Switching behaviour of stilbene molecular device: a first-principles study
The switching behaviour of stilbene molecular system (SMS) device is investigated with the help of non-equilibrium Green’s function (NEGF) approach using first principles calculation. The transmission spectrum of cisisomers confirmed that more electrons are transferred across the SMS-device using op...
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nasplib_isofts_kiev_ua-123456789-1574662025-02-09T17:09:31Z Switching behaviour of stilbene molecular device: a first-principles study Перемикальна поведiнка стильбенового молекулярного пристрою: дослiдження з перших принципiв Nagarajan, V. Chandiramouli, R. The switching behaviour of stilbene molecular system (SMS) device is investigated with the help of non-equilibrium Green’s function (NEGF) approach using first principles calculation. The transmission spectrum of cisisomers confirmed that more electrons are transferred across the SMS-device using optical excitation by the spin of C=C bond by torsion angle (θ = 180◦ ). The current-voltage characteristics show the lower magnitude of current for trans-stilbene and higher magnitude of current for cis-stilbene for an externally applied bias voltage. The outcome of the proposed work suggests that cis and trans-stilbene molecular device can be used as a switch. Перемикальна поведiнка пристроїв, що працюють на основi стильбенової молекулярної системи (SMS) дослiджується з використанням методу нерiвноважних функцiй Грiна та першопринципних розрахункiв. Спектр трансмiсiї cis-iзомерiв пiдтвердив, що бiльша кiлькiсть електронiв переходить через SMS-пристрiй, використовуючи оптичне збудження спiном зв’язку C=C на торсiйний кут (θ = 180◦ ). Вольт-ампернi характеристики вказують на iснування нижчих величин струму для trans-стильбенових пристроїв та вищих величин струму для cis-стильбенових пристроїв при накладаннi зовнiшньої змiщувальної напруги. В результатi проведеної роботи доведено, що cis i trans-стильбеновий пристрiй можна використовувати в якостi перемикача. The authors wish to express their sincere thanks to Nano Mission Council (No. SR/NM/NS1011/2017(G)) Department of Science & Technology, India for financial support. 2018 Article Switching behaviour of stilbene molecular device: a first-principles study / V. Nagarajan, R. Chandiramouli // Condensed Matter Physics. — 2018. — Т. 21, № 4. — С. 43301: 1–12 . — Бібліогр.: 52 назв. — англ. 1607-324X PACS: 33.15.Mt, 61.43.Bn, 61.46.Bc, 78.20.Bh DOI:10.5488/CMP.21.43301 arXiv:1812.08532 https://nasplib.isofts.kiev.ua/handle/123456789/157466 en Condensed Matter Physics application/pdf Інститут фізики конденсованих систем НАН України |
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The switching behaviour of stilbene molecular system (SMS) device is investigated with the help of non-equilibrium Green’s function (NEGF) approach using first principles calculation. The transmission spectrum of cisisomers confirmed that more electrons are transferred across the SMS-device using optical excitation by the
spin of C=C bond by torsion angle (θ = 180◦
). The current-voltage characteristics show the lower magnitude
of current for trans-stilbene and higher magnitude of current for cis-stilbene for an externally applied bias
voltage. The outcome of the proposed work suggests that cis and trans-stilbene molecular device can be used
as a switch. |
| format |
Article |
| author |
Nagarajan, V. Chandiramouli, R. |
| spellingShingle |
Nagarajan, V. Chandiramouli, R. Switching behaviour of stilbene molecular device: a first-principles study Condensed Matter Physics |
| author_facet |
Nagarajan, V. Chandiramouli, R. |
| author_sort |
Nagarajan, V. |
| title |
Switching behaviour of stilbene molecular device: a first-principles study |
| title_short |
Switching behaviour of stilbene molecular device: a first-principles study |
| title_full |
Switching behaviour of stilbene molecular device: a first-principles study |
| title_fullStr |
Switching behaviour of stilbene molecular device: a first-principles study |
| title_full_unstemmed |
Switching behaviour of stilbene molecular device: a first-principles study |
| title_sort |
switching behaviour of stilbene molecular device: a first-principles study |
| publisher |
Інститут фізики конденсованих систем НАН України |
| publishDate |
2018 |
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https://nasplib.isofts.kiev.ua/handle/123456789/157466 |
| citation_txt |
Switching behaviour of stilbene molecular device: a first-principles study / V. Nagarajan, R. Chandiramouli // Condensed Matter Physics. — 2018. — Т. 21, № 4. — С. 43301: 1–12
. — Бібліогр.: 52 назв. — англ. |
| series |
Condensed Matter Physics |
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2025-11-28T11:09:59Z |
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| fulltext |
Condensed Matter Physics, 2018, Vol. 21, No 4, 43301: 1–12
DOI: 10.5488/CMP.21.43301
http://www.icmp.lviv.ua/journal
Switching behaviour of stilbene molecular device: a
first-principles study
V. Nagarajan, R. Chandiramouli∗
School of Electrical and Electronics Engineering, SASTRA Deemed University,
Tirumalaisamudram, Thanjavur— 613 401, India
Received May 21, 2018, in final form August 29, 2018
The switching behaviour of stilbene molecular system (SMS) device is investigated with the help of non-equilib-
rium Green’s function (NEGF) approach using first principles calculation. The transmission spectrum of cis-
isomers confirmed that more electrons are transferred across the SMS-device using optical excitation by the
spin of C=C bond by torsion angle (θ = 180◦). The current-voltage characteristics show the lower magnitude
of current for trans-stilbene and higher magnitude of current for cis-stilbene for an externally applied bias
voltage. The outcome of the proposed work suggests that cis and trans-stilbene molecular device can be used
as a switch.
