Synthesis and spectroscopy of novel branched fluorescent dyes containing benzophenone parts and the possibility as fluorescence probes

Article abstract of DOI:10.1007/s10895-010-0699-9

This paper describes a new fluorescent family of branched dyes containing benzophenone unit including 4-N, N-diphenylamino-4′-phenacyl-stilbene (C1), 4,4′-di(4-benzoylphenylethylene)yl-triphenylamine (C2) and 4,4′,4″-tri(4-benzoylphenylethylene)yl-triphenylamine (C3). Benzophenone part is coupled with core through C-C double bond. The chemical structures of the derivatives are characterized with ¹H and ¹³C nuclear magnetic resonance and elemental analysis. Strong π-π stacking interactions are discovered with the analysis of the X-ray crystallographic data of C1. The absorption maxima and emission maxima of the derivatives exhibit gradual bathochromic shift from C1 to C3. The optical density of C1, C2 and C3 are shown to be related to the number of branches. The changes of dipole moments between the excited and ground states for C1, C2 and C3 were estimated to be 4.356, 8.091 and 8.479 Derby, respectively by Lippert equation, confirming that the internal charge transfer (ICT) dominates the process of excited singlet state. The possibility as fluorescence probes of the derivatives on the estimation of what region of micelles interacting with samples was evaluated.

Full text of DOI:10.1007/s10895-010-0699-9

J Fluoresc (2011) 21:149–159
DOI 10.1007/s10895-010-0699-9
ORIGINAL PAPER
Synthesis and Spectroscopy of Novel Branched Fluorescent
Dyes Containing Benzophenone Parts and the Possibility
as Fluorescence Probes
Fang Gao & Lanying Niu & Nvdan Hu & Jianchao Wang &
Hongru Li & Shengtao Zhang
Received: 15 March 2010 /Accepted: 22 June 2010 /Published online: 29 June 2010
#
Springer Science+Business Media, LLC 2010
Abstract This paper describes a new fluorescent family of
branched dyes containing benzophenone unit including 4-N,
N-diphenylamino-4′-phenacyl-stilbene (C1), 4,4′-di(4-ben-
zoylphenylethylene)yl-triphenylamine (C2) and 4,4′,4″-tri
(4-benzoylphenylethylene)yl-triphenylamine (C3). Benzo-
phenone part is coupled with core through C–C double
bond. The chemical structures of the derivatives are
Introduction
It is of significance to design and synthesize highly fluorescent
organic dyes due to their fascinating functions as fluorescence
sensors [1–5], biomarkers [6–8], organic electroluminescence
devices (OLED) [9–14] and non-linear optical materials [15–
17] and so on. Fluorescent dyes, whose emission spectra and
fluorescence quantum yields are often markedly sensitive to
solvent polarity [18–21], are important for the investigation
of chemical, biochemical, and biological phenomena as
probes. Although different applications requirements may
vary, for most applications an ideal dye should have spectral
characteristics such as high fluorescence quantum yield and
large molar extinction coefficient, thus it is possible to use of
lower dye concentrations in application.
Many efforts have been devoted to improve optical
properties of several fluorescent families of dyes including
perylene [22–25], rhodamine [26–28] and coumarin [29–
31], which are currently applied in chemistry, biomedical
and material fields intensively. While to meet the vast
requirements as fluorescence devices in various fields, the
development of new class of highly fluorescent dyes is
needed urgently. A common strategy of molecular design of
the photofunctional fluorescent compounds is to couple the
functional molecule with a known chromophore group.
However, this generally causes fluorescence attenuation of
chromophore part due to interaction of chromophore part
and functional molecule [32, 33]. Recently, we were
interested in developing chromophore part-linked benzo-
phenone compounds with bridged single bond because the
fluorescent quantum yields could be enhanced abnormally
via the introduction of benzophenone part caused by the
enhanced molecular rigidity although benzophenone is a
typical triplet compound [34]. In our continuous efforts to
develop such derivatives, we propose that the emission of
1
characterized with H and 13C nuclear magnetic resonance
and elemental analysis. Strong π–π stacking interactions are
discovered with the analysis of the X-ray crystallographic
data of C1. The absorption maxima and emission maxima of
the derivatives exhibit gradual bathochromic shift from C1
to C3. The optical density of C1, C2 and C3 are shown to be
related to the number of branches. The changes of dipole
moments between the excited and ground states for C1, C2
and C3 were estimated to be 4.356, 8.091 and 8.479 Derby,
respectively by Lippert equation, confirming that the internal
charge transfer (ICT) dominates the process of excited
singlet state. The possibility as fluorescence probes of the
derivatives on the estimation of what region of micelles
interacting with samples was evaluated.
