A BODIPY-Based Fluorescent Probe to Visually Detect Phosgene: Toward the Development of a Handheld Phosgene Detector.

TL;DR: A prototypical handheld phosGene detector with a promising sensing capability that expedites the detection of gaseous phosgene without sophisticated instrumentation was developed and involves a rapid response period suitable for issuing early warnings during emergency situations.

Abstract: A boron-dipyrromethene (BODIPY)-based fluorescent probe with a phosgene-specific reactive motif shows remarkable selectivity toward phosgene, in the presence of which the nonfluorescent dye rapidly transforms into a new structure and induces a fluorescent response clearly observable to the naked eye under ultraviolet light. Given that dynamic, a prototypical handheld phosgene detector with a promising sensing capability that expedites the detection of gaseous phosgene without sophisticated instrumentation was developed. The proposed method using the handheld detector involves a rapid response period suitable for issuing early warnings during emergency situations.

Summary

Introduction

• Shows remarkable selectivity toward phosgene, in the presence of which the nonfluorescent dye rapidly transforms into a new structure and induces a fluorescent response clearly observable to the naked eye under ultraviolet light.
• The need for its detection is critical not only to protect civilians against terrorist plots, but also to alert workers to its leakage in industrial plants.
• For the spectral investigation, the authors used triphosgene as a comparatively safe phosgene source, which instantly transforms into phosgene in the presence of tertiary amines.

Synthesis of BOD-SYR

• The reaction mixture was heated at reflux under.
• The liquid phases residue was purified by column chromatography.

Synthesis of BOD-UREA

• Then, triphosgene solution (125 mm in dry DCM) was added drop by drop to the BOD-SYR solution under Ar for 10 min.
• After evaporation of solvent, the resultant residue was purified by column chromatography (2:1 hexane/ethyl acetate) to afford BOD-UREA (3 mg, 26 % yield).

Conflict of interest

• The authors declare no conflict of interest.
• For more details see the Supporting Information. [13].

Figures

Figure 3. a) Image of the black-box apparatus and paper-based indicator cartridge. b) Image of indicator cartridge prior to UV illumination. c) Image of indicator cartridge under UV illumination (top row: concentration=0, 10 and 25 ppm; bottom row: concentration=50, 75 and 100 ppm).

Figure 2. Fluorescence intensity change of BOD-SYR [10 mm, in CH3CN/ Et3N (0.1%)] recorded 2 min after the addition of various analytes (10 equiv; lex=460 nm). 1) Triphosgene, 2) POCl3, 3) DCP, 4) (COCl)2, 5) SOCl2, 6) TsCl, 7) CH3COCl.

Figure 1. Absorbance and fluorescence spectra of BOD-SYR (10 mm) upon gradual addition of a solution of triphosgene (0–50 mm) in acetonitrile (CH3CN, with 0.1% Et3N), lex=460 nm.

Figure 4. a) Colour code analysis (0–255) of phosgene-exposed indicator cartridge based on the red component. b) Colour code analysis of phosgeneexposed indicator cartridge based on the green component. c) Calibration curve based on red component versus phosgene concentration.

Figure 5. a) Fluorescence intensity change of BOD-SYR-loaded paper strips in the presence of 50 ppm gaseous phosgene as a function of time (lex=460 nm). b) Fluorescence intensity change of BOD-SYR-loaded paper strips as a function of phosgene concentration (0–100 ppm).