Key words: stilbene, molecular device, electron density, switching, transmission
PACS: 33.15.Mt, 61.43.Bn, 61.46.Bc, 78.20.Bh
1. Introduction
Photochromes, generally represented as molecular switches, allow tuning their functional properties,
which arose due to their molecular structure through excitation of a light source of suitable wavelengths.
Thus, themolecules can be inter-converted reversibly among the twometastable isomers as a consequence
of photocyclization, i.e., cis
trans isomerization or combination of both. Among the most significant
photochromes, azobenzene, stilbene, and their derivatives exhibit reversible photo-induced cis
trans
isomerization. Moreover, thermodynamically trans-isomer is more stable than cis form [1]. Optical
excitation developed by rotation of N=N (C=C) double bond in azobenzene (stilbene) or C inversion in
stilbene drives the photoisomerization. Azobenzene isomers and its derivatives can be thermally initiated
for cis→trans reaction. However, in the case of stilbenoid isomers, the thermal-back reaction is not
feasible, because the activation barrier is noticed to be higher by the order of 1.9 eV [2] compared to
azobenzenes (1 eV) [3]. The switching behaviour of stilbene highly depends on the structure of both
stilbene conformations (cis and trans). The switching properties of stilbene from trans to cis switching
is observed by ultraviolet irradiation (340–400 nm), whereas cis form to trans switching is noticed with
the exposure of visible radiation (400–500 nm) [2]. The lifetime for excitation of cis and trans form is
noticed to be around 300 fs and 10–100 ps, respectively. In addition, the energy barrier of cis and trans
conformations in the gas phase has been found experimentally to be < 0.05 eV and 0.15 eV, respectively.
Nowadays, much effort has been taken by researchers toward molecular switches owing to their
potential application in nanotechnology including information storage and developing adaptive surfaces
[4]. The primary goal of the future applications is to control and understand the geometrical variations of
molecular switches, such as stilbenes and azobenzenes adsorbed on the surface of a solid substrate. For
this reason, it is essential to gather a detailed knowledge regarding the electronic structure (occupied and
unoccupied orbitals) and the adsorption structure (molecular orientation) of the molecules in contact with
solid substrates. Many researchers, particularly, Kaloni group, have extensively studied the structural and
∗Corresponding author
This work is licensed under a Creative Commons Attribution 4.0 International License . Further distribution
of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
43301-1
https://doi.org/10.5488/CMP.21.43301
http://www.icmp.lviv.ua/journal
http://creativecommons.org/licenses/by/4.0/
V. Nagarajan, R. Chandiramouli
electron properties of organic polymers, especially polythiophene, to be utilized for future optical and
electronic devices [5–10].
Photochromic molecules can experience reversible photo-triggered isomerization among the two
meta-stable states. Recently, a larger quantity of photochromic molecules have been synthesized and de-
signed, includingE/Z isomerization, cycloadditions, valence isomerization and tautomerizations.Usually,
the photochromic molecules can be segregated into numerous classes based on their type of chemical
process concerned [11]: (1) photo-induced bond cleavages, namely perchlorotoluene; (2) pericyclic reac-
tions, such as electrocyclizations, such as oxazines/-spiropyrans, cycloaditions, diarylethenes and fulgides
in aromatic compounds; (3) electron transfers; (4) intramolecular group/hydrogen transfer such as poly-
cyclic and anilsquinones; (5) E/Z isomerizations including stilibenes, azobenzenes and so on. Among
these photochromic molecules, the extensively used are stilbenes [12], diarylethenes [13], azobenzenes
[1] and oxazines/-spiropyrans [14]. Moreover, oxazines/-spiropyrans, stilbenes and azobenzenes can be
switched between the possible two isomers either thermally or photochemically, whereas the diarylethenes
can be reverted either electrochemically or photochemically. The functionalization of carbon-dependent
materials with photochromic molecules is an extensively used technique to observe their capability to
respond towards light stimuli at particular wavelengths. Furthermore, the photochromic isomers adopt
various significant properties on a single molecule, which leads to considerably diverse macroscopic
properties at the ensemble level [15]. Thus, the decoration of carbon-dependent materials along with
photochromic moieties to regulate local changes in the electrostatic, mechanical, optical environment
through a light source input has shown great interest in the subject of materials science, physics and
chemistry.
Leyssner et al. [16] reported themolecular switches onAu(111) electrodes and compared the switching
properties of stilbene and azobenzene derivatives. Zhang and co-workers [17] proposed the optical
response of photochromic molecules with the coupling of carbon nanomaterials. Gutierrez et al. [18]
reported the transport properties of cis/trans stilbenoid with a carbon-based molecular system using DFT
technique. DFT is a significant technique to explore the electronic properties of an organic molecule,
which can be investigated at the atomistic level. The inspiration behind the proposed study is to investigate
the molecular switching behaviour of trans and cis isomers of stilbene, which are sandwiched amongst
Au(111) electrodes in order to investigate the transport characteristics.
2. Computational methods
In this work, the electron transport property of SMS device is investigated using NEGF and DFT
approach executed in TranSIESTA utility in SIESTA package [19]. So far, the NEGF technique has
been utilized to explore the coherent transport via molecular device [20]. It infers that the quantum-
mechanical-phase provides a coherent transfer of electrons between two electrodes, via the molecular
region. Nevertheless, the NEGF approach is also a promising technique for phonon scattering and
determining the external parameters, magnetic field for instance. All structural optimization in the present
work is carried out by adjusting the gridmesh cut-off and vacuum slab about 550 eV and 16Å, respectively.
