed by recrystallization from ethanol gave 2-tert-butylethy-
nylnaphthalene (2BuENp, 694 mg, 67 % yield). Data for 2BuENp: colorless
(
1
needles; mp 63–65 °C; H NMR (300 MHz, CDCl ) d 1.36 (s, 9H), 7.41–7.48 (m,
3
3
H), 7.72–7.80 (m, 3H), 7.89 (s, 1H) ppm; GC–MS (EI) m/z (relative intensity, %)
?
08 (49, M ), 193 (100, M - CH ).
?
2
3
2
,6-Bis(trimethylsilylethynyl)naphthalene (26TMSENp)
26TMSENp was synthesized by Sonogashira coupling reaction of 2,6-dibromo-
naphthalene with trimethylsilylacetylene, in a similar manner to the synthesis of
1
7TMSENp (see below), in 95 % yield. Data for 26TMSENp: H NMR (400 MHz,
2
CDCl ): d 0.27 (s, 18H), 7.49 (dd, J = 8.4, 1.0 Hz, 2H), 7.69 (d, J = 8.4 Hz, 2H),
3
7
1
.94 (d, J = 1.0 Hz, 2H) ppm; IR (KBr) m 2956, 2898, 2152 (C:C), 1593, 1482,
-1
410, 1367, 1248, 1217, 1160, 1125, 969, 939, 898, 841 cm
.
2
,6-Bis(tert-butylethynyl)naphthalene (26BuENp)
26BuENp was synthesized sulfonylation of naphthalene-2,6-diol followed by
Sonogashira coupling with tert-butylacetylene in a similar manner to the synthesis
of 1TMSENp (see above). Data for 2,6-bis(trifluoromethanesulfonyloxy)naphtha-
1
lene: H NMR (300 MHz, CDCl ) d 7.49 (dd, J = 9.0, 2.5 Hz, 2H), 7.83 (d,
3
J = 2.5 Hz, 2H), 7.99 (d, J = 9.0 Hz, 2H) ppm. Data for 26BuENp: (300 MHz,
CDCl ) d 1.35 (s, 18H), 7.41 (dd-like, J = 8.3, 1.8 Hz, 2H), 7.64 (d, J = 8.3 Hz,
3
2
H), 7.83 (d-like, J = 1.8 Hz, 2H) ppm; GC–MS (EI) m/z (relative intensity, %)
?
?
88 (63, M ), 273 (100, M - CH ).
2
3
2
,7-Bis(trimethylsilylethynyl)naphthalene (27TMSENp)
2
,7-Dibromonaphthalene (0.86 g, 3.0 mmol), anhydrous THF (30 mL), Et N
3
(
2.02 g, 2.80 mL, 20.0 mmol), Pd(PPh3)4 (0.17 g, 0.16 mmol), CuI (0.033 g,
.17 mmol), and trimethylsilylacetylene (1.81 g, 2.60 mL, 18.4 mmol) were placed
0
in a round-bottomed flask. The solution was stirred at room temperature for 3 h, and
then at 40 °C for 14 h. After cooling to room temperature, the solvents were
removed under reduced pressure. The product was purified by column chromatog-
raphy on silica gel (eluent CHCl –hexane 1:1). The solid obtained by evaporation of
3
the fraction was washed with methanol at 0 °C to give 2,7-bis(trimethylsilylethy-
nyl)naphthalene (27TMSENp, 0.92 g, 96 % yield). Data for 27TMSENp: H NMR
1
(
400 MHz, CDCl ) d 0.28 (s, 18H), 7.50 (dd, J = 1.7, 8.3 Hz, 2H), 7.71 (d,
3
J = 8.3 Hz, 2H), 7.91 (d, J = 1.7 Hz, 2H) ppm; IR (KBr) m 2963 (C–H), 2155
-
1
(
C:C), 1250 (Si-CH ), 840 (Si(CH ) ) cm .
3
3 3
123

340
M. Yamaji et al.
1
,2,5,6-Tetrakis(trimethylsilylethynyl)naphthalene (1256TMSENp)
Naphthalene-1,5-diol (1.60 g, 10.0 mmol), N-bromosuccinimide (3.56 g,
0.0 mmol), and dry CH CN (40 mL) were placed in a round-bottomed flask.
2
3
The solution was stirred at room temperature for 4 h under an argon atmosphere.
