Fluorescence properties of 1-(silylethynyl)naphthalenes and 1,4-bis(silylethynyl)naphthalenes in solutions, thin films and solid states

Article abstract of DOI:10.1016/j.jphotochem.2017.04.005

1-(Silylethynyl)naphthalenes (1a-e) and 1,4-bis(silylethynyl)naphthalenes (2a-c) were prepared, and their fluorescence properties were evaluated in solutions, thin films and solid states. In dilute solutions, monomer emission is observed from substances in both groups and the relative fluorescence quantum yields of 1a-e increase as the steric bulk of the substituents on silicon increase. The observed concentration dependence of fluorescence intensities indicates that the self-quenching has a more pronounced effect on emission in shorter wavelength regions than that in longer wavelength regions. Analysis of Stern–Volmer type plots shows that formation of both an excimer and a termolecular excited complex is involved in fluorescence quenching of 1 in solution, whereas only an excimer is involved in quenching of 2. Fluorescence in thin films and solid states dispersion in KBr is dependent on number of silylethynyl groups present in the naphthalene derivatives. For example, excimer emission occurs from 1 while monomer emission occurs mainly from 2. X-ray crystallographic analysis of the crystal packing structure shows that 2b would have difficulty with forming an excimer because of steric hindrance, but that 2a can partially form an excimer owing to the slipped head-to-tail parallel orientation of naphthalene rings on neighboring molecules. The results of this effort demonstrate that the emission properties of 1- and 1,4-bis(silylethynyl)naphthalenes are influenced by the number of silylethynyl groups, the steric bulk of substituents on silicon atoms, and the compound's present state.

Full text of DOI:10.1016/j.jphotochem.2017.04.005

Journal of Photochemistry and Photobiology A: Chemistry 342 (2017) 153–160
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Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Fluorescence properties of 1-(silylethynyl)naphthalenes and 1,4-bis
(silylethynyl)naphthalenes in solutions, thin films and solid states
*
**
Hajime Maeda , Takayuki Fujii, Keita Minamida, Kazuhiko Mizuno
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
1-(Silylethynyl)naphthalenes (1a-e) and 1,4-bis(silylethynyl)naphthalenes (2a-c) were prepared, and
their fluorescence properties were evaluated in solutions, thin films and solid states. In dilute solutions,
monomer emission is observed from substances in both groups and the relative fluorescence quantum
yields of 1a-e increase as the steric bulk of the substituents on silicon increase. The observed
concentration dependence of fluorescence intensities indicates that the self-quenching has a more
pronounced effect on emission in shorter wavelength regions than that in longer wavelength regions.
Analysis of Stern–Volmer type plots shows that formation of both an excimer and a termolecular excited
complex is involved in fluorescence quenching of 1 in solution, whereas only an excimer is involved in
quenching of 2. Fluorescence in thin films and solid states dispersion in KBr is dependent on number of
silylethynyl groups present in the naphthalene derivatives. For example, excimer emission occurs from 1
while monomer emission occurs mainly from 2. X-ray crystallographic analysis of the crystal packing
structure shows that 2b would have difficulty with forming an excimer because of steric hindrance, but
that 2a can partially form an excimer owing to the slipped head-to-tail parallel orientation of
naphthalene rings on neighboring molecules. The results of this effort demonstrate that the emission
properties of 1- and 1,4-bis(silylethynyl)naphthalenes are influenced by the number of silylethynyl
groups, the steric bulk of substituents on silicon atoms, and the compound’s present state.
© 2017 Elsevier B.V. All rights reserved.
Received 9 March 2017
Received in revised form 5 April 2017
Accepted 6 April 2017
Available online 8 April 2017
Keywords:
Silylethynylnaphthalenes
Fluorescence
Absorption
Substituent
Excimer
1. Introduction
fluorescence intensities generally decrease as the concentrations
of solutions increase. Furthermore, fluorescence efficiencies are
The development of highly efficient luminescent materials is
important in fields of material science related to light-illumination,
organic electroluminescence and luminescent diodes. Organic
substances have some advantages in applications to photoactive
materials because they possess unique luminescence properties
that are governed by precise molecular designs [1–6]. Previously,
we and others observed that linking silyl and silylethynyl groups to
fused aromatic substances such as naphthalene [7–9], anthracene
[7,10,11], pyrene [7,12–17] and perylene [18] often increases
fluorescence efficiency. However, the highly emissive character
of these molecules is limited to highly dilute solutions because
often low in the solid states of these arenes. These phenomena are
caused by intermolecular stacking, and energy and electron
transfer between neighboring molecules [19–21].
p-p
In the study described below, we prepared mono(silylethynyl)
substituted naphthalenes 1a-e and bis(silylethynyl) substituted
naphthalenes 2a-c (Scheme 1), and explored the effects of
substituents on their fluorescence properties in dilute and
concentrated solutions, thin films and in solid states. Special
emphasis was given to probing the influence of the sterically bulky
silicon substituents and the number of silylethynyl groups on
emission efficiencies.
2. Results and discussion
* Corresponding author. Present address: Division of Material Chemistry,
Graduate School of Natural Science and Technology, Kanazawa University,
Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan
** Corresponding author. Present address: Graduate School of Materials Science,
Nara Institute of Science and Technology (NAIST), 8916-5, Takayama-cho, Ikoma,
Nara 630-0192, Japan.
