Formation of Halogen Bond-Based 2D Supramolecular Assemblies by Electric Manipulation

Transcription

1 Formation of Halogen Bond-Based 2D Supramolecular Assemblies by Electric Manipulation Qing-Na Zheng, a,b Xuan-He Liu, a,b Ting Chen, a Hui-Juan Yan, a Timothy Cook, c Dong Wang* a, Peter J. Stang, c Li-Jun Wan* a a Key Laboratory of Molecular Nanostructure and Nanotechnology and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences (CAS), Beijing , P.R. China b Graduate University of the Chinese Academy of Sciences, China c Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112, United States Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York, 14260, United States Contents: 1. Experimental method S2 2. The adsorption behavior of mono-component XB acceptors S3 3. Details of honeycomb structure S5 4. The effect of electric pulse to 3N/3F3I honeycomb structure S7 5. Details of 3N/4F2I porous structure S10 6. The effect of molecular structure on XB binary assembly S11 7. Detail of 2N/4F2I linear structure S12 8. Detail of 4N/4F2I porous structure S13 9. Control experiments to investigate the effect of tip-modification method S Chemical state of C-I bond in 3F3I molecule after electric manipulation S17 S1

2 1. Experimental Method STM experiment STM experiments were conducted by using a NanoscopeIIIa SPM (Digital Instruments, Santa Barbara, CA) under ambient air condition at room temperature. Mechanically cut Pt/Ir wire (90/10) tips were used. All images were taken in the constant current mode. The XB donors and acceptors were dissolved in octylbenzene (OB) at concentration of 10-5 M. Typically, the adlayer were prepared by drop-casting of ~2 µl mono-component or mixture solution onto freshly cleaved highly oriented pyrolytic graphite (HOPG, grade ZYB) surface. The well-ordered binary assembly typically formed only after applying the electric pulse ranged from 3.6 ~ 4.2 V during scanning. When 3N was used as XB donor, the typical sample preparation didn t produce binary network. A tip modification method was adapted. Briefly, a clean STM tip was immersed into a mixed solution of XB donor and acceptor for about 60s to pollute the STM tip. The XB donor and acceptor molecules were stuck to the STM tip. The polluted STM tip was applied to the OB/HOPG interface without any molecules. Then, the electric pluse was applied to the modified STM tip during the scanning process. The well ordered supramolecular assemblies can be observed. Time-of-flight secondary ion mass spectrometer (TOF-SIMS) Secondary ion mass spectra were obtained using a time-of-flight secondary ion mass spectrometer TOF-SIMS 5 from ION-TOF GmbH (Munster, Germany). A Bi 3+ liquid metal ion gun operating at a 30 kev beam voltage with a 45 incident angle was used. Charge compensation with an electron flood gun was used during the analysis cycles. Negative ion mode spectra were calibrated on the C, CH, C 2 and C 2 H peaks. X-ray photoelectron spectroscopy (XPS) XPS spectra were obtained with a VG Scientific ESCALAB250XI X-ray photoelectron spectrometer with a monochromatized Al-Kα X-ray source ( ev). X-ray power supply was run at 15 kv and ma. The typical operating pressure was around mbar in the sample chamber. The binding energy values of all core level spectra were referenced to the C1s neutral-carbon peak at ev. S2

3 2. The adsorption behavior of mono-component XB acceptors Figure S1.Close-packed structure of mono-component 3N. (a) Large-scale STM image of pure 3N close-packed structure on OB/HOPG surface. Tunneling conditions: V bias = 725 mv, I t = 419 pa. (b) High-resolution STM image of pure 3N close-packed structure. Tunneling conditions: V bias = 725 mv, I t = 461 pa. (c) Tentatively proposed structural model of pure 3N close-packed structure. Figure S1 shows the close-packed structure of the pure 3N molecules on OB/HOPG surface. The crystalline domains of the close-packed structure can reach hundreds of square nanometers. The unit cell of the pure 3N was measured to be: a = b= 1.3 ± 0.1 nm, γ = 60 ± 2º, which was agreement with the literature reported. The proposed model of pure 3N was illustrated in Figure S1c. S3

