Naphthalimide-based fluorescent dyes: Impact of extension of φ-conjugation and introduction of an electron-donating moiety on the photophysical properties

Article abstract of DOI:10.1246/bcsj.20180151

Concerning a series of naphthalimide-based fluorescence dyes in which the φ-system is extended with oligothiophene units, it has been revealed that the absorption and fluorescence maxima can be tuned over ca. 100 nm and ca. 180 nm range by extending φ-conjugation, respectively. The effects of the solvent on the fluorescence quantum yield depend on the conjugation length. For the same series but with an electron-donating moiety (push-pull type dyes), the absorption and fluorescence maxima are less dependent on the conjugation length. The fluorescence quantum yields of the push-pull type dyes are large in toluene (>0.3) but extremely low in DMSO. These results will be a guide for the design of naphthalimide-based sensors and probes.

Full text of DOI:10.1246/bcsj.20180151

Naphthalimide-Based Fluorescent Dyes: Impact of Extension
of π-Conjugation and Introduction of an Electron-Donating
Moiety on the Photophysical Properties
Joe Otsuki,* Minori Yamano, Tae Yamano, and Kosuke Sugawa
College of Science and Technology, Nihon University, 1-8-14 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8308, Japan
E-mail: otsuki.joe@nihon-u.ac.jp
Received: May 28, 2018; Accepted: July 11, 2018; Web Released: September 28, 2018
Joe Otsuki
Joe Otsuki received his Ph.D. in chemistry from the University of Tokyo in 1991. He then worked as a
research associate at the Institute of Industrial Science, University of Tokyo until 1999. In 1993, he worked
as a postdoctoral research fellow at Université Louis Pasteur (presently, Université de Strasbourg) in the
group of Jean-Marie Lehn. He then moved to the College of Science and Technology, Nihon University,
where he currently works as a professor. His research focuses on photo-/electro-active (supra)molecular
devices and materials. More information at http://www.chem.cst.nihon-u.ac.jp/>otsuki/otsuki.html.
Abstract
and ratiometric analysis as well as Förster-type resonance
energy transfer (FRET) applications. There are two typical
ways to shift the absorption/fluorescence wavelengths towards
the red. One is to extend the π-conjugation. The other is to
introduce an electron-donating or electron-withdrawing moi-
ety. Introduction of both electron-donating and electron-
withdrawing moieties to make the molecule a push-pull type
is particularly effective in red-shifting the electronic transitions.
To apply the latter strategy to the naphthalimide derivatives,
introducing an electron-donating moiety via a π-bridge to the
naphthalimide framework suffices as the naphthalimide unit
serves an electron withdrawing group.
With these backgrounds in mind, we need to know how
much the absorption and fluorescence are red-shifted by π-
extension and/or introduction of an electron-donating moi-
ety as a practical guide for the design of elaborate multicolor
sensors. While photophysical properties have been extensively
investigated for the parent naphthalimide and its derivatives, in
which substituents are directly introduced onto the naphthalene
core,9-16 less is known for π-extended naphthalimide deriva-
tives. We have chosen a thiophene group, which is chemically
stable and has attracted attention as a functional π-system for
optoelectronic applications,17-19 as a component for the π-
bridge. The choice of thiophene as a π-bridge may be justified
in light of the purpose of bringing the optical transitions to
longer wavelength regions because oligothiophenes are among
π-conjugated oligomers that show the lowest-energy absorp-
tion. For example, the absorption energy of oligothiophenes20
are the lowest when compared to oligophenylenes,21 oligopyr-
roles,22 and oligoynes23 with the same numbers of monomeric
units. We report herein the preparation and photophysics of
naphthalimide derivatives which are π-extended with oligo-
Concerning a series of naphthalimide-based fluorescence
dyes in which the π-system is extended with oligothiophene
units, it has been revealed that the absorption and fluorescence
maxima can be tuned over ca. 100 nm and ca. 180 nm range by
extending π-conjugation, respectively. The effects of the sol-
vent on the fluorescence quantum yield depend on the conju-
gation length. For the same series but with an electron-donating
moiety (push-pull type dyes), the absorption and fluorescence
maxima are less dependent on the conjugation length. The
fluorescence quantum yields of the push-pull type dyes are
large in toluene (>0.3) but extremely low in DMSO. These
results will be a guide for the design of naphthalimide-based
sensors and probes.
Keywords: Fluorescent dye
j
Naphthalimide
j
π-Conjugation
1. Introduction
Fluorescent dyes represent an important class of compounds
for applications to fluorescent sensors and probes. Fluorescent
dyes based on 1,8-naphthalimide have been attracting partic-
ularly intense attention as manifested in a surge of reports
aiming at applications to DNA-binding agents,1,2 pH indica-
tors,3 sensors for various cationic and anionic species,3-5 and
emitters for organic light-emitting diodes.6,7 As the π-system of
naphthalimide is relatively small, it absorbs at ca. 340 nm in the
UV region,8 although substitution by an amino group at the 4-
position brings the absorption to ca. 420 nm. It is desirable to
bring the absorption further towards the red to allow visible
light excitation/detection and prepare a multiple color set of
dyes to allow simultaneous quantification of multiple analytes
1506 | Bull. Chem. Soc. Jpn. 2018, 91, 1506–1514 | doi:10.1246/bcsj.20180151
© 2018 The Chemical Society of Japan

the excitation optics was performed with a SID-844 calibrated
detector and spectral correction of the emission optics was
performed with a ESC-842 secondary standard light source
such that the intensity corresponds to the relative number of
photons per unit wavelength. Fluorescence lifetimes were ob-
tained using Hamamatsu Quantaurus-Tau C11367 instrument.
R1 = 2,5-di-t-butylphenyl
R2 = 2,6-di-isopropylphenyl
R3 = 2-pyridyl
S
S
R4 = 1-hexylheptyl
S
S
S
2.2 Computational Details.
Density functional theory
(DFT) calculations were performed on Gaussian09 (Revision
E.01)27 interfaced with GaussView 5.0 running on an iMac
computer. The combination of the BMK functional28 and the
6-31G* basis set was used throughout the study. The imide
Rn group (n = 1-4, see Chart 1) was replaced by a hydrogen
atom in computation. The polarizable continuum model29 as
the self-consistent reaction field model (SCRF) was used with
toluene and DMSO as solvents. First, geometry optimiza-
tion was performed for each molecule in each solvent model.