Measurements of UV absorption and fluorescence spectra of 1a-
e and 2a-c in dilute aerated cyclohexane solutions (Figs. 1 and 2)
gave the data summarized in Table 1. While the wavelengths of the
absorption maxima of 1a-e are similar, their molar absorption
coefficients (e) roughly increase with the increasing steric bulk of
E-mail addresses: maeda-h@se.kanazawa-u.ac.jp (H. Maeda),
kmizuno@ms.naist.jp (K. Mizuno).
the silyl groups (1a < 1b-d < 1e). In contrast, the absorption
http://dx.doi.org/10.1016/j.jphotochem.2017.04.005
1010-6030/© 2017 Elsevier B.V. All rights reserved.

154
H. Maeda et al. / Journal of Photochemistry and Photobiology A: Chemistry 342 (2017) 153–160
results shows that, both presence of phenyl group on silicon and
attachment of a second silylethynyl group on the naphthalene ring
lower both the HOMO and LUMO energies. The fact that the LUMO
energies are lowered by these substituents indicates that they act
as electon-withdrawing groups. The calculated energy gaps
between HOMO and LUMO are 4.24–4.25 eV (1a-e) and 3.73–
3.75 eV (2a-c), which are in good agreement with the wavelengths
of the absorption maxima.
Log-log plots of concentration versus fluorescence intensity of
1a and 2a in cyclohexane solutions are shown in Fig. 3. The plots
show that the intensities of fluorescence from these substances
gradually increase as the concentration is increased in low
concentration range from log[1a] = ꢀ6 to ꢀ4.3 and log[2a] = ꢀ6
to ꢀ4.6. Conversely, increases in the concentrations of 1a above
5 ꢁ10ꢀ5 M and 2a above 2 ꢁ10ꢀ5 M result in decreasing fluores-
cence intensities. Finally, in contrast to fluorescence in the shorter
wavelength regions, emission from 1a and 2a in longer wavelength
regions (349 nm and 431 nm, respectively) does not disappear
when the concentrations of the solutions are high (log[1a or
2a] = ꢀ3 to ꢀ2).
Scheme 1. Silylethynylnaphthalenes.
maxima of 2a-c shift to longer wavelengths with increasing bulk of
silicon substituents (2a < 2b < 2c). However, does not depend on
e
the bulk of these groups. Fluorescence spectra of 1a-e contain
broad signals, whose maximum wavelengths are not appreciably
dependent on Si-substituents. However, the relative fluorescence
quantum yields (Frel) of 1a-e increase as the steric bulk of the silyl
groups increase (1a < 1b < 1c < 1d < 1e). Peaks in the fluorescence
spectra of 2a-c contain fine structure, and the maxima shift to
longer wavelengths in the order of 2a < 2b < 2c which parallels the
bathochromic shift occurring in the corresponding absorption
spectra. Relative fluorescence quantum yields of 2a-c are not
influenced appreciably by Si-substituents. Finally, the fluorescence
lifetimes of the silylethynylnaphthalene derivatives in dilute
aerated cyclohexane are 7.4–8.7 ns (1a-e) and 1.5–1.7 ns (2a-c),
and they decrease as the steric bulk of the silyl groups increases.
The lifetimes are longer (10.4–14.4 ns for 1a-e and 1.6–1.8 ns for
2a-c) in degassed solutions of these substances created by argon
bubbling for 10 min as a consequence of the absence of dioxygen as
the fluorescence quencher [22–25].
Absorption and fluorescence spectra of 2a in dilute (10ꢀ5 M)
and concentrated (10ꢀ2 M) aerated cyclohexane solutions are
displayed in Fig. 4. The absorption spectrum of the 10ꢀ5 M solution
contains maxima at 347 and 331 nm. In contrast, because
absorption in the 350–400 nm region is strong in the spectrum
of a 10ꢀ2 M solution of 2a, the absorption edge shifts from 350 nm
to 400 nm. The fluorescence spectrum of a 10ꢀ5 M solution of this
substance contains emission maxima at 353, 368, and 388 nm. The
intensity of emission in the 400–500 nm region is larger for a
10ꢀ2
M solution, but, because emitted light in the shorter
wavelength region (<400 nm) is re-absorbed by 2a, the band
appears to shift by ca. 50 nm to longer wavelength in comparison to
that of the 10ꢀ5 M solution.
Typically, when a fluorescence quencher (Q) is added to a
solution of a fluorescent molecule (A), quenching of emission takes
place following the Stern–Volmer relationship,
The calculated energies of the HOMOs and LUMOs of the
silylethynyl-napahthalenes are listed in Table 1. Inspection of these
Fig. 2. Fluorescence spectra of (a) 1a-e and (b) 2a-c in aerated cyclohexane
solutions (ca. 1.0 ꢁ10ꢀ5 M). Absorbances at the exciting wavelengths were adjusted
to 0.6.
Fig. 1. UV–vis absorption spectra of (a) 1a-e and (b) 2a-c in aerated cyclohexane
solutions (ca. 5.0 ꢁ10ꢀ5 M).

