ARTICLE pubs.acs.org/JPCC
Highly Oriented J-Aggregates of Bisazomethine Dye on Aligned Poly(tetrafluoroethylene) Surfaces Toshihiko 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 significance for their possible applications. J-aggregates are supramolecules organized on low dimensions in nanoscales, thus showing peculiar remarkable optical properties with interesting functions.1 Hence, their orientation should make efficient use of the functions in terms of their low dimensions. For instance, the orientation is favorable for their nonlinear optical devices, for which the aggregates recently have attracted much attention because of their large χ(3) and ultrafast response.2 A high degree of orientation should give them a significant χ(3) increase with huge optical anisotropy because of their peculiar low dimensionality. It is also favorable for their possible polariton lasing applications,3 in which the coupling between excitons and polaritons should be enhanced by the orientation. Therefore, the high degree of orientation has been needed in these interesting fields. Highly oriented J-aggregates have been uncommon, although pioneers have developed a number of aligning methods, such as vertical spin coating,4 electrospinning,5 anisotropic evaporation of solution,6 magnetic fields,7 LangmuirBlodgett films,8,9 adsorption on single crystal surface,10 and laser microfixation.11 The dichroic ratio (D) in polarized absorption expresses the degree of orientation there, and according to the best of our knowledge, D values over 20 were reported only for a monolayer of the cyanine J-aggregates ordered by a gypsum crystal surface.8 We report herein highly oriented J-aggregates in solid thin films of a bisazomethine dye on aligned poly(tetrafluoroethylene) (PTFE) surfaces. This is also the first report on the oriented r 2011 American Chemical Society
)
)
ABSTRACT: Highly oriented J-aggregates have been obtained in solid, thin films of a bisazomethine dye on aligned poly(tetrafluoroethylene) (PTFE) surfaces. The aggregates show remarkable optical anisotropy resulting from their high orientational order: the dichroic ratios at their J peaks in polarized absorption spectra reach 25. Moreover, this orientation also brings about a remarkable increase in the third-order nonlinear optical susceptibility [χ(3)] of the films of over 10 times that of their isotropic films. Major molecules do not form the aggregates, but rather, form crystalline domains where the aggregates should be dispersed. Polarized absorption spectra (visible and IR) and X-ray diffraction measurements reveal that the molecules are oriented with their long axis parallel to the PTFE chains both in the aggregates and in the crystalline domains ([2 0 1] axis PTFE chains, (010) plane substrate surface). The growth mechanism of the aggregates is discussed on the basis of both the morphology observed by atomic force microscopy and the structural affinity between the crystal and the aggregate.
J-aggregates of a bisazomethine dye. Its isotropic film was vacuumdeposited on substrates without PTFE layers, thereby containing their J-aggregates.12 By modifying the substrates with aligned PTFE layers, the aggregates are oriented and show remarkable D values up to 25. The oriented growth on aligned PTFE layers is a promising process for preparation of highly ordered films: since the seminal report of Wittmann and Smith,13 a large number of works have been dedicated to the oriented growth of various materials, including inorganic crystals,13 small molecules,1316 and polymers.10,17 However, the oriented growth of J-aggregates on the PTFE also have been uncommon. Only a squarium derivative 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. Glass slides and silicon wafers were used as substrates. For electroabsorption (EA) measurements, Al electrodes with a 0.5 mm gap were deposited on the glass slides. Silicon substrates were used for IR absorption measurement instead of glass. Then an aligned PTFE thin layer was deposited on the substrates by evaporation and rubbing (ER):15 a PTFE film (50 nm thick) was deposited on the substrates under vacuum by evaporating PTFE (molecular weight, Received: July 5, 2011 Revised: September 5, 2011 Published: September 06, 2011 19598
dx.doi.org/10.1021/jp2063436 | J. Phys. Chem. C 2011, 115, 19598–19605
The Journal of Physical Chemistry C
ARTICLE
Figure 1. Molecule of bisazomehine dye 1.
