Electrospun nanofibrous sheet doped with a novel triphenylamine based salicylaldehyde fluorophore for hydrazine vapor detection

Article abstract of DOI:10.1016/j.jphotochem.2020.112879

Successful synthesis of a novel triphenylamine based salicylaldehyde fluorophore (compound 1) was performed via Suzuki cross-coupling reaction. Subsequently, the identification the hydrazine vapor of an electrospun nanofiber sheet combined with compound 1 depending on solid condition was described. Furthermore, cellulose acetate (CA) combined with the electrospun nanofiber sheet based on compound 1 was formed by applying the electrospinning technique where the average diameter was 324.6 ± 91.6 nm. The sensing nanofiber sheet exhibited a sensitive and selective reaction to hydrazine vapor with a linear concentration range of 0.2-1 %w/v in aqueous solution according to the analysis of fluorescence images using ImageJ. Moreover, it exhibited the elevated selectivity with hydrazine across 21 convenient interferences. Initial findings revealed the nanofibrous mat's sensitivity and selectivity in terms of the identification of hydrazine via naked-eye detection under backlight 365 nm with fluorescent turn-off mode. Additionally, the generation of compound 1 and the hydrazone product (compound 1-HZ) was investigated through the use of ¹H-NMR titration and HRMS, which affirmed the formation of hydrazine with a proton chemical shift at 7.95 ppm, HRMS of compound 1-HZ at m/z = 380.1764 [1-HZ+H]⁺). It has been demonstrated that the nanofibrous mat offers a basic and suitable method for detecting water vapour in water environments as well as industrial chemical setting.

Full text of DOI:10.1016/j.jphotochem.2020.112879

Journal of Photochemistry & Photobiology, A: Chemistry 404 (2021) 112879
Contents lists available at ScienceDirect
Journal of Photochemistry & Photobiology, A: Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Electrospun nanofibrous sheet doped with a novel triphenylamine based
salicylaldehyde fluorophore for hydrazine vapor detection
Apisit Karaweka, Pipattra Mayurachayakula, Thanapich Santiwata, Mongkol Sukwattanasinittb,
,
Nakorn Niamnonta *
a Organic Synthesis, Electrochemistry & Natural Product Research Unit, Department of Chemistry, Faculty of Science, King Mongkut’s University of Technology Thonburi,
Bangkok, 10140, Thailand
b Organic Synthesis Research Unit, Department of Chemistry, Faculty of Science and Nanotec-CU Center of Excellence on Food and Agriculture, Chulalongkorn
University, Bangkok, 10330, Thailand
A R T I C L E I N F O
A B S T R A C T
Keywords:
Successful synthesis of a novel triphenylamine based salicylaldehyde fluorophore (compound 1) was performed
via Suzuki cross-coupling reaction. Subsequently, the identification the hydrazine vapor of an electrospun
nanofiber sheet combined with compound 1 depending on solid condition was described. Furthermore, cellulose
acetate (CA) combined with the electrospun nanofiber sheet based on compound 1 was formed by applying the
electrospinning technique where the average diameter was 324.6 ± 91.6 nm. The sensing nanofiber sheet
exhibited a sensitive and selective reaction to hydrazine vapor with a linear concentration range of 0.2-1 %w/v
in aqueous solution according to the analysis of fluorescence images using ImageJ. Moreover, it exhibited the
elevated selectivity with hydrazine across 21 convenient interferences. Initial findings revealed the nanofibrous
mat’s sensitivity and selectivity in terms of the identification of hydrazine via naked-eye detection under
backlight 365 nm with fluorescent turn-off mode. Additionally, the generation of compound 1 and the hydrazone
product (compound 1-HZ) was investigated through the use of 1H-NMR titration and HRMS, which affirmed the
formation of hydrazine with a proton chemical shift at 7.95 ppm, HRMS of compound 1-HZ at m/z = 380.1764
[1-HZ+H]+). It has been demonstrated that the nanofibrous mat offers a basic and suitable method for detecting
water vapour in water environments as well as industrial chemical setting.
Electrospun nanofibrous
Hydrazine
Salicylaldehyde
1. Introduction
potable water, with limits typically being low micromolar levels [10].
