Photoinduced Reversible Heteroepitaxial Microcrystal Growth of a

Article pubs.acs.org/crystal

Photoinduced Reversible Heteroepitaxial Microcrystal Growth of a Photochromic Diarylethene on (110) Surface of SrTiO3 Shingo Sakiyama,† Seiji Yamazoe,*,† Ayaka Uyama,† Masakazu Morimoto,‡ Satoshi Yokojima,§,∥ Yuko Kojima,⊥ Shinichiro Nakamura,∥ and Kingo Uchida*,† †

Department of Materials Chemistry, Faculty of Science and Technology, Ryukoku University, Seta, Otsu 520-2194, Japan Department of Chemistry and Research Center for Smart Molecules, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan § Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan ∥ Nakamura Laboratory, RIKEN Research Cluster for Innovation, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan ⊥ Mitsubishi Chemical Group, Science and Technology Research Center, Inc., 1000 Kamoshida, Yokohama 227-8502, Japan ‡

S Supporting Information *

ABSTRACT: Diarylethene 1 shows reversible transformation between the open-ring isomer (1o) and the closed-ring isomer (1c) by alternate UV and visible light irradiation, accompanied with reversible melting and crystallization of the microcrystalline film of 1 at 67 °C, which is the eutectic temperature of 1o and 1c. The reversible epitaxial crystal growth of an 1o of a diarylethene derivative was observed on a 110 surface of a strontium titanate (SrTiO3) single crystal by maintaining a constant temperature and monitoring six reversible intensity changes (within 2 h of repeating cycles) of the reflection of 004 of 1o on XRD measurements.

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INTRODUCTION Photochromic molecules show reversible color changes associated with photoisomerization by photoirradiation.1 In photochromic families, diarylethene exhibits excellent fatigue resistance and high thermal stability of both isomers and shows photoreactivity even in the crystalline state.2 Recently, two reversible photoresponsive crystal systems were reported using the photoresponse of photochromic diarylethene derivatives. One is the photoinduced shape changes of the crystals, which is due to the reversible volume changes of the molecules in the crystalline state.3 Such photoinduced shape changes were also observed with thermally unstable photochromic compounds.4 The other is the reversible topographical changes on crystalline surfaces, and such phenomena were not reported in the thermally unstable system. We previously reported such changes, which occur via the eutectic melted state of both isomers of diarylethene derivatives.5 Kobatake et al. reported similar ones due to the thermal phase changes of other diarylethene derivatives.6 In our previous study, reversible topographical changes were observed on a microcrystalline surface of diarylethene 1 between the rough crystalline surface of an open-ring isomer (Scheme 1) and flat eutectic surfaces by alternate UV and visible light irradiation. The peak intensity changes of open-ring isomer 1o in XRD patterns were observed within 2 h of a repeating cycle.7 The results indicated that reversibly photogenerated rod-shaped crystals on the surface were produced based on the lattice of the open-ring isomer crystals in the subphase. Encouraged by the results, we fabricated a system in which photoinduced reversible crystal © 2012 American Chemical Society

Scheme 1. Molecular Structures of Open- and Closed-Ring Isomers of Diarylethene

growth was controlled on an inorganic crystal whose lattice parameter resembles that of 1o. For decades, the heteroepitaxial growth of organic materials has received much attention because of its importance and unique characteristics.8−13 Organic heteroepitaxial techniques are useful for the fabrication of electronic and photonic devices.14 In device fields, single crystal substrates of metal oxides, such as SrTiO3 (STO), MgO, and sapphire, are used to obtain heteroepitaxial thin films.15 Among single crystal substrates, STO substrates are often used in the ferroelectric field. STO has a perovskite structure with a cubic phase (space group, Pm3̅m; lattice constant, a = 3.905 Å; ICSD number, #23076). Figure 1 shows the 110 surface of STO. The 110 surface has 1̅12̅ and 1̅11 axes on a plane, and the 1̅12̅ axis is perpendicular to the 11̅ 1 axis. The distance of Sr1−Sr2 is 6.763 Received: November 25, 2011 Revised: January 16, 2012 Published: February 13, 2012 1464

