Photoinduced Four-State Three-Step Ordering Transformation of

May 25, 2015 - The open-ring and annulated isomers of the terthiophene formed two-dimensional molecular orderings with different patterns while the cl...
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Photoinduced Four-State Three-Step Ordering Transformation of Photochromic Terthiophene at a Liquid/Solid Interface Based on Two Principles: Photochromism and Polymorphism Soichi Yokoyama, Takashi Hirose, and Kenji Matsuda* Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan S Supporting Information *

ABSTRACT: We have investigated photoinduced ordering transformation of a photochromic terthiophene derivative by scanning tunneling microscopy (STM) at the trichlorobenzene (TCB)/highly oriented pyrolytic graphite (HOPG) interface. The open-ring and annulated isomers of the terthiophene formed two-dimensional molecular orderings with different patterns while the closed-ring isomer did not form any ordering. The ordering of the open-ring isomer exhibited polymorphism depending on the concentration of supernatant solution. Upon UV light irradiation to a solution of the openring isomer or the closed-ring isomer, ordering composed of the annulated isomer was irreversibly formed. Upon visible light irradiation or thermal stimulus to the closed-ring isomer, the two kinds of polymorph composed of the open-ring isomer were formed due to the polymorphism. By controlling photochromism and polymorphism among four states made of three photochemical isomers, four-state three-step transformation was achieved by in situ photoirradiation from a solution of the closed-ring isomer (no ordering) into the ordering composed of the open-ring isomer (ordering α and β) followed by the orderings composed of the annulated isomer (ordering γ).

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INTRODUCTION Supramolecular chemistry at two-dimensional (2-D) surface or interface is attracting interest because surface functionalization becomes possible by assembling molecules with desired orientation at surface. The functionalized surface thus prepared can be developed into sophisticated molecular devices. In principle, self-assembled structure of molecules can be designed by tuning molecular shape and intermolecular interactions; slight change in the molecular shape or intermolecular interaction affects the resulting self-assembled structure. Surface-confined self-assemblies formed at a liquid/solid interface can be investigated by scanning tunneling microscopy (STM) at the single-molecule resolution at ambient conditions, and information on the process of 2-D self-assembly can be obtained by this technique.1 Among several assembly motifs, porous networks are attracting interest because the pore is expected to selectively immobilize and recognize functional guest molecules.2−16 Since sophisticated functions using surface can be provided by dynamic changes in 2-D self-assembly, much effort has been made to study stimuli-responsive properties of surface assemblies. Different stimuli such as temperature,17−19 electric field,20−22 addition of guests,23−27 and changing solvents28−31 have been used to induce changes in 2-D assemblies. Photocontrol of molecular assembly becomes possible by using photochromic molecules as assembling molecules © 2015 American Chemical Society

because photochromic molecules switch their geometrical shape and electronic properties by light irradiation.32 Photocontrol of 2-D self-assembly monitored by STM at a liquid/ highly oriented pyrolytic graphite (HOPG) interface using azobenzenes and diarylethenes as a photochromic unit has been reported by several groups including our group.33−39 Photocontrol of porous network has also been reported in a couple of reports.40−43 Another interesting phenomenon is a 2-D polymorphism arising from a difference in the concentration of the solution phase.44−49 It provides important insights into thermodynamic properties of surface-confined self-assemblies. De Feyter et al. have rationally interpreted an origin of polymorphs by considering the surface density of two different phases and the adsorption energies per molecule.44 In this work, we synthesized a photochromic terthiophene derivative with pseudo-C3 symmetry bearing six alkyl chains and investigated photoinduced 2-D ordering transformation of its surface-confined assemblies at the 1,2,4-trichlorobenzene (TCB)/HOPG interface. Photoswitching between porous orderings with different patterns was achieved using photoisomerization of the terthiophene derivative among three Received: April 17, 2015 Revised: May 21, 2015 Published: May 25, 2015 6404

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(Scheme 1). Thermal back-reaction from the closed- to the open-ring isomer of the derivative without alkyl chain is reported to be slow enough to trace by STM.51 Synthesis, Optical Property, and Thermal Stability of Terthiophene 1. Terthiophene 1o was synthesized by two steps from commercially available bromothiophenes as shown in Scheme 2. Nonsubstituted precursor 4 was obtained by Suzuki−Miyaura coupling of 2,3-dibromothiophene (3) with (2-methyl-3-thienyl)boronic acid, which was prepared from 3bromo-2-methylthiophene (2) by lithiation. Subsequently, terthiophene 1o was obtained by a direct C−H arylation.63 Phenyl groups bearing hexadecyloxy alkyl chain were introduced at the 5-position of three thiophene rings of the precursor 4 by the arylation reaction with 3,5-dihexadecyloxyiodobenzene (5) in the presence of paradium(II) chloride, silver(I) carbonate, and 2,2′-bipyridyl. The closed-ring isomer 1c and the annulated isomer 1a were synthesized by typical photochemical reactions in hexane from dilute solution of the open-ring isomer 1o (for the details of synthesis, see the Supporting Information). In either case of the photogeneration affording 1c and 1a, a 50:50 mixture of enantiomer should be obtained upon UV irradiation. All spectroscopic and STM measurements were carried out without isolation of the stereoisomers. Absorption spectral change of terthiophene 1 was measured in TCB which was used in STM measurements (Figure 2). Upon UV light irradiation to a solution of the open-ring isomer 1o, the absorption band corresponding to the closed-ring isomer 1c (absorption maximum, λmax = 672 nm) increased until 20 min of irradiation (Figure 2a). However, the absorption band in the visible region started to decrease by further UV light irradiation (Figure 2b). On the basis of the absorption spectrum of the pure closed-ring isomer isolated by HPLC, ca. 77% of the open-ring isomer 1o was converted to the closed-ring isomer 1c during the first 20 min irradiation. By subsequent irradiation with visible light to the solution, the initial absorption spectrum corresponding to 1o (λmax = 312 nm) was almost restored, but the absorption band in the visible region (500−750 nm) did not completely disappear (Figure 2c,d). The remaining absorption band, appeared at shorter wavelength than that of 1c, suggests the formation of a photoirreversible productthe annulated isomer 1a. The fraction of photogenerated isomers 1c and 1a can be modulated by choosing different photoirradiation protocols with UV and visible light because in general the annulated isomer is photogenerated from the closed-ring isomer with small quantum yield.59 The closed-ring isomer 1c can be obtained as a main product by a short UV light irradiation to the open-ring isomer 1o, but a small yet significant amount of 1a can be generated by a long-time UV light irradiation. Since long-time UV light irradiation provides a multicomponent

isomers, i.e., the open-ring, the closed-ring, and the annulated isomers. In addition to the photochromism, 2-D polymorphism is found to be involved in the ordering change. By combining photochromism and polymorphism, control over four states made of three photochemical isomers was achieved. Moreover, by setting up appropriate condition, in situ photoinduced fourstate three-step ordering transformation was successfully demonstrated.