Resultantly, it is necessary to develop robust and simple analytical
Hydrazine (N2H4) is a critical chemical reagent that plays a pivotal
role in various fields, including medicines, chemicals used in photog-
raphy, pigments, textile dyes and materials for reducing the rate of
corrosion in a variety of chemical industries [1–2]. Additionally, it is
recognised for its use in rocket propulsion due to its increased enthalpy
of combustion [3–4]. Despite its different benefits, it is known to be a
carcinogen with high toxicity that has the potential to cause significant
pollution to the environment along with a risk of damaging health as a
result of the processes involved in manufacturing, using, transporting
and disposing of the substance [5–6]. It has the potential to cause serious
damage to the liver, lungs, kidneys and the nervous system as absor-
bance of hydrazine can occur easily via the mouth, skin or by being
inhaled subsequent to exposure [7–9]. Authorities around the world
have placed strict regulations on the amount of hydrazine permissible in
techniques that can detect trace amounts of hydrazine.
A variety of analytical approaches can be implemented for detecting
molecules of hydrazine, including chromatography [11], titrimetry
[12], voltammetry [13] and spectrophotometry [14–15]. From these
different approaches, fluorescence is considered the most suitable as a
result of its ease of use, cost effectiveness, increased sensitivity and
flexible toolbox in the area of environmental monitoring [16–17].
Nevertheless, studies in the field have largely focused on the use of novel
fluorophores in monitoring hydrazine including various halo-esters
[18–20], keto ester [21–22], acetoxy group [23–27], phthalimide de-
rivative [28–30], active methylene groups [31–34] aldehyde group
[35–38] and various other functional groups [39]. Hence, the develop-
ment of novel fluorophores for the purpose of quantitatively detecting
hydrazine in vapor phase is still significantly challenging.
* Corresponding author.
E-mail address: nakorn.nia@kmutt.ac.th (N. Niamnont).
https://doi.org/10.1016/j.jphotochem.2020.112879
Received 13 July 2020; Received in revised form 17 August 2020; Accepted 30 August 2020
Available online 6 September 2020
1010-6030/© 2020 Elsevier B.V. All rights reserved.

A. Karawek et al.
Journal of Photochemistry & Photobiology, A: Chemistry 404 (2021) 112879
Electrospinning is a basic and notable flexible approach that can
spectrophotometer. Finally, a JEOL (JSM-6301 F) SEM analyser was
utilised for the analysis of the electrospun nanofibrous sheet’s
morphology.
directly produce nanofibers from various different polymers and com-
posite materials under the application of high voltage [40–41]. The
surface to volume ratio of nanofibers is high, thus promoting their
successful application in various fields including for sensors [42–43],
biomedical and biosensing materials [44–46], electrode materials
[47–48], controlled drug delivery [49–50], wound dressings [51–52],
oily wastewater separation [53–55] and air filtration [56–57].
Non-woven nanofiber mats exhibit increased porosity and a large sur-
face area, making them perfect for use as scaffolds in sensor applications
[58]. Recent studies have reported the use of chemical sensors of fluo-
rophores formed from electrospun nanofibers for a variety of different
analytes, including metal ions (Cu2+ and Cr3+) [59] explosives [60–61],
proteins [62] and volatile organic compounds [63]. The current
research focuses on the development of a compound 1 with CA via the
application of the electrospinning method for selectively detecting hy-
drazine in vapor phase, and is the first study to attempt such an
approach. Compound 1 consisting of an aldehyde group as hydrazine
probe was designed and successfully synthesized. The CA was chosen as
the substrate for its nontoxic, high-performance, and biodegradable
material, along with the CA which it has been utilized in many previous
studies to fabricate the nanofibrous by electrospinning technique [64].
Moreover, examination of the fluorescent images was performed to
quantitatively determine the concentration of hydrazine, selectivity test,
reversibility test and mechanistic of the probes for hydrazine detection.
2.3. One pot synthesis of compound 1
A combination of (4-(diphenylamino)phenylboronic acid (500.0 mg,
1.72 mmol), tetrakis(triphenyl phosphine)palladium(0) (180 mg,
0.16 mmol), 4-brosalicylaldehyde (346.1 mg, 1.72 mmol) in THF
(10 mL) and water (1 mL) was added to K2CO3 (500 mg, 3.62 mmol) in
an environment of N2 gas, and stirring of the resulting mixture was
performed at 70 ℃. The reaction was allowed to proceed for 4 hours,
after which 1 M HCl (20 mL) was added to the mixture and extraction
was performed with EtOAC (2 × 15 ml). After being evaporated, the
residue was eluted through a column of silica gel via pure hexane to
hexane/DCM (2/3) as the eluent to yield a solid with bright yellow
colour.