500020000; purchased from Wako Pure Chemical Co., Ltd.). The deposition was monitored by the frequency change of a quartz resonator. After that, the PTFE layer was rubbed at a pressure of about 5 kg/cm2 with a cloth sliding in a direction at a constant speed of 5 mm/s, thereby oriented with its chains parallel to the sliding direction. Deposition of the Dyes. Oriented thin films of bisazomethine dye 1 (Figure 1) were deposited onto the aligned PTFE layers by evaporating the dye in a vacuum at a pressure of ∼105 Torr with a growth rate of 0.050.15 nm/s. The dye was synthesized by the procedure reported.18 The deposition was monitored by the frequency change of a quartz resonator. Characterization of the dye films. The polarized UVvisible absorption spectra of the dye films on the glass substrates were recorded on a Cary 5E UVvisibleNIR spectrophotometer equipped with a highly efficient Gran-Thomson polarizer before the sample on the optical path. The spectra were obtained at normal incidence in the transmission mode with polarization both parallel and perpendicular to the sliding direction separately. The reference spectrum taken with the PTFE layer on a glass substrate for each polarization was subtracted from each sample spectrum during data processing. The polarized IR absorption spectra of the dye films on ER silicon substrates were recorded on a Nicolet Magna 860 FT-IR spectrometer equipped with a TGS detector. The infrared beam was polarized using an Al wire grid KRS-5 polarizer. The spectra were obtained at normal incidence in the transmission mode with polarization both parallel and perpendicular to the sliding direction separately. The reference spectrum was taken with the PTFE layer on a silicon substrate for each polarization. The reference spectrum with each polarization of the silicon substrate was subtracted from each sample spectrum during data processing. All IR spectra were taken at 2 cm1 resolution by collecting 500 interferograms for each spectrum. The spectra of dye powders dispersed in KBr disks were obtained in the transmission mode at normal incidence without polarizers. The X-ray diffractions of the films were recorded on a Mac Science M21X X-ray diffractometer. Source light (Cu Kα) was monochromated and collimated using a parabolic multilayer monochromator. For in-plane measurements, the incident angle of the X-ray beam was 0.3 to the substrate surface, and the scattering 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 equipped with a SiN cantilever employing its tapping mode in air at room temperature. 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 spectrofluorometer equipped with two polarizers: one for the EM beam and the other for the EX beam at 550 nm. The EM at an oblique angle (22.5 from normal to the film surface) was recorded with the EX at normal incidence: the two polarizing directions
Figure 2. UVvisible polarized absorption spectra of dye 1 oriented films 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 the aligned PTFE chains in a, b, and c, and it is perpendicular to the chains in d, e, and f.
were aligned. The EM and EX spectra were obtained with the aligned direction parallel and perpendicular to the sliding direction, respectively. The EA measurements of the film were carried out according to the method reported previously.19 The probing light was polarized parallel to the sliding direction, and a modulating electric field was also applied along the direction. The electrodes were not deposited on the dye film, but instead, they were predeposited as we mentioned earlier.
3. RESULTS AND DISCUSSION 3.1. J-Aggregates and Orientation of Long Axes. J-aggregates were grown in the films. A sharp absorption peak grew in the region 600650 nm, increasing the film thickness, as shown in Figure 1ac. This peak growth behavior is similar to that of their isotropic film vacuum-deposited on glass without PTFE layers: some of the authors indicated by the EA technique that the sharp peak from the isotropic film is due to Frenkel excitons,12 thereby showing that the sharp peak exactly comes from J-aggregates 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 mixed with the dye molecules not forming the aggregates, as also previously shown for their isotropic films. Some of us revealed 19599
dx.doi.org/10.1021/jp2063436 |J. Phys. Chem. C 2011, 115, 19598–19605
The Journal of Physical Chemistry C
Figure 3. Polarized IR absorption spectra of 1: (a) powder in a KBr disk with no polarizer; (b, c) the dye oriented film (thickness of 60 nm); (d) peaks (∼822 cm1) 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.
