Four new two-photon polymerization initiators with varying donor and conjugated bridge: Synthesis and two-photon activity

Article abstract of DOI:10.1016/j.saa.2013.09.051

A specific series of dumbbell-shaped bis-carbazoles or bis-phenothiazines dyes (1, 2, 3 and 4) constructed with styrene or biphenylethyne as the π-bridge have been synthesized and characterized. Detailed spectral properties including linear absorption, one and two-photon fluorescence properties were investigated. The results show that extending conjugated chain and introducing donors have substantial effect on their photophysical properties. Among them, two-photon absorption cross sections (σ) of the four dyes in DMF determined by the Z-scan technique are successively increased from 1 to 4 with enhancing electron-donating ability and extending conjugated chain, but electron-donating ability has larger contribution to the σ values than extending conjugated chain based on the comparison of small molecules (D-π-D). Two-photon initiation polymerization (TPIP) microfabrication experiments have been carried out using compound 4 as an initiator under irradiation of 200 fs, 76 MHz femtosecond laser at 760 nm. The results confirm that the four dyes can be effectively used as organic two-photon photopolymerization initiators.

Full text of DOI:10.1016/j.saa.2013.09.051

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 538–542
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Four new two-photon polymerization initiators with varying donor
and conjugated bridge: Synthesis and two-photon activity
Fuying Hao a,b, Zhaodi Liu a,b, Mingliang Zhang b, Jie Liu a,b, Shengyi Zhang b, Jieying Wu b, Hongping Zhou b,
YuPeng Tian b,
⇑
a Department of Chemistry, Fuyang Normal College, Fuyang 236036, China
b Department of Chemistry and Chemical Engineering, Anhui University, Hefei 230039, China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A new series of dumbbell-shaped bis-carbazoles and bis-phenothiazines chromophores (1, 2, 3 and 4)
constructed with styrene or biphenylethyne as the -bridge have been synthesized and characterized.
Experimental results revealed that extending conjugated chain and introducing donors have substantial
effect on their photophysical properties. Compared with extending conjugated chain, enhancing electron-
donating ability play a major role in enlarging two-photon absorption cross-sections (r). Moreover, those
four chromophores can be used as effectively organic two-photon photopolymerization initiators.
ꢀ
ꢀ
We have synthesized four D–p–D
p
dyes with two-photon absorption.
Four dyes contain phenothiazines/
carbazoles with styrene/
biphenylethyne as bridge.
Photophysical properties of four dyes
were investigated.
ꢀ
ꢀ
ꢀ
Donors have larger contribution to
r
value than that of conjugated bridge.
Four dyes can be used as organic two-
photon photopolymerization
initiators.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 August 2013
Received in revised form 30 August 2013
Accepted 7 September 2013
Available online 18 September 2013
A specific series of dumbbell-shaped bis-carbazoles or bis-phenothiazines dyes (1, 2, 3 and 4) constructed
with styrene or biphenylethyne as the p-bridge have been synthesized and characterized. Detailed spec-
tral properties including linear absorption, one and two-photon fluorescence properties were investi-
gated. The results show that extending conjugated chain and introducing donors have substantial
effect on their photophysical properties. Among them, two-photon absorption cross sections (r) of the
four dyes in DMF determined by the Z-scan technique are successively increased from 1 to 4 with
enhancing electron-donating ability and extending conjugated chain, but electron-donating ability has
Keywords:
Two-photon absorption
Dyes
Photopolymerization initiator
Z-scan technique
larger contribution to the
r values than extending conjugated chain based on the comparison of small
molecules (D– –D). Two-photon initiation polymerization (TPIP) microfabrication experiments have
p
been carried out using compound 4 as an initiator under irradiation of 200 fs, 76 MHz femtosecond laser
at 760 nm. The results confirm that the four dyes can be effectively used as organic two-photon photo-
polymerization initiators.
Ó 2013 Elsevier B.V. All rights reserved.
⇑
Corresponding author. Tel.: +86 55165108151; fax: +86 55163861279.
