Force-Activated Isomerization of a Single Molecule

Article abstract of DOI:10.1021/jacs.0c00192

Understanding and controlling isomerization at the single molecular level should provide new insight into the molecular dynamics and design guidelines of functional devices. Scanning tunneling microscopy (STM) has been demonstrated to be a powerful tool to study isomerization of single molecules on a substrate, by either electric field or inelastic electron tunneling mechanisms. A similar molecular isomerization process can in principle be induced by mechanical force; however, relevant study has remained elusive. Here, we demonstrate that isomerization of a N,N-dimethylamino-dianthryl-benzene molecule on Ag(100) can be mechanically driven by the STM tip. The existence of an out-of-plane dimethylamino group in the molecule is found to play a pivotal role in the isomerization process by providing a steric hindrance effect for asymmetric interaction between the STM tip and the molecule. This underlying mechanism is further confirmed by performing molecular dynamics simulations, which show agreement with experimental results. Our work opens the opportunity to manipulate the molecular configuration on the basis of mechanical force.

Full text of DOI:10.1021/jacs.0c00192

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Article
Force-Activated Isomerization of a Single Molecule
Jing Qi, Yixuan Gao, Haihong Jia, Marcus Richter, Li Huang, Yun Cao,
Huan Yang, Qi Zheng, Reinhard Berger, Junzhi Liu, Xiao Lin, Hongliang Lu,
Zhihai Cheng, Min Ouyang, Xinliang Feng, Shixuan Du, and Hong-Jun Gao
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.0c00192 • Publication Date (Web): 27 May 2020
Downloaded from pubs.acs.org on May 28, 2020
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Force-Activated Isomerization of a Single Molecule
, ,
,
Jing Qi,† ¶ ▲ Yixuan Gao,† ▲ Haihong Jia,† Marcus Richter,‡ Li Huang,† Yun Cao,† Huan Yang,† Qi Zheng,†
,
Reinhard Berger,‡ Junzhi Liu,‡ ∞ Xiao Lin,† Hongliang Lu,† Zhihai Cheng,§ Min Ouyang,ǁ Xinliang
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Feng,*,‡,⊥ Shixuan Du*,† and Hong-Jun Gao*,†
†Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, 100190 Beijing,
China
‡Center for Advancing Electronics Dresden (cfaed) & Department of Chemistry and Food Chemistry, Technische
Universität Dresden, 01069 Dresden, Germany
§Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-nano Devices,
Renmin University of China, 100872 Beijing, China
‖Department of Physics and Center for Nanophysics and Advanced Materials, University of Maryland, College Park,
20742 Maryland, USA
⊥School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 200240 Shanghai, China
ABSTRACT: Understanding and controlling isomerization at single molecular level should provide new insight into molecular
dynamics and design guidelines of functional devices. Scanning tunneling microscopy (STM) has been demonstrated to be a
powerful tool to study isomerization of single molecules on substrate, by either electric field or inelastic electron tunneling
mechanisms. Similar molecular isomerization process can in principle be induced by mechanical force, however relevant
study has remained elusive. Here we demonstrate that isomerization of a N,N-dimethylamino-dianthryl-benzene molecule on
Ag(100) can be mechanically driven by STM tip. The existence of out-of-plane dimethylamino group in the molecule is found
to play a pivotal role in isomerization process by providing a steric hindrance effect for asymmetric interaction between the
STM tip and molecule. This underlying mechanism is further confirmed by performing molecular dynamics simulations,
showing agreement with experimental results. Our work opens up opportunity to manipulate molecular configuration based
on mechanical force.
