Two-photon absorption and fluorescence fluoride-sensing properties of N-octyl-3,6-bis[4-(4-(diphenylamino)phenyl)phenyl]-1,4-diketo-pyrrolo[3,4-c] pyrrole

Article abstract of DOI:10.1016/j.dyepig.2013.12.031

A fully aromatic D-π-A-π-D-type molecule 3,6-bis[4-(4-(diphenylamino) -phenyl)phenyl]-N-octyl-1,4-diketo-pyrrolo[3,4-c]pyrrole (TDP) was synthesized, and the one- and two-photon absorption and emission properties in the absence or presence of fluoride anion were investigated. The results show that TDP not only exhibits large two-photon absorption (2PA) cross section (δ) up to 1030 GM and strong red two-photon excitation fluorescence, but also could operate as one- and two-photon chemosensor selectively for fluoride anion. Interestingly, it is observed that both the detection sensitivity of TDP to fluoride anion and the ratiometric change in emission spectra upon two-photon induced by fluoride anion are higher than one-photon excitation, implying that TDP could serve better as two-photon fluorescence sensor for fluoride anion. The large δ and red-shifted 2PA band promoted by triphenylamine end-group enable TDP to sense fluoride anion under longer excitation wavelength and lower input laser power.

Full text of DOI:10.1016/j.dyepig.2013.12.031

Dyes and Pigments 104 (2014) 97e101
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Two-photon absorption and fluorescence fluoride-sensing properties
of N-octyl-3,6-bis[4-(4-(diphenylamino)phenyl)phenyl]-1,4-diketo-
pyrrolo[3,4-c]pyrrole
*
Yiping Li, Meng Zheng, Jianfeng Wang, Yangyang Gao, Baoliang Zhang, Wenjun Yang
Key Laboratory of Rubber-Plastics of Ministry of Education/Shandong Province (QUST), School of Polymer Science & Engineering,
Qingdao University of Science & Technology, 53-Zhengzhou Road, Qingdao 266042, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A fully aromatic DepeAepeD-type molecule 3,6-bis[4-(4-(diphenylamino)-phenyl)phenyl]-N-octyl-1,4-
diketo-pyrrolo[3,4-c]pyrrole (TDP) was synthesized, and the one- and two-photon absorption and
emission properties in the absence or presence of fluoride anion were investigated. The results show that
Received 8 November 2013
Received in revised form
24 December 2013
Accepted 30 December 2013
Available online 8 January 2014
TDP not only exhibits large two-photon absorption (2PA) cross section (d) up to 1030 GM and strong red
two-photon excitation fluorescence, but also could operate as one- and two-photon chemosensor
selectively for fluoride anion. Interestingly, it is observed that both the detection sensitivity of TDP to
fluoride anion and the ratiometric change in emission spectra upon two-photon induced by fluoride
anion are higher than one-photon excitation, implying that TDP could serve better as two-photon
Keywords:
1,4-Diketo-pyrrolo[3,4-c]pyrrole derivative
Suzuki coupling reaction
Fluorescence chemosensor
Fluoride anion
fluorescence sensor for fluoride anion. The large
d and red-shifted 2PA band promoted by triphenyl-
amine end-group enable TDP to sense fluoride anion under longer excitation wavelength and lower
input laser power.
Two-photon absorption
Two-photon excitation fluorescence
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
instability problems [8]. It is expected that the 2PA molecules
with fully aromatic structure should be stable to laser light and
Organic two-photon absorption (2PA) molecules exhibiting
large 2PA cross-sections ( ) have received much attention due to
heat, however, such compounds exhibiting large
are still rather rare at present.
