Synthesis and photophysical properties of three ladder-type chromophores with large and rigid conjugation structures

Article abstract of DOI:10.1016/j.dyepig.2013.10.030

Three novel ladder-conjugated chromophores indicated as LT1–LT3 were synthesized and characterized. Further studies on linear, nonlinear optics and electrochemical properties demonstrated their photophysical features respectively. Compound LT1 shows good two-photon absorption cross-section (δ) up to?～1200?GM at 810?nm in tetrahydrofuran, which is attributed to intramolecular charge transfer effect, as supported by density functional theory theoretical calculations. Compound LT2 and LT3 show considerable molar extinction coefficients, which are more than 10⁵, and higher quantum yields. Structure–function relationship is further discussed, suggesting a rational strategy to develop ladder-conjugated small molecules.

Full text of DOI:10.1016/j.dyepig.2013.10.030

Dyes and Pigments 102 (2014) 1e5
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis and photophysical properties of three ladder-type
chromophores with large and rigid conjugation structures
,
a
a,
Kaichen Zhang a, Yong Dai b , Xinfu Zhang , Yi Xiao
**
*
a State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, China
b Department of Criminal Science and Technology, Sichuan Police College, Luzhou 646000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three novel ladder-conjugated chromophores indicated as LT1eLT3 were synthesized and characterized.
Further studies on linear, nonlinear optics and electrochemical properties demonstrated their photo-
physical features respectively. Compound LT1 shows good two-photon absorption cross-section (d) up
to w1200 GM at 810 nm in tetrahydrofuran, which is attributed to intramolecular charge transfer effect,
as supported by density functional theory theoretical calculations. Compound LT2 and LT3 show
considerable molar extinction coefficients, which are more than 105, and higher quantum yields.
Structureefunction relationship is further discussed, suggesting a rational strategy to develop ladder-
conjugated small molecules.
Received 16 September 2013
Received in revised form
18 October 2013
Accepted 21 October 2013
Available online 28 October 2013
Keywords:
Synthesis
Linear optics properties
Electrochemical
Ó 2013 Elsevier Ltd. All rights reserved.
Two-photon absorption
Intramolecular charge transfer
Ladder-conjugated chromophore
1. Introduction
Herein, three novel ladder conjugated chromophores were syn-
thesized by condensation reaction using TABEF (2, 3, 6, 7-
Two-photon absorption (TPA) has obtained lots of attention
since it was first proposed by M. Goppert-Mayer in her doctoral
dissertation in 1931 [1]. Due to their potential applications in
photonics [2e6], including, three-dimensional optical data storage
[7,8], two-photon-excited fluorescence microscopy [9,10], optical
power limiting [11,12], and photodynamic therapy [13], etc, inten-
sive efforts are put into the manufacture of new two-photon ma-
terials in the recent years. The applications of TPA need dyes having
large two-photon absorption cross section [14,15]. Simultaneously,
due to the popularity and easy availability of 800 nm laser sources,
designing and synthesizing TPA chromophores with the optimal
performance at this wavelength is the main goal [4].
tetraamino-9, 9-bis (2-ethylhexyl) fluorene). Quadrupolar mole-
cules are usually considered to be more effectively polarized
resulting in larger transition moment and higher TPA cross-section,
and chromophores LT1eLT3 had structures of completely rigid
planar. And most importantly, they had similar structure and con-
jugated length. The changes of two sides of them may bring about
different optical and physical properties for these materials. To
obtain an effective ICT process, a
used to facilitate the intramolecular electronic flow. At the same
time, it could play as -donor owing to its higher electron density
compared with the electron-deficient parts. Thirdly, to release
intermolecular stacking resulting in increasing solubility, two
p-conjugated bridge-fluorene was
p
pep
In 2012, our group reported one dye, which has excellent two-
isooctyl groups were introduced to the fluorene moiety.