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
INTRODUCTION
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Molecular isomers possessing subtle structural variations often manifest dramatic differences in physical and chemical
properties.1-4 Investigation on isomerization5-7 can boost the research in enantioselective synthesis,8-10 chiral catalysis6, 11-13
and chiral pharmaceutical synthesis.14-15 However, probing or even controlling exact configuration of isomers at single
molecular level in solution has posed substantial challenges due to the three-dimensional rotation of isomers.16 Recently,
studying on-surface isomerization has offered an alternative route.17-22 In this context, scanning probe microscopy (SPM) has
been proved to be a powerful technique in relevant studies. In addition to its atomic spatial resolution,19, 23-25 the SPM can be
utilized to manipulate molecules through different mechanisms,26-27 making it an ideal tool to study isomerization at single
molecular level. Although mechanisms involving light and/or electrical activation has been investigated,17, 19, 25-26, 28-32 using
mechanical force to induce isomerization has been relatively rare.33-35
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Here, we have employed scanning tunneling microscope (STM) tip to apply force interactions with N,N-dimethylamino-2,6-
di(2-anthryl)-benzene (DMADAB) molecules on the Ag substrate to trigger its isomerization, which can be directly
characterized by atomic imaging. The underlying mechanism uncovered by performing molecular dynamics simulations and
control experiment confirms that the out-of-plane dimethylamino group is essential for isomerization in this case.

RESULTS AND DISCUSSION
The synthesis of DMADAB was carried out in two steps starting from the commercially available 2,6-bromoaniline (see
Supporting Information). The DMADAB consists of a central benzene ring functionalized with an out-of-plane dimethylamino
group and two anthryl groups at the ortho-positions. Due to the rotation of the two C–C bonds between the anthryl groups
and the central benzene ring during sublimation, three isomers were formed on substrate. Figure 1a is a large-area STM
topographic image showing the three isomers of DMADAB after deposition, as marked by DMADAB-1, DMADAB-2 and
DMADAB-3. Figure 1b–d show zoom-in STM images, and the optimized structures of the three DMADAB isomers on Ag(100)
substrate. The two anthryl groups in DMADAB-1 are almost parallel, while in DMADAB-2 one anthryl group turns inwards,
forming an “L” shaped configuration. Isomer DMADAB-3 has both anthryl groups turn inwards, forming a “V” shaped
configuration. The angle between the two anthryl groups in a DMADAB molecule is used as a criterion to classify the three
isomers, as depicted in Figure S1. In the STM topographic images in the upper panels of Figure 1b–d, the three DMADAB
isomers show bright protrusions in the middle due to the out-of-plane dimethylamino groups. The lower panels of Figure 1b–
d are the top and side view of the most stable configurations of DMADAB isomers on Ag(100) surface obtained by density
functional theory (DFT) calculations. To exclude other configurations, we also intentionally used a configuration in which
both the anthryl groups are standing on the surface as the initial structure in DFT calculation, and the anthryl groups become
lying flat on the substrate after structural relaxation (Figure S2), confirming the configurations in Figure 1b-d are the most
energetically favorable ones. The side view of the isomers on the substrate display that the topmost hydrogen atom of the
protuberant methyl groups is about 0.38 nm higher than the average plane of the two anthryl groups.
The DFT calculated adsorption energies are -3.192 eV, -3.327 eV, and -3.355 eV, for DMADAB-1, DMADAB-2, DMADAB-3 on
Ag(100), respectively. It means that we should observe more DMADAB-3 on Ag(100) substrate. However, from STM image
(Figure 1a) and the quantitative populations for these three isomers (Figure S1c), we found that there are much more
DMADAB-2 isomers than others. To explain this, we optimized the structures of DMADAB isomers in vacuum and calculated
their total energies relative to DMADAB-1 (Figure S3). The respective total energy of DMADAB-2 and DMADAB-3 are 0.035
eV and 0.066 eV higher than that of DMADAB-1, suggesting that DMADAB-1 is the dominant isomer in vacuum before landing
on surface. The adsorption energy determines which isomer is easier to adsorb on the surface, while the total energy in
vacuum determines the initial quantities of each isomers. DMADAB-1 has the largest initial quantity but is the hardest to
adsorb on surface, while DMADAB-3 is the easiest to adsorb on the surface but have the smallest initial quantity. The
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competition between the two factors results in DMADAB-2, which has medium adsorption energy and total energy in vacuum,
becoming the most favorable isomer on Ag(100) surface.
