Preparation of pyrene-functionalized fluorescent film with a benzene ring in spacer and sensitive detection to picric acid in aqueous phase

Article abstract of DOI:10.1016/j.jphotochem.2010.11.004

A fluorescent sensing film was fabricated by chemical assembling pyrene moieties on a glass plate surface via a spacer containing a benzene ring. The film was used for the detection of nitroaromatic compounds (NACs), particularly picric acid (PA), in aque

Full text of DOI:10.1016/j.jphotochem.2010.11.004

Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 356–362
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Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Preparation of pyrene-functionalized fluorescent film with a benzene ring in
spacer and sensitive detection to picric acid in aqueous phase
Haiying Du, Gang He, Taihong Liu, Liping Ding, Yu Fang∗
Key Laboratory of Applied Surface and Colloid Chemistry (Ministry of Education), School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an 710062, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 August 2010
Received in revised form 21 October 2010
Accepted 5 November 2010
Available online 13 November 2010
A fluorescent sensing film was fabricated by chemical assembling pyrene moieties on a glass plate surface
via a spacer containing a benzene ring. The film was used for the detection of nitroaromatic compounds
(NACs), particularly picric acid (PA), in aqueous phase. Introduction of benzene structure in the spacer
favors ␲–␲ stacking between pyrene moieties on the end of each spacer, which encourages direct expo-
sure of the fluorophore residues to aqueous phase, and thus the film is able to quickly monitor NACs.
The advantages of this design have been demonstrated experimentally in terms of the highly sensitive
response of the above-mentioned film to the presence of trace amounts of NACs in aqueous solution. The
detection limit (DL) of the film to PA reaches 1.0 × 10−8 mol/L. Further experiments demonstrated that
the sensing process is fully reversible and is free of interference from common chemicals like toluene,
benzene, trichlormethane, ethanol, artificial seawater, NaOH, HCl, etc. Furthermore, fluorescence lifetime
measurement revealed that the quenching is static in nature.
Keywords:
Pyrene
Nitroaromatics
Picric acid
Film sensor
Fluorescence
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
elements. Compared with aromatics-based films, CPs-based films
are more sensitive even though they are, generally speaking, more
Contamination of soil and water at sites where nitroaromatic
compounds (NACs) are manufactured or used is a serious environ-
mental problem because ingestion of them may cause impair vision,
liver or kidney damage, gastritis, aplastic anemia, cyanosis, der-
matitis, etc. [1,2]. Therefore, fast, sensitive and low cost detection
of NACs, in particular picric acid (PA), 2,4,6-trinitrotoluene (TNT),
2,4-dinitrotoluene (DNT), and nitrobenzene (NB), in soil and aque-
ous phase is of great interest. Up to now, various methods such
as canines [3], gas chromatography coupled with mass spectrome-
try [4], high-pressure liquid chromatography [5], surface enhanced
Raman spectrometry [6], and electrochemical method [7,8] have
been developed for the detection of NACs in liquid phase. Although
these techniques are effective, some need to handle with com-
plex sample preparation, some are expensive and time-consuming,
and others are difficultly fielded in small, low-power package.
Compared with the above mentioned techniques, fluorescent film
sensors have gained great attention because of their high sensitivity
and selectivity, multiple choices in signals or parameters, and low
cost in instrumentation. Furthermore, films sensors are easy to be
made into devices, and in theory, they are re-usable and contami-
nation free. Clearly, these advantages must benefit on site analysis.
Among fluorescent film sensors [9–11], both conjugated poly-
mers (CPs) and fluorescent aromatics have been used as sensing
difficult to be prepared. However, these films, except a few ones
reported by our group, are prepared by using spin-coating, dip-
coating or other physical methods, and thereby suffer from issues
such as fluorophore leaking, thickness control, and inner-layer ana-
lyte diffusion [11–14].
