Effect of single atom substitution in benzochalcogendiazole acceptors on the performance of ternary memory devices

Article abstract of DOI:10.1039/c5tc02274f

Herein, three conjugated organic molecules comprised of the diethylamine donor, pyrimidine and benzochalcogenodiazole acceptors (where the chalcogen atoms are varied from O, S to Se), named PBOP, PBTP, and PBSeP, were synthesized and fabricated into resis

Full text of DOI:10.1039/c5tc02274f

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Effect of single atom substitution in Benzochalcogendiazole
Acceptors on the performance of ternary Memory Devices
Received 00th January 20xx,
Accepted 00th January 20xx
Zhaojun Liu,a Jinghui He,b Hao Zhuang, b Hua Li,b* Najun Li,b Dongyun Chen,b Qingfeng Xu,b Jianmei
Lu,*bc Keqin Zhang,a and Lihua Wangb
DOI: 10.1039/x0xx00000x
Herein, three conjugated organic molecules comprised of diethylamine donor, pyrimidine and benzochalcogenodiazole
acceptors (where the chalcogen atom are vaired from O, S to Se), named as PBOP, PBTP, and PBSeP, were synthesized and
fabricated into resistive random access memory devices. Structural analysis and theoretical calculations show that the
three molecules have almost the same crystal structures and orientations in film state but different backbone planarities,
electron affinities, intra- and intermolecular interactions, which tune the molecular packing and optical absorption. All the
compounds exhibited non-volatile ternary memory characteristics while PBOP showed the lowest switching threshold
voltages (1.2 V) and highest Ion/Ioff ratios (105 and 103) .
www.rsc.org/
desirable, but scarcely reported.10,11b,11c One category of
heterocycles, benzochalcogenadiazoles including benzooxadiazole
(BO), benzothiadiazole (BT), benzoselenadiazole (BSe), are typical
Introduction
Organic conjugated materials, especially small molecules, have
attracted extensive attention in recent years since their potential
examples of single atom substitution and intensively employed as
conjugative building blocks for improving device performance.11
Organic materials containing BT show relatively higher electron
mobilities and Ion/Ioff ratios in devices due to its stronger electron
withdrawing ability and more intrinsic S···N interactions between
1
2
applications in the fields of solar cells, field effect transistors,
3
4, 5
sensors and memories
owing to their low cost, flexibility and
6
tunability through structural design.
For example, as one
promising kind of application of organic materials, resistive random
access memory (RRAM) received considerable attention because of
the capability of layer-by-layer stacking and/or multilevel
information storage and multilevel RRAMs have been achieved by
12
the thiadiazole rings. BSe can effectively tune the polarizability,
13
optical and electronic properties of organic conjugated chain. BO
was not widely studied but several studies examining molecular
backbones show that BO is a stronger acceptor than BT and BSe due
4,
5
rationally designing of molecular structure.
Generally,
14
to the larger electron affinity of oxygen. In addition, BO’s ability
incorporation of heterocyclic units with electron donating (donors)
and withdrawing (acceptor) group into molecule backbones can
to form coplanar and quinoid structures enhance the air stability of
as-fabricated devices. 15
greatly improve the conjugation and tune the performance of
7
Nevertheless, their effects on device performances are reported
to be contradictory. It was also reported recently that BO/BSe as
organic electronic devices.
To explore structure−property
relationships of organic memory devices, researchers varied types,
positions, numbers and ratios 8 of the donor and acceptors of the
9
building blocks can guarantee stronger polarity, atomic interaction
15, 16
and electron affinity of the target molecules than BT.
The
active organic molecule and investigated their effects on the device
performances. However, in such cases, the molecular structure
changes too much and induces complexity to correctly correlate the
microscopic structural effect to macroscopic device phenomena. In
this context, the choice of a series of “infinitesimal” variations of
obtained BO/BSe-based devices show the higher redox stability,
higher Ion/Ioff ratio, longer cycle life, lower bandgap and lower
operation voltage than that of BT. 11a, 17 More confusingly, when BO
and BSe is located in electron-donating building block, the
optoelectronic performance of devices are only slightly improved or
the molecules—substitution of
a single atom of particular
11c, 18
even decreased.
Herein, the questions remain on how and
donor/acceptors in the molecule appear to be more elegant and
why those organic electronic devices were tuned so significantly by
these three benzochalcogenadiazoles. Any study toward this
question will be useful for device optimizations through structural
design of new organic materials.
a College of Textile and Clothing Engineering, Soochow University, Suzhou 215123,China
b College of Chemistry, Chemical Engineering and Materials Science, Collaborative
Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou
215123, P. R. China. E-mail: lujm@suda.edu.cn; Fax: +86 512 65880367; Tel: +86 512
65880368China
In this report, we synthesized three benzochalcogenadiazoles
derivatives where the chalcogen of the benzodiazole moiety is
systematically varied from oxygen to sulfur to selenium (Figure 1).
The RRAMs devices based on these molecules were fabricated and
investigated. The results of experimental measurements and
c State Key Laboratory of Treatments and Recycling for Organic Effluents by Adsorption
in Petroleum and Chemical Industry, Suzhou 215123, P. R.
†Electronic supplementary informaꢀon (ESI) available: Experimental procedures,
The compositions of the small molecules, TGA, memory device stability, SEM
images, DFT molecular simulation results. See DOI: 10.1039/ b000000x/.
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theoretical simulations surprisingly demonstrated exotic trends of CDCl3) δ = 160.53, 156.89, 148.80, 125.35, 123.08, 116.61, 42.25,
the device performances, different from previous research results.
