Study on synthesis, characterization, and nonvolatile memory behavior of ferrocene-containing metallopolymers

Article abstract of DOI:10.1016/j.jorganchem.2019.04.025

In this work, two metallopolymers (P1 and P2)were designed and synthesized through coupling of ferrocene-anchored fluorene derivatives with porphyrin and benzene based diethynyl ligand, respectively. The chemical structure and physical properties of these two metallpolymers were fully characterized, which indicate that these two metallopolymers are thermally stable and semiconducting. Then, sandwich-like organic resistive memory based on P1 and P2 for data storage were explored. The memory device testing results manifest that both P1 and P2 are of the stable electric bistability and show write once read many times memory (WORM)characteristics.

Full text of DOI:10.1016/j.jorganchem.2019.04.025

Accepted Manuscript
Study on synthesis, characterization, and nonvolatile memory behavior of ferrocene-
containing metallopolymers
Xiaozhe Cheng, Md Asaduzzaman, Hong Lian, Zheng Zhong, Hongen Guo,
Qingchen Dong, V.A.L. Roy
PII:
S0022-328X(19)30095-6
DOI:
https://doi.org/10.1016/j.jorganchem.2019.04.025
JOM 20775
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 13 March 2019
Revised Date: 22 April 2019
Accepted Date: 23 April 2019
Please cite this article as: X. Cheng, M. Asaduzzaman, H. Lian, Z. Zhong, H. Guo, Q. Dong,
V.A.L. Roy, Study on synthesis, characterization, and nonvolatile memory behavior of ferrocene-
containing metallopolymers, Journal of Organometallic Chemistry (2019), doi: https://doi.org/10.1016/
j.jorganchem.2019.04.025.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Study on Synthesis, Characterization, and Nonvolatile Memory
Behavior of Ferrocene-containing Metallopolymers
Xiaozhe Chenga†, Asaduzzaman Mdb†, Hong Liana, Zheng Zhonga, Hongen Guoa,
Qingchen Donga,*, V. A. L. Royb,*
aMinistry of Education Key Laboratory of Interface Science and Engineering in Advanced
Materials, Research Center of Advanced Materials Science and Technology, Taiyuan University
of Technology, Taiyuan 030024, China. Tel/Fax: +86-351-6010311.
bState Key Laboratory for THz and Millimeter Waves and Department of Materials Science &
Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong.
Corresponding author: dongqingchen@tyut.edu.cn; val.roy@cityu.edu.hk
†These people contribute equally to this work.
Abstract
In this work, two metallopolymers (P1 and P2) were designed and synthesized
through coupling of ferrocene-anchored fluorene derivatives with porphyrin and
benzene based diethynyl ligand, respectively. The chemical structure and physical
properties of these two metallpolymers were fully characterized, which indicate that
these two metallopolymers are thermally stable and semiconducting. Then,
sandwich-like organic resistive memory based on P1 and P2 for data storage were
explored. The memory device testing results manifest that both P1 and P2 are of the
stable electric bistability and show write once read many times memory (WORM)
characteristics.
Keywords: metallopolymer; synthesis; characterization; information storage; write
once read many times memory (WORM)
1. Introduction
With the rapid development of economy and technology, human society has
entered into the era of big data. It is reported that there will be over 40 trillion
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gigabytes of data generated by year 2020[1,2]. Therefore, it is very urgent for the
exploration of memory device with high density and specific characteristics, such as
flexible, nonvolatile, high speed, low cost, etc.[3-5] In the past few decades,
traditional inorganic materials especially the silicon-based semiconductors have been
widely studied and applied in the every aspect of human daily life[6]. However,
conventional silicon-based semiconductor devices are encountering severe
downscaling constraints due to the poor data fidelity, heat death, and high cost,
etc.[7,8] Moreover, flexible memories are extremely desired for constructing
e-textiles, which can integrate us into internet electronic systems and facilitate our
daily life[1,9,10]. Nevertheless, silicon-based semiconductor is intrinsically
unsuitable for soft deformation scenario due to its primarily brittle electronic
components. Therefore, design and physical realization of alternative information
storage materials and devices operating on completely different mechanisms have
attracted increasingly wide research interest and attention[11-14]. Among the new
information storage materials and devices, organic materials-based resistive random
access memory (RRAM or resistive switching memory) have been explored as the
promising candidates for next-generation information storage technology, because the
RRAM device has a simple sandwich-like structure with wide range of materials for
selection and diverse switching mechanisms for flexible implementation. Moreover,