H. Maeda et al. / Journal of Photochemistry and Photobiology A: Chemistry 342 (2017) 153–160
155
Table 1
UV absorption, fluorescence and calculated energies of the HOMOs and LUMOs of silylethynylnaphthalenes
Compound
Absorptiona
Fluorescenceb
Eigenvaluesc
HOMO (eV)
d
f
g
labs (nm)
log ee
lem (nm)
Frel
tfh (aerated) (ns)
tfi (Ar) (ns)
LUMO (eV)
energy gap (eV)
1a
1b
1c
1d
1e
2a
2b
2c
316
316
317
317
317
347
349
351
4.06
4.11
4.14
4.11
4.15
4.89
4.53
4.93
336
335
337
335
341
368
370
373
1.00
1.10
1.22
1.28
1.48
1.00
1.05
1.04
8.7
8.1
7.7
8.0
7.4
1.7
1.6
1.5
14.4
12.9
12.2
11.3
10.4
1.8
ꢀ5.66
ꢀ5.67
ꢀ5.67
ꢀ5.71
ꢀ5.75
ꢀ5.55
ꢀ5.66
ꢀ5.69
ꢀ1.41
ꢀ1.42
ꢀ1.43
ꢀ1.46
ꢀ1.51
ꢀ1.80
ꢀ1.91
ꢀ1.96
4.25
4.25
4.24
4.25
4.24
3.75
3.75
3.73
1.7
1.6
a
Ca. 5.0 ꢁ10ꢀ5 M in aerated cyclohexane.
b
c
d
e
f
Ca. 1.0 ꢁ10ꢀ5 M in aerated cyclohexane. The compounds were excited at wavelengths labs in this table.
Calculated by using B3LYP/6-31G(d,p).
Peak-top at the longest wavelength.
Logarithm of molar absorption coefficient (e).
Peak-top at highest intensity.
Relative fluorescence quantum yield based on 1a (1b-e) or based on 2a (2b-c).
Fluorescence lifetimes in aerated cyclohexane solutions.
g
h
i
Fluorescence lifetimes in cyclohexane solutions degassed by argon bubbling for 10 min.
I0/I = kqt[Q] + 1
(1)
I0’/I’ = 7.0 ꢁ104[2a] + 1
(4)
where I0 and I are emission intensities in the absence and presence
of quencher Q, is the singlet excited state lifetime and kq is the
t
The linear terms for the concentrations of 1a or 2a in each of
these equations corresponds to the situation in which one
molecule acts to quench the fluorescence of one molecule,
associated with formation of excimers (excited dimers). The
quadratic term in the equation (Eq. (3)), fitting data for quenching
by 1a, corresponds to the situation in which two molecules of 1a
are involved in quenching one fluorescent molecule via formation
of a termolecular excited complex.
quenching rate constant. However, when the quencher is also the
fluorescent molecule (as in the cases of 1a and 2a), the Stern–
Volmer equation changes to
I0’/I’ = kqt[A] + 1
(2)
where
I;0 ¼ lim ðI=½AꢂÞ
½Aꢂ!0
The difference between the quenching behaviors of 1a and 2a
can be explained by invoking a steric argument. As can be seen by
viewing CPK models [26] (Fig. 6), the mono(silylethynyl)
By using this analysis, plots of I0’/I’ versus the concentrations of
1a and 2a in low concentration ranges (Fig. 5) fit the respective
equations Eqs. (3) and (4).
derivatives 1a-e are capable of undergoing naphthalene
p-p
stacking in a head-to-tail manner to form excimers. Moreover, in
this case formation of even a termolecular excited complex is not
blocked by steric hindrance. However, in the case of bis
(silylethynyl) derivatives 2a-c, the presence of sterically bulky
substituents causes weakening of excimer forming intermolecular
I0’/I’ = 7.4 ꢁ108[1a]2 + 1.7 ꢁ104[1a] + 1
(3)
p-p stacking interactions between even two molecules and it
completely prevents formation of termolecular excited complexes.
Because of these factors, the efficiencies of fluorescence quenching
depends on the number of silylethynyl groups present in the
naphthalene derivatives.
The fluorescence behaviors of these substances in thin films and
solid states were investigated next. Thin films were prepared by
spin-coating of CHCl3 solutions of compounds 1e and 2a on glass
Fig. 3. Concentration dependence of fluorescence intensities of (a) 1a and (b) 2a in
aerated cyclohexane solutions.
Fig. 4. Absorption and fluorescence spectra of 2a in aerated cyclohexane.

156
H. Maeda et al. / Journal of Photochemistry and Photobiology A: Chemistry 342 (2017) 153–160
Fig. 5. Plots of I0'/I' versus concentration of (a) 1a and (b) 2a.