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RESULTS AND DISCUSSION Molecular Design. Terarylene derivatives, reported by Kawai group and others, are known to undergo thermally reversible photochromic reaction.50−55 Terarylene derivatives have highly planar geometry in comparison with common diarylethenes with perfluorocyclopentene ring.56 Besides the planarity, three aryl rings consisting of terarylene molecule are pointing to the directions separated by 120°. Reflecting this structural feature, the 2-D molecular ordering of terarylene can be trigonal or hexagonal. Since porous ordering is often observed in trigonal or hexagonal orderings, porous packing is expected for terarylene derivatives.6−16 In addition to the photoisomerization between the open- and closed-ring isomers, the formation of the annulated isomer is expected likewise common diarylethenes with perfluorocyclopentene ring (Figure 1).57−59 Isomerization among photo-

Figure 1. Molecular structure of photochromic terthiophene.

chromic isomers of terarylene induces a significant change in flexibility of the molecules; while the open-ring isomer has a flexible structure owing to rotatable single bonds, the closedring and the annulated isomers have a rigid planar structure. The difference in flexibility should have an effect on the ordering pattern between the photochromic isomers. Furthermore, the closed-ring isomer of terarylene is known to thermally isomerize to the open-ring isomer at room temperature.51,52 The rate of thermal ring-opening reaction depends on the molecular structure. 2-D ordering transformation can be induced not only by photoirradiation but also by heating when photochromic molecular component thermally isomerizes. In situ transformation of multistimuliresponsive molecular orderings60−62 can be visualized at the single-molecule resolution using real-time STM measurement. With above considerations, we designed terthiophene 1o, in which six alkyl chains are introduced with C3 symmetry Scheme 1. Photochromic Reaction of Terthiophene 1

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Langmuir Scheme 2. Synthetic Scheme of Terthiophene 1o

Figure 2. Absorption spectral change of terthiophene 1 upon photoirradiation in TCB. Initial concentration of 1o was 230 μM (optical path length: 1 mm). (a) Irradiation with UV light (365 nm, ∼20 mW/cm2): black line, initial spectrum of 1o; gray line, after UV light irradiation for 0.5, 2, 5, and 10 min from bottom to top; blue line, 20 min; red line, pure closed-ring isomer 1c at the same concentration. The conversion ratio from 1o to 1c reached 77% at 20 min. (b) Further UV light irradiation: blue line, after UV light irradiation for 20 min (same as blue line in part a); purple line, 30 min; red line, 40 min. (c) Visible light (>560 nm, ∼5 W/cm2) irradiation for 10 min until absorption spectrum does not change. (d) Expansion of part c. The remaining absorption band was derived from annulated isomer 1a.

Figure 3. (a) Absorption spectra of isolated photochromic isomers of terthiophene 1 in TCB: black line, the open-ring isomer 1o; blue line, the closed-ring isomer 1c; red line, the annulated isomer 1a. Theoretical oscillator strengths calculated by a TD-DFT at the B3LYP/6-31g(d) level are shown in bars. (b) Photographs of isolated photochemical isomers in TCB.

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Langmuir mixture consisting of all the three isomers, visible light irradiation was subsequently conducted before isolating the annulated isomer 1a. All the isomers, the open-ring isomer 1o, the closed-ring isomer 1c, and the annulated isomer 1a, were separated by HPLC. The isolated pure isomers were characterized by NMR spectroscopy and high-resolution mass spectrometry and then used in spectroscopy and STM. In the 1 H NMR spectrum of the annulated isomer 1a, signals of methyl proton of the annulated core were downfield-shifted to ca. 2.8 ppm in comparison with those of the other isomers, 1o and 1a (ca. 2.2 ppm), as observed for diarylethenes with the same 5-phenyl-3-thienyl group.57,59 Absorption spectra of the isolated three isomers of terthiophene 1 were measured in TCB (Figure 3). A solution of the open-ring isomer 1o was colorless with λmax at 312 nm, while the closed-ring isomer 1c was blue with λmax at 672 nm. The λmax of the annulated isomer 1a appeared at 668 nm, and the color was similar to 1c (Figure 3b). The absorption spectral change shown in Figure 2 could be reasonably explained by the sum of spectra of isolated three isomers shown in Figure 3. Moreover, the shape of the absorption spectra were well reproduced by DFT calculations at the B3LYP/6-31g(d) level; the maximum wavelength in the visible region for the annulated isomer 1a appeared at slightly shorter wavelength than the closed-ring isomer 1c. The calculated oscillator strengths are shown with experimental spectra in Figure 3. Thus, the photogeneration of the annulated isomer 1a upon long-time UV irradiation was characterized by absorption spectroscopy, 1 H NMR, and DFT calculations. Thermally induced ring-opening reaction of the closed-ring isomer 1c to the open-ring isomer 1o was investigated using UV−vis spectroscopy. The thermal reaction of the closed-ring isomer 1c in toluene was first order with the activation energy Ea = 95 kJ mol−1 and half-life t1/2 = 38 h at 20 °C in toluene according to the Arrhenius plot, which are comparable to reported terarylene derivatives (Supporting Information Figures S3 and S4 and Table S1). In TCB that is used in STM measurement, the half-life of 1c was 84 h at 20 °C. The half-life significantly decreases to 36 min at 50 °C. This means that less than 2% of the closed-ring isomer 1c thermally isomerizes to the open-ring isomer 1o during 120 min at 20 °C, while more than 90% of 1c isomerizes at 50 °C. Thus, the closed-ring isomer 1c is thermally stable at room temperature for several hours, and thermally induced isomerization from 1c to 1o is possible by heating a TCB solution to 50 °C. STM Observation of Terthiophene 1o at the TCB/ HOPG Interface. Molecular ordering composed of the openring isomer 1o was investigated by STM at the TCB/HOPG interface. We found that 1o formed two different polymorphs on 2-D surface depending on its concentration in solution phase (Figure 4). One was a 2-D porous network with larger pore and thinner framework, named as α-ordering, and the other was another porous network with smaller pore and thicker framework, named as β-ordering (Figure 4a). The framework consisting of terthiophene 1o has two different contrasts in STM image, bright spots and dark lines, which correspond to terthiophene aromatic core and alkyl side chain moieties, respectively. From the inspection of STM images, the size of a bright spot of the β-ordering is almost twice as large as that of α-ordering, suggesting that a bright spot in β-ordering consists of two molecules of 1o (red triangle in Figure 4e) and that in α-ordering corresponds to one molecule (Figure 4c). Figure 4b shows concentration dependence of the