)
)
)
that this peak is due to a crystalline phase: an exposure to chloroform vapor causes the decrease in the J peak as well as the increase both in X-ray diffraction intensities and in the second peak, thus promoting crystallization from J-aggregates to the crystalline phase.12 Shoulders (∼500 nm) (Figure 2a, b, c, f) also should be assigned to the crystalline phase because it is an intrinsic absorption (such as a vibrating subband for the second peak possibly) of 1 molecule: both its isotropic film and its dilute chloroform solution show this shoulder on their spectra.12 Although Figure 2 d shows the shoulder at a shorter wavelength (∼450 nm), it is not clear whether a small amount of another species exists in the film: in the perpendicular polarization, we should be very careful with its baseline, which is sometimes influenced in its absorbance scale under 0.1 by the UV absorption tail accompanied by some scattering. Even if this shoulder is due to another species, such as Davydov splitting from disordered molecules, its content would be negligible because of the tiny absorbance with respect to that of 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 to the sliding direction, which is parallel to the PTFE chains. The dichroic ratio D = A /A^ (A and A^: absorbance for each polarization) reaches 25 (at 622 nm), as shown in Figure 1a and d, thus showing that their uniaxial orientational order S = (D 1)/(D + 2) is 0.89. Moreover, an intrinsic D value for the J-aggregates should be >25 because the J band proportion of A^ is significantly smaller than that of A : Figure 2d does not show a sharp peak at 622 nm. The motional narrowing in the aggregates should take place,20 thereby averaging the transition moments of the molecules for each aggregate to a smaller distribution. Hence, both the molecular orientation and the motional narrowing account 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 forming the aggregates are also highly oriented with their molecular long axes parallel to the PTFE chains. Assuming that the integral of the absorption peak is proportional to the numbers of its species, we can estimate that major molecules do not form the aggregates in the 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 several peaks in the region from 1120 to 1609 cm1: 1120 (D = 22), 1142 (D = 23), 1271 (D = 10), 1353 (D = 16), 1439 (D = 25), 1516 (D = 40), 1565 (D = 15), and 1609 cm1 (D = 9.5). These peaks should be combinations of local vibrations along the molecular long axis because there is a lot of local stretching along the axis from p-phenylenes, CdC, CdN, and CN in this region.21 The local vibrations along the axis couple to form several molecular vibrations parallel to the axis. We can attribute the peak at 1516 cm1 to the mode of vibration originating mainly from asymmetric p-phenylene (19a[A1]), according to its empirical assignment.21 3.2. Planar Orientation. The dye molecules in the film also have a planar orientation. The peak at 822 cm1 on the spectra for the dye powder (Figure 3a) can be assigned to an out-of-plane mode for the p-phenylene moiety (11[B1]) according to its empirical assignment.21 The film has a tiny peak at the wavenumber for both polarization directions, thereby showing that their phenylene planes are parallel in some extent to the substrate surface (Figure 3b, c). Such planar orientation on aligned PTFE
ARTICLE
was also reported for bisazo dyes,15 napthoquinones,22 p-nitrophenol,23 and 2-methyl-4-nitroaniline.24 These peaks give us an estimate of moderate planar orientation according to the method reported previously.15 The Æcos2 ϕ0 æ value 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 uniaxial orientation, ϕ0 virtually expresses the angle between the substrate surface and the director normal to the phenyl plane for each molecule.15 Hence, ϕ0 should be nearly 57 (33 tilted from the perfect planar orientation) if all molecules in the film have the same ϕ0 value. 3.3. Orientation of Crystals. The X-ray diffraction measurements of the films reveal that the crystals of 1 are oriented in the direction where their [2 0 1] axes are parallel to the PTFE chains and their (010) planes are parallel to the substrate surface. The structure of a single crystal from 1 was determined by some of the authors previously.25 Figure 4a and b then shows that its (030), (1 1 2), and (122) planes are observed by the out-ofplane mode and its (102), (122), and (1 1 2) planes are observed by the in-plane mode. If we assume the orientation ([2 0 1]||PTFE chains and (010)||substrate, illustrated in Figure 5), its (030) planes should be observed only by the outof-plane mode, and its (102) plane should be observed only by the in-plane mode. The degree of the (010) orientation is not so high that the (1 1 2) and (122) planes are observed by both modes. Moreover, the molecular plane (phenyl rings) in the crystal are tilted at ∼13 to the (010) plane, as shown in Figure 5b. Hence, the orientation degree of molecular plane is likewise smaller, thus corresponding well to the estimate of Æcos2 ϕ0 æ = 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 a bisazo dye both on the FT layer and on the ER layer,15 thus showing that the surface of the FT layers is identical to that of the ER layers. Hence, the ER layer should also show a similar diffraction through the thin dye layer. 19600