E-mail address: yptian@ahu.edu.cn (Y. Tian).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.09.051

F. Hao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 538–542
539
Introduction
Results and discussion
Two-photon excitation of fluorophores results from the simul-
taneous absorption of two photons. The excitation process has a
number of unique advantages, such as reduced specimen photo-
damage, enhanced penetration depth and high spatial resolution
in three dimensions and has made possible the development of
three-dimensional fluorescence imaging and photodynamic ther-
apy [1–7], 3D microfabrication [8,9], optical data storage [10,11]
and optical limiting [12]. In fact, these applications are limited
Linear absorption spectra
The photophysical properties for all dyes were summarized in
Table 1. The linear absorption spectra were measured in different
solvents such as Benzene, CH2Cl2, Benzyl alcohol and DMF
(c = 1 Â 10À5 mol LÀ1). From Fig. 1, there is no obvious linear
absorption in the spectral range of 450–800 nm. Moreover, the
absorption spectrum of each dye exhibits two bands, the one cen-
due to the lack of dyes with a large
method.
Over the past twenty years, numerous organic dyes with large
two-photon absorption (TPA) cross-sections and high photochem-
ical quantum yield (U) having a general structure of the types D–
r
value and facile synthetic
tered in the region 298–318 nm due to non-directional
p
–
p
à exci-
tation, and the other centered at 330–380 nm, corresponding to
intramolecular charge transfer (ICT) excitation [30]. The former
band remains relatively constant with the chain extension/donor
change from 1 to 3 compared to the absorption of 4. Whereas
the latter band shows obvious red shift from 1 to 4, which can
be explained by extending the conjugation length via the insertion
of a benzene ring between the two donors such as 2 and 4 com-
pared with 1 and 3, respectively. On the other hand, the absorption
peaks of 3 and 4 (containing phenothiazine group) are red-shifted
about 35 nm relative to those of their analogues of carbazole group
for 1 and 2 because the lone pair electrons of sulfur atom from phe-
p–D, A–p–A, D–p–A (A: an acceptor group, D: a donating group,
and : a conjugating moiety) have been investigated both experi-
p
mentally and theoretically in order to understand their struc-
ture–property relationships. Generally, there are several essential
parameters are required for two-photon dyes [13–20], namely (i)
increasing the strength of the donor and acceptor (ii) changing
the character of the conjugated bridge (iii) increasing the planarity
of the chromophores and (iv) extending length of the mobile
bridge.
p
-
nothiazine delocalize into two benzene rings, which form p–p con-
jugated bond and hence there is some double-bond character in
the bonds of the molecule, resulting in red-shift. In other words
it suggested that electron-donating abilities of phenothiazine
group is stronger than that of carbazole group. The results seem
similar to those of the reported molecules [31]. Furthermore, the
absorption bands of the four dyes show no specific solvatochro-
mism, indicating that the surrounding solvent molecules have little
Although great progresses in the study of these materials have
been made, more and further investigations are still needed. In or-
der to systematically increase the two-photon cross section and
tune the position of the two-photon absorption peak, the design
of new materials must combine improved two-photon absorption
with other molecular properties, such as high fluorescence quan-
tum yield, efficient intersystem crossing, and low oxidation poten-
tial, which make them suitable for the given applications. Our
group has made great efforts to develop a series of two-photon ac-
tive dyes bearing heteroaromatic-based derivatives [21–24].
Carbazole and phenothiazine commercial available are well-
known heterocyclic dyes with electron-rich nitrogen or sulfur het-
eroatoms, exhibiting good optical properties [25–28]. Based on
molecular designing consideration, the carbazolyl and phenothiaz-
inyl were introduced to the target molecules as electron donors
and styrene or biphenylethyne as the conjugated chain (Scheme 1
is placed in supporting information). Herein, we designed and
synthesized four novel heteroaromatic-based TPA dyes with
influence on the
Table 1).