The product was shaken with Et O and H O. The organic layer was dried over
MgSO , filtered, and evaporated. Purification by column chromatography on silica
2
2
4
gel (eluent CHCl –hexane 2:1) gave 2,6-dibromonaphthalene-1,5-diol (807 mg,
3
1
6 % yield). Data for 2,6-dibromonaphthalene-1,5-diol: yellow solid; mp[290 °C;
1
H NMR (300 MHz, CDCl ) d 5.97 (s, 2H), 7.50 (d, J = 8.9 Hz, 2H), 7.69 (d,
3
J = 8.9 Hz, 2H) ppm.
2,6-Dibromonaphthalene-1,5-diol (319 mg, 1.0 mmol), (CF SO ) O (0.40 mL,
3 2 2
2
.4 mmol), dry Et N (0.30 mL, 2.2 mmol), and dry CH Cl (5 mL) were placed in a
3 2 2
round-bottomed flask. The solution was stirred at room temperature for 48 h under an
argon atmosphere. After evaporation of the solution, the residue was dissolved in
EtOH. Addition of H O produced a colorless solid, which was collected by suction
2
filtration. Purification by column chromatography on silica gel (eluent CHCl –hexane
3
2
5
:1) gave 2,6-dibromo-1,5-bis(trifluoromethanesulfonyloxy)naphthalene (236 mg,
2 % yield). Data for 2,6-dibromo-1,5-bis(trifluoromethanesulfonyloxy)naphthalene:
1
colorless solid; mp 153–157 °C; H NMR (300 MHz, CDCl ) d 7.87 (d, J = 9.2 Hz,
3
2
H), 8.02 (d, J = 9.2 Hz, 2H) ppm.
,6-Dibromo-1,5-bis(trifluoromethanesulfonyloxy)naphthalene (227 mg, 0.5 mmol),
Pd(OAc) (11.4 mg, 0.05 mmol), PPh (26.4 mg, 0.1 mmol), trimethylsilylacetylene
2
2
3
(0.37 mL, 2.6 mmol), dry Et N (2 mL), and dry CH CN (1 mL) were placed in a round-
3 3
bottomed flask equipped with a Dimroth condenser. The solution was stirred and heated
under reflux for 19 h under an argon atmosphere. After cooling to room temperature,
Et O and H O were added and the mixture was shaken. The organic extract was dried
2
2
over MgSO , filtered, and evaporated. Purification by column chromatography on silica
4
gel (eluent EtOAc–hexane 1:10, and then CHCl –hexane 1:10) followed by recrystal-
3
lization from EtOH gave 1,2,5,6-tetrakis(trimethylsilylethynyl)naphthalene (1256TM
SENp, 68.5 mg, 27 % yield). Data for 1256TMSENp: colorless solid; mp 171–173 °C;
1
H NMR (300 MHz, CDCl ) d 0.31 (s, 18H), 0.35 (s, 18H), 7.56 (d, J = 8.6 Hz, 2H),
3
13
8
.20 (d, J = 8.6 Hz, 2H) ppm; C NMR (75 MHz, CDCl ) d 0.47 (6C), 0.54 (6C), 100.7
3
(
2C), 100.9 (2C), 103.9 (2C), 105.3 (2C), 124.1 (2C), 125.3 (2C), 126.6 (2C), 129.8 (2C),
?
32.3 (2C) ppm; GC–MS (EI) m/z (relative intensity, %) 513 (46, M ), 73 (100,
1
Si(CH ) ).
?
3
3
2
-Methoxy-6-(trimethylsilylethynyl)naphthalene (2TMSE6MeONp)
2
-Bromo-6-methoxynaphthalene (207 mg, 1.0 mmol), dry Et N (10 mL), dry THF
3
(
10 mL), CuI (61 mg, 0.32 mmol), Pd(PPh ) Cl (215 mg, 0.31 mmol), and
3 2 2
trimethylsilylacetylene (4.2 mL, 30 mmol) were placed in a round-bottomed flask
equipped with a Dimroth condenser. The solution was stirred and heated under
reflux for 20 h under an argon atmosphere. After neutralization of the solution with
conc. HCl aq., CHCl and H O were added. The organic extract was dried over
3
2
Na SO , filtered, and then evaporated to give a residue. Purification by column
2
4
1
23

Emission and transient absorption measurements
341
chromatography on silica gel (eluent hexane–EtOAc 3:1, then hexane–EtOAc 20:1)
followed by recrystallization from ethanol gave 2-methoxy-6-(trimethylsilylethy-
nyl)naphthalene (2TMSE6MeONp, 1.63 g, 64 % yield). Data for 2TMSE6MeONp:
1
colorless needles, mp 98–100 °C; H NMR (300 MHz, CDCl ) d 0.28 (s, 9H), 3.92
3
(
s, 3H), 7.67 (d, J = 2.4 Hz, 1H), 7.14 (dd, J = 9.0, 2.4 Hz, 1H), 7.47 (dd, J = 8.4,
.5 Hz, 1H), 7.65 (d, J = 8.4 Hz, 1H), 7.68 (d, J = 9.0 Hz, 1H), 7.92 (m, 1H) ppm;
1
GC–MS (EI) m/z (relative intensity, %) 254 (89, M ), 239 (100, M - CH ).