Figure 4. STM image of terthiophene 1o at the TCB/HOPG interface. (a) c = 60 μM, It = 50 pA, Vbias = −500 mV. (b) Surface coverage against concentration. Green square and blue circle denotes surface coverage of α- and β-ordering, respectively. (c) c = 40 μM, It = 50 pA, Vbais = −500 mV. The lattice parameters for α-ordering are a = 5.41 ± 0.03 nm, b = 4.71 ± 0.05 nm, α = 85 ± 1°. (d) Ordering model of α-ordering simulated by MM calculation. (e) c = 300 μM, It = 25 pA, Vbias = −500 mV. The lattice parameters for β-ordering are a = 4.34 ± 0.02 nm, b = 3.82 ± 0.03 nm, α = 80 ± 1°. (f) Ordering model of β-ordering simulated by MM calculation. Red dotted circle denotes the position of alkyl chain floating in supernatant solution. Yellow region denotes the area of pore where TCB molecules are coadsorbed. Red triangle denotes terthiophene core moiety of 1o and three vertexes show phenyl groups of 1o.

appearance of the two polymorphs composed of 1o, indicating that α-ordering is dominant when the concentration is lower than 40 μM, while β-ordering is dominant when the concentration is higher than 40 μM. From high-resolution STM images, lattice parameters of αordering (space group p2, a = 5.41 nm, b = 4.71 nm, α = 85°, Z = 2) and β-ordering (space group p2, a = 4.34 nm, b = 3.82 nm, α = 80°, Z = 2) were determined. From the lattice parameters, the area occupied by one molecule (S) was calculated for each ordering: for α-ordering, S = 13 ± 1 nm2; for β-ordering, S = 8.2 ± 0.3 nm2. This result indicates that the β-ordering is denser packing, which corresponds to the fact that β-ordering tends to be observed at higher concentrations of supernatant solution. Focusing on alkyl chain part reveals that alkyl chains extend to four directions from a bright spot both in α- and β-orderings (Figure 4c,e). In β-ordering, all alkyl chains are parallel to the main symmetry axis of underlying HOPG (i.e., the ⟨112̅1⟩ 6407

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Langmuir zigzag directions). On the other hand, in α-ordering, two directions of alkyl chains are almost parallel to the main axis of HOPG, while the others not. Difference of contrast seen in alkyl chain moiety in α-ordering would originate from the orientation of alkyl chain relative to the HOPG axis (Figure 4c). The patterns of 2-D molecular assemblies were carefully analyzed with the molecular mechanics/molecular dynamics (MM/MD) approach. Among several models considering different orientation of molecules, we adopted the best model that satisfactorily reproduce the experimental lattice parameters, the direction of alkyl chains, and thickness of frameworks (Figure 4d,f). As clearly seen in the ordering models, the size and shape of pores in these two polymorphs are significantly different from each other (yellow region in Figure 4d,f). The monomeric αordering has distorted hexagonal pores in each of which eight TCB molecules are coadsorbed, while the dimeric β-ordering has parallelogram pores in each of which only six TCB molecules are coadsorbed. Interestingly, coadsorbed TCB molecules in pores were experimentally distinguished at the single-molecule resolution by tuning bias voltage for STM scans; the result was sufficiently consistent with the ordering models (Supporting Information Figure S14). Moreover, the ordering model provides a detailed insight into molecular geometry in the 2-D self-assembled structure. In α-ordering, one alkyl chain out of six alkyl chains of terthiophene 1o floats in supernatant solution and the others extend to four different directions from one molecule. Because of the helical structure of central hexatriene moiety of the openring isomer, one terminal thiophene ring twists out of the molecular plane. Interestingly, the alkyl chain floating in supernatant solution is connected to the phenyl group next to the twisted thiophene ring (red dotted circle in Figure 4d and Supporting Information Figure S7). The same feature can be seen in the dimeric β-ordering; two molecules of 1o formed dimer structure in close contact with each other so that the part of the twisted thiophene rings arranges in a head-to-head orientation. Two alkyl chains directing to the solution phase extend from the inner part of the dimer structure (red dotted circle in Figure 4f and Supporting Information Figure S9). STM Observation of Terthiophene 1c and 1a at the TCB/HOPG Interface. Contrary to our expectations, the closed-ring isomer 1c did not form any ordering below 94 μM, which is in marked contrast to the open-ring isomer 1o that forms α-ordering even at 10 μM (Supporting Information Figure S10). These results suggest that the closed-ring isomer 1c is difficult to form ordering at the TCB/HOPG interface in comparison with the open-ring isomer 1o. In the case that one of the photochromic isomer shows an ordering and the other does not, photoswitching of ordering formation/disappearance becomes possible. Actually, we have demonstrated photoinduced ordering formation/disappearance of 2-thienyl-type diarylethene; the open-ring isomer forms ordering, but the closed-ring isomer does not in that case.38 In contrast to the closed-ring isomer 1c, the annulated isomer 1a formed a 2-D ordering different from α- or βordering in the ordering motif (Figure 5). The ordering consisting of 1a has a porous honeycomb structure, named as γordering, with almost rhombic lattice parameters (space group preudo-p6, a = 5.3 ± 0.1 nm, b = 5.18 ± 0.04 nm, α = 61 ± 1°, Z = 2).64 The porous structure is significantly similar to the ordering of dehydrobenzo[12]annulene (DBA) with the

Figure 5. (a−c) STM images of γ-ordering of 1a at the TCB/HOPG interface. (a) It = 50 pA, Vbias = 50 mV. Blue broken line denotes domain boundary. Orientation of alkyl chain in left domain is CCW while the orientation in right domain is CW. (b) High-resolution STM image of γ-ordering with CCW orientation. It = 50 pA, Vbias = 50 mV. (c) High-resolution STM image of γ-ordering with CW orientation. It = 100 pA, Vbias = 50 mV. The lattice parameters for γ-ordering are a = 5.3 ± 0.1 nm, b = 5.18 ± 0.04 nm, α = 61 ± 1°. (d) Ordering model simulated by MM calculation. Yellow region denotes the area of pore where TCB molecules are coadsorbed. Red triangle denotes terthiophene core moiety of 1a, and three vertexes show phenyl groups of 1a. While concentration is unknown, absorption was recorded; absorbance at 668 nm was 0.30 with optical path of 5 mm.

hexadecyl alkyl chain.19,44,65 Interestingly, the annulated isomer 1a was observed at very high resolution in STM image under ambient conditions; the triangular shape of the terthiophene core was clearly recognized as a bright spot, suggesting that the molecules are tightly fixed in the porous honeycomb 2-D network (Supporting Information Figure S13). The same ordering was observed in experiments at different concentrations; no polymorph was observed for the annulated isomer 1a unlike the open-ring isomer 1o (Supporting Information Figure S11). According to the high-resolution STM images and ordering model obtained by MM/MD calculations for γ-ordering, all the alkyl chains are almost parallel to the main symmetry axis of HOPG, and there are no alkyl chains floating in supernatant solution (Figure 5b−d). The diameter of the hexagonal pore (edge-to-edge) is ca. 4.3 nm, and 19 TCB molecules are coadsorbed in a pore (Supporting Information Figure S14). As reported for porous honeycomb 2-D networks consisting of triangular molecules,13−16 a pair of 2-D chiral domains were experimentally observed concerning the rotating direction of alkyl chains forming the pore; one is clockwise (CW) and the other is counterclockwise (CCW), which are separated by domain boundary (Figure 5a−c). While the annulated isomer 1a formed ordering pattern, the closed-ring isomer 1c having similar structure to 1a did not form any ordering. The annulated isomer is reported to have 6408