p
–pà transition energy of the dye molecules (see
Single-photon excited fluorescence (SPEF) and quantum yield
One-photon excited fluorescence (SPEF) spectra were measured
at the same concentration as those of the linear absorption spectra
and the maxima wavelength display in the blue–green spectra
range (seen Table 1). From Fig. 2, one can see that under identical
experimental conditions, SPEF spectra showed a similar trend with
the linear absorption spectra. The spectra of 1–4 exhibit a large
red-shifted with changing conjugation length/donor group (D). As
dumbbell-shape (D–p–D) by solvent-free Wittig reaction, and
investigated the influence of donors (phenothiazine or carbazole)
and the conjugated frame on TPA properties, The results reveal that
compared with extending conjugated chain, enhancing electron-
donating ability play a major role in enlarging two-photon absorp-
tion cross-sections (r) and those four dyes exhibit highly efficient
two-photon initiated polymerization abilities.
Table 1
Photophysical data of four target dyes in different solvents.
ka
U c
sd
SPEF,b
max
TPEF,e
k
max
Molecule
1
Solvent
max
k
Benzene
CH2Cl2
Benzyl alcohol
DMF
298, 332
299, 329
300, 331
299, 330
394
396
401
397
0.74
0.72
0.63
0.75
3.22
2.55
2.31
2.59
417
410
419
2
3
4
Benzene
CH2Cl2
Benzyl alcohol
DMF
300, 343
302, 341
302, 345
300, 343
426
430
432
423
0.75
0.65
0.61
0.73
0.80
0.58
0.76
0.78
Experimental
436
421
441
Materials and methods
Benzene
CH2Cl2
Benzyl alcohol
DMF
298, 357
300, 358
298, 361
298, 362
475
502
500
506
0.63
0.64
0.52
0.66
3.48
4.85
5.29
5.34
498
438
505
All materials and methods in the article have been shown in the
supporting information.
Benzene
CH2Cl2
Benzyl alcohol
DMF
316, 376
318, 377
315, 381
318, 380
496
514
516
519
0.58
0.56
0.47
0.61
3.06
4.43
4.59
4.47
520
525
537
Synthesis
The synthetic route and general procedure are were placed in
the supporting information, respectively. Four target dyes 1–4
were synthesized by solvent-free Witting reaction. The intermedi-
ates a–d were synthesized with reference to the reported methods
[29].
a
b
c
kmax of the absorption spectra in nm.
kmax of the one-photon fluorescence spectra in nm.
Fluorescence quantum yield.
The lifetime of one-photon fluorescence in ns.
kmax of the two-photon fluorescence spectra in nm.
d
e

540
F. Hao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 538–542
nor or phenyl type bridge are longer relative to those of carbazole
donor or diphenylethyl bridge because the rotation of C–C in the
diphenylethylenes bridge leads to an easier transformation to
non-radiation ‘‘TICT’’ state.
Two-photon excited fluorescence
As shown in Fig. 1, there is no linear absorption in the wave-
length range of 450–800 nm for the four dyes, which indicate that
there are no energy levels corresponding to an electron transition
in this spectral range. If frequency up-converted fluorescence ap-
pears upon excitation with laser in this range, it should be safely
attributed to multi-photon absorption mechanism. As shown in
Fig. 3 (inset figure), the fluorescence intensity has a square depen-
dence on the input laser intensity for 1. This gives direct experi-
mental evidence of a two-photon excitation mechanism for the
four dyes due to their similar structures.
While the concentrated solution of the dyes (c = 1 Â 10À3
mol LÀ1) were excited by the femtosecond laser beam at 760 nm,
the two-photon excited fluorescence of all dyes can be observed
and detected in three different solvents (see Table 1). Fig. 3 shows
the TPEF of 1–4 in DMF. From Table 1 and Fig. 3, One finds that
there are similar vibronic structures in the TPEF and SPEF spectra
of the four dyes. The positions of the TPEF peaks are about 20 nm
red-shifted compared with their corresponding SPEF peaks, which
is attributed to large re-absorption effects of the sample solution in
high concentration [35]. In addition, with the increase of solvent
polarity, the peaks were slightly red-shifted. The TPEF peak posi-
tion are also independent of the laser wavelength used. Although
the electrons can be pumped to the different excited states by lin-
ear absorption (g ? u) or TPA (g ? g) owing to different selection
rules for the centrosymmetric structures, both SPEF and TPEF emis-
sion processes, with only one photon involved, should abide by the
same rule (u ? g) between TPEF and SPEF, though their initial
Frank–Condon states may be different [36].
