Published: September 06, 2011

r 2011 American Chemical Society 19598 dx.doi.org/10.1021/jp2063436 | J. Phys. Chem. C 2011, 115, 19598–19605

ARTICLE

pubs.acs.org/JPCC

Highly Oriented J-Aggregates of Bisazomethine Dye on AlignedPoly(tetrafluoroethylene) SurfacesToshihiko Tanaka,*,†,‡,§ Shinya Matsumoto,§ Takashi Kobayashi,‡ Miei Satoh,‡,§ and Tetsuya Aoyama‡

†Tsukuba Research Laboratory, Sumitomo Chemical Co. Ltd., 6 Kitahara, Tsukuba, Ibaraki 300-3294, Japan‡RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan§Department of Environmental Sciences, Faculty of Education and Human Sciences, Yokohama National University, 79-2 Tokiwadai,Hodogaya-ku, Yokohama, Kanagawa 240-8501, Japan

1. INTRODUCTION

Macroscopic orientation of J-aggregates has great significancefor their possible applications. J-aggregates are supramoleculesorganized on low dimensions in nanoscales, thus showing peculiarremarkable optical properties with interesting functions.1 Hence,their orientation should make efficient use of the functions interms of their low dimensions. For instance, the orientation isfavorable for their nonlinear optical devices, for which the aggregatesrecently have attracted much attention because of their large χ(3)

and ultrafast response.2 A high degree of orientation should givethem a significant χ(3) increase with huge optical anisotropy becauseof their peculiar low dimensionality. It is also favorable for theirpossible polariton lasing applications,3 in which the couplingbetween excitons and polaritons should be enhanced by theorientation. Therefore, the high degree of orientation has beenneeded in these interesting fields.

Highly oriented J-aggregates have been uncommon, althoughpioneers have developed a number of aligning methods, suchas vertical spin coating,4 electrospinning,5 anisotropic evapora-tion of solution,6 magnetic fields,7 Langmuir�Blodgett films,8,9

adsorption on single crystal surface,10 and laser microfixation.11

The dichroic ratio (D) in polarized absorption expresses the degreeof orientation there, and according to the best of our knowledge,D values over 20 were reported only for a monolayer of thecyanine J-aggregates ordered by a gypsum crystal surface.8

We report herein highly oriented J-aggregates in solid thinfilms of a bisazomethine dye on aligned poly(tetrafluoroethylene)(PTFE) surfaces. This is also the first report on the oriented

J-aggregates of a bisazomethine dye. Its isotropic film was vacuum-deposited on substrates without PTFE layers, thereby containingtheir J-aggregates.12 By modifying the substrates with alignedPTFE layers, the aggregates are oriented and show remarkableD values up to 25. The oriented growth on aligned PTFE layers isa promising process for preparation of highly ordered films: sincethe seminal report of Wittmann and Smith,13 a large number ofworks have been dedicated to the oriented growth of variousmaterials, including inorganic crystals,13 small molecules,13�16

and polymers.10,17 However, the oriented growth of J-aggregateson the PTFE also have been uncommon. Only a squariumderivative shows its J-band polarized on the aligned PTFE layers,thus showing its D to be ∼2.16

2. EXPERIMENTAL SECTION

Preparation of the Substrate Modified with PTFE. Glassslides and silicon wafers were used as substrates. For electro-absorption (EA) measurements, Al electrodes with a 0.5 mm gapwere deposited on the glass slides. Silicon substrates were used forIR absorptionmeasurement instead of glass. Then an aligned PTFEthin layer was deposited on the substrates by evaporation andrubbing (ER):15 a PTFE film (50 nm thick) was deposited on thesubstrates under vacuum by evaporating PTFE (molecular weight,