dx.doi.org/10.1021/cg201560f | Cryst. Growth Des. 2012, 12, 1464−1468

Crystal Growth & Design

Article

Figure 1. SrTiO3(STO) 110 plane with a space group of Pm3̅m (a = 3.905 Å). Distance between Sr atoms (Sr1−Sr2) on 1̅11 axis is 6.763 Å, and this value is close to the length of the b axis of rod-shaped 1o. The 1̅12̅ axis of STO is perpendicular to the 1̅11 axis. Distance between Sr1−Sr3 on 1̅12̅ axis (38.261 Å) is close to three times the length of a axis (12.9908 Å) of rod-shaped 1o. Therefore, the a axis of rod-shaped 1o fits the 1̅12̅ axis on the 110 plane of STO.

Å in the 1̅11 axis, and this value is close to lattice constant b (6.3593 Å) of rod-shaped 1o. The Sr1−Sr3 distance on the 1̅12̅ axis (38.261 Å) is close to three times the length of the a axis (12.9908 Å) of the rod-shaped 1o. Therefore, the a axis of rodshaped 1o fits the 1̅12̅ axis on the 110 plane of the STO. Thus, rod-shaped 1o can grow on the 110 surface of the STO. We used STO substrate with a 110 plane ((110) STO) to epitaxially grow 1o on the substrate. To the best of our knowledge, this article is the first report of photoinduced reversible epitaxial crystal growth of open-ring isomer 1o by alternate UV and visible light irradiation. We must promote the technique of heteroepitaxial crystal growth, which controls crystal habits or polymorphism.

the surface. A scanning electron microscope (KEYENCE VE8800) and an optical microscope (Leica DMLP) were used to study the surface microstructure. Crystal Data of 1o. The intensity data of the 1o crystal were collected by ω scan at a width of 0.3°/frame on a Bruker SMART APEX CCD diffractometer with graphite-monochromatized Mo Kα radiation (λ = 0.71073 Å) at 93 K. Data reduction was performed using SAINT software, which corrects for Lorentz and polarization effects and decay. The cell constants were determined by the global refinement. The structure was solved by direct methods using SHELXS-9716 and refined by full-matrix least-squares on F2 using SHELXL-97.17 The positions of the hydrogen atoms were calculated geometrically and refined by the riding model. Crystal data for the rod-shaped crystals of 1o: C17H14F6O2S2, monoclinic, P21/c, a = 12.9908(12) Å, b = 6.3593(6) Å, c = 22.098(2) Å, β = 106.1430(10)°, V = 1753.6(3) Å3, Z = 4, Dcalcd = 1.623 Mg m−3, R1 (I > 2σ(I)) = 0.0409, wR2 (I > 2σ(I)) = 0.0992, T = 93(2) K; CCDC 796675. These data can be obtained free of charge from The Cambridge Crystallographic Data Center: www.ccdc.cam.ac.uk/data_request/cif.

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MATERIALS AND METHODS Absorption spectra were measured on a HITACHI U-3500 spectrophotometer. Photoirradiation (visible light, λ > 430 nm) was carried out using an Ushio 500-W xenon lamp with a cutoff filter (Toshiba color filter Y-43), and UV irradiation was carried out with a Topcon UV lamp Fi5L (λ = 365 nm, 12 W). Photoirradiation experiments at eutectic temperature were done on a Mettler Toledo FP90 with a FP82HT hot stage. XRD was measured on a Rigaku RINT2000. The diarylethene, 1-(2,5-dimethyl-1,1-dioxa-3-thienyl)-2-(2,5-dimethyl-3-thienyl)-3,3,4,4,5,5-hexafluorocyclopentene 1o, was prepared as reported in a previous article.7 STO crystal plates with (100), (110), and (111) surfaces were purchased from the Furuuchi Chemical Corporation. Preparation of Film and Characterization. The film was prepared by coating a chloroform solution containing 1o (100 mg/mL) on the substrate (10 × 10 mm, glass or STO crystal plates). It was stored at room temperature to evaporate the solvent and placed in a desiccator. The residual solvent was removed under 58 mmHg for 30 min for SEM observation. Residual chloroform was not observed in 1H NMR in C6D6. The film was found to be approximately 20 μm thick, by a surface profiler (KLA Tencor, Alpha-Step IQR) after scratching

