Highly sensitive iridium(III) complex-based phosphorescent probe for thiophenol detection

Article abstract of DOI:10.1039/c7dt02263h

A cyclometalated iridium(iii) complex (Ir-DNBS) was designed and synthesized as a high-performance phosphorescent thiophenol probe. Ir-DNBS displays a distinct phosphorescence off-on response toward thiophenol with high selectivity, high sensitivity (detection limit: 2.5 nM) and fast response (10 min). It is noteworthy that the signaling phosphore of Ir-DNBS possesses relatively high photoluminescence quantum efficiency (Φ_PL = 0.21) together with relatively long lifetime (τ = 2.07 μs), indicative of its potential in achieving high temporal resolution. Ir-DNBS is also applicable to the detection of thiophenol in actual water samples with high recovery rate. Photophysical and spectral characterization results revealed that the probing mechanism of Ir-DNBS toward thiophenol lies in the thiolate-mediated cleavage reaction, resulting in suppressed photo-induced excited state electron transfer process in the reaction product.

Full text of DOI:10.1039/c7dt02263h

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Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
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a Zr-metal–organic
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Table of Content
Iridium (III) complex could serve as a highly sensitive, long-lifetime phosphorescence thiophenol probe through rational
design.
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Journal Name
ARTICLE
Highly Sensitive Iridium(III) Complex-Based Phosphorescent Probe
for Thiopheol Detection
Received 00th January 20xx,
Accepted 00th January 20xx
Li Xiong, Lin Yang, Shuai Luo, Yan Huang, and Zhiyun Lu*
A cyclometalated iridium (III) complex (Ir-DNBS) was designed and synthesized as a high-performance phosphorescent
thiophenol probe. Ir-DNBS displays distinct phosphorescence “off-on” response toward thiophenol with high selectivity,
high sensitivity (detection limit: 2.5 nM) and fast response (10 min). It is noteworthy that the signaling phosphore of Ir-
DNBS possesses relatively high photoluminescent (PL) quantum efficiency (ΦPL = 0.21) together with relatively long
lifetime (τ = 2.07 μs), indicative of its potential in acquiring high temporal resolution. Ir-DNBS is also applicableto the
detection of thiophenol in actual water sample with high recovery rate. Photophysical and spectral characterization results
revealed that the probing mechanism of Ir-DNBS toward thiophenol lies in the thiolate-mediated cleavage reaction,
resulting in suppressed photo-induced excited state electron transfer (PET) process in the reaction product.
DOI: 10.1039/x0xx00000x
www.rsc.org/
Nevertheless, all the above-mentioned excellent responding
characters toward thiophenols could merely be realized,
without exception, through fluorescent thiophenol probes
Introduction
Owing to the high toxicity1−6 yet wide distribution of
thiophenols in environments as pollutant species, it is highly
demanded to develop high-performance optical thiophenols
probes for their handy operation, noninvasiveness and real-
time characters.7,8 Generally, thiophenol fluorescent probes
will suffer from interference from thiol species because of
their similar nucleophilicity with thiophenol, but recent
research finding revealed that thiophenols could be easily
differentiated from thiols in neutral environments (pH = 7.3)
since they could be dissociated into more nucleophilic thiolate
species (Scheme 1).9 Based on this differentiation mechanism,
dozens of optical probes showing high selectivity toward
whose emission band locates in the visible region, which are
not perspective for biological sample studies.15,16 Although far-
red/infrared (FR/NIR) fluorescence probes whose λem > 630 nm
are more promising for bio-system applications due to their
capability to avoid the background endogenous fluorescence
interference,17,18 they generally suffer from relatively low ΦPL
stemming from their narrow band-gaps,19−22 leading to much
inferior thiophenol-responding performance than their visible
counterparts.23,24
In comparison with pure organic fluorophores,
phosphorescent heavy-metal complexes based on metal-to-
ligand charge-transfer transitions (MLCT) exhibit not only
larger Stokes shifts for easy separation of excitation and
emission, but also much longer lifetimes capable of showing
excellent temporal resolution to avoid autofluorescence in PL
bioimaging and biolabeling.25−33 As a result, the FR/NIR
emission character is no longer indispensable for
phosphorescent probes in bio-system applications, hence
luminogens with relatively high PL efficiency could be readily
acquired. However, in terms of phosphorescent thiophenol
probes, there are only two relevant reports up to date. Using
Ru(II)-bipyridine complex as the phosphore, Yuan et al.34
reported the first example of phosphorescent thiophenol
probe in 2012. The resultant probes show relative low LOD of
32.9 nM, but their reaction time is as long as 30 min.