Different from what occurs in CPs-based film sensors, the
response of fluorescent sensing films fabricated in a self-assembled
monolayer (SAMs) way is significantly faster due to direct exposure
of fluorophore moieties, avoiding, at least in principle, inner-layer
diffusion problem encountered by CPs-based physically fabricated
sensing films. Reinhoudt and co-workers prepared some fluores-
cent sensing films via immobilizing dansyl, pyrene, or coumarin
on glass plate surfaces in a SAMs way. It was reported that
those films are highly sensitive and selective to ␤-cyclodextrin,
Na+, or Pb2+ [15–17]. Gulino and co-workers reported a sensi-
tive, reversible, and fast response optical NO2 sensor via covalently
binding porphyrin molecules onto silica substrate [18]. Recently,
similar strategy has been employed by Raymo and co-workers to
prepare fluorescent sensing films for dopamine of catecholamine
neurotransmitters [19]. The principles behind the sensing is that
the association of the 2,7-diazapyrenium, which is the sensing ele-
ment and functions as an acceptor, with dopamine, a donor, via
charge–transfer interaction produces a fluorescence quenching at
the solid–liquid interface.
Over the past decade, our group has been seeking to develop
a new family of fluorescent sensing films via a SAMs way and has
realized sensitive and selective detection of NACs in vapor phase
∗
Corresponding author. Tel.: +86 29 85310081; fax: +86 29 85307566.
E-mail address: yfang@snnu.edu.cn (Y. Fang).
1010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.11.004

H. Du et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 356–362
357
and of other analytes in solution [20–23]. It is to be noted that the
structures of the spacers connecting the sensing elements and the
substrates have played important roles for the performances of the
films. Moreover, in studies of low-molecular mass organic gelators,
our group found that introduction of a simple benzene ring in the
spacer of two cholesteryl units resulted in a great effect upon their
assembling behaviors in solution [24]. Illuminated by this work and
considering the importance of spacer structure to the performance
of a fluorescent film sensor, and the fact that all SAMs based flu-
orescent sensing films reported till now do not contain aromatic
structures within their spacers, a novel fluorescent film has been
specially designed by employing a spacer containing a benzene
ring. It was expected that introduction of a benzene structure in
the spacer may cause a significant effect upon its fluorescent and
sensing behaviors. This paper reports the details of the fabrication
of a pyrene-functionalized fluorescent film with a benzene struc-
ture in the spacer connecting the fluorophore and a substrate, glass
plate, and its sensing behavior to PA in aqueous phase.
X-ray photoelectron spectroscopy (XPS) measurements were car-
ried out on an ESCAPHI5400 photoelectron spectrometer using a
monochromatic Mg K␣ X-ray source. Contact angles of the films
were measured on a dataphysics OCA20 contact-angle system
at ambient temperature. Fluorescence measurements were per-
formed at room temperature on a time-correlated single photon
counting Edinburgh FLS 920 fluorescence spectrometer with a
front-face method. The fabricated film was inserted into a quartz
cell with its surface facing the excitation light source. The position
of the film was kept constant during each set of measurements.
2.3. Synthesis of N-1-pyrenesulfonyl-p-xylylenediamine
(PSPXDA)
PSPXDA was prepared by adopting a modified literature method
[23,25]. The resulting solution was kept as PSPXDA solution and
used directly in the following surface assembling.
For characterization, PSPXDA was isolated from the above solu-
tion in its salt form by acidification of the solution with 0.1 mol/L
HCl in diethyl ether. The fine buff precipitate was filtered and
dried at room temperature. Anal. Calcd. for the salt of PSPXDA
2. Experimental
2.1. Reagents
C
24H21N2SO2Cl: C, 65.97; H, 4.84; N, 6.41. Found: C, 65.87; H, 4.81;
N, 6.95. 1H NMR (300 MHz, DMSO-d6): ı (ppm) 9.0 (1H), 8.2–8.8
(8H), 7.2 (4H), 4.0 (2H), 3.8 (2H). FTIR (KBr, cm−1): 3049 (m), 1625
(m), 1430 (m), 1319 (s), 1060 (m), 849 (s), 663 (s), 559 (s). Melting
point: 241–242 ◦C.