Received: July 5, 2011Revised: September 5, 2011

ABSTRACT: Highly oriented J-aggregates have been obtained in solid, thinfilms of a bisazomethine dye on aligned poly(tetrafluoroethylene) (PTFE)surfaces. The aggregates show remarkable optical anisotropy resulting fromtheir high orientational order: the dichroic ratios at their J peaks in polarizedabsorption spectra reach 25. Moreover, this orientation also brings about aremarkable increase in the third-order nonlinear optical susceptibility [χ(3)] ofthe films of over 10 times that of their isotropic films. Major molecules do notform the aggregates, but rather, form crystalline domains where the aggregatesshould be dispersed. Polarized absorption spectra (visible and IR) and X-raydiffraction measurements reveal that the molecules are oriented with theirlong axis parallel to the PTFE chains both in the aggregates and in thecrystalline domains ([2 0 �1] axis ) PTFE chains, (010) plane ) substratesurface). The growth mechanism of the aggregates is discussed on the basis ofboth the morphology observed by atomic force microscopy and the structural affinity between the crystal and the aggregate.

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5000�20000; purchased from Wako Pure Chemical Co., Ltd.).The deposition was monitored by the frequency change of aquartz resonator. After that, the PTFE layer was rubbed at a pres-sure of about 5 kg/cm2 with a cloth sliding in a direction at aconstant speed of 5 mm/s, thereby oriented with its chains parallelto the sliding direction.Deposition of theDyes.Oriented thin films of bisazomethine

dye 1 (Figure 1) were deposited onto the aligned PTFE layers byevaporating the dye in a vacuum at a pressure of∼10�5 Torr witha growth rate of 0.05�0.15 nm/s. The dye was synthesized by theprocedure reported.18 The deposition was monitored by thefrequency change of a quartz resonator.Characterization of thedye films.The polarizedUV�visible

absorption spectra of the dye films on the glass substrates wererecorded on a Cary 5E UV�visible�NIR spectrophotometerequipped with a highly efficient Gran-Thomson polarizer beforethe sample on the optical path. The spectra were obtained atnormal incidence in the transmission mode with polarization bothparallel and perpendicular to the sliding direction separately. Thereference spectrum taken with the PTFE layer on a glasssubstrate for each polarization was subtracted from each samplespectrum during data processing.The polarized IR absorption spectra of the dye films on ER

silicon substrates were recorded on a Nicolet Magna 860 FT-IRspectrometer equipped with a TGS detector. The infrared beamwas polarized using an Al wire grid KRS-5 polarizer. The spectrawere obtained at normal incidence in the transmissionmode withpolarization both parallel and perpendicular to the sliding direc-tion separately. The reference spectrumwas taken with the PTFElayer on a silicon substrate for each polarization. The referencespectrum with each polarization of the silicon substrate was sub-tracted from each sample spectrum during data processing. All IRspectra were taken at 2 cm�1 resolution by collecting 500 inter-ferograms for each spectrum. The spectra of dye powders dis-persed in KBr disks were obtained in the transmission mode atnormal incidence without polarizers.The X-ray diffractions of the films were recorded on a Mac

Science M21X X-ray diffractometer. Source light (Cu Kα) wasmonochromated and collimated using a parabolic multilayermonochromator. For in-plane measurements, the incident angleof the X-ray beam was 0.3� to the substrate surface, and the scat-tering vector was perpendicular to the sliding direction for 2θ scans.The atomic force microscope (AFM) images of the films were

recorded on a Seiko Instruments SPA-400 probe system equippedwith a SiN cantilever employing its tapping mode in air at roomtemperature. The roughness of the substrate is less than 0.4 nm,thus negligible for nanoscale topography.Emission (EM) or excitation (EX) spectra were recorded at

23 �C on a Jobin Yvon-Spex Fluorolog3 spectrofluorometerequipped with two polarizers: one for the EM beam and theother for the EX beam at 550 nm. The EM at an obliqueangle (22.5� from normal to the film surface) was recordedwith the EX at normal incidence: the two polarizing directions

were aligned. The EM and EX spectra were obtained with thealigned direction parallel and perpendicular to the sliding direc-tion, respectively.The EA measurements of the film were carried out according

to the method reported previously.19 The probing light waspolarized parallel to the sliding direction, and a modulatingelectric field was also applied along the direction. The electrodeswere not deposited on the dye film, but instead, they werepredeposited as we mentioned earlier.