Moreover, these phosphores suffer from ultralow PL quantum
yield (ΦPL ≤ 0.023) and short lifetime (τ ≤ 305 ns), which should
be ascribed
−
thiophenols have been developed subsequently.10
16
Currently, the detection limit (LOD) of the reported thiophenol
probes could be as low as 1.8 nM,10 the response time could
be less than 5 s,11 and the signaling fluorophores could show
high photoluminescence (PL) quantum efficiency (ΦPL) up to
0.85,12 Additionally, some of them were demonstrated to be
capable of detecting thiophenol concentrations in practical
water samples or cell imaging.13,14
Scheme 1. Schematic illustration of the better nucleophilicity of thiophenols
than thiols in neutral conditions.
Key Laboratory of Green Chemistry and Technology (Ministry of Education), College
of Chemistry, Sichuan University, Chengdu 610064, China.
E-mail: luzhiyun@scu.edu.cn; Tel: 86-28-85410059; Fax: 86-28-85410059
†Electronic Supplementary Information (ESI) available: Synthetic details, the 1H
NMR, 13C NMR, and HR-MS spectra, the concentration-dependent PL emission
spectra, kinetics under air conditions. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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Scheme 2. The design concept of the probe Ir-DNBS for the detection of thiophenols.
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DOI: 10.1039/C7DT02263H
to the insufficient heavy atom effect of their ruthenium central fragment of the C^N ligand to improve the water solubility of
atom.35,36 Although subsequently, Chao et al.37 developed a the objective complex. The results indicated that Ir-DNBS can
[Ir(ppy)2bpy]+-typed chelate (ppy: 2-phenylpyridine; bpy: 2,2’- act as a high-performance phosphorescence thiophenol probe
bipyridine) bearing more significant heavy atom effect hence with high selectively, high sensitively (LOD: 2.5 nM) and rapid
stronger spin-orbit coupling effect than Ru(II) complexes, it response (<10 min). Its signaling species shows not only
shows rather poor phosphorescence response toward relatively high PL quantum yield (ΦPL = 0.21), but also relatively
thiophenol: the LOD is in the order of mM, and the signaling long lifetime (τ = 2.07 μs) that could trigger better temporal
species suffers from quite low ΦPL (0.074) together with a resolution. Moreover, it was demonstrated to be capable of
relatively short life-time (295 ns), which is adverse to the detecting thiophenol concentrations in actual water samples
temporal resolution. These should be ascribed to the intrinsic with high recovery rate.
low ΦPL (< 0.20) and short lifetime (561 ns) of its parent
phorsphore [Ir(ppy)2bpy]+.38 In addition, [Ir(ppy)2bpy]+ was
found to show rather complicated dynamics of its triplet
Experimental ection
excited states involving not only MLCTbpy, but alsoMLCTppy and
LLCT transition characters.39 Hence it is difficult to design
[Ir(ppy)2bpy]+-typed phosphorescent complexes rationally with
increased ΦPL and τ.
As the performance of phosphorescent thiophenol probes
lags far behind that of their fluorescent counterparts, herein,
The experimental details, including reagents and apparatus,
synthesis, determination of PL quantum yield, kinetics
constant and half-time calculations and the determination of
thiophenol in water samples are described in the Supporting
Information.