diode structure of RRAM provides great potential to integrate into crossbar arrays
with three-dimensional stacking architecture for high storage density.[10,15,16]
Since the first discovery of resistive switching in amorphous oxides in the 1960s,
a wide variety of organic, inorganic, and organic-inorganic hybrid materials have been
explored to display resistive switching features.[1,17,18] Among them, organic
polymer materials have gradually attracted more and more attention and made great
progress because of their structure adjustable, light weight, low-cost fabrication as
well as solution processability on various substrates, especially the soft
substrates.[19,20] For example, Pan et al. successfully synthesized two D-A type
polyazomethine (PAM) derivatives PAM-1 and PAM-2, and explored their memory
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applications by fabricating device through solution processing technology.[21] It is
found that, PAM-1 shows rewritable bipolar resistive switching behavior, whereas
PAM-2 exhibits only WORM resistive switching behavior. Chen and coworkers
reported fabrication a flexible bipolar resistive switching memory with D-A
conjugated polymer (PFT-PI) as a single active layer on plastic polyethylene
naphthalate (PEN) substrate.[22]
Compared with pure organic polymers, metallopolymers exhibit more abundant
chemical and physical properties. In addition, the energy level of molecular orbital
and energy gap can be easily adjusted by changing the metal species and ligand
structures.[23] Ferrocene-containing polymers have become a research hotspot of
metallopolymers due to the well-defined and stable electrochemical property of
ferrocene moiety.[24] Choi and co-workers have reported a ferrocene-containing
conjugated polymer (PFT2-Fc) which exhibits excellent nonvolatile multilevel storage
characteristic due to the stability of ferrocene redox state (Fc3+/Fc2+).[25] Tan and
co-worker demonstrated a nonvolatile write-once-read-many times (WORD) memory
by using four ferrocene-terminated hyperbranched polyimides. It is reported that
switching mechanism was realized by the oxidation from ferrocene to ferrocenium
ions.[26] In 2016, W. Y. Wong and coworkers reported four conjugated polymers by
reacting ferrocene substituted fluorene derivative with four different π–conjugated
aromatic moieties through Sonogashira coupling reaction.[27] It was found that
structures of the main chains based on aromatic components make a huge impact on
the memory device performance.[27,28] Therefore, the memory properties of the
metallopolymers can be finely adjusted by changing the chemical structures of the
backbones. Here, we reported the synthesis of two new conjugated
ferrocene-containing metallopolymers and their organic nonvolatile memory
applications due to the characteristics of electrical bistability.
2. Experimental
2.1 General information
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All reactions were carried out under nitrogen unless otherwise stated.
Commercially available reagents were used as received without further purification.
All reactions were monitored by thin-layer chromatography (TLC) with Merck
pre-coated glass plates. Compounds were visualized with UV light irradiation at 254
and 365 nm. Separation or purification of products was achieved by column
chromatography or preparative TLC using silica gel from Merck (230–400 mesh).
NMR spectra were measured in CDCl3 on Bruker AV 400 or 600 NMR instrument
with chemical shifts being referenced against tetramethylsilane as the internal
1
13
standard for H and C NMR data. IR spectra were recorded on the Nicolet Magna
550 Series II FTIR spectrometer using KBr pellets for solid state spectroscopy.
Thermal analyses were performed with a Perkin-Elmer TGA 6 thermal analyzer. The
molecular weight of the polymer was determined by GPC using a HP 1050 series
HPLC with visible wavelength and fluorescent detectors against polystyrene
standards.
2.2 Synthesis of ferrocene-containing metallopolymers
2.2.1 Preparation of 4-(2-(trimethylsilyl)ethynyl)benzaldehyde (1)
In a 100 mL three-neck flask, 4-bromobenzaldehyde (1.5 g, 8.12 mmol ), CuI (78
mg, 0.41 mmol) and Pd(PPh3)4 (270 mg, 0.23 mmol) were dissolved in solution of
Et3N (50 ml) at 0 oC. The mixture was stirred for 30 min, then trimethylsilylacetylene
(8 mL, 56.6 mmol) were added to the three-neck flask. After reacting for 30 min, the
mixture was heated to reflux for 12 h. The resulting mixture was collected and
concentrated by a rotary evaporator. The crude material was purified by silica gel
column chromatography using a mixture of petrol ether and DCM (v:v = 4:1) as the
1
eluent to obtain the desired product as a yellow solid (785.3 mg, 47.8%). H NMR
(400 MHz, CDCl3, δ/ppm): 10.00 (s, 1H, CHO), 7.85-7.83 (m, 2H, Ar-H), 7.61 (d, J =
8.0 Hz, 2H, Ar-H), 0.27 (s, 9H, TMS); 13C NMR (125 MHz, CDCl3, δ/ppm): 191.71,
135.74, 132.68, 129.66, 129.54, 104.01, 99.24, 77.45, 0.28 (TMS).