It was confirmed that reasonable conformations were obtained
by comparing conformations among different molecules (see
Table S1) and with the related molecules in the literature.30 The
transition energies and the oscillator strength were calculated
by the time-dependent density functional theory (TDDFT)
using the same functional and basis set for the optimized
structures.
2.3 Synthesis of Novel Compounds. Recycle GPC was
conducted, using CHCl3 as the eluent, on a Japan Analytical
Industry LC-9201 system equipped with Jaigel-2H and Jaigel-
1H columns in tandem, with exclusion limits of 5000 and 1000,
respectively. Chemicals for synthesis were used as received
unless otherwise noted. Silica gel TLC plates (60 F254) were
purchased from Merck. Silica gel for column chromatography
(Silica Gel 60 N, spherical, neutral, 40-50 ¯m) was purchased
from Kanto Chemical. The preparation of Ph-T1-NI was report-
ed previously.26 The novel fluorescent dyes were prepared
according to the synthetic route shown in Scheme 1. Com-
pounds 1,31 7a,32 5c33 were prepared according to the literature.
Compound 3: An argon-purged solution of K2CO3 (92 mg,
0.82 mmol) in a mixture of H2O (1.5 mL) and 1,4-dioxane
(2 mL) was added to a flask containing bromonaphthalimide
1 (179 mg, 0.410 mmol), bithiophene boronic acid pinacol ester
2 (179 mg, 0.612 mmol), and Pd(PPh3)4 (47 mg, 0.041 mmol)
and the mixture was refluxed under argon for 17 h. The solvent
was evaporated and the residue was chromatographed (SiO2,
CHCl3) and washed with hexane to afford an orange solid
(161 mg, 0.309 mmol, 76%). TLC (SiO2, CHCl3): Rf = 0.47.
1H NMR (CDCl3): ¤ (ppm) = 1.16 (12H, d, J = 6.9 Hz), 2.7-
2.8 (2H, m), 7.09 (1H, dd, J = 3.7, 1.4 Hz), 7.3-7.4 (6H, m),
7.45 (1H, t, J = 7.8 Hz), 7.84 (1H, dd, J = 8.4, 1.1 Hz), 7.90
(1H, d, J = 7.8 Hz), 8.68 (1H, d, J = 7.3 Hz), 8.73 (1H, dd,
J = 7.3, 1.4 Hz), 8.82 (1H, dd, J = 8.4, 1.1 Hz). APCI-HRMS
(CHCl3): m/z calcd for C32H28NO2S2 ([MH]+), 522.1556;
found, 522.1565.
S
S
O
N
O
O
N
O
O
N
R2
O
O
N
R2
O
R3,4
R1
Ph-T2-NI
Ph-T4-NI
Ph-NI
Ph-T1-NI
N
N
S
S
S
S
N
For tuning
S
S
S
S
S
π-Bridge
S
Electron
withdrawing
O
N
R2
O
O
N
R2
O
O
N
R2
O
PyPh-T2-NI PyPh-T4-NI EH2NPh-T4-NI
Chart 1. Naphthalimide-based fluorescent dyes with extend-
ed π-conjugation through oligothiophenes without (upper
series) and with (lower series) an electron-donating moiety.
thiophene units with and without an electron-donating group
(dialkylamino groups). Chart 1 displays the naphthalimide
derivatives which have been analyzed in the present study. The
compounds with two (T2 dyes: Ph-T2-NI and PyPh-T2-NI) and
four (T4 dyes: Ph-T4-NI, PyPh-T4-NI, and EH2NPh-T4-NI)
thiophene units in the chart have been prepared in this study,
while the data on the dyes without the thiophene unit (T0 dye:
Ph-NI (with R3 24 or R4 25) are taken from the literature and
those on the dye with one thiophene unit (T1 dye: Ph-T1-NI) are
reported previously by us.26
2. Experimental
2.1 Physical Measurements.
1H NMR spectra were
recorded on a ECX-400 spectrometer. Tetramethylsilane was
used as an internal standard for chemical shifts (¤ = 0). Atmos-
pheric pressure chemical ionization high-resolution mass spec-
tra (APCI-HRMS) were recorded using an Agilent G1969A
system for CHCl3 solutions. Elemental analysis was performed
by the Center for Creative Materials Research, College of
Science and Technology, Nihon University.
Absorption spectra were measured using a Shimadzu UV-
2400PC spectrometer. Fluorescence spectra were measured
using a JACSO FP-8600 spectrometer. Spectral correction of
Compound 4:
AcOH (170 ¯L, 2.97 mmol) and NBS
(= N-bromosuccinimide, 101 mg, 0.567 mmol) were added to a
CHCl3 solution (1.7 mL) of 3 (297 mg, 0.569 mmol) and the
mixture was stirred at 0 °C for 2 h. The solution was washed
with H2O (4 © 3 mL) and an aqueous NaCl solution, dried over
Na2SO4, and evaporated to afford yellow powder (332 mg,
1
0.553 mmol, 97%). TLC (SiO2, CHCl3): Rf = 0.47. H NMR
(CDCl3): ¤ (ppm) = 1.17 (12H, d, J = 6.9 Hz), 2.7-2.8 (2H,
Bull. Chem. Soc. Jpn. 2018, 91, 1506–1514 | doi:10.1246/bcsj.20180151
© 2018 The Chemical Society of Japan | 1507

S
S
Br
B
O
O
S
S
S
2
S
S
S
Pd(PPh3)4
K2CO3
H2O/dioxane
PhB(OH)2 (6a)
Pd(PPh3)4, K2CO3
H2O, dioxane
Br
NBS, AcOH, CHCl3
Pri
Pri
O
N
Ar
1
O
O
N
O
O
N
O
O
N
O
Ar =
Ar
76%
Ar
Ar
3
4
97%
Ph-T2-NI 80%
S
S
N
S
S
S
S
S
S
(BPin)2
4
N
N
1. n-BuLi, THF
2. Bu3SnCl
4
PdCl2(dppf)
Pd(PPh3)4,K2CO3
H2O, dioxane
Pd(PPh3)4, THF
AcOK, dioxane
S
S
7a
SnBu3
Br
BPin
6b 66%
O
N
O
O
N
O
8a
5b
Ar
Ph-T4-NI
43% (based on 7a)
Ar
PyPh-T2-NI 39%
N(2-EH)2
S
S
S
O
N(2-EH)2
N(2-EH)2
S
S
S
2
N(2-EH)2
1. n-BuLi, THF
2. Bu3SnCl
Pd(PPh3)4, K2CO3
H2O, dioxane
4
Pd(PPh3)4, THF
S
S
SnBu3
Br
O
N
5c
7c 49%
8c
Ar
2-EH = 2-ethylhexyl
EH2NPh-T4-NI
15% (based on 7c and 4)
N
Br
S
S
S
S
S
S
S
S
S
S
S
S
S
4
6b
Pd(PPh3)4, K2CO3
H2O, dioxane
NBS, AcOH
CHCl3
Pd(PPh3)4, K2CO3
H2O, dioxane
S
BPin
2
O
N
O
O
N
O
O
N
O
Ar
Ar
Ar
9
86%
10 94%
PyPh-T4-NI 50%
Scheme 1. Preparation of naphthalimide-based fluorescent dyes π-extended with thiophene units. The compounds in parentheses
were not isolated.
