Evaluation of electron or charge transfer processes between chromenylium-based fluorophores and protonated-deprotonated aniline

Article abstract of DOI:10.1039/c6ra19831g

Three functional dyes based on a chromenylium skeleton were prepared. The chromenylium-based fluorophores were regarded as acceptor parts and the aniline served as donor parts; their pH-dependent fluorescent responses were used to evaluate the photoinduce

Full text of DOI:10.1039/c6ra19831g

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DOI: 10.1039/C6RA19831G
ARTICLE
Evaluation of electron or charge transfer processes between
chromenylium-based fluorophores and protonated-deprotonated
aniline
Received 00th January 20xx,
Accepted 00th January 20xx
Jin-Wei Xiao,a Wei-Jin Zhu,a Ru Sun,*a Yu-Jie Xu,b and Jian-Feng Ge*a
DOI: 10.1039/x0xx00000x
Three functional dyes based on chromenylium skeleton were prepared. The chromenylium-based fluorophores were
regarded as acceptor parts and the aniline part was severed as donor parts; their pH depended fluorescent responses
were used to evaluate the photoinduced electron transfer (PET) or intramolecular charge-transfer (ICT) processes between
the chromenylium-based fluorophores and aniline. Two chromenylium-indole hybrid functional dyes (1a−b) respectively
showed fluorescent enhancement and decrease with increasing acidity, while chromenylium-cumarin hybrid dye (1c) gave
OFF−ON response towards gradually decreasing pH. The three dyes gave emissions at 675‒850 nm when they were
excited at 650 nm, and the calculated pKa of 1a−c are 4.13, 3.15 and 2.48, respectively. The optical responses were also
illustrated by (TD)DFT calculaꢀon, the OFF−ON emission of dye 1c was mainly controlled by the PET process, both PET and
ICT processes were found between the aniline parts and the chromenylium-indole parts in dyes 1a−b.
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been designed for sensing mercury(II) ion by this platform.17
The chromenylium derivatives keep some advantages of
original rhodamines, such as high fluorescence quantum yield
Introduction
Near-infrared (NIR) fluorescent dyes emit at 650‒900 nm
region, they have been extensively studied in recent years.1-5
Near-infrared light can penetrate deeply into the tissue,
reduce the damage to the biological sample, decrease the
influence of background fluorescence in the test, and so on.6-9
The emissions of most of NIR dyes are located at the near
infrared region, while a few of them both have NIR excitation
and emission.10, 11 The fluorescent dyes with long excitation
and emission wavelengths are more preferable for applications,
and they have been used in the detection for the biological
species in in vivo assay.9, 12-14
and good lightfastness,18-22 therefore, more chromenylium
hybrid dyes have been researched by the spirocyclization-
induced fluorescence switching mechanism.12, 23, 24
The photoinduced electron transfer (PET) and
intramolecular charge-transfer (ICT) are the basic design
principles of fluorescent probes. There are the unique
advantages of the dyes that based on PET and ICT mechanisms,
such as satisfactory fluorescence response and clear
mechanism explanation by frontier orbital theory.25-30 In this
paper, three typical chromenylium skeletons were selected as
fluorophores, and the aniline group as a donor, which was
Chromenylium is the moiety of pyronin with bicyclic
pyrylium. Some fluorophores based on chromenylium had
been developed in recent years, they retained the rhodamine-
like fluorescence OFF−ON switching mechanism with high pKas,
and their excitation and emission were both in the NIR region
(Fig. 1, NIR 1–3).15-17 Using a dye as a platform (NIR 1), one NIR
fluorescent turn-on sensor, which was based on
spirocyclization-induced fluorescence switching mechanism,
was capable of application in imaging for endogenously
usually be used for electron donor in PET and ICT based
32
fluorescent dyes.31,
Different from spirocyclization-based
fluorescent dyes, such type of fluorescent dyes that based on
electron or charge transfer mechanisms usually have low pKas
with protonated on nitrogen atom.
produced hypochlorous acid.15
A
chromenylium-based
ratiometric fluorescent probe (NIR 3) had been developed by
the similar fluorescence switching ring-open and ring-close
mechanism, it provided a ratiometric fluorescent platform for
NIR probes; another ratiometric NIR fluorescent probe had
Fig. 1 Reported chromenylium-based functional dyes: NIR 1, NIR 2 and NIR 3.
