Synthesis, optical properties and charge transport characteristics of a series of novel thiophene-fused phenazine derivatives

Article abstract of DOI:10.1039/c3tc30346b

A series of tetrathienophenazine derivatives (t-TTP, l-TTP, m-TTP and their alkyl-substituted derivatives) have been synthesized via a simple condensation reaction between diketones and diamines. The redox potentials, UV-vis absorption spectra and fluorescence spectra of these derivatives are significantly affected by the positions of the sulfur atoms and the alkyl groups. The observed electronic properties were well reproduced by theoretical calculations based on density functional theory. X-ray analyses of these derivatives reveal extensive π-π interactions and short S...S contacts. The alkyl-substituted derivatives afford highly crystalline thin films by vapor deposition, and show reasonable field effect transistor performance. The conductivity of doped single crystals of these materials was also investigated, and showed an increase by several orders of magnitude upon I₂ vapor doping. The π-π stacked structures of these crystals and conductive properties indicate that these thiophene-fused phenazines are useful materials for application in organic electronics. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3tc30346b

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Materials Chemistry C
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Synthesis, optical properties and charge transport
characteristics of a series of novel thiophene-fused
Cite this: J. Mater. Chem. C, 2013, 1,
3467
phenazine derivatives†
Yongfa Xie,a Takuya Fujimoto,a Simon Dalgleish,a Yoshiaki Shuku,a
a
ab
*
*
Michio M. Matsushita and Kunio Awaga
A series of tetrathienophenazine derivatives (t-TTP, l-TTP, m-TTP and their alkyl-substituted derivatives)
have been synthesized via a simple condensation reaction between diketones and diamines. The redox
potentials, UV-vis absorption spectra and fluorescence spectra of these derivatives are significantly
affected by the positions of the sulfur atoms and the alkyl groups. The observed electronic properties
were well reproduced by theoretical calculations based on density functional theory. X-ray analyses of
these derivatives reveal extensive p–p interactions and short S/S contacts. The alkyl-substituted
derivatives afford highly crystalline thin films by vapor deposition, and show reasonable field effect
transistor performance. The conductivity of doped single crystals of these materials was also
investigated, and showed an increase by several orders of magnitude upon I2 vapor doping. The p–p
stacked structures of these crystals and conductive properties indicate that these thiophene-fused
phenazines are useful materials for application in organic electronics.
Received 22nd February 2013
Accepted 28th March 2013
DOI: 10.1039/c3tc30346b
www.rsc.org/MaterialsC
However, the preparation of such molecules usually involves
many steps, and utilizes toxic organometallic chemicals. In the
Introduction
Organic p-conjugated materials have attracted considerable
attention in recent years due to their potential application in
organic electronics such as organic light emitting diodes
(OLEDs),1 organic photovoltaics (OPVs)2 and organic eld
transistors (OFETs).3 Within this eld, thiophene-fused
polyaromatic compounds have received sustained interest
since the thienyl S/S contacts can contribute to the inter-
molecular charge transport in the solid state, as well as affect
the p–p stacking behavior. Some thiophene-fused poly-
aromatic compounds have shown high-performance in OFET
devices, with gures of merit rivaling that of amorphous
silicon. Diacene-fused thieno[3,2-b]-thiophenes (up to 12 cm2
Vꢀ1 sꢀ1 of eld-effect mobility),4 2,6-diaryl-NDTs (up to
0.1 cm2 Vꢀ1 sꢀ1 of eld-effect mobility)5 and 2,7-dialkyl[1]-
benzothieno[3,2-b][1]benzothiophenes (Cn-BTBTs) (up to
2.7 cm2 Vꢀ1 sꢀ1 of eld-effect mobility)6 are some represen-
tative examples.
present work, we have designed and synthesized a series of
thiophene-fused phenazines (t-TTP, l-TTP and m-TTP) and their
alkyl-substituted derivatives (Scheme 1). All of these derivatives
were obtained by a key reaction, a condensation reaction
between a diketone and a diamine, itself derived from the
diketone.7 Crystals of these derivatives were obtained by
recrystallization in solution or by sublimation, and all of the
derivatives afforded crystalline thin lms by vapor deposition.
The physical properties, crystal structures and transport prop-
erties of these molecules were compared with each other in
terms of the positions of sulfur atoms, and the effect of the
nitrogen atoms in the central aromatic ring is discussed in
comparison with the anthracene analogues reported by
Perepichka8 and Pei9 (Scheme 1).
aDepartment of Chemistry & Research Center for Materials Science, Nagoya University,
Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan. E-mail: mmmatsushita@nagoya-u.jp;
Awaga@mbox.chem.nagoya-u.ac.jp
bCREST, JST, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
† Electronic supplementary information (ESI) available: Cyclic voltammetry,
thin-lm XRD, and theoretical calculations. CCDC 924738 and 924748–924750.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3tc30346b
Scheme 1 Chemical structure of phenazine derivatives (X ¼ N) and anthracene
analogues (X ¼ CH).
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derivatives (t-TTP, l-TTP and m-TTP) showed poor solubility in
common organic solvents such as toluene, dichloromethane
and chloroform, while the solubility was much improved by
substituting the hexyl groups at the a-position of the fused
thiophene rings (t-HTTP, l-HTTP and m-HTTP).
Results
Synthesis
The synthetic route to the tetrathienophenazines (t-TTP, l-TTP,
m-TTP, t-HTTP, l-HTTP and m-HTTP) is outlined in Scheme 2.
The phenazine skeleton was formed by a condensation reaction
between a diketone and a diamine.10 For example, t-TTP was
obtained in 79% yield by reuxing the diketone 1a and the
diamine 4a in ethanol. Diamine 4a was prepared in 67% yield
from dioxime 3a by reduction with stannous chloride, and
dioxime 3a can be obtained from 1a by reaction with
hydroxylamine hydrochloride in nearly quantitative yield.
Diketones 1a and 2a were prepared in accordance with the
literature.11 Hexylated diketones 1b and 2b were synthesized
from hexyl thiophene, as shown in Scheme 3. The unsubstituted
Electrochemical properties
The electrochemical properties of these derivatives were char-
acterized by cyclic voltammetry (CV). The unsubstituted deriv-
atives did not show any redox peaks within the electrochemical
window
of
tetrabutylammonium
hexauorophosphate
((n-Bu4N)PF6) in dichloromethane (DCM) solution. On the other
hand, thin lms of these molecules deposited on an ITO elec-
trode showed gradually increasing redox waves upon cycling
Scheme 2 Synthesis of thiophene-fused phenazines. Reagents and conditions: (i) NH2OH$HCl, pyridine/EtOH, 90 ꢁC; (ii) SnCl2, HCl (con.), EtOH, 0 ꢁC to RT; (iii) EtOH,
reflux.
Scheme 3 Synthesis of diketone compounds.
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(Fig. S1†). This behavior resembles the redox properties of the
corresponding anthracene analogues, and can be explained by
the formation of small amounts of the radical cation species,
which is followed by the polymerization at the a-position.8
However, the alkyl-substituted derivatives showed reproducible
cyclic voltammograms with two oxidation peaks, although the
corresponding reduction peaks were not observed (Fig. 1). From
these redox potentials (1.06 V, 0.83 V and 1.21 V vs. Fc/Fc+ for
l-HTTP, m-HTTP and t-HTTP, respectively), the HOMO levels of
these molecules were estimated to be ꢀ6.2 eV, ꢀ5.9 eV and
ꢀ6.3 eV for l-HTTP, m-HTTP and t-HTTP, respectively.12 These
values indicate that these phenazine derivatives are weaker
donors in comparison with the corresponding tetrathienoan-
thracene analogue 8 (ꢀ5.9 eV and ꢀ6.0 eV for l-HTTA and
t-HTTA, respectively).