2.4. Photophysical properties of compound 1 in difference solvent
polarities
The stock solution compound 1 (1 mM) were dissolved in their sol-
vent ranging from low to high polarities, namely diethyl ether, THF,
DMSO, DMF, acetone and MeCN. Subsequently, then diluted concen-
tration of compound 1 from previous will be 20 μM followed by incu-
bation for 10 min under rt conditions. Recording of the UV-Vis
absorption was performed in the range between 300 nm and 700 nm,
while measurement of the fluorescence spectra was conducted in the
range between 390 nm and 700 nm where their maximum absorption
wavelength was used as the excitation wavelength.
2. Experimental
2.1. Materials and solvents
(4-(diphenylamino)phenylboronic acid and 4-brosalicylaldehyde
were acquired from Tokyo Chemical Industry (TCI). Cellulose acetate
powder, tetrakis(triphenyl phosphine)palladium(0) and Hydrazine
monohydrate 64-65% were bought from Sigma-Aldrich. Analytical re-
agent grade solvents, such as diethyl ether, tetrahydrofuran (THF),
dimethylsulfoxide (DMSO), dimethylformamide (DMF), acetone and
acetonitrile (MeCN), were bought from RCI Lab scan. Each of the
additional reagents were acquired from Sigma-Aldrich, Merck or RCI
Lab scan in a non-selective manner and were not additionally purified
unless specifically stated. Reactions were all performed in an atmo-
sphere comprised of N2. Furthermore, monitoring of the reaction’s
progress was performed with F254 thin layer chromatography (TLC) and
visualisation of the components was achieved via observation under UV
light (365 nm). Solvents for extraction and chromatography, such as
hexane, dichloromethane (DCM), ethyl acetate(EtOAc), were of com-
mercial grade and were distilled before use. All aqueous solutions were
prepared using Type II (pure) water.
2.5. Optical spectra respond of compound 1 toward hydrazine
Stock solution compounds 1 (1 mM) were dissolved in DMSO.
Dilution was performed for various samples of compounds 1, where
each was prepared individually either included and did not include the
hydrazine solution in DSMO. The final concentration of the samples was
20 μM and incubation of the samples was performed at rt for 10 min. The
UV-Vis absorption ranged between 300 nm and 700 nm, while mea-
surement of the fluorescence spectra showed values between 390 nm
and 700 nm where their maximum absorption wavelength was used as
the excitation wavelength.
2.6. Theoretical calculations
Optimisation of the ground-state molecular geometry was achieved
by utilizing the density functional theory (DFT) through the imple-
mentation of the Gaussian 09 program at the B3LYP/6-31G** basis set
[65–66]. Determination of optimal geometries was based on isolated
entities within a vacuum with no imposition of conformation con-
straints. Time-dependent density functional theory (TDDFT) calcula-
tions were performed on the optimised geometries obtained (utilising
the identical functional and basis set used in the previous calculations)
for the purpose of predicting the vertical electronic excitation energies.
Plotting of molecular orbital contours was performed with Gauss View 6.
2.2. Analytical instrument
The 1H and 13C NMR spectra were conducted for salicylaldehyde
derivatives using a Bruker Avance III HD Spectrometer (400 MHz,
1
100 MHz for H and 13C) where the internal standard used was tetra-
methylsilane. The amount of absorption signals in the 1H NMR- spectra
was classified in the following manner: s/singlet; d/doublet, t/triplet,
sd/singlet of doublet, dd/doublet of doublet, dt/doublet of triplet, td/
triplet of doublet, tt/triplet of triplets, m/multiplet. A Thermo Fisher
Scientific device (model Nicolet 8700) was used to perform infrared
spectra with KBr pellets. High resolution electrospray ionization mass
spectra (HRMS) were obtained using a Bruker maXis with ethyl acetate
as the solvent in the positive ionisation mode. Measurement of melting
points was performed with a Thomas Hoover capillary device and no
corrections were subsequently made to the generated values. A Hitachi
F-2500 fluorescence spectrophotometer was used to measure the fluo-
rescent spectra. Measurement of UV-Vis absorption spectra was per-
2.7. Fabrication of compound 1 nanofibrous sheet
The 0.01 %w/v of compound 1 was synthesized via the Suzuki-
Miyaura cross-coupling reaction and dissolved in a mixture between 1
%v/v of tween 80 and 2:1 acetone/DMF at ambient temperature. Then,
the 17 %w/v of CA powder was added into stirred for 1 h until the
polymer solution was homogenous. In the electrospinning procedure,
the compound 1-CA polymer solution was fed into a syringe with needle
and the standard parameters were as follows [64]: the electric voltage
applied was 17 kV, the solution feed rate was 2 mL h-, and the tip of the
formed with
a Perkin Elmer ltd, lambda 35/fias 300 UV-vis
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Journal of Photochemistry & Photobiology, A: Chemistry 404 (2021) 112879
Scheme 1. The one step synthetic route of compound 1.