The full geometrical optimization was performed with the help of conjugate gradient technique until the
Hellmann-Feynman force was perfectly converged to 0.02 eV/Å. In addition, the integration of Brillouin-
zone for a stilbene molecular system is sampled with (10 × 10 × 10) Γ-centered Monkhorst-pack k-grid
[21]. The electron-electron interaction on SMS-device is determined using a prominent GGA/PBE
exchange correlation functional [22, 23]. TranSIESTA also explores the switching mechanism of the
stilbene molecular device with Troullier-Martins (TM) norm-conserving pseudopotentials scheme [24].
In the present study, double zeta polarization (DZP) basis set is used for Au(111) electrode and for
stilbene molecules, during structural relaxation [25, 26]. The electronic transport characteristics of a
stilbene molecular system are studied using a two-probe method [27]. In the present model, the electrode
consists of three Au(111) layers. In this stilbene molecule device, we adopted a supercell size of 3 × 3
with a lattice constant of 19.634 Å. The stilbene 2-probe system is a bare system, the right-hand and left-
hand gold-electrode region comprises three layers of gold (111) with 3 × 3 surface atoms, that replicate
periodically, which forms the infinite Au-electrode. The stilbene-electrode distance is fixed to be constant
for all the system after the energy convergence of the stilbene molecular system, the axial distance of
43301-2
Investigation on stilbene molecular system device
Au-S varies from 1 to 5 with a minimum step variation of 0.1 Å. Finally, the total energies of the stilbene
molecule scattering region (MSR) for a 3-supercell system are computed, and the minimum value is
observed at 2.35 Å for both Au-left-hand and Au-right-hand electrodes. The methods are similar to those
used in the literature [28], which use nanostructures such as carbon nanotubes and boron nanotubes.
Along the stilbene molecular device, an external bias voltage (Vb) is applied along the right-hand-Au and
left-hand-Au electrodes for the current flow.
3. Results and discussion
3.1. Structure of SMS device
The two conformers of stilbene, namely ‘trans’ and ‘cis’, are bonded to the gold electrodes. The
stilbene photochromic molecules are bonded with gold electrodes through sulphur atoms. In general,
noble metals, namely platinum or gold, can be utilized as electrodes, which also possess a good ohmic
contact. Further, theAu-electrode is oriented along (111) plane. To investigate the transport characteristics
of stilbene based two-probe device, DFT with NEGF method is used as demonstrated by Brandbyge and
co-workers [29]. The method mainly depends on the two-probe device under applied bias condition. In
the present study, the two-probe stilbene device consists of two Au-electrodes on both left and right sides
of the scattering region and central scattering region, which include a small portion of the Au-electrodes
and stilbene molecule. At the initial stage, the electronic properties of both right-hand and left-hand
Au-electrodes are computed to get a corresponding self-consistent potential (SCP), which offers the
real-space boundary (RSB) conditions to the stilbene molecule scattering region (MSR). Moreover, from
the Green’s function (GF) of stilbene MSR, the density matrix along with electron density is found. This
stepwise procedure is repeated until the desired SCP is achieved. Further, the current flowing along the
stilbene MSR can be determined from the corresponding self-energies and GF by Landauer-Büttiker
formalism for the proposed stilbene molecular device. The stilbene molecule has properly merged to two
similar semi-infinite Au(111) electrodes, as shown in figure 1. For both isomers, namely trans and cis
of stilbene, the current transferring over the SR is investigated within the voltage range of 0.1–1.2 V.
Besides, for higher bias voltages, the stilbene SR gets damaged resulting in an open circuit. Therefore,
the applied externalVb is limited to 1.2 V and the response is conversed in the present work. The potential
difference between Au-left-hand (+V/2) and Au-right-hand (−V/2) is kept across the stilbene molecular
Figure 1. (Colour online) The pictorial representation of cis-stilbene molecular device (θ = 180◦).
Figure 2. (Colour online) The pictorial representation of trans-stilbene molecular device (θ = 0◦).
43301-3
V. Nagarajan, R. Chandiramouli
system. Interestingly, the changes in geometry and the applied external bias voltage of photochromic
organic molecules influence the charge transmission and density of states (DOS) spectrum along SMS
device. Figures 1 and 2 illustrate the pictorial representation of SMS switching device in ON (θ = 180◦)
state and OFF (θ = 0◦) state, respectively.
3.2. Device density of states (DDOS) spectrum of SMS device
To understand the electronic properties of stilbene in depth, DOS spectrum gives a clear picture
about the charge density for various energy intervals under the applied external bias voltage [30, 31].
Moreover, stilbenoid and stilbenes organic compounds exhibit photochemical cis-trans isomerization.
Thus, stilbene also serves as building blocks for organic compounds, whose properties can be utilized
in electro-optics and optical applications including nonlinear optics, optical data storage [32]. The
DDOS spectrum provides a perception on charge localization in SMS-device. Furthermore, based on
the conformers (cis or trans), the charge localization varies upon the applied external bias voltage. The
switching properties of stilbene are mainly related to the geometry of each stilbene organic molecules.