Optical properties
The UV-vis absorption spectra of the tetrathienophenazine
derivatives in CHCl3 are shown in Fig. 2, and their lmax are
summarized in Table 1. In all cases, two strong absorption
bands are observed; one absorption band lies around 310 nm
for all derivatives, while the other absorption band lies between
400 nm and 490 nm, depending on the structure. Introduction
of alkyl chains at the a-positions of the fused thiophenes results
in a bathochromic shi (3–20 nm) of the lmax values in
comparison with their unsubstituted derivatives (Fig. 2). The
lmax of the unsubstituted derivatives follows the progression
l-TTP > m-TTP > t-TTP, and this tendency of absorption bands
was also maintained in the corresponding alkyl-substituted
derivatives (Fig. 2). These features in the absorption spectra
were well reproduced by time-dependent Density Functional
Theory (TD-DFT) calculations, as discussed later.13
Fig. 2 Comparison of the UV-vis spectra of thiophene-fused phenazines in CHCl3
solution.
around 530 nm). Fig. 3 shows the uorescence spectra of these
derivatives, and the maximum emissions are listed in Table 1.
Introduction of the alkyl-chains also caused a red shi in the
uorescence peaks. The Stokes shi of each material is 0.46 eV,
0.25 eV and 0.07 eV for l-TTP, m-TTP, and t-TTP, respectively,
and a decrease in the Stokes shis was also observed in the
alkyl-substituted derivatives (Table 1). The uorescence abso-
lute quantum yields (Ff) of these materials were in the range of
0.02–0.19, as listed in Table 1.
The three unsubstituted derivatives (l-TTP, m-TTP and t-TTP)
showed light-blue uorescence (lmax: around 480 nm) in chlo-
roform while t-HTTP showed green uorescence (lmax: 501 nm),
and both m-HTTP and l-HTTP showed yellow uorescence (lm ax
:
X-ray crystallography
From the six newly prepared derivatives, four derivatives
(t-TTP, m-TTP, l-TTP and l-HTTP) could be crystallized by
solution or sublimation methods to afford single crystals
suitable for X-ray diffraction. The cell parameters of these
crystals are listed in Table 2. All of the unsubstituted deriva-
tives (t-TTP, m-TTP and l-TTP) have different space groups and
cell parameters depending on the different positions of sulfur
atoms in the skeleton. t-TTP (Fig. 4) showed nearly the same
cell parameter and packing structure as its corresponding
anthracene analogue (t-TTA), although the shortest S/S
˚
contacts and p–p intermolecular distances (3.664(1) A and
˚
˚
3.43 A) are different from those of t-TTA (3.769(1) A and
˚
3.354(3) A). l-TTP showed a different crystal structure from that
of the corresponding anthracene analogue (l-TTA).8 The l-TTP
crystal consists of two columns of slipped p-stacked (along the
Fig. 1 Cyclic voltammograms (scan rate 100 mV sꢀ1) of l-HTTP, t-HTTP and
m-HTTP recorded in DCM solution containing (n-Bu4N)PF6 (0.1 M) as an elec-
trolyte. A glassy carbon electrode and a Pt electrode were used as the working
electrode and the counter electrode, respectively. Potentials were referenced to
Fc/Fc+.
˚
b axis) molecules with a p–p intermolecular distance of 3.48 A
(Fig. 5). The l-HTTP crystal consists of slipped p-stacked
molecules along the a axis with a shorter p–p intermolecular
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Table 1 Electrochemicala and optical properties of thiophene-fused phenazines, compared to theoretical values
l-TTP
m-TTP
t-TTP
l-HTTP
m-HTTP
t-HTTP
l-TTA f
t-TTA f
Ee1x/2pa (V)
—
—
ꢀ5.60
ꢀ2.27
3.33
408
375
480
0.02
0.46
—
—
ꢀ5.64
ꢀ2.33
3.31
439
404
481
0.02
0.25
—
—
ꢀ5.68
ꢀ2.39
3.29
467
432
479
0.19
0.07
1.06
ꢀ6.21
ꢀ5.19
ꢀ2.04
3.15
411
379
526
0.15
0.66
0.83
ꢀ5.93
ꢀ5.21
ꢀ1.92
3.29
451
414
534
0.05
0.43
1.21
ꢀ6.33
ꢀ5.32
ꢀ2.11
3.21
486
444
501
0.18
0.07
—
—
exp
b
c
E
E
E
(eV)
(eV)
(eV)
ꢀ6.22
ꢀ5.18
—
3.52
379
—
398
0.17
0.16
ꢀ6.69
ꢀ5.23
—
3.50
418
—
422
0.32
0.03
HOMO
calcd
HOMO
calcd
c
LUMO
Ecgalcdc (eV)
lambasxd (nm)
lambasxd (nm)
lmaxd (nm)
Ffe
Stokes shid (eV)
a
Measured in DCM, (n-Bu4N)PF6 (0.1 M) as the supporting electrolyte and referenced to Fc/Fc+. b Estimated from the CV measurement according to
the empirical formula EHOMO ¼ ꢀ(1.4 ꢂ 0.1) ꢃ qVCV ꢀ (4.6 ꢂ 0.08) eV from ref. 12. c B3LYP/6-31G(d). d Measured in CHCl3. e Absolute uorescence
quantum yields were determined with a Hamamatsu C9920-02 calibrated integrating sphere system. f Cited from ref. 8.
Table 2 Crystal data and intermolecular contacts
t-TTP
l-TTP
m-TTP
l-HTTP
ꢀ
Space group
P21/n
P21/a
P21
P1
˚
a (A)
11.247(5)
5.014(2)
14.169(6)
—
91.668(7)
—
0.0618,
0.1027
3.664(1)
3.43
17.064(2)
3.894(4)
25.72(3)
—
108.820(2)
—
0.1284,
0.2638
3.686(2)
3.48
12.581(1)
4.8247(5)
13.718(1)
—
96.563(2)
—
0.0502,
0.1370
4.073(1)
3.46
4.894(1)
12.751(3)
17.057(5)
76.147(1)
84.810(1)
72.178(1)
0.0627,
0.0718
˚
b (A)
˚
c (A)
a (deg)
b (deg)
g (deg)
R, Rw
a
˚
S/S (A)
—
3.40
b
˚
d (A)
a
b
The shortest S/S0 contacts. d is the averaged inter-planar distance
between molecules along the p-stack.
SiO2 on the surface). X-ray diffraction analyses of the thin lms
yielded information on the molecular arrangements in the lms.
Thin-lm X-ray diffraction of l-HTTP grown under different
conditions shows sharply resolved peaks assignable to multiple
reections, indicating crystalline order in the direction of the
substrate normal (Fig. 8). Thin lms deposited on the untreated
and HMDS (hexamethyldisilazane) treated Si substrates at Tsub
¼
25 C consisted of two series of multiple (00l) and (00l0) reec-
tions, while thin lms deposited at Tsub ¼ 75 ꢁC showed only one
series of multiple (00l) reections. However, neither the (00l) nor
(00l0) peaks were assignable to the simulated powder pattern of
the single-crystal phase of l-HTTP. These results suggest that the
vapor-deposited thin lms of l-HTTP have distinct phases from
the single crystalline phase. The interlayer spacing (d), deter-
ꢁ
Fig. 3 Photoluminescence spectra of thiophene-fused phenazines in CHCl3
solution (lex 322 nm for t-TTP, 316 nm for m-TTP, 303 nm for l-TTP, 370 nm for
l-HTTP, 380 nm for t-HTTP, and 380 nm for m-HTTP).
˚
˚
distance (3.40 A) than that of l-TTP (3.48 A) (Fig. 6). The crystal
of m-TTP also showed a slipped p-stacking structure with a p–p
˚
mined from the rst-layer line of the XRD pattern, are 19.4 A and
˚
intermolecular distance of 3.46 A. Since the dipole moments of
0
˚
24.3 A for the (00l) and (00l ) reections, respectively. This result
suggests that the thin lm contains only one molecular arrange-
ment on the substrate when deposited at higher temperature. In
addition, the thin lms deposited at Tsub ¼ 75 ꢁC showed larger
grains (width: 0.25–0.5 mm and height: 10.0–30.0 nm), and tighter
packing on the substrates than thin lms deposited at room
molecular stacks do not completely compensate each other in
the crystal cell, m-TTP is a polar crystal (Fig. 7).