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RESULTS AND DISCUSSION Compound 1o undergoes a photocyclization reaction to form its closed-ring isomer 1c by UV irradiation, and 1c regenerates 1o by visible light irradiation in a hexane (Figure S1, Supporting Information). The quantum yields of cyclization and cycloreversion reactions of 1 in the hexane solution were 0.35 and 4.2 × 10−3, respectively.7 The photoisomerization of 1o to 1c was also observed in the crystalline state because the distance between the reactive carbon atoms of 1o in the needleshaped crystals was 3.606 Å. If the distance is less than 4 Å, the cyclization reaction can proceed upon UV irradiation even in the crystalline state.18 In previous work, DSC measurements of the 1o and 1c mixtures with different components were carried out, and the phase diagram was obtained.7 The melting points of 1o and 1c were 94 and 134.5−135.0 °C, respectively. The 1465



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Figure 2. Schematic illustration of crystal growths of 1o. (a−c) Photoinduced topographical changes of surface on SrTiO3 substrate (present system); (a′−c′) Photoinduced topographical changes of surface on glass substrate (previous system).

Figure 3. SEM images (×1000) of photoinduced topographical changes of surface on STO (a−c) and glass substrates (d−f); (a) crystallized surface of 1o on STO substrate, (b) melt surface of 1o after UV irradiation, (c) recrystallized surface of 1o after visible light irradiation, (d) crystallized surface of 1o on glass substrate, (e) melt surface of 1o after UV irradiation, and (f) recrystallized surface of 1o after visible light irradiation (scale bar, 10 μm).

eutectic point was 67 °C, where the ratio of 1o and 1c was 61:397 (Figure S2, Supporting Information). After UV irradiation to the surface, although the 1c content increased to 31%, it never increased beyond that of the eutectic mixture because of the higher concentration of 1o (concentration effect),7 and the depth of the photogenerated 1c layer was less than 10 μm. During the UV light irradiation on the microcrystalline surface of 1o on glass substrate, the eutectic temperature was maintained. We employed the eutectic temperature because the surface topographical changes have

been observed at eutectic temperature by the melt-recrystallization cycle mechanism which was explained by using the phase diagram.5 The crystals of 1o were melted, and a flat eutectic surface was generated within 30 min. Upon visible light irradiation to the surface, the microcrystals of 1o regenerated and covered the whole surface of the bulk film within 1.5 h.7 The crystal growth was much faster than that in the previous system5a in which a needle-shaped crystal of a closed-ring isomer was generated on the subphase of the open-ring isomer. The rapid crystal growth was due to the existence of seeds; the 1466



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substrates as a control. The film was prepared by coating the chloroform solution of 1o on the substrates, evaporation of the solvent, and heating at 94 °C to melt the 1o. The film was stored at 90 °C, and the surface was gradually cooled to 30 °C by a program controlled by 12 °C/h, then the first XRD measurement was carried out. A strong diffraction peak was observed at 16.6° and weak diffraction peaks at 8.3° and 24.9°. The diffraction peaks at 8.3°, 16.6°, and 24.9° correspond to the 002, 004, and 006 diffractions of rod-shaped 1o. Therefore, the 1o film on the STO substrate with the 110 plane has an 001 orientation. In contrast, the 1o films on (100) STO (Figure 5a), (111) STO (Figure 5b), and glass (Figure S3a, Supporting