2.2.2 Preparation of compound (2)
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In a 250 mL three-neck flask, meso-phenyldipyrromethane[29] (500 mg, 2.25
mmol), 4-((trimethylsilyl)ethynyl)benzaldehyde (455 mg, 2.25 mmol) and TFA (100
µL, 1.25 mmol) were dissolved in solution of DCM (100 mL). The mixture was
stirred for 3 h at room temperature. 2,3-Dicyano-5,6-dichlorobenzoquinone (DDQ)
(1.532 g, 6.75 mmol) were added to the three-neck flask. After reacting for 30 min,
the resulting mixture was collected and concentrated by a rotary evaporator. The
crude material was purified by silica gel column chromatography using a mixture of
petrol ether and DCM (v:v = 4:1) as the eluent to obtain the desired product as a
purple solid (170 mg, 17%). 1H NMR (400 MHz, CDCl3, δ/ppm): 8.81 (d, 8H, J = 8.0
Hz, Ar-H), 8.22-8.18 (m, 8H, Ar-H), 7.86 (d, J = 8.0 Hz, 4H, C=CH), 7.73 (d, J = 8.0
Hz, 6H, Ar-H), 0.38 (s, 18H, TMS), -2.80 (t, J = 8.0 Hz, 2H, N-H).
2.2.4 Preparation of compound (3)
In a 100 mL three-neck flask, compound 2 (100 mg, 0.124 mmol) and K2CO3 (20
mg) were dissolved in solution of DCM (20 mL) and methanol (20 mL). The mixture
was stirred for 12 h at room temperature. The resulting mixture was extracted by
dichloromethane for 3 times, and then the organic phase was collected and
concentrated by a rotary evaporator. The crude material was purified by silica gel
column chromatography using a mixture of petrol ether and DCM (v:v = 4:1) as the
1
eluent to obtain the desired product as a purple solid (60.8 mg, 74%). H NMR (600
MHz, CDCl3, δ/ppm): 8.88 (d, J = 12.3 Hz, 8H), 8.26 – 8.20 (m, 8H), 7.93 (d, J = 7.1
Hz, 4H), 7.79 (d, J = 7.4 Hz, 6H), 3.35 (s, 2H), -2.75 (t, J = 8.3 Hz, 2H). IR (KBr):
3273 (υC≡C-H) cm-1; 2148 (υC≡C) cm-1.
2.2.5 Preparation of 1,4-bis(2-(trimethylsilyl)ethynyl)benzene (4)
The procedure for the preparation of 1,4-bis(2-(trimethylsilyl)ethynyl)benzene (4)
was similar to that for compound 1. The resulting product was obtained as a yellow
solid (1.46 g, 85 %). 1H NMR (600 MHz, CDCl3, δ/ppm): 7.38 (s, 4H), 0.25 (s, 18H).
2.3 Preparation of 1,4-diethynylbenzene (5)
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The procedure for the preparation of 1,4-diethynylbenzene (5) was similar to that
for compound 3. The resulting product was obtained as a purple solid (443.3 mg,
95%). 1H NMR (600 MHz, CDCl3, δ/ppm): 7.44 (s, 4H), 3.17 (s, 2H).
2.3 Preparation of compound (6)
In a 100 mL three-neck flask, 2,7-diiodofluorene (418 mg, 1 mmol),
ferrocenecarboxaldehyde (214 mg, 1 mmol) and KOH (2 g) were dissolved in
solution of methanol (70 mL) under a nitrogen atmosphere. The mixture was heated to
reflux for 3 h. The resulting mixture was extracted by dichloromethane for 3 times,
and then the organic phase was collected and concentrated by a rotary evaporator. The
crude material was purified by silica gel column chromatography using petrol ether as
1
the eluent to obtain the desired product as a red solid (583 mg, 95 %). H NMR (600
MHz, CDCl3, δ/ppm): 8.60 (d, J = 1.4 Hz, 1H), 8.08 (d, J = 1.3 Hz, 1H), 7.68 – 7.64
(m, 2H), 7.45 (t, J = 8.5 Hz, 3H), 4.71 (t, J = 1.8 Hz, 2H), 4.57 – 4.56 (m, 2H), 4.26 –
4.24 (m, 5H).