Preparation, characterization, and FET performance of thin-
lms
Thin lms of the alkyl-substituted tetrathienophenazine deriva- temperature (width: 0.5–1.5 mm and height: 20.0–40.0 nm) as
tives were prepared by vapor deposition on Si substrates (with observed from AFM images (Fig. 9).
3470 | J. Mater. Chem. C, 2013, 1, 3467–3481
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0
˚
Fig. 4 (a) Crystal structure of t-TTP. S/S contacts. (b) p/p distance between the molecules (unit: A).
0
˚
Fig. 5 (a) Crystal structure of l-TTP. (b) S/S contacts. The p/p distance between the molecules (unit: A).
˚
Fig. 6 Crystal structure of l-HTTP. (a) View along the a axis. (b) p/p distance between the molecules (unit: A).
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˚
Fig. 7 Crystal structure of m-TTP. (a) Dipole moment of the molecular stacks. (b) p/p distance between the molecules and direction of the dipole moment (unit: A).
Fig. 9 AFM images of thin films of l-HTTP on bare substrates with Tsub ¼ 25 ꢁ
C
(a), substrates treated with HMDS with Tsub ¼ 25 ꢁC (b), bare substrates with Tsub
¼ 75 ꢁC (c) and substrates treated with HMDS with Tsub ¼ 75 ꢁC (d).
mh ¼ 6.2 ꢃ 10ꢀ6 cm2 Vꢀ1 sꢀ1 and mh ¼ 3.2 ꢃ 10ꢀ6 cm2 Vꢀ1 sꢀ1 for
untreated and treated substrates (Tsub ¼ 75 ꢁC), respectively.
The on/off ratio and threshold voltage of the FET devices are
listed in Table 3. These results suggest that the mono-oriented
Fig. 8 Out-of-plane XRD pattern of l-HTTP thin films (50 nm) at different
substrate temperatures (no in-plane signal).
Organic eld-effect transistor (OFET) devices of these deriv- phase and bigger grains in the thin lms can improve the
atives were prepared on bottom-gate, bottom-contact substrates transistor performance, while the HMDS treatment on the SiO2
by vacuum deposition. The thin lms of l-HTTP deposited at surface does not yield an obvious effect on the l-HTTP thin lm
room temperature on surface-oxidized silicon substrates transistor characteristics.
showed FET characteristics. The eld-effect mobilities for this
Thin lms of m-HTTP and t-HTTP were also prepared by
compound were mh ¼ 1.2 ꢃ 10ꢀ8 cm2 Vꢀ1 sꢀ1 and mh ¼ 4.6 ꢃ vapor deposition at Tsub ¼ 75 C on the Si substrates without
10ꢀ9 cm2 Vꢀ1 sꢀ1 for untreated and HMDS treated substrates HDMS treatment. The thin lms of these materials also showed
(Table 3), respectively. These values were greatly improved by high crystallinity, characterized by thin-lm XRD (Fig. S2†).
increasing the substrate temperature during vapor deposition: These lms also showed FET characteristics with eld-effect
ꢁ
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Table 3 Thin film properties of thiophene-fused phenazines
a
˚
Surface treatment
HMDS
Tsub
d-Spacing/A
mh/cm2 Vꢀ1 sꢀ1
1.2 ꢃ 10ꢀ8
Ion/off
103
Vth/V
—
l-HTTP
l-HTTP
25 ꢁC
25 ꢁC
24.3
19.4
24.3
19.4
19.4
19.4
19.0
20.2
Bare
4.6 ꢃ 10ꢀ9
104
—
l-HTTP
l-HTTP
t-HTTP
m-HTTP
HMDS
Bare
Bare
75 ꢁC
75 ꢁC
75 ꢁC
75 ꢁC
3.2 ꢃ 10ꢀ6
6.2 ꢃ 10ꢀ6
2.9 ꢃ 10ꢀ6
2.5 ꢃ 10ꢀ6
104
104
105
104
ꢀ33
ꢀ24
ꢀ23
ꢀ38
Bare
a
Substrate temperature upon vapor deposition.
mobilities of mh ¼ 2.9 ꢃ 10ꢀ6 cm2 Vꢀ1 sꢀ1 and mh ¼ 2.5 ꢃ accompanied by the spatial distributions of the molecular
10ꢀ6 cm2 Vꢀ1 sꢀ1 for t-HTTP and m-HTTP, respectively (Fig. S4† orbitals. The HOMO levels of the unsubstituted tetrathieno-
and Table 3). The substitution dependence of the tetrathieno- phenazine derivatives were estimated to be ꢀ5.60, ꢀ5.64, and
phenazines on the FET characteristics is similar to that of the ꢀ5.68 eV for l-TTP, m-TTP, and t-TTP, respectively. These values
anthracene analogues: the alkyl-substituted anthracene are lower than those of typical thiophene-fused aromatic
analogues showed reasonable transistor performance molecules such as the anthracene analogues (ꢀ5.18 to ꢀ5.23
(ꢄ10ꢀ2 cm2 Vꢀ1 sꢀ1), while the unsubstituted anthracene eV)8 and diacene-fused thieno[3,2-b]-thiophenes (ꢀ4.88 to
analogues did not show a eld effect.8
ꢀ5.58 eV).4a This result is consistent with the experimental
results from electrochemical measurements, and can be
attributed to the introduction of an electron-decient aromatic
ring. The energy levels of LUMOs of the unsubstituted tetra-
thienophenazine derivatives were ꢀ2.27, ꢀ2.33, and ꢀ2.39 eV
for l-TTP, m-TTP, and t-TTP, respectively. The ordering of the
LUMO energy levels follows the same progression as those of
the HOMOs, while the difference between the LUMO levels was
slightly larger than that of the HOMOs. Therefore, the HOMO–
LUMO gaps in these molecules are in the order l-TTP > m-TTP >
t-TTP. This tendency was also observed in the optical band-gaps
of these molecules, obtained experimentally, although the
observed optical transitions are not due to transitions between
the HOMO and LUMO, as discussed later.
Although the energetic orders are not usually the same for
each molecule, all the molecules show the same sets of molec-
ular orbitals because all the molecules are based on the same
shape of the p-conjugating skeleton. The energy and the coef-
cients of the molecular orbitals of each atom are affected by
the positions of sulfur atoms and the introduction of nitrogen
atoms, compared to the anthracene analogues. For example, the
LUMO of the unsubstituted derivatives have the same orbital
symmetry as each other, while the orbital symmetry of the
HOMOs was not the same, and varied depending on the posi-
tions of sulfur atoms (Fig. 10).
Chemical doping effect on transport properties
Since all of the thiophene-fused phenazine derivatives afforded
crystalline thin lms by vapor deposition (for thin-lm XRD
characterization of unsubstituted derivatives, see Fig. S3†), the
conductivities of these thin lms were studied as well. In all
cases, the conductivities were improved by several orders of
magnitude upon I2 doping (Fig. S5† and Table 4). The single
crystals of these (four) derivatives also showed an increase in
conductivity upon I2 doping. The change in conductivities of the
iodine-doped single crystals (10ꢀ7 to 10ꢀ5 Uꢀ1 cmꢀ1 to 10ꢀ2 to
10ꢀ1 Uꢀ1 cmꢀ1) was much higher than those of the thin lms
(10ꢀ11 to 10ꢀ8 Uꢀ1 cmꢀ1 to 10ꢀ7 to 10ꢀ5 Uꢀ1 cmꢀ1). This is
reasonable because the continuous molecular p-stacking struc-
ture in the single crystals should be better suited for charge
transport than that in the thin lms with many grain boundaries.
Theoretical calculations
The molecular orbital calculations on the tetrathienophenazine
derivatives and the corresponding anthracene analogues were
carried out based on density functional theory. The energy
levels of the HOMO and LUMO for each molecule are listed in
Table 1, and the energy diagrams are shown in Fig. 10
TD-DFT calculations were carried out to assign the optical
transitions. The predicted absorption spectra of the thiophene-
fused phenazines were in agreement with the experimental
values, with an energy scaling factor of 0.94, as shown in
Fig. S6–S11.† The transitions for the characteristic absorption
bands are summarized in Table S1.† The TD-DFT calculations of
the excited states of the unsubstituted derivatives also agreed
with the uorescence spectra (Fig. S14–S16†).
