5,5′-alkylsubsituted indigo for solution-processed optoelectronic devices

Article abstract of DOI:10.1016/j.tet.2016.05.069

A series of alkylated indigos were synthesized. Alkylated indigos were characterized by NMR, mass spectrometry, absorption spectra, cyclic voltammetry, and density functional theory (DFT) calculations. Propyl and butyl group substituted indigo was most soluble in chloroform and 1,2-dicrolobenzene, and these solubility were 65–89 times increased as compared to the parent indigo. DFT calculations suggested that the presence of the alkyl chains at the 5.5′-position increases the energy of the highest occupied molecular orbital, while reducing the energy of the lowest unoccupied molecular orbital. This theoretical finding was in good agreement with the experimental results. Crystal structures obtained by X-ray diffraction showed one-dimensional pi–pi stacking. Alkylated molecules were converted to leuco structure, and these structures were then converted to the corresponding indigos in the film state. After deposition of the films on TiO₂/FTO substrate, oxidative photocurrents were observed.

Full text of DOI:10.1016/j.tet.2016.05.069

Tetrahedron xxx (2016) 1e8
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
5,50-alkylsubsituted indigo for solution-processed optoelectronic
devices
,
b
a
,
,c
Motonori Watanabe a , Naoki Uemura , Shintaro Ida c, Hidehisa Hagiwara a
,
*
Kenta Goto d, Tatsumi Ishihara a
,b,c,
*
a International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
b Graduated School of Integrated Frontier Science, Department of Automotive Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395,
Japan
c Department of Applied Chemistry, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
d Institute for Materials Chemistry and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of alkylated indigos were synthesized. Alkylated indigos were characterized by NMR, mass
spectrometry, absorption spectra, cyclic voltammetry, and density functional theory (DFT) calculations.
Propyl and butyl group substituted indigo was most soluble in chloroform and 1,2-dicrolobenzene, and
these solubility were 65e89 times increased as compared to the parent indigo. DFT calculations sug-
gested that the presence of the alkyl chains at the 5.50-position increases the energy of the highest
occupied molecular orbital, while reducing the energy of the lowest unoccupied molecular orbital. This
theoretical finding was in good agreement with the experimental results. Crystal structures obtained by
X-ray diffraction showed one-dimensional piepi stacking. Alkylated molecules were converted to leuco
structure, and these structures were then converted to the corresponding indigos in the film state. After
deposition of the films on TiO2/FTO substrate, oxidative photocurrents were observed.
Received 14 April 2016
Received in revised form 27 May 2016
Accepted 27 May 2016
Available online xxx
Keywords:
Indigo
Substituent effect
Solution process
Precursor method
Photo current
Ó 2016 Published by Elsevier Ltd.
1. Introduction
indigos showed a herring-bone like structure for the halogen
substitution derivatives, whereas a brickwork arrangement of the
Indigo and its derivatives are some of the most popular dyes
used in pigments and artificial colorants. The crystal structure of
Indigo shows a two-dimensional packing orientation due to the
presence of intra- and intermolecular hydrogen bond interactions.1
The former interactions allow a planar structure of the indigo
crystal structure was observed in the case of phenyl-derivatives
because of
pep interactions arising from the functionalization
substitution at 5-position.14 The iodine derivatives showed good
ambipolar properties due to inter-molecular iodineeiodine in-
teractions leading to stronger pep interactions between the indigo
skeleton, giving rise to the
p
orbital delocalization on the indigo
skeletons.15 The group of Troshin reported a similar effect in the
indigos substituted by halogens at the 5,50- and/or 6,60-positions.16
These results indicate that in addition to changing the energy dif-
ference between the highest occupied and lowest unoccupied
molecular orbitals (HOMO and LUMO), the substituted functional
group also plays a key role in the charge transport crucial for op-
toelectronic properties of indigos. The use of an alkyl chain as
a substituent is a promising strategy for changing the crystal
packing. Furthermore, the presence of alkyl chains can increase the
solubility of low-solubility organic materials in organic solvents to
enable solution-processed fabrication for optoelectronic applica-
tions. This technique is widely applied to solution-processed op-
toelectronic devices using an organic materials such as
tetrathiafulvalene,17 oligothiophene,18,19 anthracene,20 thienoa-
cene,21 imide,22 and others.23 This approach can be used to increase
the solubility and change the charge transporting property for
skeleton. The latter interactions lead to the two-dimensional like
arrangement of the individual indigo molecules in the crystal
structure. Therefore, both intra- and intermolecular interactions
contribute to generating the herring-bone-like structure that in-
creases charge transfer, motivating considerable interest in indigos
as building blocks and charge-transporting materials.2e4 Recently,
indigos and functionalized indigos were applied for optoelectronic
devices, such as field effect transistors,5e7 solar cells,8,9 sensors,10,11
and electrodes for ion batteries.12,13 In particular, Pitayatanakul
et al., reported on the halogen or phenyl group functionalized in-
digos for organic semiconductors. In this series of compounds, the
* Corresponding authors. Tel./fax: þ81 92 802 6748; e-mail addresses: mwata@
i2cner.kyushu-u.ac.jp (M. Watanabe), ishihara@cstf.kyushu-u.ac.jp (T. Ishihara).
http://dx.doi.org/10.1016/j.tet.2016.05.069
0040-4020/Ó 2016 Published by Elsevier Ltd.
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2
M. Watanabe et al. / Tetrahedron xxx (2016) 1e8
indigo. Although Luttke et al. reported on several types of alkylated
5,50- and 6,60-position substituted indigos, a systematic study of
these dyes are necessary for understanding the relationships be-
tween the series of alkyl chain substitutions and the physical
properties of the compounds was not performed.24 Here we report
on the synthesis and physical properties of a series of 5,50-position
alkylated indigos. We also examine the photocurrent response of
films fabricated by solution processing from indigos and from
leuco-indigos for optoelectronic application (Fig. 1). Moreover, it is
found that a suitable chain size can be chosen to change the crystal
packing structure to a one-dimensional packing structure, and
good charge interaction orientation were demonstrated in the film
state. These effects can increase the photocurrent in the spin-
coated optoelectronic devices.
reaction25 in the presence of Mo(CO)6 to give the desired indigos
€
C1eC13.
2.2. Physical properties: absorption spectra, solubility, elec-
trochemical property, and DFT calculations
Absorption spectra of indigo (C0) and the alkylated indigos
(C1eC13) are shown in Fig. 2a. The parent C0 showed maximum
absorption at 600 nm. Relative to C0, the absorption peaks of
alkylated indigos C1eC13 were slightly red-shifted to approxi-
mately 615e617 nm and showed absorption intensities similar to
that of C0. Alkyl chains may improve the solubility and/or crystal-
linity in the solution state. To study the effect of the 5,50-positioned
alkyl chains on the solubility, the solubilities in DCB at 23 ꢀC of
C0eC13 were compared. The saturated amount of indigos at these
conditions was estimated using the calibration curve of the ab-
sorption spectra. Fig. 2b shows the solubility values obtained for
these dyes. The solubility of the parent indigo molecule was re-
ported as 0.038 mmol/L (ca. 10 mg/L) in chloroform.26 We found
that the solubility of C0 in chloroform at 23 ꢀC is 0.053 mmol/L, and
in DCB at 23 ꢀC is 0.012 mmol/L. In contrast, in the same conditions,
Fig. 1. Interconversion of indigo and leuco-indigo compounds.
alkylated
dyes
C1eC13
showed
solubilities
in
the
0.056e4.73 mmol/L range for chloroform, and in the
0.006e0.78 mmol/L range in DCB. As seen in Fig. 2a and Fig. S9, the
propyl (C3) and butyl chain (C4) substituted indigos showed par-
ticularly high solubility values. The hydrophobicity of alkyl chains
2. Results and discussion
2.1. Synthesis
assists the solvation of a series of p-conjugated organic molecules
in an organic solvent.23 Our work shows that the C1eC13 series of
compounds also displays this effect of alkyl chain hydrophobicity
on solvation.
