A ratiometric fluorescent probe for the quantitative detection of styrene in air

Article abstract of DOI:10.1039/d0cc05276k

A ratiometric fluorescent probe (N-butyl-4-(4-amino-styryl)-1,8-naphthalimide) was developed for the quantitative detection of styrene in air. The sensing mechanism was found to involve a Heck reaction between the pretreated probe (diazotization) and styr

Full text of DOI:10.1039/d0cc05276k

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A ratiomeric fluorescent probe for quantitative detection of
styrene in air
Kai Chen,‡ Zhenzhong Gao,‡ Jin Sun, Xianfeng Hou* and Jian Chen*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
A ratiometric fluorescent probe (N – buty – 4 - (4-amino-styryl) - 1, generated, which is based on reaction between double bond
8 - naphthalimide) was developed for quantitative detection of on styrene and electron-donor group on an ICT (intramolecular
styrene in air. The sensing mechnism was illustrated to be Heck charger transfer) fluorophore. Transformation of electron-
reaction between pretreated probe(diazotization) and styrene. A donor group, resulted from the reaction, can lead to variation
22
probe solution absorption method was established to detect of fluoresce signal of ICT fluorophore,21,
and achieving
gaseous styrene quantitatively.
detection of styrene. And the Heck reaction,23 which can be
easily triggered between aryldiazonium and styrene under the
catalytic effect of palladium(II), is a good choice.
Styrene is an important industrial material for polymer, such as
polystyrene (PS), styrene-butadiene rubber (SBR) and
unsaturated polyester reisn (UPR).1,2 As a derivative of
benzene, styrene is a toxic organic compound and be harmful
to nervous system, blood system and digestive system.3,4
Especially, airborne styrene can enter human body through the
respiratory tract, and endanger multiple physiological
systems.5,6 Thus many governments have enacted imperative
or law to limit concentration of styrene in air.7,8 According to
the directive 2004/42/CE of the European Parliament and of
the Council, concentration of styrene in air must be kept under
39 ppb to ensure a safe environment. Therefore, it is
significant to develop a convenient and practical method for
evaluating concentration level of styrene in air.
Based on this idea, 4- amino-styrene was introduced into 1,8-
naphthalimide to develop an novel ICT fluorophore, which
possesses longer operating wavelength and lesser steric
hindrance of electron-donor position. As shown in Scheme 1,
when the diazotized probe react styrene, a new fluorophore
with bigger conjugated structure emerges. Accordingly,
remarkable variation in photophysical properties can be
observed, and achieve ratiometric fluorescence detection of
styrene. To quantitatively detect styrene in air, solution
absorption method was employed. With this probe, the
convenient and accurate detection of gaseous styrene can be
carried out.
The synthesis of probe (N-buty-4-(4-amino-styryl)-1,8-
naphthalimide) is displayed in Scheme S1, and the details of
synthesizing process is described in ESI. The probe and
At present, a number of analytical techniques have been
employed for detection of styrene in air, such as gas
chromatography-mass
spectrometry,9,10
liquid
chromatography-ultraviolet detection,11,12 laser optoacoustic
detection,13 piezo-optical sensor,14 chemiresistive gas sensor15.
However, these techniques are based on expensive
instruments and complex procedure. And a handy and reliable
method is still an urgent need. Because of sensitivity,
selectivity, and convenient operation of fluorescence sensing
technique,16-20 we attempted to develop a fluorescent probe,
which can detect gaseous styrene.
A feasible strategy
Key Laboratory for Biobased Materials and Energy of Ministry of Education,
College of Materials & Energy, South China Agricultural University, Guangzhou
510642, P. R. China. E-mail: xfhou@scau.edu.cn (X. Hou), 6440998@qq.com (J.
Chen); Fax: +86 20 85280264
‡ These authors contributed equally to this work.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
Scheme 1 Schematic illustration of probe’s diazotization and response to styrene.
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intermediate products were characterized by 1H NMR, 13C
NMR and MS (Fig. S1-S12). After diazotization, the pretreated
probe shows a little change in fluorescence emission (Scheme
1). And an absorption band at 420 nm and an emission band
around 483 nm can be observed in mixed solution (same
volume of ethyl acetate and dichloromethane). Then
fluorescence spectra of the pretreated probe solution
containing different concentrations of styrene were recorded,
as shown in Fig. 1A. Upon addition of styrene, a new emission
around 550 nm emerges. As increase in amount of styrene,
emission at 483 nm declines, and emission at 550 nm arises
synchronously. To investigate the response time, the
fluorescence ratio values (I550/I483) of reaction solution was
recorded at different time. As shown in Fig. S15, the
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DOI: 10.1039/D0CC05276K
Fig. 2 (A) Molecular orbital energies and densities of the HOMOs and LUMOs of
the probe and the primary product. (B) HPLC data for the primary product N-
buty-4-(4-styryl-styryl)-1,8-naphthalimide(a), the sensing reaction solution
without styrene(b), with styrene at 2 min(c), 4 min(d), 6 min (e).
fluorescence ratio values (I550/I483) of different reaction
solution (containing different concentrations of styrene) reach
plateaus in 5 min. It indicates the fast response of probe
towards styrene. And the working curve was built by plotting
fluorescence ratio values (I550/I483) versus concentrations of
styrene (Fig. 1B). There is a good linear relationship in the
range of 0 to 10 μM (Fig. S16), and the detection limit was