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DOI: 10.1039/C6RA19831G
Fig. 2 Optical responses of dyes 1a-b (10 μM) towards various pH with Britton-Robinson
Buffer containing 30% DMSO: (a, b) dye 1a; (c, d) dye 1b; (a, c) absorption spectra (pH =
2.8−8.0 for 1a and pH = 2.0−8.0 for 1b), the inset is a pH-dependent photograph of the
samples; (b, d) emission spectra (λex = 650 nm, slit: 3 nm/3 nm and pH = 2.8−8.0 for 1a,
slit: 3 nm/5 nm and pH = 2.0−8.0 for 1b); (e) excitation spectra of dyes 1a-b; (f)
fluorescence intensity changes of dyes 1a-b towards pH at maximum emission peaks.
bonds, while dye 1a is containing a non-conjugated cyclic
structure. So the different stretching directions of indole
structures in 1a-b would have different effect towards the
optical response. Chromenylium-cumarin hybrid fluorophore
was also selected in this design (1c), it is directly constructed
with chromenylium and cumarin parts without any conjugated
linkers. The aniline part is severed as a donor, since its
donative ability could be varied during the proton promoted
protonation-deprotonation process. The PET process between
chromenylium-based fluorophores and aniline parts would be
evaluated in different pH conditions.
Scheme 1. Preparation of dyes 1a-c.
Results and discussion
Design and preparation of the functional dyes
Compared with the reported design by carboxyl group
participated reaction, the PET or ICT based response needs
two essential parts: acceptor and donor. The chromenylium-
based fluorophores with positive charge were designed as
acceptor parts. Dyes 1a and 1b are chromenylium-indole
hybrid fluorophores, more specifically, dye 1b is constructed
with chromenylium and indole parts by the conjugated double
The preparation of dyes 1a-c is shown in Scheme 1.
Compound
4
was synthesized by three-step procedures from
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4-(diethylamino)benzoic acid, it was respectively reacted with to 742 nm in acidic condition (Fig. 2(d)), the fluorescence
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cyclohexanone and acetone to produce compounds
the required dyes 1a-b were further prepared by Fisher 3.6 %. The calculated pKa values of dyes 1a
aldehyde ( ) and compound , independently. Finally, dye 1c 4.13 and 3.15 respectively (Fig. 2(f)). The basic photochemical
was synthesized from compound and 3-acetyl-7- data of 1a−b towards different pH were listed in Table 1.
diethylaminocoumarin ( ). The structures of all compounds Although dyes 1a−b gave the optical changes towards pH
5
and
6,
quantum yield was simultaneously droDpOpIe:d10.f1r0o3m9/C65R.2A19%831tGo
towards pH are
−
b
7
5-6
4
8
1
were confirmed by HNMR, 13CNMR and high resolution mass variation, the increase or decrease ratios are too low for real
spectroscopies (HRMS-ESI+).
application, other related fluorophore will be selected for next
Optical properties of the functional dyes towards pH
stage to improve the PET process.
Chromenylium-cumarin hybrid fluorophore (1c)
Chromenylium-indole hybrid fluorophores (1a-b)
To improve the optical properties of the PET process based
on chromenylium skeleton, chromenylium-cumarin hybrid
structure was further selected, the direct conjugation of two
parts would be promise candidate for PET transformation, and
OFF-ON type optical response would come true. The
absorption maxima of 1c at 583 nm were gradually red-sifted
to 668 nm when pH decreased from 7.0 to 1.6, the solutions of
1c gave colorimetric changes from navy blue in neutral
condition to light blue under acidic condition (Fig. 3(a)). The
NIR emission peak of 1c at 719 nm was immediately enhanced
Absorption and fluorescence pH titration experiments of
dyes 1a and 1b (10 μM) were performed in Britton-Robinson
(B-R) buffer (40 mM) containing 30% dimethyl sulfoxide
(DMSO). The absorbance of dye 1a was slightly decreased at
719−723 nm from pH = 8.0 to pH = 2.8, the color of solution
was accordingly changed from violet blue to light sky blue
under visible light (Fig. 2(a), Table 1). The excitation
wavelength was selected at 650 nm (Fig. 2(e)), its pH
depended fluorescent intensities gave 6.2-fold enhancement
immediately in acidic conditions, the emission maxima slightly
red-shifted from 749 nm to 758 nm (Fig. 2(b)), meanwhile, the
fluorescence quantum yield was increased from 2.0 % in
neutral condition to 9.1 % in acidic condition. The absorption
spectra of dye 1b were similar to dye 1a (Fig. 2(c)), its
absorbance was reduced at 702−711 nm from pH = 8.0 to pH =
2.0; compared with 1a, the pH depended emission spectra
gave reverse response, the fluorescent intensities were
immediately reduced to 30 % from 736 nm in neutral condition
Fig. 4.1H NMR of dye 1c in DMSO-d6 (top) and the acidic condition (bottom).