.
.
.
Keywords Synthesis Spectroscopy Benzophenone
.
.
Branched compound Fluorescence probe Micelle
:
:
:
:
:
F. Gao (*) L. Niu N. Hu J. Wang H. Li (*) S. Zhang
College of Chemistry and Chemical Engineering,
Chongqing University,
Chongqing 400044, China
e-mail: fanggao1971@gmail.com
e-mail: hrli@cqu.edu.cn
N. Hu
Department of Environmental and Chemical Engineering,
Liupanshui Normal College,
Guizhuo 553004, China

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J Fluoresc (2011) 21:149–159
such branched diphenylethylene derivatives containing ben-
zophenone moiety via C–C double bond could be improved
by the enhancement of conjugation nature. Of our particular
interests are if the optical properties of such derivatives are
related to the number of branches enhanced, and if it is
possible to act as fluorescence probes. Many dyes were
chosen as fluorescence probes on the evaluation of the
viscosity and polarity of micelles, while the probed results
sometimes exhibit large difference from each other. The main
reason could be due to different encapsulated regions of the
probes in micelles, which depends on: (1) neutral vs
zwitterionic nature, (2) hydrophobic vs hydrophilic nature,
and (3) large vs small size of micelles and probes.
Herein, we report a series of high fluorescent dyes
containing benzophenone part which have different zwitter-
ionic and hydrophobic nature, and different molecular sizes.
The dyes, 4-N,N-diphenylamino-4′-phenacyl-stilbene, 4,4′-di
(4-benzoylphenylethylene)yl-triphenylamine and 4,4′,4″-tri
(4-benzoylphenylethylene)yl-triphenylamine are shown in
Fig. 1. The presence of donor-acceptor moiety in new
derivatives caused by the electron-withdrawing effect of
carbonyl group in benzophenone unit could induce a large
internal charge transfer, so the optical properties of the
derivatives could be sensitive to environment, which could
make it possible for the derivatives to use as fluorescence
probes. Singlet crystal of C1 was obtained and its X-ray
crystallography was determined and discussed. The spectro-
scopic properties of the derivatives were investigated in
various solvents, and the possibility of the derivatives as
fluorescence probes was preliminary evaluated.
laboratory techniques according to the published methods
[35]. Other reagents were obtained from Aldrich unless
otherwise specified. C1, C2 and C3 (Fig. 1) were
synthesized in our laboratory.
Instruments
The UV/visible absorption spectra were recorded with a
Cintra spectrophotometer. The emission spectra were
checked by Shimadzu RF-531PC spectrofluorophoton-
meter. Rodamin 6G in ethanol (Φ=0.94, 1×10−6–1×
10−5 mol/l [36]) acted as reference to determine the
fluorescence quantum yields of the derivatives. The melting
point was determined using a Sichuan University 2X-1
melting point apparatus. Nuclear magnetic resonance
(NMR) was done at room temperature with a Bruker
500 MHz apparatus with tetramethylsilane (TMS) as
internal standard and CDCl3 as solvent. Element analysis
was determined with CE440 elemental analysis meter of
Exeter Analytical Inc. The fluorescence quantum yields of
the compounds in solvents with different polarities were
measured based on the following equation [37, 38]:
R
n20A0 If ðlf Þdlf
Φf ¼ Φ0f
ð1Þ
R
n2A If0ðlf Þdlf
wherein n0 and n are the refractive indices of the solvents,
A0 and A are the optical densities at excitation wavelength,
Φf and Φ0f are the quantum yields, and the integrals denote
as the area of the fluorescence bands for the reference and
sample, respectively.