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adsorption on flat substrate and would be associated with the difference in adsorbability between 1c and 1a.

higher affinity to HOPG surface than the open- or closed-ring isomer.37 Adsorbability and assembled structures of 1o, 1c, and 1a must be intrinsically related to molecular structure of the three photochemical isomers. Figure 6 shows molecular structures of

Table 1. Unit Cell Parameter and the Area Occupied by One Molecule of Three Orderings space group a/nm b/nm α/deg Zb S/nm2 c nd

a

ordering α

ordering β

ordering γ

p2 5.41 ± 0.03 4.71 ± 0.05 85 ± 1 2 13 ± 1 8

p2 4.34 ± 0.02 3.82 ± 0.03 80 ± 1 2 8.2 ± 0.3 6

pseudo-p6 5.3 ± 0.1 5.18 ± 0.04 61 ± 1 2 12 ± 1 19

a

Determined from high-resolution STM images and lattice parameters. Because of the pseudo-C3 symmetry of the annulated isomer 1a, the space group of γ-ordering is not exactly p6. bNumber of molecules in the unit cell. cThe area occupied by one molecule on HOPG substrate. dNumber of guest molecules (TCB) coadsorbed in a pore.

Ordering Change upon Photoirradiation. To investigate ordering change upon photoirradiation, first, UV light was irradiated in situ to a 1o solution (c = 200 μM) at the TCB/HOPG interface where β-ordering existed (Figure 7 and Supporting Information Figures S15−S22). Corresponding absorption spectral change was traced in the same condition (Supporting Information Figure S23). Upon UV light irradiation for the first 6 min, domain of β-ordering decreased while domain of honeycomb γ-ordering appeared and increased (Figure 7a−d). In the early stage of in situ UV irradiation, the domain size of γ-ordering tends to be small. Within 10 min of UV light irradiation, the β-ordering disappeared completely (Figure 7e). The monomeric α-ordering did not appear throughout the experiment of in situ UV light irradiation. If the concentration of terthiophene 1o had simply decreased due to the photocyclization reaction from 1o to 1c, α-ordering would have been observed because α-ordering forms below 40 μM. The experimental fact suggests that even a small amount of annulated isomer 1a, generated upon UV irradiation to the closed-ring isomer 1c, would preferably adsorb on the HOPG surface, resulting in the precedent formation of γ-ordering. We note that the appearance of γ-ordering is attributed to the photochemical generation of the annulated isomer 1a but not caused by thermal effects associated with photoirradiation since β-ordering consisting of the open-ring isomer 1o is not thermally responsive (Supporting Information Figure S24). When the time of UV light irradiation reached 30 min, the domain of γ-ordering increased and the surface coverage became eventually almost 100% (Figure 7f). When visible light was irradiated to the photogenerated γ-ordering for 120 min (Supporting Information Figure S15i), the ordering did not change and the ordering consisting of 1o (α- or β-ordering) was never restored. Thus, it is confirmed that γ-ordering composed of the annulated isomer 1a is not responsive to photoirradiation. The disordered domain, observed in the early stage of in situ UV irradiation (Figure 7d), was not observed when pure annulated isomer 1a isolated by HPLC was used for STM measurements. On the other hand, the disordered domain tends to form when the other isomers (1o or 1c) coexist with 1a. According to an ex situ UV irradiation experiment (shown in Figure S26 of the Supporting Information), the disordered domain was predominantly observed just after drop-casting of a

Figure 6. Molecular structures of the three isomers of terthiophene optimized in gas phase by DFT calculation at the B3LYP/6-31d(g) level. (a, c, e) Oblique view and (b, d, f) side view. (a, b) Helically twisted structure of the open-ring isomer 1o, (c, d) planar structure of the closed-ring isomer 1c, and (e, f) bowl-shaped structure of the annulated isomer 1a. Cartesian coordinates of these structures are shown in the Supporting Information.

the three isomers optimized in gas phase by DFT calculation at the B3LYP/6-31g(d) level. The open-ring isomer has a helically twisted structure due to the steric hindrance around two methyl groups in the center of terthiophene core moiety (Figure 6a,b), as mentioned above. The core moiety consists of five rotatable single bonds (two connecting thiophene rings and three connecting thiophene ring and 3,5-dialkoxyphenyl group), which impart flexibility to the core of the open-ring isomer 1o. The polymorphs α- and β-orderings composed of the open-ring isomer may be related to the flexible structure: flexible molecules have a greater chance to show polymorphs.66 On the other hand, the closed-ring isomer 1c and the annulated isomer 1a has a rigid structure because the two single bonds connecting thiophene rings are no longer rotatable (Figure 6c−f). In addition, the two methyl groups introduced in the center of terthiophene core orient perpendicular to the molecular plane both for 1c and 1a, which can disturb the adsorption on HOPG surface. A marked difference in molecular structure between 1c and 1a can be seen in their planarity of the core: the closed-ring isomer has a planar structure in comparison with the bowl-shaped structure of the annulated isomer (Figure 6d,f). The bowl-shaped structure of 1a which reduces the steric effect of the methyl group is suitable for 6409

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Figure 7. Continuous change of STM image of the open-ring isomer 1o (β-ordering) at the TCB/HOPG interface upon UV light (365 nm, ∼100 mW/cm2) irradiation. Time displayed at upper right corner of each STM image indicates total time of photoirradiation: (a) before irradiation c = 200 μM; (b) after UV light irradiation for 1.0, (c) 3.0, (d) 6.0, (e) 10, and (f) 30 min. It was set between 40 and 70 pA, and Vbias was set between −400 and −500 mV. The region surrounded by blue and purple dashed line denotes β- and γ-ordering, respectively.

