Solvent-dependent stoichiometry in perylene-7,7,8,8-tetracyanoquinodimethane charge transfer compound single crystals

Article abstract of DOI:10.1021/cg501206f

Perylene forms three binary compounds with TCNQ. Using a physical vapor transport (PVT) method, mixtures of P1T1 (perylene1-TCNQ1), P2T1 (perylene2-TCNQ1), and P3T1 (perylene3-TCNQ1) crystals can be grown simultaneously. Solution-grown crystals exhibit a stoichiometry that depends on the solvent used and not on the initial stoichiometry of the perylene and TCNQ: only single crystals of P1T1 were grown from toluene, and only P3T1, from benzene. Precipitation-dissolution theory was employed to explain this phenomenon. We found that P1T1 is less soluble than P3T1 in toluene, which resulted in its preponderant growth from this solvent. Using the same argument, we could also explain the growth of P3T1 from benzene. Crystallization of P2T1 from solution was not possible. In addition, steady-state and time-resolved fluorescence measurements indicate that the difference in solubility of TCNQ in benzene and toluene leads to different fluorescence spectra due to selective crystallization of P1T1 and P3T1 from toluene and benzene.

Full text of DOI:10.1021/cg501206f

Article
pubs.acs.org/crystal
Solvent-Dependent Stoichiometry in Perylene−7,7,8,8-
Tetracyanoquinodimethane Charge Transfer Compound Single
Crystals
Peng Hu,† Lin Ma,‡ Ke Jie Tan,† Hui Jiang,*,† Fengxia Wei,† Chuhuan Yu,† Katelyn P. Goetz,§
Oana D. Jurchescu,§ L. E. McNeil,∥ Gagik G. Gurzadyan,‡ and Christian Kloc*,†
†School of Materials Science and Engineering, Nanyang Technological University, 639798 Singapore
‡School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore
§Department of Physics, Wake Forest University, Winston-Salem, North Carolina 27109, United States
∥Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3255,
United States
S
* Supporting Information
ABSTRACT: Perylene forms three binary compounds with TCNQ.
Using a physical vapor transport (PVT) method, mixtures of P1T1
(perylene1−TCNQ1), P2T1 (perylene2−TCNQ1), and P3T1
(perylene3−TCNQ1) crystals can be grown simultaneously.
Solution-grown crystals exhibit a stoichiometry that depends on
the solvent used and not on the initial stoichiometry of the perylene
and TCNQ: only single crystals of P1T1 were grown from toluene,
and only P3T1, from benzene. Precipitation−dissolution theory was
employed to explain this phenomenon. We found that P1T1 is less
soluble than P3T1 in toluene, which resulted in its preponderant
growth from this solvent. Using the same argument, we could also
explain the growth of P3T1 from benzene. Crystallization of P2T1
from solution was not possible. In addition, steady-state and time-
resolved fluorescence measurements indicate that the difference in
solubility of TCNQ in benzene and toluene leads to different fluorescence spectra due to selective crystallization of P1T1 and
P3T1 from toluene and benzene.
the work on (BEDT-TTF)-(Cl2 TCNQ)2 3 [(bis-
INTRODUCTION
■
(ethylenedithio)tetrathiafulvalene)-(2,5-dichloro-7,7,8,8-tetra-
Single crystals of organic charge transfer compounds are suitable
cyanoquinodimethane)], TTF-TCNQ24 (tetrathiafulvalene-tet-
for the study of charge transfer effects1−5 due to their low
racyanoquinodimethane), and (BEDSe-TTF)-(F4TCNQ)25
concentration of structural imperfections (i.e., grain boundaries)
and high purity.6−10 The degree of charge transfer between the
[(bis(ethylene-diselena)tetrathiafulvalene-tetracyanoquinodi-
methane)], systematic studies of this topic remain rare.
donor and acceptor has been shown to play an important role in
organic superconductivity,11 antiferromagnetism,12 electron−
The majority of the reported organic charge transfer
compounds are binary compounds. In contrast to the case of
phonon interactions,12 and energy storage.13 The electrical
inorganic binary compounds, where well-documented libraries of
conductivities of single-crystal charge transfer compounds range
from insulating14 to semiconducting,15 metallic,16 and even
phase diagrams provide useful information on the stoichiometry
superconducting,17 as we described in a recent review.18
control and phase coexistence, it is striking that such phase
diagrams for organic binary compounds are rather rare.26−31 The
Therefore, these compounds are considered for use in many
applications including photovoltaic devices19−21 or field-effect
availability of this information, however, is deemed crucial for
controlling the properties of single crystals of charge transfer
binary compounds, which are strongly linked to their structures.