Synthesis of the 5e50 position alkyl chain substituent indigo is
illustrated in Scheme 1. Wittig reaction of indole-5-
carboxyaldehyde 2 with Wittig salt 3ae3l gave the alkylene-
compounds 4ae4l, and double bonds were reduced by hydrogen
with the Pd/C catalyst to give 5-position alkylated indoles 5ae5l in
good yields. The 5ae5m were directly coupled using an oxidation
To understand the electronic properties of C1eC13, cyclic vol-
tammetry (CV) measurements were performed. Due to the low
solubility of all of the synthesized compounds except for C3 and C4
at 23 ꢀC, CV measurements for all compounds were conducted at
Scheme 1. Synthetic route to obtain alkylated indigos C1eC13.
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M. Watanabe et al. / Tetrahedron xxx (2016) 1e8
3
Fig. 2. Absorption spectra of synthesized alkylated indigos (left) and their solubilities
Fig. 4. HOMO and LUMO orbitals of indigos. Energy potentials (eV) are given in
parenthesis.
in 1,2-diclorobenzene at 23 ꢀC (right).
140 ꢀC in DCB solutions. Fig. 3 shows the cyclic voltammograms for
selected compounds. In these conditions, all compounds showed
quasi-stable reduction curves and unstable oxidation curves
(Fig. S1). The reduction potentials obtained for C1eC13 varied be-
tween ꢁ0.79 to ꢁ0.85 V (vs NHE) with these values similar to the
supporting the same energy gap values for C1eC13 and the lowest
energy peaks obtained by experimental results. Although there
were some differences between the DFT results and the experi-
mental results such as the saturation of the HOMOeLUMO energy
difference at a higher alkyl chain length, the overall trends found by
DFT calculations were in good agreement with the experimental
results. The absorption energy, cyclic voltammetry, and DFT results
are summarized in Table S1.
ꢁ0.80 V (vs NHE) value for C0. Based on the onset potentials (E0e0
)
of 1.96 eV for C0 and 1.88 eV for the C1eC13 obtained from the
absorption spectra and the negative shift of LUMO energies ob-
served in cyclic voltammetry, the oxidation potentials for C0 and
C1eC13 were estimated as þ1.15 V (vs NHE) and þ1.09 to þ1.03 V
(vs NHE), respectively. This suggests that the alkylation on the 5,50-
positions slightly reduces the electron accepting properties and
increases the electron donating abilities. The reduction of electron
affinity saturated for the octyl group in the C8 (Table S1).
2.3. X-ray crystallographic study
The crystal structure of the parent indigo compound was re-
ported by Krautscheid et al.1 The structure showed a
p
e
ꢀ
p
stacking
ꢀ
at the distance of 3.41 A along the b-axis with 2.168 A NeH/O
inter-molecular hydrogen bond interaction along the c-axis, dem-
onstrating the two dimensional array crystal packing.
As described below, the C7 alkylated indigo shows the highest
photoresponse in film form. When the solution of the C7 in 1,2-
dichlorobenze was slowly evaporated, platelet blue coloured crys-
tals were obtained. The C7 structure has all-trans conformation of
alkyl chains (Fig. 5a).
Fig. 3. Cyclic voltammogram of selected indigos in 1,2-diclorobenzene with 0.1 M
Tetrabutylammonium tetrafluoroborate solution at 140 ꢀC.
The physical properties of the compounds C0eC13 were further
verified by density functional theory (DFT, B3LYP/6-31Gd) calcu-
lations. Fig. 4 shows the HOMOs and LUMOs of selected com-
pounds. For all molecules, HOMOs and LUMOs were delocalized
over the indigo skeleton, suggesting that the absorption bands at
600 nm for parent indigo and at 615e617 nm for alkylated indigos
are of the
pep* transition type (Fig. S2). Examination of the ab-
sorption spectra and cyclic voltammetry results shows that HOMO
and/or LUMO energy levels are decreased by the introduction of
alkyl chains. Comparison of DFTcalculation results for the parent C0
and alkylated indigos C1eC13 shows that the presence of alkyl
chains at the 5.50-position decreases both the HOMO and LUMO
energies. Furthermore, cyclic voltammetry measurements for
alkylated indigos C1eC13 showed a gradual decrease of electron
affinities with increasing length of the alkyl chain that saturates at
C5. The DFT HOMOeLUMO energy gaps for C1eC13 were 2.45 eV,
Fig. 5. X-ray crystallographic analysis results for C7.
These extended alkyl chains allow one dimensional packing of
indigo moieties. The indigo skeleton was
tance of 3.358 A. Furthermore, intermolecular hydrogen bonding at
pep stacked at the dis-
ꢀ
NeH/O (2.361 A) was found along the b-axis and the alkyl chains
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M. Watanabe et al. / Tetrahedron xxx (2016) 1e8
were elongated on the c-axis. This one dimensional packing
structure is different from the 2D interactions found in the struc-
ture of the parent indigo compound. The one-dimensional stacking
moiety is dominated by the interdigitation of the alkyl chain with
the van der Waals interaction as the driving force (Fig. 5b).23 We
also successively analysed the single crystal of C8. This crystal
packing structure showed similar structure with the C7 (Fig. S3).
We expected that a photocurrent will be enhanced by the
strongly increased solubility due to the alkyl chain effect as found
for the C4 compound. We first tried to spin-coat these compounds
on a fluorine-doped tin oxide (FTO) substrate; however, the coating
did not remain on the film in our fabrication conditions. Therefore,
we used a TiO2 film-coated FTO substrate to increase the adhesion
of the film by taking advantage of the higher roughness of the TiO2
film. To remove the photoresponse due to the TiO2 film, we used
a band-pass filter to filter out irradiation at wavelengths smaller
than 495 nm. Fig. 7a shows the photocurrent profiles of the C4-
coated TiO2 films. The bare substrate (TiO2 film) did not show
a photocurrent response. Conversely, in the case of the spin-coated
C4 (saturated in CHCl3, 1200 rpm, 60 s), we observed the increase
of positive photocurrent. The spin-coated film of C4L (From 40 mM
LC4 in EtOH, 1200 rpm, 60s) showed a much stronger response
than C4.