3. RESULTS AND DISCUSSION

3.1. J-Aggregates and Orientation of Long Axes. J-aggre-gates were grown in the films. A sharp absorption peak grew inthe region 600�650 nm, increasing the film thickness, as shownin Figure 1a�c. This peak growth behavior is similar to that oftheir isotropic film vacuum-deposited on glass without PTFElayers: some of the authors indicated by the EA technique thatthe sharp peak from the isotropic film is due to Frenkel excitons,12

thereby showing that the sharp peak exactly comes from J-ag-gregates grown in the films.A second peak (∼550 nm) is still significant after the J peak

grows (Figure 2a), thus showing that the aggregates are mixedwith the dye molecules not forming the aggregates, as alsopreviously shown for their isotropic films. Some of us revealed

Figure 1. Molecule of bisazomehine dye 1.

Figure 2. UV�visible polarized absorption spectra of dye 1 orientedfilms on aligned PTFE layers: film thicknesses of (a) 60, (b) 50, (c) 25,(d) 60, (e) 50, and (f) 25 nm. The light polarization is parallel to thealigned PTFE chains in a, b, and c, and it is perpendicular to the chains ind, e, and f.

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that this peak is due to a crystalline phase: an exposure to chloroformvapor causes the decrease in the J peak as well as the increase bothin X-ray diffraction intensities and in the second peak, thuspromoting crystallization from J-aggregates to the crystallinephase.12

Shoulders (∼500 nm) (Figure 2a, b, c, f) also should beassigned to the crystalline phase because it is an intrinsic absorption(such as a vibrating subband for the second peak possibly) of 1molecule: both its isotropic film and its dilute chloroform solu-tion show this shoulder on their spectra.12 Although Figure 2 dshows the shoulder at a shorter wavelength (∼450 nm), it is notclear whether a small amount of another species exists in the film:in the perpendicular polarization, we should be very careful withits baseline, which is sometimes influenced in its absorbance scaleunder 0.1 by the UV absorption tail accompanied by some scat-tering. Even if this shoulder is due to another species, such asDavydov splitting from disordered molecules, its content wouldbe negligible because of the tiny absorbance with respect to thatof the J peak or the second peak.The aggregates are highly oriented with their transition

moments (∼molecular long axis) parallel to the PTFE chains.The J peak has a maximum with the light polarization parallel tothe sliding direction, which is parallel to the PTFE chains. Thedichroic ratio D = A )/A^ (A ) and A^: absorbance for eachpolarization) reaches 25 (at 622 nm), as shown in Figure 1aand d, thus showing that their uniaxial orientational order S =(D � 1)/(D + 2) is 0.89. Moreover, an intrinsic D value for theJ-aggregates should be >25 because the J band proportion of A^is significantly smaller than that of A ): Figure 2d does not show asharp peak at 622 nm. The motional narrowing in the aggregatesshould take place,20 thereby averaging the transition moments ofthe molecules for each aggregate to a smaller distribution. Hence,both the molecular orientation and the motional narrowingaccount for such remarkable optical anisotropy.The peak at 550 nm also has large D values up to 15 (from

Figure 2a, d), thereby showing that the dye molecules not formingthe aggregates are also highly oriented with their molecular longaxes parallel to the PTFE chains. Assuming that the integral of theabsorption peak is proportional to the numbers of its species, wecan estimate that major molecules do not form the aggregates inthe oriented film.The polarized IR spectra also support the axial orientation.

