Improved ternary memory performance of donor-acceptor structured molecules through cyano substitution

Article abstract of DOI:10.1039/c5tc00839e

Organic memory devices can greatly increase the data-storage density and have attracted significant attention in recent years. Thus, two small molecules, DPHCANA and DPCNCANA, were designed and successfully synthesized to investigate the improvement of me

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Improved ternary memory performance of donor-acceptor
structured molecules through cyano substitution
Received 00th January 20xx,
Accepted 00th January 20xx
Qijian Zhang, Hao Zhuang, Jinghui He, Shugang Xia, Hua Li,* Najun Li, Qingfeng Xu and Jianmei Lu*
Organic memory devices can greatly increase the data-storage density and have attracted more and more attentions. Thus,
two small molecules DPHCANA and DPCNCANA were designed and successfully synthesized to investigate the
improvement of the memory device through introducing the strong electron withdrawing group cyano on the central
phenyl ring. It is noteworthy that DPCNCANA with cyano exhibited excellent ternary memory behavior benefited from
induced intermolecular H-bond connection and layer by layer molecular stacking in film state, which counteracted the
higher hole transport barrier lying between the film and the bottom electrode. In addition, we have also found that the
additional cyano group substitution lower the LUMO energy level, which is favorable to the stability in the air ambient
circumstance. We envisage that this study present here is very useful to the rational design of advanced next-generation
semiconductor materials.
DOI: 10.1039/x0xx00000x
www.rsc.org/
bottom ITO electrode has the fixed work function at - 4.8 eV
which generally serves as anode to inject holes under electric
field. Therefore, the enlarged energy barrier will definitely
Introduction
Over the past decade, small molecular and polymeric materials
have attracted more and more attentions as alternatives to
traditional inorganic optical or magnetic materials in binary
data storage applications due to several attractive merits as
increase the switch voltage of the ternary device, which would
not only improve the power consumption but also probably
give rise to the risk of puncturing the device. Therefore, design
and synthesis of ternary data storage materials without
increasing threshold voltage becomes very important.
low cost, well-defined structure, easy processing, 3D stacking
1-6
and super-high data-storage density.
Our group has
reported a series of ternary data storage materials and devices,
which are sure to dramatically improve the data storage
density when compared with the traditional binary system. 7-10
During this process we proposed the “charge trap” mechanism
as principle for designing multi-levels data storage materials, in
which we believe that two different electron acceptors
distributed in the conjugated molecular backbone served as
In our previous studies, we have found that well enhanced
11
intermolecular π-π stacking,
12
optimization of film
morphology, and decreasing of the molecular energy band-
13
gaps (Eg), are beneficial to reduce the threshold voltage of
the device, the former two effects are generally decided by the
molecular geometric construction and the latter is usually
decided by the selected electron acceptors. Taking into
account of combination above three effects into one molecule
is a good solution to achieve ideal ternary data storage
materials. However, the incorporation of relatively large
electron acceptor groups in the conjugated backbone would
shallow and deep charge traps is the pre-condition to achieve
7-10
ternary memory devices.
As we know, the more and
stronger the electron acceptors are in the molecule backbone,
the lower the HOMO energy level of the molecule would be.
Therefore, ternary data storage materials usually exhibit very
low HOMO levels which attributed to their contained no less
than two electron withdrawing groups. The decreased HOMO
energy level will enlarge the energy barrier between the
bottom electrode and the active film for the as-fabricated
sandwiched Al/organic film/ITO devices, because most of now
synthesized semiconductor materials are p-type and the
14
distort intermolecular close packing. To avoid this problem,
it is necessary to find one suitable electron acceptor, which
would not increase the Eg much and in contrary could improve
the intermolecular ordered arrangement.
Herein, we combined electron-donor Carbazole (CA) and
electron acceptor Naphthalimide (NA) to form
a D-A
structured organic small molecule, which is an efficient way to
narrow the Eg by utilizing intramolecular charge transfer (ICT)
transition between the D-A units in molecular backbone.