Full text

&
Sensors
ABODIPY**-Based Fluorescent ProbetoVisually Detect
Phosgene:Toward the Development of aHandheldPhosgene
Detector
Melike Sayar,
[a]
ErmanKarakus¸ ,
[a, c]
Tug
˘
rul Gener,
[b]
Busra Yildiz,
[a]
UmitHakan Yildiz,
[a, d, e]
and
Mustafa Emrullahog
˘
lu*
[a]
Abstract: Aboron-dipyrromethene (BODIPY)-based fluo-
rescentprobe with aphosgene-specific reactive motif
shows remarkable selectivity towardphosgene, in the
presence of which the nonfluorescent dye rapidly trans-
forms into anew structure and induces afluorescentre-
sponse clearly observable to the nakedeye under ultravio-
let light. Given that dynamic, aprototypical handheld
phosgene detector with apromising sensingcapability
that expedites the detection of gaseous phosgenewith-
out sophisticated instrumentation was developed. The
proposed methodusing the handhelddetector involves a
rapid response period suitablefor issuing early warnings
during emergency situations .
Phosgene(COCl
2
)isahighly toxic fumingliquid widely used to
produce bulk chemicals and pharmaceuticals. Despite its con-
temporary industrial applications, phosgene has historically
suffered abad reputationowing to its use as achemical war-
fare agent in World WarI.
[1]
Its mild odour,resembling freshly
mown hay,and its colourlessness renderphosgene nearly un-
detectable, even in excessive amounts. Phosgeneinhalation se-
verely affects the respiratory tract and lungs, and phosgene
poisoning, with symptomsthat appear hours after exposure to
the chemical, often causedeath by suffocation.
[2]
Nevertheless,
the high toxicity,easy produ ction,and widespread availability
in the chemical industry,make phosgene an attractive agent
for chemical terrorism. The need for its detection is critical not
only to protect civilians against terrorist plots, but also to alert
workerstoits leakageinindustrialplants.
Recent progress on the criticalsubjectofdetection has en-
richedcurrentknowledge for designing molecular probes, es-
pecially for phosgene.
[3–10]
In general,detecting phosgenewith
amolecular probe involves trapping the molecule using areac-
tive site (e.g.,hydroxy and amine functional groups), which,
following structural modification,generates adetectable opti-
cal signal, for example acolour change or fluorescenceemis-
sion.
The analytical performance of such probesdepends heavily
on the specificity of the recognition unit employed in the
probeskeleton. Scheme 1depicts general detection strategies,
Scheme1.Reactionschemes for trapping phosgene.
[a] M. Sayar,Dr. E. Karakus¸, B. Yildiz, Dr.U.H.Yildiz, Dr.M.Emrul lahog
˘
lu
Department of Chemistry,Faculty of Science
I
˙
zmirInstitute of Technology,Urla, 35430, Izmir (Turkey)
E-mail:mustafaemrullahoglu@iyte.edu.tr
[b] T. Gener
Department of Materials Science and Engineering
Izmir Institute of Technology,Urla, 35430, Izmir (Turkey)
[c] Dr.E.Karakus¸
ChemistryGroup Laboratories TUBITAK National Metrology Institute (UME)
41470, Gebze-Kocaeli (Turkey)
[d] Dr.U.H.Yildiz
Department of Photonic Science and Engineering
Izmir Institute of Technology,Urla, 35430, Izmir (Turkey)
[e] Dr.U.H.Yildiz
Inovasens Co. I
˙
zmir Technology Development Zone Inc.
Teknopark, 35430 Urla, I
˙
zmir (Turkey)
[**] boron-dipyrromethene
Supporting information and the ORCID identification number(s) for the au-
thor(s) of this article can be found under https://doi.org/10.1002/
chem.201705613.
Chem. Eur.J.2018, 24,3136 –3140 T 2018 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim3136
CommunicationDOI:10.1002/chem.201705613