13.07. HRMS: Anal. Calcd. For C22H26N8O [M + H]+ 419.2230 found
419.2241.
Compounds PBTP and PBSeP were synthesized use using a similar
procedure for compound PBOP.
Synthesis of compound PBTP (5,5'-(benzo[c][1,2,5]thiadi azole-4,7-
diyl)bis(N,N-diethyl pyrimidin-2-amine)). 1.63 g, 75%, crimson
solid. 1H NMR (400 MHz, CDCl3) δ = 8.98 (s, 4H), 7.67 (s, 2H), 3.70
(dd, J = 13.3, 6.5 Hz, 8H), 1.24 (t, J = 6.7 Hz, 12H). 13C NMR (101
MHz, CDCl3) δ = 160.28, 157.55, 153.75, 127.70, 125.53, 118.41,
42.14, 13.09. HRMS: Anal. Calcd. For C22H26N8S [M + H]+ 435.2001
found 435.2011.
Synthesis of compound PBSeP (5,5'-(benzo[c][1,2,5]selenadi
azole-4,7-diyl)bis(N,Ndiethyl pyrimidin-2-amine)). 2.00 g,
83%, orange solid. 1H NMR (400 MHz, CDCl3) δ = 8.88 (s, 4H),
7.50 (s, 2H), 3.73 (dd, J = 13.5, 6.6 Hz, 8H), 1.27 (t, J = 6.9 Hz,
12H). 13C NMR (101 MHz, CDCl3) δ = 160.25, 159.47, 157.81,
129.55, 126.04, 119.01, 42.13, 13.10. HRMS: Anal. Calcd. For
C22H26N8Se [M + H]+ 483.1446 found 482.1452.
Figure 1. From left to right, Schematic diagram of sandwich device.
SEM image of a cross-section view of the device. Chemical structures,
optimized geometries, electronegativity of the heteroatom, bond
length of N-X, and dihedral angles between the planes of the two
pyrimidine rings adjacent to the central benzodiazole unit.
Fabrication of the Memory Device
Experimental section
The indium-tin-oxide (ITO) glass was pre-cleaned by ultra-sonication
in solvent by sequence for 10 min, inclusive of water, acetone and
alcohol. The organic film was prepared on glass slides from the 1,2-
dichlorobenzene solution at room temperature by spin coating. The
film thickness was about 80 nm determined by a quartz oscillator. A
layer of Al, about 100 nm in thickness was thermally evaporated
and deposited onto the organic surface at a pressure of about 5×10-
Materials
5-bromo-2-iodopyrimidine, benzothiadiazole, benzofuroxan,
sodium borohydride, [1,1-Bis(diphenylphosphino)ferrocene]
dichloropalladium(II),bis(pinacolato)diboron,(β-4)-platinum
were purchased from commercial suppliers (TCI, Alfa Aesar,
Sigma-Aldrich) and used without further purification. Solvents
used were dried and distilled by standard methods prior to
use. All reactions were carried out under air atmosphere
unless stated. The following compounds were synthesized
according to the procedures reported in the literature (see
6
Torr through a shadow mask to form the top electrode of 0.0314
mm2 in area. In addition, the 5 nm thick LiF layer was evaporated
under high vacuum before the evaporation of Al when necessary.
Measurement
ESI†
for
details):
5,5'-(benzo[c][1,2,5]oxadiazole-4,7-
din-2-amine),5,5'-
All measurements of the devices were conducted under ambient
conditions, without any encapsulation, using an HP 4145B
semiconductor parameter analyzer equipped with HP 8110A pulse
generator. NMR spectra were collected by an Inova 400 MHz FT-
NMR spectrometer. High resolution mass spectra (HRMS) were
obtained using MicroMass TOF-MS spectrometer (EI). UV-vis
absorption spectra were carried out at room temperature from 250
to 750 nm with a Shimidazu UV–3600 spectrophotometer. Thermo
gravimetric analysis (TGA) was conducted on a TA instrument
Dynamic TGA 2950 at a annealing rate of 10 oC·min-1 under a
nitrogen flow rate of 50 mL min-1. SEM images were taken on a
Hitachi S-4700 scanning electron microscope. Atomic force
microscopy (AFM) measurements were performed by using a MFP-
3DTM (Digital Instruments/Asylum Research) AFM instrument in
tapping mode. X-ray diffraction (XRD) patterns were taken on an
X’Pert-Pro MPD X-ray diffractometer. 2D GISAXS measurement was
carried out on Anton Paar SAXS pace Analyzer.
diyl)bis(N,N-diethylpyrimi
(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(N,N-diethyl pyrimidin-
2-amine), 5,5'-(benzo[c][1,2,5]selenadiazole-4,7-diyl) bis(N,N-
diethylpyrimidin-2-amine).