Furthermore, we combined cyano groups on the CA group to
form another D-A unit, in addition, the cyano group can act as
the deep charge trap while the NA group would serve as the
College of Chemistry, Chemical Engineering and Materials Science, Collaborative
Innovation Center of Suzhou Nano Science and Technology, Soochow University,
Suzhou 215123, China. E-mail: lujm@suda.edu.cn;
Fax: +86 512 65880367; Tel: +86 512 65880368
†
Electronic Supplementary Information (ESI) available: [detailed experimental
procedures of the intermediates, NMR spectra of the terminal compounds and IR
absorbance spectra of the both molecules.]. See DOI: 10.1039/x0xx00000x
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General procedure for synthesis of compound 4
shallow charge trap thus to satisfy the pre-condition of the
ternary data storage materials. The most importance of
choosing cyano group here is especially reducing HOMO
without enhancing molecular band-gap, and promoting the
ordered molecules arrangement in the film by CN···CN and
CN···H interactions to facilitate the intermolecular charge
transport.15-17
Compound 3 (0.5 mmol), 2 M potassium carbonate aqueous
solution and compound 6 (0.47 g, 1.1 mmol) were dissolved in
the mixture of 20 mL water, 8 mL ethanol and 20 mL toluene.
After stirred in N2 atmosphere for about 15 min, 47 mg (0.04
mmol) Tetrakis(triphenylphosphine)palladium(0) was added
o
immediately. The mixture was refluxed in 70 C for 18h. After
extraction, the crude was dried by Na2SO4, condensed, and
purified by chromatography using CH2Cl2: Petroleum ether
(3/1; v/v) to obtain a yellow powder.
Experimental
Compound 4a (DPNCANA): yield 69%, bright yellow powder,
1H NMR (400 MHz, CDCl3) δ 8.65 (dd, J = 15.2, 7.4 Hz, 4H), 8.52
– 8.39 (m, 4H), 8.35 (s, 2H), 7.83 (d, J = 7.7 Hz, 4H), 7.75 – 7.63
(m, 10H), 7.57 (dd, J = 12.7, 8.0 Hz, 8H), 4.33 – 4.15 (t, 4H),
1.89 – 1.67 (m, 4H), 1.43 – 1.26 (m, 20H), 0.87 (t, J = 7.1 Hz,
6H).
Materials
Iodobenzene,
naphthalic anhydride, bis(pinacolato)diboron and Octylamine
were purchased from Energy Chemical,
4-Fluorophenylacetonitrile,
4-Bromo-1,8-
Tetrakis(triphenylphosphine)palladium(0) was purchased from
Aldrich, Carbazole, NBS (N-bromosuccinimide), Ferric Chloride,
Potassium Carbonate, Potassium Acetate and all the solvents
were purchased from Shanghai Chemical Reagent Co. Ltd. All
chemicals were used as received without further purification.
The two original compounds 9-phenyl-carbazole (1a), 4-(9H-
carbazol-9-yl)benzonitrile (1b), 4-(4,4,5,5-tetramethyl-1,3,2-
Compound 4b (DPCNCANA): yield 57%, orange yellow powder,
1H NMR (400 MHz, CDCl3) δ 8.66 (dd, J = 13.1, 7.4 Hz, 4H), 8.47
(s, 2H), 8.37 (d, J = 8.9 Hz, 4H), 8.00 (d, J = 8.4 Hz, 4H), 7.84 (dd,
J = 17.9, 7.9 Hz, 8H), 7.72 – 7.58 (m, 8H), 4.24 – 4.18 (t, 4H),
1.77 (m, 4H), 1.44 (d, J = 14.6 Hz, 8H), 1.29 (m, 12H), 0.87 (t, J =
6.7 Hz, 6H).
dioxaborolan-2-yl)-N-octyl-1,8-naphthalimide
prepared according to previously reported procedures.18-20
(NA)
were
Memory device fabrication
The indium-tin-oxide (ITO) glass was pre-cleaned with water,
acetone, and alcohol in an ultrasonic bath for 30 min,
respectively. The solution of 10 mg compounds in 1 mL o-
dichlorobenzene was filtered through a microfilter equipped
with a 0.22 μm sized pinhole. The solution was evaporated
under high vacuum (10−3 Torr) and the film thickness was
decided by the speed of the spin-coating machine. An
aluminum layer was thermally evaporated and deposited onto
the active film at about 10−7 Torr through a shadow mask to
form the top electrode. The sandwich-structured memory
device area of about 0.0314 mm2 was obtained.
Instrumentation and characterizations
1H NMR spectra were measured on an Inova 400 MHz FT-NMR
workstation. All the electrical characteristics of the devices
were executed by using a HP 4145B semiconductor parameter
analyzer with a HP 8110A pulse generator. Thermogravimetric
analysis (TGA) were conducted on a TA Instruments Dynamic
TGA 2950 at a heating rate of 10 oC min-1 and under an N2 flow
rate of 50 mL min-1. UV-Vis absorption spectrum was obtained
with the use of a Shimadzu UV-3600 spectrophotometer.