Figure 8. Change of STM image of the closed-ring isomer 1c (no ordering) at the TCB/HOPG interface upon visible light (>500 nm, ∼80 mW/ cm2) irradiation and thermal treatment: (a−c) initial concentration c = 34 μM; (d−f) initial concentration c = 94 μM; (a) STM image measured at room temperature after heating at 50 °C for 120 min and then 60 °C for 120 min. It = 50 pA, Vbias = −500 mV; (b) before irradiation or thermal treatment, It = 50 pA, Vbias = −500 mV; (c) after visible light irradiation for 60 min, It = 30 pA, Vbias = −600 mV; (d) STM image measured at room temperature after heating at 50 °C for 120 min. It = 50 pA, Vbias = −500 mV; (e) before irradiation or thermal treatment, It = 50 pA, Vbias = −500 mV; (f) after visible light irradiation for 60 min. It = 40 pA, Vbias = −500 mV.

solution containing 1o and 1a in TCB (concentration: [1o] + [1a] = 200 μM). The disordered domain was replaced by wellordered honeycomb network consisting of 1a after heating at 30 °C for 30 min, suggesting that (i) the disordered ordering is a kinetically controlled state and (ii) the domain size of 1a upon in situ UV irradiation significantly changes during several tens of minutes around room temperature. Second, UV and visible light irradiation was performed to a 1c solution at the TCB/HOPG interface to cause the annulation and cycloreversion reactions affording the annulated

isomer 1a and the open-ring isomer 1o, respectively. In these experiments, no ordering was observed at the initial state since the closed-ring isomer 1c does not form any ordering. UV light irradiation to 1c solution for 15 min provided γ-ordering consisting of 1a as expected, as in the case of UV light irradiation to 1o solution (Supporting Information Figure S25). Visible light irradiation to the closed-ring isomer 1c at the TCB/HOPG interface provided α- or β-ordering depending on the initial concentration of 1c (middle to right in Figure 8); monomeric α-ordering was mainly formed by visible light 6410

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Figure 9. Continuous change of STM image of the closed-ring isomer 1c at the TCB/HOPG interface upon UV (365 nm, ∼100 mW/cm2) or visible (>500 nm, ∼80 mW/cm2) light irradiation or heating: (a) schematic representation of the photoinduced continuous transformation; (b) before irradiation. c = 78 μM; (c) after visible light irradiation for 30 min; (d) after visible light irradiation for 60 min; (e) after UV light irradiation for 10 min; (f) after UV light irradiation for 30 min; (g) after annealing at 50 °C for 10 min. Region surrounded by green, blue, and purple dashed line denotes α-, β-, and γ-ordering, respectively. These STM images were modified by drift correction. It was set between 50 and 80 pA, and Vbias was set at −500 mV.

irradiation for 60 min at low concentration (34 μM) and dimeric β-ordering at high concentration (94 μM). Small domains of β-ordering tend to coexist in the photogenerated αordering in low concentration measurement (34 μM), but βordering is dominant in high concentration measurement (94 μM). This result is consistent with the result of concentration dependence of polymorphism of the open-ring isomer 1a (Figure 4b); at 34 μM both major α-ordering and minor βordering were observed, and at 94 μM the ordering was mostly β-ordering. The formation of α- and β-ordering from a 1c solution can be also triggered by thermal treatment. To induce thermal cycloreversion reaction from the closed-ring isomer 1c to the open-ring isomer 1o, a TCB solution of 1c on HOPG substrate was heated at 50−60 °C for 120−240 min. After the thermal treatment, α- or β-ordering can be selectively formed depending on the initial concentration similarly to the photoirradiation experiment (middle to left in Figure 8). In our previous reports on concentration dependence of ordering formation, the adsorption of the open-ring isomer was dependent solely on the concentration of the open-ring isomer and independent of the concentration of the closed-ring isomer.38 In this case also, the polymorphism of the open-ring isomer 1o is considered to be controlled only by the concentration of 1o in the solution phase, which is determined by the initial concentration of the closed-ring isomer 1c and the time of irradiation with visible light or thermal treatment. Continuous Three-Step Transformation of 2-D Ordering upon Photoirradiation. Because the detailed origin of three kinds of ordering, α-, β-, and γ-ordering, became clear by above experiments, we demonstrated a photoinduced continuous transformation of the porous 2-D networks with three

steps starting from the solution of closed-ring isomer 1c. Change of the STM image upon photoirradiation or annealing is shown in Figure 9, and other STM images are shown in Supporting Information Figure S31. The initial concentration of 1c was set at 78 μM. When visible light (λirrad > 500 nm) was irradiated for 30 min, the ordering appeared which mainly consists of α-ordering (Figure 9c), suggesting that the concentration of 1o in irradiated solution is below 40 μM because α-ordering was observed below 40 μM (Figure 4b). When the visible light irradiation was prolonged to 60 min, dimeric β-ordering was predominantly observed (Figure 9d). By considering that β-ordering is predominantly formed at concentrations larger than 70 μM (Figure 4b), the complete transformation to the dimeric β-ordering suggests that the closed-ring isomer 1c was mostly converted to the open-ring isomer 1o upon irradiaiton with visible light at the TCB/ HOPG interface. Subsequently, UV light irradiation was performed in order to obtain γ-ordering consisting of the annulated isomer 1a. After UV light (λirrad = 365 nm) irradiation for 10 min, the small domains of γ-ordering started to appear, yet β-ordering occupied a half area of HOPG surface (Figure 9e). Additional UV light irradiation for 20 min resulted in complete disappearance of the β-ordering of 1o (Figure 9f). In addition, domain size of γ-ordering increased with the increase of time of UV light irradiation. Finally, a thermal treatment was carried out in order to promote growth of domain of γ-ordering. After annealing at 50 °C for 10 min, the domain size of γ-ordering significantly increased and exceeded the size of scanned area, 90 × 90 nm2 (Figure 9g). As shown here, we demonstrated photoinduced four-state three-step continuous ordering transformation starting from the solution of closed-ring isomer 1c, 6411

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Langmuir which showed no ordering, to α-ordering consisting of the open-ring isomer 1o in monomeric fashion, β-ordering of 1o in dimeric fashion, and then γ-ordering of the annulated isomer 1a.