Figure 3b and c show large D values from 9.5 to 40 at the severalpeaks in the region from 1120 to 1609 cm�1: 1120 (D = 22),1142 (D = 23), 1271 (D = 10), 1353 (D = 16), 1439 (D = 25),1516 (D = 40), 1565 (D = 15), and 1609 cm�1 (D = 9.5). Thesepeaks should be combinations of local vibrations along themolecular long axis because there is a lot of local stretchingalong the axis from p-phenylenes, CdC, CdN, and C�N in thisregion.21 The local vibrations along the axis couple to formseveral molecular vibrations parallel to the axis. We can attributethe peak at 1516 cm�1 to the mode of vibration originatingmainly from asymmetric p-phenylene (19a[A1]), according to itsempirical assignment.21

3.2. Planar Orientation. The dye molecules in the film alsohave a planar orientation. The peak at 822 cm�1 on the spectrafor the dye powder (Figure 3a) can be assigned to an out-of-planemode for the p-phenylene moiety (11[B1]) according to its em-pirical assignment.21 The film has a tiny peak at the wavenumberfor both polarization directions, thereby showing that theirphenylene planes are parallel in some extent to the substratesurface (Figure 3b, c). Such planar orientation on aligned PTFE

was also reported for bisazo dyes,15 napthoquinones,22 p-nitro-phenol,23 and 2-methyl-4-nitroaniline.24

These peaks give us an estimate ofmoderate planar orientationaccording to the method reported previously.15 The Æcos2 ϕ0ævalue of 0.3 is calculated from the six intensity values in Figure 3a,b, and c (19a and 11, for each spectrum): in such a high uniaxialorientation, ϕ0 virtually expresses the angle between the substratesurface and the director normal to the phenyl plane for eachmolecule.15 Hence, ϕ0 should be nearly 57� (33� tilted from theperfect planar orientation) if all molecules in the film have thesame ϕ0 value.3.3. Orientation of Crystals. The X-ray diffraction measure-

ments of the films reveal that the crystals of 1 are oriented in thedirection where their [2 0 �1] axes are parallel to the PTFEchains and their (010) planes are parallel to the substrate surface.The structure of a single crystal from 1 was determined by someof the authors previously.25 Figure 4a and b then shows that its(030), (1 �1 2), and (122) planes are observed by the out-of-plane mode and its (102), (122), and (1 �1 2) planes areobserved by the in-plane mode. If we assume the orientation([2 0 �1]||PTFE chains and (010)||substrate, illustrated inFigure 5), its (030) planes should be observed only by the out-of-plane mode, and its (102) plane should be observed only bythe in-plane mode.The degreeof the (010) orientation is not sohigh that the (1�12)

and (122) planes are observed by both modes. Moreover, themolecular plane (phenyl rings) in the crystal are tilted at∼13� tothe (010) plane, as shown in Figure 5b. Hence, the orientationdegree of molecular plane is likewise smaller, thus correspondingwell to the estimate of Æcos2 ϕ0æ = 0.3 from the IR measurement.The crystal of PTFE accounts for the peak at 2θ = 18� because

it was also observed for friction-transferred (FT) PTFE layers.26

The remarkable orientation up to S = 0.98 was obtained for abisazo dye both on the FT layer and on the ER layer,15 thusshowing that the surface of the FT layers is identical to that of theER layers. Hence, the ER layer should also show a similar dif-fraction through the thin dye layer.

Figure 3. Polarized IR absorption spectra of 1: (a) powder in a KBr diskwith no polarizer; (b, c) the dye oriented film (thickness of 60 nm); (d)peaks (∼822 cm�1) for an out-of-plane mode of p-phenylene moiety.The light polarization is parallel to the aligned PTFE chains in trace b,but it is perpendicular to the chains in trace c.