Preparation of single crystals and X-ray crystallography
Experimental
Growing of single crystals of C1 was done with slow
volatilization of benzene solution at 25 °C (c=1×
10−2 mol/L). The crystal structure of the title compound
was determined by X-ray single crystal diffraction. XRD
Reagents
The organic solvents were purchased from Chongqing
Oriental Chemical Corporation and dried using standard
Fig. 1 Chemical structures of
compounds 1 to 3
O
O
N
N
C1
C3
C2
N
O
O
O
O

J Fluoresc (2011) 21:149–159
151
data were collected on a Bruker-AXS CCD area detector
equipped with diffractometer with Mo Ka (λ=0.71073 Å)
at 298 K. A single crystal suitable for determination was
mounted inside a glass fiber capillary. The structures of
the compounds were solved by direct methods and refined
by full-matrix least squares on F2. All the hydrogen atoms
were added in their calculated positions and all the non-
hydrogen atoms were refined with anisotropic temperature
factors. SHELXS97 were used to solve the structure and
SHELTL were used to refine the structure [39, 40].
respectively) for five hours sonication. Hence, the anionic
SDS, neutral TX-100 and cationic CTAB micelles with
solubilized dyes (1.0×10−5 mol/l) were prepared.
Synthesis of C1 to C3
The synthesis routes of derivatives 1 to 3 were depicted in
Scheme 1.
N,N-Diphenyl-benzaldehyde, N-phenyl-N-(p-formyl-
phenyl)yl-benzaldehyde and di(p-formylphenyl)yl-benzal-
dehyde were prepared by Veilser reaction using
triphenylamine (1.00 g, 4.08 mmol) and restillated POCl3
(9.5 ml, 101.9 mmol) as starting materials in dry DMF
(7.26 ml, 93.8 mmol) [41]. Purification was carried out
using benzene/AcOEt mixed solvents (v: v=30:1) as eleunt.
4-Bromomethylbenzophenone was prepared via bromide
of 4-methylbenzophenone with N-bromosuccinimide
(NBS) in CCl4 [42]. It was further purified with
recrystallization in benzene/cyclohexane mixed solvents.
4-Bromomethylbenzophenone reacted with excess triethyl
phosphite under 130–160°C for 6 h. After excess triethyl
phosphite was removed in vacuum, the crude 4-
Preparation of micellar solutions
The solutions of the dyes in aqueous detergents were
prepared by placing the appropriate amount of chloroform
stock solutions (the concentration was 1.0×10−5 mol/L for
all samples) in a dry volumetric flask, evaporating the
solvent with flushing argon, and re-dissolving the residue in
the detergent stock solution (the concentration of detergents
was 1.0×10−2, 1.0×10−3 and 2.0×10−3 mol/l for sodium
dodecyl sulfate (SDS), cetyltrimethyl ammonium bromide
(CTAB) and polyscyethylene isoctylphenyl ether (TX-100),
O
O
O
NBS
P(OCH2CH3)3
130-160 ºC
O
CCl4/reflux
P
Br
OEt
EtO
OHC
CHO
POCl3/DMF
N
N
POCl3/DMF
N
CHO
O
O
POCl3/DMF
O
THF/NaOEt
O
P
P
THF/NaOEt
OEt
EtO
OEt
EtO
OHC
CHO
N
C2
C1
CHO
O
THF/NaOEt
O
P
OEt
EtO
C3
Scheme 1 Synthesis routes of C1, C2 and C3

152
J Fluoresc (2011) 21:149–159
phosphonate benzopheonone was obtained and went
directly to the next step with no further purification.
7.68(t, J=7.3 Hz, 3H, CHCHCH), 7.64 (d, J=8.0 Hz, 6H,
CCHCH), 7.58(t, J=7.0 Hz, 6H, CHCHCH), 7.32(m, J=
16.0 Hz, 6H, CCHCH), 7.11(d, J=8.0 Hz, 6H, CCHCH).
Anal. Calcd for C63H45NO3, C, 87.57, H, 5.25, N, 1.62,
O, 5.56, Found, C, 87.43, H, 5.19, N, 1.71.
4-N, N-diphenylamino-4′-phenacyl-stilbene (C1)
4-Phosphonate benzophenone (0.939 g, 3 mmol) reacted
with N, N-diphenyl-benzaldehyde (0.903 g, 3 mmol) in dry
THF using sodium ethoxide (1.7 g, 20 mmol) as base at
room temperature overnight. After the filtration of solid
materials and evaporation of THF in vacuum, the reactant
mixture was dissolved in chloroform and washed by water.