Table 1 Photochemical properties of dyes 1a–c towards pH
Stokes
b
b
Dyes
pHa
λabs
λem
εc
Φd
pKa
4.13
3.15
2.48
shiftb
30
1a
1a+H+
1b
7.0
3.0
7.0
2.0
7.0
1.6
719
723
702
711
583
668
749
758
736
742
691
719
6.17×104
4.60×104
5.86×104
2.83×104
3.43×104
3.50×104
0.020
0.091
0.052
0.036
0.003
0.023
35
34
31
108
51
1b+H+
1c
Fig. 3 Optical responses of dye 1c (10 μM) towards various pH with Britton-Robinson
Buffer containing 30% DMSO: (a) absorption spectra (pH = 1.6−7.0), the inset is a pH-
dependent photograph of the samples; (b) emission spectra (λex = 650 nm, slit: 3 nm/5
nm, pH = 1.6−7.0); (c) excitation spectra of dye 1c; (d) absorption ratios A583 nm/A668 nm
of dye 1c at pH 1.6−7.0 and fluorescence intensity changes of dye 1c towards pH at
maximum emission peak.
1c+H+
a
b
The photochemical properties measured in B-R buffer containing 30%DMSO.
Reported in nm. Reported in M-1cm-1. Cyanine dye HPDITCP (Φ = 0.16 in
c
d
ethanol, ref.34).
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DOI: 10.1039/C6RA19831G
Fig. 5 The resonance equilibrium of 1c+ and its protonated form (a) and frontier molecular orbitals (FMOs) involved in the vertical excitation and emission of dye 1c+
and its protonated forms (c). CT stands for conformation transformation. Excitation and radiative processes are represented by solid lines and the nonradiative
processes by dotted line. For details please refer to Tables S2 and S3 (ESI†)
(b)
.
with increasing acidity (Fig. 3(b)) when the excitation emission property is 2.48 (Fig. 3d). Above all, dyes 1a-c keep
wavelength was selected at 650 nm (Fig. 3(c)). Emission some advantages like other chromenylium-based dyes, such as
spectra of dye 1c towards pH showed a typical NIR OFF−ON NIR excitation and emission and satisfactory fluorescence
fluorescence response with 79-fold enhancement in the quantum yield, but the water-solubility of them needs to be
emission intensity; the fluorescence quantum yield was improved by compared with reported pH probes.18, 33
increased from 0.3 % to 2.3 % (Table 1). Based on the ratios of
absorbance at 583 nm and 668 nm, the calculated absorbance NMR spectra of dyes 1a-c under neutral and acidic conditions
To verify the protonated structures of dyes 1a-c, the 1H
Abs
FI
related pKa is 2.71, and the calculated pKa value based on were obtained in DMSO-d6 (dyes 1a-b in Fig. S1† and dye 1c in
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Fig. 4), which reveal that the chemical shifts of the protons on
the N,N-diethylaniline ring were shifted to lower fields
following the protonation of the amine.
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DOI: 10.1039/C6RA19831G
Mechanism exploration
As discussed in the previous section, dyes 1a and 1b bearing
chromenylium-indole hybrid fluorophores show enhanced (1a
)
and reduced (1b) fluorescence response towards increasing
solution acidity respectively (Fig. 2). However, chromenylium-
cumarin hybrid fluorophore based dye 1c, without any
conjugated linkers, exhibits OFF-ON fluorescent response (Fig.
3). In order to explore the mechanism, the geometric
configuration of the ground and the lowest excited states of
dyes 1a+-c+ and their protonated forms were fully optimized.
Due to the total charge of molecular can only be defined in
Gaussian, the mere difference between resonance structures
would only be given through bond lengths, bond angles and
other parameters, such as molecular energy, etc. Take 1c for
example, dyes 1c+-i and 1c+-ii possess exactly the same
molecular energy (Table S1†) and the other bond parameters
attributing to the fully conjugated molecular skeleton, and
their protonated forms also expressed the same results. As
shown in Fig. 5, dye 1c+ had two absorption peaks from S0 to S1
and from S0 to S2, however, when the electron in the excited
state transiting back to the ground state, the HOMO energy of
the electron donor (amine) was higher than that of the
electron acceptor (fluorophore), so the PET process occurred
(Fig. 5b), which led to the fluorescence quenching of dye 1c+
.
In acidic solution, the PET process was inhibited, so the
fluorescence recovered (Fig. 5c). Because the conjugate
degrees of 1a-b were less than that of dye 1c, the calculation
results showed that the conjugated structures had very small
energy differences (Table S1†), but they exhibited different
charge transfer processes, such as 1a+-i and 1b+-ii showed PET
process (Fig. S2b†, Fig. S3c†), while only part of the ICT process
was found in 1a+-ii and 1b+-i (Fig. S2c†, Fig. S3b†), which led to
1a-b and 1c showing different fluorescence response
consistent. The detailed vertical excitation and emission
related parameters are listed in Tables S2 and S3 (ESI†).
