Conductive nanoscopic fibrous assemblies containing helical tetrathiafubalene stacks

Article abstract of DOI:10.1002/asia.200900044

Tetrathiafulvalenes (TTF) S-TTF and R-TTF having four chiral amide end groups self-organize into helical nanofibers in the presence of 2,3,5,6-tetrafluoro-7,7′,8,8′-tetracyanop-quinodimethane (F ₄TCNQ). The intermolecular hydrogen bonding among

Full text of DOI:10.1002/asia.200900044

FULL PAPERS
DOI: 10.1002/asia.200900044
Conductive Nanoscopic Fibrous Assemblies Containing Helical
Tetrathiafulvalene Stacks
Yoko Tatewaki,*[a] Tatsuya Hatanaka,[b] Ryo Tsunashima,[d] Takayoshi Nakamura,[c, d]
Mutsumi Kimura,*[a, b] and Hirofusa Shirai[a]
Abstract: Tetrathiafulvalenes (TTF)
S-TTF and R-TTF having four chiral
amide end groups self-organize into
helical nanofibers in the presence of
2,3,5,6-tetrafluoro-7,7’,8,8’-tetracyano-
p-quinodimethane (F4TCNQ). The in-
termolecular hydrogen bonding among
chiral amide end groups and the forma-
tion of charge-transfer complexes re-
sults in a long one-dimensional supra-
molecular stacking, and the chirality of
the end groups affects the molecular
orientation of TTF cores within the
S-TTF and F4TCNQ is determined to
be (7.0Æ3.0)ꢀ10À4 ScmÀ1 by point-
contact current-imaging (PCI) AFM
measurement. Nonwoven fabric com-
posed of helical nanofibers shows a
semiconducting temperature depend-
ence with an activation energy of
0.18 eV.
stacks. Electronic conductivity of
a
single helical nanoscopic fiber made of
Keywords: charge transfer · chir-
ality · helical structures · hydrogen
bonds · nanostructures
Introduction
coordination bonds, van der Waals interactions, p–p stacks,
and charge-transfer (CT) complex formations. In particular,
the assemblies of p-conjugated molecules have attracted
special interest because of their great potential for the direc-
tional transportation of electrons and energy along with
their molecular stacks.[2] Among the p-conjugated molecules,
tetrathiafulvalenes (TTFs) have been widely investigated as
molecular metals in crystalline and supramolecular states.[3]
One-dimensional assemblies of CT complexes composed of
oxidized TTFs and electron-acceptor molecules show highly
electronic conductivities.[4] Their conductivity strongly de-
pends on the magnitude of the intermolecular CT interac-
tions between the electron-donor and the electron-acceptor
molecules, and the length of one-dimensional stacks.[2,4] Pre-
cise control of intermolecular distance within one-dimen-
sional TTF stacks induces the creation of highly conductive
molecular materials.
Recently, the formation of supramolecular fibrous organi-
zations has been investigated as gelators.[5] Low-molecular-
weight molecular components assemble into fibrous molecu-
lar assemblies, and the gathering of these assemblies forms
three-dimensional-network structures. While various func-
tional segments have been introduced into the low-molecu-
lar-weight molecular components, there are few reports on
the fibrous assemblies consisting of a p-stacked columnar
structure of TTFs.[6] Shinkai and co-workers succeeded in
the formation of highly aligned self-assembled TTF fibers.[7]
Kato and co-workers reported the electronic conductivity of
Control of self-assembling processes enhances the properties
of molecular materials and devices built-up from functional
small molecules.[1] Many researchers have challenged the
design and construction of appropriate supramolecular ar-
chitectures for desired properties by controlling the intermo-
lecular noncovalent interactions involving hydrogen bonds,
[a] Dr. Y. Tatewaki, Prof. M. Kimura, Prof. H. Shirai
Collaborative Innovation Center for Nanotech FIBER
Shinshu University
Ueda 386-8567 (Japan)
Fax : (+81)268-21-5499
E-mail: ytatewa@shinshu-u.ac.jp
mkimura@shinshu-u.ac.jp
[b] T. Hatanaka, Prof. M. Kimura
Department of Functional Polymer Science
Faculty of Textile Science and Technology
Shinshu University, Ueda 386-8567 (Japan)
[c] Prof. T. Nakamura
Graduate School of Environmental Earth Science
Hokkaido University
Sapporo 060-0810 (Japan)
[d] Dr. R. Tsunashima, Prof. T. Nakamura
Research Institute for Electronic Science
Hokkaido University
Sapporo 060-0812 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.200900044.