One example is the degree of charge transfer, which is coupled to
the electrical properties. That, in turn, is affected not only by the
transistors.22
Given the presence of two different chemical species, the
donor and acceptor units, which exhibit different physical
properties (solubilities, sublimation temperatures, etc.), crystal
growth of charge transfer binary compounds is generally more
complex that of monomolecular systems, especially for systems
in which multiple stoichiometries are possible. Reports focusing
on this subject are quite limited: with few exceptions, including
Received: August 14, 2014
Revised: October 16, 2014
© XXXX American Chemical Society
A
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Solubility Measurements for Perylene, TCNQ, P1T1, and
P3T1. To measure the solubility of the charge transfer compounds and
individual components, solvent was added to a known quantity of single
crystal in a sealed test tube to avoid evaporation of solvent. The
temperature was slowly increased to the target temperature. Then, the
solution was stirred at target temperature overnight (longer than 20 h).
Saturation was confirmed by the presence of residual undissolved
crystals. Then, 1 mL quantities of the saturated solutions were placed
into glass bottles and weighed before and after solvent evaporation. The
solubility of the single crystal was calculated from the difference in
weight. The same procedure was repeated for benzene and toluene.
Characterization. The crystal structures of the P1T1 and P3T1
single crystals were obtained using a Bruker SMART APEX Π single-
crystal diffractometer (X-ray radiation, Mo Kα, λ = 0.71073 Å). The
steady-state fluorescence emission and excitation spectra were recorded
on a spectrofluorometer (Fluorolog-3, HORIBA Jobin Yvon). The time-
resolved fluorescence measurements were carried out at room
temperature by the time-correlated single photon counting (TCSPC)
technique with a resolution of 10 ps (PicoQuant PicoHarp 300). The
second harmonic of a titanium−sapphire laser (Chameleon, Coherent
Inc.) at 400 nm (100 fs, 80 MHz) was used as the excitation source.
type of molecules of which the binary compound is built but also
by the molecular packing and molecular stoichiometry.12,32
Recently, several studies also indicated that knowledge of the
stability of stoichiometric complexes is essential in tuning their
charge transfer properties.33−35 An understanding of the relation
between the stability and charge transfer properties of co-crystals
is crucial indeed for the successful growth of multiple-
stoichiometry compounds and control of stoichiometry trans-
formations in such compounds.
Perylene and TCNQ form three binary compounds with
different stoichiometries, P1T1 (perylene1−TCNQ1), P2T1
(perylene2−TCNQ1),36 and P3T1 (perylene3−TCNQ1). Two
stable compounds of perylene and TCNQ were previously
reported: P1T137,38 and P3T1.39,40 These studies report on the
effect of stoichiometry and molecular packing on the physical
properties such as charge transfer and optical and electrical
properties as a function of composition. Perylene41 is a donor
with a high ionization energy42 (6.96 eV), and TCNQ (7,7,8,8-
tetracyanoquinodimethane) is a strong electron acceptor with a
high electron affinity43 (3.0 eV). Charge transfer compounds
formed from TCNQ with various donors exhibit unique
properties such as metal-to-insulator transitions and exception-
ally high conductivity.18,44
It was also shown that the stoichiometry of a binary organic
charge transfer compound depends upon the stoichiometry of
the starting materials.24,45 Nevertheless, in the present study, we
observed an interesting phenomenon: the final stoichiometries of
single-crystal P1T1 (perylene1−TCNQ1) and P3T1 (pery-
lene3−TCNQ1) are not affected by the stoichiometry of the
starting materials but by the solvent in which the perylene−
TCNQ crystals were grown. The P1T1 crystals were grown from
toluene, whereas the P3T1 crystals were grown from benzene,
regardless of the acceptor/donor stoichiometry in the starting
materials. In contrast, when utilizing the physical vapor transport
(PVT) method, a mixture of monomolecular crystals, P1T1
(perylene1−TCNQ1), P2T1 (perylene2−TCNQ1), and P3T1
(perylene3−TCNQ1), is obtained.36 In this work, we grew P1T1
and P3T1 from solution (the only stoichiometries available using
the solution growth method) and employed solubility data to
analyze the effect of the choice of solvent on the stoichiometry of
the perylene−TCNQ charge transfer single crystals. Steady-state
optical spectra and time-resolved fluorescence were measured in
a mixture of perylene and TCNQ in toluene or benzene,
revealing that the difference in the solubilities of TCNQ in
benzene and toluene leads to different fluorescence spectra due
to selective crystallization of P1T1 and P3T1 from toluene or
benzene.