d and strong 2PEF
d
their potential applications in three-dimensional (3-D) fluores-
cence imaging [1], optical power limitation [2], lasing up-
conversion [3], 3-D optical data storage [4], 3-D microfabrication
[5] and photodynamic therapy [6]. Two-photon excitation can
provide exclusive confinement of the excitation to the focal volume
with high 3-dimensional resolution and reduced photobleaching
and phototoxicity by virtue of the low-energy NIR excitation (700e
1000 nm), which is very valuable to fluorescence chemosensor and
imaging [7]. Therefore, the construction of two-photon excitable
chemosensor has become one of the most attractive subjects in this
field. While a variety of organic molecules with large 2PA cross-
1,4-Diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) and its de-
rivatives represent a class of brilliant red and strongly fluorescent
high-performance pigments and have exceptional light, weather
and heat stability and high light fastness [9]. While a large number
of attempts have been made to use DPP-based conjugated mole-
cules as highly luminescent, electro- and photo-active materials in
optoelectronic devices, there are rather limited reports on 2PA
properties and construction of fluorescence sensors of DPP-based
derivatives [10]. Since DPP is a strong electron-withdrawing unit
and its hydrogen atom on lactam N positions could take place the
intermolecular proton transfer upon adding fluoride anion [11], it is
sections (
d
) and strong two-photon excited fluorescence (2PEF)
expected that donorebridgeeacceptorebridgeedonor (De
peAe
have been extensively developed, the 2PA molecules that can sense
ions and biological species are still limited. Moreover, most of the
2PA dyes reported to date employ carbonecarbon double bonds as
conjugation bridges, which might be subject to photo- and heat-
peD) type DPP-based molecules should be high 2PA-active dyes
and their N-monoalkylated derivatives should be promising can-
didates for the two-photon fluorescent chemosensor of fluoride
anion. The development of two-photon fluorescent sensor selec-
tively for fluoride is very necessary for both environmental and
biological systems because fluoride anion has unique chemical and
physiological properties and is associated with nerve gases, anal-
ysis of drinking water, and the refinement of uranium [12].
* Corresponding author. Tel.: þ86 532 84023670; fax: þ86 532 84023977.
E-mail address: ywjph2004@qust.edu.cn (W. Yang).
0143-7208/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.12.031

98
Y. Li et al. / Dyes and Pigments 104 (2014) 97e101
However, to our best knowledge, although a variety of one-photon
fluorescent fluoride-sensors have been presented in the literature
[13], there are only a few reports on two-photon fluorescent sensor
for fluoride [10c,10f,10g,14]. In the current work, we have connected
electron-donating triphenylamine group to the 3,6-positions of N-
monoalkylated DPP core via 1,4-phenylene conjugation bridges to
29.53, 29.07, 26.80, 22.62, 14.12 ppm. Anal. Calcd for C62H54N4O2: C,
83.94; H, 6.14; N, 6.32; O, 3.61. Found: C, 84.02; H, 6.10; N, 6.34%.
2.3. Measurement
The NMR spectra were recorded on a Bruker-AC500 spectrom-
eter in CDCl3 with teramethylsilame (TMS) as the internal standard.
The elemental analysis was performed on PerkineElmer 2400. UVe
vis absorption spectra were recorded on a Hitachi U-4100 spec-
trophotometer (Scan Speed: 600 nm/min, Sampling Interval:
1.00 nm, Slit Width: 4.00 nm). Fluorescence measurements were
carried out with Hitachi F-4600 spectrophotometer (Scan Speed:
1200 nm/min, PMT Voltage: 400 V, EX Slit: 5.0 nm, EM Slit: 5.0 nm)
and excited by the peak wavelength of the lowest energy absorp-
form a new fully aromatic DepeAepeD-type molecule (TDP,
Scheme 1), and its optical properties are investigated in the absence
or presence of fluoride anion. TDP is stable to laser light and no
changes in PL spectra and intensities are measured upon laser
irradiation many times. We now report that TDP not only exhibits
large
d and strong red TPEF but also could operate as two-photon
chemosensor for fluoride anion under longer excitation wave-
length and lower input laser power.
tion band. The fluorescence quantum yield (F) was determined in
THF at room temperature using Rhodamine B in methanol as the
reference according to the dilute solution method. The uncertainty
for measured UV or PL is <2%. The fluorometric cuvette with
1.0 ꢀ 1.0 cm2 cross section and four optically clear windows was
used.
