A BODIPY dye as a reactive chromophoric/fluorogenic probe for selective and quick detection of vapors of secondary amines

Article abstract of DOI:10.1039/c3cc46571c

A new reaction based fluorescence turn-off strategy for detection of secondary amines was developed. The probe shows fast response and high selectivity to secondary amines in solution/film at sub-ppm levels through chromogenic and fluorescent dual-mode signal changes.

Full text of DOI:10.1039/c3cc46571c

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A BODIPY dye as a reactive chromophoric/fluorogenic
probe for selective and quick detection of vapors of
secondary amines†
Cite this: Chem. Commun., 2013,
4
9, 11266
Received 28th August 2013,
Accepted 10th October 2013
a
a
a
ab
ab
Yanyan Fu, Qingguo He,* Defeng Zhu, Yuerong Wang, Yixun Gao,
a
a
Huimin Cao and Jiangong Cheng*
DOI: 10.1039/c3cc46571c
www.rsc.org/chemcomm
A new reaction based fluorescence turn-off strategy for detection of very short time? (2) Can a magic molecule be designed which
secondary amines was developed. The probe shows fast response and will trigger a significant chromophoric and/or fluorescent response
high selectivity to secondary amines in solution/film at sub-ppm levels upon interaction with the target analyte?
through chromogenic and fluorescent dual-mode signal changes.
It is known that phenyl boronate ester can be converted to
phenol through the oxidation of H or other oxidative
2 2
O
Rapid and efficient detection of trace volatile organic amines in reagents in the presence of a catalyst, which has been used in
8
air is highly desirable. It is not only because of its high toxicity biological systems or explosive detection, but never been used
to human health but also because of its potential harm to the for amine detection. Our consideration is that amine is a kind
1
environment. Traditional methods for detection of volatile of Lewis base, and under the basic conditions the reducing
organic amines, such as gas chromatography–mass spectrometry capacity of phenyl boronate ester will increase. Hence organic
(GC-MS), are time-consuming and need complicated sample amines may accelerate the photo-oxidation of arylboronates
processing. Thus, the development of real-time sensitive analytical (or aryl boronic acids) to yield the corresponding phenols.
2
methods for amine vapors still remains challenging.
Experiments were conducted with different arylboronates/aryl
Fluorescence sensing has gained considerable attention for boronic acids and organic amines as reagents. The results indicate
vapor detection because of its high sensitivity, low cost and ease that the oxidative reactions can be carried out smoothly (Scheme S1,
3
of fabrication. However, it is found that the selectivity of most ESI†) with satisfactory yield (63–91%) within a few minutes in the
of the fluorescent sensory materials for amine vapor detection presence of secondary amines. However, the primary amine and
based on p–p interaction, H-bonding interaction, photo-induced tertiary amine hardly induce this reaction which may be attributed
electron transfer and other weak interactions is far from satis- to their weaker alkalescence compared with secondary amines. The
faction, although an elaborate molecular design has been given proposed reaction mechanism is shown in Scheme S2 (ESI†). To the
4
special concern. Most of such materials cannot distinguish the best of our knowledge, this is a new reaction to prepare phenols
type of organic amine. Nevertheless, the recognition of secondary rapidly. Thus, the boronate ester can be chosen as the reactive
amines is significant in practical applications because the main recognition part in the fluorescent sensing of secondary amines.
ingredients of many famous medicaments and drugs are secondary
4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives
amines. For instance, methamphetamine is the main component are famous fluorescent building blocks for the construction of
of ‘‘ice’’ and ephedrine is the main ingredient of cold cure. sensory materials due to their high fluorescence quantum yields,
We reason that a reactive probe which possesses merits of good photochemical stability, low sensitivity to the environment,
5
–7
9
specificity and cumulative signaling effects is a possible tool and easy functionalization. Particularly, the absorption and emis-
to identify the organic secondary amines. sion properties of BODIPY-based dyes readily change when their
Generally, two major questions should be addressed to donor and/or acceptor changed because of the intramolecular
10
design a special reactive vapor probe: (1) can a selective and charge-transfer process.
efficient reaction be used under mild solid-state conditions in a
Herein, we report a simple BODIPY derivative as a probe for
organic amine vapors with an aromatic boronate ester as the
reactive unit. Probe 3 is prone to oxidative deboronation in the
presence of secondary amines and shows instant chromogenic
and fluorescent dual-mode response to secondary amine species.