?
?
3
2
-Cyano-6-(trimethylsilylethynyl)naphthalene (2TMSE6CNNp)
6
-Bromo-2-naphthol (4.463 g, 20 mmol), CuCN (1.968 g, 22 mmol), and DMF
20 mL) were placed in a round-bottomed flask equipped with a Dimroth condenser.
(
The flask was rapidly warmed to 135 °C in an oil bath previously heated to 135 °C,
and then stirred for 18 h. After cooling to room temperature, EtOAc (2 mL) was
added, then 10 % NaOH aq. (5 mL). The mixture was filtered through Celite. The
filtrate was acidified to pH 2 by addition of HCl aq., then EtOH (3 mL) and H O
2
(
10 mL) were added and evaporated. A small amount of CHCl was then added to
3
solidify the residue. The solid was collected by suction filtration, and found to be
-cyano-2-naphthol (1.933 g, 62 % yield). Data for 6-cyano-2-naphthol: brown
6
1
powder, mp 162–165 °C; H NMR (300 MHz, CDCl ) d 5.45 (s, 1H), 7.19–7.23 (m,
3
2
1
8
H), 7.55 (dd, J = 8.4, 1.5 Hz, 1H), 7.74 (d, J = 8.4 Hz, 1H), 7.81 (d, J = 8.7 Hz,
H), 8.15 (s, 1H) ppm; IR (KBr) m 3338, 2229 (C:N), 1633, 1482, 1289, 1163,
-
1
63 cm
Et N (1.1 mL, 7.9 mmol), CH Cl (10 mL), and 6-cyano-2-naphthol (1.186 g,
.
3
2
2
7
bath, (CF SO ) O (1.4 mL, 8.3 mmol) was slowly added with a syringe. The
.0 mmol) were placed in a round-bottomed flask. After cooling to 0 °C in an ice
3
2 2
solution was then warmed to room temperature, and stirred for 48 h. Solvents were
removed by evaporation. The residue was dissolved in EtOH (32 mL), and H O
2
(
48 mL) was added to give a suspension. Suction filtration gave solid 6-cyano-
2
2
-naphthyl trifluoromethanesulfonate (1.930 g, 95 % yield). Data for 6-cyano-
1
-naphthyl trifluoromethanesulfonate: brown powder, mp 84–88 °C; H NMR
(
300 MHz, CDCl ) d 7.52 (dd, J = 9.0, 2.4 Hz, 1H), 8.37 (dd, J = 8.4, 1.5 Hz,
3
1
8
1
H), 7.82 (d, J = 2.7 Hz, 1H), 7.98 (d, J = 8.7 Hz, 1H), 8.02 (d, J = 9.0 Hz, 1H),
1
3
.30 (br s, 1H) ppm; C NMR (75 MHz, CDCl ) d 111.0, 116.4, 117.2, 120.7,
3
21.7, 125.7, 126.2, 129.5, 130.1, 132.2, 134.0, 148.4 ppm; IR (KBr) m 3063, 2232
-
1
(
C:N), 142, 1343, 1205, 1137 cm
.
-Cyano-2-naphthyl trifluoromethanesulfonate (351 mg, 1.2 mmol), dry Et N
6
2 mL), dry CH CN (1 mL), PPh3 (61 mg, 0.23 mmol), Pd(OAc)2 (27 mg,
3
(
3
0.012 mmol), and trimethylsilylacetylene (0.21 mL, 1.5 mmol) were placed in a
round-bottomed flask equipped with a Dimroth condenser. The solution was heated
under reflux for 19 h under an argon atmosphere. EtOAc (20 mL) and H O were
2
added. The organic extract was dried over Na SO , filtered, and then evaporated.