2.4. Interconversion of indigos to corresponding leuco-
indigos: film state properties, and photocurrent
measurements
In addition to increasing the solubility in organic solvents, we
found that alkylation also affected the optoelectronic properties
because the hydrophobic interaction of alkyl chains between the
molecules will affect charge transport. Therefore, solution-
processed indigo-coated substrates were fabricated for the mea-
surement of the photoelectrochemical properties to elucidate the
effect of indigo alkylation in the solid state. To increase the indigo
solubility and enable the use of solution processing, we also in-
vestigated the corresponding leuco-indigos in a EtOH solution.
Fig. 6a showed the typical conversion results of C0 and C4 with
NaOH and Na2S2O4 in ethanol solution. When the indigo of ethanol
solution was added to NaOH and Na2S2O4 with heating in Ar at-
mosphere, the blue colour indigos disappeared, changing to a pale
yellow colour. In the absorption spectra, the characteristic indigos
peaks at around 600 nm disappeared for both leuco-C0 (LC0) and
leuco-C4 (LC4). Both solutions showed similar structures, sug-
gesting that alkylated indigos can also convert leuco structures.
These reaction solutions were drop-cast on a glass substrate under
Ar atmosphere with the obtained films shown in Fig. 6b. The films
showed no characteristic peaks and strong absorption intensities
due to the influence of sodium salts. Conversely, after exposure to
air with washing by water to remove the sodium salts, the sub-
strates showed characteristic new peaks at around 670 nm for
converted-C0 (C0L) and 613 nm for converted-C4 (C4L). This sug-
gested that the leuco-indigos were oxidised and converted to the
corresponding indigos under air (oxygen), indicating that alkylated
leuco-indigos could be converted to their corresponding indigos
under air in the film state. These peaks were shifted as compared to
the peak of the solutions.
Fig. 7. Photocurrent profiles of indigo dyes on TiO2 film/FTO substrate. (a) Chopped
profile of C4 coated TiO2 film on FTO. Inset: enlarged profiles at ꢁ0.25 to ꢁ0.1 V. C4 is
directly coated by C4 solution (saturated in CHCl3). C4L is coated by leuco-indigo
precursor LC4 and then converted to C4 by exposure to air. (b) and (c): Photocurrent
response of selected alkylated indigos from leuco-indigo precursors, and photocurrent
density dependence profiles of indigos between ꢁ0.28 and ꢁ0.27 V. (d) Spectral
sensitivity at 0 V (vs Ag/AgCl. 0.1 M Na2SO4, 50 mM TEOA aqueous solution (pH¼10)).
300-W Xe lamp was used. Red: C7L (from LC7 precursor) on TiO2 film/FTO substrate.
Blue: TiO2 film/FTO substrate. Black: Absorption spectra of C7L on TiO2 film/FTO
substrate.
The absorption bands of C4 and C4L on TiO2/FTO are shown in
Fig. S5. We found the similar absorption peaks of both film at ca.
615 nm, while absorption intensity of C4L was higher than C4,
suggesting that the leuco-based film showed much better adhesion
on the TiO2 film due to the higher solubility and increased com-
pound concentration in solution. However, the low solubility of C4
gives rise to poor results for the coating on the TiO2/FTO film, and
the obtained photocurrent response is therefore very weak.
We then systematically investigated the effect of alkyl chain
length on the photocurrent for the leuco-precursor compounds. We
found that the photocurrent magnitude increased when the carbon
number of the alkyl chain was increased up to 7 (C0L to C7L) and
then decreased for carbon numbers from 7 to 13 (C7L to C13L,
Fig. 7b, c and Fig. S6). The dependence of the photocurrent on the
irradiation wavelength was measured for the C7L-film that showed
the highest response (Fig. 7d). Although for wavelengths lower
Fig. 6. Absorption spectra (a) before treatment of indigos (C0 and C4) and after
treatment with NaOH and Na2S2O4 (LC0 and LC4) in EtOH. (b) spin-coated films on
glass substrates of leuco-indigos under Ar atmosphere (LC0 and LC4) and after expo-
sure to air (C0L and C4L).
When C0 and C4 of solution were drop cast to a glass substrate
directly, the peak of C0 and C4 were red shifted due to aggregate
structures were formed such as J-aggregation (Fig. S4). Comparing
the results of drop-casted indigo films and the films produced from
leuco-indigos, the film of C0L from LC0 on glass may has an ag-
gregation state such as J-aggregation, while C4L from LC4 has
amorphous-like or H-aggregation state because the film C4L of peak
was similar peak in that of solution state.
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M. Watanabe et al. / Tetrahedron xxx (2016) 1e8
5
than 500 nm, the observed spectral sensitivity included the com-
ponent due to the light response from TiO2 and FTO, the C7L-film
showed the spectral sensitivity corresponding to the original ab-
sorption spectra of C7L for wavelengths higher than 500 nm.
The differences in the photocurrent results were somewhat
different from the trends in the solubility of the corresponding
alkylated indigos. X-ray diffraction (XRD) patterns of the substrates
showed same peaks with similar intensities for anatase and FTO,
and no peaks corresponding to indigo structure were found (Fig. 8
and Fig. S7). This result indicates that all of indigo compounds are in
a poorly-crystalline or amorphous state. Therefore, the effect of
crystallinity for the difference of magnitudes of current density can
be neglected.
original peak on the glass substrate, the well-defined peak shape
suggested a more ordered orientation on the TiO2 film. Therefore,
the C7L-coated TiO2/FTO film showed a good photo current. Con-
versely, from C7L to C13L, the lowest energy peaks again became
broadened and blue-shifted to around 602 nm, indicating increased
disorder on the TiO2 film and leading to small photocurrent values.
The mechanism of the observed photocurrent measurement is
proposed in Fig. 10. The energy of the conduction bands (CB) of TiO2
is ꢁ0.5 eV (vs NHE), and the LUMO and HOMO energy levels of the
indigos were estimated to be approximately from ꢁ0.79 to ꢁ0.85 to
þ1.15 to þ1.03, respectively. The energy level of TEOA is þ0.80 eV.
Based on these energies, the injection of electrons to the CB of TiO2
from indigos in the excited state is the reasonable electron path-
way. Thus, oxidative photocurrent was observed during
photoirradiation.
Fig. 10. Schematic energy diagram and energy flow.
Fig. 8. XRD patterning of indigo-coated TiO2 film on FTO substrate. Bare: TiO2 film on
FTO.
3. Summary
A series of alkylated indigos were synthesized from 5-alkylated
indoles in the presence of Mo(CO)6. These compounds showed
similar physical properties in absorption spectra and cyclic vol-
tammetry measurements. The solubility in halogen organic sol-
vents such as 1,2-diclorobenzene was increased when the butyl
group was introduced on the 5,50-position, with further increases
obtained when longer alkyl chain were attached. X-ray diffraction
The absorption bands of indigo compounds on TiO2/FTO are
shown in Fig. 9 and Fig. S8. The peaks of the lowest energy bands in
the indigo absorption spectra first showed a red-shift from C0L to
C7L, followed by a blue-shift from C7L to C13L. For C0L on glass
substrate, the absorption peak was observed at 670 nm, the peak
for C0L on TiO2eFTO films was much broader and was blue-shifted
to around 582 nm, suggesting a disordered structure. Conversely,
the comparison of the peaks from C1L to C7L showed that the peaks
became more well-defined and showed an absorption band at
623 nm for C7L. Although this C7L peak is also blue shifted from the
showed that the C7 compound exhibits one dimensional
pep
stacking array along the a-axis. Alkylated molecules were con-
verted to leuco structures, and these structures were then con-
verted to their corresponding indigos in the film state. Upon
deposition on the TiO2/FTO substrate, the films showed oxidative
photocurrents. The alkyl chains were shown to affect the magni-
tude of ordering of orientation on the TiO2/FTO substrate. C7
showed the most ordered absorption spectra; therefore, the
strongest photocurrent was achieved for this compound. Studies of
other photoelectronic devices based on the molecules were ex-
plored in this work or the studies of their modified structures are
ongoing.