The synthesis, linear optics, two-photon absorption and the
electrochemistry properties of these chromophores were pre-
sented in this work. The TPA cross-section was measured in the
range from 700 nm to 1040 nm.
photon properties, and the maximum of
990 nm. This is caused by its large -conjugated system, completely
rigid and coplanar structure, and the intramolecular charge transfer
(ICT) effect [16]. For the two-photon absorption in the case of the
d is 11,000 GM at
p
p-
conjugated bonds, principal role begin to play dipoleedipole in-
teractions between the chromophore and the polymer chains [17].
2. Experimental
2.1. Materials and instruments
* Corresponding author. Tel.: þ86 411 84986251.
** Corresponding author.
Commercially available reagents were purchased and were used
E-mail addresses: sdy-0502@163.com (Y. Dai), xiaoyi@dlut.edu.cn (Y. Xiao).
without further purification. All the solvents were of analytic grade.
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.10.030

2
K. Zhang et al. / Dyes and Pigments 102 (2014) 1e5
NMR spectra in CDCl3 were measured with a 400 MHz Bruker
spectrometer using TMS as internal reference for 1H and 13C NMR.
Accurate mass correction was measured with MALDI Tof Mass
Spectrometer (MALDI micro MX). Electrochemical studies made
use of cyclic voltammetry (CV) with a conventional 3-electrode
system using a BAS 100W electrochemical analyzer in deoxygen-
ated and anhydrous CH2Cl2 at room temperature. UVevis absorp-
tion spectrums were measured with UVevis Spectrophotometer
(HP 8453). Fluorescence spectra were obtained with a FP-6500
spectrophotometer (Jasco, Japan). Melting points were measured
on a Digital Melting Point Apparatus without correction.
142.6,142.2,142.2,142.1,132.0,131.8, 130.4,130.3,130.1, 127.8, 127.8,
126.3, 126.0, 124.3, 124.2, 124.1, 122.8, 120.7, 54.9, 47.2, 35.2, 33.5,
27.9, 26.9, 22.7, 13.8, 10.2; TOF HRMS ES þ calcd for C57H55N4
795.4427 [M þ H] þ, found 795.4436.
Compound LT3: light yellow powder, yield 76%. m.p. 225.6e
227.3 ꢂC. 1H NMR (400 MHz, CDCl3, 25 ꢂC, TMS):
d (ppm): 8.67 (s,
2H), 8.44e8.42 (d, J ¼ 6.8 Hz, 4H), 8.31e8.29 (t, J ¼ 4.4 Hz, 2H),
8.09e8.06 (d, J ¼ 8 Hz, 4H), 7.87e7.81 (dd, J ¼ 8 Hz, 15.6 Hz, 4H),
2.38e2.31 (t, J ¼ 14.8 Hz, 4H), 0.95e0.73 (m, 18H), 0.55e0.52 (m,
12H); 13C NMR (100 MHz, CDCl3, 25 ꢂC, TMS):
d (ppm): 154.0, 153.7,
153.2, 142.0, 141.8, 141.5, 136.5, 132.0, 130.0, 129.4, 129.4, 128.8,
128.7, 124.7, 124.6, 124.5, 121.8, 120.8, 55.1, 46.6, 35.1, 33.5, 28.0,
26.8, 22.6, 13.8, 10.2; TOF HRMS ES þ calcd for C53H51N4 743.4114
[M þ H] þ, found 743.4125.
Two-photon absorption spectra were measured by using
a
femtosecond (fs) fluorescence measurement technique as
described in the literature [18]. The samples were dissolved in THF
at a concentration of 1.0*10ꢀ5 M. Fluorescence emission curve
excited by different laser wavelengths, from 700 nm to 1040 nm
Compound LT4: green yellow powder, yield 84%. m.p. 160.1e
162.3 ꢂC [23].
(10 nm per step) was detected. The TPA cross-section (
d
) of chro-
Compound LT5: milk white floc, yield 79%. m.p. 173.1e174.5 ꢂC
[24].
mophores LT1eLT3 in THF (1.0*10ꢀ5 M) were measured using
fluorescein in pH ¼ 11 NaOH aqueous solution as the reference [19].