we designed and synthesized a novel Ir(III) complex (Ir-DNBS
,
molecular structure and design concept shown in Scheme 2) as
a phosphorescence thiophenol probe. Based on our previous
research findings that the complex bis[2-(9,9-dimethylfluoren-
Result and discussion
Spectra Response of Ir-DNBS toward Thiophenol
As illustrated in Figure S1a, in 40% acetonitrile/PBS (0.01 M,
pH = 7.4) solution, Ir-DNBS displays four distinct absorption
bands at 260~520 nm. By comparing the absorption spectra of
2-yl) benzothiazolato-N,C2’]iridium(III)(acetylacetonate)40
(Ir-F,
structure shown in Figure S1) displays not only relatively low-
energy phosphorescence with emission maximum (λPL) of 600
nm, but also relatively high ΦPL of 0.33, a 2-(fluoren-2-
yl)benzo[d]thiazole derivative was employed as the
cyclometalated ligand (C^N ligand) of the sensor. To endow
Ir-F40 bearing analogous C^N ligand with Ir-DNBS and the free
ligands of Ir-DNBS, the absorption band with absorption
maximum (λabs ) of 289 nm and 349 nm could be safely
assigned to the ligand-centered (LC) 1ππ* transition of the N^N
ligand and C^N ligand of Ir-DNBS, respectively; while the two
absorption band with λabs of 406 and 463 nm could be
attributed to the MLCTC^N and/or MLCTN^N transitions.40 It
should be pointed out that for the latter two absorption bands
at lower energy region, they show relatively high molar
the complex with MLCTC^N
− rather than LLCT− and/or
MLCTN^N−dominated transition characters, 4-(5-(pyridin-2-yl)-
1H-1,2,4-triazol-3-yl)aniline showing strong σ-donor property
of the azolate and π-accepting ability of the pyridyl
subunits,41−43 together with relatively large band-gap was
chosen as the auxiliary ligand (N^N ligand).44
A 2,4-
extinction absorption coefficients (log ε: 4.37~4.67, Table S1),
which are much higher than that of the MLCT absorption band
of [Ir(ppy)2bpy]+-typed chelate (log ε: cal. 3.0).37 The strong
dinitrobenzenesulfonyl group (DNBS)45 was introduced to the
N^N ligand as not only the thiophenol recognition site, but also
the PL quenching moiety through a photo-induced electron-
transfer (PET) mechanism. In addition, two polyether segments
subunits were introduced to the 9-position of the fluorene
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Figure 1. (a) Phosphorescence spectra (λex = 420 nm, slits: 10/5) of 5 μM Ir-DNBS in the presence of different concentration of thiophenol in 40% acetonitrile/PBS
(0.01 M, pH = 7.4) under nitrogen conditions and (b) the correlation between phosphorescence intensity of 5 μM Ir-DNBS at 573 nm and concentration of thiophenol
in 40% acetonitrile/PBS (0.01 M, pH = 7.4) under nitrogen conditions. Insets: photographs of phosphorescence changes of 5 μM Ir-DNBS upon addition of thiophenol
(25 μM).
Figure 2. (a) Phosphorescence spectra (λex = 420 nm, slits: 10/5) of 5 μM Ir-DNBS in the presence of 25 μM thiophenol at different reaction time in 40% acetonitrile/PBS (0.01 M,
pH = 7.4) under nitrogen conditions. (b) Fluorescence enhancement profile of phosphorescence intensity at 573 nm of Ir-DNBS (5 μM in 0.01 M 40% acetonitrile/PBS, pH = 7.4) in
the presence of thiophenol (5 equiv) or thiol species (20 equiv) under nitrogen conditions.
MLCT transition character of Ir-DNBS will be beneficial to the
enhancement of phosphorescence efficiency of the phosphore nm (I573 nm) correlate linearly with the concentration of
hence the improvement of the sensitivity of the probe. thiophenol in the range of 0−5 μM (Figure 1b), and the slope k
For the 5 μM Ir-DNBS sample, its PL intensity values at 573
Under excitation at 420 nm, the solution sample of Ir-DNBS was as high as 91.92 × 106 M-1 (R2 = 0.9913). Taking into
in 40% acetonitrile/PBS (0.01 M, pH = 7.4) could emit rather consideration that the standard deviation (S.D.) of our
weak PL with λPL of 573 nm and a shoulder peaked at 620 nm. fluorescence spectrophotometer was 0.076, the LOD of
In fact, the ΦPL of Ir-DNBS in acetonitrile solution was nitrogen de-aerated Ir-DNBS solution sample toward
determined to be as low as 0.001. Despite the fact that the thiophenol, according to the equation of LOD = 3 × S.D./k, was
addition of thiophenols could not induce obvious changes on determined to be as low as 2.5 nM. According to kinetic
the absorption spectrum of Ir-DNBS (Figure S1b), it could studies on the thiophenol-induced PL enhancement profiles of
trigger distinct PL “turn-on”. As illustrated in Figure 1a, the Ir-DNBS (at I573 nm, vide Figure 2), the reaction equilibrium
existence of 5 equiv of thiophenol in 5 μM de-aerated Ir-DNBS could be reached within 10 min with relatively large kinetics
solution could trigger 75-fold enhanced PL intensity (measured constants and short half-time (k′ = 0.334 min-1, t1/2 = 2.08 min
at λPL = 573 nm). The nearly identical PL emission spectrum of in de-aerated sample; k′ = 0.398 min-1, t1/2 = 1.74 min in
Ir-DNBS in the absence or presence of thiophenol implies the aerated sample, vide Figure S4−6), confirming the rapid
quite similar energy band-gap characters of the lowest excited response character of Ir-DNBS toward thiophenol. Additionally,
states of the probe and the signaling luminogen (Figure S2).
