Contribution of stilbene-imine additives on the structural, ionic conductivity performance and theoretical evaluation on CMC-based biopolymer electrolytes

Article abstract of DOI:10.1016/j.carbpol.2020.116935

New solid biopolymer electrolytes (SBEs) were prepared by integrating stilbene-imine derivatives bearing vinylene (–CH[dbnd]CH–) and azomethine (–CH[dbnd]N–) as additives in carboxymethyl cellulose (CMC) based electrolyte. The investigation on their spectroscopic and theoretical assessments were conducted to alter the energy level in improving the structural and ionic conductivity performance. The simulated results from frontier molecular orbitals (FMO) and Mulliken-charge analysis revealed that -CF₃ and -NO₂ substituents significantly reduce the HOMO-LUMO gap up to 0.68 eV. The highest ionic conductivity of SBEs achieved at ambient temperature was ～8 × 10^?3 Scm^-1 upon the addition of additive, obeying an Arrhenius model with reciprocal of temperature (303 K–373 K). The coordination interaction of C–O bond and CH[dbnd]N band facilitated the dissociation of more cation (H⁺) of NH₄Cl which permits alternative route for H⁺ to hop into coordinating site in CMC. The outcomes are ideal in the development of electrochemical devices.

Full text of DOI:10.1016/j.carbpol.2020.116935

Carbohydrate Polymers 250 (2020) 116935
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Contribution of stilbene-imine additives on the structural, ionic
conductivity performance and theoretical evaluation on CMC-based
biopolymer electrolytes
,
,
Rafizah Rahamathullaha b, Wan M. Khairula *, M.I.N Isac
a Advanced Nano Materials (AnoMa), Faculty of Science and Marine Environment, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia
b Faculty of Engineering Technology, Universiti Malaysia Perlis, Level 1, Block S2, UniCITI Alam Campus, Sungai Chuchuh, Padang Besar, 02100, Perlis, Malaysia
c Energy Storage Research, Frontier of Materials Research Group, Advanced Materials Team, Ionic & Kinetic Materials Research (IKMaR) Laboratory, Faculty of Science
and Technology, Universiti Sains Islam Malaysia, Bandar Baru Nilai, 71800, Nilai, Negeri Sembilan, Malaysia
A R T I C L E I N F O
A B S T R A C T
Keywords:
New solid biopolymer electrolytes (SBEs) were prepared by integrating stilbene-imine derivatives bearing
–
–
–
–
Stilbene-imine
Additive
–
–
–
vinylene ( CH CH ) and azomethine ( CH
N ) as additives in carboxymethyl cellulose (CMC) based
–
electrolyte. The investigation on their spectroscopic and theoretical assessments were conducted to alter the
energy level in improving the structural and ionic conductivity performance. The simulated results from frontier
molecular orbitals (FMO) and Mulliken-charge analysis revealed that -CF3 and -NO2 substituents significantly
reduce the HOMO-LUMO gap up to 0.68 eV. The highest ionic conductivity of SBEs achieved at ambient tem-
perature was ~8 × 10ꢀ 3 Scm-1 upon the addition of additive, obeying an Arrhenius model with reciprocal of
DFT
Carboxymethyl cellulose
Solid polymer electrolyte
–
–
temperature (303 K–373 K). The coordination interaction of C O bond and CH N band facilitated the disso-
–
ciation of more cation (H+) of NH4Cl which permits alternative route for H+ to hop into coordinating site in CMC.
The outcomes are ideal in the development of electrochemical devices.
1. Introduction
based on different polymers such as poly(vinyl alcohol) (PVA),
polyacrylamide-co-acrylic acid (PAAC), poly(ethylene oxide) (PEO) and
Recently, the development of polymer electrolyte (PE) has attracted
enormous interest both in academia and industry as it provides prom-
ising prospect in application of advanced electrochemical energy de-
vices such as, dye-sensitized solar cell, supercapacitor, batteries, and
sensors (Ngai, Ramesh, Ramesh, & Juan, 2016; Singh et al., 2016;
Zhang, Liu, Cui, & Chen, 2015). In this context, PE plays an important
building block components that can be utilized as ionic conductors
(Ahmed & Abdullah, 2020; Youcef et al., 2020), separator in a battery
for short circuit prevention (Yue et al., 2016; Zhang, Zhao et al., 2015)
and regeneration of the oxidized dye molecules (Careem, Aziz, & Bur-
aidah, 2017) which consequently affect the performance of the devices.
Owing to this interest, many research works have been focused on the
benefits of the modification with different approach and implementa-
tion of various type of PEs, including reviews on solid polymer elec-
trolytes (SPEs) to attain good efficiencies and performances. For
instance, (Kumaran et al., 2018; Tan, Ramesh, & Liew, 2019) studied the
performance of electrochemical application for polymer electrolytes
to name a few. In recent years, Zhou, Shanmukaraj, Tkacheva, Armand,
& Wang, 2019 reviewed the non-flammable electrolyte systems to
include solid all-solid state for Li metal batteries.
In these sense, solid biopolymer electrolytes (SBEs) offer more
practical and convenient to use over liquid and gel electrolytes which
can give good mechanical stability, flexibility, lightweight, leakage free
and higher operating temperature (Singh et al., 2016; Su’ait, Rahman, &
Ahmad, 2015; Zhao et al., 2020). On top of that, the use of biodegrad-
able polymers as polymer host in solid state electrolytes can ideally
replace the harmful existing materials, owing good thermal and thin film
formation abilities for green energy applications (Ahmed & Abdullah,
2020; Bella, Mobarak, Jumaah, & Ahmad, 2015). Among various
biopolymer materials, the use of cellulose derivatives (Gupta & Var-
shney, 2019; Kostag, Gericke, Heinze, & El Seoud, 2019) namely chi-
tosan, methylcellulose (MC) and carboxymethyl cellulose (CMC),
carrageenan, pectin, chitin, lignocellulosic materials in electrolyte has
received much attention since it possesses a wide variety of advantages
* Corresponding author.