Compound LT6: milk white powder, yield 81%. m.p. 191.1e
The
d was calculated according to the following equation [20].
192.8 ꢂC [25].
ds
¼
dr ꢁ ðSs ꢁ Fr
ꢁ
hr ꢁ N Þ ðS ꢁ Fs
ꢁ
hs ꢁ NsÞ
(1)
=
r
r
3. Results and discussion
where the subscripts s and r stand for the sample and reference
molecule, S is the corrected intensity of two-photon-induced
3.1. Design and synthesis
fluorescence,
centration of the chromophore, and
the experimental setup, dr is the TPA cross section of the reference
molecule.
F
is the fluorescence quantum yield, N is the con-
is the collection efficiency of
Chromophores LT1eLT3 were synthesized by one-step
condensation reaction using TABEF$4HCl as the key intermediate,
and had the similar structures and p-conjugated length. To obtain
h
the larger two-photon absorption cross section, three quadrupolar
chromophores LT1eLT3 with the changes of the substituents at the
terminal position were synthesized. In the synthesis of compound
LT1, two isomers were found in the product. The symmetric com-
pound LT1 can be separated from them through column chroma-
tography. The other compounds LT2 and LT3 have the certain
structures without isomer. All these compounds LT1eLT6 were
synthesized as described in Scheme 1. Compounds LT1eLT3 and
compounds LT4eLT6 correspondingly have the similar structure.
2.2. Theoretical calculations
In order to understand the nature of the ground-state and the
low-lying excited states, quantum chemical calculations were
performed for chromophores LT1eLT3. The structures of them were
optimized using density functional theory (DFT) with B3LYP func-
tional and 6-31G basis set. All calculations were performed with
Gaussian 09 [21].
3.2. Linear photophysical properties
2.3. Synthesis
The comprehensive photophysical properties of these com-
pounds in CH2Cl2 and THF are listed in Table 1. Linear absorption
and single-photon excited fluorescence (SPEF) spectra of chromo-
phores LT1eLT3 in THF are respectively shown in Fig. 1(a) and (b).
A mixture of 0.133 g 1,8-Naphthalic anhydride (0.67 mmol),
0.2 g TABEF$4HCl [22] (0.335 mmol) and 5 ml glacial acetic acid
was heated to reflux for 4 h under argon. After cooling, the re-
action product was precipitated by the addition of MeOH (25 ml),
collected by vacuum filtration, and dried in air. The crude
product was dissolved in dichloromethane, preadsorbed on silica
gel, and purified by column chromatography (silica gel,
CH2Cl2:hexane ¼ 1:1 as eluent, gathering the band (Rf ¼ 0.2))
resulting in an orange solid compound LT1. (118 mg, yield: 45%)
Compounds LT2eLT6 were synthesized in the similar procedure.
Compound LT1: orange powder, yield 45%. m.p. >300 ꢂC. 1H
Due to the larger
p-conjugated system, compounds LT1eLT3
exhibit longer absorption wavelength and larger molar extinction
coefficient compared with reference compounds LT4eLT6, respec-
tively. As shown in Table 1, one can see that the absorption peak
position and emission peak position of compounds LT1eLT6 all
exhibit slight blue shift from CH2Cl2 to THF. Due to rigid structure
without geometry relaxation upon photoexcitation, compounds
LT2 and LT3, exhibit the smaller Stocks Shifts and the higher
quantum yields. Remarkably, they exhibit considerable molar
extinction coefficients, which are more than 105. Caused by the
introduction of benzimidazole unit, compounds LT1 and LT4 show
smaller molar extinction coefficients, and larger Stocks Shifts of
them were caused by the ICT effect. Notably compound LT1 has the
lower quantum yield compared with compound LT4 due to intro-
duction of one more benzimidazole unit, and this have been veri-
fied by the compounds of perylene diimide class [26].