Pyrenesulfonyl chloride (PSC) was synthesized by adopting a
literature method [25]. p-Xylylenediamine (PXDA; TCI, >99%) and
3-glycidoxypropyltrimethoxysilane (GPTS; Acros, 97%) were used
directly without further purification. Other chemicals used are of
the highest grade commercially available, and also used directly
without further purification. Water used throughout is de-ionized
and then double distilled. NACs including TNT, DNT, NB and PA were
of analytical grade and used directly without further purification.
(Caution: TNT and other NACs used in the present study are highly
explosive and should be handled only in small quantities.)
2.4. Activation and silanization of the glass plate surface
A glass plate (0.9 cm × 2.5 cm) was treated in a “piranha solu-
tion” (3/7, V/V, 30% H2O2/98% H2SO4) [26] (Warning: Piranha
solution should be handled with extreme caution because it can react
violently with organic matter.) at 98 ◦C for 1 h, rinsed thoroughly
with plenty of water, and finally dried at 100 ◦C in a dust-free oven
for 1 h. The activated glass plate was immersed in 50 ◦C toluene
solution of GPTS (0.6%, V/V), containing a trace amount of water, for
12 h. The glass plate was rinsed with toluene and trichlormethane,
successively, to remove any physisorbed material.
2.2. Measurements
Pressed KBr disks for the powder samples were used for
the transmission infrared spectroscopy measurements, and their
FTIR spectra were obtained with a Bio-Rad FTIR spectrometer.
Scheme 1. Schematic representation of the synthesis and immobilization of PSPXDA onto a glass plate surface, and the representative structure of the controlled one.

358
H. Du et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 356–362
Fig. 3. Fluorescence excitation and emission spectra of the film in aqueous solution.
Contact angles at ambient temperature of the surfaces of the
substrates to water at different stages of the functionalization
process have been measured and the results are shown in Fig. 2. Ref-
erence to the figure reveals that the static contact angle decreased
significantly from 10.5 0.5◦ to 6.9 0.5◦ after treatment with the
“piranha solution”. Further treatment with GPTS resulted in a sharp
increase in the data (42.1 0.8◦), indicating that the wettability of
the surface has reversed. The angle increased further after treat-
ment with PSPXDA solution in trichlormethane, and reached a
value of 71.1 0.4◦, a typical hydrophobic surface. These results
are consistent with the expectation from the chemical composition
of the surface, as shown in Fig. 1 and revealed by XPS measure-
ments.
Success in the chemical coupling of the pyrene moieties on the
substrate surface was further investigated by monitoring the flu-
orescence emission of remained solvent after immersion of the
film in trichlormethane for more than 15 h. The fact that no typical
pyrene emission was found indicates that the amount of physically
adsorbed pyrene moieties is negligible. In other words, pyrene had
been chemically coupled on the substrate surface.
Fig. 1. X-ray photoelectron spectra of the glass plates of various surface structures.
The numbers of 2, 3 and 4 stand for the plates of hydroxyl surface, epoxide surface,
and pyrene derivatives surface, respectively.
2.5. Chemical coupling of pyrene on the plate surface
The trialkoxysilane-treated glass plate was immerged into
a
PSPXDA solution in trichlormethane (cf. synthesis of N-
1-pyrenesulfonyl-p-xylylenediamine) at 61 ◦C for 12 h. To
remove unreacted PSPXDA, the plate was rinsed with plenty
of trichlormethane and ethanol, and then extracted with
dichloromethane in a Soxhlex extractor for 5 h. The plate was
further rinsed with dichloromethane and water, successively, after
the extraction. The synthesis of pyrene moieties and its coupling
onto a glass plate surface are shown in Scheme 1.
3. Results and discussion
3.2. Steady-state excitation and emission spectra of the film
3.1. Film characterization
Fig. 3 depicts the steady-state fluorescence excitation and emis-
sion spectra of the functional film in aqueous solution as functions
of excitation and emission wavelengths. Examination of the fig-
ure reveals that the emission is composed of two sharp peaks at
wavelengths of 380 nm and 401 nm, and one broad band centered
at 500 nm. The peaks and the band can be assigned to pyrene
monomer (M) emission and excimer (E) emission, respectively.
