Adsorption-Induced Second Harmonic Generation from the Layer-by

Oct 28, 2000 - Getting back to the layer-by-layer deposited films, the functional group would take random orientation in the layer. ...... Beyer, D.; ...
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Langmuir 2000, 16, 9478-9482

Adsorption-Induced Second Harmonic Generation from the Layer-by-Layer Deposited Ultrathin Film Based on the Charge-Transfer Interaction Yuzuru Shimazaki and Shinzaburo Ito* Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo, Kyoto 606-8501, Japan

Naoto Tsutsumi Department of Polymer Science and Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo, Kyoto 606-8585, Japan Received May 16, 2000. In Final Form: August 7, 2000 This paper is concerned with the second harmonic generation (SHG) from as deposited layer-by-layer adsorbed films. A nanolayered film was fabricated through the intermolecular charge-transfer interaction between the electron-donating carbazole (Cz) group and electron-accepting 3,5-dinitrobenzoyl group in the side chains of methacrylate-based polymers. A nonlinear optical dye was introduced in the film by using the copolymer in which Cz and disperse red 1 (DR1) groups were attached to the side chains. The DR1 moiety was highly oriented through the adsorption of PCzEMA-DR1, and the orientation was relaxed by additional adsorption of the polymers onto the DR1-containing layer. The second harmonic (SH) intensity of the multilayered film remained almost constant for the layers of even and odd numbers. This behavior could be explained by considering the change in the nonlinear susceptibility of the succeeding DR1containing layer. The SH intensity kept constant up to 120 °C for thermal stability.

Introduction Functionalization of polymeric materials is one of the main purposes for our research.1 One of the key factors for developing novel functions is the artificial control of the inner structure of the materials with a nanometer dimension. Alternate adsorption of polymers from solutions2-28 is a candidate for this purpose. This method enables one to fabricate ultrathin films in which an array * To whom correspondence should be addressed. Tel.: +81-75-753-5602. Fax: +81-75-753-5632. E-mail: a50471@ sakura.kudpc.kyoto-u.ac.jp. (1) Boyd, R. H.; Phillips, P. J. The Science of Polymer Molecules: An Introduction Concerning the Synthesis, Structure and Properties of the Individual Molecules That Constitute Polymeric Materials; Cambridge University Press: Cambridge, U.K., 1996. (2) Decher, G. Science 1997, 277, 1232. (3) Lvov, Y.; Decher, G.; Moewald. H. Langmuir 1993, 9, 481. (4) Schmitt, J.; Gruenewald, T.; Decher, G.; Pershan, P. S.; Kjaer, K.; Loesche, M. Macromolecules 1993, 26, 7058. (5) Hong, J. D.; Lowack, K.; Schmitt, J.; Decher, G. Prog. Colloid Polym. Sci. 1993, 93, 98. (6) Lvov, Y.; Decher, G.; Sukhorukov, G. Macromolecules 1993, 26, 5396. (7) Loesche, M.; Shmitt, J.; Decher, G.; Bouwman, W. G.; Kjaer, K. Macromolecules 1998, 31, 8893. (8) Bauer, J. W.; Rubner, M. F.; Reynolds, J. R.; Kim, S. Langmuir 1999, 15, 6460. (9) (a) Shimazaki, Y.; Mitsuishi, M.; Ito, S.; Yamamoto, M. Langmuir 1997, 13, 1385. (b) Shimazaki, Y.; Mitsuishi, M.; Ito, S.; Yamamoto, M. Langmuir 1998, 14, 2768. (10) Shimazaki, Y.; Mitsuishi, M.; Ito, S.; Yamamoto, M. Macromolecules 1999, 24, 8220. (11) Shimazaki, Y.; Mitsuishi, M.; Ito, S.; Yamamoto, M.; Inaki, Y. Thin Solid Films 1998, 333, 5. (12) Stockton, W. B.; Rubner, M. F. Macromolecules 1997, 30, 2717. (13) Koetse, M.; Laschewsky, A.; Mayer, B.; Rolland, O.; Wischerhoff, E. Macromolecules 1998, 31, 9316. (14) Anzai, J.; Kobayashi Y.; Nakamura, N.; Nishimura, M.; Hoshi, T. Langmuir 1999, 15, 221. (15) Serizawa, T.; Hashiguchi, S.; Akashi, M. Langmuir 1999, 15, 5363. (16) Li, D.; Jiang, Y.; Li, C.; Wu, Z.; Chen, X.; Li, Y. Polymer 1999, 40, 7065.

