Self-assembled organic microfibers for nonlinear optics

Article abstract of DOI:10.1002/adma.201204237

While highly desired in integrated optical circuits, multiresponsive and tunable nonlinear optical (NLO) active 1D (sub)wavelength scale superstructures from organic materials are rarely reported due to the strong tendency of organic molecules to self-assembly in centrosymmetric modes. Here a solution-processed assembly approach is reported to generate non-centrosymmetric single-crystalline organic microfibers with a cumulative dipole moment for anisotropic combined second- and third-order NLO. Copyright

Full text of DOI:10.1002/adma.201204237

www.advmat.de
www.MaterialsViews.com
Self-Assembled Organic Microfibers for Nonlinear Optics
Jialiang Xu, Sergey Semin, Dorota Niedzialek, Paul H. J. Kouwer, Eduard Fron,
Eduardo Coutino, Matteo Savoini, Yuliang Li,* Johan Hofkens, Hiroshi Uji-I,
David Beljonne, Theo Rasing,* and Alan E. Rowan*
For the next generation of integrated optical circuits
one-dimensional (1D) multiresponsive materials with tunable
nonlinear optical (NLO) properties are highly desired.[1] While
inorganic NLO active micro-/nanofibers have been developed
as photonic components,[2] there are few examples of organic
1D assemblies with strong NLO properties,[3] despite their
intrinsic advantages of ease of assembly and clear structure-
property correlations. One of the most commonly applied
NLO effects is second harmonic generation (SHG), in which
two incident photons combine to generate a photon with dou-
bled frequency and thus doubled energy.[4] It commonly occurs
when an intense laser beam interacts with a medium with a
high second-order susceptibility.[5] For organic materials this
is achieved by a high molecular hyperpolarizability (strongly
dipolar conjugated donor-acceptor, D-A type molecules), com-
bined with a non-centrosymmetric organization.[6] Another
independent NLO process is two-photon excitation fluorescence
(TPF). It is a third-order NLO process, in which two photons
are absorbed simultaneously to generate an excited state fol-
lowed by fluorescence processes.[4,7] Typical molecules that
display a high two-photon absorption cross section have strong
quadrupoles or octupoles (D-A-D, A-D-A, or more-complex D-A-
substituted molecular systems).[8]
The main impediment for the development of large libraries of
materials for SHG from these ICT compounds is the require-
ment of the NLO chromophores to be arranged non-centro-
symmetrically.[11] Approaches such as macromolecular scaf-
folding,[12] fi eld-assisted poled-polymer alignment,[13] controlled
Langmuir–Blodgett techniques,[14] and modern crystal engi-
neering[15] have all been developed to induce macroscopic non-
centrosymmetry. Some of these strategies, however, generate
materials that show poor photon propagation or coupling in
integrated optical circuits, for which sub-wavelength 1D crystal-
line architectures are more suitable.[16] Rubahn and co-workers
successfully fabricated the first organic nanofiber frequency
doublers from p-hexaphenylene (p6P) and other functionalized
oligo-p-phenylenes.[3a,3c,17] These nanofibers were produced in
a sophisticated high-vacuum growth procedure on a muscovite
mica substrate and the nanofibers were required to be carefully
transferred for optical examinations. Much simpler solution-
based processing techniques would be strongly favored, but
unfortunately such examples are rare.[3b,18]
We previously reported that fluorene bridged ICT compounds
are able to self-assemble via simple solution-processing steps
into 1D microfibers with interesting optical properties.[9b,19] In
this work, we report the self-assembly of a new V-shaped flu-
orenone based ICT compound 2,7-diphenyl-9H-fluoren-9-one
(DPFO) into a unique non-centrosymmetric microfiber struc-
ture with a permanent dipole along the fiber’s long axis and a
transition dipole perpendicular to it. We show that the micro-
fibers display two independent NLO responses of SHG and
TPF, and we demonstrate that we are able to separate both NLO
effects spectroscopically and spatially. The easy processability,
perfect crystalline microfiber structure, and intrinsic highly
efficient NLO effects of the microfibers offer great opportuni-
ties for applications in photonic devices.