Similar to the results reported in the literatures [16,27,28], a per-
fect “sandwich-like” structure may be adopted by the excimer since
its maximum emission centers at 500 nm. Furthermore, the exci-
tation spectrum is not varying along with the analysis wavelength
increasing to longer wavelength, suggesting that both the excimer
emission and the monomer emission originate from fluorophores
with similar micro-environment.
The films have been characterized by XPS and wettability mea-
surements. Fig. 1 shows the XPS spectra of the substrate of various
surface compositions, of which the chemical structures changed
from hydroxyl groups to epoxy groups and then to pyrene deriva-
tives along with the treatment. It can be seen that the signal of C1s
of the epoxy group covered substrate is much stronger than that
of the hydroxyl group covered one, indicating that the silanizing
reagent are somewhat exposed to the outer interface. Immobiliza-
tion of the pyrene moieties on the substrate surface made C1s signal
even stronger and the signal of N1s appeared, a strong evidence for
the successful coupling of pyrene moieties on the substrate surface.
This conclusion is further confirmed by the results from surface
wettability measurement.
Fig. 2. Static contact angles (ꢀ) of various glass plate surfaces and water. The numbers of (1), (2), (3) and (4) have similar meaning with those shown in Scheme 1 and in Fig. 1.

H. Du et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 356–362
359
is the Stern–Volmer constant. For the present system, the constant
is 5.1 × 104 M−1, a value much higher than those of other fluores-
cent chemosensors for PA, suggesting that the present film may be
exploited as an effective film sensor with enhanced sensitivity to PA
and other NACs [11,31–36]. Fig. 5 depicts the quenching results of
NACs to the fluorescence emission of the film. It can be seen that the
film is not only responsible to PA but also to other NACs tested. Each
data reported in the figure was recorded 15 min later after the injec-
tion of the quencher. It is to be noted that this is not mean that the
response of the film to the analyte is slow, but actually the response
is much faster because the time required for the equilibration of
the quenching is less than 1 min as revealed by time-dependent
measurements (cf. Fig. S1). According to the ability of drawing elec-
trons, it is expected that TNT might have the highest quenching
efficiency to the emission of the films due to the existence of three
nitro-groups on the benzene ring that make the ring have lowest
electron density if compared with PA and other NACs [31,36,37].
However, the quenching follows the order of PA > TNT > DNT > NB,
rather than TNT > PA > DNT > NB (cf. Fig. 5), suggesting that except
PA, for other NACs, electron withdrawing ability dominates the
quenching efficiency. The exceptional quenching effect of PA to the
fluorescence emission of the film may be explained by considering
its acid nature. This is because the three nitro-groups on the ben-
zene ring make the hydroxyl group affixed on the molecular frame
behaviors as a modest acid. In contrast, for the present film, there
is an imino structure in the spacer, which has a tendency to attract
proton, and thereby proton transfer may occur when the film is
inserted into the solution of PA. It is the proton transfer that makes
PA has a specific affinity to the film. As a result, the local concentra-
tion (near the film surface) of the quencher would be significantly
higher than that in the bulk phase, which explains why PA is a
more efficient quencher than other NACs to the film. To verify this
hypothesis, another film of a similar structure but with no imino
group in the spacer was specifically fabricated which is designated
as film (4)ꢀ (cf. Scheme 1). A similar quenching experiment was also
conducted with this film, and it was found: firstly, the quenching
efficiency of PA to this film is significantly lower than that to the
original film studied; second, for this film, TNT is a more efficient
quencher than PA, following the order of pure electron withdraw-
ing ability (cf. inset of Fig. 5). Clearly, all these results indicate that
the proton transfer-based specific binding contributed a lot to the
extraordinary quenching effect of PA. It is to be noted that introduc-
tion of a benzene ring in the spacer does not only compel pyrene
moieties extending to the outer side of the film as revealed by the
profile of its fluorescence emission spectrum, but also restricts the
Fig. 4. Fluorescence emission spectra of the film in the presence of PA of different
concentrations, which are 0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 × 10−5 M from top to bottom,
respectively (ꢁex = 353 nm).