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In the crystal structure of 1, there are the molecular arrayscomparable to those reported for a model of J-aggregates, asshown in Figure 5. For example, eight extracted molecules(Figure 5c) form a so-called “staircase”-like sheet [ ) (101) plane]comprising two linear arrays; the crystal structure is composed ofthe sheets as shown in Figure 5a and b. Such a close affinitybetween a crystal and J-aggregates has been studied for a longtime and thus is useful in deducing the molecular arrangement inJ-aggregates.27

The axial and planar orientation should bring about a conflictin the direction of each crystal on the PTFE layer during thedeposition because each crystal has four possible configurationsdue to its triclinic symmetry, as shown in Figure 6a�d. Hence,the staircase sheet also has four possible directions, which can beapproximately integrated into two directions (Figure 6a and c vsb and d) by neglecting the slight angle (∼4�) between the b- axisand the direction normal to the (010) plane; the sheet plane isapproximately normal to the substrate surface and is tilted at∼(26� to the sliding direction. The film, therefore, should com-prise these crystals assembling together with complicated bound-aries among them. Such conflict on an aligned PTFE layer wasreported for some crystalline molecules, such as sexithiophene,28

2-methyl-4-nitroaniline,24 and titanyl pthalocyanine.29

3.4. Morphology and Growth Mechanism. The AFMmeasurements show the crystal grains whose forms are compa-tible with the conflict. Many facets are seen on the tops and sides,and their straight brink lines often take angles from(15� to(35�to the sliding directions, as shown in Figures 7 and 8. Further-more, these lines often form parallelograms, rhombic squares, ortriangles, thus showing appreciable symmetry with respect to thesliding direction. The flatness and symmetry of the facets demon-strate to us that they come from major crystal planes. If weassume that their side facets come from the crystal planes parallelto the [1 0�1] axis, the brink lines should result from the inter-sections of (010) and these planes, such as (101). Then the linesshould take an either�or angle ((∼26�, the angle between [1 0�1]and [2 0 �1]) to the sliding direction, as illustrated in Figure 6,

and a pair of neighboring ones should be nearly parallel or shouldform wedges against the sliding direction. The lines thus wouldform those symmetrical shapes as a polycrystal comprising thecrystals conflicted there. For instance, Figure 6e shows onepossible model for a wedge, which is seen on the lower rightend in Figure 8a, as well as that for a parallelogram.Those side facets are probably the staircase sheets from (101)

planes because of the tight adhesion between their neighboringmolecules, whose mean distances are significantly shorter thanthose of the sheets from the other planes, such as (111) or(1�11). The tight staircase sheets would grow faster than othersheets, thereby being likely to appear. The features of crystalgrains are often formed by the anisotropic growth rate resultingfrom the difference in adhesion. For instance, slender grains of anα-type copper pthalocyanine are formed on a rubbed glass surfaceby fast growth with strong intermolecular adhesion along its b-axis, thus being oriented along the rubbing direction.30

However, we think that possibility of the other planes, such as(111) and (1�11), also should not be excluded instead of (101).The slope of the side facets sometimes seems to be smaller(∼40�) than that expected for the (101) planes, and there are notonly flat facets, but also curved surfaces. The flat slope for (101)should be 84� on the assumption that its (010) plane is horizontal.

Figure 5. Molecular arrangements for 1 in its crystal: (a) looking downthe b-axis, (b) looking down the [2 0 �1] direction, and (c) a layercomprising two linear arrays from eight oriented molecules in a viewingdirection normal to the [2 0 �1] direction. The molecules surroundedby the broken line rectangle form the layer like a staircase.

Figure 4. X-ray diffraction patterns of a dye 1 oriented film (thickness of80 nm) on an aligned PTFE layer: (a) by the out-of-plane mode with thescattering vector perpendicular both to the sliding direction and to thesubstrate surface; (b) by the in-plane mode with the scattering vectorperpendicular to the sliding direction. The asterisk is the peak for the(010) plane of PTFE.