Hydrogen-Bonded Host Networks. J. Phys. Chem. B 2004, 108, 5161−5165. (5) Shen, Y.; Zeng, L.; Lei, D.; Zhang, X.; Deng, K.; Feng, Y.; Feng, W.; Lei, S.; Li, S.; Gan, L.; Zeng, Q.; Wang, C. Competitive Adsorption and Dynamics of Guest Molecules in 2D Molecular Sieves. J. Mater. Chem. 2011, 21, 8787−8791. (6) Lu, J.; Zeng, Q.-d.; Wang, C.; Zheng, Q.-y.; Wan, L.; Bai, C. SelfAssembled Two-Dimensional Hexagonal Networks. J. Mater. Chem. 2002, 12, 2856−2858. (7) Lackinger, M.; Griessl, S.; Heckl, W. M.; Hietschold, M.; Flynn, G. W. Self-Assembly of Trimesic Acid at the Liquid-Solid Interfaces−a Study of Solvent-Induced Polymorphism. Langmuir 2005, 21, 4984− 4988. (8) Kampschulte, L.; Griessl, S.; Heckl, W. M.; Lackinger, M. Mediated Coadsorption at the Liquid-Solid Interface: Stabilization through Hydrogen Bonds. J. Phys. Chem. B 2005, 109, 14074−14078. (9) Li, M.; Deng, K.; Lei, S.-B.; Yang, Y.-L.; Wang, T.-S.; Shen, Y.-T.; Wang, C.-R.; Zeng, Q.-D.; Wang, C. Site-Selective Fabrication of TwoDimensional Fullerene Arrays by Using a Supramolecular Template at the Liquid-Solid Interface. Angew. Chem., Int. Ed. 2008, 47, 6717− 6721. (10) Palma, C.-A.; Bonini, M.; Llanes-Pallas, A.; Breiner, T.; Prato, M.; Bonifazi, D.; Samorì, P. Pre-Programmed Bicomponent Porous Networks at the Solid−Liquid Interface: The Low Concentration Regime. Chem. Commun. 2008, 5289−5291. (11) Adisoejoso, J.; Tahara, K.; Okuhata, S.; Lei, S.; Tobe, Y.; De Feyter, S. Two-Dimensional Crystal Engineering: A Four-Component Architecture at a Liquid−Solid Interface. Angew. Chem., Int. Ed. 2009, 48, 7353−7357. (12) Ahn, S.; Matzger, A. J. Six Different Assemblies from One Building Block: Two-Dimensional Crystallization of an Amide Amphiphile. J. Am. Chem. Soc. 2010, 132, 11364−11371. (13) Tahara, K.; Yamaga, H.; Ghijsens, E.; Inukai, K.; Adisoejoso, J.; Blunt, M. O.; De Feyter, S.; Tobe, Y. Control and Induction of Surface-Confined Homochiral Porous Molecular Networks. Nat. Chem. 2011, 3, 714−719. (14) Destoop, I.; Ghijsens, E.; Katayama, K.; Tahara, K.; Mali, K. S.; Tobe, Y.; De Feyter, S. Solvent-Induced Homochirality in SurfaceConfined Low-Density Nanoporous Molecular Networks. J. Am. Chem. Soc. 2012, 134, 19568−19571. (15) Chen, T.; Yang, W.-H.; Wang, D.; Wan, L.-J. Globally Homochiral Assembly of Two-Dimensional Molecular Networks Triggered by Co-Absorbers. Nat. Commun. 2013, 4, 1389. (16) Ghijsens, E.; Cao, H.; Noguchi, A.; Ivasenko, O.; Fang, Y.; Tahara, K.; Tobe, Y.; De Feyter, S. Towards Enantioselective Adsorption in Surface-Confined Nanoporous Systems. Chem. Commun. 2015, 51, 4766−4769. (17) Rohde, D.; Yan, C.-J.; Yan, H.-J.; Wan, L.-W. From a Lamellar to Hexagonal Self-Assembly of Bis(4,4′-(m,m′-di(dodecyloxy)phenyl)2,2′-difluoro-1,3,2-dioxaborin) Molecules: A trans-to-cis-IsomerizationInduced Structural Transition Studied with STM. Angew. Chem., Int. Ed. 2006, 45, 3996−4000. (18) Gutzler, R.; Sirtl, T.; Dienstmaier, J. F.; Mahata, K.; Heckl, W. M.; Schmittel, M.; Lackinger, M. Reversible Phase Transitions in SelfAssembled Monolayers at the Liquid−Solid Interface: TemperatureControlled Opening and Closing of Nanopores. J. Am. Chem. Soc. 2010, 132, 5084−5090. (19) Blunt, M. O.; Adisoejoso, J.; Tahara, K.; Katayama, K.; Van der Auweraer, M.; Tobe, Y.; De Feyter, S. Temperature-Induced Structural Phase Transitions in a Two-Dimensional Self-Assembled Network. J. Am. Chem. Soc. 2013, 135, 12068−12075. (20) Alemani, M.; Peters, M. V.; Hecht, S.; Rieder, K.-H.; Moresco, F.; Grill, L. Electric Field-Induced Isomerization of Azobenzene by STM. J. Am. Chem. Soc. 2006, 128, 14446−14447. (21) Lei, S.-B.; Deng, K.; Yang, Y.-L.; Zeng, Q.-D.; Wang, C.; Jiang, J.-Z. Electric Driven Molecular Switching of Asymmetric Tris(phthalocyaninato) Lutetium Triple-Decker Complex at the Liquid/ Solid Interface. Nano Lett. 2008, 8, 1836−1843.

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CONCLUSIONS Photochemical and thermal ordering transformation of a photochromic terthiophene 1 was investigated by STM at the TCB/HOPG interface. The open-ring and annulated isomers of the terthiophene formed molecular orderings with different porous structures while the closed-ring isomer did not form any ordering. The annulated isomer formed honeycomb pore structure containing 19 TCB molecules in each pore. The ordering of the open-ring isomer exhibited polymorphism depending on the concentration of supernatant solution. Upon UV light irradiation to a solution of the open-ring isomer or the closed-ring isomer, ordering composed of the annulated isomer was irreversibly formed. Upon visible light irradiation or thermal stimulus to the closed-ring isomer, two kinds of ordering composed of the open-ring isomer were formed depending on the concentration of the generated open-ring isomer. By controlling photochromism and polymorphism among four states made of three photochemical isomers, fourstate three-step transformation was demonstrated by in situ photoirradiation from the closed-ring isomer (no ordering) into the orderings composed of the open-ring isomer (ordering α and β) followed by the ordering composed of the annulated isomer (ordering γ).

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ASSOCIATED CONTENT

S Supporting Information *

Experimental procedures, additional figures, and 1H and 13C NMR spectra. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/ acs.langmuir.5b01404.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (K.M.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas “Photosynergetics” (No. 26107008) from the MEXT, Japan and a Grant-in-Aid for Young Scientists (B) (No. 25810048) from the JSPS, Japan.

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REFERENCES

(1) Elemans, J. A. A. W.; Lei, S.; De Feyter, S. Molecular and Supramolecular Networks on Surfaces: From Two-Dimensional Crystal Engineering to Reactivity. Angew. Chem., Int. Ed. 2009, 48, 7298−7332. (2) Bonifazi, D.; Mohnani, S.; Llanes-Pallas, A. Supramolecular Chemistry at Interfaces: Molecular Recognition on Nanopatterned Porous Surfaces. Chem.Eur. J. 2009, 15, 7004−7025. (3) Zhang, X.; Zeng, Q.; Wang, C. Molecular Templates and NanoReactors: Two-Dimensional Hydrogen Bonded Supramolecular Networks on Solid/Liquid Interfaces. RSC Adv. 2013, 3, 11351−11366. (4) Lu, J.; Lei, S.-b.; Zeng, Q.-d.; Kang, S.-z.; Wang, C.; Wan, L.-j.; Bai, C.-l. Template-Induced Inclusion Structures with Copper(II) Phthalocyanine and Coronene as Guests in Two-Dimensional 6412