Probe 3 was synthesized conveniently through the incomplete
palladium-catalyzed Suzuki cross-coupling reaction according to
a
State Key Lab of Transducer Technology, Shanghai Institute of Microsystem and
Information Technology, Chinese Academy of Sciences, Changning Road 865,
Shanghai 200050, China. E-mail: hqg@mail.sim.ac.cn, jgcheng@mail.sim.ac.cn
b
Graduate School of the Chinese Academy of Sciences, Yuquan Road 19,
Beijing 100039, China
†
Electronic supplementary information (ESI) available: General methods and
1
1
materials, more detailed discussion and deduction. See DOI: 10.1039/c3cc46571c a known procedure (Scheme 1).
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1266 Chem. Commun., 2013, 49, 11266--11268
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However, the addition of other amines such as n-propylamine,
n-hexylamine, triethylamine, benzylamine and aniline had
almost no effect on the color and fluorescence of the solution
which indicated the high selectivity of this probe to secondary
amines.
2 2
Scheme 1 Preparation of probe 3: key: (1) pyrrole, TFA, CH Cl , rt; (2) DDQ,
2 2 3 2 3 4 2 3
CH Cl , rt; (3) TEA, BF OEt , rt; (4) Pd(PPh ) , K CO , 9,9-dioctylfluorene-2,7-
To identify the reaction products, we performed the reaction
between 3 and several types of amines at a higher concentration
in the solution (Scheme S3, ESI†). In the presence of primary
amines and tertiary amines such as n-propylamine, n-hexyl-
amine, triethylamine, benzylamine and aniline, only a trace
amount of the new product was observed in the solution within
half an hour. However, a new purple product formed in good
isolated chemical yield (nearly 100%) within 5 minutes after
adding DIPA or DEA. And the major product was identified to
be 7-(8-(4,4-difluoro-4-bora-3a,4a-diaza-s-indacene))-2-hydroxyl-
bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane), THF.
1
13
9
,9-dioctylfluorene (4) according to its H, C-NMR spectra and
1
the high resolution mass spectrum (Scheme 2). In H-NMR
spectra, resonances of the BODIPY moiety of probe 3 are
observed at 7.93, 7.40 and 6.60 ppm. With the addition of
4 equiv. of DIPA, the resonances of the BODIPY moiety scarcely
shifted. Nevertheless, as shown in Fig. 3, the chemical shifts of
protons on the fluorene moiety and the thiophene moiety
changed greatly owing to the effect of the newly formed hydroxyl
group. In addition, a new peak centered at 5.29 ppm can be
assigned to the hydroxyl proton of the –OH group. Thus, the
NMR results further confirm that the interactive site should be
at the boronate ester position, and no strong interaction exists
between DIPA and BODIPY units because of no corresponding
chemical shift of the protons.
Fig. 1 Absorbance spectra (a) and fluorescence spectra (b) of 3 (10 mM) in the
presence of increasing diisopropylamine concentrations (0, 4, 8, 12, 16, 20, 24,
2
8, 32, 36, 40 mM) in a THF solution.
The chromogenic and fluorometric signaling behaviors of 3 to
secondary amines were investigated in a THF solution. As shown
in Fig. 1a, with the addition of diisopropylamine (DIPA), the
UV-vis absorption of 3 experienced a little red shift with a slight
increase in its maximum absorption peak at 513 nm and an
obvious enhancement of the tail between 540 and 600 nm.
Simultaneously, the color of the solution turned from red to
violet quickly. TLC (thin layer chromatography) monitoring
suggested that a new product appeared in the solution.