needle was positioned at a distance of 12 cm from the collector wheel.
After finishing the electrospun nanofibrous sheets, the compound 1
nanofibrous sheets were removed from the collector wheel and per-
formed in a vacuum oven at 60 ◦C for 6 h for the purpose of remove any
remaining solvent. Lastly, gold layers were applied to the nanofibrous
sheet via sputter coating and it was subsequently analysed with a JEOL
(JSM-6301 F) SEM machine at an accelerating voltage of 20 kV to study
the morphology.
correlation between the ratio fluorescent image intensity (I/I0)) before
(I0) and after (I) being exposed to different analytes was plotted.
2.10. Sensing mechanism of compound 1 toward hydrazine detection
1H-NMR titration was utilized to investigate the mechanism of the
reaction between compound 1 and hydrazine. Initially, the stock solu-
tions of compounds 1 (20 mM) were dissolved in DMSO-d6. Dilution of
the sample was performed for various samples of compound 1, each of
which contained hydrazine at distinct concentrations (0, 0.5, 1.0, and
2.0 equiv.) in DMSO-d6, which were prepared individually. The ultimate
concentration of the samples was 5 mM and incubation were performed
for a period of 10 min under rt conditions. Evaluation of the obtained
data was conducted using1H-NMR spectroscopy and the entire spectra
were recombined into a stacked plot using Mnova software.
2.8. Hydrazine vapor quantitative detection of compound 1 nanofibrous
sheet
In order to detect hydrazine quantitively in vapour phase, fluores-
cent images were analysed to evaluate the changes in the fluorescent
intensity of the nanofibrous sheets of compound 1 subsequent to being
fumigated with hydrazine vapor. Firstly, the nanofibrous sheets of
compound
1 were divided into segments with dimensions of
2.11. Real sample detection
1.5 cm x 1.5 cm. Secondly, photographs of the nanofibrous sheets of
compound 1 were captured prior to being exposed to hydrazine vapor
using a portable UV lamp with excitation at 365 nm. Thirdly, the sheets
were position on the top of a vial that contained hydrazine at different
concentrations (0, 0.20, 0.30, 0.40, 0.50, 0.75 and 0.10 %w/v) within an
aqueous solution for a period of 10 min; Subsequently, photographs
were captured again using a portable UV lamp with an excitation of
365 nm. an iPhone smartphone with the Pro Camera application was
used to record the photographic images using the lowest ISO and me-
dium white balance modes. Afterwards, ImageJ (ver. 1.48) software was
utilized to covert the digital colour data from the digital photos into
greyscale. Lastly, the correlation between the ratio fluorescent image
intensity (I/I0) before (I0) and after (I) being exposed to hydrazine
vapour versus the concentration of hydrazine in the aqueous solution
was plotted.
For the practical sample analysis in the laboratory, tap water was
preferred. Tap water which has become contaminated from military and
industrial wastes, wastewater treatment plant effluents, and possible
formation in tap water disinfection processes and distribution systems.
Because hydrazine is often used for removal of halogens from waste-
water treatment, it may enter drinking water sources that are impacted
by wastewater or wastewater treatment plant effluents. Fumigation of
the nanofibrous sheet of compound 1 was performed with tap water and
the introduction of various concentrations of standard hydrazine solu-
tion (0.25, 0.6, 0.9 %w/v). Photographs of the nanofibrous sheet of
compound 1 were captured prior and after being exposed to various
samples under a portable UV lamp at an excitation of 356 nm with a
fumigation period for 10 min at rt conditions. Subsequently, ImageJ (ver
1.48) was utilised to convert digital colour data in the digital photos into
greyscale. Lastly, relative standard deviation (RSD%) and recovery
percentages were calculated.