Calculation results are basically consistent with experiments.
Selectivity and Reversibility
The selectivity of dyes 1a-c for preferential binding to
protons over other potential interferents under biological
conditions was investigated at acidic and neutral conditions.
For dyes 1a or 1b (10 μM), there was no significant change in
fluorescence intensity in the presence of common cations such
as K+, Na+, Ca2+ and Mg2+, as well as most transition-metal ions,
such as Cd2+, Co2+, Mn2+, and Ni2+. Moreover, bioactive amino
acids, such as Lys, Phe, Gly, Glu, Arg, Cys, Pro, Try, and His,
were also investigated, and no obvious changes were observed.
But when heavy-metal ion such as Hg2+ was present under
neutral condition, the fluorescence intensity of dyes 1a-b
slightly decreased, moreover dye 1b also responded to Cu2+ at
acidic solution (Fig. S4†, Fig. S5†). This phenomenon may be
caused by complexation of Hg2+, and Cu2+. As shown in Fig. 6,
significant change in fluorescence intensity of dye 1c (10 μM)
Fig. 6 Selectivity and reversibility of dye 1c (10 μM). (a, b) Fluorescence
responses of dye 1c (10 μM) to different analytes, such as K+ (100 mM), Na+ (100
mM), Ca2+ (0.5 mM), Mg2+ (0.5 mM), Cd2+ (0.3 mM), Cu2+ (0.3 mM), Co2+ (0.3 mM),
Hg2+ (0.3 mM), Mn2+ (0.3 mM), Ni2+ (0.3 mM), Cys (0.1 mM), Phe (0.1 mM), Gly
(0.1 mM), Glu (0.1 mM), Arg (0.1 mM), Lys (0.1 mM), Pro (0.1 mM), Try (0.1 mM)
and His (0.1 mM): (a) tested in Britton-Robinson Buffer (pH = 7.0); (b) tested in
Britton-Robinson Buffer (pH = 1.8). (c) The reversible optical response of dye 1c
at different pH conditions
also not be observed in the presence of common cations,
metal ions and amino acids. The results illustrate that dye 1c
has better selectivity response to pH than dyes 1a-b in the
presence of potential interferents.
The reversibility of dyes 1a-c was also evaluated. When
solution of dyes 1a-c was changed to acidity or neutral for five
cycles, the emission spectra of them were no significant
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changes (dye 1a-b in Fig. S6†, and dye 1c in Fig. 6c). It can be
deduced that dyes 1a-c have good reversibility.
3-(Diethylamino)phenyl 4-(diethylamino)benzoate (3). To a
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stirred solution of 3-(diethylamino)phenol (3.30 g, 20.0 mmol),
DOI: 10.1039/C6RA19831G
triethylamine (2.6 mL, 20.0 mmol) and dichloromethane (50.0
mL), a solution of 4-(diethylamino)benzoyl chloride (20.0 mmol)
in dichloromethane (20.0 mL) was added dropwise at room
temperature. The resulting solution was stirred for further 5
hours at room temperature. The solvent was removed by
evaporation, and the residue was purified by column
chromatograph on silica gel eluting with hexane and ethyl
acetate (8:1, v/v) to afford product as white solid (1.30 g,
19.0 %). Mp: 54.0‒55.0oC. 1H NMR (400 MHz, CDCl3) δ 8.03 (d,
J = 8.5 Hz, 2H), 7.19 (t, J = 8.1 Hz, 1H), 6.65 (d, J = 8.5 Hz, 2H),
6.52 (d, J = 8.3 Hz, 1H), 6.46 (br, 2H), 3.41 (q, J = 6.9 Hz, 4H),
3.33 (q, J = 6.9 Hz, 4H), 1.19 (t, J = 7.2 Hz, 6H), 1.15 (t, J = 7.2 Hz,
6H).13C NMR (151 MHz, CDCl3) δ 165.6, 152.7, 151.3, 149.0,
132.2, 129.7, 115.5, 110.2, 108.8, 108.6, 105.2, 44.5, 44.4, 12.6,
12.5. HRMS (ESI+): m/z = 341.2221 (calcd for [M + H+]+,
341.2229).