The target compound DPFO was synthesized by a Suzuki
coupling reaction between phenylboronic acid and 2,7-diiodo-
9H-fluoren-9-one[19] (see Experimental Section for details and
Supporting Information, Scheme S1). High-quality bulk single
crystals of DPFO were readily fabricated by slowly evaporating
a saturated CHCl3 solution at room temperature (Supporting
Information, Figure S1). Single-crystal X-ray diffraction (XRD)
analysis showed that the V-shaped DPFO molecules are organ-
ized in a non-centrosymmetric orthorhombic Ccm21 space
group (Supporting Information, Figure S2) with the two side
phenyl planes twisted from the fluorenone plane by 36.4° both
in the same direction (Supporting Information, Figure S3). The
C؍O···H hydrogen bonds[20] drive the formation of molecular
chains along the c-axis (Figure 1A), and aromatic C؊H···π
interactions[21] attach these hydrogen-bonded molecular
Organic intramolecular charge transfer (ICT) compounds,[9]
with intrinsically high hyperpolarizabilities, are widely
employed as second- and/or third-order NLO chromophores.[10]
Dr. J. Xu, Prof. Y. Li
Beijing National Laboratory for
Molecular Sciences (BNLMS)
CAS Key Laboratory of Organic Solids
Institute of Chemistry
Chinese Academy of Sciences
Beijing 100190, P.R. China
E-mail: ylli@iccas.ac.cn
Dr. J. Xu, S. Semin, Dr. P. H. J. Kouwer, Dr. M. Savoini,
Prof. Th. Rasing, Prof. A. E. Rowan
Radboud University Nijmegen
Institute for Molecules and Materials (IMM)
Heyendaalseweg 135, 6525 AJ Nijmegen, the Netherlands
E-mail: th.rasing@science.ru.nl; a.rowan@science.ru.nl
D. Niedzialek, Dr. D. Beljonne
Université Mons-Hainaut
Place du Parc 20, 7000 Mons, Belgium
Dr. E. Fron, E. Coutino, Prof. J. Hofkens, Prof. H. Uji-I
Departement Chemie
Katholieke Universiteit Leuven
Celestijnenlaan 200F, B-3001 Heverlee, Belgium
DOI: 10.1002/adma.201204237
©
2084 wileyonlinelibrary.com
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Mater. 2013, 25, 2084–2089

www.advmat.de
www.MaterialsViews.com
is important for waveguiding) (Supporting
Information, Figure S5). The single-crystal
character of the DPFO fi bers was confirmed
by transmission electron microscopy (TEM)
and the corresponding selected-area elec-
tron diffraction (SAED) patterns, which were
indexed with the bulk-crystal lattice constants
and suggested that the microfibers grow along
the [001] direction (Figure 1D). Powder XRD
of the microfibers revealed that the thin axis
of the microfiber perpendicular to the sub-
strate was the b-axis (Figure 1E). The growth
rates of DPFO molecules which results in
these thin and long microfibers (Figure 1F)
are dominated by the non-convalent interac-
tions between DPFO molecules along the
different crystallographic axes (Supporting
Information, Scheme S2 and Table S2). Since
the long axis of the microfibers is the crystal-
lographic c-axis, and the permanent dipole of
the molecules is also directed along this direc-
tion (Supporting Information, Figure S6),
it is note worthy that the molecular dipoles
coherently contribute to the macroscopic per-
manent dipole moment of the microfiber.[12]
The UV–vis absorption and photolumines-
cence (PL) spectra of DPFO microcrystals are
comparable to those in solution (Figure 2A).