which involvetrapping phosgene through achemical reaction.
Amongwidely used recognition units,
[4–10]
o-phenylenediamine
(OPA) is unique given its exceptional specificityfor phosgene
(Scheme 1c). In most cases, the OPAunit appended on the flu-
orophore core can efficientlyquenchfluorophore emission
during aphoto-indu c ed electrontransfer (PET) process. Elimi-
nating the PET processbyinducing areactionwith phosgene
is the most efficient methodofrestorin gthe fluorescence
emission.
Despite notable achievements in detecting phosgene, differ-
entiatingphosgene from analytes with similar chemical struc-
tures remainsasignificant challenge, as do low sensitiv ity and
prolonged response times. New probe constructs that use
easily accessible recognition/reactive units with improved ana-
lytical performance in terms of sensitivity,analyte specificity,
and response times are therefore necessary.
In response to that need, herein we present the design,syn-
thesis, and spectral investigation of anovel probe construct
that exploits aunique reactionscheme that recognises phos-
gene with excellent selectivity over other analytes. For our
probe design, we used aboron-dipyrromethene (BODIPY) dye
as the signal reporter,given its outstanding photophysical
properties,
[11]
as wellasano-aminobenzyl amine group as the
phosgene-specific reactive motif, which marks afirst for re-
search in phosgene sensing (Scheme 1d).
Anticipating that phosgenewould interactwith the probe
reactive site to mediate acyclization reactionand thereby
block the PET process that would in turn induce aturn-onfluo-
rescent response (Scheme 2), we integratedthe reactive unit
with the BODIPY core following the synthetic route as outlined
in Scheme 3. To that end, we obtained afree-amine derivative
of aBODIPY dye, BOD-NH
2
,byreducing the meso-NO
2
-phenyl
derivative(1). Further alkylation of BOD-NH
2
with the individu-
ally prepared compo und 2 and subsequentreduction yieldeda
sufficient amount of the titlecompound, BOD-SYR.
[12]
We investigated the spectroscopic response of BOD-SYR to
the addition of phosgeneand other specieswith asimilarreac-
tive nature by using ultraviolet-visibl eand fluorescencespec-
troscopy. For the spectral investigation, we used triphosgene
as acomparatively safe phosgenesource,which instantly
transforms into phosgeneinthe presence of tertiary amines.
As expected, the BOD-SYR solution(acetonitrile, with 0.1%
Et
3
N), exhibited no emission(F
F
= 0.005)inthe visible region
owing to PET-promoted quenching arising from the meso-
amine moiety.However,upon the addition of triphosgene
(1 equiv), an intense emission band appeared at 511nm
(Figure 1). Notably,the spectroscopic response of the probe
was rapid, and we observed the complete saturation of signal
intensity within ten seconds (see Figure S2 in the Suppo rting
Information).
Upon the systematic addition of triphosgene, the emission
band at 511nmincreased linearly,and its intensity peaked
with the addition of 6equiv of triphosgene,with an enhance-
ment factor of more than 300-fold. In light of analytical data
collected from the titration experiment, we estimate the lower
limit of detection to be 179 nm given asignal-to-noise ratio (S/
Scheme2.Reaction-based detection of phosgene.
Scheme3.Stepwise synthesis of BOD-SYR.
Figure 1. Absorbance andfluorescence spectra of BOD-SYR (10 mm)upon
gradual additionofasolutionoftriphosgene (0–50 mm)inacetonitrile
(CH
3
CN, with 0.1%Et
3
N), l
ex
=460 nm.
Chem.Eur.J.2018, 24,3136 –3140
www.chemeurj.org T 2018 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim3137
Communication

N)=3.
[12]
The emission became distinctly green upon contact
with phosgene, which we attributed to amodification of the
dye structure(Scheme 2). Anew green-emis sive compound,
monitored on athin-layer chromatography plate, was also
clear evidence of the formationofanew BODIPY derivative.
After purification with columnchromatography we confirmed
the identityofthe new BODIPY structure as the cyclization
product of the probe by using nuclear magnetic resonance
spectroscopy (NMR) and mass analysis. Given the chemical
identityofthe isolated product, the recognition of phosgene
may proceed by asequential process initiated upon nucleo-
philic substitution of phosgene with the primaryaryl amine,
which promoted an intramolecular cyclizationtoyield anew
BODIPY structure, BOD-UREA (F
F
= 0.52), with acyclic urea lo-
cated on the meso position(Scheme 4).
We additionally investigated the spectroscopic behaviour of
the probe in the presence of other potentially reactive species.
Using identical sensing conditions, we observed no significant
change in fluorescence for other reactiveanalytes, including
acyl chlorides such as acetyl chloride,oxalyl chloride [(COCl)
2
],
thionyl chloride (SOCl
2
), phosphorus oxychloride (POCl
3
), tosyl
chloride(TsCl), and the nerve agent mimic diethylchlorophos-
phate (DCP;Figure 2). With electrophiles such as acetyl chlo-
ride, mono substitution from the primary amine eliminated the
cyclization step (Scheme 4), which clearly accountsfor the ex-
ceptional selectivity of BOD-SYR towards phosgene.
[12]
The promising efficiency of BOD-SYR in sensing phosgene
in the solution encouraged us to furtherassess its feasibility to
detect gaseous phosgene generated in situ. Seekingtodevel-
op an alternative detectionstrategy that could immediately
detect phosgene at exposure sites, we designed apaper-based
indicator cartridge to facilitateimage capturing and the differ-
entiationofcolour development. We treated the paper circles
on the cartridgewith afixed concentration (1.0 mm)ofBOD-
SYR to yield aphysisorbed layer of the probe,after which we
placed the cartridge in sealed tubes and exposed it to varying
concentrations of phosgene (0–100 ppm) generated in situ
from the triphosgene–Et
3
Ncoupling.Next, we placed the car-
tridge in ablack-box apparatus equipped with ultraviolet light-
emitting diodes in front of smartphone camera (Figure 3a).
[12]
We captured the digital images of the cartridge in Figure 3b
prior to phosgene exposure. As Figure 3c illustrates, an intensi-
fying colourdevelopment wasobserva ble as the concentration
increased.Shownfrom left to right, the concentration of ana-
Scheme4.Proposed reaction mechanism for the trapping of triphosgene.
Figure 2. Fluorescence intensity change of BOD-SYR [10 mm,inCH
3
CN/ Et
3
N
(0.1%)] recorded2min after the addition of various analytes (10 equiv;
l
ex
= 460 nm). 1) Triphosgene,2)POCl
3
,3)DCP,4)(COCl)
2
,5)SOCl
2
,6)TsCl,
7) CH
3
COCl.
Figure 3. a) Image of the black-boxapparatus and paper-based indicator
cartridge. b) Image of indicator cartridge prior to UV illumination. c) Image
of indicator cartridge under UV illumination (top row: concentration =0, 10
and 25 ppm; bottom row: concentration = 50, 75 and 100 ppm).
Chem. Eur.J.2018, 24,3136 –3140 www.chemeurj.org T 2018 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim3138
Communication