Conclusions
In summary, three chromenylium-based NIR dyes 1a-c have
been designed and synthesized. These dyes based on PET or
ICT
mechanism
instead
of
spirocyclization-induced
fluorescence switching mechanism. Dyes 1a and 1b are
chromenylium-indole hybrid fluorophore, but they have
different effect towards the optical response because of the
different stretching directions of indole structures. This
phenomenon can attribute to both PET and ICT processes exist
in aniline parts and the chromenylium-indole parts. Dye 1c is
chromenylium-cumarin hybrid fluorophores, and it is a typical
OFF-ON fluorescent dye that mainly controlled by the PET
process. All of these optical mechanism successfully be verified
by (TD)DFT calculations. Moreover, all these dyes have good
reversibility, and dye 1c also has better selectivity response to
pH than dyes 1a-b. Therefore, the dye 1c is expected to
become an excellent near infrared pH probe for the
determination of the acidity of cancer cells.
(4-(Diethylamino)-2-hydroxyphenyl)(4-(diethylamino)phenyl)
methanone (
4). A mixture of anhydrous aluminum chloride
(640.0 mg, 4.80 mmol) and
3
(412.0 mg, 1.20 mmol) were
o
heated for 2 h at 175 C. The reaction mixture was cooled to
room temperature, and slowly hydrolysed with iced water and
1.0 mL concentrated hydrochloric acid. The mixture was stirred
for 2 hours at room temperature, and then it was extracted
with dichloromethane (20.0 mL × 3). The organic phase was
removed by evaporation, and the residue was purified by
column chromatograph on silica gel eluting with
dichloromethane to afford product as yellow oil (118.0 mg,
Experimental Section
Materials and apparatus
All reagents and solvents (analytical grade) were purchased
from TCI Development Co., Ltd. (Tokyo, Japan), Energy
Chemical Co., Ltd. (Shanghai, China) and Sinopharm Chemical
Reagent Co., Ltd. (Shanghai, China) and used directly. Flash
chromatography was performed with silica gel (200−300 mesh).
Britton-Robinson (B-R) Buffer Solution (40 mM, pH = 1.6‒8.0)
were used. And their pH values were finally tested by a pH
meter.
1
28.0%). H NMR (400 MHz, CDCl3) δ 13.19 (s, 1H), 7.63 (d, J =
8.6 Hz, 2H), 7.56 (d, J = 8.7 Hz, 1H), 6.67 (d, J = 8.5 Hz, 2H), 6.16
(br, 2H), 3.45‒3.37 (m, 8H), 1.21 (t, J = 6.9 Hz, 12H).13C NMR
(101 MHz, CDCl3) δ 195.9, 165.3, 152.6, 149.5, 134.6, 131.3,
124.9, 109.7, 108.8, 102.4, 97.0, 44.10, 44.05, 12.21, 12.06.
HRMS (ESI+): m/z = 341.2259 (calcd for [M + H+]+, 341.2229).
6-(Diethylamino)-9-(4-(diethylamino)phenyl)-1,2,3,4-
1H NMR and 13C NMR spectra were recorded on a Varian
400 MHz spectrometer, and tetramethylsilane (TMS) or
solvent peaks were used as an internal standard. High-
resolution mass spectra were recorded on a micrOTOF-Q III
mass spectrometer in ESI+ mode. UV-vis spectra were obtained
tetrahydroxanthylium perchlorate (5). A solution of 4 (72.0 mg,
0.21 mmol) and cyclohexanone (22 μL, 0.21 mmol) in
o
concentrated H2SO4 (2.0 mL) was stirred at 90 C for 6 h. After
cooling to room temperature, the reaction mixture was poured
into cold water (10.0 mL), and then 70% perchloric acid (200
μL) was added. The solution was extracted with
dichloromethane (30.0 mL × 3), and the organic layer was
evaporated in vacuum. The residue was purified by column
chromatograph on silica gel eluting with dichloromethane and
methanol (25:1, v/v) to afford product as dark brown solid
(70.0 mg 52.0%). Mp: 211.0‒212.0 oC. 1H NMR (400 MHz,
CDCl3) δ 7.66 (d, J = 9.6 Hz, 1H), 7.26 (d, J = 9.4 Hz, 2H), 7.13 (d,
J = 9.5 Hz, 1H), 6.84 (br, 3H), 3.64 (q, J = 6.9 Hz, 4H), 3.49 (q, J =
6.8 Hz, 4H), 3.09 (t, J = 6.3 Hz, 2H), 2.68 (t, J = 5.3 Hz, 2H),
2.00‒2.05 (m, 2H), 1.82‒1.77 (m, 2H), 1.33 (t, J = 7.0 Hz, 6H),
1.26 (t, J = 7.0 Hz, 6H).13C NMR (151 MHz, CDCl3) δ 169.2,
163.0, 159.3, 155.0, 132.21, 132.16, 121.1, 119.65, 117.1,
116.9, 111.5, 110.9, 95.5, 46.0, 44.7, 29.7, 26.5, 22.2, 21.1,
with
a
Shimadzu UV-1800 spectrophotometer, and
fluorescence emission spectra were performed with fused
quartz cuvette (10 mm × 10 mm) on Shimadzu RF-5301PC
spectroscope with R-928 photomultiplier at room temperature.