4 Figure S2. Close-packed structure of mono-component 4N. (a) Large-scale STM image of pure 4N close-packed structure on OB/HOPG surface. Tunneling conditions: V bias = 630 mv, I t = 523 pa. (b) High-resolution STM image of pure 4N close-packed structure. Tunneling conditions: V bias = 608 mv, I t = 502 pa. (c) Tentatively proposed structural model of pure 4N close-packed structure. Each unit cell contained two 4N molecules. For clear inspection, the 4N molecules were colored pink and blue. Figure S2a shows the close-packed of pure 4N on OB/HOPG surface. The typical domain size can reach nm 2. Figure S2b was the high-resolution STM image of mono-component 4N adlayer. Two molecular lines of close-packed 4N molecules can be observed. The parameter of the outlined unit cell is a = 1.4 ± 0.2 nm, b = 3.7 ± 0.2 nm and γ = 74 ± 2. Proposed structure was provided in Figure S2c. There are two 4N molecules in each unit cell, as illustrated by pink and blue color respectively. S4

5 3. Details of honeycomb structure \ Figure S3. A composite STM image of 3N/3I3F honeycomb structure (19 nm 38 nm, the upper part) and the HOPG substrate (4 nm 8 nm, the lower part). Imaging conditions: V bias = 888 mv, I t = 1060 pa (the upper part); V bias = 45 mv, I t = 1024 pa (the lower part). The scanning direction was from the bottom up. The scan lines and drift of STM image was attributed to the sudden change of tunnelling conditions. S5

6 Figure S4. The expected model of 3N/4F2I honeycomb structure if N-I XB is the only intermolecular interaction to sustain the assembly. The hexagonal structure can be constructed from ditopic module (4F2I) and tritopic module (3N) via linear lineage (I-N XB). This expected structure has quite a large pore size (4.8 nm). The XBs were not strong enough to stabilize such a large network at the surface. The observed 3N/4F2I XB-based structure was the result of the combination of hydrogen bonds and XBs. S6

7 4. The effect of electric pulse to 3N/3F3I honeycomb structure Figure S5. STM images demonstrated the formation of the 3N/3F3I honeycomb structure was associated with the voltage of the electric pulse (height of the electric pulse). The 3N/3F3I honeycomb structure can be formed when the voltage of pulse ranged from 3.4 to 4.2 V. The 3N/3F3I honeycomb structure was disturbed when the voltage of pulse was bigger than 4.2 V. Tunnelling conditions: (a) V bias = 847 mv, I t = 659 pa. (b) V bias = 698 mv, I t = 450 pa. (c) V bias = 957 mv, I t = 605 pa. (d) V bias = 770 mv, I t = 550 pa. (e) V bias = 755 mv, I t = 659 pa. Image size: nm 2. Width of the electric pulse was 3 ms. Both 3N and 3I3F was stuck to the STM tip. Then the electric pulses were applied to the sample to explore the relationship of the electric pulse and the formation of XB-based structure. STM images in Figure S5 demonstrated that the formation of the 3N/3F3I honeycomb was associated with the voltage of the electric pulse. The 3N/3F3I honeycomb structure can be formed when the voltage of pulse ranged from 3.4 to 4.2 V. S7

8 Figure S6. The STM images of 3N/3F3I honeycomb XB-based structure after a serial of electric pulse with different width. (a-d) The scan direction was indicated by white arrow. The pulse position was indicated by white cross. Tunneling conditions: V bias = 700 mv, I t = 500 pa. Image size: nm 2. The parameters of electric pulse were indicated in each picture. The 3N/3F3I honeycomb XB-based structure can be formed when the width of electric pulse ranged from 3 ms to 30 ms. The shortest duration of the STM instrument was 3 ms. Upon application several voltage pulses (pulse height = 3.6 V, different pulse width) to STM tip at different positions of the scan area (indicated by blue crosses in each picture), 3N/3F3I honeycomb XB-based structure were seen to emerge clearly. Figure S6 demonstrated that the honeycomb can be obtained after continuous electric manipulation. The range of the electric pulse can be set from 3 to 30 ms. No obvious difference was observed under different electric pulse width. However STM tip was easily damaged in the long duration of time scale. Taking convenience and STM tip protection into account, the 3 ms electric pulse was applied in the experiment process. S8

9 5. Details of 3N/4F2I porous structure Figure S7.The STM images demonstrated that defects easily arise along b direction. (a) The STM image demonstrated that the defects (indicated by white arrows) were lying along the b direction. Tunneling conditions: V bias = 731 mv, I t = 627 pa. (b) The STM image demonstrated that the defects (white dashed line) were parallel to the b direction (indicated by white line). Tunneling conditions: V bias = 780 mv, I t = 662 pa. Figure S7 demonstrate that the defects easily occur along the b direction. This phenomenon was in agreement with the model of 3N/4F2I porous structure. A direction was sustained by both hydrogen bonds and XBs, while b direction was sustained by only XBs. S9