Table 4 Conductivity improvement of thiophene-fused phenazines doped by I2
vapor in the crystal state and thin-film state (unit: Uꢀ1 cmꢀ1
)
Crystal
Thin-lm
l-TTP
m-TTP
t-TTP
l-HTTP
m-HTTP
t-HTTP
10ꢀ5 / 10ꢀ1
10ꢀ7 / 10ꢀ2
10ꢀ7 / 10ꢀ2
10ꢀ6 / 10ꢀ2
—
10ꢀ10 / 10ꢀ7
10ꢀ8 / 10ꢀ5
10ꢀ9 / 10ꢀ6
10ꢀ9 / 10ꢀ5
10ꢀ11 / 10ꢀ5
10ꢀ11 / 10ꢀ5
To evaluate the charge transport properties of the obtained
crystals, the intermolecular hopping carrier mobility was
calculated on the basis of Marcus theory.14 The calculated
—
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Fig. 10 Energies and spatial distributions of frontier orbitals of l-TTP, m-TTP, t-TTP, l-TTA, and t-TTA. Characteristic transitions are also indicated.
parameters and the evaluated intermolecular carrier mobilities p-staking directions and 10ꢀ3 to 10ꢀ2 cm2 Vꢀ1 sꢀ1 in the other
along the crystal axes are listed in Table 5. In each case, hole directions. This result suggests that these crystals have
mobilities of 0.5–5.0 ꢃ 10ꢀ1 cm2 Vꢀ1 sꢀ1 were predicted along reasonable potential for organic transistors.
3474 | J. Mater. Chem. C, 2013, 1, 3467–3481
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Table 5 Calculated hopping mobilities of thiophene-fused phenazines
˚
Molecules
Contacta
Habb/meV
Sabb/meV
d/A
8.748
Vab/meV
lc/meV
mhopping/cm2 Vꢀ1 sꢀ1
l-TTP
l-TTP
l-TTP
l-TTP
a
c0
7.7
14.5
3.2
ꢀ0.7
ꢀ1.6
ꢀ0.3
13.9
0.1
12.9
ꢀ0.02
ꢀ2.6
ꢀ0.2
ꢀ7.4
2.4
3.6
5.9
1.6
153
153
153
153
169
169
169
169
174
174
174
174
155
155
6.1 ꢃ 10ꢀ3
3.5 ꢃ 10ꢀ2
2.9 ꢃ 10ꢀ3
7.6 ꢃ 10ꢀ1
8.9 ꢃ 10ꢀ5
5.0 ꢃ 10ꢀ1
1.1 ꢃ 10ꢀ3
9.5 ꢃ 10ꢀ2
1.3 ꢃ 10ꢀ4
4.7 ꢃ 10ꢀ2
5.0 ꢃ 10ꢀ2
8.4 ꢃ 10ꢀ3
8.7 ꢃ 10ꢀ2
3.8 ꢃ 10ꢀ3
13.002
13.507
3.892
12.581
4.825
(a + c)0
b0
a
ꢀ162.4
ꢀ0.7
ꢀ133.3
ꢀ1.8
25.9
0.6
59.1
ꢀ24.1
ꢀ8.3
ꢀ50.8
ꢀ3.9
ꢀ91.3
ꢀ0.3
ꢀ66.5
ꢀ1.9
11.7
m-TTP
m-TTP
m-TTP
m-TTP
t-TTP
t-TTP
t-TTP
t-TTP
l-HTTP
l-HTTP
b
c//
0
7.857
ct
11.941
12.314
5.014
9.262
11.862
4.892
b ꢀ a
ꢀ0.4
b
20.2
(a + c)0
a ꢀ c
t1
ꢀ9.3
ꢀ3.6
ꢀ25.0
ꢀ2.0
0.9
5.6
0.4
t2
12.749
Corresponding molecular contacts are indicated in Fig. S17–S20. b Calculated at the PW91/TZ2P level. c Calculated at the B3LYP/6-31G(d) level.
a
The absorption spectra of the phenazine derivatives showed
two strong absorption bands, while those of the anthracene
analogues showed only one strong absorption band, corre-
Discussion
Synthesis
In the present work, a series of thiophene-fused phenazines
have been synthesized in reasonable yields by a simple
condensation reaction using only two types of diketones (1a, 1b,
2a and 2b) as starting materials. Furthermore, both symmetric
and asymmetric molecules can be prepared by this method,
while the corresponding anthracene analogues require different
synthetic routes for each molecule.8 Recently, Reynolds et al.15
also reported the synthesis of tetrathieno[3,2-a:20,30-c:300,200-
sponding to the shorter wavelength band of the phenazine
derivatives. This result was well reproduced by theoretical
calculation: two absorption bands for all of the phenazine
derivatives, and only one absorption band for the anthracene
derivatives were predicted by TD-DFT calculations (Fig. S6–
S13†). Although the orbital symmetries around the frontier
orbitals (HOMO and LUMO) are not the same for each mole-
cule, the symmetries of the molecular orbitals that contribute to
the major two absorption bands are the same for all derivatives
(Fig. S6–S11†). Furthermore, the two absorption bands consist
of the same transitions, as summarized in Table S1.† For
example, the two absorption bands in l-TTP are represented by a
linear combination of two kinds of elemental transitions. One is
the HOMO to LUMO+2 transition (4.56 eV) and the other is the
HOMOꢀ2 to LUMO transition (3.74 eV). These transition
moments couple with each other to afford the two absorption
bands (shorter and longer). Although the origin and the tran-
h:2000,3000-j ]phenazine (l-TTP) by
a condensation reaction
between a diketone and a diamine. This method could be
utilized widely for constructing fused polyaromatic compounds.
Effects of sulfur positions, introduction of nitrogen in the
central ring, and substitution of alkyl chains on the
electrochemical and optical properties of
tetrathienophenazine derivatives
The estimated HOMO levels of the tetrathienophenazines from sition moments of the corresponding elemental transition in
electrochemical experiments and DFT calculations were lower l-TTA are almost the same as that of l-TTP, the balance of the
than those of the corresponding anthracene derivatives. This contributions of two transition moments for each band are not
seems reasonable considering the introduction of an electron the same. This could be attributed to the energy difference in
decient aromatic ring. In the case of l-TTP, the frontier orbitals the frontier orbitals. Among the four molecular orbitals of l-TTP
were estimated to be ꢀ5.60 and ꢀ2.27 eV for the HOMO and participating in these optical transitions, the HOMO and LUMO
LUMO (Fig. 10), respectively, and those of the corresponding have signicant coefficients at the nitrogen atoms in the central
anthracene analogue (l-TTA) were ꢀ5.19 and ꢀ1.69 eV (Fig. 10). ring, while HOMOꢀ2 and LUMO+2 do not have any coefficient
On the other hand, the introduction of alkyl chains at the alpha because these are the nodal positions of the MOs. Compared
positions of the fused thiophene rings increased the donor with the energy difference from the corresponding MOs of
abilities. The effect of alkyl-substitution in these molecules was l-TTA, the HOMO and LUMO of l-TTP are much lower than that
mainly seen in HOMO levels: the energy difference (increase) of the HOMOꢀ2 and LUMO+2. Since the nitrogen atoms with a
upon alkyl-substitution in the HOMO levels were 0.41, 0.43, and larger electron negativity are introduced at the central ring, the
0.36 eV for l-TTP, m-TTP and t-TTP, respectively, and these energies of HOMO and LUMO are decreased to a large extent,
values were larger than the change in LUMOs (0.23, 0.41, and while the effect on the other two orbitals was not as large, due to
0.28, respectively). This leads to bathochromic shis in the the nodal positions. In the case of l-TTA, the two transitions
absorption and uorescence spectra upon both nitrogen intro- were assigned to HOMO to LUMO+2 (4.63 eV) and HOMOꢀ1 to
duction and alkyl-substitution of the molecules.