The pH values were measured with a Lei-Ci (pH-3C) digital pH
meter (Shanghai, China) using a combined glass calomel
electrode.
Synthesis and Characterization
4-(Diethylamino)benzoyl chloride (2). To a solution of 4-
N,N-diethylaminobenzoic acid (2.00 g, 10.3 mmol) in 20.0 mL
dichloromethane, thionyl chloride (3.57 g, 30.0 mmol) and
N,N-dimethylformamide (DMF, 1 drop) were added at room
temperature. The resulting suspension was stirred for 20 h at
o
20 C. The solvent was removed by evaporation to afford the
- +
12.6, 12.5. HRMS (ESI+): m/z = 403.2733 (calcd for [M – ClO4 ] ,
acyl chloride product as green solid (2.05 g, 97.0%). The
product was used for the next step without further purification.
403.2749)
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7-(Diethylamino)-4-(4-(diethylamino)phenyl)-2-
methylchromenylium perchlorate ( ). A solution of
6H), 1.31 (t, J = 6.8 Hz, 6H), 1.25 (t, J = 6.8 Hz, V6ieHw)A.1rt3iCcleNOnMlinRe
(131.0 mg, (151 MHz, CDCl3) δ 170.9, 165.2, 157.6, 155.1, 152.6, 150.0,
DOI: 10.1039/C6RA19831G
6
4
0.38 mmol) and acetone (200 μL, 2.70 mmol) in concentrated 143.5, 143.2, 140.2, 131.4, 129.8, 128.5, 124.0, 122.0, 121.1,
H2SO4 (3.0 mL) was stirred at 90oC for 6 h. After cooling to 112.3, 111.53, 111.48, 110.8, 109.6, 100.8, 96.8, 48.5, 45.2,
room temperature, the reaction mixture was poured into cold 44.6, 31.0, 28.6, 12.57. HRMS (ESI+): m/z = 546.3453 (calcd for
- +
water (20.0 mL), and then 70% perchloric acid (300 μL) was [M – ClO4 ] , 546.3484).
added. The solution was extracted with dichloromethane (50.0
7,7'-Bis(diethylamino)-4-(4-(diethylamino)phenyl)-2'-oxo-
mL × 3), and the organic layer was evaporated by evaporation. 2'H-[2,3'-bichromen]-1-ylium perchlorate (1c). A solution of
4
The crude product was purified by column chromatograph on (118.0 mg, 0.35 mmol) and 3-acetyl-7-diethylaminocoumarin
silica gel eluting with dichloromethane and methanol (25:1, (440.0 mg, 1.70 mmol) in concentrated H2SO4 (3.0 mL) was
o
v/v) to afford product as dark brown solid (35.0 mg, 21.0%). stirred at 90 C for 12 h. After cooling to room temperature,
Mp: > 250.0 oC. 1H NMR (400 MHz, CDCl3) δ 8.03 (d, J = 9.6 Hz, the reaction mixture was poured into cold water (20.0 mL),
1H), 7.68 (d, J = 8.7 Hz, 2H), 7.19 (d, J = 9.4 Hz, 1H), 7.15 (s, 1H), and then 70% perchloric acid (400 μL) was added, the crude
6.85 (d, J = 8.8 Hz, 2H), 6.78 (s, 1H), 3.63 (q, J = 6.8 Hz, 4H), product was obtained by filtration and washed with water. It
3.51 (q, J = 6.8 Hz, 4H), 2.72 (s, 3H), 1.33 (t, J = 7.0 Hz, 6H), 1.26 was purified by column chromatograph on silica gel eluting
(t, J = 6.9 Hz, 6H).13C NMR (151 MHz, CDCl3) δ 162.7, 155.3, with dichloromethane and methanol (20:1, v/v) to afford
o
155.0, 150.0, 147.3, 129.0, 127.1, 115.0, 111.6, 108.5, 107.5, product as dark brown solid (18.0 mg 8.0%). Mp > 250.0 C. 1H
106.7, 91.5, 41.1, 40.2, 16.4, 7.83, 7.79. HRMS (ESI+): m/z = NMR (400 MHz, CDCl3) δ 9.35 (s, 1H), 8.42 (s, 1H), 8.10 (d, J =
- +
363.2448 (calcd for [M – ClO4 ] , 363.2436).