10 6. The effect of molecular structure on XB binary assembly Figure S8. Large-scale STM image of 3N/4H2I assembly structure. Tunneling conditions: V bias = 708 mv, I t = 450 pa. The absence of electro-withdrawing F on aromatic ring makes XB less strong to sustain ordered assembly. Scheme S1. Summary of experimental results for 3N and XB donors. S10

11 7. Detail of 2N/4F2I linear structure Figure S9. STM image of 2N/4F2I self-assembled linear structure. (a) Large-scale STM image of 2N/4F2I linear structure. Tunneling conditions: V bias = 758 mv, I t = 513 pa. (b) High-resolution STM image of 2N/4F2I linear structure. Tunneling conditions: V bias = 758 mv, I t = 513 pa. (c) Tentatively proposed structural model for 2N/4F2I linear structure. To explore the scope of our approach, we performed similar experiments using other compounds as a different XB acceptor. 2N has two pyridyl units that may be involved in XB interactions with iodines. Molecules self-assembled into a large-scale linear structure in Figure S9a. The typical domain size of the linear structure can reach nm 2. The Bright spots and dark rods can be clearly seen. With the help of the high-resolution STM image in Figure S9b, the 2N/4F2I linear structure could be analyzed in detail. The bright spots are ascribed to 4F2I and the dark rods are attributed to 2N. The dark rods are measured to be 1.2 nm ± 0.1 nm long, in agreement with the length of 2N. One 2N molecule was attached to two 4F2I molecules in a head-to-head configuration to form a linear structure. I atoms in 4F2I and pyridyl groups in 2N approach each other closely to form C-N I XBs. The C-N I angle is closer to 180º, in agreement with the definition of XBs. A structure model for 2N/4F2I linear structure is proposed in Figure S9c. A unit cell is outlined in Figure S9b, and the parameters are measured to be a = 1.5 ± 0.2 nm, b = 2.5 ± 0.2 nm, γ = 85 ± 2º. Two XBs have been formed in the two terminals of the 2N molecules to help stabilize the linear structure. S11

12 8. Detail of 4N/4F2I porous structure Figure S10. STM image of 4N/4F2I self-assembled porous structure.(a) Large-scale STM image of 4N/4F2I porous structure. Tunneling conditions: V bias = 649 mv, I t = 475 pa. (b) High-resolution STM image of 4N/4F2I porous structure. Tunneling conditions: V bias = 766 mv, I t = 452 pa. (c) The STM image shows the coexistence of 4N close-packed structure and 4N/4F2Iporous structure. Tunneling conditions: V bias = 686 mv, I t = 480 pa. (d) Building block of the 4N/4F2I porous structure. Possible hydrogen bonds are depicted by blue spots. Possible XBs are depicted by yellow spots. The STM image in Figure S10a shows the binary supramolecular architecture in the control experiment of 4N/4F2I. Molecules self-assemble into a large-scale 2D porous structure, as shown in Figure S10a. The typical domain of this porous structure can be reach nm 2. Figure S10b shows the coexistence of the pure 4N close-packed structure and 4N/4F2I porous structure. The right part of the STM image shows the 4N close-packed structure; meanwhile the left part of the image shows the 4N/4F2I porous structure. The boundary of the two domains was illustrated by white dashed line. Figures S10c displays the high-resolution STM image of binary 4N/4F2I. The lattice parameter outlined in Figure S10b is measured to be a = 2.5 ± 0.2 nm, b = 3.1 ± 0.2 nm, γ = 68 ± 2º. For S12

13 comparison, the 4N/4F2I porous structure model was superimposed in Figure S10c. The 4N/4F2I porous structure was sustained by both hydrogen bonds and XBs, which was similar to 3N/4F2I system. Two 4N molecules were connected by a 4F2I node in b direction. Two XBs can be formed between the two I atoms and the pyridyl groups of 4N molecules as illustrated by yellow spots in Figure S10d. The a direction was sustained by both hydrogen bonds (blue spots in Figure S10d) and XBs (yellow spots in Figure S10d) in a antiparallel manner similar to 3N/4F2I system. Figure S10d shows a tentatively proposed structural model for 3N/3I3F honeycomb structure. S13

14 9. Control experiments to investigate the effect of tip-modification method Figure S11.The STM image of 2N/4F2I on HOPG surface demonstrated that the formation of the XB-based structure was associated to the electric pulses. The 2N/4F2I linear structure can be formed when the voltage of the electric pulses ranged from 4.0 V to 4.2 V. Tunneling conditions: V bias = 800 mv, I t = 557 pa. Both 2N and 4F2I could not be observed on HOPG surface because of the low affinity of the pure molecules. In this control experiment the electric pulses were applied to the sample when the two species were both added to the surface, rather than by polluted tip. The formation of 2N/4F2I linear structure was related to the electric pulse. The voltage of the electric pulse must be bigger than 4.0 V. S14