LUMO (4.13 eV), respectively. Since the transition energies are
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close to each other, the transition moments couple effectively to theoretical predictions. This could be attributed to the different
cancel a longer absorption band, while the shorter absorption packing structures of the thin lms from the crystals. The other
band is enhanced. On the other hand, the two transition factors for decreasing the charge mobility could be the relatively
moments in l-TTP have a relatively large difference so that the low HOMO energy and relatively large reorganization energy for
longer absorption band appears due to the imperfect cancella- the hole transfer process. These factors relate to the charge
tion between them.
The positions of the sulfur atoms also yield a signicant charge transport processes in the bulk material, respectively.
difference in the orbital energies and absorption spectra. Both The alkyl-substituted phenazines (l-HTTP, m-HTTP and
injection at the electrode semiconductor interface, and the
the HOMO and LUMO energies decrease in the order of l-TTP > t-HTTP) showed nearly the same eld effect transistor charac-
m-TTP > t-TTP due to the effect of the different positions of the teristics, probably because the thin lms of these materials
sulfur atoms (Fig. 10). The longer absorption bands showed showed nearly the same crystallinity, although the positions of
obvious red shis in the order of l-TTP > m-TTP > t-TTP. This the sulfur atoms are different in these molecules. In comparison
feature was also preserved in the alkyl substituted molecules with the anthracene analogues, the alkyl-substituted phenazines
(Fig. 2). Since the longer absorption band is mainly due to tran- showed lower FET mobilities (ꢄ10ꢀ6 cm2 Vꢀ1 sꢀ1, compared
sitions related to LUMO, the decrease in the LUMO energy mainly with ꢄ10ꢀ2 cm2 Vꢀ1 sꢀ1 for the anthracene analogues). This
contributes to the red shi of the longer wavelength absorption could be due to the relatively low donor abilities and the large
bands in the order of l-TTP > m-TTP > t-TTP (Fig. 10). The position reorganization energies of the phenazines in comparison with
of the sulfur atoms in t-TTP results in the higher energy of the the corresponding anthracenes, as discussed above.
HOMO (ꢀ5.68 eV) contributing to the longer wavelength
absorption in comparison with that of l-TTP (ꢀ6.01 eV).
Conclusion
The maximum emission wavelengths of l-TTP, m-TTP and
t-TTP are nearly the same (Fig. 3) as each other in the uores- In conclusion, we have synthesized a series of novel tetrathieno-
cence spectra, probably because the symmetry and orbital phenazines by a simple condensation reaction between diketones
distribution of the excited molecular orbitals contributing to and diamines. These materials were characterized by exact EI-MS,
the emission are nearly the same, as shown in Fig. S14–S16.†
elemental analysis, NMR and single crystal X-ray crystallography.
The hexylated derivatives showed much higher solubility than the
unsubstituted derivatives in non-polar organic solvents. We
studied the optical and electronic properties of these materials
and found pronounced differences from their anthracene
analogues. These materials showed two strong absorption bands,
while the anthracene analogues only showed one strong absorp-
tion band in the UV-vis spectra. They also showed different uo-
rescence properties. The three unsubstituted derivatives (t-TTP,
m-TTP and l-TTP) showed light-blue uorescence in chloroform,
while t-HTTP showed green uorescence and both m-HTTP and
l-HTTP showed yellow uorescence. The cyclic voltammograms
indicated that the alkyl-substituted derivatives are weaker donors
than their corresponding anthracene analogues. Thin lms of
these materials were prepared by sublimation, and different
molecular packing structures and grains sizes were obtained
when depositing at room temperature and at Tsub ¼ 75 ꢁC. Thin
lms of the alkyl-substituted derivatives show maximum eld
Crystal structures
The crystals of the three isomers, l-TTP, m-TTP and t-TTP,
showed different packing structures. The different sulfur posi-
tions of these molecules lead to a difference in their molecular
shape, intermolecular S/S contacts, distributions and energies
of the molecular orbitals, and the resultant charge distribu-
tions. Since all these factors can contribute to the intermolec-
ular packing structures, it is hard to conclude which is the most
important factor to control the crystal structure in this case.
On the other hand, the difference in TTPs and TTAs is
simpler. The replacement of the –CH] moieties of the TTAs
with –N] does not change the molecular shape, and has little
effect on the intermolecular S/S contacts although the
molecular orbitals and the charge distributions should be
affected. Actually, there are clear differences in the energies of
the frontier orbitals and the charge distribution on the central
ring between these systems. Furthermore, the characters of the
HOMOs are different between t-TTP and t-TTA. Among the
obtained crystals, l-TTP has the most different crystal structure
from l-TTA, while t-TTP afforded an isostructural crystal with
t-TTA. While the charge distributions on the central ring can
mainly contribute to the p-stacking structure in this case, the
S/S contacts are considered to affect both the p-stacking and
the side-by-side interactions. The above result could be
explained by means of the balance of the effects of charge
distributions and the S/S contacts.
effect mobilities of ꢄ10ꢀ6 cm2 Vꢀ1 sꢀ1 when deposited at Tsub
¼
ꢁ
75 C, which was signicantly larger than those formed at room
temperature, due to a mono-oriented phase structure and bigger
grains in the thin lms. The conductivity of these materials can be
improved by several orders of magnitude by iodine doping in the
thin-lm state and crystal state. The crystals and the thin lms
showed conductivities of 10ꢀ2 to 10ꢀ1 ꢀ1 cmꢀ1 and 10ꢀ7 to 10ꢀ5
U
Uꢀ1 cmꢀ1 aer chemical doping, respectively. We can conclude
that these derivatives can also be utilized for organic electronics.
Experimental section
Transport properties
General procedures
The experimental results of the eld effect mobilities of thin All chemicals and solvents purchased were used without further
lms of these molecules were much lower than those of the purication, unless otherwise stated. Compound 1a,11 2a,11 88
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Journal of Materials Chemistry C
and 108 were synthesized according to reported procedures.
NMR spectra were measured using a 400 MHz or 600 MHz JEOL
WinAlpha A-600 using TMS as the internal reference. Low
resolution and high resolution EI-MS spectra were measured
using a JOEL JMS-T100GCV with peruorokerosene (PFK) as the
matrix. Cyclic voltammetry (CV) was carried out using a
HOKUTO DENKO HZ-5000 under nitrogen gas. UV-vis spectra
were measured using a JASCO V-570. Fluorescence spectra were
measured using a JASCO FP-6600 and absolute uorescence
quantum yields were determined using a Hamamatsu C9920-02
calibrated integrating sphere system.
Preparation of 3a
Benzo[1,2-b:4,3-b0]dithiophene-7,8-quinone (0.55 g, 2.5 mmol)
and hydroxylamine hydrochloride (1.75 g, 25.0 mmol) in pyri-
dine (3.0 mL) and ethanol (12.0 mL) were reuxed overnight.
The reaction mixture was evaporated and the obtained light
yellow residue was suspended in 20 mL of water, followed by
dropwise addition of concentrated hydrochloric acid until pH #
4. The mixture was ltered, washed with water and the lter
cake was dried in a desiccator to afford a red solid (0.61 g, 97%).
IR vmax ¼ 3166 (s), 3105 (s), 1653 (w), 1381 (m), 1125 (w) cmꢀ1
.
High resolution EI-MS (M+) for C10H6N2O2S2 found: 249.9865;
calcd: 249.9871. 1H NMR (acetone-d6, 400 MHz): d 7.97–7.96
(0.4H, d, J ¼ 5.20 Hz), 7.81–7.80 (1H, d, J ¼ 4.80 Hz), 7.67–7.66
(0.4H, d, J ¼ 5.20 Hz), 7.60–7.59 (2H, d, J ¼ 5.60 Hz); 13C NMR
(DMSO-d6, 100 MHz): d 143.25, 134.92, 131.78, 123.48, 122.70.