Fig. 7. Fluorescence spectra of (a) thin films and (b) 10ꢀ2 M cyclohexane solution of
1e, (c) thin films and (d) 10ꢀ2 M cyclohexane solution of 2a.
slides. Concentrations of these substances in the solutions used to
create the thin films along with fluorescence spectra of the
resulting films are shown in Fig. 7(a) and (c). In Fig. 7(b) and (d) are
displayed fluorescence spectra of 10ꢀ2 M solutions of these
substances for comparison purposes. Inspection of the spectra
shows that the fluorescence band of 1e in the thin films are shifted
to longer wavelength as compared to that in a 10ꢀ2 M solution. In
addition, the absorption band is broad, suggesting that the
emission arises from an excimer. Conversely, bands for fluores-
cence of 2a in thin films have fine structure and maxima at similar
(Fig. 7(a)). In addition, fluorescence decay of 1e in KBr contains two
components (11.2 and 57.4 ns). The results suggest that fluores-
cence of 1e in KBr is comprised of emission from both an excimer
(major) and a monomer (minor). On the other hand, solid state
fluorescence of 2a-c (Fig. 9(b)) appears in a similar wavelength
region and has a similar vibrational fine structure (especially for 2a
and 2b) as that of a thin film (Fig. 7(c)). Fluorescence decay of 2c is
also comprised of two components (3.7 and 9.7 ns), which together
with the other observations show that fluorescence of 2a-c in KBr
contains monomer (major) and excimer (minor) emissions.
It is known that distance between two simple naphthalene
molecules in an intramolecular excimer is about 3–4 Å in solutions
[27]. By using CPK models in Fig. 6, if 2a-c would form excimer by
face-to-face parallel approach, we roughly estimated the distance
between two naphthalene rings requires about 5–6 Å. Therefore,
the long distance is not suitable for formation of stable excimers.
Crystal packings of 2a and 2b obtained from X-ray crystallo-
graphic analysis are shown in Fig. 10. One pair of two molecules
(blue and red) are observed, whose benzene rings without
substituents are located close to one another. Distances between
two naphthyl groups in pairs of compounds are 3.4 (2a) and 8.1
(2b) Å, respectively. From these results, it is supposed that 2a can
partially form excimers according to the slipped head-to-tail
parallel location of naphthalene rings, whereas 2b hardly forms
excimers.
wavelengths to those in the spectrum of this substance in a 10ꢀ2
M
solution. These observations indicate that a monomer of 2a is
responsible for fluorescence in a thin film. It is reasonable to
conclude that fluorescence behavior of the naphthalene deriva-
tives in thin films is largely influenced by the number of
silylethynyl groups and less influenced by substituents on silicon
atoms.
In order to measure solid state fluorescence spectra, 1e, 2a-c,
which are solids at room temperature, were mixed with KBr (1e or
2a-c: KBr = 1: 60 wt%) and ground. The fluorescence colors and
spectra of the KBr mixtures are shown in Fig. 8 and 9. Excitation
wavelengths used to obtain these spectra were the absorption
maxima in diffuse reflection spectra of the substances (Figs. S1-S4).
As can be seen by viewing Fig. 9(a), fluorescence of 1e in KBr is
greatly shifted to longer wavelength as compared to emission in a
10ꢀ2 M cyclohexane solution. However, the emission wavalength
maximum is similar to that of a thin film of this substance
Fig. 6. CPK models of 1a, 1e, 2a, and 2c, indicating distances between two
naphthalene rings by the close approach of two molecules, calculated by B3LYP/6-
31G(d,p).
Fig. 8. Fluorescence colors of 1e and 2a-c dispersed in KBr (1e, 2a-c/KBr = 10 mg/
600 mg, lex = 365 nm).

H. Maeda et al. / Journal of Photochemistry and Photobiology A: Chemistry 342 (2017) 153–160
157
emission. In thin films and solid states dispersed in KBr as models
of high concentrated state, excimer emission was observed from 1,
which is hardly observed in solutions even at high concentration
(10ꢀ2 M). However, in thin films and solid state of 2, monomer
emission was mainly observed along with a minor contribution
from excimer emission owing to the difficulty of forming excimers
caused by steric hindrance arising from substituents. Overall, the
emission properties are influenced by the concentration of the
emissive species in the media. The ease of approach of emissive
molecules is governed by substitution numbers of silylethynyl
groups and substituents on silicon atoms.
3. Conclusions
In summary, in this effort we synthesized silylethynyl-
substituted naphthalenes and elucidated their fluorescence
properties in solutions, thin films, and the solid state. Lumines-
cence from electronically excited molecules of silylethynylnaph-
thalenes can be divided into components involving fluorescence
from monomers and excimers. The degree of aggregation of excited
molecules, which determines the major component responsible
for emission, depends on the state in which the substance exists
ranging from dilute solutions, concentrated solutions, thin films up
to solid states. The results arising from this effort might provide
valuable insight into design of luminescent materials based on
silyl-substituted aromatic compounds.
4. Experimental section
Fig. 9. Fluorescence spectra of (a) 1e and (b) 2a-c dispersed in KBr (1e, 2a-c/
KBr = 10 mg/600 mg) and 1e, 2c in aerated cyclohexane (1.0 ꢁ10ꢀ2 M).
4.1. Materials and equipment
The proposed luminescence mechanism is summarized in
Fig. 11. In solution at low concentration (10ꢀ5 M), monomer
emission is observed from 1 and 2. However, in solution at high
concentration (10ꢀ2 M), re-absorption of fluorescence occurs,
hence fluorescence was self-quenched (concentration-quenching)
especially at shorter wavelength region. The second factor related
to fluorescence quenching under concentrated conditions is the
formation of excimers (from 1 and 2) and termolecular excited
complexes (from 1), whose fluorescence intensity is not high
because of low concentration and low emission efficiency. Bulky
substituents on the silicon atoms interrupt intermolecular
interactions and lead to an enhanced intensity of monomer
Acetonitrile was distilled from CaH2 and then from P2O5.