2
4
Purification by column chromatography on silica gel (eluent hexane–EtOAc 10:1)
and then recrystallization from EtOH gave 2-cyano-6-(trimethylsilylethynyl)naph-
thalene (2TMSE6CNNp, 54 mg, 19 % yield). Data for 2TMSE6CNNp: yellow
1
plates; mp 120–122 °C; H NMR (300 MHz, CDCl ) d 0.29 (s, 9H), 7.61 (m, 2H),
3
123

342
M. Yamaji et al.
7
.83 (d, J = 9.6 Hz, 1H), 7.86 (d, J = 9.3 Hz, 1H), 8.02 (s, 1H), 8.19 (s, 1H) ppm;
-
1
IR (KBr) m 3065, 2956, 2897, 2231 (C:N), 2156 (C:C), 1247 cm ; GC–MS (EI)
?
?
m/z (relative intensity, %) 249 (34, M ), 234 (100, M - CH ).
3
1
-(Trimethylsilylbutadiynyl)naphthalene (1TMSBNp)
1
-(Trimethylsilylethynyl)naphthalene (1TMSENp, 1.13 g, 5.0 mmol), THF
(
10 mL), and n-Bu NF (1 mol/L in THF, 7.5 mL, 7.5 mmol) were placed in a
4
round-bottomed flask. The solution was stirred at room temperature for 4 h. CHCl3
and H O were added, and the organic extract was dried over Na SO . Filtration and
evaporation gave a residue. Column chromatography on silica gel (eluent hexane)
2
2
4
gave 1-ethynylnaphthalene (707 mg, 93 % yield). Data for 1-ethynylnaphthalene:
1
pale brown oil; H NMR (300 MHz, CDCl ) d 3.47 (s, 1H), 7.42 (dd, J = 8.1,
3
7
J = 8.1 Hz, 1H), 7.85 (d, J = 7.5 Hz, 1H), 8.35 (d, J = 8.4 Hz, 1H) ppm; GC–
.2 Hz, 1H), 7.49–7.61 (m, 2H), 7.73 (dd, J = 7.2, 1.2 Hz, 1H), 7.85 (d,
?
MS (EI) m/z (relative intensity, %) 152 (M ); IR (neat) m 3292 (C:C–H), 3058,
-
1
2
101 (C:C) cm
CuI (79.1 mg, 0.80 mmol), CH Cl (5 mL), and TMEDA (0.12 mL, 0.80 mmol)
.
2
2
were placed in a round-bottomed flask. The solution was stirred at room temperature
for 30 min under open-air conditions. Open-air conditions are necessary, but
bubbling of oxygen is not recommended because it led to decomposition of the
product. Trimethylsilylacetylene (1.13 mL, 8.0 mmol), 1-ethynylnaphthalene
(
609 mg, 4.00 mmol), and CH Cl (10 mL) were then added, and the mixture
2 2
was stirred at room temperature for 2 h under open-air conditions. Solids were
removed by filtration through Celite. The filtrate was evaporated to give a residue.
Purification by column chromatography on silica gel (eluent hexane) and HPLC
(
GPC, eluent CHCl ) gave 1-(trimethylsilylbutadiynyl)naphthalene (1TMSBNp,
3
1
86 mg, 56 % yield). Data for 1TMSBNp: pale yellow oil; H NMR (300 MHz,
5
CDCl ) d 0.28 (s, 9H), 7.42 (dd, J = 8.1, 7.2 Hz, 1H), 7.50–7.61 (m, 2H), 7.75 (dd,
3
J = 7.2, 0.9 Hz, 1H), 7.84–7.88 (m, 2H), 8.32 (dd, J = 8.1, 0.6 Hz, 1H) ppm; IR
1
-
(
MS (EI) m/z (relative intensity, %) 248 (59, M ), 233 (100, M - CH ).
neat) m 3059, 2959, 2898, 2198 (C:C), 2098 (C:C), 1250 (Si-CH ) cm ; GC–
3
? ?
3
2
-(Trimethylsilylbutadiynyl)naphthalene (2TMSBNp)
2
-(Trimethylsilylethynyl)naphthalene (2TMSENp, 3.37 g, 15.0 mmol), THF
(
30 mL), and n-Bu NF (1 mol/L in THF, 22.5 mL, 22.5 mmol) were placed in a
4
round-bottomed flask. The solution was stirred at room temperature for 4 h. CHCl3
and H O were added, and the organic extract was dried over Na SO . Filtration and
evaporation gave a residue. Column chromatography on silica gel (eluent hexane)
2
2
4
gave 2-ethynylnaphthalene (2.13 g, 93 % yield). Data for 2-ethynylnaphthalene:
1
colorless solid; H NMR (300 MHz, CDCl ) d 3.15 (s, 1H), 7.47–7.54 (m, 3H),
3
?