RESULTS AND DISCUSSION
■
The single-crystal charge transfer compounds (peryle-
ne)n(TCNQ)1 with perylene and TCNQ stoichiometries of
1:1 (P1T1) and 3:1 (P3T1) were grown from toluene and
benzene, respectively, for all three ratios of starting materials.
The stoichiometry of the final single crystals was found to be
influenced only by the solvent, not by the stoichiometry of the
starting materials. Furthermore, we dissolved P1T1 crystals in
benzene to make a saturated solution at 80 °C and placed the test
tubes in a temperature-controlled water bath. The initial
temperature of the water bath was set at 80 °C, with a cooling
rate of 0.5 °C/h. When the solution returned to room
temperature, we obtained P3T1 crystals. Similarly, we dissolved
P3T1 crystals in toluene to make a saturated solution at 80 °C
and cooled it slowly to room temperature, obtaining P1T1
crystals. Needle-like P1T1 single crystals (Figure 1A) were
EXPERIMENTAL SECTION
■
Figure 1. Optical images of P1T1 crystals from toluene (A) and P3T1
crystals from benzene (B).
Single-Crystal Growth. All reagents (99% purity), including
perylene, TCNQ, benzene, and toluene, were purchased from Sigma-
Aldrich. The perylene and TCNQ were purified at 180 and 220 °C,
respectively, via physical vapor transport (PVT).46,47 The solvents were
used without further purification. Perylene and TCNQ with mole ratios
of 3:1, 2:1, and 1:1 were weighed and placed in capped test tubes.
Benzene or toluene was added to each test tube for crystal growth. After
ultrasonication at room temperature for 15 min, the test tubes were
placed in a temperature-controlled water bath. The initial temperature
of the water bath was set at 80 °C, with a cooling rate of 0.5 °C/h. The
starting materials were nearly all dissolved at 80 °C after 2 h. A small
quantity of precipitated starting materials remained in the tube,
indicating that the solution was saturated. Single crystal growth was
observed with decreasing temperature, and crystals were isolated from
the solution when the bath reached 20 °C.
grown from toluene, and cube-like P3T1 crystals (Figure 1B)
were grown from benzene. The P2T1 stoichiometry was not
obtained from any solvent investigated in this study. The
molecular packing of P1T1 and P3T1 is depicted in Figure 2A,B.
In the P1T1 crystals, the layers of perylene molecules are
separated by layers of TCNQ molecules. The molecular packing
of P3T1 differs significantly from that of P1T1: here, two
perylene molecules are located between each pair of TCNQ
molecules, and a third perylene molecule is located between the
perylene−TCNQ stacks. Selected crystal structure information is
listed in Table 1.
B
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Figure 2. Molecular packing of P1T1 (A) and P3T1 (B).
Table 1. Crystallographic Data for P1T1 and P3T1 Derived
Using Single-Crystal X-ray Diffraction
in which [D] is the donor concentration and [A] is the acceptor
concentration in the solvent.