4. Experimental section
4.1. General information
1H and 13C NMR spectra were recorded on Bruker (ascend 400/
ascend 600 MHz) spectrometer in CDCl3. Chemical shifts are
Fig. 9. Absorption spectra of indigo-coated TiO2 films on FTO substrates.
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6
M. Watanabe et al. / Tetrahedron xxx (2016) 1e8
reported in
d
scale downfield from the peak for tetramethylsilane.
4.5. X-ray crystallographic study
Absorption spectra were recorded on a Shimadzu UV-3600 spec-
trophotometer and Hamamatsu photonics PMA-11. The redox po-
tentials were measured by using cyclic voltammetry on BAS
ALS1200B. All measurements were carried out in 1,2-
Single crystals of the C7 and C8 form suitable for X-ray analysis
were obtained by recrystallization from DCB. The X-ray data were
collected on a Rigaku Saturn724 diffractometer using multi-layer
ꢀ
diclorobenzene (DCB) solutions containing 0.1
M
tetrabuty-
mirror monochromatic Mo K
a
radiation (
l
¼0.71075 A). The struc-
lammonium hexafluorophosphate (TBAPF6) as supporting electro-
lyte at ambient condition after purging with Ar. The conventional
three electrode configuration was employed, which consists of
a glassy carbon working electrode, a platinum counter electrode,
and a Ag/Agþ reference electrode calibrated with ferrocene/ferro-
cenium (Fc/Fcþ) as an external reference. Mass spectra were
recorded on a JEOL JMS-700 MStation double focusing mass spec-
trometer. XRD pattern of C0eC13/TiO2/FTO substrates were mea-
sured with Rigaku SmartLab. Chromatographic separations were
carried out by using silica gel from Kanto Kieselgel si 60
tural determination was performed using the direct method tech-
nique with SIR 2011. All calculations were performed using the
CrystalStructure crystallographic software package except for re-
finement, which was performed using SHELXL2013. All-non-
hydrogen atoms were refined with anisotropically. Crystallo-
graphic data for the structural analyses of C7 and C8 have been
deposited to the Cambridge Crystallographic Data Centre (CCDC) as
1469332 and 1469331, respectively.
4.6. Theoretical computations
(40e63
mm). 5-methylindole (5m) was purchased from Sigma-
eAldrich, which was used without further purification.
Geometry optimization of C0eC13 were carried out by the DFT
method at the B3LYP/6-31G(d) level using Gaussian09 Rev. C.01
suite of programs. The frequency analyses were carried out for the
optimized structures to give no imaginary frequency.
4.2. Conversion of indigos to leuco-indigos
For spin-coated thin-film on TiO2/FTO substrate or glass sub-
strate, 0.04 mmol of indigo, 160 mg (4 mmol) of NaOH, 35 mg
(0.2 mmol) of Na2S2O4 was added in ethanol (1 mL) under Ar at-
mosphere, and it was heated 70 ꢀC until the suspended indigo was
solved and solution colour was turned from blue to pale yellow.
After conversion from leuco-indigos to indigos, it was used for
fabrication without further purifications. The conversion was con-
firmed by absorption spectra.
4.7. Synthesis of dyes
4.7.1. 5-Ethyl-1H-indole (5a). To a three-necked flask containing
a
mixture of methyltriphenylphosphonium bromide (2.58 g,
7.23 mmol) and THF was dropwise hexamethyldisilazane lithium
salt (7.23 mmol, 1.6 M in THF) at ꢁ10 ꢀC. After soluble of methyl-
triphenylphosphonium bromide, the mixture was dropwise indole-
5-carboxyaldehyde (700 mg, 4.83 mmol) in THF (10 mL) at ꢁ78 ꢀC
over 30 min. The reaction mixture was stirred at ꢁ78 ꢀC for addi-
tional 1 h, then allowed to stirring at room temperature overnight.
The mixture was quenched with satd NH4Cl (aq), then extracted
with ethyl acetate. The organic phase was combined and washed
with brine, and dried over anhydrous MgSO4. Evaporation of the
solvent gave a crude product, which was purified by silica gel
chromatograph by EA:hexane (1:5) as eluent. The pale yellow liquid
was isolated product of 5-vinyl-1H-indole 4a (459 mg), which was
used next reaction without further purification. The mixture of 4a,
ethanol (10 mL), and 10%Pd/C (46 mg, 10wt % of vinyl indole) was
bubbled 10 min with hydrogen gas, then the mixture was stirred at
room temperature under hydrogen atmosphere (760 Torr) for 12 h.
After reaction, Pd/C was removed by filtration through Celite, then
evaporated of solvent to dryness. The product was purified by silica
gel column chromatograph by EA:hexane (1:5) as eluent. Pale-
yellow oil of 5a was obtained in 35% yield (in two steps, 242 mg,
1.67 mmol). dH (400 MHz, CDCl3) 8.05 (br s, 1H), 7.46 (s, 1H), 7.31 (d,
1H, J¼8.3 Hz), 7.17 (t, 1H, J¼2.8 Hz), 7.06 (dd, 1H, J¼8.3, 1.4 Hz).
6.51e6.48 (m, 1H), 2.74, (dd, 2H, J¼15.2, 7.6 Hz), 1.28 (t, 3H,
J¼7.6 Hz), dC (100 MHz, CDCl3) 135.8, 134.2, 128.1, 124.2, 122.6, 119.1,
110.7, 102.3, 29.0, 16.5.
4.3. Fabrication of indigo-coated TiO2/FTO substrate
The FTO conducting glass (FTO glass, fluorine doped tin oxide
over-layer, transmission >90% in the visible, sheet resistance 7
squareꢁ1), titania-oxide pastes of Ti-Nanoxide T/SP was purchased
from Solaronix. A thin film of TiO2 (8 m) was coated on a FTO glass
U
m
substrate. The CHCl3 solution of indigos were spin-coated
(1200 rpm, 60s) on the TiO2/FTO substrate through membrane fil-
ter in grove box (MBRAUN MB150B-G, >1 ppm O2 and H2O). The
precursor methods, leuco-indigos that were also prepared in the
glove box, were fabricated as same manner with CHCl3 solution.
After spin-coated of leuco-indigo on substrates, there were exposed
on air (O2) to convert indigo and washed with DI water to remove
sodium salt. The active area was controlled at a dimension of
1.5 cm2.