DPFO absorbs at 433 nm in tetrahydrofuran
(THF) and at 425 nm in microfibers sus-
pended in heptane. When excited at 430 nm,
the solution gave PL centered at 537 nm
and the aggregates emitted at 541 nm. The
quantum yield in solution and the solid state
are also similar: 21% in THF and 28% in the
microfibers.
The molecular dipolar structure of DPFO
in combination with its Ccm21 space group
results in its second-order NLO properties.
When probing the NLO properties of the
microfibers by a home-built femtosecond
laser scanning microscope (Supporting
Information, Figure S7,S8), a sharp SHG
band was observed at half the wavelength of
the incident beam and a much broader band
is observed at higher wavelength (Figure 2B).
The broad band is similar to the fluorescence
spectrum, and is attributed to TPF. Whereas
Figure 1. Morphology and molecular packing of DPFO microfibers. A) Hydrogen-bonded DPFO
molecular chains. B) Packed molecular columns along the a-axis, viewed along the b-axis.
C) SEM image of a typical self-assembled DPFO microfiber. Inset: Fluorescent picture. Exci-
tation: 800 nm, at the circled spot. The brighter emission at the end and edges of the fiber
suggests a strong waveguiding behavior. D) TEM image and its corresponding SAED pattern
of a DPFO microfiber (inset). Scale bars in C and D: 10 μm. E) Powder XRD patterns of the
as-prepared microfibers (red) and after grinding into a powder (blue), compared with the simu-
lated pattern (black). F) Schematic representation of a microfiber and the packing modes of the
DPFO molecules in the microfiber. Hydrogen atoms have been omitted for clarity.
chains in the second dimension along the a-axis to form the
2D lamellar structure (Figure 1B and Supporting Information,
Figure S4).
the wavelength of the SHG band depends on the frequency of
the incident laser, the TPF is always centered at 530 nm and
only a variation in the intensity of the peak is observed (Figure
2B and Supporting Information, Figure S9). Power-depend-
ence measurements (Figure 2C) show that the intensity of
both SHG and TPF scale quadratically with the power of the
input laser, which confirms the two-photon origin of both NLO
processes.[22]
Yellow DPFO microcrystals were fabricated by cooling a
refluxing saturated DPFO solution in heptane to room tempera-
ture. Scanning electron microscope (SEM) studies revealed the
crystal’s 1D microfiber morphology, with widths ranging from
several to tens of micrometers and lengths up to several mil-
limeters (Figure 1C). Atomic force microscopy (AFM) imaging
showed that these fibers were very thin in the third dimen-
sion (usually hundreds of nanometers) and flat ( 5 nm, which
The NLO processes in the single microcrystal are expected
to be strongly polarization-dependent due to its well-oriented
dipole moments.[23] The SHG is related to the permanent
©
wileyonlinelibrary.com
Adv. Mater. 2013, 25, 2084–2089
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2085

www.advmat.de
www.MaterialsViews.com
Figure 2. Linear and nonlinear optical responses of DPFO. A) UV–vis absorption (left) and PL (right) spectra of DPFO in solution and in the aggregation
state. B) Spectra collected from a fixed spot of a microfiber when pumped at different wavelengths, normalized by the power of the input laser. For clarity,
only spectra excited by wavelength between 780–940 nm with an interval of 20 nm are shown. C) Logarithmic plots of the power dependence of SHG and
TPF. Inset: Corresponding spectra. Laser pump: 800 nm, 100 fs, 82 MHz, p-polarized. Incidence and detection angles are 45° from the surface normal.
Figure 3. Polarization dependence examined by scanning SHG and TPF respectively from two crossing microfibers. A) Detecting SHG (at 360 nm) with
s-polarized excitation. B) Detecting SHG with p-polarized excitation. C) Detecting TPF (at 530 nm) with s-polarized excitation. D) Spectra taken from a fixed
spot of the horizontal fiber as a function of polarization angle θ (defined as the angle of the polarizer rotated from p-polarization clockwise, shown in the
inset). The distances of both axes in A–C are in micrometers. Pump: 720 nm. Incidence and detection angles are both 45° from the surface normal.