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Figure 3. (a) Phosphorescence intensity at 573 nm (λex = 420 nm, slits: 10/5) of 5 μM Ir-DNBS in the presence of 100 μM various thiol and other nucleophiles or 4 μM thiophenols in
40% acetonitrile/PBS (0.01 M, pH = 7.4) under nitrogen conditions, and (b) phosphorescence intensity at 573 nm (λex = 420 nm, slits: 10/5) of 5 μM Ir-DNBS in the presence of 100
μM various thiol and other nucleophiles or 4 μM thiophenols in 40% acetonitrile/PBS (0.01 M, pH = 7.4) under air conditions. Insets: photographs of optical changes of 5 μM Ir-
DNBS upon addition of various analytes. 1, free; 2, Cys; 3, Hcy; 4, GSH; 5, 3-mercaptopropionic acid; 6, aniline; 7, phenol; 8, KI; 9, Na2S; 10, Na2SO3; 11, p-nitrothiophenol; 12, p-
methylthiophenol; 13, p-methoxythiophenol; 14, thiophenol.
the phosphorescence enhancement profiles of Ir-DNBS toward μs in aerated samples. The relatively long lifetimes of the
thiophenol are nearly unaffected by the ionic activity of the signaling species as well as the oxygen-induced lifetime-
solution (Figure S7).
shortening characters of both the probe and the signaling
As the pH value is a key factor influencing the interactions species validate their phosphorescence rather than
between thiophenol and probe molecule, the effect of pH fluorescence characters. In addition, the drastically shortened
value on the I573 nm of Ir-DNBS in the absence or presence of lifetime of the probe than the signaling phosphore suggests
thiophenol was investigated. As shown in Figure S8, the I573 nm the presence of PET-induced PL quenching in the probe Ir-
of Ir-DNBS is insensitive to pH environment variations within DNBS 34,45
.
the pH range of 1.0−12.0. In acidic environments (pH < 3.0),
the coexisting thiophenol could not trigger significant Selectivity of Ir-DNBS toward Thiophenols.
variations on the I573
of the mixture, which should be
nm
To evaluate the selectivity of Ir-DNBS toward thiophenols, the
phosphorescent response of Ir-DNBS toward various
interference analyte species including aliphatic thiols (i.e., Cys,
Hcy, GSH and 3-mercaptopropionic acid) and other
nucleophiles (i.e., aniline, phenol, KI, Na2S, and Na2SO3) were
examined in parallel to thiophenols. As depicted in Figure 3,
only thiophenol derivatives could trigger obvious PL
enhancement. It should be pointed out that in comparison
ascribed to the relatively weak nucleophilic capacity of neutral
thiophenol species. But with increasing pH values from 3.0 to
11.0, significant PL enhancement could be observed in the
mixture of Ir-DNBS and thiophenol (5 equiv). This should stem
from the efficient dissociation of thiophenol into thiolate ion
species that possesses much stronger nucleophilicity. It is
noteworthy that the I573 nm of Ir-DNBS remains stable in over
1h under constant photoexcitation (Figure S9), indicative of its
good photostability. Consequently, Ir-DNBS can serve as a
photostable thiophenol probe in weakly acidic, neutral and
weakly alkaline environments.