dx.doi.org/10.1021/jp2063436 |J. Phys. Chem. C 2011, 115, 19598–19605
The Journal of Physical Chemistry C
ARTICLE
Figure 4. X-ray diffraction patterns of a dye 1 oriented film (thickness of 80 nm) on an aligned PTFE layer: (a) by the out-of-plane mode with the scattering vector perpendicular both to the sliding direction and to the substrate surface; (b) by the in-plane mode with the scattering vector perpendicular to the sliding direction. The asterisk is the peak for the (010) plane of PTFE.
)
In the crystal structure of 1, there are the molecular arrays comparable to those reported for a model of J-aggregates, as shown 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 of the sheets as shown in Figure 5a and b. Such a close affinity between a crystal and J-aggregates has been studied for a long time and thus is useful in deducing the molecular arrangement in J-aggregates.27 The axial and planar orientation should bring about a conflict in the direction of each crystal on the PTFE layer during the deposition because each crystal has four possible configurations due to its triclinic symmetry, as shown in Figure 6ad. Hence, the staircase sheet also has four possible directions, which can be approximately integrated into two directions (Figure 6a and c vs b and d) by neglecting the slight angle (∼4) between the b- axis and the direction normal to the (010) plane; the sheet plane is approximately normal to the substrate surface and is tilted at ∼(26 to the sliding direction. The film, therefore, should comprise these crystals assembling together with complicated boundaries among them. Such conflict on an aligned PTFE layer was reported for some crystalline molecules, such as sexithiophene,28 2-methyl-4-nitroaniline,24 and titanyl pthalocyanine.29 3.4. Morphology and Growth Mechanism. The AFM measurements show the crystal grains whose forms are compatible 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. Furthermore, these lines often form parallelograms, rhombic squares, or triangles, thus showing appreciable symmetry with respect to the sliding direction. The flatness and symmetry of the facets demonstrate to us that they come from major crystal planes. If we assume that their side facets come from the crystal planes parallel to the [1 0 1] axis, the brink lines should result from the intersections of (010) and these planes, such as (101). Then the lines should take an eitheror angle ((∼26, the angle between [1 0 1] and [2 0 1]) to the sliding direction, as illustrated in Figure 6,
Figure 5. Molecular arrangements for 1 in its crystal: (a) looking down the b-axis, (b) looking down the [2 0 1] direction, and (c) a layer comprising two linear arrays from eight oriented molecules in a viewing direction normal to the [2 0 1] direction. The molecules surrounded by the broken line rectangle form the layer like a staircase.
and a pair of neighboring ones should be nearly parallel or should form wedges against the sliding direction. The lines thus would form those symmetrical shapes as a polycrystal comprising the crystals conflicted there. For instance, Figure 6e shows one possible model for a wedge, which is seen on the lower right end 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 neighboring molecules, whose mean distances are significantly shorter than those of the sheets from the other planes, such as (111) or (111). The tight staircase sheets would grow faster than other sheets, thereby being likely to appear. The features of crystal grains are often formed by the anisotropic growth rate resulting from the difference in adhesion. For instance, slender grains of an α-type copper pthalocyanine are formed on a rubbed glass surface by fast growth with strong intermolecular adhesion along its baxis, thus being oriented along the rubbing direction.30 However, we think that possibility of the other planes, such as (111) and (111), 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 not only flat facets, but also curved surfaces. The flat slope for (101) should be 84 on the assumption that its (010) plane is horizontal. 19601
dx.doi.org/10.1021/jp2063436 |J. Phys. Chem. C 2011, 115, 19598–19605
The Journal of Physical Chemistry C
ARTICLE
)
Figure 6. Possible crystal arrangements on the PTFE layer where the [2 0 1] direction is parallel or antiparallel to the sliding direction: (ad) possible four arrangements; (e) examples of possible polycrystals forming the shapes that are often observed in the AFM images for the film. The lines on the column crystal show the edges of the layers comprising the molecular arrays [ (101) plane]. “R” indicates the sliding direction at rubbing.