Cyclic voltammetry was performed on
a CorrTest CS
Electrochemical Workstation analyzer at room temperature.
SEM images were measured on a Hitachi S-4700 scanning
electron microscope. X-ray diffraction (XRD) pattern was taken
on an X’Pert-Pro MPD X-ray diffractometer. Atomic force
microscopy (AFM) measurement was carried out by using a
MFP-3DTM AFM instrument in tapping mode. All electrical
measurements of the device were taken at ambient conditions
without any encapsulation. Calculations on the two molecules
investigated in this work were carried out with the Gaussian 03
program package.21 Electronic properties of DPHCANA and
DPCNCANA in ground state, including the electrostatic
potential (ESP) surfaces and molecular energy orbitals, were
calculated from the density functional theory (DFT): the
Becke's three-parameter functional combined with the Lee,
22
Yang, and Parr's correlation functional (B3LYP), along with
the 3-21G basis set.
Scheme 1. Synthesis scheme and molecular structures of DPHCANA and
DPCNCANA. Reagents and conditions: (a) FeCl3, DCM, RT; (b) NBS, CHCl3, ice
o
water to RT; (c) NA, K2CO3, (PPh3)4Pd, H2O,C2H5OH, toluene, 70 C, under N2
atmosphere.
Synthetic procedures
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nm was originated from the n-π* transition of C=O bonds
23
Results and Discussion
in naphthalimide chromophore.
For DPCNCANA in solution
(Fig. 2b), the absorption peak located at 349 nm was the
combination of the n-π* electronic transition of C=O bonds
in naphthalimide chromophore and the n-π* electronic
transition of C≡N bonds, leading to the largely increased
absorption intensity. Additionally, the ICT peak located at 390
nm was blue-shifted when compared with that of DPHCANA
(405 nm), and this was mainly caused by the increased
dihedral angel that decreased the coplanarity and was not
beneficial for the ICT throughout the molecular backbone. In
comparison with their UV-vis spectra in solution, the
absorption bands of DPCNCANA and DPHCANA in film were
red-shifted 18 nm and 13 nm, respectively, and thus showing a
strong intermolecular interaction in the DPCNCANA film state,
Molecular structures and synthesis routes
Scheme 1 shows the molecular structures of DPHCANA and
DPCNCANA, and the synthesis routes of both molecules. The
1
detailed synthesis steps of the intermediates and the H NMR
spectra of DPHCANA and DPCNCANA are depicted in the
Supplementary Information part.
Thermal properties
24
which maybe also arise from the more ordered
intermolecular stacking than that of DPHCANA.
Electrochemical properties
Fig. 1 TGA curves of the two small molecules under an air flow rate of 50
mL·min-1.
Thermal properties were investigated by TGA, as shown in
figure 1. The thermal decomposition temperatures with 5%
weight loss were measured to be 208 oC and 232 oC for
DPHCANA and DPCNCANA, respectively. The higher
decomposition temperature of DPCNCANA maybe arises from
the condensed molecular interactions in solid state.
Fig. 3 Cyclic voltammogram of DPHCANA and DPCNCANA on ITO substrates
in acetonitrile solution with 0.1M tetrabutylammonium perchlorate as
electrolyte and ITO glass as the working electrode.
Photophysical properties
Cyclic voltammetry (CV) measurements were carried out to
understand the electronic properties of the films spin-coated
on ITO glasses in anhydrous acetonitrile solution. As we can
see in figure 3, the onset oxidations (Eonset) of DPHCANA and
DPCNCANA films are 0.73 eV and 1.12 eV, respectively. The
highest occupied molecular orbital (HOMO) level and the
lowest unoccupied molecular orbital (LUMO) level can be
calculated by the equations: HOMO = - [Eonset + 4.8 - EFerrocence],
LUMO
=
HOMO
+
Eg
.
Where EFerrocene is the
ferrocene/ferrocenium redox standard potential which can be
deduced from the inset of figure 3 and Eg is the optical
bandgap which can be estimated from the onset of UV-Vis
absorption spectra. The detailed CV data are summarized in
Table 1.
Fig. 2 UV-Vis absorption spectra of (a) DPHCANA and (b) DPCNCANA in
tetrahydrofuran solution and film states.