3.3. Fluorescence quenching studies with NACs
As it is well known, NACs are electron poor compounds if
compared to that of polycyclic aromatics, and thereby they are
effective fluorescence quenchers to most aromatic fluorophores
[29]. Accordingly, the effects of commonly found NACs, including
TNT, DNT, NB, and PA, to the fluorescence emission of the film were
examined. The test has been conducted in the following way: firstly,
the film was adhered to one inner-side of a quartz cell with a volume
of ca. 3.5 cm3; secondly, distilled water with a volume of 2.5 cm3
was added into the cell; and finally, the spectra were recorded when
the fluorescence intensity became stable after a certain amount of
NAC was injected into the cell. As expected, all the NACs quenched,
with different efficiencies, the emission of the film. As an exam-
ple, Fig. 4 shows the fluorescence emission spectra of the film as
a function of the concentration of PA. Clearly, the emission, par-
ticularly the excimer emission, of the film decreased significantly
with increasing PA concentration. It is to be noted that the position
of the excimer emission does not change significantly, indicat-
ing that the interaction between the analyte, PA, and the pyrene
moieties does not afford emissive states [30]. The fluorescence
quenching results can be treated with the Stern–Volmer equation,
I0/I = 1 + Ksv [PA], where I0 and I are the fluorescence intensity of
the film in the absence and presence of PA, respectively, and Ksv
Fig. 5. Quenching results of NACs and commonly found interferents, including toluene, benzene, trichlormethane, ethanol, artificial seawater, NaOH and HCl, to the fluores-
cence emission of the film with a spacer containing an imino group. Inset: quenching results from control experiments where a similar film has been employed, of which
there is no imino group in the spacer.

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H. Du et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 356–362
motions of them (cf. Fig. 3). Similar observations have never been
found before in the fluorescence studies of the films with similar
structures to the present one. As an example, Figures S2, S3 and S4
show the structure, the fluorescence emission spectrum and the
sensing performances to NACs in aqueous phase of one of such
films (cf. Supporting Information). These differences may be only
attributed to the ␲–␲ interaction between benzene rings of neigh-
boring spacers. It is this interaction that restricted the motion of
the spacers, and favors excimer formation of neighboring pyrene
moieties.
As expected, calculation of the detection limit (DL) once again
proved that the response of the film to PA is super-sensitive.
The DL for this analyte is 1.0 × 10−8 mol/L, a value quite close to
that of 6.0 × 10−9 mol/L and that of 2.1 × 10−8 mol/L reported by
Trogler, and our group, respectively. Moreover, the film employed
by Trogler’s group and that by our group before were all fabricated
in a physical way with polysilole or aggregated hexaphenylsilole
(HPS) as sensing elements, both suffer from a stability problem
[11,38]. The super-sensitivity of this film to PA must be attributed
to the specific design of the film, of which a benzene struc-
ture had been specially introduced into the spacer. The DL of
the film to PA has been determined according to the following
functions:
Fig. 6. Plots of I0/I and ꢃ0/ꢃ against the concentrations of PA (ꢁex/ꢁem = 353/500 nm).
3.4. Quenching mechanism of the sensing process
The results from lifetime measurements were illustrated in
Fig. 6. It is obvious that the lifetime of the sensing molecules does
not change obviously with increasing concentration of PA and ꢃ0/ꢃ
is nearly equal to 1, where ꢃ0 and ꢃ stand for the lifetimes of
the surface-bound fluorophore in the absence and presence of the
quencher, respectively. This result indicates that the quenching is
mainly caused by the formation of a non-fluorescent complex (F–Q)
in a ground-state, which is in support of the hypothesis that the film
has a specific binding to PA.
ꢀ
ꢁ
n
i=1
(xi − x¯)2
sb
=
(1)
n − 1
ꢂI
S =
(2)
(3)
ꢂc
Based upon the discussions made at Sections 3.3 and 3.4, a
schematicrepresentation ofthe quenchingofPAto thefluorescence
emission of the film is presented in Fig. 7.
3sb
S
DL =
The standard deviation (sb) was calculated by measuring the
intensity of the film in blank solution for more than 10 times and
then got the average intensity (x) firstly. By fitting the data into
function 1, the value of standard deviation (sb) was obtained. Sec-
ondly, a certain amount of PA was added into the blank solution and
the resulting variation of the intensity (ꢂI) was recorded. By fitting
the data into function 2, where ꢂc is the variation of quencher con-
centration, the value of precision S was calculated. Finally, the DL
was calculated according to function 3.