microcrystals of 1o that remained in the subphase play as the seed for the crystallization of 1o regenerated. The results suggest that if the subphase crystals were generated by epitaxial growth on a crystal matrix, then photochemically reversible crystal growth could be performed (Figure 2). The needle-shaped crystal of 1o was monoclinic, and the data are summarized in the experimental section and the Supporting Information. When comparing the unit lengths and angles, we selected the 110 plane of a strontium titanate (SrTiO3 (STO)) single crystal as the subphase. Figure 1 shows the 110 surface of the STO. The 110 surface has 1̅12̅ and 1̅11 axes in the plane, and the 1̅12̅ axis is perpendicular to the 1̅11 axis. The distance between the Sr atoms (Sr1−Sr2) is 6.763 Å in the 1̅11 axis, and this value is close to the lattice constant b (6.3593 Å) of rod-shaped 1o. Therefore, reversible photoinduced crystal growth of 1o on the surface was expected. The reversible topographical changes of the microcrystalline of 1o on the STO substrate are summarized in Figure 3 by comparison with those on the glass substrate. The SEM image of the microcrystalline surface of 1o on STO is shown in Figure 3a. The crystal surface was covered with scale-shaped, 3−4 μm microcrystals. The film was kept at a eutectic temperature of 67 °C and was irradiated by UV light. After 30 min, the surface was melted to make a flat surface due to the formation of the eutectic mixture as well as the surface on the glass substrate (Figure 3b,e). On the surface, visible light was irradiated for 1.5 h at eutectic temperature, and regeneration of the microcrystal of 1o was observed (Figure 3c). Because of the differences of the substrate, the shape of the microcrystalline surface was different. The surface over the STO was covered with lying rod-shaped microcrystals, and the surface on the glass substrate was covered with random standing rod-shaped ones. The situations in Figure 3b,c could be repeated by alternate UV and visible light irradiation. The appropriate reversible reflection pattern profiles of 1o on the STO substrate were monitored by XRD measurements (Figure 4). Diffraction intensities were normalized using the diffraction intensity of the 110 diffraction of the STO substrate. The results were compared on glass and (100) and (111) STO

Figure 5. XRD patterns of 1o films fabricated on (a) (100) SrTiO3(STO) and (b) (111) STO substrates. Both films showed 100 preferential orientation. Moreover, several diffraction peaks were observed. Therefore, 1o film was not epitaxially grown on (100) and (111) STO substrates.

Information) substrates had major orientations of 100, 100, and 302̅, respectively, but minor orientations as well. We examined the surface roughness of (100), (110), and (111) STO substrate by AFM and found that all the substrates are flat (Figure S4, Supporting Information). This result clearly shows that the surface lattice structure of the substrates is important for the orientation growth of the films. In comparison with the orientation of the film on the other substrates, that on the (110) STO substrate is exceptionally aligned. Therefore, 1o film was epitaxially grown on the (110) STO substrate. During the storing period of 30 min at 67 °C, the film was irradiated with 366 nm of UV light for initially 10 min, then the last 20 min, the film was stored under dark to monitor the second XRD of the eutectic surface. The XRD pattern shows that the reflection of 004 remains but is drastically weakened due to the melt of the surface crystals. The remaining small intensity of the peak indicates the crystal of 1o stayed in the subphase, a domain that is very close to the STO crystal surface. By visible light irradiation to the surface at a constant 67 °C for 1.5 h, the signal intensity was recovered. The cycle was repeated six times. The results of the XRD changes are summarized in Figure 4, and the intensity profile of the reflection of 004 is shown in Figure 6. The photorepeated profile of the XRD of 1o on the glass substrate was previously reported7 (Figure S3, Supporting Information). The microcrystalline film of 1o on the glass substrate shows many reflection peaks, but that on the STO substrate shows only one reflection. The purity of the reflections was maintained after several UV induced crystal melting and visible light induced crystal growing cycles. To the best of our knowledge, such a crystal growing technique is novel and will