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self-assembled fibers consisting of TTF-based low-molecu-
lar-weight gelators.[8] Very recently, Iyoda and co-workers
reported highly conductive self-assembled fibers from a
disk-like TTF hexamer.[9] These self-assembled fibers based
on the stacks of TTF molecules can apply to the construc-
tion of conductive nanowires.[10] However, no conductivities
of single self-assembled fibers were measured. We report
here the formation of long fibers of molecular diameter and
micrometer length containing TTF stacks. The combination
of intermolecular hydrogen bonding and charge-transfer
complex formation may lead to the formation of stable TTF
stacks. The electronic conductivities of self-assembled fibers
containing stable TTF stacks were measured by PCI-AFM.
formation). In contrast, the stoichiometric mixture of S-TTF
and the electron-acceptor F4TCNQ yielded a stiff dark-col-
ored gel. The solution color of S-TTF did not change by
mixing with 2,5-difluoro-7,7’,8,8’-tetracyanoquinodimethane
(F2TCNQ) and 7,7’,8,8’-tetracyanoquinodimethane (TCNQ),
suggesting that charge transfer from S-TTF to these TCNQ
derivatives did not occur (see Figure S2 in the Supporting
Information). The color change indicates the oxidation of
TTF molecules by the addition of F4TCNQ and the forma-
tion of a CT complex between S-TTF and F4TCNQ. The
morphology of aggregates changed from spheres to twisted
fibers as observed by TEM and AFM (Figure 1a and 1d).
Results and Discussion
Tetrathiafulvalenes bearing four (R)- and (S)-methylben-
ACHTUNGTRENNUNGzylamide end groups, R-TTF and S-TTF, were prepared by
following the reaction sequence given in Scheme 1.[11] The
Figure 1. a) and b) Transmission electron micrographs of assemblies
made of the stoichiometric mixtures of S-TTF with F4TCNQ, c) R-TTF
with F4TCNQ (bar=200 nm). d) AFM image of helical nanofibrous as-
semblies made of S-TTF and F4TCNQ.
The diameter of the fibrous assemblies was approximately
30–60 nm and the length of fibers was above 10 mm. The
mixture of S-TTF and F4TCNQ aggregated to form left-
handed helical assemblies with a 60 nm helical pitch as ana-
lyzed by TEM (Figure 1b). In contrast, R-TTF and F4TCNQ
formed opposite right-handed helical fibers as shown in Fig-
ure 1c. The details of the molecular information in the heli-
cal fibers has been analyzed by UV/Vis/NIR spectroscopy,
FTIR spectroscopy, cyclic voltammetry (CV), ESR, CD
spectra, and powdered XRD patterns.
Scheme 1.
The electronic spectra in the UV/Vis/NIR and IR region
for the gel of S-TTF and F4TCNQ were measured
(Figure 2). The gel exhibited a broad absorption band in the
IR region (2500–3500 cmÀ1), which is attributable to the
key starting material, 4,5-bis(2’-cyanoethylthio)-1,3-dithiole-
2-thione, was reacted with hexylbromide, possessing an (S)-
methylbenzylamide end group, in the presence of CsCO3 to
yield compound S-1, which was subsequently converted into
the 1,3-dithiol-2-one derivative S-2 by reaction with Hg-
ACHTUNGTRENNUNG(OAc)2. The conversion of S-2 into the target S-TTF was
achieved by the reaction in triethyl phosphite at 1108C,
which produced S-TTF as an air-stable orange powder. R-
TTF was synthesized by the same procedure as that for S-
TTF. All the compounds were fully characterized by
1
MALDI-TOF-mass spectra, and H and 13C NMR spectra.
When S-TTF was dissolved in hot toluene and then
cooled to room temperature, a loose gel was formed, indi-
cating the formation of aggregated S-TTF in solution. A
TEM image of the loose gel showed spherical objects having
100–200 nm diameters (see Figure S1 in the Supporting In-
Figure 2. a) UV/Vis/NIR of i) S-TTF and ii) mixture of S-TTF with
F4TCNQ. b) FTIR spectrum for toluene gel of i) S-TTF and ii) mixture of
S-TTF with F4TCNQ.