3.5. Interference from other chemicals
Interestingly, no significant change in fluorescence emission
was observed upon exposing the film to common organic solvents,
such as toluene, benzene, trichlormethane, ethanol, and their mix-
tures with water. Furthermore, the aqueous solutions of NaOH or
HCl, and artificial seawater have also been tested as interferents,
and it is revealed that these solutions show little effect upon the
fluorescence emission of the film (cf. Fig. 5).
Fig. 7. A schematic representation of the surface enrichment effect of pyrene functionalized film to picric acid and the non-fluorescent complex, pyrene–picric acid, formation.

H. Du et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 356–362
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[2] F.D. Marvin-Sikkema, J.A.M. de Bont, Degradation of nitroaromatic compounds
by microorganisms, Appl. Microbiol. Biotechnol. 42 (1994) 499–507.
[3] A.W. Czarnik, A sense for landmines, Nature 394 (1998) 417–418.
[4] K. Hakansson, R.V. Coorey, R.A. Zubarev, V.L. Talrose, P. Hakansson, Low-mass
ions observed in plasma desorption mass spectrometry of high explosives, J.
Mass Spectrom. 35 (2000) 337–346.
[5] D.S. Moore, Instrumentation for trace detection of high explosives, Rev. Sci.
Instrum. 75 (2004) 2499–2512.
[6] J.M. Sylvia, J.A. Janni, J.D. Klein, K.M. Spencer, Surface-enhanced Raman detec-
tion of 2,4-dinitrotoluene impurity vapor as a marker to locate landmines, Anal.
Chem. 72 (2000) 5834–5840.
[7] R.J. Dijkstra, A.N. Bader, G.P. Hoornweg, U.A.T. Brinkman, C. Gooijer, On-line
coupling of column liquid chromate graphy and Raman spectroscopy using a
liquid core waveguide, Anal. Chem. 71 (1999) 4575–4579.
[8] R. Hodyss, J.L. Beauchamp, Multidimensional detection of nitroorganic explo-
sives by gas chromatography–pyrolysis-ultraviolet detection, Anal. Chem. 77
(2005) 3607–3610.
[9] D.T. McQuade, A.E. Pullen, T.M. Swager, Conjugated polymer-based chemical
sensors, Chem. Rev. 100 (2000) 2537–2574.
[10] K.J. Albert, N.S. Lewis, C.L. Schauer, G.A. Sotzing, S.E. Stitzel, T.P. Vaid, D.R. Walt,
Cross-reactive chemical sensor arrays, Chem. Rev. 100 (2000) 2595–2626.
[11] G. He, H.N. Peng, T.H. Liu, M.N. Yang, Y. Zhang, Y. Fang, A novel picric acid film
sensor via combination of the surface enrichment effect of chitosan films and
the aggregation-induced emission effect of siloles, J. Mater. Chem. 19 (2009)
7347–7353.
Fig. 8. Results from reversibility measurements, where the fluorescence of the
film in pure water and PA solution (6.0 × 10−5 M) was measured alternatively
(ꢁex/ꢁem = 353/500 nm).
[12] J.S. Yang, T.M. Swager, Porous shape persistent fluorescent polymer films: an
approach to TNT sensory materials, J. Am. Chem. Soc. 120 (1998) 5321–5322.
[13] S.W. Thomas III, G.D. Joly, T.M. Swager, Chemical sensors based on amplifying
fluorescent conjugated polymers, Chem. Rev. 107 (2007) 1339–1386.
[14] Y.Y. Long, H.B. Chem, Y. Yang, H.M. Wang, Y.F. Yang, N. Li, K. Li, J. Pei, F. Liu,
Electrospun nanofibrous film doped with a conjugated polymer for DNT fluo-
rescence sensor, Macromolecules 42 (2009) 6501–6509.