Benzene was distilled from CaH2 and then from Na. Melting points
were determined on a Yanagimoto Micro Melting Point apparatus,
Yanaco MP-500 and are reported uncorrected. 1H and 13C NMR
spectra were recorded using a Varian MERCURY-300 (300 MHz and
75 MHz, respectively) spectrometer with Me4Si as an internal
standard. IR spectra were determined using a Jasco FT/IR-230
spectrometer. UV–vis spectra were recorded using a Jasco V-530
spectrophotometer. Diffuse reflection spectra were obtained by
using a Jasco V-570 spectrophotometer. Fluorescence spectra were
recorded using a Jasco FP-6300 spectrophotometer. Fluorescence
lifetimes were measured by using time correlation and a single
photon counting methodology, with a HORIBA NanoLED-370/
Monochrometor/TBX-05C/TBX-PS fluorometer. Mass spectra (EI)
were recorded on a SHIMADZU GCMS-QP5050 operating in the
electron impact mode (70 eV) equipped with GC-17A and DB-5MS
column (J&W Scientific Inc., Serial: 8696181). HPLC separations
were performed on a recycling preparative HPLC equipped with
Jasco PU-2086 Plus, RI-2031 Plus differential refractometer,
Megapak GEL 201C columns (GPC) using CHCl3 as an eluent.
Column chromatography was conducted by using Kanto-Chemical
Co. Ltd., silica gel 60 N (spherical, neutral, 0.063–0.200 mm). X-ray
crystallographic data for single crystals were obtained using a
Rigaku RAXIS RAPID imaging plate area detector with graphite
monochromated Mo-Ka radiation. The structure was solved by
using direct methods (SIR92) and expanded by using Fourier
techniques. All calculations were performed using the Crystal
Structure crystallographic software package.
4.2. Preparation of 1-(trimethylsilylethynyl)naphthalene (1a)
A mixture of 1-bromonaphthalene (2.8 mL, 20 mmol), CuI
(0.114 g, 0.6 mmol), Pd(PPh3)2Cl2 (0.403 g, 0.57 mmol), Et3N
(10 mL), THF (5 mL) and trimethylsilylacetylene (4.2 mL, 30 mmol)
was stirred at reflux for 20 h under argon. Conc HCl aq was added to
Fig. 10. Crystal packings in ORTEP plots of X-ray crystallographic data of 2a and 2b.

158
H. Maeda et al. / Journal of Photochemistry and Photobiology A: Chemistry 342 (2017) 153–160
Fig. 11. Luminescence mechanism in solution, thin film, and solid state.
neutralize the solution. CHCl3 (20 mL) and H2O (20 mL) were added
and the organic layer was separated, dried over Na2SO4, filtered,
and concentrated in vacuo. The residue was subjected to silica gel
column chromatography (n-hexane:CHCl3 = 10:1) followed by
distillation under reduced pressure to give 1-(trimethylsilyle-
thynyl)naphthalene (1a, 3.2 g, 72% yield) [28]. Pale yellow oil; bp
silica gel column chromatography (n-hexane) followed by HPLC
(GPC) to give 1-(tert-butyldimethylsilylethynyl)naphthalene (1b,
179 mg, 79% yield). Pale yellow oil; 1H NMR (300 MHz, CDCl3)
d
0.27 (s, 6H), 1.06 (s, 9H), 7.40 (dd, J = 8.3, 7.2 Hz, 1H), 7.50–7.59 (m,
2H), 7.70 (dd, J = 7.1, 1.2 Hz,1H), 7.80–7.85 (m, 2H), 8.34 (d, J = 8.2 Hz,
1H) ppm; 13C NMR (75 MHz, CDCl3)
d
ꢀ4.0, 17.2, 26.6, 97.8, 103.8,
156 ꢃC/4 mmHg; 1H NMR (300 MHz, CDCl3)
d 0.34 (s, 9H), 7.41 (dd,
120.9, 125.1, 126.2, 126.3, 126.8, 128.2, 128.9, 130.9, 133.1,
J = 8.2, 7.1 Hz, 1H), 7.49–7.61 (m, 2H), 7.70 (dd, J = 7.1, 1.2 Hz, 1H),
133.4 ppm; IR (neat) n
2153, 2856, 2884, 2952, 3059 cmꢀ1; MS
7.80–7.85 (m, 2H), 8.33 (d, J = 8.9 Hz, 1H) ppm; 13C NMR (75 MHz,
(EI) m/z (relative intensity) 209 (100, M+-tBu), 266 (11, M+).
CDCl3)
d 0.55, 99.5, 103.1, 120.7, 125.1, 126.2, 126.3, 126.8, 128.2,
128.9, 130.8, 133.0, 133.3 ppm; IR (neat)
n 1250, 1392, 2147, 2959,
4.4. Preparation of 1-(triisopropylsilylethynyl)naphthalene (1c)
3059 cmꢀ1; MS (EI) m/z (relative intensity) 179 (10, M+-C3H9), 209
(100, M+-CH3), 224 (43, M+).