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Figure 1. Isomers of DMADAB on Ag(100) substrate. (a) 30×50 nm2 STM topographic image of DMADAB after deposition at room
temperature (RT). The three isomers are labeled in dashed circles with different colors (DMADAB-1 = yellow; DMADAB-2 = white
and DMADAB-3 = magenta). Scale bar: 5 nm. (b–d) STM topographic images, and top and front view of the DFT optimized structures
of DMADAB-1, DMADAB-2 and DMADAB-3 on Ag(100) substrate, respectively. The C–C bonds in red in the lower panels indicate the
rotatable C–C bonds. The red arrows indicate the crystal orientations of the substrate. Scanning parameters are Vsample = −100 mV
and I = 30 pA. Scale bars: 1 nm.
We performed STM tip manipulation on the isomers to investigate their on-surface isomerization. The manipulations were
done by opening the feedback loop, decreasing the bias voltage to zero, then approaching the STM tip to the target isomer
and then lifting the tip up (Figure 2a). Figure 2b–f demonstrate manipulations on one DMADAB molecule (as indicated by
dashed circles) that triggers the transitions between isomers. Isomer DMADAB-1 in Figure 2a had one of its anthryl groups
(marked with green ellipse) rotated upon manipulation, which resulted in DMADAB-2 (Figure 2b–c). Further manipulation
on the isomer DMADAB-2 made the other anthryl group rotate and isomerize to DMADAB-3 (Figure 2c–d). This process is
reversed, as shown in Figure 2d, when DMADAB-3 was manipulated, one anthryl group rotated and turned to DMADAB-2
(Figure 2d–e). Further manipulation made the other anthryl group rotate and turn to DMADAB-1 (Figure 2e–f). We have
performed 223 manipulations on DMADAB molecules, and the overall success rate was 28.7%, as shown in the statistics in
Figure 2g. We didn’t observe the direct isomerization between DMADAB-1 and DMADAB-3 which involves the rotation of
both anthryl groups, indicating a large energy barrier of rotating both anthryl groups simultaneously. Meanwhile, from the
statistics in Figure 2g, the successful isomerization rate for DMADAB-1 to DMADAB-2, DMADAB-2 to DMADAB-1/3 and
DMADAB-3 to DMADAB-2 are comparable, suggesting comparable energy barriers of rotating one anthryl group in all the
three isomers.
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Figure 2. Reversible isomerization of DMADAB on Ag(100) surface by STM tip manipulation. (a) Schematic of the tip vertical
manipulation. The tip approaches to the target DMADAB isomer and then retracts, causing the transition. (b–f) STM images show
STM tip manipulation induced isomerization on the same DMADAB molecule on Ag(100) substrate. The images are in time order,
but not consecutive. Some images with the same configurations are omitted. The dashed circles indicate the isomers being
manipulated. Reversible isomerization between all three isomers of DMADAB has been achieved. The corresponding molecular
structures are depicted in the images, in which the bonds marked green highlight the rotated C-C bond and the green ellipses
highlight the rotating anthryl groups. Scanning parameters are Vsample = −100 mV and I = 30 pA. Scale bars: 2 nm. (g) Statistics of tip
manipulations on DMADAB isomers. The overall success rate of isomerization is 28.7% in 223 manipulations.
With the support of steered molecular dynamics (SMD) simulations, we tried to elucidate the mechanism behind the
isomerization of DMADABs. Taken the isomerization process from DMADAB-1 to DMADAB-2 as an example, the simulated
movie demonstrates the process starting from the tip (metal apex, no carbon monoxide functionalized) approaching to the
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molecule and ending with the tip retracting (See Movie S1 in Supporting Material and snapshots in Figure S4 in Supporting
Information). The four typical states from the simulation are depicted in Figure 3. First, the tip is approaching on a DMADAB-1
isomer on Ag(100) substrate. When the tip is far away from the molecule, the DMADAB-1 keeps its original adsorption
configuration with its two anthryl groups aligned parallel to the substrate and the dimethylamino group pointed straight
upwards, as indicated in Figure 3a. When the tip approaches to the surface, the DMADAB-1 isomer moves towards the tip.
