Two-Dimensional Structures of Anthracene Derivatives

Nov 29, 2010 - The functionality of the patterned surface was demonstrated by activating host−guest chemistry as the solvent molecules could be repl...
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Two-Dimensional Structures of Anthracene Derivatives: Photodimerization and Host-Guest Chemistry Yoshihiro Kikkawa,*,† Hideyuki Kihara,† Mayuko Takahashi,† Masatoshi Kanesato,† Teodor Silviu Balaban,‡,§,| and Jean-Marie Lehn‡,⊥ Photonics Research Institute and Nanosystem Research Institute, National Institute of AdVanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562, Japan; Karlsruhe Institute of Technology, Campus Nord, Institute for Nanotechnology, Postfach 3640, D-76021 Karlsruhe, Germany; Karlsruhe Institute of Technology, Campus Su¨d, Center for Functional Nanostructures, UniVersite´ Paul Ce´zanne Aix-Marseille III, ISM2-Chirosciences, UMR 6263, Campus Saint Je´roˆme, F-13397 Marseille, France; and Institut de Science et d’Inge´nierie Supramole´culiares, UniVersite´ de Strasbourg, F-67083 Strasbourg, France ReceiVed: August 25, 2010; ReVised Manuscript ReceiVed: NoVember 7, 2010

By using a simple anthracene derivative with four alkoxy tails, a two-dimensional patterned surface was fabricated. The two-dimensional structures were directly visualized by scanning tunneling microscopy (STM) at the solid/liquid interface. The anthracene derivative formed highly ordered structures displaying cavities into which solvent molecules of 1-phenyloctane were coadsorbed. The functionality of the patterned surface was demonstrated by activating host-guest chemistry as the solvent molecules could be replaced by coronene, whose size is almost identical to the cavities formed by the anthracene derivative. Furthermore, [4 + 4] photodimerization of the anthracene derivative was performed at the solid/liquid interface and revealed that the physical height and electron density of the states were changed, resulting in the increase of an apparent height in the STM images. We demonstrate thus that the porous network of the two-dimensional pattern created by the anthracene derivative can be applied for selectively incorporating guest molecules and for photoprocessing. Introduction Precise integrations and arrangements of functional molecules by self-assembly are essential for realizing molecule-based devices and circuits.1-3 Therefore, understanding the intermolecular as well as molecule-substrate interactions is important to control the lateral and spatial arrangements of well-designed building blocks on a surface.4-8 It is well-known that scanning tunneling microscopy (STM) is one of the powerful scanning probe methods for analyzing the molecular organizations, which have been fabricated based on concepts of supramolecular chemistry.9-13 From the viewpoint of photopatterning, anthracene and its derivatives are one of the most important chromophores.14-17 One characteristic of the anthracene moiety is its ability to photodimerize under UV irradiation (>300 nm wavelength), resulting in the formation of a photodimer connected by covalent bonds due to a [4 + 4] cycloaddition (Scheme 1).18,19 Most of the photodimerizations of an anthracene moiety have been investigated in solution or in the bulk phase. To our knowledge, there is no report on the STM observation of photodimerization in the monolayer of an anthracene derivative at solid/liquid interface. * Corresponding author. Phone: +81-29-861-2955. Fax: +81-29-8613029. E-mail: [email protected]. † National Institute of Advanced Industrial Science and Technology (AIST). ‡ Karlsruhe Institute of Technology, Institute for Nanotechnology. § Karlsruhe Institute of Technology, Center for Functional Nanostructures. | Present address: Universite´ Paul Ce´zanne Aix-Marseille III. ⊥ Universite´ de Strasbourg.