2.9. Selective and competitive studies of compound 1 nanofibrous sheet
Photographs of the nanofibrous sheet of compound 1 prior and
subsequent to being exposed to various analytes (1%w/v) and adding
hydrazine (1%w/v) were captured under a portable UV lamp at an
excitation of 365 nm for a fumigation period of 10 min at rt condition.
Subsequently, ImageJ (ver. 1.48) software was utilised in order to covert
the digital colour data from the digital photos into greyscale. Lastly, the
3. Results and discussion
3.1. Design and characterization of compound 1
Successful synthesis of the compound 1 was achieved in one step via
the Suzuki-Miyaura cross-coupling reaction among (4-(diphenyl amino)
Fig. 1. Fabrication process of the compound 1 (B) mixed with CA nanofibrous sheet.
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Journal of Photochemistry & Photobiology, A: Chemistry 404 (2021) 112879
Fig. 2. (A) Normalized fluorescence emission spectra of compound 1 in various solvents at 20
μ
M using their longest absorption wavelength as excitation wave-
length. (B) Lippert-Mataga plots showing the Stokes shift versus the orientation polarization (Δf) of the solvents for compound 1
Fig. 3. Changes in normalized absorption (A) and emission spectra (B) for compound 1 (30 μM) before (red line) and after (black line) the addition of N2H4 (100 μM)
in DMSO. and the inset photo show the colorimetric and fluorogenic changes induced by N2H4 treatment, under white light and a 365 nm handheld UV lamp,
respectively.
phenyl)boronic acid and 4-Bromo salicylaldehyde to produce an excel-
lent yield of compound 1 (91%), as demonstrated in Scheme 1. The
chemical framework of compound 1 includes amine group as an electron
donor (D) unit with a salicylaldehyde as electron acceptor (A) unit that
exhibits excellent charge transfer ability, while the formation of a novel
compound 1 by the large stokes shift in high polar solvents [69–70] as
shown in Fig. 2B. The emission wavelength shifts as well as the rela-
tionship among solvent polarity and emission colour are indications of
the potential capacity of compound 1 as a fluorescent probe with the
potential to be applied in environmental detection processes.
fluorescent molecule with a D-π–A structure occurs. Characterisation
and confirmation of compound 1 was performed by 1H-NMR, 13C-NMR,
and HRMS information as demonstrated in (Fig S1-S3†). Furthermore,
the aldehyde group reacted with nucleophilic targets including hydra-
zine at rt conditions. Hydrazine attraction causes transformation of
formyl into hydrazone, which induces the rupture of the conjugated
system and the distribution of electron density. Such a reaction causes
distinctive changes in absorption of UV-vis and fluorescence spectra, as
well as facilitates fluorogenic and colorimetric detection (Fig. 1).
3.3. Optical spectral responses of compound 1 toward hydrazine
To examine the possibility of using compound 1 in the detection of
hydrazine, the UV-Vis absorption and fluorescence spectra of compound
1 were analysed both with and without hydrazine, as demonstrated in
Fig. 3. Compound 1 exhibits a pair of characteristic absorption bands at
377 nm and 280 nm in DMSO, as illustrated in Fig. 3A. These absorption
bands can be attributed to the excited-state intramolecular proton-
transfer (ESIPT) procedure of planar triphenylamine derivatives. A
substitute novel individual maximum absorption wavelength emerged
3.2. Photophysical properties of compound 1 in difference solvent
polarities
at 355 nm, which disrupted the π-conjugation and impact the intra-
molecular electron density distribution. It was observed that the solution
colour transformed from yellow to no color, which allowed hydrazine to
be colorimetrically detected via the naked eye.
Fig. 2A shows the fluorescence spectra of compound 1 in solvents
with distinct polarities. A marginal rise in the emission wavelength was
demonstrated in polar solvents to shift compared with those in low polar
solvents. This finding implies that the excitation causes the dipole
moment of the molecules to increase, while the ground and excited state
dipoles exhibit similarities [67–68], suggesting an intramolecular
charge transfer (ICT) procedure in the molecules throughout optical
excitation. Additionally, comparatively good linear correlations exist
among the orientation polarization (Δf) of the solvent and Stokes shift
(Δʋ) where R2 is calculated as 0.99. It is to confirm the ICT process
Hence, when excited at 370 nm, the maximum emission wavelength
of compound 1 was 535 nm after hydrazine was added. The intensity of
the fluorescence spectra marginally decreased with a blue shift to
455 nm due to the formation of hydrazone by aldehyde and hydrazine,
as illustrated in Fig. 3B. Accordingly, the fluorescence color shifted from
light yellow to pale blue under UV light at 365 nm (Fig. 3B, inset). The
finding indicating the instantaneous formation between compound 1
hydrazine at rt is an advantageous characteristic for the ratio metric
fluorescence detection of hydrazine.