1508 | Bull. Chem. Soc. Jpn. 2018, 91, 1506–1514 | doi:10.1246/bcsj.20180151
© 2018 The Chemical Society of Japan

m), 7.04 (2H, s), 7.2-7.4 (4H, m), 7.48 (1H, t, J = 7.8 Hz), 7.84
(1H, dd, J = 7.3, 0.92 Hz), 7.88 (1H, d, J = 7.8 Hz), 8.68 (1H,
d, J = 7.3 Hz), 8.7-8.8 (2H, m). APCI-HRMS (CHCl3): m/z
calcd for C32H27BrNO2S2 ([MH]+), 600.0661 and 602.0641;
found, 600.0652 and 602.0638.
Ph-T4-NI: A 2.5 M hexane solution of n-BuLi (0.20 mL,
0.49 mmol) was added dropwise to a dry THF solution (5 mL)
of phenylbithiophene 7a (119 mg, 0.49 mmol) at ¹78 °C and
the mixture was stirred for 3 h. SnBu3Cl (0.15 mL, 0.54 mmol)
was added and the reaction mixture was stirred at room tem-
perature for 1 h. H2O (2 mL) was added to the reaction mixture
followed by extraction with CHCl3, which was dried over
Na2SO4 and evaporated. A solution of this crude tributylstannyl
derivative of phenylbithiophene (8a) (315 mg), which was
found unstable toward SiO2 and used without further purifi-
cation, and bromobithienylnaphthalimide 4 (320 mg, 0.533
mmol) and Pd(PPh3)4 (70 mg, 0.060 mmol) in dry THF (20 mL)
was refluxed under argon for 22 h. The precipitate formed was
collected and washed with CHCl3. A crystallization proce-
dure for the precipitate from CHCl3 and hexane afforded a
red powdery solid (159 mg, 0.209 mmol, 43%). TLC (SiO2,
Ph-T2-NI: An argon-purged solution of K2CO3 (56 mg,
0.50 mmol) in a mixture of H2O (750 ¯L) and 1,4-dioxane
(3 mL) was added to a flask containing bromobithienylnaph-
thalimide 4 (121 mg, 0.201 mmol), phenylboronic acid (38 mg,
0.41 mmol), and Pd(PPh3)4 (10 mg, 0.0087 mmol) and the mix-
ture was refluxed under argon overnight. The reaction mixture
was extracted with CHCl3, which was dried over Na2SO4 and
evaporated. The residue was chromatographed (SiO2, CHCl3/
hexane = 2:1) to collect an overlapped band containing a
byproduct. The collected material was crystallized from CHCl3
and 1-propanol to afford orange powder (98 mg, 0.16 mmol,
80%). TLC (SiO2, CHCl3): Rf = 0.62. 1H NMR (CDCl3):
¤ (ppm) = 1.17 (12H, d, J = 6.9 Hz), 2.7-2.8 (2H, m), 7.2-7.4
(7H, m), 7.40-7.45 (2H, m), 7.48 (1H, t, J = 7.8 Hz), 7.6-7.7
(2H, m), 7.85 (1H, dd, J = 8.7, 1.3 Hz), 7.91 (1H, d, J = 7.3
Hz), 8.69 (1H, d, J = 7.8 Hz), 8.73 (1H, dd, J = 7.1, 1.1 Hz),
8.82 (1H, dd, J = 8.7, 0.9 Hz). APCI-HRMS (CHCl3): m/z
calcd for C38H32NO2S2 ([MH]+), 598.1869; found, 598.1909.
Analysis: calcd for C38H31NO2S2, C 76.35, H 5.23, N 2.34%;
found, C 76.20, H 5.12, N, 2.22%.
1
CHCl3): Rf = 0.48. H NMR (CDCl3): ¤ (ppm) = 1.18 (12H,
d, J = 6.9 Hz), 2.7-2.8 (2H, m), 7.1-7.2 (4H, m), 7.23 (1H,
d, J = 3.7 Hz), 7.3-7.4 (6H, m), 7.41 (1H, dd, J = 7.8, 7.3
Hz), 7.49 (1H, t, J = 7.8 Hz), 7.63 (2H, dd, J = 8.3, 1.4 Hz),
7.86 (1H, dd, J = 8.3, 0.9 Hz), 7.91 (1H, d, J = 7.8 Hz), 8.69
(1H, d, J = 7.2 Hz), 8.74 (1H, dd, J = 7.2, 1.1 Hz), 8.81 (1H,
d, J = 8.3, 1.1 Hz). APCI-HRMS (CHCl3): m/z calcd for
C46H36NO2S4 ([MH]+), 762.1623; found, 762.1691.
Compound 7c: A solution of K2CO3 (340 mg, 2.46 mmol)
in a mixture of H2O (5 mL) and 1,4-dioxane (15 mL) was
added to a flask containing bithiopheneboronic acid pinacol
ester 2 (525 mg, 1.80 mmol) and p-bromoaniline derivative 5c
(501 mg, 1.80 mmol). After the solution was purged with N2,
Pd(Ph3P)4 (56 mg, 0.048 mmol) was added and the mixture was
refluxed under N2 for 16 h. The reaction mixture, after H2O
(15 mL) was added, was extracted with EtOAc, which was
dried over Na2SO4 and evaporated. The residue was chromato-
graphed (SiO2, hexane) to afford yellow powder (299 mg,
Compound 6b: An argon-purged 1,4-dioxane (30 mL) was
added to a flask containing bromophenylpyrrolidine 5b (722
mg, 3.19 mmol), (BPin)2 (= bis(pinacolato)diboron (1.21 g,
4.78 mmol), AcOK (939 mg, 9.56 mmol), and PdCl2(dppf)
(dppf = 1,1¤-bis(diphenylphosphino)ferrocene, 79 mg, 0.097
mmol) and the mixture was refluxed under argon for 14 h.