Preparation of PBOP, PBTP and PBSeP
Synthesis of compound PBOP (5,5'-(benzo[c][1,2,5] oxadi azole-
4,7-diyl)bis(N,N-diethylpyrimidin-2 -amine). A mixture of 4, 7-
dibromo-2, 1, 3-benzooxadiazole (1.38 g, 5 mmol), compound 2
(2.25 g, 15 mmol), potassium carbonate (2.76 g, 20 mmol),
Pd(PPh3)4(47 mg, 0.04 mmol), H2O (20 mL) and toluene (30 mL) was
heated at 90oC for 10 h. After cooling, the mixture was poured into
water and extracted with dichloromethane. The organic layer was
washed with water and then dried with anhydrous Na2SO4. After
the solvent was evaporated, the crude product was recrystallized
1
from ethanol to afford PBOP (1.29 g, 62%) as a crimson solid. H
NMR (400 MHz, CDCl3) δ = 9.01 (s, 4H), 7.51 (s, 2H), 3.72 (dd, J =
13.9, 6.9 Hz, 8H), 1.26 (t, J = 6.9 Hz, 12H). 13C NMR (101 MHz,
2 | J. Name., 2012, 00, 1-3
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62−83%, respecꢀvely. The chemical structures of the moieꢀes
and the molecules were verified by 1H NMR, 13C NMR and
HRMS spectroscopy. More details are described in the
Supporting Information. Thermal stability of the molecules was
investigated with thermogravimetric analysis as shown in
Figure S2 and Table 1. The TGA analysis reveals that the
temperatures (Td) to lose 5% weight of PBOP, PBTP, and PBSeP
were 192.5, 282.2, and 280.7 ºC, respectively. Therefore the
thermal stabilities of three molecules are adequate for their
applications in memory as well as other optoelectronic
devices.
Results and Discussion
Synthesis and Characterization
The structures and the synthetic methods for the synthesis of
three molecules are presented in Figure S1. Molecule 1 (M1),
M2, M3, M4, M5, M6, and M7 were prepared as described
elsewhere. 19 From Suzuki-Miyaura couplings of M3, M5, and
M7 with M2 in the presence of Pd[P(C6H5)3]4 as the catalyst
and K2CO3 as the base in Toluene/H2O at 90°C for 12 h, we
obtained the compounds PBOP, PBTP and PBSeP in yields of
Figure 2. Typical I–V curves of the (A) ITO/PBOP or (B) PBTP or (C) PBSeP/Al memory device; A,B,C-1) the statistical data of reproducibility and
ON1 state switching threshold voltages distribution, (A,B,C-2) ON2 state switching threshold voltages distribution.
when the negative sweep was repeated or followed by a reversed
scanning (sweep 3). Therefore, this device exhibits typical ternary
Current–voltage (I–V) Characteristics
memory behaviour.
The memory devices based on PBOP, PBTP and PBSeP were
Another cell of the device was measured over a voltage range of
fabricated as ITO/small-molecule/Al sandwiched devices and the
0 to −2 V (sweep 4) and showed the first onset Vths at −1.1 V, which
current–voltage (I-V) characteristics of these devices are shown in
suggests switching from “OFF” to “ON1”. Subsequent forward and
Figure 2. In the first sweep from 0 to −4 V (sweep 1), the compound
reverse scans from 0 to –2 V (sweep 5 and 6) indicate that this
PBOP based devices display two sharp transitions from a low
device remains in its ON1 state, even when the external voltage was
conductive (OFF, “0”) state to an intermediately conductive (ON1,
removed. A following sweep 7 from 0 to −4 V convert the ON1 to
“1”) state, finally to a high conductive (ON2, “2”) state at voltages
ON2 state at the −2.2 V. Again, the ON2 state could survive from
(Vths) of −1.2 and −2.3 V. The OFF to-ON1 and -ON1 to -ON2
following negative and positive sweeps of a large voltage (Sweeps 8
transitions can be regarded as a “writing” operation for the
and 9). The above three states distinguish themselves by a current
memory device. As shown by Sweep 2, it remains in the ON2 state
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ratio of 1:105:108 for “OFF”, “ON1”, and “ON2” states. In short,
ternary WORM (write-once-read-many-times) memory behaviour
was achieved in our experiments.
small molecules (E1/2(ferrocene) was measured to be 0.34 V vs.
Ag/AgCl in CH3CN).
Optical and Electrochemical Properties
Similarly, the other two molecules, PBTP and PBSeP based
devices were sequentially investigated and both show ternary
WORM characteristics. PBTP based devices are of switching
threshold voltages (Vths) at –1.4 V and –2.8 V, while –1.8 V and –3.1
V are found for that of PBSeP (Figure 2 B-1, C-1). One should be
noted that the threshold voltages of PBOP are markedly lower than
that of PBTP and PBSeP. Moreover, the conductance of PBOP-
device at OFF state is obviously lower than that of PBTP and PBSeP,
which indicates that PBOP-devices may be more favorable for
potential application because of its lower online power
consumption and lower operation voltages.
The UV-vis spectra of all compounds in dichloromethane
solution and film state are investigated to reveal the molecular
electronic properties and the stacking manner in the film
(
Figure 3 and in Table 1). The absorption spectra of three
molecules showed dual-band absorption: the higher energy
bands (~300 nm) due to conjugation and the lower energy
21
bands (~450nm) from intramolecular charge transfer.
It’s
worth noting that, some interesting trends are observed in
these spectra. First, the λmax values of both peaks exhibit red
shift when heavier chalcogens are substituted into the
benzodiazole unit. This could be attributed to the increasing
electron density and atomic radius of the heteroatom (from O
to Se) and resulting in an improved intramolecular charge
transfer (ICT). Second, the absorption bands are broader in the
film than in solution, indicating improved planarity of the
molecular backbone and enhanced intermolecular interactions
in film state. Third, the absorption coefficient of the low-
energy band decreases in intensity while the high-energy band
remains constant upon moving from O to S to Se, which can be
ascribed to the loss of electronegativity of the heteroatom and
the acceptor unit’s ability to produce and stabilize a charge-
In order to rule out the possible metal filaments phenomenon
happened in above devices, we deposited a layer of LiF (5 nm)
between the film and aluminium electrode to prevent aluminium
nanoparticles penetrating into the functional film. Herein, the
formed devices all exhibit original WORM behaviour as shown in
Figure S6, which indicated that the observed WORM behaviour is
irrelevant to the metal filament.