Two-dimensional porous networks have been fabricated via noncovalent interactions such as hydrogen bonds, metal coordination, and van der Waals interactions.20-27 In addition, synthetic macrocycles have also been used as their cavities can accommodate some functional guest molecules.28,29 By taking advantage of such porous features, host-guest chemistry at the solid/liquid interface has been studied in order to create a multifunctional system by accumulating various kinds of molecules. In this contribution, we used the anthracene derivative 1 (2,3,6,7-tetradecyloxyanthracene, Scheme 1), described earlier30 and its two-dimensional structures were investigated by STM at a highly oriented pyrolytic graphite (HOPG)/1-phenyloctane interface. The molecules self-assemble and construct nanoporous network structures, in which the solvent molecules are coadsorbed. The solvent molecules could then be replaced by coronene, a large polyaromatic hydrocarbon, so that well-defined coronene arrays can be fabricated on a HOPG surface. Photodimerization of 1 could be performed at the solid/liquid interface, resulting in the production of the photodimer 2 in high yield. The STM image contrast is changed by the UV irradiation due to the alteration in the physical height and electron density of the states for the anthracene moiety. Thus, a sole anthracene derivative can provide multifunctional abilities such as displaying host-guest chemistry and photodimerization over relatively large areas. Experimental Section Materials. The synthesis of the anthracene derivative 1 was reported previously.30 The 1-phenyloctane which was used as solvent for the STM observation was purchased from Kanto

10.1021/jp108069a  2010 American Chemical Society Published on Web 11/29/2010

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SCHEME 1: Chemical Structures of the Anthracene Derivative 1 and Its Photodimer 2

Chemicals and used as received. Coronene was obtained from Aldrich. HOPG (ZYB grade, NT-MDT, Russia) was used as a substrate for the self-assembled monolayer formation. STM Observation. The anthracene derivative 1 was dissolved in 1-phenyloctane (c < 0.25 mM) by heating gently. The solution was drop-casted on a freshly cleaved HOPG surface. STM observation was performed in a constant current mode by using a Nanoscope IIIa system (Veeco Insturuments, Santa Barbara, CA) at the HOPG/1-phenyloctane interface. Mechanically cut Pt/Ir wire (90/10) was used as the STM tip. The reproducibility of each image was checked by using different samples and tips. The molecules and the HOPG lattice under the compounds were simultaneously obtained, and the HOPG lattice was used as an internal standard to determine the lattice constants of the (co)adsorbed molecules. All the images were analyzed by the SPIP software (Image Metrology, Denmark). Photodimerization. Two-kinds of experiments defined as “ex situ” and “in situ” were performed for photodimerization. “Ex situ” in this paper means that the photodimerization of 1 was performed in solution, and the photodimer 2 was spread on a HOPG to observe the two-dimensional structure. In contrast, “in situ” is defined as the photodimerization conducted at the solid/liquid interface in a STM setup. Ex situ [4 + 4] photocyclodimerization was performed in the tetrahydrofuran solution of the anthracene derivative 1 at a concentration of 0.03 mM. The solution was bubbled with Ar gas for 10 min in order to eliminate the possibility of oxidation during the reaction. Irradiation with UV light (365 nm, 6.7 mW · cm-2: Ushio Inc., Japan) enabled the photodimerization of the anthracene moiety, which was confirmed by UV-vis spectra (JASCO Corp.) and by the 500 MHz 1H NMR spectrum (Bruker Avance 500). The tetrahydrofuran was evaporated and the residue was dissolved in 1-phenyloctane. Then, the twodimensional structure of the photodimer 2 was observed by STM at the HOPG/1-phenyloctane interface. In situ photodimerization of anthracene derivative 1 was carried out by using UV light (365 nm, 10 mW cm-2). The 1-phenyloctane solution of the anthracene derivative 1 was bubbled with N2 gas and placed on HOPG. The two-dimensional structure was observed by STM at the solid/liquid interface under N2 flow. Then UV light was irradiated to induce the photodimerization of the anthracene derivative. During the UV irradiation, STM observation was quite difficult and no image could be obtained. Therefore, UV was switched off for the STM observation after 30 min of irradiation. The [4 + 4] cycloaddition of the anthracene moiety was also confirmed in a different solution by using a UV-vis spectrometer. Results and Discussion 1. Anthracene Derivative. Figure 1 shows the STM images of the anthracene derivative 1 at the HOPG/1-phenyloctane interface. A well-ordered pattern was visualized through out the HOPG surface (Figure 1A). Figure 1B shows the highresolution STM image of the compound 1. It is evident that the three bright dots were derived from the anthracene moiety. Four

dark lines of L1 ) 1.24 ( 0.08 nm in length were elongated from the anthracene moiety, suggesting that these correspond to the decyl chains. The alkyl chains formed a cavity structure, in which there are two linear objects of L2 ) 1.21 ( 0.07 nm in length, as indicated by the red arrows. This result suggests