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Hence, one should be quite cautious about identifying all the sidefacets with (101), although we also have to consider whether theAFM tip can trace such a steep slope correctly. Moreover, com-plicated growth also should be taken into account there becauseof the deformation expected for the polycrystals, including theaggregates, which should modify their morphology, particularlybeyond 50 nm of the thickness (containing appreciable aggregates).The curved surfaces then are possibly grown through such com-plicated processes. In contrast, the case with the symmetry andflatness demonstrates to us the conflict, as mentioned earlier,according to the crystal orientation observed.The growth of the aggregates takes place while the grains are

contacting each other during the deposition. Figure 7 shows thata significant area on the PTFE layer is still not covered with thedye crystals for the average thickness of 25 nm, whereas Figure 8shows that the surface is almost covered for 60 nm. The ag-gregates precisely grow in the interval between them as theemerging J peak is shown in Figure 2b. The PTFE layers do notshow their peculiar dewetting here because the isotropic dyefilms not closed were also shown on glass previously.31

We think, therefore, that the aggregates are provided by somestress through the contact between the crystals crowded on the

surface. Slight modification in molecular arrangement can formsimple arrays from the crystal because of the structural affinitymentioned earlier. Without appreciable translation of molecules,some rotation of themolecular planes can form a typical array of aJ-aggregate having a large slip angle with the unit cell of onemolecule. Hence, one-dimensional molecular arrays are orientedin the film. The 1D array with a slip angle has been a promisingmodel for J-aggregates, explaining well some features of theaggregates, such as bathochromic shift and flow orientation.32 Wealso should not exclude two-dimensional models such as staircases

Figure 7. AFM images of an aligned PTFE layer and of the dye-orientedfilm (average thickness of 25 nm) on aligned PTFE layers: (a) for a3000 nm square, (b) for a 1000 nm square, and (c) an aligned PTFElayer for a 1000 nm square. “R” indicates the sliding direction.

Figure 6. Possible crystal arrangements on the PTFE layer where the[2 0�1] direction is parallel or antiparallel to the sliding direction: (a�d)possible four arrangements; (e) examples of possible polycrystals formingthe shapes that are often observed in the AFM images for the film. The lineson the column crystal show the edges of the layers comprising themoleculararrays [ ) (101) plane]. “R” indicates the sliding direction at rubbing.

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comprising such arrays here because it still is an open questionwhether J-aggregates are 1D or 2D. Even if it is 2D, the 1D arraysalso exist as basic elements in which each molecule is oriented withits long axis parallel to the PTFE chains, as illustrated in Figure 9.3.5. Energy Transfer from J-Aggregates to Crystals. Some

excited energy of the J-aggregates transfers to the crystallinedomains. The film shows some strongly polarized fluorescence,as shown in Figure 10, and the observed peak (652 nm) and its

shoulder (∼680 nm) should be identical to those reported forthe crystalline phase in their isotropic films: their time-resolvedphotoluminescence (PL) revealed that the peak and the shoulderare radiated from the free excitons in the crystalline domains andfrom those vibronic replicas, recpectively.33 A broadened J peak(629 nm) is also shown on the excitation spectrum in Figure 10(a), thereby demonstrating the energy transfer from the aggre-gates to the crystalline domains in the film. The PL under 160 Kin the previous study also shows that the emission intensity fromtrapped excitons (∼676 nm) depends on the content of theJ-aggregates, also supporting the energy transfer from the aggregatesto the traps in the crystalline domains.33 The dispersed structureor the axial orientation deduced is favorable for efficient transferfrom the aggregates to crystalline domains with respect to theinteraction between them.Another shoulder on the parallel emission (Figure 10c) and a

peak on the perpendicular emission (Figure 10d) were located at∼643 nm on the spectrum. They cannot be assigned to theJ-aggregates because of its too large Stokes shift (14�20 nm) forJ-aggregates, although their correct assignment is not clear. Weconsider that this emission is also radiated from the free excitonsin the crystalline domains: their emission peak wavelength of theisotropic film slightly depends on some experimental conditions,such as temperature, excitation power, and the content of theaggregates, etc.33 In such a rough film, its structure should not beuniform: it varies slightly, depending on each site in the film. Theslight change then should perturb the energy level of exitons, thuspossibly providing the shorter shoulder. Hence, the emissionfrom J-aggregates should be quenched anyway, showing no directemission from them.3.6. Electroabsorption. The EA measurements of the J peak