4.4. Photocurrent measurement
Photocurrent was measured on BAS ALS1200B. All measure-
ments were carried out in DI-water solutions containing 0.1 M
Na2SO4 as supporting electrolyte and 50 mM triethanol amine for
electron donor. The aqueous solution showed 10 pH. Measure-
ments were accomplished at ambient condition. The conventional
three electrode configuration was employed, which consists of
indigo-coated TiO2 film/FTO substrate as working electrode,
a platinum mesh as counter electrode, and Ag/AgCl as reference
electrode.
The photo-current properties were obtained under a 300 W Xe
lamp (ASAHI SPECTRA, MAX-303), and passed through a long-pass
filter (Edmund optics, >495 nm cut off). The spectra sensitivity was
measured with band-pass filter (ASAHI SPECTRA) and further
calibrated using a reference Si-photo diode (Hamamatsu photonics
K. K., S1337-1010BQ).
Compound 5bel were synthesized according to the similar
procedure as that of 5a.
4.7.2. 5-Propyl-1H-indole (5b). Pale yellow oil. 65% yield. dH
(400 MHz, CDCl3) 8.06 (br s, 1H), 7.44 (s, 1H), 7.32 (d, 1H, J¼8.3 Hz),
7.17 (t, 1H, J¼2.8 Hz), 7.03 (dd, 1H, J¼8.3, 1.4 Hz). 6.49 (t, 1H,
J¼2.0 Hz), 2.67, (t, 2H, J¼7.4 Hz), 1.73e1.63 (m, 2H), 0.97 (t, 3H,
J¼3.4) dC (100 MHz, CDCl3) 134.3, 134.1, 128.0, 124.1, 123.1, 119.9,
110.6, 102.3, 38.2, 25.3, 13.9.
4.7.3. 5-Butyl-1H-indole (5c). Pale yellow oil. 69% yield. dH
(400 MHz, CDCl3) 8.06 (br s, 1H), 7.44 (s, 1H), 7.31 (d, 1H, J¼8.3 Hz),
7.17 (t, 1H, J¼2.8 Hz), 7.04 (dd, 1H, J¼8.3, 1.4 Hz). 6.49 (t, 1H,
J¼2.1 Hz), 2.70 (t, 2H, J¼7.6 Hz), 1.68e1.60 (m, 2H), 1.42e1.33 (m,
Please cite this article in press as: Watanabe, M.; et al., Tetrahedron (2016), http://dx.doi.org/10.1016/j.tet.2016.05.069

M. Watanabe et al. / Tetrahedron xxx (2016) 1e8
7
2H), 0.93 (t, 3H, J¼7.3) dC (100 MHz, CDCl3) 134.3, 134.2, 128.0,
0.88 (t, 3H, J¼6.5) dC (100 MHz, CDCl3) 134.4, 134.3, 128.1, 124.1,
123.1, 119.8, 110.6, 102.3, 36.1, 32.33, 32.3, 31.9, 29.7, 29.66, 29.62,
29.42, 29.4, 29.3, 22.3, 14.14, 14.1.
124.2, 123.1, 119.8, 110.6, 102.2, 35.7, 34.5, 22.4, 14.0.
4.7.4. 5-Pentyl-1H-indole (5d). Pale yellow oil. 66% yield. dH
(400 MHz, CDCl3) 8.06 (br s, 1H), 7.44 (s, 1H), 7.31 (d, 1H, J¼8.3 Hz),
7.18 (t, 1H, J¼2.8 Hz), 7.04 (dd, 1H, J¼8.3, 1.4 Hz). 6.49 (t, 1H,
J¼2.1 Hz), 2.69 (t, 2H, J¼7.6 Hz), 1.70e1.62 (m, 2H), 1.36e1.31 (m,
4H), 0.89 (t, 3H, J¼6.9) dC (100 MHz, CDCl3) 134.4,134.3,128.0,124.1,
123.1, 119.8, 110.6, 102.3, 36.0, 32.0, 31.6, 22.6, 14.1.
4.7.13. 5,50-Dimethyl indigo (C1). A mixture of 5-methylindole 5m
(165 mg,1.26 mmol), tBuOH (500 mg), Cumene hydroperoxide (80%
grade, 120 mg), acetic acid (2 mg), and Mo(CO)6 (0.2 mg) was
heated to reflux for 30 min. During reaction at reflux temperature,
the pale yellow reaction mixture of color was changed to red-green,
dark red, then precipitated blue solids. After cooling, the suspended
reaction mixture was filtered and successively washed with EtOH,
hexane, and CH2Cl2. Blue solid was obtained in 57% yield (103 mg,
4.7.5. 5-Hexyl-1H-indole (5e). Pale yellow oil. 65% yield. dH
(400 MHz, CDCl3) 8.04 (br s, 1H), 7.44 (s, 1H), 7.30 (d, 1H, J¼8.3 Hz),
7.17 (t, 1H, J¼2.8 Hz), 7.03 (dd, 1H, J¼8.3, 1.6 Hz). 6.49e6.47 (m, 1H),
2.69 (t, 2H, J¼7.8 Hz), 1.69e1.61 (m, 2H), 1.40e1.25 (m, 6H), 0.88 (t,
3H, J¼7.0) dC (100 MHz, CDCl3) 134.4, 134.3, 128.0, 124.2, 123.1,
119.8, 110.6, 102.3, 36.1, 32.3, 31.8, 29.1, 22.7, 14.1.
0.36 mmol), mp: >300 ꢀC. UV/Vis: lmax (1,2-DCB), 615 nm (log
,
3
4.23). dH (600 MHz, CDCl3) 8.80 (s, 2H, J¼8.4 Hz), 7.53 (s, 2H), 7.31
(d, 2H, J¼8.4 Hz), 6.94 (d, 2H, J¼8.6 Hz), 2.35 (s, 6H). HRMS (FAB,
[MþH]þ): calcd for C18H15N2O2: 291.1134, found 291.1169. IR
(KBr):
1633, 1620, 1587 cmꢁ1
n , n , n(C]O)
(NH) 3295 cmꢁ1 (CH) 3027, 2915, 2858 cmꢁ1
4.7.6. 5-Heptyl-1H-indole (5f). Pale yellow oil. 73% yield. dH
(600 MHz, CDCl3) 8.03 (br s, 1H), 7.43 (s, 1H), 7.29 (d, 1H, J¼8.3 Hz),
7.16 (t, 1H, J¼2.9 Hz), 7.03 (dd, 1H, J¼8.3, 1.4 Hz). 6.49e6.47 (m, 1H),
2.69, (t, 2H, J¼7.7 Hz), 1.69e1.61 (m, 2H), 1.39e1.22 (m, 8H), 0.88 (t,
3H, J¼6.8) dC (125 MHz, CDCl3) 134.4,134.3,128.1,124.3,123.1,119.8,
110.7, 102.2, 36.2, 32.4, 32.0, 29.5, 29.4, 22.8, 14.2.
.
Compound C2eC13 were synthesized according to the similar
procedure as that of C1.
4.7.14. 5,50-Diethyl indigo (C2). Blue solid. 48% yield. Mp: >300 ꢀC.