Figure 1. STM images of the anthracene derivative 1 at HOPG/1phenyloctane interface. The red arrows indicate the coadsorbed 1-phenyloctane molecules. A molecular model is depicted on the basis of the STM image (C). Two 1-phenyloctane molecules indicated in yellow are coadsorbed in the cavities. Tunneling conditions: I ) 1.1 pA, V ) -266 mV (A); I ) 1.2 pA, V ) -265 mV (B).

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TABLE 1: Lattice Constants of Anthracene Derivative 1 1 + coronene 2

a (nm)

b (nm)

γ (deg)

2.21 ( 0.09 2.09 ( 0.16 2.19 ( 0.15

2.37 ( 0.11 2.20 ( 0.19 2.32 ( 0.17

71.5 ( 6.0 83.4 ( 6.5 75.5 ( 4.6

that a pair of solvent molecules of 1-phenyloctane coadsorb within the cavity. A molecular model was constructed on the basis of the STM image and is shown in Figure 1C. The lattice constants of the anthracene derivative were measured as a ) 2.21 ( 0.09 nm, b ) 2.37 ( 0.11 nm, and γ ) 71.5 ( 6.0°, and all the lattice constant data are summarized in Table 1. For demonstrating functionality of the nanopatterns, host-guest chemistry and photodimerization were studied (vide infra). 2. Host-Guest Chemistry. Since the anthracene derivative 1 formed a porous network structure filled with solvent molecules, we tried to immobilize a guest molecule in the cavities. Coronene, which has unique electronic and optoelectronic properties,31-33 was selected as a model compound to be accommodated within the porous network. Excess amount of coronene was added to an initial drop of 1 on HOPG. The subsequent STM observation revealed that bright disks were found in addition to the rectangular objects composed of three dots, suggesting coadsorption of the coronene, now visible as a polygon with several bright spots between rows of the threespotted anthracene derivative 1 (Figure 2). The lattice constants of 1 after the coadsorption of coronene were a ) 2.09 ( 0.16 nm, b ) 2.20 ( 0.19 nm, and γ ) 83.4 ( 6.5°, and the values within the error margins are almost identical to those of 1 containing solvent molecules except for the dihedral angle γ. This result suggests that the coronene molecules are well incorporated into the cavities by an induced fit mechanism22 and that regular patterns of coronene could thus be fabricated on a surface. 3. Photodimerization. 3.1. Ex Situ Experiment. Before UV irradiation (365 nm), typically three peaks at around 330-370 nm derived from the anthracene moiety were recognized (Figure 3). During the UV irradiation, the absorbance of these three peaks decreased whereas a band centered around 300 nm increased. This result suggests that the UV light causes the π-π* excitation of the anthracene moiety, resulting in the formation of photodimer 2. The photodimerization of the compounds was further confirmed by 1H NMR. The characteristic for the dimerization is an upfield shift for the proton at 9,10-positions, and the δ value was actually shifted upfield from 7.82 ppm in compound 1 to 5.74 ppm in compound 2. The two-dimensional structure of photodimer 2 was observed by STM ex situ at HOPG/1-phenyloctane interface, and the image contrast of 2 was compared to that of 1. Figure 4 shows the anthracene derivative 1 and its photodimer 2. It is evident that the image contrast of parts A and B of Figure 4 was different, and the cross-sectional data indicates that the apparent height of 2 is larger than that of 1. In these STM images, the cross-sectional data include not only the physical height but also the electron density of the states.34,35 For drawings of the HOMO and LUMO orbitals calculated with extended Hu¨ckel theory, see the Supporting Information. Therefore, the image contrast change is derived from the increase of physical height and electron density of the states for the anthracene moiety. Thus, the effective photodimerization of the anthracene moiety could be tentatively inferred from the apparent height. For the STM image, the apparent height can be affected by the tip condition. To eliminate such possible tip effect, we tried the in situ experiment to observe the monomer and photodimer at the

Figure 2. STM images of the anthracene derivative 1 with coronene molecules at the HOPG/1-phenyloctane interface. A molecular model is depicted in the frame (C). Tunneling condition: I ) 1.0 pA, V ) -414 mV.