Fig. 1. Linear absorption spectra of 1–4 in DMF with c = 1.0 Â 10À5 mol LÀ1
.
Two-photon absorption (TPA) cross-section
The open-aperture spectra of 1 and 4 are shown in Figs. 4 and 5,
Fig. 2. Single-photon-excited fluorescence spectra of 1–4 in DMF with
c = 1.0 Â 105 mol LÀ1
.
respectively. Table 2 gives b,
r
data. The TPA cross-sections (
r
) for
val-
1–4 are 4660, 6520, 8700 and 10,870 GM, respectively. The
r
ues of diphenylethyl dyes type (2 and 4) are larger than those of
phenyl analogues (1 and 3) due to the increase of mobile -bridge
length. Similarly, the values of 3 and 4 are larger than those of 1
summarized in Table 1, it is obvious that there is only marginally
solvatochromism for 1 and 2, belonging to intermediate quadrupo-
lar character (class II) (10 nm excursion in a wide range of solvent
polarities). This reveals that solvation effects are not able to break
the symmetry of the system. Whereas, dyes 3 and 4 show strong
fluorescence solvatochromism in slightly polar solvents, while
the absorption spectra are almost independent of the solvent
polarity, belonging to class I, because of coupling between elec-
tronic and vibrational degree of freedom in the delocalized elec-
trons. [32,33].
p
r
The change of solvent polarity influences not only the emission
energy but also the fluorescence quantum yield as well as the fluo-
rescence lifetimes (Table 1): (1) All the dyes show relatively high
SPEF quantum yields, which makes them interesting for applica-
tion in imaging techniques based on the detection of fluorescence.
(2) Quantum yields of the dyes with phenothiazine group or conju-
gation chain of diphenyl bridge are much less than corresponding
carbazole group or phenyl bridge due to TICT (Twisted Intramolec-
ular Charge Transfer.) (3) Quantum yields in benzyl alcohol solu-
tion are the lowest for all the studied dyes. This phenomenon
may be derived from the effect of hydrogen bonds between the
H atom of hydroxyl group in benzyl alcohol and the N or S atom
from phenothiazin or carbazole group in the excited-state besides
TICT [34] (4) The fluorescence lifetimes of the phenothiazinyl do-
Fig. 3. Two-photon-excited fluorescence spectra of 1–4 in DMF with
c = 1.0 Â 10À3 mol LÀ1. The inset shows the linear squared dependence of Log IF
on Log Iin of compound 1 versus excitation wavelengths of 760 nm.

F. Hao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 538–542
541
and 0.5% dyes (1–4) as an initiator and a little 1, 2-dichloroethane
(increasing the compatibility and controlling the viscosity). The la-
ser was tightly focused via an objective lens (50 Â NA = 0.45), and
the focal point was modulated in the gel resin that was on a xyz-
step monitorized stage controlled by computer. The polymeriza-
tion results were observed with a polarization microscope (Opton,
Germany) and the photographs of microstructures (see Fig. S1 in
the supporting information) using 4 as the initiator. It shows a
1.0 mm  1.0 mm polymerization region with a six layer stereo
structure. The distance of every two neighboring polymerization
1.1
1.0
0.9
0.8
0.7
streaks is 10.0 lm. The polymerization reaction did not take place
in the part out of the laser focus, where could be easily washed out
by tetrahydrofuran.