[15] M. Crego-Calama, D.N. Reinhoudt, New materials for metal ion sensing by self-
assembled monolayers on glass, Adv. Mater. 13 (2001) 1171–1174.
[16] N.J. van der Veen, S. Flink, M.A. Deij, R.J.M. Egberink, F.C.J.M. van Veggel, D.N.
Reinhoudt, Monolayer of a Na+-Selective fluoroionophore on glass: connecting
the fields of monolayers and optical detection of metal ions, J. Am. Chem. Soc.
122 (2000) 6112–6113.
[17] S. Flink, F.C.J.M. van Veggel, D.N. Reinhoudt, A self-assembled monolayer of a
fluorescent guest for the screening of host molecules, Chem. Commun. (1999)
2229–2230.
[18] A. Gulino, P. Mineo, E. Scamporrino, D. Vitalini, I. Fragala, Molecularly engi-
neered silica surfaces with an assembled porphyrin monolayer as optical NO2
molecular recognizers, Chem. Mater. 16 (2004) 1838–1840.
3.6. Reversibility of the quenching process
The procedures adopted for examination of the reversibility of
the sensing process are as follows: the film was inserted into a
cell with 2.5 cm3 of distilled water, and the fluorescence emis-
sion of the film was recorded firstly. Secondly, 60 ␮L PA solution
(2.5 × 10−3 mol/L) was added, and after 10 min equilibration the
fluorescence emission of the film was recorded again. Thirdly, after
the measurement the film was taken out of the cell, and immersed
in an ethanol solution for 15 min and then washed with plenty of
distilled water. The film was re-used after the treatment, and the
whole process was repeated several times. The results are shown in
Fig. 8. It is clear that the response of the film to PA is fully reversible,
and furthermore, the film is stable for at least two months provided
it is properly preserved. Therefore, it offers opportunity to be made
into devices.
[19] M.A. Cejas, F.M. Raymo, Fluorescent diazapyrenium films and their response to
dopamine, Langmuir 21 (2005) 5795–5802.
[20] S.J. Zhang, F.T. Lü, L.N. Gao, L.P. Ding, Y. Fang, Fluorescent sensors for nitroaro-
matic compounds based on monolayer assembly of polycyclic aromatics,
Langmuir 23 (2007) 1584–1590.
[21] H.H. Li, J.P. Kang, L.P. Ding, F.T. Lü, Y. Fang, A dansyl-based fluorescent film:
preparation and sensitive detection of nitroaromatics in aqueous phase, J. Pho-
tochem. Photobiol. A: Chem. 197 (2008) 226–231.
4. Conclusion
[22] F.T. Lü, L.N. Gao, L.P. Ding, L.L. Jiang, Y. Fang, Spacer layer screening effect: a
novel fluorescent film sensor for organic copper(II) salts, Langmuir 22 (2006)
841–845.
[23] L.N. Gao, Y. Fang, X.P. Wen, Y.G. Li, D.D. Hu, Monomolecular layers of pyrene as
a sensor to dicarboxylic acids, J. Phys. Chem. B 108 (2004) 1207–1213.
[24] M. Xue, K.Q. Liu, J.X. Peng, Q.H. Zhang, Y. Fang, Novel dimeric cholesteryl-based
A(LS)2 low-molecular-mass gelators with a benzene ring in the linker, J. Colloid
Interface Sci. 327 (2008) 94–101.
[25] S.A. Ezzell, C.L. McCormick, Synthesis and solution characterization of pyrene-
labeled polyacrylamides, in: S.W. Shalaby, C.L. McCormick, G.B. Butler (Eds.),
Water-Soluble Polymers, ACS Symposium Series, Washington, DC, 1991, pp.
130–150.
[26] F.S. Xiao, M. Ichikawa, Oxide-supported triruthenium ketenylidene cluster:
evidence for metal–metal bonds from laser Raman spectroscopy, Langmuir 9
(1993) 2963–2964.
A stable and bright SAM-based fluorescent film was fabricated
with a benzene ring in the spacer. Sensing performance studies
demonstrated that the fluorescence emission of the film is sensi-
tive to the presence of NACs, especially PA, with the DL being as low
as 1.0 × 10−8 mol/L. Common interferents including toluene, ben-
zene, trichlormethane, ethanol, artificial seawater, NaOH and HCl
had little effect upon the emission of the film in aqueous phase.