Figure 3. Time-dependent changes of UV-vis spectra of the anthracene derivative 1.

same time, as shown in the following section 3.2. In the case of photodimerized molecules, coronene was not included into the cavities formed by them at the present experimental condition. After the addition of coronene into the solution on HOPG, the STM observation was interrupted to display featureless images

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Figure 6. UV-vis spectra of 1 during UV irradiation at 365 nm. The data were taken in 1-phenyloctane, and collected at 5 min intervals (blue to green). For spectra with a wider wavelength range in THF see the Supporting Information.

Figure 4. STM images of the anthracene derivative 1 (A) and photodimer 2 (B). The graphs under the STM images are line profile data at the white line region in each image. Tunneling conditions for (A) and (B): I ) 1.0 pA, V ) -1000 mV.

possibly due to the complex equilibrium between the solvent molecule, coronene, and photodimer at solid/liquid interface. 3.2. In Situ Experiment. In order to investigate the photoprocessing of the anthracene derivative 1 at the HOPG/solvent interface, in situ photodimerization was performed. After the observation of 1 (Figure 5), the 1-phenyloctane solution of 1 on HOPG was irradiated with UV light at 365 nm, and the STM observation was performed in the dark condition. After only 30 min of UV irradiation, the observation of patterns as shown Figure 5B became possible in a reproducible manner. Comparing the two parts A and B of Figure 5, the image contrast of the bright part is different in some regions. The cross sections at the white line region in Figure 5B indicate that there are two components with different heights, which are highlighted by blue and red arrows, respectively (Figure 5E). This result indicates that coexistence of 1 and 2 is visible in Figure 5B. Further STM observation without UV light for 10 min provided

Figure 5C. Almost all the area is now occupied by the photodimer 2, as confirmed by the STM image contrast (Figure 5C) and the cross-sectional data (Figure 5F). The lattice constants of 2 are a ) 2.19 ( 0.15 nm, b ) 2.32 ( 0.17 nm, and γ ) 75.5 ( 4.6°, which are similar to those of 1, suggesting that the molecular arrangements of 2 are basically almost the same as 1, regardless of the physical height. In the present solid/liquid interface system, the reaction in the solution phase is more likely to occur than that on the substrate, and the original adsorbed molecules of 1 are replaced by the products 2 which have accumulated in the solution phase.36 Therefore, the mixture of 1 and 2 after the photoirradiation for 30 min is observed as an intermediate state (Figure 5B). Then, the major components 2 become gradually adsorbed due to the equilibrium (Figure 5C), whereas the minor components of unreacted 1 are left in the solution phase. The histogram analysis of the apparent height in Figure 5G clearly revealed the photodimerization and following adsorption/desorption of 1 and 2. The occurrence of photocycloaddition in 1-phenyloctane solution was also confirmed by UV-vis spectroscopy (Figure 6) and gel permeation chromatography (see Supporting Information). The typical peaks of the anthracene moiety were decreased with the reaction time, and the reaction was completed after the UV irradiation for more than 30 min but well less than

Figure 5. STM images of the anthracene derivative 1 (A) and its photodimer 2 (C). The photodimerization was performed at the solid/liquid interface. Panel B was obtained just after the UV irradiation for 30 min, whereas further 10 min of continuous scanning provided the image in the panel C. Panels B and C were obtained in the similar area. The STM imaging was performed in the same tunneling conditions: I ) 5.0 pA, V ) -1000 mV. Panels D-F show the cross-sectional data at the white lined regions in the panels A-C, respectively. In panel E, the blue and red arrows in the data indicate anthracene derivative 1 and photodimer 2, respectively. Panel G shows the histograms of apparent height data collected from the large area STM images corresponding to the panels A-C.