Considering the reproducibility of the switching
phenomenon is an important parameter for memory devices,
we count on 50 cells to investigate the cell-to-cell uniformity
for the three molecules based devices. The statistical data
shows that the thresholds voltages of ON1 have narrower
distribution than that of ON2 (Figure 2), which indicates that
the ON1 states of the fabricated devices compared to ON2 are
more stable. Regarding the stability, it is noteworthy that all
the storage states of the memory devices of PBOP, PBTP and
PBSeP are highly stable for more than one million (106)
continuous read pulses at –1 V without any significant
degradation (see Figures. S3a, b and c). In addition, the
currents of all the states in the three devices are stable under
a constant voltage stress of –1 V for up to 10 hours (see Figure.
S3 A, B and C).
8
separated state. Fourth, energy gap variation trend from
solution UV and electrochemical spectra are the same with
PBSeP<PBOP<PBTP whereas the film gaps has a different
sequence of PBOP<PBTP<PBSeP. Since both solution UV and
electrochemical spectra represent the electronic properties of
individual molecules, the varied sequence of energy gaps of
the films in fact reflect that the stacking and crystallinity play
an crucial role to determine the ensemble of molecules. The
maximum absorption peaks of PBOP, PBTP, and PBSeP in the
films show redshift of 65.5 nm, 34.3 nm and 12.2 nm,
respectively compared to their solution spectra which indicate
considerable intermolecular interaction and ordered molecular
stacking in the solid state. The lowest band gap and the largest
red-shift of PBOP than PBTP and PBSeP suggest the more
planar configuration between the pyrimidine ring and BO
moiety in PBOP, which we will discuss later.
The electrochemical properties of the three molecules films on
an indium–tin oxide (ITO) glass substrate were studied through
cyclic voltammetry (CV) in anhydrous acetonitrile. In Figure 3d, the
onset oxidation (reduction) potentials of compounds PBOP, PBTP
and PBSeP are 1.13 (-1.10) eV, 1.12 (-1.14) eV, 1.07 (-1.08) eV,
respectively. On the basis of these values, we estimated the HOMO
and LUMO energy levels according to the energy level of the
ferrocene reference (4.8 eV below vacuum level) by the following
equation: 12
EHOMO = - (Eonset ox + 4.8 - EFerrocene
ELUMO = - (Eonset red + 4.8 - EFerrocene
)
①
②
)
As shown in Table 1 the HOMO energy levels of PBOP, PBTP
and PBSeP are -5.59, -5.58 and -5.53 eV, respectively. The low
HOMO levels suggest that all compounds would be stable
against oxidation in air. The LUMO energy levels of PBOP, PBTP
and PBSeP are -3.36,-3.32 and -3.38 eV, respectively. Thus, by
Figure 3. a, b, c) UV-Visible absorption spectra of the three compounds
in CH2Cl2 solution and film. d) Cyclic voltammetry (CV) curves of the
three compounds on the ITO electrode in 0.1M Bu4NPF6/CH3CN
solution with Ag/AgCl as the reference electrode and Pt wire as the
counter electrode. The scan rate was 100 mV s−1. The inset shows the
CV curve of ferrocene, swept in the same conditions as for the three
4 | J. Name., 2012, 00, 1-3
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replacing O atoms with S atoms or Se atoms, the degree of limited charge transport in the thin-film state. Above all, the
electron-deficient characteristic of benzooxadiazole unit photoelectric properties of the conjugated compounds can be
decreases, resulting in stabilization of the HOMO, easily tuned by simply incorporating different electron-
destabilization of the LUMO. Moreover, all molecules show deficient atoms.
poor reversibility of the reduction processes, which indicates
Table 1. Optical and electrochemical properties of the three synthesized molecular films
optical
optical
red
ox
e
electrical
a λonset
(nm)
a Eg
b λonset
(nm)
bEg
c Eonset
bEonset
(eV)
d HOMO
(eV)
d LUMO
(eV)
Eg
ΦITO-EHOMO
(eV)
ELUMO-ΦAl
(eV)
Index
(eV)
(eV)
(eV)
-1.10
-1.14
(eV)
2.23
2.28
PBOP
PBTP
523.2
511.4
544.3
2.37
2.42
2.28
605
570
560
2.05
2.17
2.21
1.13
1.12
1.07
-5.59
-5.58
-5.53
-3.36
-3.32
-3.38
0.79
0.78
0.73
0.94
0.98
0.92
PBSeP
-1.08
2.15
a The data were calculated by the following equation: bandgap = 1240/λonset of the synthesized molecule in CH2Cl2. b the three synthesized
molecular films. c Vs Ag/AgCl in acetonitrile. d Calculated from cyclic voltammetry. e Calculated from the HOMO and LUMO energy level.