14
I0 = 6.88*10 W / m2
β = 1.5*10-12 m / W
At present, the mechanism of two-photon initiated photopoly-
merization is still unclear. According to the previous work by Mar-
der et al. [38], strong donor substituents would make the
conjugation system electron rich, and after single or two-photon
excitation, these dyes would transfer an electron to relatively weak
acceptors, and this process could be to some chemical reactions,
such as free radical polymerization. As mentioned above, 1–4 pos-
sessed relatively high electron density due to the extending conju-
gation system in molecules and the stronger electron-donating
ability of the carbazole and phenothiazine. Therefore, the initiators
1–4 possess very rich electrons, which benefit for charge transfer at
the excited state. So they can effectively initiate two-photon
polymerization.
-30
-20
-10
0
10
20
30
40
Z (mm)
Fig. 4. Open-aperture Z-scan profile for 1 in DMF with c = 1.0 Â 10À3 mol LÀ1
.
Excitation carried out at 760 nm.
1.1
1.0
0.9
0.8
Conclusions
In conclusion, we have successfully synthesized a series of
dumbbell shaped bis phenothiazines/carbazoles bridged by
diphenylethyl and phenyl derivatives with large two-photon
14
2
0.7
0.6
I0 = 6.61*10 W / m
absorption cross section (r). The r values increase gradually in
β = 3.5*10-12 m / W
the order 1 < 2 < 3 < 4, reaching a maximum value of 10,870 GM
for 4. Although donor substitution and conjugated chain can
greatly affect on the one and two-photon properties of the dyes,
donor substitution have larger contribution to the
r values than
-30
-20
-10
0
10
20
30
extending conjugated chain length based on the comparison of
small molecules. Therefore, to avoid large amounts of synthesis,
the findings revealed that strong donor substitution should be se-
lected, which provides a new idea and pathway to design and syn-
thesize novel two-photon fluorescence materials. In addition, all
dyes can be used for two-photon polymerization and possess po-
tential applications due to simple preparation.
Z (mm)
Fig. 5. Open-aperture Z-scan profile for 4 in DMF with c = 1.0 Â 10À3 mol LÀ1
.
Excitation carried out at 760 nm.
Table 2
Fitted b,
r
data for dyes 1–4 in DMF.
1
2
3
4
Acknowledgements
b (cm/GW)
(GM)
0.15
4660
0.21
6520
0.28
8700
0.35
10,870
r
This work was supported by the National Natural Science Foun-
dation of China (21271004, 21071001, 21271003, 21275006 and
20875001), the Natural Science Foundation of Anhui Province
(1208085MB22), Education Committee of Anhui Province
(KJ2013B205, KJ2013B204), Focus on returned overseas scholar of
Ministry of Education of China, Program for New Century Excellent
Talents in University (China), Doctoral Program Foundation of Min-
istry of Education of China (20113401110004).
b is the TPA coefficient (cm/GW) and
r is the TPA cross-section (GM).
and 2, respectively, which further prove that electron-donating
ability of phenothiazine is larger than that of carbazole group.
Interestingly, the
that of 1 and 3, respectively [37]. Thus, a conclusion was drawn
that the effect of electron donor has larger contribution to the
values than that of extending conjugated chain length.
r values of 3 and 4 are nearly twice as much as
r
Appendix A. Supplementary materiel
Two-photon initiating polymerization microfabrication (TPIP)
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.09.051.
Taking into account of the TPA cross-section, TPIP was finished
with the same mode-locked Ti: sapphire laser that was used in the
TPEF measurements with 760 nm, 200 fs lasing source, and 20 mW
average power. Three-dimensional crosslinked woodpile periodic
microstructures were fabricated with negative resins system,
which contained oligomer (bisphenyl A epoxide dimethylacrylate)
References
[1] W. Denk, J.H. Strickler, W.W. Webb, Science 248 (1990) 73–76.
[2] M. Velusamy, J.Y. Shen, J.T. Lin, Y.C. Lin, C.C. Hsieh, C.H. Lai, C.W. Lai, M.L. Ho,
Y.C. Chen, P.T. Chou, J.K. Hsiao, Adv. Funct. Mater. 19 (2009) 2388–2397.