9.0 Hz, 1H), 7.88 (d, J = 9.4 Hz, 1H), 7.63 (d, J = 8.5 Hz, 2H), 7.52
(s, 1H), 6.99 (d, J = 9.2 Hz, 1H), 6.83 (br, 2H), 6.74 (d, J = 8.7 Hz,
1H), 6.45 (s, 1H), 3.67 (q, J = 5.9 Hz, 4H), 3.55‒3.47 (m, 8H),
5
(105.6 1.36 (t, J = 6.4 Hz, 6H), 1.27 (br, 12H).13C NMR (151 MHz, CDCl3)
6-(Diethylamino)-9-(4-(diethylamino)phenyl)-4-(2-(1,3,3-
trimethylindolin-2-ylidene)ethylidene)-1,2,3,4-
tetrahydroxanthylium perchlorate (1a). A solution of
mg, 0.21 mmol) and Fisher aldehyde (43.0 mg, 0.21 mmol) in δ 160.2, 159.1, 158.9, 158.8, 158.1, 154.6, 154.1, 147.4, 134.2,
acetic anhydride (8.0 mL) was heated to 50 °C for 40 min. Then, 132.8, 130.6, 115.2, 113.2, 111.8, 111.0, 110.7, 110.1, 106.6,
water (8.0 mL) was added to the mixture to quench the 98.1, 98.0, 96.2, 96.1, 45.9, 45.4, 44.9, 12.7, 12.6, 12.5. HRMS
- +
reaction. The solvent was removed under reduced pressure to (ESI+): m/z = 564.3236 (calcd for [M – ClO4 ] , 564.3226).
give the crude product. The crude product was purified by Absorption and fluorescence titration experiment
column chromatograph on silica gel eluting with
Stock solutions of dyes 1a-c (100 μM) were prepared in a
dichloromethane and methanol (20:1, v/v) to afford product as
volumetric flask (100 mL) with DMSO. Each test solution (10
1
dark brown solid (52.0 mg, 36.0%). Mp > 250.0 oC. H NMR
μM) was prepared in a volumetric flask (10 mL) with 1.0 mL
stock solution, 2.0 mL DMSO and the corresponding buffer
solution to give a total volume of 10.0 mL. Absorption and
fluorescence spectra were obtained with 1.0 cm*1.0 cm quartz
(400 MHz, CDCl3) δ 8.52 (d, J = 14.0 Hz, 1H), 7.41 (d, J = 7.4 Hz,
1H), 7.36 (d, J = 7.7 Hz, 1H), 7.31 (d, J = 9.3 Hz, 1H), 7.20 (t, J =
7.4 Hz, 1H), 7.13 (br, 3H), 6.77 (d, J = 8.6 Hz, 2H), 6.71 (d, J =
9.2 Hz, 1H), 6.58 (br, 1H), 5.99 (d, J = 13.9 Hz, 1H), 3.65 (s, 3H),
cells.
3.56 (q, J = 6.9 Hz, 4H), 3.45 (q, J = 6.8 Hz, 4H), 2.69 (t, J = 5.8
Selectivity experiment
Hz, 2H), 2.65 (t, J = 5.8 Hz, 2H), 1.81‒1.85 (m, 2H), 1.78 (s, 6H),
1.30 (t, J = 7.0 Hz, 6H), 1.25 (t, J = 7.0 Hz, 6H).13C NMR (101
Stock solutions of dyes 1a-c (100 μM) were prepared in a
volumetric flask (100 mL) with DMSO. Stock solutions of
MHz, CDCl3) δ 172.1, 163.7, 156.6, 153.5, 152.2, 148.7, 143.3,
various ions were prepared in volumetric flasks (10 mL) with
140.9, 140.5, 131.0, 130.2, 128.9, 124.8, 122.4, 121.1, 119.6,
concentrations of KCl (1.0 M), NaCl (1.0 M), CaCl2 (5 mM),
116.5, 113.8, 112.4, 111.0, 110.3, 98.6, 95.9, 49.0, 45.4, 44.6,
31.6, 28.7, 27.6, 24.6, 21.3, 12.8, 12.7. HRMS (ESI+): m/z =
MgSO4 (5 mM), CdCl2 (3 mM), CuSO4 (3 mM), CoCl2 (3 mM),
- +
HgCl2 (3 mM), MnCl2 (3 mM), NiCl2 (3 mM) in doubly distilled
water. Stock solutions of all kinds of amino acids were all
prepared in volumetric flasks (10 mL) with concentrations of 1
mM in twice distilled water. Each test solution was prepared in
586.3799 (calcd for [M – ClO4 ] , 586.3797).