X-ray Diffraction and Single crystal structure Analysis
The ordering in the organic thin films was investigated using X- crystal structure variation, rendering the further analysis on
ray diffraction as displayed in Figure 4a. The X-ray pattern of structural-properties relationship much more convincing. The
PBSeP film is distinct from the above PBOP and PBTP. There X-ray pattern of PBSeP film is distinct from the above two
are three diffraction peaks for PBOP appeared at 5.86º, 11.78º, curves.
and 17.68º and 23.58º, respectively, which have multiple
To further investigate the molecular stacking in the film, we
relationships, indicating a highly ordered structure with a d- prepared the single crystal of PBSeP and resolve its structure
spacing of 15.1 Å (d1). According to those reported literatures, as shown in Figure 4b. PBSeP is found to crystalize in a layer-
it is reasonable to assume that d1 corresponds to the distance by-layer manner. Visually, its alky side groups condense
between π-conjugated molecular backbones separated by the together by van der waals interaction while its conjugated
alkyl side chain21. Similarly, PBTP also has four diffraction backbone stacks by π-π interaction. The lattice constant c is
peaks in film state: 5.87º, 11.72º, 17.66º and 22.61º, which 15.0 Å, in agreement with the strongest peak for these films
appear almost at the same positions of PBOP-curves. PBSeP (but not detected by XRD in the case of PBSeP, only (003) was
has only a visible feature at 18.82o, with a slightly shrunk d1 detected to offer a d1 of 4.95*3=14.9Å). Based on the multiple
value. These curves indicate that the crystal structure of the relationships between these peaks, they could be assigned as
grains of two molecules should be the same, despite that their (001), (002), (003) and (004), respectively. Single crystals of the
lattice constants are slightly varied. Such a small distortion of other two molecules would offer more structural information
the same stacking show the success of our design strategy— but are difficult to prepare thus not reported here.
change of single atoms of molecules does not cause unwanted
Figure 4. (a) X-ray diffraction patterns of the compounds in solid films. The inset shows amplified features of PBTP curves; (b) Schematic of PBSeP single
crystallites in the film stacking orientation. Dashed parallelograms mark the unit cell boundary. The Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as deposition No. CCDC 1415038.
become more acute (18.3° [O] <24.6° [S] <25.2° [Se]). Meanwhile,
In order to further understand the stacking discrepancies, we the nitrogen−heteroatom (N-X) bond length increases (Figure 1). On
examined geometric torsions of individual molecules by theoretical the other hand, experimentally, in the case of PBSeP, the above
calculations. With increasing heteroatom sizes (O < S < Se), the torsion angle even grows and splits into two: 39.9º and 51.6º,
torsions between heteroatom rings and the adjoining pyrimidines rendering the molecule asymmetric. Comprehensively, the larger
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torsion angles and longer N-X bonds result in deterioration of Figure 5 (a, b, c) displays the surface morphologies of compounds
aromaticity and weaken the conjugation among donor and acceptor PBOP, PBTP and PBSeP, indicating good film-forming property with
units. The larger torsion angle will also hinder the closer contact of root-mean-square (RMS) surface roughness of 2.2, 4.4 and 5.0 nm,
neighbouring backbone, thus the intermolecular π-π interactions respectively. The films of PBOP and PBTP showed the formation of
will be attenuated even though the molecular packing keeps larger grain-like domains (Figure S4). PBSeP film exhibited fiber-like
unchanged. Thus it is evident that although of the almost the same domains, which might be produced from molecules aggregation in
crystal structure, PBOP is of the best π-π interaction, demonstrating solution. According to the AFM phase images as shown in Figure
the single atom substitution effect.
5(d, e, f), we found that compounds PBOP and PBTP displayed
homogeneous and continuous films while PBSeP film exhibited
partial phase separation. As previously noted, the more severe
Morphology of the thin films
Since the film morphology has a considerable impact on the phase segregation and rougher surface of the PBSeP film
18a, 22a
efficiency of optoelectronic devices,
we obtained the presumably arose because of poor solubility and interchain π−π
topographies of the thin film by atomic force microscopy (AFM). stacking of PBSeP molecule. 23
Figure 5. Tapping-mode AFM images (5μm × 5μm): topography image and phase image of the films of PBOP (a, d), PBTP (b, e), and PBSeP (c, f).
because of the energy barrier between the donor (D) and
Proposed memory mechanisms
acceptor-1 (A1), which blocks the electron migration. When
To gain insight into the electrical switching behaviour of the
the external voltage rises to the first Vths, the shallow traps
memory devices, theoretical calculations have been performed
from pyrimidine acceptors will be filled, switching the storage
using the density functional theory (DFT) method of B3LYP
cell from OFF to ON1 state. With increasing the applied electric
with the 6-31G (d) basis set. The result shows that the
field, the traps arising from the benzochalcogendiazole unit
molecular surface has continuous positive molecular
will be filled up sequentially, resulting in the current transition
electrostatic potential (ESP, in red, Figure S5), which can serve
from the ON1 to the ON2 state. The energy levels of the
as open channels for charge carrier migration throughout the
HOMO and LUMO for the memory devices are summarized in
conjugated backbone. The negative ESP regions (in blue)
Figure 6b. The energy barriers between the work function of
caused by the electron-deficient groups, such as pyrimidine
ITO and HOMO are all lower than the energy barriers between
and benzochalcogendiazole segments, can serve as “traps”
the work functions of Al and LUMO. Thus, holes-migration
with different energetic depths to block the motion of charge
should dominate the conduction process in three compounds-
carriers. Figure 6a shows a schematic diagram of the charge
based devices. Upon undergoing the HOMO to LUMO
transport process in the ternary memory device. Under a low
excitation, intramolecular charge transfer could form a charge-
voltage bias, the device is in a low-conductivity (OFF) state
separated state, the trapped electrons are hard to de-trapped
6 | J. Name., 2012, 00, 1-3
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after turning off the power or under reverse voltage, and the planarity and enhanced intermolecular π–π stacking resulting
formative charge-separated state will not revert to the pristine in tighter face-on packing orientation which correlated with
state and the high-conductivity could be permanently good charge transport properties. Therefore, the fabricated
maintained. Therefore, the device exhibits WORM behavior. 4
PBOP-devices exhibit improved ternary memory performances
Apparently in these systems, oxygen containing heterocycle with the lowest switching threshold voltages and highest Ion/Ioff
device shows significantly lower threshold voltages compared the ratios. These results imply that benzooxadiazole-based
other two. This distinction can be ascribed to the better planarity of compounds can serve as a predominant choice of material for
benzooxadiazole based molecular backbone, which guarantees a organic multilevel data storage device.
stronger interchain π−π stacking and ordered face-on packing
orientation. These advances benefit the formation of free charge
Acknowledgements
transport pathways, making PBOP-based device a promising
candidate for high performance OMD applications.