The switching behaviour of stilbene from cis to trans form is observed by the exposure of visible radiation
(400–500 nm) [33], whereas trans form to cis switching is noticed with the ultraviolet irradiation (340–
400 nm) [2]. The main objective of the present study is to model the photoisomerization along with
its response coordinate described by the torsion angle around the central C=C bond [34]. In general,
isomerization mechanism may be observed from two significant models: (1) conventional one-bond flip
(OBF) model, the substituents of the C=C bond transfer along the cone surface, (2) hula-twist (HT) [34]
model, only the C=H group rotates out of plane and the remaining parts reorient within the plane. After
excitation, the trans isomer transforms to cis stilbene upon the shining ultraviolet radiation, the C=C bond
twists by 180◦, and an excitation energy (S1) minimum at a normal conformer (P∗) is observed for both cis
and trans isomers [35]. In order to leave the fluorescent region on both excitation trans∗ and cis∗ isomers
towards P∗, the organic molecules should overcome a very small barrier. The lifetime for excitation of
trans population is observed between 10 to 100 ps based on the excess energy [36] and for cis photo-exited
population 300 fs [37]. Further, the energy barrier of an initial geometry of trans and cis stilbene in the gas
phase has been found experimentally about 0.15 eV [38] and < 0.05 eV [39], respectively. The switching
behaviour along the stilbene arises owing to the distribution of free electrons in C=C, the free electrons in
two sides of trans isomer transfer to one side in cis isomer upon the exposure to the radiation of ultraviolet
light. Precisely, the two π-conjugated arms of stilbene by-products participate in the switching amongst
cis and trans isomers. Interestingly, the variation in electronic structures is noticed to be significant on
both trans and cis photoisomerization. Therefore, the free lone pair of electrons of C=C is engaged in
the variation of DOS. The electron density (ED) of cis and trans SMS-device at zero bias condition is
displayed in figures 3 and 4, respectively.
The electron density is noticed to be high beside the Au-electrodes regions owing to its metallic-
nature. Nevertheless, in SR-region, the electron density is detected to be low. Furthermore, on changing
the external Vb through the π-conjugated isomers, the ED varies upon the applied external Vb. Besides,
Figure 3. (Colour online) The electron density of cis-stilbene molecular device.
43301-4
Investigation on stilbene molecular system device
Figure 4. (Colour online) The electron density of trans-stilbene molecular device.
the changes inVb along SMS device result in the variation of the charge density across energy intervals. In
this work, the changes in DOS spectrum are noticed only beyond an external bias voltage value of 0.1 V,
which is proved through the considerable changes in the charge density. Moreover, a significant change in
output current is observed only within the Vb range of 0.1 to 1.2 V; beyond 1.2 V, the stilbene MSR gets
damaged. Moreover, the Fermi level energy (EF) is kept at zero, the bias window among Au-left-hand
and Au-right-hand electrode is adjusted to +V/2 and −V/2 in a stilbene molecular system. Figures 5 and
6 refer the DOS-spectrum of SMS device in ON (cis) and OFF (trans) states, respectively. Diligently,
Figure 5. (Colour online) The device density of states (DDOS) spectrum of cis-stilbene molecular device.
43301-5
V. Nagarajan, R. Chandiramouli
Figure 6. (Colour online) The device density of states (DDOS) spectrum of trans-stilbene molecular
device.
the orbital overlapping of stilbene hydrocarbons bonded between phenyl rings and Au atoms results in a
peak maximum (Pmax) and is detected on both the valence band (VB) and on the conduction band (CB).
Moreover, the switching between cis and trans isomers is noticed upon the exposure to UV radiation due
to a bond flip process across C=C, with twisting of phenyl rings to 180◦ along the surface of a cone.
Besides, when the SMS device is in ON (cis) state, the Pmax is observed near CB. When Vb is set to
0.1 V, the Pmax is noticed around 1.12 eV at CB. Upon increasing the external bias voltage between
the Au-left-hand and Au-right-hand electrodes, the Pmax are detected in both CB as well as in VB with
a peak shift owing to the variation in the highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO). Furthermore, for higher voltages, peak maxima are noticed at
higher energy intervals on both VB and CB. It is inferred that in cis isomers of a stilbene molecular
device, the external bias voltage leads to a charge delocalization in various energy intervals.
The variation in HOMO-LUMO orbitals along the SMS device arises owing to the one-bond flip
mechanism of C=C bond in phenyl ring with respect to the Au-electrodes. Further, the variation in LUMO
and HOMO molecular orbitals is observed at higher bias voltages, which infers that the applied external
Vb drives the density of charge along the SMS-device. For trans-isomers (OFF) condition, the charge
density is less, which is revealed from the decrease in peak maxima in CB of DOS-spectrum as shown in
figure 6.
The torsion barrier for trans-isomers is reported to be around 3 kcal/mol [40]. In the present work,
more peaks are detected and the peak shift in different energy intervals is noticed in the conduction band
of cis-isomers (ON) state of SMS device rather than of trans-isomers (OFF) state. Therefore, the charge
density along the stilbene molecular system changes with the help of the applied Vb and the spin of the
photochromic molecule through a desired angle in different conformations.