The reaction mixture was extracted with hexane, which was
dried over Na2SO4 and evaporated. The obtained residue
was chromatographed (SiO2, hexane/AcOEt = 17:3) to afford
black-red needles (575 mg, 2.10 mmol, 66%). TLC (SiO2,
1
0.620 mmol, 49%). TLC (SiO2, hexane):Rf = 0.21. H NMR
1
CHCl3): Rf = 0.60. H NMR (CDCl3): ¤ (ppm) = 1.32 (12H,
(CDCl3): ¤ (ppm) = 0.8-1.0 (12H, m), 1.1-1.4 (14H, m), 1.7-
1.9 (2H, m), 3.1-3.4 (4H, m), 6.9-7.1 (2H, m), 7.09 (1H, d,
J = 3.7 Hz), 7.14 (1H, d, J = 3.2 Hz), 7.16 (1H, d, J = 5.0 Hz),
7.43 (2H, d, J = 9.2 Hz). APCI-HRMS (CHCl3): m/z calcd for
C30H44NS2 ([MH]+), 482.2910; found, 482.3218.
s), 1.9-2.1 (4H, m), 3.2-3.4 (4H, m), 6.53 (2H, dd, J = 6.5,
1.8 Hz), 7.67 (2H, dd, J = 6.5, 1.8 Hz). APCI-MS (CHCl3):
m/z calcd for C16H25BNO2 ([MH]+), 274.1973; found,
274.2256.
PyPh-T2-NI: An argon-purged solution of K2CO3 (210 mg,
1.52 mmol) in a mixture of H2O (1 mL) and 1,4-dioxane (4 mL)
was added to a flask containing bromobithienylnaphthalimide 4
(232 mg, 0.386 mmol), boronic acid pinacol ester 6b (101 mg,
0.370 mmol), and Pd(PPh3)4 (18 mg, 0.015 mmol) and the mix-
ture was refluxed under argon for 16 h. The reaction mixture
was extracted with CHCl3, which was dried over Na2SO4 and
evaporated. The residue was chromatographed (SiO2, CHCl3/
hexane = 2:1) to collect an overlapped band containing a
byproduct. The collected material was precipitated from CHCl3
and hexane to afford red powder (969 mg, 0.15 mmol, 39%).
EH2NPh-T4-NI:
A hexane solution of n-BuLi (2.5 M,
0.25 mL, 0.62 mmol) was added dropwise to a solution of the
bithiophene derivative 7c (225 mg, 0.467 mmol) in dry THF
(8 mL) at ¹78 °C under N2 and the reaction mixture was stirred
for 1 h. SnBu3Cl (0.13 mL, 0.47 mmol) was added and the
reaction mixture was stirred at room temperature for a day. To
the reaction mixture containing tributylstannyl derivative 8c
was added bromobithienylnaphthalimide 4 (281 mg, 0.467
mmol) and Pd(PPh3)4 (56 mg, 0.048 mmol) and the mixture
was refluxed under N2 for 20 h. The reaction mixture was
extracted with CHCl3, which was dried over Na2SO4 and evap-
orated. The residue was chromatographed (SiO2, CHCl3) and
reprecipitated from CHCl3 and hexane to afford red powder
(71 mg, 0.071 mmol, 15% from 7c and 4). TLC (SiO2, CHCl3):
Rf = 0.53. 1H NMR (CDCl3): ¤ (ppm) = 0.8-1.0 (12H, m),
1.17 (12H, d, J = 6.8 Hz), 1.2-1.4 (16H, m), 1.7-1.9 (16H, m),
2.7-2.8 (2H, m), 3.1-3.4 (4H, m), 6.66 (2H, d, J = 8.7 Hz),
7.05 (1H, d, J = 3.7 Hz), 7.08 (1H, d, J = 3.7 Hz), 7.1-7.2 (3H,
m), 7.21 (1H, d, J = 3.7 Hz), 7.33 (4H, dd, J = 7.8, 3.7 Hz),
1
TLC (SiO2, CHCl3): Rf = 0.66. H NMR (CDCl3): ¤ (ppm) =
1.17 (12H, d, J = 6.9 Hz), 2.0-2.1 (4H, m), 2.7-2.8 (2H, m),
3.3-3.4 (4H, m), 6.59 (2H, d, J = 8.7 Hz), 7.11 (1H, t, J = 3.7
Hz), 7.24 (1H, d, J = 3.7 Hz), 7.3-7.4 (4H, m), 7.4-7.5 (3H,
m), 7.85 (1H, dd, J = 7.3, 1.4 Hz), 7.90 (1H, d, J = 7.8 Hz),
8.68 (1H, d, J = 7.8 Hz), 8.73 (1H, dd, J = 7.3, 0.9 Hz), 8.83
(1H, dd, J = 8.7, 1.4 Hz). APCI-HRMS (CHCl3): m/z calcd for
C42H39N2O2S2 ([MH]+), 667.2447; found, 667.2404.
Bull. Chem. Soc. Jpn. 2018, 91, 1506–1514 | doi:10.1246/bcsj.20180151
© 2018 The Chemical Society of Japan | 1509

7.4-7.5 (3H, m), 7.85 (1H, dd, J = 7.3, 0.9 Hz), 7.90 (1H, d,
J = 7.3 Hz), 8.68 (1H, d, J = 7.8 Hz), 8.73 (1H, dd, J = 7.3,
0.9 Hz), 8.80 (1H, dd, J = 8.5, 0.9 Hz). APCI-HRMS (CHCl3):
m/z calcd for C62H69N2O2S4 ([MH]+), 1001.4236; found,
1001.4121. Analysis: calcd for C62H68N2O2S4¢H2O, C 73.04,
H 6.92, N 2.75%; found, C 73.26, H 6.67, N, 2.78%.
m/z calcd for C50H43N2O2S4 ([MH]+), 831.2202; found,
831.2203.
3. Results and Discussion
The naphthalimide derivatives with two and four thiophene
units were prepared through Suzuki-Miyaura coupling and
Stille coupling reactions between the building blocks, i.e., the
naphthalimide part, the bithiophene unit, and the terminal
phenyl or aliphatic amine-substituted phenyl group as the key
steps, as shown in Scheme 1.