In a precipitation−dissolution equilibrium state, the following
P1T1
P3T1
relationship between the donor and acceptor is attained:
formula
C32H16N4
Monoclinic
P21/c
C72H40N4
Triclinic
m[D] = n[A]
(3)
crystal system
space group
P1
̅
Equation 2 can be presented as follows:
lattice parameter a (Å)
lattice parameter b (Å)
lattice parameter c (Å)
lattice parameter α (deg)
lattice parameter β (deg)
lattice parameter γ (deg)
cell volume (Å3)
7.3116(19)
10.858(3)
14.500(4)
90
10.411(3)
10.862(1)
12.574(2)
66.456(1)
66.295(3)
89.225(4)
1175.1(4)
1
n
n
⎡
⎤
n
n
m
Ksp
=
[A] [A]m =
[A]m+n
⎢
⎣
⎥
⎦
{m }
(4)
The relationship between the solubility and solubility product
constant is
90.276(5)
90
1151.2(5)
2
Ksp
(n/m)nmm+n
Ksp
mmnn
[A]
m
[D]
n
m + n
formula units per cell Z
temperature (K)
m + n
s =
=
=
=
(5)
293
293
R-factors
0.0450
0.0496
For P1T1 and P3T1, the precipitation−dissolution equili-
brium equations are as follows:
Precipitation−dissolution equilibrium theory is widely used to
explain the salt effect and common-ion effect in a separate
precipitation of ionic compounds from solution.26,29,30,48,49
Recently, it has been successfully applied to organic co-
crystals.26,50 Here, we adopted the same theory to understand
the growth of the organic charge transfer compounds. Donors
partly transfer electrons to acceptors; thus, the donors are partly
positively charged (δ+), whereas the acceptors are partly
negatively charged (δ−). Therefore, precipitation−dissolution
equilibrium theory can also be applied to organic charge transfer
systems. The charge transfer compound can be written as DnAm,
in which D represents the donor, A, the acceptor, and n and m
describe the stoichiometry of the donors and acceptors. Thus,
the precipitation−dissolution equilibrium of DnAm in a given
solvent can be presented as follows:
dissolve
(Perylene)1(TCNQ)1 XoooooooooY Perylene + TCNQ
precipitate
(6)
(7)
dissolve
(Perylene)3(TCNQ)1 XoooooooooY 3Perylene + TCNQ
precipitate
Therefore, according to eq 5, the relationships between the
solubility and the solubility product constant for P1T1 and P3T1
are
s(P1T1) = Ksp
(8)
Ksp
4
s(P3T1) =
(9)
27
dissolve
The enthalpy and entropy for reactions 6 and 7 can be
calculated from the solubility product constant according to the
following equation:49
D Am XoooooooooY nD + mA
n
precipitate
(1)
(2)
The solubility product constant (Ksp) is
Ksp = [D]n[A]m
ΔH
ΔS
R
ln Ksp = −
+
(10)
RT
Table 2. Solubility of P3T1 and P1T1 in Toluene at Different Temperatures (mol/L)
40 °C
50 °C
60 °C
70 °C
80 °C
toluene
P1T1
P3T1
P1T1
P3T1
0.0006(7)
0.0029(6)
0.0025(4)
0.0014(1)
0.0008(3)
0.0031(7)
0.0025(8)
0.0016(6)
0.0008(6)
0.0037(4)
0.0030(2)
0.0017(6)
0.0009(2)
0.0048(3)
0.0032(9)
0.0021(1)
0.0010(1)
0.0056(7)
0.0046(4)
0.0026(4)
benzene
C
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Equation 10 is linear in 1/T, with a slope equal to −ΔH/R and a
y intercept of ΔS/R. The enthalpy and entropy of dissolution can
be calculated using the temperature dependence of the solubility
product constant.
The solubility data of P1T1 and P3T1 are listed in Table 2.
Note that in solution the chemicals with low solubility will
precipitate first.51 The solubility of P1T1 is greater than that of
P3T1 in benzene and lower than that of P3T1 in toluene.
Consequently, P1T1 will precipitate first in toluene, and P3T1
will precipitate first in benzene.
°C, whereas the opposite is true for the values corresponding to
P3T1. The Ksp data indicate that P1T1 is more soluble than P3T1
in benzene and that P3T1 is more soluble than P1T1 in toluene.
The relationship between Ksp and solubility depends on the
stoichiometry of the dissociation reaction.52 Accordingly, any
direct comparison of Ksp values can be made only if the
compounds have the same dissociation stoichiometry. To
determine the thermodynamic data, the relationship between
ln Ksp and 1/T was plotted in Figure 4.
The slope and intercept were determined from the linear fit
(see eq 10). The enthalpy (ΔH) and entropy (ΔS) are presented
in Table 5. The solubility product constants calculated for P1T1
and P3T1 in toluene and benzene at 25 °C are presented in Table
6.
From eq 1, the precipitation constant, which indicates the
ability to form the charge transfer compound from the donor and
acceptor, is the reciprocal of Ksp. The Gibbs energy can be
determined by using the Ksp values at different temperatures. The
temperature dependence of the Gibbs energy to form P1T1 and
P3T1 in the two selected solvents is shown in Figure 5. The
Gibbs energy for P1T1 in toluene (∼−40 kJ/mol) is lower than
that in benzene (∼−30 kJ/mol); the Gibbs energy of P3T1 in
benzene (∼−60 kJ/mol) is lower than that in toluene (∼−52 kJ/
mol). This is the reason that P1T1 is formed in toluene and
P3T1, in benzene.