43301-6
Investigation on stilbene molecular system device
3.3. Transport properties of SMS device
The electronic transport characteristics of SMS device can be illustrated with the help of transmission
spectrum (TS) [41–43] The transport properties of SMS device are explored using TranSIESTA utility in
SIESTA code. The current flowing through the stilbene molecular device is given by Landauer-Büttiker
formula [44]
I =
2e
h
−∞∫
+∞
T (E,Vb) [ fL (E − µL) − fR (E − µR)] dE, (3.1)
T(E,Vb) = Tr[ΓL(E)GR(E)ΓR(E)GA(E)], (3.2)
where µL and µR illustrates the chemical potential (CP) of Au-left-hand and Au-right-hand electrodes,
respectively. fL and fR refer to the electronic Fermi functions of the Au-left-hand and Au-right-hand
electrodes, respectively. Vb is the applied external bias voltage of Au-left-hand and Au-right-hand elec-
trodes [45]. T(E,Vb) refers to transmittance of a stilbene molecular system at the bias voltage Vb and
energy level E [46]. ΓL,R is referred to as a coupling function of left-hand and right-hand self-energies,
respectively. The corresponding retarded and advanced Green’s function has been utilized to find the
transmission of the stilbene molecular device and it is denoted by GR and GA. The expansion of each
term including transmittance and CP on the above equations (3.1) and (3.2) is clearly discussed in our
previously reported work [1, 30]
If Vb is set to zero voltage, the transmission energy at Fermi level T(EF) provides the conductance
G = G0 T(EF), whereG0 = (2e2)/h is the unit of quantum conductance [29, 47]. The orbital delocalization
along the stilbene molecular system directs to enhance the concentration of free electrons, where it is
noticed on particular peak amplitudes Pamp in the transmission spectrum of SMS device [48–51]. The
conductance G is explored for various lengths of Au-electrodes. The conductance of stilbene at EF
decreases exponentially as the gold electrodes length increases. An exponential decrease of conductance
with an increasing length of an electrode has been reported in the literature [52]. Therefore, a suitable
length of Au-electrode must be selected to explore the transport characteristics of a stilbene device.
Further, the applied external Vb acts as a driving force along the stilbene device, which results in the
shift of the peak amplitudes on both CB and VB. Figures 7 and 8 refer to the transmission spectrum of
Figure 7. (Colour online) The transmission spectrum of stilbene device in cis state.
43301-7
V. Nagarajan, R. Chandiramouli
Figure 8. (Colour online) The transmission spectrum of stilbene device in trans state.
SMS device in cis state and trans state, respectively. The variations in the geometrical structure introduce
the deviation in molecular dipole. Moreover, for cis-SMS device, for the applied external Vb, the Pamp is
noticed in VB and CB with a higher amplitude. In addition, an increase in Vb pushes the charges through
the stilbene molecule, that is why the peak shifts are noticed in the transmission spectrum of cis-SMS
device. Nevertheless, observing the transmission spectrum of trans-stilbene device, almost all the peaks
are noticed nearer to the Fermi energy level and in the valence band with lower peak amplitudes.
From the observation, it is precisely inferred that a greater peak shift and high amplitudes are
noticed in CB of 180◦ phase variation of SMS device rather than in 0◦ phase shift of SMS device.
The photoisomerization can be stimulated by optical excitation of a prominent wavelength of visible
radiation (cis→ trans) and UV radiation (trans→ cis) owing to C inversion. Thus, it is evident that the
concentration of electrons across the cis-stilbene is high, which facilitates the electronic transport across
the scattering region. Furthermore, the charge transmission in different energy intervals upon increasing
Vb is noticed via the shift in Pamp. From the outcome, it is clearly proved that the variation in transmission
spectrum along the stilbene molecular system device arose due to the one-bond flip mechanism of C=C
bond in the phenyl ring. For trans-isomers, the transfer of electrons across the stilbene junction is less,
which is proved by a decrease of peak amplitude on both VB and CB of the transmission spectrum
as depicted in figure 8. Moreover, the variation in the transmission spectrum between the cis and trans
conformers is governed by the fact that there is a potential barrier of around 3 kcal/mol [40] for torsion
angle (θ = 0◦) in trans-isomer. On the other hand, there is a much less barrier noticed for cis-isomer
[39]. From the observation of transmission spectrum, it is precisely proved that the Vb applied across the
phenyl ring with a desired torsion angle governs the transition of electrons along SMS device.
3.4. Current-voltage characteristics of stilbene molecular device
The I−V characteristics provide a perception on the switching properties of cis-SMS and trans-SMS
device. Figure 9 refers to the I−V characteristics of trans and cis isomers of stilbene device.
As mentioned above, the current for the applied Vb of stilbene device is given by Landauer-Büttiker
expression from equation. The current passing over the scattering region in stilbene is noticed to be
favorable for cis-SMS device. Besides, the cis→trans isomerization occurs spontaneously owing to the
43301-8
Investigation on stilbene molecular system device
Figure 9. (Colour online) The I−V characteristics of trans and cis isomers of stilbene device.
lack in energy barrier. Nevertheless, substituents in stilbene may convert cis isomer optically more stable
than trans isomer upon optical excitation. The current flowing through the cis conformation in stilbene
device is comparatively larger than the trans-conformation in stilbene device as noticed in figure 9. The
question arises why the trans-isomer has a lower magnitude of current than cis isomer? This is due to
the existance of a low energy barrier (< 0.05 eV) [39] noticed for cis-isomer, whereas the trans-isomer
has the barrier of 3 kcal/mol [40], where the electrons flowing across the scattering region must cross
this barrier. Thus, the current flowing through the trans stilbene device is found to be of lower magnitude
than cis stilbene device. At low bias voltages (0.1–0.5 V), there is no significant current flow through
the device observed both for cis and trans isomer. Beyond 0.5 to 1.2 V, the current transient through the
stilbenemolecular device is found to be significant. How cis and trans conformers can be used as a switch?