Compound 9: A solution of K2CO3 (259 mg, 1.88 mmol)
in a mixture of H2O (2 mL) and 1,4-dioxane (8 mL) was added
to a flask containing bithiophene boronic acid pinacol ester
2 (402 mg, 1.38 mmol) and bromobithienylnaphthalimide 4
(284 mg, 0.474 mmol). After the mixture was purged with N2,
Pd(PPh3)4 (47 mg, 0.041 mmol) was added and the mixture
was refluxed under N2 for 21 h. After H2O (15 mL) was added,
the reaction mixture was extracted with CHCl3, which was
dried over Na2SO4 and evaporated. The residue was chro-
matographed (SiO2, CHCl3) to afford red powder (259 mg,
The absorption spectra for the dyes which have an extended
π-system with thiophene units with or without an electron-
donating moiety are shown in Figure 1. The solvents used are
toluene as a representative of nonpolar solvents and DMSO as a
representative of polar solvents. Before discussing the absorp-
tion features, it is important that the observed spectra represent
the monomeric species in solution, since in general, it is known
that some dye compounds tend to aggregate and show spectra
distinct from those derived from monomeric species.34 We have
therefore investigated concentration dependence of the absorp-
tion spectra from 2 to 20 ¯M as shown in Figure S1. Some
dyes strictly follow the Lambert-Beer law, while other dyes
show slight deviations from linearity. However, the absorption
maximum values are nearly independent of the concentration in
any case and, therefore, we can safely assume that the values
for absorption maxima represent those of monomeric species.
On the other hand, the absorption coefficients for Ph-T4-NI
both in toluene and DMSO and PyPh-T4-NI in DMSO are
smaller than those of other compounds, as well as expectations
from calculated oscillator strengths (vide infra). For the latter,
while dissolving PyPh-T4-NI in DMSO in concentrations of 2-
20 ¯M gave apparently clear transparent solutions, some pre-
cipitates were observed upon allowing the solutions to stand
still. Therefore, it is likely that PyPh-T4-NI forms some aggre-
gates in DMSO, which is supported by the observation that
DMSO solutions of this compound do not follow the Lambert-
Beer law (Figure S1, d, right). EH2NPh-T4-NI, which belongs
to the same T4 dye but with different terminal N,N-dialkyl
moieties, is more soluble and exhibits a large absorption coeffi-
cient in DMSO as expected. In the meantime, we do not have
a clear explanation of the low absorption coefficients for Ph-
T4-NI both in toluene and DMSO; these solutions follow the
Lambert-Beer law (Figure S1, b).
A common feature to note in the range >300 nm is that
the dyes with one and two thiophene units exhibit two-peaked
absorption while dyes with four thiophene units exhibit a single
extremely broad absorption peak. To assign these absorption
peaks, DFT calculations were performed. The BMK func-
tional28 was used, because it is known that the most popular
B3LYP functional underestimates the charge transfer transition
energies35,36 and the BMK reasonably reproduced the transition
energies for T1 dyes.26 The solvent effects were incorporated
via the SCRF model. The substituents on the nitrogen of
naphthalimide is replaced by a hydrogen atom to simplify the
calculations, which may be justified because the imide nitrogen
has little electron density both in the HOMOs and LUMOs.
First, the structures were optimized and the results on the di-
hedral angles between neighboring aromatic rings are compiled
in Table S1. For the bond between the naphthalimide unit and
1
0.378 mmol, 86%). TLC (SiO2, CHCl3): Rf = 0.57. H NMR
(CDCl3): ¤ (ppm) = 1.17 (12H, d, J = 6.9 Hz), 2.7-2.8 (2H,
m), 7.05 (1H, dd, J = 1.8, 3.2 Hz), 7.1-7.2 (3H, m), 7.2-7.3
(3H, m), 7.3-7.4 (4H, m), 7.49 (1H, t, J = 7.8 Hz), 7.85 (1H,
dd, J = 7.3 Hz), 7.90 (1H, d, J = 7.8 Hz), 8.69 (1H, dd, J =
7.8 Hz), 8.74 (1H, d, J = 0.9, 7.1 Hz), 8.80 (1H, d, J = 0.9,
8.7 Hz). APCI-HRMS (CHCl3): m/z calcd for C40H32NO2S4
([MH]+), 686.1310; found, 686.1574.
Compound 10: AcOH (100 ¯L, 1.8 mmol) and NBS (26
mg, 0.15 mmol) were added to a solution of terthienylnaph-
thalimide 9 (100 mg, 0.146 mmol) in CHCl3 (10 mL) and the
mixture was stirred at 0 °C for 1 h. The reaction mixture was
washed with H2O (4 © 3 mL) and an aqueous NaCl solution,
dried over Na2SO4, and evaporated to afford red powder
(105 mg, 0.137 mmol, 94%). TLC (SiO2, CHCl3): Rf = 0.57.
1H NMR (CDCl3): ¤ (ppm) = 1.17 (12H, d, J = 6.4 Hz), 2.7-
2.8 (2H, m), 6.94 (1H, d, J = 3.7 Hz), 7.00 (1H, d, J = 3.7 Hz),
7.05 (1H, d, J = 4.1 Hz), 7.12 (1H, d, J = 3.7 Hz), 7.15 (1H, d,
J = 3.7 Hz), 7.22 (1H, d, J = 3.7 Hz), 7.3-7.4 (4H, m), 7.49
(1H, t, J = 7.8 Hz), 7.86 (1H, dd, J = 0.9, 7.3 Hz), 7.90 (1H, d,
J = 7.3 Hz), 8.69 (1H, d, J = 7.3 Hz), 8.74 (1H, dd, J = 0.9,
8.0 Hz), 8.78 (1H, dd, J = 0.9, 8.0 Hz). APCI-HRMS (CHCl3):
m/z calcd for C40H31BrNO2S4 ([MH]+), 764.0416 and
766.0395; found, 764.0537 and 766.0602.