This work was financially supported by the Chinese Natural
Science Foundation (21176164, 21206102, 21476152 and
21336005), the NSF of Jiangsu Province (BE2013052).Suzhou
Nano-project (ZXG2012023) and the Project supported by the
Specialized Research Fund for the Doctoral Program of Higher
Education of China (Grant no.20113201130003 and
20123201120005) and National Excellent Doctoral Dissertation
funds (201455).
Author contributions
Zhaojun Liu synthesized the molecules and was involved in
devices measurements. Jinghui He executed the simulation
calculations. Jianmei Lu and Hua Li conceived the molecular
design and supervised the whole experiments. All authors
contributed to the scientific discussion, writing and revision of
the manuscript.
Notes and references
1
(a) Y. S. Liu, C. C. Chen, Z. R. Hong, J. Gao, Y. Yang, H. P. Zhou, L.
T. Dou, G. Li, Y. Yang, Sci. Rep. 2013, 3, 3356. (b) A. K. K. Kyaw,
D. H. Wang, D. Wynands, J. Zhang, T. Q. Nguyen, G. C.Bazan, A.
J. Heeger, Nano Lett. 2013, 13, 3796. (c) Y. S. Liu, Y. Yang, C. C.
Chen, Q. Chen, L. T. Dou, Z. R. Hong, G. Li, Y. Yang. Adv. Mater.
2013, 25, 4657. (d) H. W. Lin, J. H. Chang, W. C. Huang, Y. T. Lin,
L. Y . Lin, F. Lin, K. T. Wong, H. F. Wang, R. M . Ho, H. F. Meng. J.
Mater. Chem. A, 2014, 2, 3709.
2
(a) Y. C. Mei, M. A. Loth, M. Payne, W. M. Zhang, J. Smith, C. S.
Day, S. R. Parkin, M. Heeney, L. McCulloch, T. D. Anthopoulos,
J. E. Anthony, O. D. Jurchescu, Adv. Mater. 2013, 25, 4352. (b) J.
Y
.
Figure 6. a) HOMO orbital, LUMO orbital, and molecular ESP from DFT
calculations. Schematic diagram of the charge carrier transport process in
the FKAZO 2-based memory device. b) LUMO and HOMO energy levels for
the three molecules, calculation based on CV.
Zhou, Y. Zuo. X. J. Wan, G. K. Long, Q. Zhang, W. Ni, Y. S. Liu, Z.
Li, G. R. He, C. X. Li, B. Kan, M. M. Li, Y. S. Chen, J. Am. Chem.
Soc. 2013, 135, 8484. (c) M. M.. Torrent, C. Rovira, Chem. Soc.
Rev. 2008, 37, 827. (d) K. Y. Chi, H. W. Hsw, S. H. Tung, C. L. Liu,
ACS Appl. Mater. Interface., 2015, 7, 5663. (e) J. B. Giguuere, N.
S. Sariciftci, J. F. Morin, J. Mater. Chem. C, 2015, 3, 601. (f) T.
Takahashi, S. Tamura, Y. Akiyama, T. Kadoya, T. Kawamoto, T.
Mori, Appl. Phys. Express. 2012, 5, 061601.
(a) B. R. Baker, R. Y. Lai, M. S. Wood, E. H. Doctor, A. J. Heeger,
K. W. Plaxco, J. Am. Chem. Soc., 2006, 128, 3138. (b) J. M. Zhou,
W. Shi, N. Xu, P. Cheng, Inorg. Chem. 2013, 52, 8082. (c) M. H.
Zheng, M. M. Zhang, H. H. Li, J. Y. Jin, J. Fluoresc., 2012, 22,
1421.
Conclusions
In conclusion, a series of benzochalcogendiazole containing
molecules (PBOP, PBTP and PBSeP) have been synthesized and
fabricated to memory devices. These compounds stacking in
the same crystal structures, thus clearly demonstrating the
effect of a single atom substitution on the electrochemical, UV
absorption, film morphology, and the molecular packing
performance of the system. Among these molecules, the
oxygen-containing conjugated backbone allows for increased
3
4
(a) 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. (b) 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. (c) S. F. Miao, H. Li, Q. F. Xu, Y.
This journal is © The Royal Society of Chemistry 20xx
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ARTICLE
Journal Name
Y. Li, S. J. Ji, N. J. Li, L. H. Wang, J.W. Zheng and J. M. Lu, Adv.
Mater., 2012, 24, 6210. (d) H. Zhuang, Q. J. Zhang, Y. X. Zhu, X.
Koppe, P. Denk, C. Waldauf, A. J. Heeger, C. J. Brabec, Adv.
Mater.,2006, 18, 789.
F. Xu, H. F.Liu, N. J. Li, Q. F. Xu, H. Li, J. M. Lu and L. H. Wang, J. 16 (a) A. Patra , Y. H. Wijsboom , S. S. Zade , M. Li , Y. Sheynin ,
Mater. Chem. C, 2013, 1, 3816. (e) G. Wang, S. F. Miao, Q. J.