calculated to be 120 nM (details in ESI).
In order to investigate the selectivity, fluorescence responses
of pretreated probe towards different substances were tested.
As shown in Fig. S17, the probe exhibits high selectivity for
styrene over other species, which include common VOCs
(acetone, methylbenzene, formaldehyde, petroleum ether,
ethyl acetate, cyclohexane, propylene glycol, ethylbenzene
and butyl amine) and metal salts (FeSO4, KCl, Na2SO4, NaNO2,
MgSO4, KH2PO4 and CuSO4). Fluorescence response of
pretreated probe to styrene in the presence of these
substances was recorded (Fig. S17 C and D). And the results
suggest excellent anti-interference performance of probe.
Moreover, responses towards alkenes were also recorded (Fig.
2C and D). It is clear that pretreated probe shows no change in
the presence of methyl acrylate, vinyl acetate, and hexene.
However, 4-amino-styrene and 2-chloro-styrene can trigger
variation of fluorescence signal. And they exhibit the same
effect as styrene in quantitative detection. It suggests the
selectivity of probe towards styryl compound.
To illustrate the sensing mechanism, a series of experiments
were executed. At first, the primary product of sensing
reaction was isolated and purified. And it was confirmed to be
N-buty-4-(4-styryl-styryl)-1, 8-naphthalimide by 1H NMR and
ESI-MASS (Fig. S18-S19). The change in molecular structure
also can be observed in FTIR spectra (Fig. S20). The density
functional theory (DFT) calculations within the B3LYP hybrid
function were performed in
a Gaussian program, and
molecular orbital distributions of the probe and the primary
product are displayed in Fig. 2A. When the probe turns into
the product by adding styrene, HOMO-LUMO gap became
small, and it is verified by the red shift of fluorescence
emission. Moreover, the sensing reaction process was
explored by high performance liquid chromatography (HPLC).
As shown in Fig. 2B, the primary product N-buty-4-(4-styryl-
styryl)-1,8-naphthalimide exhibits a retention time of 24.6 min
(a in Fig. 2B), at which the sensing reaction solution without
styrene show no signal (b in Fig. 2B). Upon addition of styrene,
the peak at 24.6 min increase as extension of time, that
indicates generation of the primary product. These results
suggest the Heck reaction between the diazotized probe and
styrene under the catalysis of palladium(II), which leads to the
molecular structure transformation and photophysical
properties change.
Fig. 1 (A) Fluorescence response of probe (5 μM) to different concentration of
styrene (0-30 μM) in solution. (B) The fluorescence emission ratio (I550/I483) as a
function of styrene concentration. And fluorescence response of probe (5 μM)
to alkenes (C, D). Excitation wavelength is 420 nm. The mixed solution consists
of equal volumes of ethyl acetate and dichloromethane.
2 | J. Name., 2012, 00, 1-3
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For the quantitative detection of airborne styrene, a probe
solution absorption method (details in ESI) was developed.
Moreover, double wavelength UV spectrum method was used
as the reference method to assess this probe method. As
shown in Table 1, five air samples, containing different
concentrations of styrene, were measured by this probe based
on the working curve (A in Fig. S22). It is obvious that results
from this two method are very close, which suggests accuracy
and reliability of this probe solution absorption method. It's
worth noting that concentration of styrene in Sample 1 is 8.34
ppb, which is far below the limit value (39 ppb) in the directive
2004/42/CE of the European Parliament and of the Council. It
indicates the excellent sensitivity and practicability of this
probe solution absorption method.
To evaluate selectivity of this probe solution absorption
method, air samples containing common VOCs (acetone,
methylbenzene, formaldehyde, petroleum ether, ethyl
acetate, and styrene respectively) are tested. And results show
that the probe solution absorption has a response to styrene
only (Table S1). Furthermore, mixed samples, which consist of
styrene and these VOCs respectively, were inlet to the
sampling system to investigate anti-interference of this
method. As shown in Table S2, this method can detect styrene
well in the presence of different VOCs. These results above
suggest that the probe solution absorption method would be a
promising tool for monitoring styrene in air.
Notes and references
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In summary, we successfully developed
a ratiometric
fluorescent probe for styrene with excellent selectivity, high
sensitivity and fast response. The sensing mechanism was
demonstrated to be Heck reaction between the diazotized
probe and styrene under the catalytic effect of palladium(II).
Moreover, the probe solution absorption method, developed
for quantitative detection of styrene in air, exhibited good
accuracy and reliability. This work provides a reference for
quantitatively detecting VOCs in air.
We gratefully acknowledge the financial support by National
Key R&D Program of China (No.2018YFD0600305), Natural
Science Foundation of Guangdong Province, China (No.
2018A030310348) and Guangzhou Science and Technology
Plan (No. 201803030031).
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Conflicts of interest
There are no conflicts to declare.
Table 1 Results of air samples from double wavelength UV spectrum method and
this probe method.
Double wavelength UV
spectrum method (ppb)
Samples
This method(ppb)
1
2
3
4
5
7.91 ± 0.38
8.34 ± 0.34
9.79 ± 0.52
16.88 ± 0.76
29.34 ± 0.96
48.55 ± 1.59
8.92 ± 0.40
16.66 ± 0.89
31.90 ± 1.04
49.57 ± 1.83
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J. Name., 2013, 00, 1-3 | 3
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A ratiomeric fluorescent probe for quantitative detection of styrene in air.