2. Experimental section
2.1. Materials
N-Octyl-3,6-bis(4-bromophenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-
dione and 4-(5,5-dimethyl-1,3,2-dioxaborinan-2-yl)-triphenylamine
were from previous works [14e,15]. Other reagents and solvents were
analytical grade and used as received, unless otherwise claimed.
The two-photon absorption (2PA) cross-sections
(d) were
measured with the two-photon-induced fluorescence method by
using femto-second laser pulses as described before by us and
others [15,16]. The excitation light source was a mode-locked
Ti:sapphire fs laser (Spectra-Physics, Tsunami 3941, 700e910 nm,
80 MHz, <120 fs) pumped by a compact cw prolite diode laser
(Spectra-physics, Millennia Pro 5S). The fluorescence signal was
recorded by a spectrofluorometer (Ocean Optics, USB2000). Sam-
2.2. Synthesis of N-octyl-3,6-bis[4-(4-(diphenylamino)phenyl)
phenyl]-1,4-diketo-pyrrolo[3,4-c]pyrrole (TDP)
ples were dissolved in THF at the concentrations of 1.0 ꢀ 10ꢁ5
M
N-Octyl-3,6-bis(4-bromophenyl)pyrrolo[3,4-c]pyrrole-
and the two-photon induced fluorescence intensity was measured
at 710e850 nm by using Rhodamine B (1.0 ꢀ 10ꢁ5 M in methanol)
as the reference [17]. The intensities of the two-photon induced
fluorescence spectra of the reference and sample under the same
measurement conditions were determined and compared. The
two-photon absorption cross section of sample (ds) was calculated
by using the equation: ds ¼ ½ðSsFrn2r crÞ=ðSrFsn2s csÞꢂdr, the sub-
scripts s and r stand for the sample and reference molecules
respectively. S was the integral area of the two-photon excitation
1,4(2H,5H)-dione (0.22 g, 0.39 mmol), 4-(5,5-dimethyl-1,3,2-
dioxaborinan-2-yl)-triphenylamine (0.35 g, 0.98 mmol) and
Pd(PPh3)4 (15 mg, 0.013 mmol) were added to the mixture of 2 M
K2CO3 aqueous solution (5 mL) and toluene (7 mL) under nitrogen.
The resulting mixture was purged with nitrogen and refluxed un-
der stirring for 2 days under nitrogen atmosphere. After cooling,
100 mL of dichloromethane was added, and the organic phase was
washed with water and dried over MgSO4. The crude product was
purified by column chromatography using dichloromethane/ethyl
acetate ¼ 10/1 as the eluent. After drying, 0.29 g of deep red solids
fluorescence;
F
was the fluorescence quantum yield (assuming that
remains
was obtained (84% yield). 1H NMR (500 MHz, CDCl3):
d 8.49 (b, 1H),
both in two-photon and one-photon excitation, the
F
unchanged), n was the refractive indices of the solvents for the
sample and reference, and c was the number density of the mole-
cules in solution. dr was the TPA cross section of the reference
8.30 (d, 2H), 7.88 (d, 2H), 7.73 (d, 2H), 7.69 (d, 2H), 7.49 (m, 4H), 7.27
(m, 12H), 7.07 (m, 12H), 3.87 (t, 2H), 1.69 (m, 2H), 1.22 (m, 10H),
0.84 ppm (t, 3H). 13C NMR (125 MHz, CDCl3):
d 163.10, 162.75,
molecule. The whole experimental uncertainty in
d is about 15%.