of functional groups in the molecular dimension can be made by simply dipping a substrate alternately into the solutions. With this technique, many functionalized films,17-29 such as multilayers with proteins for orchestrated enzymatic reactions,17,18 have been prepared and investigated. Meanwhile, second harmonic generation (SHG) from polymeric materials30 is one of the functions that has been investigated for years. SHG can be achieved by arranging nonlinear optical (NLO) dyes noncentrosymmetrically in the materials. One method to arrange the dyes in that way is poling the materials by an electric field. Another way is to self-assemble the dyes by use of the Langmuir(17) Lvov, Y.; Ariga, K.; Ichinose, I.; Kunitake, T. J. Am. Chem. Soc. 1995, 117, 6117. (18) Sun, Y.; Zhang, X.; Sun, C.; Wang, B.; Shen, J. Macromol. Chem. Phys. 1996, 197, 147. (19) Chen, W.; McCarthy, T. J. Macromolecules 1997, 30, 78. (20) Schmitt, J.; Decher, G.; Dressick, W. J.; Brandow, S. L.; Geer, R. E.; Shashidhar, R.; Calvert, J. M. Adv. Mater. 1997, 9, 61. (21) Feldheim, D. L.; Grabar, K. C.; Natan, M. J.; Mallouk, T. E. J. Am. Chem. Soc. 1996, 118, 7640. (22) Lvov, Y.; Yamada, S.; Kunitake, T. Thin Solid Films 1997, 300, 107. (23) Yamada, S.; Harada, A.; Matsuo, T.; Ohno, S.; Ichinose, I.; Kunitake, T. Jpn. J. Appl. Phys. 1997, 36, L1110. (24) Wang, X.; Balasubramanian, S.; Li, L.; Jiang, X.; Sandman, D. J.; Rubner, M. F.; Kumar, J.; Tripathy, S. K. Macromol. Rapid Commun. 1997, 18, 451. (25) Balasubramanian, S.; Wang, X.; Wang, H. C.; Yang, K.; Kumar, J.; Tripathy, S. K.; Li, L. Chem. Mater. 1998, 10, 1554. (26) Heflin, J. R.; Figura, C.; Marciu, D.; Liu, Y.; Claus, R. O. App. Phys. Lett. 1999, 74, 495. (27) Roberts, M. J.; Lindsay, G. A.; Herman, W. N.; Wynne, K. J. J. Am. Chem. Soc. 1998, 120, 11 202. (28) Lindsay, G. A.; Roberts, M. J.; Chafin, A. P.; Hollins, R. A.; Merwin, L. H.; Stenger-Smith, J. D.; Yee, R. Y.; Zarras, P.; Wynne, K. J. Chem. Mater. 1999, 11, 924. (29) He, J. A.; Samuelson, L.; Li, L.; Kumar, J.; Triphathy, S. K. Langmuir 1998, 14, 1674. (30) Prasad, P. N.; Williams, D. J. Introduction to Nonlinear Optical Effects in Molecules and Polymers; Wiley-Interscience: New York, 1991.

10.1021/la000681b CCC: $19.00 © 2000 American Chemical Society Published on Web 10/28/2000

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Figure 2. Absorption spectra of the samples alternately adsorbed with PCzEMA-DR1 and PDNBMA on the 6-layer DR1free films. Inset shows dependence of the absorbance (500 nm) on the number of layers.

Experimental Section Figure 1. Chemical structures of the polymers used in this study.