From the results of current-voltage characteristics, for cis configuration, the magnitude of current is of
the order of microampere for the applied Vb of 1.2 V. However, the current flowing to trans configuration
of stilbene device is only of the order of nanoampere. Thus, using a proper signal conditioning circuit,
the magnitude can be discriminated and can be used as a switch. Moreover, the higher applied bias
facilitates the transition across the stilbene scattering region. A drastic variation in the current between
the cis and trans configuration can be demonstrated with the help of charge transfer between the HOMO
and LUMO levels. Moreover, the variation of current in the stilbene molecular junction is influenced
by HOMO-LUMO levels of stilbene conformers and the gold electrodes. Based on the torsion angle
θ, the junction barrier differs. As discussed earlier, there is a negligible value of barrier found for the
torsion angle (θ = 180◦) in cis-isomer, but for trans-isomer, the barrier is observed with a reported
value of 3 kcal/mol [40]. Previously we have demonstrated the switching properties of cis-trans isomer
of azobenzene molecular device [1]. Leyssner and co-worker [16] demonstrated the molecular switches
adsorbed on Au(111) and compared the switching behaviour of azobenzene and stilbene derivatives.
This further confirms and validates the switching properties of stilbene with the present research work.
Therefore, it is clearly proved that cis and trans-SMS device can be utilized as a switching element.
Figure 10 gives the insights on the switching behaviour of cis and trans stilbene molecular device.
The stilbene isomerization is mainly utilized for varying supramolecular geometry and domains.
Upon visible or ultraviolet irradiation, the cis and trans configuration can be changed in the stilbene
device. Thus, we may induce a phase change, a solubility change, surface activity of a surfactant, and
the critical micelle concentration can be varied upon shining a particular wavelength of radiation on
stilbene molecule. Moreover, it can be recommended that stilbene molecular device should be utilized
as a photo-switch as well as may be used for different potential applications including photo-actuation,
lithographic patterning and optical switches.
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V. Nagarajan, R. Chandiramouli
Figure 10. (Colour online) The insights on the switching behaviour of cis and trans stilbene molecular
device.
4. Conclusions
In conclusion, the switching behaviour of a stilbene molecular system device is investigated using
DFT and NEGF technique. The scattering region of stilbene single molecule encompasses cis and trans
isomers of stilbene, and its switching properties are investigated. The DDOS spectrum of trans isomer
reveals less peak maxima than cis isomer of a stilbene device. By contrast, the Pmax in cis isomer is
observed to be high in both the conduction band and in the valence band, which arise owing to the rotation
of the torsion angle of C=C bond (θ = 180◦). The transmission spectrum also proves the presence of a
higher peak amplitude in cis-stilbene molecular device (ON state) compared to the trans-stilbene device
(OFF state). The current-voltage characteristics reveal a closed configuration of a cis-stilbene molecular
device. The magnitude of current flowing though the cis stilbene device is found to be higher than the
trans stilbene device. The findings of the proposed research work verify the switching behaviour of SMS
device, which is investigated at an atomistic level. Besides, a stilbene based molecular system can have a
variety of potential applications including photo-actuation and optical switches.
Acknowledgements
The authors wish to express their sincere thanks to Nano Mission Council (No. SR/NM/NS-
1011/2017(G)) Department of Science & Technology, India for financial support.
References
1. Dhivya G., Nagarajan V., Chandiramouli R., Chem. Phys. Lett., 2016, 660, 27, doi:10.1016/j.cplett.2016.07.061.
2. Meier H., Angew. Chem. Int. Ed., 1992, 31, 1399, doi:10.1002/anie.199213993.
3. Tamai N., Miyasaka H., Chem. Rev., 2000, 100, 1875, doi:10.1021/cr9800816.
4. Balzani V., Credi A., Venturi M., ChemPhysChem, 2008, 9, 202, doi:10.1002/cphc.200700528.
5. Kaloni T.P., Giesbrecht P.K., Schreckenbach G., Freund M.S., Chem. Mater., 2017, 29, 10248,
doi:10.1021/acs.chemmater.7b03035.
43301-10
https://doi.org/10.1016/j.cplett.2016.07.061
https://doi.org/10.1002/anie.199213993
https://doi.org/10.1021/cr9800816
https://doi.org/10.1002/cphc.200700528
https://doi.org/10.1021/acs.chemmater.7b03035
Investigation on stilbene molecular system device
6. Kaloni T.P., Schreckenbach G., Freund M.S., Sci. Rep., 2016, 6, 36554, doi:10.1038/srep36554.
7. Kaloni T.P., Schreckenbach G., Freund M.S., J. Phys. Chem. C, 2015, 119, 3979, doi:10.1021/jp511396n.
8. Mehmood U., Al-Ahmed A., Hussein I.A., Renewable Sustainable Energy Rev., 2016, 57, 550,
doi:10.1016/j.rser.2015.12.177.
9. Dediu V., Murgia M., Matacotta F.C., Taliani C., Barbanera S., Solid State Commun., 2002, 122, 181,
doi:10.1016/S0038-1098(02)00090-X.
10. Majumdar S., Laiho R., Laukkanen P., Väyrynen I.J., Majumdar H.S., Österbacka R., Appl. Phys. Lett., 2006,
89, 122114, doi:10.1063/1.2356463.