DOI: 10.1021/acs.langmuir.5b01404 Langmuir 2015, 31, 6404−6414

Article

Langmuir (22) Mali, K. S.; Wu, D.; Feng, X.; Müllen, K.; Van der Auweraer, M.; De Feyter, S. Scanning Tunneling Microscopy-Induced Reversible Phase Transformation in the Two-Dimensional Crystal of a Positively Charged Discotic Polycyclic Aromatic Hydrocarbon. J. Am. Chem. Soc. 2011, 133, 5686−5688. (23) Furukawa, S.; Tahara, K.; De Schryver, F. C.; Van der Auweraer, M.; Tobe, Y.; De Feyter, S. Structural Transformation of a TwoDimensional Molecular Network in Response to Selective Guest Inclusion. Angew. Chem., Int. Ed. 2007, 46, 2831−2834. (24) Ciesielski, A.; Lena, S.; Masiero, S.; Spada, G. P.; Samorì, P. Dynamers at the Solid−Liquid Interface: Controlling the Reversible Assembly/Reassembly Process between Two Highly Ordered Supramolecular Guanine Motifs. Angew. Chem., Int. Ed. 2010, 49, 1963− 1966. (25) Blunt, M. O.; Russell, J. C.; Gimenez-Lopez, M. C.; Taleb, N.; Lin, X.; Schröder, M.; Champness, N. R.; Beton, P. H. Guest-Induced Growth of a Surface-Based Supramolecular Bilayer. Nat. Chem. 2011, 3, 74−78. (26) Shen, Y.; Zeng, L.; Lei, D.; Zhang, X.; Deng, K.; Feng, Y.; Feng, W.; Lei, S.; Li, S.; Gan, L.; Zeng, Q.; Wang, C. Competitive Adsorption and Dynamics of Guest Molecules in 2D Molecular Sieves. J. Mater. Chem. 2011, 21, 8787−8791. (27) Ahn, S.; Matzger, A. J. Additive Perturbed Molecular Assembly in Two-Dimensional Crystals: Differentiating Kinetic and Thermodynamic Pathways. J. Am. Chem. Soc. 2012, 134, 3208−3214. (28) Yang, Y.; Wang, C. Solvent Effects on Two-Dimensional Molecular Self-Assemblies Investigated by Using Scanning Tunneling Microscopy. Curr. Opin. Colloid Interface Sci. 2009, 14, 135−147. (29) Liu, J.; Zhang, X.; Yan, H.-J.; Wang, D.; Wang, J.-Y.; Pei, J.; Wan, L.-J. Solvent-Controlled 2D Host-Guest (2,7,12-Trihexyloxytruxene/ Coronene) Molecular Nanostructures at Organic Liquid/Solid Interface Investigated by Scanning Tunneling Microscopy. Langmuir 2010, 26, 8195−8200. (30) Xu, L.; Miao, X.; Zha, B.; Deng, W. Self-Assembly Polymorphism: Solvent-Responsive Two-Dimensional Morphologies of 2,7-Ditridecyloxy-9-fluorenone by Scanning Tunneling Microscopy. J. Phys. Chem. C 2012, 116, 16014−16022. (31) Destoop, I.; Ghijsens, E.; Katayama, K.; Tahara, K.; Mali, K. S.; Tobe, Y.; De Feyter, S. Solvent-Induced Homochirality in SurfaceConfined Low-Density Nanoporous Molecular Networks. J. Am. Chem. Soc. 2012, 134, 19568−19571. (32) Heinz, R.; Stabel, A.; Rabe, J. P.; Wegner, G.; De Schryver, F. C.; Corens, D.; Dehaen, W.; Süling, C. Photodecomposition of 10-Diazo2-hexadecylanthrone on Graphite Studied by Scanning Tunneling Microscopy. Angew. Chem., Int. Ed. Engl. 1994, 33, 2080−2083. (33) Zhang, X.-M.; Zeng, Q.-D.; Wang, C. Reversible Phase Transformation at the Solid−Liquid Interface: STM Reveals. Chem.Asian J. 2013, 8, 2330−2340. (34) Xu, L.-P.; Wan, L.-J. STM Investigation of the Photoisomerization of an Azobis-(benzo-15-crown-5) Molecule and Its Self-assembly on Au(111). J. Phys. Chem. B 2006, 110, 3185−3188. (35) Arai, R.; Uemura, S.; Irie, M.; Matsuda, K. Reversible Photoinduced Change in Molecular Ordering of Diarylethene Derivatives at a Solution−HOPG Interface. J. Am. Chem. Soc. 2008, 130, 9371−9379. (36) Zhang, X.; Xu, S.; Li, M.; Shen, Y.; Wei, Z.; Wang, S.; Zeng, Q.; Wang, C. Photo-Induced Polymerization and Isomerization on the Surface Observed by Scanning Tunneling Microscopy. J. Phys. Chem. C 2012, 116, 8950−8955. (37) Sakano, T.; Imaizumi, Y.; Hirose, T.; Matsuda, K. Formation of Two-dimensionally Ordered Diarylethene Annulated Isomer at the Liquid/HOPG Interface upon In Situ UV Irradiation. Chem. Lett. 2013, 42, 1537−1539. (38) Yokoyama, S.; Hirose, T.; Matsuda, K. Phototriggered Formation and Disappearance of Surface-Confined Self-Assembly Composed of Photochromic 2-Thienyl-Type Diarylethene: A Cooperative Model at the Liquid/Solid Interface. Chem. Commun. 2014, 50, 5964−5966.