©
2086 wileyonlinelibrary.com
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Mater. 2013, 25, 2084–2089

www.advmat.de
www.MaterialsViews.com
and the change of the permanent dipole
(Δμ) along the long fiber axis (the c-axis,
Supporting Information, Scheme S3C and
Figure S6). Figure 3A shows a scanned
map of the signal at 360 nm of two crossing
microfibers (excited by an s-polarized 720 nm
pump beam). Clearly, perpendicularly ori-
ented fiber B which is nearly parallel to the
incident polarization direction radiates more
strongly than fiber A. Swapping to p-polari-
zation reverses the intensity profiles of the
fibers (Figure 3B and Supporting Informa-
tion, Figure S10). TPF however, which is
associated with μge of the molecules in the
crystals,[26] is not pronouncedly polarized
(Figure 3C,D).
To further determine the effects of μge and
Δμ on the two NLO processes, quantitative
polarization dependence of both SHG and
TPF process have been determined by stud-
ying the signal at 400 and 530 nm, respec-
tively, as a function of the polarization angle
of the incident beam. The signal was recorded
on a single microfiber along all three crystallo-
graphic axes in reflection (along the b-axis) or
transmission (along the a- and c-axes) geom-
etry. The data is summarized in Figure 4. Exci-
tation perpendicular to the substrate, along
the b-axis (Figure 4A) shows a well-polarized
SHG signal. The excitation beam is perpen-
dicular to the permanent dipole, which is
expected to maximize the polarization ratio
ρ = (Imax − Imin)/(Imax + Imin). Calculation of ρ,
in fact, gives a value of virtually unity, which
is higher than any reported organic crystal[17]
and even higher than inorganic nanowires.[27]
Excitation along the b-axis, which is parallel to
μge of the molecules in the microfiber, results
in a small isotropic TPF response, which is in
agreement with our computational analysis
as discussed previously (Supporting Informa-
tion, Scheme S3). The microfiber was also
excited parallel to the substrate, detected in
a transmission mode. SHG after excitation
along the c-axis (Figure 4B) was measured and
found to also give a high polarization ratio of
0.997 0.02. With the excitation parallel to Δμ
of the molecules in this geometry, the polari-
zation dependence originate solely from the
Figure 4. Schematic representation of the reflection or transmission geometries (left), and
their corresponding angular dependence of SHG and TPF intensity on the excitation polariza-
tion examined along the crystallographic axes (right). The insets represent the orientation of
DPFO molecule, and its corresponding transition dipole (μge, double-headed arrows) and state
dipole change (Δμ, single-headed arrows). Laser pump: 800 nm, 16 mW. A) Reflection geom-
etry along the b-axis. A reflection geometry is used because the substrate and the sample holder
are not transparent for a transmission detecting geometry along the b-axis. In this geometry,
the p-polarization is parallel to Δμ, and μge is not affected by the polarization. B) Transmission
geometry along the c-axis. The p-polarization is parallel to μge, and Δμ is not involved. C) Trans-
mission geometry along the a-axis. The polarization rotates from p-polarization (parallel to μge)
to s-polarization (parallel to Δμ). The reflection geometry along b-axis was realized by adjusting
both incidence and detection angles at 0° from the surface normal, while the transmission
geometries along a- or c-axis have both angles of 90° (Supporting Information, Figure S8).