Zhang, H. F. Liu, H. Li, N. J. Li,Q. F. Xu, J. M. Lu, L. H. Wang.
Chem. Commun. 2013, 28, 947. (f) P. Y. Gu, F. Zhou, J. K. Gao, G.
G. Leitus , M. Bendikov, J. Am. Chem. Soc. 2008 , 130 , 6734. (b)
J. Hou, M. H. Park, S. Zhang, Y. Yao, L. M. Chen, J. H. Li, Y. Yang,
Macromolecules., 2008, 41, 6012.
Li, C. Y. Wang, Q. F. Xu, Q. C. Zhang, J. M. Lu, J. Am. Chem. Soc., 17 (a) J. H. Hou, T. L. Chen, S. Q. Zhang, H. Y. Chen, Y. Yang, J. Phys.
2013, 135, 14086. (g) Z. J. Liu, E. B. Shi, Y. Wan, N. J. Li, D. Y.
Chen, Q. F. Xu, H. Li, J. M. Lu, K. Q. Zhang, L. H. Wang, J. Mater.
Chem. C, 2015, 3, 2033
Chem. C., 2009, 113, 1601. (b) J. H. Kim, J. B. Park, S. A. Shin, M.
H. Hyun, D. H. Hwang, Polymer., 2014, 55, 3605. (c) A. Cihaner,
F. Algi, Adv. Funct. Mater., 2008, 18, 3583.
5
(a) Y. L. Shang, Y. Q. Wen, S. L. Li, S. X. Du, X. B. He, L. Cai, Y. F. 18 (a) J. Warnan, A. E. Labban, C. Cabanetos, E. T. Hoke, P. K.
Li, L. M. Yang, H. J. Gao, Y. L. Song, J. Am. Chem. Soc., 2007, 129,
11674. (b) C. Q. Ye, Q. Peng, M. Z. Li, J. Luo, Z. M. Tang, J. Pei, J.
M. Chen, Z. G. Shuai, L. Jiang and Y. L. Song, J. Am.
Chem. Soc., 2012, 134, 20053; (c) S. J. Liu, P. Wang, Q. Zhao, H.
Y. Yang, J. Wong, H. B. Sun, X. C. Dong, W. P. Lin and W. Huang,
Adv. Mater., 2012, 24, 2901. (d) G. Li, K. Zhang, C. Y. Wang, K.
Shukla, C. Risko, J. L. Bredas, M. D. McGehee, P. M. Beaujuge,
Chem. Mater. 2014, 26, 2299. (b) H. W. Lin, W. Y. Lee,; C. Lu, C.
J. Lin, H. C. Wu, Y. W. Lin, B. Ahn, Y. Rho, M. Ree, W. C. Chen,
Polym. Chem., 2012, 3, 767. (c) W. H. Lee, S. K. Son, K. Kim,; S.
K. Lee, W. S. Shin, S. J. Moon, I. N. Kang, Macromolecules.,
2012, 45, 1303.
S. Leck, F. Z. Hu, X. W. Sun, Q. C. Zhang, ACS Appl. Mater. 19 (a) A. Yassin, P. Leriche, M. Allain, J. Roncali, New J. Chem.,
Interfaces., 2013, 5, 6458.
2013, 37, 502. (b) J. Zhang, G. L. Wu, C. He, D. Deng, Y. F. Li, J.
Mater. Chem., 2011, 21, 3768. (c) W. Ni, X. Q. Wan, M. M. Li, Y.
C. Wang, Y. S. Chen, Chem. Commun., 2015, 51, 4936.
6
7
(a) S. Moller, C. Perlov, W. Jackson, C. Taussig, S. R. Forrest,
Nature., 2003, 426, 166. (b) J. C. Scott and L. D. Bozano, Adv.
Mater. , 2007, 19, 1452.
(a) Y. S. Park, T. S. Kale, C.-Y. Nam, D. Choi and R. B. Grubbs.,
Chem. C ommun., 2014, 50, 7964. (b) G. L. Gibson, D. Gao, A. A.
Jahnke, J. Sun, A. J. Tilley, D. S. Seferos, J. Mater. Chem. A, 2014,
20 (a) W.-Y. Lee, T. Kurosawa, S.-T. Lin, T. Higashihara, M. Ueda,
W.-C. Chen, Chem. Mater., 2011, 23, 4487. (b) M. Hagiri, N.
Ichinose, C. Zhao, H. Horiuchi, H. Hirtasuka, T. Nakayama,
Chem. Phys. Lett., 2004, 391, 297.
2, 14468. (c) B. Nicolas, M. Alexandre, G. David, W. Salem, 21 J. M. Jiang, P. A. Yang, T. H. Hsieh, K. H. Wei, Macromolecules
B. Emily, N. P. Rodica, B. Michel, D. Gilles, T. Ye, L. Mario, J. Am. 2011, 44, 9155.
Chem. Soc., 2008, 130, 732. (d) J. Soloducho, J. Cabaj, K. 22 (a) J. Rivnay, S. C. B. Mannsfeld, C. E. Miller, A. Salleo, M. F.
Olech, P. Data, M. Lapkowski, Curr. Org. Chem,.2013, 17, 283.
(a) A. Yassin, P. Leriche, M. Allain, J. Roncali, New J. Chem.,
2013, 37, 502. (b) J. Zhang, G. L. Wu, C. He, D. Deng, Y. F. Li, J.
Mater. Chem., 2011, 21, 3768. (c) W. Ni, X. Q. Wan, M. M. Li, Y.