Due to the repulsive force induced by the out-of-plane dimethylamino group (marked by green halo), one of its anthryl group
goes closer to the tip and rotates to have an attractive force with the tip, as shown by purple halo and red arrow in Figure 3b.
Afterwards, when the tip retracts from the substrate, the strong interaction from the tip pulls up the rotated the anthryl group
along with the central benzene ring (Figure 3c). However, with the other anthryl group still adsorbing on the substrate, the
molecule detaches from the tip when the tip further retracts and falls on the surface with one of the anthryl group completely
rotated to isomer DMADAB-2 (Figure 3d). Furthermore, the SMD simulations also show that the rotation direction of the
anthryl group is outward, i.e., away from the dimethylamino group, due to the steric hindrance (Figure S5).
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Figure 3. The four typical states in tip manipulation on DMADAB taken from the SMD simulations and the △f(Z) curve on a successful
isomerization. (a) The tip is approaching a DMADAB-1. (b) When the tip is close to the DMADAB-1, the out-of-plane dimethylamino
group (in green halo) gives the tip a repulsive force, which induces the tip to go to one side of the molecule and have attractive force
with one of the anthryl groups (in purple halo). As a result, the anthryl group rotates as indicated by the red arrow. (c) When the tip
retracts, the anthryl group and the central benzene ring are lifted up by the tip, with the other anthryl group still lies on substrate.
(d) When the tip further retracts, the contact of the anthryl group and the tip breaks, the anthryl group rotates completely when falls
back to the substrate and transit to DMADAB-2. (e) The △f(Z) curve recorded during a successful manipulation on a DMADAB
molecule. Insets are STM images of the DMADAB molecule before (left) and after (right) manipulation. Scale bars are 1 nm. Z = 0 pm
is defined as a tunneling junction height of -300 mV, 10 pA on top of the dimethylamino group. Regions I and II correspond to tip
approaching to the molecule from 0 pm to -700 pm. Region III is where the tip stays at -700 pm for 3 seconds. Regions IV and V
correspond to tip retracting from -700 pm to 0 pm. The feedback loop was open during the △f(Z) measurements. (f) The short-range
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force curve calculated from the △f(Z) curve in region I. The red star marks the Z position at -476 pm, where △f(Z) suddenly drops
at the boundary of regions I and II. The force curve is calculated by using the Sader-Jarvis method.36
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We have recorded the curves of frequency shift (△f) versus tip-molecule distance (Z) that of successful manipulations on
DMADAB molecules (Figure 3e, Figure S6). As shown in Figure 3e, the △f(Z) curve in regions I and II displays the tip-molecule
interaction when the tip approached to the molecule for 700 pm from a tunneling junction height of -300 mV, 10 pA, where
Z is defined as 0 pm. In region I, the curve features Lennard-Jones force law, and the corresponding short-range force curve
is calculated and displayed in Figure 3f, which indicates that the force between the tip and the molecule is a repulsive force of
3.38 nN at -476 pm. When further approaching the tip, the frequency shift suddenly drops at -476 pm and then undergoes
drastic changes in region II. This sudden drop, which is defined as the “bonding point”, is attributed to the involvement of
nonconservative processes between the tip and the molecule, such as the formation of chemical bonds. For different
manipulations, the bonding points in △f(Z) varies around an average value of -492±30 pm (Figure S6). In region III, the tip
stayed at -700 pm for 3 seconds, where the frequency shift may change, suggesting unstable structures under the tip. The
△f(Z) curve with tip retraction is displayed in regions IV and V. In region IV, the frequency shift shows large variations, which
should correspond to the lifting of one of the anthryl groups by the tip along with cleavages of the bonds that were formed in
region II. Further retracting from -243 pm to 0 pm, the △f(Z) curve becomes monotonically increasing, suggesting the anthryl
group has detached from the tip at -243 pm. Note that the detachment of the anthryl group may also happen at 0 pm or even
higher tip positions (Figure S6). Given the complex interactions involved in the process, the change of the detachment height
is reasonable. The deduced isomerization process from the △f(Z) curves fits well with the SMD simulations. In this whole
process, the dimethylamino group plays a key role in inducing the molecule to interact with the tip with one of its anthryl
groups by providing a repulsive force in the middle part of the molecule. It is predictable that without this out-of-plane
dimethylamino group, the molecule and tip are likely to interact at the central benzene ring, which makes the isomerization
unlikely to happen.