2.3 Preparation of polymer P1
In a 100 mL three-neck flask, compound 3 (100 mg, 0.151mmol) and compound 6
(92.6 mg, 0.151 mmol) were dissolved in solution of THF (20 mL) and NEt3 (20 mL),
followed by addition of CuI (2 mg) under a nitrogen atmosphere. The mixture was
allowed to stir at room temperature for 24 h. Afterwards the solvent was removed by
evaporation and the mixture was redissolved in a small amount of DCM (5 mL) and
reprecipitated with the addition of methanol. Centrifugation was done to give a
residual solid. The ferrocene-based metallopolymer P1 was isolated as a red solid
(180 mg, 94%). IR (KBr): 2193 (υC≡C) cm-1. GPC (THF): Mw = 2782, Mn = 1986,
Mw/Mn = 1.40.
2.3 Preparation of polymer P2
Polymer P2 was synthesized by reaction of compound 5 (20 mg, 0.151mmol)
and 6 (92.6 mg, 0.151 mmol). The preparation procedure is similar to that for P1. The
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final product was obtained as a red solid (105 mg, 96%). IR (KBr): 2203 (υC≡C) cm-1.
GPC (THF): Mw = 4143, Mn = 3821, Mw/Mn = 1.08.
3 Results and discussion
3.1 Synthesis and characterization of the target metallopolymer
Scheme 1. Synthetic route of targeted metallopolymers P1 and P2.
The synthetic routes of the target ferrocene-containing metallopolymers P1 and
P2 were displayed in scheme 1. The key intermediate of porphyrin derivative with
diethynyl terminal groups was synthesized in the same way as reported by our
group.[30] 1,4-dibromobenzene was used as starting material to generate the other
diethynyl intermediate 5 through the similar synthetic reactions for compound 3.
Finally, the diethynyl derivatives 3 and 5 were allowed to couple with the
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ferrocene-containing diiodofluorene compound 6 through the Sonogashira coupling
reaction to provide ferrocene-containing metallopolymers P1 and P2, respectively. All
these polymerization reactions proceeded with satisfactory yields and purified by
repeated precipitation in a small amount of DCM from methanol for 2-3 times. The
resulting polymers were well characterized by NMR, IR, GPC and TGA.
3.2 Optical and thermal properties
The optical features of P1 and P2 were investigated by UV-Vis absorption
spectroscopy. Fig. 1 shows the normalized absorption spectra of the
ferrocene-containing metallopolymers obtained in dichloromethane at room
temperature. The intense absorption peaks of the porphyrin-coupled polymer are
located at 417 nm, which is assigned to the π → π* (S0 → S2) transition.[31] While
the benzyl-coupled polymer exhibits four sets of absorption peaks at 264, 320, 350
and 505 nm, respectively. The absorption peaks at around 264 nm correspond to the
electronic transitions of the moiety of benzene in the conjugated polymer chains,
while the peaks at around 320, 350 and 505 nm are assigned to the
ferrocene-containing fluorene unit, which further proved the successful Sonogashira
polycondensation.[27]
Fig. 1. Absorption spectra of P1 and P2 in dichloromethane solution at room
temperature.
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The thermal stabilities of P1 and P2 were investigated by thermogravimetric
o
o
analyses (TGA), which were performed by heating them to 900 C at a rate of 10 C
min-1 under a nitrogen atmosphere. The decomposition temperature (Td) of P1 and P2
o
are 320 and 407 C, respectively with a weight loss of 5% (as shown in Fig. 2). The
relative high decomposition temperature of P2 may be attributed to its more rigid
backbone structure. The high thermal stability is beneficial for long operating lifetime
of the corresponding memory devices.
o
Fig. 2. TGA plots of P1 and P2 with a heating rate of 10 C min-1 under N2
atmosphere.
Table 1. The physical properties of metallopolymers P1 and P2.
UV-vis (nm)a
b
Eg
Eox(onset)c HOMOd/LUMOe
f
Polymers
Tg (oC)
(eV)
(V)
(eV)
λmax
417
264
λedge
443
505
2.86
2.06
0.57
0.58
-4.97/-2.17
-4.98/-2.92
320
407
P1
P2
a Measured in THF;
b Estimated from onset of the absorption spectra (Eg = 1240/λonset).
c Measured from cyclic voltammetry.