UV/Vis: lmax (1,2-DCB), 615 nm (log , 4.25). dH (400 MHz, CDCl3)
3
8.82 (s, 2H), 7.56 (s, 2H), 7.34 (d, 2H, J¼8.7 Hz), 6.97 (d, 2H,
4.7.7. 5-Octyl-1H-indole (5g). Pale yellow oil. 53% yield. dH
(400 MHz, CDCl3) 8.06 (br s, 1H), 7.43 (s, 1H), 7.30 (d, 1H, J¼8.3 Hz),
7.17 (t, 1H, J¼2.8 Hz), 7.03 (dd, 1H, J¼8.3, 1.5 Hz). 6.50e6.47 (m, 1H),
2.69, (t, 2H, J¼7.6 Hz), 1.69e1.60 (m, 2H), 1.40e1.21 (m, 10H), 0.88 (t,
3H, J¼7.0) dC (100 MHz, CDCl3) 134.4, 134.3, 128.1, 124.1, 123.1, 119.8,
110.6, 102.3, 36.1, 32.3, 31.9, 29.6, 29.4, 29.3, 22.7, 14.1.
J¼8.1 Hz), 2.65 (dd, 4H, J¼14.5, 7.5 Hz), 1.25 (t, 6H, J¼7.5 Hz). HRMS
(FAB, [M]þ): calcd for C20H18N2O2: 318.1368, found 318.1371. lit24
.
Mp: 373e374 ꢀC (chlorobenzene), UV/Vis: lmax 610e612 nm (KBr,
n.b.). IR (KBr):
n , n(CH) 3018, 2960, 2932,
(NH) 3306 cmꢁ1
2871 cmꢁ1 (C]O) 1634, 1620, 1588 cmꢁ1
,
n
.
4.7.15. 5,50-Dipropyl indigo (C3). Blue solid. 33% yield. Mp:
>300 ꢀC. UV/Vis: lmax (DCB), 615 nm (log
, 4.27). dH (400 MHz,
4.7.8. 5-Nonyl-1H-indole (5h). Pale yellow solid. 48% yield. Mp:
41e42 ꢀC. dH (400 MHz, CDCl3) 8.02 (br s, 1H), 7.43 (s, 1H), 7.29
(d, 1H, J¼8.3 Hz), 7.16 (t, 1H, J¼2.5 Hz), 7.03 (d, 1H, J¼8.3 Hz). 6.48
(s, 1H), 2.69, (t, 2H, J¼7.6 Hz), 1.69e1.60 (m, 2H), 1.40e1.20 (m,
12H), 0.87 (t, 3H, J¼7.9) dC (100 MHz, CDCl3) 134.41, 134.4, 128.1,
124.1, 123.1, 119.8, 110.6, 102.3, 36.1, 32.3, 31.9, 29.6, 29.4, 29.3,
22.7, 14.1.
3
CDCl3) 8.82 (s, 2H), 7.54 (s, 2H), 7.31 (dd, 2H, J¼8.2, 1.4 Hz), 6.96 (d,
2H, J¼8.2 Hz), 2.59 (t, 4H, J¼7.4 Hz), 1.71e1.58 (m, 4H), 0.94 (t, 6H,
J¼7.4 Hz). dC (100 MHz, CDCl3) 188.9, 150.4, 136.8, 135.4, 123.6,
121.9, 120.2, 111.9, 37.3, 24.6, 13.6. HRMS (FAB, [M]þ): calcd for
C
22H22N2O2: 346.1681, found 346.1682.
IR (KBr):
(NH) 3297 cmꢁ1
(C]O) 1632, 1618, 1588 cmꢁ1
n
, n ,
(CH) 3017, 2956, 2927, 2863 cmꢁ1
.
n
4.7.9. 5-Decyl-1H-indole (5i). Pale yellow solid. 89% yield. Mp:
298e299 ꢀC. dH (400 MHz, CDCl3) 8.03 (br s,1H), 7.43 (s,1H), 7.30 (d,
1H, J¼8.2 Hz), 7.16 (s, 1H), 7.03 (d,1H, J¼8.3 Hz). 6.48 (s, 1H), 2.70, (t,
2H, J¼7.6 Hz), 1.69e1.60 (m, 2H), 1.41e1.18 (m, 14H), 0.87 (t, 3H,
J¼6.2) dC (100 MHz, CDCl3) 134.42, 134.4, 128.1, 124.1, 123.1, 119.8,
110.6, 102.3, 36.1, 32.3, 31.9, 29.7, 29.6, 29.4, 29.3, 22.7, 14.1.
4.7.16. 5,50-Dibuthyl indigo (C4). Blue solid. 31% yield. Mp: >300 ꢀC
UV/Vis: lmax (DCB), 616 nm (log , 4.28). dH (400 MHz, CDCl3) 8.82 (s,
3
2H), 7.54 (s, 2H), 7.32 (dd, 2H, J¼6.8, 1.5 Hz), 6.96 (d, 2H, J¼8.2 Hz),
2.61 (t, 4H, J¼7.5 Hz), 1.67e1.55 (m, 4H), 1.40e1.31 (m, 4H), 0.93 (t,
6H, J¼7.3 Hz). dC (100 MHz, CDCl3) 188.9, 150.3, 136.7, 135.6, 123.6,
121.9, 120.2, 111.9, 34.9, 33.7, 22.1, 13.9. HRMS (FAB, [M]þ): calcd for
4.7.10. 5-Undecyl-1H-indole (5j). Pale yellow solid. 55% yield. Mp:
53e54 ꢀC. dH (400 MHz, CDCl3) 8.02 (br s, 1H), 7.43 (s, 1H), 7.29 (d,
1H, J¼8.3 Hz), 7.16 (t, 1H, J¼2.6 Hz), 7.03 (d, 1H, J¼8.3 Hz). 6.48 (s,
1H), 2.69, (t, 2H, J¼7.6 Hz), 1.69e1.60 (m, 2H), 1.41e1.18 (m, 16H),
0.87 (t, 3H, J¼6.4) dC (100 MHz, CDCl3) 134.4, 134.3, 128.1, 124.1,
123.1, 119.8, 110.6, 102.3, 36.1, 32.3, 31.9, 29.7, 29.63, 29.6, 29.4, 29.3,
22.7, 14.1.
C
24H26N2O2: 374.1194, found 374.1193. lit24. Mp: 322e324 ꢀC
(benzene), UV/Vis: lmax 615 nm (benzene, 4.32). IR (KBr):
3372 cmꢁ1 (CH) 2955, 2926, 2868, 2853 cmꢁ1
(C]O) 1630,
1588 cmꢁ1
n(NH)
,
n
, n
.
4.7.17. 5,50-Dipenthyl indigo (C5). Blue solid. 32% yield. Mp:
>300 ꢀC. UV/Vis: lmax (DCB), 617 nm (log
, 4.29). dH (400 MHz,
3
CDCl3) 8.82 (s, 2H), 7.54 (s, 2H), 7.32 (dd, 2H, J¼6.8, 1.5 Hz), 6.96 (d,
2H, J¼8 L.2 Hz), 2.60 (t, 4H, J¼7.6 Hz), 1.67e1.55 (m, 4H), 1.37e1.25
(m, 8H), 0.89 (t, 6H, J¼6.8 Hz). dC (100 MHz, CDCl3) 188.9, 150.3,
136.7, 135.7, 123.6, 121.9, 120.2, 111.9, 35.2, 31.3, 31.2, 22.5, 14.0.