Preparation of 1b
n-Butyllithium (48 mL, 1.6 M in hexane, 76.8 mmol) was
added dropwise to a solution of compound 11 (10.6 g,
31.6 mmol) in THF (150 mL) at ꢀ78 ꢁC under N2 gas. The
Preparation of 3b
ꢁ
mixture was stirred at ꢀ78 C for 1 hour and diethyl oxalate
Compound 1b (0.388 g, 1.0 mmol) and hydroxylamine hydro-
chloride (0.7 g, 10.0 mmol) in pyridine (3.0 mL) and ethanol
(15.0 mL) were stirred at 70 ꢁC for 3 hours. The reaction mixture
was evaporated and the obtained light yellow residue was sus-
pended in 40 mL water–methanol ¼ 2/1, followed by dropwise
addition of concentrated hydrochloric acid until pH # 4. The
mixture was ltered, washed with water and the lter cake was
(6.2 g, 42 mmol) was added to the mixture via a syringe at
ꢀ78 ꢁC. The mixture was stirred at ꢀ78 ꢁC for 2 hours and
then the temperature was allowed to slowly rise to room
temperature. Aer stirring overnight, the obtained dark red
mixture was quenched with saturated aqueous NH4Cl,
extracted by ethyl ether (200 mL ꢃ 3), and the combined
organic layers were dried over Na2SO4. Aer removing the
solvent, the residue was recrystallized from methanol–ethyl
acetate (2/1) at ꢀ20 ꢁC to yield a red solid (5.24 g, yield: 43%).
IR vmax ¼ 3076 (w), 2924 (s), 2850 (s), 1645 (s), 1450 (m), 1404
(s), 1298 (m), 860 (w) cmꢀ1. High resolution EI-MS (M+) for
dried in a desiccator to afford a red solid (0.39 g, 93%). IR vmax
¼
3151 (m), 3045 (m), 2924 (s), 2857 (s), 1397 (m), 1275 (m),
821 (m) cmꢀ1. High resolution EI-MS (M+) for C22H30N2O2S2
found: 418.1756; calcd: 418.1749. 1H NMR (CDCl3, 400 MHz): d
6.94 (2H, s), 2.85–2.81 (4H, t, J ¼ 7.58 Hz), 1.74–1.70 (4H, m),
1.38–1.31 (12H, m), 0.91–0.88 (6H, t, J ¼ 6.60 Hz); 13C NMR
(CDCl3, 100 MHz): d 153.6, 138.3, 137.0, 120.7, 120.0, 31.6, 31.3,
30.3, 28.9, 22.6, 14.1.
C
22H28O2S2 found: 388.15234; calcd: 388.1531. 1H NMR
(CDCl3, 400 MHz): d 6.91 (2H, s), 2.88–2.84 (4H, t, J ¼ 7.58 Hz),
1.76–1.68 (4H, m), 1.41–1.29 (12H, m), 0.92–0.88 (6H, t, J ¼
7.08 Hz); 13C NMR (CDCl3, 100 MHz): d 173.56, 161.27, 143.00,
122.44, 122.29, 31.42, 31.06, 31.01, 28.64, 22.49, 14.10.
Preparation of 4a
A solution of SnCl2 (anhydrous, 1.9 g, 10.0 mmol) in concen-
trated hydrochloric acid (5 mL) was added to a mixture of
compound 3a (0.5 g, 2.0 mmol) in ethanol (10 mL) at 0 ꢁC. Aer
stirring for 10 min, the mixture was taken to reux for 3 h. The
reaction mixture was ltered and washed with water and
ethanol. The lter cake was suspended in saturated aqueous
NaHCO3 (30 mL) and extracted with CH2Cl2 (30 mL ꢃ 3). The
organic phases were combined and dried over Na2SO4. Evapo-
ration of the solvent afforded a beige powder (0.296 g, 67%). IR
vmax ¼ 3394 (m), 3325 (m), 3272 (m), 3091 (w), 1486 (s), 1443 (s),
701 (s) cmꢀ1. High resolution EI-MS (M+) for C10H8N2S2 found:
Preparation of 2b
n-Butyllithium (67 mL, 1.6 M in hexane, 101 mmol) was added
dropwise to a mixture solution of compound 9 (22.95 g,
ꢁ
46.6 mmol) in anhydrous THF (150 mL) at ꢀ78 C under N2
ꢁ
gas. The mixture was stirred at ꢀ78 C for 1 hour and diethyl
oxalate (9.64 g, 66 mmol) was added to the mixture via a
syringe at ꢀ78 ꢁC. The mixture was stirred at ꢀ78 ꢁC for 2
hours and then the temperature was allowed to slowly rise to 0
ꢁC. The obtained dark blue mixture was quenched with satu-
rated aqueous NH4Cl, extracted with ethyl ether (300 mL ꢃ 3)
and the combined organic layers were dried over Na2SO4. Aer
removing the solvent, the residue was puried by chroma-
tography, eluting with hexane–ethyl acetate (20 : 1, 10 : 1) to
afford 8.06 g of a black solid ( yield: 44%). IR vmax ¼ 2925 (s),
2857 (m), 1653 (s), 1397 (m), 845 (w) cmꢀ1. High resolution EI-
1
220.0136; calcd: 220.0129. H NMR (CDCl3, 600 MHz): d 7.64–
7.63 (2H, d, J ¼ 5.16 Hz), 7.35–7.34 (4H, 2H, d, J ¼ 4.38 Hz), 3.66
(br, s); 13C NMR (CDCl3, 150 MHz): d 130.14, 129.05, 124.74,
122.94, 122.37.
MS (M+) for C22H28O2S2 found: 388.1527; calcd: 388.1531. H
NMR (CDCl3, 400 MHz): d 7.12 (2H, s), 2.78–2.74 (4H, t, J ¼ 7.40
1
Preparation of 4b
Hz), 1.69–1.62 (4H, m), 1.38–1.31 (12H, m), 0.91–0.88 (6H, t, A solution of SnCl2 (anhydrous, 0.90 g, 4.7 mmol) in concen-
J ¼ 6.80 Hz); 13C NMR (CDCl3, 100 MHz): d 174.67, 146.51, trated hydrochloric acid (3 mL) was added to a mixture of
ꢁ
142.63, 134.59, 124.0 (ꢃ2), 31.42, 30.94, 29.84, 28.57 (ꢃ2), compound 3b (0.387 g, 0.9 mmol) in ethanol (20 mL) at 0 C.
22.54 (ꢃ2), 14.09 (ꢃ2).
The yellow solution became black immediately, and then it was
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Journal of Materials Chemistry C
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stirred at room temperature overnight. The reaction mixture
was ltered and washed with water and ethanol. The lter cake
was suspended in saturated aqueous NaHCO3 (30 mL) and
extracted with CH2Cl2 (30 mL ꢃ 3). The organic phases were
combined and dried over Na2SO4. Evaporation of the solvent
afforded a dark yellow solid (0.287 g, 80%). IR vmax ¼ 3409 (w),
Preparation of 9 (ref. 16)
n-Butyllithium (72.4 mL, 1.6 M in hexane, 115.8 mmol) was added
dropwise to the mixture of diisopropylamine (19.8 mL, 139 mmol)
in anhydrous THF (80 mL) at ꢀ78 ꢁC under N2 gas. The mixture
ꢁ
was stirred at ꢀ78 C for 30 min and then the temperature was
allowed to rise slowly to room temperature for 30 min. This freshly
prepared LDA was added dropwise to the mixture of compound 8
(26.0 g, 105.2 mmol) in anhydrous THF (100 mL) at ꢀ78 ꢁC under
3325 (w), 2924 (s), 2850 (m), 1616 (w), 1465 (m), 845 (w) cmꢀ1
.
High resolution EI-MS (M+) for C22H32N2S2 found: 388.2006;
calcd: 388.2007. 1H NMR (CDCl3, 400 MHz): d 7.19 (2H, s), 3.46
(4H, s, br), 2.92–2.88 (4H, t, J ¼ 7.08 Hz), 1.78–1.71 (4H, m),
1.40–1.30 (12H, m), 0.91–0.87 (6H, t, J ¼ 7.08 Hz); 13C NMR
(CDCl3, 100 MHz): d 142.84, 128.63, 128.45, 124.00, 119.49,
31.61, 31.35, 30.87, 28.77, 22.56, 14.19.