E-mail address: wmkhairul@umt.edu.my (W.M. Khairul).
https://doi.org/10.1016/j.carbpol.2020.116935
Received 27 May 2020; Received in revised form 27 July 2020; Accepted 11 August 2020
Available online 20 August 2020
0144-8617/© 2020 Elsevier Ltd. All rights reserved.

R. Rahamathullah et al.
Carbohydrate Polymers 250 (2020) 116935
such as having low density materials, high specific length film forming
ability and exhibit biodegradable properties which can be used as SBEs.
Noor & Isa, 2019; Samsudin & Saadiah, 2018 have developed and
investigated new proton conducting biopolymer electrolytes based on
carboxymethyl cellulose (CMC) doped with different ammonium salt for
advanced materials application. The correlation between impedance
approach, mechanism ionic conduction and dielectric parameter were
also thoroughly described (Mazuki, Majeed, Nagao, & Samsudin, 2020;
Zainuddin, Rasali, Mazuki, Saadiah, & Samsudin, 2020). Nevertheless,
in-depth studies are still desired to optimize their performances due to
their major drawbacks of low ionic conductivity which limits their
practical technological applications and performance.
this present work is to examine the capability of conjugated π-systems of
alkoxy stilbene-imine to act as additive in biopolymer-salt electrolyte on
CMC doped with ammonium chloride (NH4Cl) system. The coordination
–
–
–
chemistry of hybrid moieties of vinylene ( CH CH ) and azomethine
–
–
–
–
CH
–
N
(
) exert a great deal in semiconducting properties as it
possess extensive conjugated system which able to conduct electron
through their π-system and can afford good charge transport to the
polymer electrolyte matrix. On top of that, the uniqueness features of
alkoxy stilbene-imine are ascribed by the existence of possible active site
–
–
of C O bond and CH N band for alternative pathway for electron flow
–
to biopolymer-salt electrolyte. Therefore, the involvement of hybrid
moieties system of stilbene-imine was carried out in order to overcome
the limitations inherent in a mixture of biopolymer-salt electrolyte. The
evaluation on how far these types of molecular compounds can be able
to improve ionic conductivity and alter structural of SBEs film was also
intensively investigated. Within this interest, stilbene-imine based ad-
ditives are expected to have good interaction with biopolymer-salt
electrolyte that leads to the effective properties of ionic conductivity
in SBEs system.
Alternatively, numerous approaches are attempted with the goal to
enhance the ionic conductivity performance and sustain interior prop-
erties of SBEs including blending of polymers, incorporated filler, ionic
liquid and additives/plasticizer into the polymer host matrix (Ambika
et al., 2018; Chai & Isa, 2016; Yang et al., 2017). Within this interest, the
incorporation of a small amount of other chemical species into the
electrolyte composition becomes another promising alternative that can
alter the structural stability and influence the SBEs performance (Kar-
thika, Ganesan, Thomas, Rani, & Prakash, 2019). Based on previous
literatures, 4-tertbutylpyridine (TBP), organic nitrogenous compound
(Ganesan, Mathew, Paul, Maruthamuthu, & Suthanthiraraj, 2013),
pyridine, thiourea (Pavithra, Velayutham, Sorrentino, & Anandan,
2017) and benzimidazole (Muthuraaman, Will, Wang, Moonie, & Bell,
2013) are some examples of small molecules employed in polymer
electrolyte to improve the conductivity and efficiency of the system.
Regarding to this interest, the motivation which led to this contri-
bution arises on the extensive studies involving organic additives in
electrolytes based on semiconducting materials system. The devotions in
2. Experimental section
2.1. Materials
All chemicals, solvent and materials were used as received without
further purification. 1-iodo-4-nitrobenzene, 4-iodoaniline, 4-vinylani-
line and carboxymethyl cellulose (CMC, Mw ~90,000 g/mol) were
purchased from Sigma-Aldrich, 4-cyanostyrene, 4-chlorostyrene, 4-
vinylaniline, 4-(trifluoromethyl)styrene and methyl 4-iodobenzoate
´
were provided by Acros Organic. Whilst, ammonium chloride,
Scheme 1. The synthetic approach for the preparation of alkoxy stilbene-imine (3a-2C)-(3b-10C).
2

R. Rahamathullah et al.
Carbohydrate Polymers 250 (2020) 116935
acetonitrile, ethanol, triethylamine, and tetrahydrofuran were obtained
from Merck.
S2, S3).
2.3.2. Synthesis of 4-[[(4-hexyloxyphenyl)methylene]amino)]-4’-
(trifluoromethyl)stilbene (3a-6C)-additive 2
2.2. Instrumentations
Yellow precipitate of (3a-6C) (0.73 g, 85 %) was synthesized from 1a
(0.50 g, 1.90 mmol) and 2b (0.39 g, 1.90 mmol) in the same manner as
CHN elemental analyses were acquired using FLASHEA 1112 CHNS
analyzer. IR spectra were obtained from Perkin Elmer Spectrum 100
Fourier Transform Infrared Spectrometer in KBr pellets within the fre-
quency region of 4000ꢀ 400 cmꢀ 1. The 1H (400.11 MHz) and 13C
(100.61 MHz) spectra were recorded on Bruker Avance III 400 Spec-
trometer with deuterated chloroform (CDCl3) solvent and tetrame-
thylsilane (TMS) as an internal standard. The density functional theory
(DFT) calculation were analyzed via Gaussian 09 software package
employing with basis set function of B3LYP/6-31 G (d,p). The electronic
properties of HOMO-LUMO gap with corresponding absorption wave-
lengths were performed by time-dependent DFT (TD-DFT) method.