The UV-vis absorption spectra of both molecules in
tetrahydrofuran (THF) solution and in film states are shown in
figure 2. As shown in Fig. 2a, the absorption peak located at
304 nm was attributed to the carbazole segment while that
observed at 405 nm was consistent with the intramolecular
charge transfer (ICT) from electron-donors to the electron-
acceptors. Meanwhile, the shoulder peak between 332-379
The results are almost in accordance with the previous
assumption; as the cyano group was introduced into the
molecular backbone, the HOMO level decreased from -5.02 eV
for DPHCANA to -5.41 eV for DPCNCANA, however, the energy
gaps for both molecules are very close and only 0.07 eV
different. As shown in Table 1, the energy barrier between
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work function of ITO and HOMO energy levels for DPHCANA for DPCNCANA is much higher than that of DPHCANA.
and DPCNCANA is 0.22 eV and 0.61 eV, respectively, both are According to this situation, the threshold voltage based on
much smaller than that between work function of Al and DPHCANA would be much smaller than that based on
LUMO energy level being 1.84 eV and 1.52 eV, indicating that DPCNCANA. The LUMO of DPCNCANA is -2.76 eV which is
it is more convenient for hole injection from ITO into the much smaller than that of DPHCANA around at -2.46 eV,
HOMO levels of both molecules. Therefore, both molecules are suggesting the DPCNCANA molecule has a better stability in
dominated by hole-transporting and the hole injection barrier the air ambient circumstance.
Table 1 Optical and electrochemical properties of the films fabricated with DPHCANA and DPCNCANA
Molecule
DPHCANA
DPCNCANA
λonset (nm)
485
Eg (eV)a
2.56
Eonset (eV)b
0.73
HOMO (eV)c
-5.02
LUMO (eV)d
-2.46
ΦAl-HOMO (eV)
0.22
LUMO-ΦAl (eV)
1.84
471
2.63
1.12
-5.41
-2.78
0.61
1.52
a
b
Estimated from the onset of absorption: bandgap = 1240/λonset
.
Potential vs. Ag/AgCl in a 0.1 M anhydrous acetonitrile solution of
c
tetrabutylammonium perchlorate (TBAP). The HOMO energy levels were calculated from cyclic voltammetry with reference to ferrocene (0.51 eV):
HOMO = - [Eonset + 4.8 - EFerrocence]. d LUMO = HOMO + Eg.
sweep from 0 to -5.0 V, an abrupt current increase was
Current–voltage (I–V) characteristics of the memory devices
observed at a threshold voltage of -2.23 V, indicating that this
In order to verify the analysis of the CV measurements above, memory device undergoes a transition from low-conductivity
we measured the current-voltage (I-V) characteristics of state (OFF state) to intermediate-conductivity state (ON1
memory devices fabricated with DPHCANA and DPCNCANA state). And the current could further increase to the high-
respectively. Figure S3a is the scheme of the sandwich- conductivity state (ON2 state) with the voltage increasing to -
structured memory devices, which consists of an indium-tin 2.86 V. The cell remained in this high-conductivity state during
oxide (ITO) bottom electrode, a spin-coated organic active- the subsequent scan from 0 to -5.0 V (sweep 2). The three
layer and an Al top electrode. The thickness of the spin-coated current states can be corresponding to 0, 1 and 2 ternary data
active layer is about 90 nm while that of Al electrode is storage utilities. Sweep 3 was operated on another cell of the
estimated to be 150 nm according to the SEM image of the device over a voltage ranging from 0 to -2.7 V, and a sharp
devices (Fig. S3b). The current-voltage (I-V) characteristics of increase in current was showed at a threshold voltage of -2.28
ITO/DPHCANA/Al device were measured under an external V. The intermediate-conductivity stage was maintained during
electric field, as shown in Fig. 4a. The current was initially in the subsequent scan from 0 to -2.7 V (sweep 4). Sweep 5 was
low-conductivity (OFF) state, when a voltage from 0 to -5 V carried out in the same cell of the device over a voltage from 0
was applied on one cell of the device, a sharp increase in to -5 V, an abrupt increase in current occurred from 10-4 A to
current was observed at switching threshold of -2.11 V, 10-2 A at a switching threshold voltage of about -2.84 V. As
indicating the transition from low-conductivity (OFF) state to long as the devices reaching the ON state, neither the
high-conductivity (ON) state (sweep 1). This electrical subsequent voltage sweep (sweep 6) nor the reverse voltage
transition can serve as the “writing” process for sweep (sweep 7) would return the memory device to the
ITO/DPHCANA/Al device. Upon reaching the high-conductivity original OFF state. Therefore, due to the introducing of CN
state, the current still remained in the ON state in the group into the molecular backbone, we successfully fabricated
subsequent voltage sweep (sweep 2). In the reverse voltage a memory device with typical ternary WORM (write once read
sweep from 0 to 5 V (sweep 3), an abrupt decrease in current many times) memory behaviour. Additionally, no obvious
was observed at a threshold voltage of about 2.74 V, which degradation in current was observed for about 4 h under a
indicates that the memory device undergoes a transition from constant stress of -1 V for both memory devices, as shown in
ON state to the original OFF state. This electrical transition Figure 5. Unexpectedly, the threshold voltage of DPCNCANA
serves as the “erase” process for data-storage devices. device is nearly the same as that of DPHCANA, which is not
Therefore, the memory device fabricated with DPHCANA is a consistent with the analysis of the CV measurements above.
binary Flash data-storage device.