μ
ge in the molecules.[28] TPF also shows a clear
polarization dependence with a maximum in
the emission when the polarization direction is parallel to μge
and a ρ = 0.67 0.04. A polarization ratio, ρ = 0.34 0.04 was
observed for TPF when the pump beam was parallel to the a-axis
(Figure 4C). The beam in this case is perpendicular to both Δμ
and μge, and consequently the SHG signal shows a quadrupolar
pattern with maxima in respect to both dipoles.[29]
dipole moment difference between the ground and excited
states (Δμ = μe − μg) and the transition dipole (μge).[24] INDO[25]
/
SCI excited-state calculations indicate that the lowest opti-
cally allowed excitation involves mainly (89%) the electronic
transition from HOMO to LUMO (Supporting Information,
Scheme S3A) and is calculated at about 3.4 eV (368 nm) with
the transition dipole (μge) oriented along the molecule (the
crystallographic b-axis; Supporting Information, Scheme S3B),
To spatially separate the two NLO signals their difference in
propagation behaviour was exploited. A microfiber was excited
©
wileyonlinelibrary.com
Adv. Mater. 2013, 25, 2084–2089
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2087

www.advmat.de
www.MaterialsViews.com
The reaction mixture was refluxed overnight. After
cooling and removing most of the solvent in
vacuum, the mixture was dissolved in 300 mL of
CH2Cl2, the organic phase was washed with water
(50 mL × 3) and dried over Na2SO4. The crude
product was purified by column chromatography
(silica gel, petroleum ether: dichloromethane =
5:1) to give 260 mg of yellow needle-like crystals
with a yield of 78%. Rf = 0.4 (petroleum ether:
dichloromethane = 3:1). Mp 235.3 °C. 1H NMR
(400 MHz, CDCl3, δ): 7.39 (t, J = 7.2 Hz, 2H, Ar H),
7.47 (t, J = 7.2 Hz, 4H, Ar H), 7.62 (t, J = 8.0 Hz,
6H, Ar H), 7.74 (d, J = 8.0 Hz, 2H, Ar H), 7.93 (m,
2H, Ar H). 13C NMR (100 MHz, CDCl3, δ): 120.84,
123.21, 124.57, 126.96, 128.10, 129.12, 133.36,
133.48, 135.39, 140.00, 142.40, 143.24 (C = O).
MS (EI m/z) [M+] calcd for C25H16O: 332.1, found
332.2. Elemental analysis calcd (%) for C25H16O: C
Figure 5. Waveguiding behaviours of SHG and TPF. (A) Microscopy image of a DPFO micro-
fiber excited in the middle spot; excitation: 800 nm; substrate: MgF2; scale bars: 5 μm. (B) Cor-
responding spectra of the excitation spot (blue circled) and outcoupled spot (green circled).
under a vertical reflection incidence and detection geom-
etry (Figure 4A), and the signals at the excitation spot and at
the edges of the microfiber were detected. When pumped at
800 nm, a bright blue spot appeared at the excitation location
of the fiber, while the green TPF propagated to the edges of
the microfiber (Figure 5A). Spectra taken from the excitation
spot of the microfiber showed exclusively SHG; in contrast, the
spectra taken from the guided spot at the edge of the microfiber
gave mostly TPF signal (Figure 5B). The non-propagation of the
SHG is a direct consequence of its highly directional property
(conservation of the wave vector makes it reflect on the sub-
strate). The TPF signal, however, easily propagates to the edges
of the microfiber, showing that the microfiber acts a waveguide
for this emitted light. Combining the polarization dependence
with the difference in wave guiding behaviour as described
above, allows us to tune the intensity at both separated emis-
sion sites as a function of polarization angle.
In conclusion, the DPFO crystalline microfiber described
above combines strong NLO of SHG and TPF. Both effects are
correlated to the molecular organization in the crystal where
both the permanent dipole difference, and in particular, the
transition dipole play principle roles. The observed properties
highlight the importance of the orientations of the dipoles as
essential design parameters in future organic NLO materials.
The (relative) intensity of both processes can be readily tuned
by changing the polarization and incidence angle of the light.
The observed extremely high polarization ratio, unusual for
organic materials, makes this material ideal for logic devices.