described above. IR (KBr):
ν
(C–H aromatic) 3023 cmꢀ 1
;
ν
(C–H aliphatic)
2935 cmꢀ 1, 2874 cmꢀ 1
;
ν
(C C, vinyl) 1585 cm
; ν(C C, aromatic)
ꢀ 1
–
–
–
–
1567 cmꢀ 1 and 1511 cmꢀ 1
;
ν
(C N) 1606 cm
;
ν
(C O, ether) 1165
ꢀ 1
–
–
–
cmꢀ 1
;
ν
(C-F) 844 cmꢀ 1. 1H NMR (400.11 MHz, CDCl3): δ 0.92 (t, J = 7.0
Hz, 3H, CH3); 1.26–1.85 (m, 8H, CH2); 4.03 (t, J = 6.6 Hz, 2H, OCH2);
6.99 (d, J = 8.4 Hz, 2H, Ar-H); 7.08–7.22 (d-d, 2H, HC=CH); 7.24 (d,
J=8.4 Hz, 2H, Ar-H); 7.55 (d, J = 8.4 Hz, 2H, Ar-H); 7.60 (s, 4H, Ar-H);
7.84 (d, J = 8.8 Hz, 2H, Ar-H); 8.42 (s, 1H, NH). 13C NMR (100.61 MHz,
CDCl3): δ 13.00 (s, CH3); 21.58, 24.67, 28.13, 30.55 (4 x s, CH2); 67.24
–
–
(s, CH -O); 129.58, 129.75 (2 x s, C C); 127.94 (s, C-CF); 113.74,
2
120.44, 124.60, 124.63, 125.35, 125.46, 126.63, 133.08, 139.96,
–
–
151.29, 158.59 (12 × s, Ar); 161.03 (s, C N). Elemental analysis for
2.3. Synthesis of stilbene-imine as organic additive
C
28H28F3NO: [Found (Calcd.)]: C = 74.48 (73.88); H = 6.25 (5.74); N =
3.10 (2.89). (See Supp. data S4, S5, S6).
All reactions and work up were performed under an ambient envi-
ronment and no special precaution steps were taken during the synthetic
work to eliminate air or moisture unless otherwise stated. In the syn-
thetic work, stilbene-imine additive consists of three major steps which
were begun with the preparation of precursors over aerobic condition of
palladium-catalysed Heck cross-coupling reactions (1a-1b). Next, re-
actions were continued with the preparation of alkoxybenzaldehydes
acting as another precursors (2a-2c) via Williamson ether synthesis with
various alkyl bromide and 4-hydroxybenzaldehyde. Subsequently, pre-
cursors (1a-1b) were reacted with 2a-2c to yield the focal targeted
compounds of stilbene-imine (3a-2C)–(3b-10C) derivatives via Schiff
Base condensation reactions. Precursors (1a-1b and 2a-2c) only used to
synthesize the stilbene-imine additives and did not involve directly in
this study. Scheme 1 depicts the overall synthetic route applied in this
work. The 3a-6C (additive- 2) has been prepared and reported at some
extends in previous occasions (Rahamathullah & Khairul, 2018).
Nevertheless, the study on the capability of this conjugated molecular
system as organic additives have never been carried out although the
existence of lone pair of electrons in oxygen and nitrogen atoms is ex-
pected to have interaction with polymer matrix which can enhance ionic
conductivity of the electrolytes. Therefore, for this contribution, the
influence of the synthesized additives (3a-2C)–(3b-10C) were investi-
gated on the performance of CMC-biopolymer based electrolyte.
2.3.3. Synthesis of 4-[[(4-decyloxyphenyl)methylene]amino)]-4’-
(trifluoromethyl)stilbene (3a-10C)-additive 3
Yellow precipitate of (3a-10C) (0.83 g, 86 %) was synthesized from
1a (0.50 g, 1.90 mmol) and 2c (0.50 g, 1.90 mmol) in the same manner
as described above. IR (KBr):
ν
(C–H aromatic) 3022 cmꢀ 1
;
ν
(C–H
aliphatic) 2919 cmꢀ 1, 2875 cmꢀ 1
;
ν
(C C, vinyl) 1587 cm
;
ν
(C C,
ꢀ 1
–
–
–
–
aromatic) 1570cmꢀ 1 and 1511 cmꢀ 1
;
ν
(C N) 1607 cm
;
ν
(C O,
ꢀ 1
–
–
–
ether) 1166 cmꢀ 1
;
ν
(C-F) 847 cmꢀ 1
.
1H NMR (400.11 MHz, CDCl3): δ
0.89 (t, J = 6.8 Hz, 3H, CH3); 1.26–1.85 (m, 8H, CH2); 4.03 (t, J = 6.4
Hz, 2H, OCH2); 6.99 (d, J = 8.8 Hz, 2H, Ar-H); 7.08–7.22 (d-d, 2H,
HC=CH); 7.24 (d, J=8.4 Hz, 2H, Ar-H); 7.55 (d, J = 8.4 Hz, 2H, Ar-H);
7.61 (s, 4H, Ar-H); 7.84 (d, J = 8.4 Hz, 2H, Ar-H); 8.42 (s, 1H, NH). 13C
NMR (100.61 MHz, CDCl3): δ 14.13 (s, CH3); 22.69, 26.02, 29.18, 29.33,
29.39, 29.56, 29.58, 31.91 (8 × s, CH2); 68.25 (s, CH2-O); 126.37,
–
126.48 (2 x s, C C); 127.66 (s, C-CF); 114.75, 121.47, 125.62, 125.65,
–
127.66, 128.88, 130.62, 130.73, 134.11, 151.29, 159.66 (12 × s, Ar);
–
162.05 (s, C N). Elemental analysis for C32H36F3NO: [Found (Calcd.)]:
–
C = 75.71 (75.18); H = 7.15 (7.74); N = 2.76 (2.89). (See Supp. data S7,
S8, S9).
2.3.4. Synthesis of 4-[[(4-ethoxyphenyl)methylene]amino)]-4′-
nitrostilbene (3b-2C)-additive 4
Yellow precipitate of (3b-2C) (0.68 g, 88 %) was synthesized from 1b
(0.50 g, 2.08 mmol) and 2a (0.31 g, 2.08 mmol) in the same manner as
2.3.1. Synthesis of 4-[[(4-ethoxyphenyl)methylene]amino)]-4’-
(trifluoromethyl)stilbene (3a-2C)-additive 1
described above. IR (KBr):
ν
(C–H aromatic) 3234 cmꢀ 1
;
ν
(C–H aliphatic)
An equimolar amount of 1a (0.50 g, 1.90 mmol) and 2a (0.29 g, 1.90
mmol) were dissolved in 50 mL of ethanol equipped with a Dean-Stark
condenser. The mixture was then put at reflux with constant stirring
at the solvent distillation temperature (79 ◦C) for ca. 6 h and monitored
via TLC (hexane: ethyl acetate) (3:2). Upon completion, the solution was
dried over anhydrous Na2SO4, filtered and cooled at room temperature.