148.54, 148.43, 147.46, 146.23, 146.17, 144.70, 144.64, 144.04, 143.32,
132.23, 123.10, 129.33, 128.38, 127.60, 126.77, 126.60, 126.17, 125.63,
124.49, 124.45, 122.45, 122.33, 110.81, 109.80, 53.43, 42.36, 31.48,
3. Results and discussion
3.1. Synthesis and one-photon absorption and excitation
fluorescence of TDP
C8H17
Br
N
O
O
O
B
N
TDP was synthesized facilely by the Suzuki coupling of N-octyl-
3,6-bis(4-bromophenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione
O
N
H
and
4-(5,5-dimethyl-1,3,2-dioxa-borinan-2-yl)-triphenylamine
Br
DP
(Scheme 1) in a high yield of 84%. The target product TDP was
unambiguously characterized by NMR spectra (1H and 13C) and
element analysis. The one-photon absorption and emission spectra
of TDP in THF and film state are shown in Fig. 1. The maximal ab-
sorption and peak emission wavelengths of TDP in THF are located
at 534 and 594 nm, respectively. This is a red-emitting dye, and the
fluorescence quantum yield in THF solution is 27%.
Pd(PPh3)4/K2CO3(aq.)/PhMe
C8H17
O
N
N
N
N
H
O
3.2. One-photon responses of TDP to fluoride anion
TDP
Fig. 2 depicts the photographs of fluorescence color changes of
TDP in THF with different equiv of n-Bu4NF (TBAF), where the TBAF
Scheme 1. Synthesis and structure of N-monoalkylated DPP capped with triphenyl-
amine (TDP).

Y. Li et al. / Dyes and Pigments 104 (2014) 97e101
99
ca. 594 nm is gradually decreased, at the same time, a new emission
shoulder at 645 nm turns to be obvious gradually with the addition
of fluoride anion (Fig. 3(b)). The former absorption and emission
bands could be ascribed to the electrically neutral TDP, the latter
absorption and emission bands (shoulder) are from the negatively
charged species (i.e. deprotonated TDP by fluoride). The addition of
TBAF decreases the fluorescence quantum yield (V) due to the low
band gap and self-absorption of deprotonated TDP by fluoride.
Nevertheless, TDP solution with 6.0 equiv of TBAF still shows a
commendable V of 19%.
3.3. Two-photon absorption and excited fluorescence
TDP and its deprotonated counterpart are all DepeAepeD-
type molecules and should be high 2PA-active dyes. Since there are
no linear (one-photon) absorptions beyond 700 nm (Fig. 3(a)), the
fluorescence emissions excited by low-energy NIR light must be
from the nonlinear absorption. Fig. 4 shows the two-photon excited
fluorescence (2PEF) spectra measured by femto-second laser pulses
(120 fs) at 800 nm under different input laser power. The fluores-
cence intensities without (Fig. 4(a)) and with (Fig. 4(b)) fluoride are
both increased gradually with the input laser power, and the plots
of logarithmic output fluorescence intensity (up-conversion signal)
versus logarithmic input laser power give the slops of 2.04 and 1.98
for TDP without and with fluoride, respectively (insets in Fig. 4).
This power-law dependence indicates that both TDP and its
deprotonated counterpart are both 2PA dyes, and the fluorescence
emission observed is from the two-photon excitation (absorption)
process. It is noted that the 2PEF spectrum of TDP without fluoride
(Fig. 4(a)) is very similar to its one-photon excited fluorescence
(OPEF) spectrum (Fig. 1) except of different full width at half
maxima. In contrast, the spectral profile of 2PEF spectrum of TDP
with fluoride (Fig. 4(b)) is different from that of OPEF spectrum
(Fig. 3(b)). However, both 2PEF and OPEF spectra remain two spe-
cial emission peaks corresponding to TDP and its deprotonated
counterpart. Therefore, it could be concluded that the one- and
two-photon excited fluorescence occurred from the same excited
states, regardless of the mode of excitation.
Fig. 1. Absorption (UV) and emission (PL) spectra of TDP in THF at 1.0 ꢀ 10ꢁ5 M.
was used as a fluoride source. Naked-eye-visible fluorescence color
changes are observed only when more than 4 equiv of TBAF is
added probably due to the red emission of solution itself. It has
been shown that monoalkyl-DPP derivatives are highly selective
sensor for fluoride since the hard electronically negative Fe can
break the NeH bond of the lactam unit to form negatively charged
and red-shifted emission species. Here we examine the effect of
some anions, such as Cle, Bre, Ie and other anions on fluorescence
emission of TDP solution. The results show that there are no
noticeable changes in the fluorescence color upon adding excess of
other anions (Fig. 2), and TDP is also fluorometric and selective
sensor for fluoride anion.