Fig. 1b shows the change in emission spectra upon addition
of DIPA. Upon excitation at 513 nm, the emission intensity at
To better understand the photophysical change before and
after the addition of secondary amines, the optical properties
of 3 and 4 were compared. The absorption peak positions of
both 3 and 4 were observed at 513 nm, but 4 demonstrated a
bigger absorbance with a broad and strong tail peak at around
592 nm decreased 25-fold while the concentration of DIPA
changed from 0 to 40 mM. A similar phenomenon was observed
when the DIPA was displaced by diethylamine (DEA) (Fig. S1,
ESI†). To demonstrate the selectivity to various amines in the
solution, both visible color change and visual fluorescence
change of 3 after addition of different amines are presented in
Fig. 2. The free probe exhibited red color and red emission in the
solution. After the addition of DEA or DIPA, the color of the solution
turned violet and the fluorescence was quenched immediately.
Scheme 2 Signaling of secondary amines by 3.
À3
Fig. 2 Visible color (a) and visual fluorescence color change (b) of 3 (10 M) with
representative amines after mixing for 5 minutes (100 equiv. for each amine in
1
À3
THF): (1) free 3; (2) 3 + n-propylamine; (3) 3 + n-hexylamine; (4) 3 + diethylamine;
Fig. 3 Partial H NMR spectra of 3 only, and 3 + diisopropylamine. [3] = 5.0 Â 10 M,
À2
(
5) 3 + diisopropylamine; (6) 3 + triethylamine; (7) 3 + benzylamine; (8) 3 + aniline.
[diisopropylamine] = 2 Â 10 M in CDCl
3
.
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formation of trace 4. While in DEA and DIPA vapors, the
quenching efficiency was 87.9% and 88.3%, respectively.
Obviously, this probe exhibited excellent selectivity to secondary
amines in the solid films.
In summary, chemosensing of secondary amines was inves-
tigated by virtue of its particular characteristic that catalyzes
the oxidation of boronate esters (or boronic acids) in air to yield
the corresponding phenols. The BODIPY-based probe exhibits both
color and fluorescence response to secondary amines either in
solution or in solid films even in the form of test papers exhibiting
its wide potential applications. Besides, the probe showed remark-
Fig. 4 (a) Changes in fluorescence intensity of 3 films exposed to air and the
saturated diisopropylamine vapor for 300 s at 25 1C at their wavelength of the
maximum emission. The inset picture was the fluorescence response of 3 films ably high selectivity to secondary amines over other amine species.
before (i) and after (ii) exposure in DIPA for 300 s. (b) Fluorescence quenching This work offers a new strategy for solid-state fluorescence sensing,
efficiency of 3 deposited on a quartz slide exposed to the saturated vapor of various
and also provides an efficient and quick method to synthesize
some special phenols starting from the corresponding boronate
organic amines for 300 s: 1. n-propylamine; 2. n-hexylamine; 3. diethylamine;
4
. diisopropylamine; 5. triethylamine; 6. aniline; and 7. benzylamine.
esters. Endeavors to further modify the sensory materials so as to
increase the sensitivity of BODIPY-based conjugates are in progress,
5
4
70 nm (Fig. S2, ESI†). The molar absorption coefficients are and studies to expand the analytes based on different sensing
5 700 M cm and 50 500 M cm for 3 and 4, respectively. mechanisms via various functionalizations of BODIPY are also
À1
À1
À1
À1
The higher molar absorptivity of 4 indicated the higher sensi- underway in our laboratory.
tivity for secondary amines using a colorimetric technique. The
This work was supported by a fund from the National
relative fluorescence quantum yields (FFL) of 3 and 4 were Natural Science Foundation of China (No. 51003118, 50973128,
evaluated to be 2.6% and 0.14% in THF, with Rhodamine B as and 61007066), the research programs of the Ministry of Science
the standard. In addition, the FFL of 3 and 4 in the solid state and Technology of China (No. 2012BAK06B03), and the Shanghai
determined by a calibrated integrating sphere are 0.31% and Science and Technology Committee (No. 11JC1414700).
0.01%, respectively, which corresponded very well with the fact
that the fluorescence of 3 was quenched rapidly when the Notes and references
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5
6
7
8
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2
À2
paper (2 Â 0.5 cm ) into the THF solution of 3 (1.0 Â 10 M)
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9
2
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1
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1
1268 Chem. Commun., 2013, 49, 11266--11268
This journal is c The Royal Society of Chemistry 2013