A pale yellow precipitate formed from the solution mixture were then
filtered, collected and recrystallized from acetonitrile to obtain the
yellow flakes of the title compound of 3a-2C (0.63 g, 84 %). IR (KBr):
2985 cmꢀ 1 and 2875 cmꢀ 1
;
ν
(C C, vinyl) 1582 cm
; ν(C C, aromatic)
ꢀ 1
–
–
–
–
1560 cmꢀ 1 and 1515 cmꢀ 1
;
ν
(NO2) 1424 cmꢀ 1 and 1339 cmꢀ 1
;
ν
(C N)
–
–
1604 cmꢀ 1
;
ν
(C O, ether) 1163 cmꢀ 1. 1H NMR (400.11 MHz, CDCl3): δ
–
1.39 (t, J = 7.0 Hz, 3H, CH3); 4.03 (q, J = 7.0 Hz, 2H, OCH2); 6.92 (d, J =
–
–
8.8 Hz, 2H, Ar-H); 7.04–7.24 (d-d, 2H, HC CH); 7.17 (d, J=8.0 Hz, 2H,
Ar-H); 7.50 (d, J = 8.4 Hz, 2H, Ar-H); 7.57 (d, J = 8.8 Hz, 2H, Ar-H);
7.77 (d, J = 8.8 Hz, 2H, Ar-H); 8.14 (d, J = 8.8 Hz, 2H, Ar-H); 8.35 (s,
1H, NH). 13C NMR (100.61 MHz, CDCl3): δ 13.72 (s, CH3); 62.69 (s, CH2-
(C–H aromatic) 3020 cmꢀ 1
;
ν
(C–H aliphatic) 2980 cmꢀ 1, 2882 cmꢀ 1
;
;
–
–
O); 126.95, 127.90 (2 × s, C C); 113.72, 120.53, 123.16, 124.46,
ν
ν
ν
-1
(C C, aromatic) 1567 cmꢀ 1 and 1511 cmꢀ 1
–
–
125.71, 129.65, 131.88, 132.58, 143.01, 145.62, 151.78, 158.79 (12 ×
(C C, vinyl) 1588 cm ;
ν
–
–
ꢀ 1
ꢀ 1
(C-F) 841 cmꢀ 1
.
1H
–
–
–
–
s, Ar); 160.88 (s, C N). Elemental analysis for C23H20N2O3: [Found
(C N)1604 cm
;
ν
(C O, ether) 1166 cm
;
ν
–
(Calcd.)]: C = 74.18 (74.74); H = 5.41 (5.74); N = 7.52 (7.13). (See
NMR (400.11 MHz, CDCl3): δ 1.39 (t, J = 7.0 Hz, 3H, CH3); 4.03 (q, J =
Supp. data S10, S11, S12).
7.0 Hz, 2H, OCH2); 6.92 (d, J = 8.8 Hz, 2H, Ar-H); 7.01–7.12 (d-d, 2H,
–
–
HC CH); 7.17 (d, J=8.4 Hz, 2H, Ar-H); 7.48 (d, J = 8.4 Hz, 2H, Ar-H);
7.54 (s, 4H, Ar-H); 7.77 (d, J = 8.8 Hz, 2H, Ar-H); 8.35 (s, 1H, NH). 13
C
2.3.5. Synthesis of 4-[[(4-hexyloxyphenyl)methylene]amino)]-4’-
nitrostilbene (3b-6C)-additive 5
NMR (100.61 MHz, CDCl3): δ 13.72 (s, CH3); 62.69 (s, CH2-O); 129.60,
–
–
Yellow precipitate of (3b-6C) (0.78 g, 87 %) was synthesized from 1b
(0.50 g, 2.08 mmol) and 2b (0.43 g, 2.08 mmol) in the same manner as
129.77 (2 x s, C C); 128.03 (s, C-CF); 113.73, 120.43, 124.60, 124.64,
125.37, 125.46, 126.64, 133.11, 139.96, 151.28., 15856 (12 × s, Ar);
described above. IR (KBr):
ν
(C–H aromatic) 3234 cmꢀ 1
;
ν
(C–H aliphatic)
–
–
160.82 (s, C N). Elemental analysis for C24H20F3NO: [Found (Calcd.)]:
2920 cmꢀ 1, 2852 cmꢀ 1
;
ν
(C C, vinyl) 1583 cm
; ν(C C, aromatic)
ꢀ 1
–
–
–
–
C = 72.90 (72.48); H = 5.10 (5.04); N = 3.54 (3.44). (See Supp. data S1,
3

R. Rahamathullah et al.
Carbohydrate Polymers 250 (2020) 116935
1561 cmꢀ 1 and 1519 cmꢀ 1
;
ν
(NO2) 1424 cmꢀ 1 and 1340 cmꢀ 1
; ν(C N)
–
quantum mechanical software employing DFT approach with basis set of
B3LYP/6-31 G (d,p). The energy separation between HOMO and LUMO,
frontier molecular orbital (FMO) and the corresponding absorption
wavelengths were performed by time-dependent density functional
theory (TD-DFT). The molecular geometry optimization was employed
using polarizable continuum model (PCM) with the integral equation
formalism variant (IEF-PCM) in dichloromethane solvent.