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Y. Tatewaki, M. Kimura et al.
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charge transfer between electron-donating TTFs and elec-
tron-accepting F4TCNQ.[12] The absorption band in the NIR
region was unambiguously assigned to the F4TCNQ anion
radicals. A cyclic voltammetric study was performed on S-
TTF in a dry, degassed acetonitrile solution (see Figure S3
in the Supporting Information). The homogeneous solution
of S-TTF displayed two reversible one-electron-oxidation
waves at E1/2 =+0.45 and +0.89 V versus SCE in the anodic
window, which indicated the formation of stable radical cat-
ions. These redox potentials almost coincided with those of
alkyl-substituted TTFs, which lack chiral amide groups.[13]
Because the redox potential for the oxidation of F4TCNQ
(+0.70 V vs SCE) was higher than the first oxidation poten-
tial of S-TTF, the TTF segment could be oxidized to the rad-
ical cation by the addition of F4TCNQ. The nCN band was
observed at 2193 cmÀ1 in the FTIR spectrum of the dried
gel. Because the nCN bands for neutral F4TCNQ and
F4TCNQÀ anion radicals have been observed at 2227 and
2193 cmÀ1, respectively, the observed electronic ground state
of the complex was close to a completely ionic state.[14] The
supramolecular gel of S-TTF and F4TCNQ in toluene exhib-
ited an ESR signal at room temperature, also indicating the
generation of radical species (see Figure S4 in the Support-
ing Information). The line width was around 0.44 mT, and
the g value was 2.0047. The g values for bis(ethylenedithio)-
tetrathiafulvalene (BEDT-TTF) cation and the F4TCNQ
anion radicals have been reported to be at 2.007 and 2.0025,
respectively.[15] The observed g value was the intermediate
between BEDT-TTF cation and F4TCNQ anion radicals, re-
vealing that the supramolecular gel consists of the charge-
transfer complex between the S-TTF cation and F4TCNQ
anion radicals. These results supported the formation of
charge-transfer complexes by the electron transfer from
TTF to F4TCNQ within the fibrous assemblies.
389 nm can be ascribed to helical dipole coupling between
oxidized TTF rings through the hydrogen-network forma-
tion of peripheral chiral amides.[17] In contrast, the gel of R-
TTF and F4TCNQ showed a mirror CD spectrum to that of
S-TTF and F4TCNQ, indicating the opposite molecular ar-
rangement of TTF rings within the stacks. XRD patterns of
the nanofiber composed of the TTF derivative-F4TCNQ
were characterized by three reflection peaks, 3.27, 1.56, and
0.99 nm, which were in the ratio of 1:1/2:1/3 (see Figure S5
in the Supporting Information). These diffraction patterns
indicate that the nanofiber of TTF–F4TCNQ consists of a la-
mellar structure. The observed spacing at 3.27 nm indicates
the width of one layer of the lamellar structure. Judging
from the molecular dimension of S-TTF, as estimated from
the computer-generated molecular model (Scheme 1), the
interlamellar distance observed in the XRD study is close to
the estimated length of S-TTF (3.3 nm). From these results,
we can conclude that the hierarchical molecular organiza-
tion of synthesized TTF molecules is a combination of the
formation of one-dimensional charge-transfer stacks and hy-
drogen bonding among chiral amide groups. Moreover, the
chirality affects the molecular orientation of TTFs within
the stacks.
Since the discovery of metallic properties in a tetracyano-
p-quinodimethane (TCNQ) complex of TTF over a relative-
ly wide temperature range, extensive work has been carried
out in the design of organic metals and superconductors of
CT complexes.[18] Precise control of the molecular arrange-
ment in CT complexes is essential for obtaining highly con-
ductive organic materials.[19] The electrical conductivity of
the supramolecular gel of S-TTF–F4TCNQ was measured by
using evaporated gold electrodes with a gap distance of
500 mm. The substrate was fully covered with the organic
film by drop-casting the diluted gel solution. The film thick-
ness and the covering ratio of the organic film on the elec-
trode were measured by SEM and AFM measurements. The
electrical conductivity of the organic film was 5.0ꢀ
10À4 ScmÀ1 at room temperature. Akutagawa et al. reported
the electronic conductivities of molecular nanowires com-
posed of the CT complex of a TTF-substituted macrocycle
and F4TCNQ.[20] The obtained value for the electrical con-
ductivity was almost the same as the reported value, sug-
gesting that the three-dimensional network structures of
nanofibers provide pathways for electron transportation.