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d Calculated from cyclic voltammetry.
e Calculated by the equation EHOMO = ELUMO –Eg.
f Measured by TGA.
3.3 Electrochemical properties
To understand the electrochemical properties of P1 and P2 these two
ferrocene-containing metallopolymers bearing different aromatic backbones, cyclic
voltammetry (CV) measurements of P1 and P2 were undertaken in anhydrous
dichloromethane (0.1 M tetra(n-butyl)ammoniumhexafluorophosphate as the
supporting electrolyte; scan rate: 100 mV s-1) , with SCE reference electrode
(ferrocene/ferrocenium (Fc/Fc+) redox couple as the external standard), a
glassy-carbon working electrode and a platinum-wire counter electrode. The
onset oxidation potentials of P1 and P2 were measured to be 0.57 and 0.58 eV,
respectively, from the cyclic voltammograms (as displayed in Fig. 3). The
HOMO values for P1 and P2 were calculated to be -4.97 and -4.98 eV by the
equation of EHOMO = -(Eox(onset) + 4.4) eV. According to the formula ELUMO
HOMO + Eg, the corresponding LUMO values of P1 and P2 were determined to
be -2.17 and -2.92 eV.[31]
=
E
Fig. 3. Cyclic voltammograms of P1 and P2 in dichloromethane with
tetra(n-butyl)ammoniumhexafluorophosphate (0.1 M) as the supporting
electrolyte for the oxidation scan.
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3.4 Metallopolymer based organic memory devices
3.4.1 Device preparation
The polymer solutions were prepared by dissolving P1 and P2 (40 mg/mL) in
o
1,2-dichlorobenzene (DCB). The resulting solution was stirred for 1h at 60 C for
obtaining a well-dissolved solution. Fig. 4 shows the device structure
(Au/Polymer/ITO/Glass) of resistive memory devices. To obtain better
reproducibility and higher surface coverage, ITO (indium tin oxide) coated glass
substrate was used as a bottom electrode for all the devices. For device fabrication,
ITO coated glass substrates were successively cleaned in ultrasonic baths of
Decon-90, acetone and deionized water for at least 30 min. The polymer solutions
were filtered through a 0.2 µm PTFE membrane and spin coated on ITO coated glass
substrates at 1000 rpm for 40 sec followed by baking the substrate at 110 oC for 1 h.
The thickness of the films was about 120 nm for P1, and 80 nm for P2 measured via
Ellipsometer. After that, Au-electrodes were deposited by thermal evaporation of 80
nm thick onto the polymer layer through a shadow mask at a rate of 0.1 Ao s-1 to
create memory cells with an area of 1.96×10-4 cm2. The resulting devices based on
P1 and P2 were recorded as Device1 and Device2, respectively.
Fig. 4. Schematic of polymer film sandwiched between Au and ITO electrodes.
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3.4.2 Organic memory behaviors
The current-voltage (I-V) curves of nonvolatile resistive memory devices are
shown in Fig. 5 (a, b). The devices exhibit typical resistance switching characteristics
under a direct voltage sweeping mode. The applied voltage is varied in a cycle from 0
V to +5 V to 0 V to –5 V to 0 V with compliance current of 1 mA. During the first
voltage sweep from 0 V to 5V, the devices initially possess a high resistance state
(HRS). These devices switch from HRS to low resistance state (LRS) at 2.5 V for
Device1, and 1.5 V for Device2 follows stage I, respectively, as a result, current
increase abruptly (9.3551×10-4 to 0.03095 for Device1 and 9.1217×10-4 to 0.0011 for
Device2) follows stage II, corresponds to the SET process. When the voltage is swept
back from 5 V to 0 V (stage III), the device kept at LRS. It is observed that the
devices remain in its LRS state (SET process) during the subsequent negative voltage
sweep stages (stage IV (0 V to -5 V) and stage V (-5 V to 0V)), representing that the
data cannot be erased after the writing process. Therefore, both Device1 and Device2
show write once read many times memory (WORM) characteristics, which exhibit
stable non-volatile memory property with unipolar switching from HRS to LRS and
the ON/OFF current ratios in the order of <102. The good stability in the LRS state is
observed when the voltage swept (5 V to 0V to -5V) from stage III to stage IV
representing the data cannot be erased after the writing process. The most significant
features of these devices are the low resistance states does not go back to high
resistance state by applying the subsequent negative voltage sweeps (Stage IV and
Stage V) Therefore, these devices reveal WORM memory effect. The detailed device
performances were summarized in Table 2. By analysis from the above CV curves, it
can be learnt that P2 shows higher peak current and larger slope (1.26 A and 7.24 for
P1; 2.05 A and 15.7 for P2), implying its better reactivity and faster electron transfer
kinetics.[27] Moreover, the LUMO energy level of P2 is relatively lower than that of
P1. The higher reactively, faster electron transfer kinetics as well as lower LUMO
energy level of P2 contribute to the lower threshold voltage of the ON state of
Device2. All above results indicate that the device based on polymer P1 and P2
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behave as a write-once read many-times (WORM) device.