2-(3-(7-(Diethylamino)-4-(4-(diethylamino)phenyl)-2H-
chromen-2-ylidene)prop-1-en-1-yl)-1,3,3-trimethyl-3H-indol-1-
ium perchlorate (1b). A solution of
6 (35.0 mg, 0.10 mmol) and
a volumetric flask (10 mL) with 1 mL stock solution of Dyes, 2
mL DMSO and 1.0 mL stock solutions of corresponding ions or
amino acids, diluted with neutral (pH 7.0 for dyes 1a-c) and
acidic (pH 3.0, 2.0, 1.6 for dyes 1a-c respectively) B-R Buffer
Solution to give a total volume of 10.0 mL. Their fluorescence
spectra were then recorded.
Fisher aldehyde (20.0 mg, 0.10 mmol) in acetic anhydride (4.0
mL) was heated to 50 °C for 40 min. Then, water (4.0 mL) was
added to the mixture to quench the reaction. The solvent was
removed under reduced pressure to give the crude product.
The crude product was purified by column chromatograph on
silica gel eluting with dichloromethane and methanol (20:1,
v/v) to afford product as dark brown solid (15.0 mg, 23.0%).
Mp > 250.0 oC. 1H NMR (400 MHz, CDCl3) δ 8.26 (t, J = 13.4 Hz,
Determination of quantum yield
All the relative fluorescence quantum yields were
1H), 7.74 (d, J = 9.1 Hz, 1H), 7.50 (d, J = 8.3 Hz, 2H), 7.33 (br, determined and calculated with the following equation:
2
2H), 7.15 (t, J = 7.3 Hz, 1H), 7.03 (d, J = 7.6 Hz, 1H), 6.80 (br,
Φx/Φst = [Ast/Ax][nx /nst2][Dx/Dst]
3H), 6.70 (s, 1H), 6.68 (s, 1H), 6.26 (d, J = 13.5 Hz, 1H), 6.10 (d, J Where st: standard; x: sample; Φ: quantum yield; A:
= 12.9 Hz, 1H), 3.58 (br, 7H), 3.48 (q, J = 6.6 Hz, 4H), 1.73 (s, absorbance at the excitation wavelength; D: area under the
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fluorescence spectra on an energy scale; n: the refractive index 12. K. Zheng, W. Lin, W. Huang, X. Guan, D. ChVeienwgAratinclde OJn.-linYe.
of the solution calculated from reported data (DMSO/water Wang, J. Mater. Chem. B., 2015,
, 8D7O1I-:81707.1.039/C6RA19831G
(v/v = 3.0/7.0)). The Cyanine dye HPDITCP (Φ = 0.16 in ethanol) 13. T. Liu, J. Lin, Z. Li, L. Lin, Y. Shen, H. Zhu and Y. Qian,
3
was used as standard.
Analyst, 2015, 140, 7165-7169.
Calculation details
–
The geometries of the dyes 1a+ c+ and their protonated
14. P. Anees, J. Joseph, S. Sreejith, N. V. Menon, Y. Kang, S.
Wing-Kwong Yu, A. Ajayaghosh and Y. Zhao, Chem. Sci.,
2016, 7, 4110-4116.
forms at the ground state (S0 state) were optimized by density
functional theory (DFT) at B3LYP/6-31+G(d) level, and the
geometries at the lowest excited state (S1 state) were
optimized by TDDFT methods with the B3LYP/6-31G(d) using
the Gaussian program package.35 In some cases, higher excited
states were optimized. There are no imaginary frequencies in
frequency analysis of all the calculated structures; therefore,
each calculated structures are in the local energy minimum.
The energy gap between the S0 state and the lowest excited
state was calculated with (TD)DFT//BP86/TZVP method based
on the optimized S0 state geometry (for absorption) and the
lowest excited state geometry (for fluorescence), respectively.
Water was used as the solvent for the (TD)DFT calculations
(CPCM model).
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Acknowledgements
The project is supported from the National Nature Science
Foundation of China (51273136), Natural Science Fund of
Jiangsu Province (BK20151262) and the Priority Academic
Program Development of Jiangsu Higher Education Institutions
(PAPD).
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8 | RSC Adv., 2016, 00, 1-9
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Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K.
ARTICLE
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DOI: 10.1039/C6RA19831G
Raghavachari, A. P. Rendell, J. C. Burant, S. S. Iyengar, J.
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Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox, Gaussian
09, revision B.01, 2010.
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DOI: 10.1039/C6RA19831G
PET and ICT processes in chromenylium hybrid fluorescent dyes.
Et
Et
N
Et
Et
Et
Et
N
O
N
O
PET / ICT
PET / ICT
H3C
N
Et
O
N
Et
O
Et
Et
N
Et
O
N
CH3
CH3
Et
H3C
H3C
CH3
N
Et
+ H+
N
Et
+ H+
+ H+