One-photon absorption and emission spectra of TDP in THF with
the progressively addition of TBAF are shown in Fig. 3. It is observed
that the absorption band centered at ca. 538 nm is gradually
decreased, and a new absorption band at 608 nm is developed with
the addition of fluoride anion (Fig. 3(a)), indicating the formation of
a new optical species with stronger pushepull electron effect. The
emission spectra shows that the original emission band peaked at
Fig. 2. Fluorescence photographs of TDP in THF (1.0 ꢀ 10ꢁ5 M) with different equiv of fluoride anion (left) and other anions (right) under illumination of a 365 nm UV lamp.
300
0.5
F_ equiv
0
(a)
(b)
F_ equiv
0
250
200
150
100
50
0.4
0.3
0.2
0.1
0.0
0.5
1.5
2.0
3.0
6.0
8.0
12.0
16.0
0.5
1.5
2.0
3.0
6.0
8.0
12.0
16.0
645 nm
F_
0
550
600
650
700
400
450
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
Fig. 3. Absorption and emission spectra of TDP in THF at 1.0 ꢀ 10ꢁ5 M with different equiv of fluoride anion (TBAF).

100
Y. Li et al. / Dyes and Pigments 104 (2014) 97e101
_
595 nm
(a)
TDP
300
(b)
400
300
200
100
0
TDP with F
645nm
Input Laser
(mW)
50
without F_
Input Power
595nm
250
200
150
100
50
4.8
4.5
4.2
3.9
3.6
Experimental data
Linear fit, Slop 1.95
(mW)
50
70
Experimental data
4.4
4.2
4.0
3.8
3.6
3.4
3.2
Linear fit, Slop 2.04
70
100
120
130
90
110
130
150
150
Log (Input Laser Power)
Log (Input Laser Power)
1.7 1.8 1.9 2.0 2.1 2.2
1.7 1.8 1.9 2.0 2.1 2.2
0
200
300
400
500
600
700
300
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Fig. 4. Two-photon excited fluorescence (2PEF) spectra of TDP (1.0 ꢀ 10ꢁ5 M) before (a) and after (b) adding 6.0 equiv of TBAF in THF excited at 800 nm under different input laser
power. The insets are the dependence of output fluorescence intensity on the input laser power.
2PA cross section (
d
) of TDP with and without TBAF are
shift the main 2PA bands to longer wavelength regions (750e
840 nm), which could enable DPP-based dyes to be excited under
lower laser powers and longer wavelengths.
measured in THF by 2PEF method, and the two-photon excitation
spectra under 100 mW of input laser power (which falls within the
power range of two-photon excitation, Fig. 4) are shown in Fig. 5.
Overall, the d values of TDP with fluoride are larger than that of TDP
3.4. Two-photon responses of TDP to fluoride anion
itself (without fluoride), which could be ascribed to stronger
intramolecular charge transfer effect of deprotonated TDP by
fluoride (Fig. 3). However, it is not clear whether they have even
stronger 2PA bands at longer wavelength regions (>850 nm) as a
result of our instrument limitation. It is noted that, in comparison
with the DPP core (TDP without donor end groups) in which the
As shown above, TDP and its deprotonated counterpart both
exhibit large d and commendable F, which should be enable TDP to
be a promising candidate for the two-photon fluorescent sensor of
fluoride anion. Fig. 6(a) shows the 2PEF spectra of TDP in THF upon
addition of different equiv of TBAF. The input laser power is
100 mW and the excitation wavelength is at 800 nm, which is lower
than that used in TDP without triphenylamine end groups in terms
of photon energy and intensity [14e]. It is observed that 2PEF in-
tensity peaked at 594 nm is also gradually decreased, while a new
emission band emerges at 645 nm and increases rapidly with the
addition of TBAF. This indicates that TDP can be used as the ratio-
metric and fluorometric two-photon sensor for fluoride anion.