NMR (400 MHz, CDCl3, 25 ꢂC, TMS):
d (ppm): 9.08 (s, 2H), 8.89e8.88
(d, J ¼ 5.6 Hz, 4H), 8.31e8.29 (d, J ¼ 7.2 Hz, 2H), 8.16e8.14 (d,
J ¼ 7.6 Hz, 2H), 7.89e7.82 (m, 6H), 2.20 (s, 4H), 0.91e0.73 (m, 18H),
0.59e0.51 (m, 12H); 13C NMR (100 MHz, CDCl3, 25 ꢂC, TMS):
d
(ppm): 161.0, 149.9, 149.7, 144.0, 139.8, 135.5, 132.6, 131.9, 127.7,
127.7, 127.2, 123.7,121.2,115.5,107.5, 54.7, 46.2, 34.8, 33.7, 28.2, 26.8,
22.9, 14.1, 10.3; TOF HRMS ES þ calcd for C53H51N4O2 775.4012
[M þ H] þ, found 775.3949.
Compound LT2: yellow powder, yield 72%. m.p. 243.1e245.7 ꢂC.
1H NMR (400 MHz, CDCl3, 25 ꢂC, TMS):
d
(ppm): 9.34e9.19 (m, 4H),
3.3. Electrochemical properties
8.70e8.66 (t, J ¼ 6.4 Hz, 2H), 8.46e8.37 (m, 6H), 7.78e7.67 (m, 8H),
2.46e2.45 (d, J ¼ 5.2 Hz, 4H), 1.04e0.73 (m, 18H), 0.59e0.51 (m,
In order to investigate the electrochemical behavior of these
compounds, CV measurements were performed in CH2Cl2 solution
12H); 13C NMR (100 MHz, CDCl3, 25 ꢂC, TMS):
d (ppm): 153.7, 142.9,

K. Zhang et al. / Dyes and Pigments 102 (2014) 1e5
3
Scheme 1. Synthesis of compounds LT1eLT6.
containing 0.05 M Bu4NPF6 as supporting electrolyte with a glassy
carbon as working electrode and SCE (saturated calomel electrode)
as the reference electrode. These results are summarized in Table 2.
Compounds LT2 and LT3 demonstrate two reversible reduction
processes and no oxidation process, while compound LT1 exhibits
one reversible oxidation process and one reversible reduction
process. These could confirm the problem why compound LT1
had ICT effect and the other two didn’t. Compounds LT1eLT3
respectively exhibit the lower LUMO compared with reference
compounds LT4eLT6, and compounds LT1 and LT2 show the lower
LUMO in these six molecules.
3.4. DFT calculations
The electron density distributions of HOMO (highest occupied
molecular orbital) and LUMO (lowest unoccupied molecular
Table 1
Linear photophysical properties of compounds LT1eLT6.
abs
Compound
l
[nm]
εmax[104cmꢀ1molꢀ1L]
lfmluaox[nm]
Stocks Shifts[nm]
CH2Cl2
F
max
CH2Cl2
THF
CH2Cl2
THF
CH2Cl2
THF
THF
CH2Cl2
THF
LT1
LT2
LT3
LT4
LT5
LT6
460
450
424
384
393
318
455
448
421
382
392
317
3.55
12.88
10.95
1.34
1.76
6.71
2.46
14.00
11.50
1.35
1.90
5.92
581
455
429
493
ec
569
452
425
485
ec
121
5
5
109
e
114
4
4
103
e
0.096a
0.701b
0.694b
0.544b
e
0.207a
0.519b
0.625b
0.625b
e
ec
ec
e
e
e
e
a
Fluorescence quantum yields were obtained using fluorescein (
Fluorescence quantum yields were obtained using 0.05 M H2SO4 solution of quinine sulfate (
Not detected.
F
¼ 0.95 in 0.01 M NaOH) as a reference.
b
c
F
¼ 0.55) as a reference.