The films showed a semiconducting behavior in the mea-
surement of the temperature dependence of the electrical
conductivity (sRT) value, and the activated energy (Ea) ob-
tained from the slope was found to be 0.18 eV (Figure 4a).
The electrical conductivity of each individual nanofiber
was measured by PCI-AFM. The PCI-AFM method devel-
oped by Kawai and co-workers is a useful technique for
measuring I–V characteristics in nanoscale materials.[21] This
method can simultaneously measure the nanostructure and
electrical properties of a material on the insulated substrate.
The electrical properties of single-wall carbon nanotubes
(SWNTs), DNA, and porphyrin assemblies adsorbed on
SWNTs have been successfully evaluated by the PCI-AFM
The FTIR spectrum of the gel composed of S-TTF and
F4TCNQ showed that the 1535 and 1639 cmÀ1 peaks are as-
signable to the amide groups, indicating that the hydrogen-
bonding network is formed among the chiral side chain.[16]
Thus, S-TTF can be assembled through two different nonco-
valent interactions: charge-transfer complex formation and
hydrogen bonding. The formation of the hydrogen network
among the chiral side chains may affect the molecular ar-
rangement of TTF stacks. Although the CD spectrum of the
loose gel of only S-TTF was almost silent, the gel of S-TTF
and F4TCNQ exhibited CD activities corresponding to every
absorption band (Figure 3). The Cotton effect centered at
Figure 3. UV/Vis and circular dichroism spectra of toluene gel of S-TTF
and F4TCNQ at room temperature.
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Conductive Nanoscopic Fibrous Assemblies
TTFs and F4TCNQ. The mechanistic pathway of the self-as-
sembly processes are postulated in Figure 5. The synthesized
TTFs assemble into one-dimensional stacks by the forma-
tion of CT complexes with F4TCNQ and intermolecular hy-
Figure 4. a) Temperature-dependence of electrical conductivity (sRT
)
value for the film made of S-TTF and F4TCNQ on the gold electrodes
having an electrode gap of 500 mm. b) I–V characteristics by PCI-AFM at
the point X in the topographic image as shown in the inset of Figure 4c.
c) Current image obtained by PCI-AFM of a nanofiber made of S-TTF
and F4TCNQ. The inset shows the topographic image of the same region
as the current image.
method.[22] We also applied this method to measure the elec-
trical conductivities of individual nanofibers composed of
CT complexes between an S-TTF derivative and F4TCNQ.
Topographic and current images of the cast film are shown
in Figure 4c, and the I–V curve at point X on the nanofiber
is shown in Figure 4b. The sample was covered with a gold
electrode on the left side to form an electrical contact with
the nanofibers. The length of the nanofibers was above
1.0 mm and their height was about 15–30 nm, as determined
by the topological image. The current image indicates the
spatially resolved current map at a bias voltage of 1.8 V. The
current image is uniform as is the topological image, and the
current image gradually becomes darker with increasing dis-
tance from the gold electrode. One-dimensional resistivity
can be estimated from the slope of the I–V curve, the dis-
tance between the gold electrode and the point contacting
the conductive AFM tip, and the cross-sectional area of the
nanofiber. The resistivity at the point on the single nanofib-
er was estimated to be (7.0Æ3.0)ꢀ10À4 ScmÀ1.
Figure 5. Schematic illustration of the formation of conductive nanoscop-
ic fibers of TTF having chiral side chains in the presence of F4TCNQ.
drogen bonding among the chiral amide end groups. The in-
termolecular hydrogen bonding surrounding the one-dimen-
sional stack affects the orientation of the TTFs. The organi-
zation of one-dimensional stacks forms long helical nanofib-
ers with approximately 30–60 nm diameters and above
10 mm length. Finally, the partial cross-linking of these heli-
cal nanofibers results in a physical gelation. Large network
structures of conductive nanofibers will open new possibili-
ties for the construction of soft electronic nanocircuits such
as neuronal networks.