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To concrete the role of the dimethylamino group in isomerization, we removed the dimethylamino group in DMADABs by
annealing the substrate at 670 K for 40 minutes, which converted all DMADABs to 1,3-di(2-anthryl)-benzene (DAB) species.
The DABs have three isomers on surface as counterparts of the DMADAB isomers. Similar with DMADAB, the angle between
the two anthryl groups in a DAB molecule is used as a criterion to classify the three isomers (Figure S1). Figure 4a shows the
STM and non-contact atomic force microscope (nc-AFM) images of a DAB-1 molecule, which yield unambiguous evidence for
the detachment of the dimethylamino group, leaving two anthryl groups intact at the meta-position of the central benzene
ring and resulting in a planar configuration. The STM and nc-AFM images of DAB-2 and DAB-3 also show the similar planar
configurations (see Figure S7 in Supporting Information). The nc-AFM images show a hexagon feature at the center with two
neighboring anthryl groups, which is in good agreement with the planar configuration of DAB molecules. The planar
configuration is distinct from those of DMADAB isomers. The nc-AFM images of DMADAB-2 (Figure S8) with decreasing tip
heights clearly resolve an out-of-plane group. The disappearance of the out-of-plane group in DAB nc-AFM images is a strong
evidence for the detachment of the dimethylamino group after annealing. For comparison, experimental and DFT simulated
STM images for DMADABs and DABs are shown in Figure S9 and Figure S10. The simulated DMADAB images all have a bright
protrusion in the center, which corresponds to the dimethylamino group, and flat arms on both sides, which are the anthryl
groups. While for the DAB molecules, the simulated images show flat electronic states along the molecular skeleton. All the
simulated images fit well with our STM images.
The STM tip manipulation was also performed to investigate the isomerization behavior of DAB isomers. However, with
multiple combinations of manipulation heights and rates, only lateral displacement but no isomerization was observed (DAB-
1 in Figure 4b and DAB-2, DAB-3 in Figure S11 in Supporting Information, respectively). Of all the 147 trials that we have
performed on DAB molecules, no isomerization was induced (the statistics is shown in Figure S12). This result demonstrates
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that without the out-of-plane dimethylamino group, the isomerization is blocked, although the force between the tip and the
molecule is large enough to move the molecule on the surface.
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Figure 4. Control experiment on DAB molecule on Ag(100). (a) STM topographic images and constant-height frequency shift nc-
AFM images of DAB-1 on Ag(100) substrate. STM scanning parameters: VSample = −30 mV and I = 10 pA. AFM scanning parameters:
amplitude = 100 pm. Scale bars: 1 nm. (b) Continuous tip manipulation of DAB-1 shows that DAB-1 can move around and rotate, but
not transit to another isomer. Dashed circles indicate the molecule being manipulated. Scanning parameters: VSample = −100 mV and
I = 10 pA. Scale bars: 3 nm. (c) Schematic drawing of the typical states in tip manipulation on DAB-1 taken from the SMD simulations.