4
K. Zhang et al. / Dyes and Pigments 102 (2014) 1e5
Fig. 1. Linear absorption spectra (a) and single-photon excited fluorescence (SPEF) spectra (b) of compounds LT1eLT3 in THF.
Table 2
Fig. 2 also reveals that efficient charge migration occurs from the
unit of fluorene to its bilateral moieties upon electronic excitation,
therefore calculations indicate that ICT occurred in it. Moreover,
there are significant overlaps between the HOMOs and LUMOs for
compounds LT2 and LT3, and these may explain they have smaller
Stocks Shifts and the higher quantum yields [29,30].
Electrochemical properties of compounds LT1eLT6.
Compound
Ered1/2
Ered1/2
Eox1/2
Eg(eV)b
LUMOc
HOMOd
1(eV)a
2(eV)a
1 (eV)a
LT1
LT2
LT3
LT4
LT5
LT6
ꢀ1.76
ꢀ1.75
ꢀ1.96
ꢀ1.82
ꢀ1.90
ꢀ2.06
ee
0.85
ee
2.36
2.70
2.86
2.80
3.06
3.30
3.32
3.33
3.12
3.26
3.18
3.02
5.68
6.03
5.98
6.06
6.24
6.32
ꢀ2.02
ꢀ2.17
ee
ee
ee
ee
ee
ee
3.5. Two-photon absorption properties
ee
Compound LT1 shows a large maximal
d value 1226 GM at
a
Measured in 0.05 M solution of Bu4NPF6 in CH2Cl2 with a scan rate of 100 mV/s.
b
c
810 nm by the method of two-photon excited fluorescence (TPEF)
measurement technique. The two-photon absorption spectra (700e
1040 nm) of compounds LT1eLT3 in THF are plotted in Fig. 3. Their
peak position and spectra shapes of TPEF are very similar with SPEF.
The compounds LT2 and LT3 respectivelyexhibit smaller 194 GM and
71 GM at 700 nm in THF compared with compound LT1. Limited by
the femtosecond laser excitation source, we cannot measure in the
short wavelength spectral range below 700 nm, and the maximal
Calculated from UVevis absorption edge, Eg ¼ 1240/
l.
Based on the assumption that the energy of Fc/Fcþ is 5.08 eV relative to vacuum
[27].
d
Calculated from the LUMO level and Eg.
Not detected.
e
orbital) of compounds LT1eLT3 are illustrated in Fig. 2. The refer-
ences devoted to the quantum chemical simulations of such kinds
of compounds have unambiguously shown that here principle role
begin to play vibration subsystem [28]. Due to the rigidly coplanar
geometry, the p-electrons in the HOMO of compounds LT1eLT3 are
delocalized over the entire molecule backbone. For compound LT1,
d
values of compounds LT2 and LT3 may exist below 700 nm. In
contrast to compounds LT2 and LT3, the significant enhancement of
the TPA for compound LT1 may be attributed to ICT effect, although
they have the similar structural features: the large
p-conjugated
system, overall molecular rigidity and planarity. Compound LT1
shows promise of applications in nonlinear optical area.
4. Conclusion
In this article, according to rational strategy combining
DFT calculations we developed three novel ladder-conjugated
Fig. 2. HOMO and LUMO electron density of compounds LT1eLT3 obtained at the
B3LYP/6-31G level.
Fig. 3. Two-photon absorption spectra of compounds LT1eLT3 in THF.

K. Zhang et al. / Dyes and Pigments 102 (2014) 1e5
5
[12] Bouit P-A, Wetzel G, Berginc G, Loiseaux B, Toupet L, Feneyrou P, et al. Near IR
nonlinear absorbing chromophores with optical limiting properties at tele-
communication wavelengths. Chem Mater 2007;19(22):5325e35.