The organic layer was dried with anhydrous magnesium
sulphate. After evaporated in vacuum, C1 was purified with
column chromophgraphty using benzene as eluent, which
was further purified with recrystallization in methylene
chloride. C1: color: yellow, yield: 55%, m.p.: 49–51 °C,
1H-NMR (500 MHz, CDCl3, δ: ppm, J: Hz): 7.78(d, J=
7.0 Hz, 4H, CHCHC), 7.71(d, J=8.5 Hz, 2H, CHCHC), 7.65
(t, J=7.5 Hz, 1H, CHCHCH), 7.55(t, J=.8.5 Hz, 4H,
CCHCH), 7.31(t, J=8.0 Hz, 4H, CHCHCH), 7.22(d, J=
16.5 Hz, 2H, CCHCH), 7.08(t, J=7.3 Hz, 6H, CCHCH),
7.00(d, J=8.5 Hz, 2H, CHCHCH). 13C-NMR: (123.472,
124.887, 125.741, 126.118, 127.880, 128.484, 129.505
130.065, 130.943 131.046, 132.365, 135.983, 138.063,
142.067, 147.504, 148.150, 196.209). Anal. Calcd for
C33H25NO, C, 87.77, H, 5.58, N, 3.10, O, 3.54, Found,
C, 87.59, H, 5.69, N, 3.21.
Results and discussion
Synthesis
Formyl groups could be easily introduced to triphenylamine
with Vilsmeier reaction. While remarkably low yields of tri
(p-formylphenyl)yl-benzaldehyde were observed even if
much excess of POCl3/DMF were used. This is mostly
caused by the deactivation of the remaining benzene ring
by the imine groups on the other two phenyl groups in the
third formylation step. The reaction of 4-phosphonate
benzopheonone and p-amino-benzaldehyde easily occurred
using sodium ethoxide as base. Stronger base such as
sodium hydride led to more byproducts in the final step.
Owing to poor solubility in most of solvents caused by
excess phenyl rings of C2 and C3, the purification and
characterization had to be carried out carefully.
X-ray crystallographic analysis
4,4′-Di(4-benzoylphenylethylene)yl-triphenylamine
(C2)The reaction of N,N-diphenyl-benzaldehyde (0.452 g,
1.5 mmol) and 4-phosphonate benzopheonone (0.903 g,
3 mmol) was carried out in THF using sodium ethoxide
(1.7 g, 10 mmol) as base at room temperature. Purification
of C2 was the same as that of C1. C2: color: yellow, yield:
53%, m.p. 172–174 °C, 1H-NMR (CDCl3): 7.82(t, J=
6.8 Hz, 8H, CHCHC), 7.60(t, J=6.8 Hz, 6H, CHCHC),
7.50(t, J=7.5 Hz, 4H, CHCHCH),7.45 (d, J=8.5 Hz, 4H,
CCHCH), 7.31(t, J=7.8 Hz, 2H, CHCHCH), 7.21(d, J=
16.0 Hz, 2H, CCHCH), 7.16(d, J=8.0 Hz, 2H, CHCHC),
7.10(t, J=9.2 Hz, 6H, CCHCH). 13C-NMR: (123.986,
125.332, 126.18, 127.9721, 128.435, 129.650, 130.083,
130.956 131.440, 132.405, 136.123, 138.50, 141.961,
147.114, 147.628, 196.228). Anal. Calcd for
C48H35NO2, C, 87.64, H, 5.36, N, 2.13, O, 4.86, Found,
C, 87.55, H, 5.279, N, 2.03.