Hence, one should be quite cautious about identifying all the side facets with (101), although we also have to consider whether the AFM tip can trace such a steep slope correctly. Moreover, complicated growth also should be taken into account there because of the deformation expected for the polycrystals, including the aggregates, which should modify their morphology, particularly beyond 50 nm of the thickness (containing appreciable aggregates). The curved surfaces then are possibly grown through such complicated processes. In contrast, the case with the symmetry and flatness 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 that a significant area on the PTFE layer is still not covered with the dye crystals for the average thickness of 25 nm, whereas Figure 8 shows that the surface is almost covered for 60 nm. The aggregates precisely grow in the interval between them as the emerging J peak is shown in Figure 2b. The PTFE layers do not show their peculiar dewetting here because the isotropic dye films not closed were also shown on glass previously.31 We think, therefore, that the aggregates are provided by some stress through the contact between the crystals crowded on the
Figure 7. AFM images of an aligned PTFE layer and of the dye-oriented film (average thickness of 25 nm) on aligned PTFE layers: (a) for a 3000 nm square, (b) for a 1000 nm square, and (c) an aligned PTFE layer for a 1000 nm square. “R” indicates the sliding direction.
surface. Slight modification in molecular arrangement can form simple arrays from the crystal because of the structural affinity mentioned earlier. Without appreciable translation of molecules, some rotation of the molecular planes can form a typical array of a J-aggregate having a large slip angle with the unit cell of one molecule. Hence, one-dimensional molecular arrays are oriented in the film. The 1D array with a slip angle has been a promising model for J-aggregates, explaining well some features of the aggregates, such as bathochromic shift and flow orientation.32 We also should not exclude two-dimensional models such as staircases 19602
dx.doi.org/10.1021/jp2063436 |J. Phys. Chem. C 2011, 115, 19598–19605
The Journal of Physical Chemistry C
ARTICLE
Figure 10. Excitation and emission spectra of a dye 1 oriented film (thickness of 60 nm): (a) the excitation spectrum by the emission at 680 nm with the excitation and emission polarized parallel to the sliding direction, (b) the excitation spectrum with that polarized perpendicular to the sliding direction, (c) the emission spectrum by the excitation at 550 nm with the excitation and emission polarized parallel to the sliding direction, and (d) the emission spectrum with that polarized perpendicular to the direction.
Figure 8. AFM images of the dye-oriented film (average thickness of 60 nm) on aligned PTFE layers: (a) for a 3000 nm square and (b) for a 1000 nm square. “R” indicates the sliding direction.
Figure 9. A 1D chain schematic model for the oriented J-aggregate on aligned PTFE chains. The aggregate is a linear chain of dye molecules stacked face-to-face, growing upward with a slip angle.