lytes in the top rowranged from 0–25 ppm and, in the bottom
row,from 50–100 ppm.
We analysed each spot by using simple colour code detec-
tion, which revealed the changeinred and green components
on ascale of 0–255 correlated to the concentratio nofphos-
gene. As Figure 4a depicts, the red component changed from
98 to 45 :8asthe concentration varied from 0to100 ppm,
whereas the green component increased from 100 to 190. This
promising colour-code correlation to the concentration of
phosgene yieldedacalibration curve enabling the quantifica-
tion of gaseous phosgene (Figure 4c). The linear relationship
of red and green components with variable concentration
show promise for detecting and quantifying phosgene using
simple image analysis. The BOD-SYR indicator cartridges and
black-box apparatus may therefore be applicable to translating
ordinary smartphones into phosgen edetectors without com-
plicatedfabrication processes.
The analytical performance of paper strips toward gaseous
phosgene wasalso investigated by fluorescencespectrosco py.
The emission intensity increased immediatelyupon exposure
to phosgene (e.g.,50ppm) then reached to aplateau within
10 s(Figure 5). The limit of detection (LOD) based on fluoro-
metric analysis was found to be as 10 ppm (Supporting Infor-
mation), which is considerably lower than fatal levels.
[13]
In summary,wehave developedaphosgene-specific fluores-
cent probe that uses aBODIPY dye as avisible light-harvesting
chromophore and an o-aminobenzyl amineunit as the new-
generation reactivemotif. Our probe system relying on asix-
membered cyclizationprocess exhibits comparable analytical
performance to previously describedsystems in terms of selec-
tivity and sensitivity,yet with an improved response time
(< 10 s; Table S1).
[12]
Along with its rapid, specific response to
Figure 5. a) Fluorescence intensity change of BOD-SYR-loaded paper strips
in the presence of 50 ppm gaseous phosgene as afunction of time
(l
ex
= 460 nm). b) Fluorescence intensity change of BOD-SYR-loaded paper
stripsasafunction of phosgene concentration (0–100ppm).
Figure 4. a) Colourcode analysis (0–255)ofphosgene-exposedindicator car-
tridge basedonthe red component. b) Colour code analysisofphosgene-
exposedindicatorcartridge based on the green component. c) Calibration
curve based on red component versus phosgene concentration.
Chem. Eur.J.2018, 24,3136 –3140 www.chemeurj.org T 2018 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim3139
Communication