–
1605 cmꢀ 1
;
ν
(C O, ether) 1163 cmꢀ 1. 1H NMR (400.11 MHz, CDCl3): δ
–
0.85 (t, J = 7.0 Hz, 3H, CH3); 0.84–1.78 (m, 8H, CH2); 3.96 (t, J = 6.6
Hz, 2H, OCH2); 6.92 (d, J = 8.8 Hz, 2H, Ar-H); 7.04–7.24 (d-d, 2H,
HC=CH); 7.17 (d, J=8.4 Hz, 2H, Ar-H); 7.50 (d, J = 8.4 Hz, 2H, Ar-H);
7.57 (d, J = 8.8 Hz, 2H, Ar-H); 7.77 (d, J = 8.8 Hz, 2H, Ar-H); 8.14 (d, J
= 8.8 Hz, 2H, Ar-H); 8.34 (s, 1H, NH). 13C NMR (100.61 MHz, CDCl3): δ
13.00 (s, CH3); 21.57, 24.67, 28.12, 30.55 (4 × s, CH2); 67.25 (s, CH2-
–
–
O); 126.95, 127.85 (2 × s, C C); 113.76, 120.54, 123.17, 124.47,
2.5. Preparation of solid biopolymer electrolyte (SBEs) Film
125.72, 129.65, 131.89, 132.59, 143.03, 145.64, 151.80, 158.82 (12 ×
–
–
s, Ar); 161.12 (s, C N). Elemental analysis for C27H28N2O3: [Found
An amount of 2.0 g of carboxymethyl cellulose (CMC) powder was
dissolved in 100 mL of distilled water and stirred constantly for ca. 12 h
at ambient environment. The amount of 16 wt.%, 0.38 g of ammonium
chloride (NH4Cl) was added into CMC solution and stirred for another
ca. 5 h until completely homogenous. The amount of ammonium salt
used in this work was fixed which referred to the highest conductivity of
CMC-NH4Cl that was reported in previous literature (Ahmad & Isa,
2016), in order to use this previously developed system as reference
before adding our synthesized additive. The homogenous solution was
then casted into glass petri dishes and dried in an oven at 55 ◦C for ca. 30
h to allow CMC-NH4Cl film to form. The SBEs were kept in desiccators
for further drying prior being characterized to ensure the removal of
residual moisture in the film.
(Calcd.)]: C = 75.68 (75.74); H = 6.59 (5.74); N = 6.54 (7.13). (See
Supp. data S13, S14, S15).
2.3.6. Synthesis of 4-[[(4-decyloxyphenyl)methylene]amino)]-4’-
nitrostilbene (3b-10C)-additive 6
Yellow precipitate of (3b-10C) (0.86 g, 85 %) was synthesized from
1b (0.50 g, 2.08 mmol) and 2c (0.55 g, 2.08 mmol) in the same manner
as described above. IR (KBr):
ν
(C–H aromatic) 3234 cmꢀ 1
;
ν
(C–H
aliphatic) 2920 cmꢀ 1, 2852 cmꢀ 1
;
ν
(C C, vinyl) 1583 cm
;
ν
(C C,
ꢀ 1
–
–
–
–
aromatic) 1561 cmꢀ 1 and 1519 cmꢀ 1
;
ν
(NO2) 1424 cmꢀ 1 and 1340
ꢀ 1
cmꢀ 1
;
ν
(C N) 1605 cm
(C O, ether) 1163 cmꢀ 1. 1H NMR (400.11
–
; ν
–
–
MHz, CDCl3): δ 0.82 (t, J = 6.8 Hz, 3H, CH3); 1.18–1.78 (m, 16H, CH2);
3.96 (t, J = 6.6 Hz, 2H, OCH2); 6.92 (d, J = 8.4 Hz, 2H, Ar-H); 7.03–7.23
–
–
(d-d, 2H, HC CH); 7.17 (d, J=8.4 Hz, 2H, Ar-H); 7.50 (d, J = 8.4 Hz,
2.5.1. Preparation of SBEs containing stilbene-imine as additive
2H, Ar-H); 7.57 (d, J = 8.8 Hz, 2H, Ar-H); 7.77 (d, J = 8.4 Hz, 2H, Ar-H);
8.14 (d, J = 8.8 Hz, 2H, Ar-H); 8.34 (s, 1H, NH). 13C NMR (100.61 MHz,
CDCl3): δ 13.08 (s, CH3); 21.66, 25.00, 28.16, 28.30, 28.36, 28.53,
28.55, 30.88 (8 x s, CH2); 67.26 (s, CH2-O); 126.95, 127.88 (2 × s,
An amount of 1 milliMolar (mM) of synthesized stilbene-imine was
dissolved in 5 mL organic solvent. Then, the solution was added drop-
wise into CMC-NH4Cl solution with constant stirring to form clear ho-
mogenous dissolution. In this work, only 1 mM of stilbene-imine was
used as additives in order to avoid phase separation and form clear film
due to the effect of alkoxy chain and aromatic group that can form
heterogeneous mixture in water and form non-uniform film. The prep-
aration of CMC-NH4Cl was carried out in the same manner as described
in 2.5. Then, the solution was casted into glass petri dishes and heated in
an oven at 55 ◦C for ca. 30 h to allow film to form. The SBEs were then
transferred into desiccator for extended the drying process for solvent
evaporation purpose. Fig. 1 illustrates the stepwise preparation of SBEs
in this study and compositions of CMC-NH4Cl-(stilbene-imine) coded as
–
–
C
C); 113.77, 120.54, 123.16, 124.47, 125.72, 129.64, 131.91, 132.59,
–
143.03, 145.66, 151.84, 158.79 (12 × s, Ar); 161.12 (s, C N).
–
Elemental analysis for C31H36N2O3: [Found (Calcd.)]: C = 76.83
(76.14); H = 7.49 (6.74); N = 5.78 (5.13). (See Supp. data S16, S17,
S18).
2.4. Computational method: DFT studies
The theoretical studies were evaluated through Gaussian 09
Fig. 1. Schematic diagram of SBEs preparation.
4

R. Rahamathullah et al.
Carbohydrate Polymers 250 (2020) 116935
Table 1
Frontier molecular orbitals (FMOs) of stilbene-imine additives.
Compound/Eg (Ev)
HOMO
LUMO
Trifluoromethyl (CF3) series
Additive 1
3.495 eV
ꢀ 5.387 eV
ꢀ 1.892 eV
Additive 2
3.498 eV
Additive 3
3.495 eV
ꢀ 5.377 eV
ꢀ 5.375 eV
ꢀ 1.879 eV
ꢀ 1.880 eV
Nitro (NO2) series
Additive 4
3.078 eV
ꢀ 5.567 eV
ꢀ 5.555 eV
ꢀ 2.489 eV
ꢀ 2.484 eV
Additive 5
3.071 eV
Additive 6
3.070 eV
ꢀ 5.552 eV
ꢀ 2.482 eV
F(3a-2C)-F(3b-10C).