with
p-methylthiophenol,
p-methoxythiophenol
and
thiophenol, p-nitrothiophenol could trigger much less
significant optical changes of Ir-DNBS, which should be
ascribed to the much weakened nucleophilicity of its mercapto
functional group due to the existence of an electron-deficient
nitro- substituent.13 In fact, as depicted in Figure 2b and Figure
PL Lifetime Characters of Ir-DNBS
To gain insight into the intrinsic excited state characters and S5b, the addition of a great excess of thiol species (20 equiv) to
thiophenol-probing mechanism of Ir-DNBS transient PL Ir-DNBS still could not induce competitive optical responses of
,
measurements were carried out on the 40% acetonitrile /PBS Ir-DNBS, implying that Ir-DNBS is not susceptible to the
(0.01 M, pH = 7.4) 5 μM Ir-DNBS solution samples in the interference from thiols and other nucleophiles. Upon further
absence or presence of 5 equiv thiophenol under either addition of 0.8 equiv of thiophenol to the mixture of Ir-DNBS
nitrogen de-aerated or aerated conditions. As depicted in and the previously mentioned interference species, drastically
Figure S10 and Table S2, for pristine Ir-DNBS, relatively short enhanced phosphorescence intensity could be discerned.
average lifetimes of 31.0 ns and 18.7 ns were observed in de-
aerated and aerated solution samples, respectively; but upon
addition of thiophenol, the PL lifetimes of the resultant
mixture were determined to be 1.99 μs in de-aerated and 0.50
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Figure 4. Partial 1H NNMR spectra of Ir-DNBS
,
Ir-DNBS + thiophenol (2 equiv), Ir-NH2 in DMSO-d6 and DN in CDCl3.
These competition experimental results indicated that Ir-DNBS
These deductions were confirmed by spectral comparison of
shows high specificity toward thiophenols, and could be used Ir-NH2 with the mixture of Ir-DNBS and thiophenol. As
to detect thiophenol derivatives in relatively complicated illustrated in Figure S1b, S2, the absorption and emission
environments.
spectra of Ir-NH2 resemble the corresponding absorption and
emission spectra of Ir-DNBS + thiophenol (5 equiv); the PL
lifetime characters of Ir-NH2 (0.51 μs and 2.07 μs in aerated
and de-aerated samples, respectively, vide Figure S10 and
Table S2) are quite analogous to that of Ir-DNBS in the
presence of 5 equiv of thiophenol (0.50 μs and 1.99 μs in
sequence); in the presence of thiophenol, the m/z signal of
931.7664 corresponding to the[Ir-DNBS + H + Na]2+ species
disappears, but an m/z signal of 816.7839 that could be
assigned to the [Ir-NH2 + H + Na]2+ species is discernible (Figure
S15). Therefore, the optical response of Ir-DNBS toward
thiophenols should be attributed to the thiolate-mediated
cleavage mechanism.
Probing Mechanism of Ir-DNBS toward Thiophenols.
For thiophenol probes bearing a 2,4-dinitrobenzenesulfonyl
(DNBS) recognition site, they will generally undergo a thiolate-
mediated cleavage process with SNAr,12,13,46 as illustrated in
Figure 4. To elucidate the probing mechanism of Ir-DNBS
toward thiophenol, 1H NMR spectrum of Ir-DNBS in the
absence or presence of 2 equiv of thiophenol was recorded. As
shown in Figure 4, in the presence of thiophenol, the proton
signals corresponding to the 2,4-dinitrobenzenesulfonamide
group of Ir-DNBS (11.02 ppm for proton
a
, 8.83 ppm for
) were
proton , 8.51 ppm for proton , 8.10 ppm for proton 3
1
2
As the complex Ir-NH2 was demonstrated to be the signaling
phosphore of Ir-DNBS, we measured its phosphorescence
quantum yield (Table S1). The result indicated that in de-
aerated acetonitrile solution, Ir-NH2 displays a satisfactory ΦPL
of 0.21. Taking into consideration that Ir-DNBS and Ir-NH2
display quite similar PL emission spectra, but the ΦPL and the
average lifetime of Ir-DNBS are much lower and shorter than
those of Ir-NH2, a PET PL-quenching mechanism could be
all found to disappear; concurrently, the characteristic proton
signals of (2,4-dinitrophenyl)(phenyl)sulfane (DN) at 8.92, 8.36,
and 7.03 ppm (corresponding to protons I, II, and III in
sequence47) were found to emerge. In addition, in the
presence of thiophenol, the proton signals of Ir-DNBS at 7.80
and 7.08 ppm corresponding to protons
5 and 4 were found to
be upfield-shifted to 7.58 and 6.46 ppm (5′ and 4′ of Ir-NH2),
respectively, which should originate from the more electron-
donating capacity of amino substituent of Ir-NH2 than
rationally assigned to Ir-DNBS 34,45,48
Upon reaction with
.