through D-π-A system from amine as D to salicylaldehyde group as A of
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Journal of Photochemistry & Photobiology, A: Chemistry 404 (2021) 112879
Fig. 4. HOMO-LUMO energy levels and the interfacial plots of the molecular orbitals for compound 1 and its reacted form with hydrazine compound 1-HZ calculated
at the TDDFT level using a B3LYP/6-31G** basis sets in the Gaussian 09 program.
Fig. 5. Typical SEM images and histograms of fiber diameter distribution of pure CA of pure CA (A and B) nanofibers and compound 1 mixed with CA nanofibrous
sheet (C and D), respectively.
3.4. Theoretical calculations
the lowest unoccupied molecular orbital (LUMO). Furthermore, the
dispersal of the electron densities across the -conjugated system on the
π
To increase the comprehension of the blue shift of the fluorescence
response of compound 1 when hydrazine is present, theoretical calcu-
lations were performed using TDDFT with the B3LYP/6-31G** basis set
with the application of a suite of Gaussian 09 software, as illustrated in
Fig. 4. The electronic distributions of the compounds prior and after
reaction with hydrazine (compound 1 and compound 1-HZ) are found to
significantly different. For compound 1, the electron densities were
localised in the triphenylamine moiety on the highest occupied molec-
ular orbital (HOMO) and transitioned to the salicylaldehyde moiety on
HOMO of the hydrazone product (compound 1-HZ), but migration to
the salicylhydrazone moiety on the LUMO. Additionally, calculation of
the energy discrepancy between the HOMO and LUMO of compound 1-
HZ returned a value of 3.5858 eV, while the energy gap for compound 1
was determined to be 3.2129 eV. Hence, the greater energy gap for
compound 1-HZ compared to compound 1 conforms with the blue shift
observed in the absorption and emission when compound 1 was treated
with hydrazine.
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Journal of Photochemistry & Photobiology, A: Chemistry 404 (2021) 112879
Fig. 6. (A) Fluorescence photo under UV light (365 nm) of compound 1 nanofibrous sheet after fumigation with different concentration of hydrazine aqueous
solution. (B) Calibration curves and LOD value of compound 1 nanofibrous sheet (B): Plot of I/I0 against I and I0 are the grayscale intensities of fluorescent image
before and after fumigation with hydrazine various concentration. Error bars represent mean ± s.d. (n = 5 independent experiments)
3.5. Morphology of compound 1 nanofibrous sheet
3-dimensional (3-D) nanoarchitecture utilises a basic electrospinning
approach. It is anticipated that the increased surface areas surrounding
and inside the porous nanofiber film can potentially offer atypically
elevated sensitive and rapid response times for sensing applications
[71].
The standard SEM images of the electrospun nanofibrous sheet
formed from the pure CA (A) and compound 1 (0.01%w/v) combined
with CA (C) are displayed in Fig. 5. Adding compound 1 to the nano-
fibers does not impact the morphology while nanofibers generated a
non-woven mat with a random orientation created space between the
nanofibers. Hence, the nanofibers formed from mixing compound 1 with
CA are uniform and bead free on surface of nanofiber sheet. The data
provided in Fig. 5B indicates that the nanofibers had an average diam-
eter of 324.6 ± 91.6 nm. Moreover, mechanical properties of compound
1 nanofibrous sheet were studied as shown in Figure S8. Evidently, this
3.6. Hydrazine vapor quantitative detection of compound 1 nanofibrous
sheet
For the purpose of developing methods for easily and efficiently
detecting hydrazine, preparation of the nanofibrous sheet of compound
1 was performed with the electrospinning method and it was
Fig. 7. (A) Fluorescence photo under UV light (365 nm) of
compound 1 nanofibrous sheet after 10 min of fumigation with
various analytes at r.t. (B) Florescence image intensity ratio (I/
I0) of compound 1 nanofibrous sheet expose for 10 min at r.t.
with several analytes (1%w/v) and the addition of hydrazine
(1%w/v): Hydrazine (1), DI water (2), hydrogen peroxide (3),
hydroxylamine (4), sodium hydroxide (5), sodium bicarbonate
(6), ammonia (7), urea(8), ethylenediamine(9), ethanolamine
(10), ethylene glycol (11), diethanolamine (12), diethanol-
amine (13), diethylene glycol (14), triethylamine (15), meth-
anol (16), ethanol (17), iso-propanol (18), n-butanol (19),
dimethylformamide (20), dimethyl sulfoxide (21), hydrochlo-
ric acid(22), sulfuric acid (23) and acetic acid (24).