[13] Collins HA, Khurana M, Moriyama EH, Mariampillai A, Dahlstedt E, Balaz M,
et al. Blood-vessel closure using photosensitizers engineered for two-photon
excitation. Nat Photonics 2008;2(7):420e4.
[14] Yan Z-Q, Xu B, Dong Y-J, Tian W-J, Li A-W. The photophysical properties and
two-photon absorption of novel triphenylamine-based dendrimers. Dye
Pigment 2011;90(3):269e74.
chromophores LT1eLT3, and investigated their linear photo-
physical properties, electrochemical properties and TPA absorption
properties. Structureefunction relationship is further discussed,
suggesting a rational strategy to develop ladder-conjugated small
molecules. Compounds LT2 and LT3 show considerable molar
extinction coefficients (more than 105), which are larger than many
small molecules with optoelectronic functional. In agreement with
the theoretical calculations, they exhibit high quantum yields and
smaller Stocks Shifts. The chromophores LT1eLT3 have similar
[15] Poronik YM, Hugues V, Blanchard-Desce M, Gryko DT. Octupolar merocyanine
dyes:
a new class of nonlinear optical chromophores. Chem e Eur J
2012;18(30):9258e66.
structure and
and LT3, the process of effective ICT caused compound LT1’s larger
, and this may provide one strategy to get large in TPA area.
Compound LT1’s is w1200 GM at 810 nm, and fluorescence
quantum efficiency is 0.207 in THF. These good data indicated
p-conjugated length. Compared with compounds LT2
[16] Xie Y, Zhang X, Xiao Y, Zhang Y, Zhou F, Qi J, et al. Fusing three per-
ylenebisimide branches and a truxene core into a star-shaped chromophore
with strong two-photon excited fluorescence and high photostability. Chem
Commun 2012;48(36):4338e40.
[17] Kulhanek J, Bures F, Wojciechowski A, Makowska-Janusik M, Gondek E,
Kityk IV. Optical operation by chromophores featuring 4,5-dicyanoimidazole
d
d
d
F
embedded within poly(methyl methacrylate) matrices.
J Phys Chem A
that compound LT1 is competitive chromophore for TPEF micro-
scopy and other TPA-involving applications.
2010;114(35):9440e6.
[18] Lee SK, Yang WJ, Choi JJ, Kim CH, Jeon S-J, Cho BR. 2,6-Bis[4-(p-dihex-
ylaminostyryl)styryl]anthracene derivatives with large two-photon cross
sections. Org Lett 2005;7(2):323e6.
[19] Makarov NS, Drobizhev M, Rebane A. Two-photon absorption standards in
the 550e1600 nm excitation wavelength range. Opt Express 2008;16(6):
4029e47.
Acknowledgments
[20] Rumi M, Ehrlich JE, Heikal AA, Perry JW, Barlow S, Hu Z, et al. Structure-
property relationships for two-photon absorbing chromophores: bis-donor
The authors thank National Natural Science Foundation of China
(No. 21174022) and the Fundamental Research Funds for the Cen-
tral Universities (No. DUT10ZD114) for financial support.
diphenylpolyene and bis(styryl)benzene derivatives.
J Am Chem Soc
2000;122(39):9500e10.
[21] Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, Cheeseman JR, et al.
Gaussian 09, revision B. 01. Wallingford CT: Gaussian Inc; 2010.
[22] Li X, Xiao Y, Qian X. 2,3,6,7-Tetraamino-9,9-bis(2-ethylhexyl)fluorene: new
multifunctional monomer for soluble ladder-conjugated molecules and
polymers. Org Lett 2008;10(13):2885e8.
[23] Tamuly C, Barooah N, Laskar M, Sarma RJ, Baruah JB. Fluorescence quenching
and enhancement by h-bonding interactions in some nitrogen containing
fluorophores. Supramolecular Chem 2006;18(8):605e13.
[24] Niknam K, Saberi D, Mohagheghnejad M. Silica bonded S-sulfonic acid: a
recyclable catalyst for the synthesis of quinoxalines at room temperature.