Blodgett (LB) method, which allows one to arrange the molecules along the surface normal. Kajikawa et al. reported that SHG from the LB films containing disperse red 1 (DR1) moieties was observed and that the SH intensity increased quadratically with the increase in film thickness.31 Getting back to the layer-by-layer deposited films, the functional group would take random orientation in the layer. However, it is natural to think that the functional group orients preferentially to some direction at the interface between layers, because the functional group could be drawn together with the groups responsible for adsorption such as ionic groups. In fact, Yamada and Kunitake reported that SHG was observed from the layerby-layer deposited film with a dye-containing polyelectrolyte.22,23 Other researchers also observed SHG from the NLO dye-containing layer-by-layer deposited films.24-29 Tripathy and Kumar reported that the layer-by-layer deposited film with azobenzene chromophores showed SHG activity.24,25 Furthermore, Heflin and Claus reported that the SH intensity from the layer-by-layer deposited film with NLO dyes showed quadratic increase against the number of layers.26 However, most of the papers reported that the SH intensity saturated or decreased as the number of layers increased,22,23,25,27,28 and the reason for this discrepancy between the theory and experimental results has not been elucidated in detail. Previously,9,10 we reported that the layer-by-layer deposited films can be fabricated through the intermolecular charge-transfer (CT) interaction between the methacrylate-based polymers having electron-donating carbazole (Cz) group (PCzEMA) and electron-accepting 3,5-dinitrobenzoyl (DNB) group (PDNBMA) in the side chains. The use of the CT interaction is advantageous in that the film can be fabricated in organic solvents, which allows a large variety of hydrophobic functional groups to be incorporated into the film. In this paper, we report on the SHG from the NLO dye-introduced layer-by-layer deposited films without any additional forces such as an electric field. As the NLO dye, DR1 was introduced into the film by using the copolymer having both Cz and DR1 groups in the side chains (PCzEMA-DR1). In addition to the observation of the SHG, a thermal stability measurement was also performed for the SHG from the layer-by-layer deposited films. (31) Kajikawa, K.; Anzai, T.; Takezoe, H.; Fukuda, A.; Okada, S.; Matsuda, H.; Nakanishi, H.; Abe, T.; Ito, H. Appl. Phys. Lett. 1993, 62, 2161.

Materials. Figure 1 shows the chemical structures of the compounds used in this study. These polymers, poly [2-(9carbazolyl)ethyl methacrylate] (PCzEMA, Mn ) 37 000) and poly [2-[(3,5-dinitrobenzoyl)oxy]ethyl methacrylate] (PDNBMA, Mn ) 20 000), have an electron-donating carbazole group and electron-accepting 3,5-dinitrobenzoyl group, respectively, in the side chains. These polymers were synthesized as reported.32,33 PCzEMA-DR1 was synthesized by random copolymerization of CzEMA and 4′-[[2-(methacryloyloxy)ethyl]-ethylamino]-4-nitroazobenzene (DR1MA) in DMF at 60 °C for 24 h with AIBN as an initiator. The fraction of DR1MA introduced in PCzEMA-DR1 was determined to be 11.4% by elemental analysis. Quartz substrates were treated in piranha solution prior to use. All the solvents used were of spectrophotometric grade. Preparation of the Layer-by-Layer Deposited Films. The layer-by-layer deposited film was prepared by alternate adsorption of the polymers onto a quartz substrate through the intermolecular CT interaction between the carbazole group and DNB group in the side chains. In all cases, the polymer was allowed to adsorb from the solution in DCE for 5 min. Then, the substrate was rinsed in DCE and left in air to dry for 5 min each. The concentration of the solution was ca. 1.0 × 10-4 mol unit L-1. For all the films prepared in this study, the substrates used were precoated with the 6-layer alternately adsorbed film with PCzEMA and PDNBMA to eliminate the effect of the quartz surface on the SHG behavior. The procedure described above was performed at room temperature under the relative humidity of 20%. Measurement. SHG measurement was performed on the DR1-introduced layer-by-layer deposited films. A picosecond Nd: YAG laser (10 Hz, EKSPLA) was used as a light source. P-polarized SH light emerged from the sample was detected by a photomultiplier and recorded in a PC through a boxcar integrator (Stanford Research System). The SH intensity of the sample was normalized by that of a Y-cut quartz plate (d11 ) 0.5 pm/V), determined by drawing an envelope for the fringe pattern, and the value at 45 degrees was reported. UV-Vis absorption spectra were recorded by a Hitachi U-3500 spectrophotometer. The glass transition temperature (Tg) was determined by differential scanning calorimetry (DSC) at the scan rate of 10 °C/min. The Tg was taken as the midpoint of the endothermic transition in the second scan.

Results and Discussion UV-Vis Absorption Measurement. Figure 2 shows the absorption spectra of the film alternately adsorbed with PCzEMA-DR1 and PDNBMA. Previously, we showed that the layer-by-layer deposited film could be fabricated with PCzEMA and PDNBMA through the CT interaction. In ref 9, the surface plasmon measurements and the UVVis absorption measurements demonstrated that the alternate adsorption with PCzEMA and PDNBMA takes place successfully. In the UV-Vis absorption measurements, the absorbance of the Cz group and the CT complex (32) Simionescu, C. I.; Percec, V.; Natansohn, A. Polym. Bull. 1980, 3, 535. (33) Ito, S.; Ohmori, S.; Yamamoto, M. Macromolecules 1992, 25, 185.