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Journal of Photochemistry & Photobiology, A: Chemistry 404 (2021) 112879
Fig. 8. Sensing mechanism of compound 1 to hydrazine detection. (A) Reaction scheme representing the formation of the hydrazone (compound 1-HZ). (B) 1H NMR
spectra titration of compound 1 (10
compound 1-HZ.
μM) upon addition of various equivalents (0, 0.5, 1 and 2 equiv.) in DMSO-d6. (C) ESI-HRMS of compound 1 and (D) ESI-HRMS of
subsequently divided into segments with dimensions of 1.5 cm x 1.5 cm.
The nanofibrous sheet of compound 1 was placed at the opening of a vial
that contained an aqueous solution of hydrazine and was then fumigated
for 10 min at rt as illustrated in Fig. 6A. The fluorescent emissions of the
nanofibrous sheet diminished from a powerful green light to a signal
with no fluorescence based on the hydrazine concentration within the
aqueous solution. In order to discriminate hydrazine, a smart phone was
used to capture photographs of the fluorescent images under a portable
UV lamp at an excitation of 365 nm. Subsequently, the ImageJ (ver
1.48) programme was utilised to convert digital colour information from
the digital photographs into grayscale values. Lastly preparation of the
calibration curve was made by plotting the ratio fluorescent image
density (I/I0) prior (I0) and subsequent (I) to being exposed to hydrazine
vapor for different concentrations of hydrazine (0.2, 0.3, 0.4, 0.5, 0.75
and 1.0%w/v) in an aqueous solution as shown in Fig. 6B. The con-
centration ranged linearly from 0.2-1.0 %w/v. The limit of detection
(LOD) for hydrazine was determined to be 0.03 %w/v (~ 9 mM)
utilising the conventional technique (3 s/K, s = standard derivation of
blank, K = slope of calibration), which seemed to be the optimal value
lower than has been reported by previous experiments (see Table S1).
3.7. Vapor phase selectivity and competition of compound 1 nanofibrous
sheet
The selectivity study of the nanofibrous sheet of compound 1 to-
wards hydrazine vapor was additionally investigated by utilizing 22
compounds, including Hydrazine (1), DI water (2), hydrogen peroxide
(3), hydroxylamine (4), ammonia (5), urea(6), ethylenediamine(7),
ethanolamine(8), ethylene glycol (9), diethanolamine (10), diethanol-
amine (11), diethylene glycol (12), triethylamine (13), methanol (14),
ethanol (15), iso-propanol (16), n-butanol (17), dimethylformamide
(18), dimethyl sulfoxide (19), hydrochloric acid(20), sulfuric acid (21)
and acetic acid (22). The findings indicate that the emissions of com-
pound 1 did not change significantly in fluorescent mode with various
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Journal of Photochemistry & Photobiology, A: Chemistry 404 (2021) 112879
detecting hydrazine in vapor phase. The nanofibrous sheet exhibits
multiple functionalities as it acts as a fluorescence quencher and chemo
selective toward hydrazine. For the purposes of convenience, we applied
fluorescence image analysis to the nanofibrous sheet using Image J
software, which enabled the concentration of hydrazine to be effectively
determined by just examining the changes in the intensity of the fluo-
rescent images. In comparison to different solid state fluorogenic for the
detection of hydrazine gases, the proposed nanofibrous sheet could offer
an easy but advantageous technique for practically detecting chemicals
in environmental settings. The detection threshold for hydrazine vapor
for the nanofibrous sheet of compound 1 was 0.03 %w/v. Accordingly,
Compound 1 showed selectivity and sensitive to hydrazine, while the
turn-off mode of detection materialised via a reduced ESPIT procedure
induced by hydrazine. Additionally, the reusability of nanofiber sheet
exhibited less than 15% change of signal change in a 4-cycle test for
hydrazine vapor detection. Lastly, it is possible to achieve acceptable
results by applying Compound 1 for the detection of hydrazine in actual
samples of water.