comprising such arrays here because it still is an open question whether J-aggregates are 1D or 2D. Even if it is 2D, the 1D arrays also exist as basic elements in which each molecule is oriented with its 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 crystalline domains. 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 for the crystalline phase in their isotropic films: their time-resolved photoluminescence (PL) revealed that the peak and the shoulder are radiated from the free excitons in the crystalline domains and from 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 aggregates to the crystalline domains in the film. The PL under 160 K in the previous study also shows that the emission intensity from trapped excitons (∼676 nm) depends on the content of the J-aggregates, also supporting the energy transfer from the aggregates to the traps in the crystalline domains.33 The dispersed structure or the axial orientation deduced is favorable for efficient transfer from the aggregates to crystalline domains with respect to the interaction 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 the J-aggregates because of its too large Stokes shift (1420 nm) for J-aggregates, although their correct assignment is not clear. We consider that this emission is also radiated from the free excitons in the crystalline domains: their emission peak wavelength of the isotropic film slightly depends on some experimental conditions, such as temperature, excitation power, and the content of the aggregates, etc.33 In such a rough film, its structure should not be uniform: it varies slightly, depending on each site in the film. The slight change then should perturb the energy level of exitons, thus possibly providing the shorter shoulder. Hence, the emission from J-aggregates should be quenched anyway, showing no direct emission from them. 3.6. Electroabsorption. The EA measurements of the J peak make an estimate that the |χ(3)| value is ∼1.1 108 esu for the oriented film as shown in Figure 11b, whereas their isotropic film has values from 1.5 1010 to 9 1010 esu previously.19 The EA spectrum around the J peak agrees with the first derivative of the absorbance (Figure 11a, b), thereby confirming that the J peak originates from Frenkel excitons. Hence, it demonstrates the remarkable χ(3) increase, over 10 times, by the orientation of the J-aggregates. 19603
dx.doi.org/10.1021/jp2063436 |J. Phys. Chem. C 2011, 115, 19598–19605
The Journal of Physical Chemistry C
ARTICLE
away 9 years ago. We thank Mr. Byung-Soon Kim and Mr. Yuki Yokota at Yokohama National University for preparing a few graphics. A part of this work was performed under the management of the Association of Super-Advanced Electronic Technologies (ASET) in the Ministry of International Trade and Industry (MITI) Program of Super-Advanced Electronic Technologies supported by the New Energy and Industrial Technology Development Organization (NEDO).
’ REFERENCES
)
Figure 11. (a) The electroabsorption (Δα) spectrum of a dye 1 oriented film (thickness of 60 nm); (b) the first derivative of absorbance, α (= A ), by photon energy for the oriented film; (c) the χ(3) spectrum for the oriented film. Both the light polarization and the applied electric field are parallel to the sliding direction.