The asymmetric unit contains one crystallographically
unique organic product, one propa-1, 2-diene molecule
and one solvent molecule, benzene (Fig. 2). Crystallo-
graphic disorder of single crystal of C1 induce that two
carbon have two positions ((C14), and C(14)′), (C(15), and
C(15)′), which have 50% rate of the occupancy respective-
ly. The organic product consists of five phenyl rings. As
shown in Figs. 2 and 3, rings 1–5 were composed of C
atoms from C2 to C7, C8 to C13, C16 to C21, C22 to C27
and C28 to C33, respectively. Rings 1 and 3 are almost
coplanar (Dihedral angle: 16.3°). The dihedral angles
between planes 1 and 2, 2 and 4, 2 and 5 were 58°, 61.8°
and 69.1°, respectively. X1 and X2 are the centers of rings
2 and 4. The X1⋯H27A and X2⋯H33B distance are
3.194 Å and 3.007 Å, respectively (atom with additional
labels A, B refers to the symmetry operations. A: x−1, 1.5−y,
0.5+z; B: x, 1.5−y, z−0.5), indicating strong edge-to-face π–π
stacking interactions existed (Fig. 3).
4,4′,4″-Tri(4-benzoylphenylethylene)yl-triphenylamine
(C3) The reaction of di(p-formylphenyl)yl-benzaldehyde
(0.330 g, 1 mmol) and 4-phosphonate benzopheonone
(0.903 g, 3 mmol) was performed in dry THF containing
sodium ethoxide (1.7 g, 20 mmol) for overnight at room
temperature. The purification was carried out as that of C1
and C2. C3: color: yellow, yield: 50%, m.p.:171–172 °C,
1H-NMR (d6-DMSO): 7.75(d, J=10.5 Hz, 18H, CHCHC),
UV/visible absorption spectroscopy
Due to electron-withdrawing effect of carbonyl group in
benzophenone unit and electron-donating effect of N core,
the derivatives exhibit typical D-π-A character. As shown
in Fig. 4, a gradual red-shift of the maximal absorption

J Fluoresc (2011) 21:149–159
153
Fig. 2 ORTEP drawing of C1 with thermal ellipsoids at 50% probability
wavelength indicates that there exists internal charge character
of (π, π*). Three absorption bands are observed for the
derivatives. The first absorption band from 225–275 nm could
be attributed to benzophenone part, and its optical density
increases with the increasing number of the branches. It is
amazing to observe that the optical density of the second
absorption band 275–350 nm also increases with the number
of the branches although the derivatives have only one
triphenylamine part. We further determined the UV/visible
absorption of different molar ratio triphenylamine/4-methyl-
benzophenone (1:1, 1:2, 1:3), and no large change on the
second absorption of 275–350 nm was observed with the
Fig. 3 π–π Stacking interac-
tions in C1

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J Fluoresc (2011) 21:149–159
Fluorescence spectroscopy and the fluorescence quantum
yields
The maximal emission maxima of C1, C2 and C3 exhibit
gradual red-shift in various solvents from the derivatives 1
to 3, as shown in Fig. 5. As compared with the maximal
emission wavelength of the derivatives in low polar
solvents, it exhibits remarkable red-shift in polar solvents,
as shown Table 2. The results imply that large internal
charge transfer occurs in the excited singlet state of the
derivatives, which means a large dipole moment exists in
the excited state. This could be mainly ascribed to donor-
acceptor moiety effect as coupling with benzophenone part
through double bond. The change of the dipole moments
between the excited state and the ground state can be
estimated based on Lippert equation [44, 45]:
Fig. 4 Absorption spectroscopy of the derivatives and 4-methyl-
benzophenone in methylene chloride c: 1×10−5 mol/L (C0: 4-methyl-
benzophenone, in black line, C1: in red line, C2: in green line, C3: in
blue line)
ꢀ
ꢁ
2
2 me ꢀ mg
hcðnabs ꢀ nemÞ ¼
Δf þ const
ð2Þ
4p"0a3
ꢂ
ꢃ
increasing molar of 4-methylbenzophenone. Hence, the
absorption band of 275–350 nm could not be simply assigned
to triphenylamine core. The second band may be from the
overlap of local electron transition of triphenylamine core and
overall molecular (π, π) transition, thus the optical density of
this absorption band is enhanced with the increasing of the
number of the arms. The optical density of third absorption
band from (350–525 nm), namely, the maximal absorption
band, shows a linear increasing with the number of arms of
the derivatives. Furthermore, Table 1 shows that the maximal
emission exhibits somewhat bathochromic shift with the
increasing of solvent polarity. The results suggest the
molecular (π, π) transition has internal charge transfer
character [43]. The data demonstrate that that the ratio of the
molar extinction coefficients of derivatives is close to the ratio
of the number of arms, namely 1:2:3. It could be easily
understood from their chemical features. C1, C2 and C3 are
" ꢀ 1
n2 ꢀ 1
Δf ¼
ꢀ
ð3Þ
2" þ 1 2n2 þ 1
Wherein h is Planck’s constant, c is the speed of light,
and Δƒ is called as the orientation polarizability. υabs, υem
are the wavenumbers of the absorption and emission, n is
the refractive index, and ε is the relative low-frequency
dielectric constant of the solvents. In Lippert equation,
chromophore acts as a dipole, which locates in a cavity
with a radius of a in a continuous solvent-dipole environ-
ment, and this equation presents a solvent effect of the
index of refraction and relative dielicetric constant. Conse-
quently, the linear correlation between Stokes shifts and Δƒ
do not reflect some special interaction between the
fluorophore and solvent molecules such as hydrogen
bonding.