11. Bouas-Laurent H., Dürr H., Pure Appl. Chem., 2001, 73, 639, doi:10.1351/pac200173040639.
12. Oudar J.L., J. Chem. Phys., 2008, 67, 446, doi:10.1063/1.434888.
13. Tian H., Yang S.J., Chem. Soc. Rev., 2004, 33, 85, doi:10.1039/b302356g.
14. Lukyanov B.S., Lukyanova M.B., Chem. Heterocycl. Compd., 2005, 41, 281, doi:10.1007/s10593-005-0148-x.
15. Klajn R., Chem. Soc. Rev., 2014, 43, 148, doi:10.1039/C3CS60181A.
16. Leyssner F., Hagen S., Óvári L., Dokić J., Saalfrank P., Peters M.V., Hecht S., Klamroth T., Tegeder P., J. Phys.
Chem. C, 2010, 114, 1231, doi:10.1021/jp909684x.
17. Zhang X., Hou L., Samorì P., Nat. Commun., 2016, 7, 11118, doi:10.1038/ncomms11118.
18. Gutiérrez R., Grossmann F., Schmidt R., ChemPhysChem, 2003, 4, 1252, doi:10.1002/cphc.200300768.
19. Soler J.M., Artacho E., Gale J.D., García A., Junquera J., Ordejón P., Sánchez-Portal D., J. Phys.: Condens.
Matter, 2002, 14, 2745, doi:10.1088/0953-8984/14/11/302.
20. Taylor J., Guo H., Wang J., Phys. Rev. B, 2001, 63, 121104(R), doi:10.1103/PhysRevB.63.121104.
21. Monkhorst H.J., Pack J.D., Phys. Rev. B, 1976, 13, 5188, doi:10.1103/PhysRevB.13.5188.
22. Perdew J.P., Burke K., Wang Y., Phys. Rev. B, 1996, 54, 16533, doi:10.1103/PhysRevB.54.16533.
23. Perdew J.P., Chevary J.A., Vosko S.H., Jackson K.A., Pederson M.R., Singh D.J., Fiolhais C., Phys. Rev. B,
1992, 46, 6671, doi:10.1103/PhysRevB.46.6671.
24. Troullier N., Martins J.L., Phys. Rev. B, 1992, 46, 1754, doi:10.1103/PhysRevB.46.1754.
25. Bhuvaneswari R., Nagarajan V., Chandiramouli R., Chem. Phys. Lett., 2018, 691, 37,
doi:10.1016/j.cplett.2017.10.058.
26. Nagarajan V., Dharani S., Chandiramouli R., Comput. Theor. Chem., 2018, 1125, 86,
doi:10.1016/j.comptc.2018.01.004.
27. Nagarajan V., Bhattacharyya A., Chandiramouli R., J. Mol. Graphics Modell., 2018, 79, 149,
doi:10.1016/j.jmgm.2017.11.009.
28. Pomorski P., Roland C., Guo H., Phys. Rev. B, 2004, 70, 115408, doi:10.1103/PhysRevB.70.115408.
29. Brandbyge M., Mozos J.-L., Ordejón P., Taylor J., Stokbro K., Phys. Rev. B, 2002, 65, 165401,
doi:10.1103/PhysRevB.65.165401.
30. Bhuvaneswari R., Nagarajan V., Chandiramouli R., Chem. Phys., 2018, 501, 78,
doi:10.1016/j.chemphys.2017.12.003.
31. Nagarajan V., Chandiramouli R., IEEE Sens. J., 2018, 18, No. 3, 948, doi:10.1109/JSEN.2017.2781728.
32. Evans C.H., Reynisson J., Geirsson J.K.F., Kvaran Á., McGimpsey W.G., J. Photochem. Photobiol., A, 1998,
115, 57, doi:10.1016/S1010-6030(98)00243-3.
33. Hub W., Schneider S., Doerr F., Oxman J.D., Lewis F.D., J. Am. Chem. Soc., 1984, 106, 701,
doi:10.1021/ja00315a040.
34. Fuß W., Kosmidis C., Schmid W.E., Trushin S.A., Angew. Chem. Int. Ed., 2004, 43, 4178,
doi:10.1002/anie.200454221.
35. Waldeck D.H., Chem. Rev., 1991, 91, 415, doi:10.1021/cr00003a007.
36. Baskin J.S., Bañares L., Pedersen S., Zewail A.H., J. Phys. Chem., 1996, 100, 11920, doi:10.1021/jp960909x.
37. Fuß W., Kosmidis C., Schmid W.E., Trushin S.A., Chem. Phys. Lett., 2004, 385, 423,
doi:10.1016/j.cplett.2003.12.114.
38. Syage J.A., Felker P.M., Zewail A.H., J. Chem. Phys., 1998, 81, 4706, doi:10.1063/1.447520.
39. Abrash S., Repinec S., Hochstrasser R.M., J. Chem. Phys., 1998, 93, 1041, doi:10.1063/1.459168.
40. Quenneville J., Martínez T.J., J. Phys. Chem. A, 2003, 107, 829, doi:10.1021/jp021210w.
41. Deekshitha M., Nagarajan V., Chandiramouli R., Chem. Phys. Lett., 2015, 641, 129,
doi:10.1016/j.cplett.2015.10.070.