In such highly oriented films, almost all the molecules effectively interact with the light polarized along their molecular long axes.
4. CONCLUSION We have demonstrated that the anisotropic film containing highly oriented J-aggregates can be obtained by depositing dye 1 on the aligned PTFE layer through evaporation. We have reached the following four conclusions: (1) major molecules do not form the aggregates but, rather, form the crystalline domains in which the aggregates should be dispersed; (2) in the films, the long axes of the dye molecules are highly oriented along the PTFE chains both in the aggregates and in the crystals; (3) the crystalline 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 has the large |χ(3)| values of ∼1.1 108 esu, over 10 times greater than those from their isotropic films. The remarkable optical anisotropy is also favorable for studying the intrinsic nature of the excitons in J-aggregates. Unlike common cyanine derivatives, dye 1 does not have counterions, which should complicate EA responses. Hence, we are still trying to investigate further their structure, growth mechanism, and functions. We thus expect the upcoming results of further EA measurements will give us some information on their intrinsic nature, a matter of exquisite scientific concern. ’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT We dedicate this work to the late Prof. Masaru Matsuoka, who actually suggested this work to us just before his passing
(1) (a) Jelly, E. E. Nature 1936, 138, 1009–10. (b) Scheibe, G. Amgew. Chem. 1936, 49, 563. (c) J-aggregates; Kobayashi, T., Ed.; World Scientific: Singapore, 1996. (d) Hranisavijevic, J.; Dimitrijevic, N. D.; Wurtz, G. A.; Wiederrecht, G. P. J. Am. Chem. Soc. 2002, 124, 4536–37. (e) Wurthner, F; Kaiser, T. E.; Saha-Moller, C. R. Angew. Chem., Int. Ed. 2011, 50, 3376–3410. (2) (a) Wang, Y. Chem. Phys. Lett. 1986, 126, 209–210. (b) Spano, F. C.; Mukamei, S. Phys. Rev. A 1989, 40, 5783. (c) Johnson, A. E.; Kumazaki, S.; Yoshihara, K. Chem. Phys. Lett. 1993, 211, 511–15. (d) Fedder, H.; Knoester, J.; Wiersm, D. A. J. Chem. Phys. 1993, 98, 6564–6. (e) Sato, Y.; Furuki, M.; Tian, M; Iwasa., I.; Pu, L. S.; Tatsuura, S. Appl. Phys. Lett. 2002, 80, 2254–6. (3) (a) Lidzey, D. G.; Bradley, D. D. C.; Virgili, T.; Armitage, A.; Skolnick, M. S.; Walker, S. Phys. Rev. Lett. 1999, 82, 3316–9. (b) Finlayson, C. E.; Parakash, G. V.; Baumberg, J. J. Appl. Phys. Lett. 2005, 86, 41110–1-3. (c) Michetti, P; La Rocca, G. C. Phys. Rev. B 2009, 79, 35325–1-6. (d) Bradley, M. S.; Bulovic, V. Phys Rev.B 2010, 82, 33305–1-4. (4) (a) Misawa, K.; Kobayashi, T. Nonlinear Opt. 1995, 14, 103. (b) Misawa, K.; Ono, H.; Minoshima, K.; Kobayashi, T. Appl. Phys. Lett. 1993, 63, 577–9. (c) Gulen, D.; Atasoylu, O.; Ozcelik, S. Chem. Phys. 2009, 355, 73. (5) Demir, M. M.; Ozen, B.; Ozcelik, S. J. Phys. Chem.B 2009, 113, 11568–73. (6) Takazawa, K.; Kitahama, Y.; Kimura, Y. Chem. Commun. 2004, 2272–3. (7) (a) Shklyarevskiy, I. O.; Boamfa, M. I.; Christianen, P. C. M.; Touhari, F.; van Kempen, H.; Deroover, G.; Callant, P.; Maan, J. C. J. Chem. Phys. 2002, 116, 8407–10. (b) Shklyarevskiy, I. O.; Christianen, P. C. M.; Aret, E.; Meeks, H.; Vlieg, E.; Deroover, G.; Callant, P.; Meervelt, L. V.; Maan, J. C. J. Phys. Chem.B 2004, 108, 16386–91. (c) Kitahama, Y.; Kimura, Y.; Takazawa, K. Langmuir 2006, 22, 7600–4. (8) Bird, G. R.; Debuch, G.; Mobius, D. J. Phys. Chem. 1977, 81, 2657–63. (9) Tabe, Y.; Ikegami, K.; Kuroda, S.; Saito, K.; Saito, M.; Sugi, M. Appl. Phys. Lett. 1990, 57, 1191–3. (10) Miyamoto, N.; Kuroda, K. J. Am. Chem. Soc. 2001, 123, 6949–50. (11) Tanaka, Y.; Yoshikawa, N.; Asahi, T.; Masuhara, H. Appl. Phys. Lett. 2001, 91, 41102–1-3. (12) Matsumoto, S.; Kobayashi, T.; Aoyama, T.; Wada, T. Chem. Commun. 