ꢁ
N2 gas. The mixture was stirred at ꢀ78 C for 1 hour and a red
solution was observed. The temperature was allowed to rise slowly
to ꢀ50 ꢁC, and then CuCl2 (15.6 g, 116 mmol) powder was added
to the reaction, and the mixture was stirred overnight at ꢀ50 ꢁC to
RT. The dark green mixture was quenched with saturated aqueous
NH4Cl and a suspension was obtained. Aqueous HCl (20%) was
added to the mixture until dissolution. The solution was extracted
with ethyl ether (300 mL ꢃ 3) and the combined organic layers
were dried over Na2SO4. Aer removing the solvent, the residue
was recrystallized from methanol–ethyl acetate (2/1) at ꢀ20 ꢁC.
22.08 g of a white crystalline solid was obtained ( yield: 84%). High
resolution EI-MS (M+) for C20H28Br2S2 found: 490.0007; calcd:
489.9999. 1H NMR (CDCl3, 400 MHz): d 6.71 (2H, s), 2.76–2.72 (4H,
t, J ¼ 7.80 Hz), 1.69–1.62 (4H, m), 1.40–1.28 (12H, m), 0.89–0.87
(6H, t, J ¼ 5.84 Hz); 13C NMR (CDCl3, 100 MHz): d 147.26, 127.54,
127.37, 110.84, 31.45, 30.97, 30.13, 28.69, 22.49, 14.09.
Preparation of 5a
The preparation procedure was similar to that of compound 3a.
Yellow solid ( yield: 99%). IR vmax ¼ 3228 (s), 3182 (s), 3113 (s),
2924 (m), 1600 (m), 1291 (m), 1125 (s) cmꢀ1. High resolution EI-
1
MS (M+) for C10H6N2O2S2 found: 249.9867; calcd: 249.9871. H
NMR (DMSO-d6, 400 MHz): d 14.72 (0.4H, s), 12.36 (0.7H, s),
8.19–8.17 (0.7H, d, J ¼ 5.36 Hz), 8.02–8.01 (0.8H, d, J ¼ 5.36 Hz),
7.60–7.59 (0.7H, d, J ¼ 5.36 Hz), 7.59–7.57 (0.5H, d, J ¼ 5.36 Hz),
7.53–7.52 (0.8H, d, J ¼ 5.36 Hz), 7.48–7.46 (0.5H, d, J ¼ 5.36 Hz);
13C NMR (DMSO-d6, 150 MHz): d 140.93, 134.82, 132.72, 130.56,
130.21, 127.38, 126.49, 125.44, 124.16, 124.03.
Preparation of 11 (ref. 16)
Preparation of 5b
n-Butyllithium (84 mL, 1.6 M in hexane, 134 mmol) was added
dropwise to a solution of compound 10 (26.0 g, 105.2 mmol) in
anhydrous ethyl ether (200 mL) at ꢀ78 ꢁC under N2 gas. The
The preparation procedure was similar to that of compound 3b.
Yellow solid ( yield: 95%). IR vmax ¼ 2924 (s), 2857 (s), 2691 (br,
m), 1132 (m), 1055 (m), 995 (m) cmꢀ1. High resolution EI-MS
(M+) for C22H30N2O2S2 found: 418.1700; calcd: 418.1749. 1H
NMR (acetone-d6, 600 MHz): d 14.77 (0.5H, s), 11.94 (0.5H, s),
7.97 (1H, s), 7.22 (1H, s), 2.88–2.83 (4H, m), 1.73–1.68 (4H, m),
1.42–1.30 (12H, m), 0.90–0.88 (6H, m); 13C NMR (CDCl3,
100 MHz): d 145.40, 145.13, 142.61, 141.20, 136.88, 130.73,
130.51, 127.38, 124.25, 120.72, 31.61, 31.57, 31.33, 31.11, 30.28,
30.19, 28.86, 28.80, 22.63, 22.57, 14.12, 13.97.
ꢁ
mixture was stirred at ꢀ78 C for 1 hour and then the temper-
ature was allowed to rise slowly to ꢀ50 ꢁC, and then CuCl2 (18 g,
134 mmol) powder was added to the reaction, and the mixture
was stirred overnight at ꢀ50 ꢁC to RT. The dark green
mixture was quenched with saturated aqueous NH4Cl, and a
suspension was obtained. Aqueous HCl (20%) was added to the
mixture to dissolve the precipitate. The solution was extracted
with ethyl ether (200 mL ꢃ 3) and the combined organic layers
were dried over Na2SO4. Aer removing the solvent, the residue
was recrystallized from methanol–ethyl acetate (2/1) at ꢀ20 ꢁC.
Preparation of 6a
10.64 g of a white solid was obtained ( yield: 52%). IR vmax
¼
The preparation procedure was similar to that of compound 4a.
2932 (s), 2857 (m), 1532 (w), 1457 (w), 792 (w) cmꢀ1. High
resolution EI-MS (M+) for C20H30S2 found: 334.1788; calcd:
334.1789. 1H NMR (CDCl3, 400 MHz): d 7.08 (2H, s), 6.97 (2H, s),
2.82–2.78 (4H, t, J ¼ 7.56 Hz), 1.72–1.64 (4H, m), 1.41–1.29 (12H,
m), 0.91–0.87 (6H, t, J ¼ 7.08 Hz); 13C NMR (CDCl3, 100 MHz): d
146.37, 137.11, 123.34 (ꢃ2), 116.91 (ꢃ2), 31.57, 30.13, 28.77,
22.56, 14.15, 13.99.
Yellow solid ( yield: 71%). High resolution EI-MS (M+) for
1
C
10H8N2S2 found: 220.0133; calcd: 220.0129. H NMR (DMSO-
d6, 600 MHz): d 7.33–7.32 (2H, d, J ¼ 5.46 Hz), 7.31–7.30 (2H, d,
J ¼ 5.10 Hz), 3.67 (4H, br, s); 13C NMR (DMSO-d6, 150 MHz): d
126.22, 125.36, 124.98, 123.72, 120.28.
Preparation of 6b
The preparation procedure was similar to that of compound 4b.
Yellow-green solid ( yield: 72%). IR vmax ¼ 2925 (s), 2857 (m),
Preparation of t-TTP
1412 (w), 1313 (w), 836 (w) cmꢀ1. High resolution EI-MS (M+) for Benzo[1,2-b:4,3-b0]dithiophene-7,8-quinone (0.29 g, 1.3 mmol)
1
C
22H32N2S2 found: 388.2042; calcd: 388.2007. H NMR (CDCl3, and compound 4a (0.29 g, 1.3 mmol) in ethanol (10.0 mL) were
400 MHz): d 6.92 (2H, s), 3.58 (4H, s, br), 2.90–2.86 (4H, t, J ¼ reuxed for 16 h. The reaction mixture was cooled to RT, ltered
7.60 Hz), 1.77–1.70 (4H, m), 1.41–1.23 (12H, m), 0.90–0.87 (6H, t, and washed with ethanol. The lter cake was dried in the
J ¼ 6.40 Hz); 13C NMR (CDCl3, 150 MHz): d 143.94, 129.59, desiccator to afford an orange crude powder (0.42 g). The crude
ꢁ
124.77, 124.51, 116.74, 31.58, 31.28, 30.86, 28.76, 22.55, 14.07.
product was sublimed (280 C) to obtain 310 mg of an orange
3478 | J. Mater. Chem. C, 2013, 1, 3467–3481
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Journal of Materials Chemistry C
crystalline solid. The crystals were of suitable quality to be used
for X-ray characterization. NMR data are not available due to
poor solubility. IR vmax ¼ 3097 (m), 1532 (m), 1404 (s), 1344 (m),
1214 (m), 723 (m) cmꢀ1. High resolution EI-MS (M+) for
Preparation of m-HTTP
The preparation procedure was similar to that of compound
t-HTTP. Yellow solid ( yield: 56%). IR vmax ¼ 2924 (s), 2850 (m),
1518 (w), 1412 (w), 814 (w) cmꢀ1. High resolution EI-MS (M+) for
C
20H8N2S4 found: 403.9565; calcd: 403.9570. Elemental analysis
1
C
44H56N2S4 found: 740.3325; calcd: 740.3326. H NMR (CDCl3,
(%) for C20H8N2S4 found: C 59.24, H 2.03, N 6.68; calcd: C 59.38,
H 1.99, N 6.92%.
