긴알킬사슬을 가진 spiropyran막의 분석

이상우, 민준홍, 최정우, 이원홍, 김의락*

서강대학교 화학공학과, 계명대학교 화학과*

Analysis of the spiropyran film with a long alkyl chain

Sangwoo Lee, Junhong Min, Jeong-Woo Choi, Won Hong Lee, Ui Rak Kim*

Dept. of Chem. Eng., Sogang Univ., C.P.O. BOX 1142, Seoul 100-611 Korea.

Dept. of Chemistry, Keimyung Univ. Dae-Gu, Korea*

INTRODUCTION

In this paper, the Langmuir-Blodgett techniques and the basic method for the coating films, spin coating technique, are used for the fabrication film with the long alkylchain-contained spiropyran The photochromic phenomena of the Langmuir-Blodgett films are investigated for the air-water interface and solid state. In the films by the spin coating method, the effect of the long alkyl chain on the photochromic properties of films are observed. The optical properties of the spin coating films are compared with that of the films by Langmuir-Blodgett technique.

EXPERIMENTAL DETAILS

1.Materials

The spiropyran with long-alkyl chain( 3',3',Dimethyl-1'- hexadecyl-6- nitrospiro-(2H-1-benzoypyran-2,2'-indoline) was synthesized by Gruda's method.[1] Spiropyran without long-chain was purchased in Tokyo Chemical Industry (Japan).

2.LB technique

1mM of synthesized spiropyran with long-alkyl chain in chloroform was spread on the water(>18M□cm) surface. The monolayer at the air-water interface was established with the evaporation of chloroform. The experiments for film deposition and obtaining □-A isotherm were performed with Langmuir trough (Nima, Model 2022, UK) under UV irradiating condition. All spiropyran films was deposited upto 10 layers.

3.Spincoating

12□L of spiropyran with long-alkyl chain in chloroform (0.5M) was dropped on the quartz slides rotating with 2000rpm for 40sec with the photoresist spiner (Headway Research Inc., Model 1-EC-101DR790, U.S.A.). The coated spiropyran films were dried for 30min at 60oC.

RESULTS AND DISCUSSION

The Fig.1 (a) represented the □-A curve of spiropyran at air-water interface under UV light irradiation. The compression for the spiropyran monolayer was stopped before the collapse of the monolayer occurred at the 40 mN/m of surface pressure. The molecular area of spiropyran (12Å2) at zero pressure in the □-A curve was smaller than that of photomerocyanine (45Å2) after 5 hour of UV light irradiation. It is considered that the area occupied by head group of spiropyran was increased due to the reaction of 'ring opening' occurred during the irradiation of UV light. Based on this result, during the irradiation of UV light, the film of spiropyran was deposited to occupy the space for the reaction of 'ring opening' of spiropyran. Fig. 1 (b),(c) and (d) represensted the AFM topographies of spiropyran film monolayer fabricated by horizontal dipping LB technique with various UV light irradiation time. As shown in Fig. 1 (b), The spiropyran film before UV light irradiation had the rod-type aggregate of spiropyran. But, as UV light irradiated, the size of aggregate was reduced. It is considered that the photoreaction, 'ring opening', by UV light irradiation affects the interaction between molecules of spiropyran.

(a)                           (b)

(c)                         (d)

Figure 1. □-A isotherm of spiropyran, (a); AFM topogrpies of spiropyran with changing UV irradiation time, (b) 0 hr. (c) 1 hr. (d) 10 hr.

The absorption spectra of spiropyran in ethanol and spiropyran LB film deposited with 20 mN/m of surface pressure were shown in Fig. 2. In the spiropyran LB films as well as in solution, the photochromism was occurred by the photoreaction when UV light irradiated. But the absorption peak of films was shifted to the longer wavelength (580 nm) in comparison with that (548 nm) of spiropyran solution in ethanol. It is likely that this shift of absorbance peak was induced by the J-aggregate due to the effect of molecular order, one of the characteristics of LB technique [2].

Figure 2. Comparison of absorbance spectrum LB film with that of solution.

The Fig. 3 showed that the absorbance of spiropyran films fabricated by the spin coating technique was changed by UV irradiation. While UV light irradiated on the spiropyran film, the peak of absorbance spectrum was shifted from 59.5 Å to 54.8 Å. But the peak value of absorbance was decreased. It can be considered that in the early stage, upto 30 min, the red-shift (59.5 Å) occurred due to the J-aggregate induced by uniform molecular orientation to the radial direction resulted from the film rotation and then the re-shift (54.8 Å) of spiropyran films occurred due to the rearrangement by the ring opening of spiropyran, which induces the increase of randomness of molecular orientation. The conformation of molecular orientation might be due that the shape of a spiropyran molecules is rod-type with large aspect ratio because spiropyran contains the long alkyl chain (C16). But it should be considered that the J-aggregate of spiropyran fabricated by spin coating technique might be weaker than that by LB technique because J-aggregate disappeared more easily. The maximum change of absorbance was about 0.4 in spiropyran films by the spin coating technique. It can be concluded that spiropyran films fabricated by spin coating technique was appropriate than spiropyran LB film because the magnitude of absorbance change was larger.

Figure 3. Absorbance spectrum of spiropyran fabricated by spin coating technique

Fig. 4 represented that the absorbance of the double layer of spiropyran by the spincoating technique was changed by UV light irradiation. While UV light irradiated on the spiropyran film, the peak of absorbance spectrum was shifted from 56.5 Å to 54.8 Å with the increase of absorbance peak value comparing to the phenomena of monolayer of spiropyran as shown in Fig. 3. This small J-aggregate of double layer might be due to rearrangement of spiropyran by the solvent for the fabrication of a second layer.

Figure 4. Absorbance of the double layer of spiropyran by spin coating technique

ACKNOWLEDGEMENT

This work was supported by grants from Korea Science and Engineering Foundation (KOSEF : 95-0502-02-01-3)

REFERENCES

1. Gruda, I. and Leblanc, R. M.: Can. J. Chem., 54, 576(1976).

2. Miyata, A., Unuma, Y. and Higashigaki, Y.: The Chemical Society of Japan, 66, 993(1993).