To understand this phenomenon, measurements regarding the
The current-voltage characteristics of the sandwich microstructures and the crystalline ordering of the two films
structured memory device fabricated with DPCNCANA were were carried out.
measured in the same condition (Fig. 4b). In the first voltage
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Fig. 4 The current-voltage (I-V) characteristics of the memory devices fabricated with (a) DPHCANA and (b) DPCNCANA.
Fig. 5 Stability test of the memory devices in all states under stimulus by read pulses at -1 V; (a) DPHCANA and (b) DPCNCANA.
Morphology of the thin films
To characterize the microstructure of the spin-coated thin
films of DPHCANA and DPCNCANA, atomic force microscopy
(AFM) measurements were carried out. As shown in Fig. 6a,
the surface morphology of DPHCANA film shows no distinct
structure, indicating poor stacking in solid state. In contrast,
figure 6b shows that DPCNCANA formed a well-organized
grain-like structure, which is deduced to be resulted from the
progressively ordered stacking by CN···CN and CN···H
interactions. Thus, DPCNCANA formed a crystalline structure in
the film state and the introducing of cyano groups into the
molecular backbone resulted in the total different film surface
morphology of DPCNCANA. In addition, the surface root-mean-
square (RMS) roughness of DPCNCANA is estimated to be 1.69
nm. The ordered stacking and small RMS of DPCNCANA are
beneficial to improve charge transport mobility through the
organic active layers and decrease the energy barriers
between the active layers and the electrodes. Thus, less power
was needed to overcome the energy barrier and the threshold
voltage of DPCNCANA based memory device was not much
larger than that of DPHCANA. 25
Fig. 6 The tapping-mode AFM height images of (a) DPHCANA and (b)
DPCNCANA films spin-coated onto ITO glass.
IR spectra of the thin films
To demonstrate the intermolecular H-bond (H···N-C) that was
generated between the neighbouring molecules, we measured
the IR absorbance spectra of molecule DPHCANA and
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DPCNCANA in both solution and film states. Firstly, as shown in
Figure S4, the IR absorbance spectrum of molecule DPHCANA
in solution state was almost the same to that of the IR
absorbance spectrum in film state. However, Figure S5 showed
a little difference between the IR absorbance spectra of
molecule DPCNCANA in film and solution states. Compared
with the absorbance spectrum in solution state, the peak
located at 2232 cm-1 arising from the CN group blue-shifted for
about 6 cm-1, as shown in Figure 7a. Additionally, the peak
located between 2800 cm-1 and 3000 cm-1 that corresponds to
the frequencies of C-H stretching mode also had a blue shift
for about
6
cm-1.
These results demonstrate that
intermolecular H-bond was generated in the films due to the
introducing of CN groups in the molecular backbones. 26
Fig. 8 The XRD patterns of DPHCANA and DPCNCANA films spin-coated onto
ITO glass substrates.
Fig. 7 IR absorbance spectra of DPCNCANA in solution and in film state. The
red line represented the IR spectra in film state and the black line
represented the IR in solution state. (a). CN-group. (b). C-H stretching mode.
Fig. 9 The dihedral angles of DFT-optimized geometries of DPHCANA and
DPCNCANA.
Density functional theory (DFT) method has been used in the
theoretical calculations of B3LYP, with the 3-21G basis set to
calculate the structural optimizations of these two molecules,
as shown in figure 9. The dihedral angle between the carbazole
core and the end-capping moiety naphthalimide group was
nearly the same. At the meantime, the 9-phenylcarbazole
derivative core of both DPHCANA and DPCNCANA possesses
the nonplanar structure at ground state. The dihedral angle of
DPCNCANA core is calculated to be 44.5° while that of
DPHCANA core is estimated to be 41.2°. The larger dihedral
angle means the larger twist of the molecular backbones and is
not beneficial for decreasing the distance between the
neighbouring molecules in film state, which may commendably
explain the larger microstructure ordering distance for
molecule DPCNCANA in the XRD measurements. Although the
microstructure ordering distance of molecule DPHCANA is a
little smaller than that of DPCNCANA, the stacking of molecule
DPHCANA in film state is not as better as that of DPCNCANA.