make an estimate that the |χ(3)| value is ∼1.1 � 10�8 esu for theoriented film as shown in Figure 11b, whereas their isotropic film hasvalues from 1.5 � 10�10 to 9 � 10�10 esu previously.19 The EAspectrum around the J peak agrees with the first derivative of theabsorbance (Figure 11a, b), thereby confirming that the J peak orig-inates from Frenkel excitons. Hence, it demonstrates the remarkableχ(3) increase, over 10 times, by the orientation of the J-aggregates.

Figure 9. A 1D chain schematic model for the oriented J-aggregate onaligned PTFE chains. The aggregate is a linear chain of dye moleculesstacked face-to-face, growing upward with a slip angle.

Figure 10. Excitation and emission spectra of a dye 1 oriented film(thickness of 60 nm): (a) the excitation spectrum by the emission at680 nm with the excitation and emission polarized parallel to the slidingdirection, (b) the excitation spectrum with that polarized perpendicularto the sliding direction, (c) the emission spectrum by the excitation at550 nm with the excitation and emission polarized parallel to the slidingdirection, and (d) the emission spectrum with that polarized perpendi-cular to the direction.

Figure 8. AFM images of the dye-oriented film (average thickness of60 nm) on aligned PTFE layers: (a) for a 3000 nm square and (b) for a1000 nm square. “R” indicates the sliding direction.

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In such highly oriented films, almost all the molecules effectivelyinteract with the light polarized along their molecular long axes.

4. CONCLUSION

We have demonstrated that the anisotropic film containinghighly oriented J-aggregates can be obtained by depositing dye1 on the aligned PTFE layer through evaporation. We havereached the following four conclusions: (1) major molecules donot form the aggregates but, rather, form the crystalline domainsin which the aggregates should be dispersed; (2) in the films, thelong axes of the dye molecules are highly oriented along thePTFE chains both in the aggregates and in the crystals; (3) thecrystalline domains of 1 are oriented in the direction where their[2 0 �1] axes are parallel to the PTFE chains and their (010)planes are also parallel to the substrate surface; (4) the film hasthe large |χ(3)| values of∼1.1 � 10�8 esu, over 10 times greaterthan those from their isotropic films.

The remarkable optical anisotropy is also favorable for study-ing the intrinsic nature of the excitons in J-aggregates. Unlike com-mon cyanine derivatives, dye 1 does not have counterions, whichshould complicate EA responses. Hence, we are still trying toinvestigate further their structure, growth mechanism, and func-tions. We thus expect the upcoming results of further EA mea-surements will give us some information on their intrinsic nature,a matter of exquisite scientific concern.

’AUTHOR INFORMATION

Corresponding Author*E-mail: 3116566701@jcom.home.ne.jp.

’ACKNOWLEDGMENT

We dedicate this work to the late Prof. Masaru Matsuoka,who actually suggested this work to us just before his passing

away 9 years ago. We thank Mr. Byung-Soon Kim and Mr. YukiYokota at Yokohama National University for preparing a fewgraphics. A part of this work was performed under the manage-ment of the Association of Super-Advanced Electronic Technol-ogies (ASET) in the Ministry of International Trade and Industry(MITI) Program of Super-Advanced Electronic Technologiessupported by the New Energy and Industrial Technology Devel-opment Organization (NEDO).

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Figure 11. (a) The electroabsorption (Δα) spectrum of a dye 1oriented film (thickness of 60 nm); (b) the first derivative of absorbance,α (= A )), by photon energy for the oriented film; (c) the χ(3) spectrumfor the oriented film. Both the light polarization and the applied electricfield are parallel to the sliding direction.

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