542
F. Hao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 538–542
[3] J.H. Lee, C.S. Lim, Y.S. Tian, J.H. Han, B.R. Cho, J. Am. Chem. Soc. 132 (2010)
1216–1217.
[20] T.C. Lin, Y.H. Lee, C.Y. Liu, B.R. Huang, M.Y. Tsai, Y.J. Huang, J.H. Lin, Y.K. Shen,
C.Y. Wu, Chem. Eur. J. 19 (2013) 749–760.
[4] X.H. Wang, D.M. Nguyen, C.O. Yanez, L. Rodriguez, H.Y. Ahn, M.V. Bondar, K.D.
Belfield, J. Am. Chem. Soc. 132 (2010) 12237–12239.
[5] N.G. Horton, K. Wang, D. Kobat, C.G. Clark, F.W. Wise, C.B. Schaffer, C. Xu Nat,
Photonics 7 (2013) 205–209.
[6] C. Cepraga, T. Gallavardin, S. Marotte, P.-H. Lanoe, J.-C. Mulatier, F. Lerouge, S.
Parola, M. Lindgren, P.L. Baldeck, J. Marvel, O. Maury, C. Monnereau, A. Favier,
C. Andraud, Y. Leverrier, M.-T. Charreyre, Polym. Chem. 4 (2013) 61–67.
[7] W.R. Zipfel, R.M. Williams, W.W. Webb, Nat. Biotechnol. 21 (2003) 1369–1377.
[8] K.S. Lee, R.H. Kim, D.Y. Yang, S.H. Park, Prog. Polym. Sci. 33 (2008) 631–681.
[9] B. Tan, K. Venkatakrishnan, A. Makaronets, Des. Monomers Polym. 16 (2013)
145–150.
[21] Y.P. Tian, M.L. Zhang, X.Q. Yu, G.B. Xu, Y. Ren, J.X. Yang, J.Y. Wu, X.J. Zhang, X.T.
Tao, S.Y. Zhang, M.H. Jiang, Chem. Phys. Lett. 388 (2004) 325–329.
[22] D.M. Li, R.T. Hu, W. Zhou, P.P. Sun, Y.H. Kan, Y.P. Tian, H.P. Zhou, J.Y. Wu, X.T.
Tao, M.H. Jiang, Eur. J. Inorg. Chem. 2009 (2009) 2664–2672.
[23] L. Kong, J.X. Yang, X.P. Hao, H.P. Zhou, J.Y. Wu, F.Y. Hao, L. Li, S.Y. Zhang, B.K. Jin,
X.T. Tao, M.H. Jiang, Y.P. Tian, J. Mater. Chem. 20 (2010) 7372–7377.
[24] H.P. Zhou, X.P. Gan, X.L. Li, Z.D. Liu, W.Q. Geng, F.X. Zhou, W.Z. Ke, P. Wang, L.
Kong, F.Y. Hao, J.Y. Wu, Y.P. Tian, Cryst. Growth Des. 10 (2010) 1767–1776.
[25] H. Hoegl, J. Phys. Chem. 69 (1965) 755–766.
[26] Y.N. Li, J.F. Ding, M. Day, Y. Tao, J.P. Lu, M. Diorio, Chem. Mater. 16 (2004)
2165–2173.
[10] A.S. Dvornikov, E.P. Walker, P.M. Rentzepis, J. Phys. Chem. A 113 (2009)
13633–13644.
[27] T. Okamoto, M. Kuratsu, M. Kozaki, K. Hirotsu, A. Ichimura, T. Matsushita, K.
Okada, Org. Lett. 6 (2004) 3493–3496.
[11] K. Iliopoulos, O. Krupka, D. Gindre, M. Sallé, J. Am. Chem. Soc. 132 (2010)
14343–14345.
[28] C.S. Krämer, T.J.J. Müller, Eur. J. Org. Chem. 18 (2003) 3534–3548.
[29] H. Bredereck, G. Simchen, W. Griebenow, Chem. Ber. 106 (1973) 3732–3742.
[30] S.A. Jenekhe, L. Lu, M.M. Alam, Macromolecules 34 (2001) 7315–7324.