To a THF (10 mL) solution of 1-ethynylnaphthalene (111 mg,
0.73 mmol) was slowly added n-BuLi (1.6 M hexane solution,
0.7 mL, 1.1 mmol) at ꢀ78 ꢃC under argon. The solution was then
stirred for 1 h at ꢀ78 ꢃC. A THF (10 mL) solution of i-Pr3SiCl
(0.47 mL, 2.2 mmol) was slowly added, and the solution was stirred
at reflux for 8 h. Et2O (20 mL) and sat NH4Cl aq (20 mL) were added
and the organic layer was separated, dried over Na2SO4, filtered,
and concentrated in vacuo. The residue was subjected to silica gel
column chromatography (n-hexane) followed by HPLC (GPC) to
give 1-(triisopropylsilylethynyl)naphthalene (1c, 110 mg, 49%
4.3. Preparation of 1-(tert-butyldimethylsilylethynyl)naphthalene (
1b)
To a THF (5.0 mL) solution of 1-(trimethylsilylethynyl)naphtha-
lene (1a, 337 mg, 1.5 mmol) was added n-Bu4N+Fꢀ (1 M THF
solution, 2.2 mL, 2.2 mmol) under an argon atmosphere, and the
resulting solution was stirred for 4 h at room temperature. CHCl3
(20 mL) and H2O (20 mL) were added and the organic layer was
separated, dried over Na2SO4, filtered, and concentrated in vacuo.
The residue was subjected to silica gel column chromatography (n-
hexane) to give 1-ethynylnaphthalene (205 mg, 90% yield) [29].
yield) [30]. Pale yellow oil; 1H NMR (300 MHz, CDCl3)
d 1.20–
1.21 (m, 21H), 7.41 (dd, J = 8.3, 7.1 Hz, 1H), 7.48–7.60 (m, 2H), 7.72
(dd, J = 7.1, 1.2 Hz, 1H), 7.80–7.85 (m, 2H), 8.39 (d, J = 8.3 Hz, 1H)
Colorless oil; 1H NMR (300 MHz, CDCl3)
d
3.47 (s, 1H), 7.42 (dd,
ppm; 13C NMR (75 MHz, CDCl3)
d
11.8, 19.1, 95.9, 105.0, 121.2, 125.1,
J = 8.2, 7.0 Hz, 1H), 7.50–7.60 (m, 2H), 7.73 (d, J = 8.0 Hz, 1H), 7.85 (d,
J = 8.1 Hz, 2H), 8.35 (d, J = 8.7 Hz,1H); MS (EI) m/z (relative intensity)
76 (78, M+-C6H4), 152 (100, M+).
126.3, 126.3, 126.8, 128.2, 128.7, 131.0, 133.1, 133.4 ppm; IR (neat)
n
737, 772, 798, 881, 996, 1013, 1074, 1392, 1462, 2815, 2864, 2889,
2941 cmꢀ1; MS (EI) m/z (relative intensity) 105 (100), 265 (78, M+-
C3H7), 308 (32, M+).
To a THF (10 mL) solution of 1-ethynylnaphthalene (127 mg,
0.83 mmol) was slowly added n-BuLi (1.6 M hexane solution,
0.8 mL, 1.3 mmol) at ꢀ78 ꢃC under argon. The solution was then
stirred for 1 h at ꢀ78 ꢃC. A THF (10 mL) solution of t-BuMe2SiCl
(376 mg, 2.5 mmol) was slowly added, and the solution was stirred
at reflux for 20 h. Et2O (20 mL) and sat NH4Cl aq (20 mL) were
added and the organic layer was separated, dried over Na2SO4,
filtered, and concentrated in vacuo. The residue was subjected to
4.5. Preparation of 1-(dimethylphenylsilylethynyl)naphthalene (1d)
To a THF (10 mL) solution of 1-ethynylnaphthalene (173 mg,
1.1 mmol) was slowly added n-BuLi (1.6 M hexane solution, 1.1 mL,
1.7 mmol) at ꢀ78 ꢃC under an argon atmosphere. The resulting
solution was stirred for 1 h at ꢀ78 ꢃC. A THF (10 mL) solution of

H. Maeda et al. / Journal of Photochemistry and Photobiology A: Chemistry 342 (2017) 153–160
159
PhMe2SiCl (0.35 mL, 3.4 mmol) was slowly added, and the solution
was stirred at reflux for 14 h. Et2O (20 mL) and sat NH4Cl aq (20 mL)
were added and the organic layer was separated, dried over
Na2SO4, filtered, and concentrated in vacuo. The residue was
subjected to silica gel column chromatography (n-hexane)
followed by HPLC (GPC) to give 1-(dimethylphenylsilylethynyl)
naphthalene (1d, 219 mg, 67% yield). Pale yellow oil; 1H NMR
4.8. Preparation of 1,4-bis(dimethylphenylsilylethynyl)naphthalene
(2b)
To a THF (10 mL) solution of 1,4-bis(trimethylsilylethynyl)
naphthalene (2a, 624 mg, 1.0 mmol) was added n-Bu4N+Fꢀ (1 M
THF solution, 6.0 mL, 6.0 mmol) under argon. The resulting solution
was stirred for 4 h at room temperature. CHCl3 (20 mL) and H2O
(20 mL) were added and the organic layer was separated, dried
over Na2SO4, filtered, and concentrated in vacuo. The residue was
subjected to silica gel column chromatography (n-hexane) to give
1,4-diethynylnaphthalene (304 mg, 86% yield) [32]. Blood red
(300 MHz, CDCl3)
2H), 7.74–7.78 (m, 3H), 7.83–7.85 (m, 2H), 8.35 (d, J = 8.0 Hz, 1H)
ppm; 13C NMR (75 MHz, CDCl3)
d 0.58 (s, 6H), 7.39–7.45 (m, 4H), 7.49–7.59 (m,
d
ꢀ0.2, 97.4, 104.8, 120.6, 125.1,
126.2, 126.4, 126.9, 127.9, 128.2, 129.2, 129.4, 131.0, 133.0, 133.4,
133.8, 137.0 ppm; MS (EI) m/z (relative intensity) 271 (100, M+-
CH3). 286 (34, M+).