Conclusions
In conclusion, we have demonstrated that the amphiphilic
TTFs having chiral side chains can form conductive helical
nanofibers in solvents through spontaneous self-assembly
processes. The hydrogen bonding of chiral side chains and
the CT complex formation have been shown to be the main
driving forces for the formation of long and flexible nanofib-
ers, which contain one-dimensional stacks made of oxidized
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Y. Tatewaki, M. Kimura et al.
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as an orange powder (128 mg, 57%). FTIR (ATR): n˜ =3306 (-NH-), 1533
(-NH-), 2930 (-CH2-), 2955 (-CH2-), 1495 (-C6H5), 1488 cmÀ1 (-C6H5);
1H NMR (400.13 MHz, CDCl3) d=7.31 (m, 20H, Ar-H), 6.10 (d, J=
8.00 Hz, 4H, N-H), 5.09 (m, 4H, -COCNHCHCH3-), 2.77 (t, J=6.60 Hz,
8H, -SCH2-), 2.15 (t, 8H, J=7.20 Hz -CH2CONH-), 1.62 (m, 18H,
-SCH2CH2-, -CONHCHCH3-), 1.46 ppm (m, 16H, -SCH2CH2CH2CH2-);
13C NMR (100.61 MHz, CDCl3) d=21.85, 25.22, 28.07, 29.19, 29.47, 36.51,
48.65, 126.20, 127.29, 127.75, 128.64, 143.44, 171.87 ppm; MS (MALDI-
TOF): m/z (%) calcd for C52H90O4: 1201.85 [M+H]+; found: 1201.
Experimental Section
General
NMR spectra were recorded on a Bruker AVANCE 400 FT NMR spec-
trometer at 399.65 MHz and 100.62 MHz for 1H and 13C in CDCl3 solu-
tion. Chemical shifts are reported relative to internal TMS. Supramolec-
ular assemblies were transferred onto quarts substrates for UV/Vis/NIR,
FTIR, and CD measurements. FTIR spectra were obtained on a Shimad-
zu IR Prestige-21 spectrophotometer with DuraSample IR II. UV/Vis
spectra were measured on a Jasco V-650 and UV/Vis/NIR spectrum was
measured on a Hitachi U-4100 spectrophotometer. CD spectra were
measured on a Jasco J-720 spectrophotometer at room temperature.
MALDI-TOF mass spectra were obtained on a PerSeptive Biosystems
Voyager-De-Pro spectrometer with dithranol as matrix. TEM were ob-
served in a JEOL JEM-2010 electron microscope at an acceleration volt-
age of 200 KV without any staining. The specimens for TEM were pre-
pared by drop-casting of toluene solutions of 1 onto amorphous carbon-
coated copper grids (400 mesh). AFM images were obtained using a
JEOL 5400 scanning probe microscope operating under the dynamic
force mode. Redox potentials were obtained by using CV, and the experi-
mental was carried out in dry degassed acetonitrile solutions of
nBu4NBF4 (0.1m). The XRD patterns were recorded on a Rigaku Geiger-
flex diffractometer with CuKa radiation.
R-1 was synthesized according to the same procedure as S-1.
Preparation of Helical Nanofibers
Helical nanofibers of 1 and F4TCNQ were prepared by mixing a solution
of
1 (0.23 mm) in hot toluene (1 mL) with a solution of F4TCNQ
(11.4 mm) in acetonitrile (20 mL). The loose gels were created after cool-
ing. The color of the solution changed from orange to green by the for-
mation of loose gels.
Electrical Conductivity
Temperature-dependent electrical conductivities of a cast film composed
of 1 and F4TCNQ were measured by using a DC two-prove method.
Temperature-dependent DC conductivity and current–voltage (I–V) char-
acteristics were measured using a homemade cryostat with a temperature
control system over a range from 300 to 78 K. The current was monitored
with a Keithley 6517 electrometer, with a constant bias voltage ranging
from À100 to +100 V. Gold electrodes with 500 mm gap were formed by
vacuum evaporation on glass substrate, followed by deposition of the
films. Electrical contacts were constructed by using silver paste to attach
with the 25 mm-diameter gold wires.