2.6. SBEs characterization
additives is found to be at around 3.49 eV - 3.07 eV. This value ex-
plains the eventual charge transfer interaction with the molecule where
-CF3 substituent has slightly large HOMO-LUMO gap which reflects low
chemical reactivity and high kinetic stability compared to -NO2 sub-
stituent. Nonetheless, in overall results, we can conclude that the
HOMO-LUMO gaps of both series are comparatively small and fall in the
range of semiconducting materials. The low HOMO-LUMO energy gaps
of additives indicate the molecule are soft and also possess higher
thermal and kinetic stabilities according to softness-hardness rule. From
2.6.1. Fourier transform infrared (FT-IR) spectroscopy
The structural and intermolecular interaction of the developed SBEs
have been examined via FTIR spectra on Thermo Nicolet 380 FTIR
spectrometer equipped with an Attenuated Total Reflection (ATR) mode
within the vibration frequency ranging from 4000 to 450 cmꢀ 1
.
2.6.2. Electrical impedance spectroscopy (EIS)
Table 2
The excitation energy, oscillator strengths (f) and major contributions of the
transitions from ground state (S0) to excited states (Sn).
For ionic conductivity characterization, the SBE samples were eval-
uated via EIS using HIOKI LCR Hi Tester (model 3532–50) at varies
frequency range between 50 Hz to 1 MHz. The samples were cut into a
fitting size of small discs with 2 cm diameter and sandwiched between
blocking stainless steel electrodes of the sample holder which connected
Wavelength
Major
Electronic
transition
Oscillator
strength
Molecule
contribution (in
%)
Exp
360
360
360
Cal
Additive
S0→S1
S0→S1
S0→S1
401
401
401
1.8743
1.8991
1.8758
H→L (98)
H→L (98)
H→L (98)
to the LCR tester. The ionic conductivity,
σ was calculated using the
1
relation in following equation (Shukur & Kadir, 2015).
Additive
t
2
σ
=
(1)
Additive
3
RbA
From the equation, t (cm) is the thickness of the sample, A (cm2) is
S0→S1
S0→S2
–
475
373
1.3296
0.3423
H→L (99)
Additive
4
396
H-1→L (73)
H→L+1 (24)
H-1→L (26)
H→L+1(71)
H→L (99)
the surface area of electrode-electrolyte contact area of SBE and Rb is
bulk resistance obtained from plotting the negative imaginary imped-
ance (-Zi) versus real part (Zr) of impedance.
S0→S3
293
359
0.2834
S0→S1
S0→S2
–
396
475
373
1.3449
0.3436
Additive
5
H-1→L (74)
H→L+1 (23)
H-1→L (25)
H→L+1 (72)
3. Results and discussion
S0→S3
293
359
0.3015
3.1. Computational detailed on stilbene-imine additives
Additive
6
S0→S1
S0→S2
396
293
451
360
1.5114
0.3772
H→L (99)
The frontier molecular orbital (FMOs) of all additives along with
their respective ΔEHOMO-LUMO energy values in eV are depicted in
Table 1. The energy gap between HOMO and LUMO for stilbene-imine
H-1→L (74)
H→L+1 (23)
5

R. Rahamathullah et al.
Carbohydrate Polymers 250 (2020) 116935
Table 3
Table 4
Value of squared effective charges (-Ln χ2) of all carbon atoms in the aromatic
Thickness, bulk resistance and ionic conductivity of all SBEs involved in this
study.
ring of substituted stibene-imine additives.
SBEs
Thickness,
Bulk Resistance, Rb (Ω)
Conductivity,
σ
(S/cmꢀ 1
)
t (cm)
References
CMC-
0.015
2.82
1.69 × 10ꢀ 3
NH4Cl
Trifluoromethyl (CF3) series
F(3a-2C)
F(3a-6C)
F(3a-10C)
0.017
0.018
0.018
0.94
0.78
0.69
5.76 × 10ꢀ 3
7.34 × 10ꢀ 3
8.30 × 10ꢀ 3
Σ Ln (χ2) of carbons in aromatic rings
Compound
Aromatic ring 1
Aromatic ring 2
Aromatic ring 3
Total
Nitro (NO2) series
F(3b-2C)
F(3b-6C)
F(3b-10C)
0.018
0.90
0.81
0.61
6.37 × 10ꢀ 3
7.07 × 10ꢀ 3
8.86 × 10ꢀ 3
Trifluoromethyl (CF3) series
0.018
0.017
Additive 1
Additive 2
Additive 3
23.5950
23.6189
23.6184
23.9003
23.9200
23.9200
27.3470
27.3470
27.4370
74.8423
74.8859
74.9754
Nitro (NO2) series
are predominantly arises from H→L (98–99 %) with high oscillator
strength (f > 1.5) in first excited singlet state S0→S1. While, the evident
that excited singlet state S0→S2 attributed to HOMO-1→LUMO (72–74
%) and HOMO→LUMO+1 (23–25 %) configuration corresponds to
Additive 4
Additive 5
Additive 6
23.6359
23.9615
23.9695
23.9924
29.9052
29.9052
29.9052
77.5026
77.5291
77.5335
23.6544
23.6359
π→π* and n→π* transitions as tabulated in Table 2. Nonetheless, the
the FMO distribution, the filled
π-orbital (HOMO) and unfilled anti
contribution of excited singlet states S0→S3 for is sizably reduced by
small calculated oscillator strength (f < 0.4) and nearly forbidden and
undetectable for considerations. As an overall result, the resulting
calculated λmax is in good agreement with the experimental value where
significantly red shifted occurred due to the superposition of the bath-
ochromic shift and effect of the conjugation targeted system.