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an hour. Accordingly, photodimerization of anthracene derivative could be first visualized at a solid/liquid interface, and the present results would be helpful for providing a simple approach for such surface modifications and/or patterning at a molecular level. Conclusion In conclusion, two-dimensional patterning was performed using the anthracene derivative 1, and surface modification was induced by host-guest chemistry or photodimerization. Assembly of four molecules of 1 created cavernous structures, in which 1-phenyloctane molecules coadsorbed. Coronene was selected as a guest molecule, which could be accommodated in the porous network structure of 1. In a separate series of experiments, photodimerization was performed at the solid/liquid interface. The apparent height of the anthracene moiety increased after the UV irradiation at 365 nm, indicating the formation of the photodimer 2. To the best of our knowledge, this is the first example of STM observation during photodimerization of anthracene derivatives at the solid/liquid interface. Thus, the present self-assembling anthracene derivative displayed bifunctionality serving as the template for the host-guest chemistry as well as for photodimerization. Acknowledgment. This work was partly supported by a grant from the Sumitomo Foundation and Grant-in-Aid for Scientific Research on Innovative Areas (21106522) from the Ministry of Education, Culture, Science, Sports, and Technology, Japan (to Y.K.). S.T.B. thanks the Colle`ge de France for support which enabled the synthesis of 1 in Strasbourg. Supporting Information Available: HOMO-LUMO orbitals and GPC chart. This material is available free of charge via the Internet at http://pubs.acs.org. References and Notes (1) Whitesides, G. M.; Grzybowski, B. Science 2002, 295, 2418–2421. (2) Barth, J. V.; Costantini, G.; Kern, K. Nature 2005, 437, 671–679. (3) Gomar-Nadal, E.; Puigmartı´-Luis, J.; Amabilino, D. B. Chem. Soc. ReV. 2008, 37, 490–504. (4) Samorı`, P.; Rabe, J. P. J. Phys.: Condens. Matter 2002, 14, 9955– 9973. (5) De Feyter, S.; Uji-i, H.; Mamodouh, W.; Miura, A.; Zhang, J.; Jonkheijm, P.; Schenning, A. P. H. J.; Meijer, E. W.; Chen, Z.; Wu¨rthner, F.; Schuurmans, N.; van Esch, J.; Feringa, B. L. Int. J. Nanotechnol. 2006, 3, 462–479. (6) Surin, M.; Lecle`re, P.; De Feyter, S.; Abdel-Mottaleb, M. M. S.; De Schryver, F. C.; Henze, O.; Feast, W. J.; Lazzaroni, R. J. Phys. Chem. B 2006, 110, 7898–7908.