(39) Bonacchi, S.; El Garah, M.; Ciesielski, A.; Herder, M.; Conti, S.; Cecchini, M.; Hecht, S.; Samorì, P. Surface-Induced Selection During In Situ Photoswitching at the Solid/Liquid Interface. Angew. Chem., Int. Ed. 2015, 54, 4865−4869. (40) Tahara, K.; Inukai, K.; Adisoejoso, J.; Yamaga, H.; Balandina, T.; Blunt, M. O.; De Feyter, S.; Tobe, Y. Tailoring Surface-Confined Nanopores with Photoresponsive Groups. Angew. Chem., Int. Ed. 2013, 52, 8373−8376. (41) Shen, Y.-T.; Guan, L.; Zhu, X.-Y.; Zeng, Q.-D.; Wang, C. Submolecular Observation of Photosensitive Macrocycles and Their Isomerization Effects on Host−Guest Network. J. Am. Chem. Soc. 2009, 131, 6174−6180. (42) Zhang, X.; Wang, S.; Shen, Y.; Guo, Y.; Zeng, Q.; Wang, C. Two-Dimensional Networks of an Azobenzene Derivative: Bi-Pyridine Mediation and Photo Regulation. Nanoscale 2012, 4, 5039−5042. (43) Shen, Y. T.; Deng, K.; Zhang, X. M.; Feng, W.; Zeng, Q. D.; Wang, C.; Gong, J. R. Switchable Ternary Nanoporous Supramolecular Network on Photo-Regulation. Nano Lett. 2011, 11, 3245− 3250. (44) Lei, S.; Tahara, K.; De Schryver, F. C.; Van der Auweraer, M.; Tobe, Y.; De Feyter, S. One Building Block, Two Different Supramolecular Surface-Confined Patterns: Concentration in Control at the Solid−Liquid Interface. Angew. Chem., Int. Ed. 2008, 47, 2964− 2968. (45) Kampschulte, L.; Werblowsky, T. L.; Kishore, R. S. K.; Schmittel, M.; Heckl, W. M.; Lackinger, M. Thermodynamical Equilibrium of Binary Supramolecular Networks at the Liquid−Solid Interface. J. Am. Chem. Soc. 2008, 130, 8502−8507. (46) Palma, C.-A.; Bjork, J.; Bonini, M.; Dyer, M. S.; Llanes-Pallas, A.; Bonifazi, D.; Persson, M.; Samorì, P. Tailoring Bicomponent Supramolecular Nanoporous Networks: Phase Segregation, Polymorphism, and Glasses at the Solid−Liquid Interface. J. Am. Chem. Soc. 2009, 131, 13062−13071. (47) Bellec, A.; Arrigoni, C.; Schull, G.; Douillard, L.; FioriniDebuisschert, C.; Mathevet, F.; Kreher, D.; Attias, A.-J.; Charra, F. Solution-Growth Kinetics and Thermodynamics of Nanoporous SelfAssembled Molecular Monolayers. J. Chem. Phys. 2011, 134, 124702. (48) Ha, N. T. N.; Gopakumar, T. G.; Hietschold, M. Polymorphism Driven by Concentration at the Solid−Liquid Interface. J. Phys. Chem. C 2011, 115, 21743−21749. (49) Ciesielski, A.; Szabelski, P. J.; Rżysko, W.; Cadeddu, A.; Cook, T. R.; Stang, P. J.; Samorì, P. Concentration-Dependent Supramolecular Engineering of Hydrogen-Bonded Nanostructures at Surfaces: Predicting Self-Assembly in 2D. J. Am. Chem. Soc. 2013, 135, 6942−6950. (50) Kawai, T.; Iseda, T.; Irie, M. Photochromism of Triangle Terthiophene Derivatives as Molecular Re-Router. Chem. Commun. 2004, 72−73. (51) Nakashima, T.; Atsumi, K.; Kawai, S.; Nakagawa, T.; Hasegawa, Y.; Kawai, T. Photochromism of Thiazole-Containing Triangle Terarylenes. Eur. J. Org. Chem. 2007, 3212−3218. (52) Kawai, S.; Nakashima, T.; Atsumi, K.; Sakai, T.; Harigai, M.; Imamoto, Y.; Kamikubo, H.; Kataoka, M.; Kawai, T. Novel Photochromic Molecules Based on 4,5-Dithienyl Thiazole with Fast Thermal Bleaching Rate. Chem. Mater. 2007, 19, 3479−3483. (53) Nakashima, T.; Goto, M.; Kawai, S.; Kawai, T. Photomodulation of Ionic Interaction and Reactivity: Reversible Photoconversion between Imidazolium and Imidazolinium. J. Am. Chem. Soc. 2008, 130, 14570−14575. (54) Jeong, Y.-C.; Cao, C.; Lee, I. S.; Yang, S. I.; Ahn, K.-H. The Considerable Photostability Improvement of Photochromic Terarylene by Sulfone Group. Tetrahedron Lett. 2009, 50, 5288−5290. (55) Fukumoto, S.; Nakashima, T.; Kawai, T. Photon-Quantitative Reaction of a Dithiazolylarylene in Solution. Angew. Chem., Int. Ed. 2011, 50, 1565−1568. (56) Irie, M.; Fukaminato, T.; Matsuda, K.; Kobatake, S. Photochromism of Diarylethene Molecules and Crystals: Memories, Switches, and Actuators. Chem. Rev. 2014, 114, 12174−12277. 6413

DOI: 10.1021/acs.langmuir.5b01404 Langmuir 2015, 31, 6404−6414

Article

Langmuir (57) Irie, M.; Lifka, T.; Uchida, K.; Kobatake, S.; Shindo, Y. One-Pot Synthesis of New Liquid Crystalline Indeno Heterocyclic Materials. Chem. Commun. 1999, 747−750. (58) Higashiguchi, K.; Matsuda, K.; Kobatake, S.; Yamada, T.; Kawai, T.; Irie, M. Fatigue Mechanism of Photochromic 1,2-Bis(2,5-dimethyl3-thienyl)perfluorocyclopentene. Bull. Chem. Soc. Jpn. 2000, 73, 2389− 2394. (59) Herder, M.; Schmidt, B. M.; Grubert, L.; Pätzel, M.; Schwarz, J.; Hecht, S. Improving the Fatigue Resistance of Diarylethene Switches. J. Am. Chem. Soc. 2015, 137, 2738−2747. (60) Miura, A.; De Feyter, S.; Abdel-Mottaleb, M. M. S.; Gesquière, A.; Grim, P. C. M.; Moessner, G.; Sieffert, M.; Klapper, M.; Müllen, K.; De Schryver, F. C. Light- and STM-Tip-Induced Formation of OneDimensional and Two-Dimensional Organic Nanostructures. Langmuir 2003, 19, 6474−6482. (61) Miao, X.; Xu, L.; Li, Z.; Deng, W. Solvent-Induced Structural Transitions of a 1,3,5-Tris(10-ethoxycarbonyldecyloxy)benzene Assembly Revealed by Scanning Tunneling Microscopy. J. Phys. Chem. C 2011, 115, 3358−3367. (62) Hirsch, B. E.; McDonald, K. P.; Qiao, B.; Flood, A. H.; Tait, S. L. Selective Anion-Induced Crystal Switching and Binding in Surface Monolayers Modulated by Electric Fields from Scanning Probes. ACS Nano 2014, 8, 10858−10869. (63) Kamiya, H.; Yanagisawa, S.; Hiroto, S.; Itami, K.; Shinokubo, H. Functionalization of a Simple Dithienylethene via Palladium-Catalyzed Regioselective Direct Arylation. Org. Lett. 2011, 13, 6394−6397. (64) Because of the pseudo-C3 symmetry of the annulated isomer 1a, the space group of γ-ordering is not exactly p6. (65) Lei, S.; Tahara, K.; Feng, X.; Furukawa, S.; De Schryver, F. C.; Müllen, K.; Tobe, Y.; De Feyter, S. Molecular Clusters in TwoDimensional Surface-Confined Nanoporous Molecular Networks: Structure, Rigidity, and Dynamics. J. Am. Chem. Soc. 2008, 130, 7119−7129. (66) Nangia, A. Conformational Polymorphism in Organic Crystals. Acc. Chem. Res. 2008, 41, 595−604.

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DOI: 10.1021/acs.langmuir.5b01404 Langmuir 2015, 31, 6404−6414