42. Nagarajan V., Chandiramouli R., Solid State Commun., 2018, 269, 50, doi:10.1016/j.ssc.2017.09.023.
43. Nagarajan V., Chandiramouli R., Comput. Theor. Chem., 2017, 1105, 52, doi:10.1016/j.comptc.2017.02.023.
44. Büttiker M., Imry Y., Landauer R., Pinhas S., Phys. Rev. B, 1985, 31, 6207, doi:10.1103/PhysRevB.31.6207.
45. Stokbro K., J. Phys.: Condens. Matter, 2008, 20, 064216, doi:10.1088/0953-8984/20/6/064216.
46. BrandbygeM., SørensenM.R., Jacobsen K.W., Phys. Rev. B, 1997, 56, 14956, doi:10.1103/PhysRevB.56.14956.
47. Taylor J., Guo H., Wang J., Phys. Rev. B, 2001, 63, 245407, doi:10.1103/PhysRevB.63.245407.
43301-11
https://doi.org/10.1038/srep36554
https://doi.org/10.1021/jp511396n
https://doi.org/10.1016/j.rser.2015.12.177
https://doi.org/10.1016/S0038-1098(02)00090-X
https://doi.org/10.1063/1.2356463
https://doi.org/10.1351/pac200173040639
https://doi.org/10.1063/1.434888
https://doi.org/10.1039/b302356g
https://doi.org/10.1007/s10593-005-0148-x
https://doi.org/10.1039/C3CS60181A
https://doi.org/10.1021/jp909684x
https://doi.org/10.1038/ncomms11118
https://doi.org/10.1002/cphc.200300768
https://doi.org/10.1088/0953-8984/14/11/302
https://doi.org/10.1103/PhysRevB.63.121104
https://doi.org/10.1103/PhysRevB.13.5188
https://doi.org/10.1103/PhysRevB.54.16533
https://doi.org/10.1103/PhysRevB.46.6671
https://doi.org/10.1103/PhysRevB.46.1754
https://doi.org/10.1016/j.cplett.2017.10.058
https://doi.org/10.1016/j.comptc.2018.01.004
https://doi.org/10.1016/j.jmgm.2017.11.009
https://doi.org/10.1103/PhysRevB.70.115408
https://doi.org/10.1103/PhysRevB.65.165401
https://doi.org/10.1016/j.chemphys.2017.12.003
https://doi.org/10.1109/JSEN.2017.2781728
https://doi.org/10.1016/S1010-6030(98)00243-3
https://doi.org/10.1021/ja00315a040
https://doi.org/10.1002/anie.200454221
https://doi.org/10.1021/cr00003a007
https://doi.org/10.1021/jp960909x
https://doi.org/10.1016/j.cplett.2003.12.114
https://doi.org/10.1063/1.447520
https://doi.org/10.1063/1.459168
https://doi.org/10.1021/jp021210w
https://doi.org/10.1016/j.cplett.2015.10.070
https://doi.org/10.1016/j.ssc.2017.09.023
https://doi.org/10.1016/j.comptc.2017.02.023
https://doi.org/10.1103/PhysRevB.31.6207
https://doi.org/10.1088/0953-8984/20/6/064216
https://doi.org/10.1103/PhysRevB.56.14956
https://doi.org/10.1103/PhysRevB.63.245407
V. Nagarajan, R. Chandiramouli
48. Chandiramouli R., Nagarajan V., J. Comput. Electron., 2017, 16, 316, doi:10.1007/s10825-017-0956-0.
49. NagarajanV., Chandiramouli R., IEEETrans. Nanotechnol., 2017, 16, 445, doi:10.1109/TNANO.2017.2682125.
50. Nagarajan V., Chandiramouli R., Chem. Phys. Lett., 2017, 675, 131, doi:10.1016/j.cplett.2017.03.031.
51. Nagarajan V., Dhivya G., Chandiramouli R., J. Comput. Electron., 2018, 17, 1, doi:10.1007/s10825-017-1047-y.
52. Zhou Y.H., Zheng X.H., Xu Y., Zeng Z.Y., J. Chem. Phys., 2006, 125, 244701, doi:10.1063/1.2409689.
Перемикальна поведiнка стильбенового молекулярного
пристрою: дослiдження з перших принципiв
В. Нагараджан, Р. Чандiрамулi
Школа електротехнiки та електронiки, унiверситет SASTRA,
Тiрумалайсамудрам, Танджавур— 613 401, Iндiя
Перемикальна поведiнка пристроїв, що працюють на основi стильбенової молекулярної системи (SMS)
дослiджується з використанням методу нерiвноважних функцiй Грiна та першопринципних розрахункiв.
Спектр трансмiсiї cis-iзомерiв пiдтвердив,що бiльша кiлькiсть електронiв переходить через SMS-пристрiй,
використовуючи оптичне збудження спiном зв’язку C=C на торсiйний кут (θ = 180◦). Вольт-ампернi ха-
рактеристики вказують на iснування нижчих величин струму для trans-стильбенових пристроїв та вищих
величин струму для cis-стильбенових пристроїв при накладаннi зовнiшньої змiщувальної напруги. В ре-
зультатi проведеної роботи доведено, що cis i trans-стильбеновий пристрiй можна використовувати в
якостi перемикача.
Ключовi слова: стильбен, молекулярний пристрiй, електронна густина, перемикання, трансмiсiя
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https://doi.org/10.1007/s10825-017-0956-0
https://doi.org/10.1109/TNANO.2017.2682125
https://doi.org/10.1016/j.cplett.2017.03.031
https://doi.org/10.1007/s10825-017-1047-y
https://doi.org/10.1063/1.2409689
Introduction
Computational methods
Results and discussion
Structure of SMS device
Device density of states (DDOS) spectrum of SMS device
Transport properties of SMS device
Current-voltage characteristics of stilbene molecular device
Conclusions
|