.77–7.83 (m, 3H), 8.02 (s, 1H) ppm; GC–MS (EI) m/z 152 (M ).
7
CuI (129 mg, 1.30 mmol), CH Cl (5 mL), and TMEDA (0.195 mL, 1.30 mmol)
2
2
were placed in a round-bottomed flask. The solution was stirred at room temperature
for 30 min under open-air conditions. The open-air conditions are necessary, but
1
23

Emission and transient absorption measurements
343
bubbling of oxygen is not recommended because it led to decomposition of the
product. Trimethylsilylacetylene (1.85 mL, 13.0 mmol), 2-ethynylnaphthalene (990
mg, 6.50 mmol), and CH Cl (10 mL) were then added, and the mixture was stirred
2
2
at room temperature for 2 h under open-air conditions. Solids were removed by
filtration through Celite. The filtrate was evaporated to give a residue. Purification
by column chromatography on silica gel (eluent hexane) and HPLC (GPC, eluent:
CHCl ) gave 2-(trimethylsilylbutadiynyl)naphthalene (2TMSBNp, 990 mg, 61 %
3
1
yield). Data for 2TMSB: colorless solid; mp 75–77 °C; H NMR (300 MHz,
CDCl ) d 0.26 (s, 9H), 7.48–7.53 (m, 3H), 7.76–7.82 (m, 3H), 8.03 (s, 1H) ppm;
3
?
GC–MS (EI) m/z (relative intensity, %) 248 (43, M ), 233 (100, M - CH ).
?
3
Instruments for spectroscopic measurements
Absorption spectra were recorded on a Jasco Ubest 50 spectrophotometer. Emission
spectra were recorded on a Hitachi F-7000 fluorescence spectrometer. Nanosecond
fluorescence lifetimes (s ) were determined by use of a time-correlated single-
f
photon counting fluorimeter (FL-900CDT; Edinburgh Analytical Instruments).
Picosecond fluorescence lifetimes were determined with the third harmonics
(
266 nm) from a femtosecond laser system equipped with a mode-locked
Ti:sapphire laser (Tsunami; Spectra Physics), which had a center wavelength of
00 nm, a pulse width of 70 fs, and a repetition rate of 82 MHz, with a CW green
8
laser (532 nm, 4.5 W, Millennia V; Spectra Physics) for pumping. The excitation
and detection systems for obtaining the time profile of fluorescence are detailed
elsewhere [30]. Fluorescence lifetime and transient absorption measurements were
performed at 295 K. The fluorescence quantum yields (U ) were determined by
F
comparing the fluorescence spectrum of the studied compound with that of
naphthalene in cyclohexane (U = 0.23 ± 0.02 [31]) or anthracene in ethanol
F
(
0.27 ± 0.02 [31]). A XeCl excimer laser (308 nm, Lextra 50; Lambda Physik) and
3
?
the fourth harmonics (266 nm) of a Nd :YAG laser (JK Lasers HY-500; pulse
width 8 ns) were used as the light sources for flash photolysis. The number of laser
pulses for each sample was less than four to avoid excess exposure. Details of the
detection system for the time profiles of the transient absorption have been reported
elsewhere [32]. The transient absorption spectra were obtained by use of an USP-
554 system from Unisoku, which provides a transient absorption spectrum with one
laser pulse.
Cyclohexane (CH, spectroscopic grade from Sigma-Aldrich), methylcyclohexane
Uvasol from Dojin), and isopentane (UV-spectroscopy grade from Fluka) were
(
used as supplied. CH was used as the solvent at 295 K whereas a mixture of
methylcyclohexane and isopentane (3:1 v/v) was used as a matrix for the
phosphorescence measurement at 77 K. All the samples for fluorescence and
transient absorption measurements were degassed in a quartz cell with a 1 cm path
length by means of several freeze–pump–thaw cycles on a high vacuum line. The
concentrations of the samples for emission measurement and laser photolysis were
adjusted to achieve optical densities of less than 0.2 and 1.0, respectively, at the
excitation wavelength.
123

344
M. Yamaji et al.
Acknowledgements
This work was supported by Grants-in-Aid for Scientific Research (KAKENHI)
from JSPS (no. 23350059) and the ‘‘Element Innovation’’ Project by the Ministry of
Education, Culture, Sports, Science, and Technology, Japan (to MY). HM and KM
acknowledge Grants-in-Aid for Scientific Research Scientific Research (KA-
KENHI) from JSPS (nos 20550049 and 23550047), and Cooperation for Innovative
Technology and Advanced Research in Evolutional Areas (CITY AREA) program
from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
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