thiopheols, the cleavage of the strong electron-deficient 2,4-
dinitrosulfonyl group in Ir-DNBS will result in significantly
suppressed PET process in Ir-NH2, leading to much enhanced
ΦPL. Based on the experimental findings that: 1) the proton
signals of the N^N ligand of Ir-NH2 differ obviously from those
sulfonylamino substituent of Ir-DNBS
. Based on these
observations, Ir-DNBS should undergo a thiolate-mediated
SNAr cleavage process to yield Ir-NH2 as the signaling species,
and DN as the byproduct.
of the N^N ligand of Ir-DNBS (e.g., proton
5 vs 5′, 4 vs 4′); 2)
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the absorption spectra of Ir-DNBS and Ir-NH2 only differ in the optical response (< 10 min) toward thiophenol, but also
View Article Online
1
region of 250
~
320 nm corresponding to the LCN^N transition, potentially high temporal resolution. FuDrtOhI:e1r0m.1o03r9e/,Ct7hDeT0p2r2o6b3He
but quite similar in the region of 320
~
550 nm; and 3) the PL Ir-DNBS allows precise quantification of thiophenol in water
emission spectra of Ir-DNBS and Ir-NH2 are near identical, it samples. Note that the thiophenol-responding performance of
could be inferred that the N^N ligand of Ir-DNBS and Ir-NH2 Ir-DNBS far exceeds that of phosphorescent thiophenol probes
should contribute insignificantly to both their visible reported so far. Our research will shed light on the molecular
absorption characters at 400
~
550 nm and phosphorescent design
strategy
for
high-performance
thiophenol
emission characters, i.e., it should be the MLCTC^N rather than phosphorescent probes.
MLCTN^N or LLCT transitions that dominates the formation and
deactivation processes of the lowest triplet excited states of Ir-
Acknowledgements
DNBS and Ir-NH2
.
The authors acknowledge the financial support for this work by
the National Natural Science Foundation of China (Grant Nos.
21372168 and 51573108). We are grateful to the Analytical &
Testing Center of Sichuan University for providing NMR data
for the intermediates and objective molecules.
Real Water Sample Application.
To validate if Ir-DNBS could be used for practical application,
Ir-DNBS was imployed to quantify thiophenol concentrations
in water samples with the standard addition method,2,9 and
the crude water samples were obtained from Jinjiang River,
East Lake of Chengdu, and the tap water in Chengdu city. As
depicted in Table 1, for all the pristine water samples, they
could not induce significant optical response of Ir-DNBS with
regard to the PL intensity. After spiking different concentration
of thiophenol (1 μM, 2 μM, or 4 μM) into the water samples,
obvious phosphorescence enhancement was observed, and
the thiophenol concentration in these water samples could be
accurately measured by the probe Ir-DNBS with good recovery
(95−104%). These results indicated that Ir-DNBS is quite
promising in the quantitative detection of thiophenols in water
samples.
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Table 1. Determination of Thiophenol Concentration in Water Samples
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thiophenol
recovered (μM)
sample
recovery (%)
(μM)
0
Not detected
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Jinjiang
River
1
0.96 ± 0.021
96
water
2
4
0
1
2
4
0
1
2
4
2.06 ± 0.049
3.98 ± 0.056
Not detected
1.01 ± 0.013
1.99 ± 0.023
4.00 ± 0.031
Not detected
0.95 ± 0.12
103
100
−
101
99
100
−
95
East
Lake
water
,
tap
water
2.08 ± 0.042
3.97 ± 0.045
104
99
Wang, F. Pan, W. Zhang and W. Zhao, Anal. Chem., 2015, 87
399-405.
,
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,
,
In summary, though rational molecular design, an iridium(III)
complex Ir-DNBS has been exploited to act as
phosphorescence thiophenol probe. By taking advantage of its
strong MLCTC^N transition characters, the signaling phosphore
of Ir-DNBS displays a relatively long lifetime of 2.07 μs and
high phosphorsecent quantum yield of 0.21, leading to not
only high selectivity, high sensitive (LOD: 2.5 nM) and rapid
8835-8841.
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6 | J. Name., 2012, 00, 1-3
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