[31] B.A. Reinhardt, L.L. Brott, S.J. Clarson, A.G. Dillard, J.C. Bhatt, R. Kannan, L. Yuan,
G.S. He, P.N. Prasad, Chem. Mater. 10 (1998) 1863–1874.
[12] P. Chantharasupawong, R. Philip, N.T. Narayanan, P.M. Sudeep, A. Mathkar,
P.M. Ajayan, J. Thomas, J. Phys. Chem. C 116 (2012) 25955–25961.
[13] M. Rumi, J.E. Ehrlich, A.A. Heikal, J.W. Perry, S. Barlow, Z. Hu, D. McCord-
Maughon, T.C. Parker, H. Röckel, S. Thayumanavan, S.R. Marder, D. Beljonne,
J.L. Bredas, J. Am. Chem. Soc. 122 (2000) 9500–9510.
[32] F. Terenziani, A. Painelli, C. Katan, M. Charlot, M. Blanchard-Desce, J. Am.
Chem. Soc. 128 (2006) 15742–15755.
[14] M. Albota, D. Beljonne, J.L. Bredas, J.E. Ehrlich, J.Y. Fu, A.A. Heikal, S.E. Hess, T.
Kogej, M.D. Levin, S.R. Marder, D. McCord-Maughon, J.W. Perry, H. Röckel, M.
Rumi, G. Subramaniam, W.W. Webb, X.L. Wu, C. Xu, Science 281 (1998) 1653–
1656.
[33] Z.Q. Liu, Q. Fang, D.X. Cao, D. Wang, G.B. Xu, Org. Lett. 6 (17) (2004) 2933–
2936.
[34] M. Maus, W. Rettig, D. Bonafoux, R. Lapouyade, J. Phys. Chem. A 103 (1999)
3388–3401.
[15] G.S. He, L.-S. Tan, Q.D. Zheng, P.N. Prasad, Chem. Rev. 108 (2008) 1245–1330.
[16] M.H.V. Werts, S. Gmouh, O. Mongin, T. Pons, M. Blanchard-Desce, J. Am. Chem.
Soc. 126 (2004) 16294–16295.
[17] J.C. Collings, S.-Y. Poon, C.L. Droumaguet, M. Charlot, C. Katan, L.-O. Palsson, A.
Beeby, J.A. Mosely, H.M. Kaiser, D. Kaufmann, W.-Y. Wong, M. Blanchard-
Desce, T.B. Marder, Chem. Eur. J. 15 (2009) 198–208.
[35] F.Y. Hao, X.J. Zhang, Y.P. Tian, H.P. Zhou, L. Li, J.Y. Wu, S.Y. Zhang, J.X. Yang, B.K.
Jin, X.T. Tao, G.Y. Zhou, M.H. Jiang, J. Mater. Chem. 19 (2009) 9163–9169.
[36] L.Z. Wu, X.J. Tang, M.H. Jiang, C.H. Tung, Chem. Phys. Lett. 315 (1999) 379–382.
[37] O.K. Kim, K.S. Lee, H.Y. Woo, K.S. Kim, G.S. He, J. Swiatkiewicz, P.N. Prasad,
Chem. Mater. 12 (2000) 284–286.
[38] B.H. Cumpston, S.P. Ananthaval, S. Barlow, D.L. Dyer, J.E. Ehrlich, L.L. Erskine,
A.A. Heikal, S.M. Kuebler, I.Y.S. Lee, D. McCord-Maughon, J. Qin, H. Röckel, M.
Rumi, X.L. Wu, S.R. Marder, J.W. Perry, Nature 398 (1999) 51–54.
[18] Y.M. Poronik, V. Hugues, M. Blanchard-Desce, D.T. Gryko, Chem. Eur. J. 18
(2012) 9258–9266.
[19] D. Firmansyah, A.I. Ciuciu, V. Hugues, M. Blanchard-Desce, L. Flamigni, D.T.
Gryko, Chem. Asian J. 8 (2013) 1279–1294.