The stacking of the molecules in solid states is an extreme
important element in the properties of the semi-conductive
layers. Thus, due to the ordered crystalline stacking in the film
state, the energy barriers that the charges should overcome
through the films of DPCNCANA is smaller than that of
DPHCANA, leading to the decreasing of the threshold voltage
of the memory device. Thus, the threshold voltage of
DPCNCANA is nearly the same as that of DPHCANA.
Molecular stacking in the thin films
X-ray diffraction (XRD) measurements of the two molecules
spin-coated on ITO substrates were preformed to further
understand the effects of CN groups in the molecular
backbone (Figure 8). The diffraction peak observed at 2θ =
18.96° for molecule DPHCANA corresponded to a d-spacing of
4.67 Å which indicated a relative ordered arrangement in the
films. This result was mainly due to the large conjugated
planarity of carbazole moieties. In addition, the diffraction
peaks at 2θ = 6.58° (13.42 Å), 9.89° (8.93 Å), 13.19° (6.72 Å)
and 16.45° (5.38 Å) are also observed for molecule DPCNCANA.
The d-spacing of 5.38 Å belongs to the microstructure ordering
distance while the diffraction peak at 2θ = 6.58° (13.42 Å)
means a long-range order, which indicates that the ordered
stacking is formed in solid state. Moreover, the 2θ = 13.19° is
almost twice of 2θ = 6.58°, indicating that DPCNCANA formed
a well-organized layer by layer stacking in the film. This result
may be caused by three reasons: (1) The large conjugated
plane of carbazole moieties; (2) The alkyl chains serving as the
spacer to control the distance of the conjugated backbones;
(3) the strong π-stacking of molecules by CN···CN and CN···H
interactions. Therefore, DPCNCANA self-assembled into
ordered crystalline and formed close layer by layer stacking in
the thin film state which is consistent with the UV analysis and
the AFM image. The stacking of DPCNCANA in film state is
beneficial for promoting the mobility of charge carriers, which
also attributes to decrease the threshold voltage.
Proposed memory mechanisms
Finally, in order to better understand the electrical switching
mechanism of the memory devices, electrostatic potential
(ESP) surfaces and the HOMO and LUMO orbital surfaces of
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DPHCANA and DPCNCANA were calculated through density nonvolatile memory behaviour. Meantime, the current can be
functional theory with the B3LYP/3-21G basis set, as shown in transited from the ON state back to the OFF state under the
Fig. 10. DFT molecular simulation results showed an open forward voltage, which indicates that the electron-
channel with continuous positive molecular electrostatic withdrawing ability of naphthalimide group is weak and the
potential (in red) which is formed from the molecular surface trapped electron can be de-trapped in the reverse voltage.
throughout the conjugated backbone, indicating that the Therefore the device we fabricated with DPHCANA exhibits
charge carriers can migrate through this open channel. typical nonvolatile binary FLASH memory behaviour. For
Meantime, the negative molecular ESP regions (in blue) were DPCNCANA, the transition from OFF state to ON1 state is the
attributed to the naphthalimide chromophores for molecule same to that of DPHCANA. Then the deep trap arising from
DPHCANA and to the naphthalimide chromophores and cyano cyano group will be filled with electron to full gradually with
groups for DPCNCANA. These negative regions can serve as the the increase of the voltage, leading to the transition from ON1
“traps” to block the mobility of the charge carriers, and the to ON2 state. Upon finishing the HOMO to LUMO+1 transition,
depth of these “traps” is in consistent with the electron- the electron density distribution is mainly located on the cyano
27
withdrawing ability of the electron-deficient groups.
For group and becomes more stable than initial state. Due to the
DPHCANA, the electron is initially located on the electron- strong electron-withdrawing ability of cyano group, the
donor carbazole moieties, and the “charge trap” arising from trapped electron is not easy to be de-trapped even the power
naphthalimide will be filled with electron quickly when an is shut down or reversed, leading to a high conductivity state
external voltage was applied on the cell of the device, which that can be maintained in a long time. Therefore the device we
indicates that the current transits from OFF to ON state. The fabricated with DPCNCANA exhibits typical nonvolatile ternary
high conductivity state (ON state) is very stable, which exhibits WORM memory characteristics.
Fig. 10 Molecular electrostatic potential (ESP) surfaces and molecular orbital energy levels of DPHCANA and DPCNCANA.