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Figure 3. Angular dependence of SH intensity from a single NLO layer on the 6-layer DR1-free film for p-polarized (a) and s-polarized (b) incident light. In both cases, p-polarized SH light was detected.

increased linearly with the number of adsorption cycles. Therefore, the spectra in the figure include the absorption by the 6-layer precoated film. In Figure 2, the absorbance further increased with the increase in the number of adsorption cycles with PCzEMA-DR1 and PDNBMA. The inset in Figure 2 shows the absorbance at 500 nm, at which the absorption of DR1 moieties is dominant, plotted against the number of adsorption cycles. The absorbance at 500 nm increased after immersion of the substrate in the solution of PCzEMA-DR1 and the absorbance increased linearly with the number of bilayers. This clearly indicates that the layer-by-layer deposited film could be fabricated with PCzEMA-DR1 and PDNBMA. SHG from a Single DR1-Containing Layer. Figure 3 shows the angular dependence of the SHG signals from a single PCzEMA-DR1 layer (NLO layer) adsorbed on the 6-layer deposited film for p-polarized (Figure 3a) and s-polarized (Figure 3b) incident light. In both cases, p-polarized SH light was detected. The SH intensity (I2ω) from ultrathin films on both sides of a substrate can be described by eq 1.34

I2ω ) Aχeffl2 Iω2(1 + cos Ψ)

(1)

in which χeff is the effective nonlinear susceptibility of the film at a certain incident angle, l is the thickness of the film, Iω is intensity of the incident light, Ψ is the phase difference of the SH lights from the film on the front and rear sides of the substrate, and A is a constant. The fringes in both figures originate from the interference of emerged SH light from both sides of the substrate, and the fringe pattern can be determined mainly by the optical parameters of the substrate used.35 Several kinds of origins for the SHG are possible. One possibility is that the second harmonic light is generated from the CT complex in the deposited film. Eisenthal et al. reported that catechol can form a CT complex on TiO2 surfaces and determined the free energy of adsorption of catechol onto the surface of colloidal TiO2 particles through the observation of SHG from the CT complex.36 However, (34) Wijekoon, W. M. K. P.; Asgharian, B.; Prasad, P, N.; Geisler, T.; Rosenkilde, S. Thin Solid Films 1992, 208, 137. (35) While the fringe minima for p-polarized incident light (Figure 4a) fell to zero, those for s-polarized (Figure 4b) took nonzero values. According to Kajikawa et al., these nonzero values are due to the difference in SH intensity that emerged from the front and rear sides of the substrate (ref 38).

the 6-layer deposited film adsorbed alternately with PCzEMA and PDNBMA is not SHG active. This means that the SHG from the film originates from the DR1 moieties aligned noncentrosymmetrically in the film through the adsorption of PCzEMA-DR1. The DR1 moieties have both electron-donating and electron-accepting sites and, therefore, one might consider that the preferential orientation of the DR1 moieties is due to the interaction of the electron-donating site in the DR1 moiety with the DNB group at the surface of PDNBMA layer. However, these electron-donating and electron-accepting sites in the DR1 moieties are charge-transferred intramolecularly,37 resulting in the inability of the electrondonating site to interact with the DNB group at the surface. The DR1 moieties and the Cz groups are linked with a main chain and, therefore, when the adsorption takes place through the CT interaction between Cz and DNB groups, the DR1 moieties are drawn together with the Cz groups. This probably results in the DR1 moieties becoming aligned noncentrosymmetrically along the surface normal at the interface. Since s-polarized SH light was negligibly small, the DR1 moieties in the film were preferentially oriented along the surface normal. Since the ratio of the SH intensity for p-polarized incident light (Ip-p) against that for s-polarized incident light (Is-p) could be measured, the average tilt angle (θtilt) of the DR1 moieties could be calculated with eqs 2 and 338,39 when the fundamental light is incident at 45°.