C. Wang, Y. S. Chen, Chem. Commun., 2015, 51, 4936.
Toney, Chem. Rev. 2012, 112, 5488. (b) M. S. Chen, J. R. Niskala,
D. A. Unruh, C. K. Chu, O. P. Lee, J. M. J. Frechet, Chem. Mater.
2013, 25, 4088. (c) T. L. Nelson , T. M. Young , J. Y. Liu , S. P.
Mishra , J. A. Belot , C. L. Balliet , A. E. Javier , T. Kowalewski , R.
D. McCullough, Adv. Mater. 2010, 22, 4617. (d) V. S. Gevaerts,
E. M. Herzig, M. Kirkus, K. H. Hendriks, M. M. Wienk, J. Perlich,
P. M. Buschbaum, R. A. J. Janssen, Chem. Mater. 2014, 26, 916.
8
9
(a) P. M. Beaujuge, S. Ellinger, J. R. Reynolds, Nat. Mater. 2008,
7, 795. (b) Q. Peng, K. Park, T. Lin, M. Durstock, L. Dai, J. Phys.
Chem. B., 2008, 112, 2801. (c) P. M. Beaujuge, W. Pisula, H. N. 23 (a) A. Patra, Y. H. Wijsboom, S. S. Zade, M. Li, Y. Sheynin, G.
Tsao, S. Ellinger, K. Müllen, J. R. Reynolds, J. Am. Chem. Soc.
2009, 131, 7514.
Leitus, M. Bendikov, J. Am. Chem. Soc., 2008, 130, 6734. (b) J.
Hou, T. L. Chen, S. Zhang, H. Y. Chen, Y. Yang, J. Phys. Chem. C.,
2009, 113, 1601. (c) W. Zhao, W. Cai, R. Xu, W. Yang, X. Gong,
H. Wu, Y. Cao, Polymer., 2010, 51, 3196.
10 (a) W. Elsawy, H. Kang, K. Yu, A. Elbarbary, K. Lee, J. S. Lee, J.
Polym. Sci., Part A: Polym. Chem. 2014, 52, 2926. (b) B. A.
Coombs, B. D. Lindner, R. M. Edkins, F. Rominger, A. Beeby, U.
H. F. Bunz, New J. Chem., 2012, 36, 550. (c) S. Q. Zhang, L.
Ye,W.C Zhao, D. L. Liu, H. F. Yao, J. H. Hou,
Macromolecules, 2014, 47, 4653.
11 (a) G. L. Gibson, T. M. McCormick, D. S. Seferos, J. Am. Chem.
Soc., 2012, 134, 539. (b) P. Elena, Z. Natalia, P. Asit, R. Yonatan,
B. Michael, J. Am. Chem. Soc., 2014, 136, 5138. (c) P. B. Pati, S.
P. Senanayak, K. S. Narayan, S. S. Zade, ACS Appl. Mater.
Interfaces., 2013, 5, 12460. (d) S. Das, P. B. Pati, S. S. Zade,
Macromolecules, 2012, 45, 5410.
12 (a) M. Zhang, H. N. Tsao, W. Pisula, C. Yang, A. K. Mishra, K.
Mullen, J. Am. Chem. Soc. 2007, 129, 3472 −3473. (b) J. K. Lee,
M. C. Gwinner, R. Berger, C. Newby, R. Zentel, R. H. Friend, H.
Sirringhaus, C. K. Ober, J. Am. Chem. Soc. 2011, 133, 9949. (c) Y.
Lin, H. Fan, Y. Li, X. Zhan, Adv. Mater. 2012, 24, 3087.
13 (a) D. S. Chung, H. Kong, W. M. Yun, H. Cha, H.K. Shim,; Y.H.
Kim, C. E. Park, Org. Electron., 2010, 11, 899. (b) S. Das,; S. S.
Zade, Chem. Commun., 2010, 46, 1168. (c) S. Haid, A. Mishra, C.
Uhrich, M. Pfeiffer, P. Bauerle, Chem. Mater., 2011, 23, 4435.
14 (a) J. M. Jiang, P. A. Yang, H. C. Chen, K. H. Wei, Chem.
Commun., 2011, 47, 8877. (b) P. Ding, C. Zhong, Y. Zou, C. Pan,
Wu, H.; Cao, Y. J. Phys. Chem. C., 2011, 115, 16211. (c) J. M.
Jiang, P. Raghunath, H. K. Lin, Y. C. Lin, M. C. Lin, K. H. Wei,
Macromolecules., 2014, 47, 7070.
15 (a) B. Zhang, X. Hu, M. Wang, H. Xiao, X. Gong, W. Yang, Y. Cao,
New J. Chem., 2012, 36, 2042. (b) Z.G. Zhang, J. Wang, J. Mater.
Chem., 2012, 22, 4178. (c) M. C. Scharber, D. Muhlbacher, M.
8 | J. Name., 2012, 00, 1-3
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Journal of Materials Chemistry C
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Effect of single atom substitution in Benzochalcogendiazole
Acceptors on the performance of ternary Memory Devices
Zhaojun Liu, Jinghui He, Hao Zhuang, Hua Li,* Najun Li, Dongyun Chen, Qingfeng
Xu, Keqin Zhang, Jianmei Lu,* and Lihua Wang,
Table of Contents
Novelty: Ternary memory storage performances of three Benzooxadiazoleꢀderivatives based
devices clearly demonstrate the effect of a single atom substitution from oxygen to sulfur,
selenium on the molecular planarity, πꢀπ stacking, film morphologies and device threshold
voltages.