4.7.11. 5-Dodecyl-1H-indole (5k). Pale yellow solid. 72% yield. Mp:
48e50 ꢀC. dH (400 MHz, CDCl3) 8.03 (br s, 1H), 7.43 (s, 1H), 7.29 (d,
1H, J¼8.3 Hz), 7.16 (t, 1H, J¼2.6 Hz), 7.03 (d, 1H, J¼8.3 Hz). 6.48 (s,
1H), 2.69, (t, 2H, J¼7.6 Hz), 1.69e1.60 (m, 2H), 1.41e1.17 (m, 18H),
0.88 (t, 3H, J¼6.4) dC (100 MHz, CDCl3) 134.4, 134.3, 128.1, 124.1,
123.1, 119.8, 110.6, 102.3, 36.1, 32.3, 31.9, 29.7, 29.63, 29.6, 29.4, 29.3,
22.7, 14.1.
HRMS (FAB, [M]þ): calcd for
402.2305. lit24. Mp: 314 ꢀC (benzene), UV/Vis: lmax 619 nm (CHCl3,
4.28) IR (KBr): (CH) 2956, 2924, 2864,
(NH) 3370 cmꢁ1
2854 cmꢁ1 (C]O) 1630, 1616, 1587 cmꢁ1
C26H30N2O2: 402.2307, found
n
, n
,
n
.
4.7.12. 5-Tridecyl-1H-indole (5l). Pale yellow solid. 57% yield. Mp:
63e64 ꢀC. dH (400 MHz, CDCl3) 8.03 (br s, 1H), 7.43 (s, 1H), 7.30 (d,
1H, J¼8.3 Hz), 7.17 (t, 1H, J¼2.5 Hz), 7.03 (d, 1H, J¼8.3 Hz). 6.49 (s,
1H), 2.69, (t, 2H, J¼7.6 Hz), 1.69e1.60 (m, 2H), 1.41e1.17 (m, 20H),
4.7.18. 5,50-Dihexyl indigo (C6). Blue solid. 42% yield. Mp: >300 ꢀC.
UV/Vis: lmax (DCB), 617 nm (log , 4.30). dH (400 MHz, CDCl3) dH
3
(400 MHz, CDCl3) 8.82 (s, 2H), 7.54 (s, 2H), 7.31 (d, 2H, J¼8.8 Hz),
6.96 (d, 2H, J¼8.6 Hz), 2.60 (t, 4H, J¼8.1 Hz), 1.67e1.55 (m, 4H),
Please cite this article in press as: Watanabe, M.; et al., Tetrahedron (2016), http://dx.doi.org/10.1016/j.tet.2016.05.069

8
M. Watanabe et al. / Tetrahedron xxx (2016) 1e8
1.36e1.25 (m, 12H), 0.88 (t, 6H, J¼6.5 Hz). HRMS (FAB, [M]þ):
calcd for C28H34N2O2: 430.2620, found 430.2602. IR (KBr): (NH)
3371 cmꢁ1 (CH) 2953, 2919, 2848 cmꢁ1
(C]O) 1638,
1584 cmꢁ1
C
n
42H62N2O2: 626.4811 found 626.4820. IR (KBr):
n ,
(NH) 3380 cmꢁ1
n
(CH) 2955, 2917, 2846 cmꢁ1 (C]O) 1629, 1612, 1585 cmꢁ1
,
n
.
,
n
, n
.
Acknowledgements
4.7.19. 5,50-Diheptyl indigo (C7). Blue solid. 41% yield. Mp: >300 ꢀC.
UV/Vis: lmax (DCB), 617 nm (log , 4.27). dH (400 MHz, CDCl3) dH
This work was supported by a Grant-in-Aid for Science Research
(YB 26810107) from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), Japan, and was performed under
the Cooperative Research Program of “Network Joint Research
Centre for Materials and Devices (IMCE, Kyushu University)”. MW
acknowledge support from I2CNER, funded by the World Premier
International Research Centre Initiative (WPI), Ministry of Educa-
tion, Culture, Sports, Science and Technology of Japan (MEXT), Ja-
pan. The computations were carried out by using the computer
facilities at the Research Institute for Information Technology,
Kyushu University.
3
(400 MHz, CDCl3) 8.82 (s, 2H), 7.54 (s, 2H), 7.31 (d, 2H, J¼8.0 Hz),
6.96 (d, 2H, J¼8.1 Hz), 2.60 (t, 4H, J¼7.9 Hz), 1.67e1.55 (m, 4H),
1.35e1.24 (m, 16H), 0.88 (t, 6H, J¼6.9 Hz). HRMS (FAB, [M]þ): calcd
for
3375 cmꢁ1
1584 cmꢁ1
C
30H38N2O2: 458.2933, found 458.2934. IR (KBr):
n
(NH)
,
n , n(C]O) 1628,
(CH) 2955, 2924, 2869, 2854 cmꢁ1
.
4.7.20. 5,50-Dioctyl indigo (C8). Blue solid. 42% yield. Mp: >300 ꢀC.
UV/Vis: lmax (DCB), 617 nm (log , 4.26). dH (400 MHz, CDCl3) dH
3
(400 MHz, CDCl3) 8.81 (s, 2H), 7.54 (s, 2H), 7.31 (d, 2H, J¼9.5 Hz),
6.96 (d, 2H, J¼8.2 Hz), 2.60 (t, 4H, J¼7.4 Hz), 1.67e1.55 (m, 4H),
1.35e1.24 (m, 20H), 0.88 (t, 6H, J¼6.4 Hz). HRMS (FAB, [M]þ): calcd
for C32H42N2O2: 486.3246, found 486.3244. lit24. Mp: 284e285 ꢀC
Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2016.05.069.
(benzene), UV/Vis: lmax 605 nm (KBr, n.b.) IR (KBr):
3375 cmꢁ1 (CH) 2954, 2924, 2850 cmꢁ1
(C]O) 1630, 1614,
1586 cmꢁ1
n(NH)
,
n
, n
.
References and notes
4.7.21. 5,50-Dinonyl indigo (C9). Blue solid. 37% yield. Mp:
298e299 ꢀC. UV/Vis: lmax (DCB), 617 nm (log
, 4.26). dH (400 MHz,
€
€
€
1. Kettner, F.; Huter, L.; Schafer, J.; Roder, K.; Purgahn, U.; Krautscheid, H. Acta
Cryst. Sec. E 2011, 67, o2867.
3
CDCl3) dH (400 MHz, CDCl3) 8.81 (s, 2H), 7.54 (s, 2H), 7.31 (d, 2H,
J¼8.2 Hz), 6.96 (d, 2H, J¼9.3 Hz), 2.60 (t, 4H, J¼7.5 Hz),1.65e1.55 (m,
4H), 1.36e1.20 (m, 24H), 0.88 (t, 6H, J¼6.6 Hz). HRMS (FAB, [M]þ):
2. Kojima, H.; Mori, T. Chem. Lett. 2013, 42, 68.
ꢁ
3. Moreno, M.; Ortiz-Sanchez, J. M.; Gelabert, R.; Lluch, J. M. Phys. Chem. Chem.
Phys. 2013, 15, 20236.