solid; 1H NMR (300 MHz, CDCl3)
d 3.55 (s, 2H), 7.62 (dd, J = 6.5,
3.4 Hz, 2H), 7.67 (s, 2H), 8.45 (dd, J = 6.0, 3.1 Hz, 2H) ppm; MS (EI) m/
z (relative intensity) 150 (13, M+-C2H), 176 (100, M+).
To a THF (7.5 mL) solution of 1,4-diethynylnaphthalene (275 mg,
1.56 mmol) was slowly added n-BuLi (1.6 M hexane solution,
5.0 mL, 7.8 mmol) at ꢀ78 ꢃC under an argon atmosphere, then the
solution was stirred for 1 h at ꢀ78 ꢃC. A THF (7.5 mL) solution of
PhMe2SiCl (1.05 mL, 6.2 mmol) was slowly added, and the solution
was stirred at reflux for 20 h. Et2O (20 mL) and sat NH4Cl aq (20 mL)
were added and the organic layer was separated, dried over
Na2SO4, filtered, and concentrated in vacuo. The residue was
subjected to silica gel column chromatography (n-hexane)
followed by crystallization by azeotropic distillation with MeOH
to give 1,4-bis(dimethylphenylsilylethynyl)naphthalene (2b,
4.6. Preparation of 1-(tert-butyldiphenylsilylethynyl)naphthalene (
1e)
To a THF (10 mL) solution of 1-ethynylnaphthalene (181 mg,
1.2 mmol) was slowly added n-BuLi (1.6 M hexane solution, 1.2 mL,
1.8 mmol) at ꢀ78 ꢃC under an argon atmosphere. The solution was
t
then stirred for 1 h at ꢀ78 ꢃC. A THF (10 mL) solution of Ph2 BuSiCl
(0.92 mL, 3.6 mmol) was slowly added, and the solution was stirred
at reflux for 20 h. Et2O (20 mL) and sat NH4Cl aq (20 mL) were
added and the organic layer was separated, dried over Na2SO4,
filtered, and concentrated in vacuo. The residue was subjected to
silica gel column chromatography (n-hexane) followed by HPLC
(GPC) to give 1-(tert-butyldiphenylsilylethynyl)naphthalene (1e,
328 mg, 72% yield). Pale yellow solid; mp 70–74 ꢃC; 1H NMR
106 mg, 15% yield). Colorless solid; 1H NMR (300 MHz, CDCl3)
d
0.60 (s, 12H), 7.42–7,46 (m, 6H), 7.61 (dd, J = 6.3, 3.3 Hz, 2H), 7.69 (s,
2H), 7.76–7.79 (m, 4H), 8.39 (dd, J = 6.2, 3.2 Hz, 2H) ppm; 13C NMR
(75 MHz, CDCl3)
d
ꢀ0.3, 99.5, 104.5, 121.5, 126.6, 127.3, 128.0, 129.5,
(300 MHz, CDCl3)
2H), 7.84–7.95 (m, 7H), 8.47 (d, J = 8.2 Hz, 1H) ppm; 13C NMR
(75 MHz, CDCl3) 19.2, 27.6, 94.7, 107.2, 120.7, 125.1, 126.2, 126.5,
127.0,127.8,128.3,129.3,129.5,131.4,133.1,133.4,133.5,135.6 ppm;
d 1.22 (s, 9H), 7.37–7.49 (m, 7H), 7.52–7.62 (m,
130.1, 133.1, 133.7, 136.7 ppm; MS (EI) m/z (relative intensity) 207
(94), 429 (100, M+-CH3), 444 (76, M+).
d
IR (KBr)
n
1107, 1428, 2156, 2856, 2952, 3069 cmꢀ1; MS (EI) m/z
4.9. Preparation of 1,4-bis(tert-butyldiphenylsilylethynyl)
naphthalene (2c)
(relative intensity) 255 (17, M+-tBuPh), 333 (100, M+-tBu), 390 (3,
M+).
To a THF (5 mL) solution of 1,4-diethynylnaphthalene (111 mg,
0.63 mmol) was slowly added n-BuLi (1.6 M hexane solution,
2.0 mL, 3.1 mmol) at ꢀ78 ꢃC under argon. The resulting solution
4.7. Preparation of 1,4-bis(trimethylsilylethynyl)naphthalene (2a)
t
was stirred for 1 h at ꢀ78 ꢃC. A THF (5 mL) solution of Ph2 BuSiCl
To a mixture of naphthalene (25.635 g, 200 mmol), Fe powder
(113 mg, 2 mmol) and CCl4 (190 mL) was slowly added Br2 (20 mL,
400 mmol). The mixture was then stirred for 5 h at room
temperature. NaOH aq was added to neutralize the solution.