PyPh-T4-NI: A solution of K2CO3 (42 mg, 0.30 mmol) in
a mixture of H2O (5 mL), 1,4-dioxane (20 mL), and toluene
(20 mL) was added to a flask containing boronic acid pinacol
ester 6b (54 mg, 0.20 mmol) and bromoterthienylnaphthalimide
10 (100 mg, 0.13 mmol). After the mixture was purged with N2,
Pd(PPh3)4 (10 mg, 0.087 mmol) was added and the mixture was
refluxed under N2 overnight. After H2O (15 mL) was added,
the reaction mixture was extracted with CHCl3, which was
dried over Na2SO4 and evaporated. The residue was chromato-
graphed (SiO2, CHCl3) and the collected fraction was repre-
cipitated from CHCl3 and hexane to afford red powder (55 mg,
1
0.066 mmol, 50%). TLC (SiO2, CHCl3): Rf = 0.40. H NMR
(CDCl3): ¤ (ppm) = 1.17 (12H, d, J = 6.9 Hz), 2.0-2.1 (4H,
m), 2.7-2.8 (2H, m), 3.3-3.4 (4H, m), 7.07 (2H, d, J = 3.7 Hz),
7.09 (1H, d, J = 3.7 Hz), 7.13 (1H, d, J = 1.4 Hz), 7.14 (1H, d,
J = 1.4 Hz), 7.22 (1H, d, J = 3.7 Hz), 7.34 (4H, d, J = 7.8 Hz),
7.4-7.6 (3H, m), 7.86 (1H, dd, J = 0.9, 8.2 Hz), 7.91 (1H, d,
J = 7.8 Hz), 8.69 (1H, d, J = 7.8 Hz), 8.74 (1H, dd, J = 0.9,
7.9 Hz), 8.81 (1H, dd, J = 0.9, 7.9 Hz). APCI-HRMS (CHCl3):
1510 | Bull. Chem. Soc. Jpn. 2018, 91, 1506–1514 | doi:10.1246/bcsj.20180151
© 2018 The Chemical Society of Japan

tion: 0.8°) which roughly agrees with those reported for 4-
thienylnaphthalimide moieties in other compounds.30 The
dihedral angles between one thiophene ring to the next are
smaller with an average of 9° (standard deviation: 5°) and the
average dihedral angle between the phenyl ring and the directly
connected thiophene ring is 23° (standard deviation: 3°). The
calculated frontier molecular orbitals (HOMO, LUMO, and
LUMO+1) are displayed in Table S2.
The TDDFT calculations were done for these optimized
structures employing the same functional and basis set. The
transition wavelengths and oscillator strengths are indicated
by the vertical bars in Figure 1 and main numerical values are
collected in Table S3. It is seen from comparison that the
calculations are in reasonable agreement with the experimental
absorption spectra with slight overestimation of the transition
energies for the T1 and T2 dyes and slight underestimation for
the T4 dyes. The calculations indicate that the lowest-energy
transition corresponds mostly to the HOMO to LUMO transi-
tion. For every dye, the HOMO is distributed over the terminal
phenyl group (including the amino nitrogen in the case of
donor-containing dyes) and the oligothiophene units, while the
LUMO is mainly distributed over the naphthalimide moiety.
Thus, the HOMO to LUMO transitions are associated with the
ππ* transition involving charge transfer over large distances.
The second lowest-energy absorption bands observed for Ph-
T2-NI and PyPh-T2-NI correspond to the HOMO to LUMO+1
transition. These absorption bands also correspond to a ππ*
transition with a charge transfer nature because the LUMO+1
is distributed over the thiophene units admixed with some
contribution from the naphthalimide moiety.
The fluorescence spectra are shown in Figure 2. Each of
the dyes (10 ¯M) was excited at its lowest-energy absorption
maxima and the relative number of photons per unit wave-
length as measured are plotted as a qualitative guide for the
trend in fluorescence intensity. The spectra for the dyes with an
electron-donating moiety in DMSO are not included because
the fluorescence is so weak that it was difficult to obtain
reliable spectra. Photos of these dye solutions under UV lamp
irradiations are shown in Figure S2. The fluorescence quantum
yields together with other spectroscopic and photophysical
data, including excited-state lifetimes (see Figure S3), radiative
rate constants, and nonradiative rate constants, are compiled in
Table 1. Some notable features are gleaned from these data on
the excited states. For one, in the case of Ph-T1-NI, the shortest
derivative among those without an electron-donating moiety,
the fluorescence intensity increases significantly on going from
toluene to DMSO. However, it is found that this property can-
not be generalized to the longer series of dyes; The fluores-
cence intensity of Ph-T2-NI does not show a significant change
and that of Ph-T4-NI even decreases on going from toluene to
DMSO. The major factor accounting for these behaviors is the
changes in the rates of nonradiative decay. Upon going from
toluene to DMSO, the nonradiative rate for Ph-T1-NI decreases
significantly, that for Ph-T2-NI decreases but by a less magni-
tude, and that for Ph-T4-NI increases.
Figure 1. Absorption spectra of naphthalimide dyes (10
¯M). The curves are experimental spectra (left axis) and
the bars are calculated oscillator strengths (right axis). The
calculations are based on TDDFT (BMK/6-31G* with
SCRF). (a) Dyes without an electron-donating moiety in
toluene. (b) Dyes with an electron-donating moiety in
toluene. (c) Dyes without an electron-donating moiety in
DMSO. (d) Dyes with and electron-donating moiety in
DMSO.
the thiophene unit, the calculations show that a conformation
in which the thiophene S atom is oriented away from the H5
of naphthalimide is more stable than a conformation in which
the thiophene S is oriented oppositely. The average dihedral
angle between the naphthalene ring and the directly connected
thiophene ring for these compounds is 41.5° (standard devia-
Another notable feature is that for those with an electron-
donating moiety, the fluorescence quantum yields are high in
toluene (0.29-0.56). However, these dyes exhibit very weak
fluorescence in DMSO. We have previously shown that the
Bull. Chem. Soc. Jpn. 2018, 91, 1506–1514 | doi:10.1246/bcsj.20180151
© 2018 The Chemical Society of Japan | 1511

of further introduction of an electron-donating moiety are
shown in Figure 3b.
The experimental absorption maxima for the series of dyes
without an electron-donating moiety are red-shifted on going
from the T0 through T2 dyes nearly as expected from calcu-
lations. The absorption maxima are further red-shifted on going
from the T2 to T4 dyes but the magnitude of the shift is less
than predicted from the calculations. As for the effects of the
introduction of an electron-donating moiety, it is reported that
the absorption maximum in toluene is shifted from 347 nm to
418 nm (Á¯ = 4900 cm¹1) upon going from Ph-NI to a donor-
ꢀ
containing counterpart in which a dimethylamino substituent is
introduced at the para position of the phenyl group (M2NPh-
NI).25 Introduction of an electron-donating moiety to the T2
ꢀ
dye results in red-shifted absorption by ca. 40 nm (Á¯ = ca.