θtilt ) arctan χzzz )2 χzxx

x

x

2χzxx χzzz

Ip-p -3 Is-p

(2)

(3)

where χzzz and χzxx are tensor components of the nonlinear susceptibility of the film. Since the value of Is-p includes an enhanced contribution from the film on the rear side of the substrate,38 the absolute tilt angle of the DR1 moieties in the film could not be determined. However, the tilt angle is smaller than 20° because the overestimation of Is-p results in a higher tilt angle. This means that the DR1 moieties in the film were highly oriented toward the surface normal. Figure 4 shows the plots of (a) SH intensity (IN) and (b) normalized nonlinear susceptibility (χN/χ1) of the NLO layer onto which the N - 1 layers of the polymers without DR1 moieties were additionally adsorbed. The schematic illustration of the sample is shown in Figure 4c. The value of χN/χ1 can be evaluated by taking the square root of IN/I1. These figures show that the SH intensity decays with the increase in the number of layers deposited on the NLO layer, indicating that the adsorption of the polymers onto the NLO layer induces orientational relaxation of the DR1 moieties, and lowers the nonlinear susceptibility of the NLO layer. From Figure 4b, it is apparent that the nonlinear susceptibility decayed to ca. 70% of the initial value by the deposition of a single polymer layer. SHG from NLO Multilayers. Figure 5 shows the SH intensities at 45° on the number of layers for the film (36) Liu, Y.; Dadap, J. I.; Zimdars, D.; Eisenthal, K. B. J. Phys. Chem. B 1999, 103, 2480. (37) Meng, X.; Natansohn, A.; Rochon, P.J. Polym. Sci. Part B: Polym. Phys. 1996, 34, 1461. (38) Kajikawa, K.; Kigata, K.; Takezoe, H.; Fukuda, A. Mol. Cryst. Liq. Cryst. 1990, 182A, 91. (39) Beyer, D.; Paulus, W.; Seitz, M.; Maxein, G.; Ringsdorf, H.; Eich M. Thin Solid Films 1995, 271, 73.

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Figure 6. Simulated results for the SH intensity of the samples with the structure shown in Figure 5c for the p-polarized incident light: (‚) measured value and (×) simulated value calculated with eq 4.

Figure 4. Dependence of (a) SH intensity (IN) and (b) χN/χ1 on the number of layers for the samples with the structure shown in (c). (‚) p-polarized incident light and (3) s-polarized incident light.

the SH intensity will increase quadratically with the increase in the thickness (eq 1). However, as in Figure 4, the single NLO layer in the film showed the decay in the nonlinear susceptibility with the increase in the number of additionally adsorbed polymer layers. This is one reason for the saturation in SH intensity against the number of NLO layers. The SH intensity of the N-layered film alternately adsorbed with PCzEMA-DR1 and PDNBMA (I(N)) can be calculated by eq 4 with the data in Figure 4b if one assumes that each NLO layer in the sample contributes independently to the SHG.

I(N) )

I(N) )

Figure 5. Dependence of SH intensity on the number of layers for the samples with the structure shown in (c) for p-polarized incident light (a) and s-polarized incident light (b). In both cases, p-polarized SH light was detected.

alternately adsorbed with PCzEMA-DR1 and PDNBMA. The data for p-polarized and s-polarized incident lights are shown in Figure 5a and 5b, respectively. The schematic illustration of the sample is shown in Figure 5c. It is apparent in Figure 5 that the SH intensity increased after the adsorption of PCzEMA-DR1 (odd layers), but decreased when PDNBMA was adsorbed (even layers). Lindsay and Roberts also observed the same tendency for the systems with NLO-active side chain polycations and NLO-inactive poly(styrenesulfonate).28 Furthermore, one can also see that the intensity remained almost constant for both the even and odd numbered layers. This is inconsistent with the theory for the ultrathin films with a constant nonlinear susceptibility, which predicts that

(∑ ) (∑ ) (N+1)/2

χ2i-1

i)1

χ1

N/2

χ2i

i)1

χ1

2

I(1) (for odd layers) (4)

2

I(1)

(for even layers)

Because the sample has a few NLO layers, the nonlinear susceptibilities of all the NLO layers are summed up in eq 4 to obtain the nonlinear susceptibility of the film. The simulated data are shown in Figure 6 with the experimental data for p-polarized incident light. The same trend was observed for s-polarized incident light (data not shown). In this figure, the calculated values were larger than the experimental data. This suggests that an additional factor exists which causes the SHG decay. This factor will be discussed in the following paragraphs. Figure 7 shows plots of SH intensity from the single NLO layer at the top of N-layered film. The schematic illustration of the sample is shown in Figure 7b. It is apparent that the SH intensities remain constant for both p-polarized and s-polarized incident light. This indicates that the orientational state of the DR1 moieties, that is, the nonlinear susceptibility of the top DR1-containing layer, is the same irrespective of the number of underlying DR1-free layers. Thus, the simulated data calculated with eq 4 should be fitted with the experimental data if one does not consider some interaction between NLO layers in the film. We are not sure at present why the SH intensity was smaller than expected. However, two reasons are possible. First, although DR1 moieties were introduced in PCzEMA-DR1 by only 11.4%, the introduction of large DR1 moieties into the donor polymer may roughen the surface of the layer-by-layer deposited film, thereby making the succeeding NLO layers less effective for SHG. Second, since the DR1 moiety has a distinct and strong dipole moment, the dipole-dipole interaction between the DR1 moieties may disturb the preferential orientation of the DR1 moieties in the succeeding layers, resulting in the smaller SH intensity from the NLO multilayers compared with that calculated by eq 4.