Lippert plots of the derivatives are presented in Fig. 6, in
which larger spectral shifts are observed. The linearity of
the plot is strong evidence for the dominant importance of
solvent effects in the spectral shifts, and three equations are
characterized by D-π-A, D-(π-A)2, D-(π-A)3 respectively
.
This results in the cooperative effect on the molar extinction
coefficients of derivatives 2 and 3.
Table 1 Absorption spectral da-
ta of the derivatives in various
solvents
Solvents
C1
C2
C3
λmax (abs)
10−5
ε
λmax (abs)
10−5
ε
λmax(abs)
10−5
ε
Benzene
395
391
396
420
393
0.215
0.232
0.255
0.268
0.282
417
414
418
423
416
0.502
0.460
0.470
0.507
0.554
420
415
422
425
424
0.783
0.914
0.843
0.815
–
Ethyl acetate
Tetrahydrofuran
Methylene chloride
Acetonitrile
ε mol−1 ·l·cm−1

J Fluoresc (2011) 21:149–159
155
1.2
7500
7000
6500
6000
5500
5000
4500
4000
3500
3000
2500
2000
C1
C2
C3
linear(C1)
linear(C2)
C1
C2
C3
1.0
0.8
0.6
0.4
0.2
0.0
linear(C3)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
400
450
500
550
600
650
700
Solvent orientation polarizability
Wavelength (nm)
Fig. 6 Relationship between Stokes’ shifts of the derivatives and the
orientation polarizability (Δƒ) of solvents respectively
Fig. 5 Emission spectroscopy of the derivatives in THF
mechanism is a so-called “positive solvatokinetic effect”,
according to which, fluorescence quantum yields are much
reduced by the strong intra-molecular charge transfer for the
larger polarity of solvents. As the attaching benzophenone
unit to core through C–C double bond, C1, C2 and C3 show
D-π-A, D-(π-A)2, D-(π-A)3 character respectively and thus
C2 and C3 show larger internal charge transfer nature at the
excited states due to branch cooperative effect. Generally,
internal charge transfer of organic compounds is strongly
dependent on the solvent polarity [48], thus the emission of
C2 and C3 should be more sensitive to solvent polarity. As
shown in Fig. 7, the emission of C3 varies larger change
with the increasing of methylene chloride volume ratio in
benzene/methylene chloride binary solvents than that of C1.
We have to point out that the fluorescence quantum
yields of the derivatives 1 to 3 are much larger than that of
simple stilbene, and even greater than stilbenoid dendrimers
carrying with dibutylamino groups [49]. It is well demon-
strated that for a simple stilbene, cis-tran isomerization is
the main approach of de-activation of the excited singlet
states [50]. In the present study, “internal charge transfer”
might dominate the decay of the excited singlet states rather
than “cis-trans” twist due to “D-π-A” nature of the
derivatives as the withdrawing effect of carbonyl group in
benzophenone unit. Furthermore, the stiffness, rigidity and
conjugation of the derivatives are enhanced by the
benzophenone part. As a consequence, the derivatives
exhibit strong fluorescence emission in non-polar solvents.
obtained as: C1: Y=9635.5X+4142.6, C2: Y=11573X+
2760.9, C3: Y=11377X+2911.3. The estimated changes of
the dipole moments between the ground and excited singlet
states confirm a great internal charge transfer and a large
conformational change in the excited state (Table 3). The
order of the change of dipole moments decreases gradually
from the derivatives 3 to 1. This could explain the gradual
red-shift of the maximal absorption and fluorescence
wavelength from the derivatives 1 to 3.