The tip interacts with the central region of the molecule (in purple halo) after approaching to the substrate. Thus, none of the anthryl
groups rotates in the manipulation process and no transition can be triggered.
In the SMD simulated movie (See Movie S2 in Supporting Material), DAB-1 shows dramatic difference from DMADABs upon
tip manipulation. First, the molecule has a planar adsorption configuration on the substrate. As the tip approaches the surface,
the DAB-1 moves towards the tip with its middle region (in purple halo in Figure 4c) directly interact with the tip. The
molecule remains the planar configuration during the manipulation process, thus makes it rather unlikely for either of the
anthryl groups to rotate. When the tip retracts, the molecule either stays on surface with its original configuration, or is picked
up by the tip. From this control experiment on the manipulation of molecules without dimethylamino groups, we have
confirmed that the impulsive force interaction between the tip and the out-of-plane dimethylamino group is essential for
isomerization of DMADABs.

CONCLUSION
We studied isomerization for DMADABs by STM tip manipulation on Ag(100) substrate. The DMADABs can reversibly and
reproducibly isomerize between three configurations. The SMD simulations demonstrate that the impulsive force between
the tip and the out-of-plane dimethylamino group is essential for the isomerization. After detachment of the dimethylamino
group, the resulting planar molecules DAB no longer change their configurations upon tip manipulation. Our work
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demonstrates that it is feasible to use out-of-plane functional groups to tune on-surface molecular isomerization, opens up
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the possibility to manipulate molecular configurations via mechanical forces.
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EXPERIMENTAL METHODS
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Sample preparation. Synthesis method and characterization data for DMADAB molecule is supplied in Supporting
Information. Experiments were done in an ultra-high vacuum (UHV) chamber with the base pressure of 2 × 10-10 mbar. The
Ag(100) surface was prepared by repeated circles of Ar+ ion sputtering and annealed to 660 K for 20 minutes. The DMADAB
was sublimed onto clean Ag(100) surface at 470 K for 3 minutes while keeping the substrate at RT, allowing possible on-
surface isomerization to happen. Fully deamination of DADBAMs were done by annealing the substrate to 670 K for 40
minutes.
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SPM measurements. All STM and nc-AFM measurements were performed at LHe temperature with the base pressure
lower than 2 × 10-10 mbar. All STM topographic images were acquired in constant-current mode. All nc-AFM measurements
were performed using a commercial qPlus tuning fork sensor in frequency modulation mode with a carbon monoxide (CO)
functionalized Pt/Ir tip.37 The resonance frequency is about 27.9 kHz, and stiffness about 1800 N/m. The imaging heights for
all nc-AFM measurements are reported in figure captions referred to the STM tunneling junction height on clean Ag(100)
substrate which is −30 mV and 10 pA. All STM and nc-AFM images were processed using free and open source software
Gwyddion.
STM tip manipulation. We first scan the sample to make sure the tip is not decorated with molecules. The tip is clean if the
shape of molecule can be clearly resolved in STM images. Tip manipulation was done by stabilizing the STM tip on Ag(100)
surface after some certain time. Afterwards, we move the tip to the center of the target molecule, open feedback loop,
subsequently decrease the bias to zero and approach the tip to the target molecule for a certain distance before retracting the
tip. STM feedback loop was then turned back on and STM scan was performed subsequently to confirm the result after each
manipulation. For most of the manipulations, when opening the feedback loop, the tunneling junction was at tunneling bias
−100 mV and tunneling current 30 pA, the approaching distance was about 550 pm for around 60 ms before the tip was
retracted by 1 nm. A tunneling junction height of -300 mV, 10 pA was also tried, for which the approaching distance for
activating the isomerization was about 700 pm. At other initial heights the isomerization can also be activated at a proper
approaching distance.