π
-orbital (LUMO) are delocalized throughout the entire molecule
–
–
–
–
N
including aromatic rings, trans-stilbene and double bonds of CH
moiety except alkoxy chain length. The alkoxy chains length had no
significant effect and did not show much different on the distribution of
electronic clouds in FMOs even though electron donating (ED) effect
becomes stronger with increasing alkoxy chain lengths to the conjugated
backbone. In contrast, by further tuning of electron withdrawing (EW)
substituents namely -CF3 and -NO2 of stilbene-imine additive, the charge
distribution of the HOMO was slightly shifted downwards around 0.13
eV ꢀ 0.43 eV and LUMO within the range 0.14 eV ꢀ 0.85 eV. These
indicate that mesomeric effect and EW strength capability shows a
crucial role in the variations of energy level. In these sense, we can see
that the EW group stabilizes LUMO energy level more than its HOMO
energy level. In conclusion, the changes in HOMO and LUMO values
resulted in the narrower band gap due to the effect of EW substituent
and hence lowering the HOMO-LUMO energy gap.
From computational study, it was revealed that different substituents
of stilbene-imine additives can influence the ionic conductivity perfor-
mance of SBEs system where it can be correlated with the energy band
gap (HOMO-LUMO). In this sense, to determine the correlation between
the substituents of stilbene-imine additive with the conductivity, effec-
tive squared charges (
χ
2) followed by –Ln
χ
2 for the aromatic rings in the
stilbene-imine derivatives were calculated at the theoretical level of
B3LYP/6-31 G (d,p) as depicted in Table 3. The
χ
2 on the
αth atom can
contribute to the prediction of the vibrational intensities, reaction
pathway and conductivity properties which can give consistent results
with the experimental approach (Ghazali, Kubulat, Isa, Samsudin, &
Khairul, 2014; Person & Kubulat, 1990). Surprisingly, the sequence of
total Ln χ2 value particularly for the third ring of stilbene-imine addi-
tives were exactly in the same order with experimental outcomes of
conductivities. The trends of the sequences are depending on the elec-
tronegativity of electron withdrawing group that attached to the ring
system namely CF3 < NO2. It revealed that the conductivity depends
much on the delocalization of the phenyl ring system of the
Additionally, the charge density of FMO for stilbene-imine additive
was evaluated in order to examine the nature of major electronic tran-
sition upon photoexcitation (Daengngern & Kungwan, 2015). In this
case, the HOMO and LUMO are assigned to
π and π* character and main
contribution are summarized in Table 2. Considering TD-DFT calcula-
tion, it can be said that the electron density contribution of all additives
Fig. 2. Cole-Cole plot for impedance diagram of CMC-NH4Cl electrolyte and
various CMC-NH4Cl-(stilbene-imine) SBEs. The inset shows the enlargement of
the SBEs at high frequency part.
Fig. 3. Temperature-dependence of ionic conductivity of CMC-NH4Cl electro-
lyte and CMC-NH4Cl-(stilbene-imine) SBEs.
6

R. Rahamathullah et al.
Carbohydrate Polymers 250 (2020) 116935
stilbene-imine derivatives. Indeed, the value of higher squared effective
computational study.
charges (Ln
χ
2) could be explained by the conjugation length and
delocalization of
π
-electrons along the molecule. From the promising
3.3. Temperature-dependent ionic conductivity
result of energy band gap (Eg) and effective charges (
χ
2) of the
stilbene-imine compounds via theoretical study and experimental result
obtained, these candidates revealed great potential to act as additives in
SBE for optoelectronic application.
To further investigate the ionic conduction mechanism and verify
that SBEs was not affected from water content towards the enhancement
of ionic conductivity, all the SBEs system were measured with a function
of temperature. Fig. 3 portrays the temperature dependence plot of
variation of log conductivity with reciprocal temperature in the range
from 303 K to 373 K. The ionic conductivity noticeably increases
monotonically with increasing temperature for all SBEs sample.
Notably, the temperature-dependence conductivity in Fig. 3 were found
to be in straight line with regression (R2) values fit to ~1 and this
linearity obeys thermal activated–Arrhenius relationship (Hafiza & Isa,
2018; Hashmi, Kumar, Maurya, & Chandra, 1990).
3.2. Ionic conductivity
The addition of additives in biopolymer-salt electrolytes is poten-
tially would enhance the conductivity performance. Hence to investi-
gate the influence of incorporation stilbene-imine additives on the
conductivity behaviour in SBEs system, highest conducting CMC-NH4Cl
in the salted system (16 wt. %) was used as a reference (Ahmad & Isa,
2016) for this type of work. In this case, the conductivity value for
CMC-NH4Cl electrolyte was identified at 1.69 × 10ꢀ 3 Scm-1 which is in
comparable with reported results by Ahmad and Isa, 2016. On top of
that, the conductivity results increase gradually upon the addition of
stilbene-imine additives into CMC-NH4Cl electrolyte within the range of
5.76 × 10-3 Scm-1 to 8.86 × 10ꢀ 3 Scm-1 at room temperature (303 K) as
depicted in Fig. 2. The enhancement in conductivity for
CMC-NH4Cl-(stilbene-imine) SBEs can be ascribed due to the decrease of
bulk resistance (Rb) in the system as illustrated in Cole-Cole plot (Fig. 2).
In this sense, the increment of conductivity with increasing tem-
perature due to the factors of enhancement in ionic mobility through
polymer chain and consequently increases the fraction of free volume at
higher temperature facilitates the ions to hop between adjacent coor-
dination sites (Moniha, Alagar, Selvasekarapandian, Sundaresan, &
Boopathi, 2018; Selvakumar, Kalaiselvimary, Rajendran, & Prabhu,
2016). The presence of stilbene-imine additives in CMC-NH4Cl electro-
lyte exhibits an enhancement in conductivity, indicate that additives
assist in salt dissociation and lead to high mobility and conductivity as
the temperature increases. Remarkably, the conductivity values of all
SBEs system did not show any abrupt changes throughout the heating
process which confirmed that ionic conductivity did not affect by water
content, but attributed from the increment in mobility of charge carrier
from doping salt and additives (Sim, Yahya, & Arof, 2016).
The summarized data for the obtained conductivity (σ) and bulk resis-
tance (Rb) is presented in Table 4.