Fluorescence lifetime measurements revealed that the quenching
is static in nature. Furthermore, the quenching is fully reversible.
Acknowledgements
[27] F.M. Winnik, Photophysics of preassociated pyrenes in aqueous polymer solu-
tions and in other organized media, Chem. Rev. 93 (1993) 587–614.
[28] J. Matsui, M. Mitsuishi, T. Miyashita, A study on fluorescence behavior of pyrene
at the interface of polymer Langmuir–Blodgett films, J. Phys. Chem. B 106 (2002)
2468–2473.
[29] S. Glazier, J.A. Barron, N. Morales, A.M. Ruschak, P.L. Houston, H.D. Abrun,
Quenching dynamics of the photoluminescence of [Ru(bpy)3]2+-pendant
PAMAM dendrimers by nitro aromatics and other materials, Macromolecules
36 (2003) 1272–1278.
We thank the Ministry of Science and Technology of China (No.
2007AA03Z349), the Natural Science Foundation of China (Nos.
20773083, 20803046 and 20927001).
Appendix A. Supplementary data
[30] Y. Liu, R.C. Mills, J.M. Boncella, K.S. Schanze, Fluorescent polyacetylene thin film
sensor for nitroaromatics, Langmuir 17 (2001) 7452–7455.
[31] H. Sohn, M.J. Sailor, D. Magde, W.C. Trogler, Detection of nitroaromatic explo-
sives based on photoluminescent polymers containing metalloles, J. Am. Chem.
Soc. 125 (2003) 3821–3830.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jphotochem.2010.11.004.
References
[32] R.Y. Tu, B.H. Liu, Z.Y. Wang, D.M. Gao, F. Wang, Q.L. Fang, Z.P. Zhang,
Amine-capped ZnS–Mn2+ nanocrystals for fluorescence detection of trace TNT
explosive, Anal. Chem. 80 (2008) 3458–3465.
[33] P. Lu, J.W.Y. Lam, J.Z. Liu, C.K.W. Jim, W.Z. Yuan, N. Xie, Y.C. Zhong, Q.
Hu, K.S. Wong, K.K.L. Cheuk, B.Z. Tang, Aggregation-induced emission in a
[1] R. Mantha, K.E. Taylor, N. Biswas, J.K. Bewtra, A continuous system for Fe0 reduc-
tion of nitrobenzene in synthetic wastewater, Environ. Sci. Technol. 35 (2001)
3231–3236.

362
H. Du et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 356–362
hyperbranched poly(silylenevinylene) and superamplification in its emission
quenching by explosivesa, Macromol. Rapid Commun. 31 (2010) 834–839.
[34] Z. Li, Y.Q. Dong, J.W.Y. Lam, J.X. Sun, A.J. Qin, M. Häußler, Y.P. Dong, l.D. Sung,
H.H.Y Williams, H.S. Kwok, B.Z Tang, Functionalized siloles: versatile synthe-
sis, aggregation-induced emission, and sensory and device applications, Adv.
Funct. Mater. 19 (2009) 905–917.
[35] Y. Zhang, G. He, T.H. Liu, M.N. Yang, L.P. Ding, Y. Fang, Sensing performances of
oligosilane functionalized fluorescent film to nitrobenzene in aqueous solution,
Sensor Lett. 7 (2009) 1141–1146.
[36] A. Saxena, M. Fujiki, R. Rai, G. Kwak, Fluoroalkylated polysilane film as a
chemosensor for explosive nitroaromatic compounds, Chem. Mater. 17 (2005)
2181–2185.
[37] S.J. Toal, W.C. Trogler, Polymer sensors for nitroaromatic explosives detection,
J. Mater. Chem. 16 (2006) 2871–2883.
[38] H. Sohn, R.M. Calhoun, M.J. Sailor, W.C. Trogler, Detection of TNT and picric acid
on surfaces and in seawater by using photoluminescent polysiloles, Angew.
Chem. Int. Ed. 40 (2001) 2104–2105.