triphosgene in solution, the probe provedsuccessful in detect-
ing gaseous phosgene when fabricated on asolid surface. The
prototypehandheld phosgenedetector using dye-loaded car-
tridges exhibited promising sensing capabilitythat expedited
the detection of phosgene gas without sophisticated instru-
mentation requiring only asmartphone as aphotometric de-
tector.Most importantly,the proposed method andthe hand-
held detector afford arapid response period suitable for the
early detection of phosgeneinemergency situations.
Experimental Section
Synthesis of BOD-SYR
BOD-NO
2
(50 mg, 0.11mmol) in EtOH (8 mL) was added to asolu-
tion of NH
2
NH
2
·H
2
O(95 mL) and Pd/C (10.1 mg, 0.01 mmol). The re-
action mixture was heated at reflux under Ar atmosphere for 2h,
then was cooled to room temperature and filtered. The solids were
washed with DCM. The liquid phases residue was purified by
column chromatography.(2:1hexane/ethyl acetate) to afford BOD-
SYR as orange solid (20 mg, 40%yield).
1
HNMR (400 MHz, CDCl
3
)
d =7.23–7.15 (m, 2H), 7.07 (td, J = 2.3, 8.6 Hz, 2H), 6.81–6.74 (m,
4H), 5.98 (s, 2H), 4.26 (br.s., 2H), 4.07 (br.s,2H), 3.96 (br.s,1H),
2.55 (s, 6H), 1.51 ppm (s, 6H).
13
CNMR (100 MHz, CDCl
3
) d= 154.9,
148.8, 145.6, 143.2, 142.6, 130.1, 129.2, 129.0, 124.3, 122.4, 120.9,
118.6, 116.1, 113.8, 46.8, 14.8, 14.6 ppm. HRMS (QTOF): m/z calcd
(%) for C
26
H
27
BF
2
N
4
:445.2330 [M++H]
+
;found:445.2443 [M ++H]
+
Synthesis of BOD-UREA
BOD-SYR (10 mg, 0.025 mmol) was dissolved in dry DCM (2 mL).
Then, triphosgene solution (125 mm in dry DCM) was added drop
by drop to the BOD-SYR solution under Ar for 10 min. After evapo-
ration of solvent, the resultant residue was purified by column
chromatography (2:1 hexane/ethyl acetate) to afford BOD-UREA
(3 mg, 26%yield).
1
HNMR (400 MHz, CDCl
3
) d = 7.54 (d, J = 8.4,
2H), 7.32 (d, J = 8.4, 2H), 7.17–7.15 (m, 1H), 7.05–7.02 (m, 1H), 6.88
(s, 1H), 6.79–6.77 (m, 1H), 5.99 (s, 2H), 4.91 (s, 2H), 2.56 (s, 6H),
1.47 ppm (s, 6H).
13
CNMR (100 MHz, CDCl
3
) d = 155.6, 153.3, 136.3,
132.1, 128.7, 128.4, 125.6, 125.0, 122.6, 121.3, 118.2, 113.6, 75.4,
51.1, 14.7, 14.6 ppm. HRMS (QTOF): m/z calcd (%) for C
27
H
25
BF
2
N
4
O:
471.2123 [M
+
+H]
+
;found:471.2223 [M++H]
+
.
Acknowledgements
The authors gratefully acknowledge I
˙
zmir Institute of Technolo-
gy and T3BA-GEBI
˙
P-2016(Turkish Academy of Science)for fi-
nancialsupport.
Conflict of interest
The authors declare no conflict of interest.
Keywords: BODIPY · fluorescence · handhelddetectors ·
phosgene · photodetection
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Acceptedmanuscript online:January 5, 2018
Version of record online:February 5, 2018
Chem. Eur.J.2018, 24,3136 –3140 www.chemeurj.org T 2018 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim3140
Communication

Frequently asked questions

Q1. What are the contributions mentioned in the paper "A bodipy**-based fluorescent probe to visually detect phosgene: toward the development of a handheld phosgene detector" ?

In general, detecting phosgene with a molecular probe involves trapping the molecule using a reactive site ( e. g., hydroxy and amine functional groups ), which, following structural modification, generates a detectable optical signal, for example a colour change or fluorescence emission. Dr. U. H. Yildiz Inovasens Co. İzmir Technology Development Zone Inc. Teknopark, 35430 Urla, İzmir ( Turkey ) [ * * ] boron-dipyrromethene Supporting information and the ORCID identification number ( s ) for the author ( s ) of this article can be found under https: //doi. org/10.