Figure 4. Photoinduced reversible XRD pattern changes of microcrystalline film of 1 on (110) surface of SrTiO3 single crystal upon alternate irradiation with UV (λ = 366 nm) and visible (λ > 500 nm) light. Purple and green arrows indicate UV and visible light irradiations, respectively. 1467



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be useful to control crystal growth for optoelectronic devices and controlling the crystal habit in polymorphological system.19

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CONCLUSIONS We successfully demonstrated the photoinduced reversible heteroepitaxial crystal growth of an open-ring isomer of a diarylethene on a (110) surface of a single crystal of strontium titanate by observing the reversible appearance of the (004) reflection of 1o. A one cycle process proceeded within 2 h, and the cycles were repeated six times. Such remarkable and rapid reversible epitaxial crystal growth on STO is supported by the remaining open-ring crystals in the subphase. This technique has the potential to control crystal habits by modifying the template lattice. It will especially be important for the polymorphological design of drugs.19 ASSOCIATED CONTENT

S Supporting Information *

Information on the absorption spectral changes of diarylethene 1; the estimated and observed XRD data of the coated film of 1o; phase diagram of mixtures of open- (1o) and closed-ring isomers (1c); AFM images of the (100), (110), and (111) STO substrate; XRD patterns of 1o films on various surfaces; schematic view of 0001 plane of Al2O3 single crystal. This material is available free of charge via the Internet at http:// pubs.acs.org.