Kikkawa et al. (7) Nath, K. G.; Ivasenko, O.; MacLeod, J. M.; Miwa, J. A.; Wuest, J. D.; Nanci, A.; Perepichka, D. F.; Rosei, F. J. Phys. Chem. C 2007, 111, 16996–17007. (8) Ziener, U. J. Phys. Chem. B 2008, 112, 14698–14717. (9) Giancarlo, L. C.; Flynn, G. W. Acc. Chem. Res. 2000, 33, 491– 501. (10) Lehn, J.-M. Science 2002, 295, 2400–2403. (11) De Feyter, S.; De Schryver, F. C. Chem. Soc. ReV. 2003, 32, 139– 150. (12) De Feyter, S.; De Schryver, F. C. J. Phys. Chem. B. 2005, 109, 4290–4302. (13) Plass, K. E.; Grzesiak, A. L.; Matzger, A. J. Acc. Chem. Res. 2007, 40, 287–293. (14) Paul, S.; Halle, O.; Einsiedel, H.; Menges, B.; Mu¨llen, K.; Knoll, W.; Mittler-Neher, S. Thin Solid Films 1996, 288, 150–154. (15) Li, T.; Chen, J.; Mitsuishi, M.; Miyashita, T. J. Mater. Chem. 2003, 13, 1565–1569. (16) Rameshbabu, K.; Kim, Y.; Kwon, T.; Yoo, J.; Kim, E. Tetrahedron Lett. 2007, 48, 4755–4760. (17) Kihara, H.; Motohashi, M.; Matsumura, K.; Yoshida, M. AdV. Funct. Mater. 2010, 20, 1561–1567. (18) Bouas-Laurent, H.; Castellan, A.; Desvergne, J.-P.; Lapouyade, R. Chem. Soc. ReV. 2000, 29, 43–55. (19) Bouas-Laurent, H.; Castellan, A.; Desvergne, J.-P.; Lapouyade, R. Chem. Soc. ReV. 2001, 30, 248–263. (20) Lu, J.; Lei, S.; Zeng, Q.; Kang, S.; Wang, C.; Wan, L.; Bai, C. J. Phys. Chem. B 2004, 108, 5161–5165. (21) Schull, G.; Douillard, L.; Debuisschert, C. F.; Charra, F.; Mathevet, F.; Kreher, D.; Attias, A. AdV. Mater. 2006, 18, 2954–2957. (22) Furukawa, S.; Tahara, K.; De Schryver, F. C.; Van der Auweraer, M.; Tobe, Y.; De Feyter, S. Angew. Chem., Int. Ed. 2007, 46, 2831–2834. (23) Blunt, M.; Lin, X.; Gimenez-Lopez, M. C.; Schro¨der, M.; Champness, N. R.; Beton, P. H. Chem. Commun. 2008, 2304–2306. (24) Madueno, R.; Ra¨isa¨nen, M. T.; Silien, C.; Buck, M. Nature 2008, 454, 618–621. (25) Shen, Y.; Deng, K.; Zeng, Q.; Wang, C. Small 2010, 6, 76–80. (26) Zhao, J.; Li, Y.; Lin, Z.; Xie, L.; Shi, N.; Wu, X.; Wang, C.; Huang, W. J. Phys. Chem. C 2010, 114, 9931–9937. (27) Arrigoni, C.; Schull, G.; Blger, D.; Douillard, L.; Fiorini-Debuisschert, C.; Mathevet, F.; Kreher, D.; Attias, A.-J.; Charra, F. J. Phys. Chem. Lett. 2010, 1, 190–194. (28) Tahara, K.; Lei, S.; Mamdouh, W.; Yamaguchi, Y.; Ichikawa, T.; Uji-i, H.; Sonoda, M.; Hirose, K.; De Schryver, F. C.; De Feyter, S.; Tobe, Y. J. Am. Chem. Soc. 2008, 130, 6666–6667. (29) Shen, Y.; Guan, L.; Zhu, X.; Zeng, Q.; Wang, C. J. Am. Chem. Soc. 2009, 131, 6174–6180. (30) Balaban, T. S.; Eichho¨fer, A.; Krische, M. J.; Lehn, J.-M. HelV. Chim. Acta 2006, 89, 333–351. (31) Nakatani, S.; Nakamura, T.; Mizuno, K.; Matsui, A. H. J. Lumin. 1994, 58, 343–346. (32) Rohr, U.; Schlichting, P.; Bo¨hm, A.; Gross, M.; Meerholz, K.; Bra¨uchle, C.; Mu¨llen, K. Angew. Chem., Int. Ed. 1998, 37, 1434–1437. (33) Jia, H.; Liu, S.; Sanguinet, L.; Levillain, E.; Decurtins, S. J. Org. Chem. 2009, 74, 5727–5729. (34) Donhauser, Z. J.; Mantooth, B. A.; Kelly, K. F.; Bumm, L. A.; Monnell, J. D.; Stapleton, J. J.; Price, D. W., Jr.; Rawlett, A. M.; Allara, D. L.; Tour, J. M.; Weiss, P. S. Science 2001, 292, 2303–2307. (35) Ishida, T.; Koyama, E.; Tokuhisa, H.; Nakamura, T.; Kanesato, M.; Mizutani, W. Jpn. J. Appl. Phys. 2006, 45, 6028–6032. (36) Elemans, J. A. A. W.; Lei, S.; De Feyter, S. Angew. Chem., Int. Ed. 2009, 48, 7298–7332.

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