4. Amat, A.; Rosi, F.; Miliani, C.; Sgamellotti, A.; Fantacci, S. J. Mol. Struct. 2011, 993,
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5. G1owacki, E. D.; Voss, G.; Sariciftci, N. S. Adv. Mater. 2013, 25, 6783.
6. G1owacki, E. D.; Voss, G.; Leonat, L.; Irimia-Vladu, M.; Bauer; Sariciftci, N. S. Isr. J.
Chem. 2012, 52, 1.
calcd for C34H46N2O2: 514.3599 found 514.3525. IR (KBr):
n
(NH)
3375 cmꢁ1
1585 cmꢁ1
,
n
(CH) 2956, 2924, 2852 cmꢁ1
,
n
(C]O) 1631, 1613,
.
7. Irimia-Vladu, M.; G1owacki, E. D.; Troshin, P. A.; Schwabegger, G.; Leonat, L.;
Susarova, D. K.; Krystal, O.; Ullah, M.; Kanbur, Y.; Bodea, M. A.; Razumov, V. F.;
Sitter, H.; Bauer; Sariciftci, N. S. Adv. Mater. 2012, 24, 375.
8. Joby, N. G.; Venkatachalam, P.; Krishnakumar, N. Int. J. Sci. Eng. Res. 2013, 4, 1317.
9. Abdullah, M. I.; Janjua, M. R. S. A.; Mahmood, A.; Ali, S.; Ali, M. Bull. Korean
Chem. Soc. 2013, 34, 2093.
10. Alexy, M.; Voss, G.; Heinze, J. Anal. Bioanal. Chem. 2005, 382, 1628.
11. Brunet, J.; Spinelle, L.; Ndiaye, A.; Dubois, M.; Monier, G.; Varenne, C.; Pauly, A.;
Lauron, B.; Guerin, K.; Hamwi, A. Thin Solid Films 2011, 520, 971.
12. Yao, M.; Araki, M.; Senoh, H.; Yamazaki, S.; Sakai, T.; Yasuda, K. Chem. Lett. 2010,
39, 950.
4.7.22. 5,50-Didecyl indigo (C10). Blue solid. 42% yield. Mp:
288e289 ꢀC. UV/Vis: lmax (DCB), 617 nm (log
, 4.27). dH (400 MHz,
3
CDCl3) 8.83 (s, 2H), 7.54 (s, 2H), 7.31 (d, 2H, J¼8.1 Hz), 6.96 (d, 2H,
J¼8.2 Hz), 2.60 (t, 4H, J¼7.3 Hz), 1.77e1.57 (m, 4H), 1.35e1.24 (m,
28H), 0.88 (t, 6H, J¼6.6 Hz). HRMS (FAB, [M]þ): calcd for
C
n
36H50N2O2: 542.3872 found 542.3871. IR (KBr): n ,
(NH) 3378 cmꢁ1
(CH) 2956, 2917, 2847 cmꢁ1 (C]O) 1631, 1613, 1587 cmꢁ1
, n .
13. Yao, M.; Kuratani, K.; Kojima, T.; Takeichi, N.; Senoh, H.; Kiyobayashi, T. Sci. Rep.
4.7.23. 5,50-Diundecyl indigo (C11). Blue solid. 39% yield. Mp:
285e286 ꢀC. UV/Vis: lmax (DCB), 617 nm (log
, 4.26). dH (400 MHz,
2014, 4, 3650.
3
14. Pitayatanakul, O.; Higashino, T.; Kadoya, T.; Tanaka, M.; Kojima, H.; Ashizawa,
M.; Kawamoto, T.; Matsumoto, H.; Ishikawa, K.; Mori, T. J. Mater. Chem. C 2014,
2, 9311.
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3, 8612.
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2014, 2, 7621.
17. Miskiewicz, P.; Mas-Torrent, M.; Jung, J.; Kotarba, S.; Glowacki, I.; Gomar-Nadal,
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2338.
CDCl3) 8.81 (s, 2H), 7.54 (s, 2H), 7.31 (d, 2H, J¼8.6 Hz), 6.96 (d, 2H,
J¼8.2 Hz), 2.60 (t, 4H, J¼7.4 Hz), 1.65e1.56 (m, 4H), 1.37e1.20 (m,
32H), 0.88 (t, 6H, J¼6.3 Hz). HRMS (FAB, [M]þ): calcd for
C
n
38H54N2O2: 570.4185 found 570.4187. IR (KBr): n ,
(NH) 3382 cmꢁ1
(CH) 2956, 2917, 2848 cmꢁ1 (C]O) 1630, 1612, 1585 cmꢁ1
, n .
4.7.24. 5,50-Didodecyl indigo (C12). Blue solid. 40% yield. UV/Vis:
lmax (DCB), 617 nm (log
, 4.27). Mp: 274e275 ꢀC dH (400 MHz,
3
CDCl3) 8.83 (s, 2H), 7.54 (s, 2H), 7.31 (d, 2H, J¼8.9, 2.2 Hz), 6.96 (d,
2H, J¼8.0 Hz), 2.60 (t, 4H, J¼7.8 Hz), 1.68e1.49 (m, 4H), 1.35e1.24
(m, 36H), 0.88 (t, 6H, J¼6.7 Hz). HRMS (FAB, [M]þ): calcd for
C
40H58N2O2: 598.4498 found 598.4499. IR (KBr):
n
(NH)
3380 cmꢁ1
1589 cmꢁ1
, n , n(C]O) 1630, 1614,
(CH) 2956, 2917, 2848 cmꢁ1
.
4.7.25. 5,50-Ditridecyl indigo (C13). Blue solid. 39% yield. Mp: 264,
265 ꢀC. UV/Vis: lmax (DCB), 617 nm (log
, 4.26). dH (600 MHz, CDCl3)
3
23. Lei, T.; Wang, J.-Y.; Pei, P. Chem. Mater. 2014, 26, 594.
8.83 (s, 2H), 7.56 (s, 2H), 7.34 (d, 2H, J¼9.5 Hz), 6.98 (d, 2H,
J¼8.2 Hz), 2.62 (t, 4H, J¼8.0 Hz), 1.67e1.57 (m, 4H), 1.38e1.22 (m,
40H), 0.90 (t, 6H, J¼6.8 Hz). HRMS (FAB, [M]þ): calcd for
€
24. Meier, H.; Lutte, W. Liebigs Ann. Chem. 1981, 1303.
25. Yamamoto, Y.; Inoue, Y.; Takaki, U.; Suzuki, H. Bull. Chem. Soc. Jpn. 2011, 84, 82.
ꢁ
ꢁ
26. Buscio, V.; Crespi, M.; Gutierrez-Bouzan, C. Materials 2014, 7, 6184.
Please cite this article in press as: Watanabe, M.; et al., Tetrahedron (2016), http://dx.doi.org/10.1016/j.tet.2016.05.069