Moreover, the SHG and TPF signals can be separated macro-
scopically by utilizing their different waveguiding behaviours.
Combining polarization and waveguiding effects, allows us to
up-convert to different frequencies, at different locations, in
the same sample. We can tune the intensity of either independ-
ently. The facile processing conditions of DPFO microfibers
allow the easy transformation of these materials into actual
optical devices.
90.33, H 4.85; Found: C 90.38, H 4.79.
Preparation of DPFO Microfibers: DPFO powder (10 mg) was mixed
with heptane (25 mL) and heated to reflux to make the saturated
solution. Upon slowly cooling (2 °C/min) to room temperature (r.t.,
25 °C) and stabilization at r.t. overnight, the compound precipitated as
microfibers. The shape and size of the microfibers can be easily tuned by
changing the concentration of the refluxing solution, and the cooling rate.
For microscopy and spectroscopy studies, the as-prepared microfibers
are transferred onto substrates (silicon, glass, etc), by simply drop-
casting the free-standing microfiber suspensions. Before the solvent was
evaporated, the microfibers are still movable, and two microfibers can be
manually moved to cross each other under the microscope to serve as
examination objects.
Set-up for NLO Examination: A home-built set-up was used for the
investigation of the NLO properties of DPFO (Supporting Information,
Figure S7). A femtosecond laser (Spectra physics Mai Tai), with a pulse
width of 100 fs and a repetition rate of 82 MHz was used as the pump,
with excitation wavelength tunable from 700 nm to 990 nm. The laser
radiation was focused by a lens (with a working distance of 3 cm and
a gradient index of refraction) into a spot with a diameter of about
6 µm at a certain angle of incidence (tunable from 0–90° from the
normal of surface), allowing the investigation of a particular position of
the microfibers. Samples were mounted on an automatic XY-scanning
table. The signal generated from the microfibers was led through a fiber
waveguide to a monochromator (Princeton instruments). The CCD
(charge-coupled device) detector in the monochromator was employed
to register the spectra. Signals were also sent via the monochromator
to a PMT (photomultiplier tube) to register the response at a particular
wavelength. The detecter can be switched between CCD and PMT by
using a flip-mirror inside the monochomator. The entrance of the fiber
waveguide was placed on a rotational arm (with angles of detection
tunable from 0–90° to the normal of surface). The ability to vary the
position of the detection part also allows to investigation of the spatial
distribution of the NLO response from the sample.
CCDC 889616 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Experimental Section
Synthesis of DPFO: Under an nitrogen atmosphere, to a stirred
mixture of phenylboronic acid (244 mg, 2.0 mmol) and 2,7-diiodo-9H-
fluoren-9-one (432 mg, 1 mmol) in THF (20 mL) and K2CO3 solution in
water (6 mL, 2 M) was added PdCl2(dppf)CH2Cl2 (50 mg, 0.06 mmol).
Acknowledgements
Financial support from the National Basic Research 973 Program of
China (2011CB932302) and the National Nature Science Foundation of
©
2088 wileyonlinelibrary.com
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Mater. 2013, 25, 2084–2089

www.advmat.de
www.MaterialsViews.com
China (21031006) (Y.L.L.), The Netherlands Organization for Scientific
Research (NWO) (Th.R., A.E.R.), EC Marie-Curie ITN-SUPERIOR
(P.H.J.K., A.E.R., D.B., J.H.), EC Marie-Curie ITN-HIERACHY (P.H.J.K.,
Th.R., A.E.R.), and VICI (A.E.R.) are acknowledged for this work. D.B.
is an FNRS research fellow. Dr. Jan Smits and Dr. Rene de Gelder
are acknowledged for analyzing the single-crystal and powder XRD.
Dr. Chengliang Wang, Mr. Chuang Zhang, Dr. Yongli Yan, and Prof.
Yongsheng Zhao are acknowledged for the fruitful discussions.