15 Figure S12. The STM image of 4N/4F2I on HOPG surface demonstrated that the formation of the XB-based structure was associated to the electric pulses. The 4N/4F2I porous structure can be formed when the voltage of the electric pulses ranged from 3.8 V to 4.4 V. Tunneling conditions: V bias = 800 mv, I t = 557 pa. In this control experiment the electric pulses were applied to the sample when the two species were both added to the surface. The formation of 4N/4F2I porous structure was related to the electric pulse. The voltage of electric pulse was range from 3.8 V to 4.4 V in order to construct the 4N/4F2I porous structure. S15

16 Figure S13. The STM image of 3N/4F2I on HOPG surface demonstrated that the affinity of 3N was so strong that only pure 3N close-packed structure can be observed when the electric pulse was ranged from 3.4 V to 4.2 V. Tunneling conditions: V bias = 847 mv, I t = 450 pa. If 3N/4F2I or 3N/3F3I was preloaded on the HOPG surface, only mono-component 3N close-packed structure can be observed, independent to the applied electric pulses. In Figure S13, both the 3N and 4F2I was added to the surface. Only 3N close-packed structure can be observed in the electric pulse ranged from 3.4 V to 4.2 V. The evidence indicated that 3N has a strong affinity to the HOPG. Comparing the results of Figure S13, S12 and S11, we can found that the electric pulses was important for the formation of XB-based structure, while the STM tip modification was not necessary for other XB-based structures. Considering the strong affinity of 3N to HOPG surface, we adopted a new method to pollute the STM tip with the mixture solution of 3N/4F2I to avoid the strong adsorption of pure 3N. The XB-based structure of 3N/4F2I can be formed under the electric manipulation of the polluted STM tip. S16

17 10. The chemical state of C-I bond in 3F3I molecule. TOF-SIMS and XPS experiments have been conducted to explore the chemical state of the C-I bond in 3F3I after electric pulses. Three samples (mono-component 3F3I, mixed adlayer of 3N/3F3I, and mixed adlayer of 3N/3F3I after electric pulses) were prepared. For the last sample, the 3N/3F3I XB-based structure was confirmed by STM. The area with the 3N/3F3I XB-based structure was marked for the TOF-SIMS and XPS characterization. Figure S14 shows the TOF-SIMS results from three set of samples. The negative ion mode of mass spectra (m/z range ) of a standard pure 3F3I were provided in Figure S14 top (blue). The molecular ion peak of 3F3I (observed (obs.) m/z , calculated (calc.) m/z ) was observed. Negative ions containing characteristic adducts were obtained, which are assignable to [3F3I - I] - (obs. m/z , calc. m/z ) and [3F3I - I + H] - (obs. m/z , calc. m/z ). Comparing the standard mass spectra of 3F3I and those of the mixed adlayer of 3N/3F3I without electric manipulation (middle) and a 3N/3F3I XB-based structure (bottom), one can see no difference, which suggested that the 3F3I was intact after the electric manipulation. We note that the mass signal of 3N is very weak in negative ion mode. We further analyzed the relative strength of characteristic molecular ion fragments. The total peak area of the 3F3I molecular ion peak was used as a reference for the normalization. Table S2 shows that the ratio of [3F3I - I] - (calc ) relative to [3F3I] - (calc ) in 3N/3F3I adlayer without electric manipulation sample was 29.3 and This ratio in 3N/3F3I adlayer under electric manipulation sample was 30.2 and 33. The peak area normalization in these two samples was very close. This result demonstrated that the C-I bond in 3F3I is intact under electric manipulation. S17

18 Figure S14. The mass spectra of mono-component 3F3I (top, blue), 3N/3F3I mixed adlayer without electric manipulation (middle, black) and with electric manipulation (bottom, red). S18

19 Table S1. Area normalization of 3N/3F3I without electric manipulation and 3N/3F3I under electric manipulation. We have conducted the XPS experiments on the mixed 3N/3F3I adlayer samples without and with electric manipulation. The XPS result of the mixed adlayer after electric manipulation is shown in Figure S15. The XPS spectra are the same for both samples (with or without electric manipulation), which indicates that the C-I bonds was intact. Figure S15. X-ray photoemission spectra of I 3d in 3N/3F3I after electric manipulation. S19