As our expectation, the derivatives exhibit strong
fluorescence in low-polar solvents. The relative fluores-
cence quantum yields of the derivatives nearly reach 1.00 in
benzene, while the fluorescence quantum yields are reduced
in methylene chloride and acetonitrile (Table 2). Such
variation of the fluorescence quantum yields suggests that
two mechanisms could dominate the decay of the excited
singlet state of the derivatives [46, 47]. One is a so-called
“negative solvatokinetic effect”, which relates to the
decreasing in the fluorescence quantum yields with the
suitable enhancement of the internal charge transfer. In
other words, in non-polar solvents, the radiative transition
decay of the excited state plays significant role. The other
Table 2 The fluorescence spectral data of compounds 1, 2 and 3 in
various solvents
Solvents
C1
C2
C3
λmax
(em)
Ф
λmax
(em)
Ф
λmax
(em)
Ф
Table 3 Estimated Changes of dipole moments between the ground
and the excited states of the derivatives from Lippert equation
Benzene
480
514
518
542
0.990
0.982
0.927
0.541
481
520
522
546
0.995
0.848
0.877
0.348
483
524
528
549
0.996
0.717
0.695
0.253
Ethyl acetate
Tetrahydrofuran
The change of dipole moments
Δμ (Derby)
C1
C2
C3
Methylene
chloride
4.356
8.091
8.479
Acetonitrile
559
0.153
562
0.0065
587
–
1 D=3.336×10−30 c.m

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J Fluoresc (2011) 21:149–159
Table 5 Some characteristics of C1, C2 and C3, and some
conventional probes and newly developed fluorescence probes
Fluorescence
probes
Size
Charge
state
Water
solubility
C1
C2
C3
Medium
Large
Large
Huge
Zwitterionic
Zwitterionic
Zwitterionic
Neutral
Hydrophobic
Hydrophobic
Hydrophobic
Hydrophobic
Pyrene-dendrimer
[55]
Water-soluble
Nile blue [56]
DBANS [57]
Medium
Ionic
Hydrophilic
Medium
Medium
Large
Zwitterionic
Zwitterionic
Ionic
Hydrophobic
Hydrophobic
Amphiphilic
APM [58]
Diaryethene
derivatives [59]
Nile-red [60, 61]
Medium
Small
Zwitterionic
Neutral
Hydrophobic
Hydrophobic
Hydrophobic
Hydrophobic
Hydrophilic
Amphiphilic
Pyrene [61]
Nile blue [56]
Medium
Small
Zwitterionic
Neutral
Coumarin 500 [62]
ANS [62, 63]
Medium
Small
Ionic
Dansylamide [61, 64]
Zwitterionic
DBANS (4,4′-(N,N-dibutylamino)-(E)-nitrostilbene, APM aminophe-
noxazone maleimide, ANS 8-anilino-1-naphthalene sulfonic acid
maximal UV/visible absorption wavelength of C3 displays
approximate 19 nm red-shift with respect to that of C2, and
approximate 46 nm red-shift with respect to that of C1. A
similar phenomenon is observed for the maximal fluores-
cence emission in various micelles. Furthermore, the
maximal absorption and emission wavelength of C1 are
red-shifted in ionic micelles with respected to that in neutral
micelle. While as contrast, the maximal fluorescence
wavelength of C2 and C3 does not exhibit large change
in various micelles. On the other hand, the fluorescence
quantum yields of C1 in various micelles are larger than
those of C2 and C3, and the fluorescence quantum yields of
the derivatives in neutral micelle are higher than those in
ionic micelles. Furthermore, the fluorescence quantum
yields of the derivatives are much reduced in micelles,
particularly in ionic micelles, indicating that the encapsu-
lated regions of micelles have a polar nature.