Interestingly, comparison between the one- and two-photon
sensing properties reveals that the new emission band at 645 nm
that is relative to negatively charged TDP species is more obvious
upon two-photon than one-photon excitation under same con-
centrations of TBAF (Figs. 3 and 6), implying that TDP is more
suitable to operate as a two-photon sensor of fluoride due to its
higher detection sensitivity to fluoride anion upon two-photon
excitation. Unexpectedly, the 2PEF spectral profile of TDP with
TBAF is affected by two-photon excitation wavelength (Fig. 6(b)).
The relative intensity ratios of fluorescence emissions at 645 and
594 nm (I645/I594) change with the two-photon excitation wave-
length. However, the origin for these intriguing experimental
phenomena is not clear at present.
d
values are smaller (<90 GM) and main 2PA bands locate the
shorter-wavelength regions (710e780 nm) [14e], the incorporation
of triphenylamine can significantly enhance (up to 1000 GM) and
d
Fig. 5. Two-photon excitation spectra of TDP measured at 1 ꢀ 10ꢁ5 M in THF in the
presence (6.0 equiv) and absence of TBAF, respectively.
645 nm
150
200
595 nm
(b)
(a)
F_ equiv
TDP With F_
594 nm
120
0
Excitation @
150
2.0
740 nm
645 nm
3.0
4.0
760 nm
800 nm
820 nm
840 nm
90
60
30
0
100
50
0
6.0
8.0
500
550
600
650
700
750
800
500
550
600
650
700
750
800
Wavelength (nm)
Wavelength (nm)
Fig. 6. 2PEF spectra of TDP in THF (1.0 ꢀ 10ꢁ5 M) with different equiv of TBAF excited at 800 nm (a) and with 6.0 equiv of TBAF excited at different wavelength (b) under the input
laser power of 100 mW.

Y. Li et al. / Dyes and Pigments 104 (2014) 97e101
(DPP) sensitizer containing
101
a
furan moiety for efficient and stable dye-
4. Conclusions
sensitized solar cells. Dyes Pigments 2012;92:1384e93;
(e) Huang W, Tang F, Li B, Su J, Tian H. Large De eAe eD structure with cyano-
and triazine-substituted for efficient AIEE solid emitters and large two-photon
absorption cross sections. J Mater Chem C 2013. http://dx.doi.org/10.1039/
C3TC31913J;
(f) Yamagata T, Kuwabara J, Kanbara T. Synthesis of highly fluorescent diketo-
pyrrolopyrrlle derivatice and two-step response of fluorescence to acid. Tet-
rahedron Lett 2010;51:1596e9;
(g) Schutting S, Borisov S, Klimant I. Diketo-pyrrolo-pyrrolo dyes an new
colorimetric and fluorescent pH indicators for optical carbon dioxide sensors.
Anal Chem 2013;85:3271e9.
p
p
We have demonstrated that N-octyl-3,6-bis[4-(4-(diphenyla-
mino)phenyl)phenyl]-1,4-diketo-pyrrolo[3,4-c]pyrrole (TDP) not
only exhibit large
rescent chemosensors selectively for fluoride anion in THF. The high
TPA activity of TDP is ascribed to the De eAe eD motif, and the
d but also operates as one- and two-photon fluo-
p
p
fluoride-sensing capacity is caused by the fluoride-induced inter-
molecular proton transfer of the hydrogen atom on lactam N posi-
tions of DPP. Other anions, including halide anions such as Cle, Bre
and Ie hardly affect the fluorescence colors of TDP in THF solution. It
is found that TDP could serve better as two-photon fluorescence
sensor for fluoride anion due to the higher detection sensitivity and
ratiometric fluorescence upon two-photon than one-photon exci-
tation. Comparing with previous simple monoalkyl-substituted DPP
[11] (a) Miyaji H, Sessler J. Off-the-shelf colorimetric anion sensors. Angew Chem
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motif exhibits larger (up to 1000 GM) and red-shifter 2PA band
(over 840 nm), as a result, TDP could sense fluoride under longer
excitation wavelength and lower input laser power.
d
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