J. Luo, W. Kaminsky, J. B. Benedict, P. J. Reid, A. K. Y. Jen,
L. R. Dalton, B. H. Robinson, J. Am. Chem. Soc. 2005, 127, 2758–2766;
c) Z. a. Li, Y. Liu, H. Kim, J. M. Hales, S.-H. Jang, J. Luo,
T. Baehr-Jones, M. Hochberg, S. R. Marder, J. W. Perry, A. K. Y. Jen,
Adv. Mater. 2012, 24, OP326–OP330.
[11] a) L. R. Dalton, A. W. Harper, R. Ghosn, W. H. Steier, M. Ziari,
H. Fetterman, Y. Shi, R. V. Mustacich, A. K. Y. Jen, K. J. Shea, Chem.
Mater. 1995, 7, 1060–1081; b) D. F. Eaton, Science 1991, 253,
281–287.
[12] M. Kauranen, T. Verbiest, C. Boutton, M. N. Teerenstra, K. Clays,
A. J. Schouten, R. J. M. Nolte, A. Persoons, Science 1995, 270,
966–969.
Received: October 10, 2012
Revised: December 17, 2012
Published online: February 21, 2013
[13] K. D. Singer, J. E. Sohn, S. J. Lalama, Appl. Phys. Lett. 1986, 49,
248–250.
[14] a) G. J. Ashwell, G. Jefferies, D. G. Hamilton, D. E. Lynch,
M. P. S. Roberts, G. S. Bahra, C. R. Brown, Nature 1995, 375,
385–388; b) T. Verbiest, S. V. Elshocht, M. Kauranen, L. Hellemans,
J. Snauwaert, C. Nuckolls, T. J. Katz, A. Persoons, Science 1998, 282,
913–915.
[15] G. R. Desiraju, Angew. Chem. Int. Ed. 1995, 34, 2311–2327.
[16] Y. Yan, Y. S. Zhao, Adv. Funct. Mater. 2012, 22, 1330–1332.
[17] K. Al-Shamery, H.-G. Rubahn, H. Sitter, Organic Nanostructures for
Next Generation Devices, Vol. 101, Springer, Verlag Berlin Heidelberg
2008.
[18] a) G. Rosenman, P. Beker, I. Koren, M. Yevnin, B. Bank-Srour,
E. Mishina, S. Semin, J. Pept. Sci. 2011, 17, 75–87; b) A. Heredia,
I. Bdikin, S. Kopyl, E. Mishina, S. Semin, A. Sigov, K. German,
V. Bystrov, J. Gracio, A. L. Kholkin, J. Phys. D: Appl. Phys. 2010, 43,
462001.
[1] a) D. Cotter, R. J. Manning, K. J. Blow, A. D. Ellis, A. E. Kelly,
D. Nesset, I. D. Phillips, A. J. Poustie, D. C. Rogers, Science 1999,
286, 1523–1528; b) S. D. Smith, Nature 1985, 316, 319–324.
[2] a) R. Yan, D. Gargas, P. Yang, Nat. Photonics 2009, 3, 569–576;
b) M. Cazzanelli, F. Bianco, E. Borga, G. Pucker, M. Ghulinyan,
E. Degoli, E. Luppi, V. Véniard, S. Ossicini, D. Modotto, S. Wabnitz,
R. Pierobon, L. Pavesi, Nat. Mater. 2012, 11, 148–154.
[3] a) J. Brewer, M. Schiek, A. Lützen, K. Al-Shamery, H. G. Rubahn,
Nano. Lett. 2006, 6, 2656–2659; b) C. Zhang, C.-L. Zou, Y. Yan,
R. Hao, F.-W. Sun, Z.-F. Han, Y. S. Zhao, J. Yao, J. Am. Chem. Soc.
2011, 133, 7276–7279; c) K. Pedersen, M. Schiek, J. Rafaelsen,
H.-G. Rubahn, Appl. Phys. B 2009, 96, 821–826.