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Figure 8. Dependence of SH intensity from the single NLO layer with (3) and without (‚) the outermost PDNBMA layer on the annealing temperature.

Figure 7. Dependence of SH intensity on the number of layers for the samples with the structure shown in (b): (‚) p-polarized incident light and (3) s-polarized incident light.

In conclusion, the orientation of DR1 moieties in the layer-by-layer deposited film is induced through the adsorption of PCzEMA-DR1, and relaxed by the additional adsorption of the polymers onto the DR1-containing layer. It should be also noted that the SH intensity remained almost constant against the number of NLO layers in the film. The saturation in SH intensity with the increase in the number of layers was also reported by Roberts27 and Tripathy25 for the electrostatic layer-by-layer self-assembly, although their system showed quadratic increase in SH intensity against the number of layers up to 72 layers (Roberts’ system) or 6 layers (Tripathy’s system). The difference in the number of layers at which the SH intensity was saturated might arise from the fact that the NLO dyes are charged and directly responsible for the adsorption in the electrostatic system, while the DR1 moieties are not responsible for the adsorption in our system. Therefore, the orientation of the DR1 moieties in our system are probably easier to relax, resulting in the earlier saturation in the SH intensity against the number of layers. Thermal Stability of the SHG signals. Figure 8 shows the annealing effect on the SHG signals from the single NLO layer (filled circle) and the single NLO layer onto which PDNBMA was adsorbed (unfilled triangles). These samples were annealed at a given temperature for 3 h and SHG measurements were performed after the samples were cooled to room temperature. Since the absorption spectra of these samples did not change after being annealed at these temperatures, it can be said that the DR1 moieties in the film survived through the annealing. The SH intensity remained constant up to 120 °C, although the intensity kept slightly increasing for the 2-layer sample. However, the intensity decreased after being annealed at higher temperatures. Roberts27 also observed this trend for the layer-by-layer deposited

polyelectrolyte multilayers. We have shown in ref 9 that the structure of the layer-by-layer deposited film with PCzEMA and PDNBMA remains up to 200 °C. Therefore, the decrease in the SH intensity is not due to the destruction of the layered structure. Since the glass transition temperatures (Tg) of PCzEMA-DR1, PDNBMA, and the 1:1 mixture of PCzEMA-DR1 with PDNBMA are 139, 98, and 115 °C, respectively, the decrease in the SH intensity is due to the orientational relaxation of the DR1 moieties induced by the micro-Brownian motion of the polymers at a temperature above Tg. Conclusion SHG was observed from as deposited layer-by-layer deposited films adsorbed through the intermolecular charge-transfer interaction between PCzEMA-DR1 and PDNBMA. Although the DR1 moiety had no interaction with the acceptor polymer, preferential orientation was induced on the process of adsorption, yielding noncentrosymmetric alignment in the surface film. The SH intensity of the film alternately adsorbed with PCzEMADR1 and PDNBMA remained almost constant for the layers of even numbers and odd numbers, respectively. This behavior could be explained by two facts: (1) the nonlinear susceptibility of the NLO layer decreased due to the orientational relaxation through additional adsorption of the polymers onto the NLO layer, and (2) the NLO layers in the film had a negative effect on the orientation of DR1 moieties in the succeeding adsorbing PCzEMADR1. The SH intensity of the DR1-containing film showed high thermal stability up to 120 °C. After being annealed at a temperature above 120 °C, the DR1 moieties in the film experience an orientational relaxation due to the micro-Brownian motion of the polymers, while keeping the layered structure at the temperatures above the glass transition temperature. Acknowledgment. This work was supported by a Grant-in-Aid for Scientific Research (No. 10555330), from the Ministry of Education, Science, Sports and Culture of Japan. The authors wish to thank Miyamoto Lab. for the DSC measurements. LA000681B