2000 cm¹1) both in toluene and in DMSO, the effect of which
is much smaller than the corresponding modification to the T0
dye (i.e., Ph-NI). The effects of the introduction of an electron-
ꢀ
donating moiety to the T4 dye is further diminished to Á¯ =
650-890 cm¹1 Indeed, the absorption maximum is blue-shifted
on going from the donor-containing T2 to T4 dyes, while the
TDDFT calculations indicate monotonic red-shifts. As the
number of thiophene units are increased, the molecule has a
greater number of rotatable bonds, which would result in a
larger fraction of molecules taking diverse, twisted conforma-
tions, less π-conjugated and higher in energy, while the calcu-
lations presented here are based on the lowest-energy optimized
conformations. This is consistent with the significantly broad
absorption bands observed for the T4 dyes, which may manifest
diverse conformations present in the solutions.
For the series of dyes without an electron-donating moiety in
toluene, the fluorescence maxima for the T0 through T4 dyes are
red-shifted from 410 nm25 to 588 nm and the red-shifting trend
is still continuing. The same series of dyes behave differently in
DMSO. The longest fluorescence wavelength is reached by the
T2 dye (Ph-T2-NI) at 660 nm. The fluorescence peak wave-
lengths for the donor-containing T2 and T4 dyes in toluene are
ca. 650 nm irrespective of the differences in the conjugation
length.
Figure 2. Fluorescence spectra of naphthalimide dyes (10
¯M) in toluene and DMSO. Each sample solution was
excited at the lowest energy absorption peak. The vertical
scale is common to all panels. (a) Dyes without an
electron-donating moiety in toluene. (b) Dyes with an
electron-donating moiety in toluene. (c) Dyes without an
electron-donating moiety in DMSO.
4. Conclusion
nonradiative rate steeply increases as the orientation polar-
izability (¦f), which is a measure of solvent polarity, exceeds a
certain value (¦f ³ 0.2) in the case of the compound in which
a diphenylamino group is introduced at the para position of
the phenyl group of Ph-T1-NI (Ph2NPh-T1-NI).26 This might
account for the large difference in the fluorescence intensities
in toluene (¦f = 0.013) and those in DMSO (¦f = 0.263),
although the radiative and nonradiative rates in DMSO cannot
be determined due to the poor fluorescence.
We are most interested in how much the absorption and
fluorescence wavelengths are shifted upon extension of the π-
system and the introduction of an electron-donating moiety,
because these are practical and critical information for the
design of multicolored sensors and probes as described in the
introduction. The effects of the number of thiophene units on
the lowest-energy absorption and fluorescence peak positions
are summarized in a wavenumber scale for the series of dyes
without an electron-donating moiety in Figure 3a. The effects
The absorption maxima can range from 350 nm to 450 nm
on the basis of the naphthalimide-based molecular design, in
which the π-conjugated system is extended with the thiophene
units. Introduction of an electron-donating moiety does red-
shift the absorption maxima for the shorter members but the
effect decreases for the longer members, ending up with the
maximum wavelength of 475 nm (Py-Ph2-NI). The fluores-
cence maxima of the series without an electron-donating moi-
ety can be tuned over the 180 nm range from 410 nm25 to 590
nm in toluene and can be tuned over the 100 nm range from
560 nm (Ph-T1-NI) to 660 nm (Ph-T2-NI) in DMSO. For the
series with an electron-donating moiety, the fluorescence
maxima are about 650 nm in toluene both for T2 and T4 dyes.
These results will be a guide for the design of functional
sensors and probes which exhibit absorption and fluorescence
at desired wavelengths. Another new finding in this study
concerns the fluorescence intensities or quantum yields, which
are (i) for the dyes without an electron-donating moiety, the
1512 | Bull. Chem. Soc. Jpn. 2018, 91, 1506–1514 | doi:10.1246/bcsj.20180151
© 2018 The Chemical Society of Japan

Table 1. Photophysical characteristics of the naphthalimide-based fluorescence dyes with extended conjugation.a
¹4
ꢀ
-
/nm
¾ © 10
-
/nm
Á¯
¸
/ns
kr
/ns
knr
/ns
abs
flu
Compounds
Ph-T1-NIb
Solvents
ºflu
/M¹1 cm
/cm
¹1
¹1
¹1
¹1
Toluene
DMSO
Toluene
DMSO
398
405
425
435
1.53
1.68
1.63
1.62
493
557
543
660
588
498
538
506
647
4841
6738
5113
7837
5929
2855
4037
2862
6003
0.06(1)
0.43(5)
0.06(2)
0.14(5)
0.21(1)
2.62(5)
0.26(1)
0.88(1)
0.29(10)
0.16(1)
0.29(6)
0.16(6)
4.28(23)
0.22(1)
3.56(19)
0.97(6)
Ph-T2-NI
Ph-T4-NI
Toluene
436
442
0.48
0.43
0.33(6)
0.03(1)
0.89(1)
0.37(7)
0.76(7)
DMSO
0.80(1)
2.51(3)
0.04(2)
0.19(2)
1.22(2)
0.20(2)
PyPh-T2-NI
PyPh-T4-NI
EH2NPh-T4-NI
Toluene
DMSO
Toluene
DMSO
Toluene
DMSO
466
475
450
460
453
455
2.62
1.63
4.28
0.49(5)
<0.01
0.38(1)
c
c
c
c
c
®
648
®
6790
®
1.01(1)
®
0.37(1)
®
0.76(1)
c
c
c
c
c
c
c
®
®
650
®
6690
®
0.29(3)
®
0.92(18)
®
0.31(7)
®
0.78(16)
3.94
4.50
c
c
c
c
c
®
®
<0.01
®
®
®
a) All measurements were done in air. Absorption and fluorescence spectra were measured at 25 °C and lifetimes were measured at
room temperature. The values followed by a parenthesis are the averages of three measurements and the numbers in the parentheses are
68.3% confidence intervals. b) Data from the literature (T. Inari, M. Yamano, A. Hirano, K. Sugawa, J. Otsuki, J. Phys. Chem. A 2014,
118, 5178). c) Difficult to determine due to poor solubility and/or poor fluorescence.
solvent (polarity) effects are different depending on the number
of thiophene units and (ii) for the dyes with an electron-
donating moiety, the quantum yields in toluene is high (>0.3)
but those in DMSO are extremely low. The latter property may
find use in polarity sensitive fluorescent probes. We are now
working on functionalization of the π-extended fluorescence
dyes presented herein.
This work was supported by the Grant-in-aid “KAKENHI”
from the JSPS (15K05486) and the Strategic Research Foun-
dation at Private Universities, from the MEXT and Nihon
University.
Supporting Information
Supporting figures and tables and supporting data for novel
compounds. This material is available on http://dx.doi.org/
10.1246/bcsj.20180151.