[4] S. R. Marder, J. E. Sohn, G. D. Stucky, Materials for Nonlinear Optics:
Chemical Perspectives, Vol. 455, American Chemical Society, Boston,
MA, USA, 1991.
[5] J. E. Reeve, H. L. Anderson, K. Clays, Phys. Chem. Chem. Phys. 2010,
12, 13484–13498.
[6] C. Wang, T. Zhang, W. Lin, Chem. Rev. 2011, 112, 1084–1104.
[7] G. S. He, L.-S. Tan, Q. Zheng, P. N. Prasad, Chem. Rev. 2008, 108,
1245–1330.
[8] a) M. Pawlicki, H. A. Collins, R. G. Denning, H. L. Anderson,
Angew. Chem. Int. Ed. 2009, 48, 3244–3266; b) B. R. Cho, K. H. Son,
S. H. Lee, Y.-S. Song, Y.-K. Lee, S.-J. Jeon, J. H. Choi, H. Lee, M. Cho,
J. Am. Chem. Soc. 2001, 123, 10039–10045; c) 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. Brédas, J. Am. Chem. Soc. 2000, 122, 9500–9510.
[19] J. Xu, H. Zheng, H. Liu, C. Zhou, Y. Zhao, Y. Li, Y. Li, J. Phys. Chem.
C 2010, 114, 2925–2931.
[20] G. R. Desiraju, Acc. Chem. Res. 2002, 35, 565–573.
[21] M. Nishio, M. Hirota, Y. Umezawa, The CH-[pi] Interaction: Evidence,
Nature, and Consequences, Wiley, 1998.
[22] C. K. Chen, A. R. B. de Castro, Y. R. Shen, Phys. Rev. Lett. 1981, 46,
145–148.
[23] S. Brasselet, V. Le Floc’h, F. Treussart, J.-F. Roch, J. Zyss,
E. Botzung-Appert, A. Ibanez, Phys. Rev. Lett. 2004, 92, 207401.
[24] a) F. Meyers, S. R. Marder, B. M. Pierce, J. L. Bredas, J. Am. Chem.
Soc. 1994, 116, 10703–10714; b) S. M. LeCours, H.-W. Guan,
S. G. DiMagno, C. H. Wang, M. J. Therien, J. Am. Chem. Soc. 1996,
118, 1497–1503.
[9] a) M. Kivala, F. Diederich, Acc. Chem. Res. 2008, 42, 235–248;
b) J. Xu, L. Wen, W. Zhou, J. Lv, Y. Guo, M. Zhu, H. Liu, Y. Li, L. Jiang,
J. Phys. Chem. C 2009, 113, 5924–5932; c) J. Xu, X. Liu, J. Lv, M. Zhu,
C. Huang, W. Zhou, X. Yin, H. Liu, Y. Li, J. Ye, Langmuir 2008, 24,
4231–4237.
[25] Materials Studio v5.0.0.0, Accelrys Software Inc., San Diego, 2009.
[26] J. Brewer, M. Schiek, H. G. Rubahn, Opt. Commun. 2010, 283,
1514–1518.
[27] J. C. Johnson, H. Yan, R. D. Schaller, P. B. Petersen, P. Yang,
R. J. Saykally, Nano. Lett. 2002, 2, 279–283.
[10] a) M. Albota, D. Beljonne, J.-L. Brédas, 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 1998, 281,
1653–1656; b) Y. Liao, B. E. Eichinger, K. A. Firestone, M. Haller,
[28] R. M. Corn, D. A. Higgins, Chem. Rev. 1994, 94, 107–125.
[29] Note that the absolute values of the radiation intensity in either
direction is dependent on the exact excitation location in the fiber,
where effects such as wave guiding, surface roughness and others
influence their ratio.
©
wileyonlinelibrary.com
Adv. Mater. 2013, 25, 2084–2089
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2089