Molecules 2009;14(5):1915e26.
[25] Yadav JS, Reddy BVS, Premalatha K, Shankar KS. Bismuth(III)-catalyzed rapid
synthesis of 2,3-disubstituted quinoxalines in water. Synthesis 2008;(23):
3787e92.
[26] Shin WS, Jeong H-H, Kim M-K, Jin S-H, Kim M-R, Lee J-K, et al. Effects of
functional groups at perylene diimide derivatives on organic photovoltaic
device application. J Mater Chem 2006;16(4):384e90.
[27] Thompson BC, Kim Y-G, McCarley TD, Reynolds JR. Soluble narrow band gap
and blue propylenedioxythiophene-cyanovinylene polymers as multifunc-
tional materials for photovoltaic and electrochromic applications. J Am Chem
Soc 2006;128(39):12714e25.
[28] Makowska-Janusik M, Gondek E, Kityk IV, Wisla J, Sanetra J, Danel A. Second-
order optical effects in several pyrazolo-quinoline derivatives. Chem Phys
2004;306(1e3):265e71.
[29] Zhang X, Chi L, Ji S, Wu Y, Song P, Han K, et al. Rational design of d-PeT
phenylethynylated-carbazole monoboronic acid fluorescent sensors for the
References
[1] Goppert-Mayer M. Elementary processes with two quantum jumps. Ann Phys
1931;9:273e94.
[2] Zhou W, Kuebler SM, Braun KL, Yu T, Cammack JK, Ober CK, et al. An efficient
two-photon-generated photoacid applied to positive-tone 3D micro-
fabrication. Science 2002;296(5570):1106e9.
[3] LaFratta CN, Fourkas JT, Baldacchini T, Farrer RA. Multiphoton fabrication.
Angew Chem Int Ed 2007;46(33):6238e58.
[4] He GS, Tan L-S, Zheng Q, Prasad PN. Multiphoton absorbing materials: mo-
lecular designs, characterizations, and applications. Chem Rev 2008;108(4):
1245e330.
[5] Terenziani F, Katan C, Badaeva E, Tretiak S, Blanchard-Desce M. Enhanced
two-photon absorption of organic chromophores: theoretical and experi-
mental assessments. Adv Mater 2008;20(24):4641e78.
[6] Kim HM, Cho BR. Two-photon probes for intracellular free metal ions, acidic
vesicles, and lipid rafts in live tissues. Acc Chem Res 2009;42(7):863e72.
[7] Kawata S, Kawata Y. Three-dimensional optical data storage using photo-
chromic materials. Chem Rev 2000;100(5):1777e88.
[8] Dvornikov AS, Walker EP, Rentzepis PM. Two-photon three-dimensional op-
tical storage memory. J Phys Chem A 2009;113(49):13633e44.
[9] Zipfel WR, Williams RM, Webb WW. Nonlinear magic: multiphoton micro-
scopy in the biosciences. Nat Biotechnol 2003;21(11):1369e77.
[10] Wang X, Nguyen DM, Yanez CO, Rodriguez L, Ahn H-Y, Bondar MV, et al. High-
fidelity hydrophilic probe for two-photon fluorescence lysosomal imaging.
J Am Chem Soc 2010;132(35):12237e9.
[11] Oliveira SL, Correa DS, Misoguti L, Constantino CJL, Aroca RF, Zilio SC, et al.
Perylene derivatives with large two-photon-absorption cross-sections for
application in optical limiting and upconversion lasing. Adv Mater
2005;17(15):1890e3.
selective detection of a-hydroxyl carboxylic acids and monosaccharides. J Am
Chem Soc 2009;131(47):17452e63.
[30] Zhang X, Wu Y, Ji S, Guo H, Song P, Han K, et al. Effect of the electron donor/
acceptor orientation on the fluorescence transduction efficiency of the d-PET
effect of carbazole-based fluorescent boronic acid sensors.
2010;75(8):2578e88.
J Org Chem