The following equilibria are assumed to occur:
precipitate
Perylene + TCNQ XoooooooooY (Perylene)1(TCNQ)1
(11)
(12)
dissolve
precipitate
3Perylene + TCNQ XoooooooooY (Perylene)3(TCNQ)1
dissolve
In toluene, because P1T1 is less soluble than P3T1, the
following equilibrium will exist:
(Perylene)3(TCNQ)1 ⇄ 3Perylene + TCNQ
⇄ (Perylene)1(TCNQ)1 + 2Perylene
(13)
Consequently, P1T1 forms in toluene, in agreement with our
experimental observations.
Similarly, in benzene, because P1T1 is more soluble than
P3T1, the following equilibrium will exist:
The reaction quotient, Q, from reactions 6 and 7, can be
calculated using concentrations of perylene in benzene or
toluene and concentrations of TCNQ in benzene or toluene
according to eqs 15 and 16.
3(Perylene)1(TCNQ)1 ⇄ 3Perylene + 3TCNQ
⇄ (Perylene)3(TCNQ)1 + 2TCNQ
(14)
Q(P1T1) = [perylene][TCNQ]
(15)
Consequently, P3T1 crystals form in benzene.
All equilibria indicating the crystal growth routes are depicted
in Figure 3.
Q(P3T1) = [Perylene]3[TCNQ]
(16)
Then, we compared Q with the Ksp values. If Q > Ksp, then
precipitation will occur, but if Q < Ksp, then no precipitates will
form.
From Figure 6, the solubilities of perylene and TCNQ
(concentration in the saturation solution) in toluene are 5.1 and
3.2 mmol/L at 25 °C, respectively. The Q values of P1T1 and
P3T1 are 1.63 × 10−5 and 4.24 × 10−10, respectively. Compared
with the data in Table 6, the reaction quotient is larger than the
solubility product constant for P1T1 (1.63 × 10−5 > 8.88 × 10−8)
and the reaction quotient is smaller than the solubility product
constant for P3T1 (4.24 × 10−10 < 4.83 × 10−10) at room
temperature. This indicates that P1T1 will form and P3T1 will
dissolve in toluene. In the same way, the solubility of perylene
and TCNQ in benzene at 25 °C is 5.4 and 0.7 mmol/L,
respectively. At room temperature, the reaction quotient is larger
Figure 3. All possible equilibria in the perylene−TCNQ system.
The Ksp values for P1T1 and P3T1 in toluene and benzene at
various temperatures calculated from the solubility data
according to eqs 8 and 9 are provided in Tables 3 and 4.
These data show that the Ksp values for P1T1 in toluene are
smaller than those in benzene for the temperature range 40−80
than the solubility product constant for P3T1 (1.10 × 10−10
>
3.48 × 10−11) and the reaction quotient is smaller than the
solubility product constant for P1T1 (3.78 × 10−6 < 3.98 ×
10−6), which indicate that P1T1 will dissolve and P3T1 will
precipitate in benzene.
Table 3. Solubility Product Constant of P1T1 in Toluene and Benzene at Different Temperatures
40 °C
50 °C
60 °C
70 °C
80 °C
toluene
1.12 × 10−7
( 0.11 × 10−7
6.46 × 10−6
1.73 × 10−7
( 0.11 × 10−7
6.68 × 10−6
1.87 × 10−7
( 0.11 × 10−7
9.14 × 10−6
2.12 × 10−7
( 0.11 × 10−7
1.08 × 10−5
2.54 × 10−7
( 0.11 × 10−7
2.16 × 10−5
)
)
)
)
)
)
)
)
)
)
benzene
( 0.25 × 10−6
( 0.25 × 10−6
( 0.25 × 10−6
( 0.25 × 10−6
( 0.25 × 10−6
D
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Table 4. Solubility Product Constant of P3T1 in Toluene and Benzene at Different Temperatures
40 °C
50 °C
60 °C
70 °C
80 °C
toluene
2.08 × 10−9
2.74 × 10−9
5.31 × 10−9
1.48 × 10−8
2.79 × 10−8
( 0.17 × 10−9
1.32 × 10−9
( 0.17 × 10−9
)
( 0.17 × 10−9
)
( 0.17 × 10−9
)
( 0.17 × 10−9
)
)
benzene
1.08 × 10−10
2.07 × 10−10
( 0.13 × 10−10
2.64 × 10−10
5.27 × 10−10
( 0.13 × 10−10
)
)
( 0.13 × 10−10
)
( 0.13 × 10−10
)
( 0.13 × 10−10
)
Figure 4. Relationship between ln Ksp and 1/T (the black lines represent
the fitting curves).
Figure 6. Solubility data of perylene and TCNQ in benzene and toluene.