Conclusions
In summary, we successfully synthesized two small molecules Specialized Research Fund for the Doctoral Program of Higher
DPHCANA and DPCNCANA, the device based on cyano Education of China (Grant No. 20123201120005), Chinese-
contained molecule DPCNCANA has a much lower HOMO Singapore Joint Project (2012DFG41900) and National
value, however, happened intermolecular H-bond connection Excellent Doctoral Dissertation funds (201455).
and led to molecular stacking and crystalline ordering in film
state, which counteracted the negative effects of the higher
Notes and references
hole transport barrier lying between the film HOMO level and
the bottom electrode, achieved almost the same switch
voltage with the counterpart molecule DPHCANA without
cyano group. This result may provide a new strategy to
synthesize conjugated molecules with novel structures and has
the potential to play a vital role development of memory
devices in the future.
1
2
3
T. Osaka, M. Takai, K. Hayashi, K. Ohashi, M. Saito and K.
Yamada, Nature, 1998, 392, 796-798.
M. Emmelius, G. Pawlowski and H. W. Vollmann, Angew.
Chem. Int. Edit., 1989, 28, 1445-1471.
G. Wang, S. F. Miao, Q. J. Zhang, H. F. Liu, H. Li, N. J. Li, Q. F.
Xu, J. M. Lu and L. H. Wang, Chem. Commun., 2013, 49, 9470-
9472.
4
5
6
Q. D. Ling, D. J. Liaw, C. X. Zhu, D. S. H. Chan, E. T. Kang and
K. G. Neoh, Prog. Polym. Sci., 2008, 33, 917-978.
J. Q. Liu, Z. Y. Yin, X. H. Cao, F. Zhao, L. H. Wang, W. Huang
and H. Zhang, Adv. Mater., 2013, 25, 233-238.
S. G. Hahm, S. Choi, S. H. Hong, T. J. Lee, S. Park, D. M. Kim,
W. S. Kwon, K. Kim, O. Kim and M. Ree, Adv. Funct. Mater.,
2008, 18, 3276-3282.
Acknowledgements
This work was financially supported by the NSF of China
(21176164, 21206102, 21336005 and 21476152), the NSF of
Jiangsu Province (BE2013052), a project supported by the
This journal is © The Royal Society of Chemistry 20xx
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DOI: 10.1039/C5TC00839E
COMMUNICATION
Journal Name
7
8
9
H. Li, Q. F. Xu, N. J. Li, R. Sun, J. F. Ge, J. M. Lu, H. W. Gu and
F. Yan, J. Am. Chem. Soc., 2010, 132, 5542-5543.
S. F. Miao, H. Li, Q. F. Xu, Y. Y. Li, S. J. Ji, N. J. Li, L. H. Wang, J.
W. Zheng and J. M. Lu, Adv. Mater., 2012, 24, 6210-6215.
P. Y. Gu, F. Zhou, J. K. Gao, G. Li, C. Y. Wang, Q. F. Xu, Q. C.
Biscarini, C. Femoni, L. Roberto and P. Leclere, J. Mate.r
Chem., 2007, 17, 728-735. (b) R. Schmidt, J. H. Oh, Y. S. Sun,
M. Deppisch, A. M. Krause, K. Radacki, H. Braunschweig, M.
Konemann, P. Erk, Z. A. Bao and F. Wurthner, J. Am. Chem.
Soc., 2009, 131, 6215-6228.
Zhang and J. M. Lu, J. Am. Chem. Soc., 2013, 135, 14086- 25 W. B. Zhang, C. Wang, G. Liu, X. J. Zhu, X. X. Chen, L. Pan, H.
14089.
W. Tan, W. H. Xue, Z. H. Ji, J. Wang, Y. Chen and R. W. Li,
Chem. Commun., 2014, 50, 11856-11858.
26 (a) D. Yokoyama, H. Sasabe, Y. Furukawa, C. Adachi, J. Kido,
Adv. Funct. Mater., 2011, 21, 1375. (b) P. Hobza, Z. Havlas,
Chem. Rev., 2000, 100, 4253. (c) X. S. Li, L. Liu, H. B. Schlegel,
J. Am. Chem. Soc., 2002, 124, 9639.
10 S. F. Miao, H. Li, Q. F. Xu, N. J. Li, J. W. Zheng, R. Sun, J. M. Lu
and C. M. Li, J. Mater. Chem., 2012, 22, 16582-16589.