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REFERENCES

(1) (a) Photochromism: Molecules and Systems; Duerr, H., BouasLaurent, H., Eds.: Elsevier: Amsterdam, The Netherlands, 1990. (b) Molecular Switches; Feringa, B. L., Ed.; Wiley-VCH: Weinheim, Germany, 2001. (2) Irie, M. Chem. Rev. 2000, 100, 1685−1716. (b) Irie, M.; Uchida, K. Bull. Chem. Soc. Jpn. 1998, 73, 985−996. (c) Kobatake, S.; Uchida, K.; Tsuchida, E.; Irie, M. Chem. Commun. 2002, 2804−2805. (3) (a) Kobatake, S.; Takami, S.; Muto, H.; Ishikawa, T.; Irie, M. Nature 2007, 446, 778−781. (b) Uchida, K.; Sukata, S.; Matsuzawa, Y.; Akazawa, M.; de Jong, J. J. D.; Katsonis, N.; Kojima, Y.; Nakamura, S.; Areephong, J.; Meetsma, A.; Feringa, B. L. Chem. Commun. 2008, 326−328. (c) Morimoto, M.; Irie, M. J. Am. Chem. Soc. 2010, 132, 14172−14178. (4) (a) Zhu, L.; Al-Kaysi, R. O.; Bardeen, C. J. J. Am. Chem. Soc. 2011, 133, 12569−12575. (b) Lange, C. W.; Foldeaki, M.; Nevodchikov, V. I.; Cherkasov, K.; Abakumov, G. A.; Pierpont, C. G. J. Am. Chem. Soc. 1992, 114, 4220−4222. (c) Koshima, H.; Ojima, N.; Uchimoto, H. J. Am. Chem. Soc. 2009, 131, 6890−6891. (5) (a) Uchida, K.; Izumi, N.; Sukata, S.; Kojima, Y.; Nakamura, S.; Irie, M. Angew. Chem., Int. Ed. 2006, 45, 6470−6473. (b) Izumi, N.; Minami, T.; Mayama, H.; Takata, A.; Nakamura, S.; Yokojima, S.; Tsujii, K.; Uchida, K. Jpn. J. Appl. Phys. 2008, 47, 7298−7302. (c) Izumi, N.; Nishikawa, N.; Yokojima, S.; Kojima, Y.; Nakamura, S.; Kobatake, S.; Irie, M.; Uchida, K. New J. Chem. 2009, 33, 1324−1326. (d) Uchida, K.; Nishikawa, N.; Izumi, N.; Yamazoe, S.; Mayama, H.; Kojima, Y.; Yokojima, S.; Nakamura, S.; Tsujii, K.; Irie, M. Angew. Chem., Int. Ed. 2010, 49, 5942−5944. (6) (a) Kitagawa, D.; Yamashita, I.; Kobatake, S. Chem. Commun. 2010, 46, 3723−3725. (b) Kitagawa, D.; Yamashita, I.; Kobatake, S. Chem.Eur. J. 2011, 17, 9825−9831. (7) Uyama, A.; Yamazoe, S.; Shigematsu, S.; Morimoto, M.; Yokojima, S.; Mayama, H.; Kojima, Y.; Nakamura, S.; Uchida, K. Langmuir 2011, 27, 6395−6400. (8) Mauritz, K. A.; Bear, E.; Hopfinger, A. J. J. Polym. Sci., Part B: Polym. Phys 1973, 11, 2185. (9) Irie, S.; Isoda, S.; Kuwamoto, K.; Miles, M. J.; Kobayashi, T.; Yamashita, Y. J. Cryst. Growth 1999, 198/199, 939. (10) Schmitz-Hübsch, T.; Sellam, F.; Staub, R.; Törker, M.; Fritz, T.; Kübel, C.; Müllen, K.; Leo, K. Surf. Sci. 2000, 445, 358−367. (11) Mannsfeld, S. C. B.; Fritz, T. Phys. Rev. B 2004, 69, 075416. (12) Mannsfeld, S. C. B.; Leo, K.; Fritz, T. Phys. Rev. Lett. 2005, 94, 056104. (13) Kubo, T.; Hondoh, H.; Nakada, T. Cryst. Growth Des. 2007, 7, 416−419. (14) Simbrunner, C.; Quochi, F.; Hernandez-Sosa, G.; Oehzelt, M.; Resel, R.; Hesser, G.; Arndt, M.; Saba, M.; Mura, A.; Bongiovanni, G.; Sitter, H. ACS Nano 2010, 4, 6244−6250. (15) (a) Yamazoe, S.; Sakurai, H.; Adachi, H.; Wada, T. Appl. Phys. Lett. 2009, 95, 062906. (b) Mino, T.; Kuwajima, S.; Suzuki, T.; Kanno, I.; Kotera, H.; Wasa, K. Jpn. J. Appl. Phys. 2007, 46, 6960. (c) Luo, H.; Thomas, M. J.; Mccleskey, M.; Bauer, E.; Burrell, A. K.; Jia, Q. Adv. Mater. 2007, 19, 3604. (16) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467−473. (17) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement; Universität Göttingen: Göttingen, Germany, 1997. (18) Kobatake, S.; Uchida, K.; Tsuchida, E.; Irie, M. Chem. Commun. 2002, 38, 2804−2805. (19) (a) Bernstein, J. Cryst. Growth Des. 2011, 11, 632−650. (b) Desiraju, G. R. Angew. Chem., Int. Ed. 2007, 46, 8342−8356. (c) Vishweshwar, P.; McMahon, J. A.; Oliveira, M.; Peterson, M. L.; Zaworotko, M. J. J. Am. Chem. Soc. 2005, 127, 16802−16803. (d) Linas, A.; Goodman, J. M. Drug Discov. Today 2008, 13, 198−210.

Figure 6. Reversible intensity changes of (004) reflection of 1o on (110) surface of SrTiO3 crystal upon alternative irradiation with UV and visible light (blue domain, under UV; yellow domain, under visible light irradiation).

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AUTHOR INFORMATION

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*Tel: +81-77-543-7462. Fax: +81-77-543-7483. E-mail: [email protected] (K.U.); [email protected]. jp (S.Y.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by Ryukoku University Science and Technology Fund and Grants-in-Aids for Scientific Research on Priority Area “New Frontiers in Photochromism (No. 471)” from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan. We are also grateful to Zeon Co., Ltd., for providing the perfluorocyclopentene. 1468


Photoinduced Reversible Heteroepitaxial Microcrystal Growth of a

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