Table 5. Thermodynamic Data for P3T1 and P1T1 in Toluene
and Benzene
The higher solubility of TCNQ in toluene than in benzene
causes the intensive steady-state absorption and fluorescence
observed in the perylene−TCNQ solution in benzene, as
discussed below.
P1T1
P3T1
toluene
benzene
toluene
benzene
ΔH (kJ/mol)
ΔS (J/mol)
17.06
26.23
62.78
32.28
54.17
−77.75
−16.98
−18.47
The steady-state absorption and fluorescence spectra of
perylene in benzene and toluene are identical (Figure 7A)
because the perylene solubility in the two solvents is equal. The
perylene fluorescence spectra in both solvents are in good
agreement with the reported perylene monomer emission when
the reabsorption effect is taken into consideration.53 The optical
absorption of TCNQ in toluene, however, is over 10 times
stronger than that in benzene due to the higher concentration. At
room temperature, the fluorescence of TCNQ is not detected in
either solvent. As a control experiment, we performed the
spectroscopic characterization of stock solutions (perylene +
TCNQ 1:1) in benzene and toluene. Figure 7B presents the
steady-state spectra of both solutions. Figure 8 shows the
fluorescence kinetics at λ = 472 nm. It can be observed that the
perylene fluorescence lifetime in the stock solution (perylene +
TCNQ 1:1) in benzene is 4.2 ns, a value that is a little longer than
the perylene radiative lifetime reported.53 This 10% lifetime
lengthening is due to reabsorption.54 However, the perylene
fluorescence lifetime in toluene is 1.6 times shorter than that in
benzene, which indicates the perylene fluorescence is quenched
by the highly concentrated TCNQ in toluene (high solubility of
TCNQ in toluene). It should be mentioned that the decay
kinetics is independent of the emission wavelength both in
benzene and in toluene. A similar situation is observed in steady-
state fluorescence (Figure 7B), but the intensity difference is
much larger. Because of the high solubility of TCNQ in toluene,
the absorption edge extends to 550 nm; therefore, the intensity
of the steady-state fluorescence from perylene in toluene is much
(4.4 times) weaker than that in benzene.
Table 6. Solubility Product Constants of P3T1 and P1T1 in
Toluene and Benzene at 25 °C
P1T1
P3T1
toluene
benzene
toluene
benzene
Ksp
8.88 × 10−8
3.98 × 10−6
4.83 × 10−10
3.48 × 10−11
Figure 5. Temperature dependence of ΔG to form P1T1 and P3T1 in
toluene and benzene.
E
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stoichiometry of the starting materials: the crystals with lower
solubility will precipitate first. As a result, only P1T1 is formed
from toluene because P1T1 is less soluble than P3T1 in this
solvent. As P3T1 is less soluble than P1T1 in benzene, only P3T1
was crystallized from benzene. Moreover, steady-state and time-
resolved fluorescence measurements indicate that the high
solubility of TCNQ in toluene results in weak fluorescence of
perylene from the toluene solution due to formation of P1T1
that utilizes the perylene from the solution.
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files and checkCif reports of P1T1 and P3T1 grown from
solutions. This material is available free of charge via the Internet
at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Authors
*(H.J.) E-mail: Jianghui@ntu.edu.sg.
*(C.K.) E-mail: Ckloc@ntu.edu.sg.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was conducted by the NTU-HUJ-BGU Nanoma-
terials for Energy and Water Management Programme under the
Campus for Research Excellence and Technological Enterprise
(CREATE), which is supported by the National Research
Foundation, Prime Minister’s Office, Singapore. K.P.G. thanks
the NSF EAPSI for supporting her work at NTU through a
fellowship. O.D.J. and L.E.M. acknowledge NSF support under
grant DMR-1105147.
Figure 7. Steady-state absorption and fluorescence spectra: (A)
Perylene and TCNQ stock solutions in benzene and toluene; (B)
perylene + TCNQ 1:1 in benzene and toluene. (The spectropho-
tometers used give correct results for the absorption only at values of A <
2.5 due to sensitivity limitations.)
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CONCLUSIONS
■
In summary, the single-crystal charge transfer compounds
(perylene)1(TCNQ)1 (P1T1) and (perylene)3(TCNQ)1
(P3T1) were grown from solvents via slow cooling. P1T1 and
P3T1 exhibit monoclinic and triclinic symmetries, respectively.
Solution-grown single crystals of P1T1 are needle-like, and P3T1
crystals are cube-like. We found that the stoichiometry of the
binary crystal is influenced by the type of solvent and not by the
F
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