Materials
All chemicals were purchased from commercial suppliers and used with-
out further purification. Column chromatography was performed with ac-
tivated alumina (Wako, 200 mesh) or Wakogel C-200. Recycling prepara-
tive gel permeation chromatography was carried out by a JAI recycling
preparative HPLC using CHCl3 as an eluent. Analytical thin-layer chro-
matography was performed with commercial Merck plates coated with
PCI-AFM Measurement
silica gel 60 F254 or aluminum oxide 60 F254
.
PCI-AFM measurements were carried out using a JSPM-5200 Environ-
mental Scanning Microscope (JEOL, JSPM-4200) equipped with two
function generators (NF, WF1946). Pt-coated conductive cantilevers with
a force constant and resonant frequency of 7.5 NmÀ1 and approximately
150 KHz, respectively, were used. Bias voltage (from À1.84 to +1.84 V)
was applied to the gold electrode on the substrate with cantilever to be
grounded. Both topographical and I–V data were obtained at 128ꢀ128
pixels. The measurements were carried out under nitrogen atmosphere at
room temperature.
S-1: A solution of CsOH·H2O (80 mg, 0.48 mmol) in methanol (0.6 mL)
was added to a solution of 4,5-bis(2’-cyanoethylthio)-1,3-dithiole-2-thione
(66 mg, 0.22 mmol) in acetonitrile (5.5 mL) over 10 min with stirring at
room temperature. After stirring for 30 min, hexylbromide having (S)-
methylbenzylamide end group[17a] (500 mg, 1.73 mmol) was added, and
the reaction mixture was stirred for 24 h. The reaction mixture was con-
centrated in vacuo, and water (50 mL) was added. The aqueous solution
was extracted with CH2Cl2 and the combined organic layer was washed
with water. After drying with NaSO4, the solvent was evaporated, and
the residue was purified by column chromatography (silica, CH2Cl2/
MeOH 98:2), to afford S-2 as an orange powder (0.15 g, 63%). FTIR
(ATR): n˜ =3304 (-NH-), 2972 (-CH2-), 1643 cmÀ1 (-C=O); 1H NMR
(400.13 MHz, CDCl3): d=7.29 (m, 10H, Ar-H), 5.11 (q, J=7.2 Hz, 2H,
Acknowledgements
NHACHTUNGTRENNUNG(CH3)CH-Ar), 2.85 (t, J=7.2 Hz, 4H, -SCH2CH2-), 2.16 (t, J=7.6 Hz,
This work was supported by a project for “Creation of Innovation Center
for Advanced Interdisciplinary Research Areas” in Special Coordination
Funds for Promoting Science and Technology from the Ministry of Edu-
cation, Culture, Sports, Science and Technology of Japan.
4H, -CH2CH2CO-), 1.68 (m, 6H, -CH CH3), 1.47 ppm (m, 12H, -CH2-);
13C NMR (100.61 MHz, CDCl3) d=21.81, 25.11, 28.09, 29.42, 36.49, 36.66,
48.77, 126.23, 127.39, 128.71, 143.44, 171.59, 207.9 ppm; MS (MALDI-
TOF): m/z (%) calcd for C31H40N2O2S5: 632.99 [M+H]+; found: 634.20.
S-2:
A mixture of S-1 (0.24 g, 0.38 mmol) and HgACHTNUGTNRUEGN(OAc)2 (0.62 g,
1.98 mmol) in the mixed solvent of CHCl3 (4.9 mL) and AcOH (2.5 mL)
was stirred under N2 at room temperature for 16 h. The resulting white
precipitate was filtered by celite and washed thoroughly with CHCl3. The
combined organic phases were refluxed with activated charcoal, cooled
to room temperature, and filtered. The filtrate was washed with NaHCO3
solution (4ꢀ200 mL), H2O (200 mL), and was dried over MgSO4. The or-
ganic layer was evaporated to dryness to afford S-2 as an orange powder
(230 mg, 99%). FTIR (ATR): n˜ =3304 (-NH-), 2972 (-CH2-), 1643 cmÀ1
(-C=O); MS (MALDI-TOF): m/z (%) calcd for C31H40N2O3S4: 616.92
[M+H]+; found: 617.5.
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triethyl phosphite (3 mL) under N2 was heated to reflux for 2.5 h at
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Conductive Nanoscopic Fibrous Assemblies
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Received: January 30, 2009
Published online: June 30, 2009
Chem. Asian J. 2009, 4, 1474 – 1479
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