References
1
2
G. Gellerman, Lett. Drug Des. Discov. 2016, 13, 47.
S. Banerjee, E. B. Veale, C. M. Phelan, S. A. Murphy,
G. M. Tocci, L. J. Gillespie, D. O. Frimannsson, J. M. Kelly, T.
Gunnlaugsson, Chem. Soc. Rev. 2013, 42, 1601.
3
D. C. Magri, A. D. Johnson, J. C. Spiteri, J. Fluoresc. 2017,
Figure 3. Dependence of lowest-energy absorption and
fluorescence maxima on the number of thiophene units.
Circles represent observed values and squares represent
calculated values. Closed and open markers are for dyes
without an electron-donating moiety and those with an
electron-donating moiety, respectively. Color codes are as
follows. Black: absorption in toluene; green: absorption in
DMSO; red: fluorescence in toluene; orange: fluorescence
in DMSO. Some markers are shifted horizontally to avoid
overlapping. (a) Data for dyes without an electron donating
moiety. (b) Comparison between the dyes with and without
an electron-donating moiety.
27, 551.
4
5
M. Saleem, M. Rafiq, M. Hanif, J. Fluoresc. 2017, 27, 31.
M. H. Lee, J. S. Kim, J. L. Sessler, Chem. Soc. Rev. 2015,
44, 4185.
6
W. Zeng, H.-Y. Lai, W.-K. Lee, M. Jiao, Y.-J. Shiu, C.
Zhong, S. Gong, T. Zhou, G. Xie, M. Sarma, K.-T. Wong, C.-C.
Wu, C. Yang, Adv. Mater. 2018, 30, 1704961.
7
W. Zhang, Y. Xu, M. Hanif, S. Zhang, J. Zhou, D. Hu, Z.
Xie, Y. Ma, J. Phys. Chem. C 2017, 121, 23218.
D. Jacquemin, E. A. Perpète, G. Scalmani, I. Ciofini, C.
Peltier, C. Adamo, Chem. Phys. 2010, 372, 61.
8
9
T. C. Barros, G. R. Molinari, P. Berci Filho, V. G. Toscano,
Bull. Chem. Soc. Jpn. 2018, 91, 1506–1514 | doi:10.1246/bcsj.20180151
© 2018 The Chemical Society of Japan | 1513

M. J. Politi, J. Photochem. Photobiol., A 1993, 76, 55.
10 A. Samanta, G. Saroja, J. Photochem. Photobiol., A 1994,
84, 19.
11 M. S. Alexiou, V. Tychopoulos, S. Ghorbanian, J. H. P.
Tyman, R. G. Brown, P. I. Brittain, J. Chem. Soc., Perkin Trans. 2
1990, 837.
12 E. C. Lim, J. Phys. Chem. A 1986, 90, 6770.
13 P. Kucheryavy, G. Li, S. Vyas, C. Hadad, K. D. Glusac,
J. Phys. Chem. A 2009, 113, 6453.
14 S. Dhar, S. S. Roy, D. K. Rana, S. Bhattacharya, S.
Bhattacharya, S. C. Bhattacharya, J. Phys. Chem. A 2011, 115,
2216.
15 S. L. Dmitruk, S. L. Druzhinin, R. A. Minakova, A. I.
Bedrik, B. M. Uzhinov, Russ. Chem. Bull. 1997, 46, 2027.
16 D. Yuan, R. G. Brown, J. Phys. Chem. A 1997, 101, 3461.
17 S. C. Rasmussen, S. J. Evenson, C. B. McCausland, Chem.
Commun. 2015, 51, 4528.
27 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B.
Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P.
Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida,
T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A.
Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd,
E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S.
Iyengar, J. Tomasi, M. Cossi, N. Rega, N. J. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R.
Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.
Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G.
Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S.
Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz,
J. Cioslowski, D. J. Fox, Gaussian 09, Gaussian, Inc., Wallingford
CT, 2013.
18 G. Barbarella, M. Melucci, G. Sotgiu, Adv. Mater. 2005, 17,
1581.
28 A. D. Boese, J. M. L. Martin, J. Chem. Phys. 2004, 121,
3405.
19 J. Zhengneng, L. Najun, W. Chuanfeng, J. Huajiang, L.
Jianmei, Z. Qizhong, Dyes Pigm. 2013, 96, 204.
20 T. Izumi, S. Kobashi, K. Takimiya, Y. Aso, T. Otsubo,
J. Am. Chem. Soc. 2003, 125, 5286.
21 K. Park, T.-W. Lee, M.-J. Yoon, J.-I. Choe, Bull. Korean
Chem. Soc. 2014, 35, 531.
22 S. Okur, U. Salzner, J. Phys. Chem. A 2008, 112, 11842.
23 T. Pino, H. Ding, F. Güthe, J. P. Maier, J. Chem. Phys.
2001, 114, 2208.
24 Y. Qu, L. Wang, J. Wu, Y. Rui, J. Cao, J. Xu, Dyes Pigm.
2018, 148, 99.
29 J. Tomasi, B. Mennucci, R. Cammi, Chem. Rev. 2005, 105,
2999.
30 J. Zhang, X. Zhang, H. Xiao, G. Li, Y. Liu, C. Li, H.
Huang, X. Chen, Z. Bo, ACS Appl. Mater. Interfaces 2016, 8,
5475.
31 T. Choppawa, M. Sukwattanasinitt, S. Sahasithiwat, V.
Ruangpornvisuti, P. Rashatasakhon, Dyes Pigm. 2014, 109, 175.
32 S. Hotta, T. Katagiri, J. Heterocycl. Chem. 2003, 40, 845.
33 W. E. Moerner, R. J. Tweig, D. W. Kline, M. He, US Patent
00099109, 2005.
34 P. Gopikrishna, N. Meher, P. K. Iyer, ACS Appl. Mater.
Interfaces 2018, 10, 12081.
35 I. A. Mikhailov, M. V. Bondar, K. D. Belfield, A. E.
Masunov, J. Phys. Chem. C 2009, 113, 20719.
25 R. Greiner, T. Schlücker, D. Zgela, H. Langhals, J. Mater.
Chem. C 2016, 4, 11244.
26 T. Inari, M. Yamano, A. Hirano, K. Sugawa, J. Otsuki,
J. Phys. Chem. A 2014, 118, 5178.
36 A. E. Masunov, Int. J. Quantum Chem. 2010, 110, 3095.
1514 | Bull. Chem. Soc. Jpn. 2018, 91, 1506–1514 | doi:10.1246/bcsj.20180151
© 2018 The Chemical Society of Japan