Fig. 7 Typical comparison of variation of emission spectroscopy of
C1 and C3 with the increasing volume of methylene chloride into
benzene/methylene chloride binary solvents
Possibility as fluorescence probes
The UV/visible absorption and fluorescence spectroscopy
of the derivatives in anionic, neutral and cationic micelles
were determined. The fluorescence quantum yields were
also measured. The spectroscopic data in micelles are
presented in Table 4. The derivatives display remarkably
different maximal absorption and fluorescence wavelength
in the same micelle. For instance, in TX-100 micelle, the
The spectroscopic data in micelles could be used to
probe what region of micelles interacting with molecules.
Table 4 Absorption and fluorescence spectral data of the derivatives in various micelles
Micelles
C1
C2
C3
λmax(abs)
λmax(em)
Ф
λmax(abs)
λmax(em)
Ф
λmax(abs)
λmax(em)
Ф
TX-100
CTAB
SDS
402
407
408
505
522
523
0.361
0.153
0.125
425
431
432
524
533
535
0.0117
443
451
453
538
552
553
0.00836
0.00362
0.00287
0.00611
0.00537

J Fluoresc (2011) 21:149–159
157
The results in Table 4 indicate that C1 lies in hydrophobic
regions of micelles, while it is more close to polar head and
surface in ionic micelles. This is mostly due to electronic
static dipole polarizability between C1 and polar head of
ionic micelles. The spectral properties of C2 and C3
suggest that they are much more near around micelle water
interface than C1, and thus the absorption and fluorescence
spectroscopy is much affected by water molecules. This is
intrigue because C2 and C3 should have stronger hydro-
phobic characteristics due to more phenyl rings and they
should be encapsulated in hydrophobic layer of micelles.
While, the results are reasonable if we consider two main
factors: (1) C2 and C3 have more dipole moments than C1,
which results in larger electronic static dipole polarizability
between C2 and C3 and polar head of ionic micelles. (2)
The radius of hydrophobic cores of SDS, CTAB and TX-
100 are about 16.7 Å, 21.7 Å and 43.5 Å respectively [51–
53]. While, the geometry optimization calculation with
AM1 method shows C2 and C3 have larger molecular size
than that of C1 respectively (the lengths are approximate
17.9 Å, 25.5 Å and 26.5 Å for C1, C2 and C3
respectively). As a consequence, C2 and C3 could be
forced to be located at micelle water interface due to large
molecular size. It is well accepted that the probed polarities
of micelles are mainly determined by the degree of
penetration into the micelles. In the present study, although
the probed polarities by different derivatives for the same
micelle could be different from each other based on the
spectroscopic data, the order of polarity (TX-
100<CTAB<SDS) is agreement for the different deriva-
tives, which is perfectly consistent with previous report
[54]. We would point out the development process of these
new fluorescence probes reported herein is not more
difficult than that of some newly reported probes [55–59].
We further summarize the characteristics of some conven-
tional fluorescence probes and novel probes. Seen from
Table 5, C1, C2 and C3 are characterized with zwitterionic
state and hydrophobic nature, which is quite similar to that
of Nile blue [56], DBANS [57], APM [58], Nile red [60,
61] while it is some different from that of pyrene dendrimer
[55], aqueous Nile blue [56], diaryethene derivatives [59],
pyrene [61], coumarin 500 [62], ANS [62, 63] and
dansylamide [60, 64]. Hence, the derivatives reported in
the present report could be employed as fluorescence
probes in some environments.
Owing to electron-withdrawing effect of carbonyl group in
benzophenone moiety, (π, π) transition of the derivatives
exhibits internal charge transfer nature, which could be
tuned by the variation of the number of arms, and thus the
spectral properties could be regulated. Our results demon-
strate that the derivatives could be employed as efficient
fluorescence probes to determine what region of micelles
interacting with molecules.
Supporting materials
CCDC 713270 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/conts/retrieving.html or from the
Cambridge Crsytallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax: 44 1223 336033).
Acknowledgements The authors appreciate financial support from
National Natural Science Foundation of China (Nos. 20776165,
20702065, 20872184). We would thank “the Foundation of Chongq-
ing Science and Technology Commission” (CSTC2008BA4020,
CSTC2009BB4216). We also appreciate warm supports from the
Key Laboratory of Functional Crystals and Laser Technology, TIPC,
Chinese Academy of Sciences. We also thank “Innovative Talent
Training Project, the Third State of “211 Project, S-09103”, Chongq-
ing University.
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