Table 1
The percent recovery data for the detection of hydrazine in spiked tap water
samples ((n = 3)a. (aMean ± SD).
Sample
Found (%w/
Spike (%
Found (%w/
v)
Recovery
(%)
RSD
(%)
v)
w/v)
0.25
0.60
0.90
0.26 ± 0.01
0.62 ± 0.03
0.89 ± 0.04
102.2
103.4
98.8
4.5
4.8
4.0
Tap
0.01 ± 0.01
water
amines, volatile organic compounds, acids and bases analytes under the
same conditions. It is interesting to note that the emissions of compound
1 only showed a significant decrease when hydrazine vapour was pre-
sent, as demonstrated in Fig. 7. It was also possible to observe the
particular reaction of the nanofibrous sheet of compound 1 to hydrazine
vapour via the naked eye (Fig. 7). Furthermore, interference studies
were conducted on additional competitive anions to verify that the
probe is capable of purely detecting hydrazine when a large number of
other molecules are present.
CRediT authorship contribution statement
3.8. Sensing mechanism of compound 1 to hydrazine detection
Apisit Karawek: Conceptualization, Formal analysis, Visualization,
Writing - original draft. Pipattra Mayurachayakul: Investigation,
Writing - review & editing. Thanapich Santiwat: Investigation, Writing
- review & editing. Mongkol Sukwattanasinitt: Conceptualization,
Writing - review & editing. Nakorn Niamnont: Conceptualization, Su-
pervision, Conceptualization, Formal analysis, Writing - review &
editing.
The sensing mechanism of the interaction between hydrazine and
compound 1 was examined via contracting various experimental ana-
lyses (Fig. 8A). Fig. 8B shows the 1H NMR titration spectra of compound
1 (10 μM) after adding several equivalents (0, 0.5, 1 and 2 equiv.) in
DMSO-d6. When hydrazine was not present, Compound 1 exhibited an
aldehyde proton at 10.23 ppm (b-H) as well as an hydroxyl proton at
10.84 ppm (a-H), which was caused by the ESIPT when an intra-
molecular hydrogen bond (H-bond) was present between the proton
donor (–OH) and the proton acceptor (–C = O) groups. Subsequent to
the addition of excess hydrazine, the aldehyde proton (b-H) was no
longer detected, indicating that aldehyde was substituted with hydra-
zine. Hydrazine formed a Schiff base and ESIPT was obstructed.
Furthermore, emergence of the new chemical shifts for the = CH- and
-NH2 group occurred at 7.95 (c-H) and 6.92 ppm (d-H), respectively.
ESI-MS analysis was conducted on the hydrazine Schiff base (compound
1-HZ), and the results showed that (compound 1-HZ) was subjected to
Declaration of Competing Interest
The authors reported no declarations of interest.
Acknowledgments
This work was supported by Thailand Research Fund under grants
MRG6180070 and RTA6180007. A.K. is grateful to the research fund for
Petchra Pra Jom Klao Master Scholarship for Master’s student of King
Mongkut’s University of Technology Thonburi (KMUTT).
(m/z = 380.1764 for
C
25H21N3O, [compound 1-HZ+H]+), which
correspond to the calculation(m/z = 380.1763) (Fig. 8C).
3.9. Real water sample
Appendix A. Supplementary data
The nanofibrous sheet of compound 1 was employed to monitor
hydrazine in samples of tap water. Each of the samples was spiked with a
determined volume of hydrazine (0.1 %w/v). Every sample was tested
three times and the findings are demonstrated in Table 1. This technique
had increased analytical precision (RSD < 5%) and acceptable accuracy
(< 5% error), thus suggesting that it has reliability for the detection of
hydrazine in actual samples. Compared with different fluorophores
utilised for detecting hydrazine in water media, compound 1 has a lower
detection threshold (Table S1). The reusability and reproducibility of
the nanofibrous mat was also investigated. To determine, the reusability
of the nanofibrous mat sensor, the compound 1 nanofibrous sheet was
controlled by alternating the fumigation of 1%v/v N2H4 and the im-
mersion of 5%wt HCl. The nanofibrous mat was then reused for sensing
the hydrazine vapor as shown in Figure S9. The result showed that the
compound 1 nanofibrous sheet was reused over 4 times. Hence, this
finding indicates the nanofibrous sheet of compound 1 has potential for
use as new option for selectively detecting hydrazine vapor.
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.jphotochem.2020.
112879.
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