The results indicate that the additives with -CF3 and –NO2 electron
withdrawing groups revealed enhancement in conductivity based on
their electronegativity and substitutions group on the additives. This
occurrence can be correlated to the increment of ionic conductivity in
which inferring information on the interaction between biopolymer-salt
electrolyte and additive increases of ion dissociation and number of
charge carriers of free ions (H+) (Alias, Chee, & Mohamad, 2017; Hafiza
3.4. Biopolymer-salt-additive interactions study
The interactions of ions in electrolyte system can be determined by
observing the changes of peak intensity, presence/or absence of new
peak and shifting in the vibrational mode of molecules which provide
crucial structural details of the polymer-salt with additives in IR analysis
(Hafiza & Isa, 2017a, 2017b; Shukur, Ithnin, Illias, & Kadir, 2013). In
this sense, the interaction of pure CMC, CMC-NH4Cl electrolyte with/-
without the addition of organic additives were analysed using FTIR. The
–
& Isa, 2017a, 2017b). The existence of nitrogen in (CH N) moiety with
–
electron donating and withdrawing group at the additives boost up the
mobility of ion for the SBEs system (Ganesan et al., 2013; Karthika et al.,
2019). Moreover, the conductivity values SBE are slightly increased
with an increasing of alkoxy chain length by tuning the electron with-
drawing group substitutions which follows the order (F(3a-2C) < (F
(3a-6C) < (F(3a-10C) < (F(3b-2C) < (F(3b-6C) < (F(3b-10C) and
affect the performance on the conductivity. Overall, the -NO2 series with
decyloxy chain of additives give the highest value in conductivity in
which confirms the electron substitution plays a crucial role in the
performance of conductivity and electron flow of the molecule in SBEs
system. Remarkably, the increments of conductivity in SBEs are in the
line with HOMO-LUMO results and Mulliken charged obtained from
Fig. 5. Proposed interaction of biopolymer-salt with stilbene-imine additives of
Fig. 4. Infrared spectra of SBE of CMC-NH4Cl with stilbene-imine additives.
SBE system.
7

R. Rahamathullah et al.
Carbohydrate Polymers 250 (2020) 116935
–
–
vibrational modes of O H stretching, carboxylate (COO ) anions of
range of 303 K – 373 K. Thus, the outcome results revealed that the small
change in conductivity upon addition of organic additives indicate that
these promising candidates could provide efficient charge transport
pathways in SBEs which leads to improvement in optoelectronic
application.
–
–
– –
O C) of CMC have been shifted in
(C O) and glycosidic group (C
wavenumbers after addition of salt suggesting that the interaction and
complexation have occurred in the biopolymer-salt of CMC-NH4Cl sys-
tem. The obtained findings were in same arguments with previous re-
ported literatures on biopolymer-salt electrolyte system (Ahmad & Isa,
2016; Shukur & Kadir, 2015).
CRediT authorship contribution statement
In contrast, noticeable changes of peak intensity and wavenumber of
certain vibrational mode were detected before and after inclusion of
additives and these have proven the interaction between biopolymer-
salt and additive occurred within the system as depicted in Fig. 4.
Nevertheless, it revealed that the main functional groups of synthesized
stilbene-imine additives disappeared and the characteristic of IR
stretching bands of new SBEs were obviously related to the vibration
Rafizah Rahamathullah: Methodology, Data curation, Visualiza-
tion, Writing - original draft. Wan M. Khairul: Supervision, Conceptu-
alization, Writing - review & editing, Validation. M.I.N Isa: Supervision,
Writing - review & editing, Validation.
Acknowledgements
–
mode of CMC NH4Cl electrolyte film (Karthika et al., 2019). This
occurrence is due to the interruption of amorphous nature by incorpo-
ration of CMC-NH4Cl electrolyte to form new SBEs film. The broadness
The authors would like to express gratitude to Organisation for the
Prohibition of Chemical Weapons (OPCW) (Grant numbers: 53309
(UMT’s referral code), OPCW’s Project Account No: L/ICA/ICB/
217568/18) for the research grant support, Ministry of Higher Educa-
tion (MOHE) Malaysia for SLAB/SLAI scholarship, Universiti Malaysia
Perlis (UNIMAP) for postgraduate scholarship, Faculty of Science and
Marine Environment, Faculty of Ocean Engineering and Informatics as
well Institute of Marine Biotechnology (IMB) Universiti Malaysia Ter-
engganu for facilities and research aids. We also would like to wish
everyone to stay safe and be strong during this hard time dealing with
COVID-19 pandemic and we will get through this very soon.
–
and wavenumber of O H band of the resulted CMC-NH4Cl-(stilbene-i-
mine) SBEs were slightly shifted to higher wavenumbers within the
range of 3360 cmꢀ 1 ꢀ 3375 cmꢀ 1. This shift indicated that the presence
–
of inter- and intramolecular hydrogen bonds acting on the OH groups
and free proton of dissociation of doping salt for SBE system. Meanwhile,
the small hump at 2916 cmꢀ 1 ascribed to aliphatic C H stretching in
–
CMC-NH4Cl was shifted within the range of 2914 cmꢀ 1 – 2920 cmꢀ 1
upon the addition of stilbene-imine additives. In these sense, the
–
wavenumbers of aliphatic C H stretch for SBEs were decreased
consistently with an increasing of chain length due to an increasing of
van der Waals interaction between the alkoxy chains in additives.
Additionally, the intensity and wavenumber of asymmetric stretching
Appendix A. Supplementary data
carboxylate (COO ) anions of (C O) bands shifted from 1597 cmꢀ 1 to
–
–
–
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.carbpol.2020.116935.
the range of 1586ꢀ 1593 cmꢀ 1 respectively. In the case of C
– –
O C
stretching band of glycosidic linkages, the SBEs with and without ad-
ditives absorbed in the same IR energy at around 1416 cmꢀ 1 - 1425
cmꢀ 1, nevertheless this peak became more intense with medium to
strong intensity with the presence of additives. These related peaks are
anticipated to be effected due to the lone pair electrons of oxygen on the
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