400 MHz): d 8.13 (2H, s), 7.42 (2H, s), 3.09–3.03 (8H, m), 1.90–
1.84 (8H, m), 1.56–1.36 (24H, m), 0.93–0.90 (12H, m); 13C NMR
(CDCl3, 100 MHz): d 150.78, 144.87, 137.15, 136.81, 136.00,
134.25, 133.76, 133.67, 121.32, 120.02, 31.69, 31.64, 31.59,
31.16, 30.79, 28.90, 28.86, 22.67, 22.63, 22.60, 14.19, 14.04.
Elemental analysis (%) for C44H56N2S4 found: C 71.19, H 7.52, N
3.61; calcd: C 71.30, H 7.62, N 3.78%.
Preparation of l-TTP
The preparation procedure was similar to compound t-TTP.
Crystals suitable for X-ray characterization were obtained. Red
solid ( yield: 53%). NMR data are not available due to poor
solubility. IR vmax ¼ 3111 (m), 1495 (m), 1411 (m), 1312 (m),
1214 (m), 723 (s) cmꢀ1. High resolution EI-MS (M+) for
Crystal growth and X-ray analysis
Crystals of t-TTP were obtained by slow evaporation of the
DCM solution or sublimation at 280–290 ꢁC, and the crystal
parameters obtained by these two methods were the same.
Crystals of m-TTP were grown by slow cooling of a saturated
benzonitrile solution from 160–90 ꢁC. Crystals of l-TTP were
obtained by sublimation at 300–320 ꢁC. Crystals of l-HTTP
were grown by slowly evaporating a DCM solution. Crystals of
m-HTTP and t-HTTP could not be obtained under various
conditions. Crystals were mounted on a loop using oil
(CryoLoop, Immersion Oil, Type B; Hampton Research Corp.)
and set on a Rigaku RA-Micro007 with a Saturn CCD detector
C
20H8N2S4 found: 403.9568; calcd: 403.9570. Elemental analysis
(%) for C20H8N2S4 found: C 59.30, H 1.88, N 6.51; calcd: C 59.38,
H 1.99, N 6.92%.
Preparation of m-TTP
The preparation procedure was similar to that of compound
t-TTP. Yellow solid ( yield: 41%). NMR data were not available
due to poor solubility. IR vmax ¼ 3090 (m), 1510 (m), 1404 (s),
1312 (s), 723 (s) cmꢀ1. High resolution EI-MS (M+) for C20H8N2S4
found: 403.9567; calcd: 403.9570. Elemental analysis (%) for
using graphite-monochromated Mo Ka radiation (l
¼
C
20H8N2S4 found: C 59.38, H 1.81, N 6.54; calcd: C 59.38, H 1.99,
˚
0.710690 A) under a cold nitrogen steam. The frame data were
integrated and corrected for absorption with the Rikagu/MSC
CrystalClear package.17 The structures were solved by direct
methods18 and standard difference map techniques, and were
rened with full-matrix least-squares procedures on F2 by a
Rikagu/MSC CrystalStructure package. Anisotropic renement
was applied to all non-hydrogen atoms. All hydrogen atoms
were placed at calculated positions and rened using a riding
model.
N 6.92%.
Preparation of t-HTTP
Compound 3b (0.160 g, 0.41 mmol) and compound 4b (0.165 g,
0.42 mmol) in ethanol (20.0 mL) were reuxed for 48 h. The
reaction mixture was cooled to RT, ltered and washed with
methanol (10.0 mL). The lter cake was dried in the desiccator
to afford a yellow solid (0.12 g, 40%). IR vmax ¼ 2924 (s), 2857
(m), 1412 (m), 966 (w), 814 (w) cmꢀ1. High resolution EI-MS (M+)
for C44H56N2S4 found: 740.3322; calcd: 740.3326. 1H NMR
(CDCl3, 600 MHz): d 7.36 (4H, s), 3.06–3.03 (8H, t, J ¼ 7.53 Hz),
1.88–1.84 (8H, m), 1.47–1.35 (24H, m), 0.92–0.90 (12H, t, J ¼
6.78 Hz); 13C NMR (CDCl3, 150 MHz): d 150.96, 136.87, 135.94,
133.39, 119.93, 31.63, 31.54, 31.14, 28.85, 22.59, 14.10.
Elemental analysis (%) for C44H56N2S4 found: C 70.73, H 7.49, N
3.56; calcd: C 71.30, H 7.62, N 3.78%.
Theoretical calculations
The molecular orbital calculations based on density functional
theory were carried out using the Gaussian09, revision C.01
program package.13 The molecular structures were optimized
using HF and B3LYP19 methods with 6-31G(d) basis sets.
Intermolecular hopping carrier mobilities were calculated
on the basis of Marcus theory.14 First, intermolecular electronic
coupling matrix elements (Vab) were calculated with eqn (1)
using intermolecular charge transfer integrals (Hab), overlap
integrals (Sab), and the energies of the two molecular orbitals
(Haa and Hbb) calculated at the PW91/TZ2P level using the ADF
2012 program package.
Preparation of l-HTTP
The preparation procedure was similar to that of compound
t-HTTP. Yellow solid ( yield: 75%). IR vmax ¼ 2924 (s), 2857 (m),
1419 (w), 1223 (w), 836 (w) cmꢀ1. High resolution EI-MS (M+) for
Hab ꢀ SabðHaa ꢀ HbbÞ=2
1
C
44H56N2S4 found: 740.3321; calcd: 740.3326. H NMR (CDCl3,
Vab
¼
(1)
2
1 ꢀ Sab
600 MHz): d 8.17 (4H, s), 3.08–3.05 (8H, t, J ¼ 7.68 Hz), 1.90–1.85
(8H, m), 1.54–1.34 (24H, m), 0.94–0.91 (12H, t, J ¼ 7.14 Hz); 13
C
Then the intermolecular charge transfer rate constants (kET
)
NMR (CDCl3, 150 MHz): d 144.93, 137.10, 134.53, 134.86,
121.24, 31.65, 31.62, 30.82, 28.89, 22.60, 14.11. Elemental
analysis (%) for C44H56N2S4 found: C 71.11, H 7.44, N 3.59;
calcd: C 71.30, H 7.62, N 3.78%.
were evaluated from eqn (2).
ꢀ
ꢁ
ꢀ
ꢁ
1=2
2
Vab
h
p
l
kET
¼
exp ꢀ
(2)
lkBT
4kBT
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Journal of Materials Chemistry C
Paper
where h, kB, and T are Planck's constant, Boltzmann constant,
and temperature, respectively. The reorganization energies
upon intermolecular hole transfer (l) were obtained from l ¼
(E+* ꢀ E+) + (E* ꢀ E), where E, E+, E*, and E+* are the heat of
formations for an optimized neutral molecule, optimized cation
molecule, neutral state on cation structure, and cation state on
neutral structure, respectively, calculated at the B3LYP/6-31G(d)
level. Intermolecular hopping mobilities (m) were estimated
from the following eqn (3).
Notes and references
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˚
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˚
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Acknowledgements
The authors gratefully acknowledge nancial support by a
Grant-in-Aid for Scientic Research from the Ministry of
Education, Culture, Sports, Science and Technology (MEXT) of
Japan. The authors also thank Prof. Shigehiro Yamaguchi,
Dr Aiko Fukuzawa and Mr Kazuhiko Nagura (Nagoya University)
for their help in measuring the absolute quantum yield of the
obtained materials.
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