Fig. 5. The I-V curves of the RS behaviors of the Au/polymer/ITO WORM memory
device. (a) Device1 and (b) Device2.
Table 2. Summary of memory performance.
Device
Device1
Device2
Memory property
ON/OFF Ratioa
ON Voltagea
(Vset)
OFF Voltage
(Vreset
)
WORM
--
27.29
1.89 V
1.54 V
(Read voltage = +1 V)
55.73
WORM
--
(Read voltage = +0.5 V)
aThe error in ON/OFF ratio and ON voltage represents the standard deviation of the
mean.
We also analyzed device-to-device reproducibility by measuring the set voltage
for 40 devices for P1 and P2. Fig. 6a and 6b show the histogram of switch-on voltage
for these two polymer WORM devices. The fabricated memory devices show
nonvolatile low transition voltage with ON/OFF ratio <102. The standard deviation of
the mean in the switch-on voltages of these devices is 1.89±0.061 V for P1 and
1.54±0.050 V for P2. These data validate control over device-to-device as well as
cycle-to-cycle stability.
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Fig. 6. Variation of ON voltages in (a) P1 and (b) P2 based RRAM devices.
3.4.3 Theoretical calculations
The electrical bistability of both P1 and P2 are mainly due to the well-known unique
reversible and stable redox property of ferrocene, namely, both ferrocene (Fe2+) and
its oxidized form ferrocenium (Fe3+) are extremely stable. This lays the foundation of
nonvolatile memory property of the as-prepared ferrocene-containing
metallopolymers. To gain deep insights into the memory behavior of P1 and P2,
theoretical electrostatic potential (ESP) were calculated by using density functional
theory (DFT) molecular simulations. Fig. 7 shows the calculated ESP of P1 and P2. It
can be found that, the molecule surface has a continuous positive ESP (in red) along
the conjugated backbone, indicating that a channel is formed from the molecular
surface throughout the polymer backbone. This continuous channel is beneficial for
the migration of charge carriers along the polymer backbone. Moreover, there are also
negative ESP regions (in sky-blue) formed due to the electron-acceptor groups, which
can serve as “traps” to impede the mobility of the charge carriers.[32] Therefore, the
conjugated backbones of the polymers benefit for the transportation of charge carriers
and regulate the threshold voltage of the ON state of memory devices.
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Fig. 7. Molecular simulation results for ESP surfaces of P1 and P2
.
4. Conclusions
In conclusion, we designed and synthesized two ferrocene-containing
metallopolymers P1 and P2 in which ferrocene is covalently linked to the fluorene
moiety as the side chain. Their structure, molecular weights, thermal and
electrochemical properties and memory behaviors were fully characterized. The I-V
characteristics of memory devices indicated the stable electric bistability of both P1
and P2. Both two memory devices show WORM memory characteristics, which
exhibit stable non-volatile memory property with unipolar switching from HRS to
LRS and the ON/OFF current ratios in the order of <102. Further modification and
optimization of materials and devices are still in progress.
Acknowledgements
We acknowledge the financial support from the National Natural Science
Foundation of China (Grant No.: 61774109). This work was also supported by
the Youth “Sanjin” Scholar Program, the Key R&D Project of Shanxi Province
(International cooperation program, No. 201603D421032), and the Natural
Science Foundation for Outstanding Young Scientists of Shanxi Province,
China (Grant No.: 201801D211007).
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Highlights
ò Two new ferrocene-based metallopolymers were designed and synthesized.
ò Nonvolatile Memory Behaviors of the ferrocene-based metallopolymers were
investigated.