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THEORETICAL METHODS
SMD simulations. The SMD simulations using constant-velocity method are employed to study the effects of STM tip on the
rotation of molecules on Ag(100) surface. We first construct a model consisting a DMADAB/DAB molecule absorbed on a
(30×30) lateral periodicity of the four-layered Ag(100) slab. The dimension of the supercell is 86.7 × 86.7 × 66.1 Å3. The STM
tip composed of 113 Pt atoms and 4 Ag atoms hangs over the substrate. Then, the vertical external forces are applied to the
STM tip for simulating the approaching and withdrawing effect of the tip, respectively. All constant-velocity SMD simulations
are performed with the pulling velocities of 0.01 nm/ps and loading rates of 16.61 pN/ps. All SMD simulations are conducted
using the GROMACS 2016 simulation package.38 The general AMBER force field (GAFF) is used to describe inter- and intra-
molecular interaction parameters of DMADAB/DAB molecule.39-40 For Ag and Pt atoms, Lennard-Jones (LJ) potential is chosen
because it is compatibility with AMBER force field and its performance is comparable to tight-binding and embedded atom
models.41 The simulations are carried out with three-dimensional periodic boundary conditions using the leap-frog integrator
with a time step of 1.0 fs. Short-range electrostatic and van der Waals interactions are calculated at a cutoff distance of 1.2
nm, whereas long-range electrostatic interactions are treated using the particle mesh Ewald method. The Berendsen
thermostat is chosen for temperature. Simulation snapshots are rendered in visual molecular dynamics.42
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DFT calculations. All DFT calculations were carried out using Vienna ab-initio simulation package (VASP)43 with the
projector augmented wave (PAW) method.44-45 Van der Waals (vdW) interactions were considered at the vdW-DF level,46 with
the optB86 functional was used for the exchange potential.47-48 The energy cutoff of the plane-wave basis sets was 400 eV,
and K-point sampling was done only at the Γ point. A slab model was used with three Ag layers as the substrate. The vacuum
layer was larger than 1.2 nm. All atoms except the bottom Ag layer were fully relaxed until the net force is smaller than 0.1
eV/nm.
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Supporting Information
The Supporting Information is available free of charge on the ACS Publications website.
Additional Supporting Material (Movie S1 and Movie S2) showing SMD simulations on DMADAB-1 and on DAB-1, respectively
(MP4)

AUTHOR INFORMATION
Corresponding Authors
*xinliang.feng@tu-dresden.de
*sxdu@iphy.ac.cn
*hjgao@iphy.ac.cn
ORCID
Jing Qi: 0000-0001-6859-750X
Yun Cao: 0000-0002-7518-2481
Junzhi Liu: 0000-0001-7146-0942
Zhihai Cheng: 0000-0003-4938-4490
Min Ouyang: 0000-0002-1721-1571
Xinliang Feng: 0000-0003-3885-2703
Shixuan Du: 0000-0001-9323-1307
Hong-Jun Gao: 0000-0002-6766-0623
Present Addresses
¶Physikalisches Institut, Experimentelle Physik II, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
∞Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong
Kong, China
Author Contributions
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▲J.Q. and Y.G. contributed equally to this work.
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The authors declare no competing financial interest.
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ACKNOWLEDGEMENT
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We acknowledge the financial support from National Key Research and Development Program of China (Grant Nos.
2016YFA0202300, 2018YFA0305800 and 2016YFA0200700), the National Natural Science Foundation of China (Grant Nos.
51761135130, 61888102, 61622116, 11604373, 21661132006, 21622304, 61674045, and 11604063), the Strategic Priority
Research Program of Chinese Academy of Sciences (Grant Nos. XDB30000000), the International Partnership Program of Chinese
Academy of Sciences (Grant Nos. 112111KYSB20160061) and the CAS Pioneer Hundred Talents Program. Furthermore, we thank
the German Research Foundation (DFG) with EnhanceNano (No. 391979941) for financial support. Part of the research was
performed in the Key Laboratory of Vacuum Physics, Chinese Academy of Sciences. Computational resources were provided by the
National Supercomputing Center in Tianjin Municipality, China.
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