2003, 1910–11. (13) Wittmann, J. C.; Smith, P. Nature 1991, 352, 414–17. (14) (a) Vallee, R.; Damman, P.; Dosiere, S. G.; Bredas, J. L. J. Phys. Chem.B 2001, 105, 6064–9. (b) Bunk, O.; Nielsen, M. M.; Soring, T. T.; Craats, A. M.; Stutzmann, N. J. Am. Chem. Soc. 2003, 125, 2252–8. (c) Brinkmann, M.; Graff, S.; Staupe, C.; Wittmann, J. C.; Chaumont, C.; Nuesch, F.; Aziz, A.; Schaer, M.; Zuppiroli, L. Phys. Chem. B 2003, 117, 10531–9. (15) Tanaka, T; Honda, Y.; Ishitobi, M. Langmuir 2001, 17, 2192–8. (16) Matsumoto, K.; Shinohara, T.; Ueda, Y. Mol. Cryst. Liq. Cryst. 2006, 445, 17–26. (17) (a) Damman, P.; Dosiere, M.; Wittmann, J. C. Macromolecules 1997, 30, 8386–91. (b) Damman, P.; Fougnies, C.; Dosiere, M.; Wittmann, J. C. Macromolecules 1995, 28, 8272–6. (c) Ueda, Y.; Kuriyama, T.; Hari, T.; Watanabe, M.; Ni, J. P.; Hattori; Uenishi, N.; Uemiya, T. Jpn. J. Appl. Phys. 1995, 34, 3876–83. (d) Brinkmann, M.; Charoenthai, N.; Traiphol, R.; Piyakulawat, P.; Wlosnewski, J.; Asawapiriom, U. Macromolecules 2009, 42, 8298–306. 19604
dx.doi.org/10.1021/jp2063436 |J. Phys. Chem. C 2011, 115, 19598–19605
The Journal of Physical Chemistry C
ARTICLE
(18) (a) Begland, R. W. US Patent 3962220 1976 (b) Shirai, K.; Matsuoka, M.; Fukunishi, K. Dyes Pigm. 2000, 47, 107–15. (19) Kobayashi, T.; Matsumoto, S.; Aoyama, T.; Wada, T. Thin Solid Films 2006, 509, 145–8. (20) Knapp, E. W. Chem. Phys. 1984, 85, 73–82. (21) Le Calve, N.; Labarbe, P. Spectrochim. Acta 1970, 26A, 77–86. (22) Tanaka, T; Matsuoka, M. Thin Solid Films 2001, 393, 148–153. (23) Damman, P; Dosiere, M; Smith., P.; Wittmann, J. C. J. Am. Chem. Soc. 1995, 177, 1117–20. (24) Vallee, R.; Damman, P.; Dosiere, M.; Toussaere, E.; Zyss, J. J. Am. Chem. Soc. 2000, 122, 6701–9. (25) Matsumoto, S.; Kobayashi, T.; Wada, T.; Shiro, M. Z. Kristallogr. 2004, 219, 239–43. (26) Fenwick, D.; Ihn, K. J.; Motamedi, F.; Wittmann, J. C.; Smith, P. J. Appl. Polym. Sci. 1970, 50, 1151–7. (27) Smith, D. L. Photogr. Sci. Eng. 1974, 18 (3), 309–322. (28) Wittmann, J. C.; Staupe, C.; Meyer, S.; Lotz, B.; Lang, P.; Horowitz, G.; Garnier, F. Thin Solid Films 1998, 333, 272–277. (29) Brinkmann, M.; Wittmann, J. C.; Barthel, M.; Hanak, M.; Chaumont, C. Chem. Mater. 2002, 14, 904–14. (30) Ofuji, M.; Inaba, K.; Omote, K.; Hoshi, H.; Takahashi, Y.; Ishikawa, K.; Takezoe, H. Jpn. J. Appl. Phys. 2003, 42, 7520–24. (31) Matsumoto, S.; Satoh, M.; Tsuchida, D.; Kobayashi, T.; Aoyama, T.; Wada, T. Trans. MRS-J. 2005, 30, 345–8. (32) (a) Scheibe, G.; Hartwig, S.; Muller, Z Elektrochem. 1943, 49, 383–7. (b) Hoppe, W. Kolloid Z. 1942, 101, 300–5. (c) Kasha, M. Molecular Excitons in Small Aggregates. In Spectroscopy of Excited State; Bardolo, B. D., Eds.; Plenum Press: New York, 1976; pp 345355. (33) Kobayashi, T.; Matsumoto, S.; Tanaka, T.; Kunugita, H.; Ema, K.; Aoyama, T.; Wada, T. M. Phys. Chem. Chem. Phys. 2005, 7, 1–6.
19605
dx.doi.org/10.1021/jp2063436 |J. Phys. Chem. C 2011, 115, 19598–19605