11 S. F. Miao, H. Li, Q. F. Xu, Y. Y. Li, S. J. Ji, N. J. Li, L. H. Wang, J.
W. Zheng and J. M. Lu, Adv. Mater., 2012, 24, 6210-6215.
12 Y. H. Zhang, H. Zhuang, Y. Yang, X. F. Xu, Q. Bao, N. J. Li, H. Li,
Q. F. Xu, J. M. Lu and L. H. Wang, J Phys Chem C, 2012, 116
22832-22839.
13 H. F. Liu, H. Zhuang, H. Li, J. M. Lu and L. H. Wang, Phys Chem
Chem Phys, 2014, 16, 17125-17132.
,
27 X. D. Zhuang, Y. Chen, G. Liu, B. Zhang, K. G. Neoh, E. T. Kang,
C. X. Zhu, Y. X. Li and L. J. Niu, Adv. Funct. Mater., 2010, 20,
2916-2922.
14 T. Lei, J. Y. Wang and J. Pei, Accounts Chem Res, 2014, 47
1117-1126.
,
15 (a) C. R. Newman, C. D. Frisbie, D. A. da Silva, J. L. Bredas, P.
C. Ewbank and K. R. Mann, Chem. Mater., 2004, 16, 4436-
4451. (b) Y. Yamashita, Sci Technol Adv Mat, 2009, 10. (c) M.
Y. Kuo, H. Y. Chen and I. Chao, Chem-Eur. J., 2007, 13, 4750-
4758.
16 (a) G. R. Hutchison, M. A. Ratner and T. J. Marks, J. Am.
Chem. Soc., 2005, 127, 2339-2350. (b) X. H. Zhang, Q. S. Li, J.
B. Ingels, A. C. Simmonett, S. E. Wheeler, Y. M. Xie, R. B. King,
H. F. Schaefer and F. A. Cotton, Chem. Commun., 2006, DOI:
Doi 10.1039/B515843e, 758-760.
17 T. M. Barclay, A. W. Cordes, C. D. MacKinnon, R. T. Oakley
and R. W. Reed, Chem. Mater., 1997, 9, 981-990.
18 J. Q. Ding, B. H. Zhang, J. H. Lu, Z. Y. Xie, L. X. Wang, X. B. Jing
and F. S. Wang, Adv. Mater., 2009, 21, 4983-4986.
19 B. J. Song, H. M. Song, I. T. Choi, S. K. Kim, K. D. Seo, M. S.
Kang, M. J. Lee, D. W. Cho, M. J. Ju and H. K. Kim, Chem-Eur.
J., 2011, 17, 11115-11121.
20 (a) G. Wang, S. F. Miao, Q. J. Zhang, H. F. Liu, H. Li, N. J. Li, Q.
F. Xu, J. M. Lu and L. H. Wang, Chem. Commun., 2013, 49,
9470-9472. (b) M. Xu, J. M. Han, Y. Q. Zhang, X. M. Yang and
L. Zang, Chem. Commun., 2013, 49, 11779-11781.
21 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K.
N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V.
Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A.
Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R.
Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J.
B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador,
J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels,
M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K.
Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A.
Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M.
W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, and
J. A. Pople, Gaussian 03, revision B.04,Gaussian, Inc.,
Wallingford CT, 2004.
22 B. Miehlich, A. Savin, H. Stoll and H. Preuss, Chem. Phys.
Lett., 1989, 157. 200-206.
23 (a) M. S. Alexiou, V. Tychopoulos, S. Ghorbanian, J. H. P.
Tyman, R. G. Brown and P. I. Brittain, J. Chem. Soc. Perk. T. 2,
1990, DOI: Doi 10.1039/P29900000837, 837-842. (b) B.
Ramachandram, G. Saroja, N. B. Sankaran and A. Samanta, J
Phys Chem B, 2000, 104, 11824-11832.
24 (a) M. Surin, P. Sonar, A. C. Grimsdale, K. Mullen, S. De
Feyter, S. Habuchi, S. Sarzi, E. Braeken, A. V. Heyen, M. Van
der Auweraer, F. C. De Schryver, M. Cavallini, J. F. Moulin, F.
8 | J. Name., 2012, 00, 1-3
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Journal of Materials Chemistry C
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DOI: 10.1039/C5TC00839E
Dramatic achievement of stable ternary data storage material
mediated by simply cyano group substitution
Qijian Zhang, Hao Zhuang, Jinghui He, Shugang Xia, Hua Li,* Najun Li, Qingfeng Xu and
Jianmei Lu*
Table of Contents
Novelty: the forming of layer by layer stacking and the realization of excellent ternary memory
device through introducing CN group in the molecular backbone.