Et2O (250 mL) and brine (100 mL) were added and the organic layer
was separated, dried over Na2SO4, filtered, and concentrated in
vacuo to give a crystalline solid. Recrystallization from EtOH
(twice) gave 1,4-dibromonaphthalene (4.226 g, 44% yield) [31].
(0.6 mL, 2.3 mmol) was slowly added, and the resulting solution
was stirred at reflux for 20 h. Et2O (20 mL) and sat NH4Cl aq (20 mL)
were added and the organic layer was separated, dried over
Na2SO4, filtered, and concentrated in vacuo. The residue was
subjected to silica gel column chromatography (n-hexane)
followed by crystallization by azeotropic distillation with MeOH
to give 1,4-bis(tert-butyldiphenylsilylethynyl)naphthalene (2c,
66 mg, 37% yield). Colorless solid; 1H NMR (300 MHz, CDCl3)
d
Pale yellow solid; 1H NMR (300 MHz, CDCl3)
d 7.63 (s, 2H), 7.65 (dd,
1.23 (s,18H), 7.39–7.47 (m,12H), 7.65 (dd, J = 6.3, 3.3 Hz, 2H), 7.81 (s,
J = 6.7, 3.4 Hz, 2H), 8.25 (dd, J = 6.1, 3.2 Hz, 2H) ppm; MS (EI) m/z
(relative intensity) 126 (100, M+-Br2), 205 (18, M+-Br), 285 (79, M+).
A mixture of 1,4-dibromonaphthalene (2.48 g, 8.7 mmol), CuI
(66.2 mg, 0.34 mmol), Pd(PPh3)2Cl2 (56.2 mg, 0.8 mmol), Et3N
(30 mL), THF (20 mL) and trimethylsilylacetylene (3.0 mL,
21.2 mmol) were stirred at reflux for 20 h under argon. Conc HCl
aq was added to neutralize the solution. CHCl3 (20 mL) and H2O
(20 mL) were added and the organic layer was separated, dried
over Na2SO4, filtered, and concentrated in vacuo. The residue was
subjected to silica gel column chromatography (n-hexane:CHCl3 =
10:1) followed by recrystallization from MeOH (twice) to give 1,4-
bis(trimethylsilylethynyl)naphthalene (2a, 1.85 g, 66% yield) [32].
2H), 7.92–7.95 (m, 8H), 8.50 (dd, J = 6.4, 3.2 Hz, 2H) ppm; 13C NMR
(75 MHz, CDCl3)
d 19.2, 27.6, 97.0, 106.8, 121.8, 126.6, 127.6, 127.8,
129.6, 130.5, 133.1, 133.3, 135.6 ppm.
4.10. Preparation of thin films
Slide glasses (Matsunami micro slide glass S-111) were
immersed in toluene for 30 min for the purpose of hydrophobic
treatment, and then dried. The slide glass was attached on a
MIKASA 1H-D7 spincoater. Respective CHCl3 solutions of com-
pounds 1e and 2a (1.0 ꢁ10ꢀ2 M, 1.0 ꢁ10ꢀ3 M, and 1.0 ꢁ10ꢀ4 M)
were dropped by a syringe on the silde glasses. The slide glass was
spun with time program of (i) 50 rpm for 5 min, (ii) 200 rpm for
10 min, (iii) 40 rpm/min increasing for 5 min, (iv) 400 rpm for
5 min, and (v) 100 rpm/min decreasing for 4 min.
Pale yellow solid; 1H NMR (300 MHz, CDCl3)
(dd, J = 6.5, 3.4 Hz, 2H), 7.62 (s, 2H), 8.34 (dd, J = 6.5, 3.3 Hz, 2H)
ppm; 13C NMR (75 MHz, CDCl3)
0.5, 101.4, 102.8, 121.5, 126.5,
d 0.33 (s, 18H), 7.61
d
127.2, 129.9, 133.0 ppm; MS (EI) m/z (relative intensity) 305 (100,
M+-CH3), 320 (79, M+).

160
H. Maeda et al. / Journal of Photochemistry and Photobiology A: Chemistry 342 (2017) 153–160
[9] M. Yamaji, H. Maeda, K. Minamida, T. Maeda, K. Asai, G. Konishi, K. Mizuno, Res.
Acknowledgements
Chem. Intermed. 39 (2013) 321–345.
[10] S. Kyushin, M. Ikarugi, M. Goto, H. Hiratsuka, H. Matsumoto, Organometallics
This study was financially supported by Cooperation for
Innovative Technology and Advanced Research in Evolutional
Areas (CITY AREA) program and Grant-in-Aids for Scientific
Research (C) (20550049, 23550047, 23550058, 26410040,
26410049) from the Ministry of Education, Culture, Sports, Science,
and Technology (MEXT) of Japan. H.M. is grateful for financial
support from A-STEP (Adaptable and Seamless Technology
Transfer Program through target